1、Designation: G150 13G150 18Standard Test Method forElectrochemical Critical Pitting Temperature Testing ofStainless Steels and Related Alloys1This standard is issued under the fixed designation G150; the number immediately following the designation indicates the year oforiginal adoption or, in the c
2、ase of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers a procedure for the evaluation of the resistance of stainless ste
3、el and related alloys to pittingcorrosion based on the concept of the determination of a potential independent critical pitting temperature (CPT).1.2 This test methodsmethod applies to wrought and cast products including but not restricted to plate, sheet, tubing, bar,forgings, and welds, (see Note
4、1).NOTE 1Examples of CPT measurements on sheet, plate, tubing, and welded specimens for various stainless steels can be found in Ref (1).2 See theresearch reports (Section 14).1.3 The standard parameters recommended in this test method are suitable for characterizing the CPT of austenitic stainlesss
5、teels and other related alloys with a corrosion resistance ranging from that corresponding to solution annealed UNS S31600 (Type316 stainless steel) to solution annealed UNS S31254 (6 % Mo stainless steel).1.4 This test method may be extended to stainless steels and other alloys related to stainless
6、 steel that have a CPT outside themeasurement range given by the standard parameters described in this test method. Appropriate test potential and solution mustthen be determined.1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this stan
7、dard.1.6 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 appropriate safety safety, health, and healthenvironmental practices and determine theapplicability of regulatory limitati
8、ons prior to use.1.7 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development of International Standards, Guides and Recommendations issuedby the World Trade Organization Technic
9、al Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3D1193 Specification for Reagent WaterD1293 Test Methods for pH of WaterE177 Practice for Use of the Terms Precision and Bias in ASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study to Determine the Prec
10、ision of a Test MethodG1 Practice for Preparing, Cleaning, and Evaluating Corrosion Test SpecimensG3 Practice for Conventions Applicable to Electrochemical Measurements in Corrosion TestingG5 Reference Test Method for Making Potentiodynamic Anodic Polarization MeasurementsG46 Guide for Examination a
11、nd Evaluation of Pitting CorrosionG107 Guide for Formats for Collection and Compilation of Corrosion Data for Metals for Computerized Database InputG193 Terminology and Acronyms Relating to Corrosion1 This test method is under the jurisdiction of G01 on Corrosion of Metals and is the direct responsi
12、bility of Subcommittee G01.11 on Electrochemical Measurements inCorrosion Testing.Current edition approved May 1, 2013May 1, 2018. Published May 2013May 2018. Originally approved in 1997. Last previous edition approved in 20102013 as G150 99 (2010). 13. DOI: 10.1520/G0150-13.10.1520/G0150-18.2 The b
13、oldface numbers in parenthesisparentheses refer to the list of references at the end of this standard.3 For referencedASTM standards, visit theASTM website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards D
14、ocument 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 to adequately depict all changes accurately, AST
15、M 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 Conshohocken, PA 19428-2959. United States13. Term
16、inology3.1 Definitions:3.1.1 critical pitting temperature (CPT)the lowest temperature on the test surface at which stable propagating pitting occursunder specified test conditions indicated by a rapid increase beyond a set limit of the measured anodic current density of thespecimen.3.1.2 pitting pot
17、ential rangethe range of measured potentials where pitting is initiated. This potential range only exists abovethe minimum critical pitting temperature; see also Appendix X1.3.1.3 potential dependent CPTthe CPT determined at a potential within the pitting potential range of the tested material; seea
18、lso Appendix X1.3.1.4 potential independent CPT the CPT determined at a potential above the pitting potential range, but below thetranspassive potential; see also Appendix X1.3.1.5 temperature rampthe rate (C/min) at which the test temperature is increased during the test.3.2 sign conventionsthe sig
19、n conventions used in this procedure are in agreement with Practice G3.3.3 Unless otherwise stated, this test method uses the general terminology relating to corrosion and corrosion testing as definedin Terminology G193.4. Summary of Test Method4.1 The test method determines the potential independen
