ASTM G102-1989(2015)e1 Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements《计算电化学测量的腐蚀速率和相关信息的标准实施规程》.pdf
《ASTM G102-1989(2015)e1 Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements《计算电化学测量的腐蚀速率和相关信息的标准实施规程》.pdf》由会员分享,可在线阅读,更多相关《ASTM G102-1989(2015)e1 Standard Practice for Calculation of Corrosion Rates and Related Information from Electrochemical Measurements《计算电化学测量的腐蚀速率和相关信息的标准实施规程》.pdf(7页珍藏版)》请在麦多课文档分享上搜索。
1、Designation: G102 89 (Reapproved 2015)1Standard Practice forCalculation of Corrosion Rates and Related Informationfrom Electrochemical Measurements1This standard is issued under the fixed designation G102; the number immediately following the designation indicates the year oforiginal adoption or, in
2、 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.1NOTEEditorially corrected the legend below Eq 1 in 4.1 in November 2015.1. Scope1.1 This pract
3、ice covers the 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
4、 guidelines for converting polarization resis-tance values to corrosion rates are provided.1.2 The values stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.2. Referenced Documents2.1 ASTM Standards:2D2776 Methods of Test for Corrosivity of W
5、ater in theAbsence of Heat Transfer (Electrical Methods) (With-drawn 1991)3G1 Practice for Preparing, Cleaning, and Evaluating Corro-sion Test SpecimensG5 Reference Test Method for Making PotentiodynamicAnodic Polarization MeasurementsG59 Test Method for Conducting Potentiodynamic Polariza-tion Resi
6、stance Measurements3. Significance and Use3.1 Electrochemical corrosion rate measurements often pro-vide results in terms of electrical current. 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 fo
7、r alloys and metals with elements havingmultiple valence values. This practice is intended to provideguidance in calculating mass loss and penetration rates for suchalloys. Some typical values of equivalent weights for a varietyof metals and alloys are provided.3.2 Electrochemical corrosion rate mea
8、surements may pro-vide results in terms of electrical resistance. The conversion ofthese results to either mass loss or penetration rates requiresadditional electrochemical information. Some approaches forestimating this information are given.3.3 Use of this practice will aid in producing more consi
9、s-tent corrosion rate data from electrochemical results. This willmake results from different studies more comparable andminimize calculation errors that may occur in transformingelectrochemical results to corrosion rate values.4. Corrosion Current Density4.1 Corrosion current values may be obtained
10、 from galvaniccells and polarization measurements, including Tafel extrapo-lations or polarization resistance measurements. (See Refer-ence Test Method G5 and Practice G59 for examples.) The firststep is to convert the measured or estimated current value tocurrent density. This is accomplished by di
11、viding the totalcurrent by the geometric area of the electrode exposed to thesolution. The surface roughness is generally not taken intoaccount when calculating the current density. It is assumed thatthe current distributes uniformly across the area used in thiscalculation. In the case of galvanic c
12、ouples, the exposed area ofthe anodic specimen should be used. This calculation may beexpressed as follows:icor5IcorA(1)where:icor= corrosion current density, A/cm2,Icor= total anodic current, A, and1This practice is under the jurisdiction of ASTM Committee G01 on Corrosionof Metalsand is the direct
13、 responsibility of Subcommittee G01.11 on Electrochemi-cal Measurements in Corrosion Testing.Current edition approved Nov. 1, 2015. Published December 2015. Originallyapproved in 1989. Last previous edition approved in 2010 as G10289 (2010). DOI:10.1520/G0102-89R15E01.2For referenced ASTM standards,
14、 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 historical standard is referenced onwww.astm.org.Copyrigh
15、t ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States1A = 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 programme
16、d into thecomputer. A sample calculation is given 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.NOTE 1The value of EW is not dependent on the unit
17、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 corrosion process, that is, the valenceof the element.4.3 For
18、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 beadjusted to reflect the observed mechanism. In addition, somerati
19、onale must be adopted for assigning values of n to theelements in the alloy because many elements exhibit more thanone valence value.4.4 To calculate the alloy equivalent weight, the followingapproach may be used. Consider a unit mass of alloy oxidized.The electron equivalent for1gofanalloy, Q is th
20、en: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 weight, EW, is the reciprocalof this quantity:EW 51(nifiWi(4)Normally only elements ab
21、ove 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 element,unless a better basis is available. A sample calculation is givenin Appendix X2 (1)
22、.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 is possible to analyze thecorrosion products and use those results to establish the pr
23、opervalence. 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 created from thermody-namic data. These diagrams are known as Potential-pH (Pour-baix)
24、 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, and pH of the contacting electro-lyte that existed during the test.NOTE 2Some of the old
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