ASTM G192-2008(2014) Standard Test Method for Determining the Crevice Repassivation Potential of Corrosion-Resistant Alloys Using a Potentiodynamic-Galvanostatic-Potentiostatic Tec.pdf

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1、Designation: G192 08 (Reapproved 2014)Standard Test Method forDetermining the Crevice Repassivation Potential ofCorrosion-Resistant Alloys Using a Potentiodynamic-Galvanostatic-Potentiostatic Technique1This standard is issued under the fixed designation G192; the number immediately following the des

2、ignation indicates 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 pro

3、cedure for conductinganodic 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 success

4、ivelypotentiodynamic, galvanostatic, and potentiostatic treatmentsfor the 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

5、 for informationonly.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 t

6、o use.2. Referenced Documents2.1 ASTM Standards:2B575 Specification for Low-Carbon Nickel-Chromium-Molybdenum, Low-Carbon Nickel-Chromium-Molybdenum-Copper, Low-Carbon Nickel-Chromium-Molybdenum-Tantalum, Low-Carbon Nickel-Chromium-Molybdenum-Tungsten, and Low-Carbon Nickel-Molybdenum-Chromium Alloy

7、 Plate, Sheet, and StripD1193 Specification for Reagent WaterE691 Practice for Conducting an Interlaboratory Study toDetermine the Precision of a Test MethodG1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG5 Reference Test Method for Making PotentiodynamicAnodic Polariza

8、tion MeasurementsG15 Terminology Relating to Corrosion and Corrosion Test-ing (Withdrawn 2010)3G48 Test Methods for Pitting and Crevice Corrosion Resis-tance of Stainless Steels and Related Alloys by Use ofFerric Chloride SolutionG61 Test Method for Conducting Cyclic PotentiodynamicPolarization Meas

9、urements for Localized Corrosion Sus-ceptibility of 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-relate

10、d termsused in this test method, see Terminology G15.4. 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 m

11、ethod tohonor the two precursors of this technique (see 1 and 2).4Thenew 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

12、used with any corrosion-resistant alloy, but it was developed by studying Alloy 22(UNS N06022). The composition and other properties ofAlloy22 are given in Specification B575. Alloy 22 is a nickelbasedalloy containing approximately 22wt% Cr, 13wt% Mo, 3wt%1This test method is under the jurisdiction

13、of ASTM Committee G01 onCorrosion of Metals and is the direct responsibility of Subcommittee G01.11 onElectrochemical Measurements in Corrosion Testing.Current edition approved Nov. 1, 2014. Published November 2014. Originallyapproved in 2008. Last previous edition approved in 2008 as G19208. DOI:10

14、.1520/G0192-08R14.2For 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.3The last approved version of this historic

15、al standard is referenced onwww.astm.org.4The boldface numbers in parentheses refer to a list of references at the end ofthis standard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1W and 3wt% Fe. The THE test method is a complement

16、to thecyclic potentiodynamic polarization (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 highlyaggressive (3-6). The THE test method has also been appl

17、ied 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. Theround robin described in Section 15 was carried out in

18、 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 corrosion potential until apreset current (or current densit

19、y) is reached (for example,2 Acm2). 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 grow a crevicecorroded area (if any develops). During the ga

20、lvanostatic 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 galvanos-tatic hold (Step 2) is read, and then 10 mV are subtracted. Theresulting value of potential is applied for a 2-h period while thecu

21、rrent 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 repassivation potential (ER,CREV) is thehighest potential in Step 3 fo

22、r 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 designed to provide highlyreproducible crevice repassivation pot

23、entials 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), corrosionresistantalloys such as Alloy 22 will resist crevi

24、ce 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 test method provides a morecontrolled way of applying the e

25、lectrical 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 tocrevice corrosion in the tested electrolyte. This is similar too

26、ther test methods to measure localized corrosion resistancesuch as Test Method G61 and Test Methods G48. The resultsfrom this test method are not intended to correlate in aquantitative manner with the rate of propagation that one mightobserve in service when localized corrosion occurs.5.3 This test

27、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) change.6. Apparatus6.1 CellThe polarization cell should be s

28、imilar to the onedescribed in Reference Test Method G5 and Test Method G61.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 electrodes, gas inletand outlet tubes, and a thermometer or th

29、ermocouple. 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 similar to the onedescribed in Figure 5 in Reference Test Method

30、 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 instrumentsshould be similar to the ones specified in Test

31、 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 0.75 by 0.75 by 0.375-in. thick (approximately 20by 20 b

32、y 10 mm). It has a drilled and tapped hole on top for theconnecting rod (as in Reference Test Method G5). The elec-trodes also have a 7-mm diameter hole in the center formounting two crevice formers, one at each side using a bolt.The test electrode could be cut from any plate or extruded bar.It is r

33、ecommended 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 formerprovides a more active path for corrosion than the freel

34、yexposed surfaces.6.5 Crevice Former or Crevice WasherThe crevice formeris a multiple crevice assembly (MCA), and it is described insubsection 5.4 of Test Methods G48, in subsection 9.2.2 inGuide G78, and in Ref 8. This MCA crevice former should befabricated using a hard non-conductive ceramic mater

35、ial suchas alumina or mullite (Fig. 2). Before mounting on the testelectrode (specimen), the crevice washers should be coveredwith a PTFE tape. This tape is 1.5-in. wide and 0.003-in. thick(standard military grade MIL-T-27730A). A corrosionresis-tant fastener is used to secure the two MCA washers, o

36、ne oneach side of the test electrode. Crevice formers made of solidG192 08 (2014)2PTFE such as in Test Methods G48 or Guide G78 are not aseffective, since they do not form a crevice gap tight enough forcertain high end corrosionresistant materials. This may resultin higher and poorly reproducible re

37、passivation potentialvalues. Two standard metal washers are used as well (Figs. 1and 2). The standard pressure on the MCAcrevice formers mayvary (depending of the study underway) but a minimum of30-in.lb (3.4-Nm) torque may be needed to form a tightcrevice. Use a calibrated torque wrench to apply th

38、e torque.Electrical contact between the bolt and the test electrode shouldbe avoided. Effective insulation may be provided by the use ofnonmetallic sleeves or by wrapping the assembly bolt withPTFE tape.6.6 Counter ElectrodeThe counter electrodes may beprepared as in Reference Test Method G5 or may

39、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 platinumcounter electrode be twice as large as the one

40、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 the proper conditions. The potential ofthe ref

41、erence 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 the requirements of SpecificationD1193, Type

42、IV reagent water.FIG. 1 Prismatic Test Electrode (0.75 by 0.75 by 0.375 in. or approximately 20 by 20 by 10 mm)G192 08 (2014)37.3 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 deaerati

43、on is necessary, nitrogen gas ofa minimum 99.99 purity should be used. Tests could also berun under normal aeration conditions or under any otheratmosphere.7.5 Prismatic-Shaped Test Electrodes of the CorrosionRe-sistant AlloyOther type of creviced test electrodes may alsobe used, depending on the sp

44、ecific 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 (specimens) areprismatic-shaped as shown in Fi

45、g. 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 carbine paper isrecommended. If surface

46、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 parallel/prismatic surfaces cannot be o

47、verstatedwith 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 of acorrosionresistant material. It i

48、s 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 the12-tooth design in Test Methods G48,

49、 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 Method 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 s