-..
.
--
-
-
.
-
+
.
.
.
:
| OF 1!
ORNL P
1430

in
i
".
.
:
.
..
1
.
*
.
.
.
.
....
-
:
C
..
.
*
*
•
.
145
. .
:50
.
.
TM 3 6
5
Tipa
240
.
7
.
I
1911.25
-
1.4 1.1.6
";
.
MICROCOPY RESOLUTION TEST CHAR
MICROCOPY RESOLUTION TEST CHART
NATIONAL BUREAU OF STANDARDS - 1963
..
-
-
-
..
3
ja::.inimesi.. : i, en
LEGAL NOTICE
This report was prepared as an account of
Government sponsored work. Neither the
United States, nor the Commission, nor any
person acting on behalf of the Commission:
A. Makes any warranty or representa-
tion, expressed or implied, with respect to
the accuracy, completeness, or usefulness
of the information contained in this report,
or that the use of any information, appa-
ratus, method, or process disclosed in this
report may not infringe privately owned
rights; or
B. Assumes any liabilities with respect
to the use of, or for damages resulting from
the use of any information, apparatus,
method, or process disclosed in this report.
As used in the above, “person acting on
behalf of the Commission”includes any em-
ployee or contractor of the Commission, or
employee of such contractor, to the extent
that such employee or contractor of the
Commission, or employee of such contractor
prepares, disseminates, or provides access
to, any information pursuant to his employ-
ment or contract with the Commission, or
his employment with such contractor.
et, ... !!
amb la inter
tention?:07 firemnat
t
A
m o
riikl
iai 101 intimate and
..
wie
in
its with
n
my
imovi, ,.
opono -------
,!!
.. !!! Ini..:::
---...---.. .......
::
iritime..
-
.
-.. ..........
: . ...
...........
----..
.-.
.
.
.. ----.
....... -
G
.
JUL 20 1965
Union Carbide Corporation.
of the Interior, and U. S. Atomic Energy Commission under contract with the
Research jointly sponsored by The Office of Saline Water, U. S. Department
APPROVED FOR PUBLIC RELEASE
Oak Ridge National Laboratory
Chemistry Division
F. A. Posey
and
Oak Ridge National Laboratory
Reactor Chemistry Division
E. G. Bohlmann
by
ALUMINUM AND TITANIUM CORROSION IN SALINE WATERS AT ELEVATED TEMPERATURES
-
ORNU-P-1430
Led W.
MASTER
UN-6510051€

