1、BRITISH STANDARD BS EN ISO 11463:2008 Corrosion of metals and alloys Evaluation of pitting corrosion ICS 77.060 BS EN ISO 11463:2008 This British Standard was published under the authority of the Standards Board and comes into effect on 15 September 1996 BSI 2008 ISBN 978 0 580 60534 5 National fore
2、word This British Standard is the UK implementation of EN ISO 11463:2008. It is identical with ISO 11463:1995. It supersedes BS ISO 11463:1995 which is withdrawn. The UK participation in its preparation was entrusted to Technical Committee ISE/NFE/8, Corrosion of metals and alloys. A list of organiz
3、ations represented on this committee can be obtained on request to its secretary. This publication does not purport to include all the necessary provisions of a contract. Users are responsible for its correct application. Compliance with a British Standard cannot confer immunity from legal obligatio
4、ns. Amendments/corrigenda issued since publication Date Comments 31 July 2008 This corrigendum renumbers BS ISO 11463:1995 as BS EN ISO 11463:2008EUROPEAN STANDARD NORME EUROPENNE EUROPISCHE NORM EN ISO 11463 April 2008 ICS 77.060 English Version Corrosion of metals and alloys - Evaluation of pittin
5、g corrosion (ISO 11463:1995) Corrosion des mtaux et alliages - valuation de la corrosion par piqres (ISO 11463:1995) Korrosion von Metallen und Legierungen - Bewertung der Lochkorrosion (ISO 11463:1995) This European Standard was approved by CEN on 21 March 2008. CEN members are bound to comply with
6、 the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard the 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 CEN Management Cen
7、tre or to any CEN member. This European Standard exists in three official versions (English, French, German). A version in any other language made by translation under the responsibility of a CEN member into its own language and notified to the CEN Management Centre has the same status as the offici
8、al versions. CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slov
9、enia, Spain, Sweden, Switzerland and United Kingdom. EUROPEAN COMMITTEE FOR STANDARDIZATION COMIT EUROPEN DE NORMALISATION EUROPISCHES KOMITEE FR NORMUNG Management Centre: rue de Stassart, 36 B-1050 Brussels 2008 CEN All rights of exploitation in any form and by any means reserved worldwide for CEN
10、 national Members. Ref. No. EN ISO 11463:2008: EForeword The text of ISO 11463:1995 has been prepared by Technical Committee ISO/TC 156 “Corrosion of metals and alloys” of the International Organization for Standardization (ISO) and has been taken over as EN ISO 11463:2008 by Technical Committee CEN
11、/TC 262 “Metallic and other inorganic coatings” the secretariat of which is held by BSI. 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 October 2008, and conflicting national standards shall be w
12、ithdrawn at the latest by October 2008. Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights. CEN and/or CENELEC shall not be held responsible for identifying any or all such patent rights. According to the CEN/CENELEC Internal Regulati
13、ons, the national standards organizations of the following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherla
14、nds, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom. Endorsement notice The text of ISO 11463:1995 has been approved by CEN as a EN ISO 11463:2008 without any modification. BS EN ISO 11463:2008 BSI 2008iii Contents Page Introduction 1 1 Scope
15、 1 2 Normative reference 1 3 Identification and examination of pits 1 4 Extent of pitting 3 5 Evaluation of pitting 5 6 Report 7 7 Additional information 7 Annex A (informative) Repeatability of measurements by use of a microscope 8 Annex B (informative) Bibliography 10 Figure 1 Variations in the cr
16、oss-sectional shape of pits 2 Figure 2 Standard rating charts for pits 6 Figure A.1 Cross-section of pit used for depth measurements in Table A.1 9 Table A.1 Microscopic pit depth 8 BS EN ISO 11463:2008 BSI 2008 blank1 Introduction It is important to be able to determine the extent of pitting, eithe
17、r 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-resistant materials for a particular service (see 1 in annex B). The application of the materials to be tested will determine the min
18、imum 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 International Standard gives guidance on the selection of procedures that can be used in the identification and examination of pits a
19、nd in the evaluation of pitting corrosion. 2 Normative reference The following standard contains provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the edition indicated was valid. All standards are subject to revision,
20、 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 below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 8407:1991, Corrosion of metals
21、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 metal surface with or without the use of a low-power magnifying glass may be used to determine the extent of corrosion and the a
22、pparent 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. 3.1.1 If the metal specimen has been exposed to an unknown environment, the composition of the corrosion products may be of va
23、lue in determining the cause of corrosion. Recommended procedures in the removal of particulate corrosion products should be followed and reserved for future identification. 3.1.2 To expose the pits fully, it is recommended that cleaning procedures should be used to remove the corrosion products and
24、 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 undercutting or subsurface corrosion (see Figure 1). However, scrubbing with a stiff-bristle brush will often enlarge the pit o
25、penings 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 approximate size and distribution of pits. Follow this procedure by a more detailed examination through a microscope using low magnifi
26、cation (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 may show a round, elongated or irregular opening, but it seldom provides an accurate indication of corrosion beneath the surface.
27、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 shown in Figure 1. 3.1.4.2 It is difficult to determine pit density by counting pits through a microscope eyepiece, but the task ma
28、y 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, and move across the grid in a systematic manner until all the surface has been covered. This approach minimizes eye-strain because
29、 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-strain. BS EN ISO 11463:2008 BSI 20082 3.1.5 To carry out a metallographic examination select and cut out a representative portion of
30、 the metal surface containing the pits and prepare a metallographic 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 whethe
31、r there is a relation between pits and inclusions or microstructure, 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
32、 cracks or cavities in a metal surface without destroying the material. 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 applicab
33、le to field applications. 3.2.1 Radiographic Radiation, such as 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
34、 image of interior imperfections. The metal thickness that can be 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 comparin
35、g specimens before and after corrosion to determine whether pitting 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
36、 defects or irregularities in the structure of electrically conductive 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. Materia
37、ls with defects will produce a magnetic field that is different 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 BS EN ISO 11463:2008 BSI 20083 3.2.2.2 The i
38、nduction 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 placed on the surface to detect the leakage fi
39、eld 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 of the material and by the limited shape o
40、f 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 signals that can be interpreted to show the locat
41、ion 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 than1mm diameter or within 1 mm of a non-pitted face, and provides instantaneous information about
42、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 that subsequently exudes from the surface afte
43、r 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 defect is shown by the intensity of the colour a
44、nd 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 removed without damaging its shape. This method
45、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 pits. 4 Extent of pitting 4.1 Mass loss Metal ma
46、ss 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 damage cannot be determined accurately from
47、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 example, mass loss along with a visual comparison
48、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
49、 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. Sectioning through a pit can be difficult and one may miss the deepest portion. The depth of the pit is measured on the flat, polished surface by the use of a microscope with a calibrated eyepiece. The method is very accurate, but it
