1、Designation: G150 99 (Reapproved 2010)Standard Test Method forElectrochemical Critical Pitting Temperature Testing ofStainless Steels1This standard is issued under the fixed designation G150; the number immediately following the designation indicates the year oforiginal adoption or, in the case of r
2、evision, 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 evaluationof the resistance of stainless steel and re
3、lated alloys to pittingcorrosion based on the concept of the determination of apotential independent critical pitting temperature (CPT).1.2 This test methods applies to wrought and cast productsincluding but not restricted to plate, sheet, tubing, bar, forgings,and welds, (see Note 1).NOTE 1Examples
4、 of CPT measurements on sheet, plate, tubing, andwelded specimens for various stainless steels can be found in Ref (1).2Seethe research reports (Section 14).1.3 The standard parameters recommended in this testmethod are suitable for characterizing the CPT of austeniticstainless steels and other rela
5、ted alloys with a corrosionresistance ranging from that corresponding to solution an-nealed UNS S31600 (Type 316 stainless steel) to solutionannealed UNS S31254 (6 % Mo stainless steel).1.4 This test method may be extended to stainless steels andother alloys related to stainless steel that have a CP
6、T outsidethe measurement range given by the standard parametersdescribed in this test method. Appropriate test potential andsolution must then be determined.1.5 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.6 This standard d
7、oes 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 safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM St
8、andards:3D1193 Specification for Reagent WaterE177 Practice for Use of the Terms Precision and Bias inASTM Test MethodsE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG3 Pract
9、ice for Conventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG15 Terminology Relating to Corrosion and CorrosionTesting4G46 Guide for Examination and Evaluation of PittingCorros
10、ionG107 Guide for Formats for Collection and Compilation ofCorrosion Data for Metals for Computerized DatabaseInput3. Terminology3.1 Definitions:3.1.1 critical pitting temperature (CPT)the lowest tem-perature on the test surface at which stable propagating pittingoccurs under specified test conditio
11、ns indicated by a rapidincrease beyond a set limit of the measured anodic currentdensity of the specimen.3.1.2 pitting potential rangethe range of measured poten-tials where pitting is initiated. This potential range only existsabove the minimum critical pitting temperature; see alsoAppendix X1.1Thi
12、s test method is under the jurisdiction of G01 on Corrosion of Metals and isthe direct responsibility of Subcommittee G01.11 on Electrochemical Measurementsin Corrosion Testing.Current edition approved May 1, 2010. Published May 2010. Originallyapproved in 1997. Last previous edition approved in 200
13、4 as G15099(2004). DOI:10.1520/G0150-99R10.2The boldface numbers in parenthesis refer to the list of references at the end ofthis standard.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume
14、 information, refer to the standards Document Summary page onthe ASTM website.4Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.3 potent
15、ial dependent CPTthe CPT determined at apotential within the pitting potential range of the testedmaterial; see also Appendix X1.3.1.4 potential independent CPT the CPT determined at apotential above the pitting potential range, but below thetranspassive potential; see also Appendix X1.3.1.5 tempera
16、ture rampthe rate (C/min) at which the testtemperature is increased during the test.3.2 sign conventionsthe sign conventions used in thisprocedure are in agreement with Practice G3.3.3 Unless otherwise stated, this test method uses thegeneral terminology relating to corrosion and corrosion testingas
17、 defined in Terminology G15.4. Summary of Test Method4.1 The test method determines the potential independentcritical pitting temperature (CPT) by way of a potentiostatictechnique using a temperature scan and a specimen holder thatis designed to eliminate the occurrence of crevice corrosion(see Fig.