ALUMINUM AND TITANIUM CORROSION IN SALINE WATERS AT ELEVATED TEMPERATURES
By E. G. Bohlmann and F. A. Posey
ABSTRACT
I. ALUMINUM
Studies on electrochemical aspects of the corrosion of aluminum alloys
5454 and 6061 were conducted in 1 M NaCl at 150°C in a titanium dynamic
loop facility. Corrosion rates were followed with time by mea surement of
the polarization resistance of the specimens. The results show that the
5454 alloy is superior to the generally recommended 6061 alloy in corrosion
resistance under all conditions studied. Polarization curves of the alloys
were mea sured under a variety of conditions in order to determine the nature
of the difference in corrosion properties. The results are generally similar
to those obtained by other workers at lower temperatures, except for certain
complications which appear mainly at the higher temperature of this study.
A pronounced minimum exists in the corrosion rate of aluminum and its
alloys in chloride solutions in the vicini'y of neutrality. Changes in the
polarization curves of anodic and cathodic processes occurring at the alumi-
num-electrolyte interface with pH provide a kinetic basis for understanding
this and other aspects of the corrosion behavior. At low potentials the rate
of the anodic or corrosion reaction is independent of the electrode potential,
but increases with increasing pH. The rate of the anodic process is controlled
by the rate of mass transport of hydroxide ions to the oxide-solution inter-
face. At higher potentials in the presence of chloride ions, the anodic
polarization curve exhibits a pitting potential which 18 independent of the
anodic current density. The pitting potential does not vary with pH but
decreases with increasing chloride concentration. The ca tuodic reaction
in alkaline solution consists of the discharge of water molecules to form
molecular hydrogen; this process is pH-independent. With increasing acidity,
discharge of hydrogen ions becomes increasingly important. The minimum cor-
rosion rate represents a compromise between the decrease in the rate of the
transport-controlled anodic reaction and the increase in the rate of ühe
ca thodic hydrogen-evolution reaction with increasing acidity.
The transport-control.led rate of the anodic process depends on solution
velocity and on the rate of the cathodic process, both of which affect the
local pH at the oxide-solution interface.
The rate of the anodic reaction
also decreases with time at constant pH and solution velocity, and is affected
by the rate of refreshment of the solution in the loop and by the ratio of
area of corroding specimens to solution volume.
These effects can probably
be understood on the basis of growth and dissolution kinetics of a porous
outer layer which is known to exist on aluminum in high-temperature aqueous
solutions. Other complications to the interpretation of polarization curves
include Ohmic effects which occur in the measurements at high current den-
sities and effects of dissolved oxygen in solution.
Comparison of polarization curves of the 5454 and 6061 alloys shows
that the rate of the cathodic hydrogen-evolution reaction on the 6061 alloy
is considerably greater than that of the 5454 alloy. The enhanced rate of
the cathodic process on the 6061 alloy accounts for its greater corrosion
rate at any pH and for its susceptibility to pitting attack. Catalysis of
the cathodic process on the 6061 alloy may be attributable to its copper
content.
II. TITANIUM
Dra stic, though extremely erratic, corrosion of titanium has been ob-
served in saline waters at temperatures of 1000 to 200°C. The corrosive
attack was first encountered in the loop studies of aluminum corrosion des-
cribed above. It has been observed in loop and autoclave experiments with
one and two molar sodium chloride solutions and synthetic sea water. Speci-
mens exposed to treated sea water in the water box of the number one effect
of the Freeport Desalination Plant also showed the attack. Crevices favor
initiation of the attack with contact areas between plastics and titanium
tending to promote the frequency of attack better than metal to metal con-
tact. Once initiated, however, the corrosion process is often self-sustain-
ing and continues beyond the confines of the crevice. Further, in a number
of instances the attack apparently Initiated at micro crevices or surface
imperfections such as laps, fissures, or inclusions. The frequency and
severity of attack vary directly with temperature and inversely with pH;
the attack was not observed at pH values higher than 8.% While very capri-
cious in terms of initiation, rate, and extent of attack, penetration rates
in excess of several hundred mils per year have often been observed. Of
nine commercially available titanium alloys which have been tested, only
the Ti-0.15% Pd alloy has shown demonstrable increased resistance to the
attack. It apparently is not immune, however, since pustules were initiated
under Teflon insulation wa shers after 82 days exposure in the Freeport Plant.
6-22-65
ALUMINUM AND TITANIUM CORROSION IN SALINE WATERS AT ELEVATED TEMPERATURES
By E. G. Bohlmann and F. A. Posey
I. ALUMINUM
Aluminum can be employed as a resistant material of construction in
contact with chloride solutions provided certain precautions are observed,
particularly with respect to solution composition, pH, and galvanic couples
with other metals.
Among commerically available aluminum alloys, important
differences exist in corrosion behavior which suggested the need for compara-
tive studies of the corrosion of aluminum alloys under dynamic conditions.
Titanium loop studies in NaCl solutions have shown the 5454 alloy (0.8% Mn,
2.7% Mg, 0.1% Cr) to be the most resistant to corrosion of eleven commer-
cially available alloys tested (EC, 1100, 3003, 3004, 4032, 5050, 5052,
5154, 5454, 6061, X8001).? Thus in short term comparative tests (~200 hr,
pH 6.5, 150°C, 1 M NaCl) the generally reccommended 6061 alloy (0.8% Si,
0.25% Cu, 1.0% Mg, 0.25% Cr) corroded three to eight times as fast as the
5454 alloy. The 5454 alloy also exhibited less pitting attack. In order
to investigate more precisely the nature of differences in corrosion be-
havior of aluminum alloys, mea surements of polarization curves and other
electrochemical aspects of aluminum corrosion were conducted in a small
titanium loop. Some results of these measurements are presented below.
High-Temperature Titanium Loop for Electrochemical Studies of Corrosion
Figure I shows schematically the corrosion loop facility which was
developed for the measurement of electorchemical behavior of aluminum and
other alloys in high-temperature salt solutions. The loop, constructed
entirely of titanium, is equipped with a heater and a pump capable of cir-
cula ting the 650 m2 volume of solution past the electrode surfaces at linear
velocities ranging, usually, from 8 to 24 ft/sec, dependirg on electrode
diameter. Provisions are available for continuous addition and withdrawal .
of fresh solution, if desired. Other features include a sampling valve, a
metering pump for injection of acid or base for control of pH, and provi-
sions for deaerating, aera ting, or oxygena ting solutions to be circw.ated
in the loop.
Details of the electrode holder assembly are shown in Fig. 2. Elec-
trodes are machined in the form of hollow cylinders from comercial stock.
Each electrode is isolated from the loop and from other electrodes by use
of silicone rubber ga sket insulators. Electrolyte circulates past the in-
terior surfaces of the electrodes, which were used in the "as-machined"
state. The polarizing electrode, constructed of titanium, occupies a cen-
tral position in the electrode holder; titanium rcds welded to this central
eleurode extend axially through the electrolyte inside the other two elec-
trodes.
This arrangement minimizes IR drops in solution between the test
specimens and the polarizing electrode and promotes uniformity of current
density distribution.
· Electrode potentials were measured on a high-impedance electrometer-
recorder combination with respect to externally situated (room temperature)
