ASTM G192-2008 Standard Test Method for Determining the Crevice Repassivation Potential of Corrosion-Resistant Alloys Using a Potentiodynamic-Galvanostatic-Potentiostatic Technique.pdf

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1、Designation: G 192 08Standard Test Method forDetermining the Crevice Repassivation Potential ofCorrosion-Resistant Alloys Using a Potentiodynamic-Galvanostatic-Potentiostatic Technique1This standard is issued under the fixed designation G 192; the number immediately following the designation indicat

2、es the year oforiginal adoption or, in the case 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 condu

3、ctinganodic polarization studies to determine the crevice repassiva-tion potential for corrosionresistant alloys. The concept of therepassivation potential is similar to that of the protectionpotential given in Reference Test Method G5.1.2 The test method consists in applying successively po-tentiod

4、ynamic, galvanostatic, and potentiostatic treatments forthe initial formation and afterward repassivation of crevicecorrosion.1.3 This test method is a complement to Test Method G61.1.4 The values stated in SI units are to be regarded as thestandard. The values given in parentheses are for informati

5、ononly.1.5 This standard does 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. Refer

6、enced Documents2.1 ASTM Standards:2B 575 Specification for Low-Carbon Nickel-Chromium-Molybdenum, Low-Carbon Nickel-Chromium-Molybdenum-Copper, Low-Carbon Nickel-Chromium-Molybdenum-Tantalum, and Low-Carbon Nickel-Chromium-Molybdenum-Tungsten Alloy Plate, Sheet, andStripD 1193 Specification for Reag

7、ent WaterE 691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG5 Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG15 Terminology

8、 Relating to Corrosion and CorrosionTestingG48 Test Methods for Pitting and Crevice Corrosion Re-sistance of Stainless Steels and Related Alloys by Use ofFerric Chloride SolutionG61 Test Method for Conducting Cyclic PotentiodynamicPolarization Measurements for Localized Corrosion Sus-ceptibility of

9、Iron-, Nickel-, or Cobalt-Based AlloysG78 Guide for Crevice Corrosion Testing of Iron-Base andNickel-Base Stainless Alloys in Seawater and OtherChloride-Containing Aqueous Environments3. Terminology3.1 DefinitionsFor definitions of corrosion-related termsused in this test method, see Terminology G15

10、.4. Summary of Test Method4.1 This anodic polarization test method combines tech-niques such as potentiodynamic, galvanostatic, and potentio-static polarization methods. This test method is called theTsujikawa-Hisamatsu Electrochemical (THE) test method tohonor the two precursors of this technique (

11、see 1 and 2).3Thenew technique will be called the THE test method. This newTHE test method is more time-consuming than the alreadywell-established cyclic potentiodynamic polarization (CPP)described in Test Method G61.4.2 The THE test method can be used with any corrosion-resistant alloy, but it was

12、developed by studying Alloy 22(UNS N06022). The composition and other properties of Alloy22 are given in Specification B 575. Alloy 22 is a nickelbasedalloy containing approximately 22wt% Cr, 13wt% Mo, 3wt%W and 3wt% Fe. The THE test method is a complement to thecyclic potentiodynamic polarization (

13、CPP) described in TestMethod G61. CPP may be used as a first fast screening methodand THE test method for fine-tuning the repassivation potentialfor crevice corrosion when the environment is not highly1This test method is under the jurisdiction of ASTM Committee G01 onCorrosion of Metals and is the

14、direct responsibility of Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved May 1, 2008. Published May 2008.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMS

15、tandards volume information, refer to the standards Document Summary page onthe ASTM website.3The boldface numbers in parentheses refer to a list of references at the end ofthis standard.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United State

16、s.aggressive (3-6). The THE test method has also been applied toother highly corrosionresistant alloys, such as Titanium grade7 (Ref 7).4.3 The THE test method can be used with any electrolytesolution. A standard 1 M NaCl solution at 90C or lowertemperature may be used to compare alloys of interest.

