1、Designation: G 102 89 (Reapproved 2004)e1Standard Practice forCalculation of Corrosion Rates and Related Informationfrom Electrochemical Measurements1This standard is issued under the fixed designation G 102; the number immediately following the designation indicates the year oforiginal adoption or,
2、 in the case of 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.e1NOTEInformation updated editorially in November 2004.1. Scope1.1 This practice covers the
3、 providing of guidance inconverting the results of electrochemical measurements to ratesof uniform corrosion. Calculation methods for convertingcorrosion current density values to either mass loss rates oraverage penetration rates are given for most engineering alloys.In addition, some guidelines fo
4、r converting polarization resis-tance values to corrosion rates are provided.2. Referenced Documents2.1 ASTM Standards:2D 2776 Test Methods for Corrosivity of Water in the Ab-sence of Heat Transfer (Electrical Methods)3G 1 Practice for Preparing, Cleaning, and Evaluating Cor-rosion Test SpecimensG5
5、Reference Test Method for Making Potentiostatic andPotentiodynamic Anodic Polarization MeasurementsG59 Practice for Conducting Potentiodynamic PolarizationResistance Measurements3. Significance and Use3.1 Electrochemical corrosion rate measurements often pro-vide results in terms of electrical curre
6、nt. Although the con-version of these current values into mass loss rates or penetra-tion rates is based on Faradays Law, the calculations can becomplicated for alloys and metals with elements havingmultiple valence values. This practice is intended to provideguidance in calculating mass loss and pe
7、netration rates for suchalloys. Some typical values of equivalent weights for a varietyof metals and alloys are provided.3.2 Electrochemical corrosion rate measurements may pro-vide results in terms of electrical resistance. The conversion ofthese results to either mass loss or penetration rates req
8、uiresadditional electrochemical information. Some approaches forestimating this information are given.3.3 Use of this practice will aid in producing more consis-tent corrosion rate data from electrochemical results. This willmake results from different studies more comparable andminimize calculation
9、 errors that may occur in transformingelectrochemical results to corrosion rate values.4. Corrosion Current Density4.1 Corrosion current values may be obtained from galvaniccells and polarization measurements, including Tafel extrapo-lations or polarization resistance measurements. (See Refer-ence T
10、est Method G5and Practice G59for examples.) Thefirst step is to convert the measured or estimated current valueto current density. This is accomplished by dividing the totalcurrent by the geometric area of the electrode exposed to thesolution. The surface roughness is generally not taken intoaccount
11、 when calculating the current density. It is assumed thatthe current distributes uniformly across the area used in thiscalculation. In the case of galvanic couples, the exposed area ofthe anodic specimen should be used. This calculation may beexpressed as follows:icor5IcorA(1)where:icor= corrosion c
