MAEINE BOILER MANAGEMENT 
 AND CONSTRUCTION 
 
 BEING A TREATISE OH 
 
 BOILER TROUBLES AND REPAIRS, CORROSION, FUELS AND HEAT 
 
 ON THE PROPERTIES OF IRON AND STEEL, ON BOILER MECHANICS 
 
 WORKSHOP PRACTICES AND BOILER DESIGN 
 
 C. E. STROMEYER, M.Inst.C.E. 
 
 M 
 
 CHIEF ENGINEER OF THE MANCHESTER STEAM USERS* ASSOCIATION FOR THE PREVENTION 
 
 OF BOILER EXPLOSIONS; FORMERLY ENGINEER SURVEYOR TO LLOYD'S REGISTER; 
 
 PAST MEMBER OF COUNCIL OF THE NATIONAL PHYSICAL LABORATORY, 
 
 KEW. 
 
 FOURTH EDITION 
 
 LONGMANS, GEEEN, AND CO. 
 
 39 PATERNOSTER ROW, LONDON 
 
 NEW YORK, BOMBAY, AND CALCUTTA 
 
 1914 
 
 All rights reserved 
 
A 
 
 
PREFACE 
 
 TO 
 
 FOUKTH EDITION 
 
 THE results of experimental researches into a variety of subjects are 
 accumulating which affect either directly or indirectly the manage- 
 ment or construction of boilers; these have been referred to in the 
 various chapters of this edition. Thus amongst physical researches may 
 be mentioned Stefan and Bolzmann's law of radiation which seems to 
 explain why the high temperature flames which are associated with 
 perfect combustion lead to furnace troubles, then there are Nicholson's 
 experiments on the influence of the speed of a gas on its heat trans- 
 mission, Coker's optical measurements of strains, and my own experi- 
 ments on fatigue of metals as yet unpublished on brittleness caused 
 by the presence of nitrogen in steel, and on water hammers in steam 
 pipes. Heyn & Bauer's exhaustive experiments on corrosion have also 
 been carefully summarised in this work. 
 
 On account of the increasing use of wrought iron and steel instead 
 of copper for steam pipes, a new chapter has been added on this sub- 
 ject. It reviews all available experiments on the losses of pressure 
 due to friction and to radiation, explains the methods of manufacture 
 and discusses steam pipe explosions, of which about two hundred have 
 been reported upon by the Board of Trade as being due either to water 
 hammer, to inelastic arrangement or to bad material. The question 
 of elasticity of pipe bends has necessitated the addition of a few 
 mathematical remarks on curved beams, and a comparison of these 
 with Prof. Bautlin's valuable experiments on full sized pipes. They 
 were found to be of great use in estimating the stresses in the flanges 
 of end plates of boilers. This subject and the staying of flat plates is 
 deserving of greater attention than is generally bestowed on it by 
 engineers. 
 
 Fortunately a large number of experiments with flat plates have 
 now been made both by the Board of Trade, the German Admiralty, 
 Prof. Bach, and others; they have been carefully summarised and 
 
 346809 
 
VI PREFACE TO FOURTH EDITION 
 
 are found to harmonise better than might have been expected. The 
 staying of annular water spaces of donkey boilers is also dealt with, 
 but only mathematically, as no experiments have been carried out. 
 
 The increasing use of high speed tool steel, and of electric and 
 oxy-acetylene welding and a few other matters are also mentioned in 
 the present edition. 
 
 The re-arrangement of the Board of Trade Rules in the early part 
 this year has necessitated a similar re-arrangement of the last chapter 
 in the present edition, but the other leading chapters on Construction 
 and on Management, have received comparatively few additions or 
 alterations. 
 
 C. E. S. 
 
 WEST DIDSBURY, 
 
 December, 1913. 
 
PEE FACE 
 
 TO 
 
 THE FIRST EDITION 
 
 WHILE reading through these pages for the last time, and thereby 
 completing a task which has proved a heavier one than could at 
 first have been imagined, numerous passages have recalled to mind 
 friendly discussions of which they are the outcome, or valuable hints 
 and sometimes exhaustive criticisms from those friends to whom 
 doubtful points were submitted. Should they find that their views 
 have not in all cases been adopted, the text will doubtless also reveal 
 to them the reasons why this could not be done; and to these 
 friends I wish to convey my warmest thanks for the encouragement 
 which their personal interest in this work has afforded me. 
 
 While collecting the material for this work a feeling that many 
 problems yet remain to be solved has rarely been absent from my 
 mind, more especially when the scientific side of a question was 
 being inquired into. Not being in a position to satisfactorily dis 
 cuss such problems, it seemed necessary at least to state them 
 concisely, so that scientists might be induced to solve them for us. 
 It would have been very easy to ignore such difficulties altogether; 
 but this course would have been contrary to my purpose, which 
 was to produce a work of a practical character. If it should be 
 objected that just because of this object even the simplest mathe- 
 matics ought to have been omitted, such critics should remember 
 that true practice, unlike abstract science, is unscrupulous in the 
 choice of means, and avails itself of the gratuitous labours of scholars 
 and scientists as readily as it adopts the more costly experiences 
 gained by repeated failures. Besides, as the object of science is 
 truth, practical men, whose sole aim is success, dare not remain in 
 the dark as regards its discoveries and deductions. 
 
 C. E. S. 
 
 GLASGOW : August 1893. 
 
INTRODUCTION 
 
 THE information contained in this work has heen collected for the use 
 of people interested in the manufacture and management of marine 
 boilers, and it is hoped that the summaries of the experiences gained 
 in one of the branches with which it deals will assist those whose 
 attention has been confined more particularly to the other. Thus, for 
 the information of manufacturers, it was necessary to discuss the 
 troubles to be expected from the use of defective materials, as well as 
 the dangers to which a boiler is exposed after it leaves their hands ; 
 while for steam users, descriptions as to the processes of construction, 
 and scientific inquiries about corrosion, fuels, and similar subjects, had 
 to be brought together. 
 
 In spite of a very exhaustive search, extending over several years, 
 little information either about the management or about workshop 
 practices could be found, most books and papers professing to deal 
 therewith doing so only in vague terms. The Author had, therefore, 
 to rely mainly on his own experiences when explaining the various 
 practices and manipulations. Although it was impossible to enter into 
 every minute detail, it is hoped that no points have been omitted to 
 which attention should be drawn. 
 
 In writing the chapter on ' Mechanics ' the Author also had to rely 
 mainly on his own resources when trying to present such problems as 
 occur in marine boilers in as simple and yet as comprehensive a form 
 as possible. Special attention has there been paid to the relations 
 existing between elastic stresses and those which make their appear- 
 ance just before rupture takes place, whereby it is hoped that the term 
 1 factor of safety ' has acquired a more precise meaning than it at 
 present possesses. A graphic method for resolving stresses, a method 
 for estimating the shearing strengths of a material from torsion experi- 
 ments, and a discussion on the irregular distribution of stresses in 
 
X INTRODUCTION 
 
 riveted joints, are some of the subjects herein discussed, and about 
 which little will be found in earlier books. 
 
 In the chapter on ' Corrosion ' attention is drawn, amongst other 
 matters, to the strange influence which apparently harmless salts exert 
 on the harmful activity of weak acids ; the action of air in feed-water 
 and the much-debated question of galvanic currents in boilers have 
 been treated in some detail. 
 
 While examining the numerous experiments on ' Heat Transmission,' 
 and before Mr. Durston's excellent paper was read, the Author was con- 
 fronted with the serious difficulty that nearly all these experiments are 
 incomplete as regards certain essential points. Sometimes the heating 
 value of the coal was not stated ; sometimes the steam pressure, funnel 
 or feed temperature was forgotten, or the ashes not weighed ; but by 
 having brought together various experiments in one chapter a better 
 idea can now be formed than has yet been possible about the resistance 
 encountered by heat when it travels from the flame through the iron 
 and scale into the water. 
 
 Somewhat similar remarks might be made on the subject of 
 ' Strength of Materials,' for metallurgists are still unable to explain 
 why a metal which can be stretched from 20 to 30 per cent, in a 
 testing machine sometimes shows no plasticity, and cracks spontane- 
 ously, when fitted in a boiler. Pains have been taken to collect all 
 references to such influences as might cause trouble when using steel, 
 and it is hoped that the Author's experience, both in engineering works 
 and in numerous English and foreign steelworks, has led him to 
 touch upon everything that is essential. 
 
 The chapter on ' Fuels and Combustion ' ought to be of value to 
 those who are entrusted with the carrying out of accurate experiments 
 on the performances of engines and boilers. Not only has it been ex- 
 plained there how necessary it is to know the heating value of the fuel 
 used, and whether it has been properly burnt, bat explanations have 
 been added showing how to carry out the experiments, and as they are 
 comparatively simple, seagoing engineers possessed of a knowledge of 
 chemistry might easily inform themselves on questions such as how 
 much heat and unconsumed fuel are escaping up the funnel, and how 
 much priming water is carried over with the steam, about which points 
 reliable information is still wanting. 
 
 For the convenience of draughtsmen the rules of the Board of 
 Trade and of Lloyd's Kegister on the scantlings of boilers have all been 
 placed near the last pages, and much trouble has been taken to make 
 
INTRODUCTION XI 
 
 the tables which are based on them not only reliable and comprehen- 
 sive, but also compact. But as these rules are liable to occasional 
 amendments, the tables may also have to be revised from time to time. 
 
 These rules and tables are preceded by a short chapter on ' Design/ 
 in which such hints have been given as will, it is hoped, facilitate 
 drawing-office work. It has not been thought advisable to reproduce 
 any drawings of complete boilers, but a long list has been compiled of 
 publications where they can be looked up, together with their prin- 
 cipal dimensions, their performances, and the builders' names. 
 
 These and the other references to publications were found to be so 
 numerous that it was necessary to abridge their titles to a few initial 
 letters, which have been rearranged in alphabetical order in the 
 following list, together with the necessary particulars for easily finding 
 the required volume. It was at first intended to quote only such 
 papers or books as had been printed in the English language ; but 
 many of these turned out to be translations, and it soon became 
 evident that they could not always be relied upon. Not only were 
 the misprints sometimes of the most serious nature, but in several 
 instances it was found impossible to trace the original paper, because 
 of the date, volume, or page being wrongly given. The plan had 
 therefore to be adopted of mentioning only the original notice of ex- 
 periments on investigation, no matter in what language they were 
 first described, 
 
LITEBATUKE 
 
 The following books and publications arc referred to in the text : 
 
 J. F. BABNABY. Effects of Heat on the Bending Qualities of Iron,' 1881. Admir- 
 alty Letter, N.S. ^ViF- 
 
 J. F. BABNABY. ' Influence of Repeated Heating and Cooling of Steel and Iron,' 
 1882. Admiralty Letter, N.S. HVs!*- 
 
 W. M. BABB. ' A Practical Treatise on High-Pressure Steam Boilers.' Indian- 
 apolis, 1880. 
 
 B. H. BABTOL. ' A Treatise on the Marine Boileru of the United States.' Phila- 
 
 delphia, 1851. 
 
 G. BEBKLEY. Experiments on the Mechanical Properties of Steel, made at Wool- 
 wich Dockyard,' 1870. 
 
 L. E. BEBTIN. 'Marine Boilers.' (Translated by L. ,G. Robertson.) London, 
 1898. 
 
 N. P. BDBOH. * A Treatise on Boilers and Boiler- Making.' London, 1873. 
 
 C. BUSLEY. 'Die Schiffsmaschine.' Kiel, 1883. (Anew edition is in progress, as 
 
 well as a translation by H. A. B. Cole. London, 1892, not completed 1901.) 
 A. LE CHATELIER. 'Influence de la Temperature sur les Proprietes Mecaniques 
 des Metaux.' Paris, 1891. 
 
 D. K. CLABK. Recent Practice in Locomotive Engineering.' London, 1858. 
 
 D. K. CLABK. ' A Manual of Rules and Tables.' London, 1878. 
 
 E. CLABK. ' Britannia and Conway Bridges.' 1850. 
 
 F. COLYEB. 4 Management of Steam Boilers.' London, 1885. 
 
 F. COLYEB. ' A Treatise on Modern Steam Engines and Boilers.' London, 1886. 
 
 J. H. COTTEBILL. ' The Steam Engine.' London, 1878. 
 
 C. C>ucHE. 'Permanent Way,' &c. (A Translation.) London, 1877. 
 
 V. DESHAYES. ' Classement et Emploi des Aciers.' Paris, 1880. 
 
 W. FAIBBAIBN. ' Useful Information for Engineers.' London, 1856. 
 
 L. FLETCHER. ' Red-hot Furnace Crown Experiments.' Manchester Steam Users, 
 
 1889. 
 
 N. FOLEY. ' The Mechanical Engineer's Reference Book.' London, 1891. 
 E. FBANKLAND. * Experimental Researches.' London, 1877. 
 DB. F. GBVSHOFF. ' Theorie der Elasticitat und Festigkeit, mit Bezug,' &c. Berlin, 
 
 1866 and 1878. 
 
 C. E. GBOVE and W. TBOBPE. ' Chemical Technology.' London, 1889. 
 H. M. HOWE. The Metallurgy of Steel.' New York, 1890. 
 W. S. HUTION. 'The Practical Engineer's Handbook.' London, 1887. 
 W. S. HUTTON. ' Steam Boiler Constructions.' London, 1891. 
 J. S. JEANS. ' Steel : its History, Manufacture, Properties, and Uses.' London, 
 
 1890. 
 
 xiii 
 
XIV LITERATURE 
 
 D. KIRKALDY. ' Results of an Experimental Enquiry into the Tensile Strength ot 
 Wrought Iron and Steel.' Glasgow, 1863. 
 
 D. KIRKALDY. ' Results of an Experimental Enquiry into the Mechanical Proper- 
 ties of Steel of Different . . . Conditions.' London, 1873. 
 
 D. KIRKALDY. ' Experimental Enquiry into the Properties of Essen and Yorkshire 
 Iron.' London, 1875. 
 
 D. KIRKALDY. ' Strength and Properties of Materials,' <fec. London, 1891. 
 
 DR. H. LANDHOLT and DR. R. BORNSTEIN. ' Physicalisch-chemische Tabellen.' 
 
 Berlin, 1894. 
 
 A. LEDEBUR. ' Handbuch fiir Eisenhuttenkunde.' Leipzig, 1884. 
 R. B. LONORIDOE. ' Strength of Riveted Joints.' Manchester, 1879. 
 M. M. P. MUIR. ' The Elements of Thermal Chemistry.' London, 1885. 
 DR. W. OSTWALD. ' Verwandschaftslehre.' Leipzig, 1887. 
 DR. J. PERCY. ' The, Metallurgy of Iron and Steel.' London, 1864. 
 H. POOLE. 'The Calorific Power of Fuels/ London, 1900. 
 
 E. J. REED. ' Ship-Building in Iron and Steel.' London, 18*59. 
 
 J. A. ROWE. ' Marine Boiler Construction and Preservation.' 1884. 
 
 SCHWARZ-FLEMMING. ' Die Kesselabtheilung auf Dampfschiffen.' Berlin, 1873. 
 
 A. E. SEATON. ' A Manual of Marine Engineering.' London, 1891. 
 
 W. H. SHOCK. 'Steam Boilers: their Construction and Management.' New York, 
 1880. 
 
 K. STIFFS. ' Iromand Steel.' (Translated by C. Sandberg.) London, 1869. 
 
 R. H. THURSTON. ' The Materials of Engineering.' New York, 1883. 
 
 R. H. THURSTON. ' A Text-book on Materials of Construction.' New York, 1885. 
 
 R. H. THURSTON. ' Steam Boiler Explosions.' New York, 1887. 
 
 J. TODHUNTER and K. PEARSON. ' A History of the Theory of Elasticity.' Cam- 
 bridge, 1886. 
 
 W. TRAIL. ' Boilers : their Construction and Strength.' London, 1888. 
 
 J. TYNDALL. ' Heat a Mode of Motion.' London, '1870. 
 
 W. C. UNWIN. ' Wrought-Iron i Bridges.' London, 1868. 
 
 W. C. UNWIN. ' The Testing of Materials of Construction.' London, 1910. 
 
 W. M. WATTS. ' Index of Spectra.' London, 1872. 
 
 C. WINKLER. Handbook of Gas Analysis.' (Translated by J. Lunge.) London, 
 1885. 
 
 J. G. WINTON. Modern* Steam Practice.' London, 1883. 
 
 List of Publications of Societies, &c., and of Periodicals, arranged in 
 the Order of the abridged Titles as Mentioned in the Text. 
 
 Am. C. E. . . Transactions of the American Society of Civil Engineers. 
 
 New York. 
 
 Am. J. S. . . American Journal of Science. Newhaven, Conn. 
 
 Am. M. E. . . Transactions of the American Society of Mechanical Engineers. 
 
 New York. 
 Am. Min. E. . Transactions of the American Institute of Mining Engineers. 
 
 New York. 
 
 An. R. M. M. A. Report of the Proceedings of the American Master Mechanics' 
 Association. New York. 
 
 An. Ch. . . . Annales de Chimie. Paris. 
 
 An. Ch. Ph. . Annales de Chimie et Physique. Paris. 
 
 An. Genie. . . Annales du Genie Civil. Paris. 
 
 An. Tnd. . . . Annales IndustrielleR. Paris. 
 
LITERATURE 
 
 Ait. Mines. . . Annales des Mines. Paris. 
 
 An. Pont. Ch. . Annales des Fonts et Chauss^es. Paris. 
 
 Army N. J. . . Army and Navy Journal. New York. 
 
 Bai. K. B. . . Bairisches Kunst- und Gewerbe-Blatt. Weimar. 
 
 Bay. A. I. V. . Zeitschrift des Bayerischen Architecten- und Ingenieur-Vereins. 
 
 (New Title : Zeitschrift fur Baukunde.) Miinchen. 
 
 Berg. H. J. . . Berg- und Hiittenmannisches Jahrbuch. Wien. 
 
 Berg. H. V. . Zeitschrift des Berg- und Hiittenmannischen Vereins 
 Berg. H. Z. . Berg- und Huttenmanmsche Zeitung. Zeipzi-r. 
 
 Brit. Assoc. . . Reports of the British Association. London. 
 
 C. E Minutes on the Proceedings of the Institution of Civil Engineers. 
 
 London. 
 
 Chem. Soc. . . Journal of the Chemical Society. London. 
 
 Chron. Ind. . Chronique d'Industrie. Bruxelles. 
 
 Civil-Ing. . . Der Civil-Ingenieur. Leipzig. 
 
 Comp. Rend. . Comptes Rendus Hebdomadaires des Seances de 1' Academic des 
 
 Sciences. Paris. 
 
 Deut. Ck. G. . Berichte der Deutschen chemis-ihen Gesellsehaft. Berlin. 
 
 Deut. Ing. . . Zeitschrift des Vereins Deutscher Ingenieure. Berh'n. 
 
 Dingler's Journal Dingler's polytechnisches Journal. Augsburg, Hanover, Stuttgart. 
 Elect. Z. . . Electrotechnische Zeitschrift. Berlin. 
 
 Eng. Min. J. . Engineering and Mining Journal. New York. 
 
 Enging. . . . Engineering. London. 
 
 Engr. . . . The Engineer. London. 
 
 Eng. Scot. . , Transactions of the Institution of Engineers and Ship-builders 
 
 in Scotland. Glasgow. 
 
 Frankl. Inst. . Journal of the Franklin Institute. Philadelphia. 
 
 Gnie C. . . Le Gnie Civil. -Paris. 
 
 G laser's An. . Annalen fur Gewerbe und Banwesen (F. C. Glaser). Berlin. 
 
 Goi-ni J. . . . Ghornu Zhurnal. St. Petersburg. 
 
 Ing. Civ. . . Comptes Rendus (a Iso Resume) des Travaux de la Societe des 
 
 Ing^nieurs Civils. Paris. 
 
 Iron Age. . . Iron Age. New York. 
 
 I. and S. I. . Journal of the Iron and Steel Institute. London. 
 
 Jahrb. B. H. . Jahrbuch fur Berg- und Hiittenwesen. Freiberg. 
 
 Manch. L. Ph. . Proceedings of the Manchester Literary and Philosophical Society 
 
 (formerly Literary and Ph. Soc. Manchester). Manchester. 
 Marine E. . . Transactions of the Institution of Marine Engineers. Stratford. 
 
 M. E Minutes of the Proceedings of the Institution of 
 
 Engineers. 
 
 Mechanical 
 London. 
 
 Mitt. Berlin . . Mitteilungen aus den koniglich-technischen Versuchsanstalten. 
 
 Berlin. 
 Mitt. Munich . Mitteilungen aus dem mechanisch-technischen Laboratorium 
 
 der Koniglichen Polytechnischen Schule. Miinchen. 
 
 Mitt. Pola . . Mitteilungen aus dem Gebiet des Seewesens. Pola. 
 
 M. S. U. A. . . Reports of the Manchester Steam Users' Association. 
 
 Manchester. 
 
 N. A Transactions of the Institution of Naval Architects. London. 
 
 N. E. C. I. . . Transactions of the North-East Coast Institution of Engineers 
 
 and Ship-builders. Newcastle. 
 
 N. Engl. I. . . Transactions of the North of England Institution of Mining and 
 
 Mechanical Engineers. Newcastle. 
 
 0. /. A. V. . . Zeitschrift des Oesterreichischen Ingenieurs- und Architecten- 
 
 Vereins. Wien. 
 
 Organ .... Organ fur die Fortschritte des Eisenbahnwesens, &c. 
 
 Wiesbaden. 
 Parliam. Rep. . Parliamentary Reports, including Board of Trade Reports. The 
 
 date, a number, and House of Commons Library Index are 
 
 given. London. 
 
 Phil. Mag. . . The London, Edinburgh, and Dublin Philosophical Magazine 
 
 and Journal of Science. London. 
 
 Phys. 5. ... Transactions of the Physical Society. London. 
 
XVI 
 
 LITERATURE 
 
 Pogg. Ann. . . Annalen der Chemie und Phyaik (Poggendorf). Leipzig. 
 
 Proceedings. . Proceedings of the Royal Society. London. 
 
 Rept. B. Eng. . Report of the Board of Engineers on Boilers, &c., 1868. 
 
 Philadelphia. 
 
 Rept. Com. P. . Report of the Commissioners of Patents, Ac., on Boiler Explo- 
 sions, 1848. Washington. 
 
 Rept. U. S. B. . Report of the United States Board appointed to Teat Iron, Steel, 
 and other Materials (Thurston, 1881, 1886). Washington. 
 
 Rev. d'Art. . . Revue d'Artillerie. Paris. 
 
 Rev. Ind. . . Revue Industrielle de Bruxelles. Bruxelles. 
 
 R. Soc. Edinb. . Transactions of the Royal Society. Edinburgh. 
 
 Soc. Arts. . . Proceedings of the Society of Arts. London. 
 
 Soc. Ch. Ind. . The Journal of the Society of Chemical Industries. Manchester. 
 
 Soc. d'Enc. . . Bulletin de la Soci6t6 d'Encouragement, ifec. Paris. 
 
 Soc. Eng. . . Transactions of the Society of Engineers. London. 
 
 Soc. I. Min. . Bulletin de la Soci^te" de PIndustrie Minerale. St. Etienne. 
 
 Soc. I. Mul. . Bulletin de la Societe" Industrielle de Mulhouse. Mulhouse. 
 
 Stahl und Eisen Stahl und Eisen : Zeitschrift des Vereins Deutscher Eisen- und 
 Stahl-Industrieller, &c. Diisseldorf. 
 
 Tel. Eng. . . Journal of the Society of Telegraph Engineers. London. 
 
 Transactions . Transactions of the Royal Society. London. 
 
 Ver.Gew. . . Zeitschrift des Vereins zur Berforderung des Gewerbefleisses. 
 
 Berlin. 
 
 Wied. Ann. . . Annalen der Physik und Chemie (Wiedinann). Leipzig. 
 
 Ze.it. Bau. . Zeitschrift fur Baukunde. Miinchen. 
 
CONTENTS 
 
 CHAPTER I 
 BOILER MANAGEMENT 
 
 PAGE 
 
 LIGHTING FIRES AND RAISING STEAM . . 1 
 
 TROUBLES CAUSED BY COLD WATER IN BOILER BOTTOMS 2 
 
 STOKING, AIR SUPPLY, FIRE BARS 3 
 
 CLEANING FIRES 14 
 
 FURNACE BRIDGES AND DAMPERS 17 
 
 Wear and Tear of Boilers 
 
 VARIOUS CAUSES OF CRACKS IN BOILERS 20 
 
 SCALE, GREASY DEPOSITS, AND COLLAPSED FURNACES 23 
 
 Boiler Repairs 
 
 REPAIRS TO FURNACES 32 
 
 ,, TO STAYS AND COMBUSTION CHAMBERS . 38 
 
 TO BoiLER-bHELL PLATES 46 
 
 Boiler Fittings 
 
 GAUGE GLASSES . 43 
 
 SABETY VALVES ..47 
 
 CHAPTER II 
 STEAM AND WATER 
 
 STEAM PRESSURE, DENSITY AND TEMPERATURE (TABLES) 48 
 
 PROPERTIES OF WATER -55 
 
 BOILING PHENOMENA AND CIRCULATION 57 
 
 xvii 
 
XV111 CONTENTS 
 
 CHAPTER III 
 CORROSION 
 
 PACK 
 
 LISTS OF EXPERIMENTS ON CORROSION 66 
 
 INFLUENCE OF ENGINE LUBRICANTS, OF ACIDS, SALTS, AND ALKALIES . . 67 
 
 AIR IN FEED AND BOILER WATER, AND PITTING 72 
 
 DISTRIBUTION OF CORROSION 76 
 
 GALVANIC CURRENTS IN BOILERS 78 
 
 CHAPTER IV 
 FUELS AND COMBUSTION 
 
 PERFECT, SLOW, AND PARTIAL COMBUSTION AND HEATING VALUE OF FUELS . . 84 
 
 BURNING QUALITIES OF FUELS 91 
 
 TEMPERATURES OF FLAMES AND AIR SUPPLY 98 
 
 PYROMETERS 96 
 
 FORCED AND NATURAL DRAUGHT AND RESISTANCES 98 
 
 MEASUREMENT OF HKAT PRODUCED AND WASTED 102 
 
 CHAPTER V 
 
 HEAT TRANSMISSION 
 
 RADIATION AND ABSORPTION OF HEAT 114 
 
 THERMAL CONDUCTIVITY .119 
 
 TEMPERATURE OF HEATING SURFACE 121 
 
 LOSSES BY R \DIATION 125 
 
 TEMPERATURE OF FIRE BARS ....... . . 127 
 
 CHAPTER VI 
 
 STRENGTH OP MATERIALS 
 
 VARIOUS PROCESSES OF MANUFACTURING IRON AND STEEL 128 
 
 INFLUENCES OF IMPURITIES ON THE QUALITIES OF STEEL 133 
 
 VARIOUS MECHANICAL TESTS OF QUALITY 137 
 
 MlCROSTRUCTURE 143 
 
 INFLUENCE OF HEAT AND COLD ON STEEL 144 
 
 INFLUENCE OF ACIDS, EXPOSURE, AND PICKLING 146 
 
 BURNT IRON, ANNEALING 147 
 
 LOCAL HEATING AND BLUE HEAT 149 
 
 TENSILE TESTS, VISCOSITY,, ELASTICITY, PLASTIC LIMIT AND ITS CHANGES, CON- 
 TRACTION AND FRACTURE 152 
 
 SHEARING AND BENDING STRESS , 156 
 
 COMPOUND STRESSES AND THEIR INFLUENCES 159 
 
CONTENTS XtX 
 
 CHAPTER VH 
 MECHANICS 
 
 PAGE 
 
 ELASTICITY 165 
 
 RESOLUTION OF STRESSES 166 
 
 DEFORMATIONS AND STRESSES PRODUCED BY BENDING BARS AND FLAT PLATES . 168 
 
 ELASTIC BEAMS AND GIRDERS 173 
 
 IRREGULARLY STAYED PLATES, MANHOLE DOORS, AND BACK END PLATES . . 177 
 
 EXPERIMENTS ON STAYED FLAT PLATES 180 
 
 CURVED BEAMS AND PLATES 185 
 
 SHEADING STRESSES IN BEAMS AND STAYS 188 
 
 PLASTIC BEAMS 189 
 
 LONGITUDINAL ELASTICITY OF FURNACES 193 
 
 BOILER SHELL PLATES AND DOMES 196 
 
 DEFORMATIONS AND STRESSES IN CYLINDRICAL FURNACES 197 
 
 THICK CYLINDRICAL SHELLS 207 
 
 DEFORMATIONS AND STRESSES IN RIVETED JOINTS . . . . . . 210 
 
 FACTOR OF SAFETY 221 
 
 LIST OF BOILER TESTS AND EXPLOSIONS . . 223 
 
 CHAPTER VIII 
 
 BOILER CONSTRUCTION 
 
 WEIGHT AND SIZES OF BOILER PLATES 225 
 
 PUNCHING OPERATIONS AND TOOLS 226 
 
 PLANING , 228 
 
 DRILLING ,, 
 
 BENDING 
 
 RIVETING ,, 
 
 HEAVY FLANGING 
 
 231 
 237 
 245 
 251 
 
 ANNEALING AND ITS TROUBLES 261 
 
 FLANGING FURNACE SADDLES AND COMBUSTION CHAMBER PLATES . . . 264 
 
 THE PLATING OF INTERNAL PARTS OF A BOILER AND RIVETING .... 267 
 
 SCREWED STAYS, GIRDERS, AND TUBES 283 
 
 CAULKING SEAMS AND RIVETS 293 
 
 WELDING OPERATIONS . 296 
 
 TESTING BOILERS BY HYDRAULIC PRESSURE AND MEASUREMENT OF DEFORMA- 
 TIONS ... . . 301 
 
 CHAPTER IX 
 DESIGN 
 
 RATIOS OF HEATING AND GRATE SURFACES AND FUNNEL DIMENSIONS . . . 804 
 
 LISTS OF WORKING DRAWINGS OF MARINE BOILERS 810 
 
 BEST PROPORTIONS FOR RIVETED JOINTS 315 
 
 LIGHTEST ARRANGEMENT OF STAYING FLAT PLATES 319 
 
 DETAILED ESTIMATE OF THE SCANTLINGS OF A MARINE BOILER .... 320 
 
 TABLES OF SCREWED STAY DIAMETERS AND AREAS 827 
 
XX CONTENTS 
 
 CHAPTER X 
 STEAM PIPES 
 
 PRESSURE LOSSES IN STEAM PIPES 829 
 
 EXPLOSIONS DUE TO WATER HAMMER 332 
 
 STEAM PIPE MANUFACTURE 335 
 
 ELASTICITY or STEAM PIPES AND FAILUUES DUE TO FATIGUE . , 388 
 
 CHAPTER XI 
 
 LLOYD'S REGISTER BOILER RULES . . .341 
 SUMMARY AND TABLES OF SCANTLINGS . . , 348 
 
 CHAPTER XII 
 
 BOARD OP TRADE BOILER RULES . . . 365 
 SUMMARY AND TABLES OF SCANTLINGS 385 
 
 INDEX ,405 
 
MARINE BOILER MANAGEMENT 
 
 AND 
 
 CONSTRUCTION, 
 
 CHAPTEE I 
 
 BOILER MANAGEMENT 
 
 SUCCESSFUL management of a boiler consists in getting the desired 
 amount of work out of it, and at the same time keeping the expenses 
 as low as possible. To be able to do this, a boiler must above all 
 things be well designed for its work ; it should be handled with the 
 proper amount of care, and any defects which may show themselves 
 should be made good at once and their causes removed. 
 
 Lighting Fires. The fires in the main boiler are usually lighted 
 by throwing some burning fuel from the donkey boiler into the main 
 furnaces ; but if this cannot be done, a small fire is kindled on one of 
 the grates and the others lighted from it. In either case the whole of 
 the fire bars are first covered with coal, so as to restrict the draught to 
 that point where the fuel is burning ; gradually, as the fire increases, the 
 hot fuel is raked back, igniting the remainder. If the coal is very dusty 
 it may be necessary to cover the bars with old matting or with paper. 
 
 If steam has to be raised quickly, the fires are started in all the 
 furnaces at once ; but this should never be done unless there is steam 
 in the donkey boiler, and appliances are available for producing arti- 
 ficial circulation. Even where this is the case, and steam has to be 
 raised with the utmost possible despatch, it is safer to force only one 
 boiler, or such a number as are sufficient to drive the engine ; for in all 
 cases of great hurry, things are likely to go wrong, and it has happened 
 over and over again that circumf erential seams of boiler bottoms have 
 cracke 1 when not sufficiently warmed during this period. The circu- 
 lating appliances used to be hydrokineters ; now it is customary to fit 
 a donkey suction to each boiler bottom, by which means the cold 
 water is drawn off there and reintroduced through the feed near the 
 water level. l Where none of these arrangements are fitted, the heating 
 of the boiler must progress slowly, taking about twelve hours. Many 
 engineers start fires only in one furnace of each boiler, usually the 
 lowest one, in the hope that the cold water, which remains undisturbed 
 
 1 These pipes should be so fitted that water cannot accidentally be forced 
 from one boiler into another if their pressures should differ. 
 

 FIG. 1 
 
 2 BOTHER MANAGEMENT 
 
 at the bottom, will get warmed. A better plan is to light fires in one 
 of the wing furnaces, F, fig. 1, of each boiler, which sets up a natural 
 circulation, the water rising on one side and descending on the other. 
 
 If steam must be raised quickly, 
 a good plan is to fill the boilers 
 to nearly full glass, to light all 
 the fires at once, and to blow 
 off all the cold water below the 
 furnaces as soon as that above 
 them is boiling. From fear of 
 subsequent leakage, the safety 
 valves are usually kept closed, 
 and the result is that the heated 
 air in the steam space shows a 
 pressure on the gauge before 
 steam has been generated, 
 which is most misleading, be- 
 cause it all disappears as soon 
 as the engines are started. 
 This air pressure on the water 
 surface also prevents the for- 
 mation of steam bubbles when 212 F. has been reached, which would 
 materially assist the circulation, by carrying water with them as they 
 rise. It is, therefore, better to keep the main or safety valves full open 
 till steam is blowing off freely, and only to close them when the boiler 
 bottom has grown hot. If closed earlier, the chances are, even with 
 slow firing, that the boiler bottoms remain cold long after the full 
 working pressure has been reached, and boiler shells being constructed 
 mainly to resist the steam pressure, are then sometimes unable to bear 
 the additional straining to which they are subjected by the very serious 
 differences of temperature between the upper two-thirds and lower 
 one-third of their circumference. (See fig. 93, p. 75.) 
 
 Cracked Shell Plates. This difference of temperature can amount 
 to as much as 270 F., and, as iron expands about one-thousandth of 
 its length between 32 F. and 212 F., the bottom of the boiler shell 
 would tend to be about one-seven-hundredth of its length shorter than 
 the top, which, in a double-ended boiler of Yl\ feet length, would 
 amount to more than J inch. Of course the upper two-thirds of the 
 boiler would be slightly compressed, but the amount of metal in the 
 lower third being the smaller, suffers the severest stress, probably 
 quite two-thirds of that which the difference of temperature would 
 warrant. But if iron or steel is prevented from contracting one- 
 thousandth of its length, which is the same thing as stretching the 
 metal by that amount, a stress of 13 tons per square inch is set up, 
 and this, then, is approximately the extra stress which the lower 
 third of the boiler shell has to resist. 
 
 As the percentage of strength of the circumferential joints is com- 
 paratively low, it is not to be wondered at that either the rivets shear 
 or that the metal tears. In either case there is no immediate danger, 
 for the leakage is slight and the water cold, at least at first. However, 
 sometimes the solid plate cracks circumferentially, and then the rush 
 of water is considerable ; but it is only amongst iron boilers that this 
 
BOILER MANAGEMENT 
 
 3 
 
 FIG. 2 
 
 happens, which is doubtless due to the fact that this material is 
 decidedly weaker across the grain than with it. As might be ex- 
 pected, double-ended boilers are more often injured in this way than 
 single-ended ones. 
 
 Those who wish to obtain numerical results on this subject should 
 fit the following arrangement to the backs of a boiler, one near the 
 water level and the 
 
 other near the bottom, 
 or wherever they think 
 it most convenient. A 
 short iron tube (fig. 2), 
 about J of an inch in 
 diameter, and closed at 
 one end, is screwed at 
 an angle of about 30 
 into the back plate, and 
 a little mercury or oil 
 poured into it. When 
 desired a thermometer 
 can be inserted, and the 
 temperature measured. 
 If mercury is used the 
 tubes must not be of 
 brass or gun metal, otherwise they will be eaten away. 
 
 Stoking. A perfect knowledge of stoking can only be gained by a 
 practical experience, which does not fall to the lot of most engineers. 
 It is not difficult to throw shovelsful of coal through the compara- 
 tively small fire doors, even when they are 4 feet above the floors, 
 but generally inexperienced hands will not be able to place the fuel 
 on those parts of the grate where it is wanted, even when the con- 
 ditions are favourable and that is one of the chief secrets of good 
 stoking, particularly with Welsh and similar coal, which may not be 
 disturbed after it has been put on the grate. North-country coal 
 has a tendency to cake, whereby the air passages are choked. While 
 breaking up this fuel with a rake or slicer an excellent opportunity is 
 afforded for levelling it. 
 
 While burning Welsh coal the case is different. The depressions 
 where the air meets with least resistance, are burnt away quickest, 
 even to such an extent 
 that the upper edge of the 
 bars becomes exposed, 
 admitting a damaging 
 excess of air (fig. 3). On 
 account of this short cut 
 very much less air finds 
 its way through the thick 
 fuel, and the combustion 
 is reduced there. Un- 
 covered bars and thin fires are readily discovered on trials by holding 
 an anemometer in each ashpit. On recoaling, the hollows will most 
 likely be more than filled up ; but even if levelled, the combustion 
 will be fiercest where the hot fuel was lying thickest, for there it is 
 
 B2 
 
 FIG. 3 
 
BOILER MANAGEMENT 
 
 all aglow (fig. 4), and these are the parts which will now burn away 
 quickest. Continued care is therefore necessary. 
 
 What is true of a single fire is true of a number, and unless all 
 the fires connected to one funnel are kept equally thick, the thin ones 
 will burn away fastest, and if there are several stokers on one watch, 
 
 he will have the lightest 
 job who chokes his fur- 
 nace with fuel. When 
 steaming under strong 
 forced draught with 
 closed stoke holes, 
 speed in coaling is of 
 the utmost importance, 
 so as not to keep the 
 doors open too long, 
 and it is customary to 
 have a right- and left-handed stoker for each fire, with a leading man 
 to direct them where to throw the fuel. In order to see better which 
 parts of the grate are bare he should wear green-glassed spectacles. 
 
 Thickness of Fires. The question as to how thick the fires ought 
 to be kept is a difficult one to answer. Less resistance will be 
 offered to the passage of the air, and the combustion will be more 
 rapid, the thinner they are. Thick fires, or rather heavy firing, offer 
 fche advantage that the furnace doors have to be opened less fre- 
 quently, and the loss and injury. due to inrushes of cold air are not 
 so great ; but such fires produce an enormous amount of volatile 
 products, which are often so cold that they cannot ignite, as they 
 should do, when mixed with the air which is admitted through the 
 doors. This loss is, of course, greater with bituminous coal. 
 
 Under natural draught the fires should be kept about 6 and 8 ins. 
 thick respectively for North-country and for Welsh coal. Under 
 forced draught they are sometimes 12 ins. thick. 
 
 Smoke Consumption. In order to consume the volatile gases 
 some firemen coal first one side of a grate and then the other, half of 
 the upper surface being thus always in a glowing condition. Another 
 plan but this can only be carried out with caking coal is to throw 
 the green coal on the front end of the grate, and to rake it back when 
 it is well alight. The combustible gases which are at first given off 
 are thoroughly mixed with the air which reaches them through the 
 doors, and passing over the red-hot coal the mixture is bound to 
 ignite. 
 
 This plan has the advantage of allowing very long grates to be 
 used. However, the ashes and clinker will be driven to the back 
 ends, against the firebrick, whence it is most inconvenient to remove 
 them. With dirty coals this trouble is so serious that firemen prefer 
 to throw them as far back as possible, and to rake them forward 
 when partly consumed, accumulating the ashes at the front end. 
 This is an uneconomical proceeding. 
 
 Side Firing consists in throwing coal first on one side of a grate, 
 and, when this has been burnt through throwing coal on the other 
 side, with the result that the radiant heat of the hot side not only 
 causes complete combustion of the smoke produced on the black side, 
 
BOILER MANAGEMENT 
 
 FIG. 4a 
 
 but it also ignites the surface of the newly added coal and checks the 
 production of smoke. Side firing, however, has the disadvantage, 
 that the firemen have to open the fire-doors twice as often as is 
 now customary, and this frequent opening results in more air being 
 admitted above the grates than is necessary. Nevertheless, there can 
 be no doubt but that this method of firing is very economical. It 
 might be simplified and im- 
 proved, leading to a saving of 
 labour if a leaf were to be taken 
 from the gasworks practice of 
 charging long retorts. In these 
 works the coal is shovelled into 
 long semi-cylindrical troughs, 
 \vhich are lifted up to the re- 
 torts, shoved in, turned round, 
 and withdrawn. Fig. 4a con- 
 tains a suggestion how this 
 method might be applied to 
 the firing of marine boilers. 
 The fire-door would have to be 
 provided with two large circular 
 holes, closed by flaps, slides, or 
 by a revolving disc. When the left side of the furnace has to be 
 charged with coal, the left-hand hole is opened and a semicircular 
 trough filled with coal inserted, turned, round and quickly with- 
 drawn. The filling of the trough is a much easier operation than 
 throwing coal on a grate which may be 6 ft. long and 3 ft. above 
 the floor, and as the hole need not be uncovered until the trough 
 is in a position to be inserted, no unnecessary air is admitted and 
 the economy would be increased. 
 
 Air Admission above the Grate. It is conceded on all hands that 
 a certain amount of air must be admitted above the grate, and that it 
 is difficult to determine how much ; but it will not be out of place to 
 illustrate the subject by drawing attention to the behaviour of the 
 flame of an ordinary paraffin lamp. If the wick is turned too low 
 disagreeable smells are produced, filling the room in a very few 
 minutes ; if too high, other smells and much soot are produced. In 
 the one case we have incomplete combustion, due to the cooling 
 action of an excess of air ; in the other case too little was supplied. 
 Smoke and smells are emitted from funnels, showing that here too 
 unconsumed gases are escaping ; for carbonic acid, as well as steam, 
 is without odour. 
 
 With present arrangements it is almost impossible to regulate 
 the air supply, or at any rate to fix it, so that the ratio of the ex- 
 cess to the total shall have a definite value, and consequently we 
 find in practice that it varies from 25% to 200%. (See pp. 94 and 
 101.) 
 
 It is clear that when the fires are thick less air passes through 
 them, less fuel is consumed, and relatively more air is drawn in 
 through the doors. With thin fires the draught through them is 
 stronger, more fuel is burnt, and less excess air drawn in. Now, 
 although the products from thick fires contain more inflammable 
 
6 
 
 gases than those from thin ones, and consequently require more 
 excess air than these, it is difficult to believe that they will receive 
 just their correct share, whatever the sizes and number of holes in 
 the doors, whatever the state of the grate, and whatever the intensity 
 of the draught or the quality of the coal ; and it is only reasonable to 
 assume that the best results will be obtained 
 
 I. If no air is admitted through the doors when the fires are 
 
 very thin and all aglow. 
 II. If much air is admitted immediately after coaling and when 
 
 the fires are thick. 
 
 III. If more air is admitted with North-country than with 
 
 Welsh coal. 
 
 IV. If less air is admitted as the fires get dirty and the combus- 
 
 tion is reduced. 
 
 But even with the most correct proportions the combustion will 
 not be perfect, if for no other reason than that the flame comes in 
 contact with the boiler plates, and gets cooled, before it is burnt out. 
 
 As regards the excess air, it is perhaps of more importance to 
 decide where to admit it than how much to admit, provided it be 
 enough. If it were possible to keep the fires very thin, it might be 
 well to admit all the air through the bars, and none above the fire ; 
 but this is impossible. To admit air through the furnace doors 
 stimulates combustion at this point, so that, before mixing with the 
 distilled furnace gases, it has already been robbed of much of its 
 oxygen. Just after coaling this is not the case; but being even 
 colder than the products of distillation, it will cool instead of igniting 
 them. As already mentioned, this result can be evaded by throwing 
 the green coal only on the front ends ; but another plan is to have 
 much brick-work at or behind the bridge, which soon grows very 
 hot, and the mixed gases ignite on coming in contact with it, and 
 burn in the combustion chamber. "Unfortunately, the distance to the 
 tubes being short, the flame is immediately extinguished on entering 
 them. 
 
 The plans have also been tried of admitting air at the bridge, or 
 through a tube passing from the shell direct into the combustion 
 chamber ; but both are open to many objections, not the least being 
 fchat the passages get choked and are certainly not under control, and 
 can neither be cleaned nor closed when desired. 
 
 With those systems of forced draught in which the ashpits are 
 closed, the funnel damper can be set so as to retard the draught 
 above the bars to such an extent that just the right amount of air is 
 admitted, even when the doors are wide open. 
 
 Flames. Interesting experiments have been made to show that 
 on mountain tops, where the air pressure is much reduced, and also 
 in partial vacuums and bad atmospheres, ordinary flames lose their 
 luminosity, while under high pressures they grow smoky, and even 
 the hydrogen and carbonic oxide flames grow luminous. From this it 
 has been argued that draught -retarders and the closing of the funnel 
 damper, when using forced draught, will improve combustion. But 
 those very experiments (E. Frankland, 1877, p. 876) go far to show 
 that the combustion is not accelerated ; besides, the increase of 
 pressure attainable by these means is so slight in comparison with the 
 
BOILER MANAGEMENT 
 
 atmospheric pressure variations, that the influence would have shown 
 itself Before now if it were true that more heat can be got out of coal 
 with a high than a low atmospheric pressure. 
 
 Some interesting facts as to the igniting temperatures of various 
 substances will be found in the chapter on ' Fuels and Combustion.' 
 There will also be found a good deal of information on the heating- 
 power of fuels, and on various methods of measuring it, as well as for 
 determining, from the funnel gases, whether the combustion is perfect 
 or not. Some of these tests are so simple that they can easily be 
 carried out at sea. 
 
 Furnace Doors. As regards economy of fuel, furnace doors 
 
 unquestionably rank amongst the most important attachments to a 
 
 boiler, and innumerable are the patents in connection with them ; but 
 
 the very fact of numberless ideas having been published makes it 
 
 impossible to deal with any of them as exhaustively as might be 
 
 wished, and only those will be mentioned which 
 
 ~""^ have found their way into the stoke-hole. 
 
 The door may consist of a single plate, fitted 
 with hinges and a latch, and perforated, chiefly at 
 the upper edge, or fitted with a gridiron or other 
 contrivance for regulating the admission of air. 
 The objection to this arrangement is that, on 
 account of the direct radiation from the fuel, the 
 door very soon gets excessively hot and warps, and 
 even cracks. The presence of an air regulator is an 
 advantage, if properly used, but the very reverse if 
 A its action is not understood (see p. 5). Some doors 
 
 j are hinged, so that they can be kept partly open. 
 
 In order to protect the door from the heat, an inside 
 screen should be fitted, which can be renewed when 
 burnt away ; for, as it cannot be kept as cool as the outer one, it 
 suffers more severely. A simple arrangement is to rivet a plate, a, 
 fig. 5, having a number of holes, to a solid one, b. The air then 
 enters at the circumference and passes through the various holes, as 
 shown by the arrows. 
 
 In other cases the internal plate is so fitted that the current of air 
 is directed either upwards or downwards, according to the views of 
 the respective engineers. (See figs. 
 6 and 7.) An idea seems to prevail 
 that by leading the air through com- 
 plicated passages it collects heat, 
 thereby facilitating combustion ; but 
 this warming is so slight that it does 
 not justify expensive arrangements. 
 Wide dead plates in combination 
 with doors which admit air only at 
 the top keep the latter cool. As 
 already mentioned, hinges are some- 
 times constructed so as to keep the 
 doors partly open ; and certainly they 
 should all be arranged so that they 
 will keep quite open when coaling, particularly during rough weather. 
 Some of the contrivances used for this purpose are very simple, as 
 
 TIG. 9 
 
 FIG 
 
 FIG. 7 
 
8 BOILER MANAGEMENT 
 
 well as fairly efficient. All of them should be strong, and capable 
 of being worked in the easiest possible manner, for a fireman's chief 
 tool is his shovel. Besides, on account of the heat, anything belong- 
 ing to a fire door cannot well be touched by hand. One way of 
 keeping the doors open is to balance them by either weights or springs, 
 but with most of these arrangements the ashpit gets closed during 
 firing, whereby that part of the air supply which passes through the 
 fuel is lessened, and that which passes through the door increased, 
 doing harm where it chills the various plates. 
 
 Door Frames suffer in the same way as the doors to which they 
 are attached, unless they too are properly protected from the heat, 
 either by baffle plates with air admissions at the back, or more gene- 
 rally by firebricks. It is never good to make the door frame in one 
 piece, as it is sure to crack. With large furnaces, of 40 ins. diameter 
 and above, two doors are sometimes fitted. Attempts have also been 
 made to fit feed heaters at these points, but evidently without success. 
 
 Fire Bars, It cannot be said that this subject has been neglected 
 by inventors, for the patents in connection with it are innumerable ; 
 but it is certainly very unsatisfactory that, after trying various novel- 
 ties, engineers always fall back on the old pattern, viz. length 2^ to 4 ft., 
 air spaces \ to J in., depth 3J to 5 ins., and thickness J to 1 in. at 
 top, tapering 1 to 1| in. per foot of depth. Even for forced draught, 
 if not excessive, the above dimensions give good results, although the 
 Admiralty, who use wrought iron or steel instead of cast iron, make 
 the bars about f in. thick, while the air spaces are reduced to f and 
 even J in. 
 
 It has been argued that by reducing the upper surface of the bars 
 a smaller area is exposed to the heat of the fire, and that such bars 
 will keep cooler ; but a glance under the grate of a furnace is suffi- 
 cient to convince anybody that as much if not more heat is received 
 by radiation by the sides of the bars as by their upper surfaces. A 
 closer examination will also show that each bar is surrounded by a 
 visible layer of trembling hot air, which is moving upwards and seems 
 to be about -fa in. thick. It is the heating of this thin film of air 
 which keeps the bars cool. These facts might lead to the conclusion 
 that a distinct advantage would be* gained by reducing the thickness 
 of each bar, and fitting more of them, because thereby relatively more 
 cooling surface is obtained. But if, as seems necessary, the air 
 spaces are left as wide as before, each bar will receive an extra 
 amount of heat, so that the thin bars will probably grow quite as hot 
 as the thick ones, and if that is the case they are at a great dis- 
 advantage, for being thin they are sure to get bent sideways. In 
 fact, the only way to use them is to pack them tightly into the 
 furnace, so that they can neither bend nor twist. 
 
 Where great trouble is experienced water in trays is placed in the 
 ashpits. This seems capable of abstracting sufficient heat, but the 
 air channels under the bars are seriously reduced, and salt water in 
 the furnaces is not a desirable object, as it causes corrosion, though 
 on forced-draught trial trips it is often necessary to spray sea 
 water into the ashpits. No doubt the accumulation of ashes and 
 red-hot small coal in the ashpits keeps the bars hotter than they 
 should be, and, as they also seriously interfere with the draught, it 
 
BOILER MANAGEMENT 
 
 would be a great advantage if means could be devised for removing 
 them. Steam blasts are used ashore to keep the bars cool. 
 
 Another plan for keeping the bars cool is to make them deeper. 
 Heat travels so very quickly in metals that the small extra distance 
 which it has to go before reaching the lower edge hardly affects the 
 result, which, roughly stated, is, that the temperature of the bars is 
 inversely proportional to their depths, or more correctly to their ex- 
 posed surface, and that their rigidity (horizontally) is proportional to 
 their depth and to the square of their thicknesses. The horizontal 
 deflection of a bar, to which a definite curvature has been given, is 
 proportional to the square of its length. These views lead to the 
 following formulae, with whose help the small table has been com- 
 piled. If not numerically correct, it can at least be used for making 
 comparisons. 
 
 I. For a given coal consumption, and for a given length of fire 
 bar, the sum of the sectional areas of the bars contained within 12 ins. 
 of the furnace diameter should be a constant value. 
 
 n.t.d. = C,. 
 
 II. For a given coal consumption the sum of the sectional areas 
 of the bars contained within 12 ins. of the furnace diameter should be 
 proportional to their lengths. 
 
 n.t.d. = C 2 .Z. 
 
 III. For equal lengths of fire bars the square of their depths should 
 be proportional to the weight of fuel burnt per square foot per hour. 
 
 d*. = 0,.Q. 
 
 In the above formulas the various letters have the following 
 meanings : 
 
 n stands for number of fire bars per foot of furnace diameter. 
 
 t stands for thickness of fire bars at their upper edges. 
 
 d stands for depth of fire bars at their centres. 
 
 I stands for length of fire bars. 
 
 GI, C 2 , C 3 are constants. 
 
 Q is consumption of coal per square foot per hour. 
 
 Values of the Products n.t.d. (This is the Sum of the Sectional 
 Areas in Square Indies of Cast-Iron Fire Bars per Foot of 
 Furnace, Diameter.) 
 
 Coal Consumption per Sq. Ft. of Grate per Hour 
 
 201bs. 
 
 401bs. 
 
 SOlbs. 
 
 100 Ibs. 
 
 Length of fire bars = 6 ft. 
 
 72 
 
 100 
 
 
 
 
 
 5ft. 
 
 40 
 
 55 
 
 80 
 
 100 
 
 4ft. 
 
 32 
 
 45 
 
 64 
 
 80 
 
 3ft. 
 
 24 
 
 34 
 
 48 
 
 60 
 
 2 ft. 6 ins. 
 
 20 
 
 28 
 
 40 
 
 50 
 
 2 ft. 
 
 16 
 
 24 
 
 32 
 
 40 
 
 1 ft. 6 ins. 
 
 12 
 
 17 
 
 24 
 
 30 
 
 With bars whose air spaces are one-half of their thickness i.e. 
 4 ins. per foot of furnace front the depths would be found by dividing 
 any of the numbers in the table by 8 ins. Thus, with bars 2 ft. 
 
10 BOILEK MANAGEMENT 
 
 6 ins. long, burning 40 Ibs. per hour, the number is 28, and the mini- 
 mum depths of such bars would be 3^ ins., while the thickness might 
 be made | in., with f -in. air spaces, or \ in. with J-in. air spaces. 
 
 In cases of forced draught these two values are very often equal 
 say | -in. bars and f -in. air spaces. To obtain the depth in their case, 
 the number in the table would have to be divided by 6 ins., so that 
 with a consumption of 40 Ibs. the 2 ft. 6 in. bars would have to be 
 4 ins. deep, and 18-in. bars would have to be 3 ins. deep. 
 
 Naturally these values are only approximate, and depend very 
 much on the fuel, but they may serve as a guide when making altera- 
 tions. 
 
 Furnace Diameters. It will be noticed that as soon as the usual 
 practice is departed from, either by increasing the length of bars or 
 the coal consumption, then their depth grows so great that it seriously 
 interferes with the draught. This influence is particularly noticeable 
 in boilers with small furnaces. Compare, for instance, two flues, the 
 one being 33 ins. in diameter and the other 48 ins. If, as is usual, the 
 lines of the dead plates pass through their centres, then the sectional 
 areas below and above these lines are 3 sq. ft. in the one furnace and 
 6'3 sq. ft. in the other. With five bars which are 3 ins. deep, the 
 ashpit areas are reduced to 2*3 and 5*3 sq. ft. respectively, or *85 and 
 1'33 sq. ft. per foot of furnace front. Under ordinary conditions this 
 means that in the one case the air entering the furnace has to travel 
 with a velocity of 12 ft. per second, in the other case its velocity is 
 only ?TJ ft., and the resistances would be as 3 to 1. An extra inch 
 added to the depth of the bars would increase the one resistance 25%, 
 and the other only about 6%, so that in cases where the performance 
 is low there is much less chance of efficient alterations if the furnaces 
 are small than if they are large. 
 
 The sum of the air spaces between the fire bars usually amounts to 
 33% of the width of the grate, so that if the length is 5 ft. we have 
 If sq. ft. of air passage for every foot of furnace front. This being 
 about twice as large as the ashpit area of the small furnace, little 
 improvement would be effected in the draught and combustion of the 
 small furnace by giving wider air spaces, for the depth of the bars 
 would also have to be increased, whereas in the large furnace, where 
 the ashpit area is sufficient, the alteration might increase the com- 
 bustion. 
 
 On trial trips, and whenever it is desired to obtain the highest per- 
 formances, the ashpits should be kept clear of ashes at all times, for 
 every inch of piled-up material restricts the draught. Ash ejectors 
 might be used with advantage. 
 
 With forced draught the case is different. Except on such trial trips, 
 where the air pressure is limited, there is practically no restriction as to 
 the pressure which may be applied, and all the above reasons for allow- 
 ing large air spaces fall to the ground, and there seem to be no objec- 
 tions against reducing them to the very narrowest limits. In fact, 
 very good results are said to have been obtained in some foreign vessels 
 where the air spaces have been reduced to Jg in. and a high-pressure 
 blast introduced into the ashpits. The necessity for opening the 
 lower doors to remove the ashes does not exist, for none can fall 
 
MANAGEMENT 
 
 11 
 
 through ; they are all fused and form clinker on the bars. Of course 
 such bars could not be used for natural draught ; but natural draught 
 in the Navy is simply another name for a very low fan pressure, which 
 could be increased if* desired. 
 
 . FIG. 8 
 
 FIG. 9 
 
 The following advantages should not be overlooked : By reducing 
 the air spaces till they are mere slits, the chief resistance to the air 
 passage is found at these points and not in the fuel, and the draught 
 will hardly be affected by considerable variations of thickness of the 
 fires. The chief combustion takes place just over the slits, and little, 
 if any, over the centre of the bars, which remain covered with compara- 
 tively cool fuel or ashes, and are therefore not exposed to so much 
 heat as the narrower bars with wide air spaces. An attempt to indi- 
 cate this difference is shown in figs. 8 and 9. 
 
 The Burning of Fire Bars is often the consequence of irregularities 
 in the upper surface of the grate. It is but natural that if several air 
 spaces are blocked (fig. 10), either by clinker or when the bars are 
 bent, then the air can cool only one side of such bars, and these must 
 grow hotter than the others. If, in addition, fuel should get wedged 
 into the wide space, nothing will prevent the corners of the bar from 
 burning, and as these waste away the fuel sinks lower and lower, and 
 it is only a question of time as to when it will have effected the 
 destruction of the bars ; naturally the adjoining ones, which are then 
 exposed to the same action, will suffer in the same way. 
 
 FIG. 10 FIG. 11 
 
 An examination of the grates of a boiler which has been worked 
 hard will show that the bars have all sagged more or less, and that 
 some are bent sideways, but that the upper edges are all uniformly 
 wasted away, presenting a regular surface. On removing and then 
 replacing them this condition is entirely altered. Possibly bars from 
 the sides have got placed near the centre, and vice versd, and a section 
 across the grate might have the appearance of fig. 11, with the 
 
12 BOILEtl MANAGEMENT 
 
 inevitable result that the tops of the projecting bars would be quickly 
 burnt away. Possibly this may lead to the worst ones falling out, 
 but at any rate the bars will generally be more quickly wasted if 
 placed together in this manner than if kept level. Where the grate 
 is made up of two lengths, it is always best to place any new bars at 
 the back end. 
 
 Ashes and Clinker. Another great trouble, and one which, like all 
 others, is aggravated under the conditions of forced draught, is the 
 accumulation of clinker on the grate. Each ton of coal contains from 
 j cwt. to 3 cwt. of ashes, according to the quality, and although a 
 portion drops into the ashpit, a considerable part remains on the grate. 
 It also depends upon the nature of the fire and on the composition of 
 the ashes whether much say f is blown up the funnel, or whether 
 only a small quantity say 25% is disposed of in this way. If the 
 fires are dull and the ashes refractory the latter remain dust and are 
 carried away ; but if they melt easily, or if the fire is a fierce one, 
 they form clinker, w T hich remains. 
 
 The following minerals are found in ashes of coal : 
 
 Silicic acid from 2% to 60% 
 
 Calcic oxide 1 20 
 
 Ferric 15 75 
 
 Alumina 2 ,,40 
 
 The most refractory ashes are those containing the smallest quan- 
 tities of silicic acid, and the most fusible those where it amounts to 
 about 50%, with 25% calcic oxide. If the alkalies were absent the 
 ashes would remain dust under the most trying circumstances. Salt 
 increases the fusibility of clinker, and the hydrochloric acid, which it 
 loses while melting, is a very active corrosive agent and injurious to 
 the boiler plates. Sea water should, therefore, not be mixed with the 
 coal, and leakages in the furnaces and combustion chambers should be 
 prevented as much as possible. 
 
 Two qualities of coal, whose respective ashes are fairly refractory, 
 will occasionally produce very fusible clinker, if used together. In 
 such cases the one probably contains an excess of silica, and the other 
 an excess of the other ingredients. The melting away of the firebricks 
 of the bridges is sometimes due to the great heat, but more often to 
 an excess of the alkalies in the clinker. They readily attack the silicic 
 acid, which is the chief constituent of the firebricks. Basic bricks 
 would not suffer under these circumstances, but cannot be used at sea, 
 as they readily absorb moisture when out of use, and then fall to pieces. 
 
 Cinders. When the ashes, which have not been blown away, melt, 
 they trickle down the sides of the partly consumed small pieces of coke, 
 and by glazing them prevent their quick combustion. This may be a 
 slight advantage, as the point of highest temperature of the fire (see 
 fig. 105, p. 97) is thereby raised a little above the grate surface. When 
 these small pieces of fuel ultimately find themselves over an air space 
 between two bars, they drop through and are wasted ; those which, at 
 the end of their downward motion, arrive on the top of a bar are con- 
 sumed there ; therefore, if a sufficient amount of forced draught is avail- 
 able, it would be more economical to reduce the air spaces to the smallest 
 possible dimensions. 
 
BOILER MANAGEMENT 
 
 13 
 
 Clinker. The slag which had adhered to the small coal is now 
 resting on the fire bars, and congeals, or at any rate its lower part, as 
 well as its extremities where it is in contact with the comparatively 
 cool air. 
 
 As more and more slag is added, troughs of thick slag are formed, 
 whose edges project over the air spaces and gradually close them (fig. 
 12), seriously interfering with the draught and combustion. With 
 worn bars (rounded tops) the closing is effected more quickly, as the 
 
 FIG. 12 
 
 FIG. 13 
 
 FIG. 14 
 
 slag trickles down the sides (fig. 13) ; and the very fact that this 
 happens is a sign that the bars are equally hot ; and this is not to be 
 wondered at, for the slag is sure to be very thin on the top, affording 
 no protection from the heat, and is very thick at the sides, preventing 
 the cold air from cooling the bars. 
 
 The necessity for guarding against this trouble has in 
 America been the cause of the adoption of fire bars with 
 hollow tops (fig. 14). The channels are soon filled with 
 ashes or clinker, and it is only their two edges which 
 absorb heat from the fire. It is stated that these fire bars, 
 which are easily cast if the pattern is made in two halves, 
 have a longer life than the ordinary ones, and also that the 
 clinker does not adhere to them so firmly. 
 
 When fires have been burning for twenty-four hours 
 they will be thoroughly dirty, the weight of mineral matter 
 resting on one square foot of grate surface amounting to from 10 to 
 40 Ibs.. or from f to 3 ins. in thickness. Of course the air spaces can 
 then only be kept open by frequently using the slicer and pricker 
 (figs. 17 and 19), but much can be done to break up the slag, which 
 adheres to the bars, by moving them as indi- 
 cated in fig. 15 ; this is only possible if they 
 are very loosely packed, and it is customary to 
 fit one bar less than the number which might 
 possibly be got into a furnace diameter. 
 They should be supported at the highest 
 possible point, so that the air spaces at the top 
 are not altered, but only the angles. 
 
 In order to allow for longitudinal expansion of the fire bars, one end, 
 where they rest on the dead plate, should be made slanting. If there 
 are two lengths, the other slant should rest on the bridge plate (fig. 16). 
 Any bodily motion is prevented by notching the other end of each bar 
 where it rests on the cross bar. 
 
14 BOILEE MANAGEMENT 
 
 If the lengths exceed 3 feet, small distance pieces, A, are cast on 
 at the centres ; they prevent excessive distortions. The bars are 
 also made decidedly taper, 1 in. to 1| in. per foot of depth, so that 
 the fuel cannot be jammed between them, which would certainly 
 happen if they were parallel and loosely fitted. The navy fire bars, 
 which are made parallel, have therefore to be packed tight. 
 
 FIG. 16 
 
 Replacing Fire Bars. In spite of all these precautions it will 
 happen that fire bars burn, or under forced draught a whole grate may 
 sometimes drop into the ashpit ; but this only happens when a large 
 amount of red-hot ashes has accumulated there. Nothing can then 
 be done but to clear out the furnace and rebuild the grate. When 
 only one or two bars have dropped out, these can be replaced by new 
 ones without drawing the fires. At the front end this is an easy 
 matter, and some men are even sufficiently skilled to be able to throw 
 a fire bar into its right position at the back of a grate ; but the safer 
 plan is to tie it to a slicer, and then to place it in position. The yarn 
 will very soon be burnt, and the slicer can then be withdrawn. 
 Wrought-iron and steel fire bars, with their high melting temperatures, 
 are said to last longer than cast-iron ones, but it is at present difficult 
 to obtain them of a taper section, as very few rolling mills produce it, 
 so that a large spare stock would have to be carried. Secondly, it is 
 difficult, or rather expensive, to thicken the ends, though it would seem 
 that with a suitable die and a steam hammer the problem could be 
 readily solved. The plan has been successfully tried of notching the 
 dead plate, bridge plate, and the cross bars, and using fire bars without 
 thickened ends. In this case the air spaces cannot be kept equal at 
 the upper edges, unless all parts are firmly fixed, which has already 
 been shown to lead to trouble. 
 
 Cleaning Fires is one of those operations which, although neces- 
 sary for the working, may cause a good deal of damage. Leakages in 
 the combustion chambers are often attributed to the rush of cold air 
 while the door is open and the grate bare. To close the funnel damper 
 seriously interferes with the generation of steam from the other 
 furnaces, and some ships have therefore been fitted with separate 
 dampers over each nest of tubes (see fig. 30, p. 19), and the results 
 are said to be satisfactory. 
 
 Another plan is to clean only half a fire at a time : one side of the 
 fire is allowed to burn down, the clinker and ashes are raked out, and 
 the bare bars covered with green coal, which is ignited by the fire at 
 the other side, which, after a time, is treated in the same way. On 
 account of the double operation firemen are not fond of this plan. 
 
 Another plan, which, to a certain extent, is indulged in by every 
 fireman when burning caking coal, is to draw the clinker forward with 
 
BOILER MANAGEMENT 15 
 
 a heavy rake (fig. 18) about one or two feet between each firing, taking 
 
 FIG. 17 
 
 PIG. 18 
 
 FIG. 19 
 
 particular care to throw the green coal on those parts of the grate 
 which have been bared. The clinker should not be allowed to get 
 cool, otherwise it will be difficult to loosen it from the bars, which is 
 done with the slicer (fig. 17). 
 
 Removal of Ashes. Having got the ashes out of the furnaces, they 
 naturally fall against the boiler, and are there slaked with sea \Yater. 
 The noxious vapours which escape are an indication that corrosive 
 acids are being generated, and it is only too well established that the 
 most serious wasting to which the external parts of a boiler are sub- 
 jected takes place here. Far better arrangements than those usually 
 adopted should be made for preventing the ashes from resting against 
 the boiler plates, or from getting into the narrow crevices which are 
 found here. Besides cementing the inside of the end seams of boilers, 
 it would not be amiss to cement the outsides as well where this cor- 
 rosive action may be expected. When guard plates are fitted, DO 
 spaces should be allowed where ashes and moisture could find a 
 lodgment. 
 
 Occasional efforts have been made to remove the ashes out of the 
 stokehold by means of ejectors, and although successful for this 
 purpose they quickly corrode, but other mechanical contrivances 
 might be tried. 
 
 The amount of ashes to be dealt with in twenty-four hours can be 
 roughly estimated as equal to the amount of mineral matter in the 
 coal burnt during that time. 
 
 Mechanical Stokers. It is unnecessary to make any remarks 
 about mechanical stokers, as every one that has yet been tried at sea 
 has been given up ; but for those who wish to study the subject the 
 following references may be of value : 
 
 J. Daglish, ' M. E.,' 1868, p. 155, mentions Stanley's and Vicar's 
 patents. J. F. Spencer, C. E.,' 1891, vol. civ. p. 54, mentions about 
 
16 
 
 BOILER MANAGEMENT 
 
 a dozen different systems. F. Colyer, 1886, also mentions several. 
 New types are perpetually appearing. Chain grates are now very 
 common for watertube boilers. 
 
 Banked Fires. An interesting table, containing the amount of coal 
 consumed under banked fires, will be found in C. Busley's work, 1883, 
 p. 157, from which it appears that from two to 
 three cwt. per furnace are consumed in twenty- 
 four hours, and that the quantity required to 
 raise steam is slightly less than this amount. 
 He does not mention whether the fires were 
 shoved back or drawn forward. The former is 
 the more correct method, because it chokes the 
 bridges, and the little air which passes there is 
 hot ; but, as the dampers can never be closed 
 sufficiently, more heat would be developed than 
 is required to maintain steam, and the more 
 general practice is to draw the fires forward, and 
 to leave the bars bare at the back. Much cold 
 air is thus admitted, which keeps down the 
 steam and reduces the draught. Of course, the 
 boilers suffer injury under both treatments, but 
 particularly under the last-mentioned one. 
 
 When the engines have to be stopped without 
 previous warning, the dampers are at once closed 
 and the smoke-box doors opened : or (but this 
 should not be allowed) all the furnace doors are 
 thrown open. This is certainly a very effective 
 means of reducing the heat of the fires, but the 
 cold inrush of air may easily cause leakage. 
 Should the steam still be rising fast the supple- 
 mentary feed should be turned on before the 
 safety valves lift. 
 
 Sweeping Tubes. On account of the soot, 
 which adheres to the tops and sides of the tubes, 
 and the ashes, which settle along their bottoms, 
 it is necessary to sweep them about once a week. 
 Wire brushes (fig. 20) are used for the soot and 
 ashes, and the split scrapers (fig. 21) to remove 
 salt. The latter tool is of little use at sea, 
 because a tube which is once plugged up with 
 salt closes up again after half an hour's steaming, 
 and need therefore not have been cleaned. The 
 brush should be strong enough to remove all the 
 are hinged at their centres for convenience of 
 handling. The sweepings of each tube naturally fall into the combus- 
 tion chamber, but the draught at once carries the greater part into 
 the adjoining tubes and up the funnel. In order not to get smothered 
 the firemen keep the damper open, and very light fires on the grates, 
 just sufficient to produce a draught. Except in large steamers, or in 
 vessels fitted with several funnels, it is usual to clean the tubes of all 
 the boilers at one operation, the whole watch being sent below for the 
 purpose ; for, as the draught is nearly non-existing during this time, 
 
 O 
 
 FIG. 20 FIG. 21 
 dust. These tools 
 
J30ILER 
 
 17 
 
 little steam can be generated, and the sooner the operation is 
 completed the better. 
 
 The efficiency of a boiler is seriously affected by accumulation of 
 soot on the heating surfaces, so much so that all land economisers 
 are fitted with scrapers which are constantly moved up and down 
 the tubes by machinery. It is found that whenever this motion 
 
 FIG. 23 
 
 FIG. 24 
 
 ceases the efficiency of the economisers is much reduced. If a 
 similar device could be introduced for the constant sweeping of boiler 
 tubes, the efficiency of the tube surface would be increased, and the 
 sizes of boilers might be reduced. Economisers probably suffer more 
 in this respect than boiler tubes would do, because they contain cold 
 water and are therefore likely to condense the tarry products of 
 combustion. 
 
 Eecently attempts have been made to clean the tubes by means 
 of steam jets which are manipulated 
 from the back ends of boilers if 
 single ended. 
 
 Soot is also a great inconvenience 
 to water-tube boilers, and may one 
 day lead to similar appliances being 
 employed on them : at present their 
 tubes are mostly cleaned by steam 
 blasts, which can of course only re- 
 move the loose soot, whereas it is 
 believed that the hard tarry deposit 
 nearest the metal is a most efficient 
 non-conductor. 
 
 Furnace Bridges. The object of 
 fitting bridges in furnaces is partly 
 to keep the fuel from falling into 
 combustion chambers, and partly 
 to reduce the air channel, so that, by imparting a momentarily high 
 velocity to the flame, a thorough mixture of its gases is effected, 
 and the combustion completed. Brick fire-bridges are arranged as 
 
 c 
 
 FIG. 25 
 
18 
 
 BOILER MANAGEMENT 
 
 shown in figs. 23-26. The space at the back of the bridge shown in 
 fig. 23 is usually quite full of ashes, even though a door is fitted at 
 the bottom by which they could be removed. 
 
 The heat which the firebricks collect may occasionally do a con- 
 siderable amount of harm to the plates against which they rest if, as 
 sometimes happens, the water is let out of the boiler before it is cold. 
 
 FIG. 26 
 
 but 
 
 Viewed from the front, the bricks are generally placed horizontally ; 
 
 where much trouble is experienced by their falling out of place, 
 which happens when clinkers are allowed to adhere to them and have 
 to be broken, or when the fires are forced, or when the furnaces are 
 large, the bricks are sometimes arranged in the form of an inverted 
 arch (fig. 27). In double-ended boilers, with through combustion 
 
 FIG. 27 
 
 FIG. 28 
 
 FIG. 29 
 
 chambers, the same plan has been tried on the central partition wall ; 
 but no advantage seems to have been gained, and where it is desired 
 to carry the wall high up, it is safer to bolt two angle irons down the 
 sides of the combustion chamber. 
 
 In cases where the furnace saddles have been cropped, or where 
 the tube plate has been flanged to meet the furnace, exposing the back 
 end seam to the direct action of the flames, it is sometimes necessary 
 to protect it by a firebrick arch (fig. 28). Here, too, it is an advantage 
 if the bridge is curved, as it gives a better support to the arch. (See 
 fig. 29.) 
 
BOILER MANAGEMENT 
 
 19 
 
 Dampers. One damper is usually fitted to each funnel, rarely one 
 damper to each boiler, and still more rarely one damper to each 
 furnace, but damper plates are provided for each ashpit. Ashore a 
 pair of dampers is always fitted to each boiler, so that the air admis- 
 sion over the bars is reduced to a minimum during the cleaning of 
 fires. With closed stokeholds the inrush of air during these cleaning 
 periods is very great, and in many cases an arrangement similar to 
 that shown in fig. 30 would be an advantage. 
 
 If forced draught is used with closed ashpits, dampers are not 
 necessary, for the suction above the bars is not always equal to the 
 pressure which is transmitted from below. In fact, when firing, it is 
 customary to restrict the blast, because otherwise so much gas is 
 generated that the funnel draught is unable to carry it off, and the 
 fumes would enter the stokehold. 
 
 FIG. 30 
 
 Flames in Stokeholds. The most series mishaps may be caused if 
 steam is suddenly generated in the combustion chambers, which is a 
 powerful reason why fusible plugs should not be fitted. With some 
 boilers in the Navy sad loss of life has several times been caused by 
 sudden leakages of the back ends of the tubes. It has been suggested 
 that this happened with H.M.S. { Barracouta, ' but a similar effect 
 might be produced by stopping the fan in one of the stokeholds, the 
 flames being at once driven into it over the bridge by the fan in the 
 other stokehold, while the funnel is unable to draw them away. The 
 difference of pressure would no doubt be increased by men anxious to 
 render assistance blocking the stokehold passages. Similar accidents 
 have also happened in single-ended and in navy-type boilers, in which 
 this action is impossible. 
 
 Alternate Heating and Cooling of Plates. Very exhaustive and 
 interesting experiments on this subject were made by E. Wehrenfennig 
 (' Organ/ 1884, vol. xxi. p. 216, &c.). He found that heating various 
 metals and cooling them had certain effects, which were reproduced 
 on repeating the experiment, and which were intensified the longer 
 the heating lasted and the higher the temperatures. His limits were 
 boiling water and red heat. (See p. 30.) 
 
 OS 
 
20 
 
 BOILER MANAGEMENT 
 
 His results are that steel and iron bars and plates shorten, but 
 grow thicker if heated and cooled, about -^V/o * rV/o ^ or one red heat. 
 Cast-iron and copper bars and plates lengthen, but grow thinner 
 if heated, say, ^VVo and / respectively. Col. H. Clerk (' Pro- 
 ceedings,' 1863, vol. xii. p. 452) and H. Caron (' Comp. Eend.,' 1863, 
 vol. Ivi. p. 828) arrive at conclusions opposed to the above, but in 
 their cases the cooling was effected suddenly. 
 
 E. Wehrenfennig also refers to experiences in connection with 
 locomotives for instance, that certain fittings grow tighter after a 
 short use if exposed to heat ; that iron nuts cannot be unscrewed 
 from copper stays after heating, but brass nuts can ; that blisters 
 crack on the fire side, being exposed to greater changes of tempera- 
 
 ture ; that rivet holes of seams in 
 iron or steel furnaces crack, in copper 
 plates they do not do so. Possibly 
 his most interesting fact is that a land 
 boiler contracted so much in length 
 that this led to various troubles about 
 the fittings. On the other hand, land 
 boiler furnaces slowly lengthen, some- 
 times as much as J inch in 30 ft. 
 
 The same thing evidently happens 
 with the through combustion cham- 
 bers of double-ended boilers, and cases 
 have repeatedly occurred where, on removing the rivets in the cir- 
 cumferential furnace seams, the holes were found to be somewhat 
 
 87 
 
 FIG. 38 
 
 FIG. 39 
 
 blind, although drilled in place, and then, having been rimered fair 
 and re-riveted, they soon grew as blind as before. 
 
 Even flanged furnace saddle seams show the same wandering of 
 rivet holes, but, for fear that this statement might be used to shield 
 bad workmanship, it is as well to point out that in all such cases 
 
BOILER MANAGEMENT 
 
 21 
 
 there is a regularity in the blindness of the holes which does not 
 exist if the holes were drilled carelessly out of place. 
 
 Pio. 40 
 
 FIG. 41 
 
 It has been suggested that the cracking of rivet holes is caused 
 by the carbonising of the iron and steel, 
 due to their contact with fuel or hydro- 
 carbons of the gases ; but as an addition 
 of carbon increases the volume of the 
 metal, it is difficult to see how this can 
 set up any tension stresses. Eecent ex- 
 periences suggest that these cracks are 
 more likely to occur in steels rich in 
 phosphorus and nitrogen than in purer 
 ones. The four accompanying sketches 
 show cracks as they occur under palm 
 stays (fig. 37), in the flat parts of com- 
 bustion chamber backs when covered 
 with scale (fig. 39), in combustion chamber back plate seams (fig. 38), 
 and in furnace saddle seams (fig. 40). 
 
 FIG. 42 
 
 FIG. 43 FIG. 44 FIG. 45 
 
 Deterioration of Materials. That this cracking of rivet holes is 
 due more to the heat than to the impinging action of the flame, is 
 
22 
 
 BOILEE MANAGEMENT 
 
 shown by the fact that the joint of the tube plate with the furnace 
 saddle does not give trouble if kept out of the fire, even though, as in 
 fig. 41, the landing is exposed to the impact of the flame, while joints 
 which are removed from this action by the depth of a furnace corruga- 
 tion (fig. 42) suffer. Cracks like those shown in figs. 43 and 44 are 
 due to severe alternating strains. 
 
 Seams in Furnaces. Kiveted joints should not be exposed to 
 the direct action of the flame. Where this cannot be helped, as in 
 
 FIG. 46 
 
 the case of patches, the greatest care should be taken to keep the 
 seams cool. Scale ought not to be allowed to accumulate there, and 
 the two plates should, if possible, be brought into metallic contact, by 
 removing the black scale, by thoroughly washing away the oil used 
 for drilling (for this is one of the worst conductors of heat), and by 
 fitting and bolting the plates so firmly together during riveting that 
 caulking is almost superfluous. It is perhaps due to the more per- 
 fect contact between the plates that double-riveted seams behave 
 better than single-riveted ones when exposed to the direction of the 
 flame. 
 
 Experience has shown that for furnace saddle seams all these 
 precautions are unavailing under the action of forced draught, and it 
 has been found that when they must be repaired in this way, instead 
 of using countersunk rivets, very large snap-headed ones should be 
 fitted (fig. 46), with the object of reducing the exposed surface of the 
 outer landing as much as possible, and at the same time carrying off 
 all the heat through the rivets into the water. (See p. 120.) Seaton 
 quotes Wye Williams, ' N.A.,' 1894, v. 35, p. 284, as having fitted 6- 
 inch studs through his furnace plates, and found that the fire ends 
 burnt off to a length of 2^ inches, so that the much shorter rivet heads 
 can take no harm. 
 
 Whenever possible, patches should be fitted on the fire sides of 
 defective plates, so that when the rivet holes crack, as shown in fig. 
 
 FIG. 47 
 
 47, it will not be necessary to cut out more material and fit a larger 
 patch, as shown in dotted lines, when a renewal is necessary. 
 
BOILER MANAGEMENT 
 
 23 
 
 Cracked Rivet Holes. One of the chief causes of these rivet holes 
 cracking is scale, and whenever possible it should be removed from 
 these patches. In the chapter on ' Heat Transmission ' explanations 
 will be found why the general efficiency of a boiler is not seriously 
 affected by accumulations of scale, but that this substance will cause 
 a considerable rise in the temperature of the plates it covers, which 
 leads, as has just been explained, to cracking or to other troubles, 
 such as leaky tubes and collapsed flues. The idea that scale prevents 
 corrosion may still prevail, and may even be a true one ; but the more 
 rational view, that there are other and better means of stopping this 
 waste, is gaining ground, and evaporators, for the supply of distilled 
 water, are coming more and more into use. The removal of one evil 
 often produces another, and recently much damage has been done 
 when using fresh water by oil deposits, which, like all scales and 
 other non-conductors, effect a considerable rise in the temperature of 
 the plates they cover. This necessitates the addition of oil niters, 
 which are inserted between the pumps and the boilers. A description 
 of one of these, together with numerous facts and analyses of boiler 
 deposits, will be found in a paper read by Mr. Edminston, ' N. E. C. I.,' 
 1892, vol. viii. 
 
 Eecently the design of these niters has been much modified, and 
 very favourable results are being obtained by means of appliances 
 which separate the grease from the steam. 
 
 Boiler Scale. Sea-water should not get into a marine boiler, but 
 when it does enter, either by accident or intentionally to form a protect- 
 ing scale, it meets with grease and iron rust, its own production, and 
 the result is scale and deposit. Professor V. Lewis, ' N.A.,' 1891, v. 32, 
 p. 67, deals with such a case, and gives analyses of scale from various 
 parts ; these have been recalculated in terms of sulphate of lime 
 calcic sulphate. 
 
 Position of Scale or Deposit 
 
 Scale. 
 Furnace 
 Top 
 
 Scale. 
 Furnace 
 Bottom 
 
 Scale. 
 Tubes 
 
 Deposit 
 Tubes 
 
 Deposit 
 Boiler 
 Bottom 
 
 Calcic sulphate 
 
 100-0 
 
 100-0 
 
 100-0 
 
 100-0 
 
 100-0 
 
 Calcic carbonate 
 
 6-9 
 
 10-2 
 
 8-2 
 
 7-0 
 
 o-o 
 
 Magnesic hydrate 
 
 3-3 
 
 19-1 
 
 27-7 
 
 193-0 
 
 31-4 
 
 Iron, alum, &c. 
 
 2-8 
 
 4-8 
 
 14-7 
 
 78-6 
 
 155-0 
 
 Organic matter. Oil 
 
 3-8 
 
 33-1 
 
 41-4 
 
 433-0 
 
 124-2 
 
 Moisture 
 
 0-9 
 
 1-9 
 
 2-2 
 
 36-8 
 
 25-7 
 
 Alkalies . 
 
 o-o 
 
 o-o 
 
 2-0 
 
 155 
 
 8-0 
 
 It will at once be seen that the composition of the scale depends 
 largely on the position from which it has been taken. Thus, for some 
 reason or other, calcic carbonate is not found in the deposits on the 
 boiler bottom, while grease is found chiefly in the deposits on the tubes, 
 showing that it has a buoyant effect on the constituents to which it 
 attaches itself. It seems to have most affinity for magnesic hydrate and 
 also much affinity for iron rust. When the latter predominates the 
 compound is so heavy that it sinks to the boiler bottom ; when magnesia 
 is in excess a deposit is formed on the tubes.. Magnesic hydrate, as 
 
24 BOILER MANAGEMENT 
 
 is well known, is the very dangerous deposit known as ' floury deposit,' 
 and is generally due to an excess of alkalies, which, as will be seen, 
 seem to accompany the magnesia in a fairly constant proportion. The 
 buoyant action of the grease shows itself in the scale on the furnace 
 bottom and on the tubes. It is strange that there is so little grease on 
 the furnace top possibly heat has driven it away; but then, one 
 would expect to find an excess of magnesia. 
 
 The Effect of Scale, It is generally believed that scale causes 
 collapses and bulges simply because it is a bad heat conductor ; but 
 a recent experience (' M. S. U. A.,' 1899, p. 6) throws some unexpected 
 light on this subject. An accident is there described in which a 
 furnace collapsed and rent although the scale was intact over the 
 bulged part. Near the rent there was another bulge which could 
 only be seen from the fire side ; on the water side it was covered by an 
 intact sheet of scale about -f in. thick. The hollow space between the 
 scale and the bulged plate must, while the boiler was at work, have 
 been filled with superheated steam, which of course is an excellent 
 non-conductor of heat. When once the plate separated from the 
 scale the hollow thus formed would effectually shield the plate from 
 the cooling contact with water, and it would grow red hot and bulge. 
 This experience suggests that hard scale is more dangerous than soft 
 scale, also that irregular working of boilers, which, on account of 
 changes of temperature, would cause the hard scale to separate from 
 the iron plate, should be avoided ; and further, that a boiler which 
 has once been emptied of water should not be refilled before at least 
 all loose scale has been removed. The suggestion that hard scale 
 may be more dangerous than soft scale derives additional support 
 from another accident to a boiler, whose furnace crowns were covered 
 2 inches deep with a thick muddy deposit ; the sides were of course 
 bare, yet it was the sides which collapsed when the water grew too 
 dense through salt. 
 
 Sea Water. A most elaborate series of chemical analyses of sea 
 water has been carried out by Prof. W. Dittmar for the ' Challenger ' 
 Beport; see article Sea Water, ' Encycl. Brit.,' 9th edition, v. xxi., 
 p. 611, from which it appears that sea water consists of 
 
 Chloride of Sodium 
 Chloride of Magnesium 
 Sulphate of Magnesia . 
 Sulphate of Lime . 
 Sulphate of Potash 
 Bromide of Magnesium 
 Carbonate of Lime 
 
 3-5990 per cent. 
 
 5034 
 
 2192 
 
 1666 
 
 1141 
 
 0100 
 
 0160 
 
 Total . . 4-6283 
 
 Sulphate of lime is practically the only constituent of sea water 
 which goes to form boiler scale, as can be seen by referring to the 
 several analyses mentioned above. Oxide of magnesium is present 
 in small quantities, say from 5 to 10 % of the sulphate of lime. The 
 moisture in the scale should of course not be counted, nor the iron 
 rust, which is due to the wasting of the boiler material. It is thus 
 
BOILER MANAGEMENT 
 
 25 
 
 evident that boiler water contains nearly all the sea water salts except 
 the sulphate of lime. These salts are : common salt, chloride of 
 potash and sulphate and chloride of magnesia. The weights of these 
 salts per 1,000 parts of water will be approximately as follows : 
 
 Chloride and Bromide of Sodium and of Potassium about . 36*0 
 
 Magnesium Chloride 5-0 
 
 Magnesium Sulphate 2*2 
 
 Sulphate of Potash ......... 1-1 
 
 Total . . 44-3 
 
 In former days these soluble salts, which were of course being 
 concentrated in the boiler, often led to overheating, and even now 
 with leaky condensers or negligent feeding such accidents sometimes 
 occur. Engineers are generally instructed not to allow their boiler 
 water to exceed -fa, which is about four times the density of sea water ; 
 but salt water does not commence to crystallise until the density when 
 cold exceeds 1-2045 or about f^. As will be seen from the follow- 
 ing table, the amount of salt dissolved by water increases with the 
 temperature, and at 350 F. a not uncommon one in modern boilers 
 the weight of salt in water probably exceeds 57 ounces per gallon, 
 whereas when cold it falls to about 50 ounces. 
 
 The following table has been calculated from Dr. H. Landholt and 
 Dr. E. Bernstein's tables, 1912, p. 485. 
 
 Saltness of Water at Saturation Point 
 
 
 Amount of Salt 
 
 
 Temperature 
 
 Added to 
 Water 
 
 Contained in the Solution 
 
 Density 
 when Gold 
 
 F. 
 
 0. 
 
 % 
 
 % 
 
 Oz. per Gallon 
 
 A 
 
 
 32 
 
 
 
 35-5 
 
 26-2 
 
 50-3 
 
 8-4 
 
 1-2027 
 
 50 
 
 10 
 
 35-8 
 
 23-3 
 
 50-5 
 
 M 
 
 1-2036 
 
 68 
 
 20 
 
 36-0 
 
 26-4 
 
 50-7 
 
 n 
 
 1-2045 
 
 86 
 
 30 
 
 36-3 
 
 26-6 
 
 51-1 
 
 8-5 
 
 
 104 
 
 40 
 
 36-6 
 
 26-8 
 
 51-4 
 
 8-6 
 
 
 122 
 
 50 
 
 37-0 
 
 27-0 
 
 51-8 
 
 
 
 140 
 
 60 
 
 37-2 
 
 27-2 
 
 52-2 
 
 8-7 
 
 
 158 
 
 70 
 
 37-9 
 
 27-4 
 
 52-6 
 
 
 
 176 
 
 80 
 
 38-2 
 
 27-6 
 
 53-0 
 
 8-8 
 
 
 194 
 
 90 
 
 38-8 
 
 27-9 
 
 53-6 
 
 8-9 
 
 
 212 
 
 100 
 
 39-6 
 
 28-3 
 
 54-4 
 
 9-0 
 
 H 
 
 Salt Deposits. The beautiful salt crystals which are found in 
 boilers, in which the density was so great as to cause collapse, are 
 not the cause of the accident ; they have been formed during the 
 period of cooling. The real injury has been done by the dense salt 
 scale, which contains only fine crystals, or still more probably by a 
 local deposit of salt which may have re-dissolved. One case is known 
 in which the furnaces did not collapse nor showed any signs of weak- 
 ness, although covered with large salt crystals about ^ in. cube. The 
 
26 BOILER MANAGEMENT 
 
 density must have exceeded 51 ounces per gallon. This boiler was 
 not worked hard. 
 
 The density as detailed in the above table is not a perfectly correct 
 guide, for boiler water also contains magnesium salts, which add to 
 the density, but which will not crystallise out at almost any tempera- 
 ture ; therefore the percentages given in the table, which refer only to 
 pure salt water, should be multiplied by 44*3 : 36'0 = T23 (see table, 
 p. 25), so that in modern high-pressure boilers the water must, at 
 least locally, contain about 70 ounces of various salts before deposits 
 occur. These remarks are not intended to encourage the use of high- 
 density water, but to enable engineers to fully understand such cases- 
 Collapses have certainly occurred before the density reached even ^, 
 but this may possibly have been the result of purely local deposits of 
 salt, due to hard firing and bad circulation. On standing idle after 
 the accident the salt would dissolve away and leave no evidence 
 except the harm it has done. 
 
 Floury Deposit consists chiefly of magnesia, and is formed in 
 boilers if their waters are treated with caustic soda, generally for the 
 purpose of preventing corrosion. This chemical certainly deposits 
 the chloride of magnesia, and unless it is carefully introduced, and 
 only in small quantities, the danger of a collapse is great. If there 
 is grease in the boiler, the magnesia and the grease and water combine 
 to form a substance of the same density as water, which can and 
 does adhere to any part of the boiler and may cause overheating. 
 See p. 122. 
 
 Grease in Boilers. After the surface condenser came into use, 
 engineers were troubled with furnace collapses, which are now 
 explained as being due to deposits of grease, especially as it is known 
 that grease is a ten times worse conductor of heat than scale ; but even 
 now the subject is a mysterious one, for whenever a furnace does 
 collapse, due to grease in the boiler, the collapsed part never shows 
 any grease at all, and even the other parts of the boiler are generally 
 only covered with sufficient grease to dirty one's clothes, its thickness 
 being probably less than r ^ inch. Seeing that this film disappears 
 from the collapsed parts, the only explanation which at present 
 suggests itself is that at the temperature which exists in a boiler this 
 grease changes its nature and becomes capable of forming tough 
 bubbles wherever the heat is greatest, while either hydro-carbon 
 vapour or super-heated steam is formed between the boiler plate and 
 the skin of the grease bubbles, thus preventing the water from coming 
 in contact with the already red-hot plate and cooling it. One 
 objection to this view is that grease acts in a very positive manner, 
 it being found that if one surface in a boiler has been overheated due 
 to grease, so have the others. In one case nine furnaces in three 
 boilers came down together ; it also seems that the growth of 
 collapses is a slow one, extending sometimes over days and even 
 months. When furnaces collapse due to scale they do this very 
 suddenly, and generally, too, it is only one furnace in a boiler which 
 comes down at a time. 
 
 Grease and Scale, It has been noticed that grease alone is far 
 more dangerous than grease and scale together ; probably the grease 
 adheres so firmly to the scale that it cannot form bubbles. This may 
 
BOILER MANAGEMENT 27 
 
 account for the experience that the furnaces of new boilers have now 
 and then come down, sometimes even on trial trips. In all such 
 cases the cause was grease without scale. On the other hand 
 steamers are running without mishap whose boilers are coated with 
 scale, and in addition with a filthy covering of grease. 
 
 Collapsed Furnaces. One of the greatest mishaps to a boiler which 
 can occur at sea is undoubtedly the collapsing of its furnaces. Gene- 
 rally, but not always, this is due to ignorance or carelessness of the 
 engineer in charge. For instance, it may happen that things have 
 been left in the boiler which, by means of the water circulation, are 
 landed on some plate exposed to the direct action of the flame, and may 
 cause a local bulge, a ludicrous instance being where the head of a 
 dead horse had been put into a Cornish boiler to prevent corrosion, and 
 
 had settled on the furnace crown. 
 With steamers it has happened 
 that while ashore, the supplemen- 
 tary feed which had to be put on 
 carried with it mud, sand, or infu- 
 sorial earth, and this settled on 
 the furnace saddles, or near the 
 upper part of the flanges of 
 v^vy. Adamson's rings. Under specially 
 favourable conditions the bulges 
 which have then been produced 
 were shaped similarly to the sec- 
 tion shown in fig. 48. 
 
 A very serious case of collapsed 
 _ furnaces occurred in a ship with 
 
 F IG . 48 lour elliptical boilers. One of them 
 
 had given trouble, had just been 
 repaired at sea, and when put into use again, all the furnaces in the 
 three other boilers came down together. No doubt the indicated pres- 
 sure of the repaired boiler was fictitious (see p. 2), and due to air in the 
 steam space, although the water was still fairly cold. On connecting 
 the boilers it disappeared, and was perhaps reduced to a partial vacuum, 
 into which steam suddenly rushed from the other boilers. The con- 
 sequent excessive ebullition, aggravated as it was in these boilers by 
 very restricted water spaces, and very little clearance below the tubes, 
 must have raised the water away from the furnace crowns, and these 
 collapsed. 
 
 Very mysterious collapses are sometimes caused by emptying and 
 refilling a boiler quickly in port, without removing the manhole doors 
 or cleaning its inside. It would appear as if, under these conditions, 
 the scale on the tubes falls off, lodges on the furnace crowns, and, as it 
 is not removed, causes overheating. It also happens that on blowing 
 out the boiler, the scum and oily matter which floated at the water 
 level adhere to the heating surfaces, even when the new water is 
 admitted. 
 
 By far the greatest number of collapses are due to scale, salt, or 
 greasy matter ; but then, instead of the furnace crowns coming down, 
 it is the sides which come in ; for, although the deposit may be uni- 
 formly distributed, the heat of the fire is greatest on either side just 
 
28 BOILEK MANAGEMENT 
 
 over the burning fuel. Shortness of water and local deposits bring 
 down the crowns, not the sides. 
 
 The collapse of furnaces may on occasion be due to very heavy 
 firing combined with one or the other above-mentioned causes. 
 Mr. Yarrow's experiments on tube plates (p. 121) show that, on 
 account of the fire side of a plate being hotter than the water side, 
 it curls towards the water. With the same fierce heat which he was 
 using on flat plates, a furnace top of 20 ins. radius would tend 
 to acquire a curvature of 20| ins. radius, and this would tend to 
 increase the horizontal diameter by 1^ ins. and reduce the vertical 
 diameter by the same amount, making the furnace 3 ins. oval. The 
 same influence is at work longitudinally. If free to move, the apex 
 of the furnace crown, heated as above, would acquire a longitudinal 
 curvature, of which the depression would be about 1J in. in a 6 ft. 
 length. Of course, the end plates and the stiffness of the cool 
 furnace bottom are opposed to these movements, but with the least 
 sediment, grease or dense water, the metal is weakened and this 
 support is much reduced and the furnace collapses. As these 
 curvatures and depressions are independent of the thickness, it is well 
 to make unstrengthened furnaces very thick if exposed to fierce heat, 
 so as to give them extra strength. 
 
 In Mr. L. E. Fletcher's experiments on 1889 red-hot furnace 
 crowns there is a case of a furnace hogging f inch in a length of 20 ft. 
 while raising steam, although the fires were very light. 
 
 Bulging of Flat Plates. Another part of the boiler where scale 
 deposits produce visible deformations is the flat plates of the combus- 
 tion chambers. With narrow water spaces the presence of much 
 steam assists in causing the plates to get hot and bulge, by keeping 
 the scale partially dry. If this treatment did not tend to make the 
 plates brittle, and cause them to crack between the stays, little harm 
 would be done, because in their bulged shape plates are stronger than 
 when flat. Possibly, too, the stretching of the plates enlarges the stay 
 holes, and causes these to leak. When the bulging is serious the 
 favourable conditions for further deformation are increased, because 
 it is now more difficult than before to remove the scale. 
 
 In boilers with two or four furnaces, leading into one large com- 
 bustion chamber, serious bulging sometimes takes place at the top of 
 the saddle between the two central furnaces, but only if they are 
 exposed to the heat of the fire, and if several angle irons have been 
 fitted underneath, as is customary for strengthening these parts; 
 the enclosed spaces form steam pockets, and the saddle plate above 
 and between them gets overheated. 
 
 Tube-Plate Troubles in warship boilers once attracted very much 
 attention, but it does not appear that any satisfactory explanations 
 have been put forward. Doubtless here, too, it is a case of over- 
 heating caused by a high temperature in the combustion chamber, 
 and an excess of steam bubbles near the plate on the water side. The 
 phenomenon (see p. 30) that steel contracts permanently when heated 
 and cooled again might account for the tubes shrinking and the tube 
 plate drawing away from them, but it is difficult to suggest a remedy 
 which has not been tried and failed. 
 
 Experiments on the subject have been made by A. F. Yarrow 
 
BOILEK MANAGEMENT 
 
 29 
 
 (' N. A.,' 1881, vol. xxxii. p. 106), who showed that tube plates 
 tend to bulge towards the fire side, and thus to draw away from the 
 tubes ; but the strong curvatures which he was able to produce are 
 not met with in practice. An idea of the temperature of a tube plate 
 will be obtained by examining the following case. (Compare p. 122.) 
 Let the thickness of a tube plate (fig. 49) be 
 1 in., if perfectly clean its temperature would 
 be 40 F. higher on the fire side than near 
 the water, while transmitting sufficient heat 
 to evaporate 20 Ibs. of water per square foot 
 per hour. The tube, being only ^ in. thick, 
 will be 4 F. hotter on the one side than on the 
 other, and therefore its average will be only 
 18 F. less than that of the tube plate, which 
 corresponds to a relative shrinkage of about 
 30*00 in. This can be neglected in compari- 
 son with the compression existing in the tube, 
 due to the expanding. If covered with scale, 
 as shown in fig. 49, or if in contact with a film 
 o( steam, so that the water can only reach the plate with difficulty, 
 then the conditions are changed. 
 
 Suppose that the scale is ^ in. thick, and that only half of the 
 above-mentioned quantity of heat is being transmitted, then the metal 
 of the tube and tube plate would be about 1,000 F. hotter than the 
 boiler water. But it is difficult to believe that the heat transmitted 
 through the tubes is equal to that passing through the plate, and cer- 
 tainly, within a very few inches from the end, the difference will exceed 
 50 %, so that it is not unreasonable to assume that the tubes are only 
 500 F. hotter than the water. With 3 -in. diameters this corresponds 
 
 FIG. 49 
 
 to a relative difference of 
 
 n. between the tube and hole. The 
 heightened temperature will re- 
 duce the elastic limit to, say, 
 13 tons, so that the pressure, 
 due to the expanding, cannot 
 dilate them more than 10 3 00 in., 
 thus leaving an opening of half 
 the difference, viz. -^ in., or 
 
 about -gjft in. all round the tube. 
 This is sufficient to cause serious 
 leakage. Salt from the boiler 
 water is supposed to choke this 
 opening as long as the heat is 
 fierce, but dissolves out and 
 renews the leakage when cold. 
 (A. J. Durston, 'N. A.,' 1893, 
 vol. xxxiv.) 
 
 In most boilers where this 
 has occurred another force was 
 at work intensifying the leakage. 
 
 It is well known that in order to reduce the crushing stress on tube 
 plates of double-ended boilers, not only the sides but also the tops and 
 bottoms of ike combustion chambers are stayed to the shell (fig. 50). 
 
 FIG. 50 
 
30 BOILER MANAGEMENT 
 
 When pressure is raised in the boiler its diameter increases, and tension 
 stresses are produced in the tube plates, which they, with their small 
 effective sections (only about 25 % of the solid plate), are unable to 
 resist, except by relieving the tubes of a little of the pressure which holds 
 them in place. At the same time the tubes contract their diameters a 
 little, due to the external steam pressure. 
 
 The chief difficulty in accepting these views is that the leakages are 
 not diminished when the fires are drawn, and the phenomenon noticed 
 by Wehrenfennig (see p. 20), that iron and steel contract permanently 
 when heated, even if only up to boiling point, may help to explain the 
 matter. The author's experiments on iron and steel bars which had 
 been drawn out cold under a hammer, on cold rolled bars, on wire 
 (drawn), and on stretched test pieces, show that they all contract 
 permanently on being heated. The distortion which takes place 
 during the annealing of flanged furnace front plates points to the 
 same conclusion, viz. that leaky tubes are caused by a partial anneal- 
 ing of the expanded tube metal, due to excessive heat. The remedy 
 which at once suggested itself is to anneal and re-expand the tube 
 ends in place. According to this view, tubes which have leaked once 
 (and have therefore been annealed) ought not to leak again after re- 
 sxpanding, but although they do, the trouble is lessened. It is curious 
 that tubes which have leaked on account of excessive scale grow tight 
 when it has been removed, even if the ends are not re-expanded. 
 
 The only effective remedy for these troubles, if they were not caused 
 by scale, appears to be the use of copper tube plates. Possibly a 
 wider pitching of the tubes, or reducing their diameters at the back 
 end, may do good. Or the tube ends might be subjected to a pre- 
 liminary compression. This, however, would require an amount of 
 care in boring the tube plate holes which is not often bestowed on 
 them. Differences of T V in. in the diameters of various holes in one 
 plate are not uncommon, and most of them are distinctly oval, some- 
 times as much as -^ in. Taking more care to make the holes circular 
 and of equal size may reduce the trouble. 
 
 In a recent experiment (discussion on A. J. Durston's paper, 
 ' N.A.,' 1893, vol. xxxiv. p. 150) a compressed tube was compared with 
 another which had been expanded in the usual way. Both were 
 fixed in a tube plate which was placed over a smith's fire and heated to 
 a temperature at which about 100 Ibs. of water were evaporated per 
 square foot per hour, but the plate was only occasionally covered with 
 water, which then remained in a spheroidal condition. After a few 
 hours' exposure the plate was allowed to grow dull red hot, when both 
 tubes grew slack. Careful measurements showed that the expanded 
 tube had contracted its diameter T \, in., while the compressed one had 
 not altered, but its hole in the tube plate had changed its taper from 
 1 : 12 to 1 : 10. This compressed tube could not be withdrawn out of 
 the hole, for its projecting end (| in.) had expanded during annealing. 
 This goes far to prove that leaky tube ends are caused by raising theii 
 temperature to redness. 
 
 Attempts are being made to electrically weld tubes into the plates, 
 but the risk of burning an internal part of a boiler which is nearly 
 finished must deter all except the most venturesome from trying this 
 plan. 
 
BOILER MANAGEMENT, 31 
 
 As a makeshift ferrules are driven into the ends of boiler tubes 
 (figs. 51 and 52), but they soon burn away. Better results are said 
 to have been obtained by making the ferrules of cast instead of 
 wrought iron, and leaving an air space between them and the tube 
 (see fig. 53 and A. J. Durston's paper). 
 
 Fm. 51 FIG. 52 FIG. 53 
 
 Cleaning Boilers. From the foregoing remarks it is clear that many 
 troubles are caused by the accumulation of scale, grease, or even salt, 
 and where this cannot be prevented, great care has to be taken that 
 the boiler shall be cleaned out and scaled as often as possible. This 
 work is never done well unless the various parts of the boiler are easily 
 accessible, not only to boys, but to the engineer, who has to see that 
 the work is properly done. None of the water spaces between the 
 tubes should, therefore, be less than 10 ins., and if that amount of space 
 cannot be provided over the wing surfaces, it ought to exist between 
 the tubes and the shell, or a manhole should be fitted in the two wings 
 of each boiler. They should not be made smaller than 10 \ x 14 ins., 
 but 12 x 16 ins. is ample. A sufficiently large manhole should also be 
 fitted between and under the furnaces, either at the front or back end 
 of the boiler. 
 
 Removal of Scale. There are several methods of removing scale. 
 The general one is to chip it off. This work is very laborious on 
 account of the hardness of the scale. Scale can be softened by 
 adding a sufficient quantity of soda to the boiler a few days before 
 reaching port. The soda converts the sulphate of lime into carbonate 
 of lime and the change has a loosening effect on the scale. After a 
 time, however, this scale would harden again and further additions oi 
 soda would have no effect. Mica powder is said to be a very effective 
 scale loosener. When the boiler is empty, the scale has to be removed 
 as rapidly as possible because air hardens it. Boilers should be cooled 
 with all their water in them. The scale can then be removed with a 
 hose pipe, brushes, and scrapers, and without chipping. The men 
 should have oil-skins, and the water in the boilers should only be 
 lowered as the cleaning progresses. Even old scale will yield to this 
 treatment if repeated. Scale grows hard in about three hours after 
 exposure to the atmosphere. Another method is to blow the boiler 
 down while steam is up, care being taken that the brickwork of the 
 firebridges is sufficiently cooled down, so as not to injure the furnace 
 plates. The boiler is then allowed to cool, no doors being removed un- 
 til the men are ready to enter the boiler. They will find the scale fairly 
 soft and so well detached from the plates that it can be scraped off. 
 
3'2 BOILER MANAGEMENT 
 
 Removal of Grease. The most effective method is to allow scale 
 to accumulate and to remove it and the grease together. Naphtha 
 and similar oils are often recommended with which the boiler surfaces 
 have to be rubbed down. Of course naked lights may not be used, 
 and as this plan is not very effective and said to be injurious to health, 
 it should not be adopted. 
 
 Corrosion. This subject is fully dealt with in a separate cnapter, 
 but here it will be necessary to make a few remarks on the external 
 wasting away of plates. This never occurs except in the presence of 
 moisture, and is found chiefly near manholes, near leaky joints, at the 
 boiler bottoms and ends, where they come in contact with bilge water, 
 and above all near the furnace fronts and combustion chamber 
 bottoms. These are exposed to the very injurious action of moist 
 ashes, containing large percentages of sulphuric and other acids, 
 which are partly liberated by the ash-cock water. By keeping the 
 boilers perfectly tight, and protecting the front plate from moist 
 ashes, all these troubles can be avoided. Naturally also leaky tubes 
 and seams cause external corrosion, for then a combination exists 
 there of heat, moisture, salt, and noxious acids. 
 
 The leakage from valve and other flanges, the drainage from test 
 cocks, and the moisture which collects in the wood of platforms ad- 
 joining the boiler backs, all tend to shorten the life of a boiler, and 
 should be prevented as much as possible. 
 
 FIG. 54 FIG. 54a 
 
 As regards manholes, an excellent practice is gaining ground 
 of flanging them and facing the edges and grooving the door, as 
 shown in fig. 54, which permits of their being faced up again when 
 worn out. 
 
 Pressed manhole doors are now very largely used and generally 
 with very satisfactory results, but it is desirable to make them of 
 fairly thick plates, for when the fillets of the flange have been 
 machined away, too little metal is sometimes left to resist the very 
 severe thrust to which these doors are subjected. This weakness, 
 in an exaggerated form, is indicated in fig. 54a. 
 
 Boiler Repairs. Sooner or later even the best managed boilers 
 will need repairs. If badly done they lead to further troubles, and 
 may prematurely necessitate the renewal of the entire boiler. Care 
 should therefore be taken that the workmanship is of the best, and 
 that no structural defects are introduced, which would either prevent 
 circulation or hinder the removal of scale 
 
 Bulged Furnaces. The most serious troubles with new boilers are 
 the furnaces. A careless engineer, or other causes, which have been 
 
BOILER MANAGEMENT r 
 
 33 
 
 already mentioned, may suddenly bring them down. If the deforma- 
 tion is not great, i.e. only a few inches, and spread over a considerable 
 area, the best remedy is to press the plates out again. Attempts have 
 repeatedly been made to do this cold, but the deformations can never 
 be perfectly removed in this way, and soon return. Besides, other 
 parts of the furnaces are thereby strained, and it has happened that 
 while pressing up a furnace crown, the welded seam at the bottom 
 cracked and had to be patched. Formerly the necessary heating was 
 done by coke fires and a blast, but it is more convenient to use a 
 powerful Wells light, for with it there are no bricks to be removed. 
 The hydraulic jack should be well bedded on timbers against the 
 bottom of the furnace, and it should have a cast-iron head of the 
 same radius as the furnace. The pressing out should be done slowly, 
 and the plate should be reheated several times during these opera- 
 tions, and once afterwards for the purpose of annealing. If the 
 operation is carried out too quickly, or in too few operations, the 
 bulge is likely to reappear after a short time. 
 
 Collapsed Furnaces. If the furnaces have collapsed thoroughly 
 they must be renewed, and it depends very much upon the boiler 
 design whether this can be done efficiently. If the furnace back end 
 was flanged inside of the tube plate, as is now generally the case, 
 there is hardly any other remedy than to cut the back end and to 
 insert an unflanged furnace (figs. 55, 58). Sufficient width should be 
 left for a double row of rivets, for such a joint seems to give better 
 
 FIG. 65 
 
 PIG. 56 
 
 results than a single-riveted one. This cutting out can be done very 
 quickly and neatly with the help of the oxy-acetylene flame. A hole 
 is drilled into the plate, its edge is raised to a white heat, and the 
 acetylene is then shut off and only the oxygen blast maintained, which 
 burns away a narrow slit of steel without much heating. Chiefly for 
 cheapness' sake, but partly for facilitating the above-mentioned repairs, 
 the tube plates, instead of the furnaces, are sometimes flanged (fig. 56). 
 Should the furnace collapse, it is then only necessary to draw it and 
 to fit a new one. Under any circumstances no expense or trouble 
 should be spared on these seams to bring the two plates into metallic 
 contact. It is well to wash the two surfaces in sal ammoniac, so as 
 to remove the scale ; also, when all the holes have been drilled, which 
 should be done in place, the furnace ought to be partly withdrawn, the 
 burrs removed, as well as every trace of oil, because this is a very bad 
 conductor of heat. The riveting should not be started from the bottom 
 
34 
 
 BOILER MANAGEMENT 
 
 otherwise, before the top is reached the plates at the 
 
 Dp is 
 It is 
 
 then practically impossible 
 
 of the seam ; 
 
 crown will be far apart (see fig. 57). 
 to make the seam per- 
 manently tight, and 
 after being in use a 
 short time it is sure to 
 leak again. Sometimes 
 it only opens on the fire 
 side, and then, though 
 the blade of a pocket 
 knife can be inserted 
 up to the other caulked 
 edge, no leakage seems 
 to take place. In order to be quite safe, it is best to fit and rivet the 
 furnace crown into position before the furnace bottom is introduced. 
 
 FIG. 57 
 
 Fto. 58 
 
 The longitudinal seam should be slightly inclined, as shown in fig. 58, 
 and then it is an easy matter to make it a very good fit. Another 
 
 FIG. 59 
 
 way of repairing a collapsed furnace is shown in fig. 59. The furnace 
 crown is cut in two, and the forward end is renewed, while the saddle 
 
BOILER MANAGEMENT 
 
 35 
 
 *s taken out, flanged, as shown, and refitted with an Adamson's 
 ring. 
 
 With a furnace whose back end is not flanged, repairs may some- 
 times be effected by removing all the rivets and turning it round, so 
 that the saddle seam is placed in the ashpit. The weld which was at 
 the bottom of the furnace is now somewhere near the crown. Central 
 
 FIG. 60 
 
 furnaces can, under certain conditions of shape, be renewed by first 
 removing the combustion chamber bottom plate. 
 
 If the furnace saddle is flanged over the tube plate, and if the 
 furnace front plate is outside the front tube plate (see fig. 60), then 
 both it and the furnace can be removed and the one renewed. But if 
 the furnace front plate is placed inside the front tube plate, and has 
 
 to be withdrawn, it is necessary to cut 
 away its two corners (fig. 61), so as to 
 be able to tilt it out of and into posi- 
 tion. The amount of metal to be re- 
 moved depends on the depth of the 
 flange. This plan cannot be carried 
 out on boilers with three furnaces, 
 unless the horizontal seam intersects 
 the central bundle of tubes. 
 
 The arrangement shown in fig. 60, 
 which facilitates these repairs, has the 
 further advantage that both the back 
 and the front seams are very easily 
 caulked from the outside. Its only 
 drawback is that one loses about 1J in. 
 of tube length. 
 
 Flanged furnaces can occasionally 
 be removed and replaced intact by 
 cutting away the lower part of their 
 back ends (fig. 62). The wing com- 
 bustion chambers would have to be specially constructed, so that no 
 part of the furnace flange is wider than the front ends of the furnaces 
 (fig. 63). 
 
 D 2 
 
 FIG. 61 
 
36 
 
 BOILER MANAGEMENT 
 
 Before attempting such repairs, careful measurements should be 
 taken, and, with the help of a board, representing the furnace front, 
 
 FIG. 63 
 
 FIG. 63 
 
 and a wooden model of the furnace (fig 64), the action of passing the 
 latter through the former should be performed. This will also enable 
 one to determine how much of the back end has to be cut away. 
 
 Furnace Patches. Furnaces sometimes suffer severely from pitting 
 along the line of fire bars. If some of the pit holes should have pierced 
 the plate, it is necessary to 
 drill them out and fit screwed 
 Btuds, or, better still, broad- 
 headed rivets, which may be 
 square, oval, or irregular in 
 section, to suit the special 
 case. Neither give trouble 
 by leakage, but they do not 
 add to the strength of the 
 furnace, and, unless abso- 
 lutely necessary, it is better 
 not to perforate it at any 
 point above the bars. If the 
 pitting is uniformly distri- 
 buted, as well as deep, there 
 is danger of this part of the 
 furnace giving way, but as 
 yet no such case seems to 
 have happened. To guard 
 against this, or to prevent 
 further pitting, some engineers bolt doubling plates, well bedded in 
 red-lead cement, along the line of fire bars (fig. 65). It is difficult to 
 imagine a more inappropriate remedy, for to place here, at the hottest 
 part of the furnace, not only two thicknesses of plate, but actually to 
 separate them by a highly non-conducting material, is little better 
 than inviting disaster. If any action is necessary, the furnace crowns 
 should be removed. 
 
 FIG. 64 
 
 FIG. 65 
 
BOILEft MANAGEMENT 
 
 37 
 
 furnace bottoms are sometimes doubled in the same way ; but 
 this is not a permanent repair, and the plates should occasionally be 
 removed for examination (see p. 38). 
 
 Blisters in the furnace crowns need only be pared away, unless they 
 are so large and deep that there is fear of theii' weakening the furnace. 
 In that case they have to be cut out and a patch fitted. 
 
 Cracked Furnaces. Plain furnaces have hardly ever been known 
 to crack except at the flanges or the seams, but every one of the 
 patented forms has done so. If due to scale or grease, the cracks 
 start on the fire side and sometimes run longitudinally; if due to 
 unequal expansion or excessive strains, they sometimes show first on 
 the water side, and generally in a circumferential direction. Similar 
 cracks (see fig. 43, p. 21) are sometimes found in the sides of the fur- 
 nace saddles, and can often be repaired by chain-pinning them. They 
 make their appearance on the fire side, and sometimes, if not interfered 
 with, do not penetrate through the plate. 
 
 When the cracks, which show themselves, are so serious that 
 tapping pins into them would not prevent leakage, the effected parts 
 have to be cut out and patches fitted. In fig. 66 the patch is fitted 
 on the fire side, and can easily be renewed if the rivet holes should 
 crack. In fig. 67 it is fitted on the water side. This is done with 
 the object of keeping the seam turned away from the fire, but it is a 
 most difficult piece of work, because the seams at A and B have to 
 
 FIG. 66 FIG. 67 FIG. 67a 
 
 be sprung open. This patch is also not to be recommended, because 
 if the rivet holes should crack, a larger corner would now have to be 
 cut out and replaced (see fig. 47, p. 22). If the tube plate or furnace 
 saddle is not too stiff, the repair shown in fig. 67a is a very con- 
 venient one. 
 
38 
 
 BOILER MANAGEMENT 
 
 FIG. 68 
 
 Cracks like those shown in figs. 43-45 (p. 26) can be repaired 
 by welding them with the oxy-acetylene flame, but such repairs will 
 not be satisfactory unless the cracks are cut out or burned out, and 
 the conditions explained on pp. 337 carried out ; the flames should be 
 applied to both sides of the plate while the new material is being 
 gradually built up. 
 
 Combustion Chamber Bottoms. These are often very seriously cor- 
 roded on the fire side, particularly near leaky seams, and, as even the 
 rivet heads retain their shape when wasted (see fig. 68), there is danger 
 that such defects will be overlooked. 
 The salt from leaky tubes when 
 mixed with ashes causes corrosion at 
 these points, and to prevent this, the 
 bottoms are sometimes cemented. 
 This is a very dangerous practice; 
 not only does this prevent any 
 
 leakage from being detected, but if there is one, or even if moisture 
 finds its way between the plates and the cement, the furnace heat 
 will convert it into steam and cause a small explosion, which may do 
 damage to bridges and fire doors, &c. Fitting doubling plates to 
 these parts may lead to the same result, but the consequences would 
 be still more serious. 
 
 The corrosion on the water side of the combustion chamber is 
 often very evenly distributed, and if the bottoms are found to be 
 thin, the backs are most likely worn away too, and before starting to 
 cut out the one it is best to drill holes in the other for measuring the 
 thickness. 
 
 The best means for detecting weak places in plates is to make a 
 thorough examination when the plates are well scaled. The shadows 
 produced by the lamp often indicate irregularities, particularly pit 
 holes. The hammer will give no reliable indication of thickness when 
 this exceeds in., and then it is of course possible to dent the plate 
 and even to knock a hole into it. When general wasting and conse- 
 quently structural weakness are suspected, drilling the plates is the 
 only means of measuring their thickness, though magnetic and electric 
 tests have been suggested and might be made available. 
 
 Before cutting out thin plates, it is well to drill test holes beyond 
 the intended new seam, for if further thin places are revealed after 
 the plate has been cut across, it will be necessary to repeat the opera- 
 tion. Patches on the lower parts of the combustion chamber usually 
 include flanges, and care should be taken that these are properly fitted, 
 for none of the seams or rivets can be caulked from the 
 water side, as is the case with new boilers. Of course 
 new stays will have to be fitted, and these should 
 always be nutted, no matter whether this was originally 
 the case or not. 
 
 Screw Stays very often lose their nuts by burning, 
 or rather bad welds open under the influence of the 
 heat (fig. 69). It is quite a common practice to cut off 
 the greater part of the projecting stay and rivet it over. This should 
 not be done, because it is due to the presence of the nuts that a 
 
 FIG. 69 
 
BOILER MANAGEMENT 
 
 39 
 
 reduction is allowed in the thickness of the plates. The better plan 
 is to cut the thread deeper (fig. 70), for which special tools exist, and 
 to fit new nuts. 
 
 This burning away of the stay nuts is generally due to their 
 not being in metallic contact either with the stay or the plate ; or, 
 in other words, they are a loose fit on the thread, and are resting 
 on a washer and two thicknesses of red-lead cement. When refitting 
 the nuts, these mistakes should not be repeated, but where the stays 
 are not normal to the inside plates, taper washers are a necessary 
 evil. This arrangement should be objected to in new boilers. 
 
 With thin plates the stay ends often leak, particularly if their 
 ends are riveted over. Instead of renewing them, some boiler-makers 
 go to the trouble of making a small cap and bolting it over the head, 
 as shown in fig. 71. Sometimes several stays in one combustion 
 chamber are hidden away in this manner, and it is only a wonder 
 that this practice has never led to a disaster. (See p. 222.) 
 
 FIG. 70 
 
 FIG. 71 
 
 FIG. 72 
 
 The excuse made for fitting these patches is that the plates had 
 become too thin for holding a new stay. If the thinning is only local, 
 a, very efficient repair is to replace the stay by one of a larger diameter. 
 But in screwing up the nut its power will perhaps be so great that 
 the thread in the plate gets stripped ; to guard against this, a check 
 nut should be fitted on the inside. It is bad for the transmission of 
 heat, but is better than no support at all. 
 
 Often it will be necessary to remove the stay, and to fit a small 
 patch and tap it, as shown in fig. 72. This is the best possible 
 arrangement, particularly if the stay is not normal to the plate, 
 because the patch could be made taper, bent or recessed so as to let 
 the nut come into metallic contact with it. 
 
 Sometimes the plates remain uninjured while the screw stays 
 waste away and will have to be renewed, generally of a larger 
 diameter, the threads having been injured. 
 
 In order to effect these various repairs, and to stop external leakages, 
 sufficient space should be left at the backs of boilers, so that a mau 
 could work there. 
 
 It will be noticed that those stays which are nearest the combus- 
 
40 
 
 BOILER MANAGEMENT 
 
 tion chamber bottoms and sides give the most trouble. This is no 
 doubt due to the very severe strains to which they are subjected 
 through the unequal expansion of furnace and shell plate, and there- 
 fore they ought to be kept as far away from the flanges as the strength 
 of the boiler back plate will allow (see p. 141). 
 
 Similar remarks apply to the top row of screw stays to boiler 
 shells ; if placed too near the combustion chamber top they also are 
 subjected to very severe 
 strains, sometimes leading 
 to rupture. 
 
 Tube-Plate Troubles. 
 The last of the troubles 
 in combustion chambers 
 is the tube plate. An ex- 
 planation as to the causes 
 of leaky tubes has already 
 been attempted, and some 
 remedies suggested. The 
 repeated re - expanding, 
 together with the injury 
 caused to the metal by 
 
 getting hot, if covered with scale, ultimately causes the tube plate to 
 crack. Fortunately, since steel and thicker tube plates have been in- 
 troduced, such cracks are rarely met with. If caulking will not stop 
 the leak, or if several spacings show cracks, it is necessary to bolt 
 little spectacle patches (fig. 73&) over them, preferably on both sides. 
 Keys, shaped like a dumb-bell (fig. 736), are said to have given good 
 results, but the fitting must be carefully done to make it a good job. 
 
 If the front tube plates of boilers are curved or bent back at the top, 
 they are subjected to very serious tension stresses, which in one case 
 led to a rupture, so that it was found necessary to fit vertical stays, aa 
 shown in fig. 74. It is, however, questionable whether the stays were 
 
 of much value, as their lower ex- 
 tremities had only been bolted to 
 the furnace tops, which, being thin, 
 could not have offered a resistance 
 if the large stays had been strained 
 to their utmost. 
 
 FIG. 73 a 
 
 FIG. 736 
 
 FIG. 74 
 
 FIG. 75 
 
 Repairs to the Boiler Shells are sometimes necessary on account 
 of the wasting away or cracking of circumferential seams. As such 
 patches are not required for strength, but only for water-tightness, they 
 need not be thick. At one time it was customary to make them of cast 
 brass, a thick sheet of lead, which was hammered over the seam, being 
 used as a pattern ; but it was found that this gave rise to very serious 
 
BOILER MANAGEMENT 
 
 41 
 
 local corrosion, caused, perhaps, by galvanic action. In their stead 
 light iron cover plates, filled with cement, are bolted over these seams, 
 as shown in fig. 75. They were very efficient in stopping leaks where 
 caulking was unavailing. Of course if the shell plate is seriously 
 weakened it is necessary either to fit an efficient doubling plate, or the 
 defective part must be cut out, and a proper patch put in its place ; 
 but it is very seldom that tnis occurs, except perhaps with donkey 
 boilers, whose bottoms cannot be properly protected from moisture. 
 
 FIG. 76 
 
 Fio. 77 
 
 D 
 
 o 
 
 It is different with the end plates of main boilers ; they are exposed 
 at one end to the hot and moist ashes, and at the other to leakages from 
 flanges and manholes, &c. As these plates are originally very thick, 
 and more than sufficiently supported, their wasting away is not so 
 much a danger as a nuisance. Most of the patches to these parts are 
 therefore simply doubling plates over the thinnest places, and it is 
 only when no other remedy is thought effective that the bad parts are 
 cut out. 
 
 The following are a few sketches of repairs which may occa- 
 sionally be necessary. Figs. 76, 77 show a case in which the 
 circumferential seams at the front ends of the shell and the furnace 
 have wasted away and have been repaired 
 by a covering patch. As it forms a ridge on 
 the inside of the furnace, against which the 
 rake will always be knocking, it is better to 
 carry out this repair as shown in figs. 78, 
 79. Part of the furnace bottom is cut 
 
 away, and the 
 patch fitted in 
 its place. Of 
 course a strap 
 will have to 
 be placed on 
 the water side, 
 as shown in 
 dotted lines 
 (fig. 79). 
 
 If only the front plate is wasted away, and if this is only between 
 the two furnaces, an internal patch can be fitted, as shown in 
 figs. 80, 81. Generally a manhole or a few large stays will be found 
 here, and as it is impossible to get a sufficiently large patch into the 
 boiler to cover them, it will be necessary to fit it from the outside. 
 
 When the lower front seams both of the furnaces and the shell are 
 in a bad condition, it may be necessary partly to renew the front plate, 
 
 P 
 
 O! 
 
 
 
 a 
 
 N 
 
 1 
 
 1 
 
 : 
 
 
 o 
 
 0; 
 
 i 
 
 
 
 
 o 
 
 Q. 
 
 
 
 0; 
 
 
 
 Q 
 
 oj 
 
 1 
 
 0: 
 
 .p. 
 
 P- 
 
 FIG 
 
 FIG. 79 
 
BOILER MANAGEMENT 
 
 and to make its flanges sufficiently deep to take in another row of 
 rivets. The joints should be placed where there is sufficient room for 
 working at them. Lap joints, as shown in fig. 83, are very difficult to 
 
 Fio. 80 
 
 Fio. 81 
 
 make, for if looked at from the back (fig. 82), it will be noticed that the 
 patch has to be fitted under the remaining plate, which cannot be done 
 efficiently. 
 
 Fio. 82 
 
 Fro. 83 
 
 A simpler plan is to butt the plates at these points, and to fit flanged 
 butt straps internally (fig. 84), or, where the space is too narrow, a solid 
 block (fig. 85). In either case this part has to be carefully fitted after 
 all the other seams have been riveted up. Of course with the solid 
 
 _/ n 
 \ 
 
 Fio. 84 
 
 Fio. 85 
 
 Fio. 86 
 
 block it will be necessary to use screwed studs and bolts, except per- 
 haps for those points marked c, for which through rivets may be used, 
 but only if the holes come opposite each other. The flanges should 
 
BOILER MANAGEMENT 
 
 43 
 
 not be cut away parallel to the axis of the boiler and furnace, but 
 should slant downwards (see dotted line, fig. 86) ; this will enable the 
 plate edges to be driven tight together. 
 
 Before deciding which plan to adopt, a 
 sketch should be made to see whether it is 
 possible to insert the various rivets. Much 
 space is gained if the rivet holes are counter- 
 sunk inside so as to do away with the heads, 
 and outside, so as to be able to use short 
 rivets (see fig. 87). 
 
 BOILER FITTINGS. 
 
 Water Gauges. Of the various boiler 
 mountings, one of the most important is the 
 gauge glass, and it ought always to be in good FIG. 87 
 
 working order, and capable of being tested at 
 
 any time. The material and construction should be of the very best. 
 Asbestos packed cocks are a great advantage, but even with them, if 
 the gun metal is bad, leakages cannot be prevented. Iron and steel 
 plates are attacked by acids, whereas copper alloys suffer severely 
 when in contact with caustic soda ; care should therefore be taken 
 never to make the boiler water too alkaline. 
 
 In some cases the gauges are fitted direct to the boiler plating, 
 but this is not a good plan ; not only does the panting of the plates 
 lead to breakages of the glass tubes, but the scum cannot be kept 
 out of the glass, and the oscillations due to the rolling of the vessel 
 and to irregularities of ebullition make it difficult to obtain good 
 readings. 
 
 The usual plan is to connect the gauge glass to the top and 
 bottom of the boiler by means of long pipes, the one reaching well up 
 into the steam space, and the lower one into the water, where little 
 circulation is expected to be found. These pipes can be fitted either 
 externally or internally. The latter arrangement is not always 
 possible, on account of the sm'oke box, and some engineers object to 
 it in toto, on the principle that no copper pipes should be fitted inside 
 a boiler. From the following table it will also be seen that, if not 
 
 Hot Water in Boiler. Cold Water (70 P.) in 
 10-foot Gauge Pipe 
 
 Hot Salt Water in Boiler. 
 Distilled Hot Water in 10-foot 
 Gauge Pipe 
 
 Boiler 
 Pressure 
 
 Tempera- 
 ture in 
 Boiler 
 
 Water Level \ 
 in Boiler H, 
 above Gauge f fig. 31 
 Reading J 
 
 Saltness of 
 Boiler Water 
 
 Water Level in 
 Boiler below 
 Gauge Reading 
 
 Lbs. 
 60 
 
 307 
 
 Inches 
 11 
 
 Oz. 
 10 
 
 1 A 7 
 
 Inches 
 
 100 
 
 338 
 
 13a 
 
 20 
 
 3-3 
 
 9 
 
 150 
 
 366 
 
 16 
 
 30 
 
 5-0 
 
 14 
 
 200 
 
 387 
 
 18 
 
 40 
 
 6-7 
 
 19 
 
 often blown through, gauges with long connections may indicate a 
 different water level from that actually existing in the boiler. When 
 
44 fcOILEB MANAGEMENT 
 
 fitted externally these pipes have the effect of cooling the water con- 
 tained in them, and as its density is thereby very much increased, 
 the indicated water level is lower than that in the boiler. Matters are 
 still further complicated by the accumulation of distilled water in the 
 upper parts of the connecting pipe, which, if there is much salt in 
 the boiler, has the effect of making the water level appear higher 
 than it really is. The possible differences caused by a connecting 
 pipe 10 ft. long are shown in the above tables, which contain the 
 corrections which should be applied to the water-gauge readings 
 under the various conditions. 
 
 The first of these tables has been calculated on the assumption 
 that the rate of expansion of water is independent of the pressure ; 
 but even if not strictly true, both tables show that a serious difference 
 may exist between the gauge-glass indication and the water level, 
 unless the cold or distilled water in the connecting pipe has first been 
 blown out. Few gauges are so fitted that this can be readily done 
 (see fig. 31), for if the water is low, the opening of the cock D, while 
 B is closed, will not necessarily clear the pipe C D of its water, or at 
 any rate not as quickly as if the cock A had been closed. This being 
 inconvenient, some gauge stands are fitted with a large cock at F. 
 
 No double bends, capable of collecting water, should be allowed 
 to exist in the gauge steam pipe, as they would cause the glass to 
 show a wrong level. 
 
 Gauge-Glass Protectors. On account of occasional personal in- 
 juries, when gauge glasses of high pressure boilers broke, they are 
 now very generally protected by glass shields of which there are 
 several patterns. These protectors should be made of stout and 
 tough glass, for their splinters can do far more harm than the much 
 smaller ones of the glass tubes. One of the safest protectors con- 
 sisted of a semicircular sheet of stout glass in which wire netting 
 was embedded, but this netting obstructed or rather confused the 
 view of the water level. Where flat plate-glass protectors are used, 
 care should be taken that there are no conspicuous horizontal objects 
 opposite to them, whose reflection might be mistaken for water-level 
 readings. 
 
 Test Cocks are intended to indicate the boiler water level. They 
 are often fitted to the gauge-glass stand, but their proper position is 
 on the boiler plating. One should be at or near the ordinary water 
 level, a second a few inches higher, and a third on a level with the 
 highest heating surface ; for, should the water have been lost out of 
 the gauge glass, it is very important to know whether a mishap can 
 still be averted by putting on all available feed, or whether it is 
 necessary to draw the fires. It is not always well to check the fires, 
 for the immediate effect of stopping ebullition is to lower the water 
 level. Sudden variations of water level are sometimes caused by the 
 drain pipe from the superheater having been fitted below the water 
 level of the boiler and not being closed on occasions when this was 
 necessary ; and more recently similar effects have been produced 
 by negligence in not closing the feed-pipe suctions from the boiler 
 bottoms, which are only intended to be open while in use, when 
 steam is being raised. 
 
BOILER MANAGEMENT 
 
 In marine boilers shortness of water is not necessarily as dangerous 
 as in land boilers, because the fur- 
 nace crowns are many feet below 
 the ordinary water level, and the 
 upper heating surfaces are not ex- 
 posed to a very high temperature ; 
 besides, in rough weather they are 
 being constantly moistened by water 
 splashing on them. But the case 
 is different in calm weather, if the 
 steamer has a strong list ; for then, 
 even if there is a reasonable height 
 of water in the glass, one of the 
 wing combustion chamber tops may 
 be laid dry for a long period and get 
 overheated. Furnace crown plates 
 would grow red-hot in about five 
 minutes after being laid bare, while 
 combustion chamber top plates would 
 require twice or four times as much 
 time. Obviously this danger is in- 
 tensified if the gauge glass is fitted 
 to the boiler side, and even the trim 
 of a vessel may expose parts of the 
 heating surface to this influence if 
 the boiler is a very long one. In 
 such cases it is advisable to fit fluid 
 levels in the engine room, which will 
 indicate how much water ought to be 
 in the glass. They are very simple 
 instruments, and can easily be made 
 with the help of a few glass tubes 
 (see figs. 32, 33). 
 
 Fusible Plugs. To guard against 
 the troubles arising from shortness 
 of water, some engineers fit fusible 
 plugs to the combustion chamber 
 tops, and in some countries this 
 practice is compulsory ; but there is 
 this serious objection, that when a 
 plug is once fused the boiler cannot 
 be used again for some hours. On 
 a ship with only one boiler such a 
 mishap might lead to her total loss, 
 and almost under any circumstances 
 which are likely to occur at sea, it 
 would be better to have the use of 
 boilers which can be worked even 
 if only at a very low pressure, than 
 not to be able to use them at all 
 till a new plug has been inserted. See p. 19.) 
 
 FIG. 31 
 
46 
 
 BOILER MANAGEMENT 
 
 5 6 
 
 Low Water Alarms. The majority of land boilers are fitted with 
 safety valves, which blow off when the minimum permissible water 
 level is reached ; they are inapplicable to marine boilers, and if 
 modified to suit the altered circumstances would, though to a less 
 degree, be open to the objections urged against fusible plugs. Water 
 
 alarms, especially such as are 
 arranged to ring an electric 
 bell, situated if necessary in 
 the engineer's berth, may in 
 some steamers be found use- 
 ful. These fittings seem to 
 FIG. 32 be reliable, but it would be 
 
 well if they could be fitted 
 
 with a cock or valve so as to produce artificially the conditions of 
 low water in the boiler, and thus ascertain whether they are in 
 working condition. In this form they would be a convenient means 
 of summoning the chief engineer in case of emergency. Water 
 alarms in which a float actuates a whistle work well, but would not 
 combine the above advantages. 
 
 7- 
 6 
 
 o ~~" 
 
 FIG. 33 
 
 Automatic Feeding Arrangements are as yet only being fitted to 
 water-tube boilers, and are hardly likely to come into use in the 
 boilers under consideration. 
 
 Safety Valves, Another very important boiler mounting is the 
 safety valve. Its action and design are so simple that little need be 
 said about it, but being practically always out of use, there is a great 
 danger that it will be found out of working order when it should act, 
 and to ensure that this shall not happen, all the working parts should 
 be lined with brass, and should be loose fits, and their working 
 condition should often be tested by lifting the valves from their seats 
 or turning them round. As it has sometimes happened that the 
 valve seats have lifted with the valves, thus preventing any escape of 
 steam, they should always be securely bolted or pinned down. 
 
 As long as low pressures were customary, weighted safety valves 
 were common and worked satisfactorily ; but now, since high pres- 
 sures are almost universal, dead weights have been replaced by 
 springs, for otherwise the working pressure would have to be reduced 
 about 30 % in rough weather, on account of weights being thrown up 
 under the combined action of the steam and the pitching of the 
 vessel. (Wilson, ' Marine E.,' 1892.) 
 
BOILER MANAGEMENT 
 
 47 
 
 Formerly spring loaded valves were very inefficient, allowing the 
 steam pressure to accumulate considerably, unless the springs were 
 made exceptionally long. This difficulty has been more than over- 
 come by utilising the reaction of the escaping steam, and, instead of 
 allowing the pressure to rise after steam has commenced to blow off, 
 there are many valves which will not close until the pressure has 
 been seriously reduced. 
 
 FIG. 35 
 
 The principles on which such safety valves can be constructed 
 are shown in figs. 34, 35, 36. In the first of these the valve diameter 
 is d, but when the steam is escaping it acts on the diameter D, and 
 keeps the valve well open until the pressure has dropped considerably. 
 
 In fig. 35 the escaping steam reacts 
 on the surrounding lip, while in fig. 36 
 it reacts, as shown, by striking against 
 the valve top. 
 
 The object of these various designs 
 is that the valve should open fully when 
 it does so at all, that it should not 
 be closed till the pressure has dropped 
 a pound or two below the working 
 pressure, and that this should be 
 effected with as short a spring as 
 possible. 
 
 Obviously all these points are 
 affected by the angle of the seat and 
 the curvature and size of the lip ; but, besides that, the diameter and 
 length of the waste steam pipe are influential factors, and it often 
 happens that safety valves which worked satisfactorily when tested 
 at the works, will not do so when fitted on board. The chattering 
 noise which they make is evidently due to the length of the pipe as 
 well as to the weight of the valve and the elasticity of the spring. 
 Every time that the valve comes down and stops the flow of steam, 
 a partial vacuum is formed by the uprushing column, and the valve 
 is lifted up again. The possible remedies are, to have an opening at 
 the lower end of the waste pipe, through which air will flow when- 
 ever a vacuum is formed, or to fit frictional appliances in the lower 
 part of the pipe, such as a series of diaphragms, wire brushes, or a 
 box of pebbles. 
 
 FIG. 36 
 
48 
 
 CHAPTEE II 
 STEAM AND WATER 
 
 THIS chapter, which did not appear in the first edition, is intended 
 to give such information about steam and water, boiling, circulating, 
 and superheating, as may be useful to boiler-makers and users. Some 
 of these items may seem to be of no great practical importance, 
 but when it is remembered that difficulties have been caused to 
 contractors by such a simple question as whether the weight of 
 water in a torpedo-boat boiler should be taken cold or when heated 
 to, say, 360 F., i.e. whether a cubic foot of water was to count as weigh- 
 ing 62*4 Ibs. or only 55 Ibs., it is evident that this information at least 
 should not be omitted from a work on boilers. Then, also, these and 
 other matters affect the measurements of evaporation. It has there- 
 fore been attempted to give the latest information on the properties 
 of steam and water, and most of these are contained in the table on 
 pages 50 to 53. 
 
 Steam Pressure, Temperature and Volume. These subjects have 
 engaged the attention of the following observers, whose results are 
 summarised in 'Wied. Ann.,' 1907, vol. xxii. p. 625, and some are 
 reproduced in the following tables : Magnus, Eegnault, Wiillner 
 and Grotrian, Batelli, Cailletet and Colardeau, Marvin, Eamsay and 
 Young, Wiebe, Knoblauch, Linde and Klebe. The results of Eeg- 
 nault and of Eamsay and Young are contained in cols. 9 and 11. 
 As will be seen, the two are not in absolute agreement, but very 
 nearly so. Cailletet and Colardeau's experiments were made by com- 
 paring steam pressures with compressed hydrogen pressure gauges 
 which had first been tested against the mercury column on the 
 Eiffel Tower. Although nearly ten years have elapsed since these 
 experiments were first published, the only details are contained in 
 a small diagram in which the height of the Eiffel Tower is represented 
 by about three inches. In that paper the experimenters also state 
 that their observations agree with the formula given by Clausius 
 (* Wied. Ann.,' 1881, vol. xiv. p. 698). Their information was 
 thought too vague to be embodied in the table, but the following are 
 the values supplied to me by the authors. 
 
STEAM AND WATER 
 
 49 
 
 Table of Steam Pressures 
 
 Temperatures 
 
 Steam Pressures 
 
 Temperatures 
 
 Steam Pressures 
 
 Clausius 
 
 Cailletet and 
 Colardeau 
 
 Olausius 
 
 Cailletet and 
 Colardeau 
 
 F. 
 
 Lbs. 
 
 Lbs. 
 
 o P 
 
 Lbs. 
 
 Lbs. 
 
 32 
 
 0-089 
 
 
 428 
 
 336-6 
 
 
 68 
 
 0-337 
 
 
 
 437 
 
 ... 
 
 368-2 
 
 104 
 
 1-07 
 
 ... 
 
 464 
 
 489-0 
 
 ... 
 
 176 
 
 2-88 
 
 ... 
 
 482 
 
 
 576-3 
 
 212 
 
 14-70 
 
 14-70 
 
 500 
 
 687-5 
 
 ... 
 
 248 
 
 28-82 
 
 ... 
 
 527 
 
 ... 
 
 873-0 
 
 257 
 
 ... 
 
 32-35 
 
 536 
 
 944-0 
 
 
 284 
 
 52-47 
 
 
 572 
 
 1267-0 
 
 1266-0 
 
 302 
 
 
 69-10 
 
 608 
 
 1675-0 
 
 ... 
 
 320 
 
 90-00 
 
 
 617 
 
 .. 
 
 1787-0 
 
 347 
 
 ... 
 
 129-20 
 
 630 
 
 1972-0 
 
 ... 
 
 356 
 
 145-80 
 
 
 662 
 
 ... 
 
 2462-0 
 
 392 
 
 * 
 
 225-70 
 
 224-9 
 
 689 
 
 ... 
 
 2946-0 
 
 Steam Density. W. Thompson ( ' Trans. R. Soc., Edinb.,' 1849, 
 vol. xvi. p. 575) showed that the second thermo-dynamic law could be 
 used to calculate the change of density which takes place during 
 a change from the fluid to the gaseous condition provided the pressure 
 temperature curve and the latent heat be known. 
 
 - 
 
 dP' T 
 
 Here V<7 and V/ are the volumes in c.c. of one gram of steam gas, 
 and of fluid water at the absolute temperature T. J. is Joule's 
 mechanical equivalent of heat, and equals 427-98 kilogram metres ; 
 it corresponds to 778-14 foot pounds per British Termal Unit (B.T.U.). 
 See E. H. Griffiths ('Trans.,' 1893, vol. 184a, p. 496). A is the 
 
 dl 
 latent heat of evaporation at and from the temperature T ; -,_ is the 
 
 increase of temperature with pressure. 
 
 Columns 14 and 15 contain the values calculated by Bankine with 
 the help of this formula, he using Regnault's formula for steam 
 pressure, which are not absolutely the same as those taken from his 
 curve, col. 9. The values of A. are those given in col. 12 (p. 51). 
 Direct experiments on density of steam have been made by Fairbairn 
 and Tate ( ' Trans.,' 1860, vol. 1. p. 192), and more recently by Ramsay 
 and Young ( ' Trans.,' 1891, vol. clxxxiii). The capacities of Fairbairn 
 and Tate's experimental glass globes were about 75 cubic inches, which 
 is satisfactory, but the calibration of their glass stem, each division in 
 each of the three globes being exactly 252'4 grains, seems to indicate 
 that they took some details for granted ; and, further, all air does not 
 appear to have been extracted from the water ; at any rate in six out 
 of fourteen experiments the differences of level of the two mercury 
 columns are such that, unless there was air in the glass globe, 
 the experimental results are impossible, while in two other experiments 
 there is similar indication that there must have been air in the 
 
50 
 
 STEAM AND WATEB 
 
 Table of Properties of Steam and Water 
 
 Steam 
 Temperatures 
 
 Heats of Water 
 
 Volume of Water 
 
 Compres- 
 sibility of 
 Water per 
 Million 
 Atmo- 
 spheres 
 
 (6) 
 
 (Begnault) 
 
 Specific 
 
 Total 
 above 32 
 
 (3) 
 
 C. 
 
 F. 
 
 At Tem- 
 perature 
 (1) 
 
 Mean 
 
 (2) 
 
 Under one 
 Atmosphere 
 (4) 
 
 Nearly 
 Boiling 
 (6) 
 
 
 
 32 
 
 1-0000 
 
 1-0000 
 
 o-o 
 
 1-000,127 
 
 1-000,178 
 
 51-77 
 
 4 
 
 39-2 
 
 1-0002 
 
 1-0001 
 
 7-2007 
 
 1-000,000 
 
 1-000,051 
 
 50-33 
 
 10 
 
 50 
 
 1-0005 
 
 1-0002 
 
 18-004 
 
 1-000,260 
 
 1-000,313 
 
 48-54 
 
 20 
 
 68 
 
 1-0012 
 
 1-0006 
 
 36-022 
 
 1-001,751 
 
 1-001,796 
 
 46-09 
 
 30 
 
 86 
 
 1-0020 
 
 1-0009 
 
 54-049 
 
 1-004,314 
 
 1-004,356 
 
 44-14 
 
 40 
 
 104 
 
 1-0030 
 
 1-0013 
 
 72-094 
 
 1-007,73 
 
 1-007,77 
 
 42-65 
 
 60 
 
 122 
 
 1-0042 
 
 1-0018 
 
 90-162 
 
 1-012,01 
 
 1-012,05 
 
 41-68 
 
 60 
 
 140 
 
 1-0056 
 
 1-0023 
 
 108-25 
 
 1-016,97 
 
 1-017,00 
 
 41-15 
 
 70 
 
 158 
 
 1-0072 
 
 1-0029 
 
 126-37 
 
 1-022,60 
 
 1-022,63 
 
 41-3 
 
 80 
 
 176 
 
 1-0098 
 
 1-0037 
 
 144-53 
 
 1-028,90 
 
 1-028,92 
 
 42-2 
 
 90 
 
 194 
 
 1-0109 
 
 1-0044 
 
 162-72 
 
 1-035,74 
 
 1-035,75 
 
 43-9 
 
 100 
 
 212 
 
 1-0130 
 
 1-0052 
 
 180-94 
 
 1-043,15 
 
 1-043,15 
 
 46-3 
 
 110 
 
 230 
 
 1-0153 
 
 1-0061 
 
 199-17 
 
 ... 
 
