1、Designation: G78 01 (Reapproved 2012)Standard Guide forCrevice Corrosion Testing of Iron-Base and Nickel-BaseStainless Alloys in Seawater and Other Chloride-ContainingAqueous Environments1This standard is issued under the fixed designation G78; the number immediately following the designation indica
2、tes the year of originaladoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.Asuperscriptepsilon () indicates an editorial change since the last revision or reapproval.INTRODUCTIONCrevice corrosion of iron-base and nickel-base s
3、tainless alloys can occur when an occlusion orcrevice limits access of the bulk environment to a localized area of the metal surface. Localizedenvironmental changes in this stagnant area can result in the formation of acidic/high chlorideconditions that may result in initiation and propagation of cr
4、evice 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 createdduring manufacturing, fabrication, assembly, or service.
5、 Crevice formers utilized in laboratory andfield studies can represent actual geometric conditions encountered in some service applications. Useof such crevice formers in service-type environments are not considered accelerated test methods.The geometry of a crevice can be described by the dimension
6、s 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. Scope1.1 This guide covers information for conducting crevice-corrosion tests and i
7、dentifies factors that may affect results andinfluence conclusions.1.2 These procedures can be used to identify conditionsmost likely to result in crevice corrosion and provide a basis forassessing the relative resistance of various alloys to crevicecorrosion under certain specified conditions.1.3 T
8、he values stated in SI units are to be regarded asstandard. The values given in parentheses are for informationonly.1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate
9、 safety and health practices and determine the applica-bility of regulatory limitations prior to use. For a specificwarning statement, see 7.1.1.2. Referenced Documents2.1 ASTM Standards:2G1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG4 Guide for Conducting Corrosion T
10、ests in Field Applica-tionsG15 Terminology Relating to Corrosion and Corrosion Test-ing (Withdrawn 2010)3G46 Guide for Examination and Evaluation of Pitting Cor-rosionG48 Test Methods for Pitting and Crevice Corrosion Resis-tance of Stainless Steels and Related Alloys by Use ofFerric Chloride Soluti
11、on1This guide is under the jurisdiction of ASTM Committee G01 on Corrosion ofMetals and is the direct responsibility of Subcommittee G01.09 on Corrosion inNatural Waters.Current edition approved Nov. 1, 2012. Published November 2012. Originallyapproved in 1983. Last previous edition approved in 2007
12、 as G7801 (2007). DOI:10.1520/G0078-01R12.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3The last approved
13、version of this historical standard is referenced onwww.astm.org.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13. Terminology3.1 Definitions of related terms can be found in Terminol-ogy G15.4. Significance and Use4.1 This guide cov
14、ers procedures for crevice-corrosion test-ing of iron-base and nickel-base stainless alloys in seawater.The guidance provided may also be applicable to crevicecor-rosion testing in other chloride containing natural waters andvarious laboratory prepared aqueous chloride environments.4.2 This guide de
15、scribes the use of a variety of creviceformers including the nonmetallic, segmented washer designreferred to as the multiple crevice assembly (MCA) as de-scribed in 9.2.2.4.3 In-service performance data provide the most reliabledetermination of whether a material would be satisfactory fora particula
16、r end use. Translation of laboratory data from asingle test program to predict service performance under avariety of conditions should be avoided. Terms, such asimmunity, superior resistance, etc., provide only a general andrelatively qualitative description of an alloys corrosion per-formance. The
17、limitations of such terms in describing resis-tance to crevice corrosion should be recognized.4.4 While the guidance provided is generally for the pur-pose of evaluating sheet and plate materials, it is also appli-cable for crevice-corrosion testing of other product forms, suchas tubing and bars.4.5
18、 The presence or absence of crevice corrosion under oneset of conditions is no guarantee that it will or will not occurunder other conditions. Because of the many interrelatedmetallurgical, environmental, and geometric factors known toaffect crevice corrosion, results from any given test may ormay n
