1、Designation: A275/A275M 15A275/A275M 18Standard Practice forMagnetic Particle Examination of Steel Forgings1This standard is issued under the fixed designation A275/A275M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of
2、 last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon () indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the U.S. Department of Defense.1. Scope*1.1 This practice2 covers a proced
3、ure for magnetic particle examination of steel forgings. The procedure will produce consistentresults upon which acceptance standards can be based. This practice does not contain acceptance standards or recommendedquality levels.1.2 Only direct current or rectified alternating (full or half wave) cu
4、rrent shall be used as the electric power source for any ofthe magnetizing methods. Alternating current is not permitted because its capability to detect subsurface discontinuities is verylimited and therefore unsuitable.1.2.1 Portable battery powered electromagnetic yokes are outside the scope of t
5、his practice.NOTE 1Guide E709 may be utilized for magnetic particle examination in the field for machinery components originally manufactured from steelforgings.1.3 The minimum requirements for magnetic particle examination shall conform to practice standards of Practice E1444/E1444M. If the require
6、ments of this practice are in conflict with the requirements of Practice E1444/E1444M, the requirementsof this practice shall prevail.1.4 This practice and the applicable material specifications are expressed in both inch-pound units and SI units. However, unlessthe order specifies the applicable “M
7、” specification designation SI units, the material shall be furnished to inch-pound units.1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in eachsystem may not be exact equivalents; therefore, each system shall be used indepen
8、dently of the other. Combining values from thetwo systems may result in non-conformance with the standard.1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety sa
9、fety, health, and healthenvironmental practices and determine theapplicability of regulatory limitations prior to use.1.7 This international standard was developed in accordance with internationally recognized principles on standardizationestablished in the Decision on Principles for the Development
10、 of International Standards, Guides and Recommendations issuedby the World Trade Organization Technical Barriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:3A508/A508M Specification for Quenched and Tempered Vacuum-Treated Carbon andAlloy Steel Forgings for Pressure VesselsA7
11、88/A788M Specification for Steel Forgings, General RequirementsE165/E165M Practice for Liquid Penetrant Examination for General IndustryE709 Guide for Magnetic Particle TestingE1351 Practice for Production and Evaluation of Field Metallographic ReplicasE1444/E1444M Practice for Magnetic Particle Tes
12、ting1 This practice is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee A01.06on Steel Forgings and Billets.Current edition approved May 1, 2015May 1, 2018. Published May 2015May 2018. Originally approved in 19
13、44. Last previous edition approved in 20132015 asA275/A275M 08 (2013).A275/A275M 15. DOI: 10.1520/A0275_A0275M-15.10.1520/A0275_A0275M-18.2 For ASME Boiler and Pressure Vessel Code applications see related Method SA-275/SA-275M in Section II of that Code.3 For referencedASTM standards, visit theASTM
14、 website, www.astm.org, or contactASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indi
15、cation of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be c
16、onsidered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States12.2 Other Document:4Recommended Practice No. SNT-TC-1A, Supplement B-Magnetic Particle Me
17、thod3. Terminology3.1 Definitions:3.1.1 indicationthe visual magnetic particle buildup resulting from leakage fields in the magnetic field.3.1.2 linear indicationan indication in which the length is at least three times the width. The minimum length of indicationsto be considered linear shall be 116
18、 in. 1.6 mm.3.1.3 magnetic fluxthe product of the magnetic induction and the area of a surface (or cross section) when the magneticinduction is uniformly distributed and normal to the plane of the surface. The concept that the magnetic field is flowing along thelines of force suggests that these lin
19、es are therefore “flux” lines, and they are called magnetic flux.3.1.4 magnetic particle method of examinationa method for detecting discontinuities on or near the surface in suitablymagnetized materials, which employs finely divided magnetic particles that tend to congregate in regions of leakage f