sa turated calomel electrodes which were bridged into the loop solution by
use of an asbestos wick assembly similar to that described by Bacarella and
Sutton.
Aluminum electrcdes (Fig. 2, specimen Nos. 1 and 3) were polarized
galvanostatically by use of a conventional current source constructed from
high-voltage batteries (135 v) of large capacity and high resistances. In-
terior surfaces of the electrodes were employed in the "as-machined" state.
Corrosion Rate Mea surements. Corrosion rates of aluminum alloys 54564
and 6061 were followed as a function of time in 1 M NaCl at 150°C by use of
polarization resistance measurements. **° The limiüing 6).ope of the polari.--
2.6
zation curve of a metal at small values of applied current (polarization
resistance) is inversely proportional to the corrosion rate. In general,
corrosion rates decrease with time until steady-state rates are attained in
periods of time which depend on experimental variables such as pH, solution
flow rate, rate of refreshment of solution, and others. Similar observations
مصمم به
on changes of corrosion potential and corrosion rate with time have been re-
ported.'-4 The rate mea surements show that the 5454 alloy is the more re-
sistent to attack under these conditions, in agreement with observations on
comparative weight loss over both short and extended periods of time. In
.
order to increase our understanding of the observed differences in corrosion
behavior of these alloys, other experiments were conducted on the electro-
chemistry of reactions occurring at the aluminum-electrolyte interface.
Variation of Corrosion Potential and Corrosion Rate with pH. Figure 3
shows how the corrosion potential (measured vs. the satura ted calomel elec-
trode) of the 5454 alloy varies with pH. The current densities of anodic
and cathodic interfacial reactions are equal at the corrosion of open-circuit
potential. In weakly acidic solutions the corrosion potential is independent
of pH, while in alkaline solutions the potential decreases with increasing
ph. This behavior is consistent with results of other investigators obtained
in chloride solutions at lower temperatures.',12,15 Experime:tal points shown
in Fig. 3 represent the average (+5 mv) of three determinations at each pH
value.
A pronounced minimum exists in the corrosion rate -pH relation of aluminum
and its alloys in chloride solutions in the vicinity of neutrality.',12,13,16-18
Cur results are quite similar to those reported by Troutner,
at a lower ter-
perature, except that corrosion rates in 1 M NaCl at 150°C are influenced more
by the solution velocity and by the accumulation of corrosion products in the
system. Increased solution velocity increases corrosion rate somewhat, parti-
cularly in alkaline solutions. The beneficial effect of corrosion products
in solution noted under these conditions is in agreement with observations
of others.,
Reasons for the existence of a minimum in the corrosion rate
20.21
of aluminum and for the observed variation of corrosion potential with pH may
be understood on a kinetic basis by reference to the polarization curves
of the anodic and ca thodic reactions which occur at the aluminum-electrolyte
interface.
Kinetic Interpretation of the Effect of pH on Aluminum Corrosion. Figure
4 shows schematic polarization curves which were constructed on the basis of
experimental data accumulated on the 5454 alloy in 1 M NaCl at 150°c. Para-
meters shown in Fig. 4 are characteristic of the potentials and current den-
sities observed in the real system: except that certain facture (discussed
below) which produce variations in behavior are ommitted. Curves ABC, A'B'C,
......?
and A "B"C represent anodic polarization curves for the aluminum disolution
reaction as a function of pH. Åt low potentials (cf. AB, A'B', and A"B")
the rate of the corrosion reaction 18 independent of the electrode potential,
but increases with increasing pH. Corrosion is uniform over the metallic
surface in this region. As shown by Kaesche, .** the corrosion rate in this
region 1.6 controlled by the rate of ma 88 transport of hydroxide ions to the
oxide-solution interface.
The interfacial reaction is so fast that the ma 68
transport process determines the over-all rate. Further verification of this
fact is provided by the work of Kolthoff and Sambucetti
who found that
hydroxide ions yield well-defined anodic diffusion currents on the aluminum
electrode.
In the presence of chloride ions, the anodic polarization curve of alumi-
num exhibits a critical potential which cannot be exceeded (in the steady
state). At this potential, the pſtting potential (BB'B'C in Fig. 4), pits
form on the electrode surface and exist simultaneously with passive area s.
The potential exhibited by the pitting surface in the steady state is essen-
tially independent of the anodic current density. The nature of the pitting
process and the properties of the pitting potential have been the object of
atendendº, +0,44,"","*-*
numerous studies.®,10,14,22,24-37 The net.
The pitting potential of aluminum es inde.
perdent of pH but becomes lese noble with increasing chloride concentration.
The cathodic reaction in alkaline solutions is independent of pH (cf.
DG in Fig. 4); this process consists of the reduction of water molecules to
form molecular hydrogen. With increasing acidity, discharge of hydrogen ions
becomes increasingly important (D'EF and D'E'F' in Fig. 4); lines D'E and D'E'
correspond to activated discharge of hydrogen ions and segments F and E'F'
correspond to diffusion-limited rates of this reaction. The reason for the
existence of a minimum in the corrosion rate -pH relation of aluminum in
chloride solutions is evident from the curves in Fig. 4. In alkaline solu-
tion the corrosion potential and corrosion current are determined by the
intersection of the anodic curve A"B" and the ca thodic curve DG (point (1)
in Fig. 4). With increasing hydroxide ion concentration, the transport-
controlled rate of the anodic or corrosion reaction increases and therefore
the intersection of the anodic polarization curve with the cathodic polari-
zation curve (DG) shifts to lower potentials and higher current densities.
This accounts for the decrease of corrosion potential with pH in alkaline
solutions observed in Fig. 3. In acidic solution the cathodic polarization
curve (D"E'F'G) intersects the anodic curve (ABC) at the pitting potential
(point (3) in Fig. 4). With increasing acidity, the corrosion potential
remains at the pitting potential (cf. lig. 3) while the corrosion current
increases as a consequence of the increased rate of reduction of hydrogen
ions; the severity of the pitting attack increases accordingly. The mini-
mum in the corrosion rate -pH relation represents a compromise between the
decrease in the rate of the trunsport-controlled anodic reaction and the in-
crease in rate of the cathodic hydrogen-evolution reaction with increasing
acidity (cf. point (2) in Fig. 4). The minimum rate occurs when the rate.
of the transport-controlled anodic reaction becomes small enough with in-
creasing acidity so that the intersection of anodic and cathodic polariza-
tion curves occurs at the pitting potential. For this reason the break in
the corrosion potential - pH relation (cf. Fig. 3) coincides with the minimum
in the corrosion rate -pH relation. One can conclude that the limit of corro-
sion resistance of aluminum and its alloys in chloride solutions is determined
,
by the position of the pitting potential, which varies with chloride ion con-
centration, in relation to the polarization curve of the cathodic proce 88.
Effect of Solution Velocity. The ideas expressed schema tically in Fig. 4
are in general agreement with the findings of Kaesche.",2903 However, cer-
tain effects occur at the higher temperature of our study (150°c) which should
be considered in the interpretation of the experimental polarization curves.
We find that the magnitude of the current corresponding to the transport-con-
trolled anodic reaction (e.8., A"B" in Fig. 4) depends on the solution velo-
city. This effeci 18 shown in Fig. 5, where curves A and B are the polariza-
