BS-ISO-17081-2004.pdf
BRITISH STANDARD BS ISO 17081:2004 Incorporating Corrigendum No. 1 Method of measurement of hydrogen permeation and determination of hydrogen uptake and transport in metals by an electrochemical technique ICS 77.060 ? Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 17081:2004 This British Standard was published under the authority of the Standards Policy and Strategy Committee on 22 November 2004 ISBN 0 580 44812 6 National foreword This British Standard reproduces verbatim ISO 17081:2004 and implements it as the UK national standard. It supersedes BS 7886:1997 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys, which has the responsibility to: A list of organizations represented on this committee can be obtained on request to its secretary. Cross-references The British Standards which implement international or European publications referred to in this document may be found in the BSI Catalogue under the section entitled “International Standards Correspondence Index”, or by using the “Search” facility of the BSI Electronic Catalogue or of British Standards Online. 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 does not of itself confer immunity from legal obligations. aid enquirers to understand the text; present to the responsible international/European committee any enquiries on the interpretation, or proposals for change, and keep the UK interests informed; monitor related international and European developments and promulgate them in the UK. Summary of pages This document comprises a front cover, an inside front cover, the ISO title page, pages ii to iv, pages 1 to 16, an inside back cover and a back cover. The BSI copyright notice displayed in this document indicates when the document was last issued. Amendments issued since publication Amd. No. DateComments 15698 Corrigendum No. 1 Addition of supersession details © BSI 28 October 2005 28 October 2005 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI INTERNATIONAL STANDARD ISO 17081 First edition 2004-11-01 Reference number ISO 17081:2004(E) Method of measurement of hydrogen permeation and determination of hydrogen uptake and transport in metals by an electrochemical technique Méthode de mesure de la perméation de l'hydrogène et détermination de l'absorption d'hydrogène et de son transport dans les métaux à l'aide d'une technique électrochimique BS ISO 17081:2004 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI ii Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iii Contents Page 1Scope 1 2Normative references 1 3Terms and definitions 1 4Symbols 3 5Principle 3 6Samples 4 6.1Dimensions 4 6.2Preparation 5 7Apparatus . 5 8Test environment considerations . 7 9Test procedure . 8 10Control and monitoring of test environment . 9 11Analysis of results . 10 11.1General . 10 11.2Analysis of steady-state current 10 11.3Analysis of permeation transient . 10 12Test report 13 Annex A (informative) Recommended test environments for specific alloys . 14 Bibliography . 16 BS ISO 17081:2004 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2. The main task of technical committees is to prepare International Standards. Draft International Standards adopted by the technical committees are circulated to the member bodies for voting. Publication as an International Standard requires approval by at least 75 % of the member bodies casting a vote. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. ISO 17081 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys. BS ISO 17081:2004 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 1 Method of measurement of hydrogen permeation and determination of hydrogen uptake and transport in metals by an electrochemical technique 1Scope 1.1This International Standard specifies a laboratory method for the measurement of hydrogen permeation and for the determination of hydrogen atom uptake and transport in metals, using an electrochemical technique. The term “metal” as used in this International Standard includes alloys. 1.2This International Standard describes a method for evaluating hydrogen uptake in metals, based on measurement of steady-state hydrogen flux. It also describes a method for determining effective diffusivity of hydrogen atoms in a metal and for distinguishing reversible and irreversible trapping. 1.3This International Standard gives requirements for the preparation of specimens, control and monitoring of the environmental variables, test procedures and analysis of results. 1.4This International Standard may be applied, in principle, to all metals for which hydrogen permeation is measurable and the method can be used to rank the relative aggressivity of different environments in terms of the hydrogen uptake of the exposed metal. 2Normative references The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. ISO 17475:1), Corrosion of metals and alloys Electrochemical test methods Guidelines for conducting potentiostatic and potentiodynamic polarization measurements 3Terms and definitions For the purposes of this document, the following terms and definitions apply. 3.1 charging method of introducing atomic hydrogen into the metal by exposure to an aqueous environment under galvanostatic control (constant charging current), potentiostatic control (constant electrode potential), free corrosion or by gaseous exposure 3.2 charging cell compartment in which hydrogen atoms are generated on the sample surface, including both aqueous and gaseous charging 1)To be published. BS ISO 17081:2004 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 2 3.3 decay current decay of the hydrogen atom oxidation current, after attainment of steady state, following a decrease in charging current 3.4 Fick's second law second-order differential equation describing, in this case, the concentration of atomic hydrogen in the sample as a function of position and time NOTEThe equation is of the form for lattice diffusion in one dimension where diffusivity is independent of concentration. See Table 1 for an explanation of the symbols. 