20、t critical pitting temperature (CPT) by way of a potentiostatic techniqueusing a temperature scan and a specimen holder that is designed to eliminate the occurrence of crevice corrosion (see Fig. 1). Thespecimen is exposed, either entirely or in part, depending on test cell configuration to a 1M NaC
21、l solution, initially at 0C. Afteran initial temperature stabilization period, the solution is heated at a rate of 1C/min. About 60 s before the temperature scan iscommenced, the specimen is anodically polarized to a potential above the pitting potential range. This potential is held constantduring
22、the whole temperature scan. A potential of 700 mV versus SCE (25C) has been found suitable for most stainless steels.The current is monitored during the temperature scan, and the CPT is defined as the temperature at which the current increasesrapidly, which for practical reasons is defined as the te
23、mperature at which the current density exceeds 100 A/cm2 for 60 s. Pittingon the specimen is confirmed visually after the test.5. Significance and Use5.1 This test method provides a prediction of the resistance to stable propagating pitting corrosion of stainless steels and relatedalloys in a standa
24、rd medium (see Note 1). The CPT test can be used for product acceptance, alloy development studies, andmanufacturing control. In the case of product acceptance, the supplier and user must agree upon the preconditioning of thespecimen with regard to surface finish. The test is not intended for design
25、 purposes since the test conditions accelerate corrosionin a manner that does not simulate any actual service environment.5.2 Another method to determine the potential independent CPT with an electrochemical technique has been discussed in theliterature (1-4). This test method involves a potentiodyn
26、amic (potential sweep) procedure performed on specimens at differenttemperatures. A comparison (2) of the test method described in this test method and the potentiodynamic technique has indicatedno difference in the test result obtained.FIG. 1 Determination of CPTG150 1826. Apparatus6.1 The apparatu
27、s necessary for determining the CPT consists of instruments for measuring electronic signals, a temperaturecontrolling apparatus, a specimen holder, and a test cell. The instruments for measuring electronic signals may be integrated intoone instrument package or may be individual components. Either
28、form of instrumentation can provide acceptable data. Typical testequipment consists of the following: (1) potentiostat (2) potential measuring instrument (3) current measuring instrument (4)temperature controller (5) temperature measuring instrument (6) test cell (7) specimen holder, and (8) electro
29、des.6.2 PotentiostatThe potentiostat shall be able to apply the constant potential to within 1 mV at a current density of 10mA/cm2. The applied potential is changed either automatically or manually by shifting the potential from the open circuit potentialto another more noble potential.6.3 Potential
30、 Measuring InstrumentRequirements shall be in accordance with the section on Potential Measuring Instrumentsin Test Method G5.6.4 Current Measuring InstrumentsAn instrument that is capable of measuring a current accurately to within 5 % of the actualvalue. The typical current densities encountered d
31、uring the CPT test are in the range of 1 A/cm2 to 10 mA/cm2.6.5 Temperature Controller:6.5.1 Thermostat equipment is required that can provide cooling and heating of the test solution in the temperature range from0C to approximately 100C. Further, the temperature controller is used to provide contro
32、lled heating, which gives the test solutiontemperature a temperature increase rate of 1C/min in the range from 0C to approximately 100C.6.5.2 Above 10C, the average rate of temperature change of the test solution shall be 1.0 6 0.3C/min, where the average iscalculated over a temperature range of 10C
33、.6.6 Temperature Measurement Instrumentation, shall be capable of measuring the temperature of the test solution with anaccuracy of 60.4C.6.7 Test Cell:6.7.1 Option 1, G5 TypeThe test cell should be similar to the one described inTest Method G5. Other similar polarization cellsmay be equally suitabl
34、e. The gas purger should distribute the gas in numerous small bubbles.6.7.2 Option 2, Flushed-port CellThis cell design is based on that published by R. Qvarfort (3) and includes the specimenholder in the design. The advantages of this cell design are that the specimen edges and back do not need to
