ASTM G78-20

Standard Guide for Crevice Corrosion Testing of Iron-Base and Nickel-Base Stainless Alloys in Seawater and Other Chloride-Containing Aqueous Environments

SIGNIFICANCE AND USE
4.1 This guide covers procedures for crevice-corrosion testing of iron-base and nickel-base stainless alloys in seawater. The guidance provided may also be applicable to crevice corrosion testing in other chloride containing natural waters and various laboratory prepared aqueous chloride environments.  
4.1.1 While this guide focuses on testing of iron-base and nickel-base stainless alloys, the procedures and evaluations methods described herein have been successfully applied to characterize the crevice corrosion performance of other alloy systems (see, for example, Aylor et al.3).
Note 1: In the case of copper alloys, the occurrence of crevice-related corrosion associated with different corrosion mechanisms takes place immediately adjacent to the crevice former rather than within the occlusion.  
4.2 This guide describes the use of a variety of crevice formers including the nonmetallic, segmented washer design referred to as the multiple crevice assembly (MCA) as described in 9.2.2.  
4.3 In-service performance data provide the most reliable determination of whether a material would be satisfactory for a particular end use. Translation of laboratory data from a single test program to predict service performance under a variety of conditions should be avoided. Terms, such as immunity, superior resistance, etc., provide only a general and relatively qualitative description of an alloy's corrosion performance. The limitations of such terms in describing resistance to crevice corrosion should be recognized.  
4.4 While the guidance provided is generally for the purpose of evaluating sheet and plate materials, it is also applicable for crevice-corrosion testing of other product forms, such as tubing and bars.  
4.5 The presence or absence of crevice corrosion under one set of conditions is no guarantee that it will or will not occur under other conditions. Because of the many interrelated metallurgical, environmental, and geometric factors known to affect crevice...
SCOPE
1.1 This guide covers information for conducting crevice-corrosion tests and identifies factors that may affect results and influence conclusions.  
1.2 These procedures can be used to identify conditions most likely to result in crevice corrosion and provide a basis for assessing the relative resistance of various alloys to crevice corrosion under certain specified conditions.  
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses after SI units are provided for information only and are not considered standard.  
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, health, and environmental practices and determine the applicability of regulatory limitations prior to use. For a specific warning statement, see 7.1.  
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.

General Information

• Status: Published
• Publication Date: 31-Oct-2020
• ICS: 77.060 - Corrosion of metals
• Technical Committee: G01 - Corrosion of Metals
• Drafting Committee: G01.04 - Corrosion of Metals in Natural Atmospheric and Aqueous Environments

Relations

• Refers: ASTM G46-94(2013) - Standard Guide for Examination and Evaluation of Pitting Corrosion
• Effective Date: 01-May-2013
• Refers: ASTM G1-03(2011) - Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
• Effective Date: 01-Dec-2011
• Refers: ASTM G52-00(2011) - Standard Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater
• Effective Date: 01-Nov-2011
• Refers: ASTM G48-11 - : Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution
• Effective Date: 01-Sep-2011
• Refers: ASTM G4-01(2008) - Standard Guide for Conducting Corrosion Tests in Field Applications
• Effective Date: 01-May-2008
• Refers: ASTM G52-00(2006) - Standard Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater
• Effective Date: 01-May-2006
• Refers: ASTM G46-94(2005) - Standard Guide for Examination and Evaluation of Pitting Corrosion
• Effective Date: 01-May-2005
• Refers: ASTM G1-03 - Standard Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
• Effective Date: 01-Oct-2003
• Refers: ASTM G48-03(2009) - Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution
• Effective Date: 10-May-2003
• Refers: ASTM G48-03 - Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution
• Effective Date: 10-May-2003
• Refers: ASTM G4-01 - Standard Guide for Conducting Corrosion Tests in Field Applications
• Effective Date: 10-Oct-2001
• Refers: ASTM G4-95 - Standard Guide for Conducting Corrosion Coupon Tests in Field Applications
• Effective Date: 10-Oct-2001
• Refers: ASTM G52-00 - Standard Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater
• Effective Date: 10-May-2000
• Refers: ASTM G48-00 - Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution
• Effective Date: 10-May-2000
• Refers: ASTM G48-99A - Standard Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride Solution
• Effective Date: 10-May-2000

