1、Designation: G78 01 (Reapproved 2012)G78 15Standard 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
2、indicates 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-
3、base stainless 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
4、 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 createdduring manufacturing, fabrication, assembly, or se
5、rvice. 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 dim
6、ensions 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
7、 and identifies factors that may affect results andinfluence conclusions.1.2 These procedures can be used to identify conditions most likely to result in crevice corrosion and provide a basis forassessing the relative resistance of various alloys to crevice corrosion under certain specified conditio
8、ns.1.3 The values stated in SI units are to be regarded as standard. The values given in parentheses are for information only.1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish a
9、ppropriate safety and health practices and determine the applicability of regulatorylimitations prior to use. For a specific warning statement, see 7.1.17.1.2. Referenced Documents2.1 ASTM Standards:2G1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test SpecimensG4 Guide for Conducting
10、Corrosion Tests in Field ApplicationsG15 Terminology Relating to Corrosion and Corrosion Testing (Withdrawn 2010)3G46 Guide for Examination and Evaluation of Pitting CorrosionG48 Test Methods for Pitting and Crevice Corrosion Resistance of Stainless Steels and RelatedAlloys by Use of Ferric Chloride
11、SolutionG193 Terminology and Acronyms Relating to Corrosion1 This guide is under the jurisdiction of ASTM Committee G01 on Corrosion of Metals and is the direct responsibility of Subcommittee G01.09 on Corrosion in NaturalWaters.Current edition approved Nov. 1, 2012June 1, 2015. Published November 2
12、012July 2015. Originally approved in 1983. Last previous edition approved in 20072012 asG7801 (2007).(2012). DOI: 10.1520/G0078-01R12.10.1520/G0078-15.2 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Stan
13、dardsvolume information, refer to the standards Document Summary page on the ASTM website.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. Becauseit may not be technically possible
14、 to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West C
15、onshohocken, PA 19428-2959. United States13. Terminology3.1 Definitions of related terms can be found in Terminology G15G193.4. Significance and Use4.1 This guide covers procedures for crevice-corrosion testing of iron-base and nickel-base stainless alloys in seawater. Theguidance provided may also
16、be applicable to crevicecorrosion crevice corrosion testing in other chloride containing natural watersand various laboratory prepared aqueous chloride environments.4.2 This guide describes the use of a variety of crevice formers including the nonmetallic, segmented washer design referredto as the m
17、ultiple 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 aparticular end use. Translation of laboratory data from a single test program to predict service performance under a variety o
18、fconditions should be avoided. Terms, such as immunity, superior resistance, etc., provide only a general and relatively qualitativedescription of an alloys corrosion performance. The limitations of such terms in describing resistance to crevice corrosion shouldbe recognized.4.4 While the guidance p
19、rovided is generally for the purpose of evaluating sheet and plate materials, it is also applicable forcrevice-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
20、 underother conditions. Because of the many interrelated metallurgical, environmental, and geometric factors known to affect crevicecorrosion, results from any given test may or may not be indicative of actual performance in service applications where theconditions may be different from those of the
21、 test.5. Apparatus5.1 Laboratory tests utilizing filtered, natural seawater, or other chloride containing aqueous environments are frequentlyconducted in tanks or troughs under low velocity (for example, ;0.5 m/s (1.64 ft/s) or less) or quiescent conditions. Containersshould be resistant to the test
22、 media.5.2 Fig. 1 shows a typical test apparatus for conducting crevice-corrosion tests under controlled temperature conditions withprovisions 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 imme
23、rsion of the test panel. Vertical positioning of thecrevice-corrosion specimens facilitates visual inspection without the need to remove them from the environments.6. Test Specimens6.1 Because of the number of variables which may affect the test results, a minimum of three specimens are suggested fo
24、r eachset of environmental, metallurgical, or geometric conditions to be evaluated. If reproducibility is unsatisfactory, additionalspecimens should be tested.6.2 Dimensions of both the test specimen and crevice former should be determined and recorded.FIG. 1 Positioning of Crevice-Corrosion Test Sp
25、ecimensTypical Arrangement in Controlled Environment ApparatusG78 1526.3 Variations in the boldly exposed (crevice-free) to shielded (crevice) area ratio of the test specimen may influence crevicecorrosion. All specimens in a test series should have the same nominal surface area. While no specific s