12、urrent density, A/cm2,Icor= total anodic current, A, andA = exposed specimen area, cm2.Other units may be used in this calculation. In somecomputerized polarization equipment, this calculation is madeautomatically after the specimen area is programmed into thecomputer. A sample calculation is given
13、in Appendix X1.4.2 Equivalent WeightEquivalent weight, EW, may bethought of as the mass of metal in grams that will be oxidizedby the passage of one Faraday (96 489 6 2 C (amp-sec) ofelectric charge.1This practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metals and is the direc
14、t responsibility of Subcommittee G01.11 on Electrochemi-cal Measurements in Corrosion Testing.Current edition approved Nov 1, 2004. Published November 2004. Originallyapproved in 1989. Last previous edition approved in 1999 as G 102 89 (1999).2For referenced ASTM standards, visit the ASTM website, w
15、ww.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.3Withdrawn.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United
16、 States.NOTE 1The value of EW is not dependent on the unit system chosenand so may be considered dimensionless.For pure elements, the equivalent weight is given by:EW 5Wn(2)where:W = the atomic weight of the element, andn = the number of electrons required to oxidize an atom ofthe element in the cor
17、rosion process, that is, thevalence of the element.4.3 For alloys, the equivalent weight is more complex. It isusually assumed that the process of oxidation is uniform anddoes not occur selectively to any component of the alloy. If thisis not true, then the calculation approach will need to beadjust
18、ed to reflect the observed mechanism. In addition, somerationale must be adopted for assigning values of n to theelements in the alloy because many elements exhibit more thanone valence value.TABLE 1 Equivalent Weight Values for a Variety of Metals and AlloysCommonDesignationUNSElementsw/ConstantVal
19、enceLowest Second Third FourthVariableValenceEquivalentWeightVariableValenceEquivalentWeightElement/ValenceEquivalentWeightElement/ValenceEquivalentWeightAluminum Alloys:AA1100AA91100 Al/3 8.99AA2024 A92024 Al/3, Mg/2 Cu/1 9.38 Cu/2 9.32AA2219 A92219 Al/3 Cu/1 9.51 Cu/2 9.42AA3003 A93003 Al/3 Mn/2 9
20、.07 Mn/4 9.03 Mn 7 8.98AA3004 A93004 Al/3, Mg/2 Mn/2 9.09 Mn/4 9.06 Mn 7 9.00AA5005 A95005 Al/3, Mg/2 9.01AA5050 A95050 Al/3, Mg/2 9.03AA5052 A95052 Al/3, Mg/2 9.05AA5083 A95083 Al/3, Mg/2 9.09AA5086 A95086 Al/3, Mg/2 9.09AA5154 A95154 Al/3, Mg/2 9.08AA5454 A95454 Al/3, Mg/2 9.06AA5456 A95456 Al/3,
21、Mg/2 9.11AA6061 A96061 Al/3, Mg/2 9.01AA6070 A96070Al/3, Mg/2,Si/48.98AA6101 A96161 Al/3 8.99AA7072 A97072 Al/3, Zn/2 9.06AA7075 A97075Al/3, Zn/2,Mg/2Cu/1 9.58 Cu/2 9.55AA7079 A97079Al/3, Zn/2,Mg/29.37AA7178 A97178Al/3, Zn/2,Mg/2Cu/1 9.71 Cu/2 9.68Copper Alloys:CDA110 C11000 Cu/1 63.55 Cu/2 31.77CDA
22、220 C22000 Zn/2 Cu/1 58.07 Cu/2 31.86CDA230 C23000 Zn/2 Cu/1 55.65 Cu/2 31.91CDA260 C26000 Zn/2 Cu/1 49.51 Cu/2 32.04CDA280 C28000 Zn/2 Cu/1 46.44 Cu/2 32.11CDA444 C44300 Zn/2 Cu/1, Sn/2 50.42 Cu/1, Sn/4 50.00 Cu/2, Sn/4 32.00CDA687 C68700 Zn/2, Al/3 Cu/1 48.03 Cu/2 30.29CDA608 C60800 Al/3 Cu/1 47.1
