1、BRITISH STANDARD BS ISO 15724:2001 Metallic and other inorganic coatings Electrochemical measurement of diffusible hydrogen in steels Barnacle electrode method ICS 25.220.40; 25.220.99 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAWBS ISO 15724:2001 This British Standard, havi
2、ng been prepared under the direction of the Sector Policy and Strategy Committee for Materials and Chemicals, was published under the authority of the Standards Policy and Strategy Committee on 21 December 2001 BSI 21 December 2001 ISBN 0 580 38800 X National foreword This British Standard reproduce
3、s verbatim ISO 15724:2001 and implements it as the UK national standard. The UK participation in its preparation was entrusted to Technical Committee STI/37, Methods of test for metallic and related inorganic coatings including corrosion tests, which has the responsibility to: A list of organization
4、s 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 Standards Catalogue under the section entitled “International Standards Corr
5、espondence Index”, or by using the “Find” facility of the BSI Standards Electronic Catalogue. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does n
6、ot 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 developm
7、ents 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 v, a blank page, pages 1 to 10, an inside back cover and a back cover. The BSI copyright date displayed in this document indicates when the document was
8、last issued. Amendments issued since publication Amd. No. Date CommentsINTERNATIONAL STANDARD ISO 15724 First edition 2001-12-01 Reference number ISO 15724:2001(E) Metallic and other inorganic coatings Electrochemical measurement of diffusible hydrogen in steels Barnacle electrode method Revtements
9、mtalliques et autres revtements inorganiques Mesurage lectrochimique de lhydrogne diffusible dans les aciers Mthode par lectrode anatifeISO 15724:2001(E) iiISO 15724:2001(E) iii Contents Page 1 Scope . 1 2 Normative references . 1 3 Principle 2 4 Reagents 2 5 Apparatus . 3 6 Test specimens . 5 7 Cal
10、ibration 5 8 Procedure . 5 9 Results 8 10 Interpretation of results . 8 11 Test report 8 Bibliography. 10ISO 15724:2001(E) iv Foreword ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing Internatio
11、nal 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
12、, 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 3. Draft International Standards
13、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 International Standard may be t
14、he subject of patent rights. ISO shall not be held responsible for identifying any or all such patent rights. International Standard ISO 15724 was prepared by Technical Committee ISO/TC 107, Metallic and other inorganic coatings, Subcommittee SC 2, Test methods.ISO 15724:2001(E) v Introduction When
15、atomic hydrogen enters steels and certain other alloys, it can cause loss of ductility or of load-carrying ability, cracking (usually submicroscopic cracks) or catastrophic brittle failure at applied stresses well below the yield strength or even the normal design strength of the alloys. This phenom
16、enon often occurs in alloys that show no significant loss in ductility when measured by conventional tensile tests and is frequently referred to as “hydrogen- induced delayed brittle failure”, “hydrogen stress cracking” or “hydrogen embrittlement”. The hydrogen can be introduced during fabrication,
17、cleaning, pickling, phosphating, electroplating, autocatalytic processes and in the service environment as a result of cathodic protection reactions or corrosion reactions. Parts that have been machined, ground, cold-formed or cold-straightened subsequent to any heat treatment are especially suscept
18、ible to hydrogen embrittlement damage.INTERNATIONAL STANDARD ISO 15724:2001(E) 1 Metallic and other inorganic coatings Electrochemical measurement of diffusible hydrogen in steels Barnacle electrode method WARNING This International Standard does not address any health hazards and safety matters ass
19、ociated with its use. It is the responsibility of the user of this International Standard to establish appropriate health and safety practices and take suitable actions for any national regulations. 1 Scope This International Standard describes a method that uses an electronic hydrogen detection ins
20、trument for measuring relative, diffusible hydrogen concentrations in bare steels or in plated steels after the coating has been removed. It is assumed that the hydrogen is uniformly distributed throughout a part. The method does not measure actual hydrogen concentration. However, oxidation current
21、densities measured against time provide a useful indication of relative hydrogen concentrations and, therefore, the measurements can be used for comparison purposes. The method may be used as a quality control procedure as it does provide a quick means of measuring the effectiveness of pre- and/or p