3.5 hydrogen flux amount of hydrogen passing through the metal sample per unit area per unit time 3.6 hydrogen uptake atomic hydrogen absorbed into the metal as a result of charging 3.7 irreversible trap microstructural site at which the residence time for a hydrogen atom is infinite or extremely long compared to the time-scale for permeation testing at the relevant temperature 3.8 mobile hydrogen atoms hydrogen atoms in interstitial sites in the lattice (lattice sites) and reversible trap sites 3.9 oxidation cell compartment in which hydrogen atoms exiting from the metal sample are oxidized 3.10 permeation current current measured in oxidation cell associated with oxidation of hydrogen atoms 3.11 permeation flux hydrogen flux exiting the test sample in the oxidation cell 3.12 permeation transient variation of the permeation current with time, from commencement of charging to the attainment of steady state, or modification of charging conditions 3.13 recombination poison chemical within the test environment in the charging cell which enhances hydrogen absorption by retarding the recombination of hydrogen atoms on the metal surface 3.14 reversible trap microstructural site at which the residence time for a hydrogen atom is greater than that for the lattice site but is small in relation to the time to attain steady-state permeation C(x,t)/t = D2C(x,t)/x2 BS ISO 17081:2004 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 3 4Symbols Table 1 gives a list of symbols and their designations. 5Principle 5.1The technique involves locating the metal sample of interest between the charging and oxidation cells, where the charging cell contains the environment of interest. Hydrogen atoms are generated on the sample surface exposed to this environment. 5.2In gaseous environments, the hydrogen atoms are generated by adsorption and dissociation of the gaseous species. In aqueous environments, hydrogen atoms are produced by electrochemical reactions. In both cases, some of the hydrogen atoms diffuse through the metal sample and are then oxidized to hydrogen cations on exiting from the other side of the metal in the oxidation cell. A palladium coating is sometimes applied to one or both sides of the membrane following initial removal of oxide films. A palladium coating on the charging face of the membrane affects the sub-surface hydrogen concentration in the substrate and the measured permeation current. It is important to verify that the calculated diffusivity is not influenced by the coating. Palladium coating is particularly useful for gaseous charging. 5.3The environment and the electrode potential on the oxidation side of the membrane are selected so that the metal is either passive or immune to corrosion. The background current established prior to hydrogen transport is steady, and small compared to the hydrogen atom oxidation current. Table 1 Symbols and their designations and units SymbolDesignationUnit Exposed area of sample in the oxidation cell Lattice concentration of hydrogen as a function of position and time Sub-surface concentration of atomic hydrogen in interstitial lattice sites on the charging side of the sample Summation of the sub-surface concentration of hydrogen in interstitial lattice sites and reversible trap sites on the charging side of the sample Lattice diffusion coefficient of atomic hydrogen Effective diffusion coefficient of atomic hydrogen based on elapsed time corresponding to Faraday's constant () Time-dependent atomic hydrogen permeation flux as measured on the oxidation side of the sample Atomic hydrogen permeation flux at steady-state as measured on the oxidation side of the sample Normalized flux of atomic hydrogen1 Time-dependent atomic hydrogen permeation current Steady-state atomic hydrogen permeation current Sample thicknessm Time elapsed from commencement of hydrogen chargings Elapsed time measured by extrapolating the linear portion of the rising permeation current transient s Time to achieve a value of s Distance in sample measured in the thickness directionm Normalized time ()1 Normalized time to achieve a value of 1 Am2 C(x,t)mol·m3 C0mol·m3 C0Rmol·m3 Dlm2·s1; Deff J(t)/Jss=0,63 m2·s1; FF =96 485 C·mol1C·mol1 J(t)mol·m2s1 Jssmol·m2s1 J(t)/Jss I(t)A·m2 IssA·m2 L t tb tlagJ(t)/Jss=0,63 x Dlt/L2 lagJ(t)/Jss=0,63 BS ISO 17081:2004 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 11:41:54 GMT+00:00 2006, Uncontrolled Copy, (c) BSI 4 5.4The electrode potential of the sample in the oxidation cell is controlled at a value sufficiently positive to ensure that the kinetics of oxidation of hydrogen atoms are limited by the flux of hydrogen atoms, i.e. the hydrogen atom oxidation current density is transport limited. NOTEPalladium coating of the oxidation side of the sample can enhance the rate of oxidation and thereby enable attainment of transport-limited oxidation of hydrogen atoms at less positive potentials than for the uncoated sample. 5.5The oxidation current is monitored as a function of time. The total oxidation current comprises the background current and the permeation current. 5.6The thickness of the sample, , is usually selected to ensure that the measured flux reflects volume (bulk) controlled hydrogen atom transport. NOTEThin specimens may be used for evaluation of the effect of surface processes on hydrogen entry (absorption kinetics or transport in oxide films). 5.7In reasonably pure metals with a sufficiently low density of microstructural trap sites, atomic hydrogen transport through the material is controlled by lattice diffusion. 5.8The effect of alloying and of microstructural features such as dislocations, grain boundaries, inclusions, and precipitate particles is to introduce traps for hydrogen atoms, which retard hydrogen transport. The rate of hydrogen atom transport through the metal during a first permeation test can be affected by both irreversible and reversible trapping. At steady state, all of the irreversible traps are occupied. If the mobile hydrogen atoms are then removed and a subsequent permeation test conducted on the sample, the difference between the first and second permeation transients may be used to evaluate the influence of irreversible trapping on transport. For some environments the conditions on the charging side of the sample may be suitably altered to induce a decay of the oxidation current after attainment of steady state. The rate of decay is determined by diffusion and reversible trapping only and hence can also be used to evaluate the effect of irreversible trapping on transport during the first transient. NOTE 1Reversible and irreversible traps can both be present in a particular metal. NOTE 2Comparison of repeated permeation transients with those obtained for the pure metal can be used, in principle, to evaluate the effect of reversible trapping on atomic hydrogen transport. NOTE 3The technique is suitable for systems in which hydrogen atoms are generated uniformly over the charging surface of the sample. It is not usually applicable to corroding systems in which pitting attack occurs,