 ... 
 
 49-5 
 
 120 
 
 248 
 
 1-0177 
 
 1-0069 
 
 217-49 
 
 ... 
 
 1-059,30 
 
 53-4 
 
 130 
 
 266 
 
 1-0204 
 
 1-0079 
 
 235-85 
 
 ... 
 
 ... 
 
 58-2 
 
 140 
 
 284 
 
 1-0232 
 
 1-0089 
 
 254-25 
 
 ... 
 
 1-078,86 
 
 63-0 
 
 150 
 
 302 
 
 1-0262 
 
 1-0100 
 
 272-70 
 
 ... 
 
 ... 
 
 69-8 
 
 160 
 
 320 
 
 1-0294 
 
 1-0111 
 
 291-20 
 
 ... 
 
 1-100,91 
 
 75-9 
 
 170 
 
 338 
 
 1-0328 
 
 1-0123 
 
 309-76 
 
 ... 
 
 ... 
 
 84-6 
 
 180 
 
 356 
 
 1-0364 
 
 1-0136 
 
 328-40 
 
 ... 
 
 1-126,43 
 
 93-2 
 
 190 
 
 374 
 
 1-0401 
 
 1-0149 
 
 347-10 
 
 ... 
 
 1-140,8 
 
 102-4 
 
 200 
 
 392 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 1-156,8 
 
 112-4 
 
 210 
 
 410 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 1-173,8 
 
 123-3 
 
 220 
 
 428 
 
 ... 
 
 ... 
 
 ... 
 
 
 1-192,2 
 
 134-9 
 
 230 
 
 446 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 1-214,3 
 
 147-0 
 
 240 
 
 464 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 1-235,8 
 
 160-1 
 
 250 
 
 482 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 1-255,8 
 
 173-9 
 
 260 
 
 500 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 1-284,5 
 
 188-5 
 
 270 
 
 518 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 
 Names of experimenters or calculators : Reg. = Regnault ; R. & Y. = Ramsay and Young ; 
 Griff. = Griffiths ; Rankine ; F. & T. = Fairbairn and Tate. 
 
 Column 2 is mean of column 1 ; column 3 is found from column 2 ; column 5 is found from 
 column 4 with help of column 6. Values from 248 to 320 are Hirn's experiments ; the values 
 for higher temperatures are by Ramsay and Young ; column 6 is from Landholt and Bornstein 
 up to 140 ; Ramsay and Young values from 374 ; the intermediate values are interpolated. 
 
STEAM AND WATER 51 
 
 Table of Properties of Steam and Water (cont.) 
 
 Steam 
 Temperatures 
 
 Absolute 
 Temperatures 
 
 Absolute Steam 
 Pressures in Pounds 
 per Square Inch 
 
 Total Heat 
 in Steam 
 above 32 F. 
 
 Latent Heat of Evapora- 
 tion at Temperature 
 
 C. 
 
 F. 
 
 F. 
 (7) 
 
 C. 
 (8) 
 
 Reg. 
 
 (9) 
 
 R.&Y. 
 
 (10) 
 
 n'ftj. 
 
 (ID 
 
 Reg. 
 B.TYU. 
 
 (12) 
 
 Griff. 
 B.T.U. 
 
 (13) 
 
 
 
 32 
 
 491 
 
 273 
 
 088 
 
 
 1091-7 
 
 1091-7 
 
 1074-1 
 
 4 
 
 39-2 
 
 498-2 
 
 277 
 
 117 
 
 ... 
 
 1093-9 
 
 1086-7 
 
 1071-7 
 
 10 
 
 50 
 
 509 
 
 283 
 
 177 
 
 ... 
 
 1097-2 
 
 1079-2 
 
 1063-3 
 
 20 
 
 68 
 
 527 
 
 293 
 
 258 
 
 
 1102-7 
 
 1066-7 
 
 1052-5 
 
 30 
 
 86 
 
 545 
 
 303 
 
 609 
 
 ... 
 
 1108-2 
 
 1054-2 
 
 1041-6 
 
 40 
 
 104 
 
 563 
 
 313 
 
 1-06 
 
 ... 
 
 1113-7 
 
 1041-5 
 
 1030-8 
 
 50 
 
 122 
 
 581 
 
 323 
 
 1-78 
 
 ... 
 
 1119-2 
 
 1029-0 
 
 1020-0 
 
 60 
 
 140 
 
 599 
 
 333 
 
 2-88 
 
 ... 
 
 1124-6 
 
 1016-1 
 
 1009-2 
 
 70 
 
 158 
 
 617 
 
 343 
 
 4-51 
 
 
 1130-1 
 
 1003-7 
 
 993-4 
 
 80 
 
 176 
 
 635 
 
 353 
 
 6-86 
 
 ... 
 
 1135-6 
 
 991-1 
 
 987-6 
 
 90 
 
 194 
 
 653 
 
 363 
 
 10-14 
 
 ... 
 
 1141-1 
 
 978-4 
 
 976-7 
 
 100 
 
 212 
 
 671 
 
 373 
 
 14-70 
 
 14-70 
 
 1146-6 
 
 965-7 
 
 965-9 
 
 110 
 
 230 
 
 689 
 
 383 
 
 20-78 
 
 20-76 
 
 1152-1 
 
 958-9 
 
 955-1 
 
 120 
 
 248 
 
 707 
 
 393 
 
 28-83 
 
 28-70 
 
 1157-6 
 
 940-1 
 
 944-3 
 
 130 
 
 266 
 
 725 
 
 403 
 
 39-25 
 
 39-03 
 
 1163-1 
 
 927-3 
 
 933-5 
 
 140 
 
 284 
 
 743 
 
 413 
 
 52-53 
 
 52-07 
 
 1168-6 
 
 914-4 
 
 927-6 
 
 150 
 
 302 
 
 761 
 
 423 
 
 69-23 
 
 69-00 
 
 1174-1 
 
 901-4 
 
 911-8 
 
 160 
 
 320 
 
 779 
 
 433 
 
 89-90 
 
 89-90 
 
 1179-5 
 
 888-3 
 
 901-0 
 
 170 
 
 338 
 
 797 
 
 443 
 
 115-2 
 
 114-7 
 
 1185-0 
 
 875-2 
 
 890-2 
 
 180 
 
 356 
 
 815 
 
 453 
 
 145-8 
 
 144-8 
 
 1190-5 
 
 862-1 
 
 879-4 
 
 190 
 
 374 
 
 833 
 
 463 
 
 182-5 
 
 181-7 
 
 1196-0 
 
 848-9 
 
 868-6 
 
 200 
 
 392 
 
 851 
 
 473 
 
 226-0 
 
 224-8 
 
 ... 
 
 ... 
 
 ... 
 
 210 
 
 410 
 
 869 
 
 483 
 
 277-2 
 
 275-3 
 
 
 ... 
 
 ... 
 
 220 
 
 428 
 
 887 
 
 493 
 
 336-3 
 
 335-7 
 
 ... 
 
 ... 
 
 ... 
 
 230 
 
 446 
 
 905 
 
 503 
 
 404-6 
 
 404-8 
 
 ... 
 
 ... 
 
 ... 
 
 240 
 
 464 
 
 923 
 
 513 
 
 ... 
 
 483-5 
 
 ... 
 
 ... 
 
 ... 
 
 250 
 
 482 
 
 941 
 
 523 
 
 ... 
 
 574-7 
 
 ... 
 
 ... 
 
 ... 
 
 260 
 
 500 
 
 959 
 
 533 
 
 ... 
 
 678-0 
 
 ... 
 
 ... 
 
 ... 
 
 270 
 
 518 
 
 977 
 
 543 
 
 ... 
 
 794-3 
 
 
 ... 
 
 ... 
 
 Columns 7 and 8. The absolute zero has been assumed 491 F. and 273 below freezing point. 
 Column 11 gives Regnault's experiments ; column 12 is found by subtracting column 3 from 
 11 ; column 13 is calculated by Griffiths from various data. 
 
 Bi 
 
STEAM AND WATER 
 Table of Properties of Steam and Water (cont.) 
 
 Steam 
 Tempera- 
 tures 
 
 Kankine 
 
 Density of Steam compared with Hydrogen = 1 
 
 F. &T. 
 
 (16) 
 
 Ramsay and Young 
 
 (17) 
 
 Amount of Superheat ' F. 
 
 o r* 
 
 F. 
 
 Specific 
 Volume of 
 Steam 
 (14) 
 
 Density 
 of 
 
 Steam 
 
 (15) 
 
 
 Sat. 
 
 4 
 
 
 Sat. 
 
 9 
 
 27 
 
 36 
 
 54 
 
 63 
 
 81 
 
 
 4 
 10 
 20 
 30 
 40 
 50 
 60 
 
 32 
 39-2 
 50 
 68 
 86 
 104 
 122 
 140 
 
 211,131 
 
 108,731 
 
 58,868 
 33,385 
 19,723 
 12,079 
 7,672 
 
 8-74 
 
 8-83 
 8-89 
 8-94 
 8-98 
 9-04 
 9-06 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 9-67 
 9-61 
 9-55 
 9-51 
 9-47 
 
 9-53 
 9-48 
 9-44 
 9-40 
 9-37 
 
 9-36 
 9-33 
 9-30 
 9-27 
 9-25 
 
 9-24 
 9-22 
 
 ... 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 9-83 
 
 70 
 
 158 
 
 5,027 
 
 9-10 
 
 ... 
 
 ... 
 
 ... 
 
 9-73 
 
 9-44 9-35 
 
 9-23 
 
 9-20 
 
 
 80 
 
 176 
 
 3,387 
 
 9-13 
 
 ... 
 
 ... 
 
 
 9-65 
 
 9-40 
 
 9-32 
 
 9-22 
 
 9-19 
 
 ... 
 
 90 
 
 194 
 
 2,340 
 
 9-18 
 
 ... 
 
 ... 
 
 9-76 
 
 9-60 
 
 9-38 
 
 9-30 
 
 9-20 
 
 9-17 
 
 
 100 
 
 212 
 
 1,658 
 
 9-20 
 
 ... 
 
 
 9-69 
 
 9-56 
 
 9-36 
 
 9-29 
 
 9-19 
 
 9-17 
 
 ... 
 
 110 
 
 230 
 
 1,192 
 
 9-29 
 
 9-93 
 
 9-84 
 
 9-64 
 
 9-52 
 
 9-34 
 
 9-28 
 
 9-19 
 
 9-16 
 
 ... 
 
 120 
 
 248 
 
 878-5 
 
 9-32 
 
 9-80 
 
 9-63 
 
 9-59 
 
 9-49 
 
 9-33 
 
 9-27 
 
 9-19 
 
 9-16 
 
 9-12 
 
 130 
 
 266 
 
 657-2 
 
 9-39 
 
 9-67 
 
 9-42 
 
 9-58 
 
 9-48 
 
 9-33 
 
 9-27 
 
 9-19 
 
 9-16 
 
 9-12 
 
 140 
 
 284 
 
 500-1 
 
 9-44 
 
 9-54 
 
 9-21 
 
 9-57 
 
 9-47 
 
 9-33 
 
 9-28 
 
 9-20 
 
 9-17 
 
 9-13 
 
 150 
 
 302 
 
 385-8 
 
 9-52 
 
 ... 
 
 ... 
 
 9-58 
 
 9-48 
 
 9-34 
 
 9-29 
 
 9-21 
 
 9-18 
 
 9-13 
 
 160 
 
 320 
 
 301-8 
 
 9-58 
 
 
 
 9-60 
 
 9-50 
 
 9-35 
 
 9-31 
 
 9-23 
 
 9-20 
 
 9-15 
 
 170 
 
 338 
 
 239-2 
 
 9-65 
 
 ... 
 
 
 9-64 
 
 9-53 
 
 9-38 
 
 9-34 
 
 9-26 
 
 9-23 
 
 9-18 
 
 180 
 
 356 
 
 191-7 
 
 9-73 
 
 ... 
 
 ... 
 
 9-70 
 
 9-59 
 
 9-43 
 
 9-38 
 
 9-31 
 
 9-28 
 
 9-22 
 
 190 
 
 374 
 
 155-3 
 
 9-81 
 
 ... 
 
 
 9-77 
 
 9-65 
 
 9-49 
 
 9-44 
 
 9-36 
 
 9-33 
 
 9-28 
 
 200 
 
 392 
 
 127-3 
 
 9-88 
 
 
 ... 
 
 9-87 
 
 9-75 
 
 9-57 
 
 9-52 
 
 9-43 
 
 9-40 
 
 9-35 
 
 210 
 
 410 
 
 105-2 
 
 9-96 
 
 
 ... 
 
 10-01 
 
 9-86 
 
 9-68 
 
 9-63 
 
 9-53 
 
 9-50 
 
 9-44 
 
 220 
 
 428 
 
 87-7 
 
 10-05 
 
 ... 
 
 
 10-18 
 
 10-01 
 
 9-82 
 
 9-75 
 
 9-66 
 
 9-63 
 
 9-57 
 
 230 
 
 446 
 
 73-8 
 
 10-13 
 
 ... 
 
 
 10-38 
 
 10-19 
 
 9-98 
 
 9-92 
 
 9-82 
 
 9-79 
 
 ... 
 
 240 
 
 464 
 
 
 ... 
 
 ... 
 
 
 10-64 
 
 10-41 
 
 10-18 
 
 10-12 
 
 10-02 
 
 9-98 
 
 
 250 
 260 
 270 
 
 482 
 500 
 518 
 
 ... 
 
 ... 
 
 ... 
 
 
 10-97 
 
 10-70 
 
 10-43 
 
 10-35 
 
 10-26 
 
 ... 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Columns 14 and 15, see p. 49. Columns 16 give Fairbairn and Tate's experiments recalculated ; 
 columns 17 give Ramsay and Young's experiments calculated by author. 
 
STEAM AND WATER 
 
 53 
 
 TABLE 
 
 The following table contains two sets of experiments on the specific heat 
 of superheated steam. Those made by the National Physical Laboratory 
 are limited to one pressure of 4*3 atmospheres, or 63 -2 pounds per square 
 inch, and to a range of 90 F. The experiments by Knoblauch and Jakob 
 range from two to eight continental atmospheres (14*3 pounds per square 
 inch), and from 300 to 673 F., but do not show as marked changes as 
 might be expected from the first-named experiments. 
 
 Specific Heats of Steam 
 
 National Physical Laboratory 
 
 Knoblauch & Jakob 
 
 Pressure 
 
 Temperature mean 
 
 Specific 
 
 Pressure 
 Atm. 
 
 Temperature mean 
 
 Specific 
 
 Atm. 
 
 C. 
 
 F. 
 
 Heat 
 
 Kg/cm, 
 
 0. 
 
 P. 
 
 Heat 
 
 ... 
 
 .. 
 
 ... 
 
 ... 
 
 2-01 
 
 149-1 
 
 300-4 
 
 0-478 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 2-02 
 
 188-2 
 
 370-8 
 
 0-470 
 
 ... 
 
 ... 
 
 M 
 
 ... 
 
 2-00 
 
 240-4 
 
 464-7 
 
 0-474 
 
 ... 
 
 ... 
 
 .. 
 
 ... 
 
 2-00 
 
 245-9 
 
 474-6 
 
 0-474 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 2-02 
 
 296-6 
 
 565-7 
 
 0-476 
 
 ... 
 
 .. . 
 
 ... 
 
 ... 
 
 2-01 
 
 345-9 
 
 654-6 
 
 0-486 
 
 ... 
 
 ... 
 
 
 
 ... 
 
 202 
 
 349-3 
 
 660-7 
 
 0-494 
 
 4-3 
 
 165 
 
 329 
 
 0-497 
 
 
 
 
 
 ... 
 
 
 ... 
 
 ... 
 
 4-00 
 
 170-6 
 
 339-1 
 
 0-502 
 
 4-3 
 
 175 
 
 347 
 
 0-472 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 4-3 
 
 185 
 
 365 
 
 0-455 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 4-3 
 
 195 
 
 383 
 
 0-442 
 
 ... 
 
 ... 
 
 ... 
 
 
 43 
 
 205 
 
 401 
 
 0-432 
 
 ... 
 
 ... 
 
 ... 
 
 
 
 ... 
 
 
 ... 
 
 3-99 
 
 210-5 
 
 410-9 
 
 0-490 
 
 4-3 
 
 215 
 
 4i9 
 
 : 424 
 
 
 
 
 ... 
 
 ... 
 
 ... 
 
 ... - 
 
 
 4-01 
 
 260-8 
 
 501-4 
 
 0-487 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 3-98 
 
 304-7 
 
 580-5 
 
 0-485 
 
 
 ... 
 
 ... 
 
 ... 
 
 3-98 
 
 3061 
 
 583-0 
 
 0-491 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 4-01 306-5 
 
 583-7 
 
 0-491 
 
 ... 
 
 ... 
 
 ... 
 
 4-00 
 
 350-3 
 
 662-5 
 
 0-500 
 
 
 
 
 
 6-00 
 
 180-2 
 
 356-4 
 
 0-531 
 
 
 
 ... 
 
 ... 
 
 6-00 
 
 217-5 
 
 423-5 
 
 0-502 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 6-01 
 
 259-8 
 
 499-6 
 
 0-492 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 5-98 
 
 306-4 
 
 583-5 
 
 0-490 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 6-01 349-6 
 
 661-3 
 
 0-502 
 
 . 
 
 ... 
 
 ... 
 
 ... 
 
 8-00 i 188-1 
 
 370-6 
 
 0-557 
 
 ... 
 
 
 ... 
 
 .. . 
 
 8-00 ; 240-0 
 
 464-0 
 
 0-500 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 8-OG 295-0 
 
 563-0 
 
 0-490 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 8-00 295-2 
 
 563-4 
 
 0-488 
 
 ... 
 
 . >. 
 
 ... 
 
 ... 
 
 8-00 ! 295-7 
 
 564-3 
 
 0-498 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 7-99 344-9 
 
 652-8 
 
 0-501 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 7-98 349-8 
 
 661-6 
 
 0-504 
 
 " 
 
 ... 
 
 ... 
 
 ... 
 
 800 356-0 
 
 672-8 
 
 0-509 
 
54 STEAM AND WATER 
 
 surrounding boiler. In their summary Fairbairn and Tate also 
 depart from the principles laid down by them, and instead of assum- 
 ing the saturation point to have been reached when the first change of 
 level was observed, they waited until a considerable difference of 
 pressure showed itself. The fluctuations recorded by them of the 
 levels of the two mercury columns are also not satisfactory; but 
 the general principle on which the experiments were carried out is a 
 good one, and, in spite of the above objections, sufficient reliance 
 was placed on their results to cause these to be recalculated. The 
 low-pressure tests were not made on the same principle and have been 
 rejected ; of the high-pressure ones only Nos. 1, 4, 7, 8, 9, 13 gave 
 marked indications as to when the point of saturation had been 
 reached, and only these have been used in col. 16. The values against 
 266 F. are the mean results. 
 
 Bamsay and Young's experiments extend over a much wider range 
 of temperature, but the volume of steam experimented on was only a 
 little larger than one cubic centimeter, or say one-thousandth of 
 the volume employed by Fairbairn and Tate. It would, therefore, 
 not be wise to rely on them absolutely, even although they may help 
 to explain the great difference to be found between the weight of 
 steam as measured on the indicator cards and the weight of feed 
 water. These experiments are, however, of great comparative value, 
 in so far as that they show a gradual decrease of density as the 
 super-heat is increased. Their experiments extend from 284 F. to 
 518 F., and also from 59 F. to 122 F., but the lower temperature 
 experiments are few, and not quite in accord with each other, and 
 certainly are in direct conflict with Rankme's deductions. They were 
 made in another apparatus. It is probable, therefore, that the 
 increase of density with decreasing low temperature shown in the 
 table may not be correct. Their experiments made at 392 F. and 
 464 F. are quite out of harmony with the rest, and have not been 
 taken into account in the compilation of the table. 
 
 The densities in cols 16 and 17 are expressed in terms of hydrogen 
 gas = 1 at C. = 32 F. = 491 F. absolute, and 760 mm. pressure 
 = 14*7 Ibs. per square inch. The weight of hydrogen is 0*089551 
 gram per liter. 
 
 The specific volume is the volume in c.c. occupied by 1 gram 
 steam and is easily found from the table. 
 
 According to the chemical analysis one would expect the density 
 of steam to be 8*98. This low value is probably only reached when 
 the steam is thoroughly superheated and under a low pressure. At 
 any rate in Eamsay and Young's experiments the value was still above 
 9'0 when the pressure was 52 Ibs., and the temperature 518 F., this 
 being a superheat of 234 F. 
 
 Total Heat of Steam. Regnault's experiments on the total heat 
 of steam, from 145 F. to 381 F., adapt themselves very closely to 
 the formula 
 
 H = 1101-5 + 0-305 T 
 
 where T is the temperature in degrees Fah. 
 
 This formula has been used in the compilation of column 11. 
 The Latent Heat of evaporation at any temperature is found 
 
STEAM AND WATER 55 
 
 by subtracting the total heat in the water from the total heat in the 
 steam. Eegnault carried out experiments on the specific heat of 
 water. Col. 1, the total heat in water, is the sum of these values 
 reckoned from 32 F. (see col. 3). These values have to be subtracted 
 from col. 11, the difference being the latent heat of steam. In recent 
 years the specific heat of water has been much enquired into, but 
 Eegnault's values may be accepted as correct. Kecently Griffiths 
 has recalculated these values (see col. 13). As Eegnault's results are 
 those generally adopted, these have been accepted throughout this 
 work. 
 
 Water Density and Compressibility. Up to a temperature of 
 212 F. experiments on density of water have usually been made 
 under a pressure of one atmosphere, whereas above this point the 
 pressures have been various. It has therefore been necessary to 
 correct the densities found by Hirn, and by Eamsay and Young, for 
 pressure, and this involves a knowledge of the elastic compressibility 
 of water at all temperatures. Col. 4 gives this value up to 500 F., 
 from 32 F. to 140 F. being values by Pagliani and Vicentini, 
 and above this point the values are taken from Eamsay and Young's 
 experiments. With the help of these values col. 5 has been compiled. 
 It contains the densities of water at the various boiling temperatures. 
 It should, however, be noted that these values are not direct observa- 
 tions, and it is more than probable (see retarded ebullitions, p. 57) 
 that just before bursting into steam there is a relatively large increase 
 of water volume. 
 
 Critical Temperature and Pressure. When a volatile fluid like 
 C0 2 is warmed under pressure, it will be noticed that at a certain 
 temperature, called the critical temperature, fluid and vapour cannot 
 be distinguished from each other. No increase of pressure will effect 
 condensation. The lowest pressure at which this change takes place 
 is caUed the critical pressure. According to Cailletet and Colardeau 
 the critical point for water is reached at 200'5 atmospheres and 680 
 F. ; above this temperature water does not exist, only steam. At 
 the critical temperature it is evident that there is no latent heat of 
 evaporation, because there is no evaporation. This means that if the 
 values of the latent heats in cols. 12 and 13 were extended to 680 F., 
 they would be reduced to nothing. Eegnault's values seem far more 
 likely to fulfil this condition than the other two. 
 
 It is also evident that at the critical temperatures the volume 
 of water must exactly equal the. volume of steam, for the two are 
 then identical; this means that if cols. 8 and 19 and 20 were 
 extended their values ought to grow equal to each other when a 
 temperature of 680 F. is reached. 
 
 Seeing that water on being heated under pressure approaches 
 nearer and nearer to the conditions of steam, and that steam and water 
 are undistinguishable from each other at the critical temperature, it is 
 more than likely that the change from steam to water or vice versd 
 even at low temperature is not so abrupt as is generally believed. 
 
 The following further properties of water may on occasion be of 
 service. 
 
 The Boiling Point of Salt Water is higher than that of pure water, 
 
56 
 
 STEAM AND WATER 
 
 so that steam evolved from brine must be slightly superheated ; but it 
 is only with the greatest difficulty, even in laboratory experiments, that 
 this has been verified. 
 
 Boiling Temperatures of Salt Water 
 
 Percentage of salt added to 
 100 water .... 
 
 
 
 14-9 
 
 25-5 
 
 35-5 
 
 1 
 40-7 ! 
 
 Boiling temperature at atmo- 
 spheric pressure . . F. 
 
 212 
 
 216-5 
 
 221 
 
 2255 
 
 226-8 
 
 Gerlach, ' Zeitschr. f. analyt. Chemie,' 1887, vol. xxvi. p. 413. 
 
 The Specific Heat of Salt Water is less than that of pure water, as 
 will be seen from the following table. As the density of water 
 increases with the added salt, the heat capacity of water does not 
 sink quite at the same rate as the specific heat. 
 
 Table of Specific Heat of Salt Water 
 
 Percentage of salt added 
 to 100 water 
 
 
 
 1-6 
 
 4-9 
 
 11-5 
 
 12-3 
 
 243 
 
 Specific heat of salt 
 water. 
 
 1-00 
 
 0-978 
 
 0-945 
 
 0-877 
 
 0-871 
 
 0-791 
 
 J. Thomson, Pogg. Ann.,' 1871, vol. cxlii. p. 337 ; A. Winkelmann, ' Wied. 
 Ann.,' 1873, vol. cxlix. p. 1 ; Marignac, ' Ann. Ch.,' 1876, vol. viii. p. 41. 
 
 > oiling" Phenomena. If one had never seen water boiling, and if 
 one were asked to describe what one would expect to occur if water 
 of a boiling temperature were placed in contact with a hotter plate, 
 one would be tempted to say that, at first, innumerable small bubbles 
 would form all over the surface, like dampness on a window pane ; 
 that these bubbles, like the water drops on the glass, would increase 
 in size, and would join together, and when an individual had 
 acquired a sufficiently large size, it would break away and rise to the 
 surface, the space thus left bare being at once re-covered with minute 
 bubbles. It is, however, well known that water does not boil like 
 this. When only .little heat is applied to the plate one may have to 
 wait for long periods between the appearances of bubbles, and when 
 they do show they grow so suddenly and tear themselves away so 
 quickly that the process cannot be watched. It will, however, be 
 noticed that, on its upward journey, each bubble increases in size, 
 especially at first. This cannot be due to the decreasing head ol 
 water over the bubble, for it would have to rise 30 ft. before its 
 diameter is increased to 30%. 
 
 The increased size cannot be due to the inertia of the water ; for 
 assuming that the bubble is formed with such rapidity as to impart 
 an appreciable velocity to the mass of water above it, and that in 
 coming to rest the water exerts a suction on the bubble and thus 
 increases its size, then clearly after the first increase the bubble woulcj 
 
STEAM AND WATEK r 57 
 
 decrease again. This does not seem to be the case ; besides a suc- 
 tion which \vouid double the volume of the bubble would have to 
 be about 7 Ibs. per square inch, and for however short a period 
 this reduced pressure might exist, it would cause the whole body 
 of the nearly boiling water to burst into steam. Only one further 
 explanation suggests itself, and that is retarded ebullition, which 
 means that the water is superheated. 
 
 Retarded Ebullition has for generations done service as an 
 explanation for boiler explosions (L. E. Fletcher, ' Experiments on Red- 
 hot Furnaces,' Manchester ; A. Witz, ' Comp. Rend.,' 1892. vol. cxiv. 
 p. 41), but since these have been carefully enquired into the theory has 
 never been confirmed. It is however well known that, if water be 
 carefully heated in a very smooth vessel, the temperature may be 
 raised several degrees above 212 F. before the water bursts into 
 steam. Chemists are sometimes troubled by retarded ebullition, 
 which now and then may eject the contents of test tubes, slight 
 superheating will produce this phenomenon ; for if ebullition takes 
 place when only \ F. superheat has been reached, then the 
 volume of steam which is evolved is about equal to the volume of 
 water. Of course if this sudden ebullition takes place in a closed 
 vessel hardly any bubbles would be seen, for the increase of pressure 
 due to half a degree of temperature is only one- sixth of a pound, and 
 this slight increase would at once check the sudden ebullition. Boiler 
 explosions from this cause are therefore impossible. If cold water be 
 heated in a glass vessel over a flame and properly illuminated, one can 
 see the change of density of the locally heated water. If boiling 
 water be gently heated, the irregular density is not very marked until 
 boiling actually commences, then it will be seen that the heating 
 surface is covered with a layer of what appears to be less dense 
 water, and in all probability this is superheated water, though judg- 
 ing by the small bubbles which are occasionally evolved from it, 
 the amount of superheat can hardly be more than 10 1 0o F. If 
 now a bubble be formed on the heating surface, the surrounding 
 superheated water gives up its steam, and rapidly enlarges the 
 bubble, which then rises to the surface. The current which its pas- 
 sage produces draws more superheated water to the bubble's birth- 
 place and along its path. Every succeeding bubble will therefore 
 most likely start at the same point and travel along a path which has 
 now become a channel for superheated water, and it is this water 
 which gives up its steam to the bubbles and causes them visibly to 
 increase in size as they rise to the surface. 
 
 After a time the superheated water will be distributed throughout 
 the mass of hot water, and if small solid particles are floating about, 
 they may form the starting points for a series of bubbles. A some- 
 what similar condition of things undoubtedly exists in effervescent 
 waters which have just been poured into a glass. These are super- 
 saturated with carbonic acid gas, which concentrates around small 
 floating cells and is there liberated, but steam is also a gas, and 
 superheated water is water supersaturated with steam. There is, 
 however, this marked difference, that steam has a much greater latent 
 heat of evaporation than carbonic acid, and its cooling effect is greater, 
 but this is in a way balanced by its greater volume, 
 
58 .STEAM AND WATER 
 
 Erratic Ebullition. If the above view be accepted, it is easy to 
 understand why the generation of steam is a jerky performance, 
 notably in water-tube boilers. Suppose that in a bottom tube of a 
 Belleville element, of say 100 ft. total length, a steam bubble be sud- 
 denly formed ; it will have to set the whole water column in motion ; 
 to arrest it a suction force would have to be applied in the lower 
 column, which means a reduction of pressure. In the early days of 
 this boiler, this action caused much trouble, for instead of setting the 
 upper 100 ft. column of water in motion, it was easier for the steam to 
 drive the water back into the downcast tube, and a backward circula- 
 tion was sometimes set up. In modern Belleville boilers, non-return 
 valves are fitted at the entrance to the lowest tubes, and the jerkiness 
 of the steam generation is now an essential advantage to this boiler, 
 for the suction which follows each outburst of steam draws fresh 
 water into the lower tube and thus materially assists circulation. 
 
 However, this boiler has gone out of use, and other water-tube 
 boilers have to depend on rapid circulation for the removal of steam 
 bubbles. They are mentioned here because they illustrate more 
 clearly than is possible with cylindrical boilers how pulsations occur. 
 If in the lower rows of water tubes there are many large bubbles 
 adhering to the upper surfaces of the tubes, these will act as powerful 
 non-conductors, reduce the rate at which steam is generated and cir- 
 culation maintained causing the tubes to overheat. Suddenly some 
 of the stagnant steam escapes, and the local circulation which it sets 
 up in one part of the boiler is communicated to other parts, and for 
 a time all the bubbles are swept out of their tubes. This period is 
 followed by one in which the overheated tubes produce much steam, 
 and the good circulation is maintained until the tubes are compara- 
 tively cold again. In a cylindrical boiler such irregularities in the 
 rate of ebullition may be brought about by the steam bubbles which 
 cling to the furnaces and tubes retarding heat transmission and 
 circulation, but on being liberated both are intensified. No experi- 
 ments seem to have been made with a view of ascertaining from 
 which plate surfaces bubbles are most easily liberated, though the 
 impression prevails that the rougher they are the better. 
 
 Priming. Information on this subject is as yet almost non-existent. 
 The generally accepted views are that low-pressure boilers prime far 
 more than high-pressure ones, and therefore require more steam space, 
 or perhaps more steam height ; also, that throttling the steam at the 
 main stop valve reduces or stops priming, and that the injection of oil, 
 particularly mineral oil, is a still more efficient remedy. Soda and 
 salt seem to increase priming, probably by forming soaps with the oils. 
 The action of mineral oils may be compared to the action of oil on 
 troubled waters : it prevents the formation of light bubbles. That the 
 partial closing of the boiler stop valve has an effect in reducing prim- 
 ing, while linking up the engine, so as to use the same reduced amount 
 of steam, has not, clearly points to the necessity of imparting violent 
 motion to the steam, or rather to the as yet uninjured froth, so as to 
 burst the bubbles. 
 
 J. T. Thornycroft (' C. E., ' 1890, vol. xcix. p. 41) argues this 
 point very clearly, and has effectively demonstrated that a very small 
 steam space will suffice, if only the mixture of steam and water ig 
 
STEAM AND WATER 
 
 59 
 
 properly guided. In his water-tube boiler he admits this mixture at 
 
 the upper circumference of the dome (fig. 88), and dashes it against an 
 
 internal baffle plate, whereupon the water falls to the level W and the 
 
 steam is carried off through the pipe A. 
 
 This small dome separated sufficient 
 
 steam for 774 I.H.P., equal to about 
 
 10 cubic ft. of steam per second, while 
 
 the internal diameter was only 26 ins., 
 
 and the clear height from water level to 
 
 crown of baffle plate only 15 ins. An 
 
 ordinary double-ended marine boiler of 
 
 the same power would require at least 
 
 48 ins. of steam-space height. It must, 
 
 however, be admitted that in his more 
 
 recent practice the steam drums are 
 
 larger than they used to be. 
 
 That this large space is necessary need not be wondered at ; for, 
 in spite of the wide water space between the nests of tubes, which are 
 primarily intended to act as downcast shafts, facilitating circulation, 
 they are very far removed from doing their work properly. Perhaps 
 
 FIG. 88 
 
 ooo 
 
 ,000 
 
 ,0005 
 
 ooo 
 
 ooo 
 
 <QOO 
 
 ooo* 
 ~oo| 
 
 00 
 
 oo* 
 
 bobodoo" 
 ooooooo 
 
 oooooo 
 
 QOOOOOQ. 
 
 ooooooo 
 
 KQOOOOOQ. 
 
 ooooooo 
 KOOOOOOO. 
 ooooooo 
 
 oooop 
 
 A 
 
 FIG. 89 
 
 Fio. 90 
 
 more than one-third of the total evaporation takes place at the furnace 
 crowns, but instead of allowing the steam to ascend to the water level 
 as freely as possible, by removing a central row of tubes (fig. 89), it 
 has to rise as best it can (fig. 90), and naturally struggles towards the 
 water spaces, where it comes in conflict with the downward current. 
 By closing up all but the wing water spaces, this struggle can be made 
 to grow so severe that the imprisoned steam raises the upper water 
 
60 STEAM AND WATER 
 
 level, as, for instance, in locomotive and navy boilers. The con- 
 sequence is that certain parts of the heating surface are more often 
 exposed to steam than to water, and even though they may not get 
 burnt, are occasionally ineffective. 
 
 A half-hearted attempt to direct the current of steam 
 and water is sometimes made by bolting a few plates 
 horizontally to the lower row of steam-space stays ; but 
 to be really effective they ought to cover the whole water 
 level, with the exception of the wings, and no downward 
 currents should be allowed at the centre water spaces. 
 
 In some boilers flat sheet-iron tubes are fitted to 
 wings, reaching to the boiler bottoms, but it is to be feared 
 that the inducement for the water to circulate through 
 them, while there are wider water spaces on either side, 
 is not a very strong one. Undoubtedly, however, the 
 water which does enter them must fall below the furnaces. 
 Improvements in circulation, though not a remedy 
 against priming, could sometimes be effected by removing 
 a central row of tubes from each nest, and securing ver- 
 tical plates to the outside rows of tubes, which would 
 prevent any steam from entering the water spaces. By 
 placing horizontal plates over each nest of tubes (fig. 90) 
 the separation of steam and water would also be effected ; 
 but all loose parts in a boiler are a nuisance. 
 
 The notions as to what takes place inside a boiler 
 are exceedingly vague, and it may be of interest to draw 
 attention to a few points. 
 
 Take, for instance, a boiler 15 ft. diameter and 11 ft. 
 long. Its steam space will be about 4 ft. high and have a 
 capacity of 450 cubic ft. It will be capable of evaporating 
 about 10,000 Ibs. of water per hour under natural, and 
 double that quantity under forced draught. The total 
 area of the water level is about 150 sq. ft., so that under 
 forced-draught conditions every square foot of this water 
 level emits 133 Ibs. of steam per hour, or-g^-lb. per second. 
 At 180 Ibs. working pressure this is equal to a volume of 
 ^2 cubic ft., or 144 cubic ins., per second, while at atmo- 
 spheric pressure the volume would be more than 10 times 
 as great. But even 144 cubic ins. of steam per square 
 foot of water surface is a large quantity, amounting to 
 about two bubbles 1 in. in diameter per second per square 
 inch of surface, or 2,000 per second if only -^ in. in dia- 
 meter. No wonder, then, if the water contains any 
 frothing substances, that the bubbles will not burst till 
 they are carried into the steam pipe, particularly as it 
 takes less than forty seconds to remove all the steam 
 contained in the steam space. 
 
 It is well known that it is quite impossible to make 
 soap bubbles in an electrified atmosphere, and it is very surprising 
 that in the days of low pressures no attempts were ever made to turn 
 this knowledge to practical account. 
 
 Attempts to measure the amount of priming water were first made 
 
STEAM AND WATEfi' 61 
 
 by Professor Thurston (' Am. C. E.,' 1874), by blowing part of the steam 
 intended for the engines into a calorimeter, and measuring its specific 
 heat. Comparing it with Eegnault's results, the amount of suspended 
 water could be calculated. This method being too complicated, the 
 author, while at sea, tried to determine the amount of salt carried over 
 by the steam, first by means of a salinometer, and then by means of 
 the chloride of silver test, but was unable to detect any. During the 
 trials of the Eesearch Committee (' M. E.,' 1890) and later C. J. Wilsor 
 has, with the help of a more delicate test, been able to measure the 
 priming water with great accuracy, and in all future trials of boilers 
 the tests, which are very simple, should be repeated. They can easily 
 be carried out at sea, and are also of special value to determine 
 whether the condenser is leaking or not. To a measured sample of 
 condensed steam a drop of a solution of yellow chromate of potash 
 is added, and a weak solution of nitrate of silver say 1 per 1,000 is 
 slowly added, until the water suddenly turns brown (fig. 91). 
 Eepeat the experiment with a much smaller sample of water drawn 
 direct from the boiler. It may require relatively from 20 to 100 times 
 as much nitrate of silver as in the last case, and the ratio between the 
 two is the ratio of priming water to steam. When testing the 
 condenser water, in order to ascertain whether there are any leaky 
 tubes, the comparison must be made with sea and not with boiler 
 water. As a check on these results add to the condensed water as 
 much boiler water as, according to the test, was primed over, and 
 repeat the experiment. The amount of nitrate of silver should then, 
 of course, be twice as much as that used in the first test. The water 
 which was drawn from the boiler has been partly evaporated by its 
 own heat. The correction is made by ascertaining the temperature 
 of the steam with the help of any reliable table. Subtract it from 
 1,178 F., then divide by 966, and multiply the previously found per- 
 centage of priming water by this quotient. 
 
 Great care has to be taken that no solid salt is contained in the 
 brine cock, as this would materially affect the result ; and it is also of 
 importance to draw the steam out of the main steam pipe as near the 
 stop valve as is possible, otherwise the priming water will have settled 
 on the walls. For rough estimates it will suffice if the drain water 
 from the high-pressure valve chest is taken. When the priming is tc 
 be measured of a marine boiler which uses no sea water, it is necessary 
 to add a little pure salt about ^ oz. per gallon of water, or 5 Ibs. per 
 ton. This quantity is sufficient, yet it is so small that it cannot possibly 
 do any harm. Probably the most convincing method is to use a 
 Carpenter separating calorimeter. Steam is taken from the main steam 
 pipe, passed through a separator, where it parts with its moisture, and 
 is then condensed ; the ratio of the two quantities of water is the amount 
 of priming. 
 
62 STEAM AND WATER 
 
 Circulation in Water-Tube Boilers. Elaborate and instructive 
 experiments have been made on this subject by Professor W. H. Wat- 
 kins, ' N.A.,' 1896, vol. xxxvii. p. 267, who constructed a large number 
 of models, using glass tubes instead of metal tubes and introducing oak 
 sawdust into the water to show the circulation. It was then found 
 that, especially in the large tube boilers, like the Belleville, the 
 movements of the steam bubbles were no indication as to the move- 
 ment of the water ; that, in fact, the water remained fairly station- 
 ary while the bubbles moved through it. It could frequently be 
 noticed that little heaps of sawdust collected in the more horizontal 
 tubes just below the points where the flames were striking them, even 
 although much steam was being generated a little further on just 
 over the flames. Occasionally in the Belleville boiler model these 
 heaps would be swept forward, due no doubt to a momentary suction 
 assisted by the action of the non-return valve. This stagnation was 
 not so marked in other large-tube boilers, and seemed to be a rare oc- 
 currence in the Babcock and Wilcox model boiler, but the finding of 
 loose scale in the lower tubes of full-sized ones shows that their 
 circulation is not as powerful as one would imagine. Certainly this 
 boiler offers very much less resistance to water circulation than the 
 Belleville boiler, but it suffers from the disadvantage that the water 
 which passes through the lower tubes has overcome more resistance 
 than that which passes through the upper ones. 
 
 In small-tubed boilers the sawdust and the bubbles travel 
 together, and while steam is being generated a most violent circulation 
 is set up. The motive force is the difference of the pressure of the 
 column of mixed steam and water moving upward as compared with 
 the pressure of the solid water in the downcast tubes. This motive 
 force can of course never exceed a head of water corresponding to the 
 height of the boiler, and a theoretical limit to the steaming power of 
 small-tubed boilers is therefore fixed. 
 
 The limit is a high one, possibly exceeding an evaporation of 200 
 or 300 Ibs. of water per square foot per hour with one-inch tubes in 
 boilers of ordinary dimensions, but this consideration shows that 
 attempts to reduce both the diameters of water tubes without increasing 
 the heights of the boilers may lead to failures. 
 
 Circulation Reversed. Another important matter revealed by 
 experiments like the above is that the currents in water tubes can be 
 reversed, that the bubbles instead of rising can be made to descend, 
 and then to rise in the upcast tube. This condition can be easilv 
 reproduced if in a U tube the downcast is first heated until mucn 
 steam is generated there, then if the flame be moved from this tube 
 to the downcast, there will be no reversal of current, the bubbles will 
 be seen to form near the flame in the old downcast, travel downwards 
 and then up the old upcast tube, which is of course not being heated. 
 On rare occasions a similar result is produced in experimental boilers, 
 and is then doubtless due to the already mentioned jerky generation 
 of steam. In some glass models, notably in that of the Sterling 
 boiler, one can notice that when the flame is just giving the proper 
 amount of heat the generation of steam in the front rows of tubes 
 may be so sudden that the bubbles are shot both upwards and 
 downwards. In water-tube boilers of the Yarrow type having no 
 
STEAM AND WATER ' 63 
 
 regular downcast tubes, it is probable that reversals of current often 
 take place in those tubes not in immediate contact with the fire. 
 This is perhaps no disadvantage. 
 
 Circulation Power of Bubbles. The following simple considerations 
 may be of some assistance in arriving at a correct view of the part 
 which steam bubbles play in producing circulation. If a beaker with 
 water be placed on a spring weighing machine, and a sphere of some 
 heavy material be raised or lowered with a velocity of v feet per 
 second, the balance will indicate an upward or downward pressure 
 
 of about -- pounds, where d is the diameter of the sphere 
 
 measured in inches. If the sphere be made to travel upwards with 
 such a velocity that the pressure is exactly equal to the weight of 
 water displaced by the sphere, then the maximum velocity is found 
 with which bubbles of the diameter d can rise towards the surface. 
 
 v = 2-7 N/<F'. 
 
 Bubbles of in. diameter could move upwards with a velocity of 
 0*9 ft. per second, the resistance encountered would be ?oooo lb., 
 equal to a head of ^5 in. If eight such bubbles combine, forming 
 one large one of f in. diameter, its upward velocity would be 
 1*22 ft. per second, and its resistance equal to a head of |- inch water 
 (C. H. E. Sankey, 'C. E.,' vol. cxli. p. 133, finds 1 ft. for inch 
 bubbles as a limit ; larger bubbles are probably too irregular in shape.) 
 The total relative resistance offered to the eight small bubbles is the 
 same as to the single large one of the same volume. The forces 
 which oppose the upward movements of the bubbles force the water 
 upwards, the available head of pressure being that just found divided 
 by the sectional area of the channel. Assume that (fig. 50, p. 29) a 
 vertical tube of 1 sq. ft. sectional area and 6 ft. high were placed 
 over a furnace which is producing 144 cubic inches of steam per 
 minute, and assume the bubbles to be inch diameter, then they 
 would rise through 6 ft. in 6 - 7 seconds and at any time the tube would 
 be filled with 6'7 x 144 = 860 cubic inches of steam or 800,000 bubbles, 
 of which each one would exert an upward force of 1 : 40,000 Ibs., 
 resulting in a total circulative force of 20 Ibs. per sq. ft. or about J 
 inch head of water. Assume another case in which the bubbles are 
 inch diameter, then their velocities will be 1-8 ft. per second and 
 they will pass up the 6 ft. tube in 3*35 seconds, so that the tube will 
 only contain half the above-mentioned volume of steam, viz. 430 cubic 
 inches, with the result that the head of pressure is reduced to about 
 ^ inch and the circulation is correspondingly reduced. Seeing that 
 the heat transmissions from a plate to water increases with increased 
 circulation, the best results will be obtained in those boilers which 
 produce the smallest bubbles. This is the most feasible explanation 
 for the fact that locomotive boilers work far more satisfactorily when 
 constantly trembling while running, than when used for stationary 
 purposes. 
 
 In water-tube boilers the movement of bubbles is based on some- 
 what more complicated conditions. Assume that the bubbles in a 
 vertical water tube are moving upwards, each bubble having a mean 
 length /, and separated from its neighbour by a water space of the 
 length L. The diameter d of the bubble is not quite as large as D, 
 
C4 STEAM AND WATER 
 
 the bore of the tube, as could be seen if a glass tube and coloured 
 water be used. The buoyancy of the bubble is y.l.d? ^, where y is 
 
 the density of water. The sum of the pressure against its upper side 
 and suction on its lower side is p y.l. or Z. = head of pressure. 
 This pressure,^?, imparts a downward velocity, v, to the film of water 
 round the bubble : v feet per second = 5 . *Sl (approximately). The 
 work performed by the bubble in its upward course at a velocity V 
 
 is V.y.Z.d. 2 j, and this is equal to the frictional work done by the 
 
 water on the walls of the tube : P = (v 3 l -f w r 'l). v. d, where ^ is the 
 coefficient of friction, and w is the upward velocity of the water above 
 the bubble which is found as follows : 
 
 (V _ W ).d*. I = v (D 2 - d 2 ) * 
 
 Combining these equations we get a cubic one which expresses the 
 velocity V in terms of the ratio D : d or vice versa ; then finding the 
 maximum value for V, the various other values can all be found 
 approximately 
 
 V= 1>5 
 
 Here V is expressed in feet per second and the dimensions in inches. 
 D. v and w are found from previous equations. If the rising bubbles 
 have to produce a downward current in other tubes, and if any of the 
 uptake tubes are not vertical, the problem grows a little more com- 
 plicated. 
 
 Whatever deductions may be drawn from these formulae, or from 
 similar considerations as to the action of bubbles, as to the least 
 height of boilers, smallest diameters of tubes and greatest inclination, 
 experiments must be undertaken before any definite decision is 
 arrived at. Only recently a case was mentioned to the author where 
 a four-inch waterpipe swelled locally to about nine inches diameter 
 before it burst, apparently without a cause. Here the material could 
 certainly not be blamed, nor was scale or grease found, and the only 
 other explanation which suggests itself is want of circulation. 
 
 Moist Steam. It has been clearly demonstrated that any moisture 
 carried over with the steam very materially reduces the efficiency of 
 an engine, especially by increasing the initial condensation and re- 
 evaporation; it is therefore desirable to fit steam traps to the main steam 
 pipes whenever these are long and likely to cause condensation. On 
 trials the moisture of steam should be measured ; this should be done 
 by a separator calorimeter, Carpenter's being a very serviceable one. 
 
 Superheated Steam. The specific heat of superheated steam under 
 constant pressure varies from 0'6 at 290 to 0'8 at 408 F., and should 
 not be confounded with the co-efficient 0'305 in Regnault's formula 
 for the total heat of evaporation, for it occupies a position between 
 the two specific heats under constant pressure and under constant 
 volume. After having expended much heat on the production of 
 saturated steam, only a little more is required to superheat it. If this 
 is done, all moisture is of course removed, and if sufficient heat has 
 
STEAM AND WATER 65 
 
 been added by this means, the condensation which would otherwise 
 take place in the engine, due to work done, will not take place. It is 
 very desirable to attain this object, but repeated attempts of a sustained 
 nature both at sea and on land have borne no lasting fruit, the mechanical 
 difficulties seeming more than to balance the economic results, which 
 maybe stated to be from 10 to 15 per cent. 1 The chief troubles have 
 been : cutting of the high-pressure cylinders and valve faces, occasional 
 burning of the superheater tubes and of the engine's cylinder lagging, 
 and then there is of course the danger of melting the brazed seams in 
 the copper pipes. These troubles are in the author's opinion due 
 chiefly to the absence of suitable bye passes for the funnel gases. It 
 should be possible to divert these from the superheater when the 
 engines are not working, or when the steam temperature has grown 
 too high. 
 
 Feed Heaters. A study of properties of steam (see tables, 
 p. 50) shows that by far the greatest amount of heat is spent in con- 
 verting water into steam, only about one fifth of this heat being used 
 for raising the temperature. All the heat of evaporation is carried 
 away by the engine condenser water, unless before the steam enters 
 the condenser a part is abstracted for feed-heating purposes. It 
 would, of course, be useless to employ the exhaust steam from the 
 low-pressure cylinder, for this is nearly as cool as the condenser and 
 the feed ; it is therefore customary to take the steam for the heaters 
 from the valve chest of the low-pressure or intermediate cylinder. 
 If the engines are of the triple expansion type, the abstracted steam 
 has then done respectively two-thirds or one-third of its share of 
 work, but the expenditure of heat is only about one-tenth of what 
 it would have been if this steam had been passed on to the condenser. 
 The saving is therefore considerable. 2 The steam for these heaters 
 should be drawn from the bottoms of the valve chests, so as to carry 
 with it any condensed water. 
 
 1 See C. E.,' 1891, vol. cviii. p. 474. 
 
 1 See J. A. Normand and others. ' N. A.,' 1895, vol. xxxvi. p. 35. 
 
66 
 
 CHAPTER III 
 CORROSION 
 
 EXPERIMENTS and papers on this subject are fairly numerous, and 
 before discussing the various theories it will be advantageous to 
 mention them. E. Mallet, ' Brit. Assoc./ 1838, vol. viii. p. 253 ; 1840, 
 vol. x. p. 221 ; 1843, vol. xiii. p. 1 ; and ' N. A.,' 1872, vol. xiii. p. 90. 
 In these experiments and papers the question of boiler corrosion 
 is hardly touched upon, but galvanic action and related subjects are 
 thoroughly discussed. Grace Calvert, ' Manch. L. Ph./ 1871, vol. x. 
 p. 99, shows that air in water causes corrosion. 
 
 ' Parliamentary Eeports,' Admiralty Committee on Corrosion in 
 Boilers, appointed in 1874, three reports, 1874, 1878, and 1880, c. 2662. 
 These experiments were very exhaustive ; they aimed at ascertaining 
 whether there was a difference between the behaviour of iron and steel, 
 whether the lubricants in the engines affected boiler corrosion, and at 
 determining the influence of zinc, of galvanic action, of various fluids, 
 and of air in water. 
 
 D. Phillips, ' C. E.,' 1881, vol. Ixv. p. 73, discusses the above reports, 
 and comes to the conclusion that iron does not corrode as fast as steel. 
 W. Parker, ' I. and S. I./ 1881, p. 39, like the Boiler Committee, exposed 
 various materials in actual boilers, but isolated each plate. The results 
 do not show a great difference between iron and steel. D. Phillips, 
 ' Marine E./ 1890-91, adds further experiments in support of the above- 
 mentioned views. 
 
 Other experiments on corrosion will be found in the following 
 papers : M. Lodin, ' Comp. Eend.,' 1870, vol. Ixx. p. 321. A. Mercier, 
 ' An. Mines,' 1879, 7th ser. vol. xv. p. 234, gives experiments on the 
 influence of fatty matter on corrosion of iron and steel. M. Lodin, 
 1 Comp. Kend.,' 1880, vol. xci. p. 217, experiments on corrosion of 
 various wires in hot fluids to which vegetable matter has been added. 
 M. B. Jamieson, ' C. E.,' 1881, vol. Ixv. p. 323. J. Norris, ' N. A., 1 
 1882, vol. xxiii. p. 151, determined the influence on corrosion of the air 
 contained in water. L. Gruner, ' An. Mines/ 1883, 8th ser. vol. iii. p. 5, 
 relative corrosion of 28 materials under 4 different conditions. This 
 paper contains an appendix by Bustein, which shows that exposures 
 of the samples for 112 days inside a boiler, and also in a boiler flue, 
 affected the mechanical properties (see p. 145). J. E. Fothergill, 
 ' M. E./ 1884, p. 339 ; F. Marshall, p. 344. Professor Lewes, ' N. A./ 
 1887, vol. xxviii. p. 247, influence on corrosion of the air contained 
 in water, and general views on corrosion, chiefly in sea water. 
 A. C. Brown, ' I. and S. I./ 1888, ii. p. 129. Professor Lewes, 
 
CORROSION 67 
 
 ' N. A.,' 1889, vol. xxx. p. 340. T. Andrews, ' C. E.,' 1884, vol. Ixxvii. 
 p. 323, and 1885, vol. Ixxxii. p. 281, gives experiments on corrosion 
 in sea water. A. Wagner, ' Bayerisches Industrie u. Gewerbe Blatt,' 
 1875, p. 102, various theories on the chemistry of corrosion, and gives 
 the results of his experiments on the action of various salts in hot 
 and cold water. Bursteyn, ' Mitt. Pola,' 1879, vol. xii. p. 503, experi- 
 ments on the influence of high pressure and fatty matter. H. Schnyder 
 ( ' Berg.- H.-Z., : vol. xxvii. p. 212), experiments on the behaviour of 
 zinc under various conditions. J. Dewrance, ' C. E./ 1900, vol. cxli. 
 p. 107, deals with air in boilers, and the discussion refers chiefly to 
 corrosion in H.M.S.'s water-tube boilers. Prof. Heyn and Bauer, 
 Iilitt. Berlin, 1908, 1909, determined the corrosive influence of about 
 forty salt solutions. J. N. Friend, ' I. and S. I.,' 1911, repeated some 
 of these experiments. 
 
 The main object of all these experiments is to ascertain the true 
 causes of corrosion, and to discover means for preventing it ; and since 
 steel has been substituted for iron the question of its relative liability 
 to corrode has repeatedly come to the front. No engineer with ex- 
 tended experience will hesitate to admit that steel does behave worse 
 than iron. Fortunately this view has not only not led them to return 
 to iron, with its numerous bad properties, but it has driven them to 
 adopt preventives which have now reduced corrosion in both iron and 
 steel boilers to very small proportions. These preventives are 
 
 I. The substitution of mineral lubricants for animal or vegetable 
 fats or oils: II. The use of fresh or even distilled water wherever 
 obtainable instead of sea- water. III. The removal ot air from the 
 feed water. IV. Electric currents. V. The use of alkalies. 
 
 In order to understand how these practices have been arrived at 
 it will be necessary to discuss the various theories of corrosion. 
 
 I. and V. Action of Engine Lubricants. All vegetable and animal 
 fats or oils are of the nature of salts, for they consist of bases and 
 acids. In fats and oils the base is glycerine, and the acids have 
 numerous names. Fats and oils, like some other neutral compounds 
 for instance, the carbonates of lime and magnesia and the sulphate 
 of iron can be split up into acids and bases by heating them. The 
 temperature at which this splitting up takes place with fats is a little 
 above 212 F. Thus stearine, which is the same substance as stearic 
 acid, is manufactured by raising tallow and water to the proper tem- 
 perature. Naturally the same process takes place in boilers, and the 
 liberated fatty acids are now capable of corroding the same amount 
 of iron as an equivalent weight of sulphuric acid would attack. The 
 resultant compound is ferric soap, which makes up the greater part 
 of the filthy greasy substance to be met with in some boilers. By 
 bringing the fatty acids in contact with other substances, other soaps 
 are formed. Thus with potash we get soft soap, with soda hard 
 soap ; with lime we get the very much harder soap called putty, 
 while with the oxides of lead and zinc medical ointments are the 
 products. Rosins which are the chief constituents of varnishes, 
 behave very much like oils and should not be introduced into boilers. 
 
 Whereas glycerine is one of the weakest bases, lime, potash, and 
 soda are the very strongest, and whereas the one is capable of re- 
 taining the fatty acids at a boiling temperature, the others will only 
 
68 CORROSION 
 
 part with them in presence of a stronger acid. Carbonic acid is in 
 a sense weaker than some oil and fat acids, and can be replaced if 
 they are brought into contact with carbonate of soda. Some of them 
 are not strong enough to do this direct, but must first attack the 
 iron, forming ferric soap. In such a case the soda does not prevent 
 corrosion, while in the previous one the liberated carbonic acid might 
 do just as much harm as the fat. When using organic lubricants 
 it is, therefore, better to add caustic soda or lime instead of the car- 
 bonate. Mineral oils are not double compouuds, and, like water, 
 consist of only two elements viz. carbon and hydrogen and these 
 are harmless. To add soda where these are in use would be useless. 
 
 II. The Use of Fresh Water. Since the introduction of surface 
 condensers sea water has gone out of use, and now that evaporators 
 are largely used the make up water is generally distilled. Neverthe- 
 less, sea water does leak past the condenser tube ends, and some of 
 its salts are decidedly injurious. See p. 24. 
 
 Chloride of Magnesia. Professor Lewes states that if sea water 
 be distilled while in contact with iron it gives off hydrochloric gas 
 when the volume of the water has been reduced to one-fifth, but it is 
 only too probable that before it is produced in sufficient quantities to 
 escape it must have been attacking the iron. He also mentions that 
 magnesic chloride and calcic carbonate (lime) react on each other, 
 and are converted into calcic chloride and magnesic oxide, the 
 carbonic acid escaping at a boiling temperature.' When exposed to 
 the influence of the air magnesic oxide absorbs carbonic acid, so that 
 on re-filling a boiler which has been opened for some time, and heat- 
 ing it, this acid gas is given off again. He looks on magnesium salts 
 as being decidedly injurious to the life of a boiler ; but, as all sea 
 water contains them, this should, if possible, never be admitted. 
 
 The Boiler Committee tube No. 21 contained chloride of magnesia 
 ?%nd attacked iron and steel very severely. 
 
 A. Wagner shows that if water contains chloride of magnesia, but 
 no air, it commences to attack iron at a temperature of about 212 F., 
 while the following chlorides will only attack it in presence of air : 
 they are arranged in the order of their corrosive power ammonium, 
 sodium, potassium, barium, calcium. 
 
 The experience which is accumulating with the Manchester Steam 
 Users' Association does not confirm these conclusions ; at any rate, 
 pure chloride of magnesia and water will not attack iron either cold 
 or at a boiling temperature even if oxygen be forced into the water, 
 and as far as can be ascertained the results mentioned above are due 
 to absence of precautions for the rigid exclusion of even a trace of 
 carbonic acid, such as distilling caustic soda solution in vacuo. Such a 
 condition cannot of course be attained in a boiler, and for practical 
 purposes the advice to exclude chlorides of magnesia is a good one. 
 
 Chloride of Lime acts similarly to chloride of magnesia. 
 
 Sulphates of potassium, sodium, calcium and magnesium seem 
 to protect iron, but sulphates of manganese and especially of ammonium 
 seem to corrode it. 
 
 Ammonium salts attack iron very energetically. 
 
 Magnesium Carbonate deserves special mention, for although it is 
 apparently in.&ctive U p to a temperature of about 350 F., corres- 
 
COBROSIOtt 69 
 
 ponding to a pressure of about 120 Ibs. per sq. inch, yet above this 
 temperature this salt splits up into carbonic acid and oxide of mag- 
 nesium which forms a floury deposit, a mud which settles on furnace 
 crowns and causes collapses. 
 
 Carbonates. According to Heyn and Bauer these salts are corrosive, 
 and the sodium and potassium carbonates unquestionably produce 
 pitting. According to the author's analysis of their results it would 
 seem that the protective power of these salts is a local one or patchy, 
 leaving the unprotected parts to be severely attacked (pitting) by gal- 
 vanic currents which are set up between the protected and unprotected 
 parts. All soda salts caused pitting, the severest actions being 
 with mixtures of common salt and soda ; the latter salt should therefore 
 not be usedif there is a chance of sea-water leakages entering the boiler. 
 
 Alkalies are not absolute protectors, for in high pressure boilers 
 they do not neutralise the free carbonic acid which is introduced with 
 the feed. In fact carbonate of soda is slowly converted to caustic 
 under high pressure conditions. 
 
 Oxygen and Carbonic Acid. Many experiments have been made 
 to prove that oxygen will or will not attack iron unless there is at 
 least a trace of carbonic acid present in the water. These researches, 
 including those of the Manchester Steam Users' Association leave no 
 doubt but that corrosion in the presence of oxygen is very materially 
 reduced if carbonic acid is excluded from the water. Nevertheless, 
 corrosion usually does occur after a time in the presence of pure 
 oxygen, but only very locally, as if some of the microscopic impurities 
 in the steel or iron had taken the place of the carbonic acid ; these 
 and silica salts cannot be entirely excluded from boilers so that even 
 when all carbonic acid is removed, corrosion may still be expected 
 unless the oxygen too is excluded. 
 
 Common Salt, if pure, seems to do no harm to iron, but even the 
 best commercial salt usually contains some chloride of magnesia. 
 
 Free Acids, which are sometimes proposed for boiler-scale solvents, 
 should not be used, nor should the feed water ever be taken from 
 a river near a chemical factory. Occasionally waste acids are dis- 
 charged there, which may do a serious amount of injury. This was 
 mentioned by Mr. Hallett (' M.E.,' 1884, p. 350). 
 
 Heyn and Bauer experimented with arsenic trioxide, which is 
 occasionally used as an anti-corrosive, and found that it had a pro- 
 tective influence when very dilute. They also tried chromic acid, 
 which, judging by their results with cold solutions, seems to give a 
 protective coating to steel plates (it is known to make steel and iron 
 passive). One ounce per 450 sq. ft. should afford complete protection, 
 one ounce per 1,800 sq. ft. affords partial protection, and one ounce 
 per 4,500 sq. ft. affords very little protection. 
 
 Oxidising Salts. Potassium chromate, potassium bi-chromate, 
 potassium chlorate are also fairly good protectors though the latter salt 
 is rather doubtful, but potassium bromate and sodate cause corrosion. 
 
 Deoxidising Salts might be expected to be protectors, but the 
 ferrous sulphate corrodes iron. Potassium cyanide and calcium 
 sulphide are practically neutral, but sodium sulphide and beet sugar 
 are fairly good protectors. Molasses according to reports from sugar 
 works are strongly corrosive. 
 
70 COKBOSION 
 
 Copper Salts seem to be an unavoidable, though only a minute, 
 constituent of all feed water, as is proved by the green scale in all old 
 boilers. For some unaccountable reason it does not deposit itself uni- 
 
 Fm. 92 
 
 formly over the inside of the boiler. Its presence is denied by many 
 engineers, therefore little information could be obtained as to the 
 points where it is most generally found. The author's experience is 
 that patches of green scale will be found on the zinc slabs, and also 
 near them on the iron. This is true even when the zinc t is suspended 
 from the steam-space stays (fig. 92). It will be found that the tubes 
 marked -f- sometimes contain thick patches of greenish-grey scale. 
 Small quantities are also found near the water lines of boilers, 
 particularly at both end plates. Larger quantities are found at 
 the front end plates, between the nests of tubes, and on the lower 
 part of the shell plates. The furnace bottoms usually contain the 
 greatest number of patches, but it is difficult to detect them, as 
 these parts are discoloured by grease. The furnace crowns and 
 combustion chambers are nearly always quite free from them, from 
 which it would appear that it is chiefly the non-heating surfaces of a 
 boiler which get covered. 
 
 If the copper would only distribute itself uniformly, it would act 
 as a protective scale, but as it is deposited on small areas, these may 
 become sources of danger by producing galvanic currents, at any rate 
 if there are any powerful chemicals in the boiler water, either acids 
 or alkalies, or even neutral salts. 
 
 Unless copper pipes are fitted inside the boiler, the only sources 
 of supply are the condenser tubes, the feed pipes, and the pumps. Here 
 again it is the use of vegetable and animal lubricants which causes the 
 mischief, for both readily attack copper or brass, as can be seen by 
 their greenish colour if either has been in contact with these metals. 
 Distilled water also seems to be a solvent ; it certainly attacks lead. 
 It is also believed that the minute particles which are worn off the 
 working parts of the pumps are carried bodily into the boiler, and J. 
 MacFarlane Gray (' N. A.,' 1861, vol. ii. p. 157) has detected specks at 
 the bottom of pit holes, and attributes pitting to that cause ; and Pro- 
 fessor Lewes (' N. A.,' 1889, vol. xxx. p. 340) also believes that the 
 presence of copper causes pitting. The author's observations do not 
 support either view, for although he has been very careful to observe 
 
COEROSION 
 
 71 
 
 green scale patches, he never could detect signs of pitting near them, 
 nor did the corrosion seem in any way to be increased at these points. 
 These views are supported by Mr. H. W.Hirman's statement, in answer 
 to Mr. MacFarlane Gray (see above), that land boilers using town 
 water pitted, although here there could be no question of the presence 
 of copper. Additional remarks on galvanic action will be found 
 further on. 
 
 Zinc Salts. There remains one set of salts which possibly play an 
 important part in boilers of the present day, but of which no mention 
 is made in any books or papers, and the following remarks are there- 
 fore purely speculative. It is a well-known fact that if boiler water is 
 often renewed the reduction of the zinc slabs is more rapid than if the 
 same water is used over and over again. A very obvious explanation 
 would be, that the more zinc salts are dissolved in the water, the less 
 corrosive it is. If this view is correct, the painting of the insides of 
 boilers with zinc oxide, and the addition of some zinc salts the 
 chloride of course excepted to the boiler water ought to have a bene- 
 ficial effect, and recent limited experiences show this to be the case. 
 
 Neutral Salts. The following experiments throw a little light on 
 the part played by what would appear to be perfectly harmless salts 
 in increasing the corrosive power of acids (' Journal of the Camera 
 Club,' London, 1892, vol. vi. p. 52). M. Gourdon's experiments in 
 1873 show that exceedingly diluted sulphuric acid could still be made 
 to attack zinc metal by adding to it various salts. 
 
 Added Salts of 
 
 Dilation of Acid in Water 
 
 Cobalt .... 
 Nickel .... 
 Platinum .... 
 Iron ..... 
 
 i 
 
 1 
 
 1 
 
 1 
 
 10,000 
 7,000 
 7,000 
 7,000 
 5,000 
 4,000 
 3,500 
 1,500 
 700 
 500 
 400 
 
 Gold 
 
 Copper .... 
 Silver 
 
 Tin 
 
 Antimony .... 
 Bismuth .... 
 Lead 
 
 
 On the same page L. Warnerke gives a table showing that by 
 adding various salts to a one per cent, solution of sulphuric acid, the 
 speed with which it attacks zinc metal can be varied considerably. 
 The amount of corrosion is given in decimals of millimeters of depth 
 per hour. 
 
 Salts added to the Dilate Salphnric Acid 
 
 Speed of 
 Corrosion 
 
 Nickel ammonio-tartrate ... 
 Cobalt chloride 
 Iridium chloride 
 Palladium chloride 
 
 13 mm. 
 11 
 09 
 085 
 077 
 
 
 070 
 
 Gold chloride 
 
 070 
 
 Silver ammonio-nitrate .... 
 
 025 
 010 
 
 
 
72 
 
 CORROSION 
 
 The interesting point about these results is, that both lead and 
 copper salts stand very low down in the two lists, showing that the 
 accepted notion, that they are very injurious, is, in one sense at least, 
 a wrong one ; and the bare fact that these various salts can influence 
 the behaviour of sulphuric acid makes it appear probable that zinc 
 salts also have an influence on the action of corrosive substances found 
 in a boiler apparently a beneficial one. l Possibly experiments carried 
 out on the above lines might show that manganese salts, which enter 
 the boiler water as the steel plates corrode, act injuriously, and this 
 might explain why the presence of this metal in steel has been looked 
 upon as increasing its corrodibility. 
 
 The Absorption of Air by a fluid is stated to take place as follows : 
 The volume of gas which a definite quantity of fluid can absorb is 
 independent of the pressure, and decreases with rising temperature. 
 Therefore, as 1,000 cubic ins. of water of C. will absorb 48-9 cubic 
 ins. of oxygen at atmospheric pressure, they will also absorb an equal 
 volume at two atmospheres, and so on. Of course, as the pressure is 
 increased the density of the oxygen is increased, so that the weight 
 of absorbed gas is proportional to the pressure. This law also holds 
 good for a mixture of gases. 
 
 Air and all gases are absorbed by water and change its density. 
 Thus H. J. Chaney ('Trans.,' 1892, vol. 183a, p. 334) finds that 
 1 cubic foot of water saturated with air is 321 grains lighter than pure 
 water, or about 0-075 per cent. (1 cubic foot weighs about 435,933 
 grains). It was formerly believed that all air could be expelled by 
 boiling, and that at a given temperature a fluid absorbs a given volume 
 of gas quite independent of the pressure ; more recent experiments 
 show that apparently neither view is quite correct. The weight 
 of absorbed gas is therefore proportional to the gas pressure. Ex- 
 periences as regards occluded gases in metals throw doubts even on 
 this theory. In the following table the volumes absorbed at various 
 temperatures are given, and also the weight of absorbed gas if the 
 
 Table of Gases absorbed by Water 
 
 
 Amount of Gas absorbed by 1,000 c.c. Water under a Pressure of one 
 
 
 Atmosphere 
 
 Name of Gas 
 
 
 
 Oxygen 
 
 Nitrogen 
 
 Carbonic Acid 
 
 Carbon Monoxide 
 
 Temperatures 
 
 
 
 
 
 
 
 
 
 
 Volume 
 
 Weight 
 
 Volume 
 
 Weight 
 
 Volume 
 
 Weight 
 
 Volume 
 
 Weight 
 
 o C . 
 
 F. 
 
 C.C. 
 
 per 1,000 
 
 c.c. 
 
 per 1,000 
 
 c.c. 
 
 per 1,000 
 
 c.c. 
 
 per 1,000 
 
 
 
 32 
 
 48-9 
 
 0-070 
 
 23-5 
 
 0-029 
 
 1713 
 
 3-38 
 
 35-4 
 
 0-044 
 
 20 
 
 68 
 
 33-3 
 
 0-044 
 
 16-5 
 
 0-019 
 
 942 
 
 1-73 
 
 24-9 
 
 0-028 
 
 25 
 
 77 
 
 31-0 
 
 0-040 
 
 15-6 
 
 0-018 
 
 830 
 
 1-49 
 
 23-4 
 
 0-026 
 
 30 
 
 86 
 
 29-0 
 
 0-037 
 
 14-9 
 
 0-017 
 
 738 
 
 1-31 
 
 22-1 
 
 0-025 
 
 40 
 
 122 
 
 26-4 
 
 0-033 
 
 13-6 
 
 0-015 
 
 607 
 
 1-04 
 
 20-4 
 
 0-022 
 
 60 
 
 150 
 
 23-8 
 
 0-028 
 
 12-5 
 
 0-013 
 
 438 
 
 0-71 
 
 18-2 
 
 0-018 
 
 100 
 
 212 
 
 23-2 
 
 0-024 
 
 12-9 
 
 0-012 
 
 
 ... 
 
 19-2 
 
 0-017 
 
 NOTE. The above are a summary from various experiments by Bunsen, also 
 A. Winkler, ' Zeitschr. f. phys. Chemie,' 1892, vol. ix. p. 171 ; and Bohn and Bock, 
 Wied. Ann.,' 1891, vol. xlviii. p. 319. The volumes in this table are for the re- 
 spective temperatures. 
 
 1 Mercury salts are known to be efficient protectors against rust. 
 
CORROSION 73 
 
 pressure is one atmosphere. When a mixture of several gases presses 
 on a fluid, the effective pressure of one of these gases is the product 
 of the combined pressure into the volumetric proportion of the gas. 
 Thus for air, where the volumetric percentages of oxygen and nitrogen 
 are as 20'8 to 79-2, oxygen only exerts a pressure of 0*208 atmosphere, 
 and nitrogen 0'792 atmosphere, and the weight of oxygen absorbed 
 by water when in contact with air is only 0*208 of what it would be 
 if pure oxygen were in contact with the water. Air and steam behave 
 in the same way. 
 
 By forcing gases into water, its temperature is slightly raised, the 
 liberated heat being apparently equal to the latent heat of evapora- 
 tion. This is certainly true for steam, and seems to be nearly true 
 for other vapours, such as carbonic acid, whose latent heat is 134 
 calories (Muir, pp. 294 and 996). The speed with which oxygen is 
 absorbed by water is according to M. Lodin (' Comp. Eend.,' 1880, 
 vol. xci. p. 217) 0-000036 Ib. per sq. Ib. per hour at 64 to 68 F. ; at 
 212 F. the rate is ten times faster. Lime water absorbs it at the 
 rate of - 000047 Ib. and eight times faster when hot. 
 
 If a closed vessel, fig. 91a, contains 1,000 c.c. water and a large 
 volume of oxygen at atmospheric pressure, the temperature being 
 0C. or 32 F., then the water will hold 6'07 gram of oxygen in 
 solution (see table). If the temperature be raised to 60 C. 
 the pressure beings till one atmosphere, the water will 
 hold only 0'028 gram of oxygen in solution, but-, at 100 C., 
 = 212 F., the quantity is but slightly less, viz. 0'024 gram, 
 and it may reasonably be assumed that at the higher tem- 
 peratures which exist in a boiler the water will absorb 
 about the same quantity. If in the above experiment the 
 pressure were increased to two atmospheres the weights 
 of absorbed oxygen would be doubled, but only if this 
 
 increase be due to added oxygen. If, for instance, enough FlG 91a 
 nitrogen were forced into the vessel to double the pressure, 
 then there would still be a partial pressure of oxygen of only one 
 atmosphere, and the water would not absorb more of this gas. It 
 would, however, absorb a certain quantity of nitrogen. The same 
 law holds good with a mixture of steam and a gas. Thus assume 
 that the oxygen in the above vessel is at a temperature of 100 C., no 
 water being present, and that water were then to be injected, it would 
 add its own pressure of one atmosphere to that of the oxygen, but 
 the water would not absorb more than 024 gram of this gas. 
 
 Feed pumps, if attached to the main engine, are usually designed 
 to deliver about four times as much water as is condensed, and 
 when working normally they naturally suck up a threefold volume 
 of air. This air is subjected to a pressure of say 200 Ibs., or about 
 14 atmospheres, and as the volumetric ratio of oxygen and nitrogen 
 in the air is as 20 to 80, the water will at 20 C. absorb (see table) 
 about 3 x 0-20 x 14 x 0-0333 = 0-28 times its own volume of 
 oxygen and 3 x 0*80 x 14 x 0'0165 = 0*55 times its own volume of 
 nitrogen, or a total gas volume of 0'83 times its own ; the remaining 
 2-17 volumes of air being compressed to one fourteenth, or say 0-16 
 of the feed-water volume. This feed water, heavily charged with 
 oxygen, say 2 ozs. per ton of water, enters the boiler. If it were 
 
74 COEBOSION 
 
 sprayed into the steam space it would at once be heated to say 390 F., 
 and as the partial pressure of the oxygen in the steam space would 
 not be more than one-eightieth atmosphere, very little oxygen would 
 remain in the heated water. If, however, the feed be allowed to 
 fall to the bottom of the boiler, it will be heated gradually under 
 conditions which prevent the escape of the absorbed air which is 
 retained until the mixture comes into contact with a heating surface. 
 Then while steam is being generated, which escapes, the liberated 
 oxygen attaches itself to the plate and attacks it. If the feed amounts 
 to one ton per hour it will, under the above conditions, contain enough 
 oxygen to corrode 4 ozs. of iron or say 6 Ibs. of iron per day. 
 
 Oxygen and Carbonic Acid. It has already been mentioned that 
 oxygen alone, or even when in company of neutral salts, will not 
 attack iron. Carbonic acid will attack iron, forming a ferrous salt 
 which is an active absorber of oxygen, and changes itself into a simple 
 oxide to which the liberated CO 2 is attached mechanically and ready 
 to attack the adjoining iron. 
 
 Red or Black Mud. In new boilers one frequently notices much 
 black or dark red mud , and the plates may appear to be rough or even 
 covered with pit holes, leading one to believe that the boiler is corrod- 
 ing fast. The true explanation will generally be found to be that as 
 in modern boilers the pressure and temperature are high, water 
 acquires the power of dissolving the silica in the mill scale on the 
 plates ; this slag contains ferric and ferrous oxide of iron in a finely 
 divided state which sink to the bottom of the boiler. The roughness 
 of the exposed iron plate is therefore a natural condition brought 
 about in the rolling mill and only shown up after the glossy scale has 
 disappeared. 
 
 Position of Feed Discharge. Having admitted the saturated feed 
 into the boiler, there are three ways of dealing with it : 
 
 1. Either lead it so that it enters the bottom of the boiler or easily 
 falls there. 
 
 2. Admit it at some point in the boiler say, over the back end of 
 the tubes, so that it gets thoroughly mixed with the hot water and 
 loses its air. 
 
 3. Lead it through pipes which are fixed inside the boiler, in order 
 that it may become sufficiently heated to part with all its air. 
 
 All these plans are in use. In the case of No. 3 the internal pipes, 
 if made of iron, suffer very seriously from pitting. If made of copper 
 they also suffer ; and in such cases much green scale will be found in 
 the boiler. 
 
 No. 2 is the general practice. Few engineers have had the courage 
 to discharge into the steam space, but where tried the plan works 
 satisfactorily, and ought to assist the water circulation, on account of 
 20% more steam being generated and condensed. Boilers liable 
 to prime could not be worked in this way, as was mentioned by 
 J. H. Hallett (' M. E.,' 1884, p. 350) ; but at any rate the feed should 
 then be introduced at a point where it will be heated as quickly as 
 possible. 
 
 No plan could be worse than to discharge the feed at the bottom 
 of a boiler, for it is clear that, in comparison with other parts, the 
 spaces under and between the furnaces can have only a very re- 
 stricted circulation. The defect is increased if they are filled with 
 cold, and therefore heavy, water (see fig. 93 : the dark spaces at the 
 
CORROSION 
 
 75 
 
 bottom represent cold water) ; then, as the fire bars, the ashes, and the 
 inrushing cold air all prevent heat from reaching the bottoms of the 
 
 HOT 
 
 FIG. 93 
 
 furnaces, the water has absolutely no chance of rising except by the 
 very slow process of being fed from below. This speed is about 5 fk 
 per hour, or 1 in. per minute. There is, therefore, no difficulty in 
 heating all the feed slowly and along one particular zone, viz. along 
 the line of the fire bars. Under these conditions the straining to which 
 both the shell and furnaces, but particularly the latter, are subjected 
 must be excessive, for not only is there a sudden jump from cold air 
 below the grate to white heat above them, but on the water side there 
 is also a sudden rise from about 100 F. to over 350 F. 
 
 Fitting. It is, however, not with stresses and circulation that we 
 are at present dealing, but with corrosion, due to air absorbed by the 
 feed water. What takes place 
 with this air is shown in fig. 94. 
 As soon as the cold water comes 
 in contact with the warm part of 
 the furnace plate, F, it is heated 
 and compelled to give up its air, 
 and being in contact with the 
 plate, the air settles on it. There 
 being no circulation, it is only 
 when the bubbles have grown 
 sufficiently large that they rise. 
 But during this period of rest the 
 air which contains oxygen and 
 carbonic acid will attack the iron, 
 and having formed small irregu- 
 larities, subsequent bubbles find a 
 still better lodgment and speedily 
 effect the formation of pit holes. 
 If the feed is led into the bottom 
 of the boiler, and if it is satu- Couo 
 rated with air, it can be shown 
 that every inch of furnace length 
 generates about four and a half 
 cubic inches of air per hour. This 
 in. diameter per second. The excessive differences of temperature 
 along this line of grate, and the consequent excessive straining of 
 
 FIG. 94 
 is equal to about one bubble 
 
76 
 
 CORROSION 
 
 Fm. 95 
 
 these parts, quickly loosen all rust as it is formed, so that metallic 
 iron or steel is always exposed to the air if allowed to be produced 
 there. Certain it is that if there is any pitting going on in a boiler, 
 the greater part is sure to be found along the 
 line of fire bars. Another part which is also 
 severely attacked is the under side of the furnace 
 and combustion chamber, for here the air bubbles 
 cannot rise if they have once been formed. 
 
 In support of these views it may be pointed 
 out that severe pitting frequently takes place on 
 the forward side of propeller blades at the 
 leading edge, as shown in fig. 95. Here the air 
 is not driven out by heat, but is abstracted by 
 the partial vacuum which is found there, and, in 
 spite of the high velocity of the water, there seems 
 to be sufficient time for the mischief to be done. 
 Even bronze blades are sometimes pitted at this 
 point. 
 
 Another confirmation is found in the severe 
 pitting of internal iron feed pipes ; even copper 
 ones waste away. Here the air is liberated by 
 the transmitted heat of the surrounding water, 
 and it has been suggested that long internal iron 
 feed pipes should be fitted to boilers, and renewed whenever they are 
 eaten through, for, whether this is due to the air or some other corro- 
 sive agent, it is cheaper to lose a regular quantity of temporary piping 
 than to have to renew furnaces. They last about eighteen months. 
 
 Distribution of Corrosion. One peculiarity about corrosion in 
 general is that boilers which suffer much at their lower parts are often 
 found to be as good as new in their steam spaces. In others the 
 stays and plates of the steam space suffer severely, while the lower 
 parts are only slightly attacked. This happens chiefly when the 
 feed is discharged near the water level, but, as it is next to impossible 
 to say in what path the circulation in a boiler takes place, and 
 whether the feed is carried up or down, definite conclusions cannot 
 be drawn. Another curious fact is, that if a number of boilers are 
 connected with a single feed pipe, that one which is farthest away 
 from the pumps suffers more than the others. 
 
 Steam-Space Corrosion. If it is the air which attacks the steam- 
 space stays and superheater plates, there is perhaps no other remedy 
 than not to admit it, unless it can be proved that zinc here also acts 
 as a protector. It seems to do so, but this can hardly be through 
 galvanic action. Possibly here again it is the presence of zinc salts, 
 of which it is not difficult to imagine that they have been carried 
 into the steam space. In some steamers these parts are whitewashed 
 with zinc white, and the result seems to be a satisfactory one. 
 
 It is of course possible that this corrosion is due to steam alone, 
 or to the hydrochloric acid which, as has been mentioned, escapes 
 from sea water when evaporated in iron boilers ; but it is safer to blame 
 the air, as it has not yet been shown that steam can attack iron at 
 temperatures ranging near the boiling point of water. If it did, the 
 action ought to be equally strong in all boilers, and that is far from being 
 
CORROSION 
 
 77 
 
 the case. That this form of corrosion may lead to serious results is 
 only to be expected, because of its rare occurrence and on account of 
 the wasting being very uniform. Thus, rivet heads and flat plates 
 in steam spaces retain their original shape even when most of their 
 substance is gone. As an instance a case may be mentioned where 
 the rivet heads of a steam dome were corroded as shown (fig. 96). 
 The head seemed to be intact, but had in reality disappeared, and 
 several of the rivets could be driven back with a hand hammer. The 
 dotted line shows the original thickness of the plate and size of rivet 
 head. 
 
 In another case the steam-space end plate of a boiler was wasted 
 as shown (fig. 97), and it was only due to the necessity of renewing 
 the stays that the corrosion of the plate was discovered, for the 
 shoulder round the nut had been mistaken for the washer which is 
 
 .* 
 
 Fio. 96 
 
 Fio. 97 
 
 sometimes placed there. The wasting of the front plates and front 
 ends of the steam stays is aggravated by the heat of the uptake ; but, 
 as equally bad cases are met with when baffle plates are fitted, the 
 temperature cannot be the sole cause. 
 
 The following is a curious illustration of this sort of corrosion. 
 On examining a pair of boilers of a ship which was barely four years 
 old, it was found that, although efficient baffle plates had been fitted, 
 five of the steam-space stays, situated about 2 ft. above the water 
 level, had lost nearly 30 % of their substance, but only close to the 
 smoke-box end. The starboard boiler was in a perfect condition. 
 Zinc had been used in both, but had been given up. There was only 
 one difference in the structure of these boilers, which is so small that 
 it would not be worth mentioning were it not in connection with the 
 feed. It was found that the knee pipes, K (fig. 98), which had been 
 screwed to the feed inlets, in order to produce downward currents, 
 had fallen off in the port boiler, and therefore a possibility exists that 
 the feed water of that boiler travelled in the direction shown by the 
 arrow F, and would part with its air sooner and deliver it into the 
 steam space. 
 
 Internal Feed Pipes burst, although their ends are open ; this is 
 no doubt due to water-hammer action. If the boiler water contains 
 salt, its boiling point will be higher (see table, p. 56) than that of the 
 
78 
 
 COKROSION 
 
 pure feed temporarily stopped ; there is every probability that the 
 pipe will have contained steam. As soon as the feed supply was 
 
 restarted the steam con- 
 densed, and the boiler 
 water was sucked towards 
 the valve with sufficient 
 velocity to injure the joints 
 or burst the pipe. A small 
 hole near the flange or an 
 uncemented joint entirely 
 prevents this action. 
 
 A most salutary lesson 
 was taught some years ago, 
 when the admixture of air 
 to the boiler feed was ad- 
 vocated as an improvement 
 to the circulation. Its in- 
 jurious effect was so great 
 that the idea very soon died 
 out. The Boiler Committee 
 also helped to convince 
 engineers on this point, and 
 in all high-class engines 
 care is taken to keep the 
 air out of the boiler, this being the simplest and safest plan for 
 guarding against its corrosive action. 
 
 Separate automatic feed pumps are the only efficient means of 
 securing this object. 
 
 Galvanic Action. The laws which have been discovered in this 
 branch of science may be briefly stated as follows : A continuous 
 electric current is only possible in a circuit. Its intensity, measured 
 in amperes, is equal at all points of this circuit, and is proportional 
 to the algebraical sum of the electromotive forces in the circuit 
 (measured in volts), and inversely proportional to the sum of the 
 electrical resistances of the circuit (measured in ohms). 
 
 The electromotive force makes its appearance under various 
 circumstances, viz. when two different substances are brought into 
 contact, or when changes of electricity or magnetism take place near 
 the circuit, or when heat is made to travel along part of a circuit. 
 Here only the former case will be dealt with. 
 
 If a circuit is constructed consisting only of solids, then no current 
 will be generated, because the sum of electromotive forces equals 
 nought. Therefore, if the electromotive force due to contact of one 
 metal with several others is known, that between two of these is 
 found by the difference. The following example will illustrate this. 
 The electromotive forces in volts due to contact with iron are 
 
 . 98 
 
 Carbon 
 
 Platinum 
 
 Copper 
 
 Iron 
 
 Tin 
 
 Lead 
 
 Zinc 
 
 -485 
 
 -369 
 
 -146 
 
 
 
 + 313 
 
 + 401 
 
 + 600 
 
 To find the value when, for instance, carbon and copper are 
 
CORROSION 
 
 79 
 
 brought into contact we have '485 (- -146) = - '339. These 
 values change considerably with rises of temperature. If, therefore, 
 one of the points of contact in a metallic circuit is heated, the 
 electromotive force at this point will be altered, and a current pro- 
 duced. Thus, at 530 F. the electromotive force between copper and 
 iron is reduced to 0, and a circuit consisting of only these two metals, 
 but with one joint heated and the other cold, would show an excess 
 of potential of - *146 volt in one direction. All thermo-electric piles 
 are constructed on this principle. With fluids, or with solids and 
 fluids, this simple law does not exist, as will be seen from the following 
 values of electromotive force which appear on immersing any of the 
 above solids in pure distilled water, and also in sea water. 
 
 Table. Electromotive Forces 
 
 Fluids 
 
 Carbon 
 
 Platinum 
 
 Copper 
 
 Iron 
 
 Tin 
 
 Lead 
 
 Zinc 
 
 Distilled water 
 
 From f + -010 
 to ( +-017 
 
 ( +-285 
 1+-345 
 
 (+100 
 
 1 + '26ft 
 
 -148 
 
 +177 
 
 +171 
 
 f-505) 
 1+-156} 
 
 Sea water 
 
 ? 
 
 -856 
 
 -475 
 
 -605 
 
 -334 
 
 -267 
 
 -565 
 
 The electromotive force in the circuit (fig. 99) would therefore be 
 as follows : 
 
 Contact copper and iron . . "146 volt 
 iron and salt water . '605 
 salt water and copper 4- -475 
 
 Electromotive force in circuit '276 volt 
 
 Jb'lti. 
 
 A Darnell's cell, consisting of copper, zinc, sulphate 
 of zinc, porous cell, sulphate of copper, has an electro- 
 motive force of about 1*10 volt. 
 
 One effect of the electric current is to produce chemical changes in 
 the fluids through which it passes, usually splitting them up into 
 the elements. It has been found that the amounts are strictly pro- 
 portional to their atomic weights. Thus a current of one ampere, 
 passing through water during one second, will produce '0001038 gram 
 of hydrogen (H 2 ), and 0'5 x 15-96 times as much oxygen (0), viz. 
 '0008283 gram. If the electricity was produced by a Daniell's cell, 
 which then of course forms part of the circuit, it would be found 
 that during this second its zinc has lost '003367 g-am, and its copper 
 gained -003279 gram, these quantities being proportional to their 
 respective atomic weights. Iron would have lost -002900 gram. 
 
 This loss of metal at the electrodes is said to be a secondary 
 action, being due to the dissolving power of the elements produced 
 there. Oxygen and hydrogen would be liberated from salt water ; 
 but the former gas, being nascent, would combine with the iron, if 
 that is the metal of the electrodes. 
 
 It is evident that the chemicals produced by these secondary 
 actions must influence the electromotive forces in the circuit ; this is 
 called polarisation. Iron shows this property in a very, marked 
 degree. 
 
 If the positive electrode be made of iron, which, as has been stated, 
 
80 COEROSION 
 
 is a distinctly electropositive metal, it will very soon change its nature, 
 and grow even more electronegative than copper. The unexposed 
 parts will still be electropositive. If the whole piece of the iron is 
 now placed in the fluid, a strong current is set up from its negative 
 to its positive end, and through the fluid back to the negative part ; 
 but very soon the current ceases, and on examination it will be found 
 that the electronegative property has spread over the whole piece. 
 Other means for making iron electronegative are dipping it into 
 chromic or nitric acid, or heating it in air in fact, any process 
 that will oxidise it ; and there seems little doubt but that this form 
 of polarisation is due to a scale of oxide of iron, which in some cases is 
 so fine as to be invisible. This would lead to the conclusion that iron 
 ought not to rust beyond its initial stage ; but, as it does so, particu- 
 larly in boilers, there is no alternative but to admit that this beneficial 
 change is not possible at a boiling temperature, or that the galvanic 
 action, which produces it and causes it to spread, does not exist in a 
 boiler, or will not act in the same way on large surfaces as on small 
 ones. Electronegative iron can be brought back to its primary con- 
 dition by making it the negative electrode. This is probably due to 
 the reducing action of the hydrogen on the oxide of iron. 
 
 The presence of hydrogen on the electrodes also influences the 
 workings of a circuit, partly increasing the resistance and partly mak- 
 ing the electrode more electropositive. It is, therefore, not surprising 
 that the galvanic actions either do not occur, or remain unnoticed 
 when the electromotive forces are weak. Some allowance should 
 therefore be made for the density of a current ; this is measured by 
 dividing its intensity by the sectional area of any particular point of a 
 circuit ; and it is of interest to note that the denser it is at the nega- 
 tive electrode, the more ozone instead of oxygen is generated there. 
 
 Irregular Potentials on iron surfaces. If a thoroughly cleaned 
 piece of iron be placed in a neutral electrolit, as for instance, dilute 
 brine, and if two short pieces of rubber tubing be placed on the iron, 
 and polished iron terminals of a sensitive galvanometer be slipped 
 into them, then, if the electromotive condition of the iron plate and 
 the two terminals were the same, there would be no current. But as 
 a matter of fact a current indicating differences of voltage will show 
 itself, and if one of the rubber tubes with its terminal be moved 
 about the plate, considerable variations of voltage will be discovered, 
 indicating either that the cleaning process was not a perfect one or 
 that there are voltage differences in the metal. These differences 
 are spread over large areas, but the microscope reveals minute 
 irregularities which, as they are selectively attacked by etching fluids, 
 must give rise to minute local currents whenever any electrolitic fluid, 
 one which is a good conductor of electricity, is present ; which 
 means that concentrated solutions of salts will assist corrosion unless 
 they are alkaline or otherwise anti-corrosive. 
 
 Centres of galvanic action can be revealed as follows (see * Cor- 
 rosion of Iron and Steel ' by Newton and Friend). Prepare a clear 
 solution of gelatine or agar-agar (1-5 per cent.), add 2 per cent, of 
 standard phenalphthalein solution (1 per cent, in strong alcohol), 
 neutralise and add 7 per cent, of a 1 per cent, solution of potassium 
 ferri-cyanide. Immerse a piece of warmed iron into this solution 
 
COEROSION 
 
 81 
 
 and allow it to cool and solidify, then some regions will develop red 
 others blue tints. The experiment illustrates very clearly the nature 
 of local corrosive action. 
 
 IV. Galvanic Action of Zinc. If slabs of zinc are fitted in such a 
 manner as to be in metallic contact with the iron (see fig. 100), a 
 current passes from zinc to water, to iron, and back, zinc 
 being dissolved and hydrogen evolved on the iron surface. 
 
 If the zinc is connected to the iron plates by means 
 of a copper wire, there will be two circuits, viz. one from 
 the zinc to water, to copper, and one from iron to water, 
 to copper; the one current wastes the zinc, the other 
 the iron. If, therefore, the zinc does protect the iron 
 from corrosion, it must be due to some other cause than 
 galvanic action. Copper pipes should produce a current 
 from iron to water, to copper, and the iron should grow 
 electronegative. 
 
 The intensities of electric currents which might be 
 expected in a boiler, if no polarisation took place, are 
 very difficult to estimate, as the laws which govern the 
 flow of electricity in conductors of large dimension have 
 not yet been clearly formulated. The resistance of a 
 conductor is proportional to its length, and inversely proportional 
 to its sectional area. For a cubic centimeter and per cubic inch we 
 have the following resistances measured in ohms : 
 
 FIG. 100 
 
 
 Per Cubic Centimeter 
 
 Per Cubic Inch 
 
 
 000,001,579 
 
 000 000 621 
 
 
 000,001,611 
 
 000 000 635 
 
 
 000,009,638 
 
 000 003 81 
 
 Mercury 
 1 water + -055 salt 
 1 + -0425 
 1 + -0212 
 1 + -0106 
 
 000,094,340 
 91-2 
 123-0 
 235-0 
 434-0 
 
 000,037,1 
 35-9 
 48-5 
 92-6 
 170-8 
 
 Prof. Heyn and Bauer (Mitt. Berlin, 1908), give full details of electromotive 
 differences and of resistances for a large number of salt solutions. 
 
 This table shows that the resistance in the metal may be neglected, 
 but it is also evident that, except when the electrodes are almost in 
 contact, the fluid resistance will reduce the intensity of the current 
 excessively. 
 
 Take, for instance, a strip of iron 1 in. 
 wide (fig. 101), from which part of the 
 scale, S, has been removed, exposing the 
 iron at Fe to the salt water, W ; then a 
 current will flow from Fe to W, to S, and 
 back. Eestricting the observation to the 
 small zone of the diameter D, the avail- 
 able section of the conductor is | say, ^ in. and its mean length 
 from Fe to S is ^^ L in. Assuming that the water contains 5'5% 
 
82 COBKOSIOtf 
 
 salt, the resistance of this small element would be (35'9 x 1 ! 507 = ) 
 54*2 ohms + the resistance of the scale and iron, say 60 ohms. 
 
 Assuming also that the electromotive force of iron scale in salt 
 water is the same as for copper, the electromotive force of such an 
 element would be -276, which would give a current of *- 2 ^f = -0046, 
 which would be capable of corroding -0022 Ib. per day, or at the rate 
 of about ^ in. in 60 days. At one inch distance from the edge of 
 the scale (see fig. 101) the action would be about 3/ of the above, 
 showing how rapidly it diminishes with the distance. 
 
 The Galvanic Action of Zinc in Boilers. If galvanic currents exist, 
 the studs by which the slabs are secured ought to remain bright, at 
 least within one-sixteenth of an inch of the metal ; but it is well known 
 to those who take much trouble in keeping up a good metallic 
 connection that corrosion takes place even at the contact surfaces, 
 which have to be scraped or filed after every voyage. The current 
 produced by zinc, iron, and sea water is about twice as strong as that 
 of scale and iron, but as it has no effect on its immediate surrounding, 
 it is hardly probable that it will have much influence on the more 
 distant parts, which are separated from it by several feet of salt 
 water. 
 
 In spite of these estimates, it can be shown experimentally that zinc 
 and iron (wire) if placed together in aerated water, but without touching 
 each other, will both corrode ; if the iron wire be attached to zinc, only 
 the zinc corrodes. This, however, is only true when certain salts are 
 present in the water, and that may explain the varied experiences as 
 regards zinc. 
 
 Some light may perhaps be thrown on this very difficult subject 
 by experiments similar to the following. Tie a small piece of 
 zinc to a piece of rusty iron and immerse in a 5/ solution of 
 caustic soda ; very soon the rust will fall off and a dull iron surface 
 appear. 
 
 Protection by Galvanic Currents. Views like the foregoing 
 naturally suggest that protection against corrosion would be afforded 
 by means of externally produced galvanic currents, which should be 
 of such an intensity and should be so directed that they would more 
 than balance any local currents. It is, however, only comparatively 
 recently that Mr. Cumberland has perfected the idea. He suspends 
 one or more iron anodes in the boilers, and passes currents of about 
 2 to 4 amperes (according to the area of the heating surface) through 
 these anodes into the boiler water, thence to the heating surface and 
 back to the dynamo. These currents are of course far cheaper than 
 those produced by zinc slabs and more certain in their action, and 
 should offer the further advantage of polarising the whole inner 
 surface of a boiler, so that after a time comparatively weak 
 currents could be used. The loss of iron from the anode should be 
 about 1 to 4 ozs. per day. Carbon anodes should not be used on 
 any account, because they do not destroy the hydrochloric acid or 
 other corrosive agents which are formed on their surfaces. Suitable 
 safeguards must be provided against passing the current in the 
 wrong direction. 
 
 Composition of Boiler Plates and Corrosion. A subject to which 
 sufficient attention has not yet been paid is the influence of the com- 
 
CORROSION 83 
 
 position of iron and steel on their behaviour in the presence of corrosive 
 fluids. It is believed that manganese increases corrosion, while there 
 can be no question that nickel reduces it. Carbon behaves very 
 strangely, and it would seem as if in one form viz. as found in annealed 
 steel it increased corrosion, whereas in hardened steel it reduces it. 
 However there is little scope for improvement, because its percentage 
 is fixed by other considerations. 
 
 A few remarks on some of the results of the experiments carried 
 out by the Admiralty Boiler Committee will not be out of place here. 
 
 As in the case of Mr. Parker's experiments, small samples of steel 
 and iron plates were exposed in various merchant and Government 
 steamers, and their losses ascertained. The unit of comparison is 
 1 grain per square foot per 10 days, equal to about -$^Q in. per annum. 
 
 It was found that when using jet condensers the corrosion was very 
 erratic, ranging from 35*5 to 281*3 grains ; but there were only four of 
 these experiments. 
 
 Influence of Condenser Tubes. In four cases copper-tubed surface 
 condensers were used, and the corrosion was slight. There were 25 
 cases of brass condenser tubes. The corrosion in their boilers was 
 slight, except in two cases, with which respectively colza and Eangoon 
 oil were used as lubricants in the cylinders. With these two excep- 
 tions the maximum and minimum losses were 128'8 and 16'8 grains. 
 In only two of these cases was zinc used, and its influence was not 
 marked. The cylinder lubricants were nearly always mineral oils. 
 There were seventeen cases of tinned condenser tubes. Their influence 
 was very marked, the corrosion being far severer than under the other 
 conditions. Mineral oil was used in four of these ships, and the 
 corrosion varied from 204'6 to 362*2 grains. In these cases the use of 
 zinc alone does not seem to do much good, the losses in three cases 
 being 129'6, 215'2, and 503'2 grains. On the other hand, when chalk, 
 Portland cement, and, strange to say, tallow were placed in the boilers 
 whose condenser tubes were tinned, the losses were much reduced, 
 two cases being as low as 32'7 and 39'7 grains. In two boilers 
 soda was used. Its action is not a decided one, for the losses were 
 30-6 and 376'3 grains. 
 
 Consumption of Zinc. In the reports of the Boiler Committee 
 information will also be found as to the loss of zinc when fitted in 
 boilers. In the case of H.M.S. ' Crocodile ' 425 to 630 Ibs. of rolled 
 zinc were consumed per boiler per annum, while in H.M.S. ' Serapis ' 
 the quantity was 236 to 420 Ibs. This is only the actual loss as found 
 by weighing the zinc before and after each voyage. J. Morris, ' N. A.,' 
 1882, vol. xxiii. p. 151, states that one slab 12 x 12 x 1J inch was com- 
 pletely consumed in 6 weeks. The use of zinc as an anti-corrosive 
 is first mentioned in 1875. 
 
 In addition to the general remarks about preventing corrosion 
 (p. 67) the following have suggested themselves. Strong chemicals, 
 either alkalies or acids, should not be used. Certain salts increase or 
 reduce the speed with which iron is attacked. Zinc salts appear to 
 reduce the action, tin salts to increase it. Air, being the probable 
 cause of pitting, should be carefully excluded. 
 
84 
 
 OHAPTEK IV 
 FUELS AND COMBUSTION 
 
 Combustion. When two substances, having a chemical affinity for 
 each other, are brought together under favourable conditions, they 
 combine, forming a new compound. During this combination heat 
 is evolved, which, if the chemical affinity is sufficiently strong, will 
 raise the temperature of the substances to such a height that they 
 grow luminous. This is called combustion. The term is not restricted 
 to the burning of coal, wood, oil, or gas in air, but is applicable to the 
 burning of these or other substances in any other gas, such as chlorine 
 or hydrogen, and is sometimes used to denote a similar process in 
 which only solids or only fluids combine. It may be illustrated by 
 igniting gunpowder, by dropping potassium metal into mercury, or by 
 heating a mixture of iron filings and sulphur. In any of these cases 
 luminous heat is generated. 
 
 Slow Combustion is a term which is commonly restricted to express 
 decay of organic matter, but the process is met with on a large scale 
 in every coal mine, where it is the cause of the increased temperature 
 of the ventilating air as it leaves the shaft. In our lungs a process of 
 slow combustion is continually proceeding, and in the tarnishing of 
 metals the same action is manifested. Thus magnesium wire if lighted 
 burns, if exposed to atmospheric influences it tarnishes. In both cases 
 oxide of magnesium has been formed. 
 
 When burning coal in a boiler furnace, the main object is to obtain 
 heat ; slow and imperfect combustion have, therefore, to be prevented. 
 The one takes place generally, but not always, if the air is in excess 
 and too cold, while the other is caused by an insufficient supply. 
 
 Heat, as is well known, is not the same thing as temperature. It 
 is a quantity and not a condition. It is measured in units of heat 
 (called calories), of which each one will raise the temperature of one 
 pound of water one degree Fahrenheit. It is often more convenient 
 to use another measure, viz. the evaporative unit. This is equal to 
 the amount of heat which will evaporate one pound of boiling water 
 from and at 212 F. One evaporative unit equals 966 calories, or 
 heat units, or thermal units (J. K. Cotterill, London, 1878, p. 314) ; 
 it is also equal to 22'63 horse-power during one minute, while one 
 calorie per second equals 1*4054 horse-power. 
 
 Heats of Combustion. Exhaustive experiments have been made 
 on numerous elements and chemical compounds to determine the 
 
FUELS AND COMBUSTION 
 
 85 
 
 amount of heat generated during the processes of combustion, 
 chemical combination, absorption, and solution. Most of these 
 results are contained in M. M. P. Muir's ' The Elements of Thermal 
 Chemistry,' 1885. In this book the kilogram and the degree centi- 
 grade are employed, and in order to reduce the values to English 
 measure they have to be multiplied by , or divided by 536f , to convert 
 them respectively into thermal or into evaporative units. 
 
 For convenience in calculating the heats of complicated chemical 
 processes the values in that and similar books are not stated per unit 
 of weight of each element or substance, but per atomic weight. Thus 
 the value for pure carbon is given for 12 His. and not for 1 kil. of 
 carbon, because the atomic weight of this clement is 12. 
 
 The following table contains a few of the most important deter- 
 minations. See also W. Ostwald, 1887. 
 
 Table of Heats of Combustion of Elements and Compounds 
 
 
 
 Heats of Combustion 
 
 Substances 
 
 Formula 
 
 Per Atom. 
 Weight 
 
 Per Pound of Fuel 
 
 Per Pound of Oxygen 
 
 
 
 B.T.U. 
 
 B.T.TJ. 
 
 Evaporative 
 Units 
 
 B.T.U. 
 
 Evaporative 
 Units 
 
 Diamond 
 
 C + 2 
 
 168,000 
 
 14,000 
 
 14-50 
 
 6,250 
 
 5-44 
 
 Native graphite . 
 
 C + 2 
 
 168,500 
 
 14,040 
 
 14-53 
 
 5,266 
 
 5-45 
 
 Carbon, amorph. . 
 
 C + 0., 
 
 174,500 
 
 14,540 
 
 15-07 
 
 5,454 
 
 5-65 
 
 Do., imperfectly 
 
 
 
 
 
 
 
 burnt . 
 
 c + o 
 
 52,100 
 
 4,340 
 
 4-50 
 
 3,257 
 
 3-37 
 
 Silicon, amorph. . 
 
 Si + 3 
 
 395,000 
 
 14,100 
 
 14-60 
 
 8,229 
 
 8-51 
 
 Sulphur (melted) . 
 
 S + 2 
 
 130,200 
 
 4,069 
 
 4-20 
 
 4,069 
 
 4-22 
 
 Phosphorus 
 
 
 
 
 
 
 
 (yellow) 
 
 Po+0 5 
 
 666,000 
 
 21,500 
 
 22-30 
 
 8,326 
 
 8-61 
 
 Hydrogen to water 
 
 H~ 2 + 
 
 123,000 
 
 61,156 
 
 63-70 
 
 7,688 
 
 7-96 
 
 to steam 
 
 H 2 + 
 
 105,720 
 
 51,322 
 
 54-70 
 
 6,608 
 
 3-84 
 
 Iron 
 
 Fe 3 + 4 
 
 477,000 
 
 2,751 
 
 2-84 
 
 7,464 
 
 7-70 
 
 Carbonic acid 
 
 CO + 
 
 122,400 
 
 4,375 
 
 4-50 
 
 7,651 
 
 7-93 
 
 perl carbon 
 
 CO + O 
 
 122,400 
 
 10,200 
 
 10-57 
 
 ... 
 
 ... 
 
 Marsh gas . 
 
 CH 4 + 4 
 
 376,200 
 
 23,512 
 
 24-30 
 
 5,878 
 
 6-09 
 
 Partial Combustion. The heat generated by the combustion of 
 28 Ibs. of carbonic oxide (CO = 12 C + 16 O) amounts to 126'9 
 English evaporative units. If this heat be added to the 53'9, which 
 are generated by imperfectly burning 12 Ibs. of carbon, 180*8 units 
 are obtained, which are exactly equal to the heat evolved by burning 
 these 12 Ibs. of carbon to carbonic acid in one operation. This shows 
 that, as regards the final result, it does not matter whether carbon 
 is burnt in one or in two stages, or, in other words, whether it is 
 completely burnt at once, or is first converted into carbonic oxide gas 
 and then burnt. Another feature of interest is that the partial 
 burning of 12 carbon, to form 28 carbonic oxide, only produces 42'5% 
 of the heat which will be evolved when 28 carbonic oxide are burnt 
 to carbonic acid. The remaining 57'5% might be looked upon as the 
 latent heat of evaporation of 12 Ibs. of carbon. This would imply 
 that it requires four and a half times as much heat to evaporate 
 
86 FUELS AND COMBUSTION 
 
 carbon as to evaporate water. But this simple relation is not supported 
 by other experiments, and from a study of the heats of combustion of 
 various chemical compounds it may be inferred that the calorific 
 value of any fuel cannot be determined accurately by calculations 
 based on chemical analysis alone. 
 
 Heating Power of Fuels. There are two methods of determining 
 the heating power of fuels : either by measuring the amount of heat 
 generated during their combustion, or by chemically analysing them, 
 and summing up the known amounts of heat which each element 
 would generate if burnt separately. The serious difficulties which at 
 one time beset the first of these methods have been successfully over- 
 come by the use of the so-called 
 
 Bomb Calorimeter. (See Berthelot and Vieille, ' An. Ch. et Ph.,' 
 1887, vi. vol. x. p. 433 ; I. Mahler, ' I. and S. I.,' 1892, p. 183.) 
 The fuel is powdered and placed in a small platinum crucible inside 
 a strong iron bomb. Moist oxygen, under a pressure of 350 Ibs., is 
 then admitted, and the whole is placed in a calorimeter, and allowed 
 to cool till the water temperature has grown steady. The fuel is ignited 
 by electricity, and is consumed rapidly and completely. The rise of 
 temperature of the calorimeter, amounting to about 5 F., is then the 
 measure of the heat evolved. 
 
 Although the combustion is a perfect one, a necessary correction 
 has to be made for the condensation of the steam produced, for it 
 must be remembered that at the temperature of the waste gases of 
 a boiler all moisture contained in them exists as steam. Assume that 
 the fuel contains 80/ carbon, 4/ moisture, and 5/ hydrogen, the 
 latter combining with an eightfold weight of oxygen and producing 
 45/ additional moisture or steam, we would obtain in the bomb 
 calorimeter from the carbon 0-80 x 14,540 = 11,632 B.T.U. 
 and from the hydrogen 0-05 x 61,156 = 1,223 B.T.U. 
 
 Total = 12,855 B.T.U. 
 
 But in a furnace 45 4- 5 = 49/ of moisture 
 
 abstract 049 x 1,016 B.T.u! at 60 F. = 498 B.T.U. 
 
 leaving a net available heat at 60 F. of 12,357 B.T.U. 
 
 or nearly 4/ less than the uncorrected bomb determination which, 
 
 it is evident, should always be accompanied by a chemical analysis. 
 
 All uncertainty about radiation, and the trouble due to the friction 
 of the mercury in the thermometer, have been overcome by the 
 arrangement adopted by C. J. Wilson, who during each experiment 
 adjusts the temperature of the surrounding envelope so as to agree 
 with the changes of the calorimeter water. 
 
 Formerly the only reliable calorific measurements had to be carried 
 out in the elaborate instrument designed by MM. Faber and Silber- 
 mann, in which the fuel was consumed in an atmosphere of oxygen 
 under normal pressure. The escaping gases were led through a long 
 cooling tube, and their temperature measured. They were then 
 collected, and analysis carried out, and accurate corrections were 
 made for incomplete combustion. 
 
 W. Thompson Calorimeter. Fig. 102 shows a simple, and, for 
 comparative purposes, a reliable instrument. The broken (not 
 powdered) fuel is weighed and placed in a small platinum crucible, F, 
 
FUELS AND COMBUSTION 
 
 87 
 
 FIG. 102 
 
 which is supported in a fork by the lower lid of an open-ended 
 bottle, C. This lid is pierced by a few tubes, D, having very small 
 holes at their ends. A tube, O, of fire- 
 proof material reaches through the upper 
 cork down to the fuel. Its one branch 
 is connected by means of an india- 
 rubber tube to an oxygen flask, and its 
 vertical branch is closed by a nipple or 
 stopper. T is a very sensitive thermo- 
 meter. 
 
 When ready the bottle C is lowered 
 into the calorimeter W, containing a 
 weighed quantity of water, and is 
 allowed to remain there till the tem- 
 perature is steady. Care has to be 
 taken not to allow any escape of air, 
 otherwise water will enter through the 
 tubes D and flood the fuel. When 
 ready, a small piece of glowing tinder 
 is dropped down the tube O, which is 
 at once closed again, and the blast of 
 oxygen turned on. The products of 
 combustion escape through the tubes D, 
 parting w r ith most of the heat which 
 they contain to the surrounding water. 
 After five or ten minutes the combustion 
 is completed ; the water is allowed to enter the bottle, cooling the 
 interior, and is then expelled, and the generated heat can now be 
 estimated by measuring the total rise of temperature of the water, 
 which amounts to from 3 to 6 F. To obtain accurate results various 
 precautions must be taken, of which some of the more important are : 
 reduction of losses by radiation ; the use of moist oxygen of the same 
 temperature as the calorimeter, so that none of the calorimeter water 
 is evaporated. This water may be 
 slightly acidulated, so that it will absorb 
 no carbonic acid. The correction for 
 complete absorption in water would be 
 a subtraction of '25 evaporative unit 
 for each pound of gas absorbed, or '92 
 for each pound of carbon burnt. If 
 caustic soda were added to the water 
 other allowances would have to be made. 
 The amount of hydrogen and moisture 
 in the coal, which is all converted 
 into water, not steam, must be allowed 
 for. 
 
 Berthier's Method is based on the 
 fallacious idea that the amount of heat 
 generated by burning a fuel is propor- 
 tional to the oxygen consumed, but being a fairly simple one, it may 
 occasionally be of use. It is carried out as follows : Accurately 
 weigh, say, 25 grains of fuel, and mix them intimately with 2 oz. of 
 pure litharge, and pour them into a crucible (fig. 103), B and F. They 
 
 FIG. 103 
 
88 FUELS AND COMBUSTION 
 
 are then covered with 1 oz. of pure litharge, L, and over all is placed 
 a layer of in. of broken glass, G. The crucible is then heated to 
 redness, care being taken that the top grows hot first, so as to melt 
 the glass, and that it is well protected from smoke. After about 
 three-quarters of an hour's heating, it is allowed to cool, and is then 
 broken up. It will be found to contain a button of lead, B. This is 
 hammered and washed to remove all impurities. It will weigh from 
 700 to 800 grains. Whatever the result, divide it by the weight of 
 fuel used, and multiply by the constant C 1? so as to obtain its calorific 
 value, or by G 2 to obtain its evaporative value. 
 
 
 Constants 
 
 
 
 
 o, 
 
 0, 
 
 Anthracite, charcoal, etc. 
 
 543 
 
 563 
 
 Welsh and similar coal, yielding, say, 90 o/o coke . 
 
 518 
 
 537 
 
 Bituminous coal, yielding 65-85 % C oke 
 
 500 
 
 517 
 
 See 'An. Ind.,' 1883, vol. i. p. 38. 
 
 The reason why the coefficients vary is because the hydrogen in 
 the fuel produces four times as much heat as an equal weight of carbon, 
 but only reduces three times as much lead. 
 
 Another way of roughly estimating the heating value of a fuel is to 
 ascertain the amount of moisture, volatile compounds, coke and ashes, 
 which it contains, and to credit every pound of the gases as being able 
 to evaporate twenty times their weight of water, while the coke less 
 ashes gives 15 evaporative units. 
 
 Coal Analysis. The calculation of the calorific value from the 
 chemical analysis is necessarily somewhat incorrect, for although the 
 heats of combustion of the various elements have been accurately 
 determined, practically nothing is known about the amount of heat 
 required to split up the chemical compounds which constitute coal. 
 It must also be remembered that the amount of oxygen in the coal 
 cannot be determined analytically, but only by difference, and is 
 therefore seriously affected by the chemical composition of the 
 mineral matter in the coal, which is entirely altered, and its weight 
 increased, while being converted into ashes. 
 
 Ashes. These also affect the calorific value of the fuels in which 
 they are contained, chiefly of course on account of the heat which 
 they carry away when being removed, but partly also on account of 
 the sulphur they contain, for in the fuel this element is combined 
 with iron as pyrites (FeS 2 ) and in the ashes it is contained as sulphide 
 (FeS). The heat necessary for this reduction has not been deter- 
 mined, but as the amount of combustible sulphur is a small quantity, 
 no great error is introduced by not making a deduction from the heat 
 value. 
 
 Coal Sampling. Little attention has been paid to the question 
 of how much coal should be put aside during a trial for purposes of 
 analysis. It is usually assumed that this quantity should bear some 
 proportion to the total quantity of coal burnt, and that if a sufficiently 
 large 'sample be taken the analysis will be correct within a certain 
 limit. That is not so, for the size of the sample depends entirely 
 
FUELS AND COMBUSTION 
 
 89 
 
 on the sizes of the largest lumps in the heap, and far from affording 
 certainty, all that can be said of any sampling is that it merely de- 
 termines the probability that a certain error as regards composition 
 will not be exceeded. Thus if the lumps of coal in a heap are all 
 of one size, and if the sample consists of 16,600 pieces, then the 
 chances are that only one sample out of 100 is likely to be wrong as 
 regards chemical composition to a greater extent than ^f/ ; 166 
 pieces, or one hundredth of the above, would ensure that an error 
 of 1/ will not occur more than once in 100 samples. This is on 
 the assumption that the irregularities in the compositions of the 
 various layers of the seam from which the coal was taken differ 
 chemically from each other to the extent of 20/ o . In good coal 
 seams the difference is less than 2/ o , and the accuracy ten times 
 greater. The chance of error is inversely proportional to the square 
 root of the number of pieces. For mixed sizes of coal the total 
 weight of the sample may be one-half of the product of the weight 
 of the largest pieces by the numbers mentioned above. 
 
 The following analyses and calorific values, as determined by the 
 bomb calorimeter, of the fuel used on the trials of the Kesearch 
 Committee and a few others have been kindly supplied by Mr. 0. J. 
 Wilson : 
 
 Vessel's Name and Fuel 
 
 Composition of Fuel in % 
 
 Calorific 
 Value 
 
 Evapora- 
 tive Value 
 
 
 
 H 
 
 0+S+N 
 
 Ash 
 
 Moist. 
 
 ' Colchester ' \ ^ ^ or ^. s ^" :e . I 
 
 71-89 
 
 5-48 
 
 14-36 
 
 4-08 
 
 4-25 
 
 13,176 
 
 13-63 
 
 Tartar' { WeffiSf } 
 
 87-98 
 
 4-22 
 
 3-31 
 
 3-42 
 
 1-07 
 
 14,765 
 
 15-28 
 
 A sample of Welsh coal . 
 A sample of coal .... 
 A sample of coke .... 
 A sample of coke .... 
 
 81-76 
 86-02 
 76-94 
 71-17 
 
 3-81 
 
 4-22 
 
 
 
 2'46 
 4-48 
 
 
 
 9-32 
 3-94 
 14-23 
 19-46 
 
 2-65 
 1-34 
 8-83 
 9-37 
 
 13,802 
 14,710 
 11,032 
 10,200 
 
 14-30 
 15-25 
 11-40 
 10-58 
 
 The following table contains summaries of some analyses and calo- 
 rific determinations (W. Thompson, ' Soc. Ch. Ind.,' 1889, vol. viii. 
 p. 525) : 
 
 
 Composition of Fuel in % 
 
 Experimental 
 
 Name of Fuel 
 
 
 
 
 
 
 
 
 Calo- 
 
 Evapo- 
 
 
 
 
 H 
 
 
 
 8 
 
 N 
 
 Moist. 
 
 Ash 
 
 rific 
 
 rative 
 
 
 
 
 
 
 
 
 
 Value 
 
 Value 
 
 Nixon Navigation Glam. 
 
 88-03 
 
 4-11 
 
 1-98 
 
 66 
 
 96 
 
 1-02 
 
 3-22 
 
 15,010 
 
 15-55 
 
 Tyldesley.Theperley &Co. 
 
 68-13 
 
 4-78 
 
 4-86 
 
 1-39 
 
 1-22 
 
 4-72 
 
 14-90 
 
 11,610 
 
 12-20 
 
 Tyldesley Coal Co. . 
 
 74-46 
 
 5-10 
 
 8-25 
 
 49 
 
 1-53 
 
 6-07 
 
 4-09 
 
 12,730 
 
 13-18 
 
 Upper ( Bottom . 
 
 75-48 
 
 4-98 
 
 7-86 
 
 75 
 
 1-59 
 
 2-78 
 
 6-55 
 
 13,300 
 
 13-77 
 
 Drnmgray J Mid rib . 
 
 72-13 
 
 4-67 
 
 6-56 
 
 54 
 
 1-25 
 
 2-26 
 
 12-58 
 
 12,520 
 
 12-96 
 
 seam ( Top seam . 
 
 75-05 
 
 5-12 
 
 9-39 
 
 86 
 
 1-76 
 
 3-53 
 
 4-29 
 
 13,560 
 
 14-05 
 
 Biokshaw Main 
 
 78-93 
 
 4-90 
 
 7-24 
 
 1-04 
 
 1-56 
 
 4-36 
 
 1-96 
 
 13,430 
 
 13-91 
 
 Pembertou 5-ft 
 
 72-41 
 
 5-16 
 
 8-84 
 
 93 
 
 1-41 
 
 6-70 
 
 4-55 
 
 13,040 
 
 13-50 
 
 Oramhawke . 
 
 69-77 
 
 4-82 
 
 12-44 
 
 1-17 
 
 1-33 
 
 7-15 
 
 3-31 
 
 13,420 
 
 13-19 
 
 Wigan 4-ft. . 
 
 76-49 
 
 4-96 
 
 8-46 
 
 1-07 
 
 1-44 
 
 4-84 
 
 2-75 
 
 13,590 
 
 14-07 
 
 Bickershaw 7-ft. 
 
 73-91 
 
 4-86 
 
 11-32 
 
 68 
 
 1-67 
 
 6-60 
 
 96 
 
 13,350 
 
 13-82 
 
 Pendleton 4-ft. 
 
 79-76 
 
 4-89 
 
 7-51 
 
 59 
 
 1-43 
 
 3-90 
 
 1-91 
 
 13,920 
 
 14-42 
 
 These calorific values were obtained in a Thompson calorimeter and 
 corrected, while the following, made by Scheurer-Kestner ( ' An, Ch, 
 
90 
 
 FUELS AND COMBUSTION 
 
 Ph.,' 1886, vi. vol. viii. p. 271), were made in the more elaborate calori- 
 meter of Faber and Silbermann. 
 
 Name of Fuel 
 
 Composition of Pure Fuel in % 
 
 Pure Coal 
 
 
 
 H 
 
 + S+N 
 
 Ash to be 
 added 
 
 Coke 
 produced 
 
 Calorific 
 Value 
 
 Evapora- 
 tive Value 
 
 Bwlf 
 Powels . 
 Altendorf 
 Ronchamp . 
 
 91-08 
 92-49 
 89-92 
 89-09 
 
 3-83 
 4-04 
 4-11 
 6-09 
 
 5-09 
 3-47 
 6-0 
 5-82 
 
 3-32 
 3-72 
 10 to 12 
 
 82-1 
 
 87-2 
 83-9 
 78-8 
 
 15,800 
 16,060 
 16,400 
 16,420 
 
 16-4 
 16-6 
 17-0 
 17-0 
 
 Nixon's Coal Scheurer-Kestner ( ' Soc. I. Mul.,' 1888, vol. Iviii. 
 p. 313) : 
 
 c 
 
 85-73 
 
 H 
 4-17 
 
 O 
 3-97 
 
 N 
 
 46 
 
 Ash 
 5-01 
 
 Calorific 
 Value 
 
 15,950 
 
 Evaporative 
 Value 
 
 16-5 
 
 In 'Soc. I. Mul./ 1891, p. 517, Scheurer-Kestner states that all his 
 previous results are too high. 
 
 Prof. H. Fritz ( ' Dingler's J.,' 1876, vol. ccxix. p. 185) gives the 
 following list : 
 
 Name of Fuel 
 
 Calorific 
 Value 
 
 Evapora- 
 tive Value 
 
 Name of Fuel 
 
 Calorific 
 Value 
 
 Evapora- 
 tive Value 
 
 Hydrogen 
 
 62,100 
 
 64-3 
 
 Coke (15 % cinder) 
 
 10,430 
 
 10-8 
 
 Coal gas 
 
 39,600 
 
 41-0 
 
 Alcohol (pure) 
 
 12,520 
 
 12-9 
 
 Petroleum 
 
 18,200 
 
 18-8 
 
 Peat coal 
 
 10,430 
 
 10-8 
 
 Olive oil 
 
 17,630 
 
 18-2 
 
 Lignite . 
 
 9,000 
 
 9-3 
 
 Wax . 
 
 15,660 
 
 16-2 
 
 Peat (dry) 
 
 8,640 
 
 8-9 
 
 Tallow . 
 
 14,930 
 
 15-4 
 
 Peat (20 % moisture) 
 
 6,480 
 
 6-7 
 
 Anthracite 
 
 14,590 
 
 15-1 
 
 Red coal 
 
 7,160 
 
 7-4 
 
 Carbon . 
 
 14,540 
 
 15-0 
 
 Dry wood 
 
 6,480 
 
 6-7 
 
 Coal (mean) 
 
 13,500 
 
 14-0 
 
 Wood (20 % moisture) 
 
 5,040 
 
 5-2 
 
 Charcoal 
 
 12,600 
 
 13-0 
 
 Straw . 
 
 3,360 
 
 35 
 
 Coal (clean) 
 
 12,600 
 
 13-0 
 
 Tan 
 
 5,580 
 
 5-7 
 
 The following table is a summary of C. Grove and W. Thorpe's 
 (1889, p. 54) analyses of 111 samples of fuel; it contains only the 
 highest and lowest values, and clearly shows how much their 
 compositions vary. 
 
 Coal Field 
 
 No. of 
 Samples 
 
 - 
 
 
 
 H 
 
 
 
 8 
 
 N 
 
 Ash 
 
 Density 
 
 Coke 
 
 -Welsh 
 
 37 | 
 
 Max. 
 
 91-4 
 
 5-8 
 
 17-9 
 
 5-1 
 
 2-2 
 
 14-7 
 
 1-38 
 
 92-2 
 
 
 ( 
 
 Miu. 
 
 71-1 
 
 3-5 
 
 4 
 
 1 
 
 
 
 1-2 
 
 1'25 
 
 55-4 
 
 Newcastle .... 
 
 18 { 
 
 Max. 
 Min. 
 
 86-8 
 78-0 
 
 6'7 
 4-5 
 
 10-3 
 2-4 
 
 2-8 
 1 
 
 1-8 
 7 
 
 9-1 
 
 2 
 
 1-31 
 1-25 
 
 72-3 
 35-6 
 
 Derbyshire .... 
 
 ' \ 
 
 Max. 
 Min. 
 
 81-9 
 78-0 
 
 5'6 
 4-8 
 
 12-4 
 8-6 
 
 1-3 
 
 7 
 
 2-1 
 8 
 
 4-6 
 1-2 
 
 1-32 
 1-27 
 
 62-5 
 
 52-8 
 
 Lancashire .... 
 
 28 \ 
 
 Max. 
 Min. 
 
 83-9 
 72-9 
 
 6'2 
 
 4'8 
 
 20-0 
 4-9 
 
 3-0 
 5 
 
 2-2 
 5 
 
 14-3 
 1-1 
 
 1-35 
 1-23 
 
 66-1 
 51-1 
 
 
 1 \ 
 
 Max. 
 
 88-5 
 
 6'5 
 
 15-5 
 
 1-6 
 
 2-0 
 
 10-7 
 
 1-32 
 
 59-1 
 
 
 \ 
 
 Min. 
 
 74-5 
 
 4'H 
 
 9 
 
 4 
 
 
 
 1'2 
 
 T23 
 
 49-3 
 
 Van Diemen's Land . . 
 
 1 
 
 Max. 
 Min. 
 
 70-4 
 57-2 
 
 4-2 
 
 2'9 
 
 9'1 
 1-0 
 
 1-3 
 7 
 
 1-6 
 9 
 
 30-4 
 14-4 
 
 
 
 Chili 
 
 6 { 
 
 Max. 
 
 78-3 
 
 6-4 
 
 173 
 
 6-1 
 
 1-1 
 
 36-9 
 
 ... 
 
 ... 
 
 
 ( 
 
 Mia. 
 
 39'0 
 
 4'0 
 
 8*4 
 
 9 
 
 5 
 
 5'7 
 
 ... 
 
 ... 
 
FUELS AND COMBUSTION 
 
 91 
 
 Coal Trials. Parliamentary Papers 
 
 Date 
 
 No. 
 
 Index 
 
 Remarks 
 
 Vol. 
 
 No. 
 
 1857-8 
 
 375 
 
 39 
 
 43 
 
 
 1859 
 
 116 
 
 25 
 
 209 
 
 Welsh and Newcastle 
 
 1860 
 
 485 
 
 42 
 
 267 
 
 
 1862 
 
 204 
 
 34 
 
 113 
 
 
 M 
 
 337 
 
 ii 
 
 11 
 
 
 n 
 
 364 
 
 
 121 
 
 Australian 
 
 1863 
 
 79 
 
 35 
 
 151 
 
 
 _ 
 
 159 
 
 
 
 141 
 
 n 
 
 1864 
 
 (80, 80-1.) 
 
 37 
 
 187, 211 
 
 Welsh and Newcastle 
 
 n 
 
 375 
 
 M 
 
 213 
 
 tt M 
 
 1865 
 
 365 
 
 35 II. 
 
 79 
 
 
 1866 
 
 440 
 
 46 
 
 35 
 
 
 1867 
 
 561 
 
 44 
 
 339 
 
 
 M 
 
 563 
 
 > 
 
 491 
 
 Lancashire and Cheshire 
 
 1868-9 
 
 212 
 
 38 
 
 443 
 
 
 > 
 
 270 
 
 
 
 447 
 
 M 
 
 1870-71 
 
 121 
 
 40 
 
 463 
 
 Newcastle 
 
 1872 
 
 165 
 
 39 
 
 349 
 
 
 1873 
 
 
 
 42 
 
 537 
 
 Indian troopships 
 
 1876 
 
 280 
 
 47 
 
 713 
 
 
 1877 
 
 397 
 
 52 
 
 515 
 
 
 1878 
 
 396 
 
 49 
 
 541 
 
 
 
 233 
 
 47 
 
 495 
 
 
 1878-9 
 
 380 
 
 45 
 
 493 
 
 
 Spontaneous Combustion of Coals. Parliamentary Papers 
 
 
 
 Index 
 
 Date 
 
 No 
 
 
 
 
 VoL 
 
 No. 
 
 1876 
 
 C. 1586-1 
 
 41 
 
 1 
 
 1878 
 
 366 
 
 47 
 
 33 
 
 1878-9 
 
 373 
 
 64 
 
 47 
 
 1880 
 
 C. 1586-1 
 
 41 
 
 1 
 
 1886 
 
 366 
 
 59 
 
 45 
 
 H. Poole gives very exhaustive information about coals of 
 the world, his tables covering about forty-two pages, of which, 
 however, English coal, coke, &c. cover about two pages. 
 
 The object of determining the heating power of a fuel is undoubtedly 
 to obtain a correct measure of its commercial value ; but heating power 
 is not everything, and there are other qualities, such as liability to 
 smoke, to flame, to cake, to ignite easily and even spontaneously, to 
 break up into dust when exposed, and various others. 
 
 Burning Qualities. Amongst these one of great importance is as 
 to whether a coal will ignite easily or not. Thus Cannel coal can be lit 
 by applying a match, while anthracite can only be kept alight under 
 carefully regulated conditions of draught, &c. The success of explo- 
 sives depends on a good knowledge of this subject ; thus we find that 
 
92 FUELS AND COMBUSTION 
 
 sulphur, which ignites at a low temperature, has to be added to gun- 
 powder in larger or smaller quantities, according as to whether it has 
 to explode quickly or slowly. More recently it has been discovered 
 that the temperature at which wood is converted into charcoal materi- 
 ally affects the temperature at which it ignites, and that where the 
 process is carried out gently and over a long period, as is the case with 
 wooden beams in houses placed close to flues, ignition ultimately takes 
 place spontaneously. Gun cotton ignites so readily that it could not 
 be used for ammunition until it was discovered that an admixture of 
 camphor or nitro -glycerine raised this temperature, and also retards 
 the burning process ; chloride of tin still further reduces its liability 
 to ignite. Some curious phenomena have bee*n noted. Thus phos- 
 phorus, which ignites at a temperature of 140 F. in an ordinary 
 atmosphere, will not burn if placed in absolutely pure oxygen. A 
 mixture of hydrogen and chlorine gas ignites at a very low tem- 
 perature if illuminated by actinic rays, but no amount of heating, 
 short of redness, will effect their chemical combination in the dark. 
 
 Table of Temperatures of Ignition 
 
 Igniting 
 
 Substance Temperature* 
 
 F. 
 
 Phosphoretted hydrogen .... 116 
 
 Phosphorus . . . . . . 140 
 
 Lignite dust 300 
 
 Sulphur 470 
 
 Carbon disulphide 300 or 440 
 
 Dried peat 435 
 
 Anthracite dnst . . . . 570 
 
 Coal 
 
 Charcoal made at 550 to 700 F. 
 
 Cokes . 
 
 2,200 to 2,300 F 
 
 600 
 
 680 
 
 1,100 or 1,400 
 
 Red Heat 
 
 Anthracite 750 
 
 Carbonic oxide ,,1,211 
 
 Hydrogen 1,030 or 1,290 
 
 Fire damp 1,200 
 
 With hydrocarbons the igniting temperature depends on the 
 chemical composition ; thus benzine ignites at about 500 F., while 
 some ( of the dense oils will quench red-hot iron without igniting. 
 Generally speaking hydrocarbons prevent both quick and spontaneous 
 combustion. More precise information on igniting temperatures 
 would greatly assist the understanding of fuel combustion. Much 
 may be learnt about the behaviour of various coals by consulting the 
 following papers : ' Memoirs of the Geological Survey of Great 
 Britain ' (London, 1848, vol. ii. p. 539) ; Eeport of Sir H. De la Beche 
 and Dr. Lyon Playfair. 
 
 Influence of Air Pressure on Combustion, Frankland's experi- 
 ments (1877, p. 863) show that, contrary to the accepted views, 
 increased pressure (not draught) does not accelerate combustion, but 
 that it increases the luminosity and smokiness of flames. At twenty 
 atmospheres air-pressure the hydrogen flame gives a perfectly con- 
 tinuous spectrum, while the carbonic oxide flame is equally luminous 
 
FUELS AND COMBUSTION 93 
 
 at fourteen atmospheres. An ordinary candle gives hardly any light 
 when burnt on the summit of Mont Blanc, but smokes under 
 pressure. 
 
 The Specific Heat of a Gas can only be accurately estimated if the 
 specific heats of individual substances are known. The following 
 small list contains all the necessary data : 
 
 Table of Specific Heats at Constant Pressure 
 
 ELEMENTS 
 
 Carbon (charcoal) . . '1935 Oxygen .... -2175 
 Hydrogen . . . 3-4090 Nitrogen , , . -2438 
 
 COMPOUNDS 
 
 Air .... '2375 Water .... 1-0000 
 
 Carbonic oxide (CO) . -2450 Marsh gas (CH 4 ) . . -5929 
 
 acid (COj) . '2163 Sulphurous acid (SO,) '1540 
 
 Steam (H 2 0) . . '4805 See also steam tables 
 
 There is some uncertainty as to the specific heat of steam, but as 
 it does not enter very largely into the composition of burnt products 
 (see p. 52), one per cent, of moisture adds about 0'003 to the specific 
 heat of air. 
 
 Air being composed of 20*8 volumes of oxygen and 79*2 volumes 
 of nitrogen, or by weight 23*07 oxygen and 76'93 nitrogen, its specific 
 heat is 
 
 23-07 x -2157^+76-93 x -2434 = 
 
 The quantity of oxygen required to consume 1 Ib. of carbon is 
 |f = 2-667, and this carries with it S'92 Ibs. of nitrogen. 
 The calculation is therefore as follows : 
 
 1-000 carbon 
 2-667 oxygen 
 
 3-667 carbonic acid x -2163 = -793 
 8-920 nitrogen x -2438 = 2-171 
 
 12-587 products x '2355 = 2-964 
 
 So that the specific heat of this mixed gas is -2355. But the amount 
 of air supplied, viz. 11-6 times as much as the carbon, is only just 
 sufficient for perfect combustion ; in practice it is above 15 and 
 sometimes even over 30. By adding 7413 Ibs. of air to the above 
 the products of combustion are increased to 20 Ibs., and the specific 
 heat would be raised to -2360. 
 
 Coal contains both hydrogen and some moisture, and, as the 
 specific heat of steam is about twice as great as that of dry air, the 
 average value is somewhat higher than the above. However, for 
 practical purposes the value -237 is sufficiently accurate. 
 
 Temperatures of Flames. When no heat is lost by radiation or 
 convection the entire quantity generated during combustion must 
 have been used to warm the products, raising their temperature 
 
94 FUELS AND COMBUSTION 
 
 sufficiently to make them glow, and the result is a flame. Its tem- 
 perature is calculated as follows : If n pounds of air are supplied 
 for every pound of carbon burnt, then the weight of the products 
 will be n + 1, the heat evolved will be 14,540 cals. per pound of fuel, 
 and if tr is the specific heat of the gases, the temperature of the flame 
 
 14540 
 <r. (n + I)' 
 
 It is now possible to determine the temperature T of the flame 
 with the help of the previous formula. Let n + 1 = 20, then T 
 = 3,080 F. above t, the mean temperature of the air and fuel. 
 Roughly speaking, the furnace temperature multiplied into the ratio 
 of products to coal (= n + -9) is 61,000 F. ; but this is true only 
 down to a limit of about n = 15. Below this point the combustion 
 of the coal is not a perfect one, and instead of 14,540 only 4,340 
 calories are evolved. 
 
 Therefore, unless much hydrocarbon gas or smoke is produced we 
 have the following three conditions : 
 
 When n = 5'8, carbonic oxide and nitrogen are the only pro- 
 ducts ; the initial temperature is 2,350 F. + t. 
 
 When n is greater than 5'8 and less than 15, the products con- 
 sist of carbonic oxide, carbonic acid, nitrogen, and oxygen, and 
 the temperature grows higher till n = 15 is reached ; then 
 no carbonic oxide is evolved. The initial temperature is 
 4,130 F. + t. 
 
 Above this point the temperature grows less and less, as stated 
 
 . 61,000 
 above, v.z. -^ 
 
 When 1 Ib. of hydrogen is being burnt, 8 times its weight of 
 oxygen is required, which is accompanied by 26'8 Ibs. of nitrogen. 
 making a total of 35'8 Ibs. of products of combustion. These consist 
 of 9 Ibs. of steam and 26'8 of nitrogen. The specific heat of this 
 
 mixtxire is, say, , 
 
 evolved being 52,860 cals., the temperature of this flame is 4,873 a 
 F. + t. 
 
 For such cases in which n + 1 exceeds, say, 50, divide 247,000 by 
 (7*7 4- n) and the quotient is the temperature. 
 
 The flame temperature of a compound containing carbon and 
 hydrogen would of course depend on some as yet undiscovered law, 
 but a fairly good guess can be made by taking a mean of the values 
 just found. Roughly 
 
 T 61,000 C + 247.000 H 
 (C + H)n + O9 + H7'7* 
 
 Of course the actual temperatures of flames are decidedly lower 
 than those found by this formula, because loss of heat takes place b\ 
 radiation during the process of combustion. 1 
 
 1 Moisture in the atmosphere seriously affects boiler performances. 
 
FUELS AND COMBUSTION 95 
 
 The following are a few particulars of temperatures of flames 
 
 (' Franklin Inst.,' 1878, vol. Ixxvi. p. 205.) 
 
 Bunsen burner using 1 vol. gas, 2'4 air gave 2,480 F. 
 
 1 vol. gas, 2-4 air, and j 2 15Q 
 
 1 nitrogen gave ) 
 
 Do. do. and 2 nitrogen gave 1,890 
 
 Bunsen burner, 1 vol. gas, 2'4 air and CO 2 , gave 2,010 
 
 2C0 2 1,434 
 
 Locatelli lamp 1,690 
 
 Stearine candle 1,723 
 
 Petroleum lamp with chimney . . . 1,885 
 
 without . 1,690 
 
 ,, sooty envelope . . . 1,434 
 
 Alcohol (-912) lamp 2,140 
 
 (-822) 2,150 
 
 H. Le Chatelier, ' Comp. Bend.,' 1892, vol. cxiv. p. 470. 
 
 Bessemer process of steel-making . . . 2,984 F. 
 Siemens ... 2,876 
 Glass-melting . . . . . 2,390 
 Electric light 3,272-3,812 
 
 The Temperature of Dissociation. When this temperature is 
 reached chemical compounds are split up. For sympathetic ink and 
 cupreous hydrate it is low, for gypsum it is higher, also for carbonate 
 of lime, sulphate of iron, &c. For steam and for carbonic acid it is 
 very high and has not yet been determined. From this it would 
 follow that the higher the initial temperatures of the fuels and air the 
 less heat is evolved, until a point is reached where no combustion 
 takes place. This is far higher than any temperature to be met 
 with even in a steel melting furnace, but its existence must not be 
 lost sight of where heated air or gas is used, for the expected benefit 
 will not be fully realised, nor will the flame temperatures be as high 
 as expected. 
 
 Furnace Temperatures. Hardly any experiments have yet been 
 made to determine furnace temperatures, but since the introduction of 
 MM. Mesure and Noel's optical pyrometer (' I. and S. I.,' 1889, p. 251) 
 at least one of the difficulties has been removed. The first of 
 these instruments is a thermopile, the heated junction of the circuit 
 consisting of wires made of two different alloys of platinum. The 
 optical pyrometer consists of a tube in which a quartz plate is fixed near 
 the centre, and a Nichol's prism at either end. One of these can be 
 turned round its own axis. On looking at a heated object, and slowly 
 turning the prism, it will be noticed that the colour changes from green 
 to red and vice versa. The angle at which this change takes place is 
 noted, and is the measure of the temperature. Care has to be taken 
 not to let any daylight be reflected from the hot object, otherwise 
 the readings will be those of the temperature of the sun. Both 
 
96 FUELS AND COMBUSTION 
 
 these instruments have to be graduated according to some reliable 
 standard. 
 
 Air Thermometer. If properly manipulated there is probably no 
 more accurate measure of temperature than an air thermometer. All 
 the permanent gases expand at the rate of '3665 
 between the freezing and the boiling point of water. 
 This is at the rate of '0020611 per F. It has been 
 assumed that the absolute zero is reached when the 
 volume of air is reduced to nothing. At the above 
 rate this would be found to be 491 below the 
 freezing point of water, or 459 F. Therefore if t 
 is the Fahrenheit temperature of an object, its abso- 
 lute temperature would be T = t + 459. The instru- 
 ment shown in fig. 104 is based on the above facts. Fl - 104 
 It consists of a small pear-shaped platinum bulb, 
 having a small pin-hole at its apex. It is carefully filled with nitrogen 
 gas, enclosed in fire clay, and placed in the furnace whose tempera- 
 ture is to be measured. When sufficiently heated the whole instru- 
 ment is plunged into cold or boiling water, and is kept there point 
 downwards till it has acquired the temperature of its surroundings. 
 The protecting scale of fire clay has of course fallen off. The bulk is 
 now carefully weighed, first in its present condition, viz. partly filled 
 with water, then when quite full, and then when quite empty. The 
 ratio of the total internal volume of the bulb, which, while in the 
 furnace, was full of hot air, to the volume of air remaining after 
 cooling in the water bath, is exactly the ratio of the absolute furnace 
 temperature to that of the bath. Any other pyrometer can be 
 graduated by placing it alongside the above. 
 
 Pyrometers. Descriptions of various pyrometers will be found in 
 the following publications. (See also p. 109.) 
 
 J. Wilson, ' M. E.,' 1852, p. 53, mentions one which consists of a 
 piece of platinum, to be thrown into a calorimeter while hot. 
 
 M. Launy, ' Comp. Bend.,' 1869, vol. Ixix. p. 347. The pressure 
 exerted by the liberated carbonic acid gas from heated lime is measured. 
 
 T. Carnelly and T. Burton, ' I. and S. I.,' 1884, p. 195. Various 
 pyrometers. 
 
 Prof. J. Wiborg, ' I. and S. I.,' 1888, ii. p. 110. An exposed bulb 
 is filled with compressed air. 
 
 M. Santignon, ' G6nie C.,' 1890, vol. xvi. p. 328. This pyrometer 
 consists of a bent metal tube which is inserted in the heated space, 
 and a steady current of water is made to flow through it. 
 
 Messrs. Heish and Folkard, ' Iron Age,' vol. xxxvii. p. 25. Platinum 
 bulb air pyrometer. 
 
 Eoberts Austin, * C.E.,' 1892, vol. ex. p. 152, describes Calendar's 
 electric resistance pyrometer sensitive to J C. up to a red heat. Le 
 Chatelier's thermo-couple is sensitive to 2 F. up to 1,800 F. Le 
 Chatelier's optical pyrometer, Mesure and Noel's optical pyrometer. 
 
 Landholt and Bornstein (1912) give a list of melting temperatures 
 of various alloys and metals and convenient boiling temperatures 
 (p. 324). 
 
 Temperatures in the Fuel. It has already been explained that the 
 temperature of a flame is proportional to the percentage of carbonic 
 acid it contains till a point is reached where carbonic oxide is formed. 
 
FUELS AND COMBUSTION 
 
 97 
 
 Fig. 105 illustrates, in a rough way, the conditions which may be ex- 
 pected in the interior of a thick fire. 1 
 
 Estimated Batio of Air to consumed 
 Carbon 
 
 Estimated Temperatures in 
 the Interior of a Fire 
 
 20 : 1. Air admitted above 
 fuel . . . . % 
 
 6-8 : 1. Chiefly CO . 
 
 10 : 1. Partly CO and C0 2 
 
 15 1 I C m P lete combus- 
 ' \ tion 
 
 2,960 F. 
 
 2,410 F. 
 2,980 F. 
 
 20: 1. 
 
 43: 1. 
 
 1: 0. 
 
 Do.. 
 Do . 
 
 A. 
 
 Of course this picture is mere guesswork, but it shows that by 
 measuring the temperatures at various depths, or by analysing the 
 gases at these points, some valuable information might still be obtained 
 as to the process of combustion (compare p. 298). 
 
