1、BSI Standards PublicationBS ISO 17918:2015Corrosion of metals and alloys Evaluation of selectivecorrosion of Cu alloys andgrey cast iron for powerplant components by visualinspection and hardnessmeasurementBS ISO 17918:2015 BRITISH STANDARDNational forewordThis British Standard is the UK implementat
2、ion of ISO 17918:2015.The 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 necessaryp
3、rovisions of a contract. Users are responsible for its correctapplication. The British Standards Institution 2015. Published by BSI StandardsLimited 2015ISBN 978 0 580 79217 5ICS 77.060Compliance with a British Standard cannot confer immunity fromlegal obligations.This British Standard was published
4、 under the authority of theStandards Policy and Strategy Committee on 31 July 2015.Amendments issued since publicationDate Text affectedBS ISO 17918:2015 ISO 2015Corrosion of metals and alloys Evaluation of selective corrosion of Cu alloys and grey cast iron for power plant components by visual insp
5、ection and hardness measurementCorrosion des mtaux et alliages valuation de la corrosion slective des alliages de cuivre et des fontes grises dans les composants des centrales lectriques par examen visuel et mesure de la duretINTERNATIONAL STANDARDISO17918First edition2015-07-01Reference numberISO 1
6、7918:2015(E)BS ISO 17918:2015ISO 17918:2015(E)ii ISO 2015 All rights reservedCOPYRIGHT PROTECTED DOCUMENT ISO 2015All 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 phot
7、ocopying, or posting 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 officeCase postale 56 CH-1211 Geneva 20Tel. + 41 22 749 01 11Fax + 41 22 749 09 47
8、E-mail copyrightiso.orgWeb www.iso.orgPublished in SwitzerlandBS ISO 17918:2015ISO 17918:2015(E)Foreword ivIntroduction v1 Scope . 12 Terms and definitions . 13 Principle 24 Procedures 24.1 Selection of components sensitive to selective corrosion and components for the test . 24.1.1 Components sensi
9、tive to selective corrosion of alloys 24.1.2 Selection of components subjected to the test for selective corrosion . 34.2 Visual inspection and hardness test for selective corrosion on alloys . 34.3 Procedure of visual inspection for selective corrosion of alloys 34.4 Procedure of hardness test for
10、selective corrosion on alloys . 44.4.2 Apparatus . 44.4.17 Precision and bias . 55 Responsibility 56 Assessment criteria and corrective actions . 66.1 Assessment criteria . 66.2 Corrective actions for unsatisfactory results 7Annex A (informative) Data sheet of visual inspection for selective corrosi
11、on of alloys . 8Annex B (informative) Description sheet for damaged area from selective corrosion of alloys . 9Annex C (informative) Evaluation sheet of hardness test results for selective corrosion of alloys10Annex D (informative) Data sheet of hardness test for selective corrosion of alloys (examp
12、le) 11Annex E (informative) Photo samples of case histories for selective corrosion 12Bibliography .21 ISO 2015 All rights reserved iiiContents PageBS ISO 17918:2015ISO 17918:2015(E)ForewordISO (the International Organization for Standardization) is a worldwide federation of national standards bodie
13、s (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,
14、 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.The procedures used to develop this document and those intended for its further ma
15、intenance 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 drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).At
16、tention 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. Details of any patent rights identified during the development of the document will be in the Introduct
17、ion 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 constitute an endorsementFor an explanation on the meaning of ISO specific terms and expressions related to conform
18、ity 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 Information The committee responsible for this document is ISO/TC 156, Corrosion of metals and alloys.iv ISO 2015 All rights rese
19、rvedBS ISO 17918:2015ISO 17918:2015(E)IntroductionSelective corrosion occurs when some alloys such as brass, bronze, and cast iron come in contact with stagnant solutions for a long time. Materials suffering from selective corrosion may show various symptoms of deterioration such as localized porous
20、 areas (crumbly and fragile), discoloration, change in colour, and so on.This kind of corrosion occurs when one of the alloying elements in alloys is dissolved from the matrix because of potential differences with other alloying elements. Most common types of selective corrosion are dezincification
21、in brass and graphitization in grey cast iron. Selective corrosion is a very slow and inconspicuous process. Once it occurs, it may have an adverse effect on the integrity of components and structures in the industry. Therefore, it is needed to distinguish the symptoms of selective corrosion and rou
22、ghly evaluate the soundness of components and structures in the field that are susceptible to selective corrosion before they are subjected to engineering evaluations.This International Standard specifies the visual inspection and the hardness test for parts made of grey cast iron and uninhibited br
23、ass containing greater than 15 % zinc, etc. in systems and components that are sensitive to selective corrosion. Susceptible materials, high temperatures, stagnant flow conditions, and a corrosive environment, such as acidic solutions for brasses with high zinc content and dissolved oxygen, are the
24、causes of selective corrosion. Components include piping, valve bodies and bonnets, pump casings, and heat exchanger components that are susceptible to selective corrosion. These components can be exposed to raw water, treated water, closed cooling water, ground water, water contaminated fuel oil, o
25、r water contaminated lube oil.The criterion is suggested in this International Standard, whether the materials suffering from selective corrosion can be continuously used or should be subjected to engineering evaluation for further and exact examination. The determination of symptoms of selective co
26、rrosion and degree of deterioration can be made with the procedures as follows: selection of components sensitive to selective corrosion and components for the test (sampling); visual inspection for selective corrosion of alloys; hardness test for selective corrosion of alloys.This International Sta
27、ndard provides examples of data sheets for descriptions and information of materials damaged by selective corrosion in the visual inspection. Provided reference photos of case histories can be used in comparing with the real damages of materials on sites. Examples of a description sheet and an evalu
