ASTM G28-97
(Test Method)Standard Test Methods of Detecting Susceptibility to Intergranular Corrosion in Wrought, Nickel-Rich, Chromium-Bearing Alloys
Standard Test Methods of Detecting Susceptibility to Intergranular Corrosion in Wrought, Nickel-Rich, Chromium-Bearing Alloys
SCOPE
1.1 These test methods cover two tests as follows:
1.1.1 Method A, Ferric Sulfate-Sulfuric Acid Test (Sections 3 through 10, inclusive)-This test method describes the procedure for conducting the boiling ferric sulfate-50% sulfuric acid test which measures the susceptibility of certain nickel-rich, chromium-bearing alloys to intergranular corrosion (see Terminology G15), which may be encountered in certain service environments. The uniform corrosion rate obtained by this test method, which is a function of minor variations in alloy composition, may easily mask the intergranular corrosion components of the overall corrosion rate on alloys N10276, N06022, N06059, and N06455.
1.1.2 Method B, Mixed Acid-Oxidizing Salt Test (Sections 11 through 18, inclusive)-This test method describes the procedure for conducting a boiling 23% sulfuric + 1.2% hydrochloric + 1% ferric chloride + 1% cupric chloride test which measures the susceptibility of certain nickel-rich, chromium-bearing alloys to display a step function increase in corrosion rate when there are high levels of grain boundary precipitation.
1.2 The purpose of these two test methods is to detect susceptibility to intergranular corrosion as influenced by variations in processing or composition, or both. Materials shown to be susceptible may or may not be intergranularly corroded in other environments. This must be established independently by specific tests or by service experience.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use. Hazard advisory statements are given in 5.1.1, 5.1.3, 5.1.9, 13.1.1, and 13.1.11.
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Designation: G 28 – 97
Standard Test Methods of
Detecting Susceptibility to Intergranular Corrosion in
Wrought, Nickel-Rich, Chromium-Bearing Alloys
This standard is issued under the fixed designation G 28; the number immediately following the designation indicates the year of original
adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A superscript
epsilon (e) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the Department of Defense.
1. Scope D 1193 Specification for Reagent Water
G 15 Terminology Relating to Corrosion and Corrosion
1.1 These test methods cover two tests as follows:
Testing
1.1.1 Method A, Ferric Sulfate-Sulfuric Acid Test (3-10 ,
inclusive)—This test method describes the procedure for
METHOD A—Ferric Sulfate—Sulfuric Acid Test
conducting the boiling ferric sulfate—50 % sulfuric acid test
which measures the susceptibility of certain nickel-rich,
3. Significance and Use
chromium-bearing alloys to intergranular corrosion (see Ter-
3.1 The boiling ferric sulfate-sulfuric acid test may be
minology G 15), which may be encountered in certain service
applied to the following alloys in the wrought condition:
environments. The uniform corrosion rate obtained by this test
Alloy Testing Time, h
method, which is a function of minor variations in alloy
N06007 120
composition, may easily mask the intergranular corrosion
N06022 24
components of the overall corrosion rate on alloys N10276,
N06030 120
N06022, N06059, and N06455.
N06059 24
1.1.2 Method B, Mixed Acid-Oxidizing Salt Test (Sections N06200 24
N06455 24
11-18, inclusive)—This test method describes the procedure
N06600 24
for conducting a boiling 23 % sulfuric + 1.2 % hydrochlo-
N06625 120
N06686 24
ric+1% ferric chloride+1% cupric chloride test which
N06985 120
measures the susceptibility of certain nickel-rich, chromium-
N08020 120
bearing alloys to display a step function increase in corrosion
N08367 24
N08800 120
rate when there are high levels of grain boundary precipitation.