 Prof. A. Ledebeur (' Stahl und Eisen,' 1882, vol. ii. p. 356) made 
 the following interesting experiments, in which the temperatures of the 
 burning charcoal (contained in a tube) were carefully regulated. To 
 a certain extent these experiments modify the above calculations : 
 
 Temperature 
 
 Percentage of Carbon burnt 
 
 Oxygen used 
 
 Degrees Fahrenheit 
 
 CO. 
 
 OO 
 
 % 
 
 660 
 710 
 Dark red . . 1,150 
 Cherry red . 1,250 
 Yellow . . 2,010 
 
 78-6 
 72-4 
 71-4 
 62-6 
 1-3 
 
 21-4 
 
 27-6 
 28-6 
 37-4 
 98-7 
 
 33-0 
 80-6 
 87-9 
 80-3 
 
 100-0 
 
 t 
 
 With thin fires it is quite possible that sufficient air for complete 
 combustion passes through the fuel. In this case the conditions above 
 the line A do not exist, and it is not necessary to admit air above the 
 bars ; but with thick fires, particularly with a weak draught, the upper 
 layers of fuel effect the reduction of carbonic acid to carbonic oxide, 
 and air must be admitted above. It will also readily suggest itself 
 that if green coal is thrown on a fire which is still evolving much car- 
 bonic oxide, the latter will be cooled to such an extent that it cannot 
 ignite when coming in contact with the upper air. Fires should, 
 therefore, be allowed to burn as low as possible before recoaling. 
 
 1 In blast furnaces no free oxygen and hardly any carbonic acid are found at a 
 greater distance than two feet from each tuyer (p. 298). 
 
 H 
 
98 FUELS AND COMBUSTION 
 
 It might seem to be an advantage, even in cases of forced draught, 
 to keep the fires thin, and thereby prevent the formation of combus- 
 tible gases. This, however, is not the case, for, unless the grate 
 surface were very much increased, there would be a serious loss, due 
 to the blowing away of unburnt coal particles. A direct test for CO 
 is described in ' Comp. Bend.,' 1897, vol. cxxiv. p. 621, and ' C. E.,' 
 vol. cxxix. p. 474. 
 
 Effects of Draught. In cases of complete combustion the weight 
 of the products is sometimes thirty times the weight of fuel burnt. 
 Now, suppose that the consumption is raised from 20 Ibs. per square 
 foot per hour to 40 Ibs. ; then the velocity of the escaping gases, 
 which amounts to 600 Ibs. per hour = 10 cubic ft. per second, would 
 be twice as great, and the power to carry away solid particles would 
 have been increased about fourfold. If, however, the fires are kept 
 thick and all the gases leave the fuel as carbonic oxide, their weight is 
 reduced to 270 Ibs., and the temperature being slightly lower, and the 
 bulk proportionately less, the power to lift up and carry away small 
 particles of coal is reduced to about one-fifth. Of course even the 
 thickest fires in a marine boiler will allow free oxygen and much car- 
 bonic acid to pass, so that the above favourable condition is hardly 
 approached ; but at any rate it is clear that with forced draught fires 
 should be kept thick, restricting the admission of air under the bars, 
 keeping the temperatures high, and giving much fuel contact to the 
 carbonic acid gases, so as to convert them into combustible ones. A 
 very large proportion of air should then be admitted at the doors or 
 bridges. Naturally the horizontal draught will be excessive unless 
 the furnaces are very large. 
 
 The air which is admitted for the combustion of the gases should 
 be as hot as possible, and when admitted at the bridges the utmost 
 has probably been done in this direction by having passed it under the 
 fire bars. When admitted at the doors artificial heating is the only 
 means of warming it, but, as all draught over the fire bed has the effect 
 of blowing away particles of coal and cinder, this trouble would only 
 be aggravated if the air temperature and bulk were increased. An 
 additional power to do harm is given to the draught if much air is also 
 driven through the bed of coal, whereby all the smaller particles are 
 carried to the top. This can only be prevented by a thick bed of coal, 
 and this again is only possible with large furnaces. 
 
 Forced and Natural Draught. A few formulae are necessary for 
 explaining this subject, but they are of the simplest. 
 
 Here v is the velocity of air, h column of air measured in feet, corre- 
 sponding to the draught pressure, and g 32'2 feet is the acceleration 
 due to gravity. Instead of an air column or mercury column, it is 
 usual to express draught pressure in inches of water. The respective 
 weights of mercury, water, and air being 13'60, 1, and '001293, the 
 formula is changed into 
 
 v 2 = 4,140 H = 56,300 M, 
 where H = pressure measured in inches of water, and M = pressure 
 
FUELS AND COMBUSTION 99 
 
 measured in inches of mercury. In practice the friction and bends 
 will seriously reduce the velocity, and the co-efficients have to be 
 reduced by about 25 %. It is also evident that with the same draught 
 an incandescent, and therefore lighter, gas is more easily moved than 
 a cold one. If T denotes its absolute temperature, while 491 is the 
 absolute temperature at 32 F., then v 2 = 8*5 . H . T theoretically, or 
 say 6 . H . T practically. 
 
 It is as well to mention that a more general formula, but without 
 the above correction, would be 
 
 * 
 
 v = 
 
 Here m is the molecular weight of a gas. This is 14-37 for air, 
 about 16 for oxygen, 14 for nitrogen, 22 for carbonic acid, and 9 for 
 steam. 
 
 In order to find V, the volume of air discharged per second, the 
 sectional area A, in square feet, of the orifice or channel has to be 
 multiplied by the velocity v. 
 
 V = v.A = A. v/6. H.T.I 
 
 The weight Q is found by multiplying this volume into the weight 
 of a cubic foot of air, and introducing the correction for temperature. 
 
 Q = A . C J7'3 , or roughly 100 . 
 
 from which it follows that the pressure H required for delivering 
 Q Ibs. of hot air per second through the section A is 
 
 O 2 T 
 
 H = ^ Ti measured in inches of water. 
 A 
 
 Resistances in Furnaces. This formula has been used in estimat- 
 ing some of the values in the following table, in which an attempt is 
 made to illustrate what takes place in two furnaces, whose diameters 
 are respectively 30 ins. and 45 ins., with 6-ft. grates. The sectional 
 areas of the ashpits and over the fuel would be 1*6 and 3*7 sq. ft. 
 20 Ibs. per square foot is to be the coal consumption under natural and 
 40 Ibs. under forced draught. The products of combustion will weigh 
 about 24 times as much as the fuel, and it is assumed that two -thirds 
 of the air passes through the fuel, and the other third through the 
 door. If the third is admitted at a temperature of 32 F., it will be 
 reasonable to assume that the temperatures in the fuel and in the 
 flame are about 2,500 F., and that as they pass into the tubes this 
 has been reduced to 1,000 F., while on entering the funnel it has 
 fallen to 600 F. 
 
 Doubtful though some of the following results are, they will at any 
 rate serve to make comparisons, and then there can be no question that 
 the large furnace has the advantage. 
 
 a 
 
100 
 
 FUELS AND COMBUSTION 
 
 Estimated Temperatures, Volumes, Velocities, and Resistances of Gases 
 in a Pair of Boiler Furnaces 
 
 Particulars 
 
 ( 
 
 Draught 
 
 Ordinary 
 
 Forced 
 
 
 30 
 1-6 
 4 
 15 
 3 
 800 
 2 
 
 45 
 3-7 
 6 
 22* 
 
 45 2 
 3 
 
 30 
 1-6 
 2 
 15 
 3 
 600 
 4 
 
 45 
 3-7 
 3 
 
 1 
 
 6 
 
 Ashpit = ^ sectional area of furnace . . sq. ft. 
 Sum of sectional area of tubes 
 
 
 Coal consumption per hour . . . Ibs. 
 Weight of products per second . . 
 
 Volume of $ air (32 F.) through ashpit . cub. ft. 
 Mean velocity in ashpit . . .ft. per sec. 
 
 Resistance ins. 
 
 15-8 
 9-9 
 
 23-7 
 6-4 
 
 31-6 
 13-1 
 
 47-5 
 8-5 
 
 076 
 
 032 
 
 31 
 
 13 
 
 Volume of 4 products in Interior of fuel } , ,, 
 (2,500 F.) f cub ' ft - 
 
 96 
 6-4 
 
 144 
 6-4 
 
 192 
 12-8 
 
 289 
 12-8 
 
 Upward velocity in fuel . . .ft. per sec. 
 Resistance (see footnote*) ... ins. 
 
 070 
 
 070 
 
 28 
 
 28 
 
 Volume of all products above fuel (2,500 F.) cub. ft. 
 Horizontal volocity over fuel . . ft. per sec. 
 
 144 216 
 90 58 
 
 289 
 119 
 
 433 
 77 
 
 ~79~ 
 
 47 
 
 20 
 
 1-68 
 
 
 Volume of products at 1,000 F. . cub. ft. 
 Velocity on entering small tubes . ft. per sec. 
 
 72 
 
 18 
 
 108 
 18 
 
 1 4 4 
 72 
 
 216 
 72 
 
 037 
 
 037 
 
 60 
 
 60 
 
 
 Volume of products at 600 F. . . cub. ft. 
 Velocity in funnel . . . .ft. per sec. 
 
 Resistance ins. 
 
 53 
 
 "4 
 
 79 105 
 17J 35 
 
 158 
 35 
 
 047 
 
 047 
 
 19 
 
 19 
 
 Total Resistances ....... \ -700 
 
 386 
 
 3-06 
 
 1-99 
 
 Closed Ashpits. When air is blown under the bars it is, perhaps, 
 an advantage to keep the air spaces between them very small, thereby 
 increasing this resistance to such an extent that all the others sink 
 into insignificance. This would ensure a fairly constant supply of air, 
 no matter what condition the fires are in. With a fierce combustion 
 and small furnaces it may then be found necessary to keep the furnace 
 doors open, so as to admit sufficient air above the bars. 
 
 Minimum Air Admission above the Grate. This question is one 
 of the most difficult that presents itself in the working of boilers, and 
 has engaged the attention of engineers for the last fifty years, with no 
 better result than the evolution of an idea that air must be admitted 
 above the bars, but as to how much and by what means has never yet 
 
 1 The values in this division have been calculated on the assumption that 
 the interstices in the fuel bed are one-fifth of the grate surfaces, the upward 
 velocity of the gases would be increased fivefold, and their resistances twenty-five 
 fold. 
 
FUELS AND COMBUSTION 
 
 been settled. The question of how little can only be determined by 
 chemistry corrected by experience. In the trials of the ' Colchester ' 
 (' M. E.,' 1890, p. 206) there are three readings in which from 1 to 2 % 
 of carbonic oxide was found in the waste products. The amount of 
 unconsumed oxygen ranged from 5'4 to 6*6 %, corresponding to from 
 17 to 18J Ibs. of waste products per Ib. of coal. On the other hand, 
 there is one sample of gas in this trial where the oxygen had been 
 reduced to 6'43 %, without evolution of carbonic oxide, and in the 
 case of the ' Ville de Douvres ' (' M. E.,' 1892, p. 8) there is one with 
 5*23 % oxygen. This may be explained by only one of the furnaces of 
 the ' Colchester ' working badly, and there, perhaps, the oxygen may 
 have been entirely consumed. To be on the safe side, 5 % of free oxy- 
 gen, corresponding to 16J Ibs. of waste products per Ib. of coal, may 
 be looked upon as the lowest limit. Under such conditions the weight 
 of the escaping gases will be a minimum, and, as their temperature ia 
 high, they will more readily part with their heat, and weighing less 
 than when more air is admitted, they move more slowly in the tubes, 
 and have more time to cool down. (See chapter on ' Heat Transmis- 
 sion.') 
 
 Maximum Air Admission above the Grate. It would, therefore, 
 appear that as little air should be admitted as is compatible with per- 
 feet combustion ; but this is not borne out in practice, as will be seeu 
 from the following table, which contains some of the results of trials by 
 the Research Committee of the Institute of Mechanical Engineers, and 
 previously referred to : 
 
 Name of Vessel 
 
 Ratio of Waste Pro- 
 ducts to Fuel 
 
 Heat carried away 
 by Waste Products 
 per Cent. 
 
 Weight of Fuel con- 
 sumed divided by 
 Total Heating Surface 
 
 ' Colchester ' . 
 
 18-5 
 
 28-0 
 
 987 
 
 ' Ville de Douvres ' 
 
 17-9 
 
 26-8 
 
 1-010 
 
 1 Fusi Yama ' . 
 
 22-8 
 
 23-5 
 
 437 
 
 'Tartar' . 
 
 31-5 
 
 22-1 
 
 367 
 
 1 lona ' . 
 
 25-5 
 
 16-2 
 
 298 
 
 It would, in fact, appear as if the order of things had been reversed, 
 and that the more air was admitted the more economical was the boiler ; 
 but this view leaves out of account the ratio of fuel burnt per hour to 
 heating surface, which value will be found in the last column, and which 
 seems to exert a far greater influence than the other condition. The 
 only way of settling this question would be to carry out progressive 
 trials with the same boiler. By a comparison of the results obtained on 
 the ' Fusi Yama ' and on the ' Tartar,' where the waste products were 
 respectively 23 and 31 J times as heavy as the fuel burnt, and the per- 
 formances of the boilers fairly equal, it will be found that, if anything, 
 less heat was carried away when a large excess (about twice as much 
 as the necessary quantity) of air had been admitted to the fires, show- 
 ing that little, if any, harm is done by such proceedings. 
 
 These remarks apply, of course, only to the economical side of the 
 question, for it is well known that by opening the doors two influences 
 %re at work to reduce the boiler performance firstly, the uptake 
 
102 
 
 HJLS AND COMBUSTION 
 
 temperature, and with it the draught is reduced, and, on account of the 
 relatively smaller resistance encountered by the air above the bars, less 
 air passes through the fuel, and its consumption is therefore seriously 
 checked. With forced draught the available pressure can be increased 
 to practically an unlimited extent, and it ought not to be difficult to 
 regulate its flow. 
 
 Velocity of Waste Products. If anemometers are placed in the 
 ashpits it will be found that their readings cannot be depended upon, 
 as these vary considerably, according to the positions of the instru- 
 ments. If placed in the uptakes they will soon get damaged by the 
 heat and dirt, and would be difficult to read. Besides, it has not yet 
 been ascertained at what point of the section of a funnel the velocity 
 of the gases is just equal to the mean. These difficulties can, to a 
 certain extent, be overcome by 
 making the arms of the anemometer 
 equal to one quarter of the diameter 
 of the funnel (see fig. 106) and 
 using four vanes, V, set at an angle 
 of 45 to the axis. It will then 
 be found that the time occupied 
 by each vane in sweeping through 
 part of any annular zone of air in the 
 funnel is nearly proportional to the 
 area of that zone, and therefore 
 the readings will be very near the 
 average velocity. A spring or 
 weight should be attached to the 
 clockwork, C, of the instrument, 
 of just sufficient force to overcome 
 the initial friction. The most ac- 
 curate results would doubtless be 
 obtained if the anemometer were 
 made of the same diameter as the 
 funnel, and its blades shaped like 
 those of the old-fashioned screw 
 propellers, their depth and pitch 
 being kept constant and their widths 
 increasing towards the extremities. 
 
 In this case it can also be shown that the mean velocity of the gas 
 for all the zones would be recorded. 
 
 Air Pressure Gauges usually consist of glass U tubes half filled 
 with water, which may be stained. They are not very accurate, for 
 the total difference of level sometimes does not exceed J in. 
 Differential gauges are therefore sometimes used ; they consist of a U 
 tube of say J in. bore, with two cylindrical bulbs at their top ends. 
 Two non-miscible fluids are put into the two arms ; any difference of 
 level in the two large top ends is then very much magnified by a rise 
 or fall of the fluid boundary in one of the arms. The magnification 
 depends partly on the difference of sectional area of the cylinders and 
 U tube, and partly on the difference of density of the two fluids. 
 Paraffin and alcohol are used, but water and aniline oil are more 
 sensitive, as their densities are nearly equal. 
 
 FIG. IOC 
 
FUELS AND COMBUSTION 103 
 
 Correction for Temperature. If possible, two or more thermo- 
 meters should be used, so as to obtain average results, and the 
 necessary data are now available for calculating the weight of the 
 waste products. Let V cubic feet be the measured volume which 
 has passed away in one hour ; then if T is its absolute temperature, 
 while 491 is the absolute temperature at F., the weight of air 
 
 per hour is Q =' Q8Q8 ^ 91 - V = 39'7 J. Here "0808 is the weight of 
 1 cubic foot of dry air. 
 
 If T = 918 and V = 1,000,000, then Q = 43,200 Ibs. 
 
 The necessary allowance should of course be made for the height 
 of the barometer, which is here assumed to be 30 ins., and for the 
 specific weight of the waste gases. 
 
 The success which has attended the author's trials to determine 
 the volume of large quantities of water by chemical means (see ' N. A.,' 
 1896, vol. xxxvii. p. 226, and ' M. S. U. A.,' 1900) encourages the hope 
 that a similar method may be employed to measure the volume and 
 weight of waste gases. In those experiments a carefully gauged 
 stream of salt water was run into the engine hotwell, samples of 
 water were drawn from the pumps, and chemical analyses of a com- 
 parative and therefore simple nature were made. The saltness thus 
 found of the salted feed, as compared with that of the added salt 
 water, would be in inverse proportion to the two volumes of water. 
 The circulating water was also measured in the same way, but car- 
 bonate of soda was used instead of salt. To measure flue gases a 
 vapour such as hydrochloric acid, or one of its organic combinations, 
 would have to be injected into the escaping gases, and samples of 
 waste gases would have to be taken from near the top of the funnel ; 
 these would have to be specially analysed for the injected vapour. 
 Its dilution with waste gases would then determine this amount. 
 
 One quart of strong hydrochloric acid per ton of coal burnt would 
 be sufficient to determine the weight of waste gases to within one 
 per cent., provided that at least one cubic yard of gases is passed 
 through the chemical absorption tube. With smaller volumes of gas, 
 especially if greater accuracy is desired, proportionately more acid 
 had to be used. Hydrochloric and hydroiodic acids have been used, 
 but without success. 
 
 Chemical Estimate of Weight of Waste Products. In outline 
 the principle is the same as that just mentioned. The quantity of 
 carbon burnt and the percentage of carbon in the waste products 
 have to be ascertained ; then their weight is equal to the weight of 
 carbon burnt multiplied by 100 and divided by the percentage of 
 carbon in the waste gases. The coal must therefore be weighed, a 
 laborious proceeding, and carefully analysed for carbon. The gas 
 analysis is a simple operation. It is also known (see p. 93) that 
 one pound of coal requires 11'587 pounds of air for complete com- 
 bustion, and that the waste products weigh 12 - 587 pounds, and 
 further the oxygen consumed and the resulting carbon dioxide are 
 nearly equal in volume, while the volumetric percentage of oxygen in 
 
104 
 
 FUELS AND COMBUSTION 
 
 the air is 20'87 - If therefore one finds 20-8/ carbonic acid and no 
 oxygen it would follow that the waste products weigh 12*587 times 
 the weight of fuel and for lesser quantities of carbonic acid the waste 
 gases are proportionately heavier. The general rule is therefore to 
 divide the percentage of carbonic acid found into 262*0, which is the 
 product 20-8 x 12 '587. This is the weight of waste products per Ib. 
 of fuel burnt. The result is, however, generally far from correct, as 
 will appear from the following remarks. 
 
 Collection of Gas Samples. In order to obtain really reliable 
 results, great care has to be taken to obtain average samples of gas. 
 It would be good if continuous supplies could slowly be drawn from a 
 central tube of every smoke box, and each one analysed ; or, if that is 
 impossible, the supplies might all be brought together in one tube, 
 and an average sample taken. 
 
 FIG. 108 
 
 In order that equal amounts may be drawn from each point, the 
 sizes of the holes should all be equal (fire-proof gas burners can be 
 used), and the section of the tubes which connect them ought to be 
 fairly large, so as to reduce the internal friction. Before bottling a 
 sample a considerable quantity of gas has to be sucked through the 
 tubes, so as to remove all trace of atmospheric air, and a certain 
 time allowance should be made for the volumetric capacity of the 
 pipes, especially if they are long and of large diameter. 
 
FUELS AND COMBUSTION 
 
 105 
 
 India rubber tubes should be used sparingly because CO 2 readily 
 diffuses through them. A lead pipe of small bore is a safe and 
 convenient connection to the gasometer (fig. 108). It is very de- 
 sirable to introduce a small wash bottle close to the cocks S, for 
 the speed with which the gases bubble through the water is an 
 indication of the rate of suction. If it ceases then most likely the 
 connecting nipples are choked. They can be cleared by a strong 
 blast through either d 2 or d 2 , whichever connection is out of use, 
 but it is more convenient to have a three way-cock close to the 
 funnel which should be so arranged that it will not admit air to the 
 gasometer. 
 
 AA 
 
 M 
 
 \ r 
 
 FIG. Ill 
 
 FIG. 110 
 
 In order to obtain average results a large number of samples 
 should be collected, analysed, and the weight of gases determined, 
 because one has to take the mean of the reciprocals of the analyses. 
 It would not be correct to take the direct mean, because the per- 
 centages of carbonic acid appear in the denominators of previous 
 equations. A convenient apparatus for collecting samples con- 
 tinuously is shown partly in section in fig. 108. Two gasometers 
 Gj G 2 are placed side by side, the air bells have guide rods, Rj R , 
 which can if necessary be loaded. The suction in Gj is produced by 
 the weight Q 15 and the connecting rope c is a clamp which prevents 
 the bell from being lifted too high. An arrangement of cocks, nos. 1 
 to 6, is suspended in front of the gasometers. Jndiarubber tubes 
 
106 FUELS AND COMBUSTION 
 
 connect d 2 to e l and d 3 to e 2) S is similarly connected to G of fig. 107, 
 while O is connected to the Orsat gas analyser (fig. 110). The cock 1 
 is permanently fixed so as to admit gas at the desired rate, 
 3 and 4 are closed and 2 opened so that gas from the chimney 
 passes through S, 1, 2, d 2 and e l into G, which should fill itself 
 in about one hour's time. While this is going on Q 2 depresses 
 the gasometer G 2 , the cocks 5 and 6 are opened and the gas 
 collected in G 2 passes to the Orsat apparatus. With a little 
 expedition duplicate analyses could be made in one hour. The 
 gasometers should be annular as shown so as to contain a minimum 
 of water, which should have a film of oil on its upper surface. 
 
 If samples are taken at definite periods, these arrangements are 
 not necessary. An air pump or aspirator draws the gases direct into 
 the sample bottle. All water used in connection with this sampling 
 should contain acidulated water which has been well shaken up with 
 waste gases ; otherwise some carbonic acid is likely to be absorbed 
 and possibly other gases given off. 
 
 Gas Analysis. It will be well to study the subject in such books 
 as that by Winkler on Gas Analysis, which deals with all its branches. 
 Doubtless the very convenient ' Orsat ' analysing apparatus will then 
 be the one selected for use. The following is a brief description: 
 E, tig. 110, is a glass vessel open at both ends ; the lower part is a tube 
 graduated from to 50 cubic centimeters. For our purposes it would 
 be better if this tube were smaller, and held only 25 cubic centimeters. 
 The upper part of E is more bulky, and the total capacity down to the 
 lowest mark of the tube is exactly 100 cubic centimeters. The tube 
 G is attached to the bottom of E, and also to the bottle J, and the 
 two contain sufficient acidulated water to more than fill E. The 
 upper end of E is connected to a glass pipe g } , a, e, g, with several 
 stopcocks. To fill E with gas, g is connected to the gas supply, the 
 cock a is opened and J lowered. The suction thus produced in E 
 empties it of water and gas flows in. The cock a is then closed. 
 The glass tube g 1 , g, has three other cocks, b,c,d; these communicate 
 with glass vessels B, C, D, of which a side view is given in fig. 111. 
 M is filled with the necessary chemical up to the stopcock. This is 
 generally closed, but after E has been filled with gas, and the cock d 
 being open, while J is raised, all the gas in E is expelled into D 
 or M, and the fluid in M passes into N. When absorption has 
 taken place in M, J is lowered until the fluid in N passes back into 
 M right up to the stopcock ; the amount of gas absorbed is then read 
 off on the scale on the tube of E. If it is desired to obtain sufficiently 
 accurate results for determining the hydrogen, as previously ex- 
 plained, it is essential to surround E with a water jacket F F and to 
 insert in it a very sensitive thermometer, whose indications have to 
 be taken with each reading, for a difference of J F., which is frequently 
 surpassed in half an hour, if working in a draughty place near a 
 boiler would affect the readings by about y 1 ^ cc. A convenient 
 arrangement for circulating the water in F is to blow air into it 
 from the bottom by means of the indiarubber ball B and the tube H. 
 When the above-mentioned accuracy is aimed at it is almost essential 
 to have an arrangement for adjusting the levels in E and J. This 
 
FUELS AND COMBUSTION 107 
 
 latter vessel should be suspended on a pulley and balanced by a 
 weight Q (fig. 110) or a spring, and behind it should be placed a 
 scale arranged as follows. The height of a column of water corre- 
 sponding to the average barometric pressure is about 400 inches ; 
 this has to be expressed in terms of the scale on the gas-vessel E 
 (fig. 110). If these divisions are J-inch the column would have a 
 height of 1,600 of these divisions. The top of this scale should 
 be placed where the zero point of E would be if parallel all the 
 way up. Its position can also be fixed by subtracting 100 from 
 the above, making it 1,500, and placing this mark on a level with 
 the 100 mark near the bottom-end of the tube E. This scale is 
 shown behind the bottle J. As ordinarily arranged the scale 
 on E is in front ; it should be behind and the figures should be 
 turned as if viewed in a looking-glass, then they will appear in 
 their right position viewed through the water. By raising or 
 lowering J, the water-level in E can now be adjusted to any 
 particular mark with the very greatest accuracy, which is not 
 possible when the scale is in front of the glass. Now read off the 
 water-level of J on the scale behind it, and add the reading of E. 
 This sum is the pressure in the arbitrary scale on the gas in E. All 
 subsequent readings have to be reduced to the first pressure. As 
 the scale behind J will in this case be 16 times as long as the 
 scale E, a tenth of one of the large divisions which are supposed to 
 be J-inch, will correspond to 0'4 inch on the J scale, so that it is 
 quite easy to read to decimals of the small divisions which is other- 
 wise impossible, and then there is no difficulty as regards accurate 
 results. 
 
 It is very essential that ample time should be allowed before each 
 reading-: firstly, to enable the gas which may have changed its 
 temperature to acquire that of the jacket F ; secondly, to allow the 
 gas to regain its original humidity ; thirdly, to allow all the water in 
 E to drain down the walls. A deliberate wait of five minutes should 
 be made before each reading. Some of the reactions, notably the 
 oxygen and carbon monoxide absorption, require much time, so that 
 with four absorbers each analysis takes up at least half an hour's 
 time, perhaps more, and the suction into the gasometer should be so 
 arranged that it fills in about one hour's time. 
 
 Chemicals Required for Analysis. 1. A solution of iodine in 
 water. This converts the sulphurous into sulphuric acid which is 
 absorbed by the fluid. 
 
 2. A solution of caustic potash in water for the absorption of the 
 carbonic acid and of the sulphurous acid if the iodine is not used. 
 
 3. (i.) Sticks of phosphorus for the absorption of oxygen. The gas 
 may be passed over these first and then through the caustic potash, 
 (ii.) A solution of pyrogallic acid in caustic potash and water. This 
 also absorbs oxygen, but is rather messy. It must not be used until 
 the carbonic acid has been removed, because it absorbs it. 
 
 4. A strong solution of subchloride of copper in hydrochloric 
 acid and water for the absorption of carbon monoxide. After treat- 
 ment the gas has to come in contact again with caustic potash so as 
 to remove the hydrochloric acid gas. 
 
108 FUELS AND COMBUSTION 
 
 Both the pyrogallic and the subchloride of copper solution have 
 to be carefully protected from the air as they both readily absorb 
 oxygen. 
 
 Analytical Operations. E (fig. 110) has to be filled from the 
 gasometer by lowering J. After waiting a few minutes the first 
 reading of E and J are taken, the water in the jacket F being 
 frequently agitated by pressure on P which sends bubbles through 
 it. The thermometer T has also to be read. The cocks e and a are 
 closed. Now raise J and open d, leading to D, of which a side view 
 is given in fig. 111. It contains say a solution of iodine in water up 
 to the top of M, as well as glass rods, so as to give a large contact 
 surface. N is nearly empty. After waiting a little, pass the gas into 
 E and back into D ; then re-introduce into E, wait a few minutes, 
 agitating the water in the jacket, and take readings E, J and T. 
 Now pass the gas into C, containing caustic potash, and treat in the 
 same way. Then pass it into B and treat in the same way. As the 
 absorption here is rather slow it will be found convenient to paste a 
 small piece of paper on B with a mark which indicates when 
 practically all the oxygen has been absorbed, then pass the gas into 
 E and back again and wait at least one minute. If B can be viewed 
 in the dark the end of the absorption is indicated by the disappear- 
 ance of phosphorescence. The gas should now be passed into the 
 vessel containing cuprous subchloride, not shown ; into E and then 
 into C and back to E. This chemical should be used last as it is a 
 powerful oxygen absorber. The cock e is now opened, the gas in E 
 blown out, and new gas admitted through e. If the cock a were 
 opened the inert gas between a and e would be removed, which 
 should not be done. 
 
 Continuous Combustion Indicators. During the last few years 
 the Ados CO 2 recorder has found great favour ashore amongst steam 
 users, and could equally well be used on steamers. It works auto- 
 matically by means of the chimney draught and makes an analysis 
 and records the carbonic acid about every ten minutes. It can at 
 any moment be switched on to any boiler, and thus enables a very 
 good idea to be formed as to the efficiency of the stoking. In 
 Mehling's gas composimeter the gas passes through a small orifice 
 into a chamber containing caustic lime and soda, which absorbs all 
 the carbonic acid. The volume of gas is now reduced, and its density 
 diminished, and the suction required for drawing off this gas through 
 another small orifice is less than the first. The two suctions are 
 measured by mercury columns and indicate the percentage of C0 2 
 absorbed. 
 
 Mr. Craig's apparatus, made by Baird and Tatlock, consists of two 
 gas meters with an absorption chamber between the two, but as the 
 gas meters contain water they could not well be used at sea. 
 
 Funnel Temperatures. The chief object of either measurement is 
 the estimating of the heat wasted, and this can now be easily done if 
 frequent readings are taken of the funnel temperatures. In this case, 
 too, care should be taken to get good average results, for it is quite 
 conceivable that if the thermometer is fixed in one position it will 
 
FUELS AND COMBUSTION 109 
 
 only record the temperature of the gases from one particular furnace, 
 which may be hotter or colder than the rest. 
 
 For a list of pyrometers see p. 96, to which should be added that 
 for funnel temperatures. A very convenient one is an ordinary mercu- 
 rial thermometer, made of glass which can stand high temperatures. 
 Quartz would be better. The vacuum end of the tube is filled with 
 nitrogen, which prevents the mercury from boiling. Such instru- 
 ments were used on the trials of the Eesearch Committee ( ' M. E.,' 
 1889-92), and registered up to 860 F. This was not quite high 
 enough for some of the trials, but the sodium and potassium thermo- 
 meter of E. C. C. Baly and J. C. Chorley is said to register up to 
 1,100 F. ; but of late Callendar's electric pyrometer is proving itself 
 to be most suitable. 
 
 Great care must be taken to screen the thermometer bulb from 
 radiant heat, and yet allow the air to come in contact with it ; other- 
 wise the readings will be wrong. Thus the temperature of waste 
 gases will apparently be very much less at the top of the funnel than 
 lower down, which is partly due to radiation into space of the heat 
 acquired by the thermometer bulb, and partly due to the cooling of 
 the gases as they travel upwards. In the same way the heated air 
 which is admitted into some furnaces is incorrectly measured if this 
 is done by an unprotected thermometer, because of the radiation, 
 either from the hot fuel or from the heated iron. The screens should 
 be at least twofold, and ought to be highly polished on their outer 
 surfaces, so as to reflect all radiant heat. 
 
 If the collecting of the waste gases and the analyses have been 
 correctly carried out then the ratio of carbon to sulphur, hydrogen 
 and nitrogen ought to be the same in the fuel as in the waste 
 gases 
 
 The following is one example from a series of twelve collections 
 and analyses taken during one trial. The fuel used during the trial 
 was analysed, after being air dried, with the following result : 
 
 Carbon ... . 74-65 
 
 Hydrogen ... . . 5*21 
 
 Sulphur ... . 2-38 
 
 Mineral matter . . . 3 '59 
 
 Remaining moisture . . 5*11 
 
 By difference oxygen, nitrogen, etc. . . 9-06 
 
 Total 100-00 
 
 Add. moisture removed by air-drying . . . 7*34 
 
 The ashes and clinker for the whole trial were weighed and analysed 
 and accounted for 2'43 % mineral matter, and 4'37 % carbon, so that 
 only 70*28 carbon were burnt. Possibly the missing 1/16 ashes 
 may have carried off 2 % or 3 % more of carbon as flue dust, and % 
 may have produced smoke, it having been found that dense black 
 smoke represents a loss of 1 % carbon. These doubtful losses will 
 however not be taken into account. 
 
 When as in this case the nitrogen has not been determined it may 
 be assumed to amount to 2 % of the carbon, equal to 2 % in the 
 above analysis, and equal to 1 % of the volume of carbonic acid found 
 in the waste gases. 
 
110 
 
 FUELS AND COMBUSTION 
 
 During the trial, which lasted from 9 15 until 5'8, the gases were 
 collected continuously and analysed about every half hour. Here 
 only the third sample will be dealt with, collected from 10-15 to 1O52. 
 Corrections were made for changes of temperature during the half 
 hour occupied in making the analysis. The nitrogen from the fuel, 
 viz. - 01 X CO 2 , and the carbonic acid in the air, viz. 0*03 %, have 
 also been subtracted. 
 
 One Flue-gas analysis collected from 10*15 to 1O52 
 
 QM 
 
 Volume 
 
 Factors 
 
 Calculated Weights 
 
 Densities of Gases and 
 Constituents air (0-0809 
 pounds per cubic foot) = TO 
 
 N 
 
 
 
 
 
 s 
 
 S0 2 
 C0 2 
 
 & 
 
 N 
 
 o.c. 
 0-07 
 7-97 
 10-80 
 0-15 
 80-02 
 
 = 1-132, 8 = 1-132 
 = 1-10601,0 = 0-41475 
 = 1-10535, 
 = 0-55267, = 0-4145 
 N = 0-9725, 
 
 77-900 
 
 0-077 
 8-814 
 11-936 
 0-083 
 
 3-306 
 0-062 
 
 0-077 
 
 Totals . 
 
 99-01 
 
 
 
 77-900 
 
 20-910 
 
 3-368 
 
 0-077 
 
 The above factors have been used in all the calculations. 
 
 The weight of the nitrogen in 100 grams of dry air free from 
 carbonic acid is 76*93 grams. All the above weights have therefore 
 to be multiplied by the ratio 76*93 -r- 77*90, and for convenience the 
 constituents of the fuel, less carbon lost in ash, can be multiplied 
 by a ratio of the carbons, viz. 3'368 -=- 70'28. 
 
 Relative Weights 
 
 
 
 Nitrogen 
 
 Oxygen 
 
 Carbon 
 
 Sulphur 
 
 Hydrogen 
 
 Consumed 
 
 Free 
 
 Total 
 
 Gas . . 
 Fuel . 
 
 76-93 
 086 
 
 8-857 
 
 11-781 
 
 20-638 
 
 3-324 
 3-324 
 
 0-076 
 0-112 
 
 0-246 
 
 Seeing that the total oxygen should be 23-07 grams per 100 grams 
 air it is evident that the 2-432 grams have disappeared. Now the 
 0'246 grams hydrogen will have consumed 7*98 times their weight, or 
 1-963 grams oxygen, so that 0'469 gjrams are still missing. These it 
 may reasonably be assumed have disappeared as carbonic acid gas 
 through the indiarubber tubing or have been absorbed by the fluid in 
 the gasometer. They should be added to the consumed oxygen, making 
 it 9-826 grams, and f , or 0'176 grams, being the equivalent loss of 
 carbon, should be added to the 3*324 grams making it 3*500 grams. 
 
 The ratio of air supplied to air required is the ratio of the total 
 to consumed oxygen viz. 23*14 to 9*326 or 2*492 to 1. If the ratio 
 of the total volumes of consumed oxygen, viz. 8*13 cc., had been 
 compared with the original volume viz. 20*8, the ratio of the two air 
 supplies would have been 2-56 to 1, and therefore not correct ; but 
 the result is nearer the truth than would have been the case if there 
 
FUELS AND COMBUSTION 111 
 
 had been either more or less leakage of carbonic acid, or if the effect 
 of the hydrogen had been taken into account. 
 
 However, with serious leakages such a determination may be 
 quite wrong. If the oxygen determination had been used the result 
 would have been 2-11 to 1. 
 
 The difference between the two sulphur determinations is within 
 the limits of observation, but may be due to the analytical combustion 
 in oxygen being more searching than that in the furnaces. 
 
 The weight of the waste gases can now be determined as per 
 following table : 
 
 Grams 
 Nitrogen in air ..... . 76'86 
 
 Oxygen in air 23-14 
 
 Carbonic acid in air 03 
 
 Moisture (by hygrometer) . . . 5'10 
 
 Carbon (from fuel) 
 Hydrogen and sulphur from fuel 
 Oxygen, nitrogen, <fec., from fuel 
 Moisture from fuel, 20-4 per cent, of C. 
 
 3-53 
 0-32 
 0-45 
 072 
 
 Total waste gases per Ib. of pure air . . HO'15 
 
 Dividing this total by the carbon (3*53) and multiplying by the 
 percentage (70'28) actually burnt the total weight of waste gases per 
 pound of fuel fired is 21*93 Ibs. This has to be multiplied by the tempera- 
 ture of the waste gases, which was 264 R in excess of that of the air, 
 and by 0'238 the specific heat of average waste gases ; the product 720 
 B.T.U. is the heat carried up the chimney for every pound of fuel. 
 
 Although the above process appears complicated it works out 
 fairly simply in practice, but the gas analysis has to be carefully 
 done. As the sulphurous acid is always a very small volume and as 
 it would be absorbed together with the carbonic acid if not already 
 dealt with, it need not, generally speaking, be determined, but then 
 f of the sulphur in the fuel has to be added to the carbon when 
 making the above estimate. An accurate gas analysis is, however, 
 a desirable check on the fuel analysis. 
 
 It is evident that if the gas analyses have to be corrected for the 
 hydrogen in the fuel it should be possible, by very carefully collecting 
 and analysing the waste gases, to determine the ratio of hydrogen to 
 carbon in the fuel, and thus dispensing with one rather costly 
 analysis. The process is simple enough. Make the necessary 
 allowances for the carbonic acid in the air and the nitrogen in the 
 fuel, and then as above find the missing oxygen, divide it by 7'98 
 the molecular weight of oxygen, and also by the weight of carbon in 
 the waste gases, and the result is the ratio of hydrogen to carbon in 
 the fuel, or rather to that portion of it which has actually been 
 consumed. 
 
 Now it will be noticed that in the above example it has been 
 assumed that the only waste of carbon is that associated with the 
 ashes and clinker, but occasionally, especially with forced draught, 
 small particles of partly burnt fuel are carried away and these, instead 
 of containing say 30 to 60 per cent, carbon, may contain much larger 
 proportions, and as in nearly all trials a very large percentage of 
 mineral matter disappears either into the flues or up the chimney, 
 
112 
 
 FUELS AND COMBUSTION 
 
 an even larger proportion of carbon is also carried away. Smoke, 
 although the densest is responsible for a loss of only about 1 % of 
 carbon, should not be entirely neglected. 
 
 Another uncertainty arises out of the very small amounts of fuel 
 used for analysis, generally only 2 to 5 grams, or perhaps, one- 
 millionth part of the fuel burnt, and what makes matters worse is 
 that the fuel has to be ground to an impalpable powder and will 
 almost certainly lose all volatile hydrocarbons which it may contain 
 and may absorb a large volume of oxygen and nitrogen. 
 
 Most fuel analyses, like the present one, contain a large item : 
 1 oxygen,' or ' oxygen &c., by difference,' but it does not appear to have 
 been shown that this difference is really oxygen, and in the present 
 example it has not been taken into account as such, otherwise the 
 percentage of hydrogen in the fuel would have had to be reduced by 
 one-eighth of this amount less the nitrogen. 
 
 On account of all these difficulties and uncertainties it would be 
 very desirable to devise a reliable anemometer as suggested on 
 page 102, and to carefully analyse the waste gases instead of as now 
 relying on an analysis of a homoeopathic dose of the fuel. 
 
 Variations in the Process of Combustion. It is evident that when 
 fresh fuel is thrown on a fire distillation takes place, that hydro- 
 carbons are freely evolved and that a careful analysis of the waste 
 products will reveal much missing oxygen, indicating that much 
 hydrogen has been evolved and consumed. When the bed of fuel is 
 all aglow, probably all hydrogen will have been driven off and only 
 carbonic acid and perhaps carbon monoxide will be found in the 
 waste gases. In the trial from which the above-mentioned example 
 has been taken firing was reduced at 3.0 and ceased at about 3.30, but 
 the fire was so thick that it continued to burn till after five o'clock. 
 The ratios of the consumed hydrogen to carbon as found by gas 
 analysis were as follows : 
 
 Times of Collection 
 
 Ratio H+0 
 
 Waste Gases 
 per Ib. of Fuel 
 
 b in* h. in. in. 
 
 per cent. 
 
 
 9.15- 9.45 = 30 
 
 11-14 
 
 20-8 
 
 9.45-10.15 = 30 
 
 10-31 
 
 21-7 
 
 10.15-10.52 = 37 
 
 10-88 
 
 21-9 
 
 10.52-11.30 = 38 
 
 9-60 
 
 22-0 
 
 11.30-12.0 = 30 
 
 6-73 
 
 21-5 
 
 12.0 -12.50 = 50 
 
 8-38 
 
 21-3 
 
 12.50- 1.35 35 
 
 10-56 
 
 21-3 
 
 1.35- 2.25 = 50 
 
 8-79 
 
 21-3 
 
 2.25- 3.0 = 35 
 
 10-68 
 
 21-8 
 
 3.0 - 3.35 = 35 
 
 7-21 
 
 22-0 
 
 3.35- 4.15 = 40 
 
 4-88 
 
 22-6 
 
 4.15- 5.8 = 53 
 
 o-oo 
 
 22-8 
 
 The average ratio of H to C is 8*06 %, whereas according to 
 the coal analysis it is 7'41 %. It will be noticed that there is 
 considerable variation in the ratio, but that it is well above the 
 average before three o'clock and fell off to nothing during the remain- 
 ing two hours. In these and similar cases where the firing is irre- 
 
FUELS AND COMBUSTION 113 
 
 gular it may be desirable to estimate tbe initial flame temperatures, 
 which are affected by the ratio of carbon to hydrogen and to the 
 total waste products. The excess temperature over the air tempera- 
 ture can be found according to the formula given on page 94, but if 
 the detailed determination of the weight of waste gases has already 
 been carried out it will be simplest to write 
 
 T _ _1 __ 0.14,540 + H. 51,322 
 Q'237 " Weight of waste products 
 
 Then the efficiency e, neglecting radiation, is found by subtracting 
 the temperature of the waste gases from T and dividing by T. Now 
 let H|, H a &c., be the heat produced in the furnaces during the 
 times ,, t 9 &c. Let S lt S 2 &c. be the heats utilised in evaporating 
 the water, and B the radiated heat which may be assumed to be a 
 constant value, then 
 
 H, . *, . e, = Si J, + R . J, ; H 2 . *, <? 2 = S 2 J 2 + R . J 2 , &c. ; 
 dividing by e, and summing up, we have 
 
 Here 2(H . t) is the total heat generated during the whole trial, which 
 is of course known, the second term can be calculated and so can 
 
 Si-). the radiation K per unit of time can therefore be determined 
 
 w 
 
 and then of course H t , H 2 , &c. It will thus be possible to determine 
 the heat generated during each time interval and also the quantity of 
 carbon and hydrogen burnt. The heat generated less the chimney 
 loss during each interval, which can now be calculated from the 
 estimated carbon consumption and other data, will, as a rule, not 
 agree with S, the heat required for the steam production, unless this 
 too has been carefully determined. 
 
 Weight of Steam Produced. All the water which is pumped into 
 a boiler is not necessarily evaporated at once : it may be in excess of 
 the heat transmission or less. In the one case the waterlevel rises 
 and the temperature and pressure sink, in the other case the reverse 
 happens. It is therefore desirable to determine the waterlevels and 
 pressures at definite intervals, or whenever the chemist has filled one 
 of his gasometers. The weight of the water in the boiler for various 
 levels should be known, the total heat contained in the water at any 
 time for which the data are available can then of course be calcu- 
 lated. This is heat which passed through the heating surface and 
 should be added to the head of evaporation during the past interval. 
 The successive sums of heats should then be subtracted from each 
 other. These are the values S, mentioned above. 
 
114 
 
 CHAPTER V 
 
 HEAT TRANSMISSION 
 
 Nature of Heat. At one time heat and light were looked upon as 
 being two different substances or conditions ; now it is universally 
 admitted that they are identical, the only difference being an objective 
 one, and depending solely on the incapability of our optic nerves to 
 perceive heat rays. Our other nerves make no distinction between 
 the two, and the back of the hand will as readily feel the radiation 
 from a blackened stove as from an electric arc, the one emitting only 
 heat and the other chiefly light. 
 
 By those who believe in the existence of a universal ether, light 
 and heat are thought to be vibrations of this medium. Every known 
 experiment on the subject points to the conclusion that these vibrations 
 are of a transverse nature, like waves on the surface of fluids, and no 
 relation seems to exist between these and the longitudinal vibrations 
 called sound. The lengths of the waves of visible heat (light) range 
 from 30,000 to 60,000 per inch. The non-luminous heat waves are 
 longer, and the ultra-violet light, invisible to our eye but very active 
 in photographic reactions and in vegetable life, consists of very much 
 smaller waves. The speed with which heat and light travel through 
 space is at the rate of about 187,000 miles per second, so that the 
 number of vibrations per second has to be counted by hundreds of 
 billions. 
 
 Radiant Heat of Gases and Solids. Heat being invisible, many of 
 the phenomena connected with radiation will be more readily under- 
 stood if exemplified by the action of light, though Prof. Langley 
 (' C. E.,' vol. c. p. 469) has done a good deal to confirm, by direct 
 experiment, the conclusions which naturally suggest themselves when 
 comparing light and heat. 
 
 It has been found that solids, when heated to incandescence, radiate 
 heat and light of every colour, which is very clearly shown in the 
 spectroscope by the fact that the spectrum of a luminous solid is a 
 continuous one, light being visible continuously from the red end to 
 the violet, and perceptible beyond both ends. Luminous gases do not 
 radiate light of every colour, and some are even monochromatic. 
 Thus the vapour of the metal caesium has a spectrum consisting of only 
 one green line. Indium shows three lines, chiefly blue ; hydrogen 
 shows four lines, placed in various parts of the entire spectrum. Arsenic 
 and sodium show several lines near the yellow ; potassium also shows 
 comparatively few lines. For further information see W. M. Watts, 
 1872. Naturally all these gases also radiate definite colours of heat, 
 if one may use this term ; but the important point is that for the same 
 intensity of colour of light or heat the heat thus radiated is very small 
 
HEAT TRANSMISSION 115 
 
 as compared with the heat radiated by a solid which shows the same 
 intensity of light and heat over the entire spectrum ; so that it will take 
 much longer to cool a gas than a solid. An idea of the enormous 
 disparity existing between the two will be obtained by examining the 
 spectrum lines of sodium with a good instrument. They will appear 
 to be no wider than very fine inked lines. The full spectrum from 
 red to violet, measured by yards, represents the amount of radiation 
 from a solid of the same temperature as the gas, whereas the breadth 
 of the lines represents the entire heat radiation of sodium vapour. 
 
 Absorption of Heat. Gases absorb only such light as they can 
 emit, but experiments as to the influence of temperature on thig 
 phenomenon are still wanting. According to present views it would 
 appear that gaseous flames are only luminous at their outer surfaces, 
 which is contrary to what one sees. 
 
 It may, therefore, be assumed that flames, unless they are quite 
 luminous, radiate and absorb little heat, and none at all when they 
 have grown cold and transparent. The heat which radiates from a 
 glowing coke fire is not absorbed by the non-luminous flame over it. 
 It also follows that when the gases are cooled below the point of 
 luminosity they cannot transmit any of their heat to the boiler plates, 
 except by actual contact, or and this is of great importance by 
 contact with the suspended particles of soot and ashes, which, as they 
 are solids, are capable of radiating heat even at low temperatures. 
 It would therefore appear probable that a little smoke is a good 
 admixture to the products of combustion. It is also probable that 
 luminous flames, such as are produced from North -country coal, will 
 be more efficient radiators in the furnace than those which are produced 
 from coke, anthracite, &c. In the former case the radiating surface, 
 i.e. the outer part of the flame, is very much larger than the exposed 
 incandescent surface of the fuel on the grate. 
 
 Another matter which should be mentioned here is the influence 
 of moisture and of carbonic acid on the radiating power of air. Prof. 
 Tyndall (1870, pp. 320, 359) states that carbonic acid absorbs (and 
 therefore also emits) 972 times as much heat as any of the permanent 
 gases, including oxygen and nitrogen, and that humid air (he does not 
 give the percentage of moisture) absorbs 90 times as much heat as 
 dry air. As the products of combustion contain from 10 to 20 % of 
 carbonic acid, this alone would raise the absorbing and radiating 
 power about one or two hundredfold, and the moisture contained in 
 the air and in the fuel would add considerably to this power. As 
 these impurities, including smoke, vary considerably in every trial, it 
 cannot be expected that much uniformity will be obtained in experi- 
 ments which do not take them into account. 
 
 Radiating Power of Solids. Physicists call those substances 
 black as regards radiating power which emit a maximum amount 
 of heat even when in an incandescent condition, and Stefan and 
 Bolzman have discovered a law, which is fully confirmed by experi- 
 ments, that this black substance, including the glowing particles 
 in coal gas flame, emit a certain amount of heat per square foot per 
 hour. 
 
 h = 16.10- 10 .T 4 
 
 i2 
 
116 
 
 HEAT TRANSMISSION 
 
 Here T is the absolute temperature, found by adding 459 to tbe 
 temperature of the incandescent substance. The heat radiated by 
 a bed of incandescent coke or anthracite is evidently proportional 
 to the grate area, that radiated by a furnace flame is proportional 
 to the heating surface of the furnace above the grate. Now the 
 furnace temperature depends on the amount of excess air mixed 
 with the flame and we have the following interesting results. See 
 page 94. 
 
 CO 2 
 
 Ratio of Air 
 
 Excess 
 
 Flame Temperature 
 
 Radiated 
 
 /o 
 
 to Fuel 
 
 Air 
 
 
 
 Heat = h 
 
 
 
 
 u Fah. 
 
 Absolute 
 
 
 16-1 
 
 15 
 
 30% 
 
 3,830 
 
 4,290 
 
 542,000 B.T U. 
 
 12-1 
 
 20 
 
 70,, 
 
 2,920 
 
 3,380 
 
 210,000 
 
 9-7 
 
 25 
 
 115,, 
 
 2,350 
 
 2,810 
 
 99,000 , 
 
 8-0 
 
 30 
 
 160,, 
 
 1,970 
 
 2,330 
 
 47,000 , 
 
 6-9 
 
 35 
 
 200,, 
 
 1,700 
 
 2,160 
 
 35,000 , 
 
 It will at once be seen that if the combustion in a furnace is 
 improved from a CO 2 percentage of say 6*9 which is a low but not 
 unusual result, to 12'1/ , which is a good result, then the quantity of 
 heat imparted to the furnace plate is sixfolded, but considerable 
 deductions must be made from the larger values on account of the 
 extremely rapid loss of heat. Thus assuming that a grate is burning 
 30 Ibs. of coal per sq. ft. per hour, or say 20 Ibs. per sq. ft. of upper 
 furnace surface, this combustion will produce 20 x 15,000 = 300,000 
 B.T.U. per sq. ft. of furnace surface, and if the combustion was so 
 perfect as to result in a temperature of 2,920 F., and if this temperature 
 could have been maintained 210,000 B.T.U. would have been abstracted 
 by the furnace plates and only 90,000 B.T.U. would be found in the 
 gases passing over the bridge, whose temperature would be reduced 
 to about 1,300 F. Of course with the reductions of temperature the 
 radiation will diminish and the above result will not be attained, but 
 there is every reason to believe that very intense local heat productions 
 are attained which would do much damage by local overheating (blow- 
 pipe effect) in scaly or greasy boilers if they were not of a temporary 
 nature, at least in hand-fired furnaces. With mechanical stokers local 
 productions of intense heat are of a more persistent nature and are the 
 cause of occasional serious damage. 
 
 Surface Resistance. The furnace plates radiate heat into the 
 furnace according to the law mentioned above, but as the steam 
 temperatures are low the maximum deductions to be made from the 
 values in the above table do not amount to 1,000 B.T.U. and are 
 negligible.* The case is different when there is scale or grease in the 
 boiler and the plates attain a high temperature, say 1,000 F. or 1,500 
 absolute, then the plate radiation, which has to be deducted from the 
 flame radiation amounts to 8,000 B.T.U. which is quite appreciable 
 against a low temperature flame or fire, and the net heat supplied to 
 the boiler is materially reduced. 
 
 Coatings of Soot and Tar intensify this effect, for as they are ex- 
 
HEAT TEANSMISSION 117 
 
 cellent non-conductors their outer surfaces can be brought to an 
 incandescent condition, when a flame unless it is very much heated will 
 not be able to transfer much of its heat to the plate. Soot and tar 
 deposit most readily on the cooler parts of boilers, i.e. in or on the 
 tubes, and especially on the surfaces of feed economiser pipes, for 
 which reason they have to be scraped continuously. It has not been 
 found possible to introduce scrapers for boiler tubes, but attempts 
 have been made to keep them clean by means of occasional steam 
 blasts. 
 
 Surface Resistances. In addition to the resistance which heat 
 meets in its passage through the plates, there is the resistance to its 
 entrance on one side and to its exit on the other side. This differs 
 for different plate materials, perhaps also for different hot gases, and 
 stands in no relation to the thermal conductivity. Thus cast iron, 
 which has a much lower thermal conductivity than copper, is never- 
 theless a better transmitter of heat for all reasonable thicknesses, 
 because it is the better absorber and emitter of heat. Even earthen- 
 ware tiles in. thickness are 70 % better than copper. (See p. 126.) 
 From various experiments and practical experiences it would appear 
 that when air is in contact with metal the heat transmission is 
 very low. 
 
 Some meagre results are to be gleaned from the performances of 
 steamers fitted with Howden's system of hot-air draught, according to 
 which about 2f units of heat are transmitted per hour through one 
 square foot for every degree of difference. The amount would be 
 double for each surface on the assumption that the metal acquires the 
 mean temperature. Plates which are exposed to the direct action of 
 the flame also receive heat by radiation. (See p. 115.) 
 
 Considerable light has recently been thrown on this subject by 
 some very careful experiments which were carried out by Miss E. M. 
 Bryant (' C. E.,' 1897, vol. clxxxii. p. 274), who measured the tempera- 
 ture gradient in the heated plate of an experimental boiler by electric 
 methods. In the first set of experiments a copper plate was heated by 
 a flame, in four other experiments the heating of steel and copper plates 
 was done by radiation from a cast-iron hemisphere which was placed, 
 concave side upwards, below the plate, while the heat was applied to 
 the outside of this casting. Its temperature was measured electrically. 
 The heated plates formed the bottoms of dishes filled with water. Com- 
 paring the amount of water evaporated with the measured tempera- 
 ture gradient in the plates, it appears that the thermal conductivity of 
 steel (across the grain) is O093 G.C.S. This is the mean of 44 experi- 
 ments, but, as will be seen on comparison with the previous table, it 
 is a rather low value. For copper the average of 25 experiments 
 gave 0'409 thermal conductivity. The ratio of the two conductivities 
 has usually been found to be about 1 to 8 ; here it is 2 to 9. It is 
 of course well known that impure copper is a very bad conductor of 
 heat, and the experimental plate may have been a bad one. 
 
 According to Miss Bryant's summary, the heat radiated from the 
 cast-iron hemisphere to the boiler plate is proportional to the square 
 of the difference of temperature between the two, 
 
118 HEAT TRANSMISSION 
 
 in which H is expressed in evaporative units per square foot per hour. 
 The values of k are as follows : 
 
 Copper Plate 
 
 I. Experiments. Underside oxidised . . . fr = 0-000,007,65 
 I. slightly smoked . . k = 0-000,011,76 
 
 I. smoked . . . k = 0-000,011,52 
 
 Mild Steel Plate 
 
 III. Experiments. Underside clean . . . . k - 0-000,006,7 
 
 IV. smoked . . . k = 0-000,010,9 
 II. rusted . . . . k = 0-000,008,8 
 II. rusted and smoked . k = 0-000,013,1 
 
 It will be seen that smoked heating surfaces are much more 
 efficient than clean ones, but contrary to expectations, rusted surfaces 
 are very inefficient even if covered with soot. This matter deserves 
 further consideration. It is also a practical experience that the 
 scraping of heating surfaces whereby the tarry film is removed im- 
 proves a heating surface. 
 
 Convection. Miss Bryan's experiments, and in fact all practical 
 experiments on heat transmission from flames, are mixed up with 
 the question of convection or heat transmission by contact between 
 gases and solids, which differs materially from the question of heat 
 transmission in solids, because gases have very low thermal con- 
 ductivities and also because they can be agitated, unused warm 
 portions replacing those which have been in contact with the heating 
 surface. The desirability of agitating flue gases has always been felt 
 by boiler inventors and has led some of them to design marvellous 
 complications, which look as if they were expected to trap or cheat 
 the gases out of their heat. There have also not been wanting very 
 forcible reminders, such as bulged and cracked plates over fire bridges 
 and other obstruction in furnaces or flues, that heat transmission is 
 intensified by disturbing obstructions, but the first man to suggest this 
 idea to scientists of the day (1875) was Prof. Osb. Eeynolds. Since 
 then a large number of experiments have been made on the effect of 
 velocity of water on the rate of heat transmission, and more recently 
 Mr. P. Jordan (' M. E.' 1909, parts 3 and 4, page 1317) experimented 
 on the velocity influence of air. His paper is a somewhat difficult 
 one to study, on account of absence of actual measurements ; his 
 results have therefore had to be resummarised as follows : 
 
 Five series of experiments were carried out : (E) on a copper pipe 
 of -J-inch bore, (F) on l^-inch bore, (D) on 2-inch bore, (C and B) on 
 one or the other of these pipes with a central core, leaving an angular 
 space. Let H be the heat (B.T.U.) transmitted per square foot per 
 second from air of the temperature Ta to the copper tube whose 
 surface temperature is Tc. Let V be the velocity of the air in feet 
 per second = Q x 13-141 . Ta:a . 491, where Q is the weight in Ibs. 
 per second of the air passing through the tube section a, and where 
 Ta is the absolute temperature of the air then 
 
 H - (Ta - Tc)(X + G!?) or H ^ (Ta - Tc) (K 2 + C 2 V). 
 
 \ a/ 
 
HEAT TRANSMISSION 119 
 
 Table of Values of Constants Deduced from Experiments. 
 
 Experiment 
 
 Diameter Inch 
 
 Ki 
 
 Cj 
 
 K 2 
 
 C, 
 
 E 
 F 
 D 
 C 
 B 
 
 1 
 
 Annular 
 Annular 
 
 0-001,43 
 0-001,76 
 0-001,20 
 0-001,62 
 0-002,14 
 
 0-000,80 
 0-000,70 
 0-000,70 
 0-000,71 
 0-000,67 
 
 0-002,36 
 0-001,34 
 0-001,15 
 0-001,12 
 0-001,58 
 
 0-000,036 
 0-000,031 
 0-000,032 
 0-000,036 
 0-000,037 
 
 Mean of above 
 
 0-001,65 
 
 0-000,72 
 
 0-001,53 
 
 0-000,034 
 
 H can be converted into B.T.U. per square foot per hour by multi- 
 plying both K and C by 3,600 seconds, but if and V are expressed 
 
 respectively in pounds weight or feet per hour the G values remain as 
 they are. In ordinary boiler practice V is about 10 ft. per second, so 
 that H = (Ta - Tc) 0-002 B.T.U. per second. If it should be desired 
 to reduce the heating surface to one-half by increasing the coefficient 
 from 002 to 0'004, this would have to be done by increasing the 
 velocity of the gases so that V x 0-000,039 is about 0'002,5, which 
 means that an air velocity of 70 ft. per second or 45 miles an hour 
 must be reached instead of 10 ft. per second. Leaving the furnace 
 diameter unchanged, the tubes which are usually 3 inches bore and 
 11 ft. long would have to be altered to 1| inch tubes 11 ft. long, or 
 if the number of tubes be increased by 30/ with diameters reduced 
 to 1 inch, the lengths could be reduced to 7f feet. The very important 
 fact must not be overlooked that the air friction increases as the 
 square of the velocity, and that an increase from 10 to 70 ft. per 
 second means that the resistance is fifty-folded. Even this resistance 
 is no very serious matter in comparison with the resistance through 
 the fuel, but ordinary chimney draft would now be out of the question, 
 and forced draft would have to be resorted to. 
 
 Another matter which must not be overlooked is that an J inch 
 coating of soot, which would reduce the sectional area of a 3 inch 
 tube by 16/ , would in 1-inch tube cause a reduction of 44/ o , and 
 the respective increases of friction would be 42 and 215%, which 
 would almost certainly mean that small tubes wou!d have to be 
 cleaned constantly as is done with economiser tubes of land boilers. 
 
 The Heat Transmission from the tube surface to the water is also 
 affected by velocity say 
 
 = (Te - Tw) (0-05 + 0-003 3\ 
 
 but as the heat transmission for stationary water is very much better 
 than that of air even when moving rapidly, practically no improvement 
 could be attained by increasing the water velocity in ordinary boilers. 
 In water-tube boilers rapid circulation is of importance because the 
 steam bubbles have to be carried away. 
 
 Thermal Conductivities. The law which regulates the flow of heat 
 through plates is a very simple one. Let ^ and t 2 be the temperatures 
 inside of a plate, measured at two points which are / inches apart, 
 
 then -* j * is the temperature gradient, and if C is the thermal con- 
 
120 
 
 HEAT TRANSMISSION 
 
 ductivity of the material of the plate, the amount of heat which passes 
 across an area A of the plate in one hour is H = C . A . 2 "7 1 . The 
 table on this page gives the values of C for various substances. 
 Thermal Conductivity of Solids =G. 
 
 Materials 
 
 G.C.S. Scale 
 
 Fahrenheit Scales 
 
 Observers 
 
 Thermal Units 
 
 Evaporative Units 
 
 Steel (hard) . 
 
 062 
 
 180 
 
 186 
 
 Kohlrausch 
 
 ' Steel (soft) . 
 
 111 
 
 321 
 
 333 
 
 M 
 
 Iron at 32 F. . 
 
 207 to -154 
 
 603 to 449 
 
 621 to -462 
 
 Forbes 
 
 at 212 F. . 
 
 157 to -129 
 
 456 to 375 
 
 472 to -387 
 
 H 
 
 at 527 F. . 
 
 124 to -112 
 
 361 to 297 
 
 372 to -306 
 
 M 
 
 > 
 
 164 
 
 477 
 
 492 
 
 Neumann 
 
 
 
 199(1 --00290 
 
 610(1- -0015 O 
 
 6(1- -001 5 
 
 Angstrom 
 
 Copper . 
 
 1'027(1--0021 
 
 8140(1 --00115 
 
 3-08(l--0015 I) 
 
 M 
 
 i> 
 
 1-108 
 
 3220 
 
 3-024 
 
 Neumann 
 
 Brass 
 
 302 
 
 878 
 
 906 
 
 
 B 
 
 150 
 
 434 
 
 450 
 
 Weber 
 
 Zinc 
 
 307 
 
 892 
 
 921 
 
 Neumann 
 
 German silver 
 
 109 
 
 317 
 
 327 
 
 
 Slate, along cleavage 
 across cleavage 
 
 0055 to -0065 
 00315 to -0036 
 
 160 to 190 
 92 to 105 
 
 0165 to -0195 
 0095 to -0108 
 
 H 
 H 
 
 i 
 
 00081 
 
 23-5 
 
 00243 
 
 Forbes 
 
 Clay, sun-dried . 
 
 00223 
 
 6-6 
 
 00669 
 
 Neumann 
 
 Chalk . 
 
 0020 to -0033 
 
 5-8 to 9-6 
 
 006 to -010 
 
 H 
 
 Glass . 
 
 00143 to -00179 
 
 4-14 to 5-18 
 
 00429 to -00537 
 
 Meyer 
 
 Fire-Brick . . ' -00174 
 
 5-1 
 
 00522 
 
 Neumann 
 
 Plaster of Paris, wet 
 
 00164 
 
 4-8 
 
 00492 
 
 M 
 
 Coal . 
 
 00057 to -00113 
 
 1-65 to 3-3 
 
 0017 to -0034 
 
 It 
 
 Pumice stone 
 
 00055 
 
 1-60 
 
 00165 
 
 II 
 
 Sand (quartz) 
 
 00013 
 
 376 
 
 00039 
 
 Forbes 
 
 Various woods 
 
 00026 to -00359 
 
 76 to 1-71 
 
 00078 to -00177 
 
 Peclet 
 
 Caoutchouc . 
 
 00041 
 
 1-19 
 
 00123 
 
 H 
 
 vulcanised 
 
 000089 
 
 258 
 
 000267 
 
 Forbes 
 
 Guttapercha 
 
 00048 
 
 1-40 
 
 00144 
 
 Peclet 
 
 Powdered charcoal 
 
 00022 
 
 64 
 
 00066 
 
 it 
 
 coke 
 
 00044 
 
 1-28 
 
 00132 
 
 t| 
 
 Charred wood 
 
 000122 
 
 35 
 
 000366 
 
 if 
 
 Grey paper 
 
 000094 
 
 273 
 
 000282 
 
 
 Pasteboard 
 
 000453 
 
 1-33 
 
 00186 
 
 Forbes 
 
 Paraffin 
 
 00014 
 
 41 
 
 00042 
 
 H 
 
 Flannel 
 
 0000335 
 
 097 
 
 0001 
 
 
 Water . 
 
 00136 
 
 4-00 
 
 004 
 
 Weber 
 
 In this table the values given in the column headed ' Thermal 
 Units ' are the number of units of heat which one square foot of 
 heating surface 1 in. thick will transmit per hour, if the difference 
 of temperature of the two surfaces of the plate itself is one degree 
 Fahrenheit. The values in the column ' Evaporative Units ' are 
 found from the last by dividing them by 966, which is the number 
 of thermal units required to evaporate one pound of water from and 
 at 212 F. These values can also be obtained direct from the G.C.S. 
 values by multiplying them by 3. 
 
 It should be mentioned that all these experiments have been 
 carried out on rods or rings, and that they are not absolutely reliable, 
 because they are based on an imperfect knowledge of the changes 
 of the specific heat and of the radiating power of the substances. If 
 carried out on a plan similar to the one adopted by A. F. Yarrow for 
 
HEAT TEANSMISSION 121 
 
 showing the curving of heated plates, these difficulties might be 
 overcome, and, what is of almost greater importance, the coefficients 
 of transmission of heat across the fibre of the material could thus 
 be measured. (See below.) 
 
 Of more importance than the theories as to how the heat trans- 
 mission takes place is the question of how much heat can be trans- 
 mitted. This very soon resolves itself into the oft-debated subject as 
 to the relative merits of the heating surfaces of the furnaces and of 
 the tubes. Unfortunately few experiments have been carried out, 
 and those few are very incomplete. 
 
 De Pambour was the first to raise the question (' Comp. Rend.,' 
 1840, vol. x. pp. 32, 111, 480), and to make comparisons, but these are 
 valueless. 
 
 C. W. Williams (' Engineer/ 1858, vol. v. pp. 223, 243, and ' N.A.,' 
 1862, vol. iii. pp. 122) made experiments on the heat transmission of 
 tubes. 
 
 J. Graham (' Manch. L. Ph.,' 1860, vol. xv. p. 8) experimented on 
 the heat transmission of flat surfaces. 
 
 M. Geoffroy (' Couche,' 1877, vol. iii. p. 28) made experiments on a 
 locomotive boiler whose length was subdivided. 
 
 P. Havrez (' An. Genie,' 1874, 2nd ser. vol. iii. p. 520) and J. A. 
 Lougridge (' C. E.,' 1878, vol. Iii. p. 101) give analyses of these experi- 
 ments. J. Durston, ' N. A.,' 1893, vol. xxxiv. p. 130. 
 
 Eeference is also repeatedly made to M. Petit's experiments, but 
 details are wanting. They seem to have consisted of two series : in 
 the one lot coke was burnt, and in the other briquettes ; and the 
 draught was f in. in the one case and 4 ins. in the other. Compare 
 P. Havrez (see above), p. 550, and ' Chron. Ind.,' 1873, vol. ii. p. 425. 
 
 C. W. Williams ('Engineer,' 1858, vol. v. p. 206) also mentions 
 experiments on a subdivided boiler carried out by Messrs. Wood and 
 Dewrance, but all details are wanting. 
 
 The experiments detailed by A. F. Yarrow (' N. A.,' 1891, vol. xxxii. 
 p. 108) can be used for determining the amount of heat transmitted 
 through a plate. He measured the curvature of a tube plate which 
 was covered with water and heated over a smith's fire. Its acquired 
 radius was 550 ins., i.e. one of its surfaces had expanded ^ J-^ of its 
 length more than the other side (assuming the plate to have been 1 in. 
 thick). But this can only have been brought about by the fire side of 
 the plate being 330 F. hotter than the other, and as experiments made 
 on the flow of heat in iron bars (see table, p. 120) show that this 
 difference of heat per inch of distance can only exist if sufficient heat 
 is being transmitted to evaporate 142 Ibs. from and at 212 F., this 
 must have been the evaporation under these conditions. 
 
 A. F. Yarrow also made similar comparative experiments on iron 
 and copper plates placed over gas jets, and found that 57 Ibs. per square 
 foot were evaporated over the iron plates, and only 32 Ibs. over the 
 copper plates, which is in accordance with other experiments. (See 
 pp. 118 and 126.) 
 
 Mean Temperatures of Heating Surfaces. Another set of interesting 
 experiments were carried out by J. Hirsh (' Soc. d'Enc.,' 1890, vol. v. 
 p. 302), and are mentioned in the second part of his paper. He con- 
 structed a small kettle about JO ins. in diameter, which had an iron 
 
122 
 
 HEAT TRANSMISSION 
 
 bottom about f in. thick. Arrangements were made for keeping the 
 water level at a constant height, while a strong gas and air blast was 
 directed against the bottom, of which a small area of 4 ins. in diameter 
 was exposed. Twenty-four holes were drilled into the bottom of this 
 plate | in. in diameter and J in. deep, and these were filled with lead 
 and tin alloys. In all 38 experiments were carried out, of which the 
 results of a few are given in the following table. 
 
 Conditions 
 
 Water Evaporated from 
 and at 212 ' P. 
 per Sq. Foot per Hour 
 
 Melting Temperature of Alloys 
 
 Above 
 
 Near 
 
 Below 
 
 Lbs. 
 
 P. 
 
 P. 
 
 c F 
 
 Distilled water . \ 
 
 26-8 
 35-6 
 64-5 
 82-5 
 93-5 
 
 428 
 > 
 
 335 
 
 369 
 
 428 
 
 482 
 
 Water which contained \/o 
 starch . { 
 
 35-8 
 59-2 
 77-0 
 
 369 
 
 428 
 
 428 
 
 428 
 
 482 
 
 Distilled water. ^ in. scale f 
 on plate 1 
 
 33-8 
 46-1 
 
 369 
 
 428 
 
 482 
 
 Distilled water. f in. / 
 scale on plate 
 
 34-6 
 53-2 
 
 428 
 
 842 
 
 482 
 
 Distilled water. Plate 
 greased with mineral oil 
 
 33-8 
 34-3 
 47-1 
 62-6 
 63-2 
 
 482 
 
 
 428 
 428 
 428 
 
 635 
 n 
 
 Sir John Durston (' N. A.,' 1893, vol. xxxiv. p. 133) has carried 
 out similar experiments in open and closed vessels. See following 
 tables : 
 
 Conditions 
 
 Temperatures 
 
 Flame 
 
 Plate on 
 Fire side 
 
 Water 
 
 Dish | in. thick 
 
 F. 
 
 1500 
 1500 
 2200 
 2300 
 2100 
 2500 
 2500 
 
 1500 
 2000 
 2000 
 2000 
 2000 
 
 F. 
 
 240 
 330 
 280 
 310 
 330 
 300 
 550 + 
 
 430 
 430 
 510 
 550 
 617 
 
 F. 
 
 212 
 212 
 212 
 212 
 212 
 212 
 212 
 
 363 
 344-5 
 358 
 351 
 
 80 
 
 Do. Grease ^ in. do. 
 Fresh water. Forge fire 
 Do. and 5 per cent, mineral oil. Forge fire 
 Do. and 2| per cent, paraffin. Forge fire . 
 Do. and 2| per cent, methylated spirits. Forge fire . 
 Do. Greasy deposit ~ in. thick. Forge fire 
 Dish f in. thick 
 
 Do. Forge fire 
 Do. Greasy deposit ^ in. Forge fire 
 Do. Dry greasy deposit ~ in. Forge fire . 
 Do. do. do. 
 
HEAT TRANSMISSION 
 
 123 
 
 In the above experiments the fusible alloys were soldered to the 
 fire sides of the plates ; in the following experiments they were round 
 or cubic plugs driven or placed in cavities in the plates. On account 
 of the insufficient contact the recorded temperatures are probably too 
 low. See Miss Bryant's paper (' C. B.,' 1897, vol. cxxxii. p. 274) for 
 remarks on the reliability of measuring temperatures by means of 
 alloys. It is also well known that fusible plugs in boilers are not as 
 reliable as they should be. 
 
 Conditions 
 
 Temperatures 
 
 Flame 
 
 Plate on 
 Fire side 
 
 Plate Centre 
 
 Water 
 
 Dish with tubes. Fresh water . 
 Boiler tube plate 
 
 2000 
 3100 
 2750 
 2500 
 
 3100 
 3200 
 
 F. 
 
 690 f 
 750 + 
 
 750-1060 
 1060 
 
 F. 
 290-336 
 540 
 
 680-750 
 
 F. 
 212 
 366 
 363 
 362 
 
 360 
 363 
 
 Do. 
 
 Do. Fresh water and 0'07 per cent, 
 mineral oil 
 Do. Fresh water and further 0'07 per 
 cent, mineral oil .... 
 
 In order to compare these values with the estimated transmis- 
 sion in A. F. Yarrow's experiments, the excess temperatures above 212 C 
 must be divided by f , that being the ratio of the thicknesses of plates, 
 and it will then be seen that in this case the heat transmitted is 
 less, but grave doubts are entertained whether the indications of 
 the alloys can be relied upon. Their outer surface is not iron, and 
 they are not soldered to the bottoms of the holes, as they should 
 be, and according to some supplementary experiments in which two 
 thicknesses of plate were bolted together, the resistance to the passage 
 of heat across the boundary of the two metals will have been very 
 great, and the indicated temperatures must therefore be looked upon 
 as excessive. 
 
 This is particularly the case where the plate has been covered with 
 scale, and it is of interest to note that when this is \ in. thick the tem- 
 perature of the fire side of the iron plate has to be increased an extra 
 460 when evaporating 55 Ibs. of water per hour. According to this 
 experiment, scale offers about five times as much resistance to the pas- 
 sage of heat as iron does, whereas laboratory experiments show the 
 ratio between iron and plaster of Paris to be as 1 to 100. This may be 
 due to the thermal conductivity of iron having been measured along the 
 fibre, while in these experiments the heat travelled across the plate 
 and across the various layers of fine slag. Then, too, the boiler scale 
 is in a saturated condition. 
 
 A very important point to be noted is, that even a f -in. plate can 
 be heated to above the melting temperature of lead, if coated with a 
 little scale on the water side, provided the fire is so hot that 55 Ibs. of 
 water are evaporated per square foot per hour, and it is therefore not 
 unreasonable to suppose that most of the late troubles with the tube 
 plates of Navy boilers are due to over-heating, particularly when it is 
 
124 HEAT TRANSMISSION 
 
 remembered that it is probably not water, but moist steam which is in 
 contact with these plates. 
 
 The last set of experiments also show that an injurious effect is 
 obtained by allowing grease to settle on heating surfaces. 
 
 Somewhat similar experiments have recently been made by the late 
 Dr. Kirk (' Enging.,' 1892, vol. liv. p. 333). As in the above case, 
 plugs of alloys were fitted into the bottom of a plate for determining 
 its temperature. It was originally 2| ins. thick, and was gradually 
 reduced to -J^- in. As no measurements were taken of the water 
 evaporated, the results are of less value than the above. 
 
 Wye Williams (' N. A.,' 1894, vol. xxxv. p. 284) fitted thousands 
 of studs into some furnace plates in order to increase the heating sur- 
 face. They projected 3 ins. on both sides, but on the fire side they burnt 
 away to 2^ ins. As oxidation (blue) commences at about 500 F., the 
 ends of these studs were doubtless heated to 1,000 F. or more and 
 must have been effective as heat transmitters. Some patent boilers 
 consist of tubes partly filled with water, sealed at both ends, and 
 fitted like these studs, half in the fire, half in the water ; the heat 
 transmission is a more rapid one than by conductivity, but these 
 boilers are not satisfactory. 
 
 Transmission of Heat. The table on p. 125 contains the results 
 of some interesting experiments, in which one side of the plate 
 or tube was exposed to hot steam and the other side to the atmo- 
 sphere. 
 
 Other experiments will be found in the following publications : 
 
 M. Burnat, ' C. E.,' 1874, vol. xli. Straw and similar coverings. 
 
 W. J. Bird, ' N. Engl. T.,' 1879, vol. xxix. p. 7 ; 1881, vol. xxxi 
 p. 77 ; 1882, vol. xxxii. p. 35 ; 1885, vol. xxxv. p. 159 ; 1886, vol. xxxvii 
 p. 13. Steam losses in pipes exposed to atmospheric influences. 
 
 J. J. Coleman, ' Phil. Soc.,' Glasgow, 1883, p. 73. 
 
 H. Collins, ' Brit. Assoc.,' 1891, p. 780. 
 
 J. M. Ordway (' Am. M. E.,' 1883, vol. v. p. 95, 1884, vol. vi.) gives 
 relative heat transmission through 1 inch of 50 substances, but, as he 
 changes his standard of comparison, it is difficult to analyse his results. 
 
 ' C. E./ 1891, vol. cviii. states that the loss of heat through covered 
 steam pipes through which super-heated steam was passing is at the 
 rate of 1 F. per 3J square ft. of surface. 
 
 Comparing these values with those obtained for the transmission of 
 heat through tube surfaces, it will be noticed that the external surface 
 of a boiler would seem to be relatively about ten times more efficient 
 as a heat dissipater than are the very much thinner tubes as heat 
 absorbers. This is of importance, because it may happen that a 
 boiler is made so long that the last foot of tube length supplies less 
 heat than is given away by the last foot of shell. Generally the 
 entire circumference of the boiler shell is about one-fourth to one- 
 sixth of the sum of the circumferences of the boiler tubes, and if this 
 boiler is unlagged there would be no advantage in allowing the gases 
 to escape at any temperature less than about 400 F. above that of 
 the water in the boiler, or say 750 F. If properly lagged the gases 
 may be cooled much lower. 
 
 In the above-mentioned experiments heat was supplied to the 
 pipes or plates by steam, and the cooling took place in air f With 
 
Coefficients of Heat Transmission 
 
 125 
 
 Material and Conditions 
 
 Difference of 
 Temperature 
 
 Steam Con- 
 densed per 
 Square Foot 
 per Hour 
 
 B.T.U. 
 
 transmitted 
 per Hour 
 per Square Foot 
 per Degree of 
 Difference 
 
 Observer 
 
 
 P. 
 
 Lbs. 
 
 
 
 Locomotive boiler . 
 
 213 
 
 1-611 
 
 7-5 
 
 Isherwood ' 
 
 ^-in. iron plate 
 
 
 ... 
 
 2-93 
 
 Franklin 
 
 covered with 
 
 
 
 
 Inst.' 2 
 
 cow-hair in. . 
 
 ... 
 
 
 
 1-05 
 
 >i ii 
 
 Do. do. ^ in. . 
 
 ... 
 
 
 
 57 
 
 ii 
 
 1 in. . 
 
 ... 
 
 ... 
 
 41 
 
 ii 
 
 1 in. . 
 
 ... 
 
 ... 
 
 31 
 
 _ 
 
 H in. . . 
 
 ... 
 
 ... 
 
 -27 
 
 jj 
 
 H- in. . 
 
 ... 
 
 
 25 
 
 jt 
 
 Cast-iron pipe 
 
 
 71 
 
 4-75 
 
 Meunier * 
 
 Wrought-iron pipe 
 
 ... 
 
 80 
 
 5-32 
 
 ii 
 
 Copper pipe .... 
 
 ... 
 
 575 
 
 3-83 
 
 ii 
 
 Cast-iron pipe 
 
 226 
 
 1-04 
 
 6-27 
 
 Meunier 4 
 
 Wrought-iron pipe 
 
 222 
 
 1-04 
 
 6-42 
 
 ii 
 
 Copper pipe .... 
 
 227 
 
 828 
 
 4-96 
 
 *i 
 
 Lagged cast-iron pipe . 
 
 234 
 
 465 
 
 2-67 
 
 n 
 
 wrought-iron pipe 
 
 217 
 
 405 
 
 2-58 
 
 it 
 
 copper pipe 
 
 229 
 
 541 
 
 3-20 
 
 ii 
 
 Bibbed cast-iron pipe 
 
 203 
 
 1-84 
 
 8-75 
 
 E. Deny 5 
 
 >t ii 
 
 210 
 
 
 1-04 
 
 H. Fischer 
 
 Cast-iron pipe 
 
 360 
 
 l-i69 
 
 3-13 
 
 N. N.' 
 
 ,,'.... 
 
 307 
 
 0-937 
 
 2-94 
 
 ii 
 
 Do. and 2 in. papier mache 
 
 
 
 
 
 composition 
 
 360 
 
 0-294 
 
 0-79 
 
 > 
 
 and 2| in. hair-felt . 
 
 360 
 
 0-216 
 
 0-58 
 
 H 
 
 and 2 in. Kieselguhr, 10% 
 
 
 
 
 
 binding material 
 
 360 
 
 0-226 
 
 0-61 
 
 It 
 
 II II II l 
 
 307 
 
 0-166 
 
 0-52 
 
 
 and 2| in. hair-felt 
 
 360 
 
 0-188 
 
 0-50 
 
 M 
 
 II M > II 
 
 307 
 
 0-125 
 
 0-39 
 
 II 
 
 f in. cork strips 2 layers 
 
 
 
 
 
 canvas . 
 
 360 
 
 0-198 
 
 0-53 
 
 
 
 n 
 
 307 
 
 0-152 
 
 0-48 
 
 II 
 
 Cast-iron pipe, Strong S.W. 
 
 
 
 
 
 wind 
 
 250 
 
 1-19 
 
 4-60 
 
 D. K. Clark 8 
 
 Do. East wind 
 
 247 
 
 0-732 
 
 2-85 
 
 ii 
 
 average .... 
 
 250 
 
 1-00 
 
 3-86 
 
 ii 
 
 and 1 in. Haake compo- 
 
 
 
 
 
 sition 
 
 H 
 
 0-230 
 
 0-89 
 
 ti 
 
 1 in. Haake composition 
 
 >l 
 
 0-267 
 
 1-03 
 
 ii 
 
 1 in. Eagle composition 
 
 l 
 
 0288 
 
 1-11 
 
 
 
 1 in. Leroy composition 
 
 
 0-310 
 
 1-20 
 
 ti 
 
 1 in. Keenan composition 
 
 H 
 
 0-317 
 
 1-22 
 
 ii 
 
 1 in. Keid McFarlane 
 
 
 
 
 
 composition 
 
 II 
 
 0-340 
 
 1-31 
 
 ii 
 
 1 in. Mclvor composition 
 
 II 
 
 0-367 
 
 1-42 
 
 ii 
 
 1 in. Sutcliffe compo- 
 
 
 
 
 
 sition 
 
 II 
 
 0-374 
 
 1-45 
 
 n 
 
 Pipe. Bare .... 
 
 350 
 
 1-516 
 
 4-2 
 
 Capper 9 
 
 1-6 in. asbestos compo- 
 
 
 
 
 
 sition 
 
 ii 
 
 420 
 
 1-16 
 
 it 
 
 1-25 in. Leroy compo- 
 sition 
 
 i 
 
 399 
 
 MO 
 
 n 
 
 1-4 in. magnesia . 
 
 ii 
 
 208 
 
 0-57 
 
 ii 
 
 1-6 in. mica flakes 
 
 ! 
 
 177 
 
 0-49 
 
 11 
 
126 HEAT TRANSMISSION 
 
 the exception of Miss Bryant's experiments, no direct measurements 
 have yet been carried out to ascertain whether the chief resistance is 
 encountered on the hot or cold side. This could best be done by 
 repeating A. F. Yarrow's experiments on the curvature of heated plates 
 and estimating the mean temperature of the plate by means of its 
 lineal expansion. Some light might be thrown on the subject by 
 comparing the previous experiments with the following (W. S. Hutton, 
 1887, p. 253). The units of heat which a J-in. plate will transmit per 
 square foot per hour, if supplied with an unlimited amount of water 
 on one side and steam on the other, are there given : 
 
 Cast iron . 
 Wrought iron 
 Steel . 
 
 White metal 
 Brass Plates 
 Gun metal 
 
 265 units 
 252 
 246 
 207 
 175 
 168 , 
 
 Phosphor bronze 162 units 
 Copper . . 155 
 Tin plate . 142 
 Glass plate . 259 
 Tiles . 246 
 
 An interesting feature of W. S. Button's figures is that they show 
 that the transmission of heat is less dependent on the conductivity of 
 the material than on its other properties. Thus tiles and glass platea 
 are nearly as good as cast iron, while copper and tin plates are the 
 least efficient. 
 
 Smoke-box Radiation. Marine boiler smoke-boxes are usually 
 fitted with baffle plates, one inside and one out. The only advantage 
 they offer is cheapness combined with a reduction of radiated heat ; 
 but heat lost by convection must be greater than with a plain plate, 
 for a natural and very powerful current of air or hot gases is induced 
 between the plates. To reduce the loss of heat from smoke-boxes the 
 space between the baffle plates should be filled with non-conducting 
 material, or if this is too heavy or too costly, the edges of the baffle 
 plates should be flanged so as to press against the smoke-box plates. 
 Only one baffle plate will then be needed an inside one. If two are 
 fitted, they should both be flanged and both fitted on the hottest side, 
 so as to protect the casing and door from heat and thus prevent its 
 warping. With water-tube boilers loss of heat, warping of the casing, 
 and then leakage of air make themselves seriously felt. 
 
 From the foregoing ib is evident that our knowledge of the trans- 
 mission of heat is very limited, and possibly incorrect ; nevertheless 
 the collection of previous experiments into one chapter has the advan- 
 tage of showing in what direction further information should be sought, 
 and the following experiments readily suggest themselves : 
 
 Notes to Table on p. 125 
 
 1 Isherwood, Experimental Researches, vol. ii, 
 
 2 Franklin Inst., 1878, iii. vol. Ixxv. p. 153. 
 9 W. Meunier, Rev. Ind., 1884. 
 
 4 Ibid., Soc. I. Mul., 1879, p. 730. 
 
 * E. Deny, ibid. 1883, vol. liii. p. 575, and 1834, vol. Iv. p. 15. 
 
 * Dingler's 7., 1878, vol. ccxxviii. p. 1. 
 
 * N. N., C. E., 1895, vol. cxxi. p. 300. 
 
 ? D. K. Clark, Engr., 1884, vol. Ivii. p. 65. 
 9 Prof. Capper, Report, 8 September, 1898. 
 
HEAT TRANSMISSION 127 
 
 1st. Experiments on the flexure of plates which are being heated 
 on one side either by water, air, or radiant heat, and are being cooled 
 on the other side by any of these methods. 
 
 2nd. A repetition of M. Geoffrey's experiments on a subdivided 
 boiler, with accurate measurements of the temperatures of the waste 
 products of combustion at various points, and also analyses of the 
 gases, and calorific determinations of the fuels. 
 
 Temperature of Fire Bars. The parts of the boiler which suffer 
 most from the effects of slowness of transmission of heat are the fire 
 bars. They are exposed to an intense heat at their upper surface, to 
 radiation on part of their side surface, and the only available means of 
 cooling them is by the air which passes over their sides. When the 
 fires are thick, when much air is admitted above the bars, and when 
 the draught is forced, the bars are naturally exposed to the very 
 serious danger of overheating. 
 
 Assuming that the heat received by the upper surface of the bars 
 is at the rate of 50,000 thermal units per hour per square foot, and 
 assuming that this heat is being transmitted to the passing air at the 
 high rate of ten units for every degree of difference of temperature, 
 then if a is the width of the air space, h the depth of the fire bar, 
 b its breadth, and t its excess temperature over that of air, we have 
 
 50000. (6 + a) = 10. t. (b + 2fc), 
 
 5000 . (b + a) 
 (b + 2/i) 
 
 In order to keep the temperature t below 1,000 F. it would be 
 necessary to make h = 2 . b + 2^ a, which is perhaps fairly near the 
 truth ; but this leaves out of account the quantity of air, which is 
 certainly an important factor. With ordinary draught the air supply 
 is at the rate of about 400 Ibs. per hour per square foot of grate, or 
 about 7 Ibs. per minute, which is certainly not a large quantity. Com- 
 paring the temperatures , and 2 2 in two different sets of fire bars in 
 which the various dimensions are a, and a 2 , b l and 6 2 , h { and /i 2 , and 
 the air supply Q! and Q 2 , we have 
 
 ti b { + a,. (6 2 _+ 2/t 2 ) . Q 2 
 
 T z b 2 + a 2 . (&, + 2/i,) . Q,* 
 
 This would show that the more work a grate has got to do the 
 deeper ought the bars to be made, and the greater should be their 
 number. But as it is at first not so much the danger of burning the 
 bars as of their being bent which has to be guarded against (seep. 10), 
 making them very thin without reducing their length would increase 
 this trouble. Until their temperatures have been taken under varying 
 conditions, which is not difficult, it is idle to speculate any further on 
 their behaviour, and at any rate the above formula should be looked 
 upon more as an indication as to how much information is yet 
 wanted than as a practical guide for new departures. 
 
128 
 
 CHAPTER VI 
 8TEENGTH, OF MATERIALS 
 
 IN this country, especially during the last twenty years, steel has 
 almost entirely supplanted wrought iron for ship and boiler construc- 
 tion. No further excuse is therefore needed for discussing its peculiari- 
 ties more exhaustively than those of the older metal. Besides, the two 
 materials are so intimately related, that the large amount of research 
 expended on one must assist in explaining the other. 
 
 Wrought Iron. It is usually stated that steel is a homogeneous 
 material, while wrought iron is a conglomerate of crystals, granules, 
 or fibres cemented together by films of slag. Layers and threads of 
 slag undoubtedly exist in iron, but it is unreasonable to suppose that 
 they are as uniformly distributed as the above theory would make it 
 appear. The manner of the production of wrought iron in the puddling 
 furnace seems to be, that drops of molten pig are slowly converted 
 into plastic wrought iron, their centres always retaining a slight 
 excess of carbon and other impurities, while the flame and slag acting 
 on their outer surfaces are converting them into almost pure iron, 
 possessing, amongst other qualities, that of welding with the greatest 
 ease. That these numerous drops of white-hot metal, which may now 
 be called granules, or even lumps, should stick together is but natural, 
 and the trouble to be expected and it does exist is that numerous 
 cavities filled with slag will come into existence. 
 
 When drawn out into bars or plates wrought iron would therefore 
 consist of numerous fibres whose individual outer surfaces are very 
 pure and soft, and whose cores contain the small percentage of carbon 
 which had been allowed to remain. Professor Wedding has shown 
 how by the microscope we can distinguish between the hard and soft 
 parts, for he found that the greater the percentage of carbon, the darker 
 the colour if the iron or steel is raised to a blue heat ; and by carefully 
 polishing and etching samples of iron, and then heating them suffi- 
 ciently to make them appear of a uniform dark straw colour, the micro- 
 scope will show that this uniformity is an illusion, and that the metal 
 really consists of innumerable cells of soft iron surrounding hard cores. 
 
 Influence of Producing Temperatures. Had the temperature of 
 the puddling furnace been as great as that in any of the steel furnaces, 
 each granule would have been melted, and the product would have 
 been mild steel of the same tenacity as the puddled iron, but it is well 
 known that the first of these metals requires quite twice as much 
 horse-power for machining it as iron of the same tenacity, and there 
 
STRENGTH OF MATERIALS 129 
 
 does not seem to be a better explanation than that this is due to the 
 somewhat higher temperature at which it has been produced. 
 
 Steels from various makers, but of the same tenacity, are said to 
 show great differences as regards the power required to chip them. 
 An explanation for this might be sought for in variations in the casting 
 temperatures, and these again would depend on the firebrick lining 
 used. 
 
 J. W. Cabat (' American Inst. Mining Engs.,' vol. xiv. p. 85) deals 
 with the influence of casting temperatures, and remarks that cold- 
 blown charges of rail steel work better than hot-blown ones, and that 
 open-hearth spring steel is similarly affected by the furnace tem- 
 perature. 
 
 The Basic Bessemer Steel Process, using Phosphoric Pig Iron, and 
 usually called the Thomas Gilchrist Process. The pig is run into the 
 converter in a molten state, and subjected from below to the action of 
 a strong blast, which first removes the carbon and silicon, and then 
 attacks the phosphorus. It was at one time believed that the develop- 
 ment of heat in all the Bessemer processes was due to the burning of 
 the carbon contained in the pig, but this has been disproved. Dr. F. 
 C. G. Muller (' Deut. Ing.,' 1878, vol. vi. p. 387) mentions that silicon 
 burns away first, and that for every per cent, consumed the tempera- 
 ture of the molten metal is raised 540 F. ; that the carbon is not con- 
 sumed until a temperature of 2,550 F. has been reached, and that its 
 burning does not raise it. Phosphorus, like silicon, adds much heat 
 to the bath, but will not burn until practically all the silicon and 
 sarbon have been consumed. It has also been found that the 
 phosphorus cannot be consumed unless lime is present in the con- 
 verter, and as this would attack and melt the ganister lining, which is 
 nearly pure silicic acid, it is necessary to give the converters a basic 
 lining (dolomite), from which the steel made by this process derives 
 its name of ' basic steel.' Only very little silicon may be tolerated in 
 the pig intended for this process, as it attacks the dolomite, and in 
 order to obtain a sufficiently high temperature, which cannot be done 
 by burning carbon, phosphorus must oe present in large proportions, 
 viz. from 2 to 3%. In some pigs phosphorus is not sufficiently plenti- 
 ful, and then, in order to obtain the right heat, it has to be melted in 
 Siemens-Martin furnaces instead of cupolas. 
 
 During the process of manufacture the blast is kept up until all the 
 phosphorus is consumed, and the metal in the converter is then 
 almost absolutely pure iron. Spiegel and ferro-manganese are now 
 added in the right proportions, and the charge is ready for casting. 
 
 At present the only available means for judging of the purity of the 
 molten steel is to count the number of revolutions of the blowing 
 engines from the time when the carbon lines in the spectrum have dis- 
 appeared, but, in spite of assertions to the contrary, it does not appear 
 that sufficient reliance can be placed on this proceeding, which is as 
 follows : 
 
 The composition of the pig iron is ascertained from samples if 
 bought, or from daily returns if run direct from the blast furnace. The 
 number of revolutions of the blowing engine required for supplying all 
 the air necessary to consume all the carbon and silicon is estimated, 
 and also how many extra revolutions will be required to remove the 
 
130 STKENGTH OF MATERIALS 
 
 phosphorus. The weight of the charge, the temperature and mois- 
 ture of the air, must necessarily affect the result somewhat ; therefore 
 the foreman first notes the number of revolutions up to the point when 
 the spectroscope tells him that all the carbon has been burnt, and com- 
 pares it with the estimated number. The difference, if any, is then 
 applied to the calculated number of extra revolutions required for 
 removing the phosphorus, and it depends upon the correctness of 
 these several determinations whether the metal is pure or not. Even 
 the temperature of the charge influences them, for the colder it is the 
 more difficult is it to judge of the disappearance of the carbon lines ; 
 so that, generally speaking, it is very easy to be mistaken as to the time 
 when the blast should stop. A danger to which the charge is also 
 exposed is that due to the action of the highly phosphoric slag on the 
 added spiegeleisen and ferro-manganese. It has been confidently 
 stated, but not proved, that the affinity of carbon for oxygen, and of 
 phosphorus for iron, is so great that, unless the latter stage of the 
 process is hurried, phosphorus will leave the slag and re-enter the 
 metal. This seems to be the reason why some works put the admix- 
 tures into the ladle and not into the converter. Where this is done 
 the question arises whether the charge can then be thoroughly mixed. 
 If not, this would explain occasional irregularities in the finished 
 product, and these being more apparent in large plates than in bars 
 and wires, may account for the strong dislike entertained towards basic 
 Bessemer plates. 
 
 The Acid Bessemer Process differs from the one just described in so 
 far as the lining of the converter is acid (silicic acid = ganister) and 
 that no lime is added. The slag is generated by the combustion of the 
 silicon (to silicic acid) and the iron (to iron oxide). Not a trace of 
 phosphorus is removed by this process, and therefore the pig iron used 
 must contain less than that to be allowed in the finished product. It 
 must also contain a large percentage (2-3 %) of silicon for the produc- 
 tion of sufficient heat. 
 
 The addition of spiegeleisen and ferro-manganese is effected just 
 before casting, either in the converter or in the ladle. 
 
 The spectroscope enables the operator to judge, with reasonable 
 accuracy, as to the percentage of carbon remaining. He could, there- 
 fore, either interrupt the blowing before all the carbon is burnt, which 
 would save some of the costly admixtures, or he could wait till all the 
 carbon has disappeared, and then reintroduce it with the necessary 
 manganese. The latter of these two methods is the more reliable. 
 An incidental difference between these processes is that in the basic 
 process, during the necessary after-blow for removing the phosphorus, 
 every trace of carbon disappears, while in the acid process this is not 
 the case, so that by adding just sufficient ferro-manganese to remove 
 all redshortness one would obtain a far weaker but also a more ductile 
 material by the basic than by the acid process ; the former is therefore 
 used almost exclusively for producing the steel for soft wire. 
 
 The Open-Hearth Process was made available for producing mild 
 steel only after Dr. Siemens had invented the regenerative chamber, 
 and although the various shapes of the furnaces take the names of 
 their respective designers, his name will always be associated with 
 steel made by this process. 
 
STRENGTH OF MATERIALS 131 
 
 Heat regenerators consist of several vaults filled with loosely packed 
 firebricks. Air is admitted through one of these chambers, and gas 
 through another, and both are ignited in the furnace. The waste 
 products are led to the chimney through the two other chambers, and 
 heat them. The current is then reversed, and the air and the gas pass 
 over the white-hot bricks of the latter chambers, and the waste pro- 
 ducts heat the former. The process is then continually repeated. 
 Not only does this save nearly all the heat, which would have escaped 
 with the hot gases, but the temperature of the furnace can easily be 
 raised so high that even the firebrick lining would melt. 
 
 Within certain limits the temperatures can be regulated by admit- 
 ting more or less excess air, and by altering the frequency of 
 reversing the current. The flame might also be altered from an 
 oxidising to a reducing one, but not without raising the temperature 
 beyond the endurance of any firebrick. The gas used for firing these 
 furnaces is produced at the works either by partly burning and partly 
 distilling coal, in which case it consists of hydrocarbons, carbonic 
 oxide, and nitrogen ; or water gas is used, which contains carbonic 
 oxide, hydrogen, and a smaller percentage of nitrogen. Eecently 
 part of the heat in the waste products has been used to distil the 
 coal. 
 
 The Acid Siemens-Martin Process. Pig iron is placed in the 
 furnace, and when melted, iron ore and about 25 % scrap iron are 
 added, until all the carbon and silicon are consumed, and the ore 
 reduced to iron. Samples are repeatedly taken and tested mechani- 
 cally, to judge of the condition of the bath, and when ready, spiegel- 
 eisen and ferro-manganese are added, and the charge is run. As in 
 the Bessemer process, some of these additions may be saved by 
 stopping the process of reduction at an early stage, and in some 
 works the carbon is successfully reintroduced by adding it as powdered 
 charcoal, or anthracite placed in the ladle or into the trough leading 
 to it from the furnace. 
 
 During the early period of refining the various layers of the bath 
 are of very different composition, as can easily be ascertained by 
 taking a sample from the top or the bottom of the charge ; but a 
 natural mixing takes place, due to chemical action and to an 
 evolution of gases. However, at the final stage, when the bath is 
 nearly but not quite uniform, this action practically ceases. It is 
 revived by the addition of iron ores, or of pig, or in some works by 
 stirring with wooden poles, which evolve large quantities of gas. 
 
 The acid Siemens process does not remove either phosphorus or 
 sulphur, and the pig and scrap used should therefore contain only 
 traces of these impurities. 
 
 The Basic Siemens Process, using Pure Pig, is almost identical 
 with the above, except that, on account of the use of a basic slag, 
 almost every trace of phosphorus disappears. It is also found that 
 both the carbon and manganese are very energetically attacked by 
 the flame, and after the spiegel has been added, it is difficult to hit 
 the right moment for running the charge. This difficulty is aggravated 
 by the fact that the natural lowest limit of mild steel from these 
 furnaces is below 20 tons, whereas with the acid Siemens furnace it 
 is about 24 tons. When trying to make steel of 27 tons, a small 
 
 K2 
 
132 STRENGTH OF MATERIALS 
 
 error in the admixtures, or in the time of casting, will have two to 
 three times as much effect in the one case as in the other. However, 
 with care the very best material, and of the intended hardness, is 
 obtained. 
 
 On account of the costliness of the basic lining this process is 
 hurried as much as possible, and six or even seven charges are some- 
 times got out of a furnace in twenty-four hours. Of course this is 
 only possible if the refining process is curtailed, and with this object 
 in view not more than about 20 to 25 % of pig iron is used, while the 
 rest is scrap. A further gain has been attempted by carrying out 
 part of the process in a Bessemer converter where all the carbon and 
 silicon are removed. The final reduction takes place in the basic 
 Siemens furnace, where the last trace of phosphorus is abstracted. 
 
 'Basic Eefined Steel.' C. E. Stromeyer, ' Eng. Scot.,' 1897, 
 vol. xli. p. 227, deals fully with this and the next material. E. Bert- 
 rand, 'I. and S. I.,' 1897, vol. i. p. 115. 
 
 The Basic Siemens Process, using Phosphoric Pig, is carried out 
 at a few works in this country. It is a tedious one, lasting about 
 fifteen hours per charge ; this is made up of iron ores, lime, and 
 about 75 to 80 % of pig, too poor in phosphorus for the basic 
 converter and too rich for the acid Siemens process. The phosphoric 
 acid which is generated is not volatile, and does not rise to the 
 surface in bubbles like carbonic acid, and therefore cannot assist in 
 mixing the charge, so that the process would be indefinitely prolonged if 
 special means were not adopted, such as the occasional addition of pig 
 and of iron ores, to produce gases. This is necessary up to the last 
 stage, which, as in all other cases, consists in adding spiegeleisen and 
 ferro-manganese. 
 
 The basic slag, which floats on the molten steel, is very thick, 
 generally about 12 to 15 ins., and the furnace gases have little chance 
 of acting on the metal. Few works use this process, and there all 
 attempts to manufacture plates on which the same reliance can be 
 placed as on the acid steel have as yet failed. With care good results 
 could no doubt be obtained, but it seems that the effects of even slight 
 carelessness on the part of the operator lead to bad results, and no 
 bests have yet been devised which will detect them. Herr Knaut 
 (' Stahl und Eisen,' 1900, vol. xx. p. 783) has put about 500 tons 
 of this basic steel into boilers, and after ten years' experience 
 condemns it. 
 
 The Puddling Process has been dying out fast. In it the pig iron 
 is melted in the presence of iron ores and slags by means of flames, 
 which can be changed from oxidising to reducing ones as occasion 
 arises. The temperatures, being very much lower than in all the 
 previous processes, appear to assist at removing a large percentage of 
 phosphorus and sulphur. Much hard labour and considerable skill 
 are required to obtain good results. The final operation consists in 
 extracting the intermixed slag from the iron, which is done under a 
 blooming hammer. 
 
 Crucible Steel, as its name implies, is produced in crucibles. 
 These are filled with carefully weighed quantities of blister steel, 
 pure iron, or scrap steel. It is said to be giving way to Siemens steel 
 even for guns, and as it is a very costly process, and has never been 
 
STRENGTH OF MATERIALS 133 
 
 used for boiler plates, it is unnecessary to enter into details, except 
 to mention that when carrying out experiments on steel alloys it is of 
 importance that the right fire-proof material should be usea. Thus, 
 when wishing to produce practically pure iron, basic crucibles must 
 be employed ; if a good percentage of carbon has to be retained, and 
 for many alloys (manganese, silicon, aluminium), the melting must 
 be done in plumbago, and for some other purposes acid crucibles are 
 best, while for certain compositions the melting has to be carried out 
 in various fire-resisting materials, and the molten metal mixed before 
 casting. 
 
 The following books will be found to contain a very full account 
 of the manufacture and properties of mild steel : Dr. J. Percy, ' Iron 
 and Steel,' London, 1864 ; M. H. Howe, ' The Metallurgy of Steel/ 
 New York, 1890 ; Professor Ledebur, ' Handbuch fur Eisenhutten- 
 kunde,' Leipzig, 1884 ; V. Deshayes, 'Classement et Emploi des Aciers,' 
 Paris, 1880 ; J. S. Jeans, ' Steel,' &c., 1890 ; Prof. A. Martens, ' Mitt. 
 Berlin/ 1890, vol. ii. 
 
 The Influences of Impurities on the mechanical properties of mild 
 steel. It may be remarked that absolutely pure iron or steel has not 
 yet been produced and experimented upon, and the following re- 
 marks, therefore, only apply to the effects of additions made to 
 average qualities. 
 
 Recently the subject has shown itself to be more complicated 
 than was at first assumed, but it is hoped that microscopic researches 
 will elucidate the matter. Thus it is now known that carbon and 
 iron combine in various proportions, forming compounds which are 
 dissolved throughout the mass of steel. These compounds can be 
 distinguished under the microscope and also by attacking the metal 
 with various acids, when the gases given off or the residues enable 
 one to estimate the amount of carbon in its different conditions. 
 These compounds give varying qualities to steel. Phosphorus 
 behaves in the same way, and instead of always producing cold- 
 shortness, it is now believed that only one of its ferric compounds 
 does this, which when treated with certain acids evolves PH 3 . The 
 phosphide of iron, on the other hand, is not dissolved in the mass of 
 metal, but exists in the form of minute crystals, which, being very 
 hard, cause the edges of cutting tools to get blunt. This explains 
 why some steels with much phosphorus are not coldshort. It has 
 not yet been shown how the phosphides can be changed. Probably 
 sulphur has the effect of dissolving the phosphide of iron, and there- 
 fore accentuating coldshortness. It is known that carbon can be 
 affected by various impurities. Silicon, tin, and copper seem to 
 drive it out of the iron. Manganese, chromium, and tungsten seem 
 to assist at dissolving it, the two latter converting it into hardening 
 carbon. For action of acids, see ' I. and S. I./ 1888, p. 369, 1896, vol. i. 
 p. 239, 1897, vol. i. p. 229 ; ' Comp. Bend./ 1897, vol. cxxx. p. 148. 
 
 Hydrogen, even in small quantities, makes hard steels very brittle. 
 It enters them when being pickled and can be driven out by heat. 
 
 Nitrogen increases the tenacity, but it shares with phosphorus the 
 unenviable distinction of making steel unreliable. Neither element 
 seems to affect the ductility as measured by mechanical tests, but 
 when present in excess both elements are responsible for frequent 
 
134 STRENGTH OF MATERIALS 
 
 failures of plates when in use. When the sum of the percentage of 
 phosphorus plus five times the percentage of nitrogen (P + 5N) 
 exceeds 0'08/ then trouble may be expected. 
 
 Nitrogen combines with iron under pressure, about 0'003 / under 
 blast furnace conditions, and about 0'030/ under Bessemer converter 
 conditions. Seeing that fluid Bessemer steel or large quantities of 
 Bessemer scrap may be thrown into Basic Siemens' furnaces which 
 use pure pig (see p. 132), this process may occasionally turn out un- 
 reliable steel. This may account for the relatively numerous steel 
 plate failures in countries where basic steel is generally used. 
 
 Carbon increases the tenacity and tempering qualities (if it does 
 not even create them) ; it reduces the elongation at the rate of about 
 30/ for every l/ o C., and the ductility and weldability and melting 
 temperature. It increases liability to burn. 
 
 Boron increases tenacity, but only after tempering. It creates 
 redshortness, but only at a white heat. 
 
 Silicon increases tenacity, reduces the elongation and melting tem- 
 perature, prevents blowholes, increases red- and coldshortness, but only 
 in presence of carbon. Eeduces weldability, but only above 0'7/ . 
 
 Phosphorus has ascribed to it in company with nitrogen the chief 
 blame for coldshortness and general treacherousness. It also in- 
 creases the liability to get burnt. It reduces the melting temperature. 
 In mild steel it should not exceed 0'07/ ' In small quantities it 
 increases corrosion, in large percentages it prevents it. It gives to 
 fractures of nicked samples a stringy appearance. As it is believed 
 to improve the machining qualities, phosphoric steels are now supplied 
 for stays and other parts which are 'shaped by automatic tools. Up 
 to 6'8/ it does not affect redshortness. 
 
 Arsenic reduces elongation and tempering qualities, increases cold- 
 shortness when above O17/ > but only slightly ; 0'25/ prevents 
 welding. In chemical analysis it has been mistaken for phosphorus. 
 Like phosphorus and carbon, it reduces the melting temperature. 
 
 Bismuth causes red- and coldshortness. 
 
 Sulphur accentuates the bad effect of phosphorus, produces red- 
 shortness and greasiness as regards welding when it exceeds 0*06/ . 
 In mild steel it should not exceed 0'077 D - It facilitates machining 
 but segregates easily. 
 
 Manganese counteracts the hardening effects of carbon, and neu- 
 tralises the redshortness of sulphur up to 0*1 / 0) and of silicon up to 
 0*5/ . In large quantities it is said to give a shaly appearance to 
 fractures of torn or bent samples. 
 
 Nickel reduces tenacity and increases ductility, particularly as 
 regards impact. It neutralises the influence of carbon, and perhaps 
 of phosphorus, and it reduces corrosion. 
 
 Copper prevents blowholes, increases tenacity, reduces elongation, 
 and produces redshortness, but only when above 3/ . Its influence 
 on welding is doubtful ; it reduces corrosion. 
 
 Chromium, like Tungsten, intensifies all the influences of carbon, 
 particularly as regards the tempering qualities. 
 
 Aluminium prevents blowholes, reduces the melting temperature, 
 and hardens cast iron, quiets the molten metal, and accentuates the 
 effects of carbon. 
 
STRENGTH OF MATERIALS 
 
 135 
 
 Tin. Authorities are conflicting. It seems to drive carbon out 
 of cast iron, and 0'35% makes mild steel quite redshort. It enters 
 steel as scrap tinplates. 
 
 Oxygen is not easily determined, and it cannot be said that it 
 exists in iron either as dissolved or segregated oxide. The small 
 traces of hydrogen which are always present in steel should effect 
 a reduction when the steel is in the heating furnace, in the same way 
 that hydrogen in a laboratory furnace is expected to reduce the oxide ; 
 if heated to redness. 
 
 An attempt to summarise these remarks is made in the following 
 table : 
 
 Elements 
 
 
 
 I 
 
 s 
 
 As 
 
 Si 
 
 Sn 
 
 Al 
 
 Mn 
 
 Ni 
 
 Or 
 
 Cn 
 
 N 
 
 H 
 
 B 
 
 Elongation . 
 Resistance to impact 
 
 + 
 
 + 
 
 + 
 o 
 
 
 
 + ? 
 
 ~ 
 
 
 + ? 
 
 + 
 + 
 
 + 
 
 + 
 
 - 
 
 - 
 
 '.'.'. 
 
 + 
 
 
 Pliability cold . 
 dull red 
 white hot 
 ,, tempered 
 
 - 
 
 
 
 
 
 'o 
 
 
 > 
 
 
 
 + 
 + 
 
 + 
 
 + 
 + 
 + 
 
 + 
 + 
 
 + 
 
 -'? 
 
 
 ... 
 
 '.'.'. 
 
 
 
 
 + 
 
 Weldability 
 
 
 ? 
 
 
 
 _ 
 
 
 
 
 
 
 
 ? 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 + 
 
 
 
 
 
 Corrodibility 
 
 ? 
 
 
 
 
 
 
 
 + ? 
 
 _ 
 
 
 _ 
 
 
 
 
 Tendency to burn 
 
 + 
 
 + 
 
 
 
 
 
 
 
 
 
 
 
 
 ... 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 NOTE. means that the property is not changed, + that it is increased, - that it is diminished by 
 the impurity : ? means that the authorities are very conflicting; ... means that no information 
 
 ADDENDUM. 
 
 For insertion after the table on page 185. 
 
 The ultimate tenacity in tons per square inch can, according to recent tests, 
 be estimated to within 5 per cent, of its true value by inserting the percentages of 
 the several chemical elements in the formula 
 
 19-75 + 25 (C + C 2 ) + 11-5 Si + 30 P + 205 N + 36 AS - 9'5 S. 
 No definite relationship has yet been discovered for the elongation and other 
 properties. 
 
 years suddenly developed serious cracks. On analysis it was found 
 that its percentage of nitrogen was O0126, and the phosphorus 
 O1477 o) the sum IP + 5N being 0'210 which is above the empyrical 
 limit of O08/ . On enquiry it transpired that the front end plate 
 and first ring had once figured in an exhibition and had been bought 
 up by a boilermaker, who added the main length to this front portion, 
 which had evidently been made of cheap Bessemer steel ; hence the 
 high percentage of nitrogen in the first belt. 
 
 A vessel for holding compressed gas exploded at Innsbruck. The 
 analysis showed that it contained O01207 nitrogen and 0*077/ 
 phosphorus, the sum IP + 5N being 0'137/ . 
 
 A plate and an angle iron used in the construction of an open tank 
 in which caustic liquor was concentrated cracked while in use, whereas 
 older tanks remained intact. The analysis showed respectively 0'0062 
 
134 STRENGTH OF MATERIALS 
 
 failures of plates when in use. When the sum of the percentage of 
 phosphorus plus five times the percentage of nitrogen (P + 5N) 
 exceeds 0*08% then trouble may be expected. 
 
 Nitrogen combines with iron under pressure, about 0'003% under 
 blast furnace conditions, and about 0-030% under Bessemer converter 
 conditions. Seeing that fluid Bessemer steel or large quantities of 
 Bessemer scrap may be thrown into Basic Siemens' furnaces which 
 use pure pig (see p. 132), this process may occasionally turn out un- 
 reliable steel. This may account for the relatively numerous steel 
 plate failures in countries where basic steel is generally used. 
 
 Carbon increases the tenacity and tempering qualities (if it does 
 not even create them) ; it reduces the elongation at the rate of about 
 30% for every 1% C., and the ductility and weldability and melting 
 temperature. It increases liability to burn. 
 
 Boron increases tenacity, but only after tempering. It creates 
 redshortness, but only at a white heat. 
 
 Silicon increases tenacity, reduces the elongation and melting tem- 
 perature, prevents blowholes, increases red- and coldshortness, but only 
 in presence of carbon. Eeduces weldability, but only above 0*7%. 
 
 Phosphorus has ascribed to it in company with nitrogen the chief 
 blame for coldshortness and general treacherousness. It also in- 
 creases the liability to get burnt. It reduces the melting temperature. 
 In mild steel it should not exceed 0'07%. In small quantities it 
 
 tralises the redshortness of sulphur up to 0*1%, and of silicon up to 
 0'5%. In large quantities it is said to give a shaly appearance to 
 fractures of torn or bent samples. 
 
 Nickel reduces tenacity and increases ductility, particularly as 
 regards impact. It neutralises the influence of carbon, and perhaps 
 of phosphorus, and it reduces corrosion. 
 
 Copper prevents blowholes, increases tenacity, reduces elongation, 
 and produces redshortness, but only when above 3%. Its influence 
 on welding is doubtful ; it reduces corrosion. 
 
 Chromium, like Tungsten, intensifies all the influences of carbon, 
 particularly as regards the tempering qualities. 
 
 Aluminium prevents blowholes, reduces the melting temperature, 
 and hardens cast iron, quiets the molten metal, and accentuates the 
 effects of carbon. 
 
STRENGTH OF MATEBIALS 
 
 135 
 
 Tin. Authorities are conflicting. It seems to drive carbon out 
 of cast iron, and 0'35% makes mild steel quite redshort. It enters 
 steel as scrap tinplates. 
 
 Oxygen is not easily determined, and it cannot be said that it 
 exists in iron either as dissolved or segregated oxide. The small 
 traces of hydrogen which are always present in steel should effect 
 a reduction when the steel is in the heating furnace, in the same way 
 that hydrogen in a laboratory furnace is expected to reduce the oxide ; 
 if heated to redness. 
 
 An attempt to summarise these remarks is made in the following 
 table : 
 
 Elements 
 
 
 
 P 
 
 s 
 
 As 
 
 _!L 
 
 Sn 
 
 Al 
 
 M" 
 
 Ni 
 
 Or 
 
 Cu 
 
 N 
 
 H 
 
 B 
 
 Elongation . 
 Resistance to impact 
 
 + 
 
 + 
 
 :i 
 
 
 
 +? 
 
 ... 
 
 
 
 + ? 
 
 + 
 
 4- 
 
 + 
 
 + 
 
 - 
 
 - 
 
 :;; 
 
 + 
 
 
 Pliability cold . 
 dull red 
 
 - 
 
 
 
 
 
 - 
 
 
 ... 
 
 + 
 + 
 
 + 
 -f- 
 
 + 
 
 - 
 
 _lv 
 
 - 
 
 - 
 
 
 
 o 
 
 white hot 
 
 
 
 
 
 
 -> 
 
 _ 
 
 
 + 
 
 
 
 
 
 
 
 + 
 
 tempered 
 
 
 
 
 
 
 
 
 + 
 
 + 
 
 + 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Weldability 
 Melting temperature 
 
 - 
 
 ? 
 
 - 
 
 
 - 
 
 
 ... 
 
 
 
 - 
 
 + 
 
 ? 
 
 ... 
 
 ... 
 
 - 
 
 Corrodibility 
 
 ? 
 
 
 
 
 
 
 
 +? 
 
 _ 
 
 
 _ 
 
 
 
 
 Tendency to burn 
 
 I + 
 
 + 
 
 
 
 
 
 
 
 
 
 
 
 
 ... 
 
 
 
 
 
 
 
 
 
 11 
 
 
 
 
 
 
 ... 
 
 NOTE. means that the property is not changed, + that it is increased, - that it is diminished by 
 the impurity : ? means that the authorities are very conflicting; ... means that no information 
 could be obtained. 
 
 Recent failures of steel due to impurities, and analysed in the 
 laboratory of the Manchester Steam Users' Association, Manchester : 
 
 Some Continental angle irons intended to be used in small portable 
 locomotive boilers failed in the boiler shop. The analysis showed 
 that this steel contained 00146/ nitrogen, which fully accounts for 
 the brittleness. 
 
 A furnace plate which had been giving trouble was being cut out, 
 and was then found to be quite brittle ; it contained 0'0180% nitrogen. 
 
 A ship was being built in a Continental port with steel plates 
 which had satisfactorily withstood the usual tests, but these plates 
 and angles broke up during construction in a most unaccountable 
 manner. A sample of this steel was found to contain 0'0230/ 
 nitrogen, which is a maximum record. 
 
 The first ring of a shell of a boiler which had been in use for some 
 years suddenly developed serious cracks. On analysis it was found 
 that its percentage of nitrogen was 0*0126, and the phosphorus 
 0'1477 , the sum IP + 5N being 0*210 which is above the empyrical 
 limit of 0'08/ . On enquiry it transpired that the front end plate 
 and first ring had once figured in an exhibition and had been bought 
 up by a boilermaker, who added the main length to this front portion, 
 which had evidently been made of cheap Bessemer steel ; hence the 
 high percentage of nitrogen in the first belt. 
 
 A vessel for holding compressed gas exploded at Innsbruck. The 
 analysis showed that it contained 0'0120 J / nitrogen and 0'077/ 
 phosphorus, the sum IP + 5N being 0'137/ . 
 
 A plate and an angle iron used in the construction of an open tank 
 in which caustic liquor was concentrated cracked while in use, whereas 
 older tanks remained intact. The analysis showed respectively 0'0062 
 
136 STKENGTH OF MATERIALS 
 
 and 0-0070% nitrogen, and 0-165 and 0261% phosphorus, the sum 
 IP + 5N being respectively 0-196 and 0'296/ , which fully accounts 
 for the brittleness, no matter whether the liquor was weak or strong. 
 Drillings of another troublesome tank gave 0*006/ nitrogen and 
 0-246% phosphorus : IP + 5N = 0-276%. 
 
 A shell plate of a fairly modern high-pressure boiler developed a 
 circumferential crack outside the lap joint, which subsequently ex- 
 tended in a diagonal direction although covered with a patch. The 
 analysis showed that the nitrogen and phosphorus percentages were 
 respectively 0'0037 and 0-088, the sum IP + 5N being 0-106%. 
 
 The connecting rod bolt of an engine broke. In this material the 
 percentages were 0*0091 nitrogen, and 0-050 phosphorus, IP + 5N = 
 0-095%. 
 
 The lower parts of the shell plate of a recently constructed boiler 
 cracked where the scale, which falls from the furnaces, occasionally 
 accumalates, and where therefore the plates may have become very hot. 
 This material contained 0-0084 / nitrogen, and 0-060 / phosphorus, 
 the sum IP + 5N being 0-102%. 
 
 Some furnace rivets in a recently constructed boiler gave trouble 
 by snapping in two. This material contained 0'0151% nitrogen, 
 and 0-163% phosphorus, the sum IP + 5N being 0*238%. 
 
 A marine boiler combustion-chamber plate which had cracked 
 along the line of rivet holes showed 0-0041% nitrogen, and 0'092% 
 phosphorus, the sum IP + 5N being 0-112%. 
 
 In a recently built marine boiler some rivet heads dropped off. 
 On analysis they were found to contain 0'0036% nitrogen and 0*061% 
 phosphorus. The sum IP + 5N = 0-079% is just on the above- 
 mentioned limit between good and bad steel. 
 
 Mention is made in "The Engineer " of the s.s. " Pahud," whose 
 boiler exploded while under steam. No material was obtainable from 
 this boiler, but the boiler of a sister ship, in which the butt straps 
 leaked, and in which the shell plate was found to be dangerously 
 cracked, was cut up and analysed. The results are as follows : 
 nitrogen, 0-0060% ; phosphorus, 0-064% ; the sum IP + 5N being 
 0-094% 
 
 These last-mentioned failures are of special importance, because 
 they are the only cases of steel marine boilers having exploded, 
 although thousands have been built annually during the last thirty 
 years. These exceptions may be looked upon as proving the rule 
 that the process of manufacture (acid open-hearth steel) combined 
 with the customary tests, ensure almost absolute safety. As this 
 boiler was built on the Continent, it is possible that the steel was 
 made by the basic open-hearth process, with which it is always 
 possible to use up basic scrap, and that may contain much nitrogen 
 It is therefore doubly desirable when using basic steel to analyse for 
 nitrogen. 
 
 Mechanical Tests are called Qualitatsproben ' in German, which 
 word expresses very appropriately that they are mainly intended to 
 determine the quality, and not, as is too often assumed in this country, 
 that they should be an imitation of the conditions to which the 
 material is to be subjected in the structure. Looked at in this light 
 there is nothing unreasonable in bending a sample which has been 
 
STEENGTH OF MATEKIALS 137 
 
 cut from a plate which will never be subject to bending stresses, or 
 to test a sample by tension, when the plate will certainly only be 
 subjected to compression stresses. The object of the various tests 
 is to ascertain the quality, and that is all, the correlation between 
 a test and the quality best suited for a particular purpose having 
 been determined by practical experience. 
 
 Thus, \vhen iron came into use it was found that the better quali- 
 ties those which did not break with ordinary usage could under 
 the conditions of testing stand bending through a certain angle, and 
 when fractured showed certain peculiarities of grain called fibre. 
 Tests on this line, of a more or less severe nature, were then looked 
 upon as a criterion of the quality. Later on tensile tests were added. 
 In the early days of steel it was found that these tests did not suffice ; 
 that plates cracked without apparent cause when in use, even though 
 samples which had been cut from them had withstood all the tests 
 prescribed for the best iron in a more than satisfactory degree. It 
 was found that this material was not reliable unless it would pass the 
 temper-bending test, which was then adopted. As already mentioned, 
 nitrogen and phosphorus impart treacherous qualities to steel, but no 
 mechanical tests have yet been discovered which will detect such 
 steels. The author is carrying out an elaborate comparison of all 
 known tests, but has not discovered any correlation between them. 
 
 The following are the most important of these mechanical quality 
 tests. 
 
 Cold Bending. This test must be looked upon as a very important 
 one, and more certain to detect a defective plate than either the temper- 
 bending or tensile tests. To punch holes in the samples before bend- 
 ing does nofe appear to give a better indication as to the natural quality 
 of the steel than if the sample is bent with sheared edges ; but care 
 should be taken that the shearing is done from opposite sides of the 
 plate, and the two sharp edges should be kept on the inside of the 
 bend ; otherwise the results will be very erratic and unsatisfactory, 
 depending not so much on the injury to the metal which has been 
 caused by the shearing as on the shape of the ragged edge. If a tear 
 commences from the sharp edge, it should not be looked upon as being 
 very serious. There seems to be a difference, depending on whether 
 the concave or convex side of the sample was the upper one while the 
 ingot was heated for rolling, but nothing reliable is known about this 
 subject. 
 
 Inferior qualities of steel will not behave well, and occasionally it 
 happens that a strong steel bends better than a weak one. The bending 
 of samples after annealing them is valueless, unless they crack even 
 then, which would be an unmistakable sign that the material is quite 
 bad. The thickness of the plate is an important factor and when 1 in. 
 is exceeded only the best steel having sheared edges will stand even 
 the slightest bending. For |-in. plates and upwards it is well to plane 
 off ^ in. of the edges, but then the samples should bend quite double. 
 Care must be taken that the temperature is a reasonable one say. 
 82 F. or 100 F. for excessive cold has a bad influence, as will be 
 seen from the following experiments. (See also p. 145.) 
 
 Out of ten samples cut from one f-in. plate six bent double at 
 82 F., while the four others broke at angles varying from 90 to 100. 
 These had been bent at F. (i.e. 32 below freezing). 
 
laa 
 
 STRENGTH OF MATERIALS 
 
 Two sets of samples of -|-in. plates were cut from six separate 
 charges. The first three were bent at 82 F. to f -in. radius, while at 
 F. the duplicate samples broke at l^-in. radius. Three others were 
 bent at 82 F. and broke at 1-in. radius ; their duplicates, tested at 
 F., broke off short. There was nothing in the analysis to indicate 
 that the two qualities were different. 
 
 This cold-bending test is the only one which seems likely to detect 
 whether the steel possesses the disagreeable quality of reverting to its 
 (perhaps) naturally bad condition. When this is feared duplicate 
 samples with sheared edges should be kept for a week or more, bent, 
 and their curvatures compared with the original ones. Both samples 
 should be bent till they crack, and at identical temperatures. 
 
 The Temper-Bending Test was devised to guard against the employ- 
 ment of steel liable to crack after it had been worked. Combined with 
 the condition that the tenacity might reach thirty-two tons, it com- 
 pelled manufacturers to replace part of the carbon in the steel by 
 manganese, thereby maintaining the tenacity, but reducing the temper- 
 ing qualities (see p. 135). The test is carried out as follows : Steel 
 samples are heated to a cherry-red, and suddenly cooled in water oi 
 82 F. (=28 C.) When cold they are bent. Better bending results 
 
 9 
 
 FIG. 112 
 
 FIG. 113 
 
 FIG. 114 
 
 are always obtained if a large batch of samples is operated upon, for 
 if they are all thrown into the tank together their mass sufficiently 
 retards the cooling and hardening effect of the water, while if thrown 
 in singly none except the first few are exposed to the very cold water. 
 Should there be any doubt about the quality of particular charges, it 
 would not be difficult to retain such samples to the last, when the 
 water has grown warm. 
 
 Another means of improving the bending results is to take the 
 samples out of the water trough while still warm, and bend them in 
 this condition. The effect of quenching the samples from a dull red 
 heat seems to be a bad one, but the reverse is true if they are 
 annealed thoroughly at a good red heat for a quarter of an hour, and 
 then cooled slowly to a cherry-red before quenching. The use of a 
 bending press instead of a hammer does not seem to be an advantage; 
 in fact, experience points the other way, and an explanation may be 
 
STRENGTH OF MATEKIALS 139 
 
 sought for in the fact that most bending presses set up a greater 
 tension stress in the outer fibres than is the case with a steam 
 hammer. The removal of sheared edges before tempering at least 
 as regards the best qualities of steel seems to be injurious. J. Riley 
 arrived at a different conclusion (' I. and S. I., 1887, p. 121). 
 
 The Red-hot Bending Test is sometimes carried out on plates to be 
 flanged, but seems to be unnecessary, except for iron. With steel this 
 or a similar test is carried out on the baby ingot which is cast during 
 the running of the charge, so as to be sure that the steel will roll 
 well. 
 
 For mild steel plates the following test is occasionally adopted : 
 
 While red hot, a half -inch hole is punched in a strip of metal 
 about 1^ in. wide (see fig. 112), and is then drifted to 1 in. diameter 
 and the end slit open, as shown in fig. 113 ; the two arms are then bent 
 as shown in fig. 114, and the drifted surface should show no signs of 
 cracks. This work is done in two heats. 
 
 The Drift Test consists in forcing a cylindrical cone into a drilled 
 hole alternately from one side and then from the other. It is some- 
 times applied to steel intended for tube plates. It is a tedious and 
 very uncertain test, and gives no indication of the quality of the 
 material. This was very conclusively shown in W. Hackney's paper 
 on test pieces (' C. E., 1883, vol. Ixxv. p. 70). Locomotive tube plates 
 are sometimes tested in this way. 
 
 Alternate Bending Tests are very tedious, and have to be carried 
 out with much care, but then they are most valuable, as an indication 
 of the ductility of the material. These tests are much used for wire, 
 and they have given good comparative results in the author's investi- 
 gations on blue heat. The plan there adopted was to bend the samples 
 alternately from one side to the other through an angle of 45 over a 
 radius of 1| in. Professor Arnold has devised a machine which very 
 rapidly bends samples many times through small but definite angles. 
 Professor Wohler devised a fatigue test which will be mentioned 
 later, p. 160. 
 
 Bending Tests with Nicked Samples. This test is a very valuable 
 one if applied to iron, as it exposes the grain. With good steel the 
 result is unsatisfactory, because it is difficult, even after nicking, to 
 break it. In order to obtain a fracture the sample should be nicked 
 all round, or bent through an angle of about 30 before nicking, and 
 then broken. Fine grain indicates high carbon, coarse grain as well 
 as silky fracture indicates low carbon. An excess of manganese is 
 said to give a shaly and even a laminated fracture, and phosphorus 
 in nicked samples gives a well recognisable stringy fracture. The 
 shape of a fracture depends not only on the quality of the material, 
 but also on the method of breaking; if done slowly fibre usually 
 appears. Sudden blows produce crystals ; their size increases with 
 the softness of the material. It is a mistake to imagine that these 
 crystals exist in the material; they are the shape of the fractured 
 surface. The starting-point of most fractures can easily be found. 
 
 Samples Nicked on Edge. This has proved itself to be a very 
 discriminating test in the author's experiments on the ageing qualities 
 of steel. The samples were planed on their edges, and nicked by 
 means of a cold chisel, which penetrated to a definite depth, about 
 
140 STRENGTH OF MATERIALS 
 
 T T B - in., and then bent. The roughness near the nicked edge was filed 
 flat, and after bending the curvature of this side, which was inner- 
 most, was measured near the nick with metal templates. 
 
 Percussion Bending Test is customary with rails and with tyres. 
 The comparatively thin plates of a boiler are nearly always subjected 
 to it as they are struck with a hammer, and, as already mentioned, 
 the results are, if possible, more satisfactory than when the bending 
 is done in a press. 
 
 Brinell's Method of Testing consists in placing a hard steel ball 
 of, say, 10 mm. diameter on the polished surface of the sample, and 
 loading and measuring the diameter of the impression under a micro- 
 scope. The estimated depressions approximate very closely to the 
 load applied and inversely to the tenacity of the material. 
 
 Tensile Tests. Much importance is attached to this test. The 
 ease with which it can be explained and the uniformity now obtained 
 are powerful inducements for retaining it. It is useful for making 
 comparisons of quality independent of tenacity, though in this respect 
 it is not nearly as valuable as some of the bending tests ; they, how- 
 ever, require observers possessed of much experience. The primary 
 object of the tensile test is to ascertain the ultimate strength of the 
 material ; but the permanent elongations also give indications of the 
 ductility, while with accurate instruments the modulus and limit of 
 elasticity can also be ascertained. No relation between the contrac- 
 tion of area and general qualities has been detected, except that basic 
 steel contracts more with equal elongation than acid steel. The 
 temperature has a marked influence (Dr. J. Kollmann, ' Ver. Gew.,' 
 1880, vol. lix.). 
 
 A good deal has been written on the forms of test pieces, and the 
 influence of length, breadth, and thickness, and on the presence and 
 absence of scale on the surface E. J. Reed, 1869, p. 401 ; P. D. 
 Bennett, ' M. E.,' 1886, p. 27 ; E. Richards, ' I. and S. I.,' 1882, p. 11 ; 
 Dr. H. Zimmermann, ' C. E.,' 1883, vol. Ixxiv. p. 301 ; W. Hackney, 
 'C. E./ 1883, vol. Ixxv. pp. 70-159; D. Kirkaldy (various); J. 
 Bauschinger, ' Mitt. Munich,' 1892, vol. xxi. 
 
 The general conclusions are, that long, thin test pieces show less 
 strength and do not elongate nearly as much as short ones, but this 
 is true only for materials which contract at the point of fracture. 
 Mild steel contracts very much, so that results as to elongation would 
 be misleading unless the length of the sample is mentioned. The 
 general practices as to length are 
 Board of Trade, 10 ins. 
 
 Admiralty, Lloyd's, and Continent, 8 ins., or 200 mm. 
 Artillery experts, Whitworth, \ , , . 
 and railway tyres 
 
 This short length of 2 ins. is due to the want of dimensions in the 
 gun barrels. The removal of the scale reduces the elongation and 
 increases the tenacity. 
 
 The Testing Machines all work on the principle that the sample is 
 attached by one end to a weighted lever, and by the other end either 
 to a screw or to a press which can be adjusted to make up for the 
 elongation. With the older machines the screws can be worked only 
 after the load has been removed, and the testing of ductile materials 
 
STEENGTH OF MATERIALS 141 
 
 cannot be carried out in one operation, but this does not seem to 
 affect the results. 
 
 In some machines the samples are placed horizontally, in others 
 vertically, and the levers are either simple or compound, and the 
 loading is done either by a jockey weight travelling on a lever, by 
 weights added to the extremity of the lever, or by a fluid pressure or 
 a pendulum weight. 
 
 The oldest machines are worked by added weights. On the 
 Continent (chiefly Austria) water is run into a large bucket at the end 
 of the lever. Generally a weighing machine is permanently stationed 
 under the bucket, so that it can easily be weighed, but a gauge glass 
 is also attached. 
 
 In England single levers and jockey weights are now customary. 
 The stretch is taken up by steam power acting on a ram, and the 
 speed is about 3 inches stretch per minute. 
 
 At some German works the lever is a loaded pendulum, which rises 
 while a hydraulic ram stretches the sample. 
 
 In France and Belgium the lever is a crank, which presses on an 
 iron disc resting on a sheet of leather, which covers a basin filled with 
 mercury, and which communicates with a graduated vertical glass tube. 
 The total load can be read off on a scale. This arrangement gives very 
 accurate results, and can with advantage be used for ascertaining the 
 drop (or elastic limit) ; but it is unsatisfactory in cases of dispute, 
 because the column of mercury sinks back to zero at once when the test 
 piece is broken. The defect could be remedied, or by attaching an 
 ordinary steam indicator automatic diagrams could be obtained. 
 
 Descriptions and illustrations of testing machines will be found in 
 the following publications : J. H. Wicksteed, ' M. E.,' 1882, p. 384, and 
 1886, p. 27 ; Prof. A. B. W. Kennedy, ' C. E.,' 1887, vol. Ixxxviii. p. 1 ; 
 U. E. Towne, ' M. E.,' 1888, pp. 206, 448. 'Engineering,' vol. xxxi. 
 p. 57 ; vol. xxxiv. p. 254 ; vol. xxxv. p. 346 ; vol. xxxvi. p. 146 ; 
 vol. xli. p. 180 ; vol. xliii. pp. 414, 572 ; vol. xliv. pp. 649, 652 ; 
 vol. xlv. p. 458, &c. ; vol. xlvi. p. 21. 
 
 Many testing machines are so arranged that they can be used for 
 measuring compression-bending and torsion stresses. Appliances foi 
 bending samples can be attached to almost any machine, but that is 
 not the case as regards compression and torsion. In the former case 
 very careful adjustments are necessary, in order that the thrust may 
 be perfectly central and the bearing perfectly normal. In both respects 
 most machines are very imperfect. Almost any lathe can be used for 
 the torsion test. It is a valuable one, but not carried out often enough, 
 and then the lessons it teaches are not properly understood (see p. 157). 
 
 Strain Indicators, When the elastic limit, has to be ascertained 
 strain indicators are indispensable. A description of these will be 
 found in ' C. E.,' 1887, vol. Ixxxviii. p. 1. The principle on which 
 they are designed is the accurate measuring of the elongation or 
 contraction of a test piece when loaded, but these changes of length are 
 so minute that they have to be magnified at least 200 fold, better still 
 1,000 fold. This can be done with the help of microscopes; but 
 they are very expensive instruments, and although accurate, are very 
 inconvenient to work with. Micrometer screws have also been used, 
 but unless they make and break contact electrically, they do not seem 
 
142 STRENGTH OF MATERIALS 
 
 to be very accurate ; besides, they are liable to have their threads 
 stripped or damaged. Most of the strain indicators in practical use 
 consist of some lever arrangement, and this always involves friction, 
 which masks the effect of after-strains and may even show permanent 
 sets before they occur. Rollers can of course be used instead of levers, 
 but they are also not free from friction. The author has been very 
 successful with rolling pins consisting of hard steel wires of diameters 
 ranging down to y^ in., to which are attached light balanced, straw 
 pointers of 3 in. length ; a magnification of 300 is obtained, which for 
 many purposes is ample. The author has also adapted the phenomena 
 of interference of monochromatic light waves to the measurement of 
 strains. With such instruments a movement of one millionth inch 
 can be detected ; this is the elongation which occurs in one inch of 
 steel when a stress of 30 Ibs. per square in. is applied. The instrument 
 is the only one that seems to have given satisfaction when used 
 for the direct measurement of Poisson's Ratio. (C. E. Stromeyer, 
 ' Proceedings/ 1894, vol. Iv. p. 377.) 
 
 When using strain indicators one cannot be too careful to have the 
 pull quite central in the test piece. Thus if in a test piece of \ in. 
 thickness the pull falls 1 ^ in. to one side of the central line, or if the 
 test piece is bent ^ in., then a strain indicator placed on one side will 
 give readings which are 6 per cent, too high or too low. For this reason 
 wedges should not be used for holding test pieces when these delicate 
 instruments are to be used ; in fact, whatever the mode of attachment, 
 the correct arrangement is to surround the test piece with three iden- 
 tical strain indicators. Their readings will tell one not only whether 
 the pull is central or not, but also what the stress is at any particular 
 section. This is of great importance when investigating limits of elasti- 
 city, for then it is not the average stress, but the maximum stress which 
 is required to be known. 
 
 Speed of Testing does not seem to affect the final result, at least 
 not unless the speed is excessively great, as in percussion tests, or 
 unless the test is prolonged for hours or days. See J. Bauschinger, 
 1 Mitt. Miinchen,' 1896, vol. xx. 
 
 Percussive Tensile Tests are carried out by securing the top end of 
 a tensile test piece to a strong but narrow beam, and attaching a cross- 
 bar to its lower end. A heavy weight, whose lower end is forked, is 
 then dropped on it, striking the cross-bar. Another plan is to attach 
 the weight to the lower end of the test piece and a cross-bar to its top 
 end ; the whole is then raised and dropped ; the cross-bar is arrested 
 by stops, while the weight tears the sample asunder. This is the more 
 usual plan, and seems to be the better of the two. 
 
 Colonel Maitland (' C. E.,' 1887, vol. Ixxxix. p. 114) was able to 
 obtain a still more sudden rupture by shaping the test piece somewhat 
 like a dumb-bell, surrounding the central, thinner part with gun cotton, 
 and inserting both into a strong tube open at both ends. On firing the 
 explosive, the two ends were driven out with great violence in opposite 
 directions. It was found that during rupture the samples had elongated 
 very much. This, however, might be due to combined action of the 
 longitudinal pull and the surface pressure on the bar, acting like the 
 forces which come into play when drawing wire (see p. 160). 
 
 Chipping, Machining, and Scratching have repeatedly been pro- 
 posed for use, as they seem capable of giving valuable information. 
 
STEENGTH OF MATERIALS 143 
 
 Thus the turning tool of a lathe will show up very distinctly the 
 various slabs and layers in an iron bar, exposing, as it were, very 
 slight differences in the hardness or toughness of the material. With 
 a hammer and chisel there is no difficulty in distinguishing between 
 iron and steel, and some boiler-smiths profess to be able to tell, with 
 the help of these tools, where a particular piece of steel has been 
 manufactured. This test has not yet been made practical ; the same 
 may be said of etching and the microscope, and magnetic tests. 
 
 Micro Structure of Steel. The sample to be examined should be 
 filed flat, rough ground, and then polished. The rough and fine 
 grinding can be done on carborundum discs of medium and finest 
 grain. If the edges of the samples are to remain flat, the polishing 
 should be done with carefully washed rouge on a hard surface, if 
 necessary on pitch, but this substance has a tendency to tear small 
 specs out of the steel. If the corners of the sample be round, the 
 polishing may be done on parchment or cloth. If the polishing on 
 cloth even without rouge be continued too long, a micro structure 
 appears, which is called polish attack. 
 
 Heating the Samples in a Vacuum reveals the grain very clearly. 
 
 Heating in Air to straw colour or purple produces beautiful patterns 
 of yellow, purple, and blue patches, but as yet no meaning attaches 
 to these colours, though it is probable that they are in some way 
 related to the angles at which the iron crystals are cut. 
 
 Annealed steels are conglomerations of Pearlite and Ferrite. If 
 steel be heated to redness (700 C. = 1290 F.) and quenched in water, 
 Martensite appears as needles which are coloured yellow to black when 
 etched, according to the percentage of carbon. The needles in high 
 carbon steels are shorter than in the low carbon ones. If steel be 
 heated to 690 C. = (1270 F.) and quenched in water Troostite is 
 formed. It consists of Martensite and Ferrite, and has a marbled 
 structure. 
 
 Ferrite is iron free from carbon. 
 
 Cementite is a compound of iron and carbon, Fe 3 C. 
 
 Pearlite is an intimate striated mixture of the two, containing 
 about 0'9/ o carbon. The structure varies considerably in different 
 steels, and when of a shelly or ropy structure this is supposed to 
 indicate the presence of phosphorus. 
 
 Phosphorus segregations are revealed by etching the steel with an 
 8/ solution of copper sulphate of ammonia, and gently washing off 
 the deposited copper. The regions rich in phosphorus will appear 
 dark, but only if the percentage of carbon is low. The darkenings 
 are not strictly proportional to the percentage of phosphorus, but 
 seem to be affected by other impurities. 
 
 Sulphur Segregations are revealed, but rather roughly, by Bau- 
 mann's method. After fine grinding the steel surface place it for five 
 minutes on a piece of photographic bromide paper which has been 
 soaked in a 5/ solution of sulphuric acid for five minutes. Wash 
 the paper and fix in hypo. The sulphuretted hydrogen which is 
 produced by the acid wherever there are minute specs of sulphide in 
 the steel blackens the silver salts locally. The action is very rapid, 
 and great care should be taken not to slide the sample on the paper. 
 This test is affected by phosphorus. Dr. Heyn recommends the use 
 of silk saturated with chloride of mercury. 
 
144 
 
 STRENGTH OF MATERIALS 
 
 Etching Fluids. A very convenient etching fluid is picric acid 
 crystals dissolved in pure alcohol. The sample should remain in this 
 fluid for a few minutes, and slightly rocked, otherwise the edges will 
 be attacked more severely than the central portions ; it should then 
 be removed, washed, but not touched, dipped into alcohol, and when 
 dry examined under the microscope. Irregular dark patches of 
 pearlite will have made their appearance, which should be studied, 
 and the sample should, if desired, be repeatedly etched until fine hair 
 lines, the boundaries between the ferrite nodules, appear. Oval and 
 long dove-coloured patches may also appear ; they are sulphide of 
 manganese. 
 
 A 1/ solution of nitric acid produces nearly the same effect as 
 picric acid, but is said to develop the crystalline structure of the 
 ferrite. 
 
 A weak solution of iodine in water is sometimes used ; it does 
 not attack cementite, or, at least, it leaves it bright, but pearlite is 
 darkened. This fluid is very troublesome. 
 
 An 8/ of copper sulphate of ammonia is very effective. The 
 section is at first covered with copper ; this will wash off unless a 
 wrong percentage has been used, and then certain portions of the 
 ferrite which contain much phosphorus will appear in a brownish 
 colour. Segregations are thus clearly revealed. If the sample before 
 polishing has been severely strained, this etching fluid will also darken 
 the strained regions, which are said to show slip bands. 
 
 Hydrochloric acid, even as a l/ o solution, is very troublesome, 
 but, as it attacks the highly phosphoric segregations about eighty 
 times more severely than others, it may yet become a useful reagent. 
 The deep pit holes which it produces in some steels are now believed 
 to be the localities of highly phosphoric nodules, and the difference 
 of behaviour under this and the previous etching fluid, as well as 
 other experiments, indicate that there are two phosphide of iron 
 impurities, the one dissolved in the ferrite, is believed to be the 
 cause of brittleness. 
 
 As yet the most important revelations which can be expected of 
 an examination of the micro structure of a mild steel is with regard 
 to the previous heat treatment, the pearlite segregations being few 
 and large if the material has been wrongly heated, i.e. too long at 
 a low temperature. If a sample of such a steel be heated to a suit- 
 able temperature, and cooled slowly, it should show much smaller 
 segregations than before. 
 
 The Influence of Temperature, particularly of heat, on the strength 
 of materials is a subject of the first importance. The relation existing 
 between the boiler pressures and temperatures will be seen from the 
 following table : 
 
 Boiler Pressure 
 
 Lbs. 
 
