1、BSI Standards PublicationBS ISO 16540:2015Corrosion of metals andalloys Methodology fordetermining the resistanceof metals to stress corrosioncracking using the four-pointbend methodBS ISO 16540:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementation of ISO 16540:2015.Th
2、e UK participation in its preparation was entrusted to TechnicalCommittee ISE/NFE/8, Corrosion of metals and alloys.A list of organizations represented on this committee can beobtained on request to its secretary.This publication does not purport to include all the necessaryprovisions of a contract.
3、 Users are responsible for its correctapplication. The British Standards Institution 2015.Published by BSI Standards Limited 2015ISBN 978 0 580 73641 4ICS 77.060Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published under the authority of
4、theStandards Policy and Strategy Committee on 31 October 2015.Amendments/corrigenda issued since publicationDate T e x t a f f e c t e dBS ISO 16540:2015 ISO 2015Corrosion of metals and alloys Methodology for determining the resistance of metals to stress corrosion cracking using the four-point bend
5、 methodCorrosion des mtaux et alliages Mthodologie de dtermination de la rsistance des mtaux la fissuration par corrosion sous contrainte au moyen de la mthode de flexion quatre pointsINTERNATIONAL STANDARDISO16540First edition2015-10-01Reference numberISO 16540:2015(E)BS ISO 16540:2015ISO 16540:201
6、5(E)ii ISO 2015 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2015, Published in SwitzerlandAll rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or pos
7、ting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below or ISOs member body in the country of the requester.ISO copyright officeCh. de Blandonnet 8 CP 401CH-1214 Vernier, Geneva, SwitzerlandTel. +41 22 749 01 11Fax +41 2
8、2 749 09 47copyrightiso.orgwww.iso.orgBS ISO 16540:2015ISO 16540:2015(E)Foreword ivIntroduction v1 Scope . 12 Normative references 13 Terms and definitions . 14 Principle 15 Loading jig design 26 Specimen preparation 36.1 General . 36.2 Parent material specimens . 36.3 Welded specimens . 46.4 Clad p
9、roduct specimens 57 Strain gauging 58 Loading . 68.1 Strain level 68.2 Setting the total strain value . 68.3 Testing at elevated temperature 89 Test environment . 89.1 General . 810 Procedure for four-point bend testing 911 Failure appraisal 1011.1 Carbon steel 1011.2 Corrosion resistant alloys . 10
10、12 Test report 11Annex A (informative) Surface preparation (see also ISO 7539-1) .12Annex B (informative) Procedure for strain gauging and determining uniaxial stress-strain calibration curve .16Bibliography .18 ISO 2015 All rights reserved iiiContents PageBS ISO 16540:2015ISO 16540:2015(E)ForewordI
11、SO (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 c
12、ommittee 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 electr
13、otechnical standardization.The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the different types of ISO documents should be noted. This document was dra
14、fted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).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 ri
15、ghts. Details of any patent rights identified during the development of the document will be in the Introduction and/or on the ISO list of patent declarations received (see www.iso.org/patents).Any trade name used in this document is information given for the convenience of users and does not consti
16、tute an endorsement.For an explanation on the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISOs adherence to the WTO principles in the Technical Barriers to Trade (TBT) see the following URL: Foreword - Supplementary informationThe comm
17、ittee responsible for this document is ISO/TC 156, Corrosion of metals and alloys.This International Standard is based on a draft NACE International standard on Four-Point Bend Testing of Materials for Oil and Gas applications. NACE International grants the right to ISO to reproduce material extract
18、ed from that document.iv ISO 2015 All rights reservedBS ISO 16540:2015ISO 16540:2015(E)IntroductionThis International Standard has been prepared as a sub-set of ISO 7539 which consists of the following parts, under the general title Corrosion of metals and alloys Stress corrosion testing: Part 1: Ge
19、neral guidance on testing procedures Part 2: Preparation and use of bent-beam specimens Part 3: Preparation and use of U-bend specimens Part 4: Preparation and use of uniaxially loaded tension specimens Part 5: Preparation and use of C-ring specimens Part 6: Preparation and use of precracked specime