18、 1). The specimen is exposed, either entirely or in part,depending on test cell configuration to a 1M NaCl solution,initially at 0C. After an initial temperature stabilizationperiod, the solution is heated at a rate of 1C/min. About 60 sbefore the temperature scan is commenced, the specimen isanodic
19、ally polarized to a potential above the pitting potentialrange. This potential is held constant during the whole tem-perature scan. A potential of 700 mV versus SCE (25C) hasbeen found suitable for most stainless steels. The current ismonitored during the temperature scan, and the CPT is definedas t
20、he temperature at which the current increases rapidly, whichfor practical reasons is defined as the temperature at which thecurrent density exceeds 100 A/cm2for 60 s. Pitting on thespecimen is confirmed visually after the test.5. Significance and Use5.1 This test method provides a prediction of the
21、resistanceto stable propagating pitting corrosion of stainless steels andrelated alloys in a standard medium (see Note 1). The CPT testcan be used for product acceptance, alloy development studies,and manufacturing control. In the case of product acceptance,the supplier and user must agree upon the
22、preconditioning ofthe specimen with regard to surface finish. The test is notintended for design purposes since the test conditions acceler-ate corrosion in a manner that does not simulate any actualservice environment.5.2 Another method to determine the potential independentCPT with an electrochemi
23、cal technique has been discussed inthe literature (1-4). This test method involves a potentiody-namic (potential sweep) procedure performed on specimens atdifferent temperatures. A comparison (2) of the test methoddescribed in this test method and the potentiodynamic tech-nique has indicated no diff
24、erence in the test result obtained.6. Apparatus6.1 The apparatus necessary for determining the CPT con-sists of instruments for measuring electronic signals, a tem-perature controlling apparatus, a specimen holder, and a testcell. The instruments for measuring electronic signals may beintegrated int
25、o one instrument package or may be individualcomponents. Either form of instrumentation can provide ac-ceptable data. Typical test equipment consists of the following:(1) potentiostat (2) potential measuring instrument (3) currentmeasuring instrument (4) temperature controller (5) tempera-ture measu
26、ring instrument (6) test cell (7) specimen holder, and(8) electrodes.6.2 PotentiostatThe potentiostat shall be able to apply theconstant potential to within 1 mV at a current density of 10mA/cm2. The applied potential is changed either automaticallyor manually by shifting the potential from the open
27、 circuitpotential to another more noble potential.6.3 Potential Measuring InstrumentRequirements shallbe in accordance with the section on Potential MeasuringInstruments in Test Method G5.6.4 Current Measuring InstrumentsAn instrument that iscapable of measuring a current accurately to within 5 % of
28、 theactual value. The typical current densities encountered duringthe CPT test are in the range of 1 A/cm2to 10 mA/cm2.6.5 Temperature Controller:6.5.1 Thermostat equipment is required that can providecooling and heating of the test solution in the temperaturerange from 0C to approximately 100C. Fur
29、ther, the tempera-ture controller is used to provide controlled heating, whichgives the test solution temperature a temperature increase rateof 1C/min in the range from 0C to approximately 100C.6.5.2 Above 10C, the average rate of temperature changeof the test solution shall be 1.0 6 0.3C/min, where
30、 the averageis calculated over a temperature range of 10C.6.6 Temperature Measurement Instrumentation, shall becapable of measuring the temperature of the test solution withan accuracy of 60.4C.6.7 Test Cell:6.7.1 Option 1, G5 TypeThe test cell should be similar tothe one described in Test Method G5
31、. Other similar polariza-tion cells may be equally suitable. The gas purger shoulddistribute the gas in numerous small bubbles.6.7.2 Option 2, Flushed-port CellThis cell design is basedon that published by R. Qvarfort (3) and includes the specimenholder in the design. The advantages of this cell des
32、ign are thatthe specimen edges and back do not need to be machined, thespecimen does not have to be mounted inside the cell, andcrevice corrosion at the contact area of the cell port isFIG. 1 Determination of CPTG150 99 (2010)2completely eliminated, even at elevated test temperatures. SeeAppendix X2
33、 for a description of this cell. The gas purgershould distribute the gas in numerous small bubbles.6.7.3 The test cell shall be able to contain a test solutionvolume of minimum 100 mL per square centimetre test area. Amaximum dilution of 15 % of the test solution during the testperiod is allowed in