tion characteristics of type 5454 alloy measured in 1 M NaCl at 150°C, pH 9.0.
In alkaline solutions, where transport of hydroxide ions to the oxide-solution
interface controls the rate of the uniform dissolution reaction, an increase
of solution velocity probably causes a decrease in the diffusion layer thick-
ness at the interface. This permits a higher flux of hydroxide ions to the
electrode surface and thus a greater over-all corrosion rate. On the other
hand, velocity effects appear to be negligible in acid solutions (cf. curve
C in Fig. 5) where the electrode undergoes pitting attack at the pitting
potential, unless the rate of the cathodic proce 88 18 also influenced by ma 68
transfer of hydrogen ions.
Effect of Cathodic Polarization on Corrosion. The schematic anodic
polarization curves of Fig. 4 should be modified to reflect the phenomenon of
"cathodic corrosion" of aluminum, as studied by Kaesche.
When aluminum
is polarized with cathodic current, the reduction of hydrogen ions or water
molecules to form molecular hydrogen causes an increase of the local pH at
the interface. This increase in local pH enhances the dissolution rate of
the superficial oxide layer. One can also conclude that if impurities of
low hydrogen overvoltage are present or if aluminum 18 connected to a le88
noble metal, the corrosion rate will be increased.
Effects of the Structure of the Oxide Layer and of Mme. Our mea sure-
ments in alkaline solutions (cf. curves A and B of F?3. 5) show that the rate
of the anodic reaction decreases with time at constant pH and solution velo-
city; this is particularly noticeable during the first few hours of an experi-
nient.
Since the rate of the cathodic reaction is essentially independent of
time, we observe a corresponding enobling of the corrosion potential and a
decrease in the corrosion rate. Other variables associated with this effect
appear to be the rate of refreshment of the solution in the loop and the ratio
of area of corroding specimens to solution volune. Evidence is available for
the existence of a duplex film on aluminum corroding in high-temperature
aqueous solutions and for the beneficial effects of dissolved corrosion pro-
in note. *dyansynger Perhaps the decrease with time
ducts on the corrosion rate.
of the rate of the anodic reaction in our experiments can be accounted for
by the kinetics of growth and dissolution of the so-called "outer" film,
which is believed to possess consider ble porosity. In this case, an in-
crease in the thickness of the outer leyer could very effectively increase
the diffusion path for the transport of hydroxj.de ions to the surface of the
"inner" compact oxide layer. All other kinetic interpretations of polari-
zation curves would then remain the same as discussed above, except for
the influence of the outer film thickne 88 on concentrations of reactant
ions. If this interpretation is correct, effects of solution refreshme nt
rate, cf specimen area to solution volume ratio, and of corrosion products
in solution are probably associated with the kinetics of growth and dissolu-
tion of the outer porous oxide layer; this in turn affects the dissolution
kinetics of the inner layer by altering the flux of reactants (OH”, in par-
ticular) due to diffusion, migration, and convection.
Ohmic Effects. Still another factor which affects interpretation of
polarization curves can be seen in Fig. 5.
The polarization curve of the
cathodic process (hydrogen evolution from solvent molecules) exhibits con-
siderable curvature at the higher current densities when plotted semi-logarith-
20
mically. We find that conventional, linear polarization curves
may be ob-
tained in most cases by a correction procedure involving subtraction of an
Ohmic contribution to the electrode potential. Some measurements suggest
that the resistance contribution increases with time. Conceivably, restricted
access of solution to the surface of the inner layer imposed by the porous
outer layer could be responsible for the Ohmic resistance which is included
in the measurement of cathodic polarization curves.
This interpretation is
also consistent with an increase of the Ohmic contribution with time due to
growth of the outer oxide layer. Altervatively, the inner layer may itself
possess sufficient electronic resistance to produce significant IR drops in
the measured cathodic polarization curves. Ionic and electronic conductivi-
ties and distributions of defect concentrations in alwainum oxide layers have
40-45
been studied by a number of workers."
20
Effect of Dissolved Oxygen. In neutral chloride sclutions, molecular
oxygen dissolved in solution can be reduced at the oxide-solution interface;
in some cases the reaction rate may even be larger than that of the hydrogen-
evolution reaction so that the corrosion rate 18 essentially controlled by
the oxygen-reduction reaction. 8,24 The effect of oxygen reduction on the
corrosion of the 5454 alloy in 1 M NaC1, pH 8.1, at 150°C 18 shown in Fig. 6.
In deaerated solution at this pH, the cathodic process consists of the re-
duction of solvent molecules to form molecular hydrogen and the aluminum
corrodes uniformly at a very low rate; the corrosion potential lies below
the pitting potential. Admission of oxygen to the system increases the
total cathodic current; at the potentials in Fig. 6 the reduction reaction
of O2 is essentially under ma 88 transfer control. In oxygenated solution,
the reduction current is so large that the corrosion potential of the alumi-
num is pulled up to the pitting potential and severe, non-uniform, pitting
attack occurs. For this reason, oxygena ted solutions and traces of noble
metals which can catalyze reduction reactions should be avoided whenever
possible.
Comparison of 5454 and 6061 Alloys. A comparison of polarization curves
of the 5454 and 6061 alloys in I M Naci, pH 8.1, at 150°C is shown in Fig. 7.
Corrosion rates are rather high in this case; the loop solution was replenished
with fresh stock solution at a rate of about one loop volume per hour, so that
the full beneficial effect of accumulated corrosion products on the corrosion
rate was not achieved. Figure 7 shows that the rate of the hydrogen-evolution
reaction on the 6061 alloy 18 considerably greater than that of the 5454 alloy.
11
Other measurements show this to be true at any pH. The curvature of the
cathodic polarization curves 18 due to the Ohmic effect discussed above.
Under the conditions of Fig. 7, the 5454 alloy undergoes uniform dissolu-
tion below the pitting potential, while the high rate of the cathodic pro-
cess maintains the 6061 alloy at the pitting potential. The enhanced rate
of the cathodic process on the 6061 alloy, compared to the 5454 alloy,
therefore accounts for its greater corrosion rate at any pH and for its
susceptibility to pitting attack. We are inclined to attribute catalysis
of the cathodic process on the 6061 alloy to the copper content (0.25%.
Copper has the lowest hydrogen overvolt ge of any of the major allowing
elements in either the 5454 or 6061 alloys. Similar catalytic effects of
trace elements have been studied by others."0,"?
The differences in corrosion behavior of the 5454 and 6061 alloys
which were detected in earlier loop experiments are shown by the polari-
zation measurements to be a consequence of the enhanced rate of the ca-
thodic reaction on the 6061 alloy compared to the more resistant 5454 alloy.
Our results show that measurement of polarization curves of metals and
alloys in high-temperature loops 16 a promising technique for rapid assess-
ment and comparison of corrosion resistance. In addition, information is
obtained on the nature of ra te-controlling steps of corrosi«n reactions
which is difficult to obtain by any other method of corrosion research.
II.
TITANIUM
Titanium 18 reported to be immune to all forms of corrosive attack in
50.52
ambient sea water. 48-31 Various investigators"-5 have also shown it to
(48) H. B. Bomberger, P. J. Cambourelis, and G. E. Hutchinson,
J. Electrochem. Soc., 101: 442-427 (September 1954).
(49) F. R. LaQue and H. L. Copson, Corrosion Resistance of Metals
and Alloys, 2nd ed., pp. 654-656, Reinhoid, New York, 1963.
