ASTM G28-22

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Designation: G28 − 02 (Reapproved 2015) G28 − 22
Standard Test Methods for
Detecting Susceptibility to Intergranular Corrosion in
Wrought, Nickel-Rich, Chromium-Bearing Alloys
This standard is issued under the fixed designation G28; 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 (´) indicates an editorial change since the last revision or reapproval.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope
1.1 These test methods cover two tests as follows:
1.1.1 Method A, Ferric Sulfate-Sulfuric Acid Test (Sections 3 – 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 G15G193), 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 – 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 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3.1 Exception—Some desired corrosion rate units in 8.1.1 are given in inch-pound units.
These test methods are under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and are the direct responsibility of Subcommittee G01.05 on Laboratory
Corrosion Tests.
Current edition approved Nov. 1, 2015Dec. 1, 2022. Published November 2015January 2023. Originally approved in 1971. Last previous edition approved in 20082015
as G28–02 (2008).(2015). DOI: 10.1520/G0028-02R15.10.1520/G0028-22.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G28 − 22
1.4 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use. Warning statements are given in 5.1.1, 5.1.3, 5.1.9, 13.1.1, and 13.1.11.
1.5 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
A262 Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels
D1193 Specification for Reagent Water
G15G193 Terminology and Acronyms Relating to Corrosion and Corrosion Testing (Withdrawn 2010)
METHOD A—Ferric Sulfate—Sulfuric Acid Test
3. Significance and Use
3.1 The boiling ferric sulfate-sulfuric acid test may be applied to the following alloys in the wrought condition:
Alloy Testing Time, h
N06007 120
N06007 120
N06022 24
N06030 120
N06059 24
N06200 24
N06455 24
N06600 24
N06625 120
N06686 24
N06985 120
N08020 120
N08367 24
Alloy Testing Time, h
N08800 120
A
N08825 120
N10276 24
A
While the ferric sulfate-sulfuric acid test does detect susceptibility to inter- granular corrosion in Alloy N08825, the boiling 65 % nitric acid test, Practices A262, Practice
C, for detecting susceptibility to intergranular corrosion in stainless steels is more sensitive and should be used if the intended service is nitric acid.
3.2 This test method may be used to evaluate as-received material and to evaluate the effects of subsequent heat treatments. In
the case of nickel-rich, chromium-bearing alloys, the test method may be applied to wrought and weldments of products. The test
method is not applicable to cast products.
4. Apparatus
4.1 The apparatus (Note 1) is illustrated in Fig. 1.
4.1.1 Allihn or Soxhlet Condenser, 4-bulb, with a 45/50 ground-glass joint, overall length about 330 mm, condensing section
about 240 mm.
4.1.2 Erlenmeyer Flask, 1-L, 1 L, with a 45/50 ground-glass joint. The ground-glass opening shall be 40 mm wide.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
To avoid frequent chipping of the drip-tip of the condenser during handling, the modified condenser described by Streicher, M. A., and Sweet, A. J., Corrosion, Vol 25,
1969, pp. 1, has been found suitable for this use.
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FIG. 1 Apparatus for Ferric Sulfate-Sulfuric Acid Test
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FIG. 2 Glass Cradle
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4.1.3 Glass Cradle (Fig. 2)—To pass through the ground-glass joint on the Erlenmeyer flask, the width of the cradle should not
exceed 40 mm and the front-to-back distance must be such that the cradle will fit the 40-mm40 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 or some other boiling aids must be used to prevent bumping.
4.1.5 Silicone Grease, (for example, stopcock grease) is recommended for the ground-glass joint.
4.1.6 Electrically Heated Hot Plate, or equivalent to provide 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(49.4 % to 50.9 %) solution as follows:
5.1.1 Warning—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 D1193) in a 500-mL500 mL graduate and pour into the 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 95.0
2 4
95.0 weight percent to 98.0 weight percent in a 250-mL250 mL graduate. Add the acid slowly to the water in the flask to avoid
boiling by the heat 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 solution. A trip
2 4 3 2 4
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 Warning—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
2 2
6.1 A specimen having a total surface area of 55 cm to 20 cm20 cm is recommended.
6.2 The intent is to test a specimen representing as nearly as possible the material as used in service. The specimens should be
The sole source of supply of the apparatus known to the committee at this time is amphoteric alundum Hengar Boiling Granules, available from Hengar Company, a
division of Henry Troemner, LLC, 201 Wolf Drive, Thorofare, NJ 08086. If you are aware of alternative suppliers, please provide this information to ASTM International
Headquarters. Your comments will receive careful consideration at a meeting of the responsible technical committee, which you may attend.
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cut to represent the grain flow direction that will see service, for example, specimens should not contain cross-sectional areas
unless it is the intent of the test to evaluate these. Only such surface finishing should be performed as is required to remove foreign
material and obtain a standard, uniform finish as specified in 6.4. For very heavy sections, specimens should be maintained to
represent the appropriate surface while maintaining reasonable specimen size for convenience in testing. Ordinarily, removal of
more material than necessary will have little influence on the test results. However, in the special case of surface decarburization
or of carburization (the latter is sometimes encountered in tubing when lubricants or binders containing carbonaceous materials
are employed), it may be possible by heavy grinding or machining to remove the affected layer completely. Such treatment of test
specimens is not permissible, except in tests undertaken to demonstrate such surface effects.
6.3 When specimens are cut by shearing, the deformed material must be removed by machining or grinding to a depth equal to
the thickness of the specimen to remove cold worked metal.
6.4 All surfaces of the specimen, including edges, should be finished using wet No. 80-grit80 grit or dry No. 120-grit120 grit
abrasive paper. If dry abrasive paper is used, polish slowly to avoid overheating. Sand blasting should not be used.
6.5 Residual oxide scale has been observed to cause spurious specimen activation in the test solution. Therefore, the formation
of oxide scale in stamped codes must be prevented, and all traces of oxide scale formed during heat treatment must be thoroughly
removed prior to stamping identification codes.
6.6 The specimen dimensions should be measured including the edges and inner surfaces of any holes and the total exposed area
calculated.
6.7 The specimen should then be degreased using suitable nonchlorinated agents such as soap and acetone, dried, and then
weighed to the nearest 0.001 g.0.001 g.
7. Procedure
7.1 Place the specimen in the glass cradle, remove the condenser, immerse the cradle by means of a hook in the actively boiling
solution (Fig. 1), and immediately replace the condenser. A fresh solution should be used for each test.
7.2 Mark the liquid level on the flask with wax crayon to provide a check on vapor loss which would result in concentration of
the acid. If there is an appreciable change in the level (a 0.5-cm0.5 cm or more drop), repeat the test with fresh solution and with
a fresh specimen or a reground specimen.
7.3 Continue immersion of the specimen for the length of time specified in Section 3, then remove the specimen, rinse in water
and acetone, and dry.
7.4 Weigh the specimen and subtract this mass from the original mass.
7.5 Intermediate weighing is not necessary, except as noted in 7.7. The tests can be run without interruption. However, if
preliminary results are desired, the specimen can be removed at any time for weighing.
7.6 Replacement of acid is not necessary during the test periods.
7.7 If the corrosion rate is extraordinarily high in Method A, as evidenced by a change in color (green) of the solution, additional
ferric sulfate must be added during the test. The amount of ferric sulfate that must be added, if the tot
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