17、 Theround robin described in Section 15 was carried out in 1 MNaCl solution at 90C.4.4 The test involves in polarizing the test electrode in threesteps:4.4.1 Step 1The test electrode is polarized potentiody-namically at a rate of 0.168 mV/s (as in Test Method G61)starting at or slightly below the co

18、rrosion potential until apreset current (or current density) is reached (for example,2 A/cm2). After this initial potentiodynamic polarization, thepolarization control is changed to galvanostatic mode (Step 2).4.4.2 Step 2The preset current of 2 A/cm2is keptconstant for a 2-h period to develop and g

19、row a crevicecorroded area (if any develops). During the galvanostatic Step2, the potential output is monitored.4.4.3 Step 3The polarization control is shifted to thepotentiostatic mode. The potential at the end of the galvano-static hold (Step 2) is read, and then 10 mV are subtracted. Theresulting

20、 value of potential is applied for a 2-h period while thecurrent output is monitored. Then successive potentiostatictreatments are applied, each time at 10 mV lower than theprevious treatment. A total of 10-15 potentiostatic treatmentsare usually required to finish Step 3.4.5 The crevice repassivati

21、on potential (ER,CREV) is thehighest potential in Step 3 for which current density does notincrease as a function of time. It is understood that at apotential below ER,CREV the alloy will not develop crevicecorrosion under the tested conditions.5. Significance and Use5.1 The THE test method is desig

22、ned to provide highlyreproducible crevice repassivation potentials for corrosionre-sistant alloys (for example, Alloy 22) in a wide range ofenvironments from non-aggressive to highly aggressive. Inconditions of low environmental aggressiveness (such as lowtemperature or low chloride concentration),

23、corrosionresistantalloys such as Alloy 22 will resist crevice corrosion initiationand the cyclic potentiodynamic polarization test (Test MethodG61) may fail to promote crevice corrosion mainly because itdrives the alloy into transpassive dissolution instead of nucle-ating crevice corrosion. The THE

24、test method provides a morecontrolled way of applying the electrical charge to the testelectrode, which may induce crevice corrosion without movingit into transpassive potentials.5.2 The more noble this crevice corrosion repassivationpotential (ER,CREV) value, the more resistant the alloy is tocrevi

25、ce corrosion in the tested electrolyte. This is similar toother test methods to measure localized corrosion resistancesuch as Test Method G61and Test Methods G48. The resultsfrom this test method are not intended to correlate in aquantitative manner with the rate of propagation that one mightobserve

26、 in service when localized corrosion occurs.5.3 This test method may be used to rank several alloys byusing the same testing electrolyte and temperature. It can alsobe used to determine the response of a given alloy when theenvironmental conditions (such as electrolyte composition andtemperature) ch

27、ange.6. Apparatus6.1 CellThe polarization cell should be similar to the onedescribed in Reference Test Method G5 and Test MethodG61. Other polarization cells may be equally suitable. The cellshould have a capacity of about 1 L and should have suitablenecks or seals to permit the introduction of elec

28、trodes, gas inletand outlet tubes, and a thermometer or thermocouple. TheLuggin probe-salt bridge separates the bulk solution from thesaturated calomel or saturated silver chloride reference elec-trode.6.2 Test Electrode (Specimen) HolderThe test electrodeholder and the mounting rod should be simila

29、r to the onedescribed in Figure 5 in Reference Test Method G5(repro-duced in Fig. 1). A leakproof PTFE compression gasket, asdescribed in subsection 4.6.1 in Reference Test Method G5,isalso necessary.6.3 Potentiostat and Output Potential and Current Measur-ing InstrumentsThe potentiostat and other i

30、nstrumentsshould be similar to the ones specified in Test Method G61.Most commercial potentiostat and related instruments meet thespecific requirements for these types of measurements.6.4 ElectrodesThe standard recommended working ortesting electrode is shown in Fig. 1, which is a prismaticmeasuring

31、 0.75 by 0.75 by 0.375-in. thick (approximately 20by 20 by 10 mm). It has a drilled and tapped hole on top for theconnecting rod (as in Reference Test Method G5). Theelectrodes also have a 7-mm diameter hole in the center formounting two crevice formers, one at each side using a bolt.The test electr

32、ode could be cut from any plate or extruded bar.It is recommended that the creviced faces of the test electrodecorrespond to the rolling or extruded direction. In certain testedconditions the test electrode may show end grain attack in theshort transverse direction, but generally the crevice formerp

33、rovides a more active path for corrosion than the freelyexposed surfaces.6.5 Crevice Former or Crevice WasherThe creviceformer is a multiple crevice assembly (MCA), and it isdescribed in subsection 5.4 of Test Methods G48, in subsec-tion 9.2.2 in Guide G78, and in Ref 8. This MCA creviceformer shoul

34、d be fabricated using a hard non-conductiveceramic material such as alumina or mullite (Fig. 2). Beforemounting on the test electrode (specimen), the crevice washersshould be covered with a PTFE tape. This tape is 1.5-in. wideand 0.003-in. thick (standard military grade MIL-T-27730A).Acorrosionresis