(50) L. B. Golden, I. R. Lane, and W. L. Acherman, Ind. and Eng.
Chem. 44: 1930-1939 (August 1952).
(51) D. Schlain, "Corrosion Properties of Titanium and Its Alloys,"
Bureau of Mines Bulletin No. 619, 1964.
(52) P. J. Gegner and W. L. Wilson, Corrosion, 15: 3416-350t (July
1959).
be resistant to attack in most chloride solutions at elevated temperatures.
For example, it was reported inert or nearly so in concentrated ferric,
nickel, mercuric, cupric, manganous, ammoni um, and magnesium chloride solu-
tion at temperatures of 100° to 155°c. However, under similar conditions
in other chloride solutions, such as those of zinc, calcium, or aluminum,
erratic behavior has been encountered. Gegner and Wilson 52 observed corro-
sion rates ranging from nii to >60 mpy on duplicate specimens exposed to
62% calcium chloride at 154°c. Other investigators
have also noted gross
variations in the corrosion resistance of titanium to concentrated chloride
solutions with relatively modest changes in temperature and/or concentration.
Observations oť titanium corrosion made in connection with the aluminum
studies discussed above, and in resultant other studies, suggest such erratic
corrosion of titanium in chloride solutions may be a more general, and serious
problem than has been appreciated thus far.
HIGH TEMPERATURE LOOP OBSERVATIONS
The corrosive attack was initially observed on titanium clamping bands
used in the assembly of loop specimen holders. Open and assembled holders
are shown in Fig. 8; note the three bands holding the halves of the holder
together and the Teflon sleeves used to insulate the pin specimens from the
titanium holder. Strips of Terlon are also often used to cover the ends of
the pins to eliminate the possibility of inadvertent contact between the bande
and pins, 80 both metal to metal and metal to Teflon crevices are formed under
the bands. The assembled specimen holders are fitted into la-in, titanium
pipe sections flanged into titanium loops and equipped with fittings which
direct the loop fluid flow through the channel in the holder (see Fig. 9).
Thus the bands are exposed to the test solution in a semi stagnant annulus
(~ 1/32 in. thick) between the holder and the pipe wall.
Figure 10 shows a number of clamping bands (made from 0.008-in. A55
titanium sheet) after exposure to pH 6.5 two molar sodium chloride at 150°C
for 192 hr. Seven of the twenty bands show gross attack, but the remaining
thirteen show none (the small holes in and near the welds were produced in
fabrication).
Similar attack has been observed under the Teflon sleeve 10-
sulation on pin specime 28, but in all the experiments conducted thus far
the initiation, rate, and extent of the attack has been very erratic.
This
inconsistency has made quantitative evaluation of the effects of various
parameters very difficult; however, some trends have been indicated by the
accumulated observations.
.
....
w
.
.
-
Presence of a Crevice. Crevices seem to promote initiation of the attack
and contact areas with Teflon are more effective than metal to metal contact.
A strong correlation between the areas of attack and contact with Teflon 10
the early observations suggested that the attack might result from breakdown
of the protective oxide film by small amounts of fluoride released by the
Teflon. Autoclave tests with bolted coupon crevice specimens in the absence
of Teflon, however, eliminated this hypothesis; although, the possibility that
it plays a part in the promotion of the attack in Teflon contact areas still
exists. It is our belief that the tight crevice formed in contact with 'T:llon
is the important factor. We have also observed the attack in areas of contact
with silicone rubber ga skets, see F18. 2; and others have noted similar cre-
(53) L. W. Gleekman, Chem. Eng. 70: 224 (November 11, 1963).
vice attack in areas of contact with rubber and Teflon in wet chloride service.
While macro crevices promote the attack, it is also clear that they are
not required for its initiation or cont. uation. Note in Fig. 3 that the fifth
band from the top in the middle column was severed but apparently kept on cor-
roding, as did the other bands showing attack, after the crevice was eliminated
by perforation of the band. This has also been observed in autoclave tests in
which the corrosion continued well beyond the confines of the crevice.
In addi-
tion, a number of instances have been observed where the attack was initiated
in the absence of a macro crevice. Examinations of specimens on which the at-
tack was incipient indicates laps, inclusions, etc., formed during the metal
fabrication, provide micro crevices at which the attack may be initiated.
Temperature. The effect of temperature on the frequency of attack 18
shown in Table 1. The data given are for pins and bands exposed in loop
runs. The attack has been observed only once at 100°C, on a pin specimen
under the Te'lon sleeve after 1178 hr exposure; but the frequency of attack
increases with temperature. Note, however, the extremely erratic results
shown by the wide range in the percent attacked in a given run. At 150°C
the attack on the bands usually rapidly penetrates the 8 mil metal thickness
and then spreads by consuming the entire thickness of the band along a rela-
tively sharply defined front. At 200°C the attack 18 of ten more general,
spreading over the surface on which it initiates more rapidly than it con-
sumes the band thickne88.
pH. The effect of pH is shown by the data in Table 2. The attack has
been observed at pH values as high as 8.7, and the frequency appears to be
inversely dependent on pĦ. Again, however, the initiation of attack 18 very
erratic as is the rate after initiation. Similar erratic results have been
obtained in autoclave experiments at 150°C. No data at lower pH values were
obtained from loop runs for fear of excessive damage to the equipment.
Time.
In most caseri, those specimens which are attacked begin to cor-
rode very shortly after reaching temperature. Initiation of attack on the
bands has been observed after twenty-four hours exposure at pH 6.4 (2 M NaCl)
at 150°c. Perforated bands have been observed after 188 hr at 150°C (1 M
Naci, pH 6.5) and after only 4
hr at 200°C (1 M NaCl, pH 6.0). Since the
bands were 8 mils thick, this corresponds to penetration rates of 1.6 in.
per year and 0.4, respectively. The rate of attack varies substantially,
however, and often the corrosion stops completely. Thus, of fourteen pins
T**
***
Table 1. Effect of Temperature on Titanium Corrosior.
Conditions: 1 or 2 M Naci, pH 5.5-6.5
Pins
Percent Attacked*
Average Per Run
No. of
°C Runs
100 3
150 2
2004
Total No.
Exposed
24
17
106
Bands
No. of Total No. Percent Attacked*
Runs Exposed Average Per Run
102
18 346
0-83
3 98
48-83
0-16
O
82
0-100
56-94
79
Includes all observable instances of initiation of attack.
Table 2. Effect of pH on Titanium Corrosion
Pins
PH
Bands
No. of Total No. Percent Attocked
Runs Exposed Average Range
No. of
Range Runs
4-5
5-6
6-7 2
7-8 1
8-9
8-10.3 2
Total No. Percent Attacked
Exposed Average Range
100
0 -
22
91 86-100
2
50 -
17 0-100
0 0
34
NW par
2
10
6
3
2
34
1 92
126
62
40
18-47
0-83
0-32
0-14
These runs were made before we were aware of the problem, so the bands were
not examined carefully as in the later runs, but no gross attack wa 8 noted.
exposed in a succession of loop runs (2 M Naci, pH 6.5), all showed some
attack after 98 hr at 150°C. Twenty-one of the twenty-eight areas of con-
tact with Teflon showed observable corrosion. The attack varied from a
few pustules to generalized penetration to a depth of eight or ten mils.
Exposure for an additional 219 hr produced attack in two additional
Teflon contact areas and continued corrosion in only six of the twenty-one
areas which showed attack after the first exposure.
Two hundred and sixty-
one hr of further exposure resulted in no visually observable additional
attack.
Similar results have been obtained in other loop run series.
The rapid initiation and the later termination of the attack were also
confirmed in an experiment carried out in a quartz tube so that the proce 88
could be viewed. The specimen was a strip of the 8 mil stock from which
