ASTM A967-99e1
(Specification)Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts
Standard Specification for Chemical Passivation Treatments for Stainless Steel Parts
SCOPE
1.1 This specification covers several different types of chemical passivation treatments for stainless steel parts. It includes recommendations and precautions for descaling, cleaning, and passivation of stainless steel parts. It includes several alternative tests, with acceptance criteria, for confirmation of effectiveness of such treatments for stainless steel parts.
1.2 Practices for the mechanical and chemical treatments of stainless steel surfaces are discussed more thoroughly in Practice A 380.
1.3 Several alternative chemical treatments are defined for passivation of stainless steel parts. gives some nonmandatory information and provides some general guidelines regarding the selection of passivation treatment appropriate to particular grades of stainless steel but makes no recommendations regarding the suitability of any grade, treatment, and acceptance criteria for any particular application or class of applications.
1.4 The tests in this specification are intended to confirm the effectiveness of passivation, particularly with regard to the removal of free iron and other exogenous matter. These tests include the following practices:
1.4.1 Practice A—Water Immersion Test,
1.4.2 Practice B—High Humidity Test,
1.4.3 Practice C—Salt Spray Test,
1.4.4 Practice D—Copper Sulfate Test,
1.4.5 Practice E—Potassium Ferricyanide-Nitric Acid Test, and
1.4.6 Practice F—Free Iron Test.
1.5 The values stated in inch-pound units are to be regarded as the standard. The SI units given in parentheses are for information only.
1.6 The following precautionary caveat pertains only to the test method portions, Sections 14 through 18 of this specification: 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.
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e1
Designation: A 967 – 99
Standard Specification for
Chemical Passivation Treatments for Stainless Steel Parts
This standard is issued under the fixed designation A 967; 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.
e NOTE—This Specification was corrected editorially in January 2000.
1. Scope 2. Referenced Documents
1.1 This specification covers several different types of 2.1 ASTM Standards:
chemical passivation treatments for stainless steel parts. It A 380 Practice for Cleaning and Descaling Stainless Steel
includes recommendations and precautions for descaling, Parts, Equipment, and Systems
cleaning, and passivation of stainless steel parts. It includes B 117 Practice for Operating Salt Spray (Fog) Testing
several alternative tests, with acceptance criteria, for confirma- Apparatus
tion of effectiveness of such treatments for stainless steel parts. B 254 Practice for Preparation of and Electroplating on
1.2 Practices for the mechanical and chemical treatments of Stainless Steel
stainless steel surfaces are discussed more thoroughly in 2.2 Federal Specification:
Practice A 380. QQ-P-35C Passivation Treatments for Corrosion-Resistant
1.3 Several alternative chemical treatments are defined for Steels
passivation of stainless steel parts. Appendix X1 gives some
3. Terminology
nonmandatory information and provides some general guide-
lines regarding the selection of passivation treatment appropri- 3.1 Definition of Term Specific to This Standard—It is
necessary to define which of the several commonly used
ate to particular grades of stainless steel, but makes no
recommendations regarding the suitability of any grade, treat- definitions of the term passivation will be used in this
specification. (See Discussion.)
ment, and acceptance criteria for any particular application or
class of applications. 3.1.1 Discussion—Stainless steels are autopassivating in the
sense that the protective passive film is formed spontaneously
1.4 The tests in this specification are intended to confirm the
effectiveness of passivation, particularly with regard to the on exposure to air or moisture. The presence of exogenous
surface contamination, including dirt, grease, free iron from
removal of free iron and other exogenous matter. These tests
include the following practices: contact with steel tooling, and so forth, may interfere with the
formation of the passive film. The cleaning of these contami-
1.4.1 Practice A—Water Immersion Test,
1.4.2 Practice B—High Humidity Test, nants from the stainless steel surface will facilitate the spon-
taneous passivation by allowing the oxygen uniform access to
1.4.3 Practice C—Salt Spray Test,
1.4.4 Practice D—Copper Sulfate Test, and the surface. The passive film may be augmented by chemical
treatments that provide an oxidizing environment for the
1.4.5 Practice E—Potassium Ferricyanide-Nitric Acid Test.
stainless steel surface.
1.5 The values stated in inch-pound units are to be regarded
as the standard. The SI units given in parentheses are for 3.1.1.1 In this specification, passivation, unless otherwise
specified, is defined as the chemical treatment of a stainless
information only.
1.6 The following precautionary caveat pertains only to the steel with a mild oxidant, such as a nitric acid solution, for the
purpose of the removal of free iron or other foreign matter, but
test method portions, Section 14 through 18 of this specifica-
tion: This standard does not purport to address all of the safety which is generally not effective in removal of heat tint or oxide
scale on stainless steel. In the case of stainless steels with
concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety and additions of sulfur for the purpose of improved machinability,
passivation may also include the removal of sulfides from the
health practices and determine the applicability of regulatory
limitations prior to use. surface of the metal for the purpose of maximizing corrosion
resistance.
