1、BRITISH STANDARDBS EN ISO 12732:2008Corrosion of metals and alloys Electrochemical potentiokinetic reactivation measurement using the double loop method (based on ihals method)ICS 77.060g49g50g3g38g50g51g60g44g49g42g3g58g44g55g43g50g56g55g3g37g54g44g3g51g40g53g48g44g54g54g44g50g49g3g40g59g38g40g51g5
2、5g3g36g54g3g51g40g53g48g44g55g55g40g39g3g37g60g3g38g50g51g60g53g44g42g43g55g3g47g36g58BS EN ISO 12732:2008This British Standard was published under the authority of the Standards Policy and Strategy Committee on 29 September 2006 BSI 2008ISBN 978 0 580 60547 5National forewordThis British Standard i
3、s the UK implementation of EN ISO 12732:2008. It is identical with ISO 12732:2006. It supersedes BS ISO 12732:2006 which is withdrawn.The UK participation in its preparation was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys.A list of organizations represented on this com
4、mittee can be obtained on request to its secretary.This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application.Compliance with a British Standard cannot confer immunity from legal obligations. Amendments/corrigenda issued
5、 since publicationDate Comments29 August 2008 This corrigendum renumbers BS ISO 12732:2006 as BS EN ISO 12732:2008EUROPEAN STANDARDNORME EUROPENNEEUROPISCHE NORMEN ISO 12732April 2008ICS 77.060English VersionCorrosion of metals and alloys - Electrochemical potentiokineticreactivation measurement usi
6、ng the double loop method (basedon Cihals method) (ISO 12732:2006)Corrosion des mtaux et alliages - Mesurage de laractivation lectrochimique potentiocintique par lamthode de la double boucle (drive de la mthode deCihal) (ISO 12732:2006)Korrosion von Metallen und Legierungen - Verfahren fr dieelektro
7、chemische potentiodynamischeReaktivierungsmessung mit dem Double-loop-Verfahren(Cihal-Verfahren) (ISO 12732:2006)This European Standard was approved by CEN on 21 March 2008.CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this Europe
8、anStandard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such nationalstandards may be obtained on application to the CEN Management Centre or to any CEN member.This European Standard exists in three official versions (English, F
9、rench, German). A version in any other language made by translationunder the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as theofficial versions.CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus,
10、 Czech Republic, Denmark, Estonia, Finland,France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal,Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and United Kingdom.EUROPEAN COMMITTEE FOR STANDARDIZATIONCOMIT EUR
11、OPEN DE NORMALISATIONEUROPISCHES KOMITEE FR NORMUNGManagement Centre: rue de Stassart, 36 B-1050 Brussels 2008 CEN All rights of exploitation in any form and by any means reservedworldwide for CEN national Members.Ref. No. EN ISO 12732:2008: Eii Foreword The text of ISO 12732:2006 has been prepared
12、by Technical Committee ISO/TC 156 “Corrosion of metals and alloys” of the International Organization for Standardization (ISO) and has been taken over as EN ISO 12732:2008 by Technical Committee CEN/TC 262 “Metallic and other inorganic coatings” the secretariat of which is held by BSI. This European
13、 Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by October 2008, and conflicting national standards shall be withdrawn at the latest by October 2008. Attention is drawn to the possibility that some of the element
14、s of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following countries are bound to implement this Europ
15、ean Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United
16、Kingdom. Endorsement notice The text of ISO 12732:2006 has been approved by CEN as a EN ISO 12732:2008 without any modification. iiiContents Page 1 Scope . 1 2 Normative references . 1 3 Terms and definitions. 1 4 Principle. 2 5 Apparatus. 3 6 Test solutions 5 7 Test specimen preparation 5 8 Procedu
17、re 5 9 Metallographic inspection . 6 10 Evaluation of results. 6 11 Test report . 7 Annex A (informative) Flushed port cell and flushed electrode holder 9 Annex B (informative) Potential of selected reference electrodes at 25 C with respect to the standard hydrogen electrode (SHE) . 12 Annex C (info
18、rmative) Suggested method for sensitizing test specimens 13 Annex D (informative) Correlation of Ir/Ipwith the degree of grain-boundary sensitization, Pa(ASTM G108), QGBAand QGBL14 BS EN ISO 12732:2008blank1Corrosion of metals and alloys Electrochemical potentiokinetic reactivation measurement using