the bands are made, and a crevice was formed by bending a corner of the
strip tightly over a piece of Teflon. Bubbles of gas were observed at the
edges of the crevice 105 minutes after the tube'was brought to 150°C; the
gas was later shown to be hydrogen. Sixty-six hours later the reaction, as
indicated by gas evolution, had stopped.
Alloys. A variety of titanium alloy pins has been exposed to sodium
chloride and synthetic sea water solutions in several loop runs. The alloy
compositions are given in Table 3 and the results are summarized in Table 4.
Eight of the nine alloys tested showed the usual erratic attack in areas of
contact with the Teflon insulating eleeves. Only the T1-0.15% Pd alloy con-
sistently resisted attack in the se exposures, even at 200°C. None of thirty
patlladium alloy pins exposed showed microscopically observable attack, com-
pared to 68% of the specimens of the other alloy compositions.
Table 3.
T tanium Alloy Compositions Tested
Alloy
Ta
Fe
A45
A55
Cast Ti
__ _Naniwal % Composition
Al Cr Mo V Zr Nb
(Commercial Purity - >99.2% Ti)
(Commercial Purity - >99.0% T)
(Una lloyed)
3.5 4.9
4.2 4.6
6.4
4.2
7.4
2.0
8.5 0.7
Al-Cr
0.2
Al-Mn
4.6
0.3
Al-V
0.2
0.2
821
1.1
0.5
8.2
881
Ti-Pd
0.15
.
Table 4. Corrosion of Titanium Alloys in Saline Waters
Conditions: Synthetic Sea Water and NaCl Solutions
20.5-2 M, pH 6-7, pins with Teflon Sleeves
150°C
200°C
Pins
Exposed
Pins
Attacked
Pins
Exposed
Pine
Attacked
A45
A55
Cast
Al-Cr
Al-Mn
ona ww no a w
Oo oooñito
ooo vai 16 o
AI-V
821
881
Ti-Pa
Four coupons were also exposed and all four were attacked in Teflon
contact areas.
Pretreatments such as innealing, anodizing, pickling, and air oxidation
did not alter pin specimen or band behavior significantly. Resistance to a to
tack Se:emed improved, but in all cases some specimens were attacked and the
lower frequencies may have been fortuitous.
Loop Components. In spite of the severity of the attack on the bands
and pins, little difficulty has been experienced with the titanium loops and
equipment in thousands of hours of operation. Several factors may account
for this:
1. Prior to use in these studies, the loops were used with strongly
oxidizing solutions to temperatures as high as 300°c. Consequently, the
surfaces are generally coated with heavy oxide films which may reduce the
likelihood of attack.
2. Crevices were minimized by design and welded construction.
3. Most surfaces are exposed to rapidly flowing solution.
However, some problems have been encountered.
The first of these was
observed in the areas of contact with the silicone rubber ga skets in the
test assembly for electrochemical studies (see Fig. 2). The attack initiated
in the crevices between the large titanium end flanges and the silicone rubber
ga skets and then invaded the conical flange apertures. After -5000 hr of oper-
ation on on? molar sodium chloride solution largely at 150°C, the flanges have
been damaged sufficiently to require replacement,
Fenetration of one of the one and a half inch schedule 90 titaniun pipe
sections into which the corrosion specimen holders are inserted has also been
encountered.
This occurred at the point labeled C in Fig. 9, and the large
shallow pit which resulted in the failure 18 shown in Fig. 11; the penetra-
tion occurred a little below the center of the pit.
Penetration of the 0.2-
in. pipe wall occurred after a total of 8468 hr of operation principally with
one and two molar sodium chloride solutions at pi's in the range 5.5 to 7.2.
The temperaturę history was 2808 hr at 100°C, 5374 hr at 150°C, and 286 hr at
200°C. A careful examination of the loop as a result of the above failure
revealed additional smaller areas of attack at the locations indicated by C'
in Fig. 9; these are areas exposed only to flowing solution with no macro
crevices of any kind.
Concentration. Loop runs were carried out with both one and two molar
NaCl. No consistent differences in the attack on pins and bands were observed,
so tire data were combined in this report.
Aeration. The loop experiments have been run in two ways as regards aera-
tion. In one case, the circulating solution wa is continuously refreshed with
aerated solution which was pumped into the loop at a rate of one liter per
hour (loop volume = 17 liters); in the other, the charge solution was "de-.
aerated" by over-night evacuation, charged to the evacuated loop, and run
with helium or nitrogen overpressure. Analyses of the gas from solution
samples taken during such runs usually showed no oxygen but probably had a
lower limit of detection of a few tenths of a ppm.
The results obtained
under the two conditions did not differ significantly.
Metallography. Metallographic sections through corroded areas of band 8
are shown in Figs. 12 and 13. Figure 12 shows the attack characterized by
relatively rapid penetration of the band. Figure 13 shows the surface
10
spreading type attack, note that attack initiated on both surfaces of this
band.
The surface attack occurred on the side of the band exposed to the
semi stagnant solution annulus between the specimen holder and titanium pipe
in which it was contained. The pustules shown on the other side of the band,
usually characteristic of the penetration type attack, formed in the crevice
between the band and the holder. Figure 13a shows the specimen as etched to
gray oxide was identified as hydride by this procedure.
The identification
was confirmed by subjecting the specimen to a vacuum anneal at 800°C which
decomposed the 'hydride and removed the hydrogen as shown in Fig. 13b. The
presence of hydrogen in corroded areas has also been confirmed by vacuun
fusion analyses. The light gray band at the edge of the corrosion front in
Fig. 12 has also been identified as hydride.
SEA WATER
Loop experiments with synthetic sea waters gave results consistent with
those obtained with the sodiun chloride solutions. Thus it appeared likely
that the attack would also be encountered in actual sea water exposure, but
experimental confirmation was desirable. Through the cooperation of Mr.
H. D. Singleton, Office of Saline Water Resident Engineer at the Freeport
Desalination Plant, three racks of commercially pure titanium specimens were
exposed in a representative desalination plant environment. These racks con-
tained metal-metal and metal-Teflon crevices. Two types of metal-metal cre-
vices were included: bolted coupons and one-half inch tubes rolled into a
one inch thick titanium plate to simulate a tube sheet joint. Metal-Teflon
11
crevices were formed by inserting Teflon sheet between some of the coupons
and under Teflon wa shers used to insulate specimens from the rack. One
pair of 'M-0.15% Pd coupons was included on the A rack; the crevice betwien
these plates was metal-metal, but meta l-Teflon crevices were also formed
under Teflon insulation wa shers.
The three racks were exposed in the water box of the number one effect
at the Freeport Plant; the brine conditions and exposure history are given
in Table 5. Rack A was removed for examination after 12 days exposure.
Attack had initiated in several metal-Teflon crevices but not in the coupon
metal-metal crevices. Incipient attack appeared to be present in a simu-
lated tube joint which was cut open. The Th-0.15% Pd coupons showed no
evidence of attack at this time; however, slight attack was observed in
the threads of the mounting bolt under the Teflon wa shers used to insulate
these coupons from the rest of the assembly.
The rack was reassembled and
returned for additional exposure.
Rack C was removed after 32 days and on examination gave results essen-
tially the same as those described for Rack A above.
Racks A and B were removed for examination after a total of 82 days ex-
posure. Rack B was in the same condition after 82 days as Rack A had been
after 12 days. Attack had initiated only in areas of contact with Teflon
and perhaps in simulated tube joints. If anything, the attack had progressed
less than in similar locations on Rack A. Examination of Rack A revealed it
to be unchanged except in two respects. The attack which had initiated in
the mounting bolt threads under the Teflon used to insulate the T-0.15% PU