Overview

ASTM G78-20: Standard Guide for Crevice Corrosion Testing of Iron-Base and Nickel-Base Stainless Alloys in Seawater and Other Chloride-Containing Aqueous Environments provides guidance and best practices for evaluating the crevice corrosion resistance of stainless alloys. Developed by ASTM International, this standard addresses procedures for crevice corrosion testing primarily in seawater but can also be applied to other chloride-containing natural and laboratory-prepared environments. The guide is relevant for industries where the durability and service life of stainless steels and related alloys are impacted by localized corrosion in marine or chloride-rich settings.

Key Topics

• Scope of Testing
  The guide details methods for testing iron-base and nickel-base stainless alloys, but the principles are flexible enough to assess other alloy systems as well.

• Test Environments
  Provides instructions for using natural and synthetic seawater, along with other chloride-containing solutions, ensuring environmental conditions are appropriately monitored and controlled.

• Crevice Formers
  Describes various types of crevice formers such as metallic and nonmetallic segmented washers (including multiple crevice assemblies or MCA) and their influence on test severity and reproducibility.

• Test Specimens
  Covers preparation of test specimens, recommended cleaning protocols, and specimen identification to maintain consistency and accuracy.

• Variability of Results
  Emphasizes that test results can be affected by many factors-such as crevice geometry, surface finish, and material composition-and cautions against using a single test outcome to predict long-term service behavior.

• Analysis and Evaluation
  Outlines general evaluation criteria, including visual inspections, depth and area of corrosion assessment, and the need for careful documentation to support material selection.

Applications

The ASTM G78-20 standard is widely used in:

• Materials Selection
  Guides engineers and materials scientists in evaluating and comparing the crevice corrosion resistance of stainless steels and related alloys in environments prone to chloride attack, such as seawater.

• Quality Assurance
  Supports the quality control process in the manufacturing of equipment and components exposed to marine or chloride-laden conditions, including heat exchangers, piping, marine vessels, and desalination plants.

• Research and Development
  Provides a framework for laboratory investigations into new alloys or protective coatings, accelerating the development of corrosion-resistant materials.

• Failure Analysis
  Assists in forensic analysis of corrosion failures in service by replicating field conditions to better understand mechanisms and contributing factors.

• Product Forms
  Applicable not only to sheet and plate but also tubing, bars, and cylindrical components, enhancing flexibility for diverse industrial forms.

Related Standards

ASTM G78-20 references several other important standards for corrosion testing and terminology:

• ASTM G1 - Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
• ASTM G4 - Guide for Conducting Corrosion Tests in Field Applications
• ASTM G46 - Guide for Examination and Evaluation of Pitting Corrosion
• ASTM G48 - Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels by Use of Ferric Chloride Solution
• ASTM G52 - Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater
• ASTM G193 - Terminology and Acronyms Relating to Corrosion

These documents complement ASTM G78-20, offering foundational procedures and terminology, enhancing the reliability and comparability of corrosion testing programs.

---

Keywords: crevice corrosion testing, seawater corrosion, chloride environments, stainless steel, nickel alloys, ASTM G78-20, localized corrosion, corrosion resistance, marine corrosion standards, crevice former, multiple crevice assembly, laboratory testing.

Standards Content (Sample)