 
 
 212 
 
 100 
 
 50 
 
 100 
 
 328 
 153 
 
 150 
 
 358 
 181 
 
 200 
 
 250 
 
 401 
 205 
 
 300 
 
 417 
 214 
 
 400 
 
 500 
 
 467 
 242 
 
 Temperature 
 > 
 
 F. 
 C. 
 
 281 
 138 
 
 382 
 194 
 
 445 
 230 
 
 Original researches on this subject will be found in the following 
 papers : ' Franklin Inst.,' 1836, ii. pp. 82-208 ; M. Baudrimont, ' An. 
 
STRENGTH OP MATERIALS 14o 
 
 Ch. Ph.,' 1850, iii. vol. xxx. p. 304 ; W. Naylor, ' M. E./ 1866, p. 76 ; 
 W. Fairbairn, 1856, 2nd ser. p. 96 ; Sir W. Fairbairn, ' Manch. L. Ph./ 
 1871, vol. x. p. 86 ; ' Portsmouth Dockyard Experiments/ 1877 ; C. 
 Huston, 'Frankl. Inst./ 1878, vol. Ixxv. p. 93; 'N./ ' Glaser's An./ 
 1880, vol. vii. p. 165 ; Dr. J. Kollmann, ' Ver. Gew./ 2nd ser., 1880, 
 vol. lix. p. 92 ; J. F. Barnaby, 1881 and 1882 ; J. E. Howard (Water- 
 town Arsenal), 'I. and S. I./ 1889, ii. p. 460; Le Chatelier, ' Comp. 
 Rend./ 1889, vol. cix. p. 58 ; Board of Trade Eeport (No. 257) on 
 ' Boiler Explosions ' ; Prof. Martens, ' Mitt. Berlin/ 1890, p. 159 ; 
 A. Bleichenden, ' M. E./ 1891, p. 320. See also p. 190 as regards elastic 
 limits at high temperatures. 
 
 The Influence of Cold on the tenacity of metals is dealt with by the 
 
 following experimenters: Sir W. Fairbairn, 'Parl. Eeport of the 
 
 Commissioners of Bailway Structures/ p. 321 ; ibid. ' Brit. Assoc./ 1857, 
 
 . 405 ; K. Styffe, 1869 ; ' N./ ' Glaser's An./ 1880, vol. vii. p. 165 ; 
 
 apt. Bernardo, ' Eev. d'Art./ 1890, p. 485 ; W. Brockbank, ' Manch. 
 
 L. Ph./ 1871, vol. x. p. 77 ; W. W. Beaumont, ' C. E./ 1876, vol. xlvii. 
 
 p. 43 ; T. Andrews, ' C. E./ 1887, vol. Ixxxvii. p. 340 ; Spangenberg, 
 
 ' Glaser's An./ 1879, vol. v. p. 165 ; T. Andrews, ' C. E./ 1891, vol. cv. 
 
 pp. 161, 169 ; W. Eudeloff, Mitt. Berlin/ 1897. 
 
 Experiments on the influence of temperature on copper and other 
 materials : ' Frankl. Tnst./ 1836, ii. p. 39 ; Dr. Kirk, ' Enging./ 1887, 
 vol. xliv. p. 661 ; W. Parker, ' N. A./ 1889, vol. xxx. p. 47 ; Le Chate- 
 lier, ' Comp. Bend./ 1889, vol. cix. p. 24 ; Le Chatelier, Paris, 1891. 
 
 Dr. J. Kollmann's experiments on iron and steel, 150 in number, 
 seem to be the most reliable. His conclusions are that the ultimate 
 strength of both materials decreases with rising temperature, and that 
 it shows a very serious drop at about 450 to 500 F. The elongation 
 is at a maximum at about 900 F. The contraction of the fractured 
 sectional area steadily increases till it reaches 90 % at a red heat. The 
 limit of elasticity decreases steadily. 
 
 Another result is that the ductility, as measured by bending tests, 
 increases with rising temperatures till 450 to 500 F. (blue heat) is 
 reached, when the material is rotten. At higher temperatures it is 
 pliable once more. It would seem as if medium quality steel is ex- 
 ceedingly brittle when cold (0 F.), while tougher qualities of the same 
 tenacity remain ductile ; at any rate, boiler-smiths and ship-platers 
 have come to the conclusion that it is risky to handle steel or iron 
 plates in cold weather, and where serious hammering or drifting is 
 contemplated, heaters are almost invariably applied. If the steel con- 
 tains much phosphorus it is exceedingly likely to break under the 
 percussive bending test, if carried out in cold weather. 
 
 Sudden cooling, not necessarily from a red heat, is said to produce 
 brittleness (see T. Andrews, 'C. E./ 1891, vol. ciii. p. 231); and 
 repeated heatings have also produced brittleness, but the exact con- 
 ditions for effecting this change are not known. E. Wehrenfennig, 
 ' O. I. A. V./ 1879, vol. xxxi. p. 153 ; J. P. Barnaby, 1881 and 1882 ; 
 A. Ledebur, 1884, p. 646 ; C. E. Stromeyer, ' C. E./ 1886, vol. Ixxxiv. 
 p. 122; E. B. Martens, 'Ing. Civ./ 1886, p. 607; E. Wehremennig, 
 ' Organ/ 1884, vol. xxi. p. 216 ; A. E. Sherk, Enging./ vol. xliv. 
 p. 4o8 ; C. E. S., ibid. vol. xliv. p. 491 ; B. H. Thwaite, ibid. vol. xliv. 
 pp. 505, 536 ; Th. Edington and Son, ibid. vol. xliv. p. 505. 
 
146 
 
 STRENGTH OF MATERIALS 
 
 Occlusion of Gases. In some of the above-mentioned cases the 
 brittleness may have been due to the absorption (occlusion) of inju- 
 rious gases, and experiments prove that hydrogen is readily absorbed, 
 and that it injures the material. Acids and other corrosive influences 
 are also said to produce brittleness, but the real cause may be the 
 hydrogen which is evolved during these processes. 
 
 Dr. Schahantl (' Bayrisches Kunst- und Gewerbeblatt/ June 1863) 
 gives an analysis of the various layers of an exploded boiler plate, and 
 shows that on the water side it contained an excess of oxygen, while 
 on the fire side occluded sulphurous acid was found. That solids do 
 absorb gases is proved by the well-known fact that soaped window 
 glasses turn a mauve colour after a time, which is due to a chemical 
 action of the oxygen of the air on the manganese salts in the glass. 
 
 M. Bustein ('An. Mines,' 1883, viii. vol. iii. p. 28) gives the 
 chemical analysis of three qualities of steel which had been exposed 
 for 112 days in flue gases or in boiler water. 
 
 Previous Treatment of Sample 
 
 Tenacity Tons 
 
 Elongation per Cent. 
 
 Original 
 Exposed 112 days in boiler . 
 flue . 
 
 56 50 
 51 47 
 44 41 
 
 42 
 40 
 37 
 
 17 19 
 
 15 I 16 
 16 ; 21 
 
 24 
 14 
 
 
 
 Nitrogen. The influence of nitrogen has already been mentioned. 
 
 Prof. Hughes (' Tel. Eng./ 1880) deals with this subject. 
 
 Influence of Pickling. A. Ledebur (' Stahl und Eisen,' 1887, 
 vol. vii. p. 682) gives analyses of eight qualities of steel (wire), and 
 finds that pickling reduces the elongation about 15%, and the 
 ductility 39 % ; that exposure to the atmosphere for two months 
 reduces both qualities about 50%, but that annealing puts matters 
 right again, though the ductility is not perfectly restored. The 
 action of zinc in galvanic contact with the wires is worthy of notice ; 
 it prevented corrosion, but the wires grew very brittle, and on 
 analysing them again they were found to contain from -002 to '005 % 
 of hydrogen. He points out that, on account of the low atomic 
 weight of hydrogen, these percentages should be multiplied by, say, 
 thirty to make them comparable with the volumes of- phosphorus or 
 of sulphur. Baedecker (' Deut. Ing.,' 1887, vol. xxxii. p. 187) confirms 
 these views about the action of acids. 
 
 Heyn (' Stahl und Eisen/ 1900, vol. xx. p. 780) states that by 
 heating and cooling steel in an atmosphere of hydrogen it becomes 
 brittle. 
 
 The study of this subject is as yet in its infancy, and is certainly 
 beset with many difficulties. It may, therefore, be of interest to men- 
 tion where experiments on occluded gases can be found : L. Troost 
 and P. Hautefeuille, ' Comp. Bend.,' 1875, vol. Ixxx. p. 788, and ' An. 
 Chim. Ph.,' 1876, 5th ser. vol. vii. p. 155 ; M. Eeynard, ' Ing. Civ./ 
 1877, pp. 91 and 210; A. H. Allen, 'I. and S. I./ 1879, p. 480, and 
 1880, p. 181 ; P. C. G. Miiller, ' Deut. Ch. G./ vol. xii. p. 11 ; ibid. 
 1 Glaser's An./ 1880, vol. vii. p. 138 ; ibid. ' Stahl und Eisen/ 1882, 
 vol. ii. p. 531 ; N. Zyronski, ' Soc. I. Min./ 1884, p. 101 ; H. M. Howe, 
 ' Eng. Min. J./ vol. xlv. p. 236. Nitrogen, Harbert and Tynam, 
 I. andS. I./ 1896, vol. ii. p. 161. 
 
STRENGTH OF MATERIALS 147 
 
 It would be wrong to compare occlusion by metals with the 
 absorbing power of fluids for instance, with water, which takes up 
 very much larger quantities of carbonic acid when cold than when 
 warm. On the contrary, metals behave in a most erratic manner, 
 and usually absorb certain gases while in a molten state, which they 
 give off again when cooling. Thus molten silver and copper absorb 
 oxygen, and expel it with much force as they harden. Therefore it 
 can hardly be expected that the annealing process will drive out all 
 the gases occluded by iron or steel, even if carried out in a vacuum, 
 although a certain proportion would disappear. The gas given off by 
 steel in the soaking pits is said to be hydrogen. If this gas should 
 be found to be the cause of brittleness, it may one day be necessary 
 to dry the gases used in melting-furnaces. 
 
 Burnt Iron. It has been attempted to explain the mystery of 
 burnt iron as being due to the presence of a large percentage of oc- 
 cluded oxygen ; but iron can unquestionably also be ' burnt ' in a 
 vacuum and in gases containing no oxygen. This has led to the 
 view that the occluded gases in the iron or steel chiefly hydrogen and 
 nitrogen leave the metal and form innumerable cavities, thereby de- 
 stroying its continuity and making it rotten (burnt). 
 
 W. M. Williams (' Chem. S.,' 1870, vol. xxiv. p. 790) found oxide 
 of iron in burnt iron. 
 
 H. Caron, ' Comp. Kend.,' 1872, vol. Ixxiv. p. 662. Iron could be 
 burnt in air, hydrogen or nitrogen gas. 
 
 Professor Ledebur, ' Jahrb. B. H.,' 1883, p. 19. Phosphoric iron is 
 more easily burnt than pure qualities. He believes burning not to 
 be due to oxygen, and mentions dead iron. See also ' I. and S. I./ 
 1888, vol. i. p. 386 ; 1897, vol. i. p. 234 ; 1898, vol. i. p. 145. 
 
 In spite of this diversity of opinion there can be no doubt that 
 iron and steel do get burnt if exposed to excessive heat, and are then 
 both red- and coldshort ; and also that in re-heating furnaces, and 
 even in annealing furnaces, burning can very easily be brought about 
 if the fire grates are left partly uncovered, and pure but heated air is 
 allowed to impinge on the plates. 
 
 Recalescence. This subject is a very complicated scientific one, 
 it has lead to important conclusions as re'gards annealing. 
 
 Annealing. It is well known that the annealed iron wire has an 
 initial hardness, which disappears on straining it. Basic (Siemens) 
 steel, made of pure pig and low in carbon, usually shows a slight 
 increase in its ultimate tenacity after annealing, while tempering 
 lowers its elastic limit. The reverse is the case with acid Siemens 
 steel, which generally contains more carbon and less manganese. 
 Internal strains are never entirely removed by annealing (p. 251). 
 Tool steel can be thoroughly annealed by heating it to redness and 
 cooling slowly till it is just dark, and then quenching. Mild steel 
 gives better bending tests if quenched at a cherry-red heat than if 
 quenched at a very dull red heat. The literature on the subject is 
 chiefly restricted to the question of removing the injury done by 
 punching, and to the influence of quenching on the comparatively 
 hard steel used for guns. 
 
 The well-known optic glass works, Schott Bros., Jena, have 
 adopted a novel method of annealing. They argued that, however slowly 
 
 L. 2 
 
148 STRENGTH OF MATERIALS 
 
 a glass might be cooled, the outside would always be hotter than the 
 inside until uniformly cold, and then the inside would be in tension. 
 They therefore cool their glass masses step by step, taking care to 
 maintain their annealing furnaces at constant temperatures for long 
 periods at a time, and then cooling rather rapidly to the next step. 
 By this means the glass has repeatedly passed through a period in 
 which it was of an equal temperature throughout, and can now be 
 produced so as to be without strains, which is proved by its optical 
 properties. 
 
 According to practical experience and also theoretical investiga- 
 tions by J. A. Brinell (' Stahl und Eisen,' vol. v. p. 611, also abstract 
 'I. and S. I./ 1886, vol. i. p. 365), annealing can produce both bad and 
 good results. Steel or iron which is kept at a dull red heat for a long 
 time becomes rotten; if kept at a bright red heat for a long time, it 
 partakes of the nature of burnt material. The best results are obtained 
 by heating to a good red heat for a short time and letting the object 
 cool, rapidly at first and then slowly. See also ' I. and S. I.,' 1882, 
 vol. i. p. 209 ; 1882, vol. ii. p. 532 ; 1898, vol. ii. p. 137, and W. 
 Budeloff, ' Mitt. Berlin,' 1891, p. 109. 
 
 Effects of Quenching Red-hot Steel. For thin plates it seems ad- 
 vantageous to remove the sheared edges before tempering the samples, 
 while for thick plates the reverse appears to be true. Quenching in 
 oil gives more toughness, while quenching in water, and particularly 
 in mercury, increases the hardness. Quenching at a dull red heat 
 thoroughly anneals tool steel. Large objects like armour plates 
 would become unequally chilled, warp and crack if plunged into water ; 
 they are therefore exposed to innumerable powerful jets of water 
 which produce equal chilling effects all over the surfaces, and yet 
 allow the resulting steam to escape. 
 
 Galvanised Steel. Injury, possibly due to chemical action or to 
 the absorption of vapours, is produced if iron or steel articles are 
 galvanised at too high a temperature. In order to guard against this 
 danger, the fires for heating the zinc baths should always be placed 
 round their sides ; this allows the impure zinc (containing iron) to 
 fall to the bottom, where it floats on a layer of molten lead. If mixed 
 with the other zinc, the temperature of the bath would have to be 
 raised too high in order to keep it fluid. 
 
 Electroplating with zinc has a temporary anti-corrosive effect, it 
 is of greatest value in revealing bad welds and other defects. 
 
 The Influence of Hammering or Cogging the Cast Ingots, or of 
 Rolling them direct. In England the practice is either to hammer or 
 cog the ingots, while in Germany this is not always done, which is 
 made possible by the different chemical compositions. Hammered 
 ingots show a better surface when rolled, and are said to be a little 
 denser. The question of waste is intimately bound up with the above, 
 and there can be no doubt that there is less scrap from plates whose 
 ingots were cogged or hammered than if no preliminary shaping had 
 taken place. From a boiler-maker's point of view a large amount of 
 scrap is an advantage, for the edges are sometimes overheated, and 
 are never of exactly the same quality as the rest of the plate. As 
 regards the final quality of the material several important investigations 
 have been carried out, but being in each case confined to steel of one 
 company, the deductions are not conclusive as regards other makers. 
 
STRENGTH OF MATERIALS 149 
 
 J. Riley, 'I. and S. I.,' 1887, p. 121. Influence of rolling, ham- 
 mering, and annealing. This is a very exhaustive paper, and the con- 
 clusion to be drawn from it is that an excessive amount of hammering 
 and rolling is not necessary. From one and the same charge thick 
 plates are both weaker and more ductile than thin ones, which have 
 received more work. 
 
 W. Parker (' I. and S. I.,' 1887, p. 134) mentions experiments to 
 show that tenacity and elongation increase with rolling. 
 
 H. Allen, ' C. E.,' 1888, vol. xciv. p. 240. Kolled wire and drawn 
 wire are neither much stronger nor more ductile than the billet unless 
 tested in an unannealed condition. 
 
 Dr. Kirkaldy gives a few experiments. 
 
 W. H. Greenwood, ' C. E.,' 1889, vol. xcviii. p. 83. Fluid com- 
 pressed steel. The benefit derived from this preliminary compression 
 does not seem to dissipate during the subsequent manipulations. 
 
 The immediate effects of hammering, &c., are investigated in the 
 following papers : 
 
 H. Tresca, ' M. E.,' 1878, p. 315. 
 
 Ibid., ' Comp. Rend.,' 1883, vol. xcvii. pp. 222, 515, 928. Localisa- 
 tion of heat developed by a hammer blow. 
 
 M. Lau, ' Comp. Rend.,' 1882, vol. xciv. p. 952. 
 
 M. Osmond, ' Comp. Rend.,' 1885, vol. c. p. 1228. Motive power 
 for rolling steel is 2^ times as much as for iron. 
 
 Dr. J. Kollmann, ' Ver. Gew./ 1880, 2nd ser. vol. lix. p. 6. 
 
 Local Heating. Serious injury is sometimes done to a steel plate 
 by drawing out one of its corners, even though this be done at a red 
 heat. Flanging, whether done by hand or presses, has also led to fail- 
 ures. It has never yet been reasonably demonstrated that this is due, 
 as some contend, to the local heating alone, or, as others believe, to the 
 straining produced by the unequal expansion of the locally heated 
 parts ; other influences, such as the chemical composition of the 
 material and the processes through which it has passed, are probably 
 important factors. 
 
 The following list contains published cases of cracked plates : 
 
 Sir N. Barnaby, ' I. and S. I.,' 1879, p. 242. List of forty-three steel 
 failures at Chatham in six months. 
 
 W. Denny, ' N. A.,' 1880, vol. xxi. p. 185. List of steel failures in 
 his own yard. 
 
 W. Parker, ' N. A.,' 1881, vol. xxii. p. 12. Cracked plates of the 
 steam yacht ' Livadia.' 
 
 A. C. Kirk, ' N. A.,' 1882, vol. xxiii. pp. 131 and 137. Cracked 
 flanged plate. 
 
 J. F. Barnaby, 'Enging.,' 1883, April 20; D. S. Smart, '0. E., 1 
 1884, vol. Ixxx. p. 102. Sketches of cracked plates. 
 
 W. Parker, ' N. A.,' 1885, vol. xxvi. p. 253. Failures of thick steel 
 plates. 
 
 H. Goodall, ' C. E.,' 1888, vol. xcii. p. 10. Sketches of some cracked 
 plates. (See also p. 252 ,) 
 
 Of course this list contains only a very small fraction of the number 
 of cracked plates, for as long as it is not settled whether these failures 
 are due to the material, or to the mode of working the plates, it will 
 be the custom, as now, for the steel-makers to replace the failed plates. 
 
150 STKENGTH OF MATEKIALS 
 
 Blue Heat. Perhaps some, though certainly not all, such failures 
 are due to working the steel at a blue heat. This is another mysterious 
 phenomenon connected with iron and steel. The salient features are 
 that steel will bend without fracture at temperatures ranging from F. 
 to 450 F. (see Dr. J. Kollmann, p. 151), and again above 550 F.,but it is 
 quite rotten between these limits ; and, further, a piece of steel which 
 has been bent or hammered at this particular temperature, but without 
 breaking, acquired and retained a permanent excessive brittleness 
 (see p. 256). This brittleness can be removed by annealing, but time 
 alone (8 years) does not restore the quality. Experiments on the 
 subject, as well as failures, which are attributed to working steel at a 
 blue heat, will be found in the following papers : 
 
 M. Valton, 'Berg- H.-Z.,' 1877, vol. xxxi. p. 25; D. Adamson, 'I. and 
 S. I./ 1878, p. 402 ; W. Denny, ' N. A.,' 1880, vol. xxi. p. 185 ; 
 C. E. Stromeyer, ' C. E.,' 1886, vol. Ixxxiv. p. 114 ; ibid., 1888, vol. xciii. 
 p. 89; W. Parker, 'I. and S. I.,' 1887, p. 136; G. B. Craig, 'N. A.,' 
 ]888, vol. xxix. p. 113 ; Eudeloff, ' Mitt. Berlin,' 1889, p. 97 ; Board 
 of Trade Eeport, August 31, 1886; 'Am. E. M. M. A.,' .Ib92; 
 Prof. A. Ledebur, ' Glaser's An.,' 1886, vol. xviii.p. 205 ; A. Martens, 
 1 Deut. Ing./ 1892, p. 172. 
 
 Influence of Severe Stresses. The limit of elasticity of a piece of 
 mild steel, which has been stressed beyond its original limit, is raised 
 even beyond its nominal ultimate strength, but this is no real improve- 
 ment, for the severer the strain the more is the ductility reduced even 
 down to brittleness. Possibly, however, the raising of the limit as 
 regards one stress, for instance tension, may produce brittleness as 
 regards compression and shear or vice versa. It also seems as if 
 steels rich in nitrogen and phosphorus are more liable to suffer in 
 this respect than other steels. 
 
 Influence of Time. The author's researches ('I. and S. I./ 1907) 
 have revealed that a majority out of 26 different qualities of mild 
 steel grew brittle after a time if they had been locally injured ; for 
 instance, by nicking, and that heat accelerates this ageing process. 
 There was no indication that the strengths had diminished, and that 
 therefore old boilers might be weaker than new ones, but they would 
 be more liable to suffer from any excessive strains, such as frequent 
 proof tests, and actual failures are cited in support of this contention. 
 Some Sheffield steel makers are of opinion that steel ingots improve 
 by storing. 
 
 List of Spontaneous Failures. Z. Colburn, 1860, p. 32. Old boiler 
 stays said to be brittle. 
 
 Professor Thurston, ' I. and S. I./ 1875, p. 342. Old rails had grown 
 brittle, and improved on re-rolling. 
 
 Professor Thurston, 4 Materials/ 1883, vol. ii. p. 576. Prolonged 
 excessive straining causes rupture. 
 
 Collingwood, ' Am. C. E.,' 1880, vol. ix. p. 171. Tenacity of wire 
 changes after a time. 
 
 L. Fletcher, ' C. E./ 1884, vol. Ixxx. p. 136. 
 
 A. J. Maginnis, 'Engr./ 1885, vol. Ix. p. 447; C. E. Stromeyer, 
 1 C. E./ 1886, vol. Ixxxiv. p. 187. Sketches of plates which cracked 
 spontaneously while not in use. 
 
 J. Harrison, 'Engr./ 1886, vol. Ixii. 
 
STRENGTH OF MATEKIALS 151 
 
 ' Army N. J.,' 1887, vol. xxiv. p. 65. A long list of steel armour 
 plates which cracked spontaneously hefore being fitted. 
 
 Collingwood, ' Am. C. E.,' 1880, vol. ix. p. 171, and W. Hewitt and 
 Felton, 'Am. M. E.,' 1888, vol. ix. p. 47. Strength and ductility of 
 wires and plates change 24 hours after rolling. 
 
 H. M. Howe, 1890, p. 195, old armour plates are brittle ; p. 210, 
 time removes injury caused by cold working. 
 
 For other cases, see p. 136. 
 
 Although not as yet published, there are a few cases of boiler shells 
 cracking under the hydraulic test, and particularly of furnace saddle 
 corners cracking while out of use or if struck with a hammer. One of 
 the most curious cases is perhaps the following : A steel steamer 
 which had been on fire was being repaired, and several of the buckled 
 plates had been taken out to be straightened. It was found that some 
 of these cracked spontaneously while lying on the ground, although 
 they had not cracked while being removed from the ship. 
 
 Besides these various failures other instances will readily suggest 
 themselves about the influence which time has on the quality of iron and 
 steel. There is the case of the gun of H.M.S. ' Collingwood/ which 
 burst with a light charge after two years' rest, succeeding on its trial 
 with several proof charges. These and similar failures are so very 
 mysterious that they have been attributed to hidden or incipient flaws ; 
 but they have never been seen, and if the point is conceded that certain 
 qualities of steel have a natural tendency to change and this is stoutly 
 maintained by experienced steel manufacturers then the difficulty is 
 somewhat reduced. That important changes are slowly occurring in 
 steel is proved by the fact that ordinary test samples which have been 
 successfully bent to a small radius crack spontaneously some time 
 afterwards ; that armour plates, after having been fired at, emit strange 
 sounds for a long period, and that the elastic limit of steel test pieces 
 which have been stretched a few per cent, slowly grows higher and 
 higher when at rest. 
 
 Time can hardly be called a treatment, but the mystery attaching 
 to its effects should be a sufficient excuse for most carefully investi- 
 gating all such cases as may possibly have been produced by it. 
 
 Influence of Punching. One treatment which produces injurious 
 effects in steel is punching holes into the plates. The experiments 
 on the subject are too numerous to be mentioned here, but many of 
 them will be found in the chapter on ' Mechanics/ under * Riveted 
 Joints/ p. 219. The thickness of the plate, the diameters of the 
 punch and die, as well as the hardness and chemical composition of 
 the plate, affect the pliability of such samples. It has been found 
 that rimering out yV in. of the holes removes all bad effects ; but if 
 it is true, as stated by Mr. Beck-Gerhard (' Gorni J./ 1884, p. 347), 
 that the curves of stress slowly extend at least 5 ins. away from the 
 hole, then punched plates ought to be annealed or rimered at once. 
 This experiment was as follows : A -f -in. plate was polished on one 
 side and punched (in a cold atmosphere). Spiral curves then showed 
 themselves, which were first washed with aqua regia. The piece 
 was then planed into several strips and each tested, when the spiral 
 curves reappeared and were perceptible to the touch. 
 
 This may explain the curious curved markings near punched holes 
 and sheared edges. In every one of these lines the surface scale has, 
 
152 STEENGTH OF MATEEIALS 
 
 fallen off, showing that here stresses have been at work producing 
 local deformations of at least / , for it is only after steel has been 
 stretched this amount that the mill scale falls off the plates. Illus- 
 trations of similar effects will be found in Kirkaldy's works. (See 
 p. 153.) 
 
 Modulus of Elasticity. On loading a test piece it will be noticed 
 that for steel and iron the elongation is almost proportional to 
 the stress, being at the rate of TT j^ in. in 10 ins. for about every 
 1*3 ton per square in., from which it follows that the modulus of 
 elasticity is about 13,000 tons, or 30,000,000 Ibs. per square in., or 
 20,000 kils. per square millimeter. With cast iron and various other 
 metals there seems to be a change in this modulus when the stress is 
 increased beyond a certain point, and some people have called this 
 the limit of elasticity, but a better name is limit of proportional 
 elongation. The more accurate the strain indicators are, the more 
 gradual does this change appear, and the obvious conclusion is that 
 with these metals the modulus of elasticity is a variable quantity, 
 growing smaller as the stress increases. It also decreases about 1^ 
 per cent, for every 100 F. rise of temperature (see H. Tomlinson, 
 ' Phys. S.,' 1887, vol. viii. p. 171). 
 
 Elastic Limit. It will be noticed that the pointers of the strain 
 indicators oscillate slightly for every newly added load, coming to 
 absolute rest only after a very long period. But when a certain 
 stress has been reached this action ceases and the pointers acquire a 
 slow onward motion. The elastic limit has now been reached, and 
 to verify whether this is so or not, several or all of the weights are 
 removed, and the pointers will either return to the positions 
 previously occupied or not. This check is necessary, as the giving 
 way of the attachments of the test pieces sometimes produces 
 strange effects, and may even cause one of the pointers to travel 
 backwards. For this reason also the determination of the elastic 
 limit should always be made with the help of three strain indicators. 
 Mild steel shows an elastic limit of about 15 tons. If very mild and 
 previously tempered it is sometimes as low as 10 tons, but in such 
 cases it is hardly perceptible and no breakdown point can be noticed. 
 
 Breakdown Point. Continuing the straining of properly annealed 
 samples, a point will be reached when the slow motion of the pointers 
 gives way to a very rapid one, which is not stopped even by reducing 
 the stress by several tons. This is called the ' breakdown point,' 
 because of the behaviour of the material, or the 'drop,' the lever 
 falling through a considerable angle. It has also been called the 
 limit of plasticity, because above this point the material behaves as if 
 it were plastic. This point is often mistaken for the limit of elasticity, 
 and the two points sometimes fall together. 
 
 Irregular Stretching. Even now it is of interest to watch the 
 strain indicator, for it will be found that the plastic elongation pro- 
 ceeds very irregularly. Generally after adding a weight it commences 
 slowly, increases, and then diminishes, until at last no further 
 motion can be detected. Very often, particularly if only small 
 additions are made to the load at one time, the pointers vary their 
 speed repeatedly, increasing and diminishing their velocity several 
 times without any additional weights being added to the lever. This 
 seems to be due to local elongations taking place, particularly in 
 
STRENGTH OF MATERIALS 153 
 
 long and thin test pieces, first at one point and then at another. A 
 recently tested bar, f in. square, showed four contractions in addition 
 to the fracture in a length of 10 ins. 
 
 Irregular Elongations. An explanation will suggest itself if 
 several (say, four) short strain indicators are attached along the length 
 of the sample, for it will then be noticed that first one and then the 
 other span is elongating, showing that waves of plasticity pass along 
 the samples. This may also be noticed when the breakdown point is 
 reached, for then the mill scale falls off, first at the extremities, and 
 then more towards the centre. The scale falls off when the stretch 
 exceeds i % of the length. 
 
 The same phenomena, but more marked, may be noticed when 
 twisting wire in a torsion machine. Instead of proceeding uniformly, 
 it will be noticed that the twist commences at one end (fig. 115), and 
 that, like a wave, it travels to and fro till the sample breaks. 
 
 Fm. 115 
 
 Changes in the Limit of Elasticity. The next point to be noticed 
 in a test piece is that when once the elastic limit has been passed, and 
 the sample then unloaded, it will not again elongate permanently 
 until the previous stress has been reached. This is only natural, for 
 the second testing is but a continuation of the first, and it is not 
 difficult to accept the statement that the elastic limit of a sample is 
 raised by preliminary testing. 
 
 E. EL. Thurston, 1883, p. 601, has suggested that this behaviour 
 would enable one to detect whether a broken structure had been 
 overstrained. A test piece would have to be carefully cut from the 
 plate and its limit of elasticity determined. Unfortunately experi- 
 ments show that, even with the most careful handling during prepara- 
 tion, the elastic limit of the test piece has again fallen to its original 
 value, or perhaps the shock of the rupture has produced this effect. 
 
 Influence of Time. The test piece under consideration could now 
 be stretched till it has elongated 5 %, which will raise the stress to 
 about 25 tons. It may then be left in the machine overnight with 
 the full load on it, or it may be put aside for a day or two. On 
 re-testing it will be found that the elastic limit has risen considerably 
 above 25 tons, which was the last stress to which it was subjected. 
 
 The following experimental results will illustrate this : 
 
 Sample No. 1 
 
 Elastic limit 
 Ultimate strength .... 
 
 19-3 
 29-7 
 
 tons 
 tons, 
 
 20-1 
 
 % elongation 
 
 
 Sample No. 2 
 
 First elastic limit .... 
 Then loaded to .... 
 Second elastic limit .... 
 Ultimate strength .... 
 
 16-3 tons 
 24-6 tons, 
 28-5 tons 
 29-8 tons, 
 
 5-2 < 
 
 after 
 17 $ 
 
 Yo elongation 
 an interval of 
 'o elongation 
 
 10 days 
 
154 STRENGTH OF MATERIALS 
 
 A long list of experiments on this subject by Bauschingei is 
 contained in ' Civil I.,' 1881, vol. xxvii. p. 1 ; also ' Mitt. Munich,' 
 1886, vol. xiii. 1891, vol. xx. He investigated the behaviour of 14 
 samples of iron and steel, and also copper and gunmetal. Unlike 
 the author's experiments, none of his showed an increase of elastic 
 limit beyond the ultimate strength of the material, but even with him 
 the influence of time in raising it is very marked. With copper and 
 gunmetal the elastic limits only rise as high as the preliminary stress. 
 In all these cases the second elastic limit and breakdown point 
 fall together, and the drop is now very much greater than with an 
 annealed sample. 
 
 The question naturally arises, What would happen if the sample 
 had first been subjected to a compression test ? This experiment has 
 also been carried out, and it was found that the elastic limit for tension 
 had been reduced from 19'3 and 16'3 to 11-8 tons, and the ultimate 
 tenacity raised to 30'7 tons, elongation 7'2 %. 
 
 A preliminary compression stress at right angles to the axis of the 
 sample (produced by drawing it out under a hammer) raised the limit 
 to 20'5 tons. This also increased the tenacity to 32 tons, and reduced 
 the elongation to 12 %. 
 
 These experiments readily suggest that, as the elastic limit is a 
 changeable value, it cannot be a reliable measure of the working 
 strength of a material. When a preliminary test has raised the 
 elastic limit considerably it may be dangerous to repeat it, because if 
 the new elastic limit is accidentally exceeded a very considerable 
 breakdown occurs, which may lead to rupture. Those parts of a 
 structure which have been subjected to excessive compression stresses 
 should not be exposed to severe tension stresses, as their elastic limits 
 of tension have been lowered and their ductility reduced. The reverse 
 is also probably true. 
 
 FIG. 116 FIG. 117 
 
 Contraction of Test Pieces. Continuing to follow the behaviour of 
 a test piece, and this time until fracture takes place, it will be found 
 that some materials, such as hard steel, manganese steel, bad iron, 
 and gunmetal, show no contraction previous to rupture, while mild 
 steel, iron, and brass and copper, do. The reasons for this contraction 
 are not known. It has been suggested that contraction is due to local 
 weakness, so that those metals which contract most are least uniform 
 as regards tenacity ; but if that were the case tensile tests with drilled 
 samples would be very irregular, according as to whether the hole 
 was near a weak or a strong place. The following experiments on a 
 mild steel plate whose tenacity wa 28 tons show that this is not the 
 case : 
 
 The samples were shaped as shown in figs. 116, 117. Thickness 
 of plates | in. ; diameter of hole 1 in., drilled, 
 
STRENGTH OF MATERIALS 
 
 155 
 
 (See also E. Richards, ' I. and S. I.,' 1882, p. 43.) 
 Another suggestion is, that the rise of temperature of a test piece 
 weakens the part which first contracts more than the others which 
 have accidentally not contracted. Dr. J. Kollmann's experiments 
 (' Ver. Gew.,' 1880, 2nd ser. vol. lix. p. 104) confirm this, for there it 
 will be found that the contraction steadily increases from about 20 % 
 at an ordinary temperature to 90 % at a red heat. Unfortunately for 
 this view the tenacity does not show the same regularity. An explana- 
 
 Brea 
 Bj. Inches 
 
 dth 
 B a Inches 
 
 TJlt. Strength 
 
 Tons per Square Inch 
 
 1-85 
 
 ... 
 
 30-1 
 
 1-25 
 
 ... 
 
 30-5 
 
 71 
 
 ... 
 
 30-3 
 
 ... 
 
 53 
 
 29-6 
 
 49 
 
 
 30-5 
 
 ... 
 
 43 
 
 29-8 
 
 >> 
 
 33 
 
 29-1 
 
 <> 
 
 28 
 
 28-6 
 
 t 
 
 23 
 
 30-5 
 
 , 
 
 18 
 
 28-7 
 
 
 13 
 
 28-9 
 
 
 
 075 
 
 28-6 
 
 FIG. 118 
 
 tion of this phenomenon is, therefore, still required. The subject will 
 be referred to again when discussing compound stresses. 
 
 Fractures. The next thing to be noticed in a fractured test piece 
 of mild steel is, that when placed together only the edges touch, leaving 
 a hollow, as shown in fig. 118. There can be but 
 one explanation, viz. that the rupture started near 
 the centre of the section, and that the outside fibres 
 continued to stretch after this point was reached. 
 This suggests the view that the stresses to be found 
 in the centre of a test piece differ from those on the 
 outside surfaces, and are also more injurious. An 
 examination of almost any torn sample of mild steel 
 will show that near the edge the surfaces of rupture are very much on 
 the slant and have every appearance of having been produced by 
 partial shear, suggesting the idea that this material gives way more 
 readily under shearing stress than under tension (see pp. 163). 
 
 The same tendency is noticed when tearing a sample perforated as 
 in fig. 119. The lines of fracture, instead of running as horizontal as 
 possible, will be distinctly steeper than the 
 angle at which the holes were drilled. 
 
 A few other matters which have been 
 noticed in fractures are : White specks, which 
 are due to a local excess of phosphorus and 
 other impurities (Stubbs, ' I. and S. I.,' 1881, 
 p. 379; H. Eccles, ibid., 1888, p. 72; 
 Prof. Ledebur, ' Stahl und Eisen,' 1889, vol. 
 ix. p. 13). A smell of ammonia, said to be 
 due to occluded nitrogen, is sometimes 
 noticed ; the colour also varies from bluish 
 
 FIG. 119 
 
 grey to salmon-colour tints or yellow ones. 
 
156 
 
 STBENGTH OF MATEEIALS 
 
 Shearing Stresses. The investigation of shearing stresses is beset 
 with various difficulties, one of the most important being the smallness 
 of the strains. Direct experiments have therefore only been useful in 
 determining the ultimate shearing strength of various materials. 
 
 c 
 
 y 
 
 FIG. 120 
 
 FIG. 121 
 
 It has been found that the hardness of the metal into which the 
 holes are drilled influences the results. It is therefore usual to groove 
 the samples to be tested as shown in fig. 120. Most experiments on 
 riveted joints include some carried out as above, and the general 
 conclusion is that the shearing strength is less than the tensile 
 strength. 
 
 More interesting results are obtained if the material is exposed to 
 torsion stresses. One end of a cylindrical bar is secured to the head of a 
 lathe, while the other end is supported, if possible, on a knife-edge, and 
 carries a lever, which is gradually loaded while the lathe head is being 
 turned round. The twisting of the bar is measured with the help of 
 a pair of mirrors m,, w 2 , arranged as shown in fig. 121. A graduated 
 scale is placed at a considerable distance from the test piece, and ex- 
 amined partly direct (x), and partly by doubly reflected light (y). Two 
 scales instead of one are then visible through the telescope T, and it 
 is their relative displacement which measures the angular deflection. 
 This arrangement has been devised by the author and has proved to 
 be very accurate. 
 
 By plotting down the readings, curves are obtained, which may be 
 called torsion diagrams, and represent the amount of twist which 
 various torsion moments impart to a test bar. It is usual to reduce 
 all these values so as to obtain the shearing stresses of the outside 
 fibres and their angular displacement. 
 
 The latter value is found by multiplying the angle of twist into 
 half the diameter of the bar, and dividing by the distance of centres. 
 
 The shearing stress of the outside fibre is found by the formula 
 
 16. M 
 
 Here M is the torsion moment, and d is the diameter of the bar. This 
 formula is only correct as long as the moments are strictly proportional 
 to the twist ; where this is not the case, and particularly when the 
 limit of elasticity is passed, or the point of rupture reached, it gives 
 wrong results. 
 
 The actual shearing stress a- in the outer fibre is then found as fol- 
 lows : Let the heights of the line O B C (fig. 122) represent the distri- 
 
STRENGTH OP MATERIALS 
 
 157 
 
 bution of the circumferential shearing stresses over the radius of a bar 
 whose diameter is d = 2r, and which has been twisted through an angle 
 in a length I, while the torsion moment is M. The sheer angle is p. 
 
 D C represents the sheering stress in the 
 outer fibre. Now if a thin film of metal, of the 
 thickness dr, be machined off the circumference 
 of the bar, and if it be twisted once more, till 
 the stress in the (now reduced) outer fibre is again 
 equal to D C, then, as the new curve O P C is 
 similar to, but shorter than, the original one, the 
 new twisting moment Mj will have to be some- 
 
 (r - dr)* 
 
 < 
 
 FIG. 122 
 
 what weaker than M, viz. M l = M . 
 
 7 ~ 
 
 while the angle 6 has increased from to + dO 
 
 = . L_. Now let a film of material, of the thickness dr, be placed 
 
 round the bar, so that it is ones more equal to its original dia- 
 meter, 2r. Let this outer film be twisted till it has acquired a stress of 
 
 4 
 
 10000 20000 30000 
 
 Shearing stresses per square inch 
 FIG. 123 
 
 40000 
 
 50000 
 
 0-4- -? -', then the torsion moment of the film is f + -^f\ %irr 2 dr. 
 The second term in the bracket is negligible and it follows that 
 
 which formula can easily be converted into <r = J<r + 
 
 16M : Trd 3 . 
 
 The way to construct a curve which will show the actual shearing 
 stress <r of the outside fibre, when the value <T O has been previously 
 
158 
 
 STRENGTH OF MATEKIALS 
 
 determined, can be carried out as shown in fig. 123. The line <r o is 
 copied from Platt and Haywards's paper (' C. E.,' 1887, vol. xc. plate 
 10, fig. 6). The faint tangential lines have been drawn to measure the 
 
 value -^5. The line fcr o has been constructed by proportional re- 
 duction, and to this has been added the respective values of -=-^, 
 
 with the help of which the curve o- has been constructed. The experi- 
 menters state that for this particular sample the elastic limit of shear- 
 ing stress was 46,400 Ibs. ; but an examination of the curve a- shows 
 that it was already reached at 35,000 Ibs., and that at 38,000 Ibs. a 
 very serious drop took place, and the material of the outside fibre 
 had not recovered even when the shear angle had increased to |. 
 Beyond this point it is always sufficiently accurate to adopt the value 
 
 o- = f = o- = '= , That this is fairly correct will be seen from 
 
 7T . d 
 
 the following experiments on tension, torsion, and direct shear (Platt 
 and Haywards, ' C. E.,' 1887, vol. xc. p. 408) : 
 
 Materials 
 
 Limits of Elasticity 
 
 Eatio 
 2: 1 
 
 (3) 
 
 . Ultimate Strengths 
 
 Tension 
 (1) 
 
 Estimated 
 from 
 Torsion 
 
 T-^I* 
 
 ird 3 
 (2) 
 
 Tension 
 (4) 
 
 Estimated 
 from 
 Torsion 
 
 a=l^M 
 
 ird 3 
 
 (5) 
 
 Ratio 
 5 :4 
 
 (6) 
 
 Experi- 
 mental 
 Shear on 
 Rivets 
 
 (7) 
 
 Ratio 
 7:4 
 
 (8) 
 
 Wrought iron 
 
 Bessemer st el 
 Crucible 
 Cast 
 Siemens 
 
 Mean ! ! 
 
 Tons 
 15-04 
 16-82 
 17-13 
 31-14 
 31-06 
 17-22 
 17-85 
 16-82 
 
 Tons 
 8'99 
 10-36 
 10-22 
 20-28 
 19-36 
 10-40 
 10-20 
 10-16 
 
 8-70 
 5-40 
 
 0-597 
 0-616 
 0-597 
 0-651 
 0-627 
 0-604 
 0-571 
 0-507 
 0-609 
 0-777 
 0-745 
 
 Tons 
 21-60 
 25-00 
 24-56 
 52-20 
 52-16 
 38-04 
 28-40 
 25-75 
 
 25-46 
 13-68 
 
 Tons 
 17-63 
 20-20 
 20-65 
 31-25 
 29-65 
 24-30 
 20-90 
 19-70 
 
 18-26 
 11-06 
 
 0-816 
 0-809 
 0-841 
 0-599 
 0-568 
 0-639 
 0-736 
 0-765 
 0-722 
 0-717 
 
 0-809 
 
 Tons 
 18'76 
 21-21 
 20-72 
 35-21 
 33-30 
 27-60 
 23-00 
 21-05 
 
 18-60 
 12-47 
 
 0-869 
 0-849 
 0-844 
 0-675 
 0-639 
 0-726 
 0-810 
 0-818 
 0-779 
 0-731 
 
 0-917 
 
 Muntz metal 
 Gunmetal \ 
 Cu 64, Sn 8, Zn 2 / 
 
 11-20 
 7-25 
 
 For additional references, see p. 163. 
 
 These, D. Kirkaldy's, and some similar experiments by G. Berkley, 
 1868 ,V. Appleby (' C. E./ 1883, vol. Ixxiv. p. 268), the latter including 
 compression tests, are apparently the most exhaustive ones that have 
 yet been made to ascertain the relation which exists between compres- 
 sion, tension, and shearing stresses. 
 
 The latter are certainly always smaller than either of the two 
 former, amounting to from 50 to 90 %. 
 
 Torsion tests carried out on bars from which the black scale had 
 not been removed showed that it falls off when the limit of elasticity 
 is reached, but even then only along a few axial lines, which implies 
 that the elastic limit and breakdown point fall together. 
 
 Bending Stress. After the foregoing it will be unnecessary to 
 analyse the behaviour of beams subjected to stresses beyond their 
 elastic limit ; suffice it to say that as the limits of elasticity of the top 
 and bottom fibres are not necessarily reached at the same time, it is 
 impossible to separate the one from the other ; but, assuming that they 
 
STRENGTH OF MATERIALS 
 
 159 
 
 did agree, then the stress in the outside fibre of a narrow, rectangular 
 bar would be found by the following formula : 
 
 S = -^r (-JM + C ) Here c stands for curvature. 
 
 From an examination of fig. 124, which represents a beam subjected 
 
 to an excessive load, Q, it is evident that -^ = Q, and, by carefully 
 
 measuring the various curvatures and changes of curvatures of such a 
 
 sample, it would be possible to construct a strain stress diagram with 
 
 the help of the following formula : 
 
 It must not be forgotten that p, the 
 radius of curvature, grows smaller with 
 
 increasing x, and that ~ is negative. 
 dx 
 
 As in the case of torsion experiments, 
 the second term in the bracket is very 
 small when the point of rupture is 
 reached, and to estimate the ultimate 
 strength of a plastic material, including cast iron, but not glass or 
 other brittle substances, it is sufficiently accurate to use the formula 
 
 S 
 
 4.Q.Z 
 
 This is 33 % less than obtained by the generally accepted elastic 
 formula, and accounts for the fact that beams are apparently so much 
 stronger than they should be. 
 
 Compound Stresses. It has already been pointed out that the 
 elastic limit and ultimate strength of a material are very much less in 
 shear than in tension, or in compression. But it is wefl known that 
 a shearing stress is composed of a tension and a compression stress, 
 each of equal intensity, as shown in fig. 125, and it is therefore of 
 importance to ascertain what other compound stresses exist. 
 
 There are, firstly, the simple stresses, (I.) tension, and (II.) com- 
 pression. 
 
 A combination of two of these acting at right angles produces a 
 (III.) shearing stress (fig. 125). 
 
 FIG. 125 
 
 FIG. 126 
 
160 
 
 STRENGTH OF MATERIALS 
 
 IV. Two equal compression stresses are met with chiefly in rail- 
 way axles when the wheel boss has been shrunk on them. This 
 combination might be called a shrinking or strangling stress, to 
 distinguish it from a compression stress, which acts only in one 
 direction. (See fig. 126.) 
 
 V. The reverse of this stress might be called drum tension (fig 
 127), as it is best represented by that case ; it is also met with in 
 thin spherical shells subjected to internal pressure. (See also p. 191 ) 
 
 By adding stresses at right angles to the planes in which the last 
 two are acting four others are obtained. 
 
 VI. Fluid Pressure (fig. 128). In this case there are only com- 
 pression stresses. If they are all changed into tension stresses we get 
 a combination which might be called (VII.) negative fluid pressure, 
 or solid tension (fig. 129). 
 
 FIG. 127 
 
 FIG. 128 
 
 VIII. When two of the stresses are compression, and the other 
 one tension, we have the case of wire-drawing. This might be called 
 a draw stress (fig. 130). (See p. 142.) 
 
 IX. By combining two tension stresses with one compression we 
 reproduce a condition which is found on the inner spherical surfaces of 
 very thick- walled exploding shells. This might be called a bomb stress 
 (figs. 131 and 181). Of the last six combinations there is only one 
 
 FIG. 129 
 
 FIG. 130 
 
 FIG. 131 
 
 about which anything definite is known, and that is that no material, 
 however weak it may otherwise be, has been destroyed by fluid pressure, 
 however great. 
 
 Solid tension (or negative fluid pressure) does not occur in prac- 
 
STRENGTH OF MATERIALS 
 
 161 
 
 tice, but the following two cases are an approach to this condition. 
 If a solid sphere is heated to redness, and then plunged into cold water, 
 the outer surface solidifies while the centre is still red hot. The exter- 
 nal diameter will be somewhat larger than it would have been if cooled 
 slowly ; and when the centre has grown cold, a tension will be found 
 there acting in every direction which may result in clinks in forgings, 
 i.e. violent internal fractures. In large masses of steel this tension 
 even comes into existence while the centre is still red hot, and cavitiea 
 are formed, to prevent which ingots are never cast circular, but square 
 or of polygonal shape, so that the sides may collapse. Of course it 
 it impossible to estimate the stress which has produced these holes. 
 
 A somewhat similar stress is found at the point of contraction of 
 test pieces (fig. 132) when of a circular section. The sample is being 
 stretched in the direction of the arrows, I, I, and the lines of force, s, s, 
 will adapt themselves to the fibres, at any rate at the circumference, 
 and there their curved shape will produce radial tensions, as indicated 
 by the looped arrows (fig. 133), so that at the centre of the smallest 
 section there exists a tension in every direction. 
 
 This might explain why with mild steel, where there is consider- 
 able contraction of area, the fracture starts at the centre, the material 
 being less able to withstand a solid tension than a simple one, as at 
 the circumference of the fracture. A careful analysis of the distribu- 
 tion of stresses produced by the load at the instant of rupture will 
 
 FIG. 132 
 
 FIG. 133 
 
 perhaps enable one to obtain numerical values for different materials. 
 Thus, it is not unusual for the contraction to exceed 50 %, and if the 
 load at rupture was 80 % of the maximum, or, say, 24 tons per square 
 in. instead of 30, the average stress in the reduced section must have 
 been 48 tons ; and when this is combined with the drum tension, due 
 to the shape, which also exists there, it is not unreasonable to assume 
 that the sample only gave way to a solid stress whose components 
 amounted to from 96 to 144 tons. Hard cast steel will not resist 
 these compound stresses without rupture, and therefore does not con- 
 tract ; and it might even be questioned whether for compound stresses 
 this material is as strong as the milder qualities. 
 
 Becently Mr. J. J. Guest (' Phil. Mag.,' July 1900, p. 70) has in- 
 
 M 
 
162 
 
 STEENGTH OF MATERIALS 
 
 vestigated this subject by experimenting on steel, brass, and copper 
 tubes. These were placed in a tensile testing machine and had 
 attached to them other appliances, so that stresses by tension, torsion, 
 or fluid pressure could be produced both singly and combined. Each 
 tube was tested over and over again, but only up to its elastic limit. 
 These and a few other tests suggest that a material breaks down, 
 not exactly when a certain limit of stress is passed, but when the 
 difference between any two of the three principal stresses, all acting 
 at right angles to each other, exceeds a certain limit. Thus as there 
 is no fluid pressure round an ordinary test piece, the tensile stress 
 is also the difference between itself and the cross stresses which are 
 nil. In wire drawing there is a circumferential pressure, equal to 
 two very severe cross stresses and a longitudinal pull, and as the 
 difference between a tension in one direction and a pressure in another 
 is the sum of the two stresses, the material gives way when this sum 
 reaches a certain limit. A shearing stress of the intensity or is a com- 
 
 FIG 133a 
 
 pound of one tension stress, + o-, acting across one compression stress, 
 - <r, and mild steel subjected to this compound stress break down 
 when a- is about one half of the tensile limit of elasticity. This re- 
 lationship is illustrated in fig. 133a by the dotted polygon marked 
 G . . . G. One principal stress is marked off horizontally from the 
 vertical line, and the other is marked off vertically from the horizontal 
 line. If the two stresses intersect outside the polygon, the material 
 breaks down. In fig. 133a, the lines SS represent characteristic 
 
STRENGTH OF MATERIALS 163 
 
 boundary curves for mild steel, they do not differ materially from 
 Guest law as represented by the polygon, but cast iron, marked CO, 
 has a totally different curve ; and marble, marked MM, differs from 
 both. So that with our present limited knowledge about compound 
 stresses it is safer not to believe in empyrical relations, but to assume 
 that each material has a characteristic curve of its own. According 
 to Guest's law cast iron should be weaker than mild steel both as 
 regard tension, compression, shear drum tension and strangling stress, 
 but if SS and CC correctly represent the properties of these two 
 materials, and if two hollow spheres of identical dimension were made, 
 one of cast iron and the other of steel, the former would be the 
 weaker under internal pressure, resulting in drum tension, while 
 the other would be weaker under external pressure, resulting in a 
 strangling stress. The curve marked MM reproduces the results 
 obtained by Th. v. Karman (' Deut. Ing.,' 1911, p. 1749). He sub- 
 jected a cylinder of marble to a circumferential pressure, equivalent 
 to two equal compressions which in fig. 133a meet on the diagonal, 
 and in addition he loaded the cylinder axially with a third compression 
 stress which is indicated by the curve MM. It will be seen that the 
 higher this axial stress the higher may be the two other stresses. 
 Other investigations into this matter are to be found as follows : 
 E. L. Hancock and W. E. Williams ( Phil. Mag.,' 1906, v. 12, p. 418, 
 etc., and 1908, v. 15, p. 81, etc.). Prof. Voigt (' Wied. An.,' 1894, v. 53, 
 p. 43; 1899, v. 67, p. 452). 
 
 The above-mentioned results with mild steel are to a certain 
 extent confirmed by some very interesting experiments on flat un- 
 stayed plates which were subjected to various pressures and very 
 carefully gauged by Prof. C. Bach ('Deut. Ing., 1 1897, p. 1158, etc.). 
 
 These plates, five in number, were made of mild steel of 24'5 tons 
 tenacity, with a limit of elasticity of 10*5 tons in tension and limit of 
 plasticity of 15 tons. They ranged from f to f in. in thickness. In 
 each plate the first permanent bulging occurred when the tension and 
 compression stresses in the centres of the plates, as calculated by 
 the author from the acquired curvatures, had reached from 7,000 to 
 8,000 Ibs. (7,650 Ibs. mean). This is almost exactly 30 % of the 
 limit of elasticity of tension. Now these experiments do not show 
 whether this giving way was due to V. p. 159, ' drum tension ' on the 
 outer surfaces of the plates, or to IV., ' strangling stresses ' on the 
 inner surfaces. Nor do these experiments show the drum tension 
 due to the expansion of the shell. This shell plate was J in. thick 
 and 28 ins. diameter. Its enlargement would tend to increase the 
 drum tensions (see p. 159) and reduce the strangling stresses, but 
 this influence would hardly affect the stresses by more than 10 %. 
 Should it be shown that this steel gave way at 7650 -f 765 = 8415 Ibs. 
 . drum tension, then the result is in direct conflict with Mr. Guest's 
 experiments, which show that with his harder steel the limit of elas- 
 ticity for ' drum tension ' may be in excess of that for simple tension. 
 Possibly it will one day be shown that the plates gave way under 
 a strangling stress of 7650 765 =-6885 Ibs. i.e. at one-third of the 
 elastic limit for tension, and that therefore a strangling stress is 
 severer on mild steel than a shearing stress. 
 
 The nature of fractures of different materials indicates that they 
 
 M2 
 
164 STRENGTH OF MATERIALS 
 
 do not all behave in the same way under compound stresses. Thus 
 mild steel tension fractures are always much inclined to the axis 
 except near the middle, whereas for hard steel the fractured surfaces 
 are normal to it and crystalline. Under torsion stresses mild steel 
 fractures are normal to the axis, while hard steel fractures show a 
 helical surface. Apparently mild steel yields with comparatively 
 greater ease to shear than to tension, whereas hard steel is more 
 easily torn than sheared. For this reason it is useless to speculate 
 on the discrepancies between Platt and Hargraves and J. J. Guest's 
 ratio of tensile and shearing strengths. 
 
 Further experiments dealing with this very interesting subject are 
 urgently required. 
 
 Until experiments have been made to determine the permissible 
 compound stresses, it would be useless to speculate as to their action, 
 but enough has been said to show that we are as yet groping in the 
 dark. It is even impossible to say whether a spherical boiler end may 
 be made half as thick as the cylindrical shell ; for although theory 
 shows that the stress is only one-half, it also shows that there are two 
 equal stresses, which have been called drum tension. 
 
 Fatigue. Boiler plates, except perhaps in locomotives, are not sub- 
 jected to innumerable rapid changes of stress called fatigue stresses, 
 but as the subject has a direct bearing on the lasting properties 
 of materials it requires a brief mention. It is believed, but experi- 
 ments on this subject are still too few for drawing definite conclusions, 
 that if a material be subjected to a large number of varying stresses, 
 it will break down if the difference between the high and the low 
 stresses exceeds a certain limit, no matter what the individual stresses 
 may be. Wohler was the first to make exhaustive experiments on 
 this subject, but until recently no satisfactory law of fatigue had 
 been established, and some of the early deductions are not reliable. 
 The author has shown ('C.E.,' v. 188, p. 38, and M. E.,' 1911, III., 
 p. 887) that the following relation exists. S = L + C J/TTw where 
 L is the elastic limit of fatigue, C is a constant and n is the number 
 of stress cycles (revolutions) of the intensity + S which a material 
 will stand before it breaks. The value of C varies considerably for 
 different materials both absolutely and relatively to L. L also varies 
 from say 12 to 16 for mild steels, to 20 and even 25 for hard steels. 
 Hardening either cast steel or mild steel does not seem to affect this 
 limit materially. The subject, although of extreme importance to 
 engineers generally, is of no direct importance to boiler makers 
 unless, as may be possible, fatigue tests should be able to give more 
 reliable information about the quality of materials than do the present 
 tests. 
 
165 
 
 CHAPTEK VII 
 MECHANICS 
 
 AN understanding of stresses first became possible when the laws 
 of elasticity began to get known, but since then the subject has had 
 such fascination for mathematicians, that it is now difficult for men 
 with little leisure to follow their investigations, even although they 
 have been most admirably collected and edited by Mr. K. Pearson 
 (J. Todhunter and K. Pearson). Unfortunately, too, these volumes do 
 not give the results of researches in such a form as to make them 
 of value to practical men. The matter is unquestionably a compli- 
 cated one, as can be seen by the few formulae in this chapter, most 
 of which it has been found impracticable to work out in detail, 
 although the necessary hints or references are given. One object of 
 going into these matters is to place in the hands of engineers the 
 means of analysing and criticising the various restrictive rules 
 which from time to time are evolved ; the other and more important 
 object is to place in the hands of engineers the means of analysing 
 experiences and experiments notably for ascertaining the stresses 
 when the strains or deformations have been measured. Attention 
 has therefore been paid to the relation between stresses and strains, 
 and as a consequence Poisson's ratio has often to be mentioned. Most 
 text-books content themselves with dealing with elastic deformations, 
 but in boilers, where plates sometimes grow red hot and plastic, and 
 also in all experiments where the metal ruptures, it is of importance to 
 bear in mind that we are not dealing with a purely elastic material, 
 and that factors of safety which are based on ultimate strength are 
 not all of the same standard. For this reason some remarks will be 
 made about plasticity and ultimate strengths. 
 
 Elasticity. The elasticity of solids as revealed by extensometers 
 attached to test pieces has already been dealt with. On boilers and 
 other solid structures these instruments would also reveal deformation 
 when pressures are applied, and the deformations would be measures 
 of the stresses to which the structures are subjected, provided that the 
 conditions are properly analysed, which, as will be seen from the few 
 formulae in this chapter, are but a small fraction of the formulas to 
 be found in text books on elasticity, is not always an easy matter. 
 Unfortunately, too, the few formulas on this subject which find their 
 way into pocket books are generally deficient in so far as they ignore 
 Poisson's ratio, which, as will be seen later on, affects the deforma- 
 tions of plates, and of structures subjected to compound stresses. The 
 modulus of elasticity will here be denoted by the letter E expressed 
 in pounds per square inch. 1 : E is the elongation or shortening of a 
 bar at a unit of length when subjected to a unit of stress. 
 
166 
 
 MECHANICS 
 
 Shearing Elasticity. It has been explained in connection with 
 fig. 125, that a shearing stress is a compound of tension stress and 
 compression stress. The shearing elasticity is the angular displace- 
 ment of the two diagonals as compared with the shearing stress 
 producing it. As the cross contraction due to the tension stress has 
 to be added to the contraction stress and vice versa, it is evident that 
 under this compound stress the material is more elastic and the 
 modulus of shearing elasticity a- is smaller than E, the correct formula 
 
 i ^n nnn nnn 
 
 being a- = E . A = - ' "' - = 11,600,000 Ibs. per sq. inch. 
 
 + 
 
 3 
 
 . 
 
 Experiments on this subject are to be found in the following 
 
 publications : Bauschinger, ' Civil Ing.,' 1879, vol. 25, p. 81 ; E. H. 
 Amagat, ' Comp. Bend.,' 1888-9, vol. 107-108; C. E. Stromeyer, 
 'Proceed.,' 1894, vol. 55, p. 377; J. Morrow, 'Phil. Mag.,' 1903, 
 vol. 6 ; J. B. Benton, ' Physical Beview,' 1901, vol. 12 ; P. Cardani, 
 ' Physicalische Zeitschrif t, ' 1903, vol. 6 ; E. Griineisen, ' Wied. Ann.,' 
 1908, vol. 25, p. 825. 
 
 The elastic constants for the more important metals and a few 
 others are contained in the following table : 
 
 Modulus of Material 
 
 Elasticity = E 
 Tons Per Sq. Inch 
 
 Shearing Elasticity 
 = E 
 Tons Per Sq. Inch 
 
 Poisson's 
 Ratio - 1 
 
 M 
 
 Wrought Iron \ from 
 
 13,000 
 
 4,500 
 
 1 O.QI 
 
 Mild and Hard Steel/ to 
 
 13,800 
 
 5,300 
 
 j- U Ol 
 
 Grey Cast Ironj^ 0111 
 
 4,500 
 8,000 
 
 
 
 
 
 Gun-metal, about 
 
 5,250 
 
 1,900 
 
 0-36 
 
 Brass, about . 
 
 5,000 
 
 1,700 
 
 0-35 
 
 Copper, about 
 Nickel, about . 
 
 8,300 
 13,000 
 
 3,000 
 5,000 
 
 0-34 
 0-31 
 
 Aluminum, about 
 
 4,600 
 
 1,700 
 
 0-34 
 
 Magnesium, about 
 
 2,600 
 
 1,000 
 
 
 
 Glass, about . 
 
 4,500 
 
 
 
 
 
 Flexibility, or bending elasticity, is best reduced to E. As will 
 shortly be explained, here also the co-efficient of cross contraction has 
 an important influence. 
 
 Plasticity. The elastic limit and breakdown point have already 
 been explained (p. 152). 
 
 Resolution of Stresses. Investigations in statics show that several 
 forces acting through one point can always be replaced by a single 
 resultant, and similarly several stresses can be replaced by resultants ; 
 but there will be three instead of one, unless they are all acting 
 parallel to one plane, and in that case there will be two resultant 
 stresses as against one resultant force. To resolve stresses which 
 are irregularly distributed in space is a problem which need not 
 be discussed in this chapter, particularly as it leads to rather com- 
 plicated formulae (Bankine, ' B. Soc. Edinburgh,' vol. xxvi. p. 715). 
 
 The Resolution of Stresses parallel to one plane is comparatively 
 simple. 
 
 Let there be four stresses, a, b, c, d (fig. 134), acting in the direc- 
 tions a 1? a 2 , a 3 , a 4 . Double each of these angles and construct the 
 polygon A, a, b, c, d, B (fig. 135). The points A, B may then be 
 
MECHANICS 
 
 167 
 
 looked upon as the two foci of an ellipse, the sum of the radii vectores 
 A, a,, B being equal to the sum of the stresses. By halving the 
 angles 2^ and 2/5 2 , and drawing the stresses a, and' b } from a point 
 (fig. 136), a system of two resultants is obtained which would 
 
 Fio. 134 
 
 FIG. 136 
 
 FIG. 135 
 
 produce exactly the same strain as the four original stresses; but 
 they are not necessarily at right angles to each other. In order to 
 fulfil this condition, radii vectores ACB (fig. 135) will have to be drawn 
 parallel to the major axis, and as 2y 2 = 2y! + 180 the resultants 
 will be at right angles to each other, as shown in fig. 137. Their 
 intensities are represented by the lengths AC = x and CB = y. 
 
 The following is the algebraical solution of this question. 
 
 The notations are the same as in the figures. 
 
 As regards the angles we have 
 
 AB . sin 2y, =a sin 2, + b sin 2 2 + &c. 
 AB . cos 2y! =a cos 2a, + b cos 2a 2 + &c. 
 
 tan 2 7l =- 
 
 a cos 2^ + b cos 2 2 + &c. 
 
 Divide 2yj by 2 ; this determines y l \ and add 90, which is the 
 angle y 2 . 
 
 As regards the stresses we have 
 _ (a + b + &c.) AB _ 2(8) + 
 2 2 ! 
 
 (a + b 
 y-- 
 
 . sin 2a) 2 + (SS . cos 2a) 2 
 .sin2a) 2 + (5S.cos2a) 2 . 
 
 22 2 
 
 For a combination of two axial stress X(a = 0), Y(a = 90) with 
 one axial shearing stress o-(a = 45 C and 135) we have : 
 
 tan 2y = 2<r : (X - Y) ; x = $(X + Y) + ^(X + Y) 2 + <r* ; 
 . Y) - ^/J(X + Y) 2 + cr 2 
 
168 
 
 MECHANICS 
 
 If some of the stresses are positive and the others negative, i.e. 
 tension or compression, they should be placed in proper order in the 
 polygon (fig. 135). But then instead of an ellipse, a hyperbola will 
 be the boundary line. It can also be proved that there will only be 
 one resultant to several shearing stresses. Thus, if in fig. 134 they 
 are represented by a, b, c, d, the intensity of the resultant stress 
 would be AB (fig. 135) and its angle yj. 
 
 m 
 
 FIG. 137 
 
 Fio. 138 
 
 The Elastic Beam. When loaded at one end (fig. 138) the bending 
 moment of a beam, at the distance x from its attachment, is 
 
 m = Q . (I - x). 
 
 If the longitudinal stresses at this point vary from S at the bottom 
 fibres to + S at the top fibres, they combine to form a resisting 
 moment which is equal to m, which for a rectangular section is : 
 
 m 
 
 6 
 
 Here b is the breadth of the beam, and t its thickness. 
 round bar of the diameter d we have 
 
 For a 
 
 In flat plates b can be taken as unity, provided the pressures and 
 forces are measured per unit of width. 
 
 The Radius of Curvature p can be determined from the following 
 formula : 
 
 l_^d*y__ m __2.S 
 
 p dx 2 E.I J.E' 
 
 Here x and y are the co-ordinates of any point of the elastic line, E is 
 the modulus of elasticity, and I is the moment of inertia of the section 
 
 for a flat beam 1 in. wide). When -=$ is constant we have 
 Iz / ax 
 
 I = 
 
MECHANICS 
 
 169 
 
 Cross Curvature. Besides bending lengthways, the edges of the 
 beam tend to curl up (fig. 139) ; this is due to the cross contraction of 
 the upper side caused by longitudinal 
 tension, and the cross extension of the -tf 
 
 lower side caused by longitudinal com- :' 
 
 pression. If the radius of this cross J '_' 
 
 curvature be called p } , then 
 
 111 
 
 Pi P /* 
 
 where - is the co -efficient of cross con- 
 traction. In wide plates, which cannot 
 curl crossways when bent, or in such 
 bent plates as are constrained to re- FIG. 139 
 
 main flat crossways, it is evident that 
 
 there are internal or external forces at work reducing the cross 
 curvature to a straight line, viz. p t = oc, which again means that 
 there are cross stresses C due to bending : 
 
 2.pj 2./i.p 
 
 Also that the longitudinal bending has been reduced, and p has been 
 increased to p 2 - 11 i 
 
 P2 P M'Pl 
 
 The formulae for a wide beam which remains straight axially are : 
 1 2 / C\ 2.8 
 
 S = 
 
 Compound Curvatures. If the bent beam is not straight axially, 
 then the stresses, as estimated from the curvatures, have to be 
 combined as follows. Let the radii of the two curvatures be p l and p 2> 
 
 then, always assuming - = 3 we have : 
 
 E.J.1-1 E . *. 0-33 
 
 s ' = -a^-- and Ci = ~^r 
 
 0i _E^ M t>ndSi = E. a tJfrS8 
 
 BY addition we get : 
 
 S = S, + S 2 = E . t . 0-55 . ( + 
 
 = C, 
 
170 
 
 MECHANICS 
 
 If pa has the negative value ^- = 0.3 .p lt then C = and 
 
 H 
 
 Tjl j 
 
 S = - ' , as already found. 
 
 S =E.*.0-55.-; C=E. *. 0-165. 1; 
 
 Pi Pi 
 
 this has also been found. 
 
 If ps == + PI, as for instance in a flat end plate, when elastically 
 acquiring a spherical shape, 
 
 S = C= E.J. 0-715. t. 
 Pi 
 
 In this last case, where of course the two principal stresses are 
 equal, a drum tension exists on the convex side of the plate, and 
 a shrinking stress on the concave side (see p. 160) ; but, as the latter 
 will most likely injure the material more seriously than a simple 
 tension (see p. 163), it is very important that all measurements 
 of curvature made for the determination of stresses should be taken 
 both lengthways and crossways. Conversely, a case might occur 
 
 where p, = p 2 ; then S = =-^ . -., showing that the stresses 
 
 2 . p /u + 1 
 
 are smaller than usually supposed. Combined in this way the stresses 
 constitute a shearing stress of a very peculiar nature, being directed 
 in opposite directions on either side of the plate. This condition 
 is found to exist along the pitch lines of screwed stays, near the 
 centres of the pitches. The cross curvatures of beams naturally affect 
 
 their deflections, and in this fact is 
 to be sought the explanation why 
 these curvatures do not agree with 
 what (so-called) theory makes them 
 out to be. 
 
 Stresses in Flat Plates. The 
 formulae which would have to be 
 evolved in analysing these stresses 
 are very complicated, even when 
 dealing only with circular discs, 
 and as such results are of very 
 limited value for these investiga- 
 tions, and as analyses of square 
 and rectangular plates leave out of 
 account some important points, a 
 short explanation as to the methods 
 adopted is all that can be attempted 
 here. Fig. 140 is a section through 
 the centre of a circular disc of the 
 
 Fio diameter 2r and of the thickness t. 
 
 It is loaded with a pressure p over 
 
 its entire surface, and with a load Q spread over its circumference, 
 and is supported by a central stay. Certain strains and stresses 
 will be produced, which it is desired to determine. 
 
MECHANICS 
 
 171 
 
 Imagine the disc to be subdivided by a large number of radial 
 lines ; then one of the slices so formed could be represented by fig. 141. 
 Its angle is ft. It is probable that radial bending moments exist, and 
 if the maximum radial tension stress of the upper fibres at the distance 
 x is denoted by S the resisting moment will be 
 
 If now the disc is subdivided into a number of concentric cylinders 
 the thickness of whose walls is dx (figs. 142, 144), it will be found 
 that under stress they have lost their original cylindrical, shape, and 
 have grown slightly conical. Let this angle be a. It is clear that 
 
 \ 
 
 aoe 
 
 Fio. 141 
 
 Fio. 142 
 
 Fio. 143 *IG. 144 
 
 circumferential stresses exist in these rings, tension at the upper 
 surface, and compression at the lower ones. Let the maximum value 
 of the former be C. These stresses could also have been produced 
 by an imaginary internal fluid pressure, ranging from + dp (fig. 143) 
 at the upper surface to dp at the lower. 
 
 If now a short length, /3 . x, of the ring be examined, the tilting 
 power of this imaginary fluid pressure would be found to be 
 
 /2 
 
 = dp . x ft . -, ; but, as C . dx = + dp . x, we have 
 b 
 
 dx 6 
 
 The intensities of S and of C can, therefore, be expressed in terms of 
 m } and m%. The relation existing between these moments is deter- 
 mined by the deformations of the disc. 
 
 The differential equation for the elastic line is -^ -^~, as long 
 
 dx Hj . 1 
 
 as there are no cross stresses ; but, as the circumferential tension C 
 tends to shorten the radial fibres, the coefficient of cross contraction, 
 
 -, must be introduced, and the equation of the elastic line is 
 
 &y- 2 / s _o\ 
 & nsv ?/ 
 
 a, the angle of the cone, is equal to -=^, which, by a similar reason- 
 
 ing to that of the previous case, is 
 
 dy _^x S 
 dx *. 
 
172 MECHANICS 
 
 Differentiating this, we get 
 
 __ -?+*-- V 
 t.~E>\ " dx i' dxj 
 
 Combining this with the previous value for .^, it disappears, and 
 we get 
 
 This is the fundamental equation as regards the relation of the 
 two stresses C and S. These have now to be compared with the 
 external forces producing them. 
 
 For simplicity's sake, let the perforated plate (fig. 140) be suspended 
 by a stay of the diameter d, and uniformly loaded only at its circum- 
 ference by Q. Dealing once more with a narrow slice of the angle ft, 
 it will be found that at the point x there exists a vertical shearing 
 
 force q = ^' , which acting on the lever x ^ produces a moment 
 
 The moment due to the radial stresses is 
 
 ft . t* a dm, B . * 2 / , r dS\ 
 
 m l = **-- . x . S, and -=-! = ^ ( b + x -=- ). 
 6 dx 6 \ dx) 
 
 The elementary moment, dm 2 , produced by the circumferential 
 stresses C, has to balance dm^ + dm,. 
 
 from which it follows that 
 
 By differentiating and substituting the values of C and in the 
 
 previous equation an expression is obtained containing only S and x 
 as variables. Integrating this twice, S is found, and C can then 
 also be determined for any point, as well as the deflections and 
 inclinations. 
 
 The same operation has to be carried out with a uniformly distri- 
 buted pressure p, and also with an unperforated plate; but the 
 resultant formulae, as already mentioned, are too long to be repro- 
 duced here, and have not been practically applied. See Grashoff, 
 1866, pp. 248, 254, 263. 
 
 C. Bach ( ' Dent. Ing.,' 1897, vol. xli. p. 158) gives details of 
 tests on flat plates, 28 ins. diameter, and from f in. to f in. thick. 
 Permanent sets were noticed very early, but they did not exceed^ in. 
 with the thin plates until a pressure of 100 Ibs. had been reached : 
 for the thick plates the pressure had to be 330 Ibs., also (' Deut. Ing.,' 
 
MECHANICS 
 
 173 
 
 1908, vol. lii. p. 1876), two square plates 31*5 ins. between edge rows 
 of rivets and one rectangular plate 31*5 x 15'8 ins. of respectively 
 0*315, 0'63, and 0*86 in. thickness. The first permanent sets were 
 noticed with 15, 27, and 49 Ibs. per square inch. The maximum 
 pressures were 350, 300, and 400 Ibs. None of the plates failed. 
 
 K. Wilson ('Enging.,' 1877, vol. xxiv. p. 239) gives the results 
 of five experiments on unstayed flat and dished boiler ends, the 
 diameter being 30 ins., and the thicknesses of end plates f in. and 
 f^ in. They were either flat and riveted to angle irons, or flanged. 
 The bursting pressures varied from 200 to 370 Ibs. per square inch. 
 
 Elastic Beams. A fair idea as to what happens in stayed plates 
 may be arrived at by examining the so-called continuous beams, 
 which, like railway rails, are supported at more than two points. 
 The analysis is carried out as follows : 
 
 Each span (fig. 145) should be examined separately. There will 
 be the uniformly distributed pressure j9, and the supporting forces 
 
 FIG. 145 
 
 Qi + Q2- There will also be the two external moments m l and w 2 , 
 and the deflections, a x and a 2 , and the depression y v Any of these 
 values may be zero. 
 
 The differentia] equation for the elastic line is - = ?3 = m - El, 
 
 p dx 
 
 where I is the moment of inertia of the section of the beam, for a 
 plate of the width 1 and the thickness t it is T \^ 3 . Integrating the 
 above equation between the limits x, %l, and I the values of the 
 inclinations a and the deflections y are obtained. 
 
 Conditions 
 
 Inclination a at x 
 aatjl 
 a at I 
 
 raz:EI 
 ml : El 
 
 El 
 
 El 
 
 2 ) : El 
 0-146 pi* : El 
 
 Deflection y at x 
 y at I 
 
 :EI 
 :EI 
 :EI 
 
 fr) : El 
 0-104 Qfr* : El 
 
 0-0443 pi*: 
 
 : El 
 
 As an example determine in a continuous beam the bending 
 moment m = m l = m^ over the supports. For y = I we have a = a : 
 = cu = and y = 0. 
 
 Ela = = ml - iQZ 2 + $pl* ; m = 
 
 Ely = = 
 
174 
 
 MECHANICS 
 
 From these equations it follows that Q = fypl and that m = ^pl 2 . 
 The above formula for beams can be applied to flat plates by taking 
 into account the tendency to curl up crossways (cross curvature) by 
 u? 
 
 replacing E by E 2 _ ~ or approximately by ME. The formulae 
 
 will also be required for estimating deflection of steam pipes. They 
 have to be combined with similar ones for curved beams, see later. 
 
 Girders. Let L be the total length of the girder, while I and n 
 are the pitch and number of stays ; then L = (n + 1) . I is double the 
 distance of the end stays from the girder ends. If w is the distance 
 apart of the girders, and p the pressure in the boiler, then the maxi- 
 mum bending moment in the girder is m in the following table : 
 
 No. of Stays 
 
 Value of ll?* 
 p.w 
 
 No. of Stays 
 
 Value of U? 
 p.te 
 
 1 
 
 i.I.L 
 
 9 
 
 9. .L- 40. Z 2 
 
 2 
 
 2.Z.L- 2.P 
 
 10 
 
 10. .L- 50. Z 2 
 
 3 
 
 3.Z.L- 4./ 2 
 
 11 
 
 11. .L- 60. V 
 
 4 
 
 4.Z.L- 8.J 2 
 
 12 
 
 12. .L- 72 J 2 
 
 5 
 
 6.J.L-12.J 8 
 
 13 
 
 13. .L- 84. V 
 
 6 
 
 6./.L-18.J 2 
 
 14 
 
 14. .L- 98. Z 2 
 
 7 
 
 7. J.L-24.P 
 
 15 
 
 15.LL-112./ 3 
 
 8 
 
 8.4.L-32.P 
 
 16 
 
 16.J.L-128.J 8 
 
 8 = f^-= ? . p ' w ( -~- m V Here h and t are respectively the 
 h* . t 2 P. t \p .w ) 
 
 height and thickness of the girder. 
 
 In the above formulae the product n . I is the length of the plate 
 whose load is borne by the girder. 
 
 For even numbers of stays, S = %j^nl(L fyril). 
 
 For odd numbers of stays, S = 
 
 These formulae harmonise with the Board of Trade rules if L = 
 (n + 1)Z, but generally L is somewhat longer, because the flanges of 
 the plates permit of a greater distance than I between the foot of the 
 girder and the first stay. The girder stresses which are customary 
 with marine boilers are very much exceeded in locomotives. Girders 
 of two plates, 4 ins. deep spanning fireboxes of 36 ins. between 
 plates, and placed 4 ins. apart with 8 stays of 4 ins. pitch have 
 been fitted to many locomotive boilers of 180 Ibs. pressure and 
 have been perfectly safe. The stress according to the above formula 
 works out at 19-3 tons per sq. inch ! On recalculating the stress 
 on the assumption that the firebox plate, which was f in. thick, 
 with an inch space between it and the girder, formed part of this 
 girder, the stress works out at 5-5 tons per sq. inch ; but if this view 
 be the correct one, the shearing, forces between the plates and the 
 girder should be taken into account. They amount to 15*3 tons for 
 the outer stays and 4*3 tons for the next ones, provided, as has been 
 assumed, that the plate and girders are rigidly secured to each other 
 by the stays and ferrules. It cannot, however, in this case, be 
 admitted that the stays, which were only in. diameter were equal 
 
MECHANICS 
 
 175 
 
 to the above-mentioned loads. Probably they both bent and sheared 
 a little, and thus increased the 5*5 tons bending stress by an unknown 
 amount. If the end stays are made sufficiently strong to resist the 
 shearing force in addition to the load due to the steam pressure, 
 girders might unquestionably be made much lighter than at present. 
 The hydraulic tests would overstrain these girders and reduce the 
 elastic stresses to plastic ones of 12*9 tons (see p. 189). 
 
 The shearing force on the outer stay is found by multiplying the 
 average stress in the plate between the outer stay and its neighbour 
 into the sectional area of the plate (w x ^). The 
 shearing force on the two outer stays is found in 
 the same way, and the load on the second stay 
 is found by difference. The average stress in the 
 plate is equal to the maximum stress in the girder 
 at one or the other of the stays multiplied by the 
 ratio v : x in fig. 145a. 
 
 The moment of inertia of the rigid combina- 
 tion of a girder of the heights H and a plate of 
 the width w as shown in figure is the sum of the 
 moments of inertia of the two sections plus the product of the areas 
 H and wt t into the squares of the distances u and v of the respective 
 centres of gravity of sections from the centre of gravity of the whole. 
 The distance x is found with the help of the formula 
 
 x(Rt + wtj = ($ELH + (H + h + tfjwt). 
 
 Then u and v are found by difference, and the moment of inertia is 
 I = iV (H 3 + tfw) + w 2 Hi + v*wti. The resisting moment is SI : a?, 
 where S is the maximum stress in the top fibre of the girder. 
 
 Stayed Flat Plates. The formulae which were worked out for 
 the continuous beam are not directly applicable to stayed flat plates ; 
 they only give average results for the whole width of such plates. 
 They also do not take into account the cross bending. Some idea of 
 the stresses in these plates will be gained by the following view. 
 Let it be assumed that the boiler pressure is halved, and that one 
 
 FIG. 145a 
 
 FIG. 146 
 
 half is active in producing bending along the pitch line B, fig. 146, 
 while the other half produces bending along the pitch line A. The 
 mean bending moment in either direction is then 
 
 A 2 A.x , 
 
 p. A /B 2 &.x.x*\ 
 
 ~ "a" ' Ua " "a" + 2" ) ' 
 
176 MECHANICS 
 
 On account of the easy elastic curvature of stayed plates along 
 lines which pass half way between the stays, these bending moments 
 are probably reduced to half of what they would be in a continuous 
 beam, viz. : 
 
 2.2.24' 2.2.24 
 
 Now, according to Mr. Guest's experiments (p. 170), the presence 
 of a cross tension stress does not affect the strength of the material, 
 so that on the tension side of the plate we could allow two cross proof 
 stresses of, say, 
 
 25,000 = 6.^=1^!; ^25,000=^; 
 
 This is a very high result, and would indicate, as would be imagined, 
 that stayed plates are not weakest in the spaces between the stays. 
 If we take the values deduced from Professor C. Bach's experiments 
 (p. 171) as being correct, we must admit that plastic bending due to 
 double compression on one side will take place if the stress exceeds 
 say 6,000 Ibs. per square inch : 
 
 6,000 : 
 
 This is also a very high value. 
 
 If now we look at the plate close to the stays, we may safely 
 assume that, because of the concentration of forces at these points, 
 the values of m at the supports as found above would not be reduced 
 by half, but probably increased twofold. 
 
 As the plates are perforated, and as the screwed stays cannot be 
 assumed to be part of the plate, there can be no radial stresses at the 
 circumference of the holes, and we have only simple stresses, which, up 
 to the proof pressure, might be allowed to reach 25,000 Ibs. per square 
 inch. 
 
 25,000 = ^ = ^; <^ 25,000=^. 
 
 This indicates that the stresses near the stays are about eight times 
 as severe as between the stays, though, if the deductions drawn from 
 Professor Bach's experiments are correct, the material, being more 
 plastic under the conditions near the centres of the plates, would only 
 be about 100 per cent, stronger than near the stays. If these views 
 are correct the working pressure of a stayed flat plate would be p = 
 25,000^ : A 2 , all dimensions being expressed in inches. If the thick- 
 nesses are expressed in sixteenths of an inch, then p = 97'5 2 : A 2 , and the 
 first indication of giving way would be at about double this pressure. 
 
 That even this result is not quite correct will be admitted when 
 we consider the question of size of stay. Assuming that the screwed 
 plate is not supported by screwed stays, but is resting on supports, 
 
MECHANICS 
 
 177 
 
 then we may distinguish three cases. Firstly, the plate over the 
 supports is not perforated. We have severe drum tension on the 
 one side and severe strangling stress on the other. Secondly, if we 
 drill a very small hole just over the support the compound stresses 
 giyj^Cvay to single tension and compression stresses of double inten- 
 sity, for this is a case very similar to that of a thick walled cylinder 
 of infinite external diameter. Thirdly, if the holes are made large, 
 the diameters of the supports being of course proportionately in- 
 creased, these simple stresses will be much reduced. Therefore, the 
 size of the sy u y is an important factor, all the more because of 
 the shearius/tress set up in the hole. This is fully borne out by 
 experiment/ and published rules have followed this up in so far 
 as that thej only allow a low working stress for screwed stays, and 
 that they Lllow higher working pressures to plates supported by 
 stays with l.iuts and washers. In such cases the working stress on 
 the stays i/iight also be increased, and, on the other hand, allowances 
 miofht bj^ made in the thickness of the plate when the screwed stays 
 without washers are of very large diameter as, for instance, when 
 these stays are tubes. 
 
 Irregiilarly Stayed Plates. By applying the formulae of con- 
 tinuous beams to irregularly stayed plates for instance, such as occur 
 in boiler backs (fig. 147) it can be shown that the stresses near 
 
 k i- 
 
 Fio. 147 
 
 the stays on either side of the pitch b are greater than the usually 
 accepted formulae would lead one to expect. The value of m l has to 
 be increased from 
 
 It is exceedingly difficult to arrive at a satisfactory view of the 
 case illustrated in fig. 148, where the pitches A and B are not equal. 
 The stresses set up parallel to the pitches A will certainly be affected 
 by the pitch B, for the more this is reduced the less metal will remain 
 between the stays, and in the extreme case when they nearly touch 
 each other, i.e. when B = d, the stress S,, due to the curvature at 
 
 the line of holes, would be increased to 
 
 a.. 
 
 J comparing this 
 
 with the above value S. for such cases when A and B are equal, 
 
 S, 4 A 
 ~ . -5. 
 
 . 
 we find that 
 
178 
 
 MECHANICS 
 
 A -; 
 
 On the other hand, when A and B are nearly equal, a slight 
 reduction of B will tend towards a more 
 
 | , uniform distribution of the stresses be- 
 
 D* tween the stays, thereby reducing the 
 maximum values of S; and it is possible 
 that an alteration of B may in the one 
 case reduce, and in the other case increase, 
 , B the maximum stresses. 
 
 O _ _ >. . yrx t . Diagonal Pitches. The Board of Trade 
 
 T y has adopted the view that the maximum 
 
 d stresses are proportional to the product 
 
 FIG. 148 of A into B, but certain allowances are 
 
 made for large variations (see Eules). 
 
 Formerly ' Lloyd's Register ' did not take into account the smaller 
 of the two pitches, but since the first edition of this work was 
 issued the view expressed in it, that the stresses in flat plates are 
 probably proportional to the sum of the squares of the two pitches, 
 has been accepted. This amounts to the same thing as measuring the 
 diagonal pitch and doubling the accepted constants. For irregularly 
 stayed plates the practice commonly followed on land boilers is to 
 inscribe circles which will touch the rivet centres or stays : the dia- 
 meters of these circles are taken to be the diagonals of squares. It 
 should also be noted that on land considerably higher pressures than 
 at sea are permitted on flat plates of the same dimensions. This is 
 due to the experience that thick plates frequently crack, owing to 
 
 panting ; yet there is no indica- 
 tion that these practices lead to 
 weak boilers. 
 
 Fio. 150 
 
 Manhole Flanges. A pro- 
 blem which presents itself with 
 reference to the fitting of man- 
 Fio. 149 holes in flat plates is the follow- 
 
 ing (see fig. 149) : 
 
 Let Q\=p l\, where p is the working pressure and l } is half the 
 width of the manhole door ; then the bending moment at the position 
 of the stay is 7 2 
 
 If experience has shown that for this particular thickness of 
 
MECHANICS 
 
 179 
 
 plate a pitch of stays equal to L is permissible, then evidently the 
 following equation must be true : 
 
 So that the maximum value for I = Z, + / 2 is 
 
 There L is the pitch for stays in flat plates as found by accepted 
 rules. The manhole doors must be estimated independently. 
 Valuable experiments have been made as to their strengths by the 
 German Admiralty, Danzig. 
 
 Effects of Boiler Deformations. A little familiarity with the work- 
 ing of the equations for a and y of continuous beams (see p. 173) will 
 soon lead to the conviction that the changes of form to be expected 
 in boilers often produce stresses which far exceed any that may be due 
 to the steam pressure alone. As a simple instance take the case of a 
 long double-ended boiler, a steam-space stay placed too close to the 
 shell plate (fig. 150). The stay's duty is to support the surrounding 
 flat plate ; but, on account of the longitudinal contraction of the shell, 
 the stay will be in compression and actually assist the steam pressure 
 in forcing out the plate, thereby seriously increasing the load on the 
 adjoining stays, and increasing the bending stresses in the flange. 
 
 Screwed Stays near Flanges. The reverse action is met with at 
 the edges of the combustion-chamber backs. Evidently there is a 
 pull in one direction at the flange, which is balanced by the pull on the 
 stay (see fig. 151). This load Q t is proportional to the mean of the 
 
 .V. 
 
 FIG. 151 
 
 pitches Z 2 an d l\, and if the latter dimension is the maximum which 
 practice has shown to be safe, then the distance x, measured from the 
 
 N 2 
 
180 MECHANICS 
 
 centre of the flange, is found by the formula 
 
 a fc* O 
 
 where a is the width of the water-space between the two combustion 
 chambers. 
 
 Stayed Concentric Rings It sometimes happens that a donkey 
 boiler furnace has to be strengthened by radial stays (fig. 151a), and 
 the question arises what is the safe working 
 pressure of the stayed boiler, and what are the 
 stresses in the plates and stays. Assume the 
 pressure p in the annular space to consist of 
 two pairs of partial ones of which one pair 
 P& Pi ac ^ s on the outer shell, and the other 
 jtfj, p> 2 on the inner shell. The pressure p l 
 reduces the diameter of the furnace shell, p 3 
 increases that of the outer one, the con- 
 sequent separation of the two shells is AZ, 
 FIG. 151o where I is the length of the stays. The 
 
 pressure p 2 acts on a rectangle of the inner 
 
 shell supported by one stay, p 4 acts on a similar rectangle of the 
 outer shell. The pull on the stay must, of course, be the same in 
 both directions, and as the areas of the rectangles are proportional 
 
 to the radii r t and r 2 of the two shells, we have *- = -* where r 1 is 
 
 Pz ^2 
 
 the radius of the inner shell and r 2 that of the outer. Let h be the 
 vertical pitch of the rows of stays, and n the number of stays in the 
 
 T 2?r 
 
 circumference, then the pull on the stay is p 2 h This pull elon- 
 
 gates the stay, and this elongation must be exactly equal to the 
 separation of the two shells. It is now an easy matter to determine 
 the several partial pressures and the stresses which they produce. 
 
 and the other partial pressures are found as above. The plates 
 between the stays are now in the same condition as flat plates 
 subjected to the respective partial pressures, ra is the angular pitch. 
 
 The following list contains most of the experiments that have been 
 made on flat plates : 
 
 W. Fairbairn, 1874, pp. 147 and 333. ^-in. copper and f -in. iron 
 plates, 5-in. and 4-in. pitches. 
 
 E. H. Thurston, ' Franklin Last.,' 1872, iii. vol. Ixiii. p. 93. r \-in. 
 iron plate, 8|-in. and 9^-in. pitch. 
 
 'L. E. Fletcher, 'Eep.M. S. U. A.,' Oct. 1876, p. 31. Admiralty 
 experiments on ' Thunderer ' boiler. 
 
 W. Boyd, ' M. E.,' 1878, p. 223. V in - iron iV in - steel plates, 9-in. 
 pitch. 
 
 C. Back and E. Wilson (see p. 172). Unstayed plates. 
 
 D. Greig and Max Eyth, 'M. E.,' 1879, p. 282, f-in. and ^-in. 
 plates, 4-in pitch. 
 
 W. Si Hutton, 1889, p. 180. 
 
MECHANICS 181 
 
 Board of Trade experiments on mild steel, ' Parl. Rep.,' 1881 
 (c. 2897), 1885 (c. 4572). 
 
 German Admiralty, Danzig, 1884-92. 
 
 In addition to the above experiments, a few details have come to 
 hand about three tests, but neither date nor place were obtainable nor 
 any reason for keeping back this information. They are the first 
 three tests in the following table which consist mainly of summaries 
 of the Board of Trade and German experiments. They have been 
 compiled on the following lines: the permanent elongations of the 
 stay bolts were subtracted from the permanent sets of the centres 
 of the squares or rectangles supported by these stays, and because 
 the steps through which the test pressures advanced were very large, 
 the intermediate pressures (limit pressures) under which the first 
 indication of permanent set may be assumed to have taken place were 
 estimated by interpolating the pressures for the smallest and second 
 smallest average permanent sets of the centres of the plates. These 
 estimates are detailed in the tables as well as the estimate of the 
 constants 0, to be used in the formula WP = C . t 2 : P 2 where P is 
 the pitch of stays in inches and t the thickness of plate in sixteenths 
 of an inch. C x is the constant based on the nominal thickness, C 2 
 is the constant based on the actual thickness measured at the stay 
 holes, or where this was not ascertained, it is based on the recorded 
 thicknesses of the test pieces cut from the plate. C 2 is also based 
 on a uniform tenacity of 30 tons per sq. inch, it being assumed 
 that the limit pressures for flat plates are proportional to the ultimate 
 tenacities. 
 
 A. Plates with stay ends riveted over. The mean value of C 2 is 
 503. This value is probably 2/ too high, because (see groups C and 
 E) the test pieces seem as a rule to be about -^ in. thinner than the 
 plates from which they have been cut. 
 
 B. Plates with stays having single nuts. The mean value of C 2 
 is 439 or more, and is also probably 2/ o too high. The relatively 
 higher results obtained in group A is undoubtedly due to the swelling 
 of the stay ends due to riveting, which swellings would give additional 
 support to the plates against deflections. 
 
 C. Plates with stays having double nuts. The mean value of C 2 
 is 522. 
 
 C and D. In the German experiments, G, H, the back end 
 plates of the test boxes, were much thicker than the front end ones, 
 but their actual thicknesses were not measured and their tenacity not 
 determined, as with the other German plates their average tenacity 
 is probably 27 tons per sq. inch. In each set of three experiments, 
 la, Ib, Ic, Ha, etc., the back plates were not changed for new ones, 
 and therefore the b and c tests in group D are for plates which have 
 already been subjected to the maximum test pressures noted in 
 groups C and D, after having been flattened out before retesting. 
 
 E. Plates with riveted washers and stays having double nuts. 
 The average value of C 2 is 749, but this value is affected by the 
 ratio of the thickness of the washer to that of the plate. 
 
 Value of Riveted Washers. A convenient comparison between 
 groups B, C, and JJ can be made by finding an average constant C 3 
 
182 
 
 MECHANICS 
 
 est Pressures and Mean 
 Permanent Sets 
 
 Plate 
 cknes 
 
 1 = 
 
 t a 
 
 w> 
 
 pajBiuijsg 
 
 Stay head flew off. 
 Stay threads stripped. 
 Stay threads stripped. 
 J Stay heads flew off. 
 1 Plate cracked at 300 Ibs. 
 Stay heads flew off. 
 Stay heads flew off at 475 Ibs. 
 Stay heads flew off. 
 Stay heads flew off. 
 Stay heads flew off. 
 Burst. 
 Burst. 
 
 O O "5 g O i/5 O <3 
 
 o 1/5 So O3 oo -* ?S > ift 
 
 co M t^ >* H 
 
 "5 (O * 00 
 
 . , 
 
 1 ' 
 
 Ji i i IglgSSi 
 
 .si 
 
 iiii i 
 
 III i 8gli t 
 
 
 c'ocooao ao ^^ 
 
 er nuts. 
 . 
 over nuts. 
 
 ts. 
 ts. 
 
 Plate cracked 
 Plate cracked 
 Stays tore. 
 Plate slipped 
 Plate cracked 
 Plate slipped 
 Stays tore. 
 Plate slipped 
 Plate slipped 
 
 8SSSSSSS 
 
 cO'vNicuscocq 
 
 1! IS IS? 
 
 W ^ C/3 < ^ < 75 < ^ 
 
MECHANICS 
 
 183 
 
 i 
 
 il 
 
 ure 
 anen 
 
 O J3J3UIB1Q 
 
 saoaid jsaj. 
 
 I 
 
 CO 
 
 ,. 
 
 XX 
 
 SSS 
 
 s 
 
 ~ 
 
 CO CO 
 
 i i i i 1 1 i i 
 
 i i i i 1 1 1 i 
 
 QOr-oS^QC^Oir^ 
 
 ISS8888E 
 
 S852SSSS 
 
 S ^ -5 ^ ^ -* 
 
 T 1 CO M CO 
 
 oo 
 
 oaoacw 
 rC'ftc 
 
 
 1 1 1 1 1 1 1 1 
 
 oocooooo 
 
 pped. 
 
 ut threads 
 ut threads 
 late cracked. 
 
 Plate cracked near 
 
 tay broke. 
 tay broke. 
 
 tay broke and plate cr 
 at 
 
 N 
 N 
 Pl 
 
 S 
 S 
 S 
 
 
 5 
 
 1 3 
 
 W 22! w 21 
 
 sssaa i 
 
 ^r ~ com CM 
 
 
 OOOOO O O 
 
 Works G. Steel boxes tested at the Gl 
 Several were flattened and used again onc 
 
 . D. Adam 
 lates of the test bo 
 
 s| 
 
 16 
 
 1 
 
 
184 MECHANICS 
 
 for groups B and C, in which the pitches are replaced by the diagonal 
 pitches less the nut diameters, and then estimating similar diagonal 
 pitches less effective washer diameters for group E. As the average 
 value of C 3 for groups B and C is 585, the effective diameter D of 
 riveted washers can be expressed by the formula 
 
 D e - 075DJJ* : tf 
 
 where D w and t w are the dimensions of the washer, and t p the thick- 
 ness of the plate. Let I be the diagonal pitch of the stays then the 
 probable limit pressure would be 
 
 P = 586* 2 : (I - D.) 2 = 585* 2 : (I - f D^ 2 : VD* 
 This formula applies equally well to groups B, C, and E. 
 
 Application of Test Results. Pressures calculated with the help 
 of the constants found above are those at which the first indications 
 of permanent set might be expected,. and these pressures would be 
 convenient limits for the hydraulic test pressures, a small allowance, 
 say 25/ , being made on account of uncertainties about local thick- 
 nesses, tenacities, and other irregularities. 
 
 Safety of Stayed Plates is a subject on which these experiments 
 throw little light, for amongst these forty-four tests there were only 
 eight crackings at stay holes, but twenty-four cases of stay failures, 
 which is a question of diameter and not of thickness. However, in 
 those cases where the plates did crack, the ratios of the maximum 
 pressures to limit pressures averages about four and one-half, so that 
 if the working pressure is fixed at say half the limit pressure the 
 factor of safety may be considered to be about nine. 
 
 Curved Beams. An originally curved beam behaves very much 
 in the same way as a straight one, except that the stresses are not 
 distributed so uniformly. Let the line 
 OP (fig. 152) be the neutral fibre, which 
 does not alter its length while being bent. 
 For any short length p . da. the elongation i . ^.^ / 
 
 of the fibres above or below this line is " I ^- 
 proportional to their distances from it. 
 But not so the strains, for, as the outer 
 fibres are longer than the inner ones, so 
 will the strains, and consequently also 
 the stresses, be proportionately greater the 
 nearer they are to the centre of curva- 
 ture. Let p and p be the radii of curva- 
 ture of the neutral fibre before and after FIQ 
 bending, and let x be the distance of any 
 fibre from this line; then, if E is the modulus of elasticity, it is 
 easily shown that the stress is 
 
 S==E g.fro-p). 
 
 (X + Po) P 
 
 Then, on carrying out the necessary algebraical operations, n (figs. 
 153 and 154), the distance of the neutral fibre from the concave side 
 of the rectangular beam, is found. 
 
 -Jh 
 
 (1 + m) m / 
 
 _ 
 
 log nat (1 + m) 
 
MECHANICS 
 
 185 
 
 The following are a few numerical values : 
 
 m = $ : r = oc 10 5 1 ^ 
 
 n : t = -317 "358 443 466 492 -500 
 The maximum stress S exists on the concave side of the beam. 
 
 S = C 6 . jp where M = bending moment and 
 
 nat (! + m )] 
 
 - 
 
 = * ' (m + 2) log nat (1 + m) - 1' 
 
 The following are a few numerical values : 
 
 m = : r = oc 10 5 1 ^ 
 
 C = x 2-889 2-103 1-287 1154 1-033 1-000 
 
 The practical conclusions to be drawn from these figures are that the 
 bending stresses on the concave side of plates flanged to the usual 
 radius, of, say, twice the thickness, are 15/ greater than those in the 
 adjoining flat plates ; that when the inner radius is reduced to the 
 thickness of the plate 29/ o has to be added to the stress ; while when 
 there is no round on the inside of the flange the stresses are infinitely 
 great. The end of every crack can also be looked upon as the inner 
 surface of a curved beam, and the lightest external force would extend 
 
 FIG. 153 
 
 FIG. 154 
 
 FIG. 155 
 
 it, unless there are other stresses beyond the crack holding the plate 
 together. When they are absent, or when tension stresses exist in the 
 plate, there is nothing to stop the crack from extending with the usual 
 explosive rapidity. Similarly, the concave sides of cold bend samples 
 are very weak, on account of their small radii, and, as the residual 
 stresses in the samples all tend to produce tensions at this point, it is 
 not surprising that the majority of such test pieces crack some time 
 after they have been put aside, and without any apparent cause. 
 
 Elastic Deformations of Curved Beams. As in the case of a straight 
 beam let E be the modulus of elasticity, and I the moment of inertia 
 of the section of the beam, the necessary allowance being made for 
 the radius of curvature r (see above). 
 
186 
 
 MECHANICS 
 
 Using polar co-ordinates we have the three expressions : 
 dy _ #*(Ar) _ m 
 Ts ~ r*da* '~ IO 
 
 d(8y) 
 
 = r(cos a - cos 
 
 = r( S in a - 
 
 sn 
 
 " cos 
 
 - sn 
 
 Seeing that sin ft is larger than sin a, the last expression is negative. 
 
 In these expressions Ar is measured radially from the original 
 centre line of the beam, y is the angle included between the original 
 and ultimate centre line of the beam at any angle a, and when a = 
 ft the angle y is also the tilt of the upper flange if the beam is a 
 curved pipe. A?/ is the rise of the end of the pipe, and Ao; is the 
 horizontal movement of the end of the pipe. 
 
 The moments acting on the beam at the point a are firstly m 
 = M, which is constant for any angle a, secondly m = Vr(cos a - 
 cos 13), and thirdly m = Hr(sin a - sin ft). This last moment is of 
 course negative. Introducing these values in the above equations and 
 integrating after a from o to ft, the expressions contained in the 
 following table are obtained. The table also contains the values for 
 the special case of a right-angled bend when ft = 90. 
 
 Moments 
 
 7 x El 
 
 %) x El 
 
 8(0?) x El 
 
 Deflections for any Angle ft; r& = l,rcos p = m,r sin& = n 
 
 M 
 Hn 
 
 [V(r-m) 
 
 MZ 
 H(r 2 - rm - In) 
 V(rn - lm) 
 
 M.(rn - lm) 
 H(- %r s + font*!***) 
 V($r 2 Z + rim - \rrnn] 
 
 M(r 2 -rm -In) 
 H(|r 2 Z - 2r* + %rmn-lm*) 
 V( - $f* + Imn + |rw 2 ) 
 
 Deflections for Right- Angled Bends ; = 90 
 
 M 
 Hr 
 Vr 
 
 + l'571Mr 
 - -571 Hr 2 
 
 + Vr 2 
 
 + Mr 2 
 - -50Hr 3 
 
 + -785Vr 3 
 
 - -571Mr 2 
 + -SSBHr 3 
 - -50Vr 3 
 
 Experiments have been carried out by Prof. A. Bautlin (' Deutsch. 
 Ing.,' 1910, v. 54, p. 43) on pipes and bars bent as shown in fig. 156. 
 The dimensions and deformations are given in the following table. 
 These experiments do not correctly represent the straining to which 
 steam pipes are subjected, because the flanges of these bends were 
 free to tilt, but Prof. Bautlin has compared the actual deformations 
 with the calculated ones, and finds the ratios to be as follows : A : 4 -89, 
 B : 2-60, C : 0'94, D : 1-04, E : 0-97. He attributes the great elasticity 
 of A and B : between two and five times as great as might be expected, 
 to slight puckerings on the inner surfaces of these bent steel tubes, 
 and other writers have tried to show that this greater elasticity may 
 in part be accounted for by the change of shape of a circular tube 
 when stressed. 
 
MECHANICS 
 
 187 
 
 Horizontal Thrusts : Pounds 
 
 220 
 
 440 
 
 660 
 
 880 
 
 1,320 
 
 1,980 
 
 2,420 
 
 A 
 B 
 
 C 
 D 
 E 
 
 Material 
 
 Dimensions of Bends 
 
 Deformations 6(/) of Half Loop 
 
 Diameters 
 in. 
 
 Thick- 
 ness 
 in. 
 
 n 
 
 in. 
 
 -3 
 in. 
 
 I 
 in. 
 
 in. 
 
 in. 
 
 in. 
 
 in. 
 
 in. 
 
 in. 
 
 in. 
 
 Mild Steel 
 
 Cast Iron 
 Steel Bars 
 
 8-7 x 8-2 
 5-3 x 5-1 
 8-5 x 8-4 
 3*15 square 
 3'15 square 
 
 26 
 
 ? 
 78 
 
 33-1 
 31-9 
 34-0 
 19-7 
 19'7 
 
 22-0 
 16-7 
 22'0 
 11-8 
 17-7 
 
 37-4 
 23-6 
 47-5 
 21-7 
 27-9 
 
 69 
 
 1-42 
 10 
 
 63 
 
 24 
 33 
 
 22 
 
 1-37 
 34 
 
 2-16 
 
 2-98 
 
 End-Plate Flanges. The agreement between experimental and 
 calculated deflections of the square bars shows that the calculations 
 might be applied to the determination of the deformations, and 
 therefore also of the stresses of flanges of flat and dished boiler ends. 
 That the matter is of importance will be evident from the following 
 list of boiler explosions due to the grooving through of end-plate 
 
 FIG. 156 
 
 FIG. 1ST 
 
 flanges Board of Trade Reports Nos. 148, 155, 162, 198, 226, 235, 
 290, 682, 967, 980, 1,155, 1,484, 1,699. Of these the last-named 
 is very instructive, though the important point, the smallness of the 
 radius of the flange, did not receive the attention it deserved. After 
 this explosion quite a number of dished-end plates of boilers have 
 been renewed. The above cases also include a few flat -ended boilers. 
 A general idea of the nature of the stresses can be obtained from 
 fig. 157. Let ^ be the thickness of the boiler shell plate of the 
 diameter 2B, and let t 2 be the thickness of the end plate, with a 
 flange of the radius r, then the upward force V (fig. 155) per 1 in. 
 of circumference is P(R - r), or as r is small compared with R we 
 may write JPR. This vertical force is the chief cause for the slight 
 vertical displacement (?/), but it also produces a slight horizontal 
 displacement, which has to be subtracted from 8(R) = R 2 P : ^E, then 
 
 as ft = we have according to the table 
 
 - -50|PRr 3 ) = 
 jj Hii 
 
 Assuming that the flat plate does not bulge, which however is 
 not strictly true, we have 
 
 y = = (l-571Mr - 
 
188 MECHANICS 
 
 Combining these two equations and remembering that I the 
 moment of inertia is T Vs 3 > we find the moments M and Hr ; Vr being 
 given above. 
 
 M = 
 
 Hr = PRr(Vl20 + 
 
 Near the shell plate the total bending moment is M + Vr - Hr, 
 at a v it is M, and at some intermediate angle a it is M + Vr cos a - 
 Hr(l - sin a) (see fig. 156). It is a maximum, according to dimension, 
 at about 45, so that approximately the maximum bending moment 
 is 
 
 Any bulging of the front-end plate increases the coefficient of the 
 last term very considerably. For stayed-end plates V is of course 
 less than mentioned above. 
 
 Shearing Stresses in Beams. No shearing stresses exist in a bent 
 beam when it is exposed to only two external bending moments 
 m i = ^h ( n g- 1^5). In every other case the shearing force in any 
 particular section of a beam is exactly equal to the otherwise un- 
 balanced load at that point. Thus, in fig. 145, p. 173, the upward 
 shearing force at the point x is Q 2 - p(l - x). 
 
 If this force were evenly distributed over the sectional area of the 
 beam, it would be easy to calculate it ; but there are certain condi- 
 tions which have to be fulfilled, and which lead to somewhat com- 
 plicated results, particularly if the section is an irregular one. In 
 rectangular beams, and therefore also in flat plates, the case is 
 simple. 
 
 Let a- represent the intensity of the shearing stress at a point 
 situated at the height y above the neutral fibre op of a beam (fig. 159), 
 while S is the longitudinal stress at that point ; then it is easily 
 proved that 
 
 d<r dS 
 
 7T = ~ //""' ln a rec ' ian g u l ar beam 
 
 dS 12 dm 12 f da- 
 
 dx == ~j* *y ' ~dx~~tpyQ an( * therefore T- = C . y, where C is a constant. 
 
 The maximum shearing stress at the neutral fibre is 2Q : 3t. 
 If, then, the total shearing force in the section at the distance x 
 is 3 we have 
 
 3 
 <r = K- 
 
 1 The axial shearing stresses on the threads of a screwed stay can be shown 
 to be distributed in the same manner, and instead of making the thickness of 
 the plate or nut half the diarneter, it ought to be three-quarters, 
 
MECHANICS 
 
 189 
 
 Fig. 161 represents the distribution of the longitudinal stresses, 
 and fig. 160 that of the shearing stresses. 
 
 As a shearing stress o- is a compound of a tension and compression 
 stress S, acting at angles of 45 to the line of shear, as shown in 
 fig. 125 (p. 168), it is easily proved that 
 
 o- = + S. 
 
 
 
 a?- 
 
 FIG. 160 
 
 Fia. 161 
 
 In order, then, to resolve the various stresses to be met with 
 in a beam into their respective right-angled resultants it is only 
 necessary to apply the formulae of p. 167 ; then 
 
 -- . 
 
 -_p+S+o+o S-p 
 
 X = + 
 
 Here p is the transverse pressure, but the signs of both S and p 
 will have to be changed if they are compression stresses. The distri- 
 bution of p is determined by a. 
 
 It is now possible to construct curves showing the direction and 
 intensities of the resultant stresses at any point of a beam (see figs. 
 184, 185, 186, p. 211). 
 
 Plastic Beams. "When flanging or bending plates, the elastic limit 
 of their material is always passed, and the resultant deformation is a 
 permanent one. In the chapter on ' Strength of Materials ' a formula 
 has been explained which enables one to calculate the stresses in the 
 outside fibres of narrow plastic beams, when their curvature is known. 
 
 Roughly, S= '2^ ; so that S is only two-thirds of what it would be 
 
 in an elastic beam, which means that a plastic beam is 50 % stronger 
 than the elastic theory would make it. 
 
 Another very important difference between an elastic and a plastic 
 beam is that the stresses of the former bear some relation to the 
 deformation, while those of the latter are nearly, if not quite, inde- 
 pendent of the same. 
 
 The work W t required to bend an elastic steel beam is proportional 
 to the square of its final curvature, about 
 
190 
 
 MECHANICS 
 
 Here A is the superficial area of the plate, measured in square feet, 
 and ^ the radius of curvature, measured in feet. By the time that the 
 elastic limit is reached this amounts to about 
 
 W,= foot tons, 
 
 and is independent of the radius. In other words, the maximum 
 energy which can be stored in a flat spring is proportional to its 
 volume. 
 
 The work W 2 required for bending a plastic beam or plate is pro- 
 portional to the curvature 
 
 The value of the constant C is about 
 
 6 for mild steel, cold. 
 4 blue hot. 
 0-3 red hot. 
 
 5 for wrought iron, cold. 
 
 3J blue hot. 
 
 0-25 red hot. 
 
 Thus to bend a cold steel shell plate whose dimensions are 14 feet 
 x 7 feet x 1 inch, and whose radius is 6*7 feet, a power of 88 foot 
 tons would be required. To do it at a red heat requires only 4^ foot 
 tons. 
 
 The above values have been estimated from the following experi- 
 ments and other observations. Dr. J. Kollmann (' Ver. Gew.,' 1880, 
 vol. lix. p. 107, &c.) states that he found the limits of elasticity (? plas- 
 ticity) to be as follows : 
 
 Tables of Limits of Elasticity and Plasticity 
 
 Temperature, P. 
 
 68 
 
 1,380 
 
 1,470 
 
 1,560 
 
 1,650 
 
 1,750 
 
 Iron . . . Tons 
 Mild steel . 
 
 17-5 
 25-4 
 
 2-0 
 3-0 
 
 1-3 
 
 1-0 
 
 1-5 
 
 Ml 
 
 C. E. Stromeyer, ' G. E.,' 1886, vol. Ixxxiv. p. 125, Nos. 4, 9, 10, 12, 18. 
 
 Temperatures, F. 
 Colour of Fracture 
 
 68 
 
 470 
 Straw 
 
 500 
 Blue 
 
 Hard steel . . . Tons 
 Mild . . . 
 
 19-4 
 16-3 
 
 17-0 
 
 15-9 
 10-0 
 
 From this it will be seen that at a blue heat and at a red heat 
 iron, as well as steel, grows more pliable in the ratio respectively of 
 3 to 2 and 20 to 1. The power required to permanently bend an 
 iron and a steel plate 12 inches wide and 1 inch thick is, therefore, as 
 follows : 
 
 Condition 
 
 Cold 
 
 Blue Hot 
 
 Red Hot 
 
 Iron plate . . Foot tons 
 Steel 
 
 60 
 75 
 
 40 
 50 
 
 3 
 3 
 
MECHANICS 
 
 191 
 
 Cross Deformation of Plastic Beams. When the elastic limit has 
 been passed the value of l//x, the coefficient of cross contraction, in- 
 creases from ^ to ^. For very narrow beams the ratio of p to p l (fig. 
 162) would then be as 1 to 2. In wide ones, such as shell plates, 
 this deformation is of course impossible, and it is 
 4 evident that a cross stress must have been set 
 
 '. up, whose intensity is nearly equal to half the lon- 
 
 gitudinal one, or, say, + 12 tons per square inch, 
 under the action of the bending rolls. But this 
 condition also demands supplementary longitu- 
 dinal stresses at the edges of the plate and com- 
 pression stresses near its centre. They are all 
 modified by the spring of the plate as it leaves the 
 rolls ; but it is quite clear that the residue is both 
 
 of a severe and of a 
 complicated nature. 
 Stresses of a similarly 
 complex nature also 
 exist in small bent 
 test samples; and it 
 is interesting to note 
 that when the steel is 
 of an unsatisfactory 
 quality it usually 
 F I0 . 162 FIG. 163 cracks at the centre 
 
 of the width, showing 
 
 that it was incapable of withstanding the combination called drum 
 tension (see fig. 163 and p. 160) to be found there. 
 
 The complicated nature of these stresses, particularly in wide 
 beams, readily explains that the maximum stresses to be found in 
 them when the plastic limit has once been passed differ very materially 
 
 from those found by the formula S = ' 2 W . 
 
 I 
 
 Shearing Stresses in Plastic Beams. The previously found 
 formula, a = -=-, is independent of the elasticity of the material. 
 
 If, therefore, the longitudinal stresses in a rectangular plastic beam 
 are distributed as shown in fig. 164, then the shearing stresses must 
 be distributed as in fig. 165. This illustration represents a case 
 where the bending stresses have been produced by means of a light 
 force acting on a long leverage, as, for instance, when shell plates are 
 being passed through the bending rolls. 
 
 The case is very different when a strong force with a short leverage 
 produces the same moment. Then the shearing stresses will be nearly 
 uniformly distributed over the thickness (fig. 167), and the longitudinal 
 stresses will have to accommodate themselves accordingly somewhat 
 after the fashion shown by the curves in fig. 166. In the one case the 
 beam gives way at the outside fibres, in the other at the neutral fibre. 
 An intermediate stage is worthy of mention. Suppose that the 
 plastic limit of tension and compression is 20 tons, while for shearing 
 it is 15 tons ; then both outside fibres of a beam would give way to 
 longitudinal stresses, at the same time that the centre fibres commence 
 
192 
 
 MECHANICS 
 
 to shear if these stresses are reacted on simultaneously. This happens 
 in a square bar if the bending force is applied at a distance equal to 
 i of its thickness, and doubtless most rivets behave in this way. 
 
 Fia. 165 
 
 FIG. 166 Fia. 167 
 
 Stresses in Cylindrical Shells. The circumferential stress in a 
 cylindrical shell of the mean diameter D is found by the well-known 
 
 formula S = ^ , where p is the internal pressure and t the thick- 
 2> . t 
 
 ness of the shell plate. If the ends of the shell plates are joined 
 together by riveted longitudinal seams, the percentage of their strength 
 will have to be taken into account. If the boiler shell is built up of 
 several strakes, and the longitudinal seams break joint, it has been 
 argued that the stresses are proportionally reduced, and that they 
 
 should be calculated as follows : S = g-^J ^y--^. Here I is the 
 
 A.I. 2<(A) 
 
 length of the boiler, and 2(AZ) is the sum of the widths of the plates, 
 including the flanged end plates, from which the rivet holes of only 
 one longitudinal seam have been subtracted. As 2 (A/) is often greater 
 than I, this view would lead to the conclusion that a riveted shell is 
 stronger than a solid one. Clearly, this argument is only true as 
 regards the mean stresses, and that it leads to valueless results is 
 proved by the fact that the same reasoning applied to a beam would 
 lead to a wrong conclusion, for its mean stress is just nothing, being 
 + S at the top and S at the bottom. 
 
 A point where variation of stresses in shell plates may be expected 
 is at A (fig. 168), in the solid plate near the end of a longitudinal seam. 
 Let it be assumed that this seam is more elastic than the plate, i.e. 
 that whereas a stress of one ton would stretch the latter ^-^wu^ of its 
 length, the same stress would cause the joint to spring or stretch, say, 
 four times as much. Then, as these two parts are firmly connected by 
 the circumferential seam, the solid plate at A would be subjected to a 
 four times greater stress than the joint. A solitary and perhaps not 
 very reliable experiment on this subject showed that the stress was 
 actually eight times greater, and similar results were obtained near 
 the single butt-strap joints on ship's sides (C. E. Stromeyer, ' N.A./ 
 1886, vol. xxvii. p. 34). The remedy which readily suggests itself is 
 to make the longitudinal seams more substantial say, of the double 
 butt-strap type. Now, however, this part may be more rigid than 
 the plate, and will have to bear a proportionately heavier load, and 
 being perforated is less capable of sustaining it. A more correct 
 principle would be to make the longitudinal joints exactly as elastic 
 as the solid plate. A few remarks on the elasticity of a riveted joint 
 
MECHANICS 193 
 
 will be found further on (p. 218), when discussing their theories, but 
 a true solution can be obtained only by careful experiments. 
 
 The order in which seams naturally range themselves as regards 
 rigidity is 1st. Single butt-strap joint. 2nd. Lap joint. 3rd. Butt 
 joint with one wide and one narrow strap. 4th. Butt joint with two 
 equally wide straps. 
 
 Of course the number of rows of rivets, their pitch and diameter, 
 and the thickness of the cover plates, will affect the results. 
 
 S Z 
 The Longitudinal Contraction of Cylindrical Shells is =^-, where 
 
 Ll ./A 
 
 I is the length and S the circumferential stress. In a boiler of 17 ft. 
 length this will amount to about 0'025 in. at the ordinary working 
 pressure. If no stays are fitted to take up the longitudinal stress, 
 which is one half of the above, it will be found that the elongation, 
 
 Thiscan be utiusedforthe 
 
 determination of 1/fi, the coefficient of cross contraction. By riveting 
 longitudinal strips on a boiler shell, the longitudinal contraction is 
 reduced, at least locally, and this is exactly what all riveted longi- 
 tudinal seams do. Consequently, longitudinal compression stresses 
 are set up in them, which must produce tension stresses in some 
 other part of the shell, probably along either side of the seam. A 
 longitudinal compression stress c will also be set up at A (fig. 168), 
 which, combining with the circumferential stress s, constitutes a 
 shearing stress, and that, as has been shown by experiments (see 
 fig. 123, p. 157), is far more injurious to iron and steel than a simple 
 tension. Therefore, whether elastic lap joints or the more solid butt- 
 strapped joints are used, very severe stresses will be found in the 
 adjoining plates. 
 
 Longitudinal contraction takes place in cylindrical furnaces 
 exposed to external pressure, and the two deformations, amounting 
 to large fractions of an inch, cause severe stress and grooving in end 
 plates. These can be obviated by using corrugated flues for which 
 the longitudinal elasticities have been determined as per following 
 table (p. 194). (See M.S.U.A., 1905, p. 13). 
 
 Influence of End Plates on the Stresses in Boiler Shells. In fig. 
 169 let the line CD represent the shape of half the length Z of a boiler 
 shell of the diameter D, while subjected to an internal pressure p { . 
 The shell plate will acquire this curvature if secured to the end plate 
 at C, as shown ; if unsecured it would have remained cylindrical and 
 have occupied the position at the line AB. Under that condition the 
 
 increase of half the diameter is y\ = ^ ' - , where t is the thick- 
 ness of the plate and E the modulus of elasticity. The stress will be 
 
 
 
 ; but, as will be seen in the diagram, if the ends are held 
 
 2 . t 
 
 down there is no circumferential straining of the shell at C, while at 
 D it is reduced in the ratio of y\y Q to y^ The object of this 
 investigation is to ascertain what this value is. 
 
 A little reflection will show that the circumferential stress S at any 
 point x or z is proportional to the distance of that point of the shell 
 
194 
 
 MECHANICS 
 
 M ri " 8 E - 1* . 
 
 2 
 
 P-I 
 
 & -s 
 
 THtHTHiHiH(?q>HOj6^66 O1 
 
 Oi rH 00 >-H 00 O 
 g <N CO O O CO 
 TH 6 iH rH rH 
 
 O OS Ol t> (N 
 rH 6 rH 6 ^ 
 
 
 I 
 
 QrHH 
 
 !> CO 
 
 O O O O O O O O O 
 
 660000000000 
 
 C5CO 
 O O 
 
 "^OiCOU7)W5 
 OOC<IOOU5O 
 
 w O O O O O O 
 
 666666 
 
 O O O 
 
 666 
 
 6 6 
 
 OOC^CO 
 rHr-IO 
 
 t 
 Ot-iH 
 
 OCOO<NOCOCO<NO<NOOO 
 
 lOOiCDt-COO5OOt>-'Tj<t<MO 
 UScO^THiOCOCOCO-^^kOTt* 
 
 666666666666 
 
 s pqsgiosoioocpoooo 
 
 ,H(MfHiHO-lTH<M 'COCO 
 
 C t-t-t-t-t-OiOSOSOOt-OSO* 
 
 " ifOCOCOCOCO<M(MCOCO(M<N 
 
 M5 O O O U5 O O 
 
 osbob665cb *cb 
 
 Si (M <M CO (M <N ' ' * W 
 
 1 -s 
 
 f .; 
 
 - - 
 
 > 
 
 pO 
 
 OH W 
 
MECHANICS 
 
 195 
 
 from its original position. S = S-, . ^ - = ^- But as 
 
 this stress is capable of balancing only part of the internal pressure, 
 there remains p=p\ y/y\, which has to be transmitted to the end plate, 
 
 a 
 
 o i 
 
 OJ 
 
 O O 
 O 
 
 O .-*. 
 
 "o 
 
 
 
 FIG. 168 
 
 FIG. 169 
 
 and in doing so longitudinal bending stresses are set up in the shell, 
 which have to be ascertained. This can be done by examining a long 
 strip of the boiler shell say, 1 in. wide loaded irregularly with a 
 pressure p, and supported at its ends by loads Q. A bending moment 
 } will also be found there. Evidently the load Q is proportional to 
 
 m 
 
 the area ABDC. 
 
 dz. The bending moment at the distance x is 
 
 y.(z- x}dz t 
 
 which may be written -^ 
 12 
 
 -=- 
 dx* 
 
 = m = 
 
 -h + i? 
 
 y.dz 
 
 / , r * i 
 
 x I y .dz I y .z .dz \ 
 
 Jo J* J 
 
 This leads to the equation y = \y (e* + e' 4 *) cos ax + 
 sin ax. 
 
 By integration and differentiation the values of ^y 0) A, and a can be 
 found, and numerical values obtained, when the conditions of the ex- 
 ternal forces are known. Thus, when very thick shell plates are 
 attached to thin end plates, or when these have a very weak and well- 
 rounded flange, m, = or nearly so. In the latter of these two cases 
 y } is also reduced, on account of the spring of the flange, which is pro- 
 portional to Q, and this value has therefore also to be reduced, and the 
 relief afforded to the shell plate is small. The calculations are too 
 complicated to be reproduced here. The problem has been discussed 
 on somewhat different lines by Dr. F. Grashoff, 1878, p. 316, and by 
 J. T. Nicolson, ' N.-E. 0. I.,' 1891, vol. vii. p. 205. Adapting some 
 of his results to a boiler of 15 ft. diameter, with 1-in. shell plates at 
 100 Ibs. pressure, we find the circumferential stress in the centre of 
 the length to be as follows : 
 
 1 Length between end plates (feet) 
 i Circumferential stress at centre (tons) 
 
 QC 
 
 3-35 
 
 15 
 
 3-35 
 
 10 
 
 3-34 
 
 5 
 
 3-15 
 
 2 
 
 2-96 
 
 1 
 
 70 
 
 02 
 
196 
 
 MECHANICS 
 
 But this is only true if the end plates are rigid while m^ = 0. In 
 practice this is never the case, and a very considerable deformation 
 must take place in the end plates. The back end, which is practi- 
 cally a flat plate, will be strained uniformly. If made exceptionally 
 thin, it would have to expand as much as the shell, but, not being 
 able to contract crossways, the consequent drum tension z would 
 bepD : 2(/x, - 1), or about 50/ more than the circumferential tension 
 in the shell. 
 
 With the front plate, which is perforated by furnaces, manholes, 
 and tube holes, it would at first sight appear as if locally the stresses 
 might grow to be excessive, but as in the remaining narrow flanged 
 strips there are no cross stresses, the remaining surface ones cannot 
 exceed those in the shell plate. The weakest points are to be found 
 between the furnace front holes; but, as no fractures take place 
 there, it is but reasonable to suppose that the stresses in the end 
 plates., due to their attachment to the shell, are small, the roundness 
 of the flange providing the necessary springiness. 
 
 Stresses near the Dome Holes. A problem which is often met 
 with in boiler designing is the efficient staying of the corners of two 
 
 < d * 
 
 
 
 I 
 
 
 c 
 
 
 : 
 
 
 
 /K 
 
 x^ 
 
 . c ^s* 
 
 
 
 i 
 
 
 
 iH 
 
 
 
 1 
 
 
 
 
 
 
 1 
 
 
 | 
 
 
 
 f 
 
 C 
 
 ; 
 
 
 
 1 
 
 
 
 
 
 D 
 
 
 > * 
 
 
 
 I 
 
 i 
 
 i 
 
 
 
 1 
 
 
 t 
 
 
 
 i 
 
 
 
 
 
 1 
 
 
 i 
 
 
 
 1 
 \^ 
 
 
 f 
 
 
 
 *B 
 
 
 
 FIG. 171 
 
 
 Fio. 170 
 
 intersecting cylindrical shells (fig. 171). Fig. 170 is a section through 
 tho line &%. 
 
 Assuming that the larger cylinder is cut up into numerous rings of 
 the thickness 3, and that internal pressure is p, then if the ring under 
 consideration were severed at the point G it would have to be retained 
 
 in its position by a pull Q = ^ . 3 . p. 
 
 Now the vertical component of this pull could be transmitted to 
 the straight side of the cylinder rf, but a stay would have to be fitted 
 
MECHANICS 
 
 197 
 
 to take up the horizontal component q. A little consideration will 
 show that it bears the same relation to Q as the distance ce bears to 
 half the diameter D. The same arguments show that the horizontal 
 component of the narrow strip cF is also proportional to its projected 
 area. This shows that the greater pull is found at G and the smaller 
 one at H. The sides of the holes are also severely stressed, see 
 p. 216. 
 
 Stresses in Cylindrical Flues. The same formula as for cylin- 
 drical shells may be applied here, but, when experimenting, buckles 
 will show themselves long before even the limit of elasticity for com- 
 pression has been reached, and the pressure cannot then be increased, 
 because the flue grows weaker and weaker the more it alters its shape. 
 It is important to know at what pressure this change takes place. 
 Let the elliptical dotted line (fig. 172) be the shape of the originally 
 cylindrical flue, and let the black line be the curve of thrusts. This 
 is a nearly circular line, and can be found by graphic construction, 
 as is done in the case of arches, &c. The intensity of the thrust is 
 
 -=-p, where p is the external pressure. To find the bending moment 
 
 at any position (say, at the angle a) it is only necessary to multiply 
 
 this thrust into the distance 
 h between the two lines. 
 At the major and minor axes 
 the moments are maxima 
 
 ^. For 
 
 FIG. 172 
 
 moment of inertia, we have 
 
 2 
 that p is limited : 
 
 -P<s- E - = 8 
 
 any other point m = m l 
 cos 2a. This equation is 
 practically identical with 
 that obtained for a straight 
 strut of the length DTr/4 
 - with loose ends and loaded 
 with the above force. If 
 accidentally bent, such a 
 strut would straighten itself 
 while supporting its load 
 K, provided it does not ex- 
 
 ceed K = 16 ^ tl . Sub- 
 stituting the value for K, 
 and also for I = * the 
 
 16. 
 
 , , . , . . 
 
 which it follows 
 
 Ibs. per sq. in. 
 
 As will be seen, p in this formula depends only on the modulus of 
 elasticity, and not on the working strength of the material ; or, in other 
 words, the strength of a flue to resist a collapsing or buckling pres- 
 sure depends on its rigidity, whereas its strength to resist a crushing 
 
198 
 
 pressure depends on the strength of the material. The two values 
 are equal when 
 
 S = | Et' 2 : D 2 . 
 
 o 
 
 Here S is the plastic limit of the material. This formula expresses 
 the conditions under which a flue would give way simultaneously 
 both by crushing and collapsing. Assuming that E-f-S = 1200, we 
 have ' 
 
 -y- 
 
 V 4800 
 
 40' 
 
 This means, that as long as the ratio of t to D is greater than ^, a 
 perfectly cylindrical tube, unsupported at its ends, will give way by 
 crushing and not by collapsing. Boiler tubes are not supported at 
 their ends, which is the same thing as if they were of infinite length ; 
 yet, on account of their relative great thickness, it is not wrong to 
 estimate their strength by the formula p = 2^S : D for cylindrical 
 furnaces, the ratio t : D is always less than 0-025. 
 
 Corrugated Flues. By corrugating a flue, I, the moment of 
 
 f3 /i / L2 
 
 inertia of one inch of its section is increased from -- to - s + - , 
 
 12 1J o 
 
 where h is the depth of the corrugations, and we have 
 
 t 3 
 
 Let h = 1 J in., then -^ can be neglected, and we find that the crush- 
 ing and collapsing pressures are equal when 
 
 r . t . S 4 . t . h z . E 
 P= -v~ -553- 
 
 that is, when - ^ . This shows that even very slight corru- 
 gations will make ordinary boiler flues independent of their end sup- 
 ports (see Dr. F. GrasKbff, 1866, pp. 232, 235). These deductions 
 suggest that the higher the pressures on furnaces, the wider may 
 the stiffening rings be placed apart. 
 
 Influence of Rings and Furnace Ends. The previous formulae take 
 no account of the strengthening effect of rings or furnace ends. One 
 way of dealing with this question is to regard the shell of a furnace as 
 if it were a wide flat column, supported at its ends by two solid guides 
 (fig. 173). 
 
 Let L be one-eighth of the furnace circumference, whose diameter 
 is D, and let I equal half its unsupported length, while q is the cir- 
 cumferential thrust per inch of length. 
 
 Then, if we take a narrow vertical strip (fig. 173A), the bending 
 moment would be q . y. This would produce a curvature 
 
 1 = ^y = ?.. 
 
MECHANICS 
 
 199 
 
 If, on the other hand, we divide the shell into horizontal strips, they 
 will be bent as shown in fig. 174. The external forces producing this 
 deflection are due to certain horizontal shearing forces, which when 
 
 1W111M 
 
 fio. 175A 
 
 summed up can be represented by an imaginary horizontal pressure jp, 
 which is balanced by P at either end. The slight extra relief due to 
 the action of force q on the radius p may be neglected (fig. 175). 
 We then have 
 
 m l = E . I 
 
 . y /p(x- 
 
 x l )dx 
 
 . dx, 
 
 = E . I = l- 
 
 It is evident that to work out these formulas would require more 
 space than can be spared, and as the result, like the previous ones, is 
 only applicable to perfectly circular furnaces, it will not 
 be carried further. In practice the problem is made more 
 complicated by the back end being irregularly supported. 
 This is also shown in fig. 173, which represents the case of 
 a furnace whose saddle is indicated by a vertical dotted line 
 and is supported by the tube plate, while the bottom extends 
 the whole length as far as the combustion chamber back 
 '7 plate. 
 
 FIG 175 Ribbed and Flanged Furnaces. Another way of looking 
 at the problem, and one which is intimately mixed up with the 
 above, is the relief afforded to the circumferential stresses by the endi 
 plates or stiffening rings. Thus in fig. 176 the line AB represents the 
 original position of the cylindrical part of the flue, whose section is shown 
 above. CD is its position when the diameter has decreased under pressure 
 
200 
 
 MECHANICS 
 
 if rings are fitted to the ends, while EF would be its position if no rings 
 were fitted. The circumferential stresses are, of course, proportional 
 to the compressions S l and S , 
 showing that the relief afforded 
 
 at the centre is . & . In 
 
 *i+yi 
 
 this fig. 176 y and y l have the 
 same meaning as in fig. 169, 
 p 195, and could, if required, 
 be calculated by the formulae 
 to be found there. When 
 doing this it must not be 
 
 forgotten that 
 
 dy 
 
 dx 
 that approximately 
 
 both when x = and when x l t and further 
 
 y\ 
 
 4.E . t 
 
 P.Q 
 
 2 . E . a' 
 
 where a is the excess sectional area of the strengthening ring over and 
 above that of the cylindrical part, and Q has the same value as on p. 195. 
 Oval Furnaces. The same reasoning which led (fig. 172) to a 
 limiting pressure for a perfectly cylindrical furnace has to be modified 
 if the furnace was originally elliptical. Let 2 . A be the difference 
 between the major and minor axes before straining, and let 2 . 1 be 
 the difference after the external pressure has been applied ; then it can 
 easily be shown that the furnace still remains elliptical, and that 
 
 * 16. E.I 32 . E . I 
 
 " 16 . E . 1 - K . D 2 = k ' 32 . E . I - p . D 3 * 
 
 Example : Let A = \ in., t = 
 E = 30,000,000 pounds ; then 
 
 in., D 
 
 -^ = 2-78 
 
 100 Ibs., 
 
 A 1 - 0-64 
 5 = 1-4 ins. 
 
 This is of course only true for long furnaces where the supporting 
 influence of the ends can be neglected. In a corrugated flue whose 
 moment of inertia of section is about ten times greater than the above 
 half-inch plate, the ratio would be 
 
 This shows how enormously rigid these furnaces are, even although 
 they, like long plain ones, have no effective end support. 
 
 When the furnaces are short, or when strengthening rings are 
 fitted, the problem grows to be a very complicated one, every defor- 
 mation producing secondary strains and stresses. The approximate 
 formulae which the author has worked out are far too complicated to 
 be of practical value. It may, however, be pointed out that the amount 
 of deflection is a fair measure of the stresses. Thus, in the above 
 
 example of a plain furnace, where - = 2'78 for an infinite length, it 
 
MECHANICS 201 
 
 is probable that for a length of 6 ft. the elastic deformation 3 A 
 would be reduced from 1'78 . A to about 09 . A, and that for shorter 
 lengths this deformation would diminish inversely as the square of 
 the length, being only 0*1 . A for a 2 -ft. length. 
 
 In a truly cylindrical furnace of the above dimensions the circum- 
 ferential compression stress is 4,000 Ibs. If the length is infinite, 
 and 3 = 2*78 . A, then the additional stress due to bending is 33,360 
 Ibs., making a total of 37,360 Ibs. 
 
 In a corrugated furnace of equal ellipticity the total circum- 
 ferential stress would be 16,816 Ibs. If the plain furnace is made 
 only 6 ft. long its circumferential bending stresses would be reduced 
 approximately by one half, making a total stress of, say, 25,000 Ibs., 
 and for a 2 ft. length the total stress would hardly exceed 6,000 Ibs. 
 
 As pointed out on p. 28 fierce fires tend to make furnaces oval, 
 while scale, greasy dsposits, &c., raise the mean temperature of the 
 plates so much that tie limit of elasticity is lowered (see p. 190), but 
 even then, although tie plates do give way a little, the flanged rings, 
 if fitted, give ample support to the cylindrical portions of the furnaces, 
 showing that in long furnaces their circumferential strengths are of 
 importance, whereas short furnaces may almost be treated as flat 
 plates supported between beams in this case strengthening rings. 
 
 Shearing Stresses in Furnaces. Above the furnace bars the 
 temperature of the furnace plates is higher than that below the bars. 
 This is due partly to the fire on one side and to scale or grease on 
 the other. A heated furnace top is therefore longer than its bottom, 
 resulting in a slight general bend, which is in itself of little impor- 
 tance ; but at the boundary of heat and cold very severe shearing 
 stresses are set up, particularly at the furnace ends. Suppose that 
 the mean temperature of the furnace plate above the bars is 20 F. 
 higher than below the bars, and that there is a zone of 2 in. alongside 
 the firebars where the change of temperature is a gradual one. Then, 
 if the furnace is 6 ft. long, giving a span of 3 ft. on either side of the 
 grate centre, the forward and back furnace top would grow -^ in. 
 longer than the bottom : the shearing angle produced at the front end 
 would therefore be ^ . ^^ ; and, as the modulus of shearing elasticity 
 is 11,600,000 (see p. 166), the shearing stress would be 23,200 Ibs. pei 
 square inch. In a longer furnace, with a fiercer fire, with cold wate? 
 fed into the boiler bottom, and scale on the furnace above the bars, 
 these shearing stresses may grow to be very serious. They probably 
 account for the leakages at the furnace fronts and back ends just 
 below the bars. 
 
 Longitudinal Stresses in Furnaces. As in beams and in shell 
 plates, so there will be cross stresses in furnaces, and it is of impor- 
 tance, particularly when testing them, to be able to ascertain their 
 intensities. Thus, in the case of the above-mentioned deformed oval 
 furnace there will be longitudinal tension and compression stresses 
 amounting to about 4 tons per square inch, all tending to make the 
 ends of the furnace more oval than its centre. 
 
 Perfectly circular furnaces tend to elongate under pressure, just 
 as boiler shells contract. When testing a furnace in a shell to which 
 it is firmly riveted at the ends, longitudinal stresses are set up. It 
 will be found that the furnace is then subjected to a longitudinal com- 
 pression stress, which is about 30 per cent, of its circumferential 
 
202 
 
 MECHANICS 
 
 stress, so that under these conditions, which are not necessarily 
 reproduced in practice, the plain furnace plates are subjected to a 
 shrinking stress, while this is not the case with corrugated ones. 
 Plain and also ribbed furnaces might therefore be expected to do 
 better in a boiler than in the test apparatus. 
 
 This view is supported by the fact that when experimentally test- 
 ing furnaces with welded seams they usually give way along a line 
 exactly opposite the riveted seam of the shell, being the point where 
 the longitudinal stresses would be greatest. 
 
 Experiments on Cylindrical Furnaces. The earliest experiments on 
 the influence of length on the strength of furnaces were made for the 
 Manchester Steam Users' Association, under the direction of Sir 
 William Fairbairn, who published them in 1856. With the exception 
 
 Fio. 177 
 
 of his Nos. 7, 8, 10 and 11, which differ among themselves by about 
 35 %, his results agree generally with the view that the strength of a 
 flue varies inversely as its length. But a careful examination of his 
 publications shows that he assumed the 150 sq. ft. of tinned sheet iron, 
 of which he made the tubes, to be of one thickness, whereas it is 
 more than probable that differences of at least -^ in. must have 
 existed, and this represents 20 per cent, of the thickness, or 35 per 
 cent, of the square of the thickness. It is, further, but reasonable to 
 suppose that the longer tubes would contain more weak parts than 
 the short ones, and further they would be more likely to be more 
 oval than the short ones, and would therefore be the first to collapse. 
 For these reasons the author does not attach the same importance to 
 these experiments as some of the mathematicians who have evolved 
 elaborate empirical formulae from them. Fairbairn further made a 
 few experiments on full-sized furnaces, but, as has been pointed out, 
 in one case either the furnace or the boiler diameter must be wrongly 
 stated. Further experiments were made by E. V. J. Knight, 'C. E.,' 
 1.878, vol. li. p. 133 ; by the Washington Navy Yard, 1874, published 
 by W. H. Shock, 1880, p. 113 ; by the Board of Trade ; by Carman, 
 
MECHANICS 
 
 203 
 
 ' University Illinois Bui.,' 1906, vol. 3 ; by Stewart, Am. M. E.,' 1906, 
 p. 730, and lastly, some very elaborate experiments by the German 
 Admiralty at their works at Danzig. The dimensions are given in 
 millimetres. The total number of readings taken with each furnace 
 frequently amounted to more than five hundred, and are a most 
 valuable contribution to the practical part of the science of elasticity. 
 The gauging instrument, fig. 177, consists of two stout brackets 
 carrying a boring bar with a screw in a slot, and on this bar is a 
 carriage with movable gauges, which is brought into contact with the 
 furnace plate for measuring purposes. 
 
 Hydraulic Tests of Plain and Flanged Cylindrical Furnaces 
 
 
 Lengths 
 
 Diameters 
 
 Thick- 
 ness 
 
 Collaps- 
 ing 
 
 
 J? 
 
 Joint 
 
 
 Experimenter or 
 Works 
 
 I 
 
 I S 
 
 Max. 
 External 
 
 i 
 
 | 
 
 1 
 
 3 
 
 i 
 
 S 
 
 1 
 
 i 
 
 1 
 
 ! 
 
 H 
 
 I 
 
 Remarks 
 
 
 ins. 
 
 ins. 
 
 ins. 
 
 in. 
 
 
 ins. 
 
 Ibs. 
 
 tons 
 
 
 tons 
 
 
 
 
 Fairbairn . 
 
 60 
 
 
 U 
 
 
 .. 
 
 i 
 
 125 
 
 3-3 
 
 i 
 
 
 Lap. 
 
 L 
 
 
 
 37 
 
 
 9 
 
 
 
 14 
 
 262 
 
 3-7 
 
 i 
 
 
 Lap. 
 
 
 
 
 37 
 
 
 9 
 
 
 
 14 
 
 378 
 
 5-4 
 
 i 
 
 
 Batt 
 
 
 
 
 276 
 
 
 7-87 
 
 
 [ 
 
 157 
 
 110 
 
 1-2 
 
 i 
 
 
 Lap. 
 
 L 
 
 
 
 61 
 
 360 
 
 
 
 18} 
 33i 
 
 
 
 - 
 
 I 
 
 420 
 99 
 
 7-0 
 2-2 
 
 i 
 i 
 
 
 Lap. 
 Lap. 
 
 L 
 
 L 
 
 
 
 420 
 
 
 42 
 
 \\ 
 
 M 
 
 $ 
 
 97 
 
 2-7 
 
 i 
 
 
 Lap. 
 
 L 
 
 
 
 300 
 
 
 42 
 
 
 
 
 
 127 
 
 3-2 
 
 i 
 
 
 Lap. 
 
 L 
 
 
 KM ht . . 
 
 48 
 
 48 
 
 24 
 
 36 
 
 36 
 
 
 
 
 
 
 
 235 
 217 
 
 7-5 
 7-0 
 
 i 
 i 
 
 
 Weld 
 Weld 
 
 A 
 
 
 
 48 24 
 
 36 
 
 
 I 
 
 
 
 468 
 
 10-0 
 
 i 
 
 
 Weld 
 
 A 
 
 
 
 48 
 
 36 
 
 
 
 
 
 390 
 
 8-3 
 
 i 
 
 
 Weld 
 
 
 
 Washington Navy Yard 
 
 71 35i 
 71 b5$ 
 
 54 
 54 
 
 1 
 
 
 
 
 1 
 
 105 
 120 
 
 5-0 
 5-8 
 
 i 
 i 
 
 
 Butt 
 Batt 
 
 B 
 B 
 
 
 
 71 35 
 
 54 
 
 
 
 
 
 133 
 
 6-4 
 
 i 
 
 
 Butt 
 
 A 
 
 
 
 71 36 
 
 54 
 
 
 
 
 
 130 
 
 6-3 
 
 i 
 
 
 Butt 
 
 A 
 
 
 Board of Trade . 
 
 !? 
 
 
 
 $ 
 
 - 
 
 
 
 i 
 
 j 
 
 200 
 180 
 
 5-8 
 4-6 
 
 i 
 i 
 
 
 Lap. 
 Lap. 
 
 
 Donkey boiler 
 Donkey boiler 
 
 
 86 
 
 
 38 
 
 
 
 
 
 187-5 
 
 4-2 
 
 i 
 
 
 Weld 
 
 
 
 ** 
 
 86 
 
 
 38 
 
 
 
 
 
 450 
 
 7-6 
 
 E 
 
 
 Weld 
 
 A 
 
 
 9% 
 
 108 
 
 
 37 
 
 
 
 i 
 
 -J 
 
 260 
 
 4-0 
 
 I 
 
 
 Lap. 
 
 L 
 
 Old boiler 
 
 *t 
 
 
 
 
 
 
 
 
 
 
 
 
 I 
 
 Compressive 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 strength of 
 
 . Dalzell Works 
 
 94 
 
 
 32-94 
 
 
 
 42 
 
 370 
 
 6-5 
 
 S 
 
 28-1 
 
 Weld 
 
 -1 
 
 this material 
 
 
 
 
 
 
 
 
 
 
 
 
 
 j 
 
 was under 18 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 tons 
 
 
 94 46J 
 
 32-94 
 
 
 
 42 
 
 600 
 
 10-5 
 
 s 
 
 28-1 
 
 Weld 
 
 A 1 
 
 * n 
 
 94 46 
 
 32-94 
 
 
 
 42 
 
 600 
 
 10-5 
 
 S 
 
 28-1 
 
 Weld 
 
 A 
 
 No collapse 
 
 Hall, Russell & Co. 
 
 773 18J 
 
 43 
 
 \ 
 
 '_ 
 
 i 
 
 700 
 
 13-5 
 
 s 
 
 .. 
 