22、ost-plating heat treatments or of monitoring hydrogen uptake during plating or due to corrosion. It is important to note that the absence of failure in a particular test does not provide confirmation of complete elimination of hydrogen embrittlement because no one test method can provide all the dat
23、a necessary to evaluate the degree of hydrogen degradation. For unplated parts the method is non-destructive; however, for plated parts the coating has to be removed prior to measurement by a means proven not to damage the steel or to introduce hydrogen. This test method is limited to: carbon and al
24、loy steels, excluding austenitic stainless steels (see note 1); flat specimens to which the cell can be attached (see note 2); measurements at room temperature ( ). NOTE 1 If this method is used for austenitic stainless steels and other face centred cubic (FCC) alloys, measurement times and interpre
25、tation of results will have to be determined because of the different kinetics involved. NOTE 2 For slightly curved surfaces it is essential to define an area that is reproducible. The area calculation will be different from that described in this International Standard. NOTE 3 The method can be app
26、lied to small parts, however, this necessitates some modification of the technique, procedure and interpretation of results. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this International Standard. For da
27、ted references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For 25
28、 C 1 CISO 15724:2001(E) 2 undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 9587, Metallic and other inorganic coatings Pretreatments of iron or steel to reduce the risk of h
29、ydrogen embrittlement ISO 9588, Metallic and other inorganic coatings Post-coating treatments of iron or steel to reduce the risk of hydrogen embrittlement 3P r i n c i p l e This method is an adaptation of the electrochemical permeation method for hydrogen diffusion. A hydrogen-containing steel par
30、t is made the anode in an electrochemical cell containing an alkaline solution as the electrolyte, with a nickel-nickel oxide (Ni/NiO) electrode forming the cathode. The cell maintains zero hydrogen concentration at the surface of the steel by oxidizing the hydrogen atoms to water. As there is no co
31、rrosion reaction taking place at the steel surface, the anodic current measured as a function of time is attributed to the concentration of mobile hydrogen. In this method, the actual hydrogen concentration is not determined. This is because the calculation of hydrogen concentration requires knowled
32、ge of the hydrogen diffusion coefficient in the alloy and knowledge of the decay curve, both of which are not always known, especially at very low hydrogen concentrations. However, comparative current densities can be used to indicate relative hydrogen concentrations. In this method, it is assumed t
33、hat the hydrogen is uniformly distributed throughout the steel part and that hydrogen is not appreciably lost due to diffusion during the course of the measurement. Furthermore, as the measurement is relatively rapid, it is probable that trapped hydrogen that is not easily released without stress bu
34、t that could contribute to delayed failure, will not be detected. This method is based on measurement of current that decays over a fixed period, in this case for . The current density will depend on the material as well as on the hydrogen concentration. Each material will have a background current
35、density (see 7.4). A measurement higher than background indicates the presence of hydrogen. Higher current densities indicate higher hydrogen concentrations; the higher the current densities the higher the likelihood of hydrogen embrittlement. A background correction of the actual measurement, howev
36、er, is not made (see note to 7.4). 4R e a g e n t s Reagent grade chemicals of sufficiently high purity to ensure the accuracy of the determination shall be used in all tests. 4.1 Electrolyte ( sodium hydroxide solution), dissolve of sodium hydroxide (NaOH) pellets in distilled or de-ionized water a
37、nd dilute to . 4.2 Methyl alcohol (CH 3 OH). 4.3 Ethyl alcohol (C 2 H 5 OH). 30 min 0,2 M 8 g 1lISO 15724:2001(E) 3 5A p p a r a t u s See Figures 1 and 2. 5.1 The barnacle electrode system. This consists of 5.1.1 cell, left open to the atmosphere without any purging (see Figure 2), and made of a no
38、n-metallic inert material that will not react with or contaminate the electrolyte, and the side opening of which has a recess to accommodate a silicon rubber gasket. 5.1.2 gasket, made of silicon rubber, that shall provide a reproducible contact area between the solution and the specimen, preferably
39、 . 5.1.3 cell holder, a cradle-like C-clamp. Key 1 Strip chart recorder 2E l e c t r o m e t e r 3 Known resistance 4 Driving electrode, Ni/NiO 5N a O H 6G a s k e t 7 Hydrogen-containing part Figure 1 Schematic diagram of a barnacle electrode system 0,2 M 1cm 2ISO 15724:2001(E) 4 5.1.4 anode (i.e.
