1、Designation: G61 86 (Reapproved 2018)Standard Test Method forConducting Cyclic Potentiodynamic PolarizationMeasurements for Localized Corrosion Susceptibility ofIron-, Nickel-, or Cobalt-Based Alloys1This standard is issued under the fixed designation G61; the number immediately following the design
2、ation 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.1. Scope1.1 This test method covers a procedure
3、for conductingcyclic potentiodynamic polarization measurements to deter-mine relative susceptibility to localized corrosion (pitting andcrevice corrosion) for iron-, nickel-, or cobalt-based alloys in achloride environment. This test method also describes anexperimental procedure which can be used t
4、o check onesexperimental technique and instrumentation.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.3 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is therespon
5、sibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with internationally recognized principles on standard-izat
6、ion established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D1193 Specification for Reagent WaterG3 Practice for C
7、onventions Applicable to ElectrochemicalMeasurements in Corrosion TestingG5 Reference Test Method for Making PotentiodynamicAnodic Polarization Measurements2.2 ASTM Adjuncts:Standard Samples (set of two)33. Significance and Use3.1 An indication of the susceptibility to initiation of local-ized corro
8、sion in this test method is given by the potential atwhich the anodic current increases rapidly. The more noble thispotential, obtained at a fixed scan rate in this test, the lesssusceptible is the alloy to initiation of localized corrosion. Theresults of this test are not intended to correlate in a
9、 quantitativemanner with the rate of propagation that one might observe inservice when localized corrosion occurs.3.2 In general, once initiated, localized corrosion can propa-gate at some potential more electropositive than that at whichthe hysteresis loop is completed. In this test method, thepote
10、ntial at which the hysteresis loop is completed is deter-mined at a fixed scan rate. In these cases, the more electro-positive the potential at which the hysteresis loop is completedthe less likely it is that localized corrosion will occur.3.3 If followed, this test method will provide cyclic poten-
11、tiodynamic anodic polarization measurements that will repro-duce data developed at other times in other laboratories usingthis test method for the two specified alloys discussed in 3.4.The procedure is used for iron-, nickel-, or cobalt-based alloysin a chloride environment.3.4 A standard potentiody
12、namic polarization plot is in-cluded. These reference data are based on the results from fivedifferent laboratories that followed the standard procedure,using specific alloys of Type 304 stainless steel, UNS S30400and Alloy C-276, UNS N10276.3Curves are included whichhave been constructed using stat
13、istical analysis to indicate theacceptable range of polarization curves.3.5 The availability of a standard test method, standardmaterial, and standard plots should make it easy for aninvestigator to check his techniques to evaluate susceptibilityto localized corrosion.1This test method is under the
14、jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved May 1, 2018. Published June 2018. Originallyapproved in 1986. Last previous edition approved in 2014 as G61 86
15、 (2014). DOI:10.1520/G0061-86R18.2For 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.3Available from ASTM Interna
16、tional Headquarters. Order Adjunct No.ADJG0061. Original adjunct produced before 1995.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on
17、 standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.14. Apparatus4.1 The polarization cell should be similar to the onedescribed in Refe
18、rence Test Method G5. Other polarizationcells may be equally suitable.4.1.1 The cell should have a capacity of about 1 L andshould have suitable necks or seals to permit the introductionof electrodes, gas inlet and outlet tubes, and a thermometer.The Luggin probe-salt bridge separates the bulk solut
19、ion fromthe saturated calomel reference electrode. The probe tip shouldbe adjustable so that it can be brought into close proximity withthe working electrode.4.2 Specimen Holder:4.2.1 Specimens should be mounted in a suitable holderdesigned for flat strip, exposing 1 cm2to the test solution (Fig.1).
