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1、BRITISH STANDARD BS ISO 11463:1995 Implementation of ISO 11463:1995 Corrosion of metals and alloys Evaluation of pitting corrosion ICS 77.060 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 08:48:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 11463:1995 This British Standard, having bee
2、n prepared under the direction of the Engineering Sector Board, was published under the authority of the Standards Board and comes into effect on 15 September 1996 BSI 11-1998 The following BSI references relate to the work on this standard: Committee reference ISE/NFE/8 Draft for comment 93/305910
3、DC ISBN 0 580 26047 X Committees responsible for this British Standard The preparation of this British Standard was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys, upon which the following bodies were represented: AEA Technology Aluminium Federation British Gas plc Britis
4、h Non-Ferrous Metals Federation British Iron and Steel Producers Association Department of Trade and Industry (National Physical Laboratory) Department of Transport (Transport Research Laboratory) Electricity Association Institute of Corrosion Ministry of Defence Society of Chemical Industry The Wel
5、ding Institute Zinc Development Association Amendments issued since publication Amd. No.DateComments Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 08:48:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 11463:1995 BSI 11-1998i Contents Page Committees responsibleInside front cover Nation
6、al forewordii Forewordii Introduction1 1Scope1 2Normative reference1 3Identification and examination of pits1 4Extent of pitting3 5Evaluation of pitting5 6Report7 7Additional information7 Annex A (informative) Repeatability of measurements by use of a microscope8 Annex B (informative) Bibliography10
7、 Figure 1 Variations in the cross-sectional shape of pits2 Figure 2 Standard rating charts for pits6 Figure A.1 Cross-section of pit used for depth measurements in Table A.19 Table A.1 Microscopic pit depth8 Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 08:48:11 GMT+00:00 2006, Uncontrolled
8、 Copy, (c) BSI BS ISO 11463:1995 ii BSI 11-1998 National foreword This British Standard reproduces verbatim ISO 11463:1995 and implements it as the UK national standard. This British Standard is published under the direction of the Engineering Sector Board whose Technical Committee ISE/NFE/8 has the
9、 responsibility to: aid enquirers to understand the text; present to the responsible international committee any enquiries on interpretation, or proposals for change, and keep UK interests informed; monitor related international and European developments and promulgate them in the UK. NOTEInternatio
10、nal and European Standards, as well as overseas standards, are available from Customer Services, BSI, 389 Chiswick High Road, London W4 4AL. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct applica
11、tion. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, the ISO title page, page ii, pages 1 to 10 and a back cover. This standard has been updated (see copyrigh
12、t date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 08:48:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 08:48:11 GMT+00
13、:00 2006, Uncontrolled Copy, (c) BSI BS ISO 11463:1995 ii 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 committe
14、es. 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 Inte
15、rnational Electrotechnical Commission (IEC) on all matters of electrotechnical standardization. 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
16、bodies casting a vote. International Standard ISO 11463 was prepared by Technical Committee ISO/TC 156, Corrosion of metals and alloys. Annexes A and B of this International Standard are for information only. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 08:48:11 GMT+00:00 2006, Uncontrolle
17、d Copy, (c) BSI BS ISO 11463:1995 BSI 11-19981 Introduction It is important to be able to determine the extent of pitting, either in a service application where it is necessary to estimate the remaining life in a metal structure, or in laboratory test programmes that are used to select pitting-resis
18、tant materials for a particular service (see 1 in annex B). The application of the materials to be tested will determine the minimum pit size to be evaluated and whether total area covered, average pit depth, maximum pit depth or another criterion is the most important to measure. 1 Scope This Inter
19、national Standard gives guidance on the selection of procedures that can be used in the identification and examination of pits and in the evaluation of pitting corrosion. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of
20、this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent edition of the standard indicated
21、below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 8407:1991, Corrosion of metals and alloys Removal of corrosion products from corrosion test specimens. 3 Identification and examination of pits 3.1 Visual inspection A visual examination of the corroded
22、metal surface with or without the use of a low-power magnifying glass may be used to determine the extent of corrosion and the apparent location of pits. It is often advisable to photograph the corroded surface so that it can be compared with the clean surface after the removal of corrosion products
23、. 3.1.1 If the metal specimen has been exposed to an unknown environment, the composition of the corrosion products may be of value in determining the cause of corrosion. Recommended procedures in the removal of particulate corrosion products should be followed and reserved for future identification
24、. 3.1.2 To expose the pits fully, it is recommended that cleaning procedures should be used to remove the corrosion products and avoid solutions that attack the base metal excessively (see ISO 8407). It may be advisable during cleaning to probe the pits with a pointed tool to determine the extent of
25、 undercutting or subsurface corrosion (see Figure 1). However, scrubbing with a stiff-bristle brush will often enlarge the pit openings sufficiently by removal of corrosion products or undercut metal to make the pits easier to evaluate. 3.1.3 Examine the cleaned metal surface to determine the approx
26、imate size and distribution of pits. Follow this procedure by a more detailed examination through a microscope using low magnification (approximately 20). 3.1.4 Determine the size, shape and density of pits. 3.1.4.1 Pits may have various sizes and shapes. A visual examination of the metal surface ma
27、y show a round, elongated or irregular opening, but it seldom provides an accurate indication of corrosion beneath the surface. Thus it is often necessary to cross-section the pit to see its actual shape and to determine its true depth. Several variations in the cross-sectioned shape of pits are sho