19、 the double loop method (based on ihals method) WARNING This International Standard may involve hazardous materials, operations and equipment. It is the responsibility of whoever uses this standard to consult and establish appropriate safety and health practices, and determine the applicability of r
20、egulatory limitations prior to use. 1 Scope This International Standard specifies the method for measuring the degree of sensitization (DOS) in stainless steel and nickel-based alloys using the Double Loop Electrochemical Potentiokinetic Reactivation (DL-EPR) test (based on ihals method). The method
21、 may be used for the quantitative assessment of deleterious thermal effects resulting in the formation of alloy-element-depleted zones at grain boundaries or in the matrix. However, attention should be paid when testing heat-affected weld zones, due to possible non-uniform distribution of sensitized
22、 zones along the fusion lines. The results of the test can be used as an index to identify the potential susceptibility of stainless steel and nickel-based alloys to intergranular corrosion, pitting corrosion, and intergranular-stress corrosion cracking, but prediction of these corrosion modes depen
23、ds on complementary specific testing. This International Standard describes the general methodology and, in Annex C, gives examples of suitable test exposure conditions for specific alloys. 2 Normative references The following referenced documents are indispensable for the application of this docume
24、nt. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 8044:1999, Corrosion of metals and alloys Basic terms and definitions ISO 643:2003, Steels Micrographic determination of the apparen
25、t grain size 3 Terms and definitions For the purposes of this document, the terms and definitions in ISO 8044 and the following apply. 3.1 integrated charge Q charge measured during passivation (Qp) and reactivation (Qr), given by the time integral of current below the passivation and reactivation p
26、eak of the curve BS EN ISO 12732:20082 4 Principle Heat treatment (including welding) of corrosion-resistant alloys can lead to formation of particles, such as chromium carbide in the case of 304 SS or -phase (FeCrMo) in duplex stainless steels. This will lead to local depletion of alloying elements
27、, unless replenished by matrix diffusion, the extent of which will be temperature dependent. This process is commonly referred to as sensitization, because depleted zones have an intrinsic lower resistance to localized corrosion and, where appropriate, to stress corrosion cracking. The extent to whi
28、ch these damage mechanisms develop and propagate will depend on the extent of depletion and the density of depleted zones. There was a need for a simple laboratory test to rapidly identify potentially deleterious thermal effects on stainless steels and nickel-based alloys. The EPR test was developed
29、 for that purpose. Although two methods have been used in laboratory testing, the single loop and the double loop, the former, which involves polarization scanning from the passive to the active state, has the disadvantage that the method can be sensitive to surface finish. The EPR test may also be
30、applied to in-field testing, provided some adaptation be made to the cell and assembly. The double loop version of this method is preferred. Here, the specimen is immersed in an acid solution such that it is in the active state under freely corroding conditions, but then anodically polarized into th
31、e passive domain. As surface features are dissolved during initial immersion under active corrosion conditions, the likelihood of surface preparation having an impact diminishes. From the passive state, the specimen is polarized at a controlled scan rate in the cathodic direction. A schematic illust
32、ration is shown in Figure 1. In the absence of active depleted zones, the passive film can become unstable as the potential becomes less positive and can start to dissolve (e.g. by reductive dissolution). However, the rate of dissolution is small and, with the sweep rate employed, the anodic current
33、 is not able to rise substantially, so that only a modest anodic peak current is measured. The process of anodic dissolution during the cathodic scan is referred to as reactivation. Occasionally, the current may go transiently cathodic on lowering the potential, as the passive current density may be
34、 less than the cathodic current at the potentials of relevance. When a depleted zone is present, the passive film is locally less protective and is more easily reduced. Hence, active dissolution of the depleted zones will occur more readily whilst adjacent material still retains some passive film, a