19、ot be indicative of actual performance in service appli-cations where the conditions may be different from those of thetest.5. Apparatus5.1 Laboratory tests utilizing filtered, natural seawater, orother chloride containing aqueous environments are frequentlyconducted in tanks or troughs under low ve
20、locity (for example,;0.5 m/s (1.64 ft/s) or less) or quiescent conditions. Contain-ers should be resistant to the test media.5.2 Fig. 1 shows a typical test apparatus for conductingcrevice-corrosion tests under controlled temperature conditionswith provisions for recirculation or refreshment of the
21、aqueousenvironment, or both, at a constant level.5.3 The apparatus should be suitably sized to providecomplete immersion of the test panel. Vertical positioning ofthe crevice-corrosion specimens facilitates visual inspectionwithout the need to remove them from the environments.6. Test Specimens6.1 B
22、ecause of the number of variables which may affect thetest results, a minimum of three specimens are suggested foreach set of environmental, metallurgical, or geometric condi-tions to be evaluated. If reproducibility is unsatisfactory,additional specimens should be tested.6.2 Dimensions of both the
23、test specimen and creviceformer should be determined and recorded.6.3 Variations in the boldly exposed (crevice-free) toshielded (crevice) area ratio of the test specimen may influencecrevice corrosion.All specimens in a test series should have thesame nominal surface area. While no specific specime
24、n dimen-sions are recommended, test panels measuring up to 300 by300 mm (11.81 by 11.81 in.) have been used in seawater testswith both naturally occurring and man-made crevice formers.For laboratory studies, the actual size of the specimen may belimited by the dimensions of the test apparatus and th
25、is shouldbe taken into consideration in making comparisons.6.3.1 A test program may be expanded to assess any effectof boldly exposed to shielded area ratio.FIG. 1 Positioning of Crevice-Corrosion Test SpecimensTypical Arrangement in Controlled Environment ApparatusG78 01 (2012)26.3.2 If crevice geo
26、metry aspects, such as crevice depth, areto be studied, the adoption of a constant boldly exposed toshielded area ratio is recommended to minimize the number oftest variables.6.4 When specimens are cut by shearing, it is recommendedthat the deformed material be removed by machining orgrinding. Test
27、pieces that are warped or otherwise distortedshould not be used. The need to provide parallel surfacesbetween the crevice former and the test specimen is animportant consideration in providing maximum consistency inthe application of the crevice former.6.5 Appropriate holes should be drilled (and de
28、burred) inthe test specimen to facilitate attachment of the crevice former.Punched holes are not recommended since the punchingprocess may contribute to specimen distortion or workhardening, or both. The diameter of the holes should be largeenough to allow clearance of the fastener (and insulator)ot
29、herwise additional crevice sites may be introduced.6.6 Specimens should be identified by alloy and replication.Mechanical stenciling or engraving are generally suitable,provided that the coding is on surfaces away from the intendedcrevice sites. Identification markings should be applied prior tothe
30、final specimen cleaning before test. Marking the samplesmay affect the test results. See the Identification of TestSpecimens section of Guide G4.6.7 Depending on the test objectives, mill-produced sur-faces may be left intact or specimens may be prepared byproviding a surface definable in terms of a
31、 given preparationprocess.6.7.1 Because of the possible variations between “as-produced” alloy surface finishes, the adoption of a givensurface finish is recommended if various alloys are to becompared. This will tend to minimize the variability of crevicegeometry in contact areas.6.7.2 While some s
32、pecific alloys may have proprietarysurface conditioning, some uncertainty may exist with regardto the actual end use surface finish. It is recommended thatmore than one surface condition be examined to assess anyeffect of surface finish on an individual alloys crevice corro-sion behavior.6.7.3 Surfa
33、ce grinding with 120-grit SiC abrasive paper is asuitable method for preparing laboratory test specimens. Wetgrinding is preferred to avoid any heating. Depending on thesurface roughness of the mill product, machining may berequired prior to final grinding.6.8 Cut lengths of pipe and tubing can be u
34、sed as specimensto test the crevice corrosion resistance of these product formsin the as-manufactured or surface treated condition. Othercylindrical products can be tested in the as-produced orfinished condition.6.8.1 The selection of cylindrical sample sizes should bemade with the knowledge of the
