1、Designation: G 150 99 (Reapproved 2004)Standard Test Method forElectrochemical Critical Pitting Temperature Testing ofStainless Steels1This standard is issued under the fixed designation G 150; the number immediately following the designation indicates the year oforiginal adoption or, in the case of
2、 revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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
3、 related 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 1Examp
4、les of CPT measurements on sheet, plate, tubing, andwelded specimens for various stainless steels can be found in Ref. (1).2See the research reports (Section 14).1.3 The standard parameters recommended in this testmethod are suitable for characterizing the CPT of austeniticstainless steels and other
5、 related 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
6、 a CPT 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.1.6 This standard does not purport to address all of thesafety concerns, i
7、f 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 Standards:D 1193 Specification for Reagent WaterE 177 Pra
8、ctice for Use of the Terms Precision and Bias inASTM Test MethodsE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG3 Practice for ConventionsApplicable to ElectrochemicalMeasu
9、rements in Corrosion TestingG5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG15 Terminology Relating to Corrosion and CorrosionTestingG46 Guide for Examination and Evaluation of PittingCorrosionG 107 Guide for Formats for Collection and Compilati
10、on 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 conditions indicated by a rapidincrease beyond a set limit of
11、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 X1.3.1.3 potential independent CPT the CPT determined at apot
12、ential above the pitting potential range, but below thetranspassive potential; see also Appendix X1.3.1.4 potential dependent CPTthe CPT determined at apotential within the pitting potential range of the testedmaterial; see also Appendix X1.3.1.5 temperature rampthe rate (C/min) at which the testtem
13、perature is increased during the test.3.2 sign conventionsthe sign conventions used in thisprocedure are in agreement with Practice G3.1This test method is under the jurisdiction of G01 on Corrosion of Metals and isthe direct responsibility of Subcommittee G01.11 on Electrochemical Measurementsin Co
14、rrosion Testing.Current edition approved Nov. 1, 2004. Published November 2004. Originallyapproved in 1997. Last previous edition approved in 1999 as G 150 99.2The boldface numbers in parenthesis refer to the list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbo
15、r Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.3 Unless otherwise stated, this test method uses thegeneral terminology relating to corrosion and corrosion testingas defined in Terminology G15.4. Summary of Test Method4.1 The test method determines the potential independentcr
16、itical 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. 1). The specimen is exposed, either entirely or in part,depending on test cell configuration to a 1M NaCl solu
17、tion,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 isanodically polarized to a potential above the pitting potentialrange. This potential is held constant during the whol
18、e 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 the temperature at which the current increases rapidly, whichfor practical reasons is defined as the temperature
19、 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 resistanceto stable propagating pitting corrosion of stainless steels andrelated alloys in a standard medium (s
20、ee 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 preconditioning ofthe specimen with regard to surface finish. The test is notintended for design purposes since
21、 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 electrochemical technique has been discussed inthe literature (1-4). This test method involves a potentiody-namic (potentia
22、l 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 difference in the test result obtained.6. Apparatus6.1 The apparatus necessary for determining the CPT con-sists of
23、 instruments for measuring electronic signals, a tem-perature controlling apparatus, a specimen holder, and a testcell. The instruments for measuring electronic signals may beintegrated into one instrument package or may be individualcomponents. Either form of instrumentation can provide ac-ceptable
24、 data. Typical test equipment consists of the following:(1) potentiostat (2) potential measuring instrument (3) currentmeasuring instrument (4) temperature controller (5) tempera-ture measuring instrument (6) test cell (7) specimen holder, and(8) electrodes.6.2 PotentiostatThe potentiostat shall be
25、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 circuitpotential to another more noble potential.6.3 Potential Measuring InstrumentRequirements shallbe in acc
26、ordance 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 theactual value. The typical current densities encountered duringthe CPT test are in the range of 1 A/cm2to 10
27、 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. Further, the tempera-ture controller is used to provide controlled heating, whichgives the test solution temperatu
28、re 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 the averageis calculated over a temperature range of 10C.6.6 Temperature Measurement Instrumentation, shall be
29、capable 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. Other similar polariza-tion cells may be equally suitable. The gas purger shoulddistribute the gas in numerou
30、s 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 design are thatthe specimen edges and back do not need to be machined, thespecimen does not have to be mounted ins
31、ide the cell, andcrevice corrosion at the contact area of the cell port iscompletely eliminated, even at elevated test temperatures. SeeAppendix X2 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 so
32、lutionvolume of minimum 100 mL per square centimetre test area. Amaximum dilution of 15 % of the test solution during the testperiod is allowed in case a flushed port cell or similararrangement is used.6.8 Specimen Holder:FIG. 1 Determination of CPTG 150 99 (2004)26.8.1 Any part of the specimen hold
33、er 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 that ensuresno occurrence of crevice corrosion at the contact area betweenspecimen holder and specimen.6.8.3
34、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 allowable specimen geometry and thenumber of surfaces on the specimen that are being testedsimultaneously.6.9 Electro
35、des:6.9.1 Auxiliary (Counter) ElectrodeRequirements shallbe in accordance with the section Auxiliary Electrodes in TestMethod G5with the exception that only one counter electrodeis necessary for CPT testing. The electrode material shall be ofa type which can be considered inert under the test condit
36、ions.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 potential within 65 mV during the entire testprocedure (see Note 2). Electrical contact to the test solutionsha
37、ll 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 may be difficult to ensure a fully constant referencepotential due to the large variations in temperature of the
38、 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 Note 3)compatible with the chosen specimen holder as specified in 6.8may be used.NOTE 3The state of the surface m
39、ay 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 be considered an integral part of the surface finish.7.2 SamplingWhen using this test method to meet productacc
40、eptance 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 removed from a work piece or component byshearing, cutting, burning, and so forth shall have the affectededges rem
41、oved 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 in all tests. Unless otherwise indicated, it is intended thatall reagents conform to the specifications of the
42、 Committee onAnalytical Reagents of the American Chemical Society wheresuch specifications are available.3Other grades may be used,provided it is first ascertained that the reagent is of sufficientlyhigh purity to permit its use without lessening the accuracy ofthe determination.8.2 Purity of WaterU
43、nless otherwise indicated, referencesto purified water shall be understood to mean reagent water asdefined by Type IV of Specification D 1193.8.3 Standard Test SolutionTo prepare 1 L of 1 M sodiumchloride (NaCl) solution, dissolve 58.45 g sodium chloride(NaCl) in purified water to a total solution v
44、olume 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 Standard PotentialAn anodic potential of 700 mVversus SCE (25C) is used. This has been found appropriate formost st
45、ainless 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 mV versus SCE (25C) may be performed.A significant deviation between the CPT obtained at 700 mVand 800 mV will
46、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 CPT stillis potential independent. To change the measurement range provided bythe standard test conditions, a
47、 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 bedetermined.9.2.2 Evaluation of differences in obtained CPT at the twopotentials should take into account the repea
48、tability 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 G1are to befollowed, where applica
49、ble, unless otherwise stated in thisprocedure.10.1.2 Clean the specimen just before immersion in theelectrolyte by degreasing with a suitable detergent, rinsing inpurified water, followed by ethanol or similar solvent, and airdrying. After degreasing, handle the specimen with clean3Reagent Chemicals, American Chemical Society Specifications , AmericanChemical Society, Washington, DC. For suggestions on the testing of reagents notlisted by the American Chemical Society, see Analar Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K.
