1、BRITISH STANDARD BS EN ISO 7539-3:1995 Incorporating Amendment No.1 Corrosion of metals and alloys Stresscorrosion testing Part3: Preparation and use of U-bend specimens The European Standard EN ISO7539-3:1995 has the status of a BritishStandardBSENISO7539-3:1995 This British Standard, having been p
2、repared under the directionof the Iron and Steel Standards Policy Committee andthe Non-ferrous Metals Standards Policy Committee, waspublished under the authorityof the Board of BSI andcomes into effect on 31July1990 BSI 04-2000 The following BSI references relate to the work on this standard: Commi
3、ttee reference ISM/NFM/8 Draft for comment 88/36940 DC ISBN 0 580 18792 6 Committees responsible for this BritishStandard The preparation of this BritishStandard was entrusted by the Iron and Steel Standards Policy Committee(ISM/-) and Non-ferrous Metals Standards Policy Committee(NFM/-) to Technica
4、l Committee ISM/NFM/8, upon which the following bodies were represented: Aluminium Federation British Gas plc British Steel Industry Department of Trade and Industry(National Physical Laboratory) Department of Transport(Transport and Road Research Laboratory) Electricity Supply Industry in England a
5、nd Wales Institution of Corrosion Science and Technology Institution of Structural Engineers Society of Chemical Industry United Kingdom Atomic Energy Authority Welding Institute Amendments issued since publication Amd. No. Date Comments 8712 October 1994 Indicated by a sideline in the marginBSENISO
6、7539-3:1995 BSI 04-2000 i Contents Page Committees responsible Inside front cover National foreword ii Foreword 2 1 Scope 3 2 Normative reference 3 3 Definitions 3 4 Principle 3 5 Specimens 3 6 Procedure 5 7 Assessment of results 5 8 Test report 5 Figure 1 Typical stressed U-bends 4 Figure 2 Methods
7、 of stressing U-bend specimens 4 Publications referred to Inside back coverBSENISO7539-3:1995 ii BSI 04-2000 National foreword This Part of BS EN ISO7539 has been prepared under the direction of the Engineering Sector Board. It is identical with ISO7539-3:1989 Corrosion of metals and alloys Stress c
8、orrosion testing Part3: Preparation and use of U-bend specimens, published by the International Organization for Standardization(ISO). BS EN ISO7539 comprises the following parts: Part1: General guidance on testing procedures; Part2: Preparation and use of bent-beam specimens; Part3: Preparation and
9、 use of U-bend specimens; Part4: Preparation and use of uniaxially loaded tension specimens; Part5: Preparation and use of C-ring specimens; Part6: Preparation and use of pre-cracked specimens; Part7: Slow strain rate testing. A British Standard does not purport to include all the necessary provisio
10、ns of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Cross-references International Standard Corresponding BritishStandard ISO7539-1:1987 BS EN ISO7539 Corrosion of me
11、tals and alloys Stresscorrosion testing Part1:1995 Guide to testing procedures (Identical) Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, theEN ISO title page, pages2 to6, an inside back cover and a back cover. This standard has been updated (see copyr
12、ight date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover.EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO7539-3 May1995 ICS 77.060 Descriptors: Metals, alloys, tests, corrosion tests, stress corrosion tests English version C
13、orrosion of metals and alloys Stress corrosion testing Part3: Preparation and use of U-bend specimens (ISO7539-3:1989) Corrosion des mtaux et alliages Essais de corrosion sous contrainte Partie3:Prparation et utilisation des prouvettes cintres en U (ISO7539-3:1989) Korrosion de Metalle und Legierung
14、en Prfung der Spannungsrikorrosion Teil3:Vorbereitung und Anwendung von Bgelproben (ISO7539-3:1989) This European Standard was approved by CEN on1995-04-08. CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the
15、status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national standards may be obtained on application to the Central Secretariat or to any CEN member. This European Standard exists in three official versions(English, French, German).