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.
Designation: G78 − 20
Standard Guide for
Crevice Corrosion Testing of Iron-Base and Nickel-Base
Stainless Alloys in Seawater and Other Chloride-Containing
Aqueous Environments
ThisstandardisissuedunderthefixeddesignationG78;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginal
adoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscript
epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
Crevice corrosion of iron-base and nickel-base stainless alloys can occur when an occlusion or
crevice limits access of the bulk environment to a localized area of the metal surface. Localized
environmental changes in this stagnant area can result in the formation of acidic/high chloride
conditions that may result in initiation and propagation of crevice corrosion of susceptible alloys.
In practice, crevices can generally be classified into two categories: (1) naturally occurring, that is,
those created by biofouling, sediment, debris, deposits, etc. and (2) man-made, that is, those created
during manufacturing, fabrication, assembly, or service. Crevice formers utilized in laboratory and
field studies can represent actual geometric conditions encountered in some service applications. Use
of such crevice formers in service-type environments are not considered accelerated test methods.
The geometry of a crevice can be described by the dimensions of crevice gap and crevice depth.
Crevice gap is identified as the width or space between the metal surface and the crevice former.
Crevice depth is the distance from the mouth to the center or base of the crevice.
1. Scope 1.5 This international standard was developed in accor-
dance with internationally recognized principles on standard-
1.1 This guide covers information for conducting crevice-
ization established in the Decision on Principles for the
corrosion tests and identifies factors that may affect results and
Development of International Standards, Guides and Recom-
influence conclusions.
mendations issued by the World Trade Organization Technical
1.2 These procedures can be used to identify conditions
Barriers to Trade (TBT) Committee.
mostlikelytoresultincrevicecorrosionandprovideabasisfor
assessing the relative resistance of various alloys to crevice
2. Referenced Documents
corrosion under certain specified conditions. 2
2.1 ASTM Standards:
1.3 The values stated in SI units are to be regarded as
G1Practice for Preparing, Cleaning, and Evaluating Corro-
standard. The values given in parentheses after SI units are
sion Test Specimens
provided for information only and are not considered standard.
G4Guide for Conducting Corrosion Tests in Field Applica-
tions
1.4 This standard does not purport to address all of the
G46Guide for Examination and Evaluation of Pitting Cor-
safety concerns, if any, associated with its use. It is the
rosion
responsibility of the user of this standard to establish appro-
G48Test Methods for Pitting and Crevice Corrosion Resis-
priate safety, health, and environmental practices and deter-
tance of Stainless Steels and Related Alloys by Use of
mine the applicability of regulatory limitations prior to use.
Ferric Chloride Solution
For a specific warning statement, see 7.1.
G52PracticeforExposingandEvaluatingMetalsandAlloys
in Surface Seawater
This guide is under the jurisdiction ofASTM Committee G01 on Corrosion of
Metals and is the direct responsibility of Subcommittee G01.04 on Corrosion of
Metals in Natural Atmospheric and Aqueous Environments. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved Nov. 1, 2020. Published November 2020. Originally contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
approved in 1983. Last previous edition approved in 2015 as G78–15. DOI: Standards volume information, refer to the standard’s Document Summary page on
10.1520/G0078-20. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G78−20
G193Terminology and Acronyms Relating to Corrosion 4.4 While the guidance provided is generally for the pur-
pose of evaluating sheet and plate materials, it is also appli-
3. Terminology
cableforcrevice-corrosiontestingofotherproductforms,such
3.1 Definitions of related terms can be found in Terminol- as tubing and bars.
ogy G193.
4.5 The presence or absence of crevice corrosion under one
set of conditions is no guarantee that it will or will not occur
4. Significance and Use
under other conditions. Because of the many interrelated
4.1 This guide covers procedures for crevice-corrosion test-
metallurgical, environmental, and geometric factors known to
ing of iron-base and nickel-base stainless alloys in seawater.
affect crevice corrosion, results from any given test may or
The guidance provided may also be applicable to crevice
may not be indicative of actual performance in service appli-
corrosion testing in other chloride containing natural waters
cationswheretheconditionsmaybedifferentfromthoseofthe