28、ation sheet are also provided for the hardness test of selective corrosion. ISO 2015 All rights reserved vBS ISO 17918:2015BS ISO 17918:2015Corrosion of metals and alloys Evaluation of selective corrosion of Cu alloys and grey cast iron for power plant components by visual inspection and hardness me
29、asurement1 ScopeThis International Standard specifies procedures of on-site detection and evaluation in order to determine the effects of material deterioration such as material loss from the components and structures that are sensitive to selective corrosion in industrial facilities, including nucl
30、ear power plants.The methodology involves visual inspection and hardness measurements in situ complemented by sample removal. These procedures include (a) representative sampling of components sensitive to selective corrosion, (b) the visual inspection, and (c) the hardness test, respectively. For a
31、n exact analysis, additional laboratory testing is recommended.The methodology is most applicable to grey cast iron and copper alloy with more than 15 % zinc. Extension to other alloys requires supportive evidence of validation.Assessment criteria orientated to the nuclear power plant application du
32、ring the past five years before the end of extended operation define the necessity for further engineering evaluation and action like, for example, further sampling, higher frequency of inspection, and component repair or exchange.This specification is not applicable for components used where the re
33、presentative sampling of surfaces in contact to the fluid is not detectable optically or detected with the portable hardness tester. Also, in case of non-representative component selection like in HVAC or building service application, this specification is not applicable. For components not used in
34、nuclear power plant, the assessment criteria have to be agreed by the parties. Assessment criteria of hardness test alone is not applicable to the evaluation of structural integrity of Al-bronze, NAB, and Cu-Ni.2 Terms and definitionsFor the purposes of this document, the following terms and definit
35、ions apply.2.1selective corrosioncorrosion of an alloy whereby the components react in proportions that differ from their proportions in the alloyNote 1 to entry: It is a phenomenon in which one of the alloying elements is electrochemically active and sensitive to corrosion resulting in being select
36、ively removed and the concentrations in other elements being relatively increased in alloys such as bronze, brass, and grey cast iron etc.EXAMPLE Dezincification, graphitizationSOURCE: ISO 8044:1999, 3.202.1.1dezincificationselective corrosion of brass resulting in preferential removal of zincNote 1
37、 to entry: It is a phenomenon where the more electrochemically active zinc is preferentially dissolved from copper-zinc alloys with mass fraction of zinc greater than 15 % resulting in a porous copper layer with diminished mechanical properties.INTERNATIONAL STANDARD ISO 17918:2015(E) ISO 2015 All r
38、ights reserved 1BS ISO 17918:2015ISO 17918:2015(E)SOURCE: ISO 8044:1999, 3.212.1.2graphitizationselective corrosion of grey cast iron, resulting in partial removal of metallic constituents, leaving graphiteNote 1 to entry: It is a corrosion process in which iron is selectively dissolved from grey ca
39、st iron resulting in remaining vulnerable porous graphite.SOURCE: ISO 8044:1999, 3.222.2visual inspectionone of the non-destructive tests within condition monitoring in which the inspector observes directly the materials, productions, or structures with his own eyes to determine whether surface defe
40、cts exist on the test bodies2.3hardness testindentation test carried out using a hardness testing machine to measure the hardness of a materialNote 1 to entry: Hardness is local resistance of surface by pressing an indenter with specific load to designate solidness and softness of materials. There i
41、s the Brinell hardness which can be used as measuring method with the indenter. An informative calculation to other hardness types (Rockwell hardness, Vickers hardness, etc.) can be helpful.3 PrincipleThe result of deterioration from the selective corrosion is the loss of materials followed by a los
42、s of mechanical properties creating a failure.The loss of materials, which may be the reason for failure, can be determined by the visual inspection and the hardness measurement. The visual inspection identifies corrosion, discoloration, change in colour and local porosity, and the hardness test rev
43、eals the change in mechanical properties from the corrosion process at the surface of the test material.4 Procedures4.1 Selection of components sensitive to selective corrosion and components for the testSelection of candidate systems and components for the test and test samples are entirely site-sp
44、ecific considering operating characteristics, sensitivity of materials to degradation, and accessibility. It is recommended that components which are only present in small number in the installation are subjected to 100 % sampling, but that components in large number (e.g. small valves and flanges)
45、are subject to random sampling. In this case, sampling ratio is recommended to be over 10 % of whole components.NOTE “Large number” means the quantity that the inspectors cannot afford to handle in a limited inspection period such as an overhaul period or an in-service inspection period and vice ver
46、sa for “small number”. Decision shall be made on responsibility of site engineers.4.1.1 Components sensitive to selective corrosion of alloysComponents sensitive to selective corrosion are mainly made of copper alloys, aluminium-copper alloys, copper-nickel alloys, and grey cast irons, for example:a
47、) Heat exchangers in component cooling water systems, valves in component cooling seawater systems, pumps and valves in fire protection systems, and components in similar conditions thereof;2 ISO 2015 All rights reservedBS ISO 17918:2015ISO 17918:2015(E)b) Buried pipes and fittings of grey cast iron
48、;c) Exemption for the test may be permitted for the components periodically subjected to non-destructive tests.4.1.2 Selection of components subjected to the test for selective corrosion4.1.2.1 In principle, components should be subjected to the 100 % sampling inspection for selective corrosion even
49、 though the components made of same materials are under the same environment and the same operating condition. The visual inspection and the hardness test should be performed for the surfaces of object components that have been in contact to corrosive media.4.1.2.2 When it is impossible to perform 100 % sampling because there are numerous object components sensitive to selective corrosion, random sampling can be permitted for the object components. The selected sample components should be subjected to the visual inspection and the hardness test