1 2
This specification is under the jurisdiction of ASTM Committee A-1 on Steel, Annual Book of ASTM Standards, Vol 01.03.
Stainless Steel, and Related Alloys and is the direct responsibility of Subcommittee Annual Book of ASTM Standards, Vol 03.02.
A01.14 on Methods of Corrosion Testing. Annual Book of ASTM Standards, Vol 02.05.
Current edition approved Sept. 10, 1999. Published November 1999. Originally Available from Superintendent of Documents, U.S. Government Printing
published as A 967–96. Last previoius edition A 967–96. Office, Washington, DC 20402.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
A 967
3.1.1.2 The formation of the protective passive film on a 5. Materials and Preparation for Passivation Treatments
stainless steel, also called passivation in a more general
5.1 The passivation treatments shall be of one or more of the
context, will occur spontaneously in air or other oxygen-
following types. The effectiveness of a particular treatment for
containing environment when the stainless steel surface is free
a particular grade of stainless steel in a particular application is
of oxide scale and exogenous matter.
demonstrated by meeting the specified testing requirements:
3.1.1.3 Chemical treatments, such as sodium dichromate
5.1.1 Treatments in nitric acid,
solutions, may facilitate the more rapid formation of the
5.1.2 Treatments in citric acid,
passive film on a stainless steel surface already free of scale or
5.1.3 Other chemical treatments, including electrochemical
foreign matter. Such treatments, also sometimes called passi-
treatments,
vation in common usage, are designated as post-cleaning
5.1.4 Neutralization, and
treatments in this specification in order to distinguish them
5.1.5 Post-cleaning treatments.
from chemical treatments capable of removing free iron from
5.2 Materials:
stainless steels.
5.2.1 The chemicals used for passivation treatments shall
3.1.1.4 The chemical treatments capable of removing heat
produce passivated surfaces which meet the requirements of
tint or oxide scale from stainless steel and capable of dissolving
one or more of the tests of this specification. Attention shall be
the stainless steel itself, typically called pickling, are substan-
given to maintaining adequate volume, concentration, purity,
tially more aggressive than treatments used for passivation, as
and temperature control appropriate to the size and amount of
defined in 3.1.1.1. The surface of stainless steel that has been
stainless steel to be treated.
pickled is free of scale, free iron, and exogenous foreign
5.2.2 The processor shall maintain a record with regard to
matter, and does not require a separate treatment for passiva-
concentration and temperature of the passivation solution
tion as defined in 3.1.1.1. The passivation process defined in
sufficient to demonstrate that the specified passivation condi-
3.1.1.2 will occur without further chemical treatment, but may
tions were maintained for each lot of stainless steel parts
be augmented and improved by the post-cleaning treatments
processed. Such records shall be available for inspection when
defined in 3.1.1.3.
specified in the purchase order. The processor is not required to
3.1.1.5 The chemical treatments capable of removing heat
reveal the precise composition of proprietary chemical mix-
tint or oxide scale from stainless steel and capable of dissolving
tures but shall maintain a unique identification of the mixture
the stainless steel itself, typically called pickling, are substan-
that will ensure its accurate representation for subsequent use.
tially more aggressive than treatments used for passivation, as
5.2.3 The processor shall be responsible for the safe dis-
defined in 3.1.1.1. The surface of stainless steel that has been
posal of all material generated by this process.
pickled is free of scale, free iron, and exogenous foreign
5.3 Preparation for Passivation Treatments:
matter, and does not require a separate treatment for passiva-
5.3.1 The pretreatment methods and procedures used prior
tion as defined in 3.1.1.1. The passivation process defined in
to the passivation treatment, including mechanical and chemi-
3.1.1.2 will occur without further chemical treatment, but may
cal methods, singly or in combination, for descaling and
be augmented and improved by the post-cleaning treatments
pickling, shall be in accordance with Practice A 380. When
defined in 3.1.1.3.
electrochemical cleaning is required, it shall be performed in
3.1.1.6 Electrochemical treatments, including electropick-
accordance with Practice B 254.
ling and electropolishing capable of removing heat tint or oxide
5.3.2 The resulting pretreated surface shall be substantially
scale from stainless steel and capable of dissolving the stainless
free of oil, grease, rust, scale, and other foreign matter.
steel itself, are substantially more aggressive than treatments
5.3.3 When the final pretreatment of a part includes pickling
used for passivation, as defined in 3.1.1.1. The surface of
of the entire surface of the part, no further passivation
stainless steel resulting from these treatments is free of scale,
treatment is required prior to testing of the surface unless
free iron, and exogenous foreign matter, and does not require a
specified by the purchaser.
separate treatment for passivation as defined in 3.1.1.1. The
passivation process defined in 3.1.1.2 will occur without
6. Treatments in Nitric Acid Solutions
further chemical treatment, but may be augmented and im-
6.1 Passivation Treatment:
proved by the post-cleaning treatments defined in 3.1.1.3.