and various laboratory prepared aqueous chloride environ-
test.
ments.
5. Apparatus
4.1.1 While this guide focuses on testing of iron-base and
nickel-base stainless alloys, the procedures and evaluations
5.1 Laboratory tests utilizing filtered, natural seawater, or
methods described herein have been successfully applied to
other chloride containing aqueous environments are frequently
characterize the crevice corrosion performance of other alloy
conductedintanksortroughsunderlowvelocity(forexample,
systems (see, for example, Aylor et al. ).
;0.5 m/s (1.64 ft/s) or less) or quiescent conditions. Contain-
ers should be resistant to the test media.
NOTE 1—In the case of copper alloys, the occurrence of crevice-related
corrosion associated with different corrosion mechanisms takes place
5.2 Fig. 1 shows a typical test apparatus for conducting
immediately adjacent to the crevice former rather than within the
crevice-corrosiontestsundercontrolledtemperatureconditions
occlusion.
with provisions for recirculation or refreshment of the aqueous
4.2 This guide describes the use of a variety of crevice
environment, or both, at a constant level.
formers including the nonmetallic, segmented washer design
5.3 The apparatus should be suitably sized to provide
referred to as the multiple crevice assembly (MCA) as de-
complete immersion of the test panel. Vertical positioning of
scribed in 9.2.2.
the crevice-corrosion specimens facilitates visual inspection
4.3 In-service performance data provide the most reliable
without the need to remove them from the environments.
determination of whether a material would be satisfactory for
6. Test Specimens
a particular end use. Translation of laboratory data from a
single test program to predict service performance under a
6.1 Becauseofthenumberofvariableswhichmayaffectthe
variety of conditions should be avoided. Terms, such as
test results, a minimum of three specimens are suggested for
immunity, superior resistance, etc., provide only a general and
each set of environmental, metallurgical, or geometric condi-
relatively qualitative description of an alloy’s corrosion per-
tions to be evaluated. If reproducibility is unsatisfactory,
formance. The limitations of such terms in describing resis-
additional specimens should be tested.
tance to crevice corrosion should be recognized.
6.2 Dimensions of both the test specimen and crevice
former should be determined and recorded.
Aylor, D. M., Hays, R.A., Kain, R. M., and Ferrara, R. J., “Crevice Corrosion
6.3 Variations in the boldly exposed (crevice-free) to
Performance of Candidate Naval Ship Seawater Valve Materials in Quiescent and
Flowing Natural Seawater,” CORROSION/99 Paper #329, NACE International. shielded(crevice)arearatioofthetestspecimenmayinfluence
FIG. 1 Positioning of Crevice-Corrosion Test Specimens—Typical Arrangement in Controlled Environment Apparatus
G78−20
is a test parameter, then the grit size, type of abrasive, and ideally the
crevicecorrosion.Allspecimensinatestseriesshouldhavethe
resulting surface roughness (Ra) value should be recorded.
samenominalsurfacearea.Whilenospecificspecimendimen-
sions are recommended, test panels measuring up to 300mm 6.7.4 The time between last metal removal from a mechani-
by 300 mm (11.81in. by 11.81 in.) have been used in seawater cally finished surface and immersion in the test solution can
tests with both naturally occurring and man-made crevice have a significant effect on crevice corrosion initiation and
formers. For laboratory studies, the actual size of the specimen should be standardized for comparative tests or at least
maybelimitedbythedimensionsofthetestapparatusandthis recorded.
should be taken into consideration in making comparisons.
6.8 Cutlengthsofpipeandtubingcanbeusedasspecimens
6.3.1 A test program may be expanded to assess any effect
to test the crevice corrosion resistance of these product forms
of boldly exposed to shielded area ratio.
in the as-manufactured or surface treated condition. Other
6.3.2 Ifcrevicegeometryaspects,suchascrevicedepth,are
cylindrical products can be tested in the as-produced or
to be studied, the adoption of a constant boldly exposed to
finished condition.
shielded area ratio is recommended to minimize the number of
6.8.1 The selection of cylindrical sample sizes should be
test variables.
made with the knowledge of the availability of appropriately
sized crevice formers, as described in 9.5.
6.4 Whenspecimensarecutbyshearing,itisrecommended
6.8.2 The type of crevice former selected may dictate the
that the deformed material be removed by machining or
length of the cylindrical test specimens. Specimen lengths of
grinding. Test pieces that are warped or otherwise distorted
4in. to 12 in. (10cm to 30 cm) and longer have been used.
should not be used. The need to provide parallel surfaces
between the crevice former and the test specimen is an