35、tant fastener is used to secure the two MCAwashers, one on each side of the test electrode. Crevice formersmade of solid PTFE such as in Test Methods G48or GuideG78are not as effective, since they do not form a crevice gaptight enough for certain high end corrosionresistant materials.This may result

36、 in higher and poorly reproducible repassivationpotential values. Two standard metal washers are used as well(Figs. 1 and 2). The standard pressure on the MCA creviceformers may vary (depending of the study underway) but aminimum of 30-in.lb (3.4-Nm) torque may be needed to forma tight crevice. Use

37、a calibrated torque wrench to apply theG192082torque. Electrical contact between the bolt and the test elec-trode should be avoided. Effective insulation may be providedby the use of nonmetallic sleeves or by wrapping the assemblybolt with PTFE tape.6.6 Counter ElectrodeThe counter electrodes may be

38、prepared as in Reference Test Method G5or may be preparedfrom high-purity platinum flat stock and wire. Counter elec-trodes could be easily fabricated by spot welding platinum wireto a platinum foil, which could be curved to adapt to the cellgeometry. It is recommended that the area of the platinumc

39、ounter electrode be twice as large as the one of the workingelectrode (test electrode or specimen).6.7 Reference ElectrodeReference electrodes could becommercially available saturated calomel or silver-silver chlo-ride. These electrodes are durable and reliable; however theyshould be maintained in t

40、he proper conditions. The potential ofthe reference electrodes should be checked at periodic intervalsto ensure their accuracy.7. Reagents and Materials7.1 Purity of ReagentsReagent grade chemicals should beused in all tests.7.2 Purity of WaterThe water should be distilled ordeionized conforming to

41、the requirements of SpecificationD 1193, Type IV reagent water.7.3 Sodium Chloride (NaCl)To prepare 1 L of 1 M NaClsolution, dissolve 58.45 g of NaCl in purified water to obtain atotal volume of solution of 1 L.7.4 Purging GasIf deaeration is necessary, nitrogen gas ofa minimum 99.99 purity should b

42、e used. Tests could also berun under normal aeration conditions or under any otheratmosphere.FIG. 1 Prismatic Test Electrode (0.75 by 0.75 by 0.375 in. or approximately 20 by 20 by 10 mm)G1920837.5 Prismatic-Shaped Test Electrodes of the CorrosionRe-sistant AlloyOther type of creviced test electrode

43、s may alsobe used, depending on the specific study being performed.8. Hazards8.1 Normal precautions for handling hot liquids should beobserved.8.2 Personal protective equipment for handling hot liquidsshould be used.9. Sampling, Test Electrodes, and Test Units9.1 Recommended test electrodes (specime

44、ns) areprismatic-shaped as shown in Fig. 1. The thickness of thematerial for the test electrodes is not essential, but it should beenough to handle the mounting rod mechanism. Thickermaterials are easier to prepare (polish). A fresh (or 1 h prior totesting) finish wet grinding of 600 grit silicon ca

45、rbine paper isrecommended. If surface effects are being studied, othersurface finishing may be considered.9.2 If other than mill finishes are investigated, the testelectrodes may be reused after remachining or grinding toremove all traces of previously incurred attack. The importanceof maintaining p

46、arallel/prismatic surfaces cannot be overstatedwith regard to reproducing crevice conditions and the preven-tion of possible fracture of the ceramic devices.9.3 The test electrodes could be prepared using wrought orcast material, or machined weld metal.9.4 The bolt, nut, and flat washer must be made

47、 of acorrosionresistant material. It is recommended to use Ti Gr 2(UNS R52400). Fastening devices can also be fabricated usingother readily available materials such as Alloys C-276 and 625(UNS N10276 and N06625, respectively). The crevice formeris manufactured using a ceramic material according to t

48、he12-tooth design in Test Methods G48, Guide G78, and Ref 8(Fig. 2). The ceramic washer is covered by a wide PTFE tape1.5-in. wide and 0.003-in. thick (standard military gradeMIL-T-27730A).10. Preparation of Apparatus10.1 The testing cell and test electrode holder are describedin Reference Test Meth

49、od G5.10.2 The potentiostat and other instruments should be simi-lar to the ones specified in Test Method G61. Most commercialpotentiostat and related instruments meet the specific require-ments for these types of measurements.11. Calibration and Standardization11.1 The potentiostat and its software should be calibratedin accordance with user calibration procedures. The goodoperating conditions of the potentiostat can also be assessedusing the Reference Test Method G5procedure.12. Procedure12.1 Test electrode preparation, cleaning and mounting.Practice