35、availability of appropriatelysized crevice formers, as described in 9.5.6.8.2 The type of crevice former selected may dictate thelength of the cylindrical test specimens. Lengths of 4 to 12 in.(10 to 30 cm) and longer have been used.7. Cleaning7.1 Pre-Test Cleaning:7.1.1 Cleaning procedures shall be
36、 consistent with PracticeG1. Typically, this may include degreasing with a suitablesolvent, followed by vigorous brush scrubbing with pumicepowder, followed by water rinse, clean solvent rinse, and airdrying. (WarningSolvent safety and compatibility with thetest material should be investigated and s
37、afe practices fol-lowed).7.1.2 For the most part, commercially produced stainlessalloys and surface ground materials do not require a pre-exposure pickling treatment. The use of acid cleaning orpretreatments shall be considered only when the crevice-corrosion test is designed to provide guidance for
38、 a specificapplication.7.1.3 Any use of chemical pretreatments shall be thoroughlydocumented and appropriate safety measures followed.8. Mass Loss Determinations8.1 Mass loss data calculated from specimen weighingbefore and after testing may provide some useful informationin specific cases. However,
39、 comparisons of alloy performancebased solely on mass loss may be misleading because highlylocalized corrosion, which is typical of crevice corrosion, canoften result in relatively small mass losses.9. Crevice Formers9.1 General Comments:9.1.1 The severity of a crevice-corrosion test in a givenenvir
40、onment can be influenced by the size and physicalproperties of the crevice former.9.1.2 Both metal-to-metal and nonmetal-to-metal crevicecomponents are frequently used in laboratory and field studies.9.1.3 Nonmetallic crevice formers often have the capacityfor greater elastic deformation and may pro
41、duce tighter crev-ices which are generally considered to more readily promotecrevice-corrosion initiation. Acrylic plastic, nylon,polyethylene, PTFE-fluorocarbons, and acetal resin are a fewof the commonly used nonmetallics.9.1.4 The properties of the nonmetallic crevice former mustbe compatible wit
42、h the physical and environmental demands ofthe test.9.1.5 Regardless of the material or type of crevice former,contacting surfaces should be kept as flat as possible toenhance reproducibility of crevice geometry.9.2 Various Designs for Flat Specimens:9.2.1 Fig. 2 shows the shapes of a few popular cr
43、eviceformer designs, such as coupons, strips, O-rings, blocks,continuous and segmented washers. In many cases, two creviceformers are fastened to a flat specimen, that is, one on eachside.9.2.2 Multiple crevice assemblies (MCA) consist of twononmetallic segmented washers, each having a number ofgroo
44、ves and plateaus.The design shown in Figs. 3 and 4 is onlyone of a number of variations of the multiple crevice assemblywhich are in use. Each plateau, in contact with the metalsurface, provides a possible site for initiation of crevicecorrosion. Multiple crevice assemblies fabricated of acetalG78 0
45、1 (2012)3resin have been shown to be suitable for seawater exposures.Other nonmetallics, such as PTFE-fluorocarbon and ceramic,have also been used (see 9.1.4).9.2.3 For metal-to-metal crevice-corrosion tests, flat wash-ers or coupons are often fastened to a larger test specimen. Allcomponents should
46、 be of the same material and prepared forexposure in the same manner.9.2.3.1 Crevice testing with metal to metal componentsassembled with either nonmetal or metal fasteners (withinsulator) will necessarily result in the formation of secondarycrevice sites where the fastener contacts the metallic cre
47、viceformer. In some cases, the geometry of these secondary sitesmay be more severe than the intended primary crevice site.9.3 Method of Attachment:9.3.1 Either metallic or nonmetallic fasteners, for example,nut- and bolt-type, can be used to secure the crevice formers tothe test panel.NOTE 1Various
48、crevice former designs utilized in laboratory and field test crevice-corrosion studies. Severity of the test may vary as a function ofcrevice geometry, that is, size of the crevice former and degree of tightnessFIG. 2 Crevice Former DesignsNOTE 1Inch-pound equivalents for SI units:0.5 mm = 0.0197 in
49、.1 mm = 0.039 in2.5 mm = 0.098 in.7 mm = 0.25 in.13 mm = 0.512 in.17 mm = 0.669 in.19 mm = 0.748 in.22 mm = 0.866 in.25.4 mm = 1 in.FIG. 3 Details of Multiple Crevice Washer (not to scale)FIG. 4 Multiple Crevice Assembly with Sheet SpecimenG78 01 (2012)4NOTE 1While it is recognized that rubber bands may be used in the 72h ferric chloride test method covered by Test Methods G48, rubber bandsare not recommended for long-term tests. Potential crevice sites formed byrubber bands on specimen edges may not be desirous for tests beyond thescope of Test Methods G48.9.3.2 Metallic