7. Pre-test Cleaning
important consideration in providing maximum consistency in
the application of the crevice former.
7.1 Cleaning procedures shall be consistent with Practice
G1. Typically, this may include degreasing with a suitable
6.5 Appropriate holes should be drilled (and deburred) in
solvent, followed by vigorous brush scrubbing with pumice
thetestspecimentofacilitateattachmentofthecreviceformer.
powder, followed by water rinse, clean solvent rinse, and air
Punched holes are not recommended since the punching
drying. (Warning—Solvent safety and compatibility with the
process may contribute to specimen distortion or work
test material should be investigated and safe practices fol-
hardening, or both. The diameter of the holes should be large
lowed).
enough to allow clearance of the fastener (and insulator)
otherwise additional crevice sites may be introduced.
7.2 For the most part, commercially produced stainless
alloys and surface ground materials do not require a pre-
6.6 Specimens should be identified by alloy and replication.
exposure pickling treatment. The use of acid cleaning or
Mechanical stenciling or engraving are generally suitable,
pretreatments shall be considered only when the crevice-
providedthatthecodingisonsurfacesawayfromtheintended
corrosion test is designed to provide guidance for a specific
crevicesites.Identificationmarkingsshouldbeappliedpriorto
application.
the final specimen cleaning before test. Marking the samples
may affect the test results. See the Identification of Test
7.3 Any use of chemical pretreatments shall be thoroughly
Specimens section of Guide G4.
documented and appropriate safety measures followed.
6.7 Depending on the test objectives, mill-produced sur-
8. Mass Loss Determinations
faces may be left intact or specimens may be prepared by
providing a surface definable in terms of a given preparation
8.1 Mass loss data calculated from specimen weighing
process. before and after testing may provide some useful information
6.7.1 Because of the possible variations between “as-
in specific cases. However, comparisons of alloy performance
produced” alloy surface finishes, the adoption of a given based solely on mass loss may be misleading because highly
surface finish is recommended if various alloys are to be
localized corrosion, which is typical of crevice corrosion, can
compared.This will tend to minimize the variability of crevice often result in relatively small mass losses.
geometry in contact areas.
9. Crevice Formers
6.7.2 While some specific alloys may have proprietary
surface conditioning, some uncertainty may exist with regard
9.1 General Comments:
to the actual end use surface finish. It is recommended that
9.1.1 The severity of a crevice-corrosion test in a given
more than one surface condition be examined to assess any
environment can be influenced by the size and physical
effect of surface finish on an individual alloy’s crevice corro-
properties of the crevice former.
sion behavior.
9.1.2 Both metal-to-metal and nonmetal-to-metal crevice
6.7.3 Surface grinding with 120grit SiC abrasive paper is a
components are frequently used in laboratory and field studies.
suitable method for preparing laboratory test specimens. Wet
9.1.3 Nonmetallic crevice formers often have the capacity
grindingispreferredtoavoidpossiblesuperficialmetallurgical
for greater elastic deformation and may produce tighter crev-
changes due to overheating that may affect material perfor-
ices which are generally considered to more readily promote
mance.
crevice-corrosion initiation. Acrylic plastic, nylon,
polyethylene, PTFE-fluorocarbons, and acetal resin are a few
NOTE 2—Depending on the surface roughness of the mill product,
machiningmayberequiredpriortofinalgrinding.Iftheeffectofabrasion of the commonly used nonmetallics.
G78−20
NOTE 1—Various crevice former designs utilized in laboratory and field test crevice-corrosion studies. Severity of the test may vary as a function of
crevice geometry, that is, size of the crevice former and degree of tightness
FIG. 2 Crevice Former Designs
9.1.4 The properties of the nonmetallic crevice former must
becompatiblewiththephysicalandenvironmentaldemandsof
the test.
9.1.5 Regardless of the material or type of crevice former,
contacting surfaces should be kept as flat as possible to
enhance reproducibility of crevice geometry.
9.1.6 For rigid type crevice formers, as shown for example
in Fig. 2, the prepared contact surface finish or finishes should
also be documented and reported as in 6.7.3.
NOTE 3—Footnote 4 provides examples of variations in crevice former
and test specimen surface finish/roughness.
9.2 Various Designs for Flat Specimens:
9.2.1 Fig. 2 shows the shapes of a few popular crevice
former designs, such as coupons, strips, O-rings, blocks,
continuousandsegmentedwashers.Inmanycases,twocrevice
formers are fastened to a flat specimen, that is, one on each
side.