26、pecimen dimensions arerecommended, test panels measuring up to 300 by 300 mm (11.81 by 11.81 in.) have been used in seawater tests with both naturallyoccurring and man-made crevice formers. For laboratory studies, the actual size of the specimen may be limited by the dimensionsof the test apparatus
27、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 shieldedarea
28、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
29、the creviceformer and the test specimen is an important consideration in providing maximum consistency in the application of the creviceformer.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
30、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 crevicesites may be introduced.6.6 Specimens should be identified by alloy and replicat
31、ion. Mechanical stenciling or engraving are generally suitable, providedthat the coding is on surfaces away from the intended crevice sites. Identification markings should be applied prior to the finalspecimen cleaning before test. Marking the samples may affect the test results. See the Identificat
32、ion of Test Specimens sectionof Guide G4.6.7 Depending on the test objectives, mill-produced surfaces may be left intact or specimens may be prepared by providing asurface definable in terms of a given preparation process.6.7.1 Because of the possible variations between “as-produced” alloy surface f
33、inishes, the adoption of a given surface finish isrecommended 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 th
34、eactual end use surface finish. It is recommended that more than one surface condition be examined to assess any effect of surfacefinish on an individual alloys crevice corrosion behavior.6.7.3 Surface grinding with 120-grit SiC abrasive paper is a suitable method for preparing laboratory test speci
35、mens. Wetgrinding is preferred to avoid any heating. Depending on the surface roughness of the mill product, machining may be requiredprior to final grinding. If the effect of abrasion is a test parameter, then the grit size, type of abrasive and ideally the resultingsurface roughness (Ra) value sho
36、uld be recorded.6.7.4 The time between last metal removal from a mechanically finished surface and immersion in the test solution can havea 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
37、be used as specimens to test the crevice corrosion resistance of these product forms inthe 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
38、 of the availability of appropriately sizedcrevice 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 of 4 to 12 in. (10to 30 cm) and longer have been used.7. Pre-test Cleaning7.1 Pre-Test Cleaning: Cleaning proced
39、ures shall be consistent with Practice G1. Typically, this may include degreasing witha suitable solvent, followed by vigorous brush scrubbing with pumice powder, followed by water rinse, clean solvent rinse, andair drying. (WarningSolvent safety and compatibility with the test material should be in
40、vestigated and safe practices followed).7.1.1 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.(WarningSolvent
41、 safety and compatibility with the test material should be investigated and safe practices followed).7.1.2 For the most part, commercially produced stainless alloys and surface ground materials do not require a pre-exposurepickling treatment. The use of acid cleaning or pretreatments shall be consid
42、ered only when the crevice-corrosion test is designedto provide guidance for a specific application.7.1.3 Any use of chemical pretreatments shall be thoroughly documented and appropriate safety measures followed.7.2 For the most part, commercially produced stainless alloys and surface ground materia
43、ls do not require a pre-exposurepickling treatment. The use of acid cleaning or pretreatments shall be considered only when the crevice-corrosion test is designedto provide guidance for a specific application.7.3 Any use of chemical pretreatments shall be thoroughly documented and appropriate safety
44、 measures followed.G78 1538. Mass Loss Determinations8.1 Mass loss data calculated from specimen weighing before and after testing may provide some useful information in specificcases. However, comparisons of alloy performance based solely on mass loss may be misleading because highly localizedcorro
45、sion, which is typical of crevice corrosion, can often result in relatively small mass losses.9. Crevice Formers9.1 General Comments:9.1.1 The severity of a crevice-corrosion test in a given environment can be influenced by the size and physical properties ofthe crevice former.9.1.2 Both metal-to-me
46、tal 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 creviceswhich are generally considered to more readily promote crevice-corrosion initiati
47、on. 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 thetest.9.1.5 Regardless of the material or type of crevi
48、ce former, contacting surfaces should be kept as flat as possible to enhancereproducibility 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 alsobe documented and reported as in 6.7.4.NOTE 1Footnote 4 pro
49、vides examples of variations in crevice former and test specimen surface finish/roughness.39.2 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 andsegmented 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 andplateaus. The design shown in Figs. 3 and 4 is only one of a number of variations of the