23、14 Cu/2 27.76CDA510 C51000 Cu/1, Sn/2 63.32 Cu/1, Sn/4 60.11 Cu/2, Sn/4 31.66CDA524 C52400 Cu/1, Sn/2 63.10 Cu/1, Sn/4 57.04 Cu/2, Sn/4 31.55CDA655 C65500 Si/4 Cu/1 50.21 Cu/2 28.51CDA706 C70600 Ni/2 Cu/1 56.92 Cu/2 31.51CDA715 C71500 Ni/2 Cu/1 46.69 Cu/2 30.98CDA752 C75200 Ni/2, Zn/2 Cu/1 46.38 Cu/
24、2 31.46Stainless Steels:304 S30400 Ni/2 Fe/2, Cr/3 25.12 Fe/3, Cr/3 18.99 Fe/3, Cr/6 15.72321 S32100 Ni/2 Fe/2, Cr/3 25.13 Fe/3, Cr/3 19.08 Fe/3, Cr/6 15.78309 S30900 Ni/2 Fe/2, Cr/3 24.62 Fe/3, Cr/3 19.24 Fe/3, Cr/6 15.33310 S31000 Ni/2 Fe/2, Cr/3 24.44 Fe/3, Cr/3 19.73 Fe/3, Cr/6 15.36316 S31600 N
25、i/2 Fe/2, Cr/3, Mo/3 25.50 Fe/2, Cr/3, Mo/4 25.33 Fe/3, Cr/6, Mo/6 19.14 Fe/3, Cr/6, Mo/6 16.111317 S31700 Ni/2 Fe/2, Cr/3, Mo/3 25.26 Fe/2, Cr/3, Mo/4 25.03 Fe/3, Cr/3, Mo/6 19.15 Fe/3, Cr/6, Mo/6 15.82410 S41000 Fe/2, Cr/3 25.94 Fe/3, Cr/3 18.45 Fe/3, Cr/6 16.28430 S43000 Fe/2, Cr/3 25.30 Fe/3, Cr
26、/3 18.38 Fe/3, Cr/6 15.58446 S44600 Fe/2, Cr/3 24.22 Fe/3, Cr/3 18.28 Fe/3, Cr/6 14.4620CB3AN08020 Ni/2Fe/2, Cr/3, Mo/3,Cu/123.98Fe/2, Cr/3, Mo/4, Cu/123.83Fe/3, Cr/3, Mo/6, Cu/218.88Fe/3, Cr/6, Mo/6,Cu/215.50G 102 89 (2004)e12TABLE 1 ContinuedCommonDesignationUNSElementsw/ConstantValenceLowest Seco
27、nd Third FourthVariableValenceEquivalentWeightVariableValenceEquivalentWeightElement/ValenceEquivalentWeightElement/ValenceEquivalentWeightNickel Alloys:200 N02200 NI/2 29.36 Ni/3 19.57400 N04400 Ni/2 Cu/1 35.82 Cu/2 30.12600 N06600 Ni/2 Fe/2, Cr/3 26.41 Fe/3, Cr/3 25.44 Fe/3, Cr/6 20.73800 N08800 N
28、i/2 Fe/2, Cr/3 25.10 Fe/3, Cr/3 20.76 Fe/3, Cr/6 16.59825 N08825 Ni/2Fe/2, Cr/3, Mo/3,Cu/125.52Fe/2, Cr/3, Mo/4, Cu/125.32Fe/3, Cr/3, Mo/6, Cu/221.70Fe/3, Cr/6, Mo/6,Cu/217.10B N10001 Ni/2 Mo/3, Fe/2 30.05 Mo/4, Fe/2 27.50 Mo/6, Fe/2 23.52 Mo/6, Fe/3 23.23C-22BN06022 Ni/2Fe/2, Cr/3, Mo/3,W/426.04Fe/
29、2, Cr/3, Mo/4, W/425.12Fe/2, Cr/3, Mo/6, W/623.28Fe/3, Cr/6, Mo/6,W/617.88C-276 N10276 Ni/2Fe/2, Cr/3, Mo/3,W/427.09 Cr/3, Mo/4 25.90Fe/2, Cr/3, Mo/6, W/623.63Fe/3, Cr/6, Mo/6,W/619.14G N06007 Ni/2 (1) 25.46 (2) 22.22 (3) 22.04 (4) 17.03Carbon Steel: Fe/2 27.92 Fe/3 18.62(1) = Fe/2, Cr/3, Mo/3, Cu/1
30、, Nb/4,Mn/2(3) = Fe/3, Cr/3, Mo/6, Cu/2, Nb/5, Mn/2(2) = Fe/2, Cr/3, Mo/4, Cu/2, Nb/5,Mn/2(4) = Fe/3, Cr/6, Mo/6, Cu/2, Nb/5, Mn/4Other Metals:Mg M14142 Mg/2 12.15Mo R03600 Mo/3 31.98 Mo/4 23.98 Mo/6 15.99Ag P07016 Ag/1 107.87 Ag/2 53.93Ta R05210 Ta/5 36.19Sn L13002 Sn/2 59.34 Sn/4 29.67Ti R50400 Ti
31、/2 23.95 Ti/3 15.97 Ti/4 11.98Zn Z19001 Zn/2 32.68Zr R60701 Zr/4 22.80Pb L50045 Pb/2 103.59 Pb/4 51.80ARegistered trademark Carpenter Technology.BRegistered trademark Haynes International.NOTE 1Alloying elements at concentrations below 1 % by mass were not included in the calculation, for example, t
32、hey were considered part of the basis metal.NOTE 2Mid-range values were assumed for concentrations of alloying elements.NOTE 3Only consistent valence groupings were used.NOTE 4(Eq 4) was used to make these calculations.4.4 To calculate the alloy equivalent weight, the followingapproach may be used.