20、ields.3.1.5 nonrelevant indicationsindications produced by leakage fields. However, the conditions causing them are present bydesign or accident, or other features of the part having no relation to the damaging flaws being sought. The term signifies that suchan indication has no relation to the disc
21、ontinuities that might constitute defects.4. Significance and Use4.1 For ferromagnetic materials, magnetic particle examination is widely specified for the detection of surface and near surfacediscontinuities such as cracks, laps, seams, and linearly oriented nonmetallic inclusions. Such examination
22、s are included asmandatory requirements in some forging standards such as Specification A508/A508M.4.2 Use of direct current or rectified alternating (full or half wave) current as the power source for magnetic particle examinationallows detection of subsurface discontinuities.5. Basis of Applicatio
23、n5.1 When in accordance with the requirements of the inquiry, contract, order, or specifications, forgings are furnished subjectto magnetic particle examination, the manufacturer and the purchaser shall be in agreement concerning the following:5.1.1 The locations on the forgings that are to be subje
24、cted to magnetic particle examination.5.1.2 The type, size, number, location, and orientation of indications that are to be considered injurious.5.1.3 The method of application of magnetic particles, demagnetization requirements and magnetic field strengths.5.2 In cases where large undercuts in the
25、forgings are to be taken by the purchaser, the manufacturer shall be given the privilege(when the design permits) of machining slots or grooves in the rough-machined forging to explore the internal conditions prior toshipping.5.3 Acceptance standards.6. Personnel Requirements6.1 Personnel performing
26、 the magnetic particle examination to this practice shall be qualified and certified in accordance witha written procedure conforming to Recommended Practice No. SNT-TC-1Aor another national standard that is acceptable to boththe purchaser and the supplier.7. Stage of Inspection7.1 Unless otherwise
27、specified by the purchaser, acceptance inspection shall be performed on a forging in the final machinedsurface condition and final thermally treated condition (including stress relief) or within 0.030 in. 0.8 mm of the final machinedsurface.8. Magnetizing Apparatus8.1 Rectified alternating (full or
28、half wave) or direct-current electric power sources may be used.When current is passed throughthe part itself, the equipment shall consist of contacting or clamping elements with sufficient surface area and clamping pressureto allow the required current to flow without damaging (burning) the part be
29、ing examined.8.2 Portable electromagnetic (ac-dc) yokes may be used in the dc mode as a magnetizing apparatus, provided the sensitivity todetect crack-like defects is demonstrated to be at least equivalent to that of the direct-magnetization method.8.2.1 Portable battery powered electromagnetic yoke
30、s are not included in the scope of this practice.4 Available from American Society for Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.A275/A275M 1829. Magnetic Particles9.1 The inspection medium shall consist of finely divided ferromagn
31、etic particles, which may be suspended in a suitable liquidmedium, or used in dry powder form.9.2 The size and shape of the particles, and their magnetic properties, both individually and collectively, are important (seeSection 12).10. Surface Preparation10.1 The sensitivity of the magnetic particle
32、 examination will depend to a considerable extent upon the condition of the surfacebeing tested. Defects may be satisfactorily revealed on shot-blasted or otherwise cleaned forged surfaces, or on surfaces havingsmall amounts of heat-treating scale without any special surface preparation; however, lo
33、ose scale must be removed. To reveal finedefects, the surfaces to be inspected should be smooth machined to at least a 250-in. 6.35-m finish where the definition forsurface finish is as per Specification A788/A788M.10.2 The surfaces shall be free of grease, oils, or other substances to which the par
34、ticles may adhere.10.3 Rough surfaces hamper the mobility of magnetic powders due to mechanical trapping which in turn produces falseindications. Such areas should be surface ground. If grinding is impractical, a paper tape overlay (as described in 15.1.1.2) mayeliminate the problem.11. Methods of M
35、agnetization11.1 The forging may be magnetized either by passing current through the piece or by inducing a magnetic field by means ofa central conductor or by coils.11.1.1 Continuous MethodIn the continuous method, the inspection medium is applied to the surface under inspection whilethe current is