A
N08825 120
1.2 The purpose of these two test methods is to detect
N10276 24
susceptibility to intergranular corrosion as influenced by varia-
____________
A
tions in processing or composition, or both. Materials shown to
While the ferric sulfate-sulfuric acid test does detect susceptibility to inter-
granular corrosion in Alloy N08825, the boiling 65 % nitric acid test, Practice A 262,
be susceptible may or may not be intergranularly corroded in
Practice C, for detecting susceptibility to intergranular corrosion in stainless steels
other environments. This must be established independently by
is more sensitive and should be used if the intended service is nitric acid.
specific tests or by service experience.
3.2 This test method may be used to evaluate as-received
1.3 This standard does not purport to address all of the
material and to evaluate the effects of subsequent heat treat-
safety concerns, if any, associated with its use. It is the
ments. In the case of nickel-rich, chromium-bearing alloys, the
responsibility of the user of this standard to establish appro-
test method may be applied to wrought and weldments of
priate safety and health practices and determine the applica-
products. The test method is not applicable to cast products.
bility of regulatory limitations prior to use. Hazard advisory
statements are given in 5.1.1, 5.1.3, 5.1.9, 13.1.1, and 13.1.11. 4. Apparatus
4.1 The apparatus (Note 1) is illustrated in Fig. 1.
2. Referenced Document
4.1.1 Allihn or Soxhlet Condenser, 4-bulb, with a 45/50
2.1 ASTM Standards:
ground-glass joint, overall length about 330 mm, condensing
A 262 Practices for Detecting Susceptibility to Intergranu-
section about 240 mm.
lar Attack in Austenitic Stainless Steels
4.1.2 Erlenmeyer Flask, 1-L, with a 45/50 ground-glass
These test methods are under the jurisdiction of ASTM Committee G-1 on
Annual Book of ASTM Standards, Vol 11.01.
Corrosion of Metals and are the direct responsibility of Subcommittee G01.05 on
Laboratory Corrosion Tests. Annual Book of ASTM Standards, Vol 03.02.
Current edition approved Apr. 10, 1997. Published November 1997. Originally To avoid frequent chipping of the drip-tip of the condenser during handling, the
published as G 28 – 71. Last previous edition G 28 – 95. modified condenser described by Streicher, M. A., and Sweet, A. J., Corrosion,Vol
Annual Book of ASTM Standards, Vol 01.03. 25, 1969, pp. 1, has been found suitable for this use.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G28
should not exceed 40 mm and the front-to-back distance must
be such that the cradle will fit the 40-mm diameter opening. It
should have three or four holes to increase circulation of the
test solution around the specimen (Note 2).
NOTE 1—Substitution for this equipment may not be used. The cold-
finger type of standard Erlenmeyer flask may not be used.
NOTE 2—Other equivalent means of specimen support, such as glass
hooks or stirrups, may also be used.
4.1.4 Boiling Chips, or some other boiling aids must be
used to prevent bumping.
4.1.5 Silicone Grease, is recommended for the ground-
glass joint.
4.1.6 Electrically Heated Hot Plate, or equivalent to pro-
vide heat for continuous boiling of the solution.
4.1.7 Analytical Balance, capable of weighing to the nearest
0.001 g.
5. Test Solution
5.1 Prepare 600 mL of 50 % (49.4 to 50.9 %) solution as
follows:
5.1.1 Caution—Protect the eyes and use rubber gloves for
handling acid. Place the test flask under a hood.
5.1.2 First, measure 400 mL of Type IV reagent water
(Specification D 1193) in a 500-mL graduate and pour into the
FIG. 1 Apparatus for Ferric Sulfate-Sulfuric Acid Test
flask.
5.1.3 Then measure 236 mL of reagent-grade sulfuric acid
(H SO ) of a concentration which must be in the range from
joint. The ground-glass opening shall be 40 mm wide. 2 4
95.0 to 98.0 weight percent in a 250-mL graduate. Add the acid
4.1.3 Glass Cradle (Fig. 2)—To pass through the ground-
slowly to the water in the flask to avoid boiling by the heat
glass joint on the Erlenmeyer flask, the width of the cradle
evolved (Note 3). Externally cooling the flask with water
during the mixing will also reduce overheating.
