ASTM G61-1986(2009) Standard Test Method for Conducting Cyclic Potentiodynamic Polarization Measurements for Localized Corrosion Susceptibility of Iron- Nickel- or Cobalt-Based All.pdf

1、Designation: G 61 86 (Reapproved 2009)Standard Test Method forConducting Cyclic Potentiodynamic PolarizationMeasurements for Localized Corrosion Susceptibility ofIron-, Nickel-, or Cobalt-Based Alloys1This standard is issued under the fixed designation G 61; the number immediately following the desi

2、gnation 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 procedur

3、e 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

4、 to 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 theresp

5、onsibility 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:2D 1193 Specification for Reagent WaterG3 Practice for ConventionsApplicable to Electrochemi

6、calMeasurements in Corrosion TestingG5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic 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 corrosion in this test

7、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 quantitativemanne

8、r 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, thepotential at which the

9、 hysteresis loop is completed is deter-mined at a fixed scan rate. In these cases, the more electrop-ositive 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-tiodynamic anodic

10、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 potentiodynamic polarization

11、 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 statistical analysis t

12、o 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.4. Apparatus4.1 The polarization cell should be s

13、imilar to the onedescribed in Reference 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-sa

14、lt bridge separates the bulk solution fromthe saturated calomel reference electrode. The probe tip shouldbe adjustable so that it can be brought into close proximity withthe working electrode.1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the direct re

15、sponsibility of Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved May 1, 2009. Published May 2009. Originallyapproved in 1986. Last previous edition approved in 2003 as G 6186(2003)1.2For referenced ASTM standards, visit the ASTM website, www.astm.org,

16、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 International Headquarters. Order Adjunct No.ADJG0061. Original adjunct produced before 1995.1Copyright ASTM I

17、nternational, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.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). Such specimen holders have been described in the litera-tur

18、e.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 range of applied currents should be used. For the type ands

19、ize 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.NOTE 1These instrumental requirements are based upon values

20、 typi-cal of the instruments in the five laboratories that have provided the dataused in determining the standard polarization plot.4.4 Potential-Measuring Instruments (Note 1)Thepotential-measuring circuit should have a high input imped-ance on the order of 1011to 1014V to minimize current drawnfro

21、m 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 Current-Measuring Instruments (Note 1)An instru-ment that

22、 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 forrecording purposes. For the purpose of the present test alogarit

23、hmic output is desirable.4.6 Anodic Polarization CircuitAscanning potentiostat isused for potentiodynamic measurements. Potential and currentare plotted continuously using an X-Y recorder and a logarith-mic converter (contained in the potentiostat or incorporatedinto the circuit) for the current. Co

24、mmercially 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 used in the round robin are listed in Table 1.4.7.2 Counter

25、ElectrodesThe counter electrodes may beprepared as described in Reference Test Method G5or may beprepared from high-purity platinum flat stock and wire. Asuitable method would be to seal the platinum wire in glasstubing and introduce the platinum electrode assembly througha sliding seal. Counter ele

26、ctrodes 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, andcommerically available. Precautions should be taken to ensu

27、rethat it is maintained in the proper condition. The potential ofthe calomel electrode should be checked 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 in

28、tended thatall reagents shall conform to the specifications of the Commit-tee on Analytical Reagents of the American Chemical Society,4France, 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

29、. 352.5Ives, D. J., and Janz, G. J., Reference Electrodes, Theory and Practice,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 S

30、teel(UNS S30400)Carbon 0.003 0.060Chromium 15.29 18.46Cobalt 2.05 .Columbium . 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 .G 61 86 (2009)2where such specifications

31、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 deion-ized conforming to the purity requirements of Specific

32、ationD 1193, 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 their own test procedure and equipment.6. Procedure6.1 Test

33、 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 for 5 min in detergent and water,rinse thoroughly in disti

34、lled 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 dissolving 34 g of reagent grade NaCl in 920 mLof distilled

35、water.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 1C byimmersing the test cell in a controlled-temperature

36、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 electrode.NOTE 2The levels of the solution in the reference

37、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 before specimen immersion (minimum of 1 h).6.7 Immerse the sp

38、ecimen 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, otherwise, more noble initial corrosion potentialvalues will be

39、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 scan 1 h after speci-men immersion, beginning at the corrosi

40、on 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 usually marked bya rapid increase of the anodic current at poten

41、tials below theoxygen-evolution potential. When the current reaches 5 mA(5 3 103A), reverse the scanning direction (toward moreactive potentials).6.9.2 Continue the reverse scan until the hysteresis loopcloses or until the corrosion potential is reached.6.10 Plot anodic polarization data on semiloga

42、rithmic 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 Fig. 2, Fig. 3, and Fig.4 indicate that initiation and

43、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 localized corrosion but of uniformcorrosion in the transpassive

44、 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 propagation of localized corrosionthan Type 304 stainless steel

45、.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 plots show the meanvalues and a range of 62 standard devia

46、tions.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 datashould fall within the range of 62 standard deviations

47、 sincethis includes 95 % of all data provided random variations arethe only source of error. No information is available on therepeatability when one laboratory conducts several identicaltests. Crevice corrosion under gaskets may lead to erroneousresults.8.3 When testing iron-, nickel-, and cobalt-b

48、ased alloysaccording to this test method, the repeatability and reproduc-ibility would be expected to be similar to the standard material.However, no data is currently available on other alloys.8.4 This test method, when conducted in accordance withthe procedures described herein, ranks some iron-,

49、nickel-, andcobalt-based alloys relative to their resistance to crevice andpitting corrosion in chloride-containing environments, such as6Reagent 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.G 61 86 (2009)3seawater. The test method will no