34、case a flushed port cell or similararrangement is used.6.8 Specimen Holder:6.8.1 Any part of the specimen holder coming in contactwith the test solution during testing shall be made of an inertmaterial, and any seal shall not allow leakage of electrolyte.6.8.2 The specimen holder shall have a design
35、 that ensuresno occurrence of crevice corrosion at the contact area betweenspecimen holder and specimen.6.8.3 Two examples of specimen holder designs in accor-dance with this standard are shown in Appendix X2 andAppendix X3. The major difference between the specimenholder designs lies in the allowab
36、le specimen geometry and thenumber of surfaces on the specimen that are being testedsimultaneously.6.9 Electrodes:6.9.1 Auxiliary (Counter) ElectrodeRequirements shallbe in accordance with the section Auxiliary Electrodes in TestMethod G5 with the exception that only one counter electrodeis necessar
37、y for CPT testing. The electrode material shall be ofa type which can be considered inert under the test conditions.6.9.2 Reference ElectrodeThe reference electrode shall bekept at room temperature outside the actual test cell. Thereference electrode shall be capable of ensuring a constantreference
38、potential within 65 mV during the entire testprocedure (see Note 2). Electrical contact to the test solutionshall be provided by the use of a luggin capillary placed in thetest solution. Requirements shall otherwise be in accordancewith the section on Reference Electrode in Test Method G5.NOTE 2It m
39、ay be difficult to ensure a fully constant referencepotential due to the large variations in temperature of the test solution;therefore, the allowable is 65 mV. This does, however, not affect themeasured potential independent CPT (1).7. Test Specimens7.1 FinishAny geometry and surface finish (see No
40、te 3)compatible with the chosen specimen holder as specified in 6.8may be used.NOTE 3The state of the surface may be dependent on the time andlocation of storage between the final mechanical or chemical surfacetreatment and testing. The time and location of storage may, therefore, insome situations
41、be considered an integral part of the surface finish.7.2 SamplingWhen using this test method to meet productacceptance criteria, the means of sampling of a test specimenshall be decided by agreement between the parties involved.7.3 Test AreaA minimum test area of 1 cm2shall be used.7.4 Specimens rem
42、oved from a work piece or component byshearing, cutting, burning, and so forth shall have the affectededges removed by grinding or machining, unless it is explicitlyintended to study the effects of these edge factors.8. Reagents and Materials8.1 Purity of ReagentsReagent grade chemicals shall beused
43、 in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.5Other grades may be used,provided it is first ascertained that the reagent is of su
44、fficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.8.2 Purity of WaterUnless otherwise indicated, referencesto 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
45、sodiumchloride (NaCl) solution, dissolve 58.45 g sodium chloride(NaCl) in purified water to a total solution volume of 1 L. Thesolution can be made up in bulk and stored for one month atroom temperature.8.4 Purging GasNitrogen gas of minimum 99.99 % purityshould be used.9. Applied Potential9.1 Stand
46、ard PotentialAn anodic potential of 700 mVversus SCE (25C) is used. This has been found appropriate formost stainless steels (1).9.2 Alternative Potential:9.2.1 If uncertainty exists concerning whether the standardpotential is sufficiently high to obtain the potential independentCPT, a test at 800 m
47、V versus SCE (25C) may be performed.A significant deviation between the CPT obtained at 700 mVand 800 mV will indicate a need for a reevaluation and newchoice of potential.NOTE 4Using a lower potential than the standard potential of 700 mVversus SCE (25C) is fully acceptable, provided the determined
48、 CPT stillis potential independent. To change the measurement range provided bythe standard test conditions, a new test solution composition will have tobe chosen. Following the choice of test solution, a test potential thatensures the determination of a potential independent CPT will have to bedete
49、rmined.9.2.2 Evaluation of differences in obtained CPT at the twopotentials should take into account the repeatability of the testmethod. The homogeneity of the material used for the twodifferent potentials shall also be considered before an alterna-tive potential is used.10. Procedure10.1 Sample Mounting, Cleaning and Placement:10.1.1 The recommendations given in Practice G1 are to befollowed, where applicable, unless otherwise stated in thisprocedure.10.1.2 Clean the specimen just before immersion in theelectrolyte by degreasing with a sui