9.2.2 Multiple crevice assemblies (MCA) consist of two
nonmetallic segmented washers, each having a number of
groovesa
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: G78 − 15 G78 − 20
Standard Guide for
Crevice Corrosion Testing of Iron-Base and Nickel-Base
Stainless Alloys in Seawater and Other Chloride-Containing
Aqueous Environments
This standard is issued under the fixed designation G78; 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.
INTRODUCTION
Crevice corrosion of iron-base and nickel-base stainless alloys can occur when an occlusion or
crevice limits access of the bulk environment to a localized area of the metal surface. Localized
environmental changes in this stagnant area can result in the formation of acidic/high chloride
conditions that may result in initiation and propagation of crevice corrosion of susceptible alloys.
In practice, crevices can generally be classified into two categories: (1) naturally occurring, that is,
those created by biofouling, sediment, debris, deposits, etc. and (2) man-made, that is, those created
during manufacturing, fabrication, assembly, or service. Crevice formers utilized in laboratory and
field studies can represent actual geometric conditions encountered in some service applications. Use
of such crevice formers in service-type environments are not considered accelerated test methods.
The geometry of a crevice can be described by the dimensions of crevice gap and crevice depth.
Crevice gap is identified as the width or space between the metal surface and the crevice former.
Crevice depth is the distance from the mouth to the center or base of the crevice.
1. Scope
1.1 This guide covers information for conducting crevice-corrosion tests and identifies factors that may affect results and influence
conclusions.
1.2 These procedures can be used to identify conditions most likely to result in crevice corrosion and provide a basis for assessing
the relative resistance of various alloys to crevice corrosion under certain specified conditions.
1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only. after
SI units are provided for information only and are not considered standard.
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. For a specific warning statement, see 7.1.
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.
This guide is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.04 on Corrosion of Metals
in Natural Atmospheric and Aqueous Environments.
Current edition approved June 1, 2015Nov. 1, 2020. Published July 2015November 2020. Originally approved in 1983. Last previous edition approved in 20122015 as
G78–01 (2012). –15. DOI: 10.1520/G0078-15.10.1520/G0078-20.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
G78 − 20
2. Referenced Documents
2.1 ASTM Standards:
G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test Specimens
G4 Guide for Conducting Corrosion Tests in Field Applications
G46 Guide for Examination and Evaluation of Pitting Corrosion
G48 Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and Related Alloys by Use of Ferric Chloride
Solution
G52 Practice for Exposing and Evaluating Metals and Alloys in Surface Seawater
G193 Terminology and Acronyms Relating to Corrosion
3. Terminology
3.1 Definitions of related terms can be found in Terminology G193.
4. Significance and Use
4.1 This guide covers procedures for crevice-corrosion testing of iron-base and nickel-base stainless alloys in seawater. The
guidance provided may also be applicable to crevice corrosion testing in other chloride containing natural waters and various
laboratory prepared aqueous chloride environments.
4.1.1 While this guide focuses on testing of iron-base and nickel-base stainless alloys, the procedures and evaluations methods
described herein have been successfully applied to characterize the crevice corrosion performance of other alloy systems (see, for
example, Aylor et al. ).
NOTE 1—In the case of copper alloys, the occurrence of crevice-related corrosion associated with different corrosion mechanisms takes place immediately
adjacent to the crevice former rather than within the occlusion.
4.2 This guide describes the use of a variety of crevice formers including the nonmetallic, segmented washer design referred to
as the multiple crevice assembly (MCA) as described in 9.2.2.
4.3 In-service performance data provide the most reliable determination of whether a material would be satisfactory for a
particular end use. Translation of laboratory data from a single test program to predict service performance under a variety of
conditions should be avoided. Terms, such as immunity, superior resistance, etc., provide only a general and relatively qualitative
description of an alloy’s corrosion performance. The limitations of such terms in describing resistance to crevice corrosion should
be recognized.
4.4 While the guidance provided is generally for the purpose of evaluating sheet and plate materials, it is also applicable for