28、wn in Figure 1. 3.1.4.2 It is difficult to determine pit density by counting pits through a microscope eyepiece, but the task may be made easier by the use of a plastic grid. Place the grid, containing 3 mm to 6 mm squares, on the metal surface. Count and record the number of pits in each square, an
29、d move across the grid in a systematic manner until all the surface has been covered. This approach minimizes eye-strain because the eyes can be taken from the field of view without fear of losing the area of interest. Enlarged photographs of the area of interest may also be used to reduce eye-strai
30、n. Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 08:48:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS ISO 11463:1995 2 BSI 11-1998 3.1.5 To carry out a metallographic examination select and cut out a representative portion of the metal surface containing the pits and prepare a metallograp
31、hic specimen in accordance with recommended procedures. If corrosion products are to be examined in cross-section, it may be necessary to fix the surface in a mounting compound before cutting. Examine microscopically to determine whether there is a relation between pits and inclusions or microstruct
32、ure, or whether the cavities are true pits or might have resulted from metal loss caused by intergranular corrosion, dealloying, etc. 3.2 Non-destructive inspection A number of techniques has been developed to assist in the detection of cracks or cavities in a metal surface without destroying the ma
33、terial. See 1 in annex B. These methods are less effective for locating and defining the shape of pits than some of those previously described, but they merit consideration because they are often used in situ, and thus are more applicable to field applications. 3.2.1 Radiographic Radiation, such as
34、X-rays, passes through the object. The intensity of the emergent rays varies with the thickness of the material. Imperfections may be detected if they cause a change in the absorption of X-rays. Detectors or films are used to provide an image of interior imperfections. The metal thickness that can b
35、e inspected is dependent on the available energy output. Pores or pits must be as large as 0,5 % of the metal thickness to be detected. This technique has only slight application to pitting detection, but it might be useful for comparing specimens before and after corrosion to determine whether pitt
36、ing has occurred and whether it is associated with previous porosity. It may also be useful to determine the extent of subsurface and undercutting pitting (see Figure 1). 3.2.2 Electromagnetic 3.2.2.1 Eddy currents may be used to detect defects or irregularities in the structure of electrically cond
37、uctive materials. When a specimen is exposed to a varying magnetic field, produced by connecting an alternating current to a coil, eddy currents are induced in the specimen and they in turn produce a magnetic field of their own. Materials with defects will produce a magnetic field that is different
38、from that of a reference material without defects, and an appropriate detection instrument is required to determine these differences. Figure 1 Variations in the cross-sectional shape of pits Licensed Copy: sheffieldun sheffieldun, na, Sun Nov 26 08:48:11 GMT+00:00 2006, Uncontrolled Copy, (c) BSI B
39、S ISO 11463:1995 BSI 11-19983 3.2.2.2 The induction of a magnetic field in ferromagnetic materials is another approach that is used. Discontinuities that are transverse to the direction of the magnetic field cause a leakage field to form above the surface of the part. Ferromagnetic particles are pla
40、ced on the surface to detect the leakage field and to outline the size and shape of the discontinuities. Rather small imperfections can be detected by this method. However, the method is limited by the required directionality of defects to the magnetic field, by the possible need for demagnetization
41、 of the material and by the limited shape of parts that can be examined. 3.2.3 Sonics In the use of ultrasonics, pulses of sound energy are transmitted through a couplant, such as oil or water, on to the metal surface where waves are generated. The reflected echoes are converted to electrical signal
42、s that can be interpreted to show the location of flaws or pits. Both contact and immersion methods are used. The test shall be carried out from the non-pitted face. The test has good sensitivity, although it is unlikely to detect pits of less than 1 mm diameter or within 1 mm of a non-pitted face,
43、and provides instantaneous information about the size and location of flaws. However, reference standards are required for comparison and training is needed to interpret the results properly. 3.2.4 Penetrants Defects opening to the surface can be detected by the application of a penetrating liquid t
44、hat subsequently exudes from the surface after the excess penetrant has been removed. Defects are located by spraying the surface with a developer that reacts with a dye in the penetrant, or the penetrant may contain a fluorescent material that is viewed under ultra-violet light. The size of the def
45、ect is shown by the intensity of the colour and the rate of bleed-out. This technique provides only an approximation of the depth and size of pits. 3.2.5 Replication Images of a pitted surface can be created by applying a material to the surface which conforms to the shape of the pits and can be rem
46、oved without damaging its shape. This method will not work however, for pits of subsurface or undercut type. The removed material contains a replica of the original surface which, in some cases, is easier to analyze than the original. Replication is particularly useful for analysis of very small pit
47、s. 4 Extent of pitting 4.1 Mass loss Metal mass loss is not ordinarily recommended for use as a measure of the extent of pitting unless general corrosion is slight and pitting is fairly severe. If uniform corrosion is significant, the contribution of pitting to total metal loss is small, and pitting
48、 damage cannot be determined accurately from mass loss. In any case, mass loss can only provide information about total metal loss due to pitting but nothing about density of pits and depth of penetration. However, mass loss should not be neglected in every case because it may be of value; for examp
49、le, mass loss along with a visual comparison of pitted surfaces may be adequate to evaluate the pitting resistance of alloys in laboratory tests. Mass loss may also be useful to detect the existence of subsurface metal loss. 4.2 Pit depth measurement 4.2.1 Metallography Pit depth may be determined by sectioning vertically through a preselected pit, mounting the cross-sectioned pit metallographically and polishing the surface. A better or alternative way is to section slightly away from the pit and slowly grind until the pit is in the cross-section. Sectio
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