12
Table 5.
Temperature Exposure History of Racks Exposed in Freeport Plant
11
Conditions: Exposed in water box of No. l effect to normal
concentration deaerated brine after acid treatment
and neutralization for scale control, pH 6.8-7.5.
Days Exposed
Temperature,
Rack A
Rack B
Rack C
138
128,
1.35
.
20
129
500
Removed after 12 days, examined and replaced.
°Removed after 32 days, examined and replaced.
Removed after 82 days, examined and replaced.
..
.
-
..
.-
.. --
-
.--...-------
compare any
properegowego
13
alloy coupons had progressed substantially. The threads (2-in. National
Course) were completely destroyed and pits had penetrated about one-six-
teenth inch into the bolt body beneath the thread roots. Also, the T1-().1.5%
Pd alloy coupons showed attack for the first time; a number of pustules had
formed under the insulating wa shers.
Although appreciable only in areas of contact with Teflon, the attack
observed in the Freeport Plant racks was entirely similar to that observed
in the loop experiments and is regarded as verification of the serious cre-
vice corrosion of titanium by saline waters at elevated temperatures. Ex-
posure of the specimen racks in the Freeport Plant is continuing.
DI SCUSSION
While crevice corrosion has been demonstrated not to be a problem with
titanium in ambient sea water, the observations described in this report
indic te it may be of considerable concern at temperatures above 100°C.
Thus, very aggressive but erratic corrosion has been initiated in crevices
exposed to saline waters at temperatures of 150° and 200°c. The particular
nature of the crevice plays an important, undefined part in the initiation
of the attack, contact areas between plastics and titanium tending to pro-
mote initiation of the attack better than metal to metal contact. It has
also been observed, however, that the attack may initiate at "micro crevices"
such as surface laps, fissures, or inclusions produced during metal fabrica-
tion. Once initiated the corrosion process may be self-sustaining and con-
tinue outside the confines of the crevice or it may cease after a period
of time.
The parameters governing the outcome have not been established.
The observations suggest an interesting explanation of the attack in the
absence of macro. crevices encountered in piping flow areas after thousands
of hours exposure without difficulty.
The attack has only been observed in
areas subject to mechanical deformation during the routine assembly of the
flanged joints accompanying insertion of corrosion specimen holders in the
loops. It is postulated that such deformation causes cracks in the heavy
oxide scale present on the piping with resultant formation of micro crevices
in which the attack initiates.
Metallographic sections through corroded areas bear a striking resemblence
to the blister type pitting attack observed in concentrated chloride solutions
15
ORIOL - AEC - OFFICIAL
by Golden et al. 50 They attributed this attack to impurities in the metal
such as magnesium chloride inclusions often found in powder metallurgy pro-
duced titanium, and stated that arc melted titanium with "very low magnesium
chloride content" did not show such pitting. The specimens used in these
studies were from arc melted material shown by spectrographic analyses to
contain less than ten ppm magnesium (13.mit of detection).
Thus it appears
the magnesium chloride inclusions only provided sites for initiation of a
type of attack to which titanium is generally susceptible in high tempera-
ture aqueous chloride solutions.
ORNL - AEC - OFFICIAL
u
.
ORDIL - AEC - OFFICIAL
ORNI-Air-Oisiciel.
References
1. F. W. Fink, A. C. S. Adv. in Chem. Series, No. 27, p. 27, Washington,
1960.
2. E. G. Bohlmann, Reactor Chen. Div. Ann. Prosr. Rept. Jan. 31, 1964,
ORNL-3591, p. 210.
3. A. L. Eacarella and A. L. Sutton, J. Electrochem. Soc., 112, 546 (1965).
4. M. Stern and A. L. Geary, J. Electrochemi. Soc., 104, 56 (1957).
5. A. C. Halrides, Corrosion, 18, 338t (1962).
6. F. A. Posey, in Encyclopedia of Electrochemistry, p. 263, Reinhold,
New York, 1964.
'
.
7. G. V. Akimov and A. I. Glukhova, Compt. Rend. Acad. Sci. U.R.S.S.,
49, 194 (1945).
8. Q. Masing, 2. Metallkunde, 37, 97 (1946).
9. V. V. Romanov and G. V. Akimov, Dokl. Akad. Nauk S.S.S.R., 29,
989 (1951).
20. R. Ergang, Q. Masing, and M. Möhling, 2. Elektrochem., 56, 8 (1952).
R. L. Dillon, Corrosion, 152 13t (1959).
A. Ya. Shatalov and Yu. A. Mikhailovskii, Zhur. Fiz. Khim., 27, ::
1025 (1953).
13. K. J. Pryor and D. S. Beir, J. Electrochem. Soc., 105, 629 (1958). .
14. H. Kaesche, Werkstoffe u. Korr., 14, 557 (1963).
15. F. H. Haynie and S. J. Ketcham, Corrosion, 19, 403t (1963),
16. T. Markovic and V. M. Balasa, Werkstoffe u. Korr., 8, 402 (1957).
17. V. H. Troutner, Corrosion, 15, 9t (1959).
18. K. F. Lorking and Ja E. O. Mayna, J. Appl. Chem. (London), 11,
. 170 (1961).
19. D. R. Dickdnson, Corrosion, 21, 19 (1965).
20. P. Ruetschi, in Encyclopedia of Electrochemistry, p. 939, Reinhold,
New York, 1964.
21. K. J. Vetter, "Elektrochemische Kinetik," Springer-Verlag, Berlin, 1961.
22. H. Kaesche, 2. physik. Chem., N. F., 34, 87 (1962). ..::;..
Sirini
ORNL - AEC - OFFICIAL
nou
.....
.....
.........
....
.
.
- 12 -
ORNI - AIC - OINICIAL
23. I. M. Kolthoff and C. J. Sambucetti, Anal. Chem. Acta, 21, 17 (1959).
R. Er gang and G. Masing, Nach. Akad. Wiss. Göttingen, Math. -Pr.y8. 11.,
1, 62, 65, 93 (1946).
25. R. Ergang and G. Masing, 2. Metallkunde, 40, 311 (1949).
26. R. Ergang, Q. Masing, and M. sönling, 2. Elektrochem., 55, 160 (1951).
27. C. Edeleanu and V. R. Evans, Trans. Parad. Soc., 47, 1121 (1951).
28. G. Masing and D. Altenpohi, 2. Metallkunde, 43, 401, 433 (1952).
29. K. M. Carlsen, J. Electrochem. Soc., 104, 147 (1957).
:30. T. H. Orem, J. Res. Nat. Bur. Stand., 58, 157 (1957).
31. P. J. Anderson and M. E. Hocking, J. Appl. Chem. (London), 8, 352 (1958).
32. T. Hagyard and J. R. Santhiapillai, J. Appl. Chem. (London), 2, 323 (1959).
33. H. Kaesche, 2. physik. Chem., N. F., 26, 238 (1960).
34. C. Edeleanu, J. Inst. Met., 89, 90 (1960/61).
35. T. Hagyard and M. J. Prior, Trans. Farad. Soc., 52, 2295 (1961).
36. W. Schwenk, Corr. Sci., 3, 107 (1963).
37. G. A. W. Murray, Corrosion, ,20, 329t (1964).
38. D. F. MacLennan, A. F. McMillan, and J. H. Greenblatt, Proc. 1st Inta
Congr. Met. Corr. 1961, p. 429, Butterworths, London, 1962.
39. M. A. Barrett and A. B. Winterbottom, Proc. 1st Int. Congr. Met. Corr. 1961,
p. 657, Butterworths, London, 1962.
40. M. J. Pryor, 2. Elektrochem., 62, 782 (1958).
J. J. McMullen and M. J. Pryor, Proc. 18t Int. Congr. Met. Corr. 1961,
p. 52, Butterworths, London, 1962.
42. A. F. Beck, M. A. Heine, D. S. Koir, D. van Rooyen, and M. J. Pryor,
Corr. Sci., 2, 133 (1962).
43. M. A. Heine and M. J. Pryor, J. Electrochem. Soc., 110, 1205 (1963).
2016 M. A. Heine, D. S. Koir, and M. J. Pryor, J. Electrochem. Soc.,
. 22, 24 (1965).
45. 1. A. Heine and P. R. Sperry, J. Electrochem. Soc., 112, 359 (1965).
ORNI - ACC-OFFICIAL
3 -1870
• 13 -
141001110 --
46. 1. D. Tomashov, Uspekhi. Khim., 24, 453 (1955)3 Corrosion, 2b,
229t (1958).
47. M. Stern and H. "Wissenberg, J. Electpochem. Soc., 106, 759 (1959).
8senberg
• Electpochem. So
48. 1. B. Bomberger, P. J. Camboure 13c, and G. E. Hutchinson, J. Electro-
chem. Soc. 101: 442-427 (September 1954).
49. F. R. La Que and H. L. Copson, Corrosion Resistance of Meta 16 and
Alloys, 2nd ed., pp. 654-656, Reinhold, New York, 1963.
50. L. B. Golden, I. R. Lane, and W. L. Acherman, Ind. and Eng. Chem.
Gri 1930-1939 (August 1952).
5.1. D. Schlain, "Corrosion Properties of Itanium and Its Alloys,"
Bureau of Mines Bulletin No. 619, 1964.
52. P. J. Gegner and W. L. Wilson, Corrosion, 15: 3410-350t (July 1959).
53. L. W. Gleekman, Chem. Eng. 70: 224 (November 11, 1963.)
YoDisso) - 03 V - INDO
ORNL-MEC - OFFICIAL
ORNL-OWG 65-2600A
PRESSURE
CELL
TO PRESSURE
CONTROL INSTRUMENT
SURGE
TANK
LET-DOWN V
VALVE
CALOMEL
REFERENCE
ELECTRODE-
CALOMEL
REFERENCE
ELECTRODE
1000 ml
TO
DRAIN
SPECIMEN HOLDER ASSEMBLY
ASBESTOS WICK
BRIDGE
CORROSION SPECIMENS
1/4-in. SCHED-80 PIPE
FLOW
PUMP
A
LOOP HEATER
LOOP HEATER
>
CAPILLARY
TUBE
ACIO BASE