20、ns for tests under constant load or constant displacement Part 7: Method for slow strain rate testing Part 8: Preparation and use of specimens to evaluate weldments Part 9: Preparation and use of pre-cracked specimens for tests under rising load or rising displacement Part 10: Reverse U-bend method
21、Part 11: Guidelines for testing the resistance of metals and alloys to hydrogen embrittlement and hydrogen-assisted cracking ISO 2015 All rights reserved vBS ISO 16540:2015BS ISO 16540:2015Corrosion of metals and alloys Methodology for determining the resistance of metals to stress corrosion crackin
22、g using the four-point bend method1 ScopeThis International Standard provides guidelines for the use of four-point bend testing to evaluate the resistance of metals including carbon steel, low alloy steels, and corrosion resistant alloys (CRAs) to stress corrosion cracking. The method gives guidance
23、 on testing of both parent plate and welds and includes procedures for metals that have no distinct yield point in their stress-strain behaviour as well as metals with a distinct yield point. The emphasis in this International Standard is on the generic methodology of the four-point bend test. Servi
24、ce application will be varied and the relevant industry standard is to be consulted where appropriate.2 Normative referencesThe following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cite
25、d applies. For undated references, the latest edition of the referenced document (including any amendments) applies.ISO 8407, Corrosion of metals and alloys Removal of corrosion products from corrosion test specimens3 Terms and definitionsFor the purposes of this document, the following terms and de
26、finitions apply.3.1corrosion resistant alloyCRAalloy designed to be resistant to general and localized corrosion in environments that are corrosive to carbon steel3.2heat affected zoneHAZportion of the base metal that is not melted during brazing, cutting, or welding, but whose microstructure and pr
27、operties are altered by the heat of these processes3.3soft zone crackingSZCform of sulphide stress cracking that may occur when a steel contains a local “soft zone” of low yield strength material and is exposed under stress to environments containing H2SNote 1 to entry: Under service loads, soft zon
28、es may yield and accumulate plastic strain locally increasing the susceptibility to cracking of an otherwise cracking resistant material. Such soft zones are typically associated with welds in carbon steels.4 PrincipleThe four-point bend test is a constant displacement test that is performed by supp
29、orting a beam specimen on two loading rollers (bearing cylinders) and applying a load through two other loading INTERNATIONAL STANDARD ISO 16540:2015(E) ISO 2015 All rights reserved 1BS ISO 16540:2015ISO 16540:2015(E)rollers so that one face of the specimen is in tension (and uniformly stressed betw
30、een the inner rollers) and the other is in compression. The stress at mid-thickness is zero and there will be significant gradients in stress through the thickness, this being most marked for thin specimens. As a consequence, cracks may initiate, but then arrest or their growth rate decrease. Hence,
31、 complete fracture might not always occur during the test exposure period. Important parameters are roller spacing, ratio between outer and inner span, specimen dimensions, width-to-thickness ratio, and roller diameter. Testing of as-welded specimens presents a particular challenge due to significan
32、t variations in root profile, surface roughness, extent of micro-cracks, and degree of misalignment.5 Loading jig design5.1 A loading jig similar to that shown in Figure 1 shall be used to apply a constant deflection to the specimen. The dimensions are often chosen so that A = H/4.5.2 Specimens of t
33、hickness up to 5 mm present few problems for parent material specimens as they can be easily accommodated in test vessels of modest size with typical dimensions for the loading jig of the following: spacing between inner rollers: 50 mm-60 mm; spacing between outer rollers: 100 mm-130 mm; roller diam
34、eter: 6 mm-10 mm.5.3 Thicker specimens, up to full wall thickness, are advisable for testing welded specimens. Here, there is a balance between minimizing the load by increasing the spacing between span supports and accommodating the increased size of the jig with possible constraints associated wit
35、h the size of the test vessel. This is an individual judgement.Keyt specimen thicknessA distance between the inner and outer supportsH distance between the outer supportsFigure 1 Typical four-point bend loading jig design2 ISO 2015 All rights reservedBS ISO 16540:2015ISO 16540:2015(E)5.4 The specime