crevice-corrosion testing of other product forms, such as tubing and bars.
4.5 The presence or absence of crevice corrosion under one set of conditions is no guarantee that it will or will not occur under
other conditions. Because of the many interrelated metallurgical, environmental, and geometric factors known to affect crevice
corrosion, results from any given test may or may not be indicative of actual performance in service applications where the
conditions may be different from those of the test.
5. Apparatus
5.1 Laboratory tests utilizing filtered, natural seawater, or other chloride containing aqueous environments are frequently
conducted in tanks or troughs under low velocity (for example, ;0.5 m/s (1.64 ft/s) or less) or quiescent conditions. Containers
should be resistant to the test media.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’sstandard’s Document Summary page on the ASTM website.
Aylor, D. M., Hays, R. A., Kain, R. M., and Ferrara, R. J., “Crevice Corrosion Performance of Candidate Naval Ship Seawater Valve Materials in Quiescent and Flowing
Natural Seawater,” CORROSION/99 Paper #329, NACE International.
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5.2 Fig. 1 shows a typical test apparatus for conducting crevice-corrosion tests under controlled temperature conditions with
provisions for recirculation or refreshment of the aqueous environment, or both, at a constant level.
5.3 The apparatus should be suitably sized to provide complete immersion of the test panel. Vertical positioning of the
crevice-corrosion specimens facilitates visual inspection without the need to remove them from the environments.
6. Test Specimens
6.1 Because of the number of variables which may affect the test results, a minimum of three specimens are suggested for each
set of environmental, metallurgical, or geometric conditions to be evaluated. If reproducibility is unsatisfactory, additional
specimens should be tested.
6.2 Dimensions of both the test specimen and crevice former should be determined and recorded.
6.3 Variations in the boldly exposed (crevice-free) to shielded (crevice) area ratio of the test specimen may influence crevice
corrosion. All specimens in a test series should have the same nominal surface area. While no specific specimen dimensions are
recommended, test panels measuring up to 300300 mm by 300 mm (11.81(11.81 in. by 11.81 in.) have been used in seawater tests
with both naturally occurring and man-made crevice formers. For laboratory studies, the actual size of the specimen may be limited
by the dimensions of the test apparatus and this should be taken into consideration in making comparisons.
6.3.1 A test program may be expanded to assess any effect of boldly exposed to shielded area ratio.
6.3.2 If crevice geometry aspects, such as crevice depth, are to be studied, the adoption of a constant boldly exposed to shielded
area ratio is recommended to minimize the number of test variables.
6.4 When specimens are cut by shearing, it is recommended that the deformed material be removed by machining or grinding.
Test pieces that are warped or otherwise distorted should not be used. The need to provide parallel surfaces between the crevice
former and the test specimen is an important consideration in providing maximum consistency in the application of the crevice
former.
6.5 Appropriate holes should be drilled (and deburred) in the test specimen to facilitate attachment of the crevice former. Punched
holes are not recommended since the punching process may contribute to specimen distortion or work hardening, or both. The
diameter of the holes should be large enough to allow clearance of the fastener (and insulator) otherwise additional crevice sites
may be introduced.
6.6 Specimens should be identified by alloy and replication. Mechanical stenciling or engraving are generally suitable, provided
FIG. 1 Positioning of Crevice-Corrosion Test Specimens—Typical Arrangement in Controlled Environment Apparatus
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that the coding is on surfaces away from the intended crevice sites. Identification markings should be applied prior to the final
specimen cleaning before test. Marking the samples may affect the test results. See the Identification of Test Specimens section
of Guide G4.
6.7 Depending on the test objectives, mill-produced surfaces may be left intact or specimens may be prepared by providing a
surface definable in terms of a given preparation process.
6.7.1 Because of the possible variations between “as-produced” alloy surface finishes, the adoption of a given surface finish is
recommended if various alloys are to be compared. This will tend to minimize the variability of crevice geometry in contact areas.
6.7.2 While some specific alloys may have proprietary surface conditioning, some uncertainty may exist with regard to the actual