33、Consider a unit mass of alloy oxidized.The electron equivalent for1gofanalloy, Q is then:Q 5 (nifiWi(3)where:fi = the mass fraction of the ithelement in the alloy,Wi = the atomic weight of the ithelement in the alloy, andni = the valence of the ithelement of the alloy.Therefore, the alloy equivalent
34、 weight, EW, is the reciprocalof this quantity:EW 51(nifiWi(4)Normally only elements above 1 mass percent in the alloyare included in the calculation. In cases where the actualanalysis of an alloy is not available, it is conventional to use themid-range of the composition specification for each elem
35、ent,unless a better basis is available. A sample calculation is givenin Appendix X2 (1).44.5 Valence assignments for elements that exhibit multiplevalences can create uncertainty. It is best if an independenttechnique can be used to establish the proper valence for eachalloying element. Sometimes it
36、 is possible to analyze thecorrosion products and use those results to establish the propervalence. Another approach is to measure or estimate theelectrode potential of the corroding surface. Equilibrium dia-grams showing regions of stability of various phases as afunction of potential and pH may be
37、 created from thermody-namic data. These diagrams are known as Potential-pH (Pour-baix) diagrams and have been published by several authors (2,3). The appropriate diagrams for the various alloying elementscan be consulted to estimate the stable valence of each elementat the temperature, potential, a
38、nd pH of the contacting electro-lyte that existed during the test.NOTE 2Some of the older publications used inaccurate thermody-namic data to construct the diagrams and consequently they are in error.4.6 Some typical values of EW for a variety of metals andalloys are given in Table 1.4.7 Calculation
39、 of Corrosion RateFaradays Law can beused to calculate the corrosion rate, either in terms of penetra-tion rate (CR) or mass loss rate (MR) (4):CR 5 K1icorrEW (5)4The boldface numbers in parentheses refer to the list of references at the end ofthis standard.G 102 89 (2004)e13MR 5 K2icorEW (6)where:C
40、R is given in mm/yr, icorin A/cm2,K1= 3.27 3 103, mm g/A cm yr (Note 3),r = density in g/cm3, (see Practice G 1 for density valuesfor many metals and alloys used in corrosion test-ing),MR = g/m2d, andK2= 8.954 3 103,gcm2/A m2d(Note 3).NOTE 3EW is considered dimensionless in these calculations.Other
41、values for K1and K2for different unit systems aregiven in Table 2.4.8 Errors that may arise from this procedure are discussedbelow.4.8.1 Assignment of incorrect valence values may causeserious errors (5).4.8.2 The calculation of penetration or mass loss fromelectrochemical measurements, as described
42、 in this standard,assumes that uniform corrosion is occurring. In cases wherenon-uniform corrosion processes are occurring, the use of thesemethods may result in a substantial underestimation of the truevalues.4.8.3 Alloys that include large quantities of metalloids oroxidized materials may not be a
43、ble to be treated by the aboveprocedure.4.8.4 Corrosion rates calculated by the method above whereabrasion or erosion is a significant contributor to the metal lossprocess may yield significant underestimation of the metal lossrate.5. Polarization Resistance5.1 Polarization resistance values may be
44、approximatedfrom either potentiodynamic measurements near the corrosionpotential (see Practice G59) or stepwise potentiostatic polar-ization using a single small potential step, DE, usually either 10mV or 10 mV, (see Test Method D 2776). Values of 65 and620 mV are also commonly used. In this case, t
45、he specimencurrent, DI, is measured after steady state occurs, and DE/DI iscalculated. Potentiodynamic measurements yield curves of Iversus E and the reciprocal of the slope of the curve (dE/dI) atthe corrosion potential is measured. In most programmablepotentiodynamic polarization equipment, the cu
46、rrent is con-verted to current density automatically and the resulting plot isof i versus E. In this case, the polarization resistance is givenby dE/di at the corrosion potential and 5.2 is not applicable.5.2 It is necessary to multiply the dE/dI or DE/DI valuecalculated above by the exposed specime
47、n geometric area toobtain the polarization resistance. This is equivalent to thecalculation shown in 4.1 for current density.5.3 The Stern-Geary constant B must be estimated orcalculated to convert polarization resistance values to corrosioncurrent density (6, 8).5.3.1 Calculate Stern-Geary constant
48、s from known Tafelslopes where both cathodic and anodic reactions are activationcontrolled, that is, there are distinct linear regions near thecorrosion potential on an E log i plot:B 5ba bc2.303 ba 1 bc!(7)where:ba = slope of the anodic Tafel reaction, when plotted onbase 10 logarithmic paper in V/
49、decade,bc = slope of the cathodic Tafel reaction when plotted onbase 10 logarithmic paper in V/decade, andB = Stern-Geary constant, V.5.3.2 In cases where one of the reactions is purely diffusioncontrolled, the Stern-Geary constant may be calculated:B 5b2.303(8)where:b = the activation controlled Tafel slope in V/decade.5.3.3 It should be noted in this case that the corrosioncurrent density will be equal to the diffusion limited currentdensity. A sample calculation is given in Appendix X4.5.3.4 Cases where both activation and diffusion effects aresimilar in ma