36、n shall be electrically isolated from the loading jig in order to avoid undesirable galvanic and crevice corrosion. This is best achieved by the use of ceramic rollers as these also satisfy the additional requirement that the rollers should not exhibit any yielding or creep during the test.5.5 Frict
37、ion between the rollers (bearing cylinders) and the specimen should be minimised to ensure that frictional constraint does not impact on the stress distribution in the specimen. This is best achieved by the use of ceramic rollers that have a low friction contact surface and can be further reduced if
38、 they are free to rotate while loading the test specimen. In the absence of free rotation, there will be some effect of friction on the force required to achieve the required strain. However, provided the specimen is strain gauged and the frictional forces are not excessive, this will not impact on
39、the test results. Nevertheless, an increase in friction will increase the stress and strain on the tensile surface locally at the inner loading pins and can enhance the likelihood of cracks forming in the specimen at those locations (see Clause 11). The extent of overstraining for a particular loadi
40、ng jig can be assessed by strain gauging in that region for a typical test condition.5.6 The material of construction of the loading jig shall be resistant to stress corrosion cracking in the test environment and the jig should be sufficiently rigid. Contamination of the solution with corrosion prod
41、ucts from the jig material shall be minimized to avoid impacting on the test results. This can be achieved by the use of corrosion resistant alloys or by application of a coating to the jig. When testing carbon and low alloy steels with higher alloyed jigs, electrical bridging from corrosion product
42、s is a possibility and electrical resistance checks shall be made at test termination. Where electrical isolation is not undertaken, then the material of construction of the jigs shall be similar to that of the specimens. For testing of carbon and low alloy steel specimens, adoption of low alloy ste
43、el jigs may be preferred to ensure an absence of galvanic interaction. In this case, a suitable inert coating may be applied to the jigs to minimize accumulation of corrosion products.6 Specimen preparation6.1 General6.1.1 Four-point bend specimens shall be flat strips of metal of uniform rectangula
44、r cross section and uniform thickness except in the case of testing welded specimens with one face in the as-welded condition for which a non-uniform cross section is inherent, or when testing the inner surface of piping material in its original surface state (for which the surface would be concave)
45、 or outer surface of a piping material in its original surface state (for which the surface would be convex).6.1.2 Identification marks or numbers shall be permanently inscribed on each end of the specimen. This is the region of lowest stress and the identification marks should therefore not initiat
46、e cracking.6.1.3 Specimen preparation techniques which generate hydrogen at the specimen surface, e.g. electric discharge machining, should not be used on materials that are susceptible to hydrogen-induced damage. If the use of such techniques is necessary, a final grinding of the outer surfaces of
47、the specimen shall be carried out to remove material containing retained hydrogen. The grinding shall be carried out as soon as possible to minimize the time available for the hydrogen to diffuse into the specimen from the outer surface. The thickness removed should reflect conservative evaluation o
48、f the effective hydrogen diffusivity in the material. For most corrosion resistant alloys, removal of 500 m from each surface of the specimen is sufficient. Baking out of the hydrogen can also be considered, but only where this does not introduce changes in the material microstructure/microchemistry
49、.6.2 Parent material specimens6.2.1 Parent material specimens shall be machined, avoiding sharp edges, from the pipe or plate in the longitudinal direction unless otherwise specified. ISO 2015 All rights reserved 3BS ISO 16540:2015ISO 16540:2015(E)6.2.2 A typical four-point bend parent material specimen is shown in Figure 2 a).6.2.3 The specimen width shall be 1,5 to 5 times the thickness of the specimen. Any deviation from this requirement, e.g. for very thick C-steel sections, requires demonstration that out-of-plane bendin