NOTE 3—Loss of vapor results in concentration of the acid.
5.1.4 Weigh 25 g of reagent grade ferric sulfate (contains
about 75 % Fe (SO ) (Note 4)) and add to the H SO
2 4 3 2 4
solution. A trip balance may be used.
NOTE 4—Ferritic sulfate is a specific additive that establishes and
controls the corrosion potential. Substitutions are not permitted.
5.1.5 Add boiling chips.
5.1.6 Lubricate the ground glass of the condenser joint with
silicone grease.
5.1.7 Cover the flask with the condenser and circulate
cooling water.
5.1.8 Boil the solution until all ferric sulfate is dissolved.
5.1.9 Caution—It has been reported that violent boiling can
occur resulting in acid spills. It is important to ensure that the
concentration of acid does not increase and that an adequate
number of boiling chips (which are resistant to attack by the
test solution) are present.
6. Test Specimens
6.1 A specimen having a total surface area of 5 to 20 cm is
recommended.
Amphoteric alundun: granules, Hengar Granules, from the Hengar Co.,
Swedesboro, NJ have been found satisfactory for this purpose.
FIG. 2 Glass Cradle Stopcock grease has been found satisfactory for this purpose.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G28
6.2 The intent is to test a specimen representing as nearly as 7.6 Replacement of acid is not necessary during the test
possible the material as used in service. The specimens should periods.
be cut to represent the grain flow direction that will see service, 7.7 If the corrosion rate is extraordinarily high in Method A,
for example, specimens should not contain cross-sectional as evidenced by a change in color (green) of the solution,
areas unless it is the intent of the test to evaluate these. Only additional ferric sulfate must be added during the test. The
such surface finishing should be performed as is required to amount of ferric sulfate that must be added, if the total mass
remove foreign material and obtain a standard, uniform finish loss of all specimens exceeds2gas indicated by an interme-
as specified in 6.4. For very heavy sections, specimens should diate weight, is 10 g for each1gof dissolved alloy. This does
be maintained to represent the appropriate surface while not apply to Method B.
maintaining reasonable specimen size for convenience in 7.8 In Method A, several specimens of the same alloy may
testing. Ordinarily, removal of more material than necessary be tested simultaneously. The number (3 or 4) is limited only
will have little influence on the test results. However, in the by the number of glass cradles that can be fitted into the flask
special case of surface decarburization or of carburization (the and the consumption of ferric sulfate. Only one sample should
latter is sometimes encountered in tubing when lubricants or be tested in a flask for Method B.
binders containing carbonaceous materials are employed), it 7.9 During testing, there is some deposition of iron oxides
may be possible by heavy grinding or machining to remove the on the upper part for the flask. This can be readily removed
affected layer completely. Such treatment of test specimens is after test completion by boiling a solution of 10 % hydrochlo-
not permissible, except in tests undertaken to demonstrate such ric acid (HCl) in the flask.
surface effects.
8. Calculation and Interpretation of Results
6.3 When specimens are cut by shearing, the deformed
material must be removed by machining or grinding to a depth 8.1 Calculation—Measure the effect of the acid solution on
equal to the thickness of the specimen to remove cold worked
the mat
metal.
Corrosion Rate 5 K 3 W!/ A 3 T 3 D! (1)
~ ~
6.4 All surfaces of the specimen, including edges, should be
where:
finished using wet No. 80-grit or dry No. 120-grit abrasive
K 5 a constant (see 8.1.1),
paper. If dry abrasive paper is used, polish slowly to avoid
T 5 time of exposure, h, to the nearest 0.01 h,
overheating. Sand blasting should not be used.