16、A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the Central Secretariat has the same status as the official versions. CEN members are the national standards bodies of Austria, Belgium, Denmark, Finland, France, German
17、y, Greece, Iceland, Ireland, Italy, Luxembourg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom. CEN European Committee for Standardization Comit Europen de Normalisation Europisches Komitee fr Normung Central Secretariat: rue de Stassart 36, B-1050 Brussels 1995 All rig
18、hts of reproduction and communication in any form and by any means reserved in all countries to CEN and its members. RefNo.ENISO7539-3:1995EENISO7539-3:1995 BSI 04-2000 2 Foreword This European Standard has been taken over by the Technical Committee CEN/TC262, Protection of metallic materials agains
19、t corrosion, from the work of ISO/TC156, Corrosion of metals and alloys, of the International Organization for Standardization(ISO). This European Standard shall be given the status of a national standard, either by publication of an identical text or by endorsement, at the latest by November1995, a
20、nd conflicting national standards shall be withdrawn at the latest by November1995. According to the CEN/CENELEC Internal Regulations, the following countries are bound to implement this European Standard: Austria, Belgium, Denmark, Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembou
21、rg, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.ENISO7539-3:1995 BSI 04-2000 3 WARNING U-bend specimens made from high strength materials may fracture rapidly; pieces may fly off at high velocity and can be dangerous. Personnel installing and examining specimens must
22、 be made aware of this possibility and be protected against injury. 1 Scope 1.1 This part of ISO7539 covers procedures for designing, preparing and using U-bend test specimens for investigating the susceptibility of a metal to stress corrosion. The term “metal” as used in this part of ISO7539 includ
23、es alloys. 1.2 U-bend specimens may be used to test a variety of product forms. They are used principally for sheet, plate or flat extruded material, which conveniently provides flat specimens of rectangular cross-section, but may also be employed for wire or rod, or for machined specimens of circul
24、ar cross-section. They can also be used for parts joined by welding. 1.3 The U-bend test is frequently used to establish whether a metal is susceptible to stress corrosion cracking in a given environment. It is used in laboratories to screen materials for susceptibility for specific applications and
25、 in service environments to assess the risk of failure. 1.4 The principal advantages of the test are its simplicity and its consequent adaptability for use in plant. A disadvantage is that stresses cannot be quantified with accuracy and if this is desired an alternative method of stressing should be
26、 used. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this part of ISO7539. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this pa
27、rt of ISO7539 are encouraged to investigate the possibility of applying the most recent edition of the standard indicated below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO7539-1:1987, Corrosion of metal and alloys Stress corrosion testing Part1: General
28、 guidance on testing procedures. 3 Definitions For the purposes of this part of ISO7539, the definitions given in ISO7539-1 are applicable. 4 Principle 4.1 The test consists in exposing to the corroding medium a piece of metal bent into a U-shape and held in a manner which ensures that there are ini
29、tial tensile stresses ranging up to the yield point over a proportion of the surface. In the act of forming specimens, varying amounts of cold work may be introduced and this deformation may influence the stress corrosion cracking tendency as compared to that of the material in the original conditio
30、n. 4.2 The test may be performed under laboratory conditions by exposing the specimens to simulated service conditions or it may be carried out in the actual service environment at the location of interest. 4.3 The objective of the test is either to establish whether a metal is suitable for a propos
31、ed application or to assess the risk of stress corrosion cracking of metals used in existing plant under service conditions. 4.4 Wide variations in test results may be obtained for a given metal and environment even when testing nominally identical specimens and the replication of tests is frequentl
32、y necessary. If specimens are prepared to different sizes or orientations or are subjected to different stressing procedures, test results may be even more variable. 5 Specimens 5.1 A variety of specimen shapes and sizes can be employed and Figure 1 shows examples of specimens often used. Figure 2 i
33、ndicates some methods of forming the specimens. To simulate crevice conditions, it is possible to form a second specimen over the first, thereby creating a crevice between the two, and to test the composite specimenseeFigure 1 d). 5.2 When stressing specimens by fastening after forming, care should