20、 Such specimen holders have been described in the litera-ture.4It is important that the circular TFE-fluorocarbon gasketbe drilled and machined flat in order to minimize crevices.4.3 Potentiostat (Note 1)A potentiostat that will maintainan electrode potential within 1 mV of a preset value over awide
21、 range of applied currents should be used. For the type andsize of standard specimen supplied, the potentiostat shouldhave a potential range of 1.0 to +1.6 V and an anodic currentoutput range of 1.0 to 105A. Most commercial potentiostatsmeet the specific requirements for these types of measure-ments
22、.NOTE 1These instrumental requirements are based upon valuestypical of the instruments in the five laboratories that have provided thedata used in determining the standard polarization plot.4.4 Potential-Measuring Instruments (Note 1)Thepotential-measuring circuit should have a high input imped-ance
23、 on the order of 1011to 1014 to minimize current drawnfrom the system during measurements. Instruments shouldhave sufficient sensitivity and accuracy to detect a change inpotential of 61 mV, usually included in commercial poten-tiostats. An output as a voltage is preferred for recordingpurposes.4.5
24、Current-Measuring Instruments (Note 1)An instru-ment that is capable of measuring a current accurately to within1 % of the absolute value over a current range between 1.0 and105Ashould be used. Many commercial units have a build-ininstrument with an output as a voltage, which is preferred forrecordi
25、ng purposes. For the purpose of the present test alogarithmic output is desirable.4.6 Anodic Polarization CircuitA scanning potentiostat isused for potentiodynamic measurements. Potential and currentare plotted continuously using an X-Y recorder and a logarith-mic converter (contained in the potenti
26、ostat or incorporatedinto the circuit) for the current. Commercially available unitsare suitable.4.7 Electrodes:4.7.1 The standard Type 304 stainless steel (UNS S30400)and Alloy C-276 (UNS N10276) should be machined into flat0.625-in. (14-mm) diameter disks. The chemical compositionsof the alloys us
27、ed in the round robin are listed in Table 1.4.7.2 Counter ElectrodesThe counter electrodes may beprepared as described in Reference Test Method G5 or may beprepared from high-purity platinum flat stock and wire. Asuitable method would be to seal the platinum wire in glasstubing and introduce the pla
28、tinum electrode assembly througha sliding seal. Counter electrodes should have an area at leasttwice as large as the test electrode.4.7.3 Reference Electrode5A saturated calomel electrodewith a controlled rate of leakage (about 3 L/h) is recom-mended. This type of electrode is durable, reliable, and
29、commercially available. Precautions should be taken to ensure4France, W. D., Jr., Journal of the Electrochemical Society, Vol 114, 1967, p.818; and Myers, J. R., Gruewlar, F. G., and Smulezenski, L. A., Corrosion, Vol 24,1968, p. 352.5Ives, D. J., and Janz, G. J., Reference Electrodes, Theory and Pr
30、actice,Academic Press, New York, NY, 1961.FIG. 1 Schematic Diagram of Specimen Holder (see Footnotes 3and 4)TABLE 1 Chemical Composition of Alloys Used in the RoundRobin, Weight %ElementAlloy C-276(UNS N10276)Type 304Stainless Steel(UNS S30400)Carbon 0.003 0.060Chromium 15.29 18.46Cobalt 2.05 .Colum
31、bium . 0.11Copper . 0.17Iron 5.78 balanceManganese 0.48 1.43Molybdenum 16.03 0.17Nickel balance 8.74Phosphorus 0.018 0.029Silicon 0.05 0.60Sulfur 0.006 0.014Vanadium 0.20 .Tungsten 3.62 .G61 86 (2018)2that it is maintained in the proper condition. The potential ofthe calomel electrode should be chec
32、ked at periodic intervals toensure the accuracy of the electrode.5. Reagents and Materials5.1 Purity of ReagentsReagent grade chemicals shall beused in all tests. Unless otherwise indicated, it is intended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents
33、of the American Chemical Society,where such specifications are available.6Other grades may beused, provided it is first ascertained that the reagent is ofsufficiently high purity to permit its use without lessening theaccuracy of the determination.5.2 Purity of WaterThe water shall be distilled or d
34、eion-ized conforming to the purity requirements of SpecificationD1193, Type IV reagent water.5.3 Sodium Chloride (NaCl).5.4 Samples of Standard Type 304 stainless steel (UNSS30400) and theAlloy C-276 (UNS N10276) used in obtainingthe standard reference plot are available for those who wish tocheck t