 Weld 
 
 A 
 
 
 
 772 19 
 
 43 
 
 !S 
 
 
 ft 
 
 740 
 
 15-2 
 
 s 
 
 
 Weld 
 
 A 
 
 No collapse 
 
 J. Howden <t Oa 
 
 84i 23 
 
 43-09 
 
 
 
 546 
 
 840 
 
 14-7 
 
 s 
 
 , 
 
 Weld 
 
 A 
 
 
 
 84i 23 
 
 43-09 
 
 
 
 546 
 
 760 
 
 13-3 
 
 s 
 
 
 Weld 
 
 A 
 
 
 * 
 
 84i 23 
 
 43-09 
 
 
 
 546 
 
 840 
 
 14-7 
 
 s 
 
 
 Weld 
 
 A 
 
 
 " 
 
 84f 23 
 
 43-09 
 
 
 
 
 546 
 
 835 
 
 14-6 
 
 s 
 
 
 Weld 
 
 A 
 
 1 
 
 1 A stands for Adamson's ring. The lengths between rings are variously measured from centre to 
 centre this is the case in the German Admiralty experiments or between ends of rounds of flange. If 
 the end lengths of furnaces are not flanged, the lengths are measured to centres of rivet holes. 
 
 L stands for circumferential lap joints ; they add a little to the furnace strength. 
 
 B stands for circumferential butt strap joints. They also add to the furnace strength, 
 
 As far as practicable, all these experiments mentioned above are 
 collected together in the following table; those on plain furnaces 
 will also be found in 'N. A.,' 1899, vol. li. p. 142, M.S.U.A. 1899. 
 That paper also contains a Table II. of 119 cases of accidentally 
 collapsed furnaces, about which sufficient details were known to 
 calculate the collapsing stresses ; of these, however, 16 furnaces 
 were oval and 22 doubtful. That paper also contains Table IV. of 
 
204 
 
 MECHANICS 
 
 30 cases of furnaces which, although oval, had worked safely for 
 years. 
 
 The formula deduced from these experiments is 
 
 > tons per sq. inch = 3 + 
 
 169,000 T 2 
 13?OOQ T , + 
 
 where L and T are the furnace lengths and plate thicknesses in 
 inches. Stewart obtains the following empirical formula from his 
 experiments 
 
 S = 2-75ET 2 : (1 - ^)D 2 . 
 
 Hydraulic Tests of Plain and Flanged Cylindrical Furnaces 
 made by the German Admiralty, Danzig 
 
 
 
 
 
 
 
 
 
 J ' 
 
 
 
 Lengths 
 
 Diameter 
 
 Thickness 
 
 Collapsing 
 
 
 
 Seam 
 
 
 1 
 
 If 
 
 3* 
 
 H 
 
 8 
 
 8? 
 
 . 
 
 
 
 1 
 
 1 
 
 1 
 
 1 
 
 Bern arks 
 
 I 
 
 9 
 
 -33 
 
 ton 
 
 "S fr4 
 
 1 
 
 d fl 
 1| 
 
 I 
 
 I 
 
 1 
 
 1 
 
 1 
 
 1 
 
 |i 
 
 
 
 I s 
 
 1 
 
 Aj 
 
 3 
 
 ^53 
 
 3 
 
 S 
 
 
 
 
 I 
 
 5 
 
 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 Ibs. 
 
 tons 
 
 
 tons 
 
 
 
 
 
 
 
 
 
 
 
 under 
 
 
 
 
 
 
 
 5 
 
 13 
 
 79 
 
 424 
 
 40'4 
 40-7 
 
 25 
 07 
 
 45 
 59 
 
 575 
 
 455 
 997 
 
 8-8 
 15-7 
 
 I 
 I 
 
 23-8 
 23-0 
 
 Butt 
 
 A 
 
 Collapsed at say 440 Ibs. 
 Collapsed 
 
 13 
 
 784 
 
 36 
 
 40-7 
 
 07 
 
 59 
 
 
 997 
 
 15'4 
 
 I 
 
 23-0 
 
 n 
 
 A 
 
 Uninjured 
 
 
 
 
 
 
 
 
 under 
 
 
 
 
 
 
 
 1 
 
 78 
 
 41J 
 
 40-0 
 
 10 
 
 33 
 
 323 
 
 342 
 
 9*1 
 
 I 
 
 21-7 
 
 
 
 A 
 
 Collapsed near butt 
 
 
 
 
 
 
 
 
 say 
 
 
 
 
 
 
 
 1 
 
 78 
 
 36J 
 
 40'1 
 
 20 
 
 33 
 
 
 330 
 
 8'9 
 
 I 
 
 21-7 
 
 m 
 
 A&H 
 
 Uninjured 
 
 6 
 
 78 
 
 4lj 
 
 40-3 
 
 17 
 
 45 
 
 440 641 
 
 13-1 
 
 I 
 
 26-3 
 
 >5 
 
 A 
 
 Collapsed near butt 
 
 6 
 
 78 
 
 36J 
 
 40-2 
 
 07 
 
 45 
 
 
 641 
 
 12-8 
 
 I 
 
 26-3 
 
 
 A&H 
 
 Uninjured 
 
 10 
 
 
 30 
 
 38-3 
 
 24 
 
 51 
 
 
 812 
 
 13-6 
 
 I 
 
 23-7 
 
 Weld 
 
 A 
 
 
 10 
 
 78 
 
 28 
 
 38-3 
 
 13 
 
 51 
 
 510 812 
 
 13-6 
 
 I 
 
 237 
 
 
 
 A 
 
 Collapsed 
 
 10 
 
 731 
 
 204 
 
 38-4 
 
 17 
 
 51 
 
 496 
 
 783 
 
 13'5 
 
 I 
 
 23-7 
 
 , % 
 
 A 
 
 tenacity at 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 bulge 18-4 tons 
 
 12 
 
 84 
 
 27 
 
 38-6 
 
 06 
 
 59 
 
 606 
 
 1,138 
 
 16'2 
 
 I 
 
 24-9 
 
 Butt 
 
 A 
 
 Collapsed at reduced 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 neck 
 
 12 
 
 84 
 
 30J 
 
 38-6 
 
 06 
 
 59 
 
 
 1,138 
 
 16-6 
 
 I 
 
 24-9 
 
 99 
 
 A 
 
 Uninjured 
 
 12 
 
 84 
 
 26; 
 
 38-7 
 
 16 
 
 59 
 
 
 1,138 
 
 16-6 
 
 I 
 
 24-9 
 
 
 A 
 
 
 2 
 
 78 
 
 28; 
 
 40-0 
 
 04 
 
 30 
 
 295 
 
 427 
 
 12-9 
 
 I 
 
 23-9 
 
 
 A 
 
 OoHtpMd 
 
 2 
 
 78 
 
 26i 
 
 40-0 
 
 25 
 
 30 
 
 
 427 
 
 12-7 
 
 I 
 
 23-9 
 
 
 A&H 
 
 Uninjured 
 
 2 
 
 78 
 
 23 
 
 40-0 
 
 08 
 
 30 
 
 
 427 
 
 12-7 
 
 I 
 
 23-9 
 
 
 
 
 8 
 
 78 
 
 28} 
 
 40-4 
 
 15 
 
 43 
 
 423 
 
 641 
 
 13-7 
 
 I 
 
 24-4 
 
 m 
 
 A 
 
 Collapsed 
 
 8 
 
 78 
 
 26 
 
 40-4 
 
 20 
 
 43 
 
 
 641 
 
 13'4 
 
 I 
 
 24-4 
 
 m 
 
 A&H 
 
 Uninjured 
 
 8 
 
 78 
 
 23f 
 
 40-4 
 
 14 
 
 43 
 
 
 641 
 
 13-4 
 
 I 
 
 21-4 
 
 
 
 
 3 
 
 78 
 
 41 
 
 40-0 
 
 04 
 
 32 
 
 307 
 
 427 
 
 12-4 
 
 I 
 
 26-6 
 
 n 
 
 M 
 
 Collapsed from end to 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 hoop 
 
 3 
 
 78 
 
 364 
 
 401 
 
 22 
 
 32 
 
 
 427 
 
 11-9 
 
 I 
 
 26-6 
 
 n 
 
 n 
 
 Uninjured 
 
 
 
 
 
 
 
 
 under 
 
 
 
 
 
 
 
 7 
 
 774 
 
 413 
 
 40-3 
 
 28 
 
 43 
 
 420 
 
 641 
 
 13-5 
 
 I 
 
 23-9 
 
 99 
 
 n 
 
 Collapsed from end to 
 
 
 
 
 
 
 
 
 say 
 
 
 
 
 
 
 hoop 
 
 7 
 
 774 
 
 36 
 
 40-3 
 
 63 -43 
 
 
 630 
 
 13-2 
 
 I 
 
 23-9 
 
 5> 
 
 n 
 
 Uninjured 
 
 4 
 
 78 
 
 283 
 
 40-3 
 
 24| -31 
 
 
 455 
 
 15-2 
 
 I 
 
 22-8 
 
 n 
 
 
 
 4 
 
 78 
 
 26} 
 
 40-2 
 
 24 
 
 31 
 
 307 
 
 427 
 
 12-5 
 
 I 
 
 22-8 
 
 n 
 
 _ 
 
 Collapsed. The hoop 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 rivets tore at 455 Ibs. 
 
 4 
 
 78 
 
 23 
 
 40-2 
 
 08 
 
 31 
 
 ... 
 
 455 
 
 13-2 
 
 I 
 
 22-8 
 
 m 
 
 M 
 
 Uninjured 
 
 9 
 
 78 
 
 281 
 
 40-4 
 
 11 
 
 45 
 
 
 783 
 
 15-7 
 
 I 
 
 21-9 
 
 99 
 
 
 
 9 
 
 78 
 
 26 
 
 40'4 
 
 10 
 
 46 
 
 443 
 
 783 
 
 15-7 
 
 I 
 
 21-9 
 
 
 m 
 
 Collapsed. The hoop 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 rivets tore later at 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 455 Ibs. 
 
 9 
 
 78 
 
 23^ 
 
 40-4 
 
 12 
 
 45 
 
 
 783 
 
 15-7 
 
 I 
 
 21-9 
 
 
 
 
 Uninjured 
 
 11 
 
 784 
 
 30 
 
 38-5 
 
 12 
 
 49 
 
 472 
 
 712 
 
 13-0 
 
 S 
 
 24-1 
 
 Weld 
 
 A 
 
 Collapsed 
 
 11 
 
 784 
 
 28 
 
 38-5 
 
 06 
 
 49 
 
 468 683 12-5 
 
 S 
 
 24-1 
 
 A 
 
 
 11 
 
 784 
 
 204 
 
 38-5 
 
 ... 
 
 49 
 
 ... 
 
 769 
 
 13-5 
 
 S 
 
 24-1 
 
 99 
 
 A 
 
 Uai&Jtmi 
 
 A stands for Adamson's ring. See footnote of previous table. 
 
 H stands for angle-iron hoop. The furnace lengths are measured from ring to ring or end seam, but not 
 
 to hoop. If the hoops are considered to give support, then in each line marked with H the lengths 
 
 In the third column will have to be halved. 
 
MECHANICS 
 
 205 
 
 Hydraulic Tests of Corrugated Furnaces (Fox's). Nos. 1-7, made at 
 Leeds Forge. Nos. 14-17 made by German Admiralty, Danzig 
 
 
 Length 
 
 Diameter 
 
 Thickness ' 
 
 Collapsing 
 
 
 
 1 
 
 g 
 
 S a 
 
 1 
 
 11 
 
 1 
 
 1 
 
 " 
 
 I 
 
 Remarks. Position of Bnlginga 
 
 & 
 
 1 1 11 
 
 1 
 
 1? 
 
 i 
 
 i 
 
 1 
 
 1 
 
 
 
 
 H 
 
 5 
 
 fc o 
 
 ** 
 
 
 
 CQ 
 
 
 
 
 ins. ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 Ibs. 
 
 tons 
 
 tons 
 
 
 
 81 ... 
 
 35$ 
 
 
 52 
 
 ... 
 
 900 i 13-9 22-7 
 
 No details 
 
 
 76 5| 
 
 341 
 
 JL 
 
 349 
 
 
 830 18-1 29-0 
 
 On flat 
 
 
 76 6 
 
 341 
 
 A 
 
 378 
 
 
 800 16-2 29-2 
 
 On flat. Thickness 0-331 ins. 
 
 
 79 6 i 33| 
 
 S 
 
 452 
 
 419 
 
 1,130 18-8 29-3 Second corrugation 
 
 
 80 6^! 34-5 
 
 X 
 
 468 
 
 
 1,090 17-9 ! 29-0 
 
 On flat 
 
 
 77J 6^5 33'6 
 
 S '574 
 
 551 
 
 1,400 18-3 28-5 I Eleventh corrugation 
 
 7 
 
 78 64. 1 34-9 
 
 3? ! * 575 
 
 542 
 
 1,410 19-1 29-4 Front corrugation 
 
 14 
 
 90 3| 40-2 
 
 X "492 
 
 362 
 
 925 i 16-9 23-7 Total length after standing 1 S mins. 
 
 15 
 
 79 111 40-2 ' & 1 -559 
 
 462 
 
 996 16-0 25-9 
 
 On flat. External diameter 38'5 ina. 
 
 16 
 
 79 I 4 426 ^ -642 
 
 522 
 
 1,066 15-7 24-2 : Near centre after standing 3 oiins. 
 
 17 
 
 80J :<* 
 
 48-3 A j '652 
 
 540 
 
 996 16-5 23-6 
 
 Near centre after standing 2 muis. 
 
 Hydraulic Tests of Various Corrugated Furnaces 
 
 
 Length 
 
 Diameter 
 
 Thickness ' 
 
 Collapsing 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 = 
 
 V 
 
 "8 
 
 Ifl 
 
 
 
 
 
 2 
 
 ~m 
 
 
 
 Remarks 
 
 a 
 
 to 
 
 
 
 -- 
 
 || 
 
 1 
 
 i! 
 
 - 
 
 1 
 
 2 
 
 
 
 
 
 
 5 
 
 
 S 
 
 0> o 
 
 & H 
 
 3 
 
 I 
 
 s 
 
 
 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 Ibs. 
 
 tons 
 
 tons 
 
 
 Farnley Spirally Corrugated Furnaces, 2 ins. deep, 6 ins. pitch 
 
 i 
 
 77| ... 
 
 39-2 
 
 
 559 
 
 835 
 
 13-1 
 
 
 
 2 
 
 78 
 
 
 39-1 
 
 1 \ 
 
 548 
 
 ... 
 
 850 
 
 13-8 
 
 
 
 3 
 
 78? i 
 
 38-9 
 
 
 442 
 
 ... 
 
 670 
 
 13-2 
 
 
 
 4 
 
 78| 1 ... 
 
 39-4 
 
 ] [ 
 
 446 
 
 ... 
 
 570 
 
 11-2 
 
 
 
 5 
 
 7&&| .- 
 
 39-3 
 
 
 
 354 
 
 
 515 
 
 12-8 
 
 
 
 Holmes' Corrugated Furnaces 
 
 6 
 
 84 
 
 ... 
 
 35*4 
 
 ^ 
 
 515 
 
 950 
 
 14-6 
 
 27-3 
 
 One corrugation and adjacent two 
 
 7 
 
 8 
 
 84 
 84 
 
 ... 
 
 35-6 
 35-5 
 
 1<J 
 
 452 
 557 
 
 ... 
 
 750 
 920 
 
 13'2 
 13-1 
 
 27-5 
 
 26-8 
 
 plain parts collapsed 
 One plain part collapsed 
 
 Morrison's Suspension Furnace 
 
 9 
 
 10 
 11 
 12 
 
 st 
 
 Sj 
 
 4i 
 
 3 
 
 34-1 
 34-3 
 
 34'4 
 34-7 
 
 I 
 
 325 
 373 
 470 
 452 
 
 = 
 
 795 
 
 900 
 1,100 
 1,050 
 
 18-6 
 18-5 
 18-0 
 18-0 
 
 27-6 
 27-3 
 26-9 
 26-6 
 
 Collapsed at plain part and at weld 
 second corrugation 
 .. along weld 
 
 13 
 14 
 
 w 
 
 4| 
 5 
 
 347 
 34-1 
 
 
 530 
 567 
 
 ::: 
 
 1,300 
 1,340 
 
 19-0 
 18-1 
 
 27-5 
 27-1 
 
 first to third corrugation* 
 at plain part 
 
 1 Note for last two tables. In order to obtain the true stresses in the material the total section of 
 the furnace plate should be measured. This is done in the German Admiralty experiments, where the 
 thickness of the furnace ends is multiplied into the furnace length. In the English experiment* the 
 thicknesses of the corrugated plates are taken ; they should have been multiplied into the total lengths 
 of the corrugations, and not into the furnace lengths. On an average, the corrugated plates are 
 1 1 per cent, thinner thau the ends of the furnaces ; all the English stresses should therefore be reduced 
 about 121 per cent. 
 
206 
 
 MECHANICS 
 
 Hydraulic Tests of Purves' Ribbed Furnaces 
 
 
 Length 
 
 Diameter 
 
 Thickness 
 
 Collapsing 
 
 
 
 1 
 
 3 
 
 
 3 
 
 a 
 I'. 
 
 1 
 
 '3 
 
 1 
 
 3 
 
 ' 
 
 1 
 
 Remarks 
 
 * 
 
 1 
 
 
 E 
 
 5 
 
 <T 
 
 Q 
 
 * 
 
 o 
 
 5 
 
 I 
 
 i 
 
 H 
 
 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ins. 
 
 ius. 
 
 ins. 
 
 Ibs. 
 
 tons 
 
 tons 
 
 
 
 
 Teste made a* Sir John Brown & Go's Works, Sheffield 
 
 1 
 
 78j 
 
 
 13 
 
 
 38-6 
 
 TT 
 
 568 
 
 
 740 11-2 
 
 27-2 
 
 Collapsed on flat 
 
 2 
 
 78j 
 
 
 13 
 
 I 
 
 38-7 
 
 ii 
 
 546 
 
 
 760 
 
 12-1 
 
 26-6 
 
 M 
 
 3 
 
 79, 
 
 
 7 
 
 i 
 
 38-6 
 
 '. 
 
 295 
 
 
 650 
 
 19-0 
 
 25-9 
 
 between first and second rib 
 
 4 
 
 79 
 
 
 7 
 
 
 38-6 
 
 ir\ 
 
 311 
 
 
 635 
 
 17-6 
 
 27-9 
 
 sixth auii seventh rib 
 
 5 
 
 79 
 
 
 7 
 
 
 38-8 
 
 i_5. 
 
 509 
 
 
 800 
 
 13-6 
 
 26-1 
 
 end to end 
 
 6 
 
 79, 
 
 
 7- 
 
 
 38-9 
 
 A 
 
 559 
 
 
 800 
 
 12-4 
 
 27-9 
 
 i 
 
 7 
 
 79, 
 
 
 7, 
 
 
 38-8 
 
 II 
 
 611 
 
 
 875 
 
 12-4 
 
 27-6 
 
 !> !! 
 
 8 
 
 79, 
 
 
 7. 
 
 
 38-8 
 
 ii 
 
 613 
 
 
 873 
 
 12-3 
 
 28-3 
 
 
 9 
 
 
 
 9; 
 
 
 38-8 
 
 
 307 
 
 
 675 
 
 19-0 
 
 28-8 
 
 
 10 
 
 
 
 9 
 
 
 38-7 
 
 
 362 
 
 
 700 
 
 19-0 
 
 28-0 
 
 
 11 
 
 
 
 9j 
 
 
 38-7 
 
 
 461 
 
 
 870 
 
 16-3 
 
 27-3 
 
 
 12 
 
 
 
 1 
 
 
 38-7 
 
 || 
 
 466 
 
 
 950 
 
 17-6 
 
 29-3 
 
 
 13 
 
 
 
 9J 
 
 i 
 
 38-6 
 
 
 686 
 
 " 
 
 1,065 
 
 15-7 
 
 28-7 
 
 
 14 
 
 
 
 tf 
 
 
 38-6 
 
 || 
 
 678 
 
 
 1,145 
 
 17-1 
 
 27-4 
 
 
 16 
 
 
 
 
 
 
 38-7 
 
 
 622 
 
 
 1,020 
 
 16-9 
 
 ... 
 
 
 
 
 Tes made at German Admiralty Works, Danzig 
 
 18 
 
 79 
 
 jH 
 
 38-0 
 
 A| 
 
 624 
 
 865 
 
 13-8 
 
 26-6 Collapsed end to end 
 
 Curved Plates. With oval furnaces, in which there is only a 
 slight variation of curvature, the bending stress due to m l (p. 197) 
 would be 3 . 8 : t times the mean circumferential stress. What, it 
 may be asked, will be the 
 effect if the curvature changes 
 still more rapidly, viz. from, 
 say, 24 ins. to a straight line, 
 as often happens in combus- 
 
 FIQ. 178 
 
 tion chamber tops (fig. 178) ? 
 
 or if it changes from one 
 
 side to the other, as in the 
 
 case of combustion chamber $ JG 179 
 
 bottoms (fig. 179)? When 
 
 the pressure is on the convex side, the circumferential stresses are 
 
 all compression, while when it acts on the concave side they are 
 
 tension. This is shown in fig. 179, which represents part of the 
 
 bottom of a combustion chamber with two furnaces. 
 
 As sketched, the conditions are more unfavourable than when 
 
MECHANICS 
 
 207 
 
 building an arched bridge without abutments and without any sup- 
 port, for the ends are in this case actually being pulled at. The 
 stresses which are necessarily set up are of the most complicated 
 nature. Thus there will be circumferential shearing stresses, which 
 increase very seriously towards the forward and back ends of these 
 plates, particularly along the line of change of flexure. Horizontal 
 seams should not be fitted here. These shearing stresses are also 
 
 very severe on the circumferential 
 seams of the furnace back ends and 
 of the combustion chamber backs ; 
 and the extra circumferential com- 
 pression stresses which are thereby 
 set up in the furnace saddles may 
 have been the cause of occasional 
 mishaps. The staying of these parts 
 to the boilei shell will necessarily 
 afford local relief, but very often 
 leads to excessive bending strains in 
 the screwed stay near the water level. 
 Thick Cylindrical Shells. This 
 subject would be out of place here 
 were it not that some of the mathe- 
 matical deductions will assist in 
 estimating the distribution of stresses 
 in riveted joints. 
 
 Let the left- and right-hand side of fig. 180 represent half the tube, 
 respectively with and without the internal and external pressures 
 p, and^? 2 . Then, dealing with the thin-walled ring dr of the radius r, 
 we find that if p is the radial pressure at this distance from the 
 centre, and if S is the circumferential stress, S being circumferential 
 tension, we have 
 
 S . dr = (p + dp) (r + dr) p . r. Neglecting dp . dr, we have 
 
 The radius of the ring has now decreased 
 
 FIG. 180 
 
 The thickness dr of the ring under consideration has decreased by 
 (3) Hd r) = d - d 
 
 If there are no longitudinal stresses in the cylinder, then its length 
 
 increases 
 
 (4, M. + '-JLE.). 
 
 Differentiating (2) we have 
 
 d (cr) _ _ _S p _r SdS __ dp \ 
 dr E ^ E E \dr p.dr)' 
 
208 MECHANICS 
 
 But d (<) r) = 5 (dr), and combining this with (3) 
 
 Substituting the values of S p from (1) we find 
 (5) *' 
 
 ,dS 
 
 + -=- =o. 
 dr 
 
 It follows that p + S is constant for all values of r, which 
 that 81 (4) is also constan?, and need not be taken into account. 
 Differentiating (1) leads to the equation 
 
 and combining this with (5) we get 
 
 /n\ o dp . d"*p 
 
 1 ; dr dr 2 " 
 
 Integrating this and introducing the various constants leads to the 
 following equations : 
 
 (8) 
 
 2. 
 
 - p l 
 
 2 _ r 2 
 2 r l 
 
 
 BI - .Pi = 2 * 2 _ 2 2 . According to Guest's law this difference of 
 
 ^2 ~ r l 
 
 stress which is the internal pressure added to the circumferential 
 stress should not exceed a certain limit. If r 2 = oc , Sj = - p ; the 
 combination of Sj and p is a pure shearing stress of the intensity 
 a- l =p l = - S x . At the radius r we have 
 
 /ON _ (Pi " ^ 2 ) r i% 2 
 
 \*J F" ,,.2/^2 . 2\ 
 
 2 - 
 
 (10) 
 
 s _ _ 
 
 , 
 
 From this it will be seen that p + S = o when p^r^ p\r^. In 
 that case too the metal is exposed to uniformly distributed spiral 
 shearing stresses, o-, as shown in 
 fig. 181 : its effects are often seen 
 around punched holes. 
 
 This condition is also approached, 
 at least near the internal circumfer- 
 ence, when r 2 is very large. For 
 practical illustrations see ' C. E.,' P 
 1893, vol. cxi. p. 212, and fig. 182, ! 
 which represents a piece of a steel 
 shell burst by a high explosive. All the fractured surfaces are 
 sheared and inclined at an angle of 45. 
 
MECHANICS 
 
 209 
 
 Oth or conclusions to be drawn are 
 
 1st. The maximum stresses, either tension or compression, are 
 always found at the internal circumference. 
 
 2nd. If the internal pressure p } = o, then the maximum circum- 
 ferential compression stress is 
 
 8, = 
 
 An approximately correct formula for cylindrical tubes would there- 
 
 fore be 
 
 where D is the external diameter and t the thickness of plate. 
 
 3rd. If the external pressure p 2 = o, then the maximum circum- 
 ferential tension stress is 
 
 s, - - 
 
 V - V 
 
 fore 
 
 For boiler shell plates an approximately correct formula is there- 
 
 Sl = ~ 
 
 , 
 
 and S] ~ ^1 = ~ 
 
 D, 
 
 where D x is the internal and Dj + t the mean, and Dj + %t the 
 external diameter of the shell. In both these cases, therefore, the 
 maximum simple stress has to be estimated as if the pressure were 
 acting on an imaginary tube whose diameter is a little larger than 
 the actual one, and Sj - p has to be estimated as if the internal 
 pressure were acting on the external diameter. 
 
 These corrections are too unimportant to be taken into serious 
 count in practice, except, as will shortly be explained, in the case of 
 rivet holes. 
 
210 MECHANICS 
 
 The deformations of thick-walled tubes are found by inserting the 
 values of S, and p } in equation (2) : 
 
 r, "E 
 
 ^"2 = _2 ..Pi^i 2 _ fa / ?'2 2 + ?'i 2 _ 1 
 ri E.(r 2 2 -r, 2 ) E Ir 2 2 -r, 2 / 
 
 An approximate formula for boiler shells would be 
 
 &>_.l>i 2 -ri-J 
 r 2 E ' 2* 
 
 and for boiler furnaces it would be 
 
 Plastic Tubes. As regards the distribution of stresses in thick- 
 walled cylinders when the plastic limit has been reached, little can be 
 learnt until the plastic properties of steel subjected to compound stresses 
 
 are better known. However, as the value of - changes when this 
 
 /* 
 
 limit is passed from about to ^, it is evident that it ought to be in- 
 troduced into the various formulae as a function of r, and then is not 
 
 any more a constant value, nor is S 4- p ; and what complicates matters 
 still more is that longitudinal stresses are set up which increase with 
 increasing length of tube. The stresses in a gun barrel which is on the 
 point of bursting are therefore not at all as simple as is usually assumed. 
 A thorough analysis of the shape of the 
 swelling of the material round a carefully 
 drifted hole (fig. 183), similar to that carried 
 out in the case of torsion tests, could per- 
 haps be made to throw light on this subject. 
 
 Riveted Joints. At first sight it would 
 appear that there is no simpler problem 
 than to find the stresses in a riveted joint. 
 Given the sectional area of the perforated 
 plate, and the sectional areas of the rivets, 
 the average stresses ought to be easily cal- p IG . 133 
 
 culated. But these are only the average 
 
 stresses. To find the positions and intensities of the maximum 
 stresses is far more complicated, but worth examining, not only on 
 account of the importance of the subject, but also because the diffi- 
 culty of dealing with it more in detail will make it clear how little is 
 yet known about other problems of boiler mechanics which, even at 
 first sight, strike one as more complicated than this one. 
 
 Deformation of Rivets. Fig. 184 represents part of a butt-strapped 
 joint. A force Q is being transmitted from the central (shell) plate to 
 the two butt straps and in doing so the bearing pressures pi and p^ 
 
MECHANICS 
 
 211 
 
 come into existence. They tend to give the rivet a slight bend, and 
 this deformation will cause an irregularity in their distribution, the 
 
 I 
 
 FIG. 184 
 
 pressure being proportional to the deformation. This is evidently a 
 similar case to the one which presented itself when dealing with the 
 influence of end plates on the distribution of stresses in cylindrical 
 shells, and which, as was there shown, leads to the most complicated 
 formulae. Here it will be assumed that as long as the elastic limit has 
 not been reached, p 2 is uniformly distributed over the thickness t of the 
 shell plate, and p l is distributed over the thickness of the butt straps in 
 
 O Q 
 
 the shape of a triangle. Then in the above casejpj = 2p z = ?- 
 
 Stress in Rivets. These pressures produce bending and shearing 
 stresses which, when reduced to right-angled resultants (see p. 167), act 
 in directions which are indicated in figs. 185 and 186. In both the in- 
 tensities are indicated by the shading of the various zones, and if placed 
 
 FIG. 185 
 
 over each other it would be found that for any particular point the two 
 sets of stresses cross each other at right angles. Fig. 185 shows only 
 compression stresses, and fig. 186 shows tension stresses at the left eclge, 
 which are gradually reduced and change into compression stresses at 
 the right-hand centre. The stresses and their angles have been calcu- 
 lated on the assumption that the rivet diameter is equal to the thick - 
 
212 
 
 MECHANICS 
 
 ness of the shell plate and twice as thick as the butt straps, and that 
 the pressure is distributed as in fig. 184, but rounded off at the corners. 
 
 FIG. 186 
 
 Then the mean stress along the line of shear, which is the mean of the 
 tension and compression stresses, is T13 ton per ton of mean bearing 
 pressure, and the maximum stress in this line is 1'55 ton. On the 
 upper part of the left edge there are some severe compression stresses, 
 the maximum being 2'33 tons ; and in the lower right-hand corner 
 shrinking stresses are met with, consisting of two right-angled stresses 
 of 1'2 and 1*45 ton per ton of mean bearing pressure. These diagrams 
 and values might be used for the purpose of calculating the elastic 
 deformation of the rivet, and the bearing pressures would then 
 have to be modified ; but as no very important deductions will 
 be drawn from these results, the more correct curves have not been 
 determined. 
 
 Distribution of Bearing Pressure. Another correction has to be 
 introduced on account of the irregular distribution of the bearing 
 pressure over the rivet diameter. Let the dotted 
 line (fig. 187) represent the imaginary outline of the 
 rivet section if it had been free to shift its position. 
 But having come in contact with the circumference 
 of the hole, which is shown by a black line, a pressure 
 is called into existence, which may be taken to be 
 proportional to the distance between the black and 
 dotted lines. This normal pressure between the rivet 
 and the plate is shown in fig. 188. p=p Q cos a. Here 
 p is the maximum bearing pressure. The sum of p cos a for the dia- 
 meter d of the rivet is ^ . p . d . t. This is equal to the load Q on 
 the rivet, and the maximum bearing pressure at the centre line is 
 
 Fio. 187 
 
 d.t' 
 
MECHANICS 213 
 
 In the butt straps, as has been explained, this pressure will perhaps 
 be double as much, depending on the flexure of the rivet and com- 
 pression of the rivet hole. 
 
 Fig. 188 shows that d } = d cos a, and that if the rivet were divided 
 into numerous axial laminae of equal thickness, the thrust on each one 
 
 FIG. 188 FIG. 189 FIG. 190 
 
 would be proportional to its own width, and if not connected amongst 
 each other they would be deflected by different amounts (see figs. 189 
 and 190). 
 
 As these independent motions cannot take place there must exist 
 a series of cross stresses in the rivets, which prevent the laminae from 
 slipping. It is also probable that in adjusting themselves to their 
 surrounding conditions the outer laminae do not offer as much resist- 
 tance as the inner ones, and therefore the normal pressure (fig. 188) 
 is more likely to be distributed according to the formula_p = j p cos u 3 , 
 which, if true, would lead to the conclusion that the maximum bearing 
 pressure to be found between the rivet and its hole is 
 
 . 3.Q 
 
 p ~ 
 
 which is 50 % greater than the mean. 
 
 The Shearing Stress in a Rivet increases from nothing at either of 
 its ends and at the centre of its length to a maximum at the plane of 
 shear. In this plane it is greatest at the centre of the rivet, falling 
 off in a parabolic curve towards the circumference. The maximum 
 shearing stress in the centre is therefore about double the mean, viz. 
 
 ,= 8_Q Q 
 
 TT. a* d* 
 
 which coefficient is nearly the saroe as T55 xl'5 as found above. 
 
 Shearing and Bending Stresses. If the leverage with which a 
 load acts on a beam is equal to one-third of its thickness, then the 
 limits of elasticity, both for tension compression and shear, are reached 
 simultaneously (see p. 192). In a lap joint this condition most likely 
 exists. In butt-strapped joints it will depend upon the thicknesses, 
 and on the distribution of the bearing pressure, whether this is so or 
 not. If the strap is equal to the thickness of the rivet, and the pres- 
 sure distributed as in fig. 184, or if the thickness of the strap is of 
 the rivet diameter, and p is uniformly distributed over the length, 
 then the above condition exists. In other cases the rivet gives way 
 first, either by bending alone or by shearing alone. Of course these 
 remarks only apply up to the elastic limit, and even here they are 
 
214 MECHANICS 
 
 seriously modified by the various cross stresses which it has only been 
 possible to hint at. 
 
 Plastic Rivets. As soon as the stresses increase to such an extent 
 that either at one point or another the elastic, or even the plastic, limit 
 has been reached, then the conditions are altogether changed. All the 
 pressures are more evenly distributed. The shearing stress is similarly 
 affected, and is probably uniformly distributed, as shown in fig. 167, 
 p. 192. The ultimate strength of a rivet may, therefore, be estimated 
 by those formulae which give the mean stresses, while its working 
 strength up to the elastic limit has to be found as explained above. 
 It is, therefore, very misleading to assume that the elastic limit and 
 ultimate strength of a rivet stand in the same relation as the elastic 
 limit and ultimate strength of a simple bar. In the latter case the 
 ratio is about as one to two, in the former it is more nearly as one to 
 five. A nominal factor of safety of five leads to a construction in 
 which the limit of elasticity of a rivet is just reached with the ordinary 
 working pressure. 
 
 When the dimensions of a rivet have been so arranged that the 
 limit of elasticity of the metal is reached simultaneously at various 
 parts, which is of course the most advantageous condition, then it 
 does not at all follow that, on increasing the load, rupture will also 
 take place simultaneously at all these points. In fact, there can be 
 no doubt but that the bending moments increase at a relatively 
 greater rate than the load, while the axial stresses due to them 
 increase irregularly. While this is going on, the shearing stresses 
 distribute themselves more uniformly and sink into relative insignifi- 
 cance, so that a rivet designed on the best principles for working 
 conditions would rupture primarily through bending, and at a lower 
 load than another which is so designed that all the ultimate stresses 
 are reached simultaneously. Of course in this case the rivet would 
 not be an equally efficient one under working conditions. That 
 unexplained actions of this sort do exist is proved by nearly all 
 experiments on this subject, for it will be found that it is not always 
 the part which is apparently most strained that gives way. In fact, 
 the stronger part either the rivet or the plate seems as if it were 
 always endowed with extra strength. Thus a joint may tear through 
 the plate when its stress is, say, 28 tons, while that in the rivets is 
 14 tons. But by reducing the sectional area of the latter it is possible 
 to construct a joint which will give way at, say, 20 tons, while the 
 plate remains intact, though in this case it has been strained up to 
 32 tons or more. 
 
 Rivet Holes. Circumferentially the bearing pressure in a rivet 
 hole is of course distributed exactly in the same way as on the rivet. 
 The stresses which are thereby produced in the surrounding material 
 might be determined with considerable accuracy by a careful and ex- 
 haustive analysis ; but this cannot be attempted here, and it will only 
 be possible to recapitulate some of the views on this subject, and 
 which are intended to be approximately correct. 
 
 Firstly, the stresses between the rivet holes are supposed to be 
 uniformly distributed. This is evidently incorrect. 
 
 Secondly, the shell plates, or the straps, are supposed to be built 
 up of a number of tapes or links, each one being of a sufficient section 
 
MECHANICS 
 
 215 
 
 for carrying the load which is placed on it (figs. 191, 192). The 
 depths of these links over the rivets must be made 50 % greater than 
 their widths. Although this view rather begs the question, it seems 
 
 ?.. }..*._ 
 
 Fio. 192 
 
 to give results which are well supported by practice, and if oftener 
 applied would lead to modifications in some of the complicated 
 riveted joints. Thus in fig. 191 it will be noticed that the inner row 
 of rivets is irregularly pitched. This is necessary, as otherwise the 
 
 tapes from the outer row would 
 have to be split in two and spread 
 out at an angle. 
 
 Thirdly, in order to estimate 
 the amount of metal required be- 
 tween the rivet hole and the edge 
 of the plate, this part is looked 
 upon as part of a continuous 
 beam. 
 
 Fourthly, the circumferential 
 shearing stresses are used as a basis. 
 
 Fifthly, a more thorough method is to deal with the metal 
 surrounding the rivet as if it were part of a thick-walled cylinder. 
 
 Distribution of Stresses near Rivet Holes. In fig. 193 the curves 
 A and B represent the distribution of the circumferential stresses at 
 these two points, due to the internal pressure p 0> which in this case 
 is supposed to be uniformly distributed. In the formula (8, p. 208) 
 
 _, r 2 = u, so that 
 
 for the curve A we have r, 
 
 . 
 
 01 = ~- 
 
 And for the curve B we have r, = ^ r 2 
 
 4 . P - 4 . 1. d + 2 . d 2 
 
 I 
 
 4 . Z 2 4 1. d' 
 
 Of course, as the adjoining rivet also produces stresses, S a has to be 
 added to S^ and we have 
 
216 
 
 MECHANICS 
 
 The following tables contain some numerical values of the ratios 
 of S, 1 : Po, and of S : p , for different values of d, u, I : 
 
 u : d 
 
 75 
 
 1 
 
 1-25 
 
 1-5 
 
 1-75 
 
 2 
 
 S, 1 : -P. = 
 
 2-6 
 
 1-67 
 
 1-38 
 
 1-25 
 
 1-18 
 
 1-13 
 
 
 I : d 
 
 3 
 
 3-5 
 
 4 
 
 4-5 
 
 5 
 
 6 
 
 7 
 
 8 
 
 S : -Po = 
 
 M7 
 
 1-11 
 
 1-08 
 
 1-06 
 
 1-05 
 
 1-03 
 
 1-02 
 
 1-02 
 
 From this it would appear that the tension stresses at the sides of 
 the rivet holes are slightly in excess of the rivet pressure p . Ap- 
 proximately 
 
 Similarly, the stress S 1 , maybe expressed with sufficient accuracy 
 by the formula 
 
 As has already been shown, these circumferential tension stresses 
 combine with the radial pressures p to form shearing stresses, acting 
 along spiral lines (fig. 182, p. 209) ; and, as mild steel gives way more 
 readily under this stress than under either simple tension or simple 
 compression, it is only natural that when the plate, and not the rivet, 
 gives way, the line of fracture 
 should start where shown in 
 fig. 194 ; also compare fig. 181, 
 p. 208. 
 
 It has been explained on 
 
 p. 193 that, on account of the Fw 194 
 
 axial contraction of boiler shells, 
 
 when subjected to internal pressure, the longitudinal seams are 
 subjected to a compression stress. At the edges of the plates this 
 will amount to about 30 % of the circumferential tension, and has to 
 be subtracted from S 1 ,, but it increases the spiral shearing stresses. 
 
 The above remarks apply only to the outer rows of rivets. In the 
 second and third rows the conditions are far more complicated ; but 
 if, as is usual, the rivets are placed closer together, the stresses will 
 be more uniform, and therefore relatively less severe. 
 
 Prof. B. G. Coker arM Mr. W. A. Scoble (<N. A.,' 1913) have 
 utilised the phenomena associated with the polarisation of light for 
 analysing stresses in transparent objects. Manufacturers of high 
 class lenses and prisms examine the slabs of glass from which they 
 intend to make their objects in polarised light, in order to detect 
 strains due to too rapid annealing. The colours which appear are 
 due to angular displacements of the planes of polarisation. These 
 angles are nearly proportional to the differences of the principal 
 
MECHANICS 217 
 
 stresses to which the object is subjected, and to its thickness, and 
 it is therefore an easy matter to estimate these differences of stresses 
 (x - y) by a comparison of colours. For mild steel, which nearly 
 conforms to Guest's law, and breaks down when a certain difference 
 of stress is reached, these simple observations would suffice, but if 
 the individual stresses are to be estimated it is necessary to determine 
 their sums (x + y). Professors Coker and Scoble determine these 
 sums by measuring the local contractions of thickness, which is about 
 one-third of the elongations which are being produced in the direction 
 of the stresses. Then x is half the sum of the two observations, and 
 y is half their difference. These experiments can be carried out on 
 sheets of glass, but it is a troublesome material on account of its 
 liability to break, and therefore very transparent xylonite has been 
 used. Their latest experiments were undertaken with a view to 
 determining the stresses in riveted plates, which stresses have not 
 been determined mathematically, though a formula has been con- 
 structed for stress in a plate with a hole in it which is subjected to a 
 single stress. By their optical method they found that the maximum 
 stress very near the hole was 2 '37 times the mean stress of the plate, 
 whereas the estimated stress for an infinitely wide plate is 2 '38 times 
 the mean. The theoretical maximum stress at the edge of the hole 
 is three times the mean. This mean stress includes the hole which 
 was one-quarter the width of the plate, so that the mean stress on 
 the remaining 75% of the plate is 1-33 of the above, and the maxi- 
 mum stress at the edge of the hole is theoretically 2*25 times as 
 great. Similar tests were carried out by E. Preuss (' Deut. Ing.,' 1912, 
 vol. 56, p. 1780) by measuring the elongations near holes which had 
 been drilled into test pieces of various widths, and the following 
 results were obtained. They also apply to large holes hi shells. 
 
 Ratio of Width to Hole Diameter . 
 Ratio of Maximum to Mean Stress . 
 
 8 
 2-35 
 
 4 
 2-34 
 
 2-4 
 2-13 
 
 1-71 
 2-24 
 
 These results are in fair agreement with the above, and confirm 
 the claim that this optical method of measuring stresses is reasonably 
 correct. Messrs. Coker and Scoble therefore applied it to xylonite 
 plates which were pulled by metal studs (glass studs would have 
 been better) and measured stresses for widths of four diameters and 
 three diameters which indicate that the edges of the holes are stressed 
 about four times the average, including the holes, or about three times 
 the mean stress in the remaining metal. According to the above 
 formula based on the theory of thick-walled cylinders, the ratio of 
 maximum to mean stress for I = 4d is 3 -24. 
 
 Plasticity of the Solid Plate. When the stresses have grown so 
 intense that the plastic limit has been reached they will rearrange 
 themselves; but instead of being distributed more uniformly, it is 
 probable that they will become more local, the maximum stresses 
 being found round the circumferences of the holes. Testing a set of 
 joints to destruction cannot, therefore, give a correct idea as to the 
 proportions which should exist between the thickness of the plates, 
 the rivet diameters, and the holes, 
 
218 
 
 MECHANICS 
 
 Distribution of Stresses amongst several Rows of Rivets. In 
 
 fig. 195 the slanting position of the rivets is intended to indicate that 
 a treble riveted lap-joint is being strained. If, as is generally sup- 
 posed, each rivet bears the same load, then every one will be inclined 
 to the same angle ; but then the stretch, and therefore also the 
 stress of the plate b would be equal to that of d, and the same for c 
 and e. But it is obvious that, whereas the full stress is to be found 
 
 Fio. 195 
 
 at a, two-thirds will be found at b or at e, and only one-third at c and 
 d, because in either case each rivet has only transmitted one-third of 
 the load. These two distances have, therefore, only stretched half as 
 much as b and e, and therefore the central rivet will not, as has been 
 assumed, be inclined as much as the other two, and the shearing 
 stress to which it is subjected will be less than the average, while 
 for the two outer ones it will be more. 
 
 There are obvious reasons why it is easier to calculate the distribu- 
 tion of stresses in a butt joint than in a lap joint ; but even this is a 
 
 most laborious operation, 
 
 and the results are not 
 quite reliable. The fol- 
 lowing estimate was ob- 
 tained with a joint whose 
 dimensions were taken 
 from practice, and which 
 was intended to represent 
 part of a double butt- 
 strapped joint, having a 
 percentage of 85'3. (See 
 fig. 196.) 
 
 Assuming the circum- 
 ferential stress on the 
 shell plate to be 5'05 tons 
 per inch, each rivet is 
 
 FIG. 196 supposed to be subjected 
 
 to a mean stress of 5 tons 
 
 per sq. in., and the mean stress in the plate between the rivets would 
 be 5 4 92 tons. However, it was found that the mean shearing stress 
 in the outer rivets is 5'10 tons, in the intermediate ones 4'20 tons, 
 and 5'75 in the inner ones. This joint, therefore, is only equal to 
 74* 1 % of the solid plate, which is a little less than might be obtained 
 by using the far more practical double -riveted joint, having rivets 
 1J in. diam. and a pitch of 4'9 ins. 
 
 This should be a sufficient justification for the practice of not 
 crediting a joint with a greater strength than 75 % of the solid 
 plate. 
 
MECHANICS 
 
 219 
 
 J. T. Milton (' N. A.,' 1885, vol. xxvi. p. 204) has recorded ex- 
 periments on this subject which show that, even for the ultimate 
 strength of a joint, considerable differences exist as regards the 
 stresses in the various rows of rivets, and no doubt experiments on 
 the elaborate joints to be found in bridges would show that their 
 high percentage is imaginary. 
 
 Experiments on Riveted Joints. A very exhaustive list of experi- 
 ments on riveted joints will be found, W. C. Unwin, M. E.,' 1881, 
 p. 303. These and a few subsequent ones are contained in the follow- 
 ing table : 
 
 W. Fairbairn . . , 
 E.Clark 
 
 D.K. Clark . 
 
 J. Grantham . . 
 
 D. Kirkaldy . 
 
 W. Fairbairn . . 
 
 N. Barnaby . 
 
 J. Price ... 
 
 J. Cochrane . 
 
 W. Waller 
 
 W. R. Browne . 
 
 J.G.Wright . 
 
 Report . 
 
 D. Kirkaldy . 
 
 Sir W. Fairbairn . 
 
 B. B. Stoney . 
 
 J. Barba 
 
 J. Riley . 
 
 R. B. Longridge 
 
 R. V. Knight . 
 
 W. Boyd . 
 
 B. Martell 
 
 R. V. Knight . 
 
 Dr. H. Zimmermann 
 
 N. Barnaby . 
 
 D. Greig and M. Eyth 
 
 R. B. Longridge 
 
 R. V. J. Knight 
 
 Prof. A. B. W. Kennedy 
 
 > 
 
 W. Parker 
 
 C. H. Moberley 
 R. B. Longridge 
 
 Prof. A. B. W. Kennedy 
 
 J. G. Wildish . 
 
 J. T. Milton . 
 
 Prof. A. B. W Kennedy 
 
 G. W. ManueJ 
 
 1850 . 'Phil. Transactions,' vol. ii. 
 
 p. 677. 
 . 'Britannia and Con way 
 
 Bridges,' vol. i. ch. iv. 
 1858 ' Recent Practice.' 
 
 1860 N. A.,' vol. i. p. 57 
 
 1862 
 
 1864 Soc. Arts,' vol. xiii. p. 20. 
 
 1865-6 ' Eng. Scot.,' vol. ix. p. 153. 
 
 1869-70 vol. xiii. p. 47. 
 
 1870 ' C. E.,' vol. xxx. p. 265. 
 
 1871 ' N. Eng. I.,' vol. xx. p. 117. 
 
 1872 ' M. E.,' p. 53. 
 
 PP. 77, 89. 
 
 ' N. Eng. I.,' vol. xxi. p. 67. 
 
 'Experiments on Riveted 
 
 Joints.' 
 
 1873 'R. Soc. Edinburgh.' 
 
 1875 ' R. Ir. Ac.,' vol. xxv. p. 151. 
 Ch. iii. 
 
 1876 ' N. A.,' vol. xvii. p. 135. 
 
 1877 Engr.,' vol. xliii. p. 125. 
 
 C. E.,' vol. li. p. 131. 
 
 1878 M. E.,' p. 217. 
 
 4 N. A.,' vol. xix. p. 12. 
 4 C. E.,' vol. liv. p. 161. 
 
 ' Zeit. Bauk.,' vol. i. p. 530. 
 
 1879 ' I. and S. I.,' p. 238. 
 
 M. E.,' p. 268. 
 
 'On the Strength of Riveted 
 
 Joints.' 
 
 1881 'M.E.,'p. 720. 
 
 pp. 205, 232, 717. 
 
 1882 pp. 143, 242. 
 
 C. E.,' vol. Ixix. p. 50. 
 vol. Ixix. p. 337. 
 
 1884 vol. Ixxx. p. 154. 
 
 1885 M. E.,' pp. 198, 249. 
 
 N. A.,' vol. xxvi. p. 179. 
 vol. xxvi. p. 204. 
 
 4 M. E.,' p. 538. 
 1889 . N. A.,' vol. xxx. p. 292. 
 
 The above contain chiefly those experiments in which actual joints 
 were torn. Related subjects are sometimes to be found in these papers, 
 but it will be more convenient to look for them under the following 
 headings : 
 
220 MECHANICS 
 
 Drilled and Punched Plates. 
 
 
 1868 
 
 N. A.,' vol. ix. p. 10. 
 'M. E.,'p. 97. 
 'N. A.,' vol. xvii. p. 135. 
 M. E.,'p. 97. 
 'N. A.,' vol. xviii. p. 303. 
 vol. xix. p. 1. 
 vol. xix. p. 172. 
 'M. E.,'p. 222. 
 p. 285. 
 'I. and S.I.,' p. 45. 
 ' M. E.,' p. 313. 
 I. and S. I.,' p. 43. 
 p. 49. 
 ' C. E.,' vol. Ixix. p. 50. 
 ' Gorni J.,' p. 347. 
 'N. A.,' vol. xxvi.p. 193. 
 ' M. E.,' pp. 27, 44. 
 ' C. E.,' vol. Ixxxv. p. 421. 
 1 Mitt. Berlin,' p. 97. 
 
 Torsion. 
 
 1 M. E.,' p. 268. 
 'N. A.,' vol. xxi. pp. 191, 204. 
 'M. E.,'p. 313. 
 'Land S. I.,' p. 11. 
 ' C. E.,' vol. Ixxiv. p. 268. 
 ' N. A.,' vol. xxvi. p. 198. 
 ' M. E.,' p. 249. 
 1 C. E.,' vol. xc. p. 382. 
 1 Proceedings,' vol. xlvii. p. 363. 
 
 Joints. 
 
 'M. E.,'p. 268. 
 p. 327. 
 ' Deut. Ing.,' p. 739. 
 
 J. Cochrane . 
 J Biley . .. 
 
 1872 
 1876 
 
 B.Walker 
 A. C. Kirk . 
 B. Martell 
 W. Parker 
 W Boyd .... 
 
 1877 
 1878 
 
 
 J. G. Muir . 
 N. Barnaby . 
 
 E. Bichards . 
 T. Wrightson . 
 W. Parker 
 W. Beck-Gerhard . 
 J. G. Wildish . 
 P. D. Bennett . 
 L. Tetmayer . 
 Budellof . 
 
 D. Greig and Max Eyth . 
 
 1879 
 1881 
 1882 
 
 1884 
 1885 
 1886 
 
 1889 
 
 Shearing and 
 
 1879 
 1880 
 
 D. Greig and Max Eyth . . 1881 
 E. Bichards .... 1882 
 V. Appleby .... 1883 
 J. G. Wildish .... 1885 
 Prof. W. A. B. Kennedy . 
 J. Platt and B. F. Hayward . 1887 
 C. H. Carus-Wilson . . 1890 
 
 Friction of 
 
 D. Greig and Max Eyth . . 1879 
 Clark Kaven and Lavelley . 1881 
 1897 
 
 Diagonal Joints. 
 
 J. G. Wright .... 1872 . ' M. E.,' pp. 79, 90. 
 W. H. Shock .... 1874 P. 198. 
 
 {' Numerous letters,' vols. xliii.. 
 ' E^riments,' vol. xliii. pp. 
 380, 428. 
 
 Theories about Riveted Joints. 
 
 J. H. Latham .... 1858 . P. 1. 
 T. Baldwin .... 1866 . ' Soc. Eng.,' p. 150. 
 W. C. Unwin .... 1868 
 
 C. Keilly 1870 . ' C. E.,' vol. xxix. p. 454. 
 
 W. B. Browne .... 1872 . M. E.,' p. 53. 
 
 ' Engr.,' vol. xxxiv. p. 362. 
 
 Beport ' N. Eng. I.,' vol. xxi. p. 67. 
 
 W. B. Browne . , . 1873 
 
 H. MacColl .... 1874-5 . ' Eng. Soc.,' vol. xviii. p. 111. 
 
 L. E. Fletcher .... 1876 . ' M. E.,' p. 64. 
 
 D. K. Clark .... 1878 . Eules. 
 
 D. Adamson .... ' I. and S. I.,' p. 392. 
 
 B. H. Twedell ..... 1881 . ' M. E.,' p. 293. 
 
 G. Clouzel .... . p. 167. 
 
 W. C. Unwin ... pp. 318, 333. 
 
MECHANICS 221 
 
 W. S. Hall .... 1885 . 'M. E.,' p. 231. 
 
 J. A. Rowe .... 1884-5 . N. E. C. I.,' p. 73. 
 
 J. T. Milton .... 1885 . * N. A.,' vol. xxvi. p. 204. 
 
 Factor of Safety. Having dealt with the peculiar behaviour of 
 materials under various conditions, and also with some problems con- 
 nected with the mechanics of a boiler, it is necessary to add a few 
 remarks on the term factor of safety, which from an engineering point 
 of view might be called the measure of our ignorance : it was adopted 
 at a time when practically nothing was known about the strength of 
 materials, the distribution of stresses, and their influences ; but even 
 now the ultimate strength of a structure is taken as a standard, and 
 it is assumed that if the loads which produced rupture were reduced to, 
 say, one-fifth, then the stresses would be similarly reduced ; but that 
 this is not the case has been repeatedly explained in the last few pages. 
 For instance : 
 
 1st. In a tensile test piece the ultimate stress is a compound, re- 
 sembling a negative fluid pressure, and this stands in no relation to the 
 axial tension which exists in the sample at only one-fifth the ultimate 
 load. (See fig. 132, p. 161.) 
 
 2nd. The working stresses in a narrow beam are relatively 33 % 
 severer than the ultimate stresses. A nominal factor of safety of 5 is 
 in this case actually only 3J. (See p. 192.) 
 
 3rd. The working and ultimate torsional strength of mild steel 
 stand in a similar relation, and in this case the nominal and actual 
 factors of safety stand in the relation of 5 to 3j. (See fig. 123, 
 p. .157.) 
 
 4th. The shearing stresses in rivets under working conditions and 
 during rupture have just been explained, and in this case the actual 
 factor of safety is very much smaller than the nominal. (See 
 p. 157.) 
 
 As will be seen, a great deal depends upon whether the formulae 
 by which the stresses have been calculated are sufficiently comprehen- 
 sive. If they are, and if the material is reliable, and the working 
 conditions thoroughly well known, then there ought to be no reason 
 for not reducing the factor of safety, for, from what has just been said, 
 it is evident that some parts of a boiler are even now being worked 
 with an actual factor of safety which is somewhat smaller than the 
 real one, and there is no reason why other parts, where the nominal 
 and actual factors are nearly equal, should not have the benefit, and 
 might perhaps be made somewhat weaker than they are now. 
 
 It is also evident that when analysing the facts connected with 
 the bursting, either experimental or accidental, of a boiler, it is very 
 important to take into account the various deformations, for whereas 
 elasticity of a s tincture is rightly looked upon as an extra guarantee 
 of strength, plasticity throws the stresses into parts of a structure 
 where they are least expected. To be thoroughly valuable, experi- 
 ments on large structures should not only aim at obtaining information 
 as to the weakest parts at the instant of rupture, but very careful 
 measurements should be taken to determine the elastic deformations 
 before that pressure is reached. (See p. 302.) 
 
 Barking Boiler Explosion. Explosions amongst marine boilers are 
 
222 MECHANICS 
 
 almost unknown : the case of one which exploded at Barking, January 6, 
 1899 (Board of Trade Eeport, No. 1173), due to excessive pressure, is 
 therefore of special interest, and gives some indications as to permissible 
 working stresses. 
 
 The boiler was built of iron in 1878 by Messrs. E. and W. Hawthorn, 
 Leslie & Co. Dimensions : Diameter 10 ft., length 9 ft. 10 ins. ; 
 one dome ; two furnaces 34 ins. diameter ; two separate combustion 
 chambers. Thicknesses : Shell J in., joints welded ; furnaces T ^ in. 
 (single butt straps), reduced by corrosion to -^ in. along firebars; 
 combustion chambers fe in., reduced generally to f in., except at bottom 
 of back, where thicknesses of T 5 B in. were general ; these parts had 
 also been patched. Screwed stays 1J in., riveted over ends except 
 21 in the back, which were new and nutted. Marginal stays If in. 
 diameter, nutted. One screwed stay had a cover patch (see fig. 71). 
 Pitches 8 ins. square, and also 8 ins. x 12 ins. Front end plates, top 
 }-$ in., apparently not reduced. Stays 2 in. diameter, with plus 
 threaded ends welded on ; diameter reduced to about If in. Washers 
 6 in. diameter, \ in. thick ; pitch 14 ins. square, and also 15 ins. x 
 12 ins. Tube plate -JJ- in. ; pitches of stay tubes 13J ins. x 9 ins. 
 Back plate f in. Maximum pitch of stays 8 ins. x 12 ins. 
 
 The accident was due to two successive pressure gauges being out 
 of order, whereby the man who was setting the safety valves screwed 
 them down to 240 Ibs., at which pressure the boiler exploded. 
 
 The shell tore along the top, through the dome hole, at 8^ tons per 
 square inch, but not through any weld ; it is, however, more than pro- 
 bable, there being two reports, that the first to rupture were the welds 
 of the steam space stays, say at 7*6 tons per square inch ; then the end 
 plates tore, and then the shell. The furnaces do not appear to have 
 collapsed. The stress in these plates was 4-2 tons at the thickest 
 uncorroded parts, and 5*8 tons near the firebars. The tube plate does 
 
 /2 
 
 not appear to have bulged. Using the formula W . P . = C ^, where 
 
 the thickness is expressed in sixteenths of an inch, we get C = 265. 
 The steam space plates were bulged, but it is not certain that this 
 happened before the explosion. In this case we get C = 450. 
 The combustion-chamber plates do not appear to have bulged, nor 
 were many stays drawn out. Here we have C = 310 for the T 7 ^ in. 
 plates, and C = 620 for the T % in. plates. Many of the screwed stays 
 were wasted. 
 
 The experience gained in this case is directly applicable to boiler 
 strengths, except as regards the furnaces, for in this case the fires were 
 only very light at the time of the explosion, and therefore not likely to 
 produce stresses and deformations previously discussed. The questions 
 to be decided are, therefore : what extra allowance can be made for the 
 use of steel instead of welded iron, and what factor of safety is desir- 
 able ? For here, of course, as the boiler was under working conditions 
 i.e. high pressure and high temperature our uncertainty as to what 
 happens when we calculate boiler strengths with the help of experi- 
 mental data of cold steel falls away. 
 
 A very instructive case as regards strengths of boiler girders is the 
 explosion (Board of Trade Eeport, 1900, No. 1254) of a stationary 
 loco-boiler. The girders were 74 ins. long, 7 ins. deep, 1J in. thick, 
 
MECHANICS 223 
 
 placed 5 ins. apart, and each one carrying 14 stays, pitched 4| ins., and 
 supported, but at the wrong points, by slings. It was assumed that 
 the explosion took place at a pressure of 140 Ibs., but the boiler had re- 
 cently been tested to 200 Ibs. At this pressure, neglecting the influence 
 of the slings, the stress was 33 tons per square inch, or if, as appears 
 probable, the girders gave way when hot at a pressure of 140 Ibs., then 
 the stress under these conditions was 23 tons per square inch. 
 
 List of some Boiler Tests and Explosions. 
 
 R H. Thurston, 1872, 'Frankl. Inst.,' iii. vol. Ixiii. 
 
 p 89. Tested boiler to 82 Ibs. cold, then burst at 90 Ibs. hot. 
 
 p. 93. Stayed flat plates. Tested cold to 138 Ibs., then burst at 165 Ibs. hot. 
 
 p. 95. Tested box boiler to 60 Ibs. cold. Vertical braces gave way ; repaired 
 these and tested hot. Reports were heard at 50 Ibs. pressure; boiler burst at 
 53g Ibs. pressure. 
 
 p. 99. Tested boiler to 200 Ibs. at 100 F. Several braces broke under 
 115 Ibs. steam pressure. 
 
 p. 99. U.S.A. steamer ' Algonquin ' tested cold to 150 Ibs. Some braces 
 broke under 100 Ibs. steam pressure. 
 
 R. H. Thurston, 1887, 'Explosions.' Tested boiler to 300 Ibs. steam; burst at 
 235 Ibs. on opening valve. 
 
 P. Carmichael, 'Eng. Scot.,' 1869-70, vol. xiii. ; also 1878-9, vol. xxii. Experi- 
 mental bursting of a boiler. 
 
 L. E. Fletcher, 1876, ' M. E.,' p. 59. Experimental bursting of a boiler 
 (cold). 
 
 W. Siemens, ' M. E., 1 1878. 
 
 D. Greig and Max Eyth, ' M. E.,' 1879. Experimental bursting of three boiler 
 shells. 
 
 W. Parker, ' N. A.,' 1881, vol. xxii. p. 12. 'LivadiaV boiler burst under cold 
 water test above working pressure. 
 
 Ibid., ' N. A.,' 1885, vol. xxvi. p. 253. Shell boiler burst under hydraulic test. 
 
 Ibid., 'N. A.,' 1889, vol. xxx. p. 290. Experimental bursting of a boiler (cold). 
 
 J. Scott, ' N. A.,' 1889, vol. xxx. p. 285. Experimental bursting of a Navy 
 boiler. 
 
 Parliamentary Committee on Boiler Explosions, 1817. 
 
 Report on boiler explosions. Rep. Comm. Parl., 1849. 
 
 Parliamentary Committee on Boiler Explosions, 1871. Parliamentary Reports 
 No. 186, vol. Ixvi. p. 43, No. 378, vol. Ixvi. p. 85 ; 1877, No. 361, vol. Ixviii. p. 373. 
 
 Martens, ' Rep. U.S.A.,' various dates. 
 
 'Board of Trade Reports on Boiler Explosions.' Amongst these latter the 
 following are of interest : 
 
 1861, part iv. Locomotive boiler tested to 196 Ibs. at 162 F. ; burst seven 
 months later under 120 Ibs. 
 
 ' Acrefair,' Dec. 10, 1880. Boiler locally weakened to 61 Ibs. permissible work- 
 ing pressure ; burst at 32 Ibs. 
 
 No. 228. Drying cylinder burst. Factor of safety about 20*3. 
 
 No. 229. Lancashire boiler shell burst. Factor of safety was about 2-8. 
 
 No. 237. Locomotive boiler burst. 
 
 No. 243. Boiler shell burst through manhole at 100 Ibs., after having been 
 recently tested to 150 Ibs. steam. 
 
 No. 249. Boiler shell exploded. Factor of safety 2-75. 
 
 No. 252. Boiler shell exploded. Factor of safety 11. 
 
 No. 265. Boiler shell exploded at 83 Ibs. It had recently been tested cold to 
 92 Ibs. 
 
 No. 314. Boiler shell exploded. Factor of safety 3-5. 
 
 No. 346. Furnace collapsed at 50 Ibs. It had been tested to 95 Ibs. only three 
 days previously. 
 
 Other interesting cases are Explosion on the steamer ' Mulheim No. 5,' 
 1866; explosion on the steamer 'Parana,' 1869; explosion on the steamer 
 
224 MECHANICS 
 
 'America,' 1871; explosion of a locomotive boiler, 'Engineering,' 1890, vol. 1. 
 p. 332. 
 
 T. W. Trail (' C. E.,' 1884, vol. li. p. 31) mentions the bursting of two boilers 
 whose factors of safety were 3'9. 
 
 L. E. Fletcher (' C. E.,' 1884, vol. Ixxx. pp. 136 and 139) mentions several 
 curious explosions. 
 
 J. J. Platt, ' M. E.,' 1878, p. 260. A steel fire-box plate cracked after being in 
 use five months. 
 
 MacFarlane Gray (' N. A.,' 1877, vol. xviii. p. 326) mentions that a boiler 
 intended for a working pressure of 30 Ibs. was tested to 400, repaired, and then 
 worked all right. 
 
 J. A. Eowe, 1884, p. 7. A boiler burst at 30 Ibs. working pressure after a cold 
 water test to 59 Ibs. 
 
 See list, p. 136. 
 
225 
 
 CHAPTEE VIII 
 BOILER CONSTBUCTION 
 
 IN the following pages the various workshop practices of boiler con- 
 struction will be dealt with as briefly as the subject will allow. The 
 question of cost cannot, of course, be entered upon, but occasional 
 reference will be made to the time required for the various operations ; 
 this necessarily varies in different works, depending not only on the 
 perfection of the machinery, but also on the skill and energy of the 
 men. More attention has been paid to the different practices and 
 tools for obtaining the same object, and occasionally methods have 
 been mentioned which are practically obsolete or not in use, but which 
 may have done good service or must be looked upon as warning 
 examples. Naturally, every modern device has not been discussed, 
 but it is hoped that none except unimportant ones have been 
 neglected. 
 
 The order in which boiler construction will be taken is to deal 
 firstly with the various operations to be performed on the boiler shell, 
 then with the internal parts, and then with the boiler as a whole. 
 
 The plates as they arrive from the rolling mills are never exactly 
 of the specified sizes, being usually about J in. larger hi each 
 dimension. The thickness is kept within reasonable limits by the 
 condition that any excess weight beyond, say, 5% margin will not be 
 paid for ; but difficulties are sometimes occasioned by stipulations 
 that certain weights shall not be exceeded which, when compared 
 with the plate thicknesses, are too low. The weight of 1 sq. foot 
 of iron is equal to about 40 Ibs. per inch of thickness, and 41 Ibs. for 
 steel. 
 
 The edges of plates are nearly always thinner than the centres. 
 This is almost unavoidable, for as soon as the rolls are set so that the 
 conditions are reversed the plates are seriously puckered. It is not 
 possible to give a full explanation without entering into unnecessary 
 details, but there is no difficulty in understanding that if during the 
 last pass through the rolls the thickness of a plate is reduced -$ in., 
 while its thickness is in. at the edges and T 7 ^ at the centre, then 
 these parts will stretch relatively T *g and ^ of their length, and the 
 centre must pucker. Should the rolls have been made quite parallel, 
 then as soon as they get heated their centres swell and produce the 
 above result. If they are made slightly hollow, the plates which are 
 rolled first will be thin at the edges, and perhaps frilled; but the 
 greatest trouble is experienced when the widths of the plates to be 
 
226 BOILEK CONSTRUCTION 
 
 rolled vary much, for an enormous pressure (about 500 to 1,000 tons, 
 has to be exerted, and the spring in the rolls is very appreciable. 
 
 Shearing Operations. In a boiler shop large shearing machines 
 are not required, but certain plates, such as those for the boiler ends 
 and for the combustion chambers, are often ordered with a com- 
 paratively large margin, on account of flanging, and this excess is then 
 most easily removed by shearing. A small out powerful machine, 
 capable of cutting steel plates up to 1J in. thick, will be found a very 
 handy tool. The levers and handles for working it should not project 
 in front ; otherwise they may come in contact with such of the plates 
 whose flanges have to be sheared while standing on end. The 
 arrangements for replacing the shearing blades should be such that 
 this can be done quickly, so that, as occasion arises, curved or cornered 
 shears may be substituted for straight ones. 
 
 The question as to how much material ought to be planed off 
 sheared edges in order to remove the injurious effect is, and probably 
 will remain, an unsettled one. Some engineers look on shearing and 
 punching as being perfectly harmless ; others insist on subsequently 
 planing away at least J in. Probably the experiences which led to 
 these diverging views are due to the use of various qualities of material. 
 Remarks on this subject will be found in the chapter on ' Strength of 
 Materials,' and the conclusions arrived at there are that good material 
 is not injured, while bad material grows brittle, and the more so the 
 thicker the plates are. Evidence will also be found there in support 
 of the view that the brittleness caused by shearing gradually extends 
 into the plates. Under any circumstances it is Well to guard against 
 possible failings of this sort by insisting on a cold bending test of 
 samples with sheared edges, or of samples with punched holes. In this 
 latter case a standard punch and bolster should be determined upon, 
 as their relative diameters influence the results. If a sample which 
 has been punched or sheared bends well when cold, and particularly 
 if it does so after having been put aside for a week or more, then there 
 will be little fear that the material can satisfactorily withstand this 
 and the less severe workshop treatment. 
 
 Punching Operations. The effects of punching are so very similar 
 to those produced by shearing that nothing need here be said about 
 them, except, perhaps, that it would be better if no punching machines 
 were used in a boiler shop, so that all holes could only be drilled. 
 However that is rarely, if ever, the case, and therefore it is as well to 
 fit as strong and accurate a machine as can be obtained, and to insist 
 on carefulness in setting the bolster. If carelessly placed the punched 
 hole will be a very irregular one (see fig. 197). This is particularly 
 the case if the guides of the punching press slide are a loose fit, for 
 then it will happen that one hole is quite fair, while the next has a 
 slanting form, or even a worse one (as in fig. 198), due to the punch 
 having started penetrating while its edge was actually overlapping 
 the circumference of the die. The breaking of punches under such 
 conditions is not to be wondered at. 
 
 The clearance, or rather the difference, between the diameters of 
 the punch and of the die hole is usually about 10 to 15 %. This 
 agrees fairly well with the following published recommendations : 
 
 W. H. Shock (1880, p. 166) gives 15 to 20%. J. H. Wicksteed 
 
BOILER CONSTRUCTION 
 
 227 
 
 (' M. E.,' 1878, p. 244) recommends one-sixth of the thickness of plate. 
 This amounts to 11% where the diameters of the holes are half as 
 large again as the thickness of the plate, and 17 % when they are 
 equal. 
 
 FIG. 197 
 
 FIG. 198 
 
 Spiral and Slanting Punches have been used not only to lessen 
 the injury to the plate, but also to reduce the pressure on the machine. 
 W. Barr (1880, p. 92) mentions that Kennedy's spiral punch (fig. 199) 
 requires only one-third the power of an ordinary one. Stern (' M. E.,' 
 1878, p. 239) gives the following information : 
 
 
 
 Diam. of Hole 
 
 Punching Force 
 
 Tenacity of 
 Punched Plate 
 
 Ordinary punch . . 
 Spiral 
 
 iin. 
 
 
 
 33 to 35 tons 
 22 25 
 
 26 tons 
 
 28| 
 
 L. Hill (' M. E.,' 1878, p. 244) mentions slanting punches (figs. 200, 
 201). 
 
 It is only natural that, in comparison with ordinary punches, less 
 force, though possibly just as much power, is required with spiral or 
 slanting punches, because with them only a small part of the 
 circumference is doing work, just in the same way as less force is 
 
 FIQ. 199 
 
 FIG. 200 
 
 Fio. 201 
 
 required in a shearing machine if the cutting blade is set at a steep 
 angle. When large holes have to be punched, there ought to be no 
 hesitation in substituting one of the above punches for the ordinary 
 flat one. Fig. 200 seems to be the best suited for hand holes, &c., not 
 only because of its being symmetrical, but because the greater part of 
 the edge is shaped like a good cutting tool. The reverse or V shape 
 would in this respect be the worst possible. The spiral punch leaves 
 
 Q 2 
 
228 BOILER CONSTRUCTION 
 
 a mark in the circumference, which in large holes may be an 
 inconvenience. 
 
 A favourite plan in some works is to punch the holes in all those 
 plates which for some reason, such as flanging, have to be annealed, 
 but, on account of the blindness of some of these holes when fitted 
 together, a great deal of hand labour has to be expended on them in 
 the way of chipping and rimering, so that if added together the 
 expenses for such holes would be found greater than if they had been 
 drilled ; besides, they will not be satisfactory jobs. 
 
 The holes of the seams in the furnaces are also sometimes punched ; 
 but here, particularly with the circumferential seams at the front ends, 
 there is danger that the drawing of the furnace mouth, to meet the 
 flanged front plate, will produce cracks. 
 
 Various seams in the flat plates of the front and back ends are 
 sometimes punched, even when they are $ in. thick ; but the 
 warping of the plates and the certainty of having to chip and rimer 
 a large number of holes ought to be a sufficient objection to this 
 practice. 
 
 The lower edges of the back tube plates are almost invariably 
 punched, leaving them quite ragged. In some works they are left in 
 this condition, as it is useless to caulk this edge. For appearance 
 sake, most boiler-makers chip it. Under any circumstances it would 
 be best to leave a good bevel, so as to prevent steam lodging there and 
 causing the saddle seam to heat. By using a square or rectangulai 
 punch such edges would be left in a better condition for chipping. 
 
 Punching is also resorted to for producing holes for guiding the 
 trepanning tools with which the tube plates are bored. This is 
 a bad practice, and leads to irregularities amounting to in. in 
 the various diameters of the finished holes, and even affects their 
 roundness. 
 
 A less objectionable though still unsatisfactory use of the punch 
 is the practice of perforating those points of the back end plates and 
 of the combustion chamber plates where the screwed stays are to be 
 fitted. When placed in position drills and then taps are passed 
 through them, which remove all brittleness, even if the plates have 
 not been annealed after punching. (For injury done by punching 
 see p. 220.) 
 
 Illustrations of various types of shearing and punching machines 
 will be found in the following publications : 
 
 ' Engineering,' vol. xxxix. p. 219, * Hydraulic Shearing Machine ' ; 
 vol. xiii. p. 221, ' Portable Pneumatic Punching Machine ' ; vol. xliv. 
 p. 16, ' Shearing Machine ' ; vol. 1. p. 688, ' Punching and Shearing 
 Machine', vol. 1. pp. 177-179, 243, 247, 494, 519, 'Punching 
 Machines.' 
 
 Planing Operations. Illustrations of plate-edge planing machines 
 will be found in ' Engineering,' vol. xxxvi. p. 384 ; vol. xlix. pp. 245, 
 252; vol. 1. pp. 536, 625. All the shell plates have to be planed at 
 their edges. They are bolted down on the planing machine (fig. 202), 
 and a tool in the slide rest E, l travels along its edge, at a speed of 
 about 10 to 18 ft. per minute, mean speed 12 ft. with a feed of ^ in. 
 for 1-in. plates, and proportionately more or less for thicker or thinner 
 plates, removing the superfluous material at the rate of 5 to 6 cubic 
 
BOILER CONSTRUCTION 
 
 229 
 
 inches per minute. To this has to be added the time for setting the 
 plate. The total time required to set and plane four shell plates 
 measuring 20 ft. x 5J ft. x 1 in., equal to 102 ft. running, amounted 
 to about 12 hours, from which it is clear that the proper setting of the 
 plates, which had to be repeated eight times, takes up very much more 
 time than that required for the removal of the material. The machine 
 used had two sets of frames, placed at right angles (see fig. 202). 
 
 
 . t* 
 
 _ . 
 
 
 
 
 
 
 
 1 
 
 
 7 C 
 
 ) h o o o o oo o c 
 
 
 7 
 
 . r 
 
 FIG. 202 
 
 With the old-fashioned machines, in which the plate has to be reset for 
 each edge, the time required would have been twice as long, and much 
 more space would have been required, for the plate, which is shown by 
 the dotted lines a, b, c, d, would have to be turned round to the position 
 e, f, g, h. 
 
 A little saving in time is effected if the planing tool be so fitted 
 that it can be turned round, and cut both during the forward and 
 
230 
 
 BOILER CONSTRUCTION 
 
 backward travel (see fig. 203). But when the edges have to be bevelled 
 the tool must have two cutting faces (see fig. 204). 
 
 The amount of bevel of edges to be caulked varies from nothing to 
 1 : 3 (see p. 300), but for the butts of shell plates it should be about 
 1 : 30 ; otherwise they will not close properly (see fig. 205). 
 
 FIG. 203 
 
 Fio. 204 
 
 Should the planing machine be shorter than the plates, their 
 edges will have to be planed in two operations. The usual plan is 
 to withdraw the tool gradually when it reaches the end of the stroke, 
 but in some works part of the material at this point is first removed 
 by chipping. 
 
 FIG. 205 
 
 In old machines, where the holding-down frame is secured at its 
 ends, as shown in fig. 206, only definite lengths of plates can be planed, 
 unless a bracket is bolted to the bed. 
 
 Large plates are generally ordered with a margin of J inch all round, 
 and this is occasionally exceeded by another J inch when shearing. 
 
 All this material has to be removed 
 on the planing machine, and great 
 care has to be taken that the final 
 
 -~-_^ ^^_^ dimensions are correct. They should 
 
 I* ^r~~^--~^!l^l^ nil never be marked off with anything 
 T * else but a steel or iron rule, for the 
 
 - *-"** ^ 'I differences of expansion of wood, iron, 
 
 and brass are very appreciable on 
 large dimensions. The working draw- 
 ings should always contain the widths 
 and lengths of the plates, though the 
 latter dimension is generally omitted. 
 To find the exact circumferential 
 length of a shell plate multiply the mean diameter of the particular 
 strake by 3-H16. 1 
 
 This length has to be divided by two, three, or four, according to 
 the number of joints in the shell. The length of the adjoining strake 
 
 1 A rough approximation to this value is 2 T 2 ; where very great accuracy is 
 desired the fraction fff may be used. 
 
 FIG. 206 
 
BOILER CONSTRUCTION 231 
 
 may be found in the same way, but should be checked by adding or sub- 
 tracting 6 283 times the mean thickness of the two plates as measured 
 at their overlapping edges. It is necessary to be accurate on this point, 
 otherwise the plates will not butt properly. In lap- jointed boilers one 
 width of the lap has to be added to the length of each plate. 
 
 The furnace and combustion -chamber side plates are also planed on 
 these machines, and their dimensions are either marked on the drawings 
 or have to be measured from them. The lengths should be found by 
 measuring the circumferences of the flanged plates and furnaces when 
 fitted together. 
 
 The flat edges of the front and back end plates are also planed in 
 these machines, but only after having been flanged and fitted together. 
 
 Drilling Operations. In all first-class works every hole in a boiler 
 is drilled, and generally drilled in place. A considerable amount of 
 ingenuity has therefore been expended in designing machines which 
 will do this work with speed and accuracy, and which can be adapted 
 to various uses. Naturally a great many different patterns are in use, 
 as will be seen from the following list : 
 
 W. S. Hall, M. E.,' 1878, p. 565. Drilling machinery. He men- 
 tions Hutchinson's, Welch's, Buckton and Wicksteed's, and Buckton's 
 multiple drilling machines; Adamson's, Dickinson's, Jordan's, and 
 Kennedy's drilling machines ; Hall's portable, Brown's and Thorn's 
 steam drilling machines ; McKay's equilibrium drill and other furnace 
 and manhole boring tools, and also Shaw's flexible shaft. 
 
 W. Arrol (' M. E.,' 1887, p. 312) describes the drilling machinery 
 used in the construction of the Forth Bridge. This paper is well worth 
 studying, though not intended for boiler work. In ' Engineering ' will 
 be found sketches of the following : 
 
 Ordinary drilling machines, vol. xxxiii. p. 348 ; vol. xxxv. p. 99 ; 
 vol. xlvi. p. 327 ; vol. xlviii. p. 191. 
 
 Eadial drilling machines, vol. xxxiii. p. 134 ; vol. xxxviii. p. 388 ; 
 vol. xxxix. pp. 57, 360 ; vol. xl. p. 246 ; vol. xli. p. 29 ; vol. xliii. p. 269 ; 
 vol. xliv. p. 42 ; vol. xlvi. p. 468; vol. xlviii. p. 180; vol. xlix. p. 248; 
 vol. 1. p. 184 ; vol. Ixxxv. p. 46 ; vol. Ixxxvi. p. 540 ; vol. Ixxxviii. p. 393. 
 
 Multiple drilling machines, vol. xxxiv. p. 373 ; vol. xliii. p. 69 ; 
 vol. xliv. pp. 150, 289, 292 ; vol. xlv. p. 451 ; vol. xlvi. p. 90; vol. xlix. 
 pp. 250, 251. 
 
 Shell and back end drilling machines, vol. xxxiii. p. 586 ; vol. xl. 
 p. 424 ; vol. xli. p. 620 ; vol. xlii. p. 420 ; vol. xlviii. p. 501 ; vol. Iv. 
 p. 318 ; vol. Iviii. p. 780 ; vol. Ixiv. p. 751. 
 
 Portable drilling machines (for furnaces), vol. xxxii. p. 162 ; vol. 
 xxxix. p. 570 ; vol. xlii. p. 637 ; (for shells) vol. xl. p. 320 ; (hydraulic) 
 vol. xliii. pp. 130, 131 ; vol. xliv. p. 295 ; vol. xlvii. p. 644 ; (hand) vol. 
 xlv. p. 185. Eing-shaped shell drilling machine (Forth Bridge), vol. 
 xxxix. p. 57 ; vol. xlix. p. 248. 
 
 Combined multiple and radial drill, vol. xlii. p. 613. 
 
 Drilling and tapping machine, vol. 1. p. 184 ; xciv. p. 82. 
 
 Drill grinders, vol. xl. p. 320 ; vol. xliii. p. 101 ; vol. xliv. p. 6 ; 
 vol. 1. p. 674. 
 
 These numerous references make it needless to discuss the distin- 
 guishing features of the various types, and attention will only be 
 drawn to a few points. 
 
232 
 
 BOILER CONSTRUCTION 
 
 The Ordinary Drilling Machine is used for little else but small or 
 occasional jobs. Its table can be raised or lowered, and can gene- 
 rally be turned round a vertical axis. The feeding is done by hand. 
 In shipyards, where these machines are used for countersinking holes, 
 the feeding arrangement is a balance lever. 
 
 IFliWlFli 
 
 N. 
 
 
 FIG. 207 
 
 Radial Drilling Machines are made in various forms. Sometimes 
 they are fixed against walls, and are driven by belting from above, or 
 they stand alone and are driven from underground. In that case they 
 are generally made so that their arm can sweep through 360. In 
 some cases the table is adjustable, in others the arm can be raised or 
 
 n 
 
 n 
 
 n 
 
 FIG. 208 
 
 lowered. Arrangements for doing this by power are a great con- 
 venience, and all moving parts should be balanced. It is well to make 
 the balance weights extra heavy, so as to reduce the slack of the drill 
 to a minimum. 
 
 Multiple Drilling Machines are passing out of favour in boiler shops, 
 because their chief occupation, drilling shell plates before bending, 
 
BOILER CONSTRUCTION 233 
 
 is gone. They are generally arranged to slide along a frame, and each 
 spindle can be shifted and worked independently of the others, or they 
 can be set to the proper pitch and moved along together. In some 
 machines the spindles can also be moved at right angles to the frame, 
 so that a double row of holes can be drilled without resetting the plate. 
 In these machines the various spindles cannot of course be brought 
 close together, which causes a slight waste of time at the two ends of 
 a seam, but is otherwise an advantage. In another type of machine 
 the spindles are placed very close together. Figs. 207, 208 show twc 
 arrangements for adjusting the pitch in these cases. A turn of the 
 screw S (fig. 207) will separate the nuts N,, N 2 , N 4 , N 5 from the centre 
 one N 3 , and they are then clamped. Or a turn of the spindle C (fig. 
 208) will turn the hollow right- and left-handed screws * z z , z 3 , 
 which connect the four nuts n lt n 2 , w 3 , w 4 , and these are then clamped. 
 The drill spindles are attached to these nuts and move with them. 
 Should one of the drills break, or be put out of use, all the others would 
 of course have to be stopped for a time. 
 
 f; 
 
 Fro. 209 
 
 Shell Plate Drilling Machines usually consist of two vertical 
 columns, of which one or both are movable. One, two, or even three 
 drill spindles are attached to a slide, which can be moved up or down 
 these columns into any required position. If shells are to be drilled 
 they are placed on a turntable between the two columns (sometimes 
 there are three or four). Much time is wasted over the longitudinal 
 seams, for usually only one can be attacked at a time, and in this 
 respect it is a great advantage if each column can be moved both in a 
 radial and in a circumferential direction, even if only through a limited 
 range. Then the angular adjustment need not be done by the turn- 
 table. 
 
 Another shell -drilling machine is shown in fig. 209, and more 
 fully illustrated, 'Enging.,' 1912, vol. xciv. p. 51. The boiler shell 
 rests on four wheels, W, W. A slide rest S is movable along the 
 
234 
 
 BOILER CONSTRUCTION 
 
 bed plate, and carries an arm A, which can be set to any angle by 
 means of the screw z. It carries the drilling spindle D, which can be 
 moved up or down. It is clear that the drills for there are usually 
 two can, within certain limits, be set to any required angle or position . 
 When all the holes in a given span are drilled, the boiler is turned 
 round the necessary angle and a fresh start made. 
 
 Boiler Back End Drilling Machines usually consist of two columns, 
 both movable along a strong bed plate ; the drill spindles can, as in 
 one of the previous cases, be raised or lowered to any convenient 
 height, so that every part of the back end plate of a boiler could be 
 drilled if placed in the proper position. These machines are some- 
 times fitted with the necessary gear for tapping holes and screwing in 
 the screw stays, and in some cases circular saws can be attached, with 
 which to cut off the projecting ends. 
 
 FIG. 210 
 
 A very convenient machine for drilling furnaces in place is shown 
 (fig. 210). A frame with three or four set screws is firmly screwed 
 into the mouth of the furnace ; a light drilling machine is attached to 
 the centre of this frame in such a manner that it can be clamped in 
 any radial position. The driving wheel projects beyond the mouth of 
 the furnace, and is driven by a belt or gut rope. Of late, electric 
 motors have been applied to this purpose. A somewhat similar 
 machine, but fixed, is/sometimes used for drilling the furnace fronts 
 
BOILER CONSTRUCTION 
 
 235 
 
 Fio. 211 
 
 out of place after the furnaces have been fitted and the holes 
 marked off. 
 
 Any one of the more powerful drilling machines can be used for 
 boring the tube plate holes. A small hole is first drilled or punched in 
 the centre. The guiding spindle S (fig. 211) of a special tool holder, 
 which is secured to the drilling machine, is inserted into one of 
 them, and the cutting of the circumference 
 of the large hole is then done by the parting 
 tool T while it revolves. P is the tube 
 plate which is to be bored. Unless the 
 spindle S is a very good fit in its guide hole, 
 the tube holes are very apt to be irregular 
 both as regards shape and size, and as the 
 setting of the tool T is a somewhat tedious 
 job, it is not to be wondered at that every 
 time it has to be done the diameter of the 
 hole changes. This can easily be demon- 
 strated by measuring several holes, which 
 will be found to differ sometimes by as much 
 
 as T V in. even in the same plate. No wonder, then, that tubes which are 
 somewhat less in diameter than the smallest holes should split while 
 being expanded into the larger ones. In some machines S is replaced 
 by a sliding centre which rests in a large centre punch mark and 
 guides the cutter. In some works the tube holes are rimered out 
 after boring, which is an excellent practice. Less commendable is the 
 system of tapping the stay tube holes before the plates are riveted up ; 
 some of the threads are sure to be nearly cut away. 
 
 Boring Tools. Other contrivances related to drilling machines are 
 furnace and manhole boring tools. If intended only for the former of 
 these purposes, they are practically nothing but very powerful drilling 
 machines ; only, instead of a drill, an arm with a slide rest is attached 
 to the vertical spindle. A parting tool is secured to this rest, as shown 
 in fig. 212, and the furnace 
 front plate bolted in the 
 desired position on the bed 
 plate and bored out. Most 
 of these machines are now 
 arranged in such a manner 
 that the vertical spindle 
 can be made to travel hori- 
 zontally backwards and 
 forwards, whereby the hole 
 cut into the plate will be 
 an elliptic one, as required 
 for manholes. 
 
 As regards the drills 
 themselves something may 
 be learnt from W. S. Hall's 
 
 paper ( M. E.,' 1878, p. Fl0 ' 212 ' 
 
 565), as well as from 
 W. F. Smith's (ibid. 1883, p. 56), who discusses the cutting angles of 
 
236 BOILER CONSTRUCTION 
 
 tools and drills and speeds. The oxy-acetylene blowpipe is now used 
 for cutting out large holes. 
 
 Time required for Drilling. To drill a hole 1 in. deep per minute, 
 and to spend about half a minute for setting, seems to be a fair 
 allowance for holes of from f in. to 1| in. diameter. W. F. Smith 
 gives a circumferential drill speed of 20 ft. per minute with T ^-Q in. 
 feed, while J. H. Wicksteed, in the discussion which followed, re- 
 commends 40 ft. and ^ in., so that as regards speed of feed the 
 result is the same in both cases. For 1-in. holes this means a 
 drilling speed of about 1 in. per minute, which is a very high 
 value. 
 
 Dempster Smith, ' M. E.,' 1909, vol. i. p. 315 deals very fully with 
 the question of speed, feed, thrust, and power. He had the advantage 
 of exceeding the speeds which were customary before high-speed steels 
 were invented. He looks on 60 ft. per minute as a safe circum- 
 ferential speed for drills, and finds that the drilling power for a 
 given speed and feed increases as d Q ' s , and the horse-power per 
 cubic inch of metal removed is proportional to d' 2 t' s where d is the 
 diameter of drill and t the feed per minute both measured in inches, 
 which means that this power is almost independent of the diameter 
 and the feed, as it increases very slightly when either are increased. 
 For steel the feed is about d* : 100 ins. per revolution, and as these 
 are about 230 : d, the feed per minute is about 2 -3d* ins. per minute. 
 Thus a 1-in. drill should pass through 1 in. of metal in 24 seconds, 
 and the times for -in. and 1^-in. drills are respectively 38 and 
 18 seconds. Of course these details refer to the materials used in 
 these experiments. 
 
 Hand drilling is much slower, being at the rate of about 5 to 6 ins. 
 depth of 1-in. holes per hour, and about 3 minutes for setting. 
 Smaller holes can be drilled more quickly, and, generally speaking, 
 the labour is proportional to the weight of metal removed. The 
 limiting conditions for automatic feed are the strength of the drill and 
 the clearance for the borings. In both respects the twist drill is 
 superior to the ordinary one, but very few boiler shops have retained 
 it in use. It is stated that after a time these drills wear away near 
 their ends, and grow taper, and get jammed in the holes and break. 
 Another and probably more powerful reason is that sufficient care is 
 not taken to run them perfectly true, nor to guide them as required, 
 nor to sharpen them correctly ; and if all or nearly all the work is 
 thrown on one cutting edge, it cannot be expected that the result will 
 be a satisfactory one. The irregular action which takes place with 
 ordinary drills if one cutting edge is longer than the other is some- 
 times made use of to produce taper holes. The deeper the drill pene- 
 trates when in this condition, the larger grows the diameter of the 
 hole. This is of course impossible with twist drills, as they are guided 
 by the hole they make. 
 
 Marking off Holes. Should it be necessary to drill shell plates 
 before bending, it is very important to make accurate templets both 
 for the inside and outside strakes, comprising about thirty or forty 
 holes, and the exact positions of several holes should be carefully 
 calculated as a check on the templets. In works where this plan is 
 
BOILER CONSTRUCTION 237 
 
 adopted the necessary appliances for drilling in place are doubtless 
 wanting, and then the holes in the end plate flanges and in the longi- 
 tudinal seams will have to be drilled by hand, the outer machine-drilled 
 holes acting as guides. The latter should never be drilled before bend- 
 ing the plates, as they are thereby seriously weakened at points where 
 strength is of the utmost importance. 
 
 Great care should always be taken that these holes cover each other 
 perfectly, for if blind, the sectional area of the rivet in the plane of 
 shear is reduced, or if this is put right by chipping and rimering, the 
 section of the plate round the hole is reduced. 
 
 Another practice is to punch or even to drill the holes of a smaller 
 diameter than required, and to drill away the superfluous material 
 when fitted together ; but if the view be true that the injury to the 
 material extends slowly for a considerable distance, then this practice 
 ought to be condemned. 
 
 The marking off of back plates for boilers and combustion chambers 
 can be done from the drawings, but often the combustion chamber 
 plates after being drilled are laid on the boiler plates for marking off. 
 In either case the pitch in the boiler plate should be slightly greater 
 than the other, and also higher, so as to allow of the stays being on the 
 slant. 
 
 Bending Operations. -Since the failure of the steel shell plate of 
 the steam yacht ' Livadia ' there exists a very justifiable dread of 
 bending such plates while hot, but as long as chis operation is not 
 carried out at a blue heat the plates ought to suffer no permanent 
 injury, and where the rolls are not sufficiently strong to bend cold 
 plates they will have to be heated. It must not be forgotten that the 
 ' Livadia ' case is not the only one in which the shell plates cracked, 
 and that several instances are known where this happened with plates 
 that had been bent cold. 
 
 A very strong objection against bending shell plates while hot is 
 the necessity of being possessed of a very long heating furnace, the 
 extra time required for warming and then for cooling the plates, and 
 the difficulty of obtaining a uniform temperature, which leads to 
 irregular curvatures. These, and not the supposed injury done to the 
 shell, are probably the most potent reasons which have induced manu- 
 facturers to adopt the plan of bending plates cold. 
 
 The Bending Rolls have necessarily to be proportionately stronger, 
 and the following few notes will be a guide in the matter. 
 
 The resistance to bending beyond the limit of elasticity is indepen- 
 dent of the curvature, and is approximately equal to 4 . t* . b for iron and 
 5 . P . b i or steel. Here t is the thickness and b the breadth of the plate, 
 measured in inches. If the plate is heated to redness the coefficients 
 4 and 5 are reduced to about J (see p. 190). 
 
 As the strength of the bending rolls is proportional to the cube of 
 their diameters, and inversely proportional to the square of their length, 
 and as the bending moment exerted by the rolls on the plate is, in the 
 case of three rolls, of which the two smaller ones nearly touch (see 
 fig. 215), proportional to the diameter, we find that D 2 = c . L . t 
 (see p. 169). 
 
238 
 
 BOILER CONSTRUCTION 
 
 Here D is the diameter and L the length of the rolls, and c a constant 
 which is equal to about 4^ for the lower or outer ones of a system of 
 three rolls, and the upper or inner one should be 25 % larger than these, 
 as it supports double the load. 
 
 For red-hot plates the constants may be reduced to 1*5, which 
 would allow of the rolls being reduced to about half the above diameters. 
 
 FIG. 215 
 
 FIG. 217 
 
 Fio. 216 
 
 FIG. 218 
 
 The smaller the diameters are made, the shorter will be the unbent 
 end pieces of plate, and, as this is a very desirable object, various 
 devices are in use for attaining it. 
 
 The two outer (or lower) rolls are sometimes supported by anti- 
 friction rollers, as shown in fig. 216. Or instead of three rolls four 
 are used (fig. 217). The leverage x of the bending forces of the rolls 
 can be very much reduced by this means, but on account of the greater 
 pressure the diameters have to be proportionately increased. 
 
 Another plan is to have the four rolls arranged as shown in fig. 218, 
 but the advantages are not apparent, and it would even seem that by 
 
BOILER CONSTRUCTION 239 
 
 removing the central roll C and bringing the two rolls B closer together 
 
 FIG. 219 
 
 the bending could be done better. In some machines the upper roll 
 can be moved horizontally, but this also demands that the diameters 
 should be large. 
 
 The bending rolls may be placed either 
 horizontally (fig. 219) or vertically (fig. 
 220). The latter plan is certainly the 
 most convenient, and is being generally 
 adopted. The upper framework is shown 
 in plan, and is so arranged that the inner 
 roll can be lifted out, in order that shell 
 or furnace plates may be rolled in one 
 piece. Of the horizontal rolls it is usually 
 only the two lower ones which are driven, 
 while with the vertical rolls all three turn 
 together. They thereby acquire a better 
 grip of the plate, but even in that case it 
 is advantageous to cut a few grooves into 
 the driving rolls, as they materially assist 
 in dragging in the plate. 
 
 Sketches of various types of bending 
 rolls will be found in the following 
 volumes of ' Engineering ' : Horizontal 
 plate bending rolls : vol. xxxiii. p. 134 ; 
 vol. xlix. p. 529 ; vol. 1. pp. 327, 480, 688. 
 Vertical rolls : vol. xxxii. p. 135 ; vol. xliv. 
 p. 258. Plate straightening machines 
 with five rolls : vol. xl. pp. 9, 321, 619 ; 
 vol. xlv. p. 135; vol. 1. pp. 276, 606. 
 Bending presses : vol. xliii. p. 491 ; vol. 
 xlix. p. 245 ; vol. Iviii. p. 477. 
 
 In some works the plates are passed 
 several times through the bending rolls 
 
 while these are being gradually screwed ' ' ^ 
 closer together. When possible, and par- Fro. 220 
 
 ticularly if the plates are hot, the curving 
 
 should be carried out in one pass, for, independently of the disadvan- 
 tages of punishing the material repeatedly, it will be found that less 
 
240 
 
 BOILER CONSTRUCTION 
 
 force is required for a single bending than for several, if that is 
 necessary. This, however, is only possible if the machine is in good 
 working order, and if full reliance may be placed on the marks to 
 which the rolls are set. On account of the spring of the rolls some 
 allowance has to be made, according as to whether very wide or very 
 narrow plates are being bent, and for the same reason the influence 
 
 of the extra stiffness of 
 thick plates has ali*o to 
 be taken into account. 
 After bending, the plates 
 uncurl slightly, but ab- 
 solute accuracy need 
 not be aimed at. 
 
 With vertical rolls 
 the shop floor should 
 be square to their axis, 
 and instead of using 
 round iron rolling rods 
 to support the plates, 
 small carriages (fig. 221) 
 Fio. 221 FIG. 222 will be found to follow 
 
 the curvatures of the 
 
 plate more smoothly, and not give rise to jerky motions. The speed 
 at which the rolls are worked is about 18 ft. per minute, but it takes 
 altogether about thirty minutes to bend one piece of shell plate. 
 Before commencing the bending, a circular chalk line, to judge of the 
 curvature, is drawn on the floor, passing through the roll space ; but 
 it is also necessary to have curved templets, with which the upper 
 edge is gauged, as the wear on the roller bearing is not an equal one. 
 
 FIG. 223 
 
 Hydraulic Bending Presses are sometimes used instead of rolls. 
 They seem to be most efficient for the bending of long narrow plates, 
 particularly if the curvatures are all equal, as was the case with the 
 tubes of the Forth Bridge. When the radii of the press moulds and 
 
BOILER CONSTRUCTION 
 
 241 
 
 the shell differ materially, liners have to be interposed, as in fig. 222, 
 producing a rounded polygonal, instead of a perfectly circular shape. 
 This is the case even, though to a much less extent, when no liners 
 are used, for the press is never powerful enough to force the plate into 
 absolutely close contact with both moulds. 
 
 Templets have to be applied to the plates while being pressed 
 step by step, otherwise irregularities are sure to occur. But uo 
 
 FIG. 224 
 
 amount of care can do away with the irregular distribution of the 
 stresses in the plates, and this plan cannot therefore be looked upon 
 as a good one for furnaces, because with them the stresses are 
 compressive. 
 
 A few sketches of some hydraulic bending presses are shown in 
 figs. 223, 224. In the first of these the two rams act directly on the 
 press frames, while in the other motion is imparted by means of 
 
242 
 
 BOILER CONSTRUCTION 
 
 wedges, W. In both cases it is necessary to let the two plungers move 
 together ; this is easily done by working the two force pumps from 
 one shaft, and by having an accumulator with two rams instead of one. 
 
 Shell Plate Ends. From previous remarks it will have been 
 gathered that one of the chief difficulties to contend with is the bend- 
 ing of the ends of the plates in such a manner that the general curva- 
 ture is uniform, no matter whether the joint is to be butt-strapped, 
 welded, or lap-jointed as in fig. 225. 
 
 There are various ways of producing these forms. In some works 
 the end of the plate is heated before bending ; it is then laid on a 
 slanting anvil block (fig. 226), with or without curvature, and hammered 
 
 FIG. 227 
 
 FIG. 228 
 
 FIG. 229 
 
 Fia. 230 
 
 with mallets. It is then heated over its entire length, and put through 
 the rolls, or it is bent cold. 
 
 Another plan is to give the top or inner roll an extra screw-down 
 when the end of the plate has been reached (fig. 227). In order to get 
 the correct shape on the other end of a lap-jointed plate it has to be 
 taken out of the rolls and reversed, as in fig. 228. 
 
 This plan is unsatisfactory unless carried out on hot plates, and 
 even then it is clear that the joining surfaces are not flat but irregu- 
 larly curved. 
 
 A better shape is obtained by the following plan, but it is attended 
 with great danger, because the bending may accidentally be carried 
 out at a blue heat, producing either fracture or brittleness. The plate 
 is fixed as shown (fig. 229), and a heater placed at H, and when 
 
BOILER CONSTRUCTION 
 
 243 
 
 locally warmed the bending is done by hammering. The ends of 
 
 plates to be butted are sometimes left flat, and are drawn together by 
 
 the butt straps (fig. 230). Barbarous though this method is, the 
 
 finished shape is a fairly true one, because the strength of the two 
 
 butt straps is about equal to that of 
 
 the shell plate, and the resultant 
 
 curvature is the same as for the 
 
 lest of the boiler. With thick plates 
 
 this plan gives top much trouble 
 
 while the riveting is going on, and 
 
 under any circumstances it is not a 
 
 satisfactory one. In some works the 
 
 plates are ordered extra long and the 
 
 ends cut off after bending and used 
 
 as butt straps. 
 
 The most satisfactory results are 
 undoubtedly obtained by bending the 
 ends of the plates with suitable 
 moulds in a strong riveting machine, 
 either before or after bolting the 
 plates together. The moulds (fig. 231) 
 should be about 9 or 12 ins. long, and 
 gently rounded at their ends. The bending or pressing is done cold. 
 The same moulds can also be used for curving the butt straps. 
 
 Ends of Riveted Seams. In lap-jointed shell plates the corners 
 have to be tapered off previous to bending (figs. 232, 233). This is 
 
 Fio. 231 
 
 O O \O O 
 
 o\ o o'-; o 
 
 o o/o o| 
 
 S~\. S X"N S^. tt 
 
 O 
 
 (O 
 
 o 
 
 O; 
 O- 
 
 o_ o^o 
 
 O I 
 
 o: 
 
 o 
 
 FIG. 232 
 
 Fio. 238 
 
 Fio. 234 
 
 Fio. 235 
 
 usually done by heating them and drawing them out under a steam 
 hammer or by hand. On account of the heaviness of the plates the 
 latter plan is most convenient. Pin-shaped tools should be used, at 
 least for the heavy work, and it is always well to re-heat the surround- 
 ings of such corners when finished to prevent cracking. Very 
 
 R2 
 
244 
 
 BOILER CONSTRUCTION 
 
 satisfactory results are obtained by chipping or planing the corners. 
 (See figs. 234, 235, and p. 249.) 
 
 In the case of butt-strapped joints the arrangements are various. 
 They are sometimes left square and butted at A A (tigs. 230, 237) 
 
 A 
 
 Fio. 236 
 
 FIG. 237 
 
 against the flanged end plates or the adjoining strakes, in which case 
 it is very necessary to be careful that the lengths of the butt straps 
 are correct, and also that they are correctly fitted. Another plan, but 
 one in which the advantages obtained are doubtful, is to bevel the 
 
 A 
 
 FIG. 238 
 
 Fio. 239 
 
 butt straps (fig. 238). They are more difficult to make, to fit, and to 
 caulk than the previous ones. 
 
 In both these cases, but especially in the first, it is customary 
 to fit another cover plate, as shown in fig. 239. 
 
BOILER CONSTRUCTION 
 
 245 
 
 Another plan probably the most efficient is to draw out or plane 
 the end of the outer butt strap and chip away part of the shell, as shown 
 in fig. 240. Instead of chipping these parts they may with advantage 
 
 Fio. 240 
 
 be planed before bending, and the butt straps might also be planed 
 to shape. Fig. 241 shows another, but not a satisfactory, arrange- 
 ment. Sometimes the butt ends are welded, or the end rivet in a butt 
 seam may with advantage be replaced by a screwed stud. 
 
 Fio. 241 
 
 The Fitting together of the Shell Plates is comparatively simple, 
 fchey being easily held together by temporary bolts and straps. With 
 butt-strapped joints it is an advantage to be able to draw the butts tight- 
 together, and it is best done as shown in fig. 242, by bolting brackets to 
 the circumferential seams and drawing these together by means of strong 
 bolts, but as these butts can never be watertight fits it is not necessary 
 to go to much trouble about them. The end plates, either front or 
 
 Fro. 242 
 
 back, are made in two or three pieces, unless they are small enough to 
 be made in one. The lower part of the end plate can now easily be 
 secured in its correct position by bolts, starting at the bottom ; 
 this draws the shell up, and the upper part of the end plate can now 
 be inserted and bolted to the top of the shell. Where the end plates 
 are made of three pieces, the centre one is generally fitted last, but if 
 it is desired to be prepared for having to renew the furnaces, it is the 
 lower plate which should be fitted last. 
 
 Riveting. The older types of power riveters were actuated by 
 steam, while all newer ones are worked by hydraulic pressure, 
 
246 
 
 BOILER CONSTRUCTION 
 
 Formerly, too, it was thought necessary that the pressure should be 
 applied suddenly, in imitation of the blows of a hammer ; but it has 
 been found that better results are obtained if the pressure is steady, 
 provided, of course, that it is sufficiently intense. Machines have 
 also been constructed which will form heads at both ends, so that, 
 instead of rivets, pieces of round bars might be used. The results 
 do not appear to have been very satisfactory, except that the heads 
 thus formed required little or no caulking. Practically the same 
 result can be obtained with an ordinary machine by using pan- 
 
 FIG. 243 
 
 headed rivets and a spherical die. The deformation which the head 
 experiences assists in closing it up to the plate. Under any circum- 
 stances the rivets should be inserted from the inside of the boiler. 
 Eivets should always be slightly larger than required so that they 
 will more than fill their holes ; their heads will then have short fins. 
 If these are absent it is probable that the rivets do not fill their holes. 
 Riveting Machines. Good illustrations of several types of riveters 
 will be found in the following numbers of ' Engineering ' : Vol. xxxiii, 
 

 BOILER CONSTRUCTION 
 
 247 
 
 p. 199 ; vol. xxxv. p. 462 ; vol. xxxvi. p. 492 ; vol. xl. p. 317 ; vol. xlii. 
 p. 80; vol. xlix. p. 259. Portable riveting machines: vol. xxxix. 
 pp. 471, 474 ; vol. xliv. p. 289 (vol. xliv. p. 299, pneumatic) ; vol. xlix. 
 p. 256. Hydraulic riveter with plate-closing arrangements, vol. xliii. 
 p. 531. Hydraulic riveter for using rods instead of rivets, vol. xlix. 
 p. 533. Portable riveter for the circumferential seams of boilers, 
 vol. xliii. pp. 490, 491, vol. Ixii. p. 422. Electric : vol. Ixxxvii. p. 592 
 
 The riveting of the last circumferential seams can be performed by 
 the last-mentioned tool when both end plates, having flanges turned 
 inward, have been fitted in place. The front tube plate is made in 
 three pieces, of which the centre one is not fitted till later ; the boiler is 
 laid on its back end, and the furnaces, which are not yet riveted to the 
 fronts, are dropped to the bottom, and can, as occasion requires, be 
 shifted to make room for the riveter. This consists of two long arms, 
 of which one passes through the opening of the tube plate to the 
 circumference ; the other reaches the circumference from the outside, 
 and contains the hydraulic cylinder, &c. 
 
 Another machine (fig. 243), designed for the same object, is worked 
 by steam. To the centre (C) of the end plate is bolted a long arm 
 with a powerful spring and a heavy holding-up weight (W), which 
 presses against the rivet hi the circumference of the end plate flange ; 
 a strong lever (not shown) is fitted, with which this weight can be 
 pulled back and shifted to the next hole, where the rivet has pre- 
 viously been inserted from inside. The lever is now released, whereby 
 the rivet is pressed home ; a small steam hammer (H) is then made to 
 strike the other end of the rivet, shaping it as required. 
 
 In works where either of these tools is used where, therefore, 
 both end plates can be riveted by machinery the shell seams might 
 have been riveted with the help of comparatively light machines, 
 similar to those used in the construction of the Forth Bridge. 
 
 The seam of a flanged out shell plate shown in fig. 244 allows 
 the riveting to be done by machinery, but it is a heavy design, and 
 the seam cannot be caulked 
 on the inside unless a caulk- 
 ing ring is fitted. 
 
 Riveting Pressure. Al- 
 though machine riveting 
 seems a simple matter, 
 there are a few points 
 which, if not attended to, 
 will give trouble. The 
 pressure used should not 
 be too great, otherwise the 
 plate may crack along the 
 pitch line, either at once or 
 when the boiler is in use. 
 A pressure of 100 tons per 
 square inch of section of rivet hole seems to be ample, while anything 
 above 150 tons seems to be dangerous. Allowing for the size of 
 the rivet head, and assuming the red-hot rivet to be as fluid under 
 pressure as water, this pressure would give rise to a tension of 50 tons 
 
 FIG. 244 
 
248 
 
 BOILER CONSTRUCTION 
 
 per square inch in the metal surrounding the hole. Even allowing 
 50 % for friction and other causes, the stress is still an excessive one. 
 The distance of the metal from rivet hole to edge of plate must he 
 sufficient to prevent bulging. On p. 215 it has been shown that, as 
 regards strength of joint, it is necessary that the above dimension 
 
 should be at least equal to 
 
 , where p is the pitch of rivets in 
 
 the outer row, N the total number of rivets in one pitch, and n the 
 number of rivets in the innermost row. This leads to the generally 
 
 adopted practice of making 
 this margin equal to the rivet 
 diameter. The shearing stress 
 which would be set up in this 
 ==3 part of the seam, while riveting 
 =J with a pressure of 150 tons 
 per square inch of rivet hole, 
 would be about 20 tons, which 
 is also a dangerous amount, 
 and the edges of nearly all 
 FIG. 245 machine-riveted butt straps 
 
 will be found bulged. 
 
 It must not be forgotten that, as at present constructed, hydraulic 
 riveters exert a greater pressure than their nominal one, for on open- 
 ing the valve to the cylinder the accumlator weight falls, being 
 arrested only when the rivet is struck. Of course the acquired energy 
 of the drop makes itself suddenly felt as a very serious, but at present 
 not measured, blow, exceeding by many tons the nominal pressure. 
 
 It is very important to have the various plates screwed close 
 together; otherwise, and particularly if the heads are small or 
 countersunk and the rivets hot, plastic metal will force its way 
 between the plates, as shown in fig. 245. Some riveting machines 
 are so arranged that they can exert 'a pressure on the surrounding 
 plates before and during the time that the rivet is being pressed. 
 But whether this machine be used or not> the plates should always 
 be well bolted together ; if loose the rivets may be too short and not 
 fill their holes. 
 
 Bolting Rivet Seams. The bolts may remain in place till all the 
 alternate holes are riveted up, or they can be gradually removed while 
 the holes are being successively filled. The latter plan seems to be 
 both slower and more unsatisfactory than the first one, for it tends to 
 stretch and shift the plates, and is adopted for this purpose in ship- 
 building when the butts do not meet. It is claimed that this plan has 
 the advantage of warming the plate round the succeeding hole by the 
 previous rivet, thereby preventing cracks ; but such a danger ought 
 not t6 exist with good material. 
 
 It will be found that the work can be done both better and quicker 
 if the rivet holes are not filled up in succession, for, in order to do this, 
 the bolts near the riveting machine have to be removed, and that, of 
 course, is inconvenient. If the rivets are put slightly into the holes, 
 and at once riveted up, the boiler shell has to be shifted backwards 
 and forwards over a distance of about 2 ft. before the next rivet can 
 be inserted. If, on the other hand, three or four rivets are placed 
 
BOILER CONSTRUCTION 
 
 249 
 
 simultaneously into adjoining holes, the speed of riveting can certainly 
 be increased, but that means that the second rivet is being pressed, 
 while the first one is still hot and pliable, and it will almost certainly 
 be stretched a little by the spring of the plate, so that some of the 
 beneficial influences of the powerful hydraulic pressure are being wasted. 
 On the other hand, if the pressure is kept up till the first rivet is cold 
 there is no advantage in having three others waiting all this time in 
 
 FIG. 246 
 
 adjoining holes. This practice is illustrated in fig. 246. The rivet d 
 is being closed, and e, f, g, h are waiting, while a, b, c are finished. 
 In fig. 247 the rivet b is being subjected to the hydraulic pressure ; a 
 has just been pressed, but cannot well be affected by the new operation 
 on account of a strong bolt filling the intermediate hole. The rivet c 
 bas just been placed in its hole, and can readily be acted upon when 
 the pressure on b has lasted long enough. When every alternate hole 
 
 FIG. 247 
 
 has been filled, all the bolts are removed together, and their holes are 
 then riveted. After the bolts have been inserted, and before riveting 
 is commenced, hydraulic pressure is applied all round the seam, and if 
 this should slacken some of the bolts they are tightened up. 
 
 Irregularly-shaped Rivet Head. Anybody watching the process 
 of riveting must be struck with the primitive means used for guiding 
 the rivet holes to the dies. An overhead crane, which might be more 
 usefully employed, is carrying the boiler, which is constantly swinging 
 about. Crowbars are stuck into some of the rivet holes, and the 
 men tug at these till the rivet, which has been inserted, is in the 
 right position. As the weight of the boiler shell is often nearer 20 
 tons than 10 tons, it is natural that there must be much pulling and 
 shoving till the right point is approximately reached. But even then 
 the angular position of the shell is not correct, and the centre line of the 
 riveter does not coincide with the axis of the rivet hole. Naturally, 
 when the pressure is now applied, a few small but violent oscillation^ 
 
250 
 
 BOILER CONSTRUCTION 
 
 take place, and the chances are very much against the rivet head having 
 been formed centrally round its shank. This is illustrated in fig. 248. 
 Of course, externally there is no indication of this state of affairs, except 
 perhaps that the dies leave semicircular marks 
 round the heads, as shown in fig. 249. It ought 
 not to be a difficult matter to devise appliances 
 
 FIG. 248 
 
 which would turn the boiler shell to its right 
 
 position with more certainty than is at present FIG. 249 
 
 possible. 
 
 Time required for Riveting. When the pressure has been ap- 
 plied it should not be taken off again in less than about one minuto 
 (and the longer it remains the better) ; otherwise the rivet will not 
 have cooled sufficiently, and the remaining spring in the plates will 
 stretch it and reduce its diameter. The men do not generally care to keep 
 the pressure on for so long, because the dies, &c., get hot and soft and 
 soon wear out. It takes about 15 minutes to close up 10 rivets. 
 
 The Heating of the Rivets is done in a small reverberatory fur- 
 nace. Sometimes gas or oil is used as fuel. They should not be 
 raised to too high a temperature, or else they grow too plastic under 
 hydraulic pressure and spread out between the plates (fig. 245, p. 249). 
 Nor should they be heated too quickly, or else only their outsides are 
 softened. On the other hand, it is not good to spend too much time 
 over the heating, for a long exposure, particularly in an oxidising flame, 
 reduces the strength of the material of the outer surface, and it is just 
 this which is subjected to the severest stresses when under working con- 
 dition. Fifteen to twenty minutes for heating is the general practice. 
 
 Unlike iron rivets, steel ones cannot be burnt without showing it 
 when in place. 
 
 The influence of heating rivets to a red or a white heat is dis- 
 cussed by M. Considere, ' An. Pont. Gh.,' 1885, 6th ser. vol. ix. p. 574, 
 and 1886, 6th ser. vol. xi. p. 5. 
 
 Eivets are made about T V in. less in diameter than the holes they 
 are intended to fill. The length, L, of their shanks has, therefore, to be 
 made greater than T, the combined thickness of the plates. L=1'5 D 
 + T (1 + J . D), where D is the diameter of the rivet hole. The weights 
 of rivets may be calculated by the formula 
 
 Q.cwt.=2.n. 
 
 where n is the number of rivets. 
 
BOILEK CONSTRUCTION 261 
 
 Internal Parts of Boilers. Nearly all internal plates, as well as the 
 end plates, have to be flanged. The only operations which precede 
 this one are the bending and riveting or welding of the furnaces, the 
 thinning or drawing out of some corners, and the drilling or punching 
 of a few holes for temporarily securing the plates. Welding will be 
 touched upon later, and the other preliminary operations require no 
 remark, except, perhaps, that the drawing out of the corners may be 
 done either by a steam hammer or by hand. The latter plan takes 
 longer, but seems to produce a better job. (See p. 245.) 
 
 Before discussing the various flanging operations it is well to have 
 a clear idea as to the risks attending them. 
 
 Dangers attending Flanging Operations. Whenever a piece of iron 
 or steel is being heated there is, of course, a danger of burning it. 
 This should never happen while flanging, for during this operation 
 such a heat ought hot to be approached. A more real trouble is 
 the wasting away which takes place, particularly with iron, which 
 loses a considerable part of its thickness each time that it is re-heated. 
 There is the further danger of reducing the thickness of the plate 
 by drawing it out, and also the difficulty of producing the correct 
 shape of flanges, and of preserving it, while adjoining parts are being 
 heated. 
 
 More serious than any of these troubles is the risk of cracking the 
 plates. There seem to be three ways of doing this : 1st, by using red- 
 short iron or steel ; 2nd, by not annealing the flanged plates, which 
 then retain strains that may ultimately lead to ruptures ; 3rd, the 
 working of iron or steel at a blue heat. The plates which are thus 
 injured will either break at once or, being now in a brittle condition, 
 will crack later on. 
 
 On all these subjects interesting information will be found in the 
 chapter on ' Strength of Materials.' 
 
 The Danger of not Annealing flanged plates has been demonstrated 
 over and over again in boiler yards by plates cracking. Few of the 
 manufacturers care to give details of their experience, especially as the 
 steel makers readily substitute new plates for the spoilt ones, and do 
 not care to have such oases noised abroad. Those which have been 
 published will be found in the chapter on ' Strength of Materials,' but 
 numerous others are continually occurring. Flanged tube plates (figs. 
 250, 253, 256), flanged end plates (fig. 255), furnace fronts (fig. 251), 
 and with ships the huckster plates, boss plates (fig. 254), and garboard 
 strakes, sometimes give trouble by cracking. 
 
 Stresses Due to Flanging. Here it will not be out of place to draw 
 attention to the fact, which is thoroughly supported by experiments, 
 that iron and steel are affected in their quality by severe stresses, and 
 particularly that, by subjecting test pieces to a slowly increasing but 
 severe pull, their ultimate strength can be raised, while their ductility 
 is very much reduced. The most important point is that the limit of 
 elasticity rises under this stress, until it actually exceeds the original 
 strength of the material. In other words, taking a test bar whose 
 limit of elasticity is 10 tons, and whose ultimate strength is 30 tons, 
 with 20 % elongation, it is possible, by slowly increasing the load, to 
 raise both the limit of elasticity and the ultimate strength to about 
 3d tons, while the elongation which takes place during the final loading 
 
252 
 
 BOILER CONSTRUCTION 
 
 is reduced to a very few per cent., possibly to nothing. When thia 
 point is reached, the test piece gives way completely, without any 
 additional weights being added. Now this gradual increasing of 
 stresses is reproduced while flanging a plate. The shape does not 
 matter much, except, perhaps, as regards the intensity of the stresses 
 which are set up. In forming a tube plate, first one side is flanged, 
 except at the corners, then the next one in the same way, and then 
 the third. When this is finished the corners are once more heated 
 and flanged. Now it is clear that, if the operation commences at A 
 (fig. 252), the heat will have little effect at first ; but even while B is 
 being flanged and A is cooling, strong tension stresses would be 
 produced ; these are very much increased by the time that C is finished. 
 Each one of those parts has probably had a chance of cooling slowly 
 from about 1,000 F., and if the plate were now put aside, and 
 
 FIG. 250 
 
 Fio. 251 
 
 FIG. 252 
 
 measurements could be taken, it would be found that these lengths of 
 the plate had not shortened as much as would be due to their 
 change of temperature. If a steel bar, 1 in. in area, is rigidly secured 
 at its ends, and cooled from 212 F. to 32 F., it would then exert a 
 pull of about 13 tons, so that it is not unreasonable to imagine that 
 the cooling of the flange from a red heat would produce a stress of at 
 least 20 tons. But a tension stress at one edge of a plate must produce 
 a compression stress at the centre and a tension at the circumference. 
 In other words, the plate yields a little, and possibly, instead of finding 
 a stress of 20 tons at only one edge, we find a fairly uniform stress of 
 10 tons all round the plate, and a compression stress in the centre. 
 While the second side is being flanged new stresses are set up all 
 round ; then, when the third side goes through this manipulation, the 
 stresses will be once more increased. To give a correct idea of the 
 distribution pf the stresses would be impossible, but for the purpose 
 
BOILER CONSTRUCTION 
 
 253 
 
 of illustration it may be assumed that the flange ABC is now subjected 
 to 30 tons tension, the flange D to 20 tons, and E to 10 tons. The 
 unflanged parts, F, would be subjected to 30 tons, and the centre of 
 the plate is in compression. The next operation consists in flanging 
 the corners, and there is no doubt that heating them relieves the other 
 stresses at tho circumference a little, but on cooling they will be more 
 intense than before. Even now, if the cooling were carried out 
 quickly, there might be no danger, because one or the other part 
 would gently elongate ; but, as is usually the case where a failure has 
 subsequently occurred, the plate has been put aside for the night, and 
 next morning the flat part had cracked (fig. 253). Slowly the breaking 
 stress was reached, and then, as in the case of test pieces, the material 
 gave way completely. In a case 
 mentioned by the late Dr. Kirk 
 (fig. 253), ' N. A.,' 1882, vol. xxiii. 
 p. 131, the crack extended about 
 18 ins. into the plate, and measured 
 ^ in. open at the edge. It is not 
 at all certain that, by cracking, the 
 plate was relieved of all its strains ; 
 but even assuming this, and as- 
 suming also that the stresses were 
 uniformly distributed over the total 
 circumference of about 14 ft., the 
 opening of the crack to J in. would 
 show that in this particular case the 
 circumferential stress amounted to 
 , 13,000 
 
 168 
 
 , or nearly 40 tons per 
 
 square in., showing that the above 
 
 estimate of 30 tons was not too 
 
 high. Other cases are illustrated 
 
 in figs. 250, 251, 253, 254, 255, 256. 
 
 It has not yet been possible to 
 
 obtain tensile tests of plates which 
 
 have not failed, but which might 
 
 be expected to do so. They would 
 
 certainly throw a strong light on 
 
 the subject. Test pieces should be FIG. 253 
 
 sawn (not sheared) out of the plate 
 
 all along its circumference. An accurate measurement of the limit of 
 
 elasticity would give conclusive information as to the intensity of the 
 
 stress which that particular part had been resisting ; but the greatest 
 
 care would have to be taken not to bend the sample (p. 152). 
 
 Before leaving this subject it may be as well to explain why cracks 
 of this sort extend so far beyond the overstrained part. The contrac- 
 tion of area at the edges of the crack at its inner end, and even beyond 
 this point, is a sure sign of the ductility of the metal, at least in the 
 centre of the plate. A careful study of the subject will show that at 
 the instant when a fracture takes place the two separating surfaces are 
 travelling away from each other at a velocity equal to that of sound. 
 For iron and steel it is 17,500 feet per second. The rate at which the 
 
254 
 
 BOILER CONSTRUCTION 
 
 crack mentioned above was extending towards the centre of the plate 
 must have been = 1,260,000 feet, or 550 miles, per second, and it i& 
 
 00 
 00 
 
 O O'O 
 
 uu u 
 
 00 
 
 00 
 00 
 
 FIG. 254 
 
 therefore not surprising that it had overshot its mark. Instances 
 could be mentioned where the crack had extended right across the 
 
 FIG. 255 
 
 plate, and in one case a plate actually broke in two, one piece knock- 
 ing down a man. If the above estimate of 40 tons stress per square 
 
 FIG. 256 
 
 inch is a correct one, then the amount of energy which was relieved 
 by the plate cracking was equal to lifting it bodily 16 feet into the air. 
 
BOILER CONSTRUCTION 
 
 255 
 
 The loudness of the report when these cracks occur, and the destruc- 
 tive energy which some steel armour plates have displayed when 
 cracking spontaneously, are proof that these estimates are not excessive. 
 The existence of such mischievous powers in the interior of boiler 
 plates should not be tolerated, and there ought really to be no objection 
 to the annealing of plates which have been flanged. When this 
 cannot be done at once, the centre of the plate should be heated to 
 redness immediately after flanging, and before the edges have lost 
 their heat. The compression stresses in the centre of the plate are 
 thereby partly removed. If the plates have been very much buckled 
 during flanging, they should not be flattened except during the 
 annealing process, for it is chiefly the very flat plates which crack. 
 
 Working Plates when Partly Cooled. The other danger to which 
 allusion has been made is the working of steel and iron at a blue heat. 
 Experiments on this subject will be found in the chapter on ' Strength 
 of Materials.' Here it is only necessary to draw attention to workshop 
 practices. The ease with which such failures can be attributed either 
 
 to redshortness, coldshortness, or generally unsuitable material, and 
 the absence of any chemical or mechanical test, make it difficult to be 
 sure, in any particular case, what has been the cause of the breakage ; 
 but about the following one there can be little doubt. 
 
 The flange E (lig. 257) of part of a furnace front plate was so much 
 out of shape that the furnace, /, could not be drawn up sufficiently to 
 make a good job, and it had to be knocked in a little ; but being rather 
 thick, a substantial heater, H, was first applied, as shown. A few 
 weeks later, while the boiler was being tested by hydraulic pressure, a 
 loud report was heard, and though no leakage took place, an internal 
 crack, c, was ultimately discovered, extending round one-quarter of the 
 flange, yet penetrating only to within one-sixteenth of the outside 
 surface. Too little is as yet known about this subject, though every 
 boiler-maker should be made aware of it, which can easily be done by 
 letting him make the following bends : 
 
 Strips of mild steel 6 ins. long, 1^ in. wide, and about f in. thick, 
 should be treated as follows : 
 
 No. 1 should be placed under a steam hammer (fig. 258), allowing 
 
256 BOILER CONSTRUCTION 
 
 3 ins. to project as far as a. This end should then be bent down 
 to the angle b by striking it with a sledge hammer. It should then be 
 reversed to the position c, and again bent down, and the operation 
 continued till breakage takes place. If good, the material will stand 
 20 half -bends, either with sheared edges, annealed, or hardened. 
 
 No. 2 should be placed between two heaters, H, H (fig. 259), and 
 kept there till its edge turns straw colour to violet. It should then be 
 
 taken to the steam hammer and 
 
 r= = : - _- =} bent as before. Two instead of 
 I ^^^^^l^^^^^^^^-jrj 20 bends will now suffice to 
 / _ IT"-.') break it. 
 
 ** = = = = ^ No. 3 should be treated like 
 
 FIG. 259 No. 2, but the bending should 
 
 only be carried on till there is 
 
 the first indication of a crack. The sample should then be put aside 
 for a day to cool slowly, when it can readily be broken with a hand 
 hammer or by throwing it on an anvil. 
 
 No. 4 should be heated like No. 2, and then drawn out under the 
 steam hammer till its thickness is reduced by about -fa in. After 
 waiting a day it will have become as brittle as glass. 
 
 Cases in which the influence of working flanges at a blue heat may at 
 least be suspected are shown in figs. 250, 251. Compare p. 150. 
 
 Local Heating, It may be possible that plates can be injured by 
 the influence of a blue heat even while they are partly red-hot, and 
 that is another reason why they should always be annealed after work- 
 ing them. 
 
 Fig. 260 shows a plate partly flanged, and also locally heated near 
 the centre of one edge. Evidently this red-hot part is surrounded by 
 
 FIG. 260 
 
 a zone of which one part is blue hot. There is also a strong probability 
 that one part of this zone will retain its temperature for a long while, 
 for although the whole plate is radiating heat, the colder parts do not 
 lose it as quickly as the hot ones, and are also being warmed by them, 
 so that at some point the gain and the loss must be equal during a con- 
 siderable period. If the plate is being hammered while this point of 
 permanent temperature is just blue hot, very serious injury may be 
 done to the material. It is therefore not as improbable as it might 
 otherwise seem to find that such a plate contains as many brittle zones 
 as there have been heats applied to it. The danger of these local 
 
BOILEK CONSTRUCTION 
 
 257 
 
 defects is accentuated by the adjoining parts being tough and ductile, 
 and such a plate might be compared to one made up of glass ribs and 
 sheets of lead. There is naturally much difficulty in reproducing these 
 conditions experimentally, but the danger exists all the same, and 
 should be guarded against by careful annealing. 
 
 Cases have occurred where unflanged plates whose corners had 
 been drawn out and then laid aside cracked overnight. It is difficult 
 to imagine that the quality had nothing to do with this, though the 
 tests were good, but stresses had evidently been set up in a similai 
 manner to those explained on p. 253. 
 
 Hydraulic Flanging. Formerly presses similar to that shown at 
 fig. 223, p. 240, were used for flanging, but the necessity of requiring 
 
 FIG. 261 
 
 numerous moulds and various other inconveniences have led to the 
 very extensive adoption of Tweddell's flanging press (fig. 261). See 
 also 'Enging.,' 1912, vol. xciv. p. 83. It consists of three hydraulic 
 cylinders, A, B, C, to whose rams various moulds or head-pieces 
 can be keyed, a, b, c. The whole is supported on a strong bed- 
 plate, B, to which the mould block M and the angle frame N (for 
 guiding b) can be bolted. The press is shown in the act of flanging 
 a boiler end plate, P, which is firmly held down by a, while the 
 moulding iron b is forced down the side and bends the plate. After 
 each stroke a is lifted so as to allow the plate P to be moved a little, 
 and then b descends again. When the whole length of one heat 
 has been dealt with in this way, the flange will be very irregular and 
 frilled, as shown in fig. 262. These irregularities are removed by 
 forcing the ram c against the circumference of the flange. The head- 
 
258 
 
 BOILER CONSTRUCTION 
 
 piece a should be of ample size, so as not to injure the plate, but not 
 too large, otherwise the plate remains perfectly flat after flanging, in 
 which condition it is more liable to crack than if somewhat warped 
 or buckled. The plate should be hottest at the edge, for if that part 
 is left dark red, the thickness of the plate will be reduced at the bend, 
 and the puckers cannot be easily removed. Fig. 263 shows an end 
 plate partly flanged. One part, a, is bent down, the other part, b, is 
 still straight, and the metal between a and b must have stretched 
 
 FIG. 262 
 
 FIG. 263 
 
 I'm. 204 
 
 FIG. 265 
 
 considerably. Besides this the circumference of the plate at b is greater 
 than that of the flange a, so that when finished there must be a consider- 
 able compression stress in the flange. It has the effect of slightly 
 bending the plate edgeways, as can be noticed by the curving of any 
 straight line which has been scribed on the plates before flanging. 
 
 Short lengths, varying from 4 to 6 feet of the circumference (and 
 even 8 feet of thick plates), are heated at one time and the flanging 
 completed before the next length is taken. The heating takes about 
 twenty minutes, and the flanging is at the rate of about 1 foot in 
 
 2 minutes. The extreme ends of the 
 flanges are never of the shape finally 
 required, and have to be dealt with 
 subsequently by hand. 
 
 Fig. 264 shows how tie corners of 
 the plates are cut previous to flanging. 
 The outside plate (see fig. 265) is drawn 
 FIG. 266 out at the corner, and when subse- 
 
 quently flanged has a very irregular 
 
 appearance, as shown in fig. 280, p. 265. Fig. 266 shows how the 
 corners rise up. This is due to the above-mentioned compression 
 of the material. Before allowing the flange to cool, the corners of 
 the inside flange have to be knocked in with a few blows of a hammer, 
 and the corners of the outside fLange knocked out ; otherwise these 
 
BOILER CONSTRUCTION 
 
 259 
 
 parts will have to be re-heated before fitting together, which would 
 be a great waste of time. 
 
 Flanging with a Steam Hammer is done when no other means 
 are available. The plate is placed at an angle on rollers (fig. 267). H 
 is the moulded hammer-head ; M is the lower mould, keyed to the 
 anvil block. A tie rod or plate is also bolted to it for holding 
 the pivot of the plate 
 P, which has been firmly 
 bolted to the centre. The 
 flanges occasionally get 
 torn by this rough treat- 
 ment, and must then be 
 welded. 
 
 Hand Flanging. It 
 goes without saying that 
 up to certain thicknesses 
 flanging can be done by 
 hand. It is usual to dis- 
 pense with pivots and 
 stops, which are necessary 
 with machine flanging, and 
 to be guided as regards 
 shape by deep centre punch 
 marks on the plate. For 
 end plates it is always 
 better to use a pivot ; the 
 circumference can then be 
 made more truly circular. 
 
 The size to which plates have to be sheared for flanging depends, 
 of course, on the depth of the flange, but also on the skill of the 
 operator. With some a very much greater margin must be left for 
 irregular work than with others. The following is a customary rule, 
 and produces flanges with an average of 1 in. for waste : 
 
 To the external size of the flanged plate add the depth of the 
 flange, measured inside. 
 
 For end plates of boilers this is the usual custom. The furnace 
 holes are, however, cut 2 ins. smaller in diameter than would be 
 required by this rule, while for machine-pressed dome ends the extra 
 margin for the flanges is reduced to about 75 % of the above, because 
 they draw out considerably. 
 
 Tube plates and combustion chamber back plates have to be 
 ordered with a margin which is 1 in. in excess of the depth of the 
 flange. 
 
 An extra allowance of 1 in. has to be added at the corners of 
 plates to be flanged by a steam hammer. (See fig. 264.) 
 
 Flanging Fnrnace Holes. Another operation which is carried out 
 under the press is the flanging of the holes in the furnace front plates. 
 Having been bored out to the correct diameter, as indicated above, 
 the circumference of each hole is heated and flanged separately. This 
 is also done under a Tweddell's flanging press. A strong cast-iron 
 ring mould is bolted to the bed plate, and the two plungers a and b 
 (fig. 261) are secured to a strong cast-iron die. The cocks and valves 
 
 82 
 
 FIG. 267 
 
260 BOILER CONSTRUCTION 
 
 of the press are then altered, so that the plungers work in unison, and 
 when the furnace front plate has been placed in its proper position 
 on the ring mould, the die is forced through it, producing the desired 
 flange The power required seems to be at the rate of about 5 tons 
 per foot of circumference with a |-in. plate and with a sufficient depth 
 for one row of rivets, and double this power for inch plates or for 
 treble-riveted flanges. After being heated it takes about 15 minutes 
 to carry out the flanging. 
 
 The furnace front plate should be firmly held in its proper position, 
 because a tendency exists for the die to drag down only one side of 
 the flange, and in doing this the plate gets moved. If the ring mould 
 is strong enough, the plunger c might secure the plate. The die 
 should also be as taper as the length of the stroke will allow ; less 
 force is then required, and the tendency to shift the plate is reduced 
 to a minimum. 
 
 Irregular Shapes of Furnace Holes. Simple as the operation 
 appears, it will be found that the holes produced in this w*y do 
 
 FIG. 268 
 
 not always turn out perfectly circular, unless certain precautions have 
 been taken. One of these is not to heat the plate further than is 
 absolutely necessary, so as not to warm, and thereby weaken, those 
 flanges which have already been finished. Thus, if the finished flange 
 at a (fig. 268) were to be heated while the circumference of the hole 
 O is over the furnace, a slight contraction would take place at this 
 point during flanging, and the diameter D would be reduced. 
 Similarly, a contraction would take place at b if the outside flange 
 were heated at this point. This contraction is the necessary con- 
 sequence of the stretching of every part of the circumference of O, 
 just as the closing-up action, while flanging the outer circumference 
 of end plates, tends to elongate the adjoining parts. 
 
 These deformations can be partly prevented by placing a stout 
 iron ring (fig. 269), cut as shown, inside the finished flange and tightly 
 wedging it into position, but only after the adjoining hole has been 
 heated, and just before it is placed under the press. In some works 
 all three or four furnace holes are flanged in one operation, and 
 
BOILER CONSTRUCTION 
 
 261 
 
 sometimes also the outside flange is done at the same time. This of 
 course requires a very powerful press, similar to the one shown at 
 fig. 223, p. 240. The great inconvenience of this method is the large 
 number of moulds and dies required ; but the results are highly 
 satisfactory, the only serious trouble being the drawing away of the 
 
 FIG. 
 
 FIG. 270 
 
 metal from the weaker or lower flange towards the stronger one (see 
 fig. 270), which very often leads to the outer flange being higher and 
 the inner one being lower than either should be. Fig. 271 is a section 
 through a furnace-hole flange, and shows the deformation to be 
 expected. 
 
 The actual flanging operation is easier with iron than with steel, 
 because this metal is softer, and because it can be worked at a higher 
 
 FIG. 271 
 
 temperature, and fewer heats are necessary. On the other hand, only 
 the very best qualities otyron can pass through this operation without 
 showing cracks or other defects, and there is also much waste of 
 thickness, due to the burning of the surface. That steel possesses 
 great advantages is proved by the fact that hardly any other material 
 is now used for this purpose. 
 
 Annealing. It might have been better to postpone the necessary 
 remarks about annealing until all flanging operations have been dis- 
 
262 
 
 BOILER CONSTRUCTION 
 
 cussed, but, as there is no more difficult piece to deal with than a large" 
 furnace front, the subject has been introduced here. 
 
 The heating furnace is of the ordinary reverberatory type (fig. 272). 
 It is usual to employ coal for fuel, but gas is also used, and it has been 
 affirmed that it causes plates to grow brittle. The flame travels right 
 across the furnace, and gets drawn down at the front. If the furnace 
 is very large, the firing is done at one side, and the downcast is placed 
 at the other. Doors should be fitted so that the plate can be watched, 
 
 FL a rt c/ed Boiler Plate 
 
 Fio. 272 
 
 and care should be taken to keep the temperature comparatively low, 
 partly in order not to burn the iron or steel, but particularly not to 
 heat one part of the plate before another ; otherwise serious distor- 
 tions will occur. Large plates are taken out, turned end for end, and 
 replaced before finally allowing them to cool. J. H. Brinell, ' I. and S. I.,' 
 1886, vol. i. p. 365, has shown how best to anneal. The plates should be 
 heated quickly to a good heat, cooled rapidly at first and then slowly. 
 Long heating at a low temperature is bad, and can be detected with 
 the microscope. 
 
 b 
 
 a 
 
 Fio. 273 
 
 Deformations Produced by Annealing. Even with the most uni- 
 form heating it will be found that the strains which have been pro- 
 duced while flanging will make themselves felt in the most annoying 
 manner. As already mentioned, the tilting up of the outside flange 
 shortens it, so that it is in compression, and the adjoining part of the 
 plate will be in tension. In a furnace front plate this is counteracted 
 by the stretching of the furnace-hole flanges, but only partially ; for, 
 on heating such a plate, it draws as indicated in fig. 273. The metal 
 
BOILER CONSTRUCTION 
 
 263 
 
 at a, b, and c elongates, and the outer flange comes in, sometimes as 
 much as J in. 
 
 The metal shortens at d and e, so that in one direction the 
 diameters increase and in the other they decrease, their difference 
 occasionally amounting to as much as 1 in. Partial relief is given by 
 annealing the furnace front plate after the circumference has been 
 flanged, and once more when the holes are finished. 
 
 To flange the furnace holes oval, which is sometimes done, does 
 not give good results, partly because the changes of form cannot be 
 previously estimated, but more particularly because the outside flange 
 gets drawn in during annealing, and then, although the furnace holes 
 may be circular, the outside flange is locally flattened. 
 
 FIG. 274 
 
 All these distortions depend not only on the shapes and sizes of the 
 flanges, but also on the nature and number of the heat at which the 
 various parts were bent. By making the outer flange and that of the 
 furnace hole perfectly circular, then reheating both locally, and 
 forcing them out at this point by means of a liner shown in black in 
 fig. 274, and then annealing the plate, the flanges return from the 
 position by the black line to their original shape, as shown by a dotted 
 line. If they are still oval these parts are set by hand during the process 
 
 of annealing, the plate being drawn 
 out of the furnace for this purpose 
 and partly flattened, and then re- 
 placed and reheated, and if neces- 
 sary reset. Where great accuracy 
 
 i?'m. 276 
 
 is aimed at, solid segments of 
 circles (fig. 275) are wedged into 
 the furnace holes before anneal- 
 ing ; they have to be made rather 
 FIG. 275 strong, but for all that waste away 
 
 if used too often. 
 
 A careful examination of machine-flanged holes, after they have 
 been annealed, will show that they have closed in a little at their 
 
264 BOILER CONSTRUCTION 
 
 edge (fig. 276). This, like the other deformations, is due to the 
 stresses set up by the flanging operations. It is needless to say that 
 all other flanged plates are distorted more or less by annealing. End 
 plates cannot, therefore, be fitted together before this is done. 
 
 The plates are flattened when they leave the annealing furnace ; 
 this is very necessary, especially along the edges, where the riveted 
 seams come. The operation is not difficult, but care must be taken 
 
 FIG. 277 
 
 that the necessary hammering of the flanges does not spoil them. It 
 is necessary to test the circumference by templet while the plates are 
 still hot, and to gauge the furnace holes. Occasionally the circum- 
 ferential flange will be found set up as in fig. 277. This happens 
 particularly near the furnace holes. In such cases heavy double- 
 handed hammers have to be used to knock it down again. Portable 
 steam hammers are also used for this and other purposes. 
 
 Plates in which the flanges of the edges and of furnace holes are 
 turned towards opposite sides are troublesome objects. Not only is it 
 difficult to get them level, but at the points where the two flanges are 
 nearest each other a disagreeable tendency exists for them to tilt over 
 (fig. 278), and also to bend down bodily, as shown in fig. 279. Con- 
 siderable experience is necessary to get these parts into shape. 
 
 FIG. 278 FIG. 279 
 
 Plates should remain in an annealing furnace for at least two hours 
 but it takes a few more hours before they have cooled after being laid 
 on the shop floor. A lesson in annealing may be learnt from the plan 
 adopted for optical glass, which leads to perfect results. It is heated 
 to the required temperature, and the furnace is then cooled quickly, 
 but only through a small range of temperature, and it is only when 
 the whole of the glass has adapted itself to the reduced heat that it 
 is lowered once more. This is repeated till ordinary temperatures are 
 reached. If the temperature is reduced steadily the surfaces would 
 necessarily be slightly colder than the inside, and straining could not 
 be prevented. 
 
 Final Flangings. Having been thoroughly annealed the various 
 parts of the end plates are now clamped together, care being taken 
 that the circumference is a true circle, and of the right diameter, sc 
 
BOILER CONSTRUCTION 
 
 265 
 
 as to fit the shell. A few holes are drilled through the various cross- 
 seams, and these are then screwed together by well-fitting bolts. 
 Girders, or, for small-sized plates, angle irons, are also bolted to the 
 plates, to keep them flat while suspended, and then one corner joint 
 after another is heated and brought to its correct shape by hand 
 hammering. This is rather a troublesome operation, and generally 
 requires two heats, but if the corners are carefully prepared much 
 time is saved. When, finally, the two plates are in close contact at 
 the corners templets are applied, to test whether the curvature is 
 correct. These parts should project slightly, as they get drawn in on 
 cooling. 
 
 The shaping of these corners will be best understood by referring to 
 fig. 280, which shows the irregular shape of the corner plates as they 
 
 FIG. 280 
 
 Fio. 281 
 
 have left the press. The corner is now heated, and the outer plate 
 struck, as shown in fig. 281, starting at the bottom, so that the humps 
 (which are shown in fig. 280) of both the outside and inside plate are 
 driven in. Gradually the upper parts of the flanges are reached bv the 
 hammer. In the meantime, especially for 
 light plates, heavy hammers or weights 
 have been held inside the flange, in order 
 to make the blows more effective and to 
 bring the plates well together. At a later 
 stage the inside is struck to drive that 
 flange out and to stretch the outer one a 
 little. All this hammering is performed 
 with the end plates, suspended by a 
 chain, so that the heated corner is quite 
 accessible. The final operation is per- 
 formed on a slab of iron (fig. 282). 
 If there are two horizontal seams in the 
 back end plates, it is usual to rivet up 
 one of them, either before or immediately 
 after the above operation. If these 
 corners are welded (fig. 283) none of 
 the seams may be fiveted up first ; the 
 shaping of the corners is done during 
 and immediately after welding. After this operation it is well, 
 and even necessary, to reheat the neighbourhood of these parts. 
 
 FIG. 282 
 
266 
 
 BOILER CONSTRUCTION 
 
 FIG. 283 
 
 This has to do service instead of annealing. These welded corners 
 contract about in., and it is necessary to make the proper allowances. 
 It would be well to leave these corners full and trim them cold. The 
 stay holes, unless they have been punched 
 before annealing, or if it is intended to 
 bore them in place, are now drilled, and 
 the plates can now be fitted into the shells, 
 drilled, and riveted up, as already ex- 
 plained. In some works the straight edges 
 of all flat plates are bent so as to make 
 bevelled joints; but this is unnecessary, 
 costly, and dangerous, for heaters have 
 often to be used, and the plates may thus 
 be made brittle. 
 
 Riveting End Plate Seams. The cross seams are often riveted by 
 machinery before fitting into the boiler, and as, particularly in the 
 front plate, some rivet holes are countersunk, the plates do not expand 
 equally during the riveting process, and all the trouble taken to ensure 
 perfect fits at the flanges is in vain, in fact the difference of expan- 
 sion is sometimes so great as to crack the welded corners. It is 
 therefore advisable to bolt these seams well together and to start 
 riveting from both ends (see p. 283). Even now, however, the corners 
 are not likely to fit close to the shell, so that in some works after the 
 greater part of the flange to shell riveting has been done, these corners 
 are heated to redness by small blast furnaces, then hammered to close . 
 them up to the shell and riveted. It is not an ideal proceeding, 
 but being sanctioned by Lloyd's Eegister it is not likely to be given 
 up. The subsequent cracking of one of these heated corners indicates 
 that if other means for making these corners tight can be shown to be 
 satisfactory they should be insisted on. 
 
 Flanging Furnace Saddles. Undoubtedly, one of the most diffi- 
 cult flanging operations is the shaping of furnace saddles. Eecent 
 attempts to do the work by Tweddell's flanging press are said to be 
 highly satisfactory. 
 