34、be taken to ensure that the deflection is restored to that obtained at the end of the forming operation. 5.3 Specimens for use in service conditions should be securely fixed to avoid movement through the system and should be accessible for inspection or removal. Their design and method of fixing sho
35、uld be considered as a whole. 5.4 If more than one metal is present in a system, specimens should be electrically insulated to avoid galvanic effects. 5.5 Specimens should be fabricated from representative material with due regard to such factors as rolling direction and heat treatment. If relevant,
36、 welded specimens should be tested, and the configuration in service should be borne in mind when preparing the specimens.ENISO7539-3:1995 4 BSI 04-2000 5.6 For laboratory testing a fine surface finish is frequently used since it allows early detection of cracks, but for in-service testing a surface
37、 finish representative of the plant should be employed. For further comments relating to surface condition, ISO7539-1 should be consulted. 5.7 Specimens should be degreased prior to testing and should be handled with care thereafter. 5.8 Specimens should be examined, after forming, for cracks that m
38、ay have developed before exposure to the test environment. It may also be desirable to prepare additional specimens for use as controls for later comparison(see7.4). 5.9 Where it is necessary to mark the specimen for purposes of identification, the methods given in ISO7539-1 should be followed. Figu
39、re 1 Typical stressed U-bends Figure 2 Methods of stressing U-bend specimensENISO7539-3:1995 BSI 04-2000 5 6 Procedure 6.1 The aim should be to test under all likely service conditions and over a period which includes start-up, shut-down and other changes in conditions as well as the normal design c
40、onditions. 6.2 Interfaces between fluid phases represent likely areas for stress corrosion cracking as do locations where temperature gradients exist, where condensate may form or where local boiling may occur. Locations where gradients may occur in the chemical composition of the fluid, especially
41、in the concentration of oxidizing or reducing agents, also represent hazard areas. These factors should be taken into account when planning the location of specimens. 6.3 Location of specimens to permit safe examination and removal can be a major problem, especially with equipment under pressure, an
42、d may make it impossible to test all locations. 7 Assessment of results 7.1 Before specimens are examined it is necessary to check that relaxation of tension has not invalidated the test, for example by failure of the fastening. 7.2 Examination of specimens is generally by eye or low-power microscop
43、y. In laboratory tests replicate specimens are frequently used to facilitate periodical examination and to determine exposure time when cracks are first observed. For in-service tests, the use of replicate specimens and regular examination is often impractical. In such cases, the specimens should be
44、 examined after an arbitrary exposure time sufficiently long to cover all anticipated variations in service conditions. A test period of5 weeks to10 weeks is often considered appropriate for process plant. 7.3 To open small cracks further stressing may be used. Metallographic sections through the sp
45、ecimen should be prepared to detect minor cracks. 7.4 Since some cracks may have origins other than stress corrosion it is necessary, if cracks are detected, to examine similarly stressed specimens that have not been exposed to the corroding environment for comparison. 7.5 The test should be regarde
46、d as basically a “go/no go” test and minor differences in behaviour, e.g.intime to first crack, or in size of crack, should not be considered significant. 7.6 Any cracking observed, unless positively proved to have occurred for some reason other than stress corrosion, should be considered as indicat
47、ive of failure. 7.7 Lack of cracking in service tests, after a specified period of exposure, should be regarded as indicative of behaviour in practice only so long as the conditions of service are not appreciably altered from those existing during the test. 8 Test report The test report should inclu
48、de the following information: a) full description of the test material, including composition and structural conditions, type of product and section thickness from which specimens were taken; b) orientation, type and size of test specimens and their surface preparation; c) test environment, includin
49、g location of specimens for in-service tests; d) the times at which observations were made and when cracks became visible.6 blankBSENISO7539-3:1995 BSI 04-2000 Publications referred to Seenational foreword.BS EN ISO 7539-3:1995 BSI 389 Chiswick High Road London W4 4AL BSIBritishStandardsInstitution BSI is the independent national body responsible for preparing BritishStandards. It presents the UK view on standards in Europe and at the international level. It is incorporated by Royal Charter. Revisions BritishStandards are
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