1、Designation: A275/A275M 08 (Reapproved 2013)A275/A275M 15Standard 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 rev
2、ision, the year of 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 Scope*1.1 This p
3、ractice2 covers a procedure 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 alternatin