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ASTM A 262 REV A Document Information:
Title
Standard Practices for Detecting Susceptibility to Intergranular Attack in Austenitic Stainless Steels
ASTM International
Publication Date:
Nov 10, 2002
Scope:
These practices cover the following five tests:
Practice A—Oxalic Acid Etch Test for Classification of
Etch Structures of Austenitic Stainless Steels (Sections 3 to 7,
inclusive),
Practice B—Ferric Sulfate–Sulfuric Acid Test for
Detecting Susceptibility to Intergranular Attack in Austenitic
Stainless Steels (Sections 8 to 14, inclusive),
Practice C—Nitric Acid Test for Detecting
Susceptibility to Intergranular Attack in Austenitic Stainless
Steels (Sections 15 to 21, inclusive),
Practice E—Copper–Copper Sulfate–Sulfuric Acid Test for
Detecting Susceptibility to Intergranular Attack in Austenitic
Stainless Steels (Sections 22 to 31, inclusive), and
Practice F—Copper–Copper Sulfate–50 % Sulfuric Acid
Test for Detecting Susceptibility to Intergranular Attack in
Molybdenum-Bearing Cast Austenitic Stainless Steels (Sections 32 to
38, inclusive).
The following factors govern the application of these
practices:
Susceptibility to intergranular attack associated with the
precipitation of chromium carbides is readily detected in all six
tests.
Sigma phase in wrought chromium-nickelmolybdenum steels, which
may or may not be visible in the microstructure, can result in high
corrosion rates only in nitric acid.
Sigma phase in titanium or columbium stabilized alloys and cast
molybdenum-bearing stainless alloys, which may or may not be
visible in the microstructure, can result in high corrosion rates
in both the nitric acid and ferric sulfate- –sulfuric acid
solutions.
The oxalic acid etch test is a rapid method of identifying, by
simple etching, those specimens of certain stainless steel grades
that are essentially free of susceptibility to intergranular attack
associated with chromium carbide precipitates. These specimens will
have low corrosion rates in certain corrosion tests and therefore
can be eliminated (screened) from testing as "acceptable."
The ferric sulfate–sulfuric acid test, the copper–copper
sulfate–50 % sulfuric acid test, and the nitric acid test are based
on weight loss determinations and, thus, provide a quantitative
measure of the relative performance of specimens evaluated. In
contrast, the copper–copper sulfate–16 % sulfuric acid test is
based on visual examination of bend specimens and, therefore,
classifies the specimens only as acceptable or nonacceptable.
In most cases either the 15-h copper–copper sulfate– 16 %
sulfuric acid test or the 120-h ferric sulfate–sulfuric acid test,
combined with the oxalic acid etch test, will provide the required
information in the shortest time. All stainless grades listed in
the accompanying table may be evaluated in these combinations of
screening and corrosion tests, except those specimens of
molybdenum-bearing grades (for example 316, 316L, 317, and 317L),
which represent steel intended for use in nitric acid
environments.
The 240-h nitric acid test must be applied to stabilized and
molybdenum-bearing grades intended for service in nitric acid and
to all stainless steel grades that might be subject to end grain
corrosion in nitric acid service.
Only those stainless steel grades are listed in Table 1 for
which data on the application of the oxalic acid etch test and on
their performance in various quantitative evaluation tests are
available.
Extensive test results on various types of stainless steels
evaluated by these practices have been published in Ref
(1).2
The values stated in SI units are to be regarded as standard.
The inch-pound equivalents are in parentheses and may be
approximate.
This standard does not purport to address all of the safety
problems, 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. (Specific precautionary statements
are given in 5.6, 11.1.1, 11.1.9, and 35.1.)
2 The boldface numbers in parentheses refer to the
list of references found at the end of these practices
Keywords:
- austenitic stainless steel
- copper sulfate
- corrosion
- testing
- etch structures
- ferric sulfate
- intergranular corrosion
- nitric acid
- oxalic acid
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