6.1.1 Stainless steel parts shall be treated in one of the
Statements regarding chemical treatments, unless otherwise
following aqueous solutions and maintained within the speci-
specified, are taken to include electrochemical treatments.
fied temperature range for the specified time.
4. Ordering Information
6.1.1.1 Nitric 1—The solution shall contain 20 to 25 volume
percent of nitric acid and 2.5 + 0.5 weight percent of sodium
4.1 It is the responsibility of the purchaser to specify a test
dichromate. The parts shall be immersed for a minimum of 20
practice appropriate to any particular material and application.
This specification was written for the purpose of providing an min at a temperature in the range from 120 to 130°F (49 to
54°C).
alternative to United States Federal Specification QQ-P-35C.
Determination of the suitability of this specification for that 6.1.1.2 Nitric 2—The solution shall contain 20 to 45 volume
percent of nitric acid. The parts shall be immersed for a
purpose is the responsibility of the purchaser.
4.2 Unless specified by the purchaser, the chemical treat- minimum of 30 min at a temperature in the range from 70 to
90°F (21 to 32°C).
ment applied to the stainless steel parts shall be selected by the
seller from among the listed passivation treatments. 6.1.1.3 Nitric 3—The solution shall contain 20 to 25 volume
A 967
percent nitric acid. The parts shall be immersed for a minimum exogenous matter from a stainless steel surface, including the
of 20 min at a temperature in the range from 120 to 140°F (49 removal of free iron, can be accomplished by different media,
to 60°C). with potential for benefits to be gained from use of proprietary
6.1.1.4 Nitric 4—The solution shall contain 45 to 55 volume skills and art, including proprietary passivation media. Such
percent of nitric acid. The parts shall be immersed for a treatments may include externally applying an electrical po-
minimum of 30 min at a temperature in the range from 120 to tential on the stainless steel parts, as in the case of electropol-
130°F (49 to 54°C). ishing. The suitability of such passivation treatments for use in
6.1.1.5 Nitric 5—Other combinations of temperature, time, meeting the requirements of this specification shall be deter-
and concentration of nitric acid, with or without other chemi- mined by the capability of the processed parts meeting the
cals, including accelerants, inhibitors, or proprietary solutions, specified test requirements.
capable of producing parts that pass the specified test require- 8.2 Stainless steel parts shall be treated in a specified
ments. aqueous solution, with or without externally applied electrical
6.2 Water Rinse—Immediately after removal from the pas- potential, and maintained within a specified temperature range
sivating solution the parts shall be thoroughly rinsed, using for a time sufficient for the processed parts to meet the
stagnant, countercurrent, or spray washes singly or in combi- specified test requirement.
nation, with or without a separate chemical treatment for 8.3 Water Rinse—Immediately after removal from the pas-
neutralization (see 9.1) of the passivation media, with a final sivating solution, the parts shall be thoroughly rinsed, using
rinse being carried out using water with a maximum total solids stagnant, countercurrent, or spray washes, singly or in combi-
content of 200 ppm. nation, with or without a separate chemical treatment for
neutralization of the passivation media (see 9.2), with a final
7. Treatments in Citric Acid
rinse being carried out using water with a maximum total solids
7.1 Passivation Treatment: content of 200 ppm.
7.1.1 Stainless steel parts shall be treated in one of the
9. Neutralization
following aqueous solutions and maintained within the speci-
9.1 The chemical reactions of the passivating media on the
fied temperature range for the specified time.
surface of the stainless steel shall be stopped by rinsing of the
7.1.1.1 Citric 1—The solution shall contain 4 to 10 weight
stainless steel part, with or without a separate neutralization
percent of citric acid. The parts shall be immersed for a
treatment.
minimum of 4 min at a temperature in the range from 140 to
9.2 The suitability of a neutralization procedure is deter-
160°F (60 to 71°C).
mined by the capability of the processed parts meeting the
7.1.1.2 Citric 2—The solution shall contain 4 to 10 weight
specified test requirements. (See Note 1.)
percent of citric acid. The parts shall be immersed for a
minimum of 10 min at a temperature in the range from 120 to
NOTE 1—The selection of medium and procedures for a neutralization
140°F (49 to 60°C). depends of the chemistry of the passivation and on economic consider-
ations. An example of a neutralizing treatment would be immersion of the
7.1.1.3 Citric 3—The
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