end use surface finish. It is recommended that more than one surface condition be examined to assess any effect of surface finish
on an individual alloy’s crevice corrosion behavior.
6.7.3 Surface grinding with 120-grit120 grit SiC abrasive paper is a suitable method for preparing laboratory test specimens. Wet
grinding is preferred to avoid any heating. Depending on the surface roughness of the mill product, machining may be required
prior to final grinding. If the effect of abrasion is a test parameter, then the grit size, type of abrasive and ideally the resulting
surface roughness (Ra) value should be recorded.possible superficial metallurgical changes due to overheating that may affect
material performance.
NOTE 2—Depending on the surface roughness of the mill product, machining may be required prior to final grinding. If the effect of abrasion is a test
parameter, then the grit size, type of abrasive, and ideally the resulting surface roughness (Ra) value should be recorded.
6.7.4 The time between last metal removal from a mechanically finished surface and immersion in the test solution can have a
significant effect on crevice corrosion initiation and should be standardized for comparative tests or at least recorded.
6.8 Cut lengths of pipe and tubing can be used as specimens to test the crevice corrosion resistance of these product forms in the
as-manufactured or surface treated condition. Other cylindrical products can be tested in the as-produced or finished condition.
6.8.1 The selection of cylindrical sample sizes should be made with the knowledge of the availability of appropriately sized
crevice formers, as described in 9.5.
6.8.2 The type of crevice former selected may dictate the length of the cylindrical test specimens. Lengths Specimen lengths of
44 in. to 12 in. (10(10 cm to 30 cm) and longer have been used.
7. Pre-test Cleaning
7.1 Cleaning procedures shall be consistent with Practice G1. Typically, this may include degreasing with a suitable solvent,
followed by vigorous brush scrubbing with pumice powder, followed by water rinse, clean solvent rinse, and air drying.
(Warning—Solvent safety and compatibility with the test material should be investigated and safe practices followed).
7.2 For the most part, commercially produced stainless alloys and surface ground materials do not require a pre-exposure pickling
treatment. The use of acid cleaning or pretreatments shall be considered only when the crevice-corrosion test is designed to provide
guidance for a specific application.
7.3 Any use of chemical pretreatments shall be thoroughly documented and appropriate safety measures followed.
8. Mass Loss Determinations
8.1 Mass loss data calculated from specimen weighing before and after testing may provide some useful information in specific
cases. However, comparisons of alloy performance based solely on mass loss may be misleading because highly localized
corrosion, which is typical of crevice corrosion, can often result in relatively small mass losses.
9. Crevice Formers
9.1 General Comments:
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9.1.1 The severity of a crevice-corrosion test in a given environment can be influenced by the size and physical properties of the
crevice former.
9.1.2 Both metal-to-metal and nonmetal-to-metal crevice components are frequently used in laboratory and field studies.
9.1.3 Nonmetallic crevice formers often have the capacity for greater elastic deformation and may produce tighter crevices which
are generally considered to more readily promote crevice-corrosion initiation. Acrylic plastic, nylon, polyethylene, PTFE-
fluorocarbons, and acetal resin are a few of the commonly used nonmetallics.
9.1.4 The properties of the nonmetallic crevice former must be compatible with the physical and environmental demands of the
test.
9.1.5 Regardless of the material or type of crevice former, contacting surfaces should be kept as flat as possible to enhance
reproducibility of crevice geometry.
9.1.6 For rigid type crevice formers, as shown for example in Fig. 2, the prepared contact surface finish or finishes should also
be documented and reported as in 6.7.46.7.3.
NOTE 3—Footnote 4 provides examples of variations in crevice former and test specimen surface finish/roughness.
9.2 Various Designs for Flat Specimens:
9.2.1 Fig. 2 shows the shapes of a few popular crevice former designs, such as coupons, strips, O-rings, blocks, continuous and
segmented washers. In many cases, two crevice formers are fastened to a flat specimen, that is, one on each side.
9.2.2 Multiple crevice assemblies (MCA) consist of two nonmetallic segmented washers, each having a number of grooves and
plateaus. The design shown in Figs. 3 and 4 is only one of a number of variations of the multiple crevice assembly which are in
use. Each
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