36、 still flowing. The current source generates high amperage current in pulses of up to 1-s duration. The duration of thisflow shall allow at least three pulses of current or in the case where machines supply continuous current flow a minimum shot of15 to 12-s duration should be applied.11.1.2 Surge M
37、ethodIn the surge method a high-magnetizing force is applied and then reduced to a lower continuous value,which is maintained during application of the inspection medium.11.2 At least two separate examinations shall be carried out on each area. The second examination shall be with the lines ofmagnet
38、ic flux approximately perpendicular to those used for the first examination in that area. A different means of magnetizingmay be used for the second examination. Magnetizing in more than one direction cannot be accomplished simultaneously.NOTE 2An exception to the above rule is overall sequential mu
39、ltivector magnetization whereby several magnetizing circuits are provided forsequentially magnetizing a part in multiple directions depending upon the locations of the current connectors. By this technique, flaws of any orientationcan be detected with a single application of magnetic particles.11.3
40、The two general types of magnetization with regard to direction are longitudinal and circular, as follows:11.3.1 LongitudinalWhen a forging is magnetized longitudinally, the magnetic flux lines are usually parallel to the axis of thepiece. A longitudinally magnetized piece always has definite poles
41、readily detectable by compass or magnetometer. Longitudinalmagnetization is usually accomplished by placing the forging within a solenoid, often formed by wrapping cable around the piece(Fig. 1). For special applications, magnetic yokes can be used (Fig. 2) when requirements of 8.2 are met.11.3.2 Ci
42、rcularCircular magnetization is obtained by passing a current directly through the piece (Fig. 3), or induced througha conductor (Fig. 4), or conductors threaded (Fig. 5) through an opening in the piece. Localized circular magentization may beobtained by passing current through the local areas by us
43、e of prod-type contacts (Fig. 6).FIG. 1 Longitudinal MagnetizationA275/A275M 18311.4 The magnetic field is confined almost entirely to the piece and there may be no external manifestation of the magnetizedcondition. Indications will appear strongest in the direction perpendicular to the direction of
44、 the magnetic field.11.5 Field StrengthThe minimum field strength that will reveal and permit classification of all objectionable defects shall beused. The maximum field strengths practical are the ones just below the point at which excessive adherence of the particles beginsto occur over the surfac
45、e being inspected.11.5.1 Coil MagnetizationWhen coil magnetization is used, the magnetic field strength is directly proportional to the current(ampere-turns if a coil or solenoid is used) and inversely proportional to the thickness of the section being inspected.FIG. 2 Longitudinal Magnetization, wi
46、th YokeFIG. 3 Circular Magnetization, Current Directly Through ForgingFIG. 4 Circular Magnetization, Current Through a ConductorFIG. 5 Circular Magnetization, Current Through Conductors Threaded Through ForgingA275/A275M 18411.5.1.1 Longitudinal MagnetizationFor encircling coils (Fig. 1), the turns
47、of the coil shall be kept closely together. The fieldstrength decreases as distance from the coil increases and long parts must be magnetized in sections. If the area to be inspectedextends beyond 6 in. 150 mm on either side of the coils, the adequacy of the field shall be demonstrated by the use of
48、 fieldindicators (see 11.5.6).(1) Small ForgingsMagnetizing force shall be 35 000 ampere-turns divided by the sum of 2 plus the “length over diameter”ratio of the test part. For example, a part 10 in. 250 mm long by 2 in. 50 mm in outside diameter has an L/D ratio of 5.Therefore,35 000/(2 + 5) = 500
49、0 ampere-turns; if a 5-turn coil is used, the current required is 5000/5 or 1000 A. This formula provides anadequate field strength on small parts having an L/D ratio of 4 or greater. For parts having a smaller L/D ratio, adequate fieldstrengths shall be demonstrated by the use of a field indicator (see 11.5.6). The graph in Fig. 7 may be used to determine theampere-turns required for each L/D relationship.(2) Large ForgingsFor large forgings the magnetizing force shall be in the range from 1200 to 4500 ampere-turns. A fieldindicator (see
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