35、heir own test procedure and equipment.6. Procedure6.1 Test Specimen Preparation:6.1.1 Wet grind with 240-grit SiC paper, wet polish with600-grit SiC paper until previous coarse scratches are removed,rinse, and dry.6.1.2 Prior to assembly of the specimen holder, ultrasoni-cally degrease the specimen
36、for 5 min in detergent and water,rinse thoroughly in distilled water, and dry.6.1.3 Mount the specimen in the electrode holder. Tightenthe assembly until the TFE-fluorocarbon gasket is sufficientlycompressed to avoid leakage in the gasket.6.2 Prepare a 3.56 % (by weight) sodium chloride solutionby d
37、issolving 34 g of reagent grade NaCl in 920 mLof distilledwater.6.3 Assemble the electrode holder and place in the polar-ization cell. Transfer 900 mLof test solution to the polarizationcell, ensuring that the specimen remains above the solutionlevel.6.4 Bring the temperature of the solution of 25 6
38、 1C byimmersing the test cell in a controlled-temperature water bathor by other convenient means.6.5 Place the platinum auxiliary electrodes, salt-bridgeprobe, and other components in the test cell. Fill the salt bridgewith test solution and locate the probe tip approximately 1 mmfrom the working el
39、ectrode.NOTE 2The levels of the solution in the reference and polarizationcells should be the same. If this is impossible, a closed solution-wet (notgreased) stopcock can be used in the salt bridge to eliminate siphoning.6.6 Purge the solution sufficiently with an appropriate gas toremove oxygen bef
40、ore specimen immersion (minimum of 1 h).6.7 Immerse the specimen for 1 h before initiating polariza-tion. A sliding seal can be used to ensure that an oxygen-freeenvironment is maintained while the specimen is lowered. It isimportant that all oxygen be removed by purging prior topolarization, otherw
41、ise, more noble initial corrosion potentialvalues will be observed.6.8 Record the platinum potential 50 min after immersion ofthe specimen. Record the open-circuit specimen potential, thatis, the corrosion potential, the instant before beginning polar-ization.6.9 Potential ScanStart the potential sc
42、an 1 h after speci-men immersion, beginning at the corrosion potential (Ecorr),and scan in the more noble direction at a scan rate of 0.6 V/h(65 %). Record the current continuously with change inpotential on an X-Y recorder using semilogarithmic paper.6.9.1 The onset of localized corrosion is usuall
43、y marked bya rapid increase of the anodic current at potentials below theoxygen-evolution potential. When the current reaches 5 mA(5103A), reverse the scanning direction (toward moreactive potentials).6.9.2 Continue the reverse scan until the hysteresis loopcloses or until the corrosion potential is
44、 reached.6.10 Plot anodic polarization data on semilogarithmic paperin accordance with Practice G3 (potential-ordinate, currentdensity-abscissa). A plot of representative polarization curvesgenerated by the practice is shown in Fig. 2.7. Interpretation of Results7.1 The polarization curves shown in
45、Fig. 2, Fig. 3, and Fig.4 indicate that initiation and propagation of localized corrosionoccurs at potentials more electronegative than the oxygenevolution potential on Type 304 stainless steel (UNS S30400)in the chloride environment. The curve for Alloy C-276 (UNSN10276) is not a result of localize
46、d corrosion but of uniformcorrosion in the transpassive or oxygen evolution region. Sincethe corrosion potentials (Ecorrvalues) for Alloy C-276 (UNSN10276) and Type 304 stainless steel (UNS S30400) areusually similar, these curves indicate that Alloy C-276 is moreresistant to initiation and propagat
47、ion of localized corrosionthan Type 304 stainless steel.8. Precision and Bias8.1 A standard polarization plot, based on the potentiody-namic data from five different laboratories, has been prepared.The plot has been separated into the forward (Fig. 3) andreverse (Fig. 4) scans for clarity. These plo
48、ts show the meanvalues and a range of 62 standard deviations.8.2 The spread in data obtained from a number of labora-tories and used in the preparation of the standard plot (Fig. 3and Fig. 4) demonstrates the reproducibility that is possiblewhen a standard procedure is followed. An investigators dat
49、ashould fall within the range of 62 standard deviations sincethis includes 95 % of all data provided random variations arethe only source of error. No information is available on the6Reagent Chemicals, American Chemical Society Specifications, AmericanChemical Society, Washington, DC. For Suggestions on the testing of reagents notlisted by the American Chemical Society, see Annual Standards for LaboratoryChemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeiaand National Formulary, U.S. Pharmacopeial Convention, Inc. (USPC), Rockville,MD.G61