FLOW
POLARIZING
ELECTRODE
SAMPLE
VALVE
Ultimul
(
WWIIHIIIIIIIIIT
INJECTION
PUMP
25-go!
TANK
650-ml LOOP VOL
INJECTION
PUMP
LOOP OH CONTROL SYSTEM
TV21310- )3 V - INTO

ORNL DWG. 65-4226
POLARIZING
[ELECTRODE
ASBESTOS WICK
FROM CALOMEL
ELECTRODE
SPECIMEN
NO. 1
CALOMEL
-REFERENCE
ELECTRODE
GASKET
INSULATORS
SPECIMEN
[ NO. 3
w
ekillleri.1.1.1.1.1.1.1.lil.
Primiti
LGUIDES AND INSULATORS
TEST ASSEMBLY FOR ELECTROCHEMICAL STUDIES
OF DYNAMIC CORROSION
ORNL-DWG. 65-6468
-800
DO
ELECTRODE POTENTIAL vs. S.C.E. (mv)
-1100
4
5
6
7
8
9
10
pH (measured at room temperature )
Fig. 3 Corrosion Potential of 5454 Aluminum Alloy as
a Function of pH in 1M NaCl at 150°C.

ORNL-DWG. 65-6467

-700
INCREASING (H+).
-800
PITTING
POTENTIAL
-9001
ELECTRODE POTENTIAL vs. S.C.E. (MV)
000
INCREASING (OH
CURVE
DH
Ecorri corr
... 1.000 1.0x 10*9
-850 1.5x 10-5
- 850 1.4 x 10-4
7
6
10-6A/cm2 = 0.805 mdd = 0.428 mpy
-12004-Luuletus tuuu
-6
10-7
10-6
-5
10
-
10-4
10
10-3
CURRENT DENSITY (amp/cm²)
Fig. 4 Schematic Polarization Curves of Anodic and
Cathodic Reactions on Aluminum in Chloride Solution.
-700
ORNL-DWG. 65-6466
mptomi
-800
ANODIC
PITTING
POTENTIAL
DO
ELECTRODE POTENTIAL VS. S.C.E. (mv)
CATHODIC
Ö,
ELITIL-
24
CURVE PH VEL Post Ecorr i corr
9.0
-1167 1.5 x 10-4
9.0
8 -1124 7.5 x 10°
4.2 8 or 24 -850 ~8x 10-5
للن
10-5
10-4
10-3
-1500
10-6
CURRENT DENSITY (amp/cm2)
Fig. 5 Effect of Solution Velocity on Polarization Curves
of 5454 Aluminum Alloy in 1M NaCl at 150°C.

-800mm
ORNL-DWG. 65-6465
TTTTTTTT
- PITTING
POTENTIAL

ext-tota
-900
B
-1000
ELECTRODE POTENTIAL VS. S.C.E. (MV)
प
-1100
"
CURVE SOLUTION
DE-AERATED
AERATED
OXYGENATED
OOD
-1200
10-6
10-5
10-3
-1300 ddim
10-4
CURRENT DENSITY (amp/cm2)
Fig. 6 Effect of Oxygen Concentration on Cathodic
Polarization Curves of 5454 Aluminum Alloy in 1M NaCl, pH 8.1,
at 150°C.
-800
ORNL-DWG. 65-6464
Top

-900
ANODIC
w -1000
ELECTRODE POTENTIAL vs. S.C.E. (mv)
ta
-CATHODIC-
-1200
CURVE ALLOY
aan 6061
Ato 5454
LOOP VOLUME : 650cc
REFRESHMENT RATE: 600 cc/hr
-1300
10-5
-14004
10-4
10-3
10-2
CURRENT DENSITY (amp/cm2)
Fig. 7 Comparison of Polarization Curves of 5454
and 6061 Aluminum Alloys in 1M Naci, pH 8.8, at 150°C.

PiHOTO 22808A
CLAMPING BAND
. . .
میکشند
. .
. . -ممسمن انسسسسسسستححس ششنتني.تحمت
..
.
مدد
. .
.
.
، ۰ که م .:
لم : ۸۰۰: ... . مه مهمننننمعلم ندهم...خ
مممممممممممممممم. . ب ..
:
خانم
" : 50
. .: بر ۰۰:
INCHES
العلللللللللللللللللا
TEFLON SLEEVE
::: .ان
ها .:|
I
.مهممم
سموم
. ۰۰۰
.. محمد
. !
----. .
-
|-
|
. . . . . .
.
.
*-
با
|
|
د
او
Fig. 8. Titanium Specimen Holder.

ORNL OWO. 68-6717

C-C' -- PITTING OCCURRED AT
THESE POINTS
PRESSURIZER
MIXING BY-PASS
PRESSURIZER
HEATER
-SAM”. E BARRELS
SOLUTION-SAMPLING
VALVE
100 GPM CENT.
CIRU. PUMP
LOOP HEATER
Fig. 9. Schematic Diagram of Titanium 100 gpm Solution Tost Loop.
Fig. 11. PII Feel
IOT OT
7
"
"
ORNL-DWG 65-415A
. . .
.
. . .
.
. .
.
.
..
مه مه . . .
- -
-
.
ها
يجنننننللللننضنسحمسائل
باب
'
'
متهم میهناننممممم
منفی
اما
ز من .
فخر
نینتند
م
TF
مسدن تو
تنها
به
CONDITIONS:




مخفيضا
لننتكسين
150°C
pH 6.4
2M NOCI
192 HOURS
Fig. 10. Corroded Specimen Holder Ciamping Bands.









Y62314
-
-
-
...
*PENETRATION OCCURRED AT POINT INDICATED BY P.
Fig. 11. Pit Penetration of 1/2-in. Titanium Pipe.

PHOTO 67194

r
:
.
.
.
500x1
INCHES
ETCHANT-50 % GLYCERINE, 25 % HNO3, 25 % HF
Fig. 12. Titanium Clamping Band Corrosion.


PHOTO 69983
mommy
Warning
OXIDE
HYDRIDE
METAL
@x;:
2.001.16
S 500x .
-
500X
(0) BEFORE VACUUM ANNEALING
(0) AFTER VACUUM ANNEALING AT 800 °C
ETCHANT-50 % GLYCERINE, 25 % HNO3, 25 % HF
Fig. 13. Titanium Clamping Band Corrosion.


END
DATE FILMED
9/16/651