 Two objects have to be kept in view, viz. not to burn or otherwise 
 injure the material, and not to reduce its thickness. Suppose that a 
 
 V V 
 
 FIG. 284 
 
 FIG. 285 
 
 FIG. 286 
 
 FIG. 287 
 
 cylindrical shell (fig. 284) is marked with a number of equidistant 
 longitudinal lines, and that the end of this cylinder is flanged like a 
 furnace saddle, as shown in dotted lines, the straight ones can be 
 
BOILER CONSTRUCTION 
 
 267 
 
 m&cle to take up any of the positions shown in the end views (figs. 285, 
 286, 287). In the first case the lines radiate from the furnace centre, 
 and it is clear that the metal will have been much stretched, and con- 
 sequently much thinned, at the corner. This happens if the corner is 
 made very hot during flanging, and is also flanged first In the 
 second case the lines which extend up to the corners are parallel, 
 showing that thus far the metal has not been stretched or thinned. But 
 that is not the case from the corner to the crown, where the lines spread 
 out very much. This can only happen if the centre has been heated 
 and flanged first, and kept hot while flanging the corners. Fig. 287 
 
 Fio. 288 
 
 Fio. 289 
 
 FIG. 290 
 
 shows how the lines should have distributed 
 themselves. The available means for at- 
 taining this end are : firstly, not to heat 
 the whole width of the flange, but only the 
 curved part, leaving the edges of a dull red 
 heat; secondly, to do the flanging gradu- 
 ally, and not to finish one corner outright, 
 but to partly flange first one corner, then 
 the other, and so on ; thirdly, by leaving 
 an extra amount of metal on those parts 
 of the flanges which are most easily drawn 
 thin, and then if their edges are not heated 
 too much they might even thicken some 
 parts near the curve by stumping them up. 
 The most difficult furnaces to flange are 
 those with high saddles, as shown in figs. 288 
 and 289. As nothing is gained by making 
 them of this shape, it is better to keep the flanges as low as possible, 
 as shown in figs. 290 and 291. The deep flanges usually require 
 from fifteen to twenty heats, while it is asserted that some smiths can 
 produce the low flanged saddles in five or seven heats, but in that 
 case the curvatures must be kept large. Each heat requires about 
 one hour. 
 
 FIG. 291 
 
268 
 
 BOILER CONSTRUCTION 
 
 The Flanging Operation is carried out as follows : The anvil 
 mould M is shaped as shown in section (fig. 292). It is part of a 
 segment of a circle, and is bolted to a strong 
 bed plate, B (fig. 293), to which another light 
 frame, F, and a stop, S, have been secured. 
 The furnace is heated at the point where it 
 is to be flanged, and laid on the mould, and 
 the flanging is then done with mallets. 
 
 Care has to be taken while doing this. If 
 FlQ 292 * ne edge of the plate were to be struck first, as 
 
 shown in fig. 294, it would chiefly bend and 
 
 stretch the edge (see fig. 295) ; it is therefore usual to strike at first 
 nearer the anvil block (fig. 296). This blow produces little effect at the 
 
 FIG. 293 
 
 FIG. 296 
 
 FIG. 297 
 
 edge, which therefore remains thick. Further blows produce curves, 
 as shown in figs. 297, 298, 299. 
 
 By starting from the inside more pressure is exerted there, and the 
 tendency to contracting the furnace at the saddle is reduced. It has 
 
BOILER CONSTRUCTION 
 
 269 
 
 already been pointed out that the stretching of one part of a plate sets 
 up compression stresses in other parts, which show themselves by a 
 
 FIG. 298 
 
 FIG. 299 
 
 swelling up (see fig. 300) ; but this is easily removed with the help of 
 a facing iron, as shown in fig. 301. The effect of a hard tool is to 
 
 FIG. 300 
 
 FIG. 301 
 
 stretch the metal locally, and that naturally increases the diameter of 
 the furnace at that part. 
 
 This bulging was once a very noticeable feature in some patent 
 furnaces. When allowed to re- 
 main, such faults have repeatedly 
 been mistaken for indications of 
 weakness or partial collapses, and 
 much unnecessary anxiety or ex- 
 pense might have been saved if 
 they had been removed at first. 
 Very little flanging is required at 
 the corner, for the corners help 
 to draw this part out. 
 
 When all this work has been 
 done the furnace will have the 
 appearance shown in fig. 302. To 
 
 finish it one of the corners is heated at a time, and placed on an 
 anvil mould, as shown in fig. 303. It is then hammered to the cprrecij 
 
270 
 
 BOILER CONSTRUCTION 
 
 bhape. If the preliminary flanging has not been carried out carefully, 
 troubles may be expected, not only at the corners, but also with the 
 round parts of the furnace, which easily lose their shape. 
 
 These anvil moulds 
 (fig. 303) maybe dispensed 
 with if the curvatures of 
 the corners are sufficiently 
 large, but this demands a 
 slight deviation from the 
 usual design ; either the 
 furnaces have to be flanged 
 round the tube plate, or 
 the top corners of the 
 saddle flanges have to be 
 left long, and the radius 
 of the tube-plate flange 
 increased locally, while 
 the combustion-chamber 
 plate is cut away, as 
 shown in fig. 304. This 
 entails chipping and is 
 expensive. A cheaper and 
 equally efficient plan is 
 to plane the combustion- 
 chamber sides parallel, 
 and to make the tube- 
 
 
 FIG. 303 
 
 plate flange deeper at its 
 lower end. 
 
 The furnaces should 
 now be thoroughly an- 
 nealed, gauged for round- 
 ness, and corrected before 
 FIG. 304 FIG. 305 cooling, and, above all, 
 
 the vertical part of each 
 
 saddle flange should be made perfectly flat, so that it fits the flat 
 part of the tube plate without having to be reheated. Where the 
 flues are not supplied ready flanged by the steel works it is best 
 to fit them and the tube plates together before annealing, and to heat 
 and work the corners when bolted together, as is done with the end 
 plates. If the two are fitted together after this process, it is best, but 
 difficult, only to heat the corners of the tube plate, because it is easier 
 to anneal it than an entire furnace. If these various precautions are 
 not adopted it will often be found that the furnace saddle and the 
 tube plate fit as badly as shown in fig. 305. Such work can be 
 detected by cutting out occasional rivets. 
 
 In some works this fitting is done cold, but then the use of heaters 
 cannot be prevented, and brittleness, due to working at a blue heat, 
 may be the result. 
 
 In some works the furnace saddle flange is left very deep, par- 
 ticularly at the corners, as shown in figs. 288, 289 (p. 267). In others 
 it is kept as small as possible (figs. 290, 291). The latter plan, particu- 
 larly if the curvatures are not too sharp, is by far the best ; not only 
 
BOILER CONSTRUCTION 
 
 271 
 
 is it easier to do the flanging, reducing the number of heats from over 
 twenty to less than ten, but, on account of the gentler treatment of 
 the material, its liability to crack, after the boiler has been put in use, 
 is so very much reduced that no fear need be entertained on this point. 
 
 That these troubles are not alone due to unequal expansion of 
 parts of the boiler, is proved by the fact that it is the corners of the 
 central furnaces which generally crack, while those nearest the shell, 
 where the strains are certainly most severe, do not suffer so often. 
 But recent numerous failures cannot be said to have fixed the blame 
 on the quality of the material, and the only alternative explanation is 
 that the steel has been injured during flanging, either by burning it, 
 by heating it too often or over tires giving off noxious vapours, by in- 
 sufficient annealing, by manipulating the corners at a blue heat, or by 
 overheating and straining when in use. 
 
 Flanging Tube Plates. The preceding remarks make it unneces- 
 sary to add much about the flanging of tube and combustion chamber 
 plates. As previously mentioned (p. ^53), it is usual to flange the straight 
 edges first, and to leave all the corners to the last. This practice need 
 not be adhered to when doing the work under a press. In order to 
 obtain the correct shapes, machine flanging must be done with suitable 
 moulds, and then it 
 is also of importance 
 to shear pieces off the 
 corners, not so much for 
 the purpose of saving 
 labour when trimming 
 the edges, as to prevent 
 the drawing out of the 
 material. Careful mea- 
 surements will show 
 that the thickness of 
 the metal is distributed 
 
 M 
 
 FIG. 306 
 
 FIG. 307 
 
 FIG. 308 
 
 irregularly, as shown in fig. 306. By keeping the edges of the plates 
 hotter than the curved part this thinning action is reduced to a 
 minimum. 
 
 If the edges have been flanged before the corners, the flanging 
 mould M (fig. 308) should have a good taper, so as to press the 
 finished flanges firmly against the mould block M! (fig. 307) ; for if 
 M is left nearly square there will be a strong tendency to draw the 
 plate away from M,. This is particularly the case when flanging the 
 corners first, as shown in fig. 307 ; and then strong stops, S S, S S, have 
 
272 BOILEK CONSTRUCTION 
 
 to be fitted. After this operation the plate should have the appearance 
 shown by fig. 309, and the edges can then be flanged with great accuracy. 
 
 FIG. 309 
 
 Hand Flanging. When flanging by hand stops are sometimes 
 used, though in some works it is deemed sufficient to make a few 
 chalk marks on the flanging mould, and some smiths content them- 
 selves with marking the line of flange with deep centre punch marks. 
 
 FIG. 310 
 
 The combustion chamber sides are seldom flanged. Now and then 
 designs are met with where the back edge is turned in (fig. 310). 
 
BOILER CONSTRUCTION 
 
 273 
 
 There is no advantage in this plan, and the flanging operation is 
 a more difficult one than usual. 
 
 Another arrangement is to leave the back tube plate and combustion 
 chamber plate flat, and to flange out the back and front edges of the 
 top and side plates (figs. 311, 312). Unless very much rounded at the 
 corners the flanges grow thin, or tear, and must be welded. Boilers 
 with these combustion chambers are said to be difficult to clean, and 
 objections have been raised against the caulking liners (fig. 312), but 
 they do not seem to give trouble. Some combustion chambers have 
 rounded backs (fig. 313). These must, of course, be bent in the rolls 
 before flanging. Some combustion chamber tops are flanged to meet 
 the girder plates (see fig. 375, p. 288). Instead of the furnaces, the 
 lower ends of tho back tube plates may be flanged (fig. 314) like the 
 
 Fio. 313 
 
 FIG. 314 
 
 forward outer plate of the fire-box of a locomotive. It is better not to 
 let the tube plate extend much below the centre line of the furnace, 
 because it is next to impossible to make the two a good fit. Besides, 
 an extra seam across the combustion chamber saves a seam round the 
 furnace bottom. If the tube plate is made to end at A, the top part 
 can be fitted quite close, and there will be less chance of leakage, a 
 danger to which this arrangement is specially liable. 
 
 Eeference has occasionally been made to the practice of flanging 
 the furnace saddles round the tube plate corners i.e. placing the back 
 tube plate on the fire side of the furnace flange (fig. 315). It has the 
 advantage over the ordinary style (fig. 316) of allowing both seams to 
 be caulked efficiently; nor can steam-bubbles lodge under the landing, 
 and it permits of the radius of the tube plate flange being made smaller 
 than that of the furnace flange. It is asserted that the flame 
 
274 
 
 BOILER CONSTRUCTION 
 
 impinging on the caulked edge will do harm, but no trouble has ever 
 been noticed at this point. In the one case the side corners will have 
 to be shaped as shown in end view (figs. 288-291, p. 26?); in the other, 
 as in fig. 67, p. 37. In the one case the tube plate corners, in the other 
 
 Fio. 315 
 
 FIG. 316 
 
 the furnace saddle corners, will have to be drawn out or chipped taper. 
 As these corners have often given trouble by leaking, some works have 
 adopted the plan of welding them. They ought to be annealed. 
 
 Before concluding the remarks on this subject it is necessary to 
 mention an isolated practice of flanging the shell plates, in stead of the 
 
 boiler end plate (fig. 317). There 
 does not seem to be any advan- 
 tage, except that the upper end 
 plates of boilers need not be 
 annealed. The shell plate being 
 in tension, any injury caused 
 to these parts by the flanging 
 operation would be doubly dan- 
 gerous, as it cannot be removed 
 by annealing. 
 
 The work is carried out as 
 follows : The ends of the longi- 
 
 Fio. 317 tudinal seams are welded, the 
 
 seams riveted, and the edge of 
 
 the shell heated and flanged in a Tweddell's flanging press, which, to 
 suit the requirements of the case, has to be placed on its back. 
 
 Another interesting subject is cold flanging. The results of 
 Messrs. Easton and Anderson's experience will be found in the 
 ' Journal of the Iron and Steel Institute ' for 1882, p. 528. They 
 produced annular discs of the shape shown in fig. 318 with plates ^ in. 
 thick, but the results cannot be said to have been satisfactory, for 
 out of sixty plates, Landore SS quality, nine cracked their inner 
 flanges, and one its outer flange ; five were not annealed, and of these 
 three cracked. Out of fourteen which had been twice annealed two 
 cracked. The forty-one remaining were annealed only once, but 
 
BOILER CONSTRUCTION 
 
 275 
 
 some of them as long as forty-eight hours and in ashes. Five of these 
 cracked, although one-half of the lot were flanged slowly, requiring 
 about three to four minutes instead of a quarter of a minute. 
 
 Fio. 318 
 
 No mention is made as to whether any of the plates cracked later 
 on, though it is to be expected, for nearly all bent test pieces crack at 
 their inner radius some time after leaving the press or hammer. 
 
 Fitting Together of Plates. Having completed the flanging and 
 annealing, the plates are fitted together and secured to each other by 
 means of a few bolts. Whenever possible, the various seams are 
 closed up cold by hammering. Troublesome parts are warmed by 
 heaters, but, as they often reach a blue heat, it would be better to 
 heat them properly. On this point practices differ. Some works 
 prefer heating only one plate, bolting it to the other, and hammering 
 it, so as to fit the cold one. This plan requires very great care in the 
 flanging of the plate which remains cold, as it cannot be made to 
 alter its shape, and the danger exists that it will be made blue hot. 
 Other works heat both plates while bolted together ; then, of course, 
 it is easy to correct any slight defects of form in both. Hardly any 
 works re-anneal these pieces, which may account for some cracks. 
 Less risk would be run if the corners at least were reheated. 
 
 Particular care should be taken with the flanged corners of the 
 furnaces where they meet the back tube plate and the combustion 
 chamber sides. Not only will injudicious treatment increase the 
 liability of these parts to crack after the boiler has been put in use, 
 but also, on account of the impossibility or difficulty of caulking this 
 seam at both edges, there is a greater chance of the water forcing its 
 way through here than through any other seam of the boiler 
 (see fig. 413, p. 296). Bad plating very generally leads to troublesome 
 
 Fitting Combustion Chamber Plates, The fitting together of the 
 various internal parts is done as follows : The tube plates are bolted 
 to the furnaces and hammered up close, the rivet holes drilled, and 
 the riveting carried out at once or postponed till the other parts have 
 been prepared. The combustion chamber back plate is then bolted 
 to the furnace and tube plate by means of strips of iron. The sides, 
 top and bottom plates are then successively fitted. The order in 
 which this is done depends on the position of the seams. Kepre- 
 sentations of the various plans will be found in figs. 319-327. If the 
 whole of the riveting is to be done by hydraulic power, the arrange- 
 ment shown in fig. 325 must be adopted, the top plate being riveted 
 before the sides are put in position ; and these again are riveted before 
 the bottom plate is secured. But this can only be riveted if the depth 
 of the riveter is sufficiently long to reach from the furnace mouth to 
 the back plate. If the head of the machine is a clumsy one, the 
 flanges will have to be made sufficiently deep so that the rivets can 
 
 T2 
 
276 
 
 BOILEE CONSTRUCTION 
 
 be reached. By removing the back plate after all the side plates have 
 been fitted it is possible to rivet at least the tube plate flange by 
 machinery. If the riveting of all the combustion chamber seams is to 
 be done by hand, it is immaterial in which order the plates are put on, 
 and preference will naturally be given to arrangements like those in 
 
 FIG. 319 
 
 FIG. 320 
 
 FIG. 321 
 
 figs. 319, 320. When the two plates are of equal thickness the seams 
 can be placed higher up, as in fig. 321. Should the lengths of the plates 
 be found too great, or, what is more likely, should the back combustion 
 chamber plate not be shaped exactly like the back tube plate and 
 
 FIG. 322 
 
 FIG. 323 
 
 FIG. 324 
 
 furnace, which would lead to trouble in fitting the circumferential 
 ones in one or two lengths, it may be safer to use three plates, as in 
 figs. 321, 322, 323, or even four plates (figs. 324, 325, 326, 327). The 
 arrangements shown in figs. 319, 320, 321, 322, 324, 325 require that 
 
 FIG. 325 
 
 FIG. 326 
 
 FIG. 
 
 one or the other of the plates should be bent at two points, which, for 
 fitting, is more troublesome than if each plate has got to be bent at 
 only one point, as in fig. 327. The arrangement shown in fig. 322, 
 and on a large scale in fig. 328, doubles the bending operations. The 
 
BOILER CONSTRUCTION 
 
 277 
 
 latter figure also shows how difficult it would be to caulk the internal 
 edge of such a seam if placed higher up in the curve, and also that it 
 should never be placed near a stay. (See also fig. 329.) The corners 
 of all these plates ought to be drawn out as shown in figs. 232 and 233 
 (p. 243). The various seams should also be slightly bevelled, and it 
 is as well to do this before fitting them together. 
 
 FIG. 328 
 
 FIG. 329 
 
 The combustion chamber bottoms and sides are bent cold to their 
 various curves by passing them through the bending rolls, but the 
 corners, particularly where they have to be drawn out, are heated. It 
 is difficult to obtain quite the correct shape at once, and the final 
 setting has to be done in place. Heaters are frequently used, but 
 whether it is that a blue heat is never reached, or whether the work 
 done to the plates at this temperature is not sufficiently severe, it 
 certainly does not as yet seem to have led to any failures in the shop 
 or subsequently. 
 
 Drilling Combustion Chamber Plates. When the various plates 
 have been properly fitted together, their seams are drilled in place 
 generally by hand, but also by machinery. In some works all the 
 outer plates are first removed and drilled by machinery, or even 
 punched, and then refitted, and the inner plates drilled. Sometimes 
 the outer plates are perforated before fitting. If punched, there is 
 always the danger that the plates may crack while bending them, or 
 if punched after bending they are liable to warp, and part of the fitting 
 work has to be done over again. Another plan is to drill all the 
 flanges before fitting, to mark off the holes from the inside on the 
 outer plates, and to drill these by machinery. In any case, all holes 
 in the flanges will have to be countersunk on the inside, for it is 
 difficult to caulk any other heads when so near to a corner. It is 
 also customary, but not necessary, to countersink all rivet holes on 
 the fire side of the various lap joints ; but it does not appear that 
 projecting heads burn off. Wherever there is sufficient space for 
 riveting, or when this is done by machinery, the rivets should be 
 inserted from the water side of the plates. 
 
 The angle of the countersink varies from 15 to 45. The smaller 
 the angle, the smaller is the power of the rivet to draw the plates to- 
 gether while it is cooling. It vanishes altogether when the apex of 
 the cone lies beyond the flat base of the head, or if both ends are 
 countersunk this limit is reached when both cones touch each other 
 at their apexes. 
 
278 
 
 BOILER CONSTRUCTION 
 
 Riveting Combustion Chambers. The remarks made while dis- 
 cussing the riveting of shell plates, &c., apply to a certain extent to 
 this case. The very greatest care should be taken to ensure perfect 
 contact of the plates at the saddle and its corners, for this is almost 
 the hottest part of the boiler, and any air-spaces are sure, sooner or 
 later, to lead to troubles which rapidly extend. On account of the 
 difficulty of flanging the furnace ends, these parts are not always as 
 flat as the tube plate to which they are connected, and carelessness in 
 riveting easily leads to the condition of things illustrated in fig. 305, 
 p. 270. Careless work at these seams is readily exposed by removing 
 a rivet or two. In corners the rivets may be arranged as in fig. 330 or 
 fig. 331, the latter of the two plans being the more generally adopted. 
 In some works the corner rivets are replaced by screws beaded over 
 at either end. For remarks on caulking see p. 293. 
 
 FIG. 330 
 
 FIG. 331 
 
 Planing Edges of Flanges. All the edges of the plates ought first 
 to have been machined. With the circumferential plates this is or 
 can be done before bending, and in that case they can be bevelled ; the 
 flanges, unless they are trimmed with milling tools, are left with square 
 edges. In some works they are subsequently chipped, while in others 
 they are only chipped, and, if little material has to be removed, this is 
 done after the seams have been riveted. These remarks apply as 
 well to the flanged end plates as to those of the internal parts. If 
 much material has to be removed, this can be done by the shearing 
 or the punching machine, usually before the plates are fitted ; or the 
 superfluous parts are removed by a cross-cut chisel. The furnace 
 saddle seams are often shaped by slotting machines or band saws. 
 
 Planing machine lathes with very large face plates, or turntables, 
 are also used for this work. The cutting tools or knives are made 
 very wide, sometimes more than 12 ins., and it is then possible to deal 
 with all sorts of irregular-shaped flanges. Of course, as there is always 
 only one thickness of plate, only part of the width of the tool is used 
 at a time, and the feed is a pretty heavy one. The cutting speed is 
 about 10 ft. per minute, and the depth of a cut about ^ in. Circular 
 saws, which cut off a solid piece of the flange, or milling cutters, have 
 also been tried for removing the superfluous material, but are not 
 generally used. They travel at the rate of about 2 ft. per hour. 
 See 'Enging.,' 1909, vol. Ixxxviii. p. 212. The furnace front plate 
 flanges can be machined by the same machine (fig. 212, p. 235) 
 which cuts the holes, but a tool with a very wide cutting edge 
 replaces the parting tool shown there, 
 
BOILER CONSTRUCTION 
 
 279 
 
 Fitting Internal Parts into Shell. The furnaces and combustion 
 chambers having been riveted together, each one has to be fitted into 
 the furnace front plate. If all the furnaces lead into one combustion 
 chamber, their back ends should not be riveted up without the furnace 
 front plate being in position, otherwise the most serious inconveniences 
 will be encountered when trying to put the two together. 
 
 Where each combustion chamber has a separate furnace, these are 
 fitted into the flanged front plate and their holes drilled and riveted, 
 while the stays from one combustion chamber side to the other are 
 screwed into place. Then, when this work has been completed the 
 whole of the combustion chambers, furnaces, and furnace front plate 
 are rigidly connected, and may be lifted into position in the boilei 
 shell, to which the back plate has already been riveted. 
 
 If the front tube plate is to be placed inside of the furnace front 
 plate, a little simple manoauvring may be necessary. 
 
 In some works the screwing together of the combustion chambers 
 and the riveting of the furnace front seams are carried out inside the 
 boiler shell after the furnace front plate has been riveted up. No 
 advantage is gained, and on account of the confined space the work 
 will be both slow and bad. Besides, if one of the furnaces should 
 crack while its front end is being expanded, all the work just mentioned 
 would have to be done over again. 
 
 Fitting Furnaces. On account of the difficulty of making a furnace 
 front plate with, say, three or four holes, slip easily on to as many 
 
 FIG. 332 
 
 FIG. 333 
 
 furnaces, these are generally made at least J in. smaller in diameter 
 than their respective holes. Sometimes there will be even ^ in. of 
 difference. Then, if the flange is left square, as shown in fig. 332, the 
 expanded furnace mouth will only bear at the front edge, as shown in 
 fig. 333. It is, therefore, customary to leave the flange slightly conical, 
 as shown in fig. 334. In order to get a good fit, as in fig. 335, the 
 diameter of the front edge of the furnace will occasionally have to be 
 increased even as much as \ in. It is dangerous, and in cold weather 
 impossible, to do this expanding without heaters ; and when they are 
 used there is the further danger of overheating and of making the plates 
 permanently brittle by hammering them when blue hot, and cracks at 
 these seams are not unknown. 
 
 The work is carried out as follows : The furnaces are secured as 
 centrally as possible in their respective holes, and all the holes drilled 
 in place either by hand or by the machine (fig. 210, p. 234). Numerous 
 bolts are then inserted, heaters applied, and the bolts screwed tighter, 
 
280 
 
 BOILER CONSTRUCTION 
 
 while the front seam is being hammered, until the plates are in perfect 
 contact. The troubles which these seams sometimes give have led a 
 few engineers to make them treble-riveted, but an apparently safer 
 and more convenient plan would be to make the flanges conical in the 
 
 FIG. 334 
 
 Fia. 335 
 
 FIG. 336 
 
 other direction (fig. 336), and either turn the front end of the furnace 
 or give it a slight bevel, as shown. Instead of heaters, portable coke 
 furnaces are sometimes used, which heat the seams almost to redness, 
 and they can be screwed close without hammering. 
 
 The Riveting of Furnace Front Seams is not quite so simple as 
 would at first sight appear, particularly if the water-spaces are made 
 narrow, and there is always a very strong inclination to do this in 
 order to gain space. With this object in view the flanges of the furnace 
 holes are sometimes turned the other way to those of the circumferen- 
 tial one (fig. 244, p. 247 ; fig. 278, p. 264), or the furnace is made taper 
 
 FIG. 337 
 
 FIG. 338 
 
 (fig. 337) or its front end contracted a few inches, or the furnace is 
 fitted at an angle. Gamed to extremes this principle will be recognised 
 in the arrangement shown in fig. 338, which would permit of the 
 furnaces touching each other. When, in addition, the longitudinal 
 seams both of the furnaces and the shell accidentally come together 
 (see fig. 339), the boiler bottom is practically cut off from the upper 
 part, and the consequent want of circulation may make itself seriously 
 felt. Figs. 340, 341, 342 show an arrangement which also permits of 
 the furnaces being placed very near each other and near the shell, 
 except the central one, because here both flanges are turned in the 
 same direction. (See also figs. 84-87, p. 42.) 
 
 In pases where two flanges are so close together that a rivet can 
 
BOILER CONSTRUCTION 
 
 281 
 
 neither be introduced nor subsequently caulked, the holes have to be 
 carefully drilled, tapped, and countersunk, and accurately-fitting 
 screws, with conical heads, inserted. The ends of the screws are 
 
 FIG. 339 
 
 FIG. 340 
 
 beaded over, and the heads caulked. An arrangement in which all 
 this difficulty is overcome, and in which the front plate holes need not 
 be flanged, is shown in fig. 343. The furnace front flanges will over- 
 lap each other. (See also fig. 41, p. 21.) 
 
 FIG. 341 
 
 FIG. 342 
 
 Furnace Saddles. The various designs for securing the furnaces 
 to the combustion chambers are shown in the following sketches 
 Fig. 344 is the most common, except, perhaps, when the back end 
 seam is single riveted all the way round, instead of being double 
 
 FIG. 343 
 
 FIG. 344 
 
 FIG. 345 
 
 FIG. 346 
 
 riveted from below the line of fire bars, as shown. In through 
 combustion chambers of double-ended boilers this seam is sometimes 
 double riveted above and treble riveted below (see fig. 345). The 
 increased width of the lower flange is sometimes met with in the back 
 plate of combustion chambers (see fig. 346). In both the above cases 
 fche tube plate is on the water side of the saddle plate, and it is affjrrnecj 
 
282 
 
 BOILER CONSTRUCTION 
 
 that unless the edge of the plate is well bevelled, and the rivet heads 
 countersunk on the water side, steam-bubbles will lodge there. It is 
 difficult to caulk this seam on the inside because of the furnace, and 
 on the outside because of the tubes. The curvature of the tube plate 
 side flanges is a very sharp one, in order to get the tubes as near the 
 edge as possible, and when the furnace saddle flange is inside of this 
 tube plate this curvature is often so sharp as to be more like a corner, 
 and therefore very liable to crack (see fig. 43, p. 21). One way out 
 of this difficulty is to increase the radius of curvature of the tube 
 plate side flanges where they meet the saddle corners. This part 
 
 FIG. 347 
 
 FIG. 348 
 
 FIG. 34y 
 
 must therefore be made deeper, and it is necessary to cut away the 
 combustion chamber side plates, as shown either in black or dotted 
 lines in fig. 304. p. 270. Another arrangement is shown in fig. 347 
 (see fig. 60, p. 35). The saddle being flanged over the tube plate, it 
 can be made with a gentler curve than in figs. 344 and 345. The 
 saddle seam is sometimes double riveted, and believing that the large 
 amount of metal at this point would lead to burning, some engineers 
 plane or chip this seam (see fig. 348). When it is necessary to fit very 
 thick plates to the combustion chamber bottoms, they are sometimes 
 planed thin at the seam before bending, as shown in fig. 349, but no 
 object seems to have been gained by adopting this plan. 
 
 FIG. 350 
 
 FIG. 351 
 
 Tt is objected that the saddle seams of the last three constructions 
 expose a caulked edge to the impinging action of the flame, but in 
 practice they answer well. It is certainly far easier to caulk both 
 edges of this seam, and there is no projection under which steam- 
 bubbles could find a lodgment. A similar seam is shown in fig. 350, 
 
BOILER CONSTRUCTION 
 
 283 
 
 which is adopted with ribbed furnaces and with those fitted with 
 several Adamson's rings. The tube plate hole is not flanged, and can 
 be carried to the very bottom of the combustion chamber. 
 
 The arrangement shown in fig. 351 is adopted when there is 
 little spare space between the furnace top and the tubes, but as the 
 work of flanging is doubled, and the caulking difficult, it cannot be 
 recommended. 
 
 A somewhat more objectionable arrangement is shown in fig. 352, 
 the tube plate being flanged to meet the furnace, and the seam being 
 
 FIG. 352 
 
 FIG. 353 
 
 exposed both to the radiant heat of the incandescent fuel and to the 
 convection of the hot gases and flame. 
 
 The very greatest care has to be taken to secure metallic contact 
 of the plates, and the flanged tube plate is sometimes bored to fit the 
 furnace which has been turned (see fig. 353). In order to minimise 
 the chance of leakage, and to reduce the labour of caulking, it is a 
 good plan to remove the scale of all plates by pickling them in a 
 1 per cent, solution of hydrochloric acid, or to sponge the seams with 
 sal-ammoniac. Other remarks about riveting these seams will be 
 found on p. 34. 
 
 The back end seams are sometimes welded (see figs. 424, 425, 
 p. .299), and an excellent job can be made of them, but in case of 
 collapse they are apt to crack. 
 
 Riveting Saddle Seams. While being riveted, seams invariably 
 stretch, more particularly if the holes are countersunk, and generally 
 the two plates do not stretch equally, and the result in saddle seams is 
 either that the plate with the outer flange grows longer than the 
 inner one, whereby the previously well-fitted corner opens, or else the 
 inner plate stretches more than the outer one, causing the flange of 
 the latter to crack. Therefore, under no circumstances should rivet- 
 ing be commenced at one side and carried across ; it is also not well 
 to commence in the centre and work to both sides. The best plan is 
 to commence at both sides and work towards the middle, alternately 
 riveting one side and then the other. If the reheating of corners 
 without subsequent annealing were not objectionable it would be 
 well if the saddle corners could be closed up hot after riveting 
 (see p. 266). 
 
 The Screwed Stays between the combustion chamber backs or 
 sides and the back end or shell of the boiler are sometimes fitted 
 before the circumferential seam of the front plate is riveted, some- 
 
284 BOILER CONSTRUCTION 
 
 times afterwards. This being done by hand, all the holes will have 
 been previously drilled or* punched, and the plates annealed ; they 
 are tapped when in position, and the stays screwed and beaded over, 
 or caulked and nutted. If the tapping and screwing of stays are 
 done by machinery, the drilling is also done by the same machine 
 (see p. 233). The sawing off of the ends should not be necessary, for 
 accurate measurements of the lengths could have been taken, and it 
 is certainly cheaper to saw off the correct lengths in a small machine 
 than in one of these very expensive ones. It takes about 10 minutes 
 to tap a pair of holes and to screw in the stay, and another 20 minutes 
 to caulk and to screw up the nuts. When done by hand, the whole 
 operation takes about one hour. 
 
 When screwed in by hand, these stays are often made with a 
 square head (fig. 354). The labour of cutting off the ends would be 
 
 FIG. 354 FIG. 355 
 
 saved by the use of a closed nut with a shank (figs. 355, 356). Its 
 depth should not exceed the thickness of a stay nut. Stay holes are 
 always tapped when the plates have been placed in their final position, 
 and immediately before the stays are fitted; 
 otherwise it would be impossible to enter 
 them. It does not seem to matter much that 
 the threads of the stays and of the tap are not 
 exactly alike. This difference is due both to the 
 FIG. 356 tap and the stays altering their length respec- 
 
 tively during hardening and during screwing. 
 The stays should be a tight fit, particularly at their inner end. This 
 is not always the case, even in some of the best boiler-shops, and often 
 leads to leakage with the least overheating. As the nutting of loose 
 stays is difficult, they are at once scragged with a caulking tool, and 
 inspection does not reveal the slackness. 
 
 The Pitch of Threads of the stays varies in different shops, the 
 natural tendency being to make the pitch as fine as possible, because 
 the effective diameter is measured from the bottom of the thread ; 
 but it takes longer to tap and screw them. There is little harm in 
 fine threads when nuts are screwed on the ends, but a coarse and 
 deep thread is necessary when the ends are only beaded over. 
 
 Cases in which explosions or mishaps have been traced to the use 
 of fine threads are to be found in ' Engineering,' 1887, vol. xliii. p. 396, 
 and 1890, vol. 1. p. 85. 
 
 Should the plate bulge, as it often does when hot, its inner (water) 
 side will leave the screw threads entirely (fig. 357), and only the outer 
 edge will hang on to the stay by the small riveted head and by a very 
 few threads (fig. 357) ; whereas with a coarse thread, as in fig. 358, it 
 would require a serious amount of bulging before any of the threads 
 are quite clear of each other. 
 
BOILER CONSTRUCTION 
 
 285 
 
 The threads of the taps and stays are never quite the same, which, 
 when fine ones are used, may cause them to strip. 
 
 Stay Nuts ought not to be thicker, or only a very little thicker, than 
 the plates which they have to support : not because of the danger of 
 
 Fio. 357 
 
 FIG. 358 
 
 burning them, but for fear of stripping the thread in the plate. This 
 is illustrated in fig. 359, where, if the full power which such a nut 
 could stand were applied, the threads in the plate would certainly strip. 
 The drawing office habit of showing the stays horizontal instead of 
 normal to the combustion chamber plate, and the carelessness with which 
 the holes are drilled, placing the stays at an angle, and making the 
 nuts bear on one side only, add to their power of doing harm. The 
 taper washers which are then fitted often make matters worse by turn- 
 ing round, the thick part being found where the thin part ought to be. 
 To prevent this, the bearing side of the nut should be faced. The 
 
 Fio. 359 
 
 Fio. 360 
 
 FIG. 361 
 
 thick external plates may be recessed, as shown in fig. 360. This is 
 easily done with a rose disc of the size of the nut : it is slipped over the 
 stay, the nut screwed down on it, and it is then turned with a spanner, 
 its outer edge being formed square or hexagonal. In many works the 
 stays are bent by striking long steel nuts temporarily screwed on with 
 a hammer (fig. 361). Thick stays are not likely to bend ; their fit in 
 the plate will be spoilt and their threads damaged. 
 
 One often finds red-lead cement, and also flat washers, under the 
 nuts in the combustion chambers. Neither are wanted, doing more 
 harm than good. Nobody would contend that the cement could stop 
 
286 
 
 BOILEK CONSTRUCTION 
 
 any leakage, the circumference of the stay having been caulked ; it can, 
 therefore, only act as a non-conducting layer between the boiler plate 
 and the nut, causing the latter to burn when exposed to the flame. 
 The interposition of a washer doubles this danger. The cement is also 
 sure to get into the threads between the nut and the stay, where it acts 
 as an efficient non-conductor and prevents the nut being cooled by the 
 stay. Fig. 362 shows stay bolts which are used by some builders. 
 
 FIG. 362 
 
 FIG. 363 
 
 FIG. 364 
 
 An ideally perfect stay should allow of the nut in the combustion 
 chamber being brought into as absolute a metallic contact with both 
 stay and plate as is possible : it will thereby be prevented from burn- 
 ing, and will give the most solid and efficient support to the perforated 
 plate. Taper washers ought therefore to be dispensed with as much 
 as possible on the combustion chamber ends of the stays, and in no 
 case should the angle be so large as shown in fig. 363 ; in fact, the 
 
 angle should not exceed -=, where t is the thickness of plate and d 
 
 el 
 
 the effective diameter of the stay. With a ^-in. plate and a l-in. stay 
 this would give an angle of ^, or 10 (see fig. 364). Near flanged 
 seams it is difficult to fit nuts ; then riveting should be allowed. 
 
 Caulking Screwed Stays. Screwed stays are caulked with an ordi- 
 nary tool before the nuts are fitted (fig. 365). Locomotive engineers, 
 
 who do not seem to like nutted 
 stays, have used hollow bars and 
 made them tight by drifting. 
 Mr. Yarrow has also adopted 
 this plan, but on account of the 
 impossibility of getting at the 
 outside ends, he makes the hole 
 larger at the inner end than at 
 the other, and uses both drifts 
 from the fire side (' N. A.,' 1891, 
 
 FlG> 365 vol. xxxii. p. 102, plate 22). The 
 
 drift used should be threaded 
 so that by screwing on a nut it can be drawn out again. 
 
 Girders. These are fitted to combustion chamber tops and other 
 flat parts in the inside of boilers, transmitting the pressure from these 
 parts to others which are better adapted to support it. If the girders 
 end near stays, these will have to be made of a larger sectional area, 
 in order to support the extra load which is thrown upon them. 
 
BOILER CONSTRUCTION 
 
 287 
 
 Most girders are made of two plates, one on either side of the stays 
 which they have to support (figs. 366, 367, 368, 369, 370). These are 
 connected to each other by rivets and distance pieces, and caps are fitted 
 under the nuts of the stays. 
 
 r 
 
 i r 
 
 rr 
 
 FIG. 366 
 
 FIG. 367 
 
 X 
 
 FlQ. 
 
 SI 
 
 FIG. 370 
 
 FIG. 368 
 
 Instead of riveting the plates together they are sometimes welded 
 at their ends. Cast-iron feet at the ends are also used. 
 
 Sometimes they are forged or slotted out of the solid (fig. 371) or 
 are made of cast steel (fig. 372). 
 
 FIG. 371 
 
 FIG. 372 
 
 In some works the girders are arranged alternately with an odd 
 and an even number of stays, the pitch being measured diagonally. 
 The saving in weight, however, is too slight to balance other incon- 
 veniences. 
 
 Angle Iron and Web Girders. Instead of girders with stays, 
 angle irons (fig. 373), and even beams (fig. 374), are sometimes riveted 
 
 FIG. 373 
 
 FIG. 374 
 
 to the combustion chamber tops, but this is a bad practice, as the plates 
 generally crack under the doubled parts, in the same way as they do 
 under palm stays (see fig. 37, p. 20). 
 
 Another plan, and one which is comin? into more general use, is 
 to flange the combustion chamber plates, and rivet them to vertical 
 
288 
 
 BOILER CONSTRUCTION 
 
 webs (figs. 375 and 376). The ends of these vertical plates have to be 
 forged with projecting feet (fig. 384, p. 289), which tuck in under the 
 
 Fro. 375 
 
 FIG. 376 
 
 Fio. 377 
 
 combustion chamber top plate flanges. It is not difficult either to 
 rivet these seams or to caulk them from the fire side. 
 
 Some other shapes of girders are mentioned by 
 D. S. Smart (' C. E.,' 1884, vol. Ixxx. p. 132). 
 
 Pig. 377 shows a corrugated combustion chamber 
 top which is occasionally fitted ; its strength can be 
 calculated with the help of a formula on p. 200. 
 Occasionally the tops are rounded, as in fig. 378. 
 
 Suspended Girders. Instead of allowing the gir- 
 ders to rest entirely on the corners of the combustion 
 chambers, they can be suspended by stays to the 
 FIG 378 boiler shells (figs. 379, 380), or their ends need not 
 rest on the tube plate at all ; but in either case the 
 end stays should be kept far away from the flanges, in order that 
 the expansion of the shell diameter, which amounts to about ^ a in., 
 
 FIG 379 
 
 should not open their seams. The top ends of the suspending rods 
 are attached to double angle irons, riveted to the shell. The top ends 
 are flattened out as in fig. 381, so that they may be secured by several 
 
BOILER CONSTRUCTION 
 
 rivets, but generally they end in an eye and a bolt, with a split key 
 passing through their projecting end (fig. 382). Sometimes these 
 stays are tapped both into the combustion chamber and shell plate. 
 
 Fio. 382 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 o 
 
 o 
 
 
 
 o o o 
 
 
 
 
 
 
 
 
 
 
 
 O 
 
 o 
 
 c 
 
 c 
 
 
 
 c 
 
 o o o 
 
 
 
 
 
 o 
 
 
 
 
 
 o o 
 
 
 
 
 1 
 
 D 
 
 
 
 $ 
 
 D 
 
 
 
 
 d 
 
 D 
 
 o 
 
 o 
 
 
 
 o 
 
 o o o 
 
 
 
 
 
 c 
 
 c 
 
 
 
 C 
 
 
 
 PIG. 383 
 
 FIG. 384 
 
 Vertical Stays. It also happens that girders are dispensed with 
 entirely, and every one of the combustion chamber top stays is carried 
 up to the shell. This arrangement is carried out as shown in fig. 382. 
 
290 
 
 BOILER CONSTRUCTION 
 
 The reason for fitting these stays to the shell is, in most oases, to 
 relieve the tube plate of its load. But this relief may be carried to 
 excess, and may lead to the stretching of tube plate holes if the stays 
 are fixed near the flanges. (See p. 34.) 
 
 FIG. 385 
 
 Plate Stays are shown in figs. 383, 385 ; they are carried to the 
 shell plate (figs. 383, 385) and riveted to angle irons. Fig. 384 shows 
 how the two ends of the vertical plate have to be stumped up so as to 
 fill the roundings at the end. 
 
 Fio. 
 
 These plates are usually fitted crossways (fig. 383). Holes are 
 provided, through which the steam -space stays have to pass. For 
 very deep combustion chambers, the top has to be supported by 
 
 FIG. 387 
 
 several webs, but their number depends on the thickness of the plates ; 
 SG3 also s.s. ' Iberia,' ' Enging.,' vol. Ivi. p. 207. 
 
 The Steam-Space Stays are sometimes tapped into the plates 
 (fig. 386), and sometimes fitted with nuts on either side of each plate 
 
BOLLEK CONSTRUCTION 291 
 
 (fig. 387). Both arrangements have their disadvantages. In the one 
 case the stays have to be swelled at one or both of their ends and 
 threaded, then screwed into the plates, caulked both inside and out, and 
 nutted. After being in use for some time the diameter at the front 
 end will be seriously reduced by corrosion, as indicated by the dotted 
 lines (fig. 386), and the stays must be renewed. This is not the case 
 with those stays which have been threaded without swelling, for the 
 exposed part of the stay may be very seriously reduced before making 
 it weaker than the screwed part ; in this case the thread at the front 
 ends should not extend beyond the inside nut. The objection 
 previously urged against fine threads does not apply to nutted stays 
 (see p. 285). 
 
 The trouble with these stays is that they leak, for it is only grummets 
 and washers that can be used to prevent this. The hollow space is 
 sometimes filled with sheet iron and caulked, but better results seem 
 to be obtained with asbestos packing. The outside washers for these 
 stays are very often riveted to the plate, giving it a better support. 
 In confined spaces it may be necessary to fit the stays in two lengths. 
 This is shown in figs. 388 and 389. 
 
 Fio. 389 
 
 Boiler Tubes. One of the last things to be done to a boiler is to 
 fit the tubes. This is a simple matter : the tubes arrive cut to the 
 right lengths and probably also annealed at their ends ; they are 
 passed through the two tube plates, and their ends are expanded. 
 Formerly this was done by means of conical drifts, and some people 
 still advocate their use, but the common practice is to use expanders. 
 These consist of several usually three small rollers, partly project- 
 ing out of the circumference of an iron case. A taper mandril is place 
 in the centre and driven in while being turned round, thereby causing 
 the rollers and their case to revolve, at the same time exerting a 
 pressure on the tube, which expands and gets firmly bedded against 
 the metal of the tube plate. Plain tubes can be placed in position 
 and expanded at the rate of about six per hour. 
 
 The past disasters with the tubes of Navy boilers, leading as they 
 did to the appointment of a special committee of inquiry, are a 
 sufficient proof that the mode of securing them is not a perfect one. 
 Undoubtedly the severe conditions of Navy trials search out any 
 defects which may exist, and when leakage nas once commenced it 
 seems impossible to stop it again until the tubes are re-expanded. 
 By some it is affirmed that the trouble is caused by overheating the 
 tube plate (see p. 28). Others believe that the chilling effect of 
 inrushes of cold air, or that structural peculiarities, are to blame. 
 Thus each tube has a slight twist, due to the expander having been 
 worked in one direction only. On heating the tubes, they may 
 untwist slightly. This motion will be particularly injurious if the 
 tube plate holes are not perfectly circular. The taper shape of the, 
 
 u2 
 
292 
 
 BOILER CONSTRUCTION 
 
 tube expander which is used to force a parallel tube into a parallel 
 hole may also be a cause. 
 
 Of the various attempted remedies, none have yet given per- 
 manently satisfactory results, and for the merchant service, where 
 practically no troubles are experienced, no deviation from the present 
 course would be advisable. It consists in fitting a sufficient number 
 of stay tubes. 
 
 Stay Tubes. These are fitted before the others, in order to be 
 able to screw up the nuts. If the tubes are left parallel, the back end 
 requires to be screwed sufficiently long so that the inside nut of the 
 front end can be inserted, as shown in fig. 390. The back end is 
 
 FIG. 390 
 
 Fio. 391 
 
 Fio. 392 
 
 beaded over, as in fig. 393, or nutted, as in figs 391, 394. Nowadays 
 nearly all stay tubes are swelled at their front end (fig. 392), and both 
 plates are tapped together. Fig. 395 shows a section of a tool which 
 is very convenient for screwing or unscrewing stay tubes. Two half- 
 round grooves, deeper than shown, are cut into the sides of a spindle 
 which is just large enough to enter the tube, and two short lengths of 
 steel of a lenticular section are placed into these recesses and held 
 there by any convenient means. Their outer edges, being roughened, 
 
 Fio. 393 
 
 FIG. 394 
 
 FIG. 395 
 
 grip the inside of the tube whichever way they are turned. Both 
 tube ends are expanded and also caulked, and either beaded over or 
 fitted with nuts. The other tubes are then placed in position and 
 expanded. Stay tubes are insisted on in the merchant service, while 
 the locomotives and American steamers do without them, but all the 
 ends are beaded. Exhaustive experiments on the holding power of 
 tubes are mentioned by W.H. Shock, 1880, p. 217. As regards taper- 
 ended tubes experiments were carried out by Martens (' Mitt., Berlin,' 
 1887, vol. v. p. 65). None of these results were obtained at steaming 
 temperatures. 
 
 The time required to tap the tube plate, fit a stay tube, and bead 
 
BOILER CONSTRUCTION 
 
 293 
 
 or nut it, is about one hour and a half. The taps are hollow, and can 
 be adjusted on a long spindle to suit any length of tubes ; these are 
 threaded in a lathe. 
 
 Caulking. In order to explain what takes place during the 
 duration of a blow, when the hammer, the caulking tool, and the plate 
 are in contact, it will be necessary to divide the plate into layers of, 
 say, ^ in. in thickness, as shown in fig. 396. The velocity of the 
 hammer and caulking tool is imparted to the first layer, and quickly 
 transmitted to the next, and further on. The pressure which is 
 
 PL A TE 
 
 FIG. 396 
 
 required to transmit this velocity from the caulking tool to the first 
 layer, and then from one layer to another, is at first in excess of the 
 elastic limit, and produces a permanent deformation, as shown. But 
 this pressure reacts on the caulking tool, causing it to rebound after 
 only a few layers have acquired the high velocity ; but, their mass 
 being small as compared with that of the hammer, their pressure on 
 the further layers is not sufficiently great to flatten and spread them 
 out. The permanent effect will, therefore, be that which is illustrated 
 in fig. 396. A little reflection will show that, the lighter the hammer, 
 the sooner it rebounds, and the fewer the layers acted upon, and the 
 
 Heavy Hammer 
 
 Light Hammer 
 
 FIG. 397 
 
 lighter the blow, the slower the imparted velocity, and the smaller 
 the deformations. Thus, if twenty-five layers equal to \ in. are 
 deformed by the blow of a 7-lb. hammer on a 2-lb. caulking tool, 
 only half that number, equal to in., would be spread out when 
 using a hammer weighing 3^ Ibs. and a 1-lb. tool. By increasing 
 the velocity, the force between the caulking tool and plate would be 
 increased, and the swelling would be greater, but the distance to 
 which this swelling extends would not be altered at least, not 
 materially. In an exaggerated form the effects would, therefore, be 
 
294 
 
 CONSTRUCTION 
 
 as shown in fig. 397. For this reason heavy hammers are first used, 
 and then light ones. 
 
 The next thing to he considered is the shape of the tool and the 
 shape of the edge of the plate. In fig. 398 the edge of the plate is 
 square, and the effect of the caulking tool is seen under it (fig. 399). 
 The metal has simply been swelled up. 
 
 FIG. 398 
 
 FIG. 400 
 
 FIG. 399 
 
 \ 
 
 Fro. 402 
 
 Fro. 403 
 
 Fro. 404 
 
 FIG. 406 
 
 Fro. 407 
 
 In fig. 400 the edge of the plate is bevelled, and the caulking tool is 
 placed firmly against it. The result of the blow is seen above (fig. 401). 
 Not only is the edge of the plate swelled up, as in the previous case, 
 but the lower plate is scraped up, forming a small ridge ; and, thirdly, 
 the blow being directed downward, both plates are depressed ; but as 
 
BOILER CONSTRUCTION 
 
 295 
 
 there is more spring in the outer plate (lap), it will not suffer as much 
 permanent deflection as the lower one, and the result will be that the 
 edge remains slightly, but permanently, open. This view is further 
 illustrated in figs. 402, 403. An exaggerated seam of this sort is shown 
 in fig. 404, and it is quite clear that no amount of hammering on the 
 slanting surface would caulk the joint effectively. The maximum 
 angle met with in practice is 1 : 3. 
 
 A better result would be obtained by placing the tool as shown in 
 fig. 405, but, on account of the thinness of the edge, the caulking 
 would not be very deep (fig. 406). Another method is shown in figs. 
 
 Fio. 409 
 
 Fm. 410 
 
 Fio. 411 
 
 407 and 408, and strongly recommended by locomotive engineers. The 
 effect of a blow in this case is almost the very reverse of the previous 
 one ; for while the edge of the metal is being swelled, the plate under 
 it is being struck down, and, as the hammer rebounds, the lower plate 
 springs back and presses firmly against the caulked edge (see figs. 
 409, 410). A tool of this shape will cause the swelling to extend 
 
 Fio. 412 
 
 farther into the plate, and thereby give a larger bearing surface. 
 Care should be taken not to make this tool too small, otherwise it 
 will act like a wedge, and press up the outer surface (fig. 411). 
 Special tools have to be used for inside corners and for some rivets ; 
 they are generally shaped as shown in fig. 412. It is painful to handle 
 
296 BOILER CONSTRUCTION 
 
 them, and their work is never very satisfactory. The jar of the blow 
 on all caulking tools is greatly reduced, if their ends are grooved, by 
 striking them on a coarse file in a red-hot condition. 
 
 There is no need for caulking the inside 
 edges of seams if these are well bedded ; but 
 when the plates are not close, as shown in fig. 
 413, the inside edge should at least be fullered 
 to prevent a rocking of the plates. 
 
 Most of the above remarks are also applicable 
 to pneumatic caulking, but it must not be for- 
 gotten that as it is not limited like human power, 
 much damage can be done on badly plated seams. 
 
 Electric Welding of riveted seams has been successfully carried out. 
 Pickling. Eiveted seams are said to be tighter if all black oxide 
 scale is first removed from their surfaces, and the Admiralty practice 
 with regard to tube ends is to grind them bright, so that they shall be 
 in metallic contact with the tube plate. The pickling fluid which is 
 used for removing the black scale consists of 1 per cent, of hydrochloric 
 acid in water. Sulphuric acid, more than any other, has the effect of 
 making steel brittle, particularly the hard qualities (see p. 146). 
 
 Welding Operations. Keference has already been made to the 
 fact that many of the seams of the internal parts can be welded, 
 thereby saving the labour of flanging, drilling, riveting, and caulking. 
 At one time efforts were made to weld iron shell plates, but the results 
 were not encouraging, many seams having subsequently to be covered 
 with straps. The introduction of steel, and the difficulty of welding 
 it, stopped all progress. For a time it was only the furnaces which 
 were welded ; for, as these are not subjected to circumferential tension 
 strains, the Board of Trade and ' Lloyd's Eegister ' raised no objection. 
 It is, however, well known that even now great difficulty is experienced 
 in keeping the welded seams of some patent flues intact during the 
 process of manufacture. 
 
 No doubt can be felt that better results are now obtained than 
 formerly : they are doubtless due to improvements in the production of 
 the milder qualities of steel (20 to 25 tons), which can be made almost 
 absolutely free from sulphur and phosphorus, two of the most injurious 
 impurities. The influence of various chemicals does not seem to be 
 accurately known, but what information could be collected on this 
 subject will be found on pp. 133-135. 
 
 The most reliable test for ascertaining whether steel is weldable is 
 to cut off a strip about 18 ins. long, heat its centre, bend it and weld 
 it, bend back the two ends (fig. 415), and then pull the sample asunder 
 in the testing machine. The welded surfaces will probably be smooth 
 and bright, except at the edges, where small patches of metal have left 
 one side and stuck to the other. The larger these patches, and the 
 greater their number, the more weldable is the steel. This test is not 
 applicable to iron, as this metal tears through at the corners. To test 
 it welded joints are re-heated and bent ; if good, the weld should not 
 open (see fig. 414). The ordinary tensile test is of little use when 
 applied to welded samples, for, provided the joint is sufficiently taper, 
 the strength will appear satisfactory. A far better test is to trepan 
 small rings out of a welded plate, tap them, and tear them asunder by 
 
BOILER CONSTRUCTION 
 
 297 
 
 means of two screw plugs (fig. 416). Very serious defects have 
 occasionally been exposed by this means. 
 
 Having obtained a good material, several precautions have to be 
 taken to ensure a good weld. The heating should be carried to the 
 right point. This knowledge can only be gained by practice. Steel, 
 unlike iron, should not be heated to such an extent as to cause 
 sparking. 
 
 Fio. 414 
 
 FIG. 415 
 
 FIG. 416 
 
 Both sides of the plate should be exposed to the fire. If this is 
 impossible the joint must be left wide open, to allow the flame to pass 
 to the other side, where a cap of firebrick is placed. Having completed 
 a short length of weld, and while heating the next, care should be 
 taken to let the escaping flame pass over the recently welded part so 
 as to keep it hot, otherwise the resultant irregular contraction will 
 produce cracks. 
 
 The anvil on which the welding takes place should be as solid as 
 possible. Any appreciable amount of spring affects the quality of the 
 
 FIG. 417 
 
 Fluxes are used for iron, but seldom for steel. The edges of the 
 plates, whether of steel or iron, are slightly tapered, as shown (fig. 417), 
 care being taken to keep the surfaces convex, so that the centres touch 
 
,298 
 
 BOILER CONSTRUCTION 
 
 first and the slag thereby gets driven out. Or the edges are formed 
 into V's (fig. 418). They are first pressed firmly together, and then 
 hammered. A very convenient method of welding steel plates together 
 is to insert a separately-heated good weldable iron bar into the seam. 
 Where practicable this piece is shaped like a double-headed rail 
 (fig. 419). 
 
 Fro. 420 
 
 FIG. 421 
 
 Fires for Welding. The heating of the plates is usually done over 
 coke fires, using a blast. Much time is saved if these furnaces are filled 
 and replenished with red-hot coke taken out of an adjoining furnace. 
 The air blast for welding ought not to pass through more than about 
 18 ins. of coke, otherwise the combustion is not perfect, and the flame 
 not hot enough. (See W. van Folten, ' Stahl und Eisen,' 1893, p. 26.) 
 
 Fig. 420 shows a movable furnace delivering its flame in a hori- 
 zontal direction. It can only be used with plates placed vertically, and 
 then it is usual to place one furnace on each side. 
 
 Longitudinal seams in furnaces are very conveniently heated as 
 shown in fig. 421. As the flame strikes only one side of the plate, it 
 
 \ 
 
 FIG. 422 
 
 is necessary to prevent radiation by the little firebrick cover 0. It is 
 also necessary to keep the seam wide open at this point, by bending 
 
BOILER CONSTRUCTION 
 
 299 
 
 back its edges, so that the flame can pass through it ; otherwise only 
 one side of the plate will weld. When ready, the furnace plate is lifted 
 and turned round by means of the pulley P. This can be dispen sed with 
 by placing the furnace inside of the flue, as shown in fig. 422. In this 
 case, when the seam has been sufficiently heated it is placed over the 
 projecting anvil A, and welded. 
 
 vVhere gas is used for heating purposes, the arrangement shown 
 in tig. 423 is a very convenient one, the ignited mixture of gas and air 
 
 . 423 
 
 passing down the tube T. A is the anvil, and H the steam hammer. 
 Rollers are now very largely used instead of hammers. It is 
 dangerous to use fans for supplying the air to the gas, as their action 
 is not so reliable as that of any of the positive blowers, and causes 
 explosions. 
 
 When the tube plate and furnace are to be welded together, 
 this is usually done at the corner (see tig. 424). No flanging is then 
 necessary. 
 
 FIG. 424 
 
 FIG. 425 
 
 But another plan may be mentioned, according to which tfre tube 
 plate is first flanged so as to form a saddle, and this part is then welded 
 to the furnace (fig. 425). This method is particularly convenient for 
 use with patent flues, which, with one exception, are weakest near the 
 combustion chamber end. With the above plan the thick metal of the 
 tube plate supports the flue. 
 
 Although not carried out to any great extent, all the seams of the 
 furnaces and combustion chambers can be welded, and the finished 
 article will then have the appearance shown in fig. 426. 
 
300 
 
 BOILE& CONSTRUCTION 
 
 For remarks about electric welding and oxy-acetylenQ welding, see 
 ' Steam Pipes '. 
 
 Hydraulic Test. Although not forming part of the construction, 
 the final hydraulic test is the concluding operation before the boiler is 
 put into the ship. It is usual to have a preliminary test the day before, 
 when any defective caulking can be made good, but with good work 
 
 FIG. 426 
 
 this should not be necessary. The generally adopted plan is to raise 
 the pressure step by step, and at once caulk any defect which shows 
 itself. If the full pressure is put on at once, the leakages may be so 
 excessive that they cannot all be put right. During this preliminary 
 test the stay nuts are not screwed on, so that the stays may if neces- 
 sary be recaulked. 
 
 Much has been said and written against testing boilers to double 
 the working pressure, but, in spite of assertions to the contrary, riveted 
 seams, and even welds, which were found to be perfectly tight with 
 the cold test, commenced to leak at half that pressure when hot. This 
 is probably due to the difference in the conditions of testing, and not, 
 as is often stated, to the previous excessive proof stress. 
 
 It is also argued that an hydraulic test not exceeding the working 
 pressure will detect defective material and flaws. This is not borne 
 out by experience (see p. 223). 
 
 In one sense, the hydraulic test can therefore be looked upon as a 
 guarantee of good material, although its chief object is to detect bad 
 workmanship. This will show itself by leakages. 
 
 The amount of water which has to be pressed into a boiler amounts 
 to about ^ per cent, of its gross volume, unless all the air has not been 
 removed, 'or unless the boiler is weak, in which case more water has 
 to be pumped into it. 
 
BOILER CONSTEUCTION 
 
 301 
 
 Boiler Deformations. Observations as to the deformations are also 
 made, but it cannot be said that they have been of much assistance in 
 detecting local weaknesses ; but they undoubtedly offer a means of 
 studying the actual stresses in boilers, and a few remarks on the subject 
 will not be out of place. That they are very much larger than most 
 engineers expected was shown during the discussion on J. T. Milton's 
 paper (' N. A.,' 1893, vol. xxxiv. p. 157) on this subject. 
 
 The stretching of the boiler circumference can be roughly measured 
 by coiling a wire 1J times round it (fig. 427) and weighting the two 
 
 FIG. 427 
 
 FIG. 428 
 
 FIG. 429 
 
 ends, and then marking the two wires at the top of the boiler before 
 and during the test. The stretch ought to be about ^-^-$ of the cir- 
 cumference, or, say, in. for an 11-ft. boiler, and \ in. for a 13-ft. boiler. 
 It will be found that the reading is less, and also, on relieving the 
 pressure, that the original marks do not coincide. This is not per- 
 manent set, but is due to the friction between the wire and the shell. 
 More accurate results can be obtained if one end of the wire is bolted 
 to the boiler and small rocking frames interposed between the shell 
 and the wire at other points (see fig. 428). The wire is secured by 
 means of a small bolt to the rivet-head A, and led from one rocking 
 frame to another till it reaches E, and the weight W is then hung to 
 the loose end, while a scale is secured partly to the bolt-head A and 
 
302 
 
 BOILER CONSTRUCTION 
 
 partly to the wire at V. The rocking frames (fig. 429) are made of 
 thin steel plates, sharpened at the bottom. The wire passes over the 
 notch y. By fixing several wires round one boiler the straining of the 
 various parts of the shell and the influence of the end plates and 
 seams can easily be ascertained (see p. 195). 
 
 Most of the other parts of the boiler can best be measured by rods 
 or battens having a micrometer screw or other contrivance attached 
 
 FIG. 430 
 
 to their ends. Fig. 430 shows a convenient instrument for this pur- 
 pose : S is one of a large number of small sleeves, to which ordinary 
 wood screws have been brazed, and by which means they are secured 
 to the wooden rod or batten ; E E is a steel rod which easily fits 
 the sleeve S, and is accurately graduated, preferably in millimetres ; 
 V is another sleeve, slit open on one side, and containing a vernier. 
 The two should be a sliding fit. Measurements of the various points 
 of a boiler before and after testing are taken by consecutively insert- 
 ing the rod E E with its vernier into all the sleeves S and noting 
 the readings (see p. 169). 
 
 lA 
 
 a* 
 
 \- -B 
 
 FIG. 431 
 
 For themeasurement of furnace deflections, ordinary trammels are 
 more convenient, as, by their means, it is easier to detect the major 
 and minor axes of deformation. 
 
 For instance, if measurements are taken at the axes A A and B B 
 
BOILER CONSTRUCTION 303 
 
 (fig. 431), with a deformation as shown by the dotted lines, then the 
 final readings would differ but little from the original ones. However, 
 if trammels are used, they will show that the diameters had changed 
 their angle, and the trammel resting at A would touch e instead of a, 
 while the one resting at B would touch / instead of d. This would 
 lead to further measurements being taken at jh and ik, and would 
 show that a serious deformation was taking place there. Should one 
 
 I 
 
 I ' 
 
 \ * 
 
 \ 
 
 o\ ; 
 
 i / 
 i 
 
 
 Fio. 432 
 
 of the diameters be so much reduced that the trammel cannot be got 
 into position, its points of touching must be marked along the axis of 
 the flue. 
 
 In order to reduce these measurements to absolute readings, em- 
 ploy the following formula : A t and A 2 are the difference between the 
 diameter of the furnace and the length, D, of the trammel ; x and y 
 are shown in fig. 432. 
 
 If the original reading was x and the subsequent one y, then the 
 deformation of the furnace was A! + A 2 = x "t ^ . 
 Let D = 40 ins., x = 4 ins., y = 2 ins., then 
 
 If the first measurement of x was 6 ins., and the second one 4 ins., 
 
 0> -J 
 
 then the deformation was also T ^ in., viz. -A^ 
 
 Having tested the boiler, it ought to be examined internally, after 
 it is usual to cement the lower seams of the shell, to cut the 
 various openings for steam pipes, &c., and to fit the boiler on board. 
 
 On account of the numerous recent cracks in furnace saddles, it 
 has been suggested that these parts should be severely hammered 
 after the test. 
 
304 
 
 CHAPTEE IX 
 DESIGN 
 
 The Proportions of Heating and Grate Surfaces and sectional areas 
 of tubes, funnel, and other parts of boilers vary considerably according 
 to the experiences of the manufacturers or shipowners, and it would 
 be rash to attempt to harmonise these divergent views ; all that can 
 be attempted is to reduce the problem to the simplest elements, and 
 these, it is hoped, will indicate how to make comparisons and draw 
 conclusions from authentic records. The two conflicting factors are 
 economy on the one hand, and maximum performance for a given 
 weight of boiler on the other. In the one case large heating surfaces 
 are necessary, in the other a high temperature of the escaping 
 products is unavoidable. 
 
 Assuming the case of a boiler supplied with feed water of 100 F. 
 and worked at a pressure of 150 Ibs. (water temperature 315 F.), and 
 assuming that the fuel is capable of evaporating 15 Ibs. of water at 
 and from 212 F., equal to 12'3 Ibs. under the above conditions, and 
 assuming that 15 Ibs. of steam are required for each I.H.P., then the 
 following results may be expected : 
 
 Pounds of water evaporated per square foot of "1 
 heating surface per hour . J 
 
 2 to 3 
 
 5 
 
 9 
 
 The evaporating efficiency of the boiler will be "1 
 approximately j 
 The uptake temperatures will be about 
 Weight of water in Ibs. evaporated per Ib. of fuel 
 
 70% 
 
 500 
 8-6 
 
 65% 
 
 700 
 8-0 
 
 60% 
 
 900 
 7-4 
 
 Weight of fuel per hour per I.H.P. . 
 Square feet of heating surface per I.H.P. . 
 
 1-75 
 6to7| 
 
 1-88 
 3 
 
 203 
 Ml 
 
 With the help of the above-mentioned funnel temperatures it is 
 possible to estimate the force of its draught when the height is 
 known. 
 
 Funnel Draught Measured in Inches, Water. 
 
 Mean Temperature of 
 
 Mean Height of Funnel above Fire Bars 
 
 Waste Gases 
 
 20ft. 
 
 40ft. 
 
 60ft. 
 
 80ft. 
 
 100 ft. 
 
 400 F. 
 
 14 
 
 28 
 
 42 
 
 56 
 
 70 
 
 600 P. 
 
 17 
 
 34 
 
 51 
 
 68 
 
 85 
 
 800 F. 
 
 19 
 
 38 
 
 57 
 
 76 
 
 95 
 
 1,000 F. 
 
 20 
 
 41 
 
 61 
 
 82 
 
 .1-02 
 
DESIGN 
 
 305 
 
 Any desired pressure or suction can of course be obtained by 
 mechanical means (forced draught). If the specific resistance due 
 to fuel and other obstructions were known, it would be easy to esti- 
 mate Q, the weight of air which passes through 1 square foot of 
 
 grate per hour : Q = 730 A / ^ , where h is the draught pressure 
 v 1 + r 
 
 in inches of water, and r the specific resistance to the air passage ; 
 but as this latter value can only be guessed at (see p. 102), and as the 
 weight of coal consumed is not strictly proportional to the weight oi 
 air which passes through the grate, the matter is simplified by com- 
 paring the coal consumption and funnel draught direct. 
 
 Approximate Coal Consumption in Ibs. per Square Foot of Grate. 
 
 Draught pressure, inches (water) 
 
 * ' * 1 f 1 * 
 
 2 
 
 3 
 
 4 
 
 Pounds of coal burnt per hour per sq. f from 
 ft. of grate \ to 
 
 15 i 20 
 20 | 25 
 
 25 30 
 30 40 
 
 40 
 
 50 
 
 50 
 75 
 
 GO 
 80 
 
 The following case will illustrate the use to which these tables can 
 be put. The relations between the various surfaces are to be deter- 
 mined for a boiler whose funnel height is 80 feet, and which is to give 
 economical results. The uptake temperature should therefore not 
 exceed 500 P., and the draught suction will be about '6 in. ; the con- 
 sumption per square foot of grate will be about 20 Ibs. per hour ; the 
 indicated horse -power will be about 11 per square foot of grate, and 
 the heating surface will have to be about 55 times as large as the 
 grate area. 
 
 If economy is of secondary consideration, then the uptake tempera- 
 ture will have to be about 1,000, the draught will be '85 in., the con- 
 sumption 30 Ibs. per square foot of grate, and the horse-power about 
 14, which is not much more than in the above case ; but the heating 
 surface will be very much less, viz. 23 times as large as the grate. 
 
 Had the funnel been shorter, the consumption per square foot of 
 grate would have been less, and the ratio of the heating surface would 
 also have been reduced, whereas with forced draught it would have to 
 be increased. 
 
 The absence of any reliable data on the relationship between funnel 
 height, grate area, and heating surface makes it difficult to check the 
 above values by actual performances, and the above tables and cal- 
 culations should, therefore, only be looked upon as an indication how 
 deductions could be drawn from really reliable information. The 
 necessity for doing this has occasionally made itself felt in boilers which 
 were to be exceptionally economical. In one case the lowness of the 
 funnel and its temperature reduced the boiler performance so seriously 
 that it was necessary to reduce the heating surface by blocking up a 
 large number of tubes ; and it is evident that if these boilers had 
 originally been properly designed, they could have been made of very 
 much smaller dimensions. 
 
 Funnel Dimensions. A natural desire to reduce both the height 
 and diameter of a funnel, so as to offer little resistance to the speed of 
 the ship, will, if carried too far, reduce the draught, and with it the 
 
 x 
 
306 DESIGN 
 
 boiler performance. Many people hold the view that a short funnel 
 with a large diameter is as efficient as a tall one with a reduced sectional 
 irea ; but this can only be true in cases where the resistance to the 
 motion of the products of combustion is greatest in the funnel. In 
 well-designed ones this is far from being the case, and then, within 
 certain limits, the draught is not affected by the diameter. The one 
 limit is determined by the velocity of the waste gases, which should 
 not exceed 25 ft. per second under natural draught. The other limit 
 is more difficult to fix, but it is quite certain that if a funnel is made too 
 large in section, cold air will rush down from above and interfere with 
 the up current. This happens with those funnels which occasionally 
 draw well, and at other times badly. It is well known that factory 
 chimneys parallel outside and conical inside, which were the fashion 
 some years ago, were serious offenders in this respect, from which it 
 is reasonable to conclude that not only the size and proportions, but 
 also the shapes of funnels, affect the results. 
 
 Dimensions of Grates and Furnaces. As a general rule, and for 
 ordinary work, the stoking of furnaces whose bars are longer than 5 ft. 
 cannot be done economically. When their lengths exceed 6 ft. most 
 of the extra coal burnt is simply wasted. This is particularly the case 
 with forced draught, and some engineers advocate that under such 
 conditions the grate should not be longer than 4 ft. 
 
 Stoking is seriously interfered with if the furnace diameters are 
 small, and probably the cooling influence of the plates close to the 
 fire retards combustion, whereby unconsumed gases are permitted to 
 escape. So that, unless grates are very short, furnaces should not be 
 made less than 3 ft. diameter, and where flaming coals are used they 
 should be still larger. 
 
 Builders prefer small furnaces, because with them more grate sur- 
 face and more heating surface can be got into a boiler of a given dia- 
 meter ; but steam users should see that this does not lead to their being 
 supplied with an inferior boiler. 
 
 Tubes. The furnace and tube lengths are practically identical, and 
 vary from 4 ft. for short double-ended boilers to 9 ft. for single-ended 
 boilers with forced draught. In the latter case the tube diameters are 
 about 2^ ins., while for natural draught, where a small internal 
 sectional area would offer too much resistance, the length is usually 
 about 24 diameters. 
 
 Tube Surfaces, and Space Occupied. The following table gives 
 some of the dimensions of boiler tubes. The thickness of the metal 
 is assumed to be '15 in., or about No. 9 wire 
 gauge. The external and internal heating surfaces 
 are given per foot of length. The internal sectional 
 area of a single tube is also added. The last two 
 lines of the table contain the amount of end space 
 required by one tube when it is surrounded either 
 by 1 in. or 1J in. of water space (see dotted lines, 
 
 FIG. 438 fig. 433). 
 
 In one and the same boiler the number of tubes 
 for each furnace sometimes differs considerably. This is a bad de- 
 sign, for there are either too few for the one or too many for the 
 other. The tube surface amounts to from 75 to 85 % of the total 
 heating surface. 
 
DESIGN 
 
 307 
 
 External diameter, inches . 
 
 2i 
 
 2 
 
 2f 
 
 3 
 
 3* 
 
 3 
 
 3f 
 
 Sij.ft. of external surface per ft. 
 internal 
 sectional area 
 
 59 
 51 
 021 
 
 65 
 
 57 
 029 
 
 72 
 64 
 033 
 
 79 
 71 
 040 
 
 85 
 77 
 048 
 
 92 
 84 
 056 
 
 98 
 90 
 065 
 
 Square inches of end space per tube. 
 
 Water spaces = 1 in. 
 = Uin. . 
 
 10-5 
 12-2 
 
 12-2 
 14-0 
 
 14-0 
 16-0 
 
 16-0 
 18-1 
 
 18-1 
 20-2 
 
 20-2 
 22-6 
 
 22-6 
 25-0 
 
 Boiler Diameter. Having decided how many square feet of tube 
 
 heating surface the boiler should contain, what diameter and length 
 
 the tubes should be, and what widths of water space are to be left 
 
 between the tubes, the above table will enable one to estimate how 
 
 many square inches of tube plate area will be taken up by the tubes. 
 
 These areas are represented by A and B (fig. 434), and the various 
 
 letters indicate the other 
 
 water and steam spaces, viz. : 
 
 a is the distance between 
 
 two furnace diameters. 
 
 b is the distance between 
 
 the furnace and the 
 
 shell. 
 
 c is the distance from the 
 wing furnace to the 
 lower row of tubes. 
 d is the furnace diameter. 
 e is the distance from the 
 centre furnaces to the 
 lower row of tubes. 
 / is the distance from the 
 shell to the wing tubes. 
 h is the same dimension 
 measured in the steam 
 space. 
 g is the distance between Fl - 434 
 
 the nests of tubes. 
 
 All these dimensions are to be taken, not from centre to centre, nor 
 from the circumferences, but from the squares surrounding the tubes, 
 as shown in fig. 435. 
 
 K- 
 
 .1. 
 
 9 - 
 
 FIG. 435 
 
 Let 2 (T) represent the sum of the end space required for the tubes. 
 In fig. 434 this would be 2A + B. Let D be the boiler diameter, 
 then, 2 (T) = 0'45(D-d-K) a . 
 
 X 2 
 
308 
 
 DESIGN 
 
 The value of K is found by multiplying the various water and 
 steam spaces by the numbers contained in the following table, and 
 then adding them together : 
 
 Number of Furnaces in Boiler . 
 
 Two 
 
 Three 
 
 Four 
 
 Multiply a by 
 
 20 
 60 
 
 70 
 60 
 
 45 
 45 
 
 
 
 20 
 
 70 
 
 the sum of e by . . 
 
 9 tr 
 
 /by 
 
 30 
 20 
 40 
 
 25 
 25 
 
 40 
 
 35 
 35 
 50 
 
 
 
 
 
 The above formula will be found to agree fairly well with the 
 general practice as long as his equal to one-third of the boiler diameter 
 (^ D). Where this relation does not exist, subtract from D, in., 1 in., 
 and 1J in., for two-, three-, and four-furnaced boilers respectively, for 
 every additional inch of steam space, so that if written out in extenso 
 the above formula would be 
 For two furnaces : 
 
 For three furnaces : 
 
 For four furnaces : 
 
 --- 
 o o 
 
 The sign 2 ( ) means that the letter in the bracket is the sum of 
 the several dimensions. 
 
 These formulse can be simplified by adopting the following average 
 values : a and b vary from 3 ins. to 8 ins., and are usually 5 ins. 
 
 In two-furnaced boilers c varies from 3 ins. to 11 ins., but it is 
 generally made 7| ins. In other boilers it varies from 8 to 12 ins., 
 the mean being 10 ins. 
 
 e is sometimes as much as 15 ins. Generally both c and e are 
 made 10 ins. 
 
 / and g both vary from 8 ins. to 12 ins. The usual practice is to 
 make both about 10 ins. ; this would give 10J ins. of clear water space 
 at the wings, and 11 ins. at the centres. 
 
 The mean value of h is J D. 
 
 Substituting these average values, the formulae are reduced to the 
 following : 
 
 For two furnaces and two combustion chambers 
 
 For three furnaces and three combustion chambers 
 - (H5(0-92D - d - 22J) 2 . 
 
DESIGN 309 
 
 For four furnaces and two combustion chambers 
 2(T) = 0'45(D-d-24f) 2 . 
 
 For four furnaces and three combustion chambers 
 2 (T) = 0-45 (D-d- 
 
 For the purpose of ascertaining the diameter it will be more con- 
 venient to alter these formulae as follows : 
 
 The length of the Boiler is fixed by the length of the tubes or 
 furnace, by the depth of the combustion chambers, and by the water 
 space at their backs. 
 
 The latter should not be made less than 5 ins., but cases are met 
 with where they are reduced to 3 ins. They should be made wider at 
 the top than at the bottom, the usual angle being ^ in. per foot of 
 depth. 
 
 The Combustion Chambers, measured horizontally, should be made 
 as deep as possible : 28 ins. and 36 ins. seem to be the smallest limits 
 for single- or double-ended boilers respectively. Generally this depth 
 is about 12 ins. greater than half the furnace diameter for single-ended 
 boilers, while for double-ended ones with through combustion chambers 
 it is made about 24 ins. deeper than half the furnace diameter. 
 
 The following are the relations usually existing between various 
 boiler dimensions : 
 
 Boilers with Two Furnaces. The ratio of boiler diameter to fur- 
 nace diameter is generally as 10 to 3, but sometimes 10 % more or 
 less. Custom is equally divided between leading the two furnaces 
 into two combustion chambers or into one. In the latter case the 
 central water space between the tubes is sometimes dispensed with, 
 but generally a few rows of tubes are left out along this line. The 
 diameters of these boilers range from 8 ft. to 14 ft., and the lengths 
 from 8 ft. to 10 ft. for natural draught, and up to 12 ft. for forced 
 draught. The shortest double-ended boilers are 12 ft. long, and the 
 longest 18 ft. 
 
 Boilers with Three Furnaces. The ratio of boiler diameter to 
 furnace diameter is generally as 4 to 1, but sometimes 7 % more or 
 less. Generally three combustion chambers are fitted, but sometimes 
 only one, and in that case the tubes are mostly divided into two groups 
 with a water space in the centre. In rare cases there are no water 
 spaces except at the sides. The diameters of these boilers range from 
 11 to 16 ft., and the lengths from 9 to 11 ft. for natural, and 12 ft. for 
 forced draught. Double-ended boilers are sometimes made 20 ft. 
 long. 
 
 Boilers with Four Furnaces. The ratio of boiler diameter to 
 furnace diameter is generally 5 to 1, but sometimes 5 % more or 
 less. The combustion chambers are usually so arranged that the two 
 central furnaces are led into one, and the two wing ones into separate 
 chambers, so that there are one large and two small ones. Sometimes 
 there are only two combustion chambers, and very rarely there are 
 
310 DESIGN 
 
 four, or only a single one. The diameters range from 13 to 17 ft., and 
 the lengths are the same as for three-furnaced boilers. Double-ended 
 ones are rarely built. 
 
 Boiler Performances. The following are a few rough rules for 
 estimating the heating surface and power of a boiler under natural 
 draught : 
 
 D = boiler diameter in feet. 
 L = boiler length in feet. 
 
 P = working pressure in pounds per square inch, 
 HS = heating surface in square feet. 
 Q = boiler weight in tons (no funnel, &c.). 
 W = water weight in tons. 
 C = coefficients. 
 
 IHP = indicated horse-power = from to \ HS and up to 1 HS 
 with forced draughts. With water tube boilers these coefficients 
 have to be reduced about 25 %. 
 HS = C, . D 2 . L 
 
 I = 0'9 for single-ended boilers, natural draught. 
 C, = 0'95 to 1*0 for single-ended boilers, forced draught. 
 C, = TO for double-ended boilers, natural draught. 
 GI = 1*05 for double-ended boilers, forced draught. 
 Q = C 2 (D 2 . L + HS) (P + 60). 
 
 C 2 = 27,000 for single- ended boilers to Lloyd's Eules. 
 
 C 2 = 25,700 for single-ended boilers to Board of Trade Eules. 
 
 C 2 = 30,000 for double-ended boilers to Lloyd's Eules. 
 
 C 2 = 28,600 for double-ended boilers to Board of Trade Eules. 
 
 W = 0-01 D 2 L. 
 
 In 1898 on the Clyde and before the recent rise in prices, the cost 
 of single- ended boilers working at 150 pounds and designed to Lloyd's 
 Eules, not including funnel, &c., was 
 
 Cost in = 0-35 D 2 . L + 2 (D 2 . L) H 
 
 The first term represents the cost of material and such charges as 
 are nearly proportional to weight, and therefore to pressure ; the second 
 term represents such charges as riveting, tapping, screwing, caulking 
 as are nearly proportional to the boiler surfaces. 
 
 All the above coefficients vary in different works, as they depend 
 on local practices and appliances. 
 
 The following are a few published details of boiler weights. 
 Bertin & Eobertson, p. 355, ' Weights of Water-tube Boilers ' ; also 
 ' Norman,' ' Enging.,' vol. Iviii. p. 701 ; ' Kensington,' ' Enging.,' vol. 
 Iviii. p. 199 ; U.S. ' Minneapolis,' * Enging.,' vol. Ix. p. 600. 
 
 Two lists of boiler performances have been published by F. Marshall, 
 M. E.,' 1881, p. 449, and 1891, p. 337. 
 
 The following is a list of published drawings of marine boilers : 
 
 F. Colyer, 1886. Three-furnaced oval boiler, by Maudslay, 12 ft. 
 4 ins. diam., 14 ft. 1 in. diam., 9 ft. 11 ins. long ; three-furnaced 
 cylindrical boiler, 17 ft. 4 ins. diam., 9 ft. 1 in. long. 
 
 Schwarz Flemming, 1873. Forty-nine sketches of boilers. 
 
 C. Busley, 1883. Boilers in vessels of German Navy. 
 
 B. N. Bartol, 1851. Sketches and surfaces of American boilers. 
 
DESIGN 311 
 
 J. T. Winton, 1883. Various types of boilers. 
 
 N. P. Burgh, 1873, contains drawings of about 20 boilers and 
 sketches of 90 types of patented boilers from 1852-71. 
 
 N. Foley, 1891. Plates 6, 7, 8, give full detailed drawings of the 
 three following boilers : 
 
 Single-ended, 2 furnaces, 39 ins. internal diam., 1,099 sq. ft. heat- 
 ing surface. Outside dimensions, 12 ft. x 9 ft. 8 ins. Weight, 25 
 tons. Steam pressure, 150 Ibs. 
 
 Single-ended, 3 furnaces, 35^ ins. internal diam., 1,334 sq. ft. 
 heating surface. Outside dimensions, 12 ft. 6 ins. x 9 ft. 8 ins. 
 Weight, 27 tons. Steam pressure, 150 Ibs. 
 
 Double-ended, 4 furnaces, 34 his. internal diam., 1,843 sq. ft. heat- 
 ing surface. Outside dimensions, 10 ft. 6 ins. X 16 ft. 6 ins. Weight, 
 34 tons. Steam pressure, 160 Ibs. (See also p. 318.) 
 
 Other types of boilers will be found in the following lists : 
 
 Dry Back Type.' Enging./ vol. Ixiii. p. 474. 
 
 Navy Type. ' Surprise ' and ' Alacrity/ Palmers', 'Enging.,' vol. xl. 
 pp. 447, 450 ; ' Melbourne,' Simmons & Co., ' Engr.,' vol. Ix. p. 392 ; 
 ' Yorktown/ ' Enging.,' vol. li. p. 493 ; ' Bergen,' ' Enging./ vol. xlix. 
 p. 191 ; ' Mouche/ Belliss & Co., ' Enging./ vol. xxxix. p. 81 ; ' Enging./ 
 vol. Iv. p. 694. 
 
 Locomotive Type. Schichau, ' Enging./ vol. xxxiv. p. 579 ; Yar- 
 row, ' Enging./ vol. xlii. p. 179 ; ' Sunderland/ Doxford, ' Enging./ 
 vol. xlix. p. 30 (for burning petroleum); Hick, Hargreaves, 'Enging./ 
 vol. xlix. p. 528 ; ' Barham ' and ' Bellona/ Hawthorn, Leslie & Co., 
 ' Enging./ vol. 1. p. 705 ; ' Phlegeton/ Soc. Ann. Claparede, ' Engr./ 
 vol. Ix. p. 277 ; Sectional locomotive boiler for transport, Sandycroft 
 Foundry, ' Enging./ vol. xxxviii. p. 261 ; N. Foley, 1891, pi. x. and xi. ; 
 'Enging./ vol. Iv. p. 695; H.M.S. 'Hazard/ 'Enging./ vol. Iviii. 
 p. 421. 
 
 Water Tube Boilers. J. F. Spencer, ' M. E./ 1859, p. 264 ; Z. Col- 
 burn, ibid., 1864, p. 61 ; Laybourne, ibid., 1871, p. 263 ; D. Joy, 
 ' I. and S. I./ 1874, p. 220 ; Perkins boiler, Maw, ciii. ; Adams and Co., 
 ' Enging./ vol. xxxiv. p. 251 ; J. F. Flanery, ' C. E./ 1878, vol. liv. p. 123 ; 
 J. T. Thornycroft, ' Enging./ vol. xxxv. p. 463, vol. xliv. p. 105, vol. 
 xlvii. p. 402 ; ' N. A./ 1889, vol. xxx. p. 271 ; ' C. E./ 1890, vol. xcix. 
 p. 41 ; Ward's Patent, ' Enging./ vol. xlvii. p. 322 ; Yarrow, ' Enging./ 
 vol. li. p. 79. All recent vessels of the French Navy are having 
 tubular boilers fitted (Belleville, Lagrafel-D'Allest), J. T. Milton, 
 ' N. A./ 1893, vol. xxxv. Danish cruiser ' Geiser ' (Thornycroft), 
 ' Enging./ vol. liv. p. 789 ; ' Daring ' (Thornycroft), ' Enging./ vol. 
 Ivi. p. 667; 'Algerie' (Babcox and Wilcocks), 'Enging./ vol. Iviii. 
 p. 433 ; Stirling Boiler, ' Enging./ vol. lix. p. 825 ; Stirling type, 
 ' Enging./ vol. lix. p. 825 ; H.M.S. ' Terrible ' (Belleville details), 
 ' Enging./ vol. lix. p. 822 ; Du Temple, ' Enging./ vol. Ix. p. 57 ; 
 Normand, ' Enging./ vol. Ix. p. 75 ; H.M.S. ' Surly/ ' Enging./ vol. 
 Ix. p. 630 ; Niclausse, ' Enging./ vol. Ix. p. 91 ; Thornycroft, ' Enging./ 
 vol. Ix. p. 269; Ligaudy, 'Enging./ vol. Ix. p. 541; Serpollet, 
 ' Enging./ vol. Ix. p. 501 ; Haythorn, ' Enging./ vol. Ix. p. 680 ; 
 Eussian ' Kherson' (Belleville), ' Enging./ vol. Ixii. p. 799 ; H.M S. 
 ' Spanker ' (Du Temple), ' Enging./ vol. Ixiii. p. 777 ; H.M.S. ' Pelorus ' 
 (Normand), ' Enging./ vol. Ixiii. p. 385 ; ' Laos ' (Belleville), ' Enging./ 
 
312 
 
 DESIGN 
 
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 q 
 
 ^ 
 
 I 
 
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 g g 
 
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 CM CO O <M C-J i-l rH r-l CS rH i-l -H 
 
 O O O S 
 
 acwjang s^vx 
 
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 us oo <o --(jio 
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 ,0 r-l t^ i-l O ; US U5 00 CO t- CO ; t j O5 OO CO a? US 5 g ; ; US US 
 
 00OOOOOOOO O 00 00 CO <0 <O CO 00 CO CO CO <O * CO CO CO CO O 
 
 eg S8S2; 
 
 05 oo oo cc CQ i 
 
 g _^OCO.Q. 
 
 
 I -H O 00 t t~ t- * I 
 
 i co co N e* c> CN n i 
 
 HH g O CO <M us CO O O O O eo 1-1 O CO 
 
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 CO O 55 Ol >-! O O rH US CO O CO CO US A 
 
 co ^ - co co oo ao co oo to r- co co t^ -f< 
 
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 c us T-H O 05 eo o> co o o o r-i co co o P< o co oo co co co co i~i co o 
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 fc *< 
 
 H _ 
 
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 V^ 
 
 fa? S .-s 
 
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 yii* irf*"^ ii5 ii*! **i? m 
 
 ms^>>d 'jAjgJa^l '1 '*!S ' M 55ji^ ' ^-a ^ ' ' >.ajj 
 
 >>>-3o'-3 1:=-3o-3o'-3 1 .MrilllH- . ^^ "3 "3 . . ^^' 
 
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 to xbor ^6o.bb".'> < ti) (>>-r .>t>>> 
 
 .= o 2 be ^a>obc*fl .otao sx; 
 
 fi " " * s ijflf s ' * e fSfff 1? " * S S & > * s s ^ 6 , 
 
 " 
 
 
 
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 a . a & S &C.Q o cs c - | S S ' y 
 
 ^vgll | 33;. ' - a : - g - - g ;gj(E -. ,1 4 - a '.'I 
 
 ll||?? | rirfg^l 1 :1|| illli 1 SissrM Si- 
 
 gisigg J 1 1 1 1 1 ilii I Igilf! i a 
 
DESIGN 
 
 813 
 
 : 1 ' ' *s 3 *? I ' 11 't ' s 'i 
 
 ill 
 
 e,s II > 
 
 3 3 3 cS 
 
 KL. PN&, fc 
 
 ro-LZLO'^'SO i l aoCOD'^'-^aDi 
 
 OTeoeo^^^ ( 
 
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 do to >* o os o 
 
 W CO KS .0 : CO 
 
 iftooOOO S . .0 .0 . .WHS .100 OO.t-0 O 00-*0 O 0000 000 .00 
 
 t ^X,4OOU5>0 ..^.35;:<a0;C<IlO aOO : t^. 00>OOWJOO OOlOp-l-* 00>OO ;lOlO 
 
 O O O 00 CV < O OS *CI5O O 
 
 - erj -r M cc eo >e> -^ co ej co co eo T 
 
 sgEiJsgg illi 1 llll 
 
 fe^< i PS^^^ -hsg 5 S5 
 
 ooo 
 o> o c-. 
 
 oo 
 
 c: co 
 
 H 
 
 -.osoo 
 
 CO t~ 5O CO ^H O O O O * O O W O CO u O OO O O O> O> 
 OSSOOOJOJOOOO'VO OOSOOCJ OO>OOJOOt 
 
 
 i O eo 00 O Ci O 
 
 O r* ""' 
 I 04 -H i <N i-l 
 
 "- 1 " x~"" 
 
 S =1*.*S3? !e*^S 
 
 ** ^ 00 
 '-J 5 n. 
 
 I PI il ^f 
 
 III'S'S'S I c'll'l o' o' o"|5'||'3 . "5*3 .'S -3 ^"ag^-s^ "3 "S -3-3 o' -g "So" 
 
 ti -.** to 3 e 
 
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 5? 
 
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314 DESIGN 
 
 vol. ixvii. p. 544; Maxim, 'Enging./ vol. Iviii. p. 195; Niclausse, 
 ' N.A..' 1896, vol. xxxvii. p. 119. Bertin and Eobertson. 
 
 General descriptions of water- tube boilers : ' Marine Boilers,' 
 Bertin and Eobertson ; Water-tube Boilers, J. T. Milton, ' N. A.,' 
 1893, vol. xxxv. pp. 86, 295 ; Water-tube Boilers, J. K. Eobinson, 
 U. S. Navy, Am. Soc., ' N. E.,' ' C. E./ 1895 ; also ' Enging./ vol. Ix. 
 p t 554. Circulation in Water-tube Boilers : Prof. Watkinson, ' N. A.,' 
 
 1896, vol. xxxvii. p. 267 ; also ' Enging./ vol. Ixi. p. 437 ; J. A. 
 Normand, ' N. A.,' 1896, vol. xxxvii. p. 109 ; C. C. P. Fitzgerald, ' N. A.,' 
 
 1897, vol. xxxviii. p. 165 ; A. F. Yarrow, ' N. A./ 1898, vol. xl. 
 p. 114 ; A. F. Yarrow, ' N. A.,' 1899, vol.xli.p. 333. Very, instructive 
 information about boilers in general will be found in the Admiralty 
 Eeport, 1892. 
 
 In the following list the vessel's name and reference only are 
 given. The drawings show the positions of boilers, pipes, &c., as 
 fitted on board : 
 
 W. H. Maw, 1883 : ' Gallia,' plate xv. ; ' Hohenzollern/ xxi. ; 
 H.M.S. ' Grappler,' ' Wrangler,' ' Wasp,' ' Banterer,' ' Espoir,' xlvii. 
 and xlviii. ; ' Servia/ Ixiy. ; H.M.S. ' Eover,' Ixxi. ; ' Arizona,' xcii. ; 
 ' Grecian,' cxviii. ; 'Assyrian Monarch,' cxlvi. andcxlvii.; ' Czar,'cxxxi. ; 
 H.M.S. ' Conqueror,' cxliii. ; ' Normandie,' clxviii. ' Engr.' : * Chicago,' 
 vol. Ixi. p. 86 ; ' Oroya,' vol. Ixiii. p. 234 ; ' Grace Darling,' vol. Ixv. 
 p. 236; 'Elbe,' vol. Ixiv. p. 522. 'Enging.': 'Princess Elizabeth,' 
 1 Princess Marie,' vol. xxxi. p. 119 ; ' Servia,' vol. xxxiii. p. 247 ; ' Satel- 
 lite,' ' Conqueror,' vol. xxxv. pp. 266, 267 ; ' Czar,' vol. xxxv. p. 364 ; 
 ' Churchill,' vol. xxxvii. p. 2 ; ' Normandie,' vol. xxxvii. p. 65 ; 
 ' Godiva,' ' Stokesley,' and ' Hunstanton,' vol. xxxvii. p. 380 ; 
 'County of Salop,' vol. xxxviii. p. 516; H.M.S. 'Boadicea,' 
 Bacchante,' vol. xl. pp. 325, 328 ; ' Alacrity ' and ' Surprise,' vol. xl. 
 p. 589 ; ' Kathleen Mavourneen,' vol. xli. p. 221 ; H.M.S. ' Mersey ' 
 and ' Eodney/ vol. xli. p. 449 ; ' Eoyal Prince/ vol. xli. p. 588 ; 
 ' Westmoreland/ vol. xlii. p. 70 ; ' Gladiator/ vol. xliii. p. 104 ; 
 ' County of York/ vol. xliii. p. 246 ; ' The Earl/ vol. xliv. p. 405 ; 
 H.M.S. ' Orlando/ vol. xliv. p. 492 ; ' Elbe/ vol. xliv. pp. 656, 661 ; 
 'Islander,' vol. xlvi. p. 304 ; H.M.S. 'Barracouta/ vol. xlix. p. 467; 
 ' Sunderland ' (torpedo boat), vol. xlix. p. 32 ; ' Kaiser Wilhelm II.,' 
 vol. 1. p. 126 ; H.M.S. ' Barham ' and ' Barracouta/ vol. 1. p. 628 ; 
 ' Normannia/ vol. 1. p. 252 ; ' City of Vienna ' (forced draught), vol. li. 
 p. 398 ; ' Indra/ vol. li. p. 525 ; ' Scot/ vol. lii. p. 10 ; ' Ophir/ vol. 
 lii. pp. 535, 591 ; H.M.S. ' Edgar/ vol. liii. p. 74; 'Infanta Maria 
 Theresa/ ' Enging./ vol. Ivii. p. 805 ; ' Norman/ ' Enging./ vol. Iviii. 
 p. 699 ; Eussian ' Kherson ' (Belleville), ' Enging./ vol. Ixii. p. 799 ; 
 H.M.S. ' Powerful ' (Belleville), ' Enging./ vol. Ixii. p. 403 ; ' Kaiser 
 Wilhelm der Grosse/ ' Enging./ vol. Ixiv. p. 364 ; ' Cristobal Colon/ 
 (Water-tube), ' Enging./ vol. Ixiv. p. 206 ; ' Engr./ vol. Ixxx. pp. 228, 
 523, 543 (pipes;; ' Corsican/ 'Enging.,' vol. Ixxxv. p. 46; H.M.S. 
 ' Lord Nelson/ 'Enging.,' vol. Ixxxvi. p. 421 ; 'Orsova/ 'Enging./ vol. 
 Ixxxvii. p. 715: 'Nippore Yusen Kaisha/ 'Enging./ vol. Ixxxix. p. 210; 
 ' Olympic/ ' Enging.,' vol. xc. p. 692 ; Eecalde/ vol. xciii. p. 288. 
 
 The Scantlings of Boilers are in most cases determined either ac- 
 cording to Lloyd's or the Board of Trade rules, to which a special 
 chapter is devoted. Here it will not be out of place to indicate the" 
 methods to be employed for finding the best proportions, either as 
 
DESIGN 
 
 315 
 
 regards efficiency or weight. It is, of course, impossible to make any 
 comparisons as regards cost, because the practices and available tools 
 of different shops are not known ; nor will any attempt be made to 
 deal with the subject exhaustively, and only two simple comparisons 
 will be carried out. In the one case it will be shown which form of 
 joint and which percentage of riveting gives the lightest boiler shell, 
 but only if built strictly according to Lloyd's rules. In the other 
 ease the lightest means of staying flat boiler plates will be discussed, 
 and a few remarks will be added, showing how to proceed when deal- 
 ing with such rules. 
 
 A very complete collection of rules and regulations by various 
 Governments for boiler construction, &c., will be found in Delauny- 
 Belville, 1886. 
 
 Riveted Joints. Lap joints (fig. 436) and double butt-strap joints 
 (fig. 437) are those most commonly used in boilers, though occasion- 
 
 FIG. 436 
 
 FIG. 437 
 
 ally Eowe's joint (fig. 438) is met with ; it has been designed with 
 the object of keeping the pitch of the outer row of rivets small, so 
 
 FIG. 438 
 
 FIG. 439 
 
 as to increase the water-tightness. A similar object is evident in fig. 
 439. Single butt-strapped joints (fig. 440) are only used on furnaces 
 
 FIG. 440 
 
 FIG. 441 
 
 or to cover defective welds. Fig. 441 is a design intended to save 
 weight. 
 
 When there are more than two rows of rivets in a lap joint, or 
 more than three in a double butt-strapped one, it is desirable to arrange 
 the rivets in such a manner that the percentage of strength of joint 
 is the same for every row of rivets. It will be found that this is only 
 the case in joints designed similarly to those shown in figs. 443 to 447. 
 In these cases the quotient obtained by dividing the number of rivets 
 in two adjoining rows is a constant value. If there are relatively 
 fewer rivets in the inner row than in the outer one as, for instance, 
 in fig. 442 the percentage of strength along that line is too high ; 
 while if there had been relatively more rivets, it would have been too 
 low. Let the quotient of the number of rivets in one row, when 
 divided by the number in the adjoining inner row, be denoted by m ; 
 then B, the value of percentage of the joint all rows having equai 
 
316 
 
 DESIGN 
 
 values is found in the following table. A lower percentage than 
 fchat given in this table should not be used, because the inner ro\v3 
 would be weaker than the outer ones, which gives a bad seam for 
 caulking. 
 
 Table of Percentages of Riveted Joints. 
 
 m 
 
 1* 
 
 1* 
 
 l| 
 
 If 
 
 If 
 
 2 
 
 ** 
 
 2 
 
 Lap joint, 3 rows 
 4 
 > 5 ,, 
 
 A 
 
 53-0 
 60-2 
 65-6 
 
 52-6 
 
 60-8 
 68-2 
 73-8 
 
 63-6 1 
 71-42 
 
 78-4 3 
 82-6 
 
 71-0 
 
 78-1 
 84-7 
 87-9 
 
 73-7 
 
 80-5 
 86-5 
 
 80-0 
 85-7 
 
 84-2 
 
 
 
 70-5 
 
 77-9 
 
 86-6 
 
 
 
 
 
 
 Q 
 
 74-2 
 
 81-2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Butt 2 
 
 > 11 3 ,, 
 
 ... 
 
 57-8 
 
 55-5 
 70-4 
 
 63-9 
 
 78-4 
 
 67'3 4 
 81-4 6 
 
 75-0 5 
 
 87-5 7 
 
 80-2 
 
 87-1 
 
 ) 3 
 
 l^in 
 innei 
 
 each | 
 row/ 
 
 66-7 
 
 2 in 
 innei 
 
 each I 
 row J 
 
 83-33 8 
 
 
 
 
 
 1 See fig. 455. a See fig. 446. See fin. 447. 
 
 * This is the value for Howe's joint, having two rows of rivets on each side of butt with equal 
 numbers of rivets in each (fig. 438). See fig. 443. 
 
 a This is the value for Rowe's joint, having three rows of rivets on each side of butt, there being 
 1, 1, and If rivets respectively in the 1st, 2nd, and 3rd rows (fig. 448). 7 See fig. 444. See fig. 442. 
 
 The riveted joint most commonly used is shown in fig. 442. It has 
 been explained (see p. 222) that the distance from the edge of the 
 
 FIG. 442 
 
 Fm. 443 
 
 plate to the circumference of the rivet hole should not be less than its 
 diameter. As regards the distances of the various rows of rivets from 
 
 each other, a fairly uniform practice seems 
 to exist of making the angular position of 
 the rivets equal to about 50 to 55, and 
 in some works even 60 is customary. 
 Some experiments (see p. 155) show that, 
 except for an angle of about 60, diagonal 
 joints are no stronger than longitudinal 
 ones. At this angle the longitudinal and 
 diagonal pitches are equal. For smaller 
 angles the percentage of the plate might 
 be ascertained by measuring the zigzag 
 line of all the outer rivets, subtracting 
 all their diameters, and then dividing by the zigzag length. Few 
 joints would then show the high percentage now claimed for them. 
 
 Fio. 444 
 
DESIGN 
 
 317 
 
 It has also been shown (see p. 218) that if the rows of rivets are 
 placed very wide apart, the stresses are not uniformly distributed 
 amongst them. This tends to lower the value of an ordinary joint, 
 but the unequal straining would be somewhat reduced by cutting 
 away the metal along the dotted line (fig. 444). In the absence of 
 any conclusive experiments or investigations, it is safest to adhere to 
 the general practice mentioned above. In double-ended boilers it 
 will often be found that the percentage of plate remaining between 
 the holes of the screwed stays is less than that between the rivets of 
 the longitudinal seams. The stays will then have to be pitched 
 diagonally. But some allowance might be made for the absence of 
 bearing pressure (see p. 215). 
 
 Lightest Joints. For the purpose of comparing the weight of 
 various joints, and also the amount of metal removed by drilling, 
 which is a sort of measure of the labour expended in the shops, the 
 above drawings of riveted joints have been made ; in every case 
 the holes are placed at an angle of 60. The dimensions are in ac- 
 cordance with Lloyd's Boiler Eule for a steel /plate 1 in. thick, the 
 rivet diameters not being less than 1 in., and the percentage of the 
 plate and of the rivet sections being equal. The estimates are con- 
 tained in the following table : 
 
 Comparison of various Riveted Joints. 
 
 Type of Joint 
 
 1 
 
 Rivets 
 
 -1 
 
 Weight per 1 ft. of Shell 
 
 Boiler Shell Weight | 
 
 JS 
 
 g 
 
 No. 
 per 
 Pitch 
 
 Diam. 
 
 Pitch 
 
 WP. of a 
 12-ft. Boil 
 
 3 Joints 
 includ- 
 ing 
 Rivet 
 Heads 
 
 Shell 
 Plate 
 and 
 3 Joints 
 
 Weight 
 of 
 Rivets 
 
 Inch 
 
 Inch 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Ibs. 
 
 Lap fig. 445 
 446 
 447 
 Butt (') 
 443 
 442 
 444 
 448 
 
 70 
 77 
 82-9 
 74-5 
 77-8 
 85-4 
 89-1 
 81-4 
 
 3J 
 
 5 
 
 P 
 
 5 
 
 7 
 3f 
 
 1 
 
 1 
 
 1-04 
 
 3-33 
 4-35 
 5-84 
 3-92 
 4-50 
 6-85 
 9-16 
 5-60 
 
 126 
 142 
 150 
 145 
 151 
 166 
 173 
 152 
 
 93 
 114 
 174 
 146 
 155 
 241 
 306 
 259 
 
 1643 
 1664 
 1723 
 1696 
 1705 
 1791 
 1856 
 1809 
 
 39 
 43 
 46 
 37 
 40 
 42 
 48 
 39 
 
 13-0 
 11-8 
 11-4 
 11-7 
 11-3 
 10-8 
 10-7 
 11-9 
 
 * Like part of fig. 445. 
 
 The last column contains the quotients obtained by dividing the 
 total weight of 12 ins. of length of the boiler shell by the respective 
 working pressures, as found by the 
 rules ; these are convenient measures 
 of the efficiencies of the various joints. 
 It will be seen that the quadruple lap 
 joint (fig. 446), though simpler, is almost 
 as good as the double-riveted butt joint 
 (fig. 443), and that the common butt- 
 strap joint (fig. 442) is nearly equal to 
 the one shown in fig. 444. This order 
 is slightly changed if the circumference 
 of the shell is made up of only one or two instead of three 
 plates. Of course, in works where the machines are incapable of 
 
 FIG. 445 
 
318 
 
 DESIGN 
 
 dealing with plates of more than a certain thickness it may be neces- 
 sary to use joints of the very highest percentage, and then the one 
 sketched in fig. 444 is undoubtedly the best (see p. 218). 
 
 FIG. 446 
 
 Best Arrangement of Staying Flat Plates. A comparison similar 
 to the above can be carried out for flat plates. Here it cannot be a 
 
 FIG. 447 
 
 question of variation of pitch, for it is quite clear that the total weight 
 of stays is a constant quantity, while the weight of the flat plates 
 
 FIG. 448 
 
 varies as the thickness, or inversely as the pitch of the stays, and by 
 placing these very close together the plates could be made quite thin. 
 
DESIGN 
 
 319 
 
 In the following table the pitch of the stays in the combustion chamber 
 plates is 10 ins. each way, the working pressure is 100 Ibs., and the 
 diameter of the screwed stay 1 in. 
 
 Table of Total Weight of Flat Combustion Chamber Plates 
 
 
 
 
 Total Weight of 
 
 Plate 
 
 100 sq. ins., 
 
 Thickness 
 
 including 
 
 
 Nuts, &c. 
 
 Inch 
 
 Ibs. 
 
 By Lloyd's Register 
 
 Boiler Rules { stay 
 
 ends riveted 
 nutted . 
 
 625 
 562 
 
 18-1 
 16-7 
 
 By Board of Trade 
 
 Boiler Rules! " 
 I tt 
 
 riveted 
 nutted . 
 
 730 
 580 
 
 21-1 
 17-2 
 
 In the following table the area of steam-space plating supported by 
 each stay of 2J ins. diameter is 300 square ins. 
 
 Table of Weight of Flat Steam-space Plates 
 
 Conditions of Staying Flat Plates in Steam Space 
 
 Constants 
 
 Plate 
 Thick- 
 ness 
 
 Weight of 
 300 sq. ins. 
 
 Plate 
 
 Do. and 
 
 Nuts, &c. 
 
 Inch 
 
 Ibs. 
 
 Ibs. 
 
 Lloyd's Boiler Rules. 
 
 Double nuts and no washers .... 
 
 175 
 
 82 
 
 70-0 
 
 77-5 
 
 washers ( P) 
 
 185 
 
 80 
 
 68-0 
 
 78-5 
 
 riveted (fPxiT) . 
 
 200 
 
 77 
 
 65-4 
 
 84-7 
 
 ;; (|PXT) . 
 
 220 
 
 73 
 
 62-4 
 
 95-3 
 
 strip-riveted (f P x T) . 
 
 (2201 
 1240/ 
 
 71 
 
 61-0 
 
 112-8 
 
 doubling plate (|T) 
 
 175 
 
 ( -611 
 Nl) 
 
 87-0 
 
 98-1 
 
 Board of Trade Rules. 
 
 Stay ends nutted 
 
 112-5 
 
 97 
 
 82-7 
 
 84-1 
 
 Double nuts and washers (3d x \ T) 
 
 125 
 
 91 
 
 78-0 
 
 91-7 
 
 riveted (\ P x T) 
 
 187-5 
 
 73 
 
 62-6 
 
 95-6 
 
 strips 
 
 200 
 
 71 
 
 60-5 
 
 111-9 
 
 Here, again, it will be seen that the mode of attachment which 
 permits of the use of the thinnest plate does not lead to the lightest 
 construction. 
 
 Doubling strips and plates are sometimes arranged as shown in fig. 
 449, the adjoining plates overlapping each other. In such cases the 
 corners should be cut away, so as to reduce the length of the taper. 
 
820 
 
 DESIGN 
 
 In the case illustrated in fig. 450, the plate has evidently been weakened 
 by the seam. Doubling plates are also fitted to the front tube plate 
 between the nests of tubes, and to the back plates of the boilers 
 wherever the stays are too wide apart, and here, too, the laps are 
 sometimes made very wide. Of course, the number or the sectional 
 area of the adjoining stays or stay tubes must be increased to bear the 
 extra load. Angle irons are also fitted, but usually in such a manner 
 that they give no support. 
 
 These few suggestions about the design of certain parts of boilers, 
 so that they shall be as light as possible, can readily be extended to 
 
 FIG. 449 
 
 Fio. 450 
 
 other parts, and also to the problem of cheapness and despatch ; but 
 when the main principles have been settled, care must still be exercised 
 in carrying them out, for other circumstances may come into play. 
 This occurs in the following simple design of a steel boiler in accord- 
 ance with Lloyd's Register Boiler Eules. It is intended to illustrate 
 how the various rules can be applied, and the various references to 
 the tables will show how to use them advantageously. 
 
 In order to shorten the explanations, practically no notice has been 
 taken of mechanical difficulties, which are discussed elsewhere, and 
 the design is necessarily imperfect in these respects. 
 
 The External Diameter of the shell is not to exceed 13 ft. 156 ins., 
 the heating surface is to be 2,000 square ft., and the grate surface 
 50 square ft., but the length of the grate is to be limited to 5J ft. All 
 the vertical water spaces are to be 10 ins. wide, and the steam-space 
 stays are not to be placed closer together than 16 ins. The water 
 space round each tube is to be 1 in., round the furnaces 4 ins., and 
 above them 7^ ins. Working pressure, 160 Ibs. 
 
 The Furnace Diameter is found by dividing 50 square ft. by 5J ft., 
 which gives 114 ins. of furnace fronts. Two furnaces would be too 
 large, but three of 38 ins. internal and about 39 J ins. external diameter 
 will be convenient (see pp. 100, 309, and table, p. 354). 
 
DESIGN 
 
 321 
 
 The Tube End Spaces have to be estimated, as explained on p. 307- 
 The internal diameter of the shell is about 154 ins., and the water 
 spaces, as explained on p. 307, are 9^ ins. at the wings, 9 ins. between 
 the nest of tubes, and 7 ins. above the furnaces. The steam space has 
 been made one-third of the boiler diameter. 
 
 Water Spaces (p. 313) 
 
 a 
 
 b 
 
 . 
 
 e 
 
 / 
 
 
 
 Total 
 
 Water spaces, inches . 
 
 4 
 
 4 
 
 7 
 
 7 
 
 9-5 
 
 9 
 
 __ 
 
 Multiples .... 
 
 7 
 
 6 
 
 2 
 
 25 
 
 4 
 
 2x-25 
 
 
 
 Products .... 
 
 2-8 
 
 2-4 
 
 1-4 
 
 1-7 
 
 3-8 
 
 4-5 
 
 16-6 
 
 Then 2 (T) = -45 (154 39*25 - 16'6) 2 = 4,330 square ins. This 
 is the available tube end area. 
 
 Tubes. If the tubes are made 3J ins. diameter, then each one will 
 occupy an end space of (4J) 2 = 18*1 square ins. Dividing this into 
 4,330 gives 240 as the necessary number of tubes. The tube surface 
 will be about 80 per cent, of the total say, 1,600 square ft. and 
 therefore each tube must have a surface of 6' 7 square ft., which neces- 
 sitates that its length should be 7'9 ft. (see table, p. 313). If 3-in. or 
 3J-in. tubes had been decided upon, these numbers would have been 
 respectively 272 and 7'5 ft. and 215 and 8*1 ft. These 240 tubes should 
 be arranged in bundles of as nearly as possible equal numbers (78). 
 and if possible in such a manner that the number of vertical and hori- 
 zontal rows are all odd numbers, for then the staying is very much 
 simplified. 
 
 The circular line A B (fig. 451) should be drawn ; it marks off the 
 boundary for the centres of the extreme tubes. Its radius is 66| ins. 
 Measurement or calculation will show that after deducting the central 
 water spaces there remain 121 ins. for the horizontal spacing of the 
 tubes, which, as they are placed 4J ins. apart, number 28. The lines 
 C D and E F, 7 ins. above the furnace crowns, indicate the lower 
 boundary for the tube spaces, while N M is the upper limit. The height 
 between these lines is 34J at the wings and 52 ins. at the centre, equal 
 to about 8 and 12 tube pitches. The tube nests can now be arranged 
 as shown in fig. 451, viz. 8 x 10 -f 12 x 7 + 8 x 10 = 244 (odd 
 numbers of rows being impossible). Of these, 6 fall away at the four 
 corners, leaving 3 more than required. This agreement is sufficiently 
 close for all practical purposes, but before proceeding it is advisable to 
 estimate the 
 
 Heating Surface in the Combustion Chambers, so as to be sure 
 that the total of 2,000 square ft. is reached. The clear depth, accord- 
 ing to p. 309, is 31 ins., and the heating surf ace other than that of the 
 tubes will be about 380 square ft., which, added to 238 x 6'8 = 1,620, 
 is exactly 2,000 square ft. Had this result not been obtained, then 
 the tube lengths would have had to be altered a little. The boiler 
 length is 11 ft. 3 ins. 
 
 The lengths of the Shell Plates can now be fixed, and the riveted 
 joints arranged. 
 
922 DESIGN 
 
 Longitudinal Joint* and Shell Plates. As explained in connection 
 with the tables on p. 352, the numerals there given should be so selected 
 that they are larger than the numbers of rivets in one pitch. In this 
 case we will first choose 5 rivets, then the numeral selection is 4 - 98 and 
 the percentage 85 J. With this percentage and Lloyd's formula for 
 ahell plates with steel of 27 tons we get 15'8 sixteenths of an inch and 
 a pitch of 6*74 ins. ; we naturally choose 1 in. plates and 6| in. 
 pitch of rivets. On checking this it will be found to be in excess of 
 the required pressure, and also that the 22^ feet of riveted seams will 
 require 334 rivets. 
 
 If we decide on 3 rivets we find that 78 per cent, joint leads exactly 
 to a plate of 1^ in. and that the numeral against this percentage is 
 3'03. Dividing by 3 and multiplying by 1^, the size of rivets is found 
 to be liV and thus according to the first column the pitch is 4'83 ins., 
 so that 280 rivets will be required in a length of 22J feet. The saving 
 in the cost of riveting due to using 54 less (their total weight however 
 is the same) will not balance the increased cost of the extra sixteenth 
 of thickness in the shell plate. We can therefore decide for the high 
 percentage joint and thinner plate. 
 
 The Thickness of the Front Tube Plate is determined either by the 
 distances at M (fig. 451) across the wide water spaces, by the distance 
 at N from the tubes to the shell, or by the mean pitch of the stay tubes. 
 The latter dimension is the mean, of the mean horizontal and of the 
 vertical pitches, and is most easily determined by counting the number 
 of tubes that form the four sides of a figure whose corners are occu- 
 pied by stay tubes, then multiplying this sum by one-quarter of the 
 tube pitches. In this design the tubes are placed 4J ins. apart, and 
 the mean pitch can vary from 8J to 9 T Q ff , lOf, 11 }--, or 12| ins., requir- 
 ing (see table, p. 360) that the plates should be either -f , {I, j, |, or 
 J in. thick. The plates across the 13J in. wide water spaces would 
 have to be either j[f or -J in. thick according to the method of attach- 
 ing the stay tubes. In this design the latter thickness will be used, and 
 the stay tubes have therefore to be arranged as shown in fig. 451, those 
 at the circumference being nutted. 
 
 If f-in. plates had been adopted it would have been necessary to 
 fit about 25 extra stay tubes, as well as two doubling plates, to the 
 front plate, as shown in dotted lines, whereby the cost would have been 
 raised and no weight saved. 
 
 The Back Tube Plate need only be Jg in. thick, as the mean pitch 
 of the stay tubes does not exceed 11-} J ins. 
 
 Stay Tubes. The constant for estimating the thickness of the front 
 tube plate near the water line is 140, giving a pitch of 13*1 ins. with 
 the | in. plate. The top stay tubes will therefore have to support half 
 this height and 1^ pitch, equal to 6f in. below their centre line ; but 
 the area thus found has to be diminished by the section of four tubes : 
 (6-55 + 6-37) x 8J 4 x 3J = 77 square ins. The corner stays at M 
 have each to support (6;55 +4-25) x (4-25 + 6'75) - 2J x 3J = 100 
 square ins., and those in the nests of the tubes 87 square ins. The 
 respective loads on each will be 12,300, 16,000, and 13,900 Ibs., which, 
 according to the table on p. 358, require that the minimum thick- 
 nesses of the stay tubes shall be J in. and 9 threads per in., ^ in. and 
 9 threads, and J in. and 12 threads. The latter being too fine a 
 
DESIGN 323 
 
 screw, all the tubes will be made i\ in. thick with 9 threads per 
 inch. 
 
 End Plates in Steam Space. One of the conditions of this design 
 is, that the steam -space stays must be pitched at least 16 ins. apart. 
 As previously mentioned (p. 319), the lightest construction is obtained 
 if they are secured by double nuts. The constant being 175, 1-in. end 
 plates will be required (see table, p. 358). But a trial shows that this 
 leads to an inconvenient distribution of stays. Of the various alterna- 
 tives which suggest themselves, a plate 1J in. thick will be used, pro- 
 vided that the flanging plant is sufficiently powerful to deal with it. 
 
 The maximum permissible pitch of stays is now 18 % 8 ins., and 
 allowing 1J in. for the thickness of flange, and 2 ins. for its radius, 
 the maximum distance from the shell at which the stays may be placed 
 is 22 ins. This boundary line is marked G H (fig. 451). The lower 
 boundary line, G I, is then drawn 15 ins. above the centres of the top 
 row of tubes. This height is found by taking the mean of the pitches 
 found for a J-in. plate with 140 constant and 1^-in. plate with 175 
 constant. The position of the stays can now be marked off, care being 
 taken that none of them are stationed over a water space, and all of 
 them must fall outside of the line I G H. 
 
 The Sectional Areas of the Steam-space Stays are calculated by 
 drawing the line B J, which is the lower limit of the area supported by 
 the shell : it is found by adding half the permissible pitch of 18*8 ins. 
 to the flange and its radius. B K is the upper limit of the area sup- 
 ported by the stay tubes, and, as already shown, it amounts to 6'55 ins. 
 A few vertical and horizontal lines are now drawn to mark off the areas 
 supported by the various stays, and it is then found that the load on 
 the upper left-hand one is about 22,000 Ibs., and on all the others about 
 53,000 Ibs. According to the table on p. 363, these loads would require 
 2-in. and 3-in. stays with 6 threads per inch, because the next smaller 
 sizes, 1J in. with 11 and 2J ins. with 12 threads, are not advisable. 
 
 The Combustion Chamber Side and Top Plates can now be drawn 
 as shown in thick black lines. The centre of the wing radius may be 
 placed at O, in order not to have an awkward corner at L, but then a 
 stay will have to be fitted at A, which is inconvenient, especially if 
 a manhole is fitted at the front end. The corners at M are struck with 
 a radius of 3^ ins., which allows 1 in. for the inner curve of the flange 
 and $ in. for its thickness. For the position of seams see figs. 321-7, 
 p. 276. 
 
 Combustion Chamber Backs, The centres of the furnaces, of the 
 steam-space stays, and of the combustion chamber corners are trans- 
 ferred from fig. 451 to 452. The double boundary lines abed and 
 e f g I h are then drawn. The outer one should be 3 ins. within the 
 outer plates, so that the stay nuts, which are about 3 ins. over cants, 
 will not have to rest on the curved part of the flange, which is assumed 
 to be 1 inch. The inner boundary should be determined by theoretical 
 considerations (see p. 179), but as the numerical results are unpracti- 
 cal, the line has been drawn 1J in. within the outer one, or 4^ ins. 
 from the side and top plates, so that the distance measured from the 
 commencement of the flange to the edge of the nut is about 1^ in. 
 All the stays at the circumference should fall within these two lines, 
 as shown in fig. 452. 
 
 Y2 
 
324 
 
 DESIGN 
 
 OOOO<5TOOOO 
 
 /OOOOOOOOOj 
 
 OOOOOOOO 
 
 ooc 
 
 DOO. 
 'OOO 
 
 iOOOOOOOOOC* 
 
 boooooooooi 
 
 POOOOOOQOQ 
 
 iooooooooooi 
 
 , C , _;, ----?i--.-1 
 
 DOOQ 
 -OOOC 
 
 ooc 
 
 Fro. 461 
 
DESIGN 
 
 325 
 
 a 
 
 <T ^ 
 
 j; 
 
 1 ' 
 
 
 \\ 
 
 1 1 
 
 
 v \ 
 
 VI 
 
 
 
 * * \^ 
 
 1 1 
 
 
 \\ 
 
 i< 
 
 % 
 
 \ 
 
 1 1 
 
 
 1 ( 
 
 1 
 
 
 
 *T 
 
 
 ^ 
 
 ;> 
 
 
 
 . u 
 
 1 1 
 
 
 1 1 
 
 ? 
 
 
 VT^ 
 
 i ' 
 
 
 // 
 
 t; 
 
 
 
 / 
 
 ^ j 
 
 
 / / 
 
 ,f 
 
 
 
 
 
 Fro. 
 
The maximum and minimum distances for the horizontal pitches of 
 the screwed stays are 23| to 26| ins. for the centre and 38| to 41 1 ins. 
 for the wing chambers. Using fa in. plates with nutted stays, the pitch 
 is 8J. They can be arranged as shown. It will be noticed that the 
 lower rows nave had to be shifted 4 in., and that the uppermost and 
 lowermost stays just touch the inner boundary line. The combustion 
 chamber backstays should be normal to these plates and slightly out 
 of normal to the boiler back plates. It is only a drawing office con- 
 venience to show them horizontal. 
 
 Sectional Area of Screwed Stays. The maximum permissible pitch 
 for T 9 ^ in. plates, viz. 8J ins., having been adopted, the table on p. 355 
 can be used with advantage, and the sizes of the stays are at once 
 determined, viz. 1J in. diameter and 7 threads per inch. The size of 
 the screwed stays of the circumferences are determined separately. 
 The steam-space stays support the plating down to 9*4 ins. below 
 the lowest ones, so that the top row of screwed stays has to support 
 the remaining 6'1 ins. as well as 4| ins. lower down. Multiplying 
 this sum by 8J ins. (the horizontal pitch) and 160 Ibs., the load on 
 each stay is found to be 13,500 Ibs., which, according to the table on 
 p. 363, requires a screw stay If in. diameter with 8 threads per inch. 
 
 The stays at b and e support 10J ins. X (6| ins. + 4|- ins.) x 160 
 = 17,800 Ibs., and require stays of If in. diameter with 8 threads per 
 inch. The others below these two support loads of 10J ins. x 8J ins. 
 x 160 = 14,360 Ibs., and have to be If in. diameter, with at least 
 11 threads. This size will be adopted for all the stays at the circum- 
 ference except b and e. 
 
 The Back End Plate. It will be seen that the pitch of the stays 
 across b e cannot be reduced below 13^ ins. According to the table on 
 p. 358 the thickness of the plate must be J| in., unless the stays at 
 the edge of the combustion chamber are placed at an angle (see p. 285), 
 or unless doubling strips are fitted between these stays. But neither 
 alternative will be adopted. 
 
 The permissible distance from the upper screw stays to the lower 
 steam-space stays has to be found. As drawn it measures 15J ins., 
 and a calculation shows that, for the above thickness (1 and }-| in.) 
 it might have been made 16 r ins., showing that this part is strong 
 enough (see p. 323). 
 
 Doubling Plates at Bottom of Back End. By drawing the line 
 k I, which is the width supported by the shell, and amounts to 9J ins., 
 and also the boundaries k m n and n I of the areas supported by the 
 lower screwed stays, it will be found that a small area is unsup- 
 ported ; a doubling plate has therefore to be fitted, as shown in 
 dotted lines, and the stays near its corners at k and at h have to be 
 increased to If in. diameter, in order to take their share of this extra 
 load. 
 
 There are various other details the furnaces (pp. 309, 354), the 
 girders, the combustion chamber side stays (pp. 29, 277), and the 
 manholes (pp. 32, 178, 343) but they have either been discussed 
 elsewhere or present no difficult features. 
 
 When they have been calculated, nothing remains to be done but 
 to complete the drawing by inserting the various seams and flanges, 
 and then making out a list of the full sizes of the plates (pp. 225, 
 
DESIGN 
 
 327 
 
 258), the lengths of the stay bars, and the weights of the various sized 
 rivets (p. 250), ready for ordering. All the dimensions should be 
 carefully checked, and if the boiler is to be built under the inspection 
 of any society, the working pressure for each part should be calculated 
 from the invoiced dimensions and with the help of the latest edition 
 of their rules, and preferably without the use of any tables. If re- 
 quired, a tracing should also be submitted for approval, so as to 
 obviate all risks of having to make alterations. 
 
 The two following tables, which contain the effective diameters 
 and the effective sectional areas of screwed stays, may be of use when 
 other stresses than those of the tables, pp. 362, 363, are to be adopted. 
 
 Effective Diameters of Screwed Stays. 
 
 4> 
 
 Whitworth 
 Screws 
 
 Number of Screw Threads per Inch 
 
 . | V 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 Number 
 of 
 Threads 
 
 Effective Diameters at Bottom of Threads 
 
 Inches 
 
 Inches 
 
 Inches 
 
 Inches 
 
 Inches 
 
 Inches 
 
 Inches 
 
 Inches 
 
 Inches 
 
 . 
 
 10 
 
 62 
 
 
 
 
 
 62 
 
 63 
 
 64 
 
 | 
 
 9 
 
 73 
 
 ... 
 
 ... 
 
 ... 
 
 73 
 
 75 
 
 76 
 
 76 
 
 I 
 
 8 
 
 84 
 
 
 
 84 
 
 86 
 
 87 
 
 88 
 
 89 
 
 1 f 
 
 7 
 
 94 
 
 ... 
 
 94 
 
 96 
 
 98 
 
 1-00 
 
 1-01 
 
 1-02 
 
 l| 
 
 7 
 
 1-07 
 
 ... 
 
 1-07 
 
 1-09 
 
 Ml 
 
 1-12 
 
 1-13 
 
 1-14 
 
 If 
 
 6 
 
 1-16 
 
 1-16 
 
 1-19 
 
 1-21 
 
 1-23 
 
 1-25 
 
 1-26 
 
 1-27 
 
 1J 
 
 6 
 
 1-29 
 
 1-29 
 
 1-32 
 
 1-34 
 
 1-36 
 
 1-37 
 
 1-38 
 
 1-39 
 
 1$ 
 
 5 
 
 1-37 
 
 1-41 
 
 1-44 
 
 1-46 
 
 1-48 
 
 1-50 
 
 1-51 
 
 1-52 
 
 If 
 
 5 
 
 1-49 
 
 1-54 
 
 1-57 
 
 1-59 
 
 1-61 
 
 1-62 
 
 1-63 
 
 1-64 
 
 4 
 
 4* 
 
 1-59 
 
 1-66 
 
 1-69 
 
 1-71 
 
 1-73 
 
 1-75 
 
 1-76 
 
 1-77 
 
 2 
 
 *i 
 
 1-72 
 
 1-79 
 
 1-82 
 
 1-84 
 
 1-86 
 
 1-87 
 
 1-88 
 
 1-89 
 
 
 4 
 
 1-84 
 
 191 
 
 1-94 
 
 1-96 
 
 1-98 
 
 2-00 
 
 201 
 
 2-02 
 
 2! 
 
 4 
 
 1-93 
 
 2-04 
 
 2-07 
 
 2-09 
 
 2-11 
 
 2-12 
 
 2-13 
 
 2-14 
 
 23 
 
 4 
 
 205 
 
 2-16 
 
 2-19 
 
 2-21 
 
 2-23 
 
 2-25 
 
 2-26 
 
 2-27 
 
 H 
 
 4 
 
 2-18 
 
 2-29 
 
 2-32 
 
 2-34 
 
 2-36 
 
 2-37 
 
 2-38 
 
 2-39 
 
 2| 
 
 4 
 
 2-30 
 
 2-41 
 
 2-44 
 
 2-46 
 
 2-48 
 
 2-50 
 
 2-51 
 
 2-52 
 
 2 4 
 
 4 
 
 2-43 
 
 2-54 
 
 2-57 
 
 2-59 
 
 2-61 
 
 2-62 
 
 2-63 
 
 2-64 
 
 2| 
 
 3* 
 
 2-51 
 
 266 
 
 2-69 
 
 2-71 
 
 2-73 
 
 2-75 
 
 2-76 
 
 2-77 
 
 3 
 
 3 
 
 2-63 
 
 2-79 
 
 2-82 
 
 2-84 
 
 2-86 
 
 2-87 
 
 2-88 
 
 2-89 
 
 3* 
 
 
 
 2-91 
 
 2-94 
 
 2-96 
 
 2-98 
 
 3-00 
 
 3-01 
 
 3-02 
 
 3i 
 
 "3* 
 
 2-86 
 
 3-04 
 
 3-07 
 
 3-09 
 
 3-11 
 
 3-12 
 
 3-13 
 
 3-14 
 
 H 
 
 
 ... 
 
 3-16 
 
 3-19 
 
 3-21 
 
 3-23 
 
 3-25 
 
 3-26 
 
 3-27 
 
 3 
 
 3* 
 
 3-11 
 
 3-29 
 
 3-32 
 
 3-34 
 
 3-36 
 
 3-37 
 
 3-38 
 
 3-39 
 
 H 
 
 
 
 3-41 
 
 3-44 
 
 3-46 
 
 3-48 
 
 3-50 
 
 3-51 
 
 3-52 
 
 3| 
 
 'a 
 
 3-32 
 
 3-54 
 
 3-57 
 
 3-59 
 
 361 
 
 3-62 
 
 3-63 
 
 3-64 
 
 N 
 
 ... 
 
 ... 
 
 3-66 
 
 3-69 
 
 3-71 
 
 3-73 
 
 3-75 
 
 3-76 
 
 3-77 
 
 4 
 
 3 
 
 3-57 
 
 3-79 
 
 3-82 
 
 3-84 
 
 3-86 
 
 3-87 
 
 3-88 
 
 3-89 
 
328 
 
 DESIGN 
 
 Effective Sectional Areas of Stays. 
 
 Outside 
 Diameters 
 
 1^ 
 
 Whitworth 
 Screws 
 
 Number of Screw Threads per Inch 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 12 
 
 Number 
 of 
 Threads 
 
 Effective Sectional Areas 
 
 Inches 
 
 Sq. Ins. 
 
 Sq. Ins. 
 
 Sq. Ins. 
 
 Sq. Ins. 
 
 Sq. Ins. 
 
 Sq. Ins. 
 
 Sq. Ins. 
 
 Sq. Ins. 
 
 Sq. Ins. 
 
 | 
 
 44 
 
 10 
 
 30 
 
 
 
 
 
 30 
 
 31 
 
 32 
 
 ! 
 
 60 
 
 9 
 
 42 
 
 ... 
 
 ... 
 
 ... 
 
 42 
 
 44 
 
 45 
 
 46 
 
 i 
 
 79 
 
 8 
 
 55 
 
 ... 
 
 
 55 
 
 58 
 
 60 
 
 61 
 
 63 
 
 ii 
 
 99 
 
 7 
 
 70 
 
 ... 
 
 70 
 
 73 
 
 76 
 
 78 
 
 80 
 
 81 
 
 i| 
 
 1-23 
 
 7 
 
 89 
 
 ... 
 
 89 
 
 93 
 
 96 
 
 99 
 
 1-01 
 
 1-03 
 
 if 
 
 1-48 
 
 6 
 
 1-06 
 
 1-06 
 
 1-12 
 
 1-16 
 
 1-19 
 
 1-22 
 
 1-24 
 
 1-26 
 
 H 
 
 1-77 
 
 6 
 
 1-30 
 
 1-30 
 
 1-36 
 
 1-41 
 
 1-45 
 
 1-48 
 
 1-50 
 
 1-52 
 
 i 
 
 2-07 
 
 5 
 
 1-47 
 
 1-56 
 
 1-63 
 
 1-69 
 
 1-73 
 
 1-76 
 
 1-79 
 
 1-81 
 
 if 
 
 2-40 
 
 5 
 
 1-75 
 
 1-85 
 
 1-93 
 
 1-99 
 
 2-03 
 
 2-07 
 
 2-10 
 
 2-12 
 
 i| 
 
 2-76 
 
 4| 
 
 1-99 
 
 2-17 
 
 2-25 
 
 2-31 
 
 2-36 
 
 2-40 
 
 2-43 
 
 2-45 
 
 2 
 
 3-14 
 
 ^ 
 
 2-31 
 
 2-51 
 
 2-59 
 
 2-66 
 
 2-71 
 
 2-75 
 
 2-79 
 
 2-81 
 
 21 
 
 3-55 
 
 ? 
 
 2-66 
 
 2-87 
 
 2-96 
 
 3-03 
 
 3-09 
 
 3-13 
 
 3-17 
 
 3-20 
 
 2 ? 
 
 3-98 
 
 
 2-93 
 
 3-26 
 
 3-36 
 
 3-43 
 
 3-49 
 
 3-54 
 
 3-58 
 
 3-61 
 
 2 i 
 
 4-43 
 
 
 3-32 
 
 3-67 
 
 3-77 
 
 3-85 
 
 3-91 
 
 3-96 
 
 4-01 
 
 4-04 
 
 2 
 
 4-91 
 
 
 3-73 
 
 4-11 
 
 4-22 
 
 4-30 
 
 4-37 
 
 4-42 
 
 4-46 
 
 4-50 
 
 2 
 
 5-41 
 
 
 4-17 
 
 4-57 
 
 4-68 
 
 4-77 
 
 4-84 
 
 4-90 
 
 4-94 
 
 4-98 
 
 2; 
 
 5-94 
 
 
 4-64 
 
 5-05 
 
 5-18 
 
 5-27 
 
 5-34 
 
 5-40 
 
 5-45 
 
 5-49 
 
 2| 
 
 6-49 
 
 H 
 
 4-94 
 
 5-56 
 
 5-69 
 
 6-79 
 
 5-87 
 
 5-93 
 
 5-98 
 
 6-02 
 
 3 
 
 7-07 
 
 i 
 
 5-45 
 
 6-10 
 
 6-23 
 
 6-33 
 
 6-41 
 
 6-48 
 
 6-53 
 
 6-57 
 
 3| 
 
 7-67 
 
 
 ... 
 
 6-66 
 
 6-80 
 
 6-90 
 
 6-99 
 
 7-06 
 
 7-11 
 
 7-15 
 
 H 
 
 8-29 
 
 % 
 
 6-41 
 
 7-24 
 
 7-39 
 
 7-50 
 
 7-59 
 
 7-65 
 
 7-71 
 
 7-76 
 
 4 
 
 8-95 
 
 
 ... 
 
 7-85 
 
 8-00 
 
 8-12 
 
 8-21 
 
 8-28 
 
 8-34 
 
 8-39 
 
 3 i 
 
 9-62 
 
 3* 
 
 7-58 
 
 8-48 
 
 8-64 
 
 8-76 
 
 8-85 
 
 8-93 
 
 8-99 
 
 9-04 
 
 3$ 
 
 10-32 
 
 
 ... 
 
 9-14 
 
 9-31 
 
 9-43 
 
 9-53 
 
 9-60 
 
 9-67 
 
 9-72 
 
 i 
 
 11-04 
 
 3 
 
 8-67 
 
 9-82 
 
 9-99 
 
 10-12 
 
 10-22 
 
 10-30 
 
 10-37 
 
 10-42 
 
 H 
 
 11-79 
 
 ... 
 
 ... 
 
 10-53 
 
 10-71 
 
 10-84 
 
 10-94 
 
 11-03 
 
 11-15 
 
 11-15 
 
 4 
 
 12-56 
 
 8 
 
 10-03 
 
 11-26 
 
 11-44 
 
 11-58 
 
 11-69 
 
 11-77 
 
 11-85 
 
 11-90 
 
329 
 
 CHAPTEK X 
 
 STEAM PIPES 
 
 STEAM pipes are, by the Boiler Explosions Acts, classed as boilers, 
 and now that the majority of pipes are being made of steel, they 
 have so much in common with boilers that they deserve to be 
 mentioned here. 
 
 The function of steam pipes is to convey steam from boilers to 
 engines with as little loss as possible either of pressure due to friction 
 or of volume due to radiation. Steam pipes should be safe, which 
 means that the material should be good and the thicknesses ample 
 for the intended pressure, but they should not be so rigid or heavy 
 as to cause fracture, and the general arrangement should be such 
 that water will not lodge in them and cause water hammers and 
 explosions. 
 
 The friction of steam flowing in pipes has not been the subject of 
 many experimental researches, the most reliable deductions having 
 still to be drawn from experiments with air and water, allowance 
 being made for differences of density. In short pipes the chief re- 
 sistance is due to the imparting of a certain velocity to the steam, 
 and is equal to a height of fluid of the steam density h = v 2 : %g, 
 where h is the pressure per square foot divided by the density in 
 cubic feet. The velocity in this formula is intermediate between 
 that at the centre and at the circumference of the pipe. Let Q be 
 the weight of steam in pounds per hour, and a the sectional area of 
 the pipe in square inches, then the velocity v in feet per second is 
 C x Q x T.abs. : a x P.abs., where C is 0*121 for uniformly distributed 
 velocity and about O'lOO in practice. The loss of pressure in pounds 
 per square inch would therefore be about 
 
 AP = Q 2 x T.abs. : a 2 x P x 540,000. 
 
 Here a is the smallest sectional area of the pipe or any of its valves. 
 When there are several restrictions in a pipe, AP increases to a cer- 
 tain extent, allowances having to be made for the several changes 
 from high to low velocities and vice versa, a reducing coefficient of 
 0*6 being applied at each change. It is claimed for certain steam 
 sluice valves that if the approaches to and departures from a com- 
 paratively small hole are properly shaped, then the loss due to a 
 change from slow to high velocity is regained by the change from 
 high to low. This is a subject which turbine builders are now 
 studying with the greatest attention. 
 
330 STEAM PIPES 
 
 Iri addition to the above-mentioned loss there is the surface fric- 
 tion of the pipe. If the velocity of the steam were the same all over 
 the section of the pipe, the friction would be proportional to the 
 square of the velocity and to the total internal surface of the pipe. 
 In practice the case is not so simple, and at the point where the steam 
 enters the pipe, or immediately behind a valve or other obstruction, 
 the steam is thoroughly churned up and the surface velocity may be 
 equal to or in excess of the mean velocity, but at some distance from 
 this point there will be a great difference between the central and 
 the surface velocities, so that the friction per square foot of surface 
 decreases with the length of the pipe. This decrease is not the same 
 under all conditions but is affected by the average velocity ; for if 
 this is low the difference between the centre and surface velocity will 
 be great, whereas if it is high the difference, due to whirling will 
 be slight, and thus the length influence diminishes with increasing 
 velocity. These remarks apply to steady flows of steam ; for inter- 
 mittent flows, as is mostly the case in pipes on steamers, the flow is 
 a pulsating one, and the behaviour of the steam will be as follows. 
 As soon as the slide valve is open there will be a violent rush forward 
 of the core of the steam ; this rush, on account of the viscosity of 
 steam, will affect the circumferential layers of steam, which will 
 attain a maximum velocity at the instant when the slide valve is 
 shut, and together with the core steam, will be dammed up and the 
 pressure increased near the valve. This should cause a slight flow of 
 the core away from the valve. It will thus be seen that under these 
 conditions the steam pipe is practically reduced in sectional area by 
 the circumferential layers of fairly stationary steam, and it is not 
 improbable that the enlarging of a diameter of a pipe merely increases 
 the thickness of the inert layers, and may be of less advantage than 
 is generally imagined. 
 
 As already mentioned, experiments on this subject are scarce, and 
 practical experiences are likely to be misleading unless account be 
 taken of the velocity of pressure waves in steam in relation to the 
 effective lengths of pipes. The average velocity of pressure waves 
 in saturated steam seems to be about 1,400 ft. per second, no matter 
 what the pressure. If the engine is running 300 revolutions a minute 
 or 10 strokes a second, the steam pressure pulsation waves in the 
 steam pipe will have lengths of 140 ft., so that if in one ship the 
 steam pipe is 70 ft. long there will be temporary reductions of pressure 
 at the slide valve while opening, due to the reflected suction waves 
 which were created by previous openings of the other steam part. If, 
 however, the pipe were to be made 100 ft. long, the pressure wave due 
 to the damming up of steam after the closing of a port, would travel 
 to the boiler and be back in time to add a little pressure to the 
 inflowing steam. A comparison of two such results would therefore 
 lead to the erroneous conclusion that there is less friction in a long 
 pipe than in a short one. 
 
 The following table contains the names of those who have experi- 
 mented on this subject. Fuller details are to be found in ' Deut. 
 Ing.,' 1908, vol. 52, p. 82. The same volume, p. 481, and a few sub- 
 sequent numbers, contain Mr. C. Eberle's experiments and deductions, 
 amongst which may bj mentioned that with superheated steam there 
 
STEAM PIPES 
 
 831 
 
 is a marked drop of temperature from the centre to the circumference 
 of a pipe amounting to as much as 70 F. in a 3-inch pipe. With 
 the exception of Mr. Eberle's experiments on steam all the rest deal 
 only with the friction of air. 
 
 Fritzsche has analysed previous results and compared them with 
 his own experiments, arriving at the following expression 
 
 &p = p . * . I . v* : d . T c , 
 
 where p and &p are the pressure and loss of pressure, I and d are the 
 length and diameter in metres and millimetres, T c is the absolute 
 temperature, and v is the velocity in metres per second, while ^ is a 
 coefficient for which a table has to be consulted; it is about 0'020 for 
 customary pressures and dimensions and 0'000,08 for feet and inches. 
 
 In practice a velocity of about 8,000 ft. per minute is customary 
 except with short cut-off in the engine when the mean velocity may 
 be 10,000 ft. For turbine supply the mean velocity is about 7,000 ft. 
 
 Experiments on Air Friction in Pipes. 
 
 Date 
 
 Name 
 
 Pipe 
 
 Air or Gas 
 
 Material 
 
 Diameters 
 
 Lengths 
 
 Velocities 
 
 Pressures 
 
 
 
 
 ins. 
 
 ft. 
 
 ft. per sec. 
 
 Atmos. 
 
 1819 
 
 Gerard 
 
 C. and W. Iron 
 
 0-6-3-2 
 
 23-2,050 
 
 290-1,180 
 
 1 
 
 M 
 
 G. G. Schmidt 
 
 Glass 
 
 0-9 
 
 0-5-3-3 
 
 ? 
 
 ? 
 
 1823 
 
 Koch 
 
 Brass 
 
 0-25-0-55 
 
 82-260 
 
 490-1,870 
 
 1 
 
 1829 
 
 d'Aubuisson 
 
 Tin plates 
 
 1-0-4-0 
 
 30-1270 
 
 49390 
 
 1 
 
 1837 
 
 Buff 
 
 Lead 
 
 3-3-4-2 
 
 2-6-35 
 
 98-490 
 
 1 
 
 1845 
 
 Pecqueur 
 
 Lead 
 
 0-4-1-2 
 
 13-222 
 
 780-3,330 
 
 2-5-4-5 
 
 1856 
 
 Weissbach 
 
 Glass, Brass 
 
 0-4-0-6 
 
 5-5-10-0 
 
 590-3,540 
 
 1 
 
 M 
 
 }j 
 
 Zinc 
 
 1-0 
 
 33 
 
 590-1,770 
 
 1 
 
 1857 
 
 Rittinger 
 
 Riveted W. Iron 
 
 8-2 
 
 70-200 
 
 300 
 
 1 
 
 1861 
 
 Blochmann 
 
 Drawn W. Iron 
 
 0-6-1-0 
 
 ? 
 
 483 
 
 1 
 
 1863 
 
 Arson 
 
 C. Iron, Tin plate 
 
 3-2-2-0 
 
 up to 1,000 
 
 up to 237 
 
 1 
 
 M 
 
 M 
 
 C. Iron 
 
 2-0 
 
 up to 1,000 
 
 up to 237 
 
 1 
 
 1876 
 
 Stockalper 
 
 W. Iron 
 
 6-0 
 
 1,700 
 
 93-225 
 
 3-7-5-6 
 
 M 
 
 i 
 
 W. and C. Iron 
 
 8-0 
 
 15,000 
 
 93-225 
 
 3-7-5-6 
 
 1879 
 
 Devillez 
 
 C. Iron 
 
 2-8-5-0 
 
 560-3.200 
 
 40-590 
 
 1-8-5-6 
 
 1884 
 
 Althans 
 
 C. Iron 
 
 14-3 
 
 30 
 
 69-153 
 
 1 
 
 1890 
 
 Meissner 
 
 Zinc 
 
 10-4-20-0 
 
 92-650 
 
 27-116 
 
 1 
 
 
 Riedler 
 
 C. Iron 
 
 12-0 
 
 11,000-54,300 
 
 53-170 
 
 6-3-8-0 
 
 1892 
 
 Lorenz 
 
 C. Iron 
 
 4-0 
 
 98 
 
 155-185 
 
 6-7-6-8 
 
 H 
 
 Ledoun 
 
 W. Iron 
 
 1-8-4-0 
 
 97 
 
 147-1,630 
 
 1-4-5-7 
 
 1897 
 
 Flieger 
 
 Smooth-bored 
 
 0-2 
 
 0-6 
 
 1,570-5,200 
 
 1-2-3 
 
 i> 
 
 Zeuner 
 
 Smooth brass 
 
 0-2 
 
 13 
 
 1,180-4,130 
 
 0-75 
 
 1904 
 
 Rietschel 
 
 Copper 
 
 0-9-4-0 
 
 28-78 
 
 59-295 
 
 1 
 
 M 
 
 ii 
 
 Zinc 
 
 2-0-4-0 
 
 28-78 
 
 59-295 
 
 1 
 
 n 
 
 Brabbee 
 
 Riveted W. Iron 
 
 12-0-31-5 
 
 980-2,250 
 
 59-333 
 
 1 
 
 
 
 Fritzsche 
 
 W. Iron 
 
 1-0-1-5 
 
 51 
 
 49-114 
 
 0-2-11-1 
 
 1908 
 
 Eberle 
 
 W. Iron 
 
 2-75-5-9 
 
 87 
 
 137-1,445 
 
 3-10 
 
 Radiation Losses of steam pipes. Seeing that the loss of pressure 
 due to friction diminishes inversely as the square of the diameter of 
 the pipe, and that the loss of volume due to cooling and condensation 
 increases with the diameter of the pipe, there must be a certain 
 
332 SfEAM PIPES 
 
 diameter for any length of pipe for which the sum of these two losses 
 is a minimum. To ascertain this best diameter Chr. Eberle (' Deut. 
 Ing.,' 1908, vol. 52, p. 481, etc.) carried out elaborate experiments on 
 these two losses, both with saturated and with superheated steam. 
 Unfortunately he could draw no definite conclusions as to the best 
 diameters because his results are too complicated, but some of them 
 are extremely interesting and deserve mentioning. Thus he finds 
 that water-catchers collect more water when the steam is stationary 
 than when it is flowing, which would be in contradiction to Mr. 
 Jordan's experiments (p. 118), were it not that this can be attributed 
 to inefficiency on the part of the water-catchers. On making the 
 necessary allowances, Mr. Eberle could detect no velocity influence as 
 regards radiation losses, or rather it was masked by the temperature 
 effect, all the high velocity tests having been carried out with much 
 hotter steam that the low velocity tests. One deduction to be drawn 
 from these tests by interpolation is that at about 340 C. the heat 
 loss for stationary superheated steam would probably be 3-3 B.T.U. 
 per sq. foot of wrought iron surface per hour for 1 C. difference of 
 temperature, and practically the same value was found for saturated 
 steam at the same temperature, so that this loss is independent of 
 the condition of the steam. 
 