40、the specimen to be tested). 5.1.5 cathode, a Ni/NiO electrode (e.g. from a nickel-cadmium battery), the area of which shall be approximately five times that of the anode. 5.1.6 a current measuring device. NOTE The current can be measured by any method that will not adversely affect the system; e.g.,
41、 in this International Standard, the device consists of: a) a standard resistance connected across the two electrodes via a switch; b) an electrometer to determine the current by measuring the voltage drop across the resistance (a resistor with an electrometer having an input impedance of has been f
42、ound to be satisfactory); c) a strip chart recorder to monitor the electrometer measurements (an input resistance of has been found to be satisfactory); d) a timer accurate to within in a run. Dimensions in millimetres Key 1G a s k e t s e a t Figure 2 Barnacle electrode cell 10 k 10 12 100 k 10 s 3
43、0 minISO 15724:2001(E) 5 5.2 Microscope. 5.3 Nylon cleaning pad, impregnated with aluminium oxide. 6 Test specimens The specimen can be an actual part or a coupon to thick. If a coupon is used, it shall be of the same material and form, and have the same heat treatment and surface finish as the part
44、, in order to depict the same hydrogen parameters, such as hydrogen uptake during processing, mobile versus trapped hydrogen and surface finish. The specimen shall be sufficiently large to accommodate the cell and for a duplicate measurement to be made (see 8.3.6). It shall also be sufficiently flat
45、 and smooth to prevent leakage of the electrolyte under the gasket. 7 Calibration 7.1 Calibrate the Ni/NiO electrode (5.1.5) against a saturated calomel electrode (SCE) in NaOH solution (4.1). A freshly charged Ni/NiO electrode will be at least more noble (i.e. positive) than the SCE. It shall be re
46、charged when its potential drops to less than more noble (i.e. positive) than SCE. 7.2 Charge the Ni/NiO electrode using a platinum, or similar, inert electrode as the cathode and the Ni/NiO electrode as the anode in NaOH solution for at a current density of to . NOTE To prevent a temporary drain of
47、 the charge due to repeated use of the Ni/NiO electrodes, alternate two electrodes during a series of measurements. 7.3 Calculate the cell contact area outlined by the gasket as follows. Using the cell holder (5.1.3) assemble the cell (5.1.1) on a flat specimen with a smooth piece of aluminium foil
48、or sheet, at least thick, between the specimen (5.1.4) and the gasket (5.1.2). The Ni/NiO electrode is not needed. Fill the cell with NaOH solution and allow the aluminium to be etched for about . Dismantle the cell and rinse the aluminium sample thoroughly. NOTE 1 A properly assembled cell will pro
49、duce a sharply defined circular etched area. Measure the diameter of the circle using a microscope (5.2), see 9.2. NOTE 2 A poor gasket or improper tightening of the cell can be detected by this procedure. Overtightening will produce a deformation of the gasket, resulting in an out-of-round etch. Undertightening, or a worn gasket, will cause crevices, resulting in etching under the gasket. 7.4 Measure the background current density by using uncoated specimens containing no hydrogen, or specimens that have been subjected to heat treatment
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