35、be machined, thespecimen does not have to be mounted inside the cell, and crevice corrosion at the contact area of the cell port is completelyeliminated, even at elevated test temperatures. See Appendix X2 for a description of this cell. The gas purger should distribute thegas in numerous small bubb
36、les.6.7.3 The test cell shall be able to contain a test solution volume of minimum 100 mL per square centimetre test area. Amaximum dilution of 15 % of the test solution during the test period is allowed in case a flushed port cell or similar arrangementis used.6.8 Specimen Holder:6.8.1 Any part of
37、the specimen holder coming in contact with the test solution during testing shall be made of an inert material,and any seal shall not allow leakage of electrolyte.6.8.2 The specimen holder shall have a design that ensures no occurrence of crevice corrosion at the contact area betweenspecimen holder
38、and specimen.6.8.3 Two examples of specimen holder designs in accordance with this standard are shown in Appendix X2 and Appendix X3.The major difference between the specimen holder designs lies in the allowable specimen geometry and the number of surfaceson the specimen that are being tested simult
39、aneously.6.9 Electrodes:6.9.1 Auxiliary (Counter) ElectrodeRequirements shall be in accordance with the sectionAuxiliary Electrodes in Test MethodG5 with the exception that only one counter electrode is necessary for CPT testing. The electrode material shall be of a type whichcan be considered inert
40、 under the test conditions.6.9.2 Reference ElectrodeThe reference electrode shall be kept at room temperature outside the actual test cell. The referenceelectrode shall be capable of ensuring a constant reference potential within 65 mV during the entire test procedure (see Note 2).Electrical contact
41、 to the test solution shall be provided by the use of a luggin capillary placed in the test solution. Requirementsshall otherwise be in accordance with the section on Reference Electrode in Test Method G5.NOTE 2It may be difficult to ensure a fully constant reference potential due to the large varia
42、tions in temperature of the test solution; therefore, theallowable is 65 mV. This does, however, not affect the measured potential independent CPT (1).7. Test Specimens7.1 FinishAny geometry and surface finish (see Note 3) compatible with the chosen specimen holder as specified in 6.8 maybe used.NOT
43、E 3The state of the surface may be dependent on the time and location of storage between the final mechanical or chemical surface treatmentG150 183and testing. The time and location of storage may, therefore, in some situations be considered an integral part of the surface finish.7.2 SamplingWhen us
44、ing this test method to meet product acceptance criteria, the means of sampling of a test specimen shallbe decided by agreement between the parties involved.7.3 Test AreaA minimum test area of 1 cm2 shall be used.7.4 Specimens removed from a work piece or component by shearing, cutting, burning, and
45、 so forth shall have the affectededges removed by grinding or machining, unless it is explicitly intended to study the effects of these edge factors.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall be used in all tests. Unless otherwise indicated, it is intended that allr
46、eagents conform to the specifications of the Committee on Analytical Reagents of the American Chemical Society where suchspecifications are available.4 Other grades may be used, provided it is first ascertained that the reagent is of sufficiently high purityto permit its use without lessening the ac
47、curacy of the determination.8.2 Purity of WaterUnless otherwise indicated, references to purified water shall be understood to mean reagent water asdefined by Type IV of Specification D1193.8.3 Standard Test SolutionTo prepare 1 L of 1 M sodium chloride (NaCl) solution, dissolve 58.45 g sodium chlor
48、ide (NaCl)in purified water to a total solution volume of 1 L. The solution can be made up in bulk and stored for one month at roomtemperature.8.4 Purging GasNitrogen gas of minimum 99.99 % purity should be used.9. Applied Potential9.1 Standard PotentialAn anodic potential of 700 mV versus SCE (25C)
49、 is used. This has been found appropriate for moststainless steels (1).9.2 Alternative Potential:9.2.1 If uncertainty exists concerning whether the standard potential is sufficiently high to obtain the potential independent CPT,a test at 800 mV versus SCE (25C) may be performed.Asignificant deviation between the CPT obtained at 700 mV and 800 mVwill indicate a need for a reevaluation and new choice of potential.NOTE 4Using a lower potential than the standard potential of 700 mV versus SCE (25C) is fully acceptable, provided the determine