 Safety of Steam Pipes. As long as steam pipes were made of 
 copper, a metal which is easily fashioned into bends, the designing 
 of steam-pipe arrangements presented no serious difficulty ; now 
 however that mild steel is being used, the severe stresses which it 
 may set up must be guarded against, for although it can be bent 
 much further than copper without permanent set, it is nevertheless 
 much stronger. It is therefore necessary to enquire carefully into 
 the causes which have up to the present led to failures of steam pipes 
 on steamers. 
 
 Water-Hammer. A very complete analysis of about 100 cases of 
 steam-pipe explosions due to water-hammer has been carried out by 
 the author (M.S.U.A., 1908). These include the following Board of 
 Trade reports on explosions on steamers : Nos. 1398 ; 589, 929, 
 1437; 926; 468, 580, 1056, 1109, 1295, 1515, 1582, 1738; 572, 
 1048, 1537, 1747; 512, 933, 986, 1264. Of these the last three 
 reports do not contain sufficient information to permit of the true 
 causes of the explosions being discovered. 
 
 Water Pockets. Nine other cases, No. 468 to 572, were due to 
 
 Water level 
 
 FIG 453. 
 
 the sudden admission of steam, S, into ranges of pipes containing water 
 and shown diagramatically in fig. 453. The effect of this admission 
 of steam was that a most rapid condensation took place, and the 
 resulting steam blast along the surface of the water raised waves, 
 
STEAM PIPES 333 
 
 as shown in dotted lines at H. Instantly the steam space from H 
 to E would be converted into a vacuum, the wave would be shot 
 towards E and the valve would explode at X. Such explosions could 
 not occur either if there were no water in the pipe, or if the valves 
 or pipe joints had leaked and had admitted air, which, on admitting 
 steam, would form an effective cushion. To guard against this class 
 of mishaps, which, as already stated, form the majority of marine- 
 pipe explosions, it might be well to provide steam pipes with valves 
 which would admit air whenever there is a vacuum. Most automatic 
 steam traps are arranged to admit air when cold, but they do not 
 appear to be used on steamers. 
 
 Steam-Pipe Drain Cocks. The above-mentioned explosions would, 
 of course, not have occurred if the drain cock D had been opened 
 some considerable time before steam was admitted, but the opening 
 of drain cocks with steam in the pipes is not unattended with danger, 
 as will be seen from the following further cases, Nos. 1398, 589, 929, 
 see fig. 454. The original water-level in the steam pipe is marked in 
 the diagram. Steam was admitted at S, while the drain cock at D 
 was open ; the water-level gradually sank till the condition sketched 
 
 in fig. 453 was attained ; a wave and a vacuum were formed and an 
 explosion occurred at H. In these cases the valve E was shut, but 
 the same results would have occurred if it had been opened instead 
 of the drain D. In Nos. 1437 and 926 the conditions were the 
 same as the above, but the pipe was too strong at H and did not 
 burst there ; the pressure wave travelled to the valve E, and, due to 
 reflection, its intensity was doubled locally and led to a fracture at X. 
 Submerged Valves. Explosions Nos. 1048 and 1747 were due to 
 the opening of submerged valves, like E in fig. 453, through which 
 steam entered, the water-level probably standing higher than shown. 
 If or when the steam pressure under this valve was greater than that 
 above, it would lift this valve, and the steam coming in contact with 
 cold water would immediately be condensed, the water would bang 
 against the valve and do the damage. It is practically impossible to 
 prevent this class of explosions if engineers omit to drain such pipes. 
 Case No. 1537 is probably unique. The port and starboard boiler 
 were connected by a cross pipe ; the ship had a list to starboard, and 
 as the port valve was open, steam from that boiler had condensed 
 and was resting on the starboard valve. Then the vessel took a list to 
 port, and while the cold water was flowing to port the rush of steam 
 raised a wave which shattered the starboard valve. 
 
334 STEAM PIPES 
 
 Air in Pipes. No. 512 is a case where an explosion seems to have 
 occurred in spite of the presence of air in the pipe. Imagine in 
 fig. 454 the lower portion of the pipe to be full of water with steam 
 pressure at S, and air under compression from E to the down bend ; 
 then on suddenly opening the valve E this air would rapidly escape, 
 and the following plug of water would close the valve or choke it and 
 smash its chest. 
 
 Accidents Ashore. Ashore, where steam pipes are very long and 
 arrangements are sometimes very complicated, explosions which are 
 almost inexplicable occur. They have all been dealt with in the 
 Manchester Steam Users' Association Memorandum for 1908, and the 
 following are here mentioned as they may occur on steamers. Nos. 
 1360, explosion of a downward sloping pipe ; in 1622 and 1678 the 
 pressure wave travelled a long way through a superheater and caused 
 the explosion due to the reflection of the pressure wave. No. 342 was 
 due to the starting of the engine; Nos. 1571, 1465, 1658, 1669, 1646 
 are complicated pipe arrangements which may occur on steamers. 
 In No. 1283 an isolating valve seems to have been partly to blame 
 for the explosion. In No. 1125 the opening of one submerged valve 
 resulted in an overflow of water into the main steam pipe, and the 
 explosion of another as yet closed valve. In Nos. 1162 and 1274 the 
 rush of steam from one or more boilers seems to have stowed or 
 dammed water into unused portions of the range, and a subsequent 
 change of flow of steam caused this water to flow and to bring com- 
 paratively cold portions into contact with hot steam. Amongst over 
 100 explosions enquired into there was only one wrought-iron pipe, 
 No. 1636, and one mild-steel pipe, No. 1360, but this latter one was 
 of basic material. All the other exploded pipes were either cast iron 
 or copper. 
 
 Steam-Pipe Materials. It would thus seem that wrought iron or 
 mild steel is a very suitable material for withstanding the severe 
 water-hammer blows to which steam pipes are sometimes subjected, 
 and since the use of these materials has been sanctioned on steamers, 
 steam pipes are often made of them. Nevertheless, even with these 
 materials accidents can occur, and every precaution should be adopted 
 to obviate them. These precautions are, that the boiler stop valve 
 should whenever possible be placed at a higher level than the engine 
 shop valve, so that any water in the pipe will drain towards the 
 engine. This condition is rarely fulfilled on steamers. There should 
 not be any pockets in these steam pipes in which water could lodge, 
 and if these pockets cannot be avoided, they should be well drained. 
 Nevertheless, drain cocks ought not to be opened when any of the 
 boiler shop valves are open. The safe plan is to admit a little steam 
 into the pipe, close the shop valve and then drain the pipe, repeating 
 the operation until all the water has run out or until the pipe has 
 drawn in air. The fitting of vacuum valves or automatic steam traps 
 can do no harm, and may prevent an occasional explosion. 
 
 Fatigue of Steam Pipes. The second important cause of steam- 
 pipe explosion is want of elasticity to meet the relative movements 
 of boilers and engines, which cause has been somewhat intensified 
 by the use of steel pipes, and the natural tendency to dispense with 
 costly expansion bends. Another danger associated with the rigidity 
 
STEAM PIPES 335 
 
 of steel steam pipes is that a much greater strain is now thrown on 
 shop valves than was possible when copper pipes were in use, and 
 as a safeguard against this danger it would be well to use cast-steel 
 valve cases as is now the usual practice ashore. Even then, however, 
 there remains the danger of the pipes breaking close to their flanges, 
 or their drawing out of the flanges if these are not properly designed. 
 Therefore, before dealing with expansion arrangements for pipes their 
 manufacture will be briefly reviewed. 
 
 Lap- Welded Steel Pipes are made by bending a plate having taper 
 edges to the required cylindrical shape, heating it as a whole to a 
 welding heat, and passing it through rolls which lap-weld it over a 
 bullet-shaped plug. It is usual to repeat the heating and rolling so 
 as to ensure a perfect weld. With this process there is danger of 
 burning the steel unless the greatest care be taken to maintain the 
 correct temperature over the entire length of the pipe ; which means 
 of course that pipes by certain makers are likely to be more uniformly 
 reliable than those by others, who are less painstaking in regulating 
 the heats of their furnaces. By this process the welding is done by 
 roller pressure on a bullet-shaped thorn, the lap being at the top 
 when the pipe passes into the rolls. It may however happen that 
 one or the other lap slips or stretches a little, and then the joint 
 forms a helical line on the pipe, which means that, instead of being 
 subjected to a good vertical rolling pressure over its whole length, 
 the lap-weld receives hardly any pressure where, during the rolling 
 process, it was at the side of the pipe. Pipes having a spiral weld 
 should therefore be unhesitatingly rejected. On account of the ease 
 with which the mild qualities of basic steel can be welded there is a 
 great temptation to use this material, but as it is liable to failures which 
 as yet can only be explained as being due to the unreliability of this 
 material, acid steel should be used where absolute reliability is aimed at. 
 
 Pipes of 12 ins. diameter and above are welded on short lengths 
 of a few inches at a time, the heating being done as shown in 
 fig. 423, p. 299. There seems to be very little reduction of thickness, 
 if care be taken to have a reducing flame, and plates as thin as in. 
 can be effectively lap-welded by this process. 
 
 Solid Drawn Pipes, as the name implies, are seamless ones, which 
 means that, as they have not to be welded, comparatively hard steels 
 may be used. There are said to be over 100 different processes of 
 manufacture, the chief ones being as follows : Steel ingots are cast 
 with a core hole and then drawn out. Until recently great difficulty 
 was experienced in obtaining solid castings, the air which escaped 
 from the core producing blow holes. Another process is to cast solid 
 steel ingots, bore and draw them out. Steel is also cast into moulds 
 which revolve rapidly ; after a time a thick and sound shell forms, 
 and the core is then run out and the ingot drawn out. Amongst 
 the various methods of drawing out may be mentioned a com- 
 paratively recent invention in which the axes of two or more rollers are 
 set at slight angles to the axis of the pipe ; they revolve and roll round 
 a bullet-shaped thorn over which the hot cylindrical ingot is slipped. 
 The rollers reduce the metal to the required thickness, and at the 
 same time drag it along the thorn. In those pipes the fibre is longi- 
 tudinal. In the Maunesmann process these rollers are very long, 
 
336 
 
 STEAM PIPES 
 
 and as they are necessarily taper their circumferential velocities vary, 
 which leads to the hollowing of solid bars or the thinning of the 
 cylindrical ingots. In these pipes the fibre is circumferential. 
 
 Bends in Steel Pipes. Steel pipes have to be most carefully filled 
 with dry sand which has to be firmly rammed down inch by inch ; 
 they are then slowly heated to redness, sufficient time being allowed 
 for the core of the sand to become hot, and the pipes are then bent 
 by means of halyards, windlasses, and ropes, or by turn-tables. The 
 thinning of the metal at the outside of bends, and the further bending 
 of parts which have already acquired the desired curvature is prevented 
 by spraying these parts with cold water. As soon as the bending is 
 completed and the spraying discontinued the heat in the sand in the 
 pipes anneals them. Short bends are made by sawing a number of 
 taper slots into them, bending them and electrically welding the 
 closed-up slots. 
 
 Copper Pipes are usually brazed, two sheets of copper having been 
 hammered to the desired shape and lap-jointed. Some pipes are 
 solid drawn from hollow ingots, others are made by an electric process, 
 copper being deposited on a revolving mandril over which agate rollers 
 are constantly travelling in order to harden the metal ; these and the 
 solid drawn copper pipes can be bent cold after being filled with resin. 
 Steam Pipe Flanges. The flanges for copper pipes are made of 
 gun metal to which they are brazed. The fact that several copper 
 pipes have worked satisfactorily for years and have 
 then failed shortly after rebrazing suggests that 
 occasionally injudicious heating during the brazing 
 operations may do harm. Another form of flange 
 is shown in fig. 455, the ends of the two pipe ends 
 being flanged out and clamped together by means 
 of two rings which have to be slipped over the 
 pipes before flanging. Two cases of failures of 
 these joints at the roots of the flanges are reported, 
 No. 1921 (sheet copper), No. 1069 (electro deposited 
 copper), and as the flanging was done cold the failures were not due 
 to bad heat treatment (unless the flanges were annealed), but to 
 severe straining. 
 
 Various modifications of this form of flange are in use on the 
 continent for steel pipes, whose ends are generally thickened before 
 flanging. In one modification each ring consists of four segments 
 which overlap each other. Possibly this is a makeshift for a break- 
 down, for these segments can be placed round the pipes after flanging. 
 Steel pipes of small diameter are often screwed into their flanges, 
 see fig. 456, as is customary with 
 gas and water pipes, but this is a 
 dangerous practice if the pipes are 
 subjected to severe bending strains 
 as is the usual case on steamers, 
 for these combinations are extremely 
 weak at the flanges. It must be 
 remembered that the bore of the FIG. 456 
 
 pipe may vary, whereas the diameter of the cut threads is made to 
 a standard gauge ; if then by chance the pipe diameter should be in. 
 
 FIG. 455 
 
JH- 
 
 STEAM PIPES 337 
 
 larger than intended, the remaining metal at the threaded part is 
 reduced by T ^ in. With pipes of large diameter there is the additional 
 danger that, in order to ensure tightness much force has to be used 
 for screwing the pipe into the flange, and if any caulking has to be 
 done the circumferential compression stress in the pipe should tend 
 to pucker the comparatively thin metal. At any rate large pipes are 
 rarely fitted with screwed-on flanges. 
 
 When large pipes were first made of steel, their flanges were 
 riveted on. This is unquestionably still the most reliable system, but 
 it is clumsy, expensive, and the rivet heads offer some resistance to 
 the flow of steam. 
 
 More recently the flanges have been welded on, but a few failures 
 in which the pipes drew out of their flanges had shaken confidence 
 in this method, which is however being restored 
 since two improvements have been introduced; 
 firstly, the outer edges of the flanged holes are 
 recessed, fig. 457, so that the pipe end is bended 
 over in addition to being welded, and a better weld 
 than formerly is secured by making the flange hole FlG - 457 
 
 smaller than the pipe, reducing the diameter of the end of the pipe 
 before insertion in the hole, and enlarging both pipe and flange during 
 the welding process, whereby a severer welding pressure than formerly 
 is attained. 
 
 Electric Welding if properly carried out is unquestionably a very 
 reliable method of attaching flanges to pipes, but it lends itself to 
 wash welding or surface welding. For instance, the flange shown in 
 fig. 457, but without the recess, could be welded where the fillet 
 touches the pipe and where the pipe appears on the flat of the flange, 
 but such a seam would soon open out. The more effective method 
 of electric welding is shown in fig. 458. The flange F has no fillet 
 but is cut taper along the line ab, and placed 
 close to the end of the pipe P, and the 
 V-shaped hollow between flange and pipe is 
 then slowly filled up with best Swedish iron, 
 shown as layers in the figure, by means of the 
 electric arc. Cheap filling material should not 
 be used because it may result in the cracking 
 of a very costly seam, and care should be 
 FIG. 458 taken to hold the anode as far as possible 
 
 away from the molten steel, in order that the carbon particles which 
 are carried by the electric current may have time to burn instead of 
 being transferred to the steel and making it hard. The weld should be 
 lightly hammered while hot. 
 
 Acetylene Welding of >pipes is very similar to electric welding, 
 except that in order to maintain the seam at a high temperature two 
 flames should be used, one near b, which does the actual welding, 
 and one at a for heating purposes only. The iron surfaces should be 
 very clean, otherwise the added Swedish iron will not adhere to them. 
 Pipe Failures due to defects and to movements. Amongst about 
 100 reported failures of marine pipes due to movements or vibrations 
 of engines and boilers, there were forty failures of brazed copper pipes, 
 thirty-nine failures of solid drawn copper pipes, and fifteen of electro- 
 
 z 
 
338 STEAM t>IPES 
 
 deposited pipes. There was only one failure of a steel pipe, which 
 was due to its having been screwed into its flange. There were 
 amongst the brazed, solid drawn, and electro -deposited pipes respec- 
 tively 4, 5, and 3 longitudinal fractures. They all occurred on bends 
 and along what was the neutral fibre during the bending process, which 
 seems to indicate that the severe shearing stresses to which these 
 parts of the pipes were subjected had permanently injurious effects. 
 
 The remaining eighty-two failures were circumferential cracks 
 generally close to the flanges, and they are nearly all attributable to 
 straining and vibrations. In some cases the fractures occurred while 
 the engines were racing, but there are also a few cases where pipes 
 broke close to the flanges a few days after repair or renewal. Thus 
 in the cases reported by the Board of Trade, Nos. 767 and 1355 broke 
 respectively in two and three days after renewal ; Nos. 1160 and 1616 
 in six days, and Nos. 945, 1111, 1268, 1290, 1795, 1852, and 1904 
 broke in about one month aiter renewal. 
 
 Annealed Copper Pipes. Some of the last-mentioned failures may 
 have been due to injudicious heating. Thus Nos. 1922 and 1926 had 
 been in use respectively for ten and six years without trouble, but 
 failed respectively in three and two months after annealing. Other 
 failures after annealing are : two cases after four years, two after two 
 years, two after one year, one after eight months, one after seven 
 months, two after six months, two after five months, one after four 
 months, one after three months, one after fifteen days, or fifteen 
 failures occurred on an average fourteen months after annealing, or 
 rather after unsuitable annealing. 
 
 Some of the above-mentioned failures are almost certainly attri- 
 butable to unsuitable copper, the old parts of the pipes breaking after 
 new ends had been brazed on. 
 
 Deformations. In the majority of cases the very large differences 
 of movement between engines and boilers has been the cause of 
 failures, and as this cause will have as injurious an effect on steel pipes 
 as it has had on copper pipes, it is desirable that engine-builders 
 should make careful observations of these relative movements and 
 allow for them. Eeport No. 1296 mentions a horizontal movement 
 of f in. between the boiler and engine valves on a length of 8 ft. 
 The pipe which was 5 ins. diameter had a very short bend and 
 fractured seven months after being fitted, and again one month after 
 being repaired (see p. 186 for stresses due to bending). 
 
 Expansion Bends. The most common form of expansion bend is 
 shown in fig. 459, but figs. 460 and 461 are possible modifications, the 
 
 FiQ. 459 FIG. 460 FIG. 461 
 
 later form being the most elastic. Assuming these pipes to be 6 ins. 
 in diameter and the height 4 ft., the relative displacement of flanges 
 
STEAM PIPES 
 
 339 
 
 in figs. 459 and 460 may be + f in. for steel and + f in. for copper. 
 With bends as shown in fig. 461 these amounts may be doubled. The 
 thickness of the metal of the pipes does not affect the permissible 
 movement, which is strictly proportional to the ratio of the dimensions 
 of the loops to the diameters of the pipes. Additional details will be 
 found on p. 187. In some cases where expansion bends had to be 
 provided for long lengths of pipes of large diameter, these were 
 severed and attached to boxes, the gap being bridged by a bundle 
 of small diameter tubes. 
 
 Expansion Joints. Occasionally expansion glands are fitted, but 
 seeing that about ten out of about 100 failed pipes were fitted with 
 these glands they do not seem to have been of much use. The report 
 numbers are 480*, 1011, 1113, 1172*, 
 1185*, 1187, 1207, 1214, 1666* 1852*. 
 Those marked with * deal with curved 
 pipes, for which expansion glands are of 
 course useless, because the steam pressure 
 acting on the sectional area of the pipe, 
 and with a leverage equal to the bend, 
 would produce a larger movement, if un- 
 checked, than could be taken up by the 
 gland. Even with straight pipes the thrust 
 due to the steam pressure is very severe. 
 Thus with a 6-in. pipe and a pressure of 
 200 Ibs. per sq. in. the thrust is nearly 
 3 tons. An equilibrium expansion gland 
 has been devised, but does not seem to 
 have been much used, in which the pipe, 
 whose end is closed and whose circum- 
 ference is perforated with slits over a short 
 length, passes through two glands situated 
 at the ends of a box to which the con- 
 tinuation of the pipe is attached. Swivel joints are not common 
 either ashore or on steamers. They have been used in the Main 
 Eailway Station, Munich, see fig. 462. The most effective way of 
 applying them would be to have two swivels at the ends of a bend, 
 for then every movement would find relief. For marine purposes a 
 more reliable arrangement than the spring Z would be necessary to 
 keep the socket in place when the ship vibrates, the most convenient 
 arrangement being no doubt to provide the end of the pipe with ribs, 
 F, supporting a central sphere, C, against which a set screw, C r S, 
 would have to press. 
 
 Steam-Pipe Supports. The more elastic a steam pipe is made, the 
 more is it liable to be thrown out of line and otherwise strained when 
 the ship rolls, when the boilers move or the engines vibrate. Seeing 
 that some of these movements are independent of the ship's structure, 
 they would produce very severe strains in the pipes if these were 
 secured to the ship. The general tendency therefore is to dispense 
 with hangers as much as possible, and to use them only where the 
 pipes are very long. Considerable support would be afforded to the 
 pipes without apparently any injurious effect if their weights were 
 
 z2 
 
 FIG. 462 
 
340 
 
 STEAM PIPES 
 
 
 balanced as in fig. 463. The method does not appear to have been 
 tried, and should be carefully considered before adoption. Spring 
 
 supports should not be used on 
 steam pipes ; if long and elastic they 
 must be secured against longitudinal 
 movements either at one of their 
 ends or near their middles. Here 
 also springs should not be used as 
 buffers, for they have caused break- 
 ages. In these cases (ashore) the 
 rush of steam set up longitudinal vibrations which were in no way 
 damped by two end springs ; finally one of the elbow joints (cast iron 
 on steel pipes) was fractured. 
 
 Steel Stop Valves and Bends. Marine engineers, although they 
 are giving up the use of copper, will doubtless continue to prefer 
 expansion bends to glands, but they should not overlook the fact that 
 as steel pipes are stronger than copper ones, they throw heavy strains 
 on cast-iron valves or bends. 
 
 Steam Pipe Arrangements, see p. 314. 
 
341 
 
 CHAPTER XI 
 LLOYD'S REGISTER BOILER RULES 
 
 EXTRACTS FBOM RULES PUBLISHED IN 1907-8. 
 
 Rules for Determining the Working Pressure to be allowed in New 
 
 Boilers 
 
 Cylindrical Shells of Iron Boilers. The strength of circular shells 
 of iron boilers to be calculated from the strength of the Jongitudinal 
 joints by the following formula : 
 
 C^ x T x R 
 
 ^ - =S- -- = = working pressure, 
 
 where C = coefficient as per following table, 
 T = thickness of plate in inches, 
 
 B = mean diameter of shell in inches, 
 = percentage of strength of joint found as follows the 
 least percentage to be taken. 
 
 For plate at joint B = Z- X 100 ; 
 
 forrivets at Joint B=^f x 100; 
 
 Bn x a Qn with iron rivets in iron plates 
 ~ ]TxT with drilled holes - 
 
 (In case of rivets being in double shear, T75a is to be used instead 
 of a), 
 
 where p == pitch of rivets, 
 
 d diameter of rivets, 
 
 a, = sectional area of rivets. 
 
 n = number of rows of rivets. 
 
 MEM. In any case where the strength of the longitudinal joint is 
 satisfactorily shown by experiment to be greater than given by this 
 formula, the actual strength may be taken in the calculation, 
 
342 
 
 LLOYD'S REGISTER BOILER RULES 
 Table of Coefficients. Iron Boilers 
 
 
 For Plates 
 
 For Plates 
 
 For Plates 
 
 Description of Longitudinal Joint 
 
 J-in. thick and 
 
 f-in. and above 
 
 above 
 
 
 under 
 
 HB, 
 
 |-in. thick 
 
 Lap joint, punched holes . . . 
 
 155 
 
 165 
 
 170 
 
 drilled 
 
 170 
 
 180 
 
 190 
 
 Double butt-strap joint, punched holes 
 , drilled 
 
 170 
 180 
 
 180 
 190 
 
 190 
 200 
 
 NOTE. The inside butt strap to be at least f of the strength of the longitudinal joint. 
 
 Cylindrical Shells of Steel Boilers. The strength of cylindrical 
 shells of steel boilers is to be calculated from the following formula : 
 
 working pressure in Ibs. per square inch, 
 
 f\ x /T _ o\ x p 
 ^ v ' ' - 
 
 where D = mean diameter of shell in inches, 
 
 T = thickness of plate in sixteenths of an inch, 
 
 C = 22 when the longitudinal seams are fitted with double 
 
 butt straps of equal width, 
 
 C = 21*25 when they are fitted with double butt straps of 
 unequal width, only covering on one side the reduced 
 section of plate at the outer lines of rivets (fig. 438, 
 p. 321), 
 
 C = 20'5 when the longitudinal seams are lap joints. 
 If the minimum tensile strength of shell plates is other than 
 28 tons per square inch, these values of C should be correspondingly 
 modified. 
 
 B = the least percentage of strength of longitudinal joint, 
 found as follows : 
 
 For plate at joint B = 
 for rivets at joint B = 
 
 B = 
 
 P 
 
 p x t 
 n x a 
 p x t 
 
 x 100; 
 
 x 85 where steel rivets are used, 
 
 x 70 where iron rivets are used, 
 
 where p = pitch of rivets in inches, 
 
 t = thickness of plate in inches, 
 
 d = diameter of rivet holes in inches, 
 
 n = number of rivets used per pitch in the longitudinal joint, 
 
 a = sectional area of rivet in square inches. 
 In case of rivets in double shear T75a is to be used instead of a. 
 
 NOTE. The inside butt strap to be at least | of the strength of 
 the longitudinal joint. 
 
 NOTE. For the shell plates of superheaters or steam chests en- 
 closed in the uptakes, or exposed to the direct action of the flame, the 
 coefficients should be | of those given above, 
 
LLOYD'S REGISTER BOILER RULES 343 
 
 Proper deductions are to be made for openings in shell. 
 
 All manholes in circular shells to be stiffened with compensating 
 rings. 
 
 The shell plates under domes in boilers so fitted to be stayed from 
 the top of the dome or otherwise stiffened. 
 
 Stays.- -The strength of stays supporting flat surfaces is to be cal- 
 culated from the smallest part of the stay or fastening, and the strain 
 upon them is not to exceed the following limits, namely : 
 
 Iron Stays. For stays not exceeding 1J in. smallest diameter, and 
 for all stays which are welded, 6,000 Ibs. per sq. in. ; for unwelded 
 stays above I \ in. smallest diameter, 7,500 Ibs. per sq. in. 
 
 Steel Stays. For screw stays not exceeding 1^ in. smallest 
 diameter, 8,000 Ibs. per sq. in. ; for screw stays above 1^ in. smallest 
 diameter, 9,000 Ibs. per sq. inch. For other stays not exceeding 
 1J in. smallest diameter, 9,000 Ibs. per sq. in., and for stays exceed- 
 ing IJ in. smallest diameter, 10,400 Ibs. per sq. in. No steel stays 
 are to be welded. 
 
 Stay Tubes. The stress is not to exceed 7,500 Ibs per sq. in. 
 
 Flat Plates. The strength of flat plates supported by stays to be 
 taken from the following formula : 
 
 Cx T 2 
 f=-= =s working pressure in Ibs. per square inch, 
 
 where T = thickness of plate in sixteenths of an inch, 
 
 p-=square of pitch in inches ; if the pitch in the rows is not 
 equal to that between the tows, then the mean of the 
 squares of the two pitches is to be taken, 
 
 C = 90 for iron or steel plates fa thick and under, fitted with 
 screw stays with riveted heads, 
 
 Q = 100 for iron or steel plates above fa thick, fitted with 
 screw stays with riveted heads, 
 
 C = HO for iron or steel plates fa thick and under, fitted 
 with stays and nuts, 
 
 C = 120 for iron plates above fa thick, and for steel plates 
 above fa and under fa thick, fitted with screw stays 
 and nuts, 
 
 C = 135 for steel plates fa thick and above, fitted with screw 
 stays and nuts, 
 
 C = 140 for iron plates fitted with stays with double nuts, 
 
 C = 150 for iron plates fitted with stays, with double nuts 
 and washers outside the plates, of at least ^ of the 
 pitch in diameter and \ the thickness of the plates, 
 
 C = 160 for iron plates fitted " with stays, with double nuts 
 and washers riveted to the outside of the plates, of 
 at least of the pitch in diameter and ^ the thick- 
 ness of the plates, 
 
 C = 175 for iron plates fitted with stays, with double nuts 
 and washers riveted to the outside of the plates, 
 when the washers are at least f of the pitch in 
 diameter and of the same thickness as the plates. 
 
 For iron plates fitted with stays, with double nuts and doubling 
 
344 LLOYD'S REGISTER BOILER RULES 
 
 strips riveted to the outside of the plates, of the same thickness as 
 the plates, and of a width equal to f the distance between the rows 
 of stays, C ma Y b e taken as 175, if P is taken to be the distance 
 between ^he rows, and 190 when p is taken to be the pitch between 
 the stays in the rows. 
 
 For steel plates, other than those for combustion chambers, the 
 values of C ma y be increased as follows : 
 
 C = 140 increased to 175, 
 150 185, 
 
 160 200, 
 
 175 220, 
 
 190 240. 
 
 If flat plates are strengthened with doubling plates securely riveted 
 to them, having a thickness of not less than of that of the plates, 
 the strength to be taken from 
 
 f\ w /T _i_ f/2) 2 
 
 \J LI iL -- working pressure in Ibs. per square inch ; 
 
 where t = thickness of doubling plates in sixteenths, and Q T an ^ 
 P are as above. 
 
 NOTE. In the case of front plates of boilers in the steam space 
 these numbers should be reduced 20 %, unless the plates are guarded 
 from the direct action of the heat. 
 
 For steel tube plates in the nest of tubes the strength to be taken 
 from 
 
 * ' = working pressure in Ibs. per square inch : 
 
 where T = ^ e thickness of the plates in sixteenths of an inch, 
 p = the mean pitch of stay tubes from centre to centre. 
 
 For the wide water spaces between the nests of tubes the strength 
 to be taken from 
 
 P x T 2 
 
 w D2 ' = working pressure in Ibs. per square inch ; 
 
 where p = the horizontal distance from centre to centre of the 
 
 bounding rows of tubes, and 
 C = 120 where the stay tubes are pitched with two plain 
 
 tubes between them, and are not fitted with nuts 
 
 outside the plates, 
 
 C = 130 if they are fitted with nuts outside the plates, 
 C = 140 if each alternate tube is a stay tube not fitted with 
 
 nuts, 
 
 C = 150 if they are fitted with nuts outside the plates, 
 C = 160 if every tube in these rows is a stay tube, and not 
 
 fitted with nuts, 
 C = 170 if every tube in these rows is a stay tube, and each 
 
 alternate stay tube is fitted with nuts outside the 
 
 plates. 
 
 The thickness of tube plates pf pombustipn chambers in cases 
 
LLOYD'S REGISTER BOILER RULES 345 
 
 where the pressure on the top of the chambers is borne by these 
 plates is not to be less than that given by the following rule : 
 
 T= Px Wx D . 
 
 1750 x (D-d)' 
 
 where P = working pressure in Ibs. per square inch, 
 
 W = width of combustion chamber between plates in inches, 
 D = horizontal pitch of tubes in inches, 
 d = inside diameter of plain tubes in inches, 
 T = thickness of tube plates in sixteenths of an inch. 
 Girders. The strength of girders supporting the tops of combus- 
 tion chambers and other flat surfaces to be taken from the following 
 formula : 
 
 Cx d? x T 
 _* * working pressure in Ibs. per square inch ; 
 
 where L = width between tube plates, or tube plate and back 
 
 plate of chamber, 
 P = pitch of stays in girders, 
 D = distance from centre to centre of girders, 
 d = depth of girder at centre, 
 X = thickness of girder at centre. All these dimensions to 
 
 be taken in inches. 
 Wrought Iron. 
 
 6,000 if there is one stay to each girder, 
 9,000 if there are two or three stays to each girder, 
 Q = ). 10,000 if there are four or five stays to each girder, 
 10,500 if there are six or seven stays to each girder, 
 10,800 if there are eight stays or above to each girder. 
 
 Wrought SteeL 
 
 / 7,110 if there is one stay to each girder, 
 10,660 if there are two or three stays to each girder, 
 C = -j 11,850 if there are four or five stays to each girder, 
 12,440 if there are six or seven stays to each girder, 
 1 12,800 if there are eight stays or above to each girder. 
 If the minimum tensile strength of girder plates is other than 
 28 tons per square inch, these values of C shall be correspondingly 
 modified. 
 
 Circular Furnace*. The strength of plain furnaces to resist col- 
 lapsing to be calculated as follows : 
 
 Where the length of the plain cylindrical part of the furnace 
 exceeds 120 times the thickness of the plate, the working pressure is 
 to be calculated by the following formula : 
 
 1 075 200 x T" 2 
 P^ = working pressure in Ibs. per square inch ; 
 
 L x U 
 
 where the length of the plain cylindrical part of the furnace is 
 less than 120 times the thickness of the plate, the working pressure 
 is to be calculated by the following formula : 
 
 x ^ ' Ht/ = working pressure in Ibs. per square inch ; 
 
346 LLOYD'S REGISTER BOILER RULES 
 
 where D = outside diameter of furnace in inches, 
 
 T = thickness of plate in inches, 
 
 L = length of plain cylindrical part in inches, measured 
 from the centres of the rivets connecting the furnaces 
 to the flanges of the end and tube plates, or from 
 the commencement of the curvature of the flanges 
 of the furnace where it is flanged or fitted with 
 Adamson's rings. 
 
 In the furnaces referred to below the formu'ae given are applicable 
 if the steel used has a tensile strength of not less than 26 nor more 
 than 30 tons per square inch. If the material of furnaces has 
 a less tensile strength than 26 tons per square inch, then for each 
 ton per square inch which the minimum tensile strength falls below 
 26, the coefficient is to be correspondingly decreased by ^ 6 part. 
 
 The strength of corrugated furnaces made on Fox's, Morison's, 
 Deighton's, or Beardmore's plan to be calculated from 
 
 1 259 x (T 2^ 
 
 _^ _' = working pressure in Ibs. per square inch. 
 
 The strength of spirally corrugated furnaces is to be calculated 
 from the following formula : 
 
 . x l ~ '= working pressure in Ibs. per square inch ; 
 
 where T = thickness of plate in sixteenths of an inch, 
 
 and D = outside diameter of corrugated furnaces in inches. 
 The strength of Improved Purves's furnaces with ribs 9 inches 
 apart, and of Brown's Cambered furnaces with ribs either 8 inches 
 or 9 inches apart, to be calculated from the following formula : 
 
 1 160 x (T 2^ 
 
 =A-^ ' = working pressure in Ibs. per square inch ; 
 
 where T = thickness of plate in sixteenths of an inch, 
 
 and D = smallest outside diameter of furnaces in inches. 
 The strength of the Leeds Forge bulb furnace is to be calculated 
 from the following formula : 
 
 1 259 x f T 2^ 
 
 ^_J _J = working pressure in Ibs. per square inch ; 
 
 where T = thickness of plate in sixteenths of an inch, 
 
 and D = smallest outside diameter in inches. 
 The strength of Holmes' Patent Furnaces, in which the corruga- 
 tions are not more than 16 inches apart from centre to centre, and not 
 less than 2 ins. high, to be calculated from the following formula : 
 
 945 x fT 2^ 
 
 Working pressure in Ibs. per square inch = V " 
 
 where T = thickness of plain portions of furnace in sixteenths 
 
 of an inch, 
 
 D = outside diameter of plain parts of the furnace in 
 ipches,, 
 
LLOYD'S REGISTER BOILER RULES 847 
 
 Donkey Boilers. The iron used in the construction of the fire 
 boxes, uptakes, and water tubes of donkey boilers shall be of good 
 quality, and to the satisfaction of the surveyors, who may in any cases 
 where they dectn it advisable apply the following tests : 
 
 Thickness of 
 Plates 
 
 To Bend Cold through an Angle of 
 
 With the Grain 
 
 Across the Grain 
 
 ! 
 
 80 
 70 
 55 
 40 
 
 45 
 35 
 25 
 20 
 
 The material to stand bending hot to an angle of 90, over a radius 
 not greater than 1^ time the thickness of the plates. 
 
 General Remarks about Boilers under Construction. The sur- 
 veyors will be guided in fixing the working pressure by the tables and 
 formulae annexed. 
 
 Any novelty in the construction of the machinery or boilers to be 
 reported to the Committee. 
 
 The boilers, together with the machinery, to be . inspected at 
 different stages of construction. 
 
 All the holes in steel boilers should be drilled, but if they be 
 punched the plates are to be afterwards annealed. 
 
 All plates that are dished or flanged, or in any way heated in the 
 fire for working, except those that are subjected to a compressive 
 stress only, are to be annealed after the operations are completed. 
 
 No steel stays are to be welded. 
 
 Unless otherwise specified, the rules for the construction of iron 
 boilers will apply equally to boilers made of steel. 
 
 The boilers to be tested by hydraulic pressure, in the presence of 
 the engineer-surveyor, to twice the working pressure, and carefully 
 gauged while under test. 
 
 Two safety valves to be fitted to each boiler and loaded to the 
 working pressure in the presence of the surveyor. In the case of 
 boilers of greater working pressure than 60 Ibs. per sq. in., the safety 
 valves may be loaded to 5 Ibs. above the working pressure. If 
 common valves are used, their combined areas to be at least half 
 a square inch to each square foot of grate surface. If improved 
 valves are used, they are to be tested under steam in the presence of 
 the surveyor; the accumulation in no case to exceed 10 % of the 
 working pressure. 
 
 An approved safety valve also to be fitted to the superheater. 
 
 In winch boilers one safety valve will be allowed, provided its area 
 be not less than half a square inch per square foot of grate surface. 
 
 Each valve to be arranged so that no extra load can be added 
 when steam is up, and to be fitted with easing gear which must lift 
 the valve itself. All safety-valve spindles to extend through the 
 covers and to be fitted with sockets and cross handles, allowing them 
 to be lifted and turned round in their seats, and their efficiency tested 
 at any time. 
 
 Stop valves to be fitted so that each boiler can be worfcecl 
 separately. 
 
348 LLOYD'S REGISTER BOILER RULES 
 
 
 
 Each boiler to be fitted with a separate steam-gauge, to accurately 
 indicate the pressure, 
 
 Bach boiler to be fitted with a blow-off cock independent of that 
 on the vessel's outside plating. 
 
 The machinery and boilers are to be securely fixed to the vessel to 
 the satisfaction of the surveyor. 
 
 SUMMARY. 
 
 The preceding rules are summarised in the following short table, 
 in which the method has been carried out of indicating all such 
 dimensions as are measured in inches by capitals, such as are 
 measured in sixteenths of an inch by small letters, and all coefficients, 
 &c., by black letters : 
 
 C and C' = coefficients. 
 
 W P = permissible working pressure. 
 B and B' = percentage of joint respectively of plate and of rivets. 
 
 N = number of rivets included within one pitch of external 
 
 row. 
 T and t = thicknesses of plates measured respectively in inches and 
 
 in sixteenths of an inch. 
 P = pitches in inches of rivets or stays in flat plates, or tubes 
 
 in tube plates. 
 
 P c = distance apart of girders or cross pitch of stays in inches. 
 D = mean diameter of shells and diameter of furnaces in 
 inches, measured as follows : for all plain furnaces, or 
 made with ribs (Purves's), with flanges (Adamson's 
 rings), or for Holmes's furnaces, the outside diameter of 
 the plain cylindrical part is to be taken, and the thick- 
 ness of the plates measured at these parts. For Fox's 
 and Morison's corrugated furnaces the extreme external 
 diameter is to be taken. 
 
 D and Dt = effective external and internal diameters of plain or stay 
 tubes, and effective diameter of rivets, or of stays, in 
 inches. 
 L or L'= length of plain cylindrical parts of furnaces measured 
 
 respectively in inches or feet. 
 L = length of girders measured in inches = internal distance 
 
 between tube and back plates. 
 H= depth of girders measured in inches. 
 
 A = sectional area of stays or stay tubes, or of rivets, in 
 
 square inches. 
 S A = sum of areas of holes in tube plate in square inches. 
 
 RIVETED JOINTS. (See appended Tables.) 
 
 100 
 A D 8 
 
 Percentage of plate B = ~ . 100 
 
 Percentage of rivets B' = C . N . ==-, or V . N . ^ . . 
 
LLOYD'S REGISTER BOILER RULES 
 
 849 
 
 TABLE OP COEFFICIENTS 
 
 Materials of 
 
 Double Butt Straps 
 
 Lap Joints 
 
 Plate 
 
 Rivet 
 
 
 
 0' 
 
 
 
 cy 
 
 Iron, punched . 
 drilled . 
 
 Iron .... 
 
 1750 
 157-5 
 122-5 
 
 148-7 
 
 137-4 
 123-8 
 96-3 
 116-8 
 
 100 
 90 
 70 
 85 
 
 78-5 
 70-7 
 55-0 
 66-7 
 
 Steel . . 
 
 
 Steel! ! ! ! 
 
 Iron BOILER SHELLS. W P = C . (B or B') . ^ , or C' . (B or B') . ~ . 
 
 TABLE OF COEFFICIENTS 
 
 Joint 
 
 Double Butt Straps 
 
 Lap joints 
 
 Plates 
 
 
 
 c* 
 
 C 
 
 C 1 
 
 Thickness of 
 Plates 
 
 Jin. Jin. 
 
 above 
 
 Jin. 
 
 fin. 
 
 above 
 
 1 in. j in. 
 
 above 
 
 Jin. 
 
 Jin. 
 
 above 
 
 Punched . 
 Drilled . 
 
 170 180 
 180 190 
 
 190 
 200 
 
 10-61 
 11-24 
 
 11-24 
 11-87 
 
 11-87 
 12-50 
 
 155 ' 165 
 
 170 180 
 
 i 
 
 170 
 
 190 
 
 9-68 
 10-61 
 
 10-31 
 11-24 
 
 10-61 
 11-87 
 
 Steel BOILER SHELLS. W P = C . (B or B') . 
 
 TABLE OF OOEFICIENTS C 
 
 Tenacity of Steel, Tons 
 
 26 
 
 27 
 
 28 
 
 20 
 
 30 
 
 . 
 
 31 
 
 32 | 
 
 Lap joints .... 
 Butt straps of unequal widths 
 of equal widths . 
 
 19-03 
 19-73 
 20-43 
 
 19-76 
 20-49 
 21-21 
 
 20-50 
 21-25 
 22-00 
 
 21-23 
 22-01 
 
 22-78 
 
 21-96 
 22-76 
 23-57 
 
 22-69 
 23-52 
 24-35 
 
 23-42 
 
 24-28 
 25-14 ! 
 
 FURNACES. (See appended Tables.) 
 Plain furnaces when L exceeds 120 T : 
 
 w p _ 1,075 , 200 . T 2 _ 4,200 . ** _ 350 . t* 
 D.L ~D7T S '- 
 
 Plain furnaces when L is less than 120 T 
 W P = 5Q.(300T-L) = 600 
 
 PATENT AND OTHER FURNACES. 
 For measurements of D see p. 
 
 er.L-^ 
 
 342. 
 
 C' 
 
 1,259 
 1,160 
 
 TABLE OF COEFFICIENTS FOR STEEL OF 26 TONS AND MORE 
 
 Corrugated flue, various types 
 
 . 
 
 . 
 
 Farnley's spirally corrugated flue 
 
 
 
 912 
 
 945 
 
 
 
 
 
 
350 
 
 LLOYD'S REGISTER BOILER RULES 
 
 STAYED FLAT PLATES. If pitches are equal W P = ^~ 2 - 
 (See appended Tables.) 
 
 O (~1 f'2 
 
 If pitches are unequal W P = ' ' 2 
 
 -t +-L c 
 
 diameter of the greatest inscribed circle. 
 
 2 . C . t 2 
 
 , where A is 
 
 TABLE OF COEFFICIENTS -0 
 
 Iron 
 
 Steel 
 
 Stay ends riveted plates up to ^ inch 
 
 90 
 100 
 110 
 120 
 120 
 
 90 
 100 
 110 
 120 
 135 
 
 above ^ inch , 
 
 
 M ,, -',. inch thick and above . . 
 
 Double nuts 
 
 140 
 150 
 160 
 175 
 190 
 
 175 
 185 
 200 
 220 
 240 
 
 and washers ( P x T) 
 
 and riveted washers (I P x 4 T) . 
 (fPxT) . . . . 
 and doubling strips (f P x T) lengthways . 
 
 Tube plate 
 
 140 
 
 140 
 
 Tube plate between nests of tubes 
 
 Beaded 
 
 Nutted 
 
 
 When there are two plain tubes between stays .... 
 is one plain tube between stays .... 
 M every tube is a stay tube ... . 
 
 120 
 140 
 160 
 
 130 
 150 
 170 
 
 Doubling plates W P. = C ( f^-. {' '? . th ? ** of ihe.douUing 
 2 . P 2 [ plate in sixteenths of an inch 
 
 Tube plates, W P = 1>60 ' ^-"^-^ 
 
 STAYS. (See appended Tables.) 
 STAYS. W P = C . ^J^~ or C' . 
 
 Stay tubes. W P = C . 
 
 .Pc 
 A 
 
 __ 
 P. PC 
 
 _ 
 P.P.-2 A' 'P.P C ~2A* 
 
 TABLE OF COEFFICIENTS 
 
 ( 
 
 ) 
 
 C 
 
 * 
 
 
 Iron 
 
 Steel 
 
 Iron 
 
 Stoel 
 
 Screwed stays up to 1| inch effective diameter 
 above 1 inch effective diameter . 
 Stay tubes .... 
 
 6,000 
 7,500 
 7 500 
 
 8,000 
 9,000 
 7 500 
 
 4,712 
 
 5,891 
 5 SQO 
 
 6,?83 
 7,068 
 
 UOft 
 
 
 
 
 
 
 GIRDERS. WP = C 
 
 H 2 T 
 
LLOYD'S REGISTER BOILER RULES 
 
 351 
 
 TABLE OF COEFFICIENTS 
 
 
 
 
 Number of Stays per Girder 
 
 Iron 
 
 Steel 
 
 One 
 
 6,000 
 
 7,110 
 
 
 9,000 
 
 10,660 
 
 
 10,000 
 
 11,850 
 
 
 10,500 
 
 12,440 
 
 
 10,800 
 
 12800 
 
 
 
 
 TABLES. 
 
 When used in the drawing office, it is strongly recommended that 
 those parts of the following tables which are inapplicable to the 
 particular works should be obliterated. 
 
 TABLE FOR FINDING THE DIAMETERS OP RIVETS AND OP PITCHES 
 IN RIVETED JOINTS. 
 
 A short table will be found on p. 323 which shows the smallest 
 permissible percentage for any form of joint, the condition being 
 that when that particular percentage is adopted the strength of 
 the joint shall be exactly the same for each row of rivets. If 
 this percentage is exceeded, the inner rows will be stronger than 
 the outer ones. If the joint is made of a smaller percentage, the 
 inner rows of rivets will be the weakest and must be calculated 
 separately. 
 
 Having decided on a particular percentage, the best dimensions of 
 the joint can be ascertained from the following table, which contains 
 the values of N . D -r- T = number of rivets x diameter of rivets H- 
 thickness of shell plate. Having found the number in the table 
 against the desired percentage, it is only necessary to multiply it by 
 the thickness of the plate, and then, dividing by the number of rivets 
 within one pitch, their diameters are found. The percentage and 
 therefore also the numeral should be so chosen that the latter is larger 
 than the number of rivets in one pitch. 
 
 Example. Butt-strap joint 1-inch steel plates, steel rivets, three 
 rows, with two rivets in each inner row. Then the smallest percentage 
 to be adopted for this joint is 83'33. Interpolating the values in the 
 following table, it will be found that the value of N . D -=- T is 4'28. 
 Dividing this by 5, the number of rivets, then their diameters must be 
 856. In the first column of the same table will be found the value 
 of pitch -r- rivet diameter = 6. Therefore the pitch is 6 x '856 = 
 5'136 inches. 
 
 If it is desired to make the rivet diameter equal to the thickness 
 of the plate, then a value must be selected where N . D -f- T = 5, 
 i.e. 85 per cent.; then the pitch would have to be 6'98 inches. 
 (See p. 347.) 
 
352 
 
 LLOYD'S REGISTER BOILER RULES 
 
 S3 
 
 
 ! LAP JOINT 
 
 BUTT STRAPS 
 
 1 
 
 1 
 
 jl! 
 
 II 
 
 Jl 
 
 |l 
 
 Jl 
 
 II 
 
 IT 
 
 If" 
 
 i 
 
 8 
 
 t 
 
 
 ill 
 
 cs 
 
 s; 
 
 .gfe! 
 
 o <a > 
 
 |&a 
 
 Eg 
 
 08 (* 
 
 SS 
 
 ! 
 
 1 
 
 |og 
 
 gg 
 
 II 
 
 Ig 
 
 Jgg 
 
 
 ss 
 
 So 
 
 i 
 
 a 
 
 HH 
 
 HH 
 
 
 WH 
 
 HH 
 
 HH 
 
 no 
 
 W M 
 
 a 
 
 i 
 
 
 Constants 
 
 i 
 
 * 
 
 100 
 
 90 
 
 85 
 
 70 
 
 100 
 
 |-90 
 
 1-85 
 
 1-10 
 
 2-50 
 
 60 
 
 ... 
 
 2-12 
 
 2-25 
 
 2-73 
 
 
 ... 
 
 
 
 2-55 
 
 61 
 
 ... 
 
 2-21 
 
 2-34 
 
 2-84 
 
 
 
 
 
 2-63 
 
 62 
 
 2-08 
 
 2-31 
 
 2-44 
 
 2-97 
 
 
 
 
 
 2-70 
 
 63 
 
 2-17 
 
 2-41 
 
 2-55 
 
 8-10 
 
 
 
 
 
 2-78 
 
 64 
 
 2-26 
 
 2-52 
 
 2-66 
 
 3-23 
 
 
 
 
 
 2-86 
 
 65 
 
 2-36 
 
 2-63 
 
 2-78 
 
 3-38 
 
 
 
 
 
 2-94 
 
 66 
 
 2-47 
 
 2-75 
 
 2-91 
 
 3-53 
 
 ... 
 
 ... 
 
 ... 
 
 2-02 
 
 3-03 
 
 67 
 
 2-59 
 
 2-87 
 
 3-04 
 
 3-69 
 
 ... 
 
 ... 
 
 ... 
 
 2-11 
 
 3-12 
 
 68 
 
 2-71 
 
 3-01 
 
 8-18 
 
 3-87 
 
 ... 
 
 ... 
 
 
 221 
 
 3-23 
 
 69 
 
 2-83 
 
 3-15 
 
 8-33 
 
 4-05 
 
 ... 
 
 ... 
 
 ... 
 
 2-31 
 
 3-33 
 
 70 
 
 2-97 
 
 3-30 
 
 3-49 
 
 4-24 
 
 ... 
 
 ... 
 
 ... 
 
 2-42 
 
 3-45 
 
 71 
 
 3-12 
 
 3-46 
 
 3-66 
 
 4-45 
 
 
 ... 
 
 2-ib 
 
 2-54 
 
 3-57 
 
 72 
 
 3-27 
 
 8-64 
 
 3-85 
 
 4-68 
 
 ... 
 
 2-08 
 
 2-20 
 
 2-67 
 
 3-70 
 
 73 
 
 3-44 
 
 3-82 
 
 4-05 
 
 4-92 
 
 ... 
 
 2-19 
 
 2-31 
 
 2-81 
 
 3-85 
 
 74 
 
 3-62 
 
 4-03 
 
 4-26 
 
 5-18 
 
 2-07 
 
 2-31 
 
 2-44 
 
 2-96 
 
 4-00 
 
 75 
 
 3-82 
 
 4-24 
 
 4-49 
 
 5-46 
 
 2-18 
 
 2-43 
 
 2-57 
 
 3-12 
 
 4-08 
 
 75* 
 
 3-92 
 
 4-36 
 
 4-61 
 
 5-61 
 
 2-24 
 
 2-49 
 
 2-64 
 
 3-20 
 
 4-17 
 
 76 
 
 4-03 
 
 4-48 
 
 4-74 
 
 5-76 
 
 2-30 
 
 2-56 
 
 2-71 
 
 3-29 
 
 4-26 
 
 76* 
 
 4-14 
 
 4-61 
 
 4-87 
 
 5-92 
 
 2-37 
 
 2-63 
 
 2-79 
 
 3-38 
 
 4-34 
 
 77 
 
 4-26 
 
 4-74 
 
 5-01 
 
 6-09 
 
 2-44 
 
 2-71 
 
 2-87 
 
 3-48 
 
 4-44 
 
 77* 
 
 4-38 
 
 4-87 
 
 5-16 
 
 6-27 
 
 2-51 
 
 2-78 
 
 2-95 
 
 3-58 
 
 4-55 
 
 78 
 
 4-51 
 
 5-02 
 
 5-31 
 
 6-45 
 
 2-58 
 
 2-86 
 
 3-03 
 
 3-68 
 
 4-65 
 
 78* 
 
 4-65 
 
 5-17 
 
 5-47 
 
 6-64 
 
 2-66 
 
 2-95 
 
 3-12 
 
 3-79 
 
 4-76 
 
 79 
 
 4-79 
 
 5-32 
 
 5-64 
 
 6-84 
 
 2-74 
 
 3-04 
 
 3-22 
 
 3-91 
 
 4-88 
 
 79* 
 
 4-94 
 
 5-49 
 
 5-81 
 
 7-05 
 
 2-82 
 
 3-13 
 
 3-32 
 
 4-03 
 
 5-00 
 
 80 
 
 5-09 
 
 5-66 
 
 5-99 
 
 7-28 
 
 2-91 
 
 323 
 
 3-42 
 
 4-16 
 
 6-13 
 
 80* 
 
 5-26 
 
 5-84 
 
 6-18 
 
 7-51 
 
 3-00 
 
 3-33 
 
 3-53 
 
 4-29 
 
 5-26 
 
 81 
 
 5-43 
 
 6-03 
 
 6-39 
 
 7-75 
 
 3-10 
 
 344 
 
 3-65 
 
 4-43 
 
 5-40 
 
 81* 
 
 5-61 
 
 6-23 
 
 6-60 
 
 8-01 
 
 3-21 
 
 3-56 
 
 3-77 
 
 4-58 
 
 5-56 
 
 82 
 
 5-80 
 
 6-44 
 
 6-82 
 
 8-29 
 
 3-32 
 
 3-68 
 
 3-90 
 
 4-73 
 
 6-71 
 
 82* 
 
 6-00 
 
 6-67 
 
 7-06 
 
 8-57 
 
 343 
 
 3-81 
 
 4-04 
 
 4-90 
 
 5-88 
 
 83 
 
 6-22 
 
 6-91 
 
 7-31 
 
 8-88 
 
 3-55 
 
 3-94 
 
 4-18 
 
 5-07 
 
 6-06 
 
 83* 
 
 6-44 
 
 7-16 
 
 7-58 
 
 9-20 
 
 3-68 
 
 4-08 
 
 4-33 
 
 5-26 
 
 6-25 
 
 84 
 
 6-68 
 
 7-43 
 
 7-86 
 
 9-54 
 
 3-82 
 
 4-25 
 
 4-49 
 
 5-46 
 
 6*45 
 
 84| 
 
 6-94 
 
 7-71 
 
 8-17 
 
 9-92 
 
 3-97 
 
 4-41 
 
 4-67 
 
 6-67 
 
 6-67 
 
 85 
 
 7-22 
 
 8-02 
 
 8-49 
 
 10-31 
 
 412 
 
 4-58 
 
 4-85 
 
 5-89 
 
 6-82 
 
 85* 
 
 7-41 
 
 8-23 
 
 8-72 
 
 ... 
 
 423 
 
 4-70 
 
 4-98 
 
 6-05 
 
 6-98 
 
 8*1 
 
 761 
 
 8-46 
 
 8-95 
 
 ... 
 
 4-35 
 
 4-83 
 
 5-12 
 
 6-21 
 
 7-14 
 
 86 
 
 7-82 
 
 8-69 
 
 9-20 
 
 
 4-47 
 
 4-97 
 
 5-26 
 
 6-38 
 
 7-32 
 
 86* 
 
 8-04 
 
 8-94 
 
 9-46 
 
 ... 
 
 4-60 
 
 5-11 
 
 5-41 
 
 6-57 
 
 7-50 
 
 86| 
 
 8-28 
 
 9-20 
 
 9-74 
 
 ... 
 
 4-73 
 
 5-25 
 
 5-56 
 
 6-76 
 
 7-69 
 
 87 
 
 8-52 
 
 9-47 
 
 10-02 
 
 ... 
 
 4-87 
 
 5-41 
 
 5-73 
 
 6-96 
 
 7-89 
 
 87* 
 
 8-78 
 
 9-75 
 
 ... 
 
 ... 
 
 5-02 
 
 5-57 
 
 5-90 
 
 7-17 
 
 8-10 
 
 87 
 
 9-05 
 
 10-06 
 
 ... 
 
 ... 
 
 5-17 
 
 5-75 
 
 6-08 
 
 7-39 
 
 8-33 
 
 88 
 
 9-34 
 
 ... 
 
 ... 
 
 ... 
 
 5-33 
 
 5-93 
 
 6-28 
 
 7-62 
 
 8-57 
 
 8-82 
 
 8 8 8l 
 
 9-64 
 9-96 
 
 ... 
 
 ... 
 
 ... 
 
 5-51 
 5-69 
 
 6-12 
 6-32 
 
 6-48 
 6-70 
 
 7-87 
 813 
 
 9-09 
 
 89 
 
 10-30 
 
 ... 
 
 ... 
 
 ... 
 
 5-89 
 
 6-54 
 
 6-93 
 
 8-41 
 
 9-37 
 
 89* 
 
 
 
 
 
 6-09 
 
 6-77 
 
 7-17 
 
 8-70 
 
 9-68 
 
 WWM 
 
 894 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 6-31 
 
 7-01 
 
 7-43 
 
 9-02 
 
 o-oo 
 
 90 
 
 
 
 
 
 6-55 
 
 7-28 
 
 7-70 
 
 9-36 
 
 
 
 
 
LLOYD'S REGISTER BOILER RULES 
 
 353 
 
 In many of the high-percentage joints it will be found that unless 
 the diameters of the rivets are less than the thickness of the plates the 
 most efficient proportions cannot be adopted. 
 
 The following tables contain the internal diameters of furnaces, 
 according to Lloyd's Register Boiler Rules. 
 
 INTERNAL DIAMETER OP CIRCULAR FURNACES IN INCHES. 
 
 Thickness. Inches 
 
 Plain or Flanged Furnaces 
 Kn *" SO (300 T L) 
 
 Patent Furnaces 
 
 Tenacity of Steel 
 
 = 
 
 D.L' r 
 
 D 
 
 
 Above 26 T 
 
 P 
 
 Lengths of Furnaces 
 
 3orr. 
 
 Purves 
 
 Corr. 
 
 9ft. 
 
 8ft. 
 
 7ft. 
 
 6ft. 
 
 6ft. 
 
 4ft. 
 
 3ft. 
 
 30 in. 
 
 24 in. 
 
 18 iu. 
 
 12 in. 
 
 9 in. 
 
 0.(-2)-s-D 
 
 1 
 1 
 
 * 
 
 3 \i 
 11 
 
 26-6 
 30-9 
 35-5 
 40-5 
 45-8 
 51-4 
 
 26-3 
 30-1 
 34-1 
 38-3 
 42-7 
 47-3 
 52-3 
 
 25-5 
 30-0 
 34-9 
 40-1 
 45-7 
 51-6 
 
 129-2 
 34-4 
 40-0 
 45-9 
 52-3 
 
 34-2 
 40-3 
 
 46-8 
 53-7 
 
 ( 
 41-2 
 
 48-5 
 56-3 
 
 50LB5 
 
 55-0 
 
 ;. WORKING PRESSURE. 
 63-0 68-0 | 73-0 78-0 83-0 85-5 
 
 79-9 
 
 76-6 
 
 62-5 
 
 62-2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 25-9 
 29-8 
 34-0 
 38-4 
 43-2 
 48-2 
 53-4 
 
 25-6 
 29-7 
 34-2 
 39-0 
 44-1 
 49-5 
 55-2 
 
 25-5 
 30-0 
 34-8 
 40-1 
 45-7 
 51-6 
 
 30-7 
 36-2 
 42-0 
 45-9 
 49-0 
 52-1 
 
 30 LB 
 
 41-1 
 45-3 
 51-1 
 
 3. W 
 
 47-0 
 52-8 
 
 3RKIN 
 
 50-8 
 
 G PB 
 54-5 
 
 ESSURE. 
 
 58-3 62-0 
 
 63-9 
 
 58-9 
 
 57-2 
 
 46-0; 46-5 
 52-2 52-3 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 00 LB 
 
 32-7 
 36-1 
 40-7 
 45-3 
 50-0 
 
 s. W 
 37-5 
 42-1 
 46-7 
 51-3 
 
 ORKl> 
 
 40-5 
 45-1 
 49-7 
 54-3 
 
 G Pf 
 
 43-5 
 48-1 
 52-7 
 
 tESSD 
 
 46-5 
 51-1 
 
 RE. 
 
 49-5 
 
 51-0 
 
 46-4 
 52-7 
 
 45-6 
 51-4 
 
 36-01 37-0 
 41-0 41-7 
 46-0 46-4 
 51-0 51-0 
 
 
 
 
 
 28-7 
 33-4 
 36-6 
 44-0 
 48-6 
 53-2 
 
 27-0 
 30-4 
 33-9 
 37-6 
 41-6 
 45-7 
 50-0 
 
 27 : 
 30-5 
 34-3 
 38-3 
 42-5 
 46-8 
 51-5 
 
 27-2 
 31-0 
 35-1 
 
 394 
 43-9 
 48-7 
 53-6 
 
 27-7 
 31-9 
 36-3 
 41-0 
 46-0 
 51-4 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ... 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 20 LB 
 
 27-1 
 29-9 
 33-8 
 37-6 
 41-5 
 45-3 
 
 s. W 
 31-1 
 34-9 
 38-8 
 42-6 
 46-5' 
 50-3 
 
 ORKII 
 
 33-6 
 37-4 
 41-3 
 45-1 
 49-0 
 52-8 
 
 ro Pi 
 36-1 
 39-9 
 43-8 
 47-6 
 51-5 
 
 IESSU 
 
 38-6 
 42-4 
 46-3 
 50-1 
 
 RE. 
 
 41-1 
 
 44-9 
 48-8 
 52-6 
 
 42-3 
 46-2 
 50-0 
 
 38-0 
 43-2 
 
 48-5 
 53-7 
 
 37-9 
 42-7 
 47-5 
 52-2 
 
 29-3 
 33-5 
 37-7 
 
 41-8 
 46-0 
 50-2 
 
 30-7 
 34-6 
 38-5 
 42-4 
 46-2 
 50-1 
 
 
 
 
 
 
 
 
 
 27-7 
 30-3 
 36-5 
 40-0 
 
 ... 
 
 
 
 25-7 
 29-0 
 
 26-4 
 30-1 
 34-0 
 
 
 
 
 
 
 
 
 
 
 
 
 AA 
 
354 LLOYD'S REGISTER BOILER RULES 
 
 INTERNAL DIAMETER OP CIRCULAR FURNACES IN INCHES continued. 
 
 Thickness. Inches 
 
 Plain or Flanged Furnaces 
 350 t* __50(300T-L) 
 
 
 Patent Furnaces 
 
 
 Tenacity of Steel 
 
 1 
 
 D . 
 
 L' D 
 
 
 
 Abov 26 T 
 
 i 
 
 Lengths of Furnaces 
 
 Oorr. 
 
 Furves 
 
 Oorr. 
 
 9ft. 
 
 8ft. 
 
 7ft. 
 
 6ft. 
 
 5ft. 
 
 4ft. 
 
 3ft. 
 
 30 in. 
 
 24 in. 
 
 18 in. 
 
 12in.|9in. 
 
 0.-J)+D 
 
 j| 
 
 \ 
 I 
 
 25-1 
 
 28-1 
 31-2 
 34-4 
 37-8 
 41-4 
 45-2 
 49-0 
 
 28-4 
 31-7 
 35-2 
 38-9 
 42-7 
 46-7 
 51-0 
 
 32-6 
 36-4 
 40-4 
 44-6 
 49-0 
 53-4 
 
 12 
 
 38-1 
 42-6 
 46-8 
 50-7 
 
 OLBE 
 
 44-1 
 48-0 
 51-8 
 
 i. Wo 
 
 49-1 
 53-0 
 
 RKINO PRESSURE Continued. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 140 LBS. W 
 
 25-1 
 
 ORKH 
 
 28-7 
 32-0 
 35-2 
 38-5 
 41-8 
 45-1 
 48-4 
 51-7 
 
 10 Pi 
 
 30-8 
 34-1 
 37-4 
 40-7 
 44-0 
 47-2 
 50-5 
 
 IESSURE. 
 
 33-0 35-1 
 36-2 38-4 
 39-5 41-0 
 42-8 45-0 
 46-1 48-2 
 49-4 51-5 
 
 38-2 
 39-5 
 42-7 
 46-0 
 49-0 
 52-6 
 
 32-0 
 36-5 
 41-0 
 45-5 
 50-0 
 54-4 
 
 32-4 
 36-5 
 40-6 
 44-6 
 
 48-7 
 52-8 
 
 24-6 
 28-1 
 31-7 
 35-3 
 38-9 
 42-4 
 46-0 
 49-6 
 53-1 
 
 26-2 
 29-6 
 32-9 
 36-2 
 39-5 
 42-8 
 46-1 
 49-4 
 53-7 
 
 
 
 
 
 
 25-5 
 
 28-8 
 32-1 
 35-4 
 38-7 
 42-0 
 45-2 
 48-5 
 51-8 
 
 29-8 
 33-1 
 36-4 
 39-7 
 43-0 
 46-2 
 49-6 
 52-8 
 
 
 
 
 
 
 
 
 
 
 25-6 
 31-1 
 34-4 
 37-7 
 41-0 
 44-2 
 47-5 
 50-8 
 
 26 : 6 
 29-3 
 32-2 
 35-3 
 38-5 
 44-0 
 
 27 : 
 30-0 
 33-1 
 36-4 
 39-8 
 43-5 
 47-2 
 
 24-7 
 27-8 
 31-0 
 34-4 
 38-0 
 41-8 
 45-5 
 48-8 
 52-1 
 
 25-7 
 28-9 
 32-5 
 36-4 
 40-0 
 43-2 
 46-5 
 49-8 
 53-1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 160 LBS. W 
 
 ORKD 
 
 25-0 
 27-9 
 30-7 
 33-7 
 36-5 
 39-3 
 42-2 
 45-1 
 47-9 
 50-8 
 
 JO Pi 
 
 26-9 
 29-7 
 32-6 
 36-5 
 38-3 
 41-2 
 44-1 
 46-9 
 49-8 
 52-7 
 
 IESSU 
 
 28-7 
 31-6 
 34-4 
 37-3 
 40-2 
 43-1 
 45-9 
 48-8 
 51-7 
 
 RE. 
 
 30-6 
 33-5 
 35-7 
 39-2 
 42-1 
 44-9 
 47-8 
 50-2 
 
 31-5 
 34-4 
 37-3 
 
 40-1 
 43-0 
 45-9 
 48-7 
 51-6 
 
 27-5 
 31-4 
 35-3 
 39-3 
 43-2 
 47-1 
 51-1 
 55-0 
 
 28-2 
 31-8 
 35-4 
 38-9 
 42-5 
 46-1 
 49-6 
 53-2 
 
 24-1 
 27-2 
 30-4 
 33'5 
 36-6 
 39-7 
 42-9 
 4fi-0 
 49-1 
 52-2 
 
 25-8 
 28-7 
 31-5 
 34-4 
 37-3 
 40-2 
 43-1 
 46-0 
 48-9) 
 51-8 
 j 
 
 
 
 
 
 
 
 26-0 
 28-8 
 31-7 
 34-6 
 37-4 
 40-3 
 43-2 
 46-0 
 48-9 
 51-8 
 
 
 
 
 
 
 25-1 
 28-0 
 30-8 
 33-7 
 36-6 
 39-4 
 42-3 
 45-2 
 48-0 
 50-9 
 
 
 
 
 
 
 
 
 
 
 27-1 
 29-9 
 32-8 
 35-7 
 38-5 
 41-4 
 44-3 
 47-1 
 50-0 
 
 25*5 
 
 28-0 
 30-7 
 33-5 
 36-4 
 
 26-1 
 28-8 
 31-7 
 34-7 
 37-8 
 41-1 
 
 27-0 
 30-0 
 33-1 
 36-4 
 39-6 
 43-5 
 45-4 
 
 25-2 
 28-2 
 31-7 
 34-8 
 37-7 
 40-5 
 43-4 
 46-3 
 49-1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i i 
 
LLOYD'S REGISTER BOILER RULES 355 
 
 INTERNAL DIAMETER OP CIRCULAR FURNACES IN INCHES continued. 
 
 1 
 Thickness. Inchea 
 
 Plain or Flanged Furnace 
 . / 50r300T-L 
 
 
 ) 
 
 
 
 Patent Furnaces 
 
 Tenacity of Steel 
 
 1 
 
 
 D. 
 
 
 l 
 
 r~ 
 
 Abore 86 T 
 
 ft 
 
 Lengths of Furnaces 
 
 Corr. 
 
 Purves 
 
 Oorr. 
 
 9ft. 
 
 8ft. 
 
 7ft. 
 
 6ft. 
 
 5ft. 
 
 4ft. 
 
 3ft. 
 
 30 in. 
 
 24 taJll in. 
 
 12 in. 
 
 9 in. 
 
 0.<I-I)+D 
 
 i i 
 
 180 LBS. WORKING PRESSI 
 | : ... 1 ... 
 
 nftB. 
 
 27-1 
 29-7 
 31-6 
 34-7 
 37-3 
 39-8 
 42-4 
 44-9 
 47-5 
 50-0 
 
 28-0 
 30-5 
 33-0 
 35-6 
 38-1 
 40-7 
 43-2 
 45-7 
 48-2 
 50-8 
 
 24-0 
 27-5 
 31-0 
 34-5 
 38-0 
 41-5 
 45-0 
 48-5 
 51-9 
 
 25-0 
 28-2 
 31-3 
 34-5 
 37-7 
 40-8 
 44-0 
 47-1 
 50-3 
 
 26-6 
 29-3 
 32-1 
 34-9 
 37-7 
 40-4 
 43-2 
 46-0 
 48-8 
 51-6 
 
 25*4 
 27-9 
 30-5 
 33-1 
 35-7 
 38-2 
 40-8 
 43-4 
 45-9 
 48-5 
 51-0 
 
 1 
 
 ? 
 
 'i 
 
 sa f 
 
 M 
 
 
 
 
 
 
 
 
 
 26-3 
 28-9 
 31-4 
 34-0 
 36-5 
 39-0 
 41-6 
 44-1 
 46-7 
 49-2 
 51-7 
 
 28-0 
 30-5 
 33-1 
 35-6 
 38-2 
 40-7 
 43-2 
 45-8 
 48-3 
 50-9 
 ... 
 
 
 
 
 
 
 
 25-5 
 28-1 
 30-6 
 33-2 
 35-7 
 38-3 
 40-8 
 43-3 
 45-9 
 48-4 
 51-0 
 
 27-2 
 29-7 
 32-3 
 34-8 
 37-4 
 39-9 
 42-5 
 45-0 
 47-5 
 50-1 
 
 
 
 
 
 
 
 
 
 
 
 
 27-3 
 29-8 
 32-4 
 34-7 
 37-5 
 40-0 
 42-5 
 45-1 
 47-6 
 50-2 
 
 200 u 
 
 27-1 
 29-7 
 32-1 
 
 25-5 
 28-2 
 30-6 
 34-5 
 36-4 
 
 26-5 
 29-3 
 32-3 
 35-1 
 37-6 
 40-2 
 
 25-0 
 28-0 
 30-8 
 33-3 
 35-9 
 38-4 
 41-0 
 43-5 
 
 26-5 
 29-0 
 31-6 
 34-1 
 36-7 
 39-2 
 41-7 
 44-3 
 46-8 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 BS. WORKING PRESSURE. 
 
 25-1 
 
 27-4 
 29-6 
 31-9 
 34-2 
 36-5 
 38-8 
 41-0 
 43-3 
 45-6 
 47-9 
 50-1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 25-1 26-6 
 27-4 28-4 
 29-7 31-2 
 
 32-0 33-5 
 34-2 35-7 
 
 36-5 38-0 
 38-8 39-3 
 41-1 42-6 
 43-4 44-9 
 45-6 47-1 
 47-9 48-4 
 50-2 51-7 
 
 27-5 
 30-6 
 33-8 
 36-9 
 40-1 
 43-2 
 46-4 
 49-5 
 52-6 
 
 25-3 
 28-1 
 31-0 
 33-8 
 36-6 
 39-5 
 42-3 
 45-1 
 48-0 
 50-8 
 
 26-0 
 28-5 
 31-0 
 33-5 
 36-0 
 38-5 
 41-0 
 43-5 
 46-0 
 48-5 
 
 25-0 
 27-3 
 29-6 
 31-9 
 34-3 
 36-5 
 38-7 
 41-0 
 43-3 
 45-6 
 47-9 
 
 
 
 
 
 
 
 
 
 25-9 
 28-2 
 30-5 
 32-7 
 35-0 
 37-3 
 39-6 
 41-9 
 44-1 
 46-4 
 48-7 
 51-0 
 
 
 
 
 
 
 
 25-2 
 27-5 
 
 29-7 
 32-0 
 34-3 
 36-6 
 38-9 
 41-1 
 43-4 
 45-7 
 48-0 
 
 26-7 
 29-0 
 31-2 
 33-5 
 35-8 
 38-1 
 40-4 
 43-6 
 44-9 
 47-2 
 49-5 
 
 
 
 
 
 
 
 
 
 
 
 
 26-7 
 29-0 
 31-3 
 33-6 
 35-9 
 38-1 
 40-4 
 42-7 
 45-0 
 
 
 
 
 
 26-0 
 28-3 
 30-6 
 32-9 
 35-1 
 37-4 
 39-7 
 42-0 
 
 
 
 
 
 26*5 
 
 28-8 
 
 25-1 
 27-4 
 30-0 
 32-6 
 
 ... 27-6 
 26-1 29-9 
 28-8 32-1 
 31-4 34-4 
 33-7 36-7 
 36-0 39-0 
 
 
 
 
 ... , ... , 
 
 AA 2 
 
356 
 
 LLOYD'S REGISTER BOILER RULES 
 
 TABLES FOB FINDING MAXIMUM PITCH OF STAYS. 
 
 The following two sets of tables contain the maximum permissible 
 pitches for various working pressures, thicknesses, and methods of 
 attachments, both for stays and stay tubes. When the cross pitches 
 are not equal, the square root of the mean of their squares should be 
 taken. If the stays or stay tubes are pitched irregularly the square 
 root of hatf of the square of the diameter of the largest inscribed circle 
 should be taken, for the pitch, or multiply it by v/0'5 = 0'707. 
 
 MAXIMUM PITCH IN INCHES OF STAYED FLAT PLATES. 
 
 
 STAYED IKON PLATES 
 
 STAYED STEEL PLATES 
 
 1 
 
 
 d 
 
 
 f 
 
 
 E-T 8. 
 
 o. 
 
 
 
 
 tf 
 
 
 EH Q. 
 
 3. 
 
 ! 
 
 
 
 1 
 
 11 
 
 
 
 |.gH 
 
 PH |f 
 
 tr 
 
 s o> 
 
 "a 
 
 -1 
 
 ii 
 
 Is, 
 
 fell 
 
 11 
 
 g 
 
 fj 
 
 H 
 
 M.2 
 
 ^ 
 
 "S x 
 
 
 la 
 
 Hi 
 
 ft 
 
 
 
 o 
 
 i>3 
 
 
 s x 
 
 jl.2 
 
 ft 
 
 
 CO 
 
 I 
 
 % 
 
 i 
 
 ft 
 
 & 
 
 sS 
 
 ^ 
 
 cc 
 
 03 
 
 | 
 
 r 
 
 ft 1 "" 
 
 d'| 
 
 I 3 
 
 Con- 
 
 stants 
 
 90 
 100 
 
 110 
 120 
 
 140 
 
 150 
 
 160 
 
 175 
 
 190 
 
 90 
 100 
 
 110 
 
 120 
 135 
 
 175 
 
 185 
 
 200 
 
 220 
 
 240 
 
 60LBS. WORKING 
 
 PRESSURE. 
 
 Ins. 1 
 
 Ins. ' Ins. 
 
 Ins. 
 
 Ins, 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 
 7-34 8-12 
 
 9-16 
 
 9-48 
 
 9-79 
 
 10-2 
 
 10-6 
 
 7-34 
 
 8-12 
 
 10-2 
 
 10-5 
 
 10-9 
 
 11-4 
 
 12-0 
 
 & 
 
 8-57 9-47 
 
 10-7 
 
 11-0 
 
 11-4 
 
 11-9 
 
 12-4 
 
 8-57 
 
 9-47 
 
 11-9 
 
 12-2 
 
 12-7 
 
 13-4 
 
 14-0 
 
 i 
 
 10-2 11-3 
 
 12-2 
 
 12-6 
 
 13-0 
 
 13-6 
 
 14-2 
 
 10-2 
 
 11-3 
 
 13-6 
 
 14-0 
 
 14-6 
 
 15-3 
 
 16-0 
 
 ft 
 
 11-5 
 
 12-7 
 
 13-7 
 
 14-2 
 
 14-6 
 
 15-3 
 
 16-0 
 
 11-5 
 
 13-5 
 
 15-3 
 
 15-8 
 
 16-4 
 
 17-2 
 
 18-0 
 
 f 
 
 12-8 
 
 14-1 
 
 15-2 
 
 15-8 
 
 16-3 
 
 17-0 
 
 17-7 
 
 12-8 
 
 15-0 
 
 17-0 
 
 17-5 
 
 18-2 
 
 19-1 
 
 20-0 
 
 tt 
 
 14-1 
 
 15-5 
 
 16-8 
 
 17-3 
 
 17-9 
 
 18-7 
 
 19-5 
 
 14-1 
 
 16-5 
 
 18-7 
 
 19-3 
 
 20-1 
 
 21-1 
 
 
 f 
 
 15-4 
 
 16-9 
 
 18-3 
 
 18-9 
 
 19-5 
 
 20-4 
 
 21-2 
 
 15-4 
 
 18-0 
 
 20-4 
 
 21-1 
 
 
 ... 
 
 ... 
 
 4 13 
 
 16-7 
 
 18-3 
 
 19-8 
 
 20-6 
 
 21-2 
 
 
 
 16-7 
 
 19-5 
 
 
 
 
 
 
 16 
 
 18-0 
 
 19-7 
 
 21-3 
 
 
 
 
 
 18-0 
 
 21-0 
 
 
 
 
 
 
 15 
 
 19'3 
 
 21-1 
 
 
 
 
 
 
 19-3 
 
 
 
 
 
 
 
 1 16 
 
 20-6 
 
 
 
 
 
 
 
 20-6 
 
 
 
 
 
 
 ... I 
 
 
 
 
 
 
 
 
 
 
 
 
 1 "" 
 
 
 
 80 LBS. WORKING PRESSURE. 
 
 a 
 
 6-36 
 
 7-03 
 
 7-93 
 
 8-21 
 
 8-48 
 
 8-87 
 
 9-24 
 
 6-36 
 
 7-03 
 
 8-87 
 
 9-12 
 
 9-48 
 
 9-95 
 
 10-3 
 
 ft 
 
 7-42 
 
 8-20 
 
 9-26 
 
 9-58 
 
 9-89 
 
 10-3 
 
 10-7 
 
 7-42 
 
 8-21 
 
 10-3 
 
 10-6 
 
 11-0 
 
 11-6 
 
 12-1 
 
 i 
 
 8-94 
 
 10-79 
 
 10-6 
 
 10-9 
 
 11-3 
 
 11-8 
 
 12-3 
 
 8-94 
 
 9-89 
 
 11-8 
 
 12-1 
 
 12-6 
 
 13-2 
 
 13-8 
 
 3 & 
 
 10-0 
 
 11-0 
 
 11-9 
 
 12-3 
 
 12-7 
 
 13-3 
 
 13-8 
 
 10-0 
 
 11-6 
 
 13-3 
 
 13-6 
 
 14-2 
 
 14-9 
 
 15-5 
 
 1 
 
 11-1 
 
 12-2 
 
 13-2 
 
 13-6 
 
 14-1 
 
 14-7 
 
 15-4 
 
 11-1 
 
 12-9 
 
 14-7 
 
 15-2 
 
 15-8 
 
 16-5 
 
 17-3 
 
 
 12-2 
 
 13-4 
 
 14-5 
 
 15-0 
 
 15-5 
 
 16-2 
 
 16-9 
 
 12-2 
 
 14-2 
 
 16-2 
 
 16-7 
 
 17-3 
 
 18-2 
 
 19-0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 I 
 
 f 
 
 13-4 
 
 14-6 
 
 15-8 
 
 16-4 
 
 16-9 
 
 17-7 
 
 18-4 
 
 13-4 
 
 15-5 
 
 17-7 
 
 18-2 
 
 18-9 
 
 19-9 
 
 20-8 
 
 
 14-5 
 
 15-9 
 
 17-1 
 
 17-8 
 
 18-3 
 
 19-2 
 
 20-0 
 
 14-5 
 
 16-8 
 
 19-2 
 
 19-7 
 
 20-5 
 
 21-6 
 
 
 JL 
 
 15-6 
 
 17-1 
 
 18-5 
 
 19-1 
 
 19-7 
 
 20-6 
 
 ... 
 
 15-6 
 
 18-1 
 
 20-7 
 
 21-3 
 
 ... 
 
 ... 
 
 ... 
 
 8 15 
 
 16-7 
 
 18-3 
 
 19-8 
 
 20-5 
 
 21-2 
 
 
 
 16'7 
 
 19-4 
 
 
 
 
 
 
 16 
 1 
 
 17-8 
 
 19-5 
 
 21-2 
 
 
 
 
 
 17-8 
 
 20-7 
 
 
 
 
 
 
 
 19-0 
 
 20-8 
 
 
 
 
 
 
 19-0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
LLOYD'S REGISTER BOILER RULES 
 
 357 
 
 1 
 
 STAYED IRON PLATES 
 
 STATED STEEL PLATES 
 
 1 
 
 
 i 
 
 -1 1 
 
 S rf rt E_. 
 
 *~ |x.f 
 
 h 
 
 3 
 
 1 
 
 si 
 
 of 
 
 * 
 
 x.f 
 
 a. 
 
 M 
 
 "3 'O 
 
 
 "S Hr U) f" 1 
 
 
 W S 
 
 a ^ 
 
 
 ~ 
 
 
 
 PH g OQ 
 
 
 
 
 || 
 
 s 
 
 *j I"*" 
 
 *0J 4) ,-fcl " O 
 
 
 11 
 
 3 
 
 ** 
 
 c3 r * 1 
 
 ~~ *"** 
 
 
 fccS 
 
 I 
 
 
 r 
 
 If ' 
 
 ^|pjj 
 
 jf!i 
 
 If 
 
 >> 
 
 fa 
 
 0? 
 
 si 
 
 5i 
 
 . X 
 
 d"** 
 
 1|| 
 
 tt 
 8 
 
 1 
 
 02 
 
 1 
 
 -* o 
 
 5 
 
 J 
 
 8r 
 
 cc 
 
 1 
 
 *a 
 
 6 
 
 fi 
 
 ft' ^ 
 
 1 
 
 Oon- 
 
 stauts 
 
 90 
 
 100 
 
 110 
 120 
 
 140 150 
 
 160 
 
 175 
 
 190 
 
 90 
 100 
 
 110 
 120 
 135 
 
 175 
 
 185 
 
 200 
 
 220 
 
 240 
 
 
 
 
 
 100 LBS. We 
 
 RKING 
 
 PRESSURE. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. Ins. 
 
 Ins. Ins. Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. Ins. 
 
 
 5-79 
 
 6-29 
 
 7-09 
 
 7-34 
 
 7-58 
 
 7-93 
 
 8-27 
 
 5-79 
 
 6-29 7-93 
 
 8-16 
 
 8-48 
 
 8'89 
 
 9-29 
 
 ^ 
 
 6-64 
 
 7-34 
 
 8-28 8-57! 8-85 
 
 9-26 
 
 9-64 
 
 6-64 
 
 7-34 
 
 9-26 
 
 9-52 
 
 9-89 
 
 10-3 
 
 10-8 
 
 i 
 
 8-00 8-76 
 
 9-46 9-79 
 
 10-1 
 
 10-6 
 
 11-0 
 
 8-00 
 
 8-76 
 
 10-6 
 
 10-8 
 
 11-3 
 
 11-8 
 
 12-3 
 
 2 T5 
 
 9-00 
 
 9-85 
 
 10-6 
 
 11-0 
 
 11-3 
 
 11-9 
 
 12-4 
 
 9-00 10-4 
 
 11-9 
 
 12-2 
 
 12-7 
 
 13-3 
 
 13-9 
 
 1G 
 
 10-0 
 
 10-9 
 
 11-8 
 
 12-2 
 
 12-6 
 
 13-2 
 
 13-7 
 
 10-0 
 
 11-6 
 
 13-2 
 
 13-6 
 
 14-1 
 
 14-8 
 
 15-4 
 
 11 
 
 11-0 
 
 12-0 
 
 13-0 
 
 13-4 
 
 13-9 
 
 14-5 
 
 15-1 
 
 11-0 
 
 12-7 
 
 14-5 
 
 14-9 
 
 15-5 
 
 16-3 
 
 17-0 
 
 | 
 
 12-0 
 
 13-1 
 
 14-1 
 
 14-6 
 
 15-1 
 
 15-8 
 
 16-5 
 
 12-0 
 
 13-9 
 
 15-8 
 
 16-3 
 
 16-9 
 
 17-7 
 
 18-5 
 
 4 
 
 13-0 
 
 14-2 
 
 15-3 
 
 15-9 
 
 16-4 
 
 17-1 
 
 17-9 
 
 13-0 
 
 15-1 
 
 17-1 
 
 17-6 
 
 18-3 
 
 19-2 
 
 20-1 
 
 * 
 
 14-0 
 
 15-3 
 
 16-5 
 
 17-1 
 
 17-7 
 
 18-5 
 
 19-2 
 
 14-0 
 
 16-2 
 
 18-5 
 
 19-0 
 
 19-7 
 
 20-7 
 
 ... 
 
 
 15-0 
 
 16-4 
 
 17-7 
 
 18-3 
 
 18-9 
 
 19-8 
 
 20-6 
 
 15-0 
 
 17-4 
 
 19-8 
 
 20-4 
 
 21-1 
 
 ... 
 
 
 
 1 
 
 16-0 
 
 17-5 
 
 18-9 
 
 19-5 
 
 20-2 
 
 21-1 
 
 ... 
 
 16-0 
 
 18-5 
 
 21-1 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 1 ^ 
 
 17-0 
 
 1Q.fi 
 
 20-1 
 
 20-8 
 
 
 
 
 17-0 
 
 19-7 
 
 
 
 
 
 
 11 
 
 X f U 
 
 18-0 
 
 XO \J 
 1Q.7 
 
 
 
 ... 
 
 ... 
 
 
 ift-n 
 
 20-9 
 
 
 
 
 
 
 S 
 
 XO v 
 
 J-*7 1 
 
 120 LBS. WORKING PRESSURE. 
 
 | 
 
 6-19 5-74 
 
 6-48J 6-70 
 
 6-92 
 
 7-24i 7-55 
 
 5-19 
 
 5-74 
 
 7-24 
 
 7-44 7-74 
 
 8-12 
 
 8-48 
 
 8 
 
 6-06 6-70 
 
 7-561 7-82 
 
 8-07 
 
 8-45 
 
 8-80 
 
 6-06 
 
 6-70 
 
 8-45 
 
 8-69 9-03 
 
 9-47 
 
 9-89 
 
 13 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 7-30 8-00 
 
 8-64 
 
 8-94 
 
 9-23 
 
 9-66 
 
 10-0 
 
 7-30 
 
 8-00 
 
 9-66 
 
 9-93 
 
 10-3 
 
 10-8 
 
 11-3 
 
 2 9 
 
 8-21 9-00 
 
 9-72 
 
 10-0 
 
 10-3 
 
 10-8 
 
 11-3 
 
 8-21 
 
 9-54 
 
 10-8 
 
 11-1 
 
 11-6 
 
 12-1 
 
 12-7 
 
 f^ 
 
 9-12 10-0 
 
 10-8 
 
 11-1 
 
 11-5 
 
 12-0 
 
 12-5 
 
 9-12 
 
 10-6 
 
 12-0 
 
 12-4 
 
 12-9 
 
 13-5 
 
 14-1 
 
 B 
 
 10-0 
 
 11-0 
 
 11-8 
 
 12-2 
 
 12-7 
 
 13-2 
 
 13-8 
 
 10-0 
 
 11-6 
 
 13-2 
 
 13-6 
 
 14-2 
 
 14-8 
 
 15-5 
 
 3 
 
 10-9 
 
 12-0 
 
 12-9 
 
 13-4 
 
 13-8 
 
 14-4 
 
 15-1 
 
 10-9 
 
 12-7 
 
 14-4 
 
 14-8 
 
 15-4 
 
 16-2 
 
 16-9 
 
 4 13 
 
 11-8 13-0 
 
 14-0 
 
 14-5 
 
 15-0 
 
 15-7 
 
 16-3 
 
 11-8 
 
 13-7 
 
 15-7 
 
 16-1 
 
 16-7 
 
 17-6 
 
 18-3 
 
 i" 
 
 12-7 
 
 14-0 
 
 15-1 
 
 15-6 
 
 16-1 
 
 16-9 
 
 17-6 
 
 12-7 
 
 14-8 
 
 16-9 
 
 17-4 
 
 18-0 
 
 18-9 
 
 19-7 
 
 'if 
 
 13-6 
 
 15-0 
 
 16-2 
 
 16-7 
 
 17-3 
 
 18-1 
 
 18-8 
 
 13-6 
 
 15-9 
 
 18-1 
 
 18-6 
 
 19-3 
 
 20-3 
 
 21-1 
 
 1 
 
 14-6 
 
 16-0 
 
 17-2 
 
 17-8 
 
 18-4 
 
 19-3 
 
 20-0 
 
 14-6 
 
 16-9 
 
 19-3 
 
 19-8 
 
 20-6 
 
 ... 
 
 ... 
 
 
 15-5 
 
 17-0 
 
 18-3 19-0 
 
 19-6 
 
 20-5 
 
 ... 
 
 15-5 
 
 18-0 
 
 20-5 
 
 21-0 
 
 ... 
 
 ... 
 
 ... 
 
 _ T ^"** 
 
 lfi-4. 
 
 IQ.ft ! 1Q-.1 QftO 
 
 20*8 
 
 
 
 ifi-4 
 
 iQ-n 
 
 
 
 
 
 
 XO ^ JUJ Vf 1 / "X | **v A 
 
 140 LBS. WORKING PRESSURE. 
 
 a 
 
 4-81 
 
 5-31 
 
 6-00; 6-21 
 
 6-41 
 
 6-70 
 
 7-02 
 
 4-81 
 
 5-31 
 
 6-70 
 
 6-89 
 
 7-17 
 
 7-51 
 
 7-85 
 
 JL 
 
 5-61 
 
 6-20 
 
 7-00 7-24 
 
 7-48 
 
 7-82 
 
 8-19 
 
 5-61 
 
 6-20 
 
 7-82 
 
 8-04 
 
 8-36 
 
 8-76 
 
 9-16 
 
 | 
 
 6-76 
 
 7-40 
 
 8-00! 8-28 
 
 8-55 
 
 8-94 
 
 9-36 
 
 6-76 
 
 7-40 
 
 8-94 
 
 9-19 
 
 9-56 
 
 10-0 
 
 10-5 
 
 * 
 
 7-60 
 
 8-32 
 
 9-00 1 9-31 
 
 9-62 
 
 10-0 
 
 10-5 
 
 7-60 
 
 8-83 
 
 10-0 
 
 10-3 
 
 10-7 
 
 11-2 
 
 11-8 
 
 1 
 
 8-45 9-25 
 
 10-0 
 
 10-3 
 
 10-G 
 
 11-1 
 
 11-7 
 
 8-45 
 
 9-81 
 
 11-1 
 
 11-4 
 
 11-9 
 
 12-5 
 
 13-1 
 
 ft 
 
 9-29 
 
 10-2 
 
 11-0 
 
 11-3 
 
 11-7 
 
 12-2 
 
 12-8 
 
 9-29 
 
 10-8 
 
 12-2 
 
 12-6 
 
 13-1 
 
 13-7 
 
 14-4 
 
 8 
 
 10-1 
 
 11-1 
 
 12-0 
 
 12-4 
 
 12-8 
 
 13-4 
 
 14-0 
 
 10-1 
 
 11-7 
 
 13-4 
 
 13-8 
 
 14-3 
 
 15-0 
 
 15-7 
 
 la 
 
 10-9 
 
 12-0 
 
 13-0 
 
 13-4 
 
 13-8 
 
 14-5 
 
 15-2 
 
 10-9 
 
 12-7 
 
 14-5 
 
 14-9 
 
 15-5 
 
 16-2 
 
 17-0 
 
 ? 16 
 
 11-8 
 
 12-9 
 
 14-0 
 
 14-4 
 
 14-9 
 
 15-6 
 
 16-3 
 
 11-8 
 
 13-7 
 
 15-6 
 
 16-0 
 
 16-7 
 
 17-5 
 
 18-3 
 
 8 i| 
 
 12-6 
 
 13-8 
 
 15-0 
 
 15-5 
 
 16-0 
 
 16-7 
 
 17-5 
 
 12-6 
 
 14-7 
 
 16-7 
 
 17-2 
 
 17-9 
 
 18-7 
 
 19-6 
 
 3 
 
 13-5 
 
 14-8 
 
 16-0 
 
 16-5 
 
 17-1 
 
 17-8 
 
 18-7 
 
 13-5 
 
 15-7 
 
 17-8 
 
 18-3 
 
 19-1 
 
 20-0 
 
 20-9 
 
 j_i_ 
 
 14-3 
 
 15-7 
 
 17-0 
 
 17-5 
 
 18-1 
 
 19-0 
 
 19-9 
 
 14-3 
 
 16-6 
 
 19-0 
 
 19-5 
 
 20-3 
 
 ... 
 
 ... 
 
 ( x i l< 
 
 15-2 
 
 16-6 
 
 18-0 
 
 18-6 
 
 19-2 
 
 20-1 
 
 21-1 
 
 15-2 
 
 17-6 
 
 20-1 
 
 20-fi 
 
 
 ... 
 
 
868 
 
 LLOYD'S REGISTER BOILER RULES 
 
 
 STAYED IRON" PLATES 
 
 STAYED STEEL PLATES 
 
 
 
 
 
 
 of 
 
 
 PH 
 
 
 
 
 
 
 
 
 
 H 2 
 
 55 
 
 Plate Thicknw 
 
 Stay Ends 
 Riveted 
 
 i 
 
 11 
 
 f! 
 
 "p 
 
 Do. & Washer 
 JPxJT 
 
 Do. Washers, 
 Riveted, 
 fPxJT 
 
 Do. Do., P X ' 
 or across 
 Doubling Strip 
 
 Doubling Strip 
 Lengthways 
 
 1 
 
 Stays Nutted 
 
 Stays with 
 Double Nuts 
 
 6~ 
 
 Do. Riveted, 
 fPxJT 
 
 Do. Do., P x 
 or across 
 Doubling Strip 
 
 Doubling Strip 
 Lengthways 
 
 Con- 
 stants 
 
 90 
 100 
 
 110 
 120 
 
 140 
 
 150 
 
 160 
 
 175 
 
 190 
 
 90 
 100 
 
 110 
 120 
 135 
 
 175 
 
 185 
 
 200 
 
 220 
 
 240 
 
 
 
 
 
 
 160 LBS. WORKING 
 
 PRESSURE. 
 
 
 
 
 
 Ins. 
 
 Ins. Ins. Ins. 
 
 Ins. I Ins. Ins. Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. 
 
 Ins. Ins. 
 
 Ins. 
 
 f 
 
 4-50 
 
 4-97 5-61 
 
 5-80 6-00 
 
 6-27j 6-53 
 
 4-50 
 
 4-97 
 
 6-27 
 
 6-45 
 
 6-70 7-03 
 
 7-34 
 
 T 
 
 5-25 
 
 5-80 6-54 
 
 6-77 
 
 7-00 
 
 7-31 
 
 7-62 
 
 5-25 
 
 5-80 
 
 7-31 
 
 7-52 
 
 7-82 
 
 8-20 
 
 3-57 
 
 * 9 
 
 6-32 
 
 6-93 7-48 
 
 7-74 
 
 8-00 
 
 8-36 
 
 8-71 
 
 6-32 
 
 6-93 
 
 8-36 
 
 8-60 
 
 8-94 
 
 9-38 
 
 9-80 
 
 
 7-11 
 
 7-79 8-41 
 
 8-71 9-00 
 
 9-41 
 
 9-80 
 
 7-11 
 
 8-26 
 
 9-41 
 
 9-67 
 
 10-0 
 
 10-5 
 
 11-0 
 
 4 
 
 7-90 
 
 8-66 9-35 
 
 9-68 10-0 
 
 10-4 
 
 10-8 
 
 7-90 
 
 9-18 
 
 10-4 
 
 10-7 
 
 11-1 
 
 11-7 
 
 12-2 
 
 ft 
 
 8-69 
 
 9-53, 10-2 
 
 10-6 11-0 
 
 11-5 
 
 11-9 
 
 8-69 
 
 10-1 
 
 11-5 
 
 11-8 
 
 12-2 
 
 12-9 
 
 13-4 
 
 f 
 
 9-48 
 
 10-3 
 
 11-2 
 
 11-6 
 
 12-0 
 
 12-5 
 
 13-0 
 
 9-48 
 
 11-0 
 
 12-5 
 
 12-9 
 
 13-4 
 
 14-0 
 
 14-6 
 
 7 n 
 
 10-2 
 
 11-2 
 
 12-1 
 
 12-5 
 
 13-0 
 
 13-5 
 
 14-1 
 
 10-2 
 
 11-9 
 
 13-5 
 
 13-9 
 
 14-5 
 
 15-2 
 
 15-9 
 
 
 11-0 
 
 12-1 
 
 13-0 
 
 13-5 
 
 14-0 
 
 14-6 
 
 15-2 
 
 11-0 
 
 12-8 
 
 14-6 
 
 15-0 
 
 15-6 
 
 16-4 
 
 17-1 
 
 it 
 
 11-8 
 
 12-9 
 
 14-0 
 
 14-5 
 
 15-0 
 
 15-6 
 
 16-3 
 
 11-8 
 
 13-7 
 
 15-6 
 
 16-1 
 
 16-7 
 
 17-5 
 
 18-3 
 
 1 
 
 12-6 
 
 13-8 
 
 14-9 
 
 15-4 
 
 16-0 
 
 16-7 
 
 17-4 
 
 12-6 
 
 14-7 
 
 16-7 
 
 17-2 
 
 17-8 
 
 18-7 
 
 19-5 
 
 1_L 
 
 13-4 
 
 14-7 
 
 15-9 
 
 16-4 
 
 17-0 
 
 17-7 
 
 18-5 
 
 13-4 
 
 15-6 
 
 17-7 
 
 18-2 
 
 19-0 
 
 19-9 
 
 208 
 
 1| 
 
 14-2 
 
 15-5 
 
 16-8 
 
 17-4 
 
 18-0 
 
 18-8 
 
 19-6 
 
 14-2 
 
 16-5 
 
 18-8 
 
 19-3 
 
 20-1 
 
 21-0 
 
 ... 
 
 180 LBS. WORKING PRESSURE. 
 
 f 
 
 4-24 
 
 4-69 
 
 5-29 5-47| 5-65| 5-91 6-16 
 
 4-24 
 
 4-69 5-91 
 
 6-08 6-32 
 
 6-63 6-92 
 
 ft 
 
 4-94 
 
 547 
 
 6-17 
 
 6-39 
 
 6-59 
 
 6-90 
 
 7-19 
 
 4-94 
 
 5-47 6-90 
 
 7-09 7-37 
 
 7-74 
 
 8-08 
 
 1 
 
 5-96 
 
 6-53 
 
 7-05 
 
 7-30 
 
 7-54 
 
 7-88 
 
 8-22 
 
 5-96 
 
 6-53 7-88 
 
 8-11 8-43 
 
 8-84 
 
 9-23 
 
 ft 
 
 6-70 
 
 7-34 
 
 7-93 
 
 8-21 
 
 8-48 
 
 8-87 
 
 9-24 
 
 6-70 
 
 7-79 8-87 
 
 9-12 9-48 
 
 9-94 
 
 10-3 
 
 | 
 
 7-45 
 
 8-16 
 
 8-81 
 
 9-12 
 
 9-42 
 
 9-86 
 
 10-2 
 
 7-45 
 
 8-66 9-86 
 
 10-1 jlO-5 
 
 11-0 
 
 11-5 
 
 
 8-19 
 
 8-98 
 
 9-70 
 
 10-0 
 
 10-3 
 
 10-8 
 
 11-3 
 
 8-19 
 
 9-52 
 
 10-8 
 
 11-1 
 
 11-5 
 
 12-1 
 
 12-7 
 
 ! 
 
 8-94 
 
 9-79 
 
 10-5 
 
 10-9 
 
 11-3 
 
 11-8 
 
 12-3 
 
 8-94 
 
 10-3 
 
 11-8 
 
 12-1 
 
 12-6 
 
 13-2 
 
 13-8 
 
 tf 
 
 9-68 
 
 10-6 
 
 11-4 
 
 11-8 
 
 12-2 
 
 12-8 
 
 13-3 
 
 9-68 
 
 11-2 
 
 12-8 
 
 13-1 
 
 13-7 
 
 14-3 
 
 15-0 
 
 
 10-4 
 
 11-4 
 
 12-3 
 
 12-7 
 
 13-1 
 
 13-8 
 
 14-3 
 
 10-3 
 
 12-1 
 
 13-8 
 
 14-1 
 
 14-7 
 
 15-4 
 
 16-1 
 
 H 
 
 11-1 
 
 12-2 
 
 13-2 
 
 13-6 
 
 14-1 
 
 14-7 
 
 15-4 
 
 11-1 
 
 12-9 
 
 14-7 
 
 15-2 
 
 15-8 
 
 16-5 
 
 17'3 
 
 i 
 
 11-9 
 
 13-0 
 
 14-1 
 
 14-6 
 
 15-0 
 
 157 
 
 16-4 
 
 11-9 
 
 13-8 
 
 15-7 
 
 16-2 
 
 16-8 
 
 17-6 
 
 18-4 
 
 1JL 
 
 12-6 
 
 13-8 
 
 14-9 
 
 15-5 
 
 16-0 
 
 16-7 
 
 17-4 
 
 12-6 
 
 14-7 
 
 16-7 
 
 17-2 
 
 17-9 
 
 18-7 
 
 19-6 
 
 *8 
 
 13-4 
 
 14-6 
 
 15-8 
 
 16-4 
 
 16-9 
 
 17-7 
 
 18-4 
 
 13-4 
 
 15-5 
 
 17-7 
 
 18-2 
 
 18-9 
 
 19-8 
 
 20-7 
 
 200 LBS. WORKING PRESSURE. 
 
 f 
 
 4-02 4-44 5-02 
 
 5-19 
 
 5-36 
 
 5-61 5-84 
 
 4-02 4-441 5-61 
 
 5-77 6-00 6-29 6-57 
 
 ft 
 
 4-69; 5-19 5-85 
 
 6-06 
 
 6-26 
 
 6-24 6-82 
 
 4-69 5-19 
 
 6-54 
 
 6-73 7-00 
 
 7-34 7-66 
 
 I 
 
 5-65 6-19 
 
 6-69 
 
 6-92 
 
 7-15 
 
 7-48 1 7-79 
 
 5-65 6-19 
 
 7-48 
 
 7-69 8-00 
 
 8-39 8-76 
 
 A 
 
 6-36 6-97 
 
 7-53 
 
 7-79 
 
 8-05 
 
 8-41 8-77 
 
 6-36 7-39 
 
 8-41 
 
 8-65 9-00 
 
 9-43 9-85 
 
 
 7-07 7-74 
 
 8-36 
 
 8-66 
 
 8-94 
 
 9-35 
 
 9-74 
 
 7-07 8-21 
 
 9-35 
 
 9-61 10-0 
 
 10-4 
 
 10-9 
 
 *M 
 
 7-77; 8-52 
 
 9-20 
 
 9-52 
 
 9-83 
 
 10-2 
 
 10-7 
 
 7-77 9-03 
 
 10-2 
 
 10-5 
 
 11-0 
 
 11-5 
 
 12-0 
 
 f 
 
 8-48 9-29 
 
 10-0 
 
 10-3 
 
 10-7 
 
 11-2 
 
 11-6 
 
 8-48 1 9-85 
 
 11-2 
 
 11-5 
 
 12-0 
 
 12-5 
 
 13-1 
 
 it 
 
 9-19 10-0 
 
 10-8 
 
 11-2 
 
 11-6 
 
 12-1 
 
 12-6 
 
 9-19 10-6 
 
 12-1 
 
 12-5 
 
 13-0 
 
 13-6 
 
 14-2 
 
 
 9-89 
 
 10-8 
 
 11-7 
 
 12-1 
 
 12-5 
 
 13-0 
 
 13-6 
 
 9-89 11-5 
 
 13-0 
 
 13-4 
 
 14-0 
 
 14-6 , 15-3 
 
 it 
 
 10-6 
 
 11-6 
 
 12-5 
 
 12-9 
 
 13-4 
 
 14-0 
 
 14-6 
 
 10-6 
 
 12-3 
 
 14-0 
 
 14-4 
 
 15-0 
 
 15-7 16-4 
 
 i 
 
 11-3 
 
 12-3 
 
 13-3 
 
 13-8 
 
 14-3 
 
 14-9 
 
 15-5 
 
 11-3 
 
 13-1 
 
 14-9 
 
 15-3 
 
 16-0 
 
 16-7 17-5 
 
 1JL 
 
 12-0 
 
 13-1 
 
 14-2 
 
 14-7 
 
 15-2 
 
 15-9 
 
 16-5 
 
 12-0 
 
 13-9 
 
 15-9 
 
 16-3 
 
 17-0 
 
 17-8 18-6 
 
 1* 
 
 12-7 
 
 13-9 
 
 15-0 
 
 15-5 
 
 16-1 
 
 16-8 
 
 17-5 
 
 12-7 
 
 14-7 
 
 16-8 
 
 17-3 
 
 18-0 
 
 19-8 19-7 
 
LLOYD'S REGISTER BOILER RULES 
 
 359 
 
 PITCH IN INCHES OP TUBE PLATE STAYS, CENTBE TO CENTRE. 
 
 Plate Thickness 
 
 . 1 
 
 Mean Pitch In Nest 
 of Tubea 
 
 WIDE WATEB SPACES 
 
 1 
 S^ 
 
 WIDE WATEB SPACES 
 
 Stay Ends Beaded 
 
 Stay Ends Nutted 
 
 Stay Ends Beaded 
 
 Stay Ends Nutted 
 
 Number of Plain Tubes between Stays 
 
 Number of Plain Tubes between Stays 
 
 
 
 l 
 
 2 
 
 
 
 i 
 
 2 
 
 
 
 1 
 
 3 
 
 
 
 1 
 
 s 
 
 Con- 
 stants 
 
 140 
 
 160 
 
 140 
 
 120 
 
 170 
 
 150 
 
 130 
 
 140 
 
 160 
 
 140 
 
 120 
 
 170 
 
 150 
 
 130 
 
 60 LBS. 
 
 WORKING PRESSURE. 
 
 1 
 
 100 LBS. WORKING PRESSURE. 
 
 1 
 
 A 
 
 9-16 
 10-7 
 
 9-80 
 11-4 
 
 9-16 
 10-7 
 
 8-48 
 9-90 
 
 10-1 
 U-8 
 
 9-49 
 11-1 
 
 8-83 
 10-3 
 
 7-10 
 8-28 
 
 7'59 
 8-85 
 
 7-10 
 
 8-28 
 
 6-57 
 7-67 
 
 7-82 
 9-13 
 
 7-35 
 8-57 
 
 6-84 
 7-98 
 
 i 
 
 12-2 
 
 13-1 
 
 12-2 
 
 11-3 
 
 13-5 
 
 12-6 
 
 11-8 
 
 9-47 
 
 10-1 
 
 9-47 
 
 8-76 
 
 10-4 
 
 9-80 
 
 9-12 
 
 A 
 
 13-7 
 
 14-7 
 
 13-7 
 
 12-7 
 
 15-1 
 
 14-2 
 
 13-2 
 
 10-6 
 
 11-4 
 
 10-6 
 
 9-86 
 
 11-7 
 
 11-0 
 
 10-3 
 
 1 
 
 15-3 
 
 16-3 
 
 15-3 
 
 14-1 
 
 16-8 
 
 15-8 
 
 14-7 
 
 11-8 
 
 12-6 
 
 11-8 
 
 11-0 
 
 13-0 
 
 12-2 
 
 11-4 
 
 tt 
 
 16-8 
 
 18-0 
 
 16-8 
 
 15-6 
 
 18-5 
 
 17-4 
 
 16-2 
 
 13-0 
 
 13-9 
 
 13-0 
 
 12-0 
 
 14-3 
 
 13-5 
 
 12-5 
 
 I 
 
 it 
 
 18-3 
 19-9 
 
 19-6 
 21-2 
 
 18-3 
 19-9 
 
 17-0 
 
 18-4 
 
 20-2 
 
 19-0 
 20-6 
 
 17-7 
 19-1 
 
 14-2 
 15-4 
 
 15-2 
 16-4 
 
 14-2 
 15-4 
 
 13-1 
 14-2 
 
 15-6 
 16-9 
 
 14-7 
 15-9 
 
 13-7 
 
 14-8 
 
 $ 
 
 21-4 
 
 ... 
 
 21-4 
 
 19-8 
 
 ... 
 
 ... 
 
 20-6 
 
 16-6 
 
 17-7 
 
 16-6 
 
 15-3 
 
 18-3 
 
 17-1 
 
 16-0 
 
 i 
 
 ... 
 
 ... 
 
 ... 
 
 21-1 
 
 ... 
 
 ... 
 
 ... 
 
 17-7 
 
 18-9 
 20-1 
 
 19-0 
 20-2 
 
 17-7 
 
 18-9 
 20-1 
 
 16-4 
 
 17-5 
 
 18-6 
 19-7 
 
 ORKINC 
 
 19-6 
 20-9 
 
 t PRES 
 
 19-4 
 
 19-6 
 20-8 
 
 SURE. 
 
 17-1 
 
 18-2 
 
 19-4 
 20-5 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 80 LBS. WORKING PRESSURE. 
 
 120 LBS. W 
 
 f 
 
 7-94 
 
 8-49 
 
 7-94 
 
 7-35 
 
 8-75 
 
 8-22 
 
 7-65 
 
 6-48 
 
 6-93 
 
 648 
 
 6-00 
 
 7-14 
 
 6-71 
 
 6-24 
 
 A 
 
 9-26 
 
 9-90 
 
 9-26 
 
 8-57 
 
 10-2 
 
 9-58 
 
 8-92 
 
 7-56 
 
 8-07 
 
 7-56 
 
 7-00 
 
 8-33 
 
 7-83 
 
 7-29 
 
 $ 
 
 10-7 
 
 11-3 
 
 10-7 
 
 9-79 
 
 11-7 
 
 11-0 
 
 10-2 
 
 8-64 
 
 9-24 
 
 8-64 
 
 8-00 
 
 9-52 
 
 8-94 
 
 8-33 
 
 A 
 
 11-9 
 
 12-7 
 
 11-9 
 
 11-0 
 
 13-1 
 
 12-3 
 
 11-5 
 
 9-72 
 
 10-4 
 
 9-72 
 
 9-00 
 
 10-7 
 
 10-1 
 
 9-37 
 
 f 
 
 13-2 
 
 14-1 
 
 13-2 
 
 12-2 
 
 14-6 13-7 
 
 12-7 
 
 10-8 
 
 11-5 
 
 10-8 
 
 10-0 
 
 11-9 
 
 11-2 
 
 10-4 
 
 g 
 
 14-6 
 
 15-6 
 
 14-6 
 
 13-5 
 
 16-0 15-1 
 
 14-0 
 
 11-9 
 
 12-7 
 
 11-9 
 
 11-0 
 
 13-1 
 
 12-3 
 
 11-4 
 
 1 
 
 15-9 
 
 17-0 
 
 15-9 
 
 14-7 
 
 17-5 16-4 
 
 15-3 
 
 13-0 
 
 13-9 
 
 13-0 
 
 12-0 
 
 14-3 
 
 13-4 
 
 12-5 
 
 if 
 
 17-2 
 
 18-4 
 
 17-2 
 
 15-9 
 
 18-9 17-8 
 
 16-6 
 
 14-0 
 
 15-0 
 
 14-0 
 
 13-0 
 
 15-5 
 
 14-5 
 
 13-5 
 
 ^ 
 
 18-5 
 
 19-8 
 
 18-5 
 
 17-1 
 
 20-4 
 
 19-2 
 
 17-8 
 
 15-1 
 
 16-2 
 
 15-1 
 
 14-0 
 
 16-7 
 
 15-7 
 
 14-6 
 
 it 
 
 19-8 
 
 21-2 
 
 19-8 
 
 18-4 
 
 ... 
 
 20-5 
 
 19-1 
 
 16-2 
 
 17-3 
 
 16-2 
 
 15-0 
 
 17-9 
 
 16-8 
 
 15-6 
 
 i 
 
 21-2 
 
 ... 
 
 21-2 
 
 19-6 
 
 ... 
 
 ... 
 
 20-4 
 
 17-3 
 
 18-5 
 
 17-3 
 
 16-0 
 
 19-0 
 
 17-9 
 
 16-7 
 
 M 
 
 ... 
 
 ... 
 
 ... 
 
 20-8 
 
 ... 
 
 ... 
 
 ... 
 
 18-4 
 19-4 
 
 19-6 
 20-8 
 
 18-4 
 19-4 
 
 17-0 
 18-0 
 
 20-2 
 
 19-0 
 20-1 
 
 17-7 
 18-7 
 
 i 
 
 
 
 
 
 
 
360 
 
 LLOYD'S REGISTER BOILER RULES 
 
 PITCHES IN INCHES OF TUBE PLATE STAYS, CENTBE TO CENTRE. 
 
 i 
 
 s 
 
 
 
 
 
 I 
 
 Con- 
 stants 
 
 Mean Pitch In Nest i 
 of Tubes 
 
 ! 
 
 WIDE WATER SPACES 
 
 Mean Pitch in Nest 
 of Tubes 
 
 WIDE WATER SPACES 
 
 Stay Ends Beaded 
 
 Stay Ends Nutted 
 
 Stay Ends Beaded 
 
 Stay Ends Nutted 
 
 Number of Plain Tabes between Stays 
 
 Number of Plain Tubes between Stays 
 
 
 
 l 
 
 2 
 
 
 
 1 
 
 2 
 
 
 
 1 
 
 2 
 
 
 
 i 
 
 2 
 
 140 
 
 160 
 
 1 140 
 
 120 
 
 170 
 
 150 
 
 130 
 
 140 
 
 160 
 
 140 
 
 120 
 
 170 
 
 150 
 
 130 
 
 '1 | | 1 
 140 LBS. WORKING PRESSURE. 
 
 180 LBS. WORKING PRESSURE. 
 
 1 
 
 6-00 
 
 6-41 
 
 6-00 
 
 5-55 
 
 6-61 
 
 6-21 5-82 
 
 5-29 
 
 5-66 5-29 
 
 4-90 
 
 5-83| 5-48 
 
 6-10 
 
 
 
 7-00 
 
 7-48 
 
 7-00 
 
 6-48 
 
 7-71 
 
 7-25 6-74 
 
 6-17 
 
 6-60 
 
 6-17 
 
 5-72 
 
 6-80 
 
 6-39 
 
 5-95 
 
 i 
 
 8-00 
 
 8-56 
 
 8-00 
 
 7-41 
 
 8-81 
 
 8-28 7-71 
 
 7-05 
 
 7-54 
 
 7-05 
 
 6-53 
 
 7-77 
 
 7-30 
 
 6-80 
 
 T 9 
 
 9-00 
 
 9-62 
 
 9-00 
 
 8-32 
 
 9-91 
 
 9-32 8-67 
 
 7-94 
 
 8-48 
 
 7-94 
 
 7-35 
 
 8-75 
 
 8-22 
 
 7-65 
 
 i 
 
 10-0 
 
 10-7 
 
 10-0 
 
 9-26 
 
 11-0 
 
 10-4 
 
 9-64 
 
 8-82 
 
 9-43 
 
 8-82 
 
 8-16 
 
 9-72 
 
 9-13 
 
 8-50 
 
 tt 
 
 11-0 
 
 11-8 
 
 11-0 
 
 10-2 
 
 12-1 
 
 11-4 
 
 10-6 
 
 9-70 
 
 10-4 
 
 9-70 
 
 8-98 
 
 10-7 
 
 10-0 
 
 9-35 
 
 a 
 
 4 
 
 12-0 
 
 12-8 
 
 12-0 
 
 11-1 
 
 13-2 
 
 12-4 
 
 11-6 
 
 10-6 
 
 11-3 
 
 10-6 
 
 9-78 
 
 11-7 
 
 11-0 
 
 10-2 
 
 
 
 13-0 
 
 13-9 
 
 13-0 
 
 12-0 
 
 14-3 
 
 13-5 
 
 12-5 
 
 11-5 
 
 12-3 
 
 11-5 
 
 10-6 
 
 12-6 
 
 11-9 
 
 11-0 
 
 7 
 IB 
 
 14-0 
 
 15-0 
 
 14-0 
 
 13-0 
 
 15-4 
 
 14-5 
 
 13-5 
 
 12-3 
 
 13-2 
 
 12-3 
 
 11-4 
 
 13-6 
 
 12-8 
 
 11-9 
 
 H 
 
 15-0 
 
 16-0 
 
 15-0 
 
 13-9 
 
 16-5 
 
 15-5 
 
 14-5 
 
 13-2 
 
 14-1 
 
 13-2 
 
 12-2 
 
 14-6 
 
 13-7 
 
 12-7 
 
 i 
 
 16-0 
 
 17-1 
 
 16-0 
 
 14-8 
 
 17-6 
 
 16-6 
 
 15-4 
 
 14-1 
 
 15-1 
 
 14-1 
 
 13-1 
 
 15-5 
 
 14-6 
 
 13-6 
 
 Mi 
 
 17-0 
 
 18-2 
 
 17-0 
 
 15-7 
 
 18-7 
 
 17-6 
 
 16-4 
 
 15-0 
 
 16-0 
 
 15-0 
 
 13-9 
 
 16-5 
 
 15-5 
 
 14-4 
 
 i* 
 
 18-0 
 
 19-3 
 
 18-0 
 
 16-7 
 
 19-8 
 
 18-6 17-3 
 
 15-9 
 
 17-0 
 
 15-9 
 
 14-7 
 
 175 16-4 
 
 15*3 
 
 160 LBS. WORKING PRESSURE. 
 
 200 LBS. WORKING PRESSURE. 
 
 1 
 
 5-61 
 
 6-00 
 
 5-61 
 
 5-20 
 
 6-18 5-81 5-41 
 
 5-02 
 
 5-37 
 
 5-02 4-65 5-53 
 
 5-20 4-84 
 
 & 
 
 6-55 
 
 7-00 
 
 6-55 
 
 6-07 
 
 7-22 
 
 6-78 
 
 6-31 
 
 5-86 
 
 6-26 
 
 5-86 
 
 5-42 
 
 6-45 
 
 6-06 
 
 5-64 
 
 i 
 A 
 
 7-48 
 8-42 
 
 8-00 
 9-00 
 
 7-48 
 8-42 
 
 6-93 
 7-80 
 
 8-25 
 
 9-28 
 
 7-74 7-21 
 8-71 8-11 
 
 6-69 
 7-53 
 
 7-15 
 8-05 
 
 6-69 
 7-93 
 
 6-20 
 6-97 
 
 7-39 
 8-31 
 
 6-93 
 7-80 
 
 6-45 
 7-26 
 
 l 
 
 9-35 
 
 10-0 
 
 9-35 
 
 8-67 
 
 10-3 
 
 9-68 9-01 
 
 8-37 
 
 8-94 
 
 8-37 
 
 7-75 
 
 9-22 
 
 8-66 
 
 8-06 
 
 U 
 
 10-3 
 
 11-0 
 
 10-3 
 
 9-53 
 
 11-3 
 
 10-6 9-92 
 
 9-20 
 
 9-84 
 
 9-20 
 
 8-52 
 
 10-1 
 
 9-52 
 
 8-87 
 
 I 
 
 11-2 
 
 12-0 
 
 11-2 
 
 10-4 
 
 12-4 
 
 11-6 10-8 
 
 10-0 
 
 10-7 
 
 10-0 
 
 9-29 
 
 11-1 
 
 10-4 
 
 9-67 
 
 is 
 
 TT 
 
 12-2 
 
 15-0 
 
 12-2 
 
 11-3 
 
 13-4 
 
 12-6 11-7 
 
 10-9 
 
 11-6 
 
 10-9 
 
 10-1 
 
 12-0 
 
 11-3 
 
 10-5 
 
 i 
 
 13-1 
 
 14-0 
 
 13-1 
 
 12-1 
 
 14-4 
 
 13-6 12-6 
 
 11-7 
 
 12-5 
 
 11-7 
 
 10-8 
 
 12-9 
 
 12-1 
 
 11-3 
 
 H 
 
 14-0 
 
 15-0 
 
 14-0 
 
 13-0 
 
 15-5 
 
 14-4 
 
 13-5 
 
 12-5 
 
 13-4 
 
 12-5 
 
 11-6 
 
 13-8 
 
 13-0 
 
 12-1 
 
 i 
 
 15-0 
 
 16-0 
 
 15-0 
 
 13-9 
 
 16-5 
 
 15-5 
 
 14-4 
 
 13-4 
 
 14-3 
 
 13-4 
 
 12-4 
 
 14-7 
 
 13-9 
 
 129 
 
 4 
 
 15-9 
 
 17-0 
 
 15-9 
 
 14-7 
 
 17-5 
 
 16-5 
 
 15-3 
 
 14-2 
 
 15-2 
 
 14-2 
 
 13-2 
 
 15-7 
 
 14-7 13-7 
 
 ** 
 
 16-8 
 
 18-0 
 
 16-8 
 
 15-6 
 
 18-6 
 
 17-4 16-2 
 
 15-1 
 
 16-1 
 
 16-1 
 
 13-9 
 
 16-6 
 
 15-6 
 
 14-5 
 
LLOYD'S REGISTER BOILER RULES 
 
 361 
 
 TABLE OF RELATIVE SIZES OF SCREWED STAYS AND FLAT PLATES. 
 
 A simple relation exists between the thickness of a plate and its 
 stays, and when the maximum pitch has been determined by the 
 previous tables, the sizes, i.e. external diameters and pitch of threads, 
 can be found direct by consulting the following table. Should the 
 given sizes not be convenient, then either the diameter or the number 
 of threads must be increased. Smaller numbers than those given in 
 this table may not be adopted. The process can also be reversed. 
 
 Thickness of Plates in 
 Inches 
 
 i 
 
 7 
 Te 
 
 i 
 
 & 
 
 i 
 
 y 
 
 f 
 
 *i 
 
 1 
 
 8 
 
 1 
 
 1& 
 
 U 
 
 Meth i ) n d gStat8 taCh "!^oi?i IRON PLATES AND IRON STAYS 
 
 f 
 Stay ends riveted I 
 
 Stays nutted . 1 
 Doable nuts 
 
 90 
 
 100 
 
 110 
 120 
 
 140 
 
 l 8 
 U 7 
 U 7 
 
 1ft 9 
 U 7 
 18 8 
 
 H 7 
 l* 6 
 
 nn 
 
 11 7 
 If 7 
 Ifll 
 
 13 8 
 Ifll 
 l* 6 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 11 7 
 
 2 8 
 
 2ft 10 
 
 29 6 
 
 24 7 
 
 2f 8 
 
 2}10 
 
 3 6 
 
 Do. and washers 
 (*PxlT) 
 
 150 
 
 It 7 
 
 1910 
 
 U 7 
 
 1111 
 
 li 9 
 
 mo 
 
 *i 6 
 
 2J 82| 9 
 
 2112 
 
 *f 7 
 
 2| 8 
 
 3 10 
 
 Do. do. riveted 
 (|PxlT) . 
 
 160 
 
 11 9 
 
 11 6 
 
 18 9 
 
 1*11 
 
 U 6 
 
 2 7 
 
 2ft 9 
 
 2112 
 
 21 7 
 
 2f 9 
 
 2|11 
 
 8 7 
 
 Sft 8 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 Do. do. ( PxT) . 
 
 175 
 
 U12 
 
 1) 8 
 
 Ifll 
 
 1? 6 
 
 li 7 
 
 2 10 
 
 2} 6 
 
 2| 82111 
 
 2j 7 
 
 21 9 
 
 3 12 
 
 31 7 
 
 STEEL PLATES AND STEEL STAYS 
 
 Stay ends riveted ( 
 Stays nutted . ( 
 Double nuts . 
 
 90 
 100 
 110 
 120 
 135 
 
 175 
 
 1 9 
 1 8 
 1*11 
 
 1 8 
 
 H 7 
 1? 7 
 
 1411 1112 
 11 911 7 
 11 Sigll 
 
 11121112 
 if 8 If 12 
 If 811 9 
 
 Ifll 
 11 6 
 2 12 
 
 ... 
 
 ... 
 
 ... 
 
 ~ 
 
 ... 
 
 
 21 7 
 
 *8 8 
 
 21 9 
 
 212 
 
 *i 7 
 
 3 8 
 
 Do. and washers 
 (JPxJT). . 
 
 185 
 
 U 71| 8 
 
 nioigii 
 
 1 10 2 6 
 
 2ft 7 
 
 21 92|12 
 
 2f 7 
 
 2f 82J10 
 
 3} 6 
 
 Do. do. riveted 
 (fPxiT) 
 
 200 
 
 U 81910 
 
 1 81812 
 
 18 7 
 
 2 9 
 
 2ft 12 
 
 2| 7 
 
 21 9 
 
 2f 6 
 
 25 73 10 
 
 31 6 
 
 Do. do. (f PxT) 
 
 220 
 
 111011 7 
 
 If 10 l| 8 
 
 ilia 
 
 2ft 7 
 
 2J10 
 
 2J 72| 9 
 
 2112 
 
 3 73J10 
 
 3f 7 
 
 STEEL PLATES AND IRON STAYS 
 
 Stay ends riveted 1 
 Stays nutted . ( 
 Double nuts . 
 
 90 
 100 
 110 
 120 
 135 
 
 175 
 
 1 8 
 IS 7 
 i| 6 
 
 1ft 9 
 It 7 
 11 9 
 
 19 7 
 li 6 
 Ifli 
 
 11 7 
 
 1111 
 1J 7 
 
 If 8 
 1S12 
 
 li 9 
 
 Igll 
 
 11 7 
 2 12 
 
 1| 7 
 
 2 7 
 21 7 
 
 
 
 
 
 
 
 
 
 
 
 
 
 210 
 
 *f 6 
 
 2| 8 
 
 2ill 
 
 H 7 
 
 31 9 
 
 Do. and washers 
 (*PxJT) 
 
 185 
 
 13 7 
 
 1112 
 
 1811 
 
 If 9 
 
 2 6 
 
 2ft 8211121 7 
 
 2 9 
 
 *i 6 
 
 3 8 
 
 3J12 
 
 33 7 
 
 Do. do. riveted 
 (fPxjT) 
 
 200 
 
 if 10 
 
 H 7 
 
 Ifll 
 
 1| 6 
 
 2ft 8 
 
 21 6 
 
 If 8*1 6 
 
 *f 8 
 
 2|12 
 
 Sft 8 
 
 3*113! 7 
 
 
 1 
 
 
 i 
 
 
 
 
 
 
 
 j 
 
 Do. do. if PxT) . 
 
 2201J 7 
 
 i|ll 
 
 If 71? 102$ 721112J 72|122| 8 
 
 3ft 8 
 
 31 931 63| 9 
 
 NOTE. The first of the numbers are the external diameters of the stays, the second numbers 
 (blach ) are the number of threads per inch. 
 
362 
 
 LLOYD'S REGISTER BOILER RULES 
 
 The following three tables contain respectively the maximum per- 
 missible load for screwed iron or steel stays, and for stay tubes, both 
 for Whitworth screws and for finer pitches. They will be found con - 
 venient where the pitching of the stays is unequal : 
 
 PERMISSIBLE WORKING LOADS ON Iron STAYS WITH STRESSES OB 
 
 6,000 AND 7,500 LBS. PER SQUARE INCH. FOR DIAMETERS AND 
 
 SECTIONS SEE PAGES 327 and 328. 
 
 si 
 II 
 
 H 
 
 i 
 ! Whitworth 
 Threads 
 
 Number of Threads per Inch 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 Number) 
 of Working Loads of Screwed Stays 
 ThreadSj 
 
 
 
 
 
 
 j ! 
 
 
 
 Inches 
 
 Lbs. 
 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 | 
 
 2,650 
 
 10 
 
 1,823 
 
 
 
 
 
 1,823 1,893' 1.950 
 
 4 
 7 
 
 "8 
 
 8,608 
 
 9 
 
 2,530 
 
 
 
 
 2,530 
 
 2,630 2,713 
 
 2,782 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 4,712 
 
 8 
 
 3,325 
 
 ... 
 
 ... 
 
 3,325 
 
 3,467 
 
 3,583 3,680 
 
 3,7601 
 
 i* 
 
 6,964 
 
 V 
 
 4,183 
 
 ... 
 
 4,183 
 
 4,388 
 
 4,552 
 
 4,684 
 
 4,795 
 
 4,887 
 
 it 
 
 7,363 
 
 7 
 
 5,367 
 
 ... 
 
 5,367 
 
 5,599 
 
 5,783 
 
 5,932 
 
 6,057 
 
 6,160 
 
 if 
 
 8,909 
 
 6 
 
 6,359 
 
 6,359| 6,697 
 
 6,956 
 
 7,162 
 
 7,328 
 
 7,466 
 
 7,680 
 
 i* 
 
 10,602 
 
 6 
 
 7,802 
 
 7,802 
 
 8,176 
 
 8,461 
 
 8,688 
 
 8,870 
 
 9,022 
 
 9,148 
 
 i I 
 
 15,550 
 
 5 
 
 8,831 
 
 9,391 
 
 9,802 
 
 10,114 
 
 10,361 
 
 10,561 
 
 13,407 
 
 13,579 
 
 if 
 
 18,040 
 
 5 
 
 10,518 
 
 13,910 
 
 14,467 
 
 14,892 
 
 15,227 
 
 15,497 
 
 15,721 
 
 15,907 
 
 ii 
 
 20,710 
 
 i 
 
 14,903 
 
 16,265 
 
 16,867 
 
 17,325 
 
 17,687 
 
 17,977 
 
 18,219 
 
 18,419 
 
 2 
 
 23,562 
 
 i 
 
 17,338 
 
 18,804 
 
 19,449 
 
 19,943 
 
 20,331 
 
 20,643 
 
 20,901 
 
 21,115 
 
 * 
 
 26,599 
 
 i 
 
 19,952 
 
 21,527 
 
 22,219 
 
 22,744 
 
 23,159 
 
 23,491 
 
 23,767 
 
 23,995 
 
 2* 
 
 29,820 
 
 4 
 
 21,942 
 
 24,435 
 
 25,171 
 
 25,731 
 
 26,170 
 
 26,524 
 
 26,818 
 
 27,059 
 
 H 
 
 33,225 
 
 4 
 
 24,876 
 
 27,526 
 
 28,308 
 
 28,900 
 
 29,366 
 
 29,740 
 
 30,052 
 
 30,307 
 
 2 
 
 36,813 
 
 4 
 
 27,888 
 
 80,802 
 
 31,629 
 
 32,253 
 
 32,747 
 
 33,142 
 
 33,469 
 
 33,740 
 
 * 
 
 40,591 
 
 4 
 
 31,295 
 
 34,260 
 
 35,133 
 
 35,792 
 
 36,310 
 
 36,727| 37,072 
 
 37,3571 
 
 2f 
 
 44,547 
 
 4 
 
 34,783 
 
 37,903 
 
 38,816 
 
 39,514 
 
 40,060 
 
 40,496 
 
 40,859 
 
 41,158 
 
 2* 
 
 48,689 
 
 i| 
 
 37,088 
 
 41,732 
 
 42,694 
 
 43,420 
 
 43,992 
 
 44,450 
 
 44,828 
 
 45,141 
 
 8 
 
 53,014 
 
 i| 
 
 40,874 
 
 45,744 
 
 46,751 
 
 47,511 
 
 48,107 
 
 48,586 
 
 48,984 
 
 49,309 
 
 *k 
 
 67,524 
 
 
 ... 
 
 49,940 
 
 50,991 
 
 61,785 
 
 52,407 
 
 52,907 
 
 53,322 
 
 53,662 
 
 *i 
 
 62,229 
 
 3* 
 
 48,047 
 
 54,319 
 
 55,416 
 
 56,243 
 
 56,893 
 
 57,413 
 
 57,846 
 
 58,201 
 
 &i 
 
 67,097 
 
 ... 
 
 ... 
 
 58,883 
 
 60,025 
 
 60,885 
 
 61,561 
 
 62,103 
 
 62,551 
 
 62,920 
 
 3* 
 
 72,157 
 
 3* 
 
 66,827 
 
 63,631 
 
 64,817 
 
 65,711 
 
 66,413 
 
 66,978 
 
 67,442 
 
 67,825 
 
 N 
 
 77,401 
 
 ... 
 
 ... 
 
 68,563 
 
 69,791 
 
 70,721 
 
 71,452 
 
 72,037 
 
 72,519 
 
 72,915 
 
 M 
 
 82,830 
 
 3 
 
 65,059 
 
 73,680 
 
 74,946 
 
 75,916 
 
 76,670 
 
 77,277 
 
 77,777 
 
 78,189 
 
 3* 
 
 88,446 
 
 ... 
 
 ... 
 
 78,979 
 
 80,293 
 
 81,300 
 
 82,074 
 
 82,702 
 
 83,220 
 
 83,645 
 
 
 94,145 
 
 3 
 
 75,207 
 
 84,465 
 
 85,822 
 
 86,857 
 
 87,661 
 
 88,312 
 
 88,846 
 
 89,282 
 
LLOYD'S REGISTER BOILER RULES 
 
 363 
 
 PERMISSIBLE WORKING LOADS ON Steel STAYS WITH STRESSES OF 8,000, 
 
 9,000, AND 10,000 LBS. PER SQUARE INCH. FOR DIAMETERS AND 
 
 SECTIONS SEE PAGES 327 and 328. 
 
 o cs 
 
 * 
 
 a 
 H 
 
 Whitworth 
 Threads 
 
 Number of Threads per Inch 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 Number 
 of 
 Threads 
 
 Working Loads of Screwed Stays 
 
 Inches 
 I 
 
 i 
 
 Lbs. 
 3,976 
 
 5,412 
 
 10 
 9 
 
 Lbs. 
 2,431 
 
 3,374 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 LDP. 
 2,431 
 
 3,506 
 
 Lbs. 
 2,523 
 
 3,617 
 
 Lbs. 
 2,600 
 
 3,709 
 
 ... 
 
 ... 
 
 ... 
 
 3,374 
 
 1 
 
 7,069 
 
 8 
 
 4,433 
 
 ... 
 
 ... 
 
 4,433 
 
 4,623 
 
 4,778 
 
 4,907 
 
 5,014 
 
 li 
 
 8,946 
 
 7 
 
 5,578 
 
 ... 
 
 5,578 
 
 5,851 6,069 
 
 6,245 
 
 6,393 
 
 6,515 
 
 1 
 
 11,045 
 
 7 
 
 7,156 
 
 ... 
 
 7,516 
 
 7,465 7,711 
 
 7,910 
 
 8,074 
 
 8,213 
 
 If 
 
 13,365 
 
 6 
 
 8,479 
 
 8,479 
 
 8,931 
 
 9,275 9,549 
 
 9,770 
 
 9,954 
 
 10,107 
 
 1| 
 
 17,671 
 
 6 
 
 10,402 
 
 10,402 
 
 10,902 
 
 11,282 11,584 
 
 11,827 
 
 12,030 
 
 12,198 
 
 If 
 If 
 
 H 
 
 20,740 
 24,053 
 27,612 
 
 5 
 5 
 
 11,775 
 14,024 
 17,884 
 
 12,522 
 
 16,692 
 19,518 
 
 13,069 
 17,361 
 20,241 
 
 13,486 
 
 17,870 
 20,790 
 
 13,814 
 18,273 
 21,225 
 
 14,081 
 18,596 
 21,573 
 
 16,089 
 18,866 
 21,863 
 
 16,295 
 19,089 
 22,103 
 
 2 
 
 31,416 
 
 ^ 
 
 20,805 
 
 22,565 
 
 23,341 
 
 23,932 
 
 24,397 
 
 24,771 
 
 25,081 
 
 25,338 
 
 2 5 
 
 35,466 
 
 4 
 
 23,942 
 
 25,833 
 
 26,663 
 
 27,293 
 
 27,790 
 
 28,190 
 
 28,520 
 
 28,795 
 
 2* 
 
 H 
 
 39,761 
 44,301 
 
 4 
 4 
 
 26,330 
 29,850 
 
 29,322 
 33,032 
 
 30,206 
 33,970 
 
 30,874 
 34,680 
 
 31,405 
 35,239 
 
 31,829 
 35,689 
 
 32,180 
 36,062 
 
 32,471 
 36,369 
 
 S| 
 
 49,087 
 
 4 
 
 33,590 
 
 36,962 
 
 37,955 
 
 38,704 
 
 39,295 
 
 39,770 
 
 40,163 
 
 40,488 
 
 2f 
 2f 
 
 21 
 
 54,119 
 59,396 
 64,918 
 
 4 
 4 
 
 37,560 
 41,739 
 44,506 
 
 41,112 
 45,485 
 50,079 
 
 42,160 
 46,586 
 51,233 
 
 42,951 
 47,417 
 52,105 
 
 43,573 
 48,067 
 52,780 
 
 44,073 
 48,595 
 53,340 
 
 44,487 
 49,031 
 53,794 
 
 44,828 
 49,389 
 54,169 
 
 3 
 
 70,686 
 
 3i 
 
 49,049 
 
 54,893 
 
 56,101 
 
 57,003 
 
 57,729 
 
 58,303 
 
 58,780 
 
 59,171 
 
 3 
 
 76,700 
 
 ... 
 
 
 59,928 
 
 61,190 
 
 62,143 
 
 62,889 
 
 63,490 
 
 63,987 
 
 64,395 
 
 3* 
 3f 
 
 82,958 
 89,462 
 
 ? 
 
 57,657 
 
 65,182 
 70,660 
 
 66,498 
 72,030 
 
 67,492 
 73,062 
 
 68,271 
 73,874 
 
 68,896 
 74,524 
 
 69,415 
 75,061 
 
 69,842 
 75,505 
 
 3* 
 
 H 
 
 96,211 
 103,206 
 
 3* 
 
 68,192 
 
 76,353 
 82,276 
 
 77,781 
 83,755 
 
 78,855 
 84,865 
 
 79,700 
 85,742 
 
 80,374 
 86,444 
 
 80,931 
 87,023 
 
 81,391 
 87,493 
 
 3f 
 
 110,447 
 
 3 
 
 78,171 
 
 88,416 
 
 89,948 
 
 91,098 
 
 92,006 
 
 92,732 
 
 93,333 
 
 93,824 
 
 3i 
 
 117,932 
 
 ... 
 
 ... 
 
 94,774 
 
 96,364 
 
 97,550 
 
 98,490 
 
 99,243 
 
 99,864 
 
 100,374 
 
 4 
 
 125,664 
 
 3 
 
 90,260 
 
 101,354' 102,997 
 
 104,229 
 
 105,201 
 
 105,975 106,614 
 
 107,145 
 
364 
 
 LLOYD'S KEGISTEK BOILER KULES 
 
 STAY TUBES, SECTIONAL AREAS, AND WORKING LOADS. 
 
 Nnraber of 
 
 
 
 
 
 
 Plus 
 
 
 
 
 
 
 Pius 
 
 Threads 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 Thrds. 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 Threads 
 
 per Inch 
 
 
 
 
 
 
 
 
 
 
 
 
 
 If 
 
 11 
 gS 
 
 Sectional Area of Metal 
 
 Permissible Working Load (7,600 Ibs.) 
 
 HO 
 
 g* 
 
 
 
 Ins. 
 
 In. 
 
 Sq. In.'sq. In. 
 
 Sq. In. 
 
 Sq. In. Sq. In 
 
 Sq. Iii. 
 
 Lbs. 
 
 Lbs. 
 
 Lb?. 
 
 Lbs. 
 
 Lb. 
 
 Lbs. 
 
 2 
 
 i 
 
 89 
 
 94 
 
 98 
 
 1-02 
 
 1-05 
 
 1-37 
 
 6,690 7,080 
 
 7,380 
 
 7,050 
 
 7,870 
 
 10,810 
 
 
 A 
 
 1-17 
 
 1-22 
 
 1-26 
 
 1-30 
 
 1-33 
 
 1-65 
 
 8,800 
 
 9,190 
 
 9,520 
 
 9,770 
 
 9,990 
 
 12,420 
 
 
 1 
 
 143 
 
 1-48 
 
 1-52 
 
 1-56 
 
 1-59 
 
 1-91 
 
 10,740 
 
 11,130 
 
 11,430 
 
 11,790 
 
 11,920 
 
 14,360 
 
 2* 
 
 i 
 
 1-02 
 
 1-08 
 
 1-13 
 
 1-17 
 
 1-20 
 
 1-57 
 
 7,690 
 
 8,130 
 
 8,480 
 
 8,790 
 
 9,040 
 
 11,780 
 
 
 ft 
 
 1-35 
 
 1-41 
 
 1-46 
 
 1-50 
 
 1-53 
 
 1-94 
 
 10,180 10,620 
 
 10,970 
 
 11,270 
 
 11,520 
 
 14,200 
 
 
 1 
 
 1-66 
 
 1-72 
 
 1-77 
 
 1-81 
 
 1-84 
 
 2-20 
 
 12,480 
 
 12,920 
 
 13,270 
 
 13,570 
 
 13,820 
 
 16,570 
 
 2* 
 
 i 
 
 1-16 
 
 1-22 
 
 1-27 
 
 1-32 
 
 1-35 
 
 1-76 
 
 8,680 
 
 9,180 
 
 9,670 
 
 9,910 
 
 10,190 
 
 13,230 
 
 
 A 
 
 1-54 
 
 1-60 
 
 1-05 
 
 1-70 
 
 1-74 
 
 2-14 
 
 11,540 
 
 12,040 
 
 12,430 
 
 12,770 
 
 13,050 
 
 16,100 
 
 
 1 
 
 1-89 
 
 1-96 
 
 2-01 
 
 2-05 
 
 2-09 
 
 2-50 
 
 14,210 
 
 14,710 
 
 15,100 
 
 15,440 
 
 15,720 
 
 18,770 
 
 2| 
 
 i 
 
 1-29 
 
 1-36 
 
 1-42 
 
 1-47 
 
 1-51 
 
 196 
 
 9,690| 10,230 
 
 10,670 
 
 11,040 
 
 11,340 
 
 14,730 
 
 
 A 
 
 1-72 
 
 1-79 
 
 1-85 
 
 1-90 
 
 1-94 
 
 2-39 
 
 12,920 
 
 13,470 
 
 13,890 
 
 14,270 
 
 14,580 
 
 17,940 
 
 
 f 
 
 2-12 
 
 2-20 
 
 2-25 
 
 2-30 
 
 2-34 
 
 2-79 
 
 15,850 
 
 16,500 
 
 16,820 
 
 17,300 
 
 17,610 
 
 20,990 
 
 3 
 
 
 
 1-42 
 
 1-50 
 
 1-56 
 
 1-62 
 
 1-66 
 
 2-15 
 
 10,695 
 
 11,295 
 
 11,760 
 
 12,170 
 
 12,510 
 
 16,190 
 
 
 TS 
 
 1-90 
 
 1-98 
 
 2-04 
 
 2-10 
 
 214 
 
 2-68 
 
 14,280 
 
 14,880 
 
 15,360 
 
 15,760 
 
 16,080 
 
 19,780 
 
 
 f 
 
 2-35 
 
 2-43 
 
 2-50 
 
 2-55 
 
 2-60 
 
 3-09 
 
 17,690 
 
 18,290 
 
 18,760 
 
 19,220 
 
 19,510 
 
 23,190 
 
 
 & 
 
 2-78 
 
 2-86 
 
 2-93 
 
 2-98 
 
 3-03 
 
 3-52 
 
 20,910 
 
 21,510 
 
 21,990 
 
 22,390 
 
 22,710 
 
 26,410 
 
 3* 
 
 ^ 
 
 1-56 
 
 1-64 
 
 1-71 
 
 1-77 
 
 1-82 
 
 2-35 
 
 11,700 
 
 12,360 
 
 12,870 
 
 13,310 
 
 13,650 
 
 17,670 
 
 
 A 
 
 2-08 
 
 2-17 
 
 224 
 
 2-30 
 
 2-35 
 
 2-88 
 
 15,650 
 
 16.310 
 
 16.820 
 
 17,260 
 
 17.610 
 
 21,630 
 
 
 I 
 
 2-59 
 
 2-67 
 
 2-74 
 
 2-80 
 
 2-85 
 
 3-38 
 
 19,420 
 
 20,080 
 
 20,590 
 
 21,030 
 
 21,400 
 
 25,400 
 
 
 A 
 
 3-06 
 
 3-15 
 
 322 
 
 3-28 3-33 
 
 3-86 
 
 23,020 23,670 
 
 24,180 
 
 24,630 
 
 24,990 
 
 29,000 
 
 3* 
 
 1 
 
 1-69 
 
 1-78 
 
 1-86 
 
 1-92 
 
 1-97 
 
 2-55 
 
 12,690 
 
 13,400 
 
 13,960 
 
 14,430 
 
 14,830 
 
 19,140 
 
 
 A 
 
 2-27 
 
 2-36 
 
 2-43 
 
 2-50 
 
 255 
 
 3-12 
 
 17,020 
 
 17,730 
 
 18,290 
 
 18,760 
 
 19,160 
 
 23.460 
 
 I a 
 I ff 
 
 2-82 
 
 2-91 
 
 2-99 
 
 3-05 
 
 3-10 
 
 3-68 
 
 21,170 
 
 21.870 1 22,440 
 
 22,910 
 
 23,280 
 
 27,390 
 
 
 7 
 TS 
 
 3-35 
 
 3-44 
 
 3-51 
 
 3-58 
 
 363 
 
 4-20 
 
 25,120 25,830 26,390 
 
 26,860 
 
 27,230 
 
 31,560 
 
 3 | 
 
 i 
 
 1-82 
 
 1-92 
 
 2-00 
 
 2-07 
 
 2-13 
 
 2-74 
 
 13,690 14,440 
 
 15,960 
 
 15,570 
 
 15,060 
 
 20,610 
 
 
 A 
 
 2-45 
 
 2-55 
 
 2-63 
 
 2-70 
 
 2-75 
 
 3-37 
 
 18,390 19,150 i 19,750 
 
 20,260 20,660 
 
 25,310 
 
 
 1 
 
 3-05 3-15 
 
 3-23 
 
 3-30 
 
 3-36 
 
 3-97 
 
 22,890 23,660 24,260 24,77o| 25,200 
 
 29,820 
 
 
 A 
 
 3-63 
 
 3-73 
 
 3-81 
 
 3-88 
 
 3-93 
 
 4-55 
 
 27,220 
 
 27,990 
 
 28,590 
 
 29,100 
 
 29,520 
 
 34,140 
 
365 
 
 CHAPTEK XII 
 BOARD OF TRADE BOILER RULES 
 
 EXTRACTS FROM THE ' INSTRUCTIONS AS TO THE SURVEY OP PASSENGER 
 STEAM SHIPS.' PUBLISHED BY THE BOARD OF TRADE, 1913. 
 