2 2
A 5 area, cm , to the nearest 0.01 cm ,
6.5 Residual oxide scale has been observed to cause spuri-
W 5 mass loss, g, to the nearest 0.001 g, and
ous specimen activation in the test solution. Therefore, the
D 5 density, g/cm (see 8.1.2).
formation of oxide scale in stamped codes must be prevented,
and all traces of oxide scale formed during heat treatment must
8.1.1 Many different units are used to express corrosion
be thoroughly removed prior to stamping identification codes.
rates. Using the above units for T, A, W, and D, the corrosion
6.6 The specimen dimensions should be measured including
rate can be calculated in a variety of units with the following
the edges and inner surfaces of any holes and the total exposed
appropriate value of K:
area calculated.
Constant K in Corrosion Rate
A
6.7 The specimen should then be degreased using suitable
Corrosion Rate Units Desired Equation
nonchlorinated agents such as soap and acetone, dried, and
mils per year (mpy) 3.45 3 10
then weighed to the nearest 0.001 g.
inches per year (ipy) 3.45 3 10
inches per month (ipm) 2.87 3 10
7. Procedure millimeters per year (mm/Y) 8.76 3 10
micrometers per year (μm/y) 8.76 3 10
7.1 Place the specimen in the glass cradle, remove the
picometers per second (pm/s) 2.78 3 10
2 4 B
grams per square meter-hour (g/m -h) 1.00 3 10 3 D
condenser, immerse the cradle by means of a hook in the
6 B
milligrams per square decimeter-day (mdd) 2.40 3 10 3 D
actively boiling solution (Fig. 1), and immediately replace the
2 6 B
micrograms per square meter-second (μg/m -s) 2.78 3 10 3 D
condenser. A fresh solution should be used for each test.
_______________
7.2 Mark the liquid level on the flask with wax crayon to
A
If desired, these constants may also be used to convert corrosion rates from
provide a check on vapor loss which would result in concen-
one set of units to another. To convert a corrosion rate in units X to a rate in units
Y, multiply by K /K . For example:
Y X
tration of the acid. If there is an appreciable change in the level
6 6
15 mpy 5 15 3 2.78 3 10 / 3.45 3 10 pm/s
@~ ! ~ !#
(a 0.5-cm or more drop), repeat the test with fresh solution and
with a fresh specimen or a reground specimen.
5 12.1 pm/s
B
Density is not needed to calculate the corrosion rate in these units. The density
7.3 Continue immersion of the specimen for the length of
in the constant K cancels out the density in the corrosion rate equation.
time specified in Section 3, then remove the specimen, rinse in
8.1.2
water and acetone, and dry.
UNS Designation Density, g/cm
7.4 Weigh the specimen and subtract this mass from the
original mass. N06007 8.31
N06022 8.69
7.5 Intermediate weighing is not necessary, except as noted
N06030 8.22
in 7.7. The tests can be run without interruption. However, if
N06059 8.80
preliminary results are desired, the specimen can be removed at N06200 8.50
N06455 8.64
any time for weighing.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
G28
tion s and the 95 % reproducibilty limits, R. These values were
N06600 8.41
r
N06625 8.44
related to the average corrosion rate, x¯, in mpy as follows:
N06686 8.73
N06985 8.31
s 563.02 x¯ (4)
R
N08020 8.05
N08367 8.06 R568.46 x¯ (5)
N08800 8.03
N08825 8.14
where:
N10276 8.87
R 5 2.8s
R
8.2 Interpretation of Results—The presence of intergranular The units of R and s are mpy.
R
corrosion is usually determined by comparing the calculated 10.2 The procedure in Test Method A of Test Methods G 28
corrosion rate to that for properly annealed material. Even in for determining the susceptibility to intergranular corrosion in
the absence of intergranular corrosion, the rate of general or wrought nickel rich chromium bearing alloys has no bias
grain-face corrosion of properly annealed material will vary because the Method A value for susceptibility to intergranular
from one alloy to another. These differences are demonstrated corrosion in these alloys i
...
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