35、lbeit a gradually thinning passive film. Thus significant active dissolution occurs. The reason for the gradual rise in current is probably a reflection of the spread in activity associated with a spread of the extent of depletion and corresponding variations in the passive film properties (some sec
36、tions reduced at higher potentials and some at lower potentials). Gradually, as the activity of all the sites build up, this begins to be counteracted by the decrease in potential reducing the current of the active regions because of Tafel behaviour; thus a reactivation peak is observed. The peak in
37、 the current density, and the charge passed associated with that peak, depend on the extent of alloy depletion. The ratio of the reactivation peak to the activation peak, or the reactivation charge to the activation charge, when compared with the values for the solution-annealed specimen, gives an i
38、ndex of sensitization. However, for sensitized grain boundaries, these values have to be normalized to the grain size. At the end of the test, the specimen is examined to confirm the nature of the localized corrosion process. BS EN ISO 12732:20083Key X potential Y log of current 1 anodic scan 2 reac
39、tivation scan Figure 1 Schematic polarization curves of the double loop EPR test method 5 Apparatus The apparatus necessary for obtaining EPR data consists of electronic instruments and a test cell. The electronic instruments may be integrated into one instrument package or may be individual compone
40、nts. Either form of instrumentation can provide acceptable data. 5.1 Scanning potentiostat The potentiostat should be capable of controlling the potential to within 1 mV accuracy, over the range of potential and current encountered in the EPR measurements. The potentiostat should have a potential ra
41、nge of 2 000 to +2 000 mV and a current range of 1 A to 1 A. 5.2 Electrode potential-measuring instrument The electrode potential-measuring circuit should have a high input impedance of the order of 1011 to 1014, to minimize current drawn from the system during measurements. Such circuits are provid
42、ed with most potentiostats. Instruments should have sufficient sensitivity and accuracy to detect a change of 1,0 mV over a potential range between 2 000 and +2 000 mV. BS EN ISO 12732:20084 5.3 Current-measuring instruments The current in the circuit is evaluated from the potential drop measured ac
43、ross a known resistor. In many potentiostats, this measurement is made internally but measurements can also be made externally by locating a resistor in the current line from the counter electrode to the auxiliary connection on the potentiostat. The current intensities encountered in an EPR test are
44、 usually in the range of 1 Acm2to 100 mAcm2. An instrument that is capable of measuring a current accuracy to within 1 % of the absolute value over a current density range between 1,0 Acm2and 105 Acm2, for a specimen with a surface area of approximately 1,0 cm2to 5,0 cm2, is recommended. 5.4 EPR tes
45、t cell The test cell should contain the working electrode (the metal to be polarized), a reference electrode for measuring the electrode potential and counter electrode(s). The test cell shall be constructed of materials that will not corrode, deteriorate, or otherwise contaminate the test solution.
46、 Borosilicate glass and poly-tetrafluoroethylene (PTFE) have been successfully used. The counter electrode/s should be positioned so that the current distribution about the specimen is symmetrical. The reference electrode may be inserted directly into the main cell. To avoid mutual contamination, a
47、double-junction reference electrode may be used or the reference electrode may be located in a separate chamber and linked to the main cell by a salt bridge. To minimize the potential drop between the reference electrode and the working electrode, a Luggin capillary should be used. The tip of the ca
48、pillary probe shall be positioned so that it is at a minimum distance from the working electrode of 2 times the diameter of the tip. The volume of solution in the test cell shall be such as to reduce to insignificance any change in the solution chemistry, as a consequence of the reaction processes.
49、Typically 250 ml is sufficient, with a minimum requirement of 100 mlcm2of working electrode. 5.4.1 Electrode holder. The working electrodes shall be mounted in such a way that the holder and mounting material have no influence on the measurement. An example of an electrode-mounting assembly is shown in Figure A.2. For steels with a protective oxide film, the seal of the test specimen to the holder can sometimes lead to undesired crevice attack of the steel at the interface. A method of preventing such crevice attack for certain appli