 (Paragraphs referring to Surveyor's duties and to old boilers, and the section 
 referring exclusively to iron boilers have been omitted.) 
 
 Boilers and Superheaters. 
 
 101. Fixing of Working Pressure ; and Examination of Tracings. 
 
 The Surveyor should fix the working pressure for boilers by a series 
 of calculations of the strength of the various parts, taking into con- 
 sideration the workmanship and material. The Board of Trade have 
 arranged to receive, for examination by their Surveyors, plans and 
 particulars of boilers before the commencement of manufacture, by 
 these means hoping to ; prevent questions arising after the boilers 
 are finished and on board. This practice has been found to work well 
 in saving the time of the Surveyors, and in preventing expense, incon- 
 venience, and delay to owners. 
 
 Tracings of boilers may be received for examination upon pay- 
 ment of the usual fee, and the Surveyors may proceed as far as 
 witnessing the hydraulic test and making the subsequent internal ex- 
 amination before any further instalment of the passenger certificate 
 survey fee is paid. Engineers and boil-makers should be advised of 
 this arrangement. . . . 
 
 The Surveyor cannot declare a boiler to be safe unless he is fully 
 informed as to its construction, material, and workmanship. He 
 should, therefore, be very careful how he ventures to give a declaration 
 for a boiler that he is not called upon to survey until after it is com- 
 pleted, and fixed in the ship. 
 
 105. Liquid Fuel. A declaration should not be granted for a vessel 
 in which liquid fuel is to be used without previously submitting the 
 case for the Board's consideration. In all cases in which it is in- 
 tended that such fuel should be used on board passenger vessels, a 
 full description of the fuel and of the apparatus for supplying it to the 
 boilers, and of the method and place proposed for stowing it should 
 
366 
 
 BOARD OF TRADE BOILER RULES 
 
 be given. Complete drawings should be supplied by the owners, so 
 as to enable the Board to decide whether the arrangements are such 
 as can be considered reasonably safe to be passed by the Surveyor. 
 (For the regulations regarding motor boats, see Part V.) 
 
 108. Makers of Steel. When the steel is not to be made by any 
 of the following makers, the case must receive the special considera- 
 tion of the Board, and this should be specially noted by the Surveyors. 
 
 Messrs. W. Beardmore & Co. 
 ,, J. Brown & Co. ... 
 ,, Cammel, Laird & Co. ... 
 
 The Clydebridge Steel Co. 
 D. Colville and Sons 
 The Consett Iron Co., Ltd. 
 The Glasgow Iron and Steel Co., Ltd. 
 
 Guest, Keen and Nettlefolds, Ltd. 
 The Leeds Forge Co. ... 
 ,, Palmer's Shipbuilding and Iron Co., 
 
 Ltd. 
 ,, The South Durham Steel and Iron 
 
 Co., Ltd. 
 
 John Spencer and Sons, Ltd. 
 The Steel Co. of Scotland 
 ,, The Weardale Steel, Coal and Coke 
 
 Co., Ltd. 
 Stewarts and Lloyds, Ltd. 
 
 The Pargate Iron and Steel Co. 
 
 J. Dunlop&Co 
 
 ,, Baldwins, Ltd 
 
 The Lanarkshire Steel Co., Ltd. 
 ,, Waverley Iron & Steel Co. 
 Dorman, Long & Co., Ltd. 
 The Wigan Coal and Iron Co., Ltd. 
 
 For plates, 
 
 angles, stay 
 
 and rivet bars. 
 
 Cargo Fleet Iron and Steel Co. 
 
 For plates. 
 
 For stay and 
 rivet bars. 
 
 For stay and 
 
 rivet bars, angles 
 
 and flats. 
 
 For bars of 
 
 angle, channel, 
 
 and H-sections. 
 
 109- Process of Manufacture : Annealing Shell Plates. All steel in- 
 tended for use in the construction of boilers and for forgings should 
 be made by the open-hearth process. Boiler plates should be of acid 
 quality ; but the other portions of boilers, and forgings, may be made 
 of either acid or basic steel. In the case of castings, the steel may be 
 made by any process which has been approved by the Board of Trade. 
 
 It is very desirable that all plates (especially those of great thick- 
 ness) intended for the shells of boilers should be annealed, but it is 
 important that the process should be carefully effected, the plates being 
 heated singly to a suitable temperature, in a properly constructed 
 furnace, and allowed to cool separately and uniformally out of the 
 furnace. 
 
 110. Selection and Treatment of Test-Pieces. All the test-pieces 
 required should be selected by the Surveyor, and, except where other- 
 
BOAED OF TRADE BOILER RULES 367 
 
 wise specified in these regulations, the tests should be made in his 
 presence at the place of manufacture, and before the despatch of the 
 material. 
 
 Test specimens may be cut from the rolled material either 
 lengthwise or crosswise, but cross check tests of boiler shell plates 
 and butt straps should be made occasionly, the specimens being 
 stamped by the Surveyor before they are cut from the plates. 
 
 If any material is annealed or otherwise heat-treated, the test- 
 pieces should be similarly and simultaneously treated with the 
 material before they are tested. The specimens should not be further 
 heated, excepting those of temper-bending tests which should 
 be heated to a blood red and quenched in water at a temperature not 
 exceeding 80 Fahr. 
 
 As regards forgings, the test-pieces should be taken from a part 
 of the forgings of sectional dimensions not less than those of the 
 body of the forging, and they should be machined to size without 
 further forging down. 
 
 Test-pieces should not be cut off forgings or castings until they 
 have been stamped by the Surveyor after the annealing has been com- 
 pleted. 
 
 When a number of articles are cut from one plate, bar or forging, 
 the number of tests required should be the sameias that required from 
 the original piece, provided the articles have not been further heated 
 or forged, and can be indentified as having formed part of the original 
 piec3. 
 
 When a number of small forgings are made from the same ingot, 
 or a number of small castings from the same charge of steel, the full 
 number of tests specified hereafter need not be made ; tensile and bend- 
 ing tests at the rate of one of each for every four articles will, as a rule, 
 in such cases be sufficient. 
 
 116. General Instructions. The following instructions regarding 
 boiler material refer to steel of ordinary mild quality. Where high 
 tensile steel is used, the requirements specified by the Board in each 
 case should be adhered to. 
 
 Plates. 
 
 117. Number and Nature of Tests. A tensile and a bending test 
 should be taken from each plate, as rolled ; but, when the weight of 
 the plate exceeds two and a half tons, a tensile and a bending test 
 should be taken from each end. Bending tests only, however, need 
 be made from plates for which a greater stress than is allowed for iron 
 is not desired. 
 
 The plates for man -hole doors, and for compensating rings around 
 the openings for doors, should be tested in the usual manner. 
 
 118. Tensile Strength and Elongation. The tensile strength of 
 plates not intended to be worked in the fire or exposed to flame, for 
 which special limits have not been sanctioned, should be between 27 
 and 32 tons per square inch : that of other plates, from 26 to 30 tons 
 per square inch. The elongation should not be less than 20 per cent, 
 in a length of 8 inches for material f inch in thickness and upwards 
 which is required to have a tensile strength of 27 to 32 tons per square 
 
368 BOAED OF TRADE BOILER RULES 
 
 inch, and not less than 23 per cent, if the tensile strength is required 
 to be between 26 and 30 tons per square inch. For material under f 
 inch in thickness, the elongation may be reduced ; but, for each 
 eighth of an inch of diminution in thickness, the reduction should not 
 be more than 3 per cent, below the elongations mentioned. 
 
 119. Bend Tests. Bending test-pieces should withstand being bent, 
 without fracture, until the sides are parallel at a distance apart of 
 not more than three times the thickness of the specimen. The bending 
 tests of plates not intended to be worked in the fire or exposed to 
 flame may be made with strips in the same condition as the plates : 
 those from other plates should be made with strips which have been 
 tempered. 
 
 120. Witnessing of Tests by Surveyor. It is very desirable that the 
 Surveyor should witness the whole of these tests ; but, in the case 
 of plates made from steel manufactured by any of the makers whose 
 names are given in Section 108, he need only select and witness tests 
 from one in four of the plates of each thickness, unless the weight of 
 the plate is over two and a half tons, or special limits of strength, or, 
 in the case of shell plates, a minimum tensile strength exceeding 27 
 tons is required, in which cases the Surveyor should see the tests 
 made from all the plates. 
 
 Angle, Rivet, and Stay Bars. 
 
 121. Number and Nature of Tests. One tensile test should be made 
 from each 15, or part of 15, bars rolled of each section or diameter 
 from the same charge, but not less than two tensile tests should be 
 made, unless the total number of bars rolled from the same charge 
 is 8, or less than 8, and the bars are of the same section or diameter, 
 when one test will suffice. For round bars If inches in diameter, and 
 under, the numbers 50 and 20 should be substituted for 15 and 8 re- 
 spectively, as determining the number of tests necessary. 
 
 A cold and a temper bend should be made from stay bars in the 
 same proportion as that in which tensile tests are required ; and a 
 cold or temper bend should be made from each angle or tee bar rolled. 
 No bending tests need be made from rivet bars. 
 
 122. Tensile Strength and Elongation of Stays, Angles, and Tee 
 Bars. The tensile strength of longitudinal stays, angles, and tee bars 
 should be between 27 and 32 tons per square inch, with an elongation 
 of not less than 20 per cent, measured on the appropriate standard 
 test-piece (A or B). For bars for combustion-chamber stays, the ten- 
 sile strength should be between 26 and 32 tons per square inch, with 
 an elongation of not less than 23 per cent, measured on the standard 
 test-piece. When, however, stay bars are tested on a gauge length of 
 four times the diameter (test-piece F), the elongations should be 24 
 per cent, and 28 per cent, respectively. 
 
 For tee or angle bars under f inch in thickness, the elongation 
 may be 3 per cent, below that specified for plates. 
 
 123. Bend Tests. Bending test-pieces should withstand being bent, 
 without fracture, until the sides are parallel at a distance apart of not 
 more than three times the thickness or diameter of the specimen. 
 
 124. Rivet Bars. The tensile strength of rivet bars should be be- 
 
BOARD OF TRADE BOILER RULES 369 
 
 tween 26 and 30 tons per square inch, with an elongation of not less 
 than 25 per cent, measured on the standard test-piece B, or 30 per 
 cent, if measured on test-piece F. 
 
 Rivets. 
 
 125- Nature of Tests. A few rivets of each size should be selected 
 by the Surveyor from the bulk, and should be subjected to the follow- 
 ing tests : 
 
 (a) The rivet shanks to be bent cold and hammered' until the two 
 
 parts of the shank touch, without fracture on the outside of 
 the bend. 
 
 (b) The rivet heads to be flattened, while hot, until their diameter 
 
 is two and a half times the diameter of the shank, without 
 
 cracking at the edges. 
 
 A few check tensile tests of shell rivets should also be made when 
 the Surveyor considers it necessary. The elongation should, when 
 practicable, be taken in a length of two and a half times the diameter 
 of the prepared part ; the tensile strength should be from 27 to 32 tons 
 per square inch and the contraction of area about 60 per cent. 
 
 Tubes. 
 
 126- Number and Nature of Tests. 
 
 (a) Solid-drawn Steel Steam Pipes, Boiler Tubes, etc., subject to In- 
 ternal Pressure. 
 
 The makers should take a few samples from each batch of tubes 
 and test them for tensile strength and elongation. A bending test 
 should also be made by them from the scrap end of each tube drawn. 
 
 Tensile and bending tests should also be made in the Surveyor's 
 presence from specimens selected by him in the following proportion, 
 from the tubes made from each charge : 
 
 Tubes up to and including 3 inches in diameter : 1 in 40 or part 
 thereof. 
 
 Tubes above 3 inches up to and including 4 inches in diameter : 1 in 
 20 or part thereof. 
 
 Tubes above 4 inches up to and including 5 inches in diameter : 
 1 in 10 or part thereof. 
 
 Tubes above 5 inches up to and including 7 inches in diameter : 
 1 in 6 or part thereof. 
 
 Tubes above 7 inches in diameter : 1 in 4 or part therefore. 
 
 The tensile strength should range between 23 and 30 tons per 
 square inch, and the elongation should not be less than 20 per cent, 
 in a length of 8 inches, or 18 per cent, if the thickness of the tubes is 
 less than J of an inch. 
 
 All the tubes should be tested by the makers to a suitable hydraulic 
 pressure, and the tests of at least 25 per cent, of them should be 
 witnessed by the Surveyor. The tests of all steam pipes should, 
 however, be witnessed by the Surveyor on completion of the pipes, 
 that is after they have been bent to shape and the flanges have been 
 secured in position (see Section 174). 
 
 BB 
 
370 BOARD OF TRADE BOILER RULES 
 
 (b) Solid-drawn Steel Tubes subject to External Pressure. 
 
 If no allowance over that given for iron tubes is required, a few 
 bending tests should be made from the scrap ends of the stay tubes, 
 but special tests need not be made from the ordinary tubes if the 
 Surveyor finds the general quality of the material satisfactory and he 
 is satisfied. 
 
 If allowance over iron is required, tensile and bending tests should 
 be witnessed by the Surveyor in the proportions given for solid-drawn 
 steel steam pipes. The tensile strength) should range between 23 and 
 30 tons per square inch, and the elongation should be at least that 
 required for similar solid-drawn steam pipes. 
 
 All the tubes should be tested by the makers to a suitable hydraulic 
 pressure, but the tests need not be witnessed by the Surveyor if he is 
 satisfied that the tubes have been duly tested by the makers. 
 
 (c) Steel Lap-Welded Tubes subject to External Pressure. 
 
 (i.) Steel Tubes for which no Allowance over Iron is required. 
 A few bending tests should be made from the scrap ends of the stay 
 tubes or the strips from which they are made, but special tests need 
 not be made from the ordinary tubes if the general nature of the 
 material has been found satisfactory and the Surveyor is satisfied. 
 
 (ii.) Steel Stay Tubes for which Allowance over Iron is required. 
 Tensile and bending tests should be made from 25 per cent, of the 
 strips from which the tubes are made. The tensile strength should 
 range between 23 and 30 tons per square inch, and the elongation 
 should be at least 20 per cent, in a length of 8 inches when the strips 
 are tested in their normal condition. 
 
 All the tubes should be tested by the makers to a suitable hydraulic 
 pressure, but the tests need not be witnessed by the Surveyor if he is 
 satisfied that the tubes have been duly tested by the makers. 
 
 127. General Kequirements for all Tubes. The hydraulic test should 
 not, in any case, be less than three times the working pressure, and it 
 should not exceed four times the pressure given by the rule : 
 
 6000 x thickness in inches _ 
 inside diameter in inches 
 
 in the case of lap- welded tubes, or five times that pressure in the case 
 of solid-drawn steel tubes. 
 
 All the tests mentioned should be made in the Surveyor's presence, 
 except where otherwise stated, and such means as may be necessary 
 should be taken to satisfy the Surveyor that the specimens he may 
 have to test have been cut from the tubes they represent. 
 
 If any of the aforesaid tubes are made in long lengths and passed 
 by the Surveyor in that condition, the number of tests required may 
 be calculated on the number of tubes as made, Notwithstanding that 
 they may afterwards be cut up into shorter lengths. 
 
 Steel tubes should be made of open -hearth acid steel, unless 
 material of other quality has been specially approved for the purpose. 
 Solid-drawn tubes of a thickness exceeding J inch should be finished 
 by the hot-drawn process, unless cold-drawing has been specially 
 
BOARD OF TRADE BOILER RULES 371 
 
 sanctioned, and all cold-drawn tubes should afterwards be efficiently 
 annealed. 
 
 Forgings. 
 
 128. Number and Nature of Tests. At least one tensile and one 
 bend test should be taken from each forging; but, if the weight 
 exceeds three tons, a tensile and a bending test should be taken from 
 each end. 
 
 129. Tensile Strength and Elongation. The tensile strength of steel 
 forgings' should not exceed 40 tons per square inch ; and the elongation 
 measured on the appropriate standard test-piece C, D, or E, should 
 not be less than 17 per cent, for 40-ton steel ; and in no case may 
 the sum of the tensile strength and the corresponding elongation be 
 less than 57. 
 
 130. Bend Tests. The bending test-pieces should withstand being 
 bent without fracture through an angle of 180, the internal radius of 
 the bend being not greater than that specified below : 
 
 Maximum specified tensile strength of forging. 
 
 Internal radius of test-piece after 
 bending. 
 
 Up to 32 tons per square inch 
 Above 32 tons and up to 36 tons per square inch 
 Above 36 tons and up to 40 tons per square inch 
 
 inch. 
 
 I 
 
 131. General Instructions. The forgings should be made from 
 sound ingots, and not more than the lower two-thirds of the ingot 
 may be utilised for forging. The sectional area of the body of the 
 forging may not exceed one-fifth of the sectional area of the original 
 ingot ; and no part of the forging should have more than two-thirds 
 of the sectional area of the ignot. All ignot steel forgings should, after 
 completion, be thoroughly annealed at a uniform temperature ; and, 
 if any subsequent heating is done, the forging should, if required by 
 the Surveyor, be again annealed. 
 
 Castings. 
 
 132. Number and Nature of Tests. No tests need be made from 
 unimportant steel castings or from steel castings which are used for 
 articles usually made of cast-iron, if the scantlings are not materially 
 reduced below what would be required if cast-iron were used. All 
 other steel castings should be tested as follows : 
 
 At least one tensile and one bending test should be made from the 
 castings from each charge ; and, where a casting is made from more 
 than one charge, at least four tensile and four bending tests should be 
 made from pieces cast as far apart as possible on the casting, 
 and as near the top and the bottom respectively as practicable. 
 
 Where more than one casting is made from one charge, at least 
 
372 BOARD OP TRADE BOILER RULES 
 
 one tensile and one bending test should be made from the castings run 
 from one common pouring head ; but separate tests should be made 
 from each casting or set of castings run from each separate pouring 
 head. Small castings may, however, be dealt with in accordance with 
 the provisions of Section 110. 
 
 133. Tensile Strength and Elongation. The tensile strength may 
 range from 26 to 40 tons per square inch, with an elongation, measured 
 on the standard test-piece C, D, or E, of not less than 15 per cent. 
 If, however, the castings are to be used for the more important pieces 
 of machinery, such as pistons, etc., or for articles usually made of 
 wrought material, the elongation should not be less than 20 per cent, 
 where the corresponding tensile strength is between 26 and 35 tons 
 per square inch. 
 
 134. Bend Tests. The bending test-pieces should withstand being 
 bent, without fracture, through an angle of 60 if the tensile strength 
 is between 35 and 40 tons per square inch, and, in the case of other 
 castings, through an angle of 90 : but, if they are required to be of 
 the superior quality previously referred to, the angle should not be 
 less than 120. 
 
 The internal radius of the bend in each case should not be greater 
 than one inch. 
 
 135. Annealing. All steel castings should be thoroughly annealed 
 at a uniform temperature, and should be allowed to cool down prior to 
 removal from the annealing furnace ; and, if subsequently heated, 
 with the Surveyor's approval, should again be similarly annealed, if 
 required by the Surveyor. 
 
 Steel Boilers. 
 
 136. Thickness of Plates : Drilling, Welding and Annealing. The 
 thickness of plates, other than tube strips, used in the construction of 
 boilers should not be less than ^ inch. 
 
 It is expected that the rivet holes will be drilled, and not punched. 
 Plates that are drilled in place should be taken apart and the burr 
 taken off, and the holes slightly countersunk from the outside. 
 
 Butt straps should be cut from plates, and not from bars. 
 
 Steel plates which have been welded should not be passed if sub- 
 ject to a tensile stress, and those welded and subject to a compressive 
 stress should be efficiently annealed. 
 
 Local heating of the plates should be avoided, as many plates have 
 failed from having been so treated. 
 
 All plates that have been flanged or locally heated, and all stays 
 and stay tubes which have been locally heated, should be carefully 
 annealed after being so treated. 
 
 137. Cylindrical Boiler Shells. The Board of Trade consider that 
 boilers well constructed, well designed, and made of good material 
 should be allowed an advantage in the matter of working pressure 
 over boilers inferior in any of the above respects, as, unless this is 
 done, the superior boiler is placed at a disadvantage, and good work- 
 manship and material will be discouraged. They have therefore 
 caused the following rules to be prepared : 
 
BOABD OF TBADE BOILER RULES 
 
 373 
 
 When the cylindrical shells of boilers are made of material which 
 has been duly tested and approved, with all the rivet holes drilled in 
 place and all the seams fitted with double butt straps, each of at least 
 five-eighths the thickness of the plates they cover, and all the seams 
 at least double riveted with rivets having an allowance of not more 
 than 87 '5 per cent, over the single shear, provided that the boilers 
 have been open to inspection during the whole period of construction, 
 then 4-5 may be used as the factor of safety, the minimum actual ten- 
 sile strength of the plates being used in calculating the working pres- 
 sure. 
 
 When the above conditions are not complied with, the additions 
 in the following scale should be made to the factor of safety, according 
 to the circumstances of each case : 
 
 
 At 
 
 15 
 
 
 Bt 
 
 3 
 
 1 
 
 C 
 
 2 
 
 1 
 
 D 
 
 1 
 
 1 
 
 E 
 
 3 
 
 1 
 
 P 
 
 15 
 
 o 
 
 
 
 ^ 
 
 G 
 
 1-0 
 
 
 H* 
 
 4 
 
 
 It 
 Jt 
 
 1 
 15 
 
 OQ 
 
 K 
 
 1 
 
 1 
 
 L 
 
 2 
 
 "S 
 
 -_ 
 
 M 
 
 1 
 
 1 
 
 N 
 
 1 
 
 = 
 
 1 
 
 
 
 P: 
 
 2 
 3 
 
 
 
 
 
 To be added if all the holes are fair and good, but drilled out of 
 
 place after bending. 
 To be added if all the holes are fair and good, but drilled before 
 
 bending. 
 To be added if double butt straps are not fitted, and the seams 
 
 are lapped and double riveted. 
 To be added if double butt straps are not fitted, and the seams 
 
 are lapped and treble riveted. 
 To be added if only single butt straps are fitted, and the seams 
 
 are double riveted. 
 To be added if only single butt straps are fitted, and the seams 
 
 are treble riveted. 
 
 To be added if any joint is single riveted. 
 To be added if there are two or more belts of plates, and the 
 
 seams are not properly crossed. 
 
 To be added if the holes are fair and good, but drilled out of 
 
 place after bending. 
 To be added if the holes are fair and good, but drilled before 
 
 bending. 
 To be added if the seams are fitted with single butt straps, and 
 
 are double riveted. 
 To be added if the seams are fitted with single butt straps, and 
 
 are single riveted. 
 To be added if the seams are fitted with double butt straps, and 
 
 are single riveted. 
 
 To be added if the seams are lapped and double riveted. 
 To be added if the seams are lapped and single riveted. 
 To be added if the boiler is of such a length as to fire from both 
 
 ends, or is of unusual length, as in the case of flue boilers, 
 
 and the seams are fitted as described opposite K, M, or N, 
 
 but, if the seams are as described opposite L or 0, P'4 should 
 
 be added in lieu of the addition designated by K, M, N, L 
 
 or O, as the case may be. 
 
 * The factor may be increased still further if the workmanship is such as, in 
 the Surveyor's judgment, to render such increase necessary. 
 
 t If the holes are to be rimered or bored out in place, the case should be sub- 
 mitted to the Board as to the reduction or omission of A, B, I, and J, as hereto- 
 fore. 
 
 If the middle circumferential seams are double strapped and double riveted, 
 or lapped and treble riveted, and the calculated strength is not less than 65 per 
 cent, of the solid plate, no addition to the factor need be made in respect of the 
 length of the boiler. 
 
374 BOAED OF TRADE BOILER RULES 
 
 The joints referred to in the table as circumferential seams do not 
 include the joints between the shell and end plates, which it is ex- 
 pected will be at least double riveted when the thickness of the shell 
 exceeds | inch. 
 
 When surveying boilers that have not been open to inspection 
 during construction, the case should be submitted to the Board as to 
 the factor to be used. 
 
 The strength of ordinary joints is found by the following for- 
 mulae : 
 
 100 (d - d) ^ fper-centage of strength of plate at joint as com- 
 p = \ pared with the solid plate ; and 
 
 100 xS 2 xaxwxC_ Jper-centage of strength of rivets as 
 Sj x p x T \ compared with the solid plate ; 
 
 where p = pitch of rivets, in inches ; 
 
 d = diameter of rivets, in inches ; 
 
 a = area of one rivet, in square inches ; 
 
 n = number of rows of rivets ; 
 
 T = thickness of plate, in inches ; 
 
 C = 1 for rivets in single shear ; 
 
 C = 1-875 for rivets in double shear ; 
 
 S x = minimum tensile strength of plates, in tons per square 
 inch; and 
 
 S 2 shearing strength of rivets, in tons per square inch, which 
 is taken to be 23. 
 
 If the percentage strength of the rivets in the longitudinal seams 
 is found by calculation to be less than the calculated percentage 
 strength of the plate, the working pressure of the shell should be 
 calculated in the following manner from each percentage : 
 
 Si x 2240 x % strength of joint x 2 T 
 
 ^ j- |L9 " V Y"tY*^QQ11VA 
 
 D x factor of safety x 100 
 
 D being the inside diameter of the boiler, in inches. 
 When using the percentage strength of the plate, 4*5 plus the 
 additions suitable for the method of construction should be used as 
 the nominal factor of safety ; but, when using the percentage strength 
 of the rivets, 4-5 should be used as the factor of safety. The smaller 
 of the two pressures so found is the pressure to be allowed per square 
 inch on the safety valves. (See the formulae as given in detail in 
 Section 138.) 
 
 MAXIMUM PITCHES FOR RIVETED JOINTS. 
 
 T = thickness of plate in inches ; 
 
 p = maximum pitch of rivets in inches, provided it does not 
 
 exceed 10^ inches ; and 
 C = constant applicable from the following table : 
 
BOARD OF TRADE BOILER RULES 
 
 375 
 
 Number of Rivets in 
 one Pitch. 
 
 Constants for Lap Joints. 
 
 Constants for Double Butt 
 Strap Joints. 
 
 1 
 
 1-31 
 
 1-75 
 
 2 
 
 2-62 
 
 3-50 
 
 3 
 
 3-47 
 
 4-63 
 
 4 
 
 4-14 
 
 5-52 
 
 5 
 
 ~~ 
 
 6-00 
 
 (C x T) + 1 f = p. 
 
 When the work is first class, such pitches may be adopted so far 
 as safety is concerned, yet, in some cases, it may be well not to adopt 
 the greatest pitch found by the formula. The maximum pitch should 
 not, however, exceed 10^ inches with the thickest plates for boiler 
 shells. If in any case the pitch is found to exceed that arrived at by 
 the foregoing formula, for the particular description of joint and thick- 
 ness of plate, such pitches should not be passed, but all such cases 
 should be reported. 
 
 139. Openings in Shells ; Doors, etc. The openings in the shells of 
 cylindrical boilers should have their shorter axes placed longitudin- 
 ally. 
 
 Compensating rings of at least the same effective sectional area 
 as the plates cut out, and not less in thickness than the plates to 
 which they are attached, should be fitted around all man-holes and 
 openings, or the surrounding portion of the plates otherwise efficiently 
 stiffened. 
 
 It is very desirable that the compensating rings around openings 
 in flat surfaces be made of L- or T-bars. When a ring is not fitted 
 around such an opening and the plate is flanged for compensation, 
 the total depth, D, of the flange should not be less than that given by 
 the following equation : 
 
 D = Vwidth of opening x thickness of plate. 
 
 Cast-iron doors should not be passed, and in all cases in which 
 the Surveyors find that cast-iron is employed in the construction of 
 boilers in such a manner as to be subjected to the pressure of steam or 
 water, they should report the circumstances to the Board of Trade. 
 
 The neutral part of the boiler shells under steam domes should be 
 efficiently stiffened and stayed, as serious accidents have arisen from 
 the want of such precautions. 
 
 In connection with openings in the ends of steam receivers, etc., 
 the Surveyors should bear in mind that, although the usual strengthen- 
 ing plate may be fitted around such openings, the end is still weaker 
 than if no opening had been made, and that the fact of there being a 
 plate or the flange of a neck-piece riveted around the opening may 
 not remove the necessity for having the end suitably stayed. 
 
 140. Hemispherical Ends. Hemispherical ends subject to internal 
 pressure may be allowed double the pressure that is suitable for a 
 cylinder of the same diameter and thickness^ 
 
376 BOARD OF TRADE BOILER RULES 
 
 141. Dished Ends. Ends of steam receivers which are dished and 
 flanged in a hydraulic press, the whole end being operated upon at 
 each heat, may be passed without stays, provided that the radius of 
 the end is not greater than the diameter of the shell to which it is 
 attached and does not exceed 4 feet, that the outer radius of the flange 
 at the root is not less than 3 inches, that the end is made of mild 
 steel of the usual quality, and that it is efficiently annealed after the 
 completion of the setting and flanging ; but the maximum pressure 
 allowed without stays should not exceed that found by the following 
 formula : 
 
 90000 x T x h 
 
 - = working pressure ; 
 
 where T = thickness of end, in inches ; 
 
 D = diameter of shell, inside, in inches ; 
 
 h = distance, in inches, from the centre of the end on the 
 inner side to a straight line passing through the points 
 where the curve of the end due to the inner radius, and 
 produced, would intersect the sides of the cylindrical 
 shell, produced if necessary, at the diameter D, and 
 
 = E - JjpT?, in which = ( inner radius of end> in 
 
 V 4 I inches. 
 
 If there is a man-hole in the end, T should exceed that found by 
 the formula by J- inch. 
 
 The above instructions do not apply to dished ends of vertical 
 donkey boilers, which are subject to the thrust of the uptake in 
 addition to the pressure of steam. 
 
 142- Stays for Dished Ends. Stays, properly distributed, should 
 be fitted to dished ends which are not of the thickness required for 
 flat ends, or which do not comply with the requirements stated in 
 Section 141 ; but, if the ends are sufficient for the pressure needed, 
 when considered as portions of spheres, the stays, if of solid steel, 
 may have a nominal stress of 18,000 Ibs. per square inch of net 
 section. If dished ends are not equal to the pressure needed when 
 considered as portions of spheres, they should be stayed as flat sur- 
 faces. 
 
 143. Stays for Flat Surfaces- Solid steel stays for supporting flat 
 surfaces may be allowed a working stress of 9,000 Ibs. per square 
 inch of net section, provided the tensile strength and elongation are 
 as stated in Section 122. Steel stays which have been welded should 
 not be passed. (This does not apply to stay tubes which are welded 
 longitudinally.) 
 
 When the threads of longitudinal stays are finer than six per inch, 
 the depth of the external nuts should be at least 1 J times the diameter 
 of the stay. 
 
 The areas of diagonal stays are found in the following way : Find 
 the area of a direct stay needed to support the surface, multiply this 
 area by the length of the diagonal stay, and divide the product by the 
 length of a line drawn at right angles to the surface supported to the 
 end of the diagonal stay ; the quotient will be the area of the diagonal 
 stay required. 
 
BOARD OF TRADE BOILER RULES 377 
 
 When gusset stays are used, their area should be in excess of that 
 found in the above way. 
 
 144. Stay Tubes. Stay tubes made of steel which has been tested 
 and has been found to comply with the higher requirements stated in 
 Section 126, may be allowed a stress not exceeding 7,500 Ibs. per 
 square inch of net section, provided that their net thickness is in no 
 case less than J inch. 
 
 145. Ordinary Tubes. Ordinary smoke tubes, if made of steel for 
 which no special allowance is required, should be of a thickness at 
 least equal to that found by the formula given in Section 156 for 
 similar tubes of iron. 
 
 146. Girders for Flat Surfaces. When the tops of combustion-boxes 
 or other parts of a boiler are supported by stays held by solid girders 
 of rectangular section, the following formula should be used for finding 
 the working pressure to be allowed for the girders, assuming that they 
 are not subject to a temperature greater than the ordinary heat of steam, 
 and that, in the case of combustion-boxes, the ends are properly bedded 
 to the edges of the tube-plate and the back plate of the combustion- 
 box : 
 
 C x d 2 x T 
 
 (W - P) D x L = W rkmg preSSUrG > 
 where W = width of combustion -box, in inches ; 
 P = pitch of supporting stays, in inches ; 
 D = distance between the girders from centre to centre, in 
 
 inches ; 
 
 L = length of girder, in feet ; 
 d = depth of girder, in inches ; 
 T = thickness of girder, in inches ; 
 N = number of supporting stays ; 
 
 N x 1320 * 
 C = j^- -^ when the number of stays is odd ; and 
 
 (N + 1) 1320* 
 C = - -VT 2 when the number of stays is even. 
 
 The working pressure for the supporting stays and for the plate 
 between them should be determined by the rules for ordinary stays 
 and plates. 
 
 147. Flat Surfaces. The pressure on plates forming flat surfaces is 
 found by the following formula : 
 
 C (or c) x (T + I) 2 
 
 ^ ' - L, = working pressure ; 
 
 b o 
 
 where T = thickness of the plate, in sixteenths of an inch ; 
 S = surface supported, in square inches ; and 
 C = constant for steel 1 according to the following 
 c = constant far iron] circumstances : 
 
 / when the plates are not exposed to the impact of heat 
 or flame, and the stays are fitted with nuts on both 
 C = 240 | sides of the plates, and doubling strips, not less in 
 c = 192 \ width than two-thirds the pitch of the stays and of 
 the thickness of the plates, are securely riveted to the 
 outside of the plates they cover ; 
 
 * 1,200 for iron. 
 
378 
 
 BOAED OF TEADE BOILEE EULES 
 
 C = 210 
 
 c = 168 
 
 C = 165 
 
 C = IJ2 
 
 C - 150 
 
 C = 120 
 
 when the plates are not exposed to the impact of heat 
 or flame, and the stays are fitted with nuts on both 
 sides of the plates, and with washers, not less in dia- 
 meter than two-thirds the pitch of the stays and of the 
 same thickness as the plates, securely riveted to the 
 outside of the plates they cover ; 
 
 when the plates are not exposed to the impact of heat 
 or flame, and the stays are fitted with nuts on both 
 sides of the plates, and with washers outside the 
 plates, at least three times the diameter of the stay 
 and two-thirds the thickness of the plates they cover ; 
 
 when the plates are not exposed to the impact of heat 
 or flame, and the stays are fitted with nuts on both 
 sides of the plates ; 
 
 = 1.12-5 
 = go 
 
 = 77 
 
 = 70 
 
 77 
 
 C = 75 
 
 c = 60 
 
 C = 67-5 
 c = 
 
 ( when tube-plates are not exposed toithe direct impact 
 | of heat or flame, and the stays are fitted with nuts ; 
 
 when tube-plates are not exposed to the direct impact 
 of heat or flame, and the stay tubes are screwed into 
 the plates and expanded ; 
 
 when the plates are not exposed to the impact of heat 
 or flame, and the stays are screwed into the plates and 
 riveted over ; 
 
 when the plates are not exposed to the impact of heat, 
 with steam in contact with the plates, and the stays 
 fitted with nuts and washers, the latter being at least 
 three times the diameter of the stay and two-thirds the 
 thickness of the plates they cover ; 
 when the plates are exposed to the impact of heat, 
 
 with steam in contact with the plates, and the stays 
 
 fitted with nuts only ; 
 
 !when the plates are exposed to the impact of heat 
 or flame, with water in contact with the plates, and 
 the stays screwed into the plates and fitted with 
 nuts ; 
 
 when the plates are exposed to the impact of heat 
 or flame, with water in contact with the plates, 
 and the stays screwed into the plates and having 
 the ends riveted over to form substantial heads ; 
 and 
 
 when the plates are exposed to the impact of heat, 
 with steam in contact with the plates, with 
 the stays screwed into the plates and having 
 the ends riveted over to form substantial 
 heads. 
 
 C = 66 
 c = 60 
 
 C = 39.6 | 
 c = 36 
 
 When the riveted ends of screwed stays are much worn, or when 
 the nuts are burned, the constants should be reduced, but the Surveyor 
 must act according to the circumstances that present themselves at the 
 
BOARD OF TRADE BOILER RULES 379 
 
 time of the survey, and it is expected that, in cases where the riveted 
 ends of screwed stays in the combustion-boxes and furnaces are found 
 in this state, it will be often necessary to reduce the constant 66 to 
 about 40. 
 
 When the plates are not exposed to the impact of heat or flame, 
 and doubling plates covering the whole of the flat surfaces are riveted 
 to the plates, the working pressure may be found by the following 
 formula : 
 
 C (or c) (T + I) 2 + C (or c) (T x + I) 2 
 
 g _ Q - = working pressure ; 
 
 w r here T = thickness of the plate, in sixteenths of an inch ; 
 
 T l = thickness of the doubling plate, in sixteenths of an inch ; 
 S = surface supported, in square inches ; and 
 C (or c) = constant applicable to the case, as previously given. 
 When doubling plates do not cover the whole of i the flat surfaces, 
 but are fitted between the rows of supporting stays, the strength allowed 
 for them should be two -thirds only of that which would be allowed 
 for similar doubling plates extending beyond and embracing the 
 supporting stays. 
 
 In calculating the working pressure of the portion of tube-plates 
 between the boxes of tubes, the value of S in the above formula should 
 be found as follows : 
 
 where D = horizontal pitch of the stay tubes, in inches ; 
 and d = vertical do. do. do. 
 
 The pitches should be measured from centre to centre of the stay 
 tubes, and no deduction should be made for any tubes in the con- 
 tained surface. 
 
 In the body of tube-plates, the value of S may be found in the 
 ordinary way, and the area of the tubes in the space bounded by the 
 stay tubes may be deducted. 
 
 In cases where plates are stiffened by T- or L-bars, and a greater 
 pressure is required for the plates than is allowed by the use of the 
 foregoing constants, the case should be submitted for the consideration 
 of the Board of Trade. 
 
 W 7 hen dealing with end plates in the vicinity of horizontal 
 furnaces such as are now generally used in boilers, the Surveyors 
 need not require stays to be fitted if the flat portion of the plate is 
 sufficient according to the rules for flat surfaces ; but, when the 
 furnaces and cornbustion-box stays are not efficient as through stays, 
 as in the case of certain tug-boat boilers and of other marine boilers in 
 which furnaces having coned back ends are fitted, stays are required, 
 and in the latter case it will often be found that three through stays, 
 distributed around each of the lower man-holes between the furnaces, 
 are necessary in order to afford the desired strength. The Surveyor 
 should, however, submit the particulars of such cases for consideration 
 when in doubt as to how to deal with them. 
 
 When a circular flat end is bolted or riveted to an outside ring 
 or flange of a cylindrical shell, S in the formula may be taken as the 
 
380 BOAED OF TEADE BOILEE EULES 
 
 area of the square inscribed in the circle passing through the centres 
 of the bolts or rivets securing the end, provided the ring or flange is 
 of sufficient thickness. 
 
 148. Compressive Stress on Tube-Plates. The Surveyors should not 
 in any case allow a greater compressive stress on the tube-plates than 
 14,000* Ibs. per square inch, which is that used in the following 
 formula : 
 
 (D - d) T x 28000 f 
 
 W x D. i ~ = working pressure ; 
 
 where D = least horizontal distance between centres of tubes, in 
 
 inches ; 
 
 d = inside diameter of ordinary tubes, in inches ; 
 T = thickness of tube-plate, in inches ; and 
 W = width of combustion-box, in inches, between the tube- 
 plate and back of fire-box, or distance between the com- 
 bustion-box tube-plates when the boiler is double-ended 
 and the box common to the furnaces at both ends. 
 
 149. Circular Furnaces. Circular furnaces with the longitudinal 
 joints welded, or made with single butt straps double riveted, or 
 double butt straps single riveted : 
 
 99000 J x the square of the thickness of the plate, in inches, 
 (length, in feet + 1) x diameter, in inches. 
 
 = working pressure per square inch, provided it does twt exceed that 
 found by the following formula : 
 
 9900 x thickness, in inches _ [working pressure per square 
 diameter, in inches " \inch. 
 
 The second formula limits the crushing stress on the material to 
 4,950 II Ibs. per square inch. 
 
 The length is to be measured between the rings, if the furnace is 
 made with rings. 
 
 If the longitudinal joints instead of being butted are lap-jointed in 
 the ordinary way and double riveted, then 82,500 should be used in- 
 stead of 99,000 ; but, where the lap is bevelled and so made as to give 
 the flues the form of a true circle, then 88,000 may be used. 
 
 When the workmanship is not of the best quality, the constants 
 given above, for the former rule, should be reduced, according to 
 circumstances, and the judgment of the Surveyor. Some of the con- 
 ditions of best workmanship are that the rivet holes shall be drilled 
 after the bending is done and when the plates are in place, and the 
 plates afterwards taken apart, the burr on the holes taken off, and the 
 holes slightly countersunk from the outside.** 
 
 * 11 ,000 for iron. f 22,000 for iron. J 90,000 for iron. 
 
 9,000 for iron. || 4,500 for iron. 
 
 ** In the case of upright fire-boxes of donkey or similar boilers, 10 per cent, 
 should be deducted from the constant given above, applicable to the respective 
 classes of work, and the constant for the crushing formula should bo reduced by 
 a similar amount, becoming 8,910 (or 8,100), 
 
BOARD OF TRADE BOILER RULES 381 
 
 150- Furnaces Corrugated, or Ribbed and Grooved. Machine made 
 furnaces of the Fox, Morison or Deighton corrugated types, manu- 
 factured by The Leeds Forge Company, John Brown & Co., Sheffield, 
 The Deighton Patent Flue and Tube Co., Leeds, and Wm. Beard- 
 more & Co., Glasgow ; of the Purves ribbed and grooved type, or 
 Brown's cambered type, manufactured by John Brown & Co., 
 Sheffield ; and of the Fox or Morison corrugated type manufactured 
 by Thomas Piggott & Co., Birmingham, provided they are practically 
 true circles, and the plates are not less than ^- inch thick, may be 
 allowed the working pressure found by the following formula : 
 
 C x T 
 
 ^ = working pressure ; 
 
 where C = 14,000 ; * 
 
 T = thickness, in inches, measured at the bottom of the cor- 
 rugation or camber ; and 
 
 D = outside diameter, in inches, measured at the bottom of 
 the corrugations or cambers when the furnace is of the 
 corrugated or cambered type, or over the plain parts 
 when it is of the ribbed and grooved description. 
 In the Fox furnace, the pitch of the corrugations should not 
 exceed 6 inches ; and in the Morison furnace and the Deighton 
 furnace, the pitch should not exceed 8 inches. In these kinds of 
 furnaces, the depth from top of corrugations outside to bottom of 
 corrugations inside should not be less than 2 inches. 
 
 The ribs of ribbed and grooved furnaces should not be less than 
 1^- inches above the plain parts, the depths of the grooves not more 
 than | inch, and the length between the centres of the ribs not over 
 9 inches. In Brown's cambered furnace, the thickness of metal at 
 the centre of the ribs should be at least ^ inch greater than the 
 thickness at the bottom of the camber, the tops of the ribs should be 
 curved to a radius of If inches, and the grooves beneath the ribs to 
 a radius of |-f- inch, the height of the ribs above the bottom of the 
 camber should not be less than If inches, and the pitch of the ribs 
 should not be more than 9 inches. 
 
 Machine made furnaces of the bulb type, manufactured by The 
 Leeds Forge Company, may be allowed the working pressure found 
 by the following formula, provided that they are practically true 
 circles, that the pitch of the bulbs does not exceed 8 inches, that the 
 depth from the top of the bulbs to the plain parts at the centre of the 
 pitch is not less than 2J inches, that the plates are not less than -^ 
 inch thick, and the plain parts between the bulbs are fairly uniform in 
 thickness : 
 
 15000 x T 
 
 j^ = working pressure ; 
 
 where T = thickness of the plain parts between the bulbs, in inches ; 
 
 and 
 
 D = outside diameter at the middle of the plain parts between 
 the bulbs, in inches. 
 
 * This constant only applies to the furnaces when made by the firms named. 
 The Surveyors should report full particulars of any case in which the owners or 
 builders of a passenger steamship propose to use furnaces of any of these types if 
 made by other makers. 
 
382 BOARD OP TRADE BOILER RULES 
 
 In each of these kinds of furnaces, the plain parts at the back ends 
 should be so made that the length, measured from the waterside of 
 the back tube-plate to the centre of the back end corrugation or rib, 
 does not exceed 9 inches. The plain parts at the front ends should 
 also be so made that the length of the flat, measured from the centre 
 of the rivets by which the furnace is secured to the front end plate to 
 the centre of the first corrugation or rib, does not exceed 9 inches. 
 When the plain parts at the back ends are made conical, and the 
 flange by which the attachment is made to the back tube-plate is con- 
 tinuous, a length of 10-^ inches may be allowed between the waterside 
 of the back tube-plate and the centre of the first corrugation or rib. 
 When this method of construction is adopted, the vertical section 
 through the neck-piece should be kept as circular as is practicable, 
 the set-up at the bottom should not exceed 8 inches measured over 
 the plates, and in no case should the vertical axis exceed the horizontal 
 one by more than 14 per cent. The plates at the ends should not be 
 unduly thinned in the flanging. 
 
 If the furnace is riveted in two or more lengths, the case should 
 be submitted for consideration. 
 
 151. Furnaces made up of Flanged Rings. When horizontal furnaces 
 of ordinary diameter are constructed of a series of rings welded 
 longitudinally, and the ends of each ring are flanged and riveted to the 
 next, with a caulking ring intervening, and so forming the furnace, 
 the working pressure is found by the following formula, provided that 
 the length of the rings, in inches, measured over the flanges, is not 
 greater than (120 T - 12), and the flanging is performed at one heat 
 by a suitable flanging machine, and provided also that the conditions 
 which are printed after the formula are complied with : 
 
 9900 x T/ I + 12\ 
 3 x D (5 - 60 x T j = working pressure ; 
 
 where T = thickness of plate, in inches. 
 
 I = length of rings, in inches, and measured over the flanges ; 
 D = outside diameter of furnace, in inches. 
 
 The radius of the flanges on the fire side should be about 1^- 
 inches. The depth of the flanges from the fire side should be three 
 times the diameter of the rivet plus 1| inches, and the thickness of 
 the flanges should be as near the thickness of the body of the plate as 
 practicable. The distance from the edge of the rivet holes to the edge 
 of the flange should not be less than the diameter of the rivet, and 
 the diameter of the rivets at least f inch greater than the thickness of 
 the plate. The depth of the ring between the flanges should not be 
 less than three times the diameter of the rivets, the fire edge of the 
 rings should be at about the termination of the curve of flange, and 
 the thickness not less than half the thickness of the furnace plate. It 
 is very desirable that these rings should be turned. 
 
 The holes in the flanges and rings should be drilled in place, if 
 practicable ; but, if not drilled in place, they should be drilled smaller 
 than the size required, and afterwards, when in place, rimered out 
 until the holes are quite fair ; the holes should be slightly tapered, 
 and the heads of the rivets should be of moderate size. 
 
BOARt) OF TRADE BOILER RULES 383 
 
 After all the welding, flanging, and heating is completed, each ring 
 should be efficiently annealed in one operation. 
 
 When the flanges of the back ends of the furnaces are not con- 
 tinuous, and the lower parts of the back rings are supported by sub- 
 stantial T-bars securely riveted to the plates, the first constant used 
 in the formula for these rings should not exceed 8,910. 
 
 The formula may also be used for determining the pressure which 
 may be allowed on the bottoms of combustion-chambers to which 
 furnaces, having continuous flanges at the back ends, are fitted. In 
 this case, I may be taken as the length over plates ; and no alteration 
 of any of the constants need be made unless the full thickness of the 
 plate is not maintained to the bottom row of stays at each side, when 
 40 should be substituted for 60. 
 
 IRON BOILERS. 
 
 152. Cylindrical Boiler Shells. In calculating the pressure for 
 which the cylindrical shells of iron boilers are suitable, the tensile 
 strength of the plates may be taken as equal to 47,000 Ibs. per square 
 inch with the grain, and 40,000 Ibs. across the grain ; and the shearing 
 strength, per square inch, of the rivets as equal to the tensile strength, 
 per square inch, of the plates ; and, if the boilers have been open to 
 inspection during the whole period of construction, and the workman- 
 ship, material and design are of the highest- class, then 5 may be used 
 as the factor of safety, the additions specified in the rules for steel 
 boilers being made according to the other circumstances stated. If, 
 however, the iron is tested and the elongation, measured in a length 
 of 10 inches, is not less than 14 per cent, with, and 8 per cent, across, 
 the grain, and the Surveyors are otherwise satisfied as to the quality 
 of the plates and rivets, 4*5 may be used as the factor of safety in- 
 stead of 5, in which case the minimum actual tensile strength of the 
 plates should be used in calculating the working pressure, which is to 
 be determined by the rule given on page 
 
 Butt straps should be of as good quality as the shell plates, and 
 those for the longitudinal seams should be cut across the fibre. 
 
 153. Stays for Dished Ends. Solid iron stays for supporting dished 
 ends which are found to be equal to the pressure needed, when con- 
 sidered as portions of spheres, may have a nominal stress of 14,000 
 Ibs. per square inch of net section, but the stress should not exceed 
 10,000 Ibs. when the stays have been welded. 
 
 154. Stays for Flat Surfaces. In the case of new boilers, the 
 Surveyor may allow a stress not exceeding 7,000 Ibs. per square inch 
 of net section on solid iron screwed stays supporting flat surfaces, but 
 the stress should not exceed 5,000 Ibs. when the stays have been 
 welded. 
 
 It has been brought to the notice of the Board of Trade that iron 
 screwed stays in the combustion -chambers of high pressure marine 
 boilers, when of suitable quality, have been found to resist the cross- 
 breaking stresses, to which they are subjected in working, better than 
 similar stays made of steel, and a stress of 9,000 Ibs. per square inch 
 may be allowed on such stays, if solid and unwelded, provided the 
 
384 BOAED OF TRADE BOILER RULES 
 
 bars from which they are made have been tested in the Surveyor's 
 presence, and found to have a tensile strength of not less than 21- tons 
 per square inch and an elongation, measured in a length of 8 inches, 
 of not less than 27 per cent. 
 
 Iron bars which are to be used for combustion-chamber stays in- 
 tended to be subjected to a stress of more than 7,000 Ibs. per square 
 inch should be tested for tensile strength in the same way as similar 
 steel bars, but in the following proportions : one bar in 20 when the 
 diameter of the bars does not exceed 1 inch ; one bar in 12 when not 
 over 1 inches ; and one bar in 8 when the diameter exceeds !- 
 inches. If, however, the bars are rolled at the same time and in 
 lengths not exceeding 20 feet, half these numbers of tests may be 
 accepted, provided the results are uniform and satisfactory, and the 
 Surveyor is satisfied. Two satisfactory re-tests should be made for 
 each failure in any particular batch. All the bars, as rolled, should 
 be stamped with consecutive numbers, and any pieces into which a 
 bar may be cut should be stamped with the original number of the 
 bar. 
 
 In all cases in which iron bars are to be used for the making of 
 screwed stays for which a stress of 9,000 Ibs. per square inch of net 
 section is claimed, the Surveyor should, as far as possible, satisfy him- 
 self that the bars he may select for testing purposes fairly represent 
 in quality the parcel of bars from which they are taken ; and further, 
 he should see that the material is what it purports to be, and, whenever 
 the tensile strength exceeds 24 tons per square inch, special precautions 
 should be taken, by careful examination of the fracture, and other 
 ready means, to guard against the substitution of very mild steel, or 
 of iron mixed with steel scrap, in place of iron. 
 
 In this connection, the Surveyors are informed that mild steel is 
 sometimes improperly termed "ingot iron," and must in all cases, 
 as regards tests and treatment while being worked into boilers, be dealt 
 with in accordance with the Board's instructions with respect to 
 mild steel for boilers. 
 
 Iron. 
 
 155. Stay Tubes. A stress of 6,000 Ibs. may be allowed on the net 
 section of iron stay tubes, provided that the net thickness is in no case 
 less than i inch. 
 
 156. Ordinary Tubes. The thickness of ordinary smoke tubes made 
 of iron should not be less than that found by the following formula : 
 
 or B 
 
 B x D 
 
 9000 (T - -085) 
 
 where T = thickness of tube, in inches ; 
 
 D = outside diameter of tube, in inches ; and 
 B = working pressure. 
 
 157. Girders, Flat Surfaces, Tube-Plates, and Furnaces. When 
 dealing with iron girders, flat surfaces, tube plates, and plain furnaces, 
 
BOARD OF TRADE BOILER RULES 385 
 
 the constants in the rules for steel boilers should be altered as indicated 
 in italics. 
 
 158. General Instructions. In other respects, the instructions, 
 generally, regarding steel boilers apply equally to iron boilers, excepting 
 those in which reference is made to furnaces which are not of the 
 plain type and to the welding and heat treatment of the material. 
 
 160. Iron Cylindrical Superheaters. The strength of the joints of 
 cylindrical superheaters and the factor of < safety are found in the same 
 manner as in the case of cylindrical boilers and steam receivers, but, 
 instead of using 47,000 Ibs. as the tensile strength of iron, 30,000 Ibs. 
 is adopted, unless the heat or flame impinges at, or nearly at, right 
 angles to the plate, when 22,400 Ibs. is substituted. 
 
 When a superheater is constructed with a tube subject to external 
 pressure, the working pressure should be ascertained by the rules 
 given for circular furnaces, but the constants should be reduced as 30 
 to 47. 
 
 In all cases the internal steam pipes should be so fitted that the 
 steam in flowing to them will pass over all the plates which have steam 
 in contact with them, and are exposed to the impact of heat or flame. 
 
 161. Steel for Superheaters, etc. The tubes for superheaters of the 
 type in which there is a coil, or series of small tubes, subject to inter- 
 nal pressure, should be made of solid-drawn steel ; but, excepting for 
 such parts, the use of steel for the heating surfaces of superheaters 
 should be discouraged. This applies to the unshielded uptakes of all 
 boilers, including ordinary vertical donkey boilers ; and, whenever it 
 is proposed to use steel for this purpose, the particulars should be 
 submitted to the Board of Trade for consideration. 
 
 The ends of superheaters, and the flat ends, etc., of all boilers, as 
 far as the steam space extends, should be fitted with shield or baffle 
 plates where exposed to the hot gases in the uptake. 
 
 STEAM PIPES, etc. 
 
 170. Copper Pipes. The working pressure of well-made copper 
 pipes, when the joints are brazed, is found by the following for- 
 mula : 
 
 6000 x (T - ^) 
 
 ^ -'- = working pressure ; 
 
 where T = thickness, in inches ; and 
 D = inside diameter, in inches. 
 
 When the pipes are solid-drawn and not over 10 inches in diameter, 
 substitute in the foregoing formula -^ for ^. 
 
 In any case where the Board of Trade authorise a trial to be made 
 of electro-deposited pipes, the Surveyors should continue, as at pres- 
 ent, to see that the conditions on which such trial is authorised are 
 fulfilled. All cases in which it comes to the Surveyors' knowledge 
 that electro-deposited pipes have failed, either in the copper-smiths' 
 works or in actual working, should be fully reported. 
 
 171. Wrought-Iron and Steel Pipes. The internal pressure on lap- 
 welded wroughfr-iron pipes made of good material, and on lap-welded 
 or solid-drawn steel pipes, may be determined by the following for- 
 ce 
 
380 BOARD OP TRADE BOILER RULES 
 
 mula, provided that the minimum thickness is not less than J inch, 
 and the workmanship, hydraulic test, etc., are satisfactory : 
 
 6000 x T 
 =r = working pressure ; 
 
 where T = thickness, in inches ; and 
 D = inside diameter, in inches. 
 
 Steel pipes which have welded longitudinal seams, and are subject 
 to internal pressure, should in each case be provided with a strap 
 fitted externally and riveted over the weld. All steel pipes should 
 be efficiently annealed after being heated locally for welding or bend- 
 ing them to shape. 
 
 The flanges of wrought-iron and of steel pipes should be made of 
 solid wrought material of ductile quality. 
 
 Pipes for superheated steam should be made of wrought-iron or 
 steel, and not of copper. 
 
 172. Draining Steam Pipes. Efficient means should be provided for 
 draining all steam pipes. Boiler stop- valves cannot be regarded as 
 suitable for this purpose. All drain cocks or valves should be accessible, 
 and so placed as to render it practicable to drain the water from any 
 portion of the steam pipes or chests in connection therewith. Drain 
 pipes should be fitted to drain cocks or valves when the latter are in 
 such a position that the water or steam discharged from them would 
 be likely to cause personal injury. It is desirable that the drains 
 should be automatic in their action. 
 
 173. Expansion Joints. The parts of a socket expansion joint 
 subject to rubbing action should be made of brass or of other metal 
 which will not rust. 
 
 In all cases in which such a joint is fitted to a bent steam pipe, the 
 Surveyor should require a fixed gland and bolts, or other efficient 
 means, to be provided to prevent the end of the pipe being forced out 
 of the socket. This regulation should be complied with in all cases of 
 bent pipes fitted with socket expansion joints, and it is also desirable 
 that fixed glands and bolts should be fitted to the expansion joints of 
 straight steam pipes, as cases have occurred, particularly with small 
 straight pipes, in which the ends have been forced out of the sockets. 
 
 A socket expansion joint on a bent pipe is not a desirable arrange- 
 ment, and, when adopted, the pipe should be anchored or provided with 
 a strut at the bend, to relieve it of any undue bending stresses which 
 might otherwise be produced by the internal pressure on a surface of 
 the pipe equal to the area due to its bore. 
 
 174- Examination and Testing of Steam Pipes. Surveyors should 
 pay particular attention to the examination and testing of steam pipes, 
 and a record of the tests should be kept in the office boiler book. 
 
 All new copper steam pipes should be tested by hydraulic pressure 
 to not less than twice and not more than two and one- half times the 
 working pressure. The higher test should be that usually employed. 
 When, however, special considerations arise, the case should be fully 
 submitted and instructions obtained before the Surveyor proceeds with 
 the hydraulic test. 
 
BOARD OF TRADE BOILER RULES 387 
 
 Wrought-iron lap-welded, and steel steam pipes should be tested 
 by hydraulic pressure when new, with the flanges secured in place, to 
 at least three times the working pressure, but a higher test pressure 
 need not be objected to provided that it does not exceed four times the 
 pressure found by the rule in Section 171, or five times that pressure 
 in the case of solid-drawn steel pipes. 
 
 As regards old pipes, the Surveyor may, at any time he thinks it 
 necessary, before he gives a declaration, require them to be tested by 
 hydraulic pressure to satisfy himself as to any doubtful part, or parts, 
 and he may also require the removal of any of such pipes in order 
 that their interior may be examined and their actual thickness and 
 condition ascertained, but they should be tested periodically, to not less 
 than twice the maximum working pressure to which they are subject, 
 as follows : 
 
 MAIN STEAM PIPES. 
 
 Note. Main steam pipes include the main range and its branches from the 
 various boilers and those to the propelling machinery, also all steam pipes joining 
 two or more boilers together. 
 
 (a) All copper bars having brazed longitudinal seams, whether 
 forming a complete range or only part of a range of pipes, should, 
 with the exception of those referred to in paragraph (c), be examined 
 and tested, with the lagging removed, at least once in about every 
 four years. 
 
 (b) Iron, steel, or solid-drawn copper pipes should, when the 
 diameter exceeds 3 inches, be stripped and tested by hydraulic pressure 
 at least once in six years. 
 
 (c) In the case of pipes with a diameter of 3 inches or less the 
 Surveyor may use his own discretion as to the removal of the lagging 
 for more than a few inches near each flange when the hydraulic test is 
 applied. 
 
 AUXILIARY STEAM PIPES HAVING AN INTERNAL DIAMETER EXCEEDING 
 
 6 INCHES. 
 
 (a) Copper pipes having brazed longitudinal seams should be 
 stripped and tested by hydraulic pressure at least once in four years. 
 
 (b) Iron, steel, or solid-drawn copper pipes should be stripped and 
 tested by hydraulic pressure at least once in six years. 
 
 AUXILIARY STEAM PIPES HAVING AN INTERNAL DIAMETER EXCEEDING 
 3 INCHES AND NOT EXCEEDING 6 INCHES. 
 
 (a) Copper pipes having brazed longitudinal seams should be 
 stripped for not less than 2 inches at each flange and tested by 
 hydraulic pressure at least once in every four years. 
 
 (b) Iron, steel, or solid-drawn copper pipes should be stripped for 
 not less than 2 inches at each flange and tested by hydralic pressure 
 at least once in six years. 
 
 cc 2 
 
388 BOARD OF TRADE BOILER RULES 
 
 GENERAL. 
 
 In 'all cases where the pipes are not wholly stripped, the hydraulic 
 test pressure should remain on the pipes for such time as the Surveyor 
 considers necessary, but in no case for less than 20 consecutive minutes. 
 Any length from which leakage is observed at other places than the 
 flanges should be stripped, repaired, and re-tested. 
 
 The foregoing instructions apply to all steam pipes, the bursting of 
 which would probably cause loss of life or serious injury, but it is not 
 expected that the Surveyors will insist on the testing of small pipes, 
 from which the free outflow of steam would cause no danger or in- 
 convenience, and which would not easily burst in any circumstances. 
 
 When a vessel is surveyed for a passenger certificate after trans- 
 ference from a foreign flag, or for the first time, all the steam pipes 
 should be tested as indicated in these instructions. 
 
 It has been brought to the notice of the Board that severe corrosion 
 has, in a number of cases, been found on the outer surface of copper 
 steam pipes which have been covered with non-conducting material 
 composed chiefly of asbestos combined with a binding material, more 
 particularly where the pipes have been wetted by sea water. The 
 Surveyors should therefore pay special attention to the examination 
 and condition of copper steam pipes which may be covered with 
 asbestos and other porous lagging, especially when the pipes are exposed 
 to the action of sea water, and, where they find any evidence of the 
 existence of corrosion, they should take special steps to satisfy them- 
 selves that the pipes are of sufficient thickness and otherwise safe for 
 the pressure at which they are worked. It is most desirable that 
 copper pipes which would be liable to be occasionally wetted by sea water 
 should be efficiently protected by a waterproof covering over the lagging, 
 which should, preferably, be free from acid and otherwise non-corrosive. 
 
 Safety-Valves. 
 
 175. Examination of Safety- Valves. The Surveyor, in his exami- 
 nation of the machinery and boilers, is particularly to direct his 
 attention to the safety-valves, and, whenever he considers it necessary, 
 he is to satisfy himself as to the pressure on the boiler by actual trial. 
 
 The Surveyor is to fix the limits of the weight to be placed on the 
 safety-valves, and the responsibility of issuing a declaration before he 
 is fully satisfied on the point is very grave. The law places on the 
 Surveyor the responsibility of "declaring" that the boilers are in his 
 judgment sufficient with the weights he states. 
 
 176. Surveyor to see Valves Weighted. When the Surveyor has 
 determined the working pressure, he is to see the safety-valves weighted 
 accordingly, and the weights or springs fixed in such a manner as to 
 preclude the possibility of them shifting or in any way increasing the 
 pressure. The limit of the weight on the valves is to be inserted in 
 the declaration, and should it at any time come to a Surveyor's 
 knowledge that the weights have been shifted, or the loading of the 
 valves has been otherwise altered, or that the valves have been in any 
 way interfered with, so as to increase the pressure without the 
 sanction of the Board of Trade, he is at once to report the facts to the 
 Board. 
 
BOARD OF TRADE BOILER RULES 
 
 If any person places an undue weight on the safety-valve of any 
 steamship, or in the case of steamships surveyed under the Act, 
 increases such weight beyond the limits fixed by the Engineer Surveyor, 
 he shall, in addition to any other liability he may incur by so doing, 
 be liable for each offence to a fine not exceeding one hundred pounds. 
 
 177. Provision as regards Safety- Valves. Gases have come under 
 the notice of the Board in which there were pipes between the boilers 
 and the safety-valve chests. Such arrangement is not in accordance 
 with the Act, which distinctly provides that the safety-valves shall be 
 upon the boilers. 
 
 The Surveyors are instructed that in all new boilers, and in boilers 
 in which alterations can be easily made, the valve chest should be 
 placed directly on the boiler ; and the neck, or part between the chest 
 and the flange which is bolted on to the boiler, should be as short as 
 possible and be cast in one with the chest. 
 
 The Surveyor should note that it is not intended by this instruction 
 that vessels with old boilers which have been previously passed with 
 such an arrangement should be detained for the alterations to be 
 carried out. 
 
 Of course in any case in which the Surveyor is of opinion that it is 
 positively dangerous to have a length of pipe between the boilers and 
 the safety-valve chest, it is his duty at once to insist on the requisite 
 alterations being made before granting a declaration. 
 
 179. Area of Safety-valves. The locked-up valves, i.e., those out of 
 the control of the engineer when steam is up, should have an area not 
 smaller, and a pressure not greater, than those which are not locked- 
 up, if any such valves are fitted. 
 
 When natural draught is used, the area per square foot of fire-grate 
 surface of the locked-up safety-valves should not be less than that 
 given in the following table opposite the boiler pressure intended, but 
 in no case should the valves be less than 2 inches in diameter. This 
 applies to new vessels and to vessels which have not previously received 
 a passenger certificate. 
 
 When, however, the valves are of the common description, and are 
 made in accordance with the table, it will be necessary either to fit 
 them with springs having great elasticity, or to provide other means 
 to keep the accumulation within moderate limits. 
 
 Safety -Valve Areas 
 (Natural Draught) 
 
 Boiler 
 Pressure 
 
 Area of Valve 
 per Square 
 Foot of 
 Fire Grate 
 
 Boiler 
 Pressure 
 
 Area of Valve 
 per Square 
 Foot of 
 Fire Grate 
 
 Boiler 
 Pressure 
 
 Area of Valre 
 per Square 
 Foot of 
 Fire Grate 
 
 15 
 
 16 
 17 
 18 
 19 
 20 
 21 
 22 
 
 1-250 
 1-209 
 1-171 
 1-136 
 1-102 
 1-071 
 1-041 
 1-013 
 
 23 
 24 
 25 
 26 
 27 
 28 
 29 
 30 
 
 986 
 961 
 937 
 914 
 892 
 872 
 852 
 833 
 
 31 
 32 
 33 
 34 
 35 
 36 
 37 
 38 
 
 815 
 797 
 781 
 765 
 750 
 735 
 721 
 707 
 
390 
 
 BOARD OF TRADE BOILER RULES 
 
 Safety-Valve Areas. cont. 
 
 Boiler 
 
 Pr6S8UT6 
 
 Area of Valve 
 per Square 
 Foot of 
 Fire Grate 
 
 Boiler 
 Pressure 
 
 Area of Valve 
 per Square 
 Foot of 
 Fire Grate 
 
 Boiler 
 Pressure 
 
 Area of Valve 
 per Square 
 Foot of 
 Fire Grate 
 
 39 
 
 694 
 
 93 
 
 347 
 
 147 
 
 231 
 
 40 
 
 681 
 
 94 
 
 344 
 
 148 
 
 230 
 
 41 
 
 669 
 
 95 
 
 340 
 
 149 
 
 228 
 
 42 
 
 657 
 
 96 
 
 337 
 
 150 
 
 227 
 
 43 
 
 646 
 
 97 
 
 334 
 
 151 
 
 225 
 
 44 
 
 635 
 
 98 
 
 331 
 
 152 
 
 224 
 
 45 
 
 625 
 
 99 
 
 328 
 
 153 
 
 223 
 
 46 
 
 614 
 
 100 
 
 326 
 
 154 
 
 221 
 
 47 
 
 604 
 
 101 
 
 323 
 
 155 
 
 220 
 
 48 
 
 595 
 
 102 
 
 320 
 
 156 
 
 219 
 
 49 
 
 585 
 
 103 
 
 317 
 
 157 
 
 218 
 
 50 
 
 576 
 
 104 
 
 315 
 
 158 
 
 216 
 
 51 
 
 568 
 
 105 
 
 312 
 
 159 
 
 215 
 
 52 
 
 559 
 
 106 
 
 309 
 
 160 
 
 214 
 
 53 
 
 551 
 
 107 
 
 307 
 
 161 
 
 213 
 
 54 
 
 543 
 
 108 
 
 304 
 
 162 
 
 211 
 
 55 
 
 535 
 
 109 
 
 302 
 
 163 
 
 210 
 
 56 
 
 528 
 
 110 
 
 300 
 
 164 
 
 209 
 
 57 
 
 520 
 
 111 
 
 297 
 
 165 
 
 208 
 
 58 
 
 513 
 
 112 
 
 295 
 
 166 
 
 207 
 
 59 
 
 506 
 
 113 
 
 292 
 
 167 
 
 206 
 
 60 
 
 500 
 
 114 
 
 290 
 
 168 
 
 204 
 
 61 
 
 493 
 
 115 
 
 288 
 
 169 
 
 203 
 
 62 
 
 487 
 
 116 
 
 286 
 
 170 
 
 202 
 
 63 
 
 480 
 
 117 
 
 284 
 
 171 
 
 201 
 
 64 
 
 474 
 
 118 
 
 281 
 
 172 
 
 200 
 
 65 
 
 468 
 
 119 
 
 279 
 
 173 
 
 199 
 
 66 
 
 462 
 
 120 
 
 277 
 
 174 
 
 198 
 
 67 
 
 457 
 
 121 
 
 275 
 
 175 
 
 197 
 
 68 
 
 451 
 
 122 
 
 273 
 
 176 
 
 196 
 
 69 
 
 446 
 
 123 
 
 271 
 
 177 
 
 195 
 
 70 
 
 441 
 
 124 
 
 269 
 
 178 
 
 194 
 
 71 
 
 436 
 
 125 
 
 267 
 
 179 
 
 193 
 
 72 
 
 431 
 
 126 
 
 265 
 
 180 
 
 192 
 
 73 
 
 426 
 
 127 
 
 264 
 
 181 
 
 191 
 
 74 
 
 421 
 
 128 
 
 262 
 
 182 
 
 190 
 
 75 
 
 416 
 
 129 
 
 260 
 
 183 
 
 189 
 
 76 
 
 412 
 
 130 
 
 258 
 
 184 
 
 188 
 
 77 
 
 407 
 
 131 
 
 256 
 
 185 
 
 187 
 
 78 
 
 403 
 
 132 
 
 255 
 
 186 
 
 186 
 
 79 
 
 398 
 
 133 
 
 253 
 
 187 
 
 185 
 
 80 
 
 394 
 
 134 
 
 251 
 
 188 
 
 184 
 
 81 
 
 390 
 
 135 
 
 250 
 
 189 
 
 18S 
 
 82 
 
 386 
 
 136 
 
 248 
 
 190 
 
 182 
 
 83 
 
 382 
 
 137 
 
 246 
 
 191 
 
 181 
 
 84 
 
 378 
 
 138 
 
 245 
 
 192 
 
 181 
 
 85 
 
 375 
 
 189 
 
 243 
 
 193 
 
 180 
 
 86 
 
 371 
 
 140 
 
 241 
 
 104 
 
 179 
 
 87 
 
 367 
 
 141 
 
 240 
 
 195 
 
 178 
 
 88 
 
 364 
 
 142 
 
 238 
 
 196 
 
 177 
 
 89 
 
 360 
 
 143 
 
 237 
 
 197 
 
 176 
 
 90 
 
 357 
 
 144 
 
 235 
 
 198 
 
 176 
 
 91 
 
 353 
 
 145 
 
 234 
 
 199 
 
 175 
 
 92 
 
 350 
 
 146 
 
 232 
 
 200 
 
 174 
 
BOARD OF TRADE BOILER RULES 391 
 
 When forced draught is used, the area of the safety-valves should 
 not be less than that found by the following formula : 
 
 ^ x ! estimated consumption of coal per square 
 
 \ foot of grate in Ibs. per hour area of valves 
 
 20 required ; 
 
 where A = area of valves as found from the table. 
 
 When the pressure exceeds 180 Ibs. per square inch, the accumula- 
 tion of pressure at the steam test will probably be exceptionally high, 
 unless the area of the branch leading from the valve chest is in excess 
 of the area of the valves, and the area of the main waste steam pipe 
 is correspondingly in excess of the gross area of the valves. 
 
 When ascertaining the fire-grate area, the length of the grate 
 should be measured from the inner edge of the dead-plate to the 
 front of the bridge, and the width from side to side of the furnace on 
 the top of the bars at the middle of their length. 
 
 181. Spring-loaded Safety- Valves- The Surveyor need raise no 
 question as to the sufficiency of spring-loaded valves, if the results of 
 the steam trial for accumulation of pressure are satisfactory, and if 
 the following conditions are complied with : 
 
 (1) That at least two valves are fitted to each boiler. 
 
 (2) That the valves are of the size prescribed by Section 179. 
 
 (3) That the springs and valves are so cased-in and locked-up 
 
 that they cannot be tampered with. 
 
 (4) That provision is made to prevent the valves flying off in case 
 
 of the springs breaking. 
 
 (5) That screw lifting-gear is provided to ease all the valves, as 
 
 required by Section 180. 
 
 (6) That the size of the steel of which the springs are made is in 
 
 accordance with that found by the following formula : 
 
 = d; 
 
 where s = the load on the spring, in Ibs. ; 
 
 D = the diameter of the spring (from centre to 
 
 centre of wire), in inches ; 
 d = the diameter, or side of square, of the wire, in 
 
 inches ; 
 
 c = 8,000 for round steel ; and 
 c = 11,000 for square steel. 
 
 (7) That the springs are protected from the steam and impurities 
 
 issuing from the valves. 
 
 (8) That, when valves are loaded by direct springs, the compress- 
 
 ing screws abut against metal stops or washers, when the 
 loads sanctioned by the Surveyor are on the valves. 
 
 (9) That the springs have a sufficient number of coils to allow a 
 
 compression under the working load of at least one quarter 
 the diameter of the valve. 
 The number of coils required for a given compression, or the com- 
 
392 BOARD OF TRADE BOILER RULES 
 
 pression due to the load, is given, approximately, by the following 
 formula : 
 
 K x C x d 4 
 
 K = 
 
 s x D 
 s x D 3 x N 
 C x d 4 
 
 or 
 
 where N = number of free coils in spring ; 
 K = compression, in inches ; 
 d = diameter of steel, or side of square, in sixteenths 
 
 of an inch ; 
 
 C = 22 for round, and 30 for square steel ; and 
 5 and D have the same meanings as before. 
 
 The steel of safety-valve springs should not as a rule be less than 
 J inch in diameter or side of square. 
 
 182. Spring-loaded Valves to be Tested under Steam. In no case is 
 the Surveyor to give a declaration for spring-loaded valves, unless he 
 has examined them and is acquainted with the details of their con- 
 struction, and unless he has tried them under full steam, and full 
 firing, for at least 15 minutes with the feed-water shut off and stop- 
 valve closed, and is fully satisfied with the result of the test. In 
 special cases, when the valves are of novel design or where forced 
 draught is used, the results of the test under full steam should be re- 
 ported on the form Surveys 21, but, if the Surveyor is fully satisfied 
 with them, he need not delay the granting of the declaration for the 
 vessel pending the approval of the Board of Trade. If, however, the 
 accumulation of pressure exceeds 10 per cent, of the loaded pressure, 
 he should withhold his declaration and report the case to the Board, 
 submitting a sketch, if necessary, and stating the strength pressure 
 and the working pressure of the boilers. 
 
 When witnessing safety-valve tests for accumulation of pressure, 
 the Surveyors are to use the pressure gauges supplied by the Board 
 of Trade for the purpose. No steam gauge should be used without 
 having a syphon filled with water between it and the boiler, and care 
 should be taken to see that the gauge pipe and syphon are clear before 
 attaching the gauge. 
 
 183- Plans of New Designs or of Alterations in Details to be submitted- 
 In the case of safety-valves of which the principle and details have 
 already been passed by the Board of Trade, the Surveyor need not 
 require plans to be submitted so long as the details are unaltered, as to 
 which he must fully satisfy himself ; but, in any new arrangement of 
 valves, or in any case in which any detail of approved valves is altered, 
 he should, before assuming the responsibility of passing them, report 
 particulars, with a drawing to scale, to the Board of Trade. He can 
 make this drawing himself from the actual parts of the valves fitted, 
 but, in order to save time and to faciliate the survey, the owners or 
 makers may prefer to send in tracings of their own, before the valves 
 are placed on the boiler. If they do this the survey can be more 
 readily made, and delay and expense may be saved to owners, as the 
 Surveyor will not then have to spend his time, and delay the ship, 
 in preparing drawings and comparing them with the valves. 
 
BOARD OF TRADE BOILER RULES 393 
 
 The tracings of new safety-valve designs should, where practicable, 
 be transmitted to the Board of Trade for consideration before the con- 
 struction of the valves is commenced. 
 
 The Surveyors should arrange with manufacturers to supply the 
 designs of safety-valves which they intend to make. An easy method 
 of facilitating this matter is for the manufacturer to leave in the local 
 Surveyor's office an approved plan or plans of his valve or valves, and 
 then afterwards to inform the Surveyors that the valves fitted are 
 according to (drawing A, B, or C, as the case may be. By this means, 
 when once a design has been agreed upon, and is adhered to, all sub- 
 sequent questions and delays will be prevented. 
 
 185- Stop- Valves- No boiler or steam chamber should be so con- 
 structed, fitted, or arranged that the escape of steam from it through the 
 safety-valves required by the Act of Parliament can be wholly, or 
 partially, intercepted by the action of another valve. 
 
 Combined stop- and safety-valve chests are undesirable mountings, 
 and in any case in which it is desired to adopt them, full particulars 
 should be submitted to the Board for consideration. 
 
 A stop-valve should always be fitted between the boiler and the 
 steam pipe, and, where two or more boilers are connected with a 
 steam receiver or superheater, between each boiler and the super- 
 heater or steam receiver. 
 
 The necks of stop-valve chests and other boiler mountings should 
 be as short as practicable ; and the chests should be tested when new 
 to double the working pressure. 
 
 186. Water-Gauges, Test Cocks, Steam-Gauges, etc. Each boiler 
 should be fitted with a glass water-gauge, at least three test cocks, 
 and a steam-gauge. Boilers that are fired from both ends, and those 
 of unusual width, should have a glass water-gauge and three test cocks 
 at each end or side, as the case may be. An additional glass water- 
 gauge may, however, be substituted for three test cocks. When a 
 steamship has more than one boiler, each boiler should be treated as 
 a separate one, and have all the requisite fittings. 
 
 When the water-gauge cocks are not attached directly to the shell 
 of the boiler, but to a stand-pipe or column, cocks should, as a general 
 rule, be fitted between the boiler and the stand-pipes, etc., and may 
 be placed either on the boiler or at the stand-pipe. Such cocks need 
 not, however, be insisted on in cases where the columns, stand-pipes, 
 etc., are of moderate length and of suitable strength, provided that the 
 diameter of the bore at any part is not less than 3 inches. The Sur- 
 veyors should not pass valves between the boiler and the stand-pipe. 
 
 If the column, stand-pipes, etc., are of less diameter than 3 inches, 
 and the pipes are bolted to the boiler without the intervention of cocks, 
 the arrangement need not be objected to, if (otherwise satisfactory, 
 provided that there is no difficulty in keeping the passages at the ends 
 clear and in ascertaining that they are so. To do this it will be 
 necessary that the passage in the part of the column between the top 
 and bottom gauge-glass cocks be cut off or closed, which may be done 
 permanently, or by the interposition of a cock at that part. The latter 
 is a convenient and desirable arrangement even when cocks are fitted 
 on the boiler. 
 
 In the case of high pressure boilers, it is desirable that the cocks 
 
394 BOARD OF TEADE BOILER RULES 
 
 in connection with the water-gauges should be fitted with handles 
 which can be expeditiously manipulated from a convenient position. 
 
 It is desirable in all cases that test cocks should be fitted directly 
 to the skin of the boiler, and when the water-gauge is attached to a 
 column, the opening through which is stopped or can be cut off, the 
 test cocks must be fitted directly to the skin of the boiler. 
 
 The Surveyors should satisfy themselves by actual examination 
 whether the glass water-gauges of the boilers of the vessels they survey 
 are clear, and also whether they are fitted with automatic valves or 
 fittings, as the existence of such fittings cannot always be ascertained 
 by external examination. In all cases where automatic gauges are 
 fitted, full particulars thereof should be submitted for consideration 
 and approval before the gauges are passed. 
 
 189. Circulating Pipes. When the pipes are so arranged that the 
 water in the boilers can be circulated by means of the donkey pump, 
 similar precautions should-be observed ; and a cock fitted with a spanner 
 and guard, the handle of which will stand above the level of the 
 platform, should be fitted to the circulating pipes, preferably near the 
 pump. 
 
 190- Non-return Valves to Pipes. A non-return valve having a 
 screw spindle not attached, by which the valve may be set down on 
 its seat when necessary, should be fitted to all pipes which are so led 
 or placed that water could, unless such non-return valves were fitted, 
 run from the boiler or the sea into the bilge, either by accidentally or 
 intentionally leaving a cock or valve open ; the only exception to this 
 requirement has reference to the fireman's ash cock, which must have 
 a cock or valve on the ship's side and be above the stoke-hold plates. 
 
 191. Cast-Iron Stand-Pipes, Cocks, etc Cast-iron stand-pipes or 
 cocks intended for the passage through them of hot brine should not 
 be passed. 
 
 Surveyors should also discourage the use of cast-iron chocks and 
 saddles for boilers, and particular attention should be paid to the 
 chocking of boilers, more especially when they are fired athwartships. 
 
 192. Exhaust Pipe of Donkey Engine not led through Ship's Side. 
 The exhaust pipe for the donkey engine should not be led through the 
 ship's side ; it should be led on deck or into the main waste steam pipe, 
 and in all cases it should have a drain-cock on it. 
 
BOARD OF TRADE BOILER RULES 395 
 
 SUMMARY 
 
 The preceding rules are summarised in the following short table, 
 in which the method has been carried out of indicating all such 
 dimensions as are measured in inches by capitals, such as are measured 
 in sixteenths of an inch by small letters, and all coefficients, &c., by 
 black letters. 
 
 C and C' = coefficients. 
 
 W P = permissible working pressure. 
 
 B and B' = percentage of joint, respectively of plate and of rivets. 
 N = number of rivets included within one pitch of external 
 
 row. 
 
 F = factor of safety. 
 T and t = thickness of plate, measured respectively in inches and 
 
 in sixteenths. 
 P and P = pitches of rivets, or of stays, or of stay tubes. 
 
 D = internal diameter of shells, or of plain tubes ; effective 
 diameters of rivets or of stays, or external diameter of 
 furnaces in inches, measured at the plain cylindrical 
 part or at the bottom of the corrugations. 
 
 I/ and L" = length of plain cylindrical parts of furnaces, depth of 
 combination chamber, or length of girders, measured 
 respectively in feet and in inches. 
 H = depth of girders measured in inches. 
 A = sectional area of stays or of rivets in square inches. 
 
 Percentage of plate : B = (P - D) : 100 P. 
 Percentage of rivets : 
 
 Double Butt Straps : B' = 187'5 N . A -f P . T = H7 N . D* ^ P . T. 
 Lap Joints : B' = 100 NA + PT = 78*5 N . D 2 ^ P . T. 
 
396 
 
 BOARD OF TRADE BOILER RULES 
 
 The coefficients for determining the working pressure of the shell 
 depend on the material and on conditions of workmanship, the 
 ultimate strength of the material being divided by the sum of 4-5 and 
 one or both of the following additions : 
 
 TABLE OF ADDITIONS TO THE FACTORS OP SAFETY 
 
 Type of Joint 
 
 Longitudinal Seams 
 
 Circumferential Seams 
 
 Double 
 Butt 
 Straps 
 
 Lap Joint 
 
 Double 
 Butt 
 Straps 
 
 Lap Joint 
 
 Riveting 
 
 >>-g 
 
 i 
 
 Double 
 
 | 
 
 1 
 
 a 
 
 0-25 
 0*2 
 0-1 
 
 1 
 
 0-15 
 0-10 
 
 o-o 
 
 1 
 S 
 
 0-35 
 0-3 
 0-2 
 
 3 
 
 1 
 
 1 
 
 0-15 
 0-1 
 
 o-o 
 
 Holes drilled before bending . 
 after ,, 
 > M in place ,, 
 
 0-3 
 0'15 
 
 o-o 
 
 1-3 
 1-15 
 L-0 
 
 0-6 
 0-45 
 0-3 
 
 0-4 
 0-25 
 0-1 
 
 0-25 
 0-2 
 O'l 
 
 For good but not tested iron add -5. 
 
 If there are no circumferential seams add '4. 
 
 1 In these three cases -3 has to be added for double-ended boilers, but only for the central 
 
 Iron Boiler Shells. 
 
 C (BorB') T 
 
 The value of C is 
 
 40,000 for wrought iron (across the grain), not tested. 
 47,000 (with the grain) 
 
 'If tested, C is the lowest ultimate tensile strength in Ibs. per sq. 
 inch. F<5r superheaters use 30,000, or if in contact with flame use 
 22,400. 
 
 Steel Boiler Shells. 
 
 WP = 44-8 S . T . B + F . D, or = 229 T . B' -j- D. 
 
 S in tons per sq. inch is the minimum ascertained tensile strength of 
 the shell plates. 
 
BOARD OF TRADE BOILER RULES 
 
 897 
 
 FUBNACES. (See appended Tables.) 
 
 Plain Furnaces. WP 
 
 C.T 2 . 
 
 k or 
 
 C'.* 2 
 
 D.(L' + 1)' D.(L' 
 TABLE OP VALUES OF C AND C' 
 
 
 C 
 
 C' 
 
 Material ot Furnace 
 
 
 
 
 Iron 
 
 Steel 
 
 Iron 
 
 Steel 
 
 Longitudinal Seams ol Furnace 
 
 Drilled 
 
 Punched 
 
 Drilled 
 
 Drilled 
 
 Punch'd 
 
 Drilled 
 
 Single butt straps double- 
 
 
 
 
 
 
 
 riveted, or double butt 
 
 
 
 
 
 
 
 straps single-riveted 
 
 90,000 
 
 85,000 
 
 99,000 
 
 351-6 
 
 332-0 
 
 386-7 
 
 Single butt straps single- 
 
 
 
 
 
 
 
 riveted, or lap- bevelled and 
 
 
 
 
 
 
 
 double-riveted . 
 
 80,000 
 
 75,000 
 
 88,000 
 
 312-5 
 
 293-0 
 
 343-7 
 
 Lap not bevelled, double- 
 
 
 
 
 
 
 
 riveted .... 
 
 75,000 
 
 70,000 
 
 82,500 
 
 293-0 
 
 273-4 
 
 3222 
 
 Lap bevelled, single-riveted . 
 
 70,000 
 
 65,000 
 
 77,000 
 
 273-4 
 
 255-9 
 
 300-8 
 
 Lap not bevelled, single- 
 
 
 
 
 
 
 
 riveted .... 
 
 65,000 
 
 60,000 
 
 71,500 
 
 253-9 
 
 234-4 
 
 279-3 
 
 Longitudinal seams welded . 
 
 90,000 
 
 99,000 
 
 351-6 1 386-7 
 
 In no case should the working pressure exceed the values found 
 by the following formulae : 
 
 for iron. 
 
 For short lengths of flanged furnaces use the following formulae : 
 
 wp== 9,900 ^ (5 T _ L"_ 1. 
 
 for steel plates. 
 
 These formulae can only be used as long as L" ^_ 120 T 12. 
 
 The working pressures for various patent furnaces are found by 
 the following fovtnuia : 
 
 Fox's corrugated steel furnaces ) w p _ -, * ^/^ T QI7 . t 
 Purves's ribbed D " ' D' 
 
 Leeds Forge Bulb W P = 15,000 . ^ = 937'5 i . 
 
398 
 
 BOARD OK TRADE BOILER KULKS 
 
 FLAT PLATE. (See appended Tables.) 
 
 (P- P.- 6)- 
 
 If the pitches P and P are equal, then 
 
 For unequal pitches (see T. W. Trail, 1890, pp. 67, 199) apparently 
 
 wf _ 
 
 2C. 
 
 where p = diagonal pitch or diameter of largest inscribed circle 
 TABLE OP VALUES OF C. 
 
 Material of Plate 
 
 Ifron 
 
 Steel 
 
 
 8 
 
 
 
 
 
 
 
 
 JS 
 
 
 Position of Stay and its Mode of 
 Attachment 
 
 Front Tu 
 Plate 
 
 a * 
 
 P. 
 
 q 
 
 V, ^ 
 
 m 
 
 Front Tu 
 Plate 
 
 U 
 
 1 
 
 P. 
 
 a 
 
 El 
 | S 
 
 Stay ends riveted or expanded 
 
 70 
 
 60 
 
 36 
 
 70 
 
 77 
 
 66 
 
 39-6 
 
 77 
 
 Stay screwed into plate and nutted 
 
 90 
 
 80 
 
 54 
 
 ... 
 
 112-5 
 
 100 
 
 67-5 
 
 
 Stay double nutted 
 
 
 
 , 
 
 120 
 
 
 
 
 150 
 
 washer 3D xT 1 ... 
 
 ... 
 
 60 
 
 132 
 
 ... 
 
 ... 
 
 75 
 
 165 
 
 ,, fPxT. 
 
 .. 
 
 ... 
 
 
 16ft 
 
 ... 
 
 ... 
 
 ... 
 
 210 
 
 bar f P x T . 
 
 ... 
 
 ... 
 
 ... 
 
 192 
 
 ... 
 
 ... 
 
 ... 
 
 240 
 
 INNER TUBE PLATES. 
 
 wp _ C . (P-D) T _ C' . (P - D) t 
 ' U r ^ r L". P " 
 
 TABLE OP VALUES OP C AND C'. 
 
 Material 
 
 Iron 
 
 Steel 
 
 C . 
 
 22000 
 
 28000 
 
 C' 
 
 1,375 
 
 1,750 
 
 
 
 
BOARD OF TRADE BOILER RULES 899 
 
 STAYS. (See appended Tables.) 
 
 TABLE OP VALUES OF C AND C 7 . 
 
 Material of Stays 
 
 C 
 
 C' 
 
 Welded or heated iron stays . 
 
 5,000 
 
 3,925 
 
 Iron stays 
 
 7,000 
 
 5,498 
 
 Steel 
 
 9,000 
 
 7,069 
 
 Iron stay tubes if i inch thick net 
 
 6,000 
 
 ... 
 
 Steel if i inch thick net 
 
 7,500 
 
 
 GIBBERS. WP = 
 
 C . H" T 
 
 TABLE OP VALUES OF C. 
 
 Number of Stays in Girders 
 
 Material of Girders 
 
 Iron 
 
 Steel 
 
 
 6,000 
 9,000 
 10,000 
 
 6,600 
 9,900 
 11,000 
 
 
 
 
 TABLES. 
 
 When used in the drawing office, it is strongly recommended that 
 those parts of the following tables which are inapplicable to the 
 particular works should be obliterated. 
 
 TABLE FOR FINDING THE DIAMETERS OF RIVETS AND OP PITCH IN 
 
 EIVETED JOINTS. 
 
 A short table will be found on p. 316 which shows the smallest 
 permissible percentage for any particular joint ; the conditions are 
 fully explained and illustrated. 
 
 The following table contains the values of N . D -f- T = number of 
 rivets x diameter of rivets -r thickness of steel plate. Having found 
 the number in the table corresponding to the desired percentage, it 
 has to be divided by the number of rivets and multiplied by the 
 thickness of the plate. The result is the diameter of the rivet hole. 
 This has to be multiplied by the corresponding value in the first 
 column of this table, viz. pitch -f- rivet diameter, and the product is 
 the pitch of the rivet. For examples see pp. 322, 351. 
 
 This is only true if the factor of safety is 4'5. For any other 
 
 factor F the value N . D -- T has to be multiplied by 4 _ 5 . 
 
 The pitch is limited by the formula P = If + C x T, and may not 
 exceed 10". (See p. 371) 
 
400 
 
 BOARD OF TRADE BOILER RULES 
 
 MINIMUM VALUES OF N . D -- T 
 
 Number x Diameter of Rivets 
 ""Thickness of Plate ' 
 
 Pitch* Rivet 
 Diameter 
 
 Percentage of 
 Plate 
 
 LAP JOINT 
 
 BUTT STRAPS 
 
 Iron Plates Steel Plates Steel Plates 
 Iron Rivets Steel Rivets Iron Rivets 
 
 Iron Plates i Steel Plates Steel Plates 
 Iron Rivets Steel Rivets Iron Rivets 
 
 Constants 
 
 100 
 
 iflOO 
 
 A'lOO 
 
 noo 
 
 m-ioo 
 
 l-A-100 
 
 2-50 
 
 60 
 
 ... 
 
 2-32 
 
 3-10 
 
 ... 
 
 ... 
 
 
 
 2-56 
 
 61 
 
 ... 
 
 2-42 
 
 3-24 
 
 ... 
 
 
 
 ... 
 
 2-63 
 
 62 
 
 2-08 
 
 2-53 
 
 3-38 
 
 ... 
 
 ... 
 
 ... 
 
 2-70 
 
 63 
 
 2-17 
 
 2-64 
 
 3-52 
 
 ... 
 
 ... 
 
 2-01 
 
 2-78 
 
 64 
 
 2-26 
 
 2-76 
 
 3-68 
 
 ... 
 
 ... 
 
 2-10 
 
 2-86 
 
 65 
 
 2-36 
 
 2-88 
 
 3-84 
 
 ... 
 
 ... 
 
 2-19 
 
 2-94 
 
 66 
 
 2-47 
 
 3-01 
 
 4-02 
 
 ... 
 
 ... 
 
 2-29 
 
 3-03 
 
 67 
 
 2-59 
 
 315 
 
 4-20 
 
 ... 
 
 ... 
 
 2-40 
 
 3-12 
 
 68 
 
 2-71 
 
 3-29 
 
 4-40 
 
 ... 
 
 ... 
 
 2-51 
 
 3-22 
 
 69 
 
 2-83 
 
 3-45 
 
 4-61 
 
 ... 
 
 ... 
 
 2-63 
 
 3-33 
 
 70 
 
 2-97 
 
 3-62 
 
 4-83 
 
 ... 
 
 2-07 
 
 2-76 
 
 3-45 
 
 71 
 
 3-12 
 
 3-79 
 
 5-07 
 
 ... 
 
 2-17 
 
 2-89 
 
 3-57 
 
 72 
 
 3-27 
 
 3-99 
 
 5-32 
 
 ... 
 
 2-28 
 
 3-04 
 
 3-70 
 
 73 
 
 3-44 
 
 4-19 
 
 5-59 
 
 ... 
 
 2-39 
 
 3-20 
 
 3-85 
 
 74 
 
 3-62 
 
 4-41 
 
 5-89 
 
 2-07 
 
 2-52 
 
 3-37 
 
 4-00 
 
 75 
 
 3-82 
 
 4-65 
 
 6-21 
 
 2-18 
 
 2-66 
 
 3-55 
 
 4-08 
 
 75* 
 
 3-92 
 
 4-78 
 
 6-38 
 
 2-24 
 
 2-73 
 
 3-64 
 
 4-17 
 
 76 
 
 4-03 
 
 4-91 
 
 6-55 
 
 2-30 
 
 2-80 
 
 3-74 
 
 4-26 
 
 765 
 
 4-14 
 
 5-05 
 
 674 
 
 2-37 
 
 2-88 
 
 3-85 
 
 4-35 
 
 77 
 
 4-26 
 
 5-19 
 
 6-93 
 
 2-44 
 
 2-97 
 
 3-96 
 
 4-45 
 
 77* 
 
 4-38 
 
 5-34 
 
 7-13 
 
 2-51 
 
 3-05 
 
 4-07 
 
 4-55 
 
 78 
 
 4-51 
 
 5-49 
 
 7-34 
 
 2-58 
 
 3-14 
 
 4-19 
 
 4-65 
 
 78^ 
 
 4-65 
 
 5-66 
 
 7-55 
 
 2-66 
 
 3-23 
 
 4-32 
 
 4-76 
 
 79 
 
 4-79 
 
 5-83 
 
 7-74 
 
 2-74 
 
 3-33 
 
 4-45 
 
 4-88 
 
 79* 
 
 4-94 
 
 6-01 
 
 8-02 
 
 2-82 
 
 3-43 
 
 458 
 
 5-00 
 
 80 
 
 5-09 
 
 6-20 
 
 8-28 
 
 2-91 
 
 3-54 
 
 4-73 
 
 5-13 
 
 80* 
 
 5-26 
 
 6-40 
 
 8-54 
 
 3-00 
 
 3-66 
 
 4-88 
 
 5-26 
 
 81 
 
 5-43 
 
 6-61 
 
 8-82 
 
 3-10 
 
 3-78 
 
 5-04 
 
 5-40 
 
 81* 
 
 5-61 
 
 6-83 
 
 9-11 
 
 3-21 
 
 3-90 
 
 5-21 
 
 5-55 
 
 82 
 
 5-80 
 
 7-06 
 
 9-43 
 
 3-32 
 
 4-03 
 
 5-39 
 
 5-71 
 
 82^ 
 
 6-00 
 
 7-31 
 
 9-75 
 
 3-43 
 
 4-17 
 
 6-57 
 
 5-88 
 
 83 
 
 6-22 
 
 7-57 
 
 10-10 
 
 3-55 
 
 4-32 
 
 5-77 
 
 6-06 
 
 83* 
 
 6-44 
 
 7-84 
 
 ... 
 
 3-68 
 
 4-48 
 
 5-98 
 
 6-25 
 
 84 
 
 6-68 
 
 8-14 
 
 ... 
 
 3-82 
 
 4-65 
 
 6-21 
 
 6-45 
 
 84* 
 
 6-94 
 
 8-45 
 
 ... 
 
 3-97 
 
 4-83 
 
 6-45 
 
 6-67 
 
 85 
 
 7-22 
 
 8-78 
 
 ... 
 
 4-12 
 
 5-02 6-70 
 
 6-82 
 
 85 - 
 
 7-41 
 
 9-02 
 
 ... 
 
 4-23 
 
 5-15 1 6-88 
 
 6-98 
 
 85| 
 
 7-61 
 
 9-26 
 
 ... 
 
 4-35 
 
 5-29 7-07 
 
 7-14 
 
 86 
 
 7-82 
 
 9-52 
 
 ... 
 
 4-47 
 
 5-44 
 
 7-26 
 
 7-32 
 
 88* 
 
 8-04 
 
 9-79 
 
 ... 
 
 4-60 
 
 5-60 
 
 7-47 
 
 7-50 
 
 86$ 
 
 8-28 
 
 10-07 
 
 ... 
 
 4-73 
 
 5-76 
 
 7-68 
 
 7-69 
 
 87 
 
 8*52 
 
 ... 
 
 ... 
 
 4-87 
 
 5-93 
 
 7-91 
 
 7-89 
 
 87* 
 
 8-78 
 
 ... 
 
 ... 
 
 5-02 
 
 6-11 
 
 8-15 
 
 8-10 
 
 87| 
 
 9-05 
 
 ... 
 
 ... 
 
 5-17 
 
 6-30 
 
 8-40 
 
 8-33 
 
 88 
 
 9-34 
 
 ... 
 
 ... 
 
 5-34 
 
 6-50 
 
 8-67 
 
 8-57 
 
 88* 
 
 9-64 
 
 ... 
 
 ... 
 
 5-51 
 
 6-71 
 
 8-95 
 
 8-82 
 
 88| 
 
 9-96 
 
 ... 
 
 ... 
 
 5-69 
 
 6-93 
 
 9-25 
 
 9-09 
 
 89 
 
 10-30 
 
 ... 
 
 ... 
 
 5-89 
 
 7-17 
 
 9-57 
 
 9-37 
 
 89 i 
 
 ... 
 
 ... 
 
 ... 
 
 6-09 
 
 7-42 
 
 9-90 
 
 9-68 
 
 89} 
 
 ... 
 
 ... 
 
 ... 
 
 6-31 
 
 7-69 
 
 10-26 
 
 10-00 
 
 90 
 
 ... 
 
 i 
 
 6-55 
 
 7-97 
 
 
 
BOARD OF TRADE BOILER RULES 
 
 401 
 
 The following tables contain the internal diameters of furnaces, 
 calculated according to the Board of Trade Rules : 
 
 INTERNAL DIAMETERS OP CIRCULAR FURNACES IN INCHES. 
 
 TYPE 
 
 PLAIN FLUES (Iron 
 
 PLAIN FLUES (Steel) 
 
 ADAMSON'S 
 RINGS 
 
 V 
 
 Krt 
 
 IS 
 
 -- ~ 
 
 6 
 
 Formula 
 
 90,000 
 
 T, 
 
 1 
 
 FP 
 
 os" 
 
 ""D-^FT, 
 
 H fi 
 o" 
 
 $- 
 
 -L"-089-l-07) 
 
 D.(L'+1) 
 
 L. or 0. 
 
 9 Ft. 
 
 8 Ft. 
 
 7 Ft. 6 Ft. ! 5 Ft. 
 
 9 Ft 
 
 8 Ft 
 
 7 Ft 
 
 6 Ft. 
 
 5 Ft. 
 
 a 
 
 I-H 
 
 CO 
 00 
 
 a 
 
 i 
 
 a 
 
 00 
 
 1 
 
 Plat* 
 Thickness. 
 Inches 
 
 n 
 
 *j 
 
 i 
 
 ;.: 
 % 
 
 1 
 
 : 
 
 i 
 
 i 
 
 >i 
 
 -i 
 
 1 
 
 27-8 
 32-0 
 
 36-5 
 41-3 
 463 
 51-7 
 
 26*7 
 31-0 
 35-7 
 
 40-6 
 46-0 
 51-6 
 
 25-6 
 30-1 
 85-0 
 40-2 
 
 45-9 
 51-8 
 
 29-4 
 34-5 
 40-1 
 46-1 
 
 52-5 
 
 60 L 
 
 34-4 
 40-4 
 47-0 
 54-0 
 
 B8. "fl 
 
 55-5 
 
 foRKJ 
 
 26-4 
 30-7 
 35-3 
 
 40-2 
 45-5 
 51-1 
 
 KG P 
 
 29-4 
 34-2 
 39-3 
 
 44-8 
 50-7 
 
 RESS1 
 
 28-2 
 33-2 
 38-6 
 44-4 
 
 50-6 
 
 JRE 
 
 32-4 
 
 38-1 
 44-2 
 50-8 
 
 37-9 
 44-6 
 51-7 
 
 61-0 
 
 59-1 
 
 68-2 
 
 73-7 
 
 86-7 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 .. 1 -- 
 
 80 L 
 
 25-6 
 30-1 
 35-0 
 40-3 
 
 45-9 
 51-9 
 
 00 L 
 
 BS. V 
 
 41-5 
 44-9 
 48-4 
 51-8 
 
 BS. V 
 
 33-0 
 35-8 
 38-5 
 41-3 
 
 44-0 
 46-7 
 49-5 
 52-3 
 
 .BS. T 
 
 FORKING PRESSURE 
 
 28-2 
 33-2 
 38-6 
 44-4 
 
 50-6 
 
 45-7 1 
 49-5 
 53-3 
 
 44-1 
 
 50-4 
 
 51-0 
 
 55-1 
 
 64-9 
 
 27-1 
 30-7 
 34-6 
 38-5 
 
 42-7 
 
 26-4 
 
 30-2 
 34-2 
 38-4 
 42-9 
 
 47-5 
 
 ' 
 
 26-0 
 30-0 
 
 34-2 
 38-6 
 43-4 
 
 48-4 
 
 53-7 
 
 25-7 
 29-9 
 34-4 
 
 39-2 
 44-3 
 
 49-7 
 55-5 
 
 ] 
 
 26-1 
 
 29-9 
 33-8 
 38-0 
 42-4 
 
 47-1 
 
 fORKJ 
 
 29-1 
 
 33-4 
 37-7 
 42-4 
 47-3 
 
 50-9 
 
 [NO F 
 
 28-7 
 33-0 
 
 37-7 
 42-6 
 47-8 
 53-3 
 
 28-4 
 32-9 
 37-9 
 
 43-2 
 
 48-8 
 54-8 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 RESSURE 
 
 36-4 
 
 39-4 
 42-4 
 45-4 
 
 48-5 
 51-5 
 
 35-1 
 40-1 
 45-1 
 50-2 
 
 40-6 
 45-6 
 50-6 
 
 43-9 
 48-9 
 53-9 
 
 51-7 
 
 
 
 
 
 
 
 
 
 26-3 
 30-7 
 35-5 
 
 40-2 
 45-5 
 51-1 
 
 
 
 
 
 27-8 
 32-0 
 
 36-5 
 41-3 
 46-3 
 51-7 
 
 120 i 
 
 26-8 
 30-2 
 33-7 
 
 38-4 
 YORK 
 
 ... 26-2 
 
 26-5 29-9 
 
 30-0 33-8 
 33-7 38-0 
 37-6 4*4 
 
 41-5 47-1 
 ING PRESS 
 
 26-2 
 
 30-1 
 
 34-3 
 
 38-8 
 43-6 
 48-7 
 
 54-5 
 
 URE 
 
 ... 24-0 
 24-2 27-2 
 27-4 30-5 
 30-5 34-1 
 
 33-9 36-7 
 
 27-1 
 30-7 
 34-5 
 38-4 
 
 42-7 
 
 27-3 
 
 31-1 
 35-2 
 39-6 
 44-1 
 
 49-7 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 30-2 
 32-7 
 35-2 
 37-7 
 
 40-2 
 42-7 
 45-3 
 47-8 
 
 50-3 
 
 29-0! 
 33-2 ( 
 37-4, 
 41-6 
 
 45-8 
 50-0 
 
 33-6 
 37-8 
 42-0 
 46-2 
 
 50-3 
 
 36-3 
 
 40-5 
 44-7 
 48-9 
 
 53-1 
 
 43-0 
 46-6 
 50-2 
 
 
 
 
 
 
 29-7 
 31-9 
 34-2 
 
 36-5 
 38-8 
 41-1 
 43-3 
 
 45-6 
 
 
 ! 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 26-5 
 
 30-2 
 34-2 
 38-3 
 42-9 
 
 47-6 
 
 
 
 
 
 29-2 
 
 33-4 
 37-7 
 42-3 
 47-3 
 
 52-5 
 
 25-2 
 28-0 
 
 25-2 
 28-2 
 
 31-4 
 
 25-4 
 
 28-5 
 31-9 
 
 35-4 
 
 25-8 
 29-2 
 32-8 
 36-6 
 
 41-1 
 
 27-9 
 31-0 
 
 27-9 
 31-1 
 
 34-5 
 
 28-0 
 31-5 
 35-2 
 
 39-0 
 
 28-5 
 32-2 
 36-1 
 42-0 
 
 45-3 
 
 
 
 
 ^J 
 
 DD 
 
402 
 
 BOAKD OF TKADE BOILER KULES 
 
 INTERNAL DIAMETERS OF CIRCULAR FURNACES IN INCHES cont. 
 
 TYPE 
 
 PLAIN FLUES (Iron) 
 
 PLAIN FLUES (Steel) 
 
 ADAMSON'S 
 RINGS 
 
 *t> 
 
 gg 
 &.* 
 
 Formula 
 
 *"* D^TTD 
 
 HiP 
 
 1 
 
 o 
 
 '""""IKCFTT) 
 
 H e 
 r 
 
 J><- 
 
 -L"-089-1'07) 
 
 H A 
 D 
 
 L. or 0. 
 
 9 Ft. 
 
 8 Ft. 
 
 7 Ft. 
 
 6 Ft. 
 
 5 Ft. 
 
 9 Ft 
 
 8 Ft 
 
 7 Ft 
 
 .6 Ft 
 
 .5 Ft 
 
 jj 
 i 
 
 B 
 
 i 
 
 c 
 
 00 
 
 | 
 
 Plate 
 Thickness. 
 Inches. 
 
 S 
 
 fyll 
 
 y 
 
 *: 
 
 1 
 
 fy 
 
 : 
 
 ': 
 
 t 
 
 1 _ 
 
 140 LBS. WORKING PRESSURE 
 
 28-9 
 32-4 
 35-9 
 39-5 
 
 43-1 
 46-6 
 50-1 
 
 31-2 
 34-7 
 38-2 
 41-8 
 
 45-4 
 48-9 
 52-5 
 
 27-2 
 30-2 
 33-3 
 36-4 
 
 39-6 
 42-7 
 45-8 
 49-9 
 
 52-0 
 
 36-7 
 39-8 
 42-9 
 45-9 
 
 49-0 
 52-1 
 
 [32-1 
 34-7 
 37-4 
 40-1 
 
 42-7 
 45-4 
 48-1 
 50-8 
 
 28-4 
 30-8 
 33-1 
 35-5 
 
 37-9 
 40-2 
 42-6 
 45-0 
 
 47-4 
 
 25-5 
 27-6 
 29-7 
 31-9 
 
 34-0 
 36-1 
 38-2 
 LO-4 
 
 12-5 
 
 
 
 
 
 
 
 
 
 
 
 
 27-9 
 300 
 32-2 
 
 34-3 
 36-5 
 38-7 
 40-8 
 
 42-9 
 
 28-4 
 32-0 
 35-5 
 
 39-1 
 42-7 
 
 46-2 
 49-8 
 
 53-4 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 29-2 
 
 31-1 
 33-1 
 35-1 
 37-0 
 
 39-0 
 
 ) LBS 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 28-5 
 32-2 
 36-1 
 40-4 
 
 44-8 
 
 E 
 
 
 
 
 
 29-2 
 32-8 
 3C-7 
 
 39-0 
 164 
 
 26-4 
 . Wo 
 
 28-5 
 
 RKIN( 
 
 ... 27-4 
 26-8 30-8 
 30-0 34-4 
 
 33-3 38-7 
 
 j PRESKUR 
 
 
 
 ... 24-3 27-9 
 ... 27-1 31-2 
 
 25-8 30-1 35-1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ... 28-2 
 27-9 31-3 
 31-0 34-4 
 
 84-1 37-5 
 87-2 40-6 
 40-3 43-7 
 43-4 46-8 
 
 46-5 49-9 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 29-9 
 31-9 
 33-7 
 35-5 
 
 37'4 
 
 
 
 
 
 25-5 
 28-6 
 31-9 
 
 33-9 
 180 
 
 28-8 
 30-5 
 82-2 
 
 83-9 
 
 LBS. 
 
 
 
 
 
 28-0 
 31-5 
 35-2 
 
 39-0 
 
 
 
 
 
 24-3 
 WOR 
 
 25-5 
 
 KINO 
 
 25-1 
 28-9 
 FREE 
 
 26-8 
 30-0 
 
 33-7 
 
 .SURE 
 
 ... 
 
 ... 
 
 26-2 
 
 27-1 
 30-6 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 27-7 
 30-5 
 
 33-3 
 36-0 
 
 38-8 
 41-5 
 
 44-3 
 
 29-6 
 32-3 
 
 35-1 
 37-8 
 40-6 
 43-4 
 
 46-1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 27-4 
 
 30-2 
 33-0 
 35-7 
 38-5 
 
 41-2 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 27-9 
 31-1 
 
 34-6 
 
 29-8 
 31-5 
 
 33-1 
 
 
 
 
 
 28-2 
 30-0 
 200 i 
 
 28-5 
 30-0 
 
 .BS. ^ 
 
 VORK 
 
 ING 1 
 
 ... 27-5 
 25-6 29-8 
 
 ^ESSURE 
 
 ... 
 
 ... 
 
 ... 
 
 27-0 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 4 
 
 29-0 
 
 31-5 
 34-0 
 36-5 
 38-9 
 
 U-4 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 29-9 , 
 32-3 , 
 34-8 , 
 37'3 : 
 
 39-8 '< 
 
 
 
 
 
 
 
 
 
 
 
 
 
 29-5 
 32-0 
 34-5 , 
 
 J6-9 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 , 
 
 27-9 
 31-0 
 
 29-7 
 
 
 
 
 
 27-0 1 
 
 27-0 
 
 ... 
 
 ... 
 
 ... 
 
 26-7 , 
 
BOARD OF TRADE BOILER RULES 
 
 403 
 
 PERMISSIBLE WORKING LOADS OF UNTESTED Iron STAYS WITH A 
 STRESS OF 7,000 LBS. PER SQUARE INCH. FOR DIAMETER AND 
 SECTIONS, SEE PP. 327, 328. 
 
 Outside Diameters 
 
 Working Loads for 
 Plus Threads 
 
 Whltworth 
 Threads 
 
 Number of Threads per Inch * 
 
 678 
 
 9 10 
 
 11 
 
 12 
 
 Number 
 of 
 Threads 
 
 Working Loads of Screwed Stays at 7,000 Ibs. per Square Inch 
 
 Inches 
 
 Lbs. 
 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 I 
 
 3,093 
 
 10 
 
 2,127 
 
 
 
 
 
 2,127 
 
 2,208 
 
 2,275 
 
 
 
 
 
 1 
 
 4,209 
 
 9 
 
 2,952 
 
 ... 
 
 ... 
 
 ... 
 
 2,952 
 
 3,068 
 
 3,165 
 
 3,245 
 
 1 
 
 5,498 
 
 8 
 
 3,879 
 
 ... 
 
 ... 
 
 3,879 
 
 4,045 
 
 4,180 
 
 4,293 
 
 4,387 
 
 H 
 
 6,958 
 
 7 
 
 4,880 
 
 ... 
 
 4,880 
 
 5,120 5,310 
 
 5,465 
 
 5,594 
 
 5,701 
 
 H 
 
 8,590 
 
 7 
 
 6,262 
 
 ... 
 
 6,262 
 
 6,532 
 
 6,747 
 
 6,921 
 
 7,065 
 
 7,186 
 
 if 
 
 10,394 
 
 6 
 
 7,419 
 
 7,419 7,813 
 
 8,116 
 
 8,355 
 
 8,549 
 
 8,710 
 
 8,844 
 
 ; 
 
 
 
 
 
 
 
 
 
 
 1 2 
 
 12,370 
 
 6 
 
 9,102 
 
 9,102 9,539 
 
 9,871 
 
 10,136 
 
 10,349 
 
 10,526 
 
 10,673 
 
 If 
 
 14,517 
 
 5 
 
 10,303 
 
 10,956 
 
 11,435 11,800 
 
 12,086 
 
 12,321 
 
 12,514 
 
 12,674 
 
 if 
 
 16,837 
 
 5 
 
 12,271 
 
 12,983 
 
 13,503 
 
 13,899 
 
 14,212 
 
 14,464 
 
 14,673| 14,847 
 
 *1 
 
 19,330 
 
 ^ 
 
 13,910 
 
 15,181 
 
 15,743 
 
 16,170 
 
 16,508 
 
 16,779 
 
 17,004 
 
 17,191 
 
 2 
 
 21,991 
 
 ! 
 
 16,182 
 
 17,550 
 
 18,154 
 
 18,614 
 
 18,976 
 
 19,266 
 
 19,508 
 
 19,707 
 
 N 
 
 24,826 
 
 4 5 
 
 18,623 
 
 20,092 
 
 20,738 
 
 21,228 
 
 21,616 21,925 
 
 22,182 
 
 22,396 
 
 2* 
 
 27,833 
 
 4 
 
 20,479 
 
 22,806 
 
 23,493 
 
 24,016 24,426 
 
 24,756 
 
 25,028 
 
 25,255 
 
 2f 
 
 31,011 
 
 4 
 
 23,217 
 
 25,698 
 
 26,421 
 
 26,973 27,408 
 
 27,758 
 
 28,048 
 
 28,287 
 
 2* 
 
 34,362 
 
 4 
 
 26,127 
 
 28,748 
 
 29,520 
 
 30,103 30,564 
 
 30,932 
 
 31,238 
 
 31,491 
 
 
 37,884 
 
 4 
 
 29,210 
 
 31,976 
 
 32,791 
 
 33,406 33,888 
 
 34,279 34,601 
 
 34,866 
 
 2| 
 
 41,578 
 
 4 
 
 32,464 
 
 35,377 36,233 
 
 36,880 37,361 
 
 37,796 
 
 38,135 
 
 38,413 
 
 21 
 
 45,443 
 
 4 
 
 34,616 
 
 38,950 39,848 40,526 
 
 41,059 
 
 41,487 
 
 41,840 
 
 42,131 
 
 3 
 
 49,480 
 
 H 
 
 38,149 
 
 42,694 
 
 43,634' 44,344 
 
 44,900 
 
 45,347 
 
 45,718 
 
 46,022 
 
 N 
 
 53,690 
 
 ... 
 
 ... 
 
 46,611 
 
 47,592 48,334 
 
 48,914 
 
 49,380 
 
 49,768 
 
 50,085 
 
 i* 
 
 58,071 
 
 3 T 
 
 44,844 
 
 50,697 51,719 52,494 
 
 53,100 
 
 53,586 
 
 53,990 
 
 54,321 
 
 3f 
 
 62,624 
 
 ... 
 
 ... 
 
 54,958 
 
 56,023 56,826 
 
 57,457 
 
 57,963 
 
 58,481 
 
 58,726 
 
 
 
 
 
 
 
 
 
 
 
 3i 
 
 67,347 
 
 H 
 
 53,038 
 
 59,389 
 
 60,496 61,332 
 
 61,986 
 
 62,513 
 
 62,946 
 
 63,304 
 
 3| 
 
 72,249 
 
 ... 
 
 ... 
 
 63,993 
 
 65,143 66,006 66,688 
 
 67,234 
 
 67,684 
 
 68,060 
 
 3! 
 
 77,315 
 
 3 
 
 60,722 
 
 68,768 
 
 69,960 70,854 
 
 71,560 
 
 72,125 
 
 72,592 
 
 72,986 
 
 31 
 
 82,556 
 
 ... 
 
 ... 
 
 73,713 
 
 74,950 
 
 75,874 
 
 76,605 
 
 77,189 77,672 
 
 78,069 
 
 4 
 
 87,969 
 
 3 
 
 70,192 
 
 78,834 
 
 80,111 
 
 81,067 
 
 81,823 
 
 82,425 
 
 82,924 
 
 83,340 
 
 Nuts to be 1J diameters deep. 
 
 DD2 
 
404 
 
 BOARD OF TRADE BOILER RULES 
 
 PERMISSIBLE WORKING LOADS OP Steel STAYS AND OF IRON STAYS 
 OF 21-5 TONS TENACITY WITH A STRESS OF 9,000 LBS. PER 
 SQUARE INCH. FOR DIAMETERS AND SECTIONS, SEE PP. 327, 
 328. 
 
 1 
 
 1* 
 
 3 
 
 01 0> 
 
 O "O 
 
 1! 
 jj 
 
 r 
 
 Wbitworth 
 Threads 
 
 Number of Threads per Inch 1 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 
 11 
 
 12 
 
 Number! 
 of Working Loads of Screwed Stays at 9,000 Ibs. per Square Inch 
 Threads! 
 
 Inches 
 I 
 
 i 
 
 Lb. 
 
 3,976 
 5,412 
 
 10 
 9 
 
 Lbs. 
 2,740 
 
 3,795 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs. 
 
 Lbs, 
 2,734 
 
 3,944 
 
 Lbs. 
 2,839 
 
 4,069 
 
 Lbs. 
 2,925 
 
 4,172 
 
 ... 
 
 ... 
 
 ... 
 
 3,795 
 
 i 
 
 7,069 
 
 8 
 
 4,988 
 
 ... 
 
 ... 
 
 4,988 
 
 5,201 
 
 5,375 
 
 5,520 
 
 5,641 
 
 u 
 it 
 
 i 
 
 8,946 
 11,045 
 13,365 
 
 7 
 7 
 6 
 
 6,275 
 8,051 
 9,539 
 
 9,539 
 
 6,275 
 8,051 
 10,047 
 
 6,581 
 8,398 
 10,435 
 
 6,827 
 8,675 
 10,742 
 
 7,026 
 8,898 
 10,992 
 
 7,192 
 9,085 
 11,199 
 
 7,330 
 9,240; 
 11,371 
 
 Hi 
 
 15,904 
 
 6 
 
 11,703 
 
 11,703 
 
 12,264 
 
 12,692 
 
 13,032 
 
 13,306 
 
 13,533 
 
 13,723 
 
 if 
 
 18,662 
 
 5 
 
 13,247 
 
 14,087 
 
 14,702 
 
 15,171 
 
 15,541 
 
 15,841 
 
 16,089 
 
 16,295 
 
 it 
 
 21,644 
 
 5 
 
 15,777 
 
 16,692 
 
 17,361 
 
 17,870 
 
 18,273 
 
 18,596 
 
 18,866 
 
 19,089 
 
 i* 
 
 24,845 
 
 4 
 
 17,884 
 
 19,518 
 
 20,241 
 
 20,790 
 
 21,225 
 
 21,573 
 
 21,863 
 
 22,103 
 
 2 
 
 28,275 
 
 i 
 
 20,805 
 
 22,568 
 
 23,341 
 
 23,932 
 
 24,397 
 
 24,772 
 
 25,081 
 
 25,338 
 
 21 
 
 31,916 
 
 i 
 
 23,942 
 
 25,833 
 
 26,663 
 
 27,293 
 
 27,790 
 
 28,190 
 
 28,520 
 
 28,795 
 
 2* 
 
 35,782 
 
 4 
 
 26,330 
 
 29,322 
 
 30,206 30,874 
 
 31,405 
 
 31,829 
 
 32,180 
 
 32,471 
 
 H 
 
 39,871 
 
 4 
 
 29,850 
 
 33,032 
 
 33,970 
 
 34,680 
 
 35,239 
 
 35,689 
 
 36,006 
 
 36,369 
 
 2* 
 
 H 
 
 44,177 
 48,707 
 
 4 
 4 
 
 33,590 
 37,560 
 
 36,962 
 41,112 
 
 37,955 
 42,160 
 
 38,704 
 42,951 
 
 39,295 
 43,573 
 
 39,770 
 44,073 
 
 40,163 
 
 44,487 
 
 40,488 
 44,828; 
 
 2* 
 
 53,457 
 
 4 
 
 41,739 
 
 45,485 
 
 46,586 47,417 
 
 48,067 
 
 48,595 
 
 49,031 
 
 49,389; 
 
 21 
 
 58,427 
 
 H 
 
 44,506 
 
 50,079 
 
 51,233 
 
 52,105 
 
 52,780 
 
 53,340 
 
 53,794 
 
 54,169 
 
 3 
 8* 
 H 
 
 63,617 
 69,029 
 74,660 
 
 3 
 
 4 
 
 49,049 
 53,801 
 57,657 
 
 54,893 
 59,928 
 65,182 
 
 56,101 57,003 
 61,190 62,143 
 66,498 67,492 
 
 57,729 
 62,889 
 68,271 
 
 58,303 
 63,490 
 68,896 
 
 58,781 
 63,987 
 69,415 
 
 59,171 
 64,395; 
 69,842i 
 
 3f 
 
 80,516 
 
 ... 
 
 62,814 
 
 70,660 
 
 72,030 
 
 73,062 
 
 73,874 
 
 74,524 
 
 75,061 
 
 75,505 
 
 H 
 
 85,689 
 
 H 
 
 68,192 
 
 76,353 
 
 77,791 
 
 78,855 
 
 79,700 
 
 80,374 
 
 80,930 
 
 81,391 
 
 N 
 
 92,883 
 
 ... 
 
 73,793 
 
 82,276 
 
 83,755 
 
 84,865 
 
 85,742 
 
 86,444 
 
 87,023 87,493 
 
 3| 
 
 99,398 
 
 3 
 
 78,171 
 
 88,416 
 
 89,948 
 
 91,098 
 
 92,006 
 
 92,732 
 
 93,333 93,824 
 
 H 
 
 106,134 
 
 ... 
 
 84,056 
 
 94,774 
 
 98,364 
 
 97,550 98,490 
 
 99,243 
 
 99,864100,374 
 
 4 
 
 113,090 
 
 3 
 
 90,260 
 
 101,354 
 
 102,997 
 
 104,229 105,201 105,975 
 
 106,614107,145 
 
 1 Nuts to be 1 diameters deep. 
 
INDEX 
 
 Abbreviations: B. T. = Board of Trade. L. E. = Lloyd's Register. 
 
 Absolute temperatures, 49, 51. 
 Absorption of air by water, 72, 78. 
 - by steel, 22, 133, 146. 
 Accidents due to 
 
 Brick bridges, 18. 
 
 Fine threaded stays, 28. 
 
 Grease, scale and salt, 26. 
 
 Water-level errors, 43. 
 Accidents- 
 Explosions, 135, 221, 337. 
 
 Leaky tubes, 28. 
 
 Loss of water, 1. 
 
 From flames, 19. 
 
 To internal feed pipes, 77. 
 
 To flanged plates, 149. 
 
 To flat plates, 21, 29. 
 
 To furnaces, 27. 
 
 To stays, 39. 
 Acetelyne welding, 337. 
 Acids in boilers, 69. 
 
 influence on steel, 146. 
 Adamson's furnace, strength of. 198, 203. 
 Air, admission to furnaces, 4, 9, 17, 93. 
 
 expansion of, 96. 
 
 for combustion, 4, 93. 
 
 in steam pipes, 334. 
 
 in water, 72, 78. 
 Alarms, low water, 46. 
 Alkalies, use of, 69. 
 
 Alternate heating and cooling, 19, 30. 
 Alternating stresses, 164, 255. 
 Aluminium in steel, 135. 
 Anemometers, 102. 
 Annealing, 144, 147, 274. 
 
 B. T. Rules, 366, 372. 
 
 Deformation due to, 260, 263. 
 
 Front end plates, 274. 
 
 Steam pipes, 338. 
 Arsenic in steel, 134. 
 Ashes, 12, 88. 
 
 cause corrosion, 32, 38, 41. 
 
 removal of, 15. 
 Ash-pit area, 10, 100. 
 Automatic feed, 46. 
 
 Back plates, stays in, 177. 
 
 Banked fires, 16. 
 
 Beam 
 
 Continuous, 173. 
 
 Curved, 184-8. 
 Cross curvature, 169. 
 Elastic, 168, 173. 
 Plastic, 189, 237. 
 
 Bearing pressure on rivets, 212. 
 Belleville boilers, 62. 
 Bending 
 
 Operations, 189, 237. 
 
 Bolls, 238. 
 
 Shell plate ends, 240, 243. 
 
 Stresses, 168, 184. 
 
 Test, alternating, 164, 255. 
 
 cold, 137. 
 
 tempered, 138. 
 Bessemer steel, 129. 
 Bismuth in steel, 134. 
 Black heat. See Blue heat. 
 Blisters, 37. 
 
 Blowing off boilers, 18, 25. 
 
 Blow-off cocks, L. E. Eules, 348. 
 
 Blue heat, 37, 150, 190, 242, 255, 275, 
 
 277, 279. 
 
 Board of Trade Rules, 365-82. 
 Boiling phenomena, 56. 
 Boron in steel, 141. 
 Bridges, 17. 
 
 | Brinell's method of testing steel, 140. 
 Bubbles, circulating force of, 56, 63. 
 
 formation of 75. 
 Bulged flat plates, 28, 182. 
 
 furnaces, 32. 
 Burnt iron, 147, 262. 
 
 rivet heads and nuts, 38, 124, 286. 
 Butt straps, 193, 211, 214-20, 244-8, see 
 
 Rules. 
 
 Calorie, 49, 84. 
 Calorimeters for fuels, 86. 
 
 for moisture, 61, 64. 
 Carbon in steel, 134. 
 
 (405) 
 
406 
 
 INDEX 
 
 Carbonic acid in water, 72. 
 Caulking, 292-6. 
 
 difficult seams, 230, 244, 277, 280, 
 283, 286. 
 
 Cementing furnace sides and bottoms, 
 36. 
 
 furnace fronts, 15. 
 
 shell seams, 41. 
 Chemicals for removing scale, 31. 
 Chromium in steel, 134. 
 Circulating force of bubbles, 56, 63. 
 Circulation, 56. 
 
 - bad, 27, 58, 75. 
 
 in watertube boilers, 62. 
 
 reversed, 62. 
 Circumferential cracks, 2. 
 Cleaning fires and boilers, 14. 
 Clinker, 4, 13. 
 
 Closed ash-pits, 100. 
 Coal analysis, 88-91. 
 
 consumption, 10, 91, 97, 304. 
 Cold air in furnaces, 14, 19. 
 
 influence on steel, 137, 145. 
 
 water in boiler bottoms, 3, 74. 
 Colapsed furnaces, 24, 26, 32. 
 
 (time), 45. 
 
 Combustion, 85. 
 
 Air for, 93. 
 
 Heats of, 85, 89. 
 
 Incomplete, 85. 
 
 Tests, 108. 
 
 Variation of, 112. 
 
 Compound stresses, 160, 166, 169, 202. 
 Compressibility of water, 55. 
 Conductivity, thermal, 119. 
 Construction, chapter on, 225-303. 
 Contraction of test pieces, 155, 161. 
 
 cross, 166, 169, 191, 193, 207. 
 Convection, 116. 
 
 Copper in steel, 134. 
 Copper pipes in boilers, 70. 
 
 - pipes, B. T. Rules, 385. 
 
 steam pipes, 336. 
 
 tube plate, 118, 121, 126. 
 Corners, weakness of, 185. 
 Corrosion 
 
 Chapter on, 66-83. 
 Distribution of, 76. 
 Due to air in water, 72. 
 External, 15, 32, 38, 41. 
 Of stays, 290. 
 Corrugated combustion chambers, 288. 
 
 furnaces, theories and experiments, 
 198, 205. 
 
 Cost of boilers, 310. 
 
 Cracked plates, list of, 135, 149, 150. 
 
 Cracks due to blue heat, which see. 
 
 to doubling plates, etc., 20, 27. 
 
 to local heating, 33, 149, 242, 256. 
 
 to phosphorus and nitrogen, 21, 
 
 25, 135. 
 
 racks due to riveting pressure, 247. 
 to scale and grease, 23. 
 
 in flanged plates, 252-6. 
 
 in furnace saddles, 20, 33. 
 
 in rivet holes, 21, 216, 247. 
 
 in shell plates, 2, 40. 
 
 in tube plates, 40. 
 
 under palm stays, 20. 
 
 Critical temperature for steam, 49, 55. 
 Cross stresses in beams, 169, 177, 178, 
 197. 
 
 in cylindrical shells, 2, 193. 
 
 near rivet and stay holes, 169, 209, 
 
 216. 
 
 Crucible steel, 132. 
 Curved beam, 184-8. 
 
 Cylindrical flues, experiments on longi- 
 tudinal elasticity of, 194, 209. 
 
 shells, stresses in, 196, 207-10. 
 
 Dampers, 15, 19. 
 
 Deformations due to alternate heating 
 and cooling, 19, 30. 
 
 of hard-worked furnaces, 28, 201. 
 Density of gases, 49, 103, 110. 
 
 of steam, 49, 52. 
 
 of salt-water, 25. 
 Design, Chapter on, 304-28. 
 Diagonal joints, 155, 220. 
 
 - pitch of rivets, 155, 215, 316. 
 Dished ends, B. T. Rules, 376. 
 Dome holes, stresses around, 196. 
 Double-ended boilers, list of, 312. 
 Drain cocks for steam pipes, 333. 
 Draught, forced and natural, 98, 100, 305. 
 Drilled plates, strength of, 155, 220. 
 Drilling operation, 231. 
 
 time for, 236. 
 Dryback boilers, list of, 311. 
 
 Ebullition, 56, 121. 
 
 Economisers, 16. 
 
 Effective diameters of shells, 209. 
 
 of washers, 181. 
 
 Elastic limit, 152. 
 
 for shear, 155, 166 . 
 
 hot, 190. 
 
 modulus, 152, 166. 
 Elasticity of steam pipes, 334, 338. 
 
 water, 55. 
 Electric current, 79. 
 
 welding, 296, 337. 
 
 End plates affect shell stresses, 194. 
 Etching tests, 143. 
 Evaporation, 56, 121. 
 Evaporative unit, 84. 
 Expanding tube ends, 30, 291. 
 Expansion joints, 338. 
 
 B. T. Rules, 386. 
 Explosions,marine boiler, 135, 221. 
 
 of steam pipes, 337. 
 
INDEX 
 
 407 
 
 Factor of safety, 221. 
 
 B. T. Rules, 373. 
 
 Fatigue, laws of, 164. 
 
 of steam pipes, 334. 
 Feed heaters, 65. 
 
 pipes, B. T. Rules, 385. 
 bursting of internal, 78. 
 
 positions of, 74, 78. 
 
 Ferrules, 31. 
 
 Fire bars, bending of, 8, 13, 102. 127. 
 
 Fires, cleaning of, 14. 
 
 Hunting of, 1. 
 
 - thickness of, 4, 97, 100. 
 Firing, 3. 
 
 - fierce, 28. 
 
 Flames in stokeholds, 19. 
 
 temperatures of, 94, 113. 
 
 Flanged plates, finishing corners of, 37, 
 258, 265, 272. 
 
 sizes for shearing, 225, 258. 
 
 Flanges for steam pipes, 336. 
 
 - stresses in, 184-8, 200, 252. 
 Flanging operations, 251-75. 
 Flat plates, gauging of, 169. 
 
 Staying of, 170, 175-83. 
 
 Stresses in unstayed, 163, 172. 
 Floury deposits, 24, 26. 
 Forced draught, 98, 100, 305. 
 Fractures, nature of, 140, 155, 161. 
 Friction of riveted joints, 220. 
 
 of steam in pipes, 329-32. 
 Fuel, 88-91. 
 
 Fullering, 295. 
 
 Funnel dimensions (design) 10, 305, 315. 
 
 - temperature. 103, 109. 
 Furnace 
 
 Bridges, 17. 
 
 Bulges and collapses, 24, 26, 32. 
 
 Doors, '5, 7. 
 
 Drilling machines, 234. 
 
 Front plate renewals, 35. 
 
 Holes, irregular shapes of, 266. 
 
 Patches, 37. 
 
 Resistance to draught, 98, 100, 305. 
 
 Saddles, 21, 37, 266-74. 
 
 Seams, 22, 34. 
 Furnaces 
 
 B. T. Rules, 380, 397, 401. 
 
 Fitting front ends, 279. 
 
 L. R. Rules, 345, 349, 353. 
 Fusible plugs, 45. 
 
 Galvanic action, 70, 78-83. 
 Galvanising steel, 148. 
 Gas analysis, 106-13. 
 Gases, in steel, 133, 146. 
 
 in water, 61, 73, 74, 79, 153. 
 Gauge glasses, 44. 
 
 Gauging flat plates, 169. 
 Girders, 174, 287. 
 
 Girders, B. T. Rules, 377, 384, 399. 
 
 L. R. Rules, 345, 350. 
 Grate areas, 304. 
 
 Grease in boilers, 23, 26, 67, 123. 
 
 filters, 23. 
 
 Guest's law of stresses, 162. 
 
 Hand drilling, 236. 
 Heat, 114-27. 
 
 Mechanical equivalent of, 49. 
 
 Radiant, 114. 
 
 Surface resistance to, 117. 
 
 Of combustion, 85. 
 Heaters cause cracks, 37. 
 Heating, alternate, causes leakages, 19, 
 
 30. 
 Heating surface, 304, 312. 
 
 Studded, 22, 124. 
 
 Temperatures of, 122. 
 Helical joints, 155, 220. 
 Hydraulic flanging, 257. 
 - testing, 150, 301. 
 Hydrogen in fuel, 109. 
 
 in steel, 133, 146. 
 
 Igniting temperatures, 95. 
 Internal feed pipes, 74-7. 
 Iron and Steel, 128. 
 | Dead and passive, 69, 148. 
 
 Steam pipes, B. T. Rules, 385. 
 Lap joints, 193, 215-20, 242, 315-18. 
 Latent heat of evaporation, 50, 54. 
 Leaky condenser, 60. 
 
 furnace seams, 34. 
 
 joints, manholes, etc., 32. 
 
 tubes, 28, 40. 
 
 Limit of elasticity, 158, 166, 190. 
 Lloyd's Register Rules, 341-7. 
 Local heating, B. T. Rules, 372. 
 
 danger of, 149, 256. 
 
 j of end -plate corners, 265. 
 
 Locomotive boiler circulation, 63. 
 
 boilers, list of illustrations, 311. 
 Low- water alarms, 46. 
 
 Management, Chapter on, 1-47. 
 Manganese in steel, 134. 
 Manholes, 32. 
 
 Boring, 241. 
 
 B. T. Rules, 375. 
 
 Staying of, 178. ' 
 Materials, Chapter on, 128. 
 Measurement of feed and waste products. 
 103. 
 
 of strains, 169, 301. 
 Mechanical equivalent of heat, 49. 
 Mechanics, Chapter on, 165-224. 
 Melting temperature of steel, 134. 
 Microstructure, 143. 
 
 Modulus of elasticity, 152, 166. 
 
408 
 
 INDEX 
 
 Moist air and radiation, 115. 
 and combustion, 94. 
 
 ashes cause corrosion, 12, 88. 
 
 steam, 60, 64. 
 
 Natural draught, 98, 100, 305. 
 Navy boilers, lists of drawings, 311. 
 Nickel in steel, 134. 
 Nitrogen in steel, 133. 
 Nuts, burnt, 38, 124, 286. 
 
 thickness of, 39, 285. 
 
 Occluded gases and brittleness, 133, 
 
 146. 
 Oil filters, 23. 
 
 prevents priming, 58. 
 Open-hearth steel, 129. 
 Orsat gas analyser, 105. 
 Oval furnaces, 197. 
 Oxygen in steel, 134. 
 
 in water, 72, 78. 
 
 Oxy-acetyline welding and cutting, 33, 
 38, 236. 
 
 Passive iron, 69, 80. 
 Performances of boilers, 101, 310. 
 Phosphorus in steel, 134. 
 Pickling plates, 33, 146, 288, 296. 
 Pipes for gauges, 43. 
 
 steam, B. T. Eules, 385. 
 Pitting, 11, 69, 75, 82, 180. 
 
 Planing machines and operations, 228, 
 278. 
 
 furnace saddles, 288. 
 Plate-bending rolls, etc., 238. 
 Pressure losses in steam pipes, 329-32. 
 
 on rivets, 247. 
 Priming, 58, 60. 
 
 Protectors for gauge glasses, 44. 
 
 Puddled iron, 128. 
 
 Punched holes, 151, 220, 227. 
 
 Eules, 347, 373. 
 
 Punching operation, 226. 
 Pyrometers, 96, 109. 
 
 Radiant heat, 114. 
 Radiation from boilers, 124. 
 
 from steam pipes, 331. 
 Red-hot furnace crown, 24, 26, 32. 
 Redshortness, 134, 139. 
 Renewing furnaces, 33, 36. 
 
 furnace front plates, 35. 
 
 stays, 38. 
 
 Repairs to boiler front, 22, 32-43. 
 Resolution of stresses, 166. 
 Rimering tube plates, 237. 
 Rivet stresses, 210. 
 Riveted joints 
 
 B. T. Rules, 374, 395, 400. 
 
 Designs, 243-50, 315-19. 
 
 L. R. Rules, 341, 348, 352. 
 
 Riveting operations, 246, 248, 278. 
 
 Combustion chambers, 41, 278, 280. 
 
 Furnaces saddle seams, 22. 34, 280. 
 
 Pressure, 248. 
 
 Time for, 250. 
 
 Rivets, Size and weight of, 250. 
 Rolling, influence of, 148. 
 
 
 
 
 | 
 
 1 Rules and Tables. 
 
 Rules. 
 
 Sum- 
 
 Tables. ! 
 
 
 
 mary. 
 
 
 Board of Trade 
 
 365-82 
 
 394 
 
 
 Flat plates . 
 
 377 
 
 398 
 
 
 Furnaces 
 
 380 
 
 397 
 
 401 
 
 Girders . 
 
 377, 384 
 
 399 
 
 ... 
 
 Riveted joints 
 
 374 
 
 395 
 
 400 
 
 Shell plates . 
 
 372, 383 
 
 395 
 
 
 Stays . 
 
 376 
 
 383 
 
 399 
 
 Tube plates . 
 
 380 
 
 398 
 
 ... 
 
 Lloyd's Register 
 Flat plates . 
 
 341-7 
 343 
 
 350 
 
 361 
 
 Furnaces 
 
 345 
 
 349 
 
 353 
 
 Girders . 
 
 345 
 
 350 
 
 
 Riveted joints 
 
 341 
 
 348 
 
 352 
 
 Shell plates . 
 
 341 
 
 348 
 
 ... 
 
 Stays and tubes 
 
 343 
 
 350 
 
 36 1',' 364 
 
 Tube plates . 
 
 344 
 
 350 
 
 359 
 
 Safety Valves 
 
 B. T. Rules, 388. 
 
 General, 46. 
 
 L. R. Rules, 347. 
 Salt water, boiling point, 56. 
 
 density, 25. 
 
 Sampling coal, 88. 
 
 Sawing edges of flanged plates, 278. 
 
 Screwed stays, 283-6. 
 
 Caulking of, 286, 293-6. 
 
 Effective diameters and areas, 327, 
 328. 
 
 Nuts during test, 300. 
 Seams in furnaces, 22, 33. 
 
 welded at ends, 245, 266. 
 Seawater, composition, 24. 
 Sediment, black and red, 74. 
 
 floury, 26. 
 
 Shearing Elasticity, 152, 166. 
 
 Operation, 226. 
 Shell plate drilling, 231. 
 Shell plates, effective diameters, 209. 
 
 Flanging of, 274. 
 
 Repairs to, 40. 
 Shortness of water, 43. 
 Side firing, 4. 
 Siemens-Martin steel, 131. 
 Silicon in steel, 134. 
 Single ended boilers, Ijst of, 313. 
 Smoke, its influence on heat transmis- 
 sion, 115. 
 
INDEX 
 
 409 
 
 Solid drawn steam pipes, 335. 
 Sooty surfaces, 16, 115. 
 Specific heat of gases, 93. 
 
 of steam, 64, 93. 
 
 of water, 50. 
 
 volume of steam, 52. 
 Split bridges, 5. 
 Springs, formula for, 347. 
 
 Stay hole drilling and tapping, 234. 
 - holes in shells, percentage of, 317. 
 Staying flat plates, 174-84. 
 
 manholes in cylinders, 180. 
 Stays 
 
 B. T. Kules, 376, 383, 399. 
 Diameters and areas of, 327, 328. 
 Fitting of, 277, 279. 
 In steam space, 290. 
 L. R. Rules, 343, 350, 361. 
 Rupture of, 38. 
 Strains produced by, 29. 
 Stresses in, 178, 180. 
 Steam and water, Chapter on, 48-65. 
 
 pipe arrangements, list of, 314. 
 
 pipes, chapter on, 329-40. 
 
 raising of, rapid, 1. 
 
 space, 59, 306. 
 
 - specific heat of, 64, 93. 
 Steel, 128-33. 
 
 Impurities, 133-6. 
 
 Micro-structure of, 143. 
 
 Open-hearth, 130. 
 
 Tests, B. T. Rules, 366-71. 
 Stop valves, L. R. Rules, 347. 
 Strain indicators, 141, 301. 
 Strength of materials, Chapter on, 128-64. 
 Stresses 
 
 Alternating, 164, 255. 
 
 Around holes, 215, 216. 
 
 Bending, 168. 
 
 Compound, 160, 166, 169, 202. 
 
 Due to flanging, 253. 
 
 Due to stays, 29. 
 
 In cylindrical shells, 192, 207. 
 
 In flanges, 184-5. 
 
 In flat plates, 163-73, 174-84. 
 
 In furnaces, 75, '197, 204. 
 
 In girders, 174. 
 
 In pipes, 184-5, 329-32. 
 
 In riveted joints, 210-22. 
 
 In stays, 178-80. 
 
 In thick shells, 207. 
 
 Near domehole, 196. 
 
 Resolution of, 166. 
 
 Shearing, 152, 166. 
 Sulphur in fuel, 109. 
 - in steel, 134. 
 Superheated steam, 52, 64. 
 in pipes, 332. 
 
 water, 57. 
 
 Superheaters, B. T. Rules, 372-88. 
 
 L. R. Rules, 342, 347. 
 
 Tack holes, 228. 
 
 Tapping stay holes, 234, 284. 
 Temper bending test, 138, 148. 
 Temperature, absolute, 49, 51, 96. 
 
 In funnels, 98, 103, 108. 
 
 In furnaces, 95. 
 
 Influence on steel, 144. 
 
 Of fire-bars, 127. 
 
 Of flames, 93, 113. 
 
 Of heating surfaces, 117-24. 
 
 Zero, 49, 96. 
 Test cocks, 44. 
 Testing machines, 140. 
 
 - pressure, 300. 
 
 ! Tests, various, 136-44. 
 
 Alternate bending, 164-255. 
 Temper, 138-48. 
 Tensile, 140, 152, 161. 
 Torsion and shear, 156. 
 Thermal conductivity, 119-26. 
 
 - expansion of water, 50. 
 Thermometer cups, 3. 
 
 I Thermometers. See Pyrometers. 
 Time required for 
 Annealing, 264. 
 Bending shell plates, 240. 
 Collapsing furnaces, 45. 
 Drilling, 236. 
 Flanging, 258. 
 
 furnace holes, 260. 
 Planing plate edges, 229. 
 
 fiances, 278. 
 Raising steam, 1. 
 Riveting, 250. 
 Tapping and staying, 284. 
 Testing, 152. 
 
 Tubing, 292. 
 Tin in steel, 134. 
 Torsion test for shear, 156. 
 Tube dimensions, 306. 
 heating surface, 307. 
 Tube plates. 
 
 B. T. Rules, 380, 398. 
 
 Boring of, 28. 
 
 Dimensions of, 306. 
 
 L. R. Rules, 344, 350, 359. 
 
 Troubles with, 28, 40, 291. 
 
 Of copper, 30, 118, 121, 126. 
 Tube scrapers, etc., 16. 
 Tubes 
 
 Expanding of, 28, 292. 
 
 Overheated, 29. 
 
 Pitch of, 40, 307. 
 
 Sections of, 307. 
 
 Stay, 292. 
 
 Sweeping of, 15. 
 Types of boilers, 313. 
 Washers for screwed stays, 39, 285. 
 Waste product, 106-9. 
 Water 
 
 Density, 43, 55. 
 
410 
 
 INDEX 
 
 Water 
 
 Gauges, 43. 
 
 B. T. Bules, 393. 
 
 Hammers in steam pipes, 78. 
 
 Loss of, 1, 43. 
 Water spaces, 31, 307. 
 Water tube boilers, list of, 311. 
 
 boiler steam space, 59. 
 
 Weight of boilers, 310. 
 
 of plates, 225. 
 
 of rivets, 250. 
 
 of water in boilers, 310. 
 Weldability of steel, 134, 135. 
 Welded stays, B. T. Rules, 372. 
 L. B. Bules, 347. 
 
 Welded steam pipes, 335, 337. 
 Welding 
 
 Combustion chambers, 296, 300. 
 
 Electric, 296. 
 
 End-plate corners, 266. 
 
 Furnace, 299. 
 
 Girder ends, 286. 
 
 Operation, 296. 
 
 Test, 297. 
 
 I Welds exposed to heat, 38. 
 I Wrought iron, 128. 
 
 I Zero temperature, 49, 96. 
 Zinc on boilers, 70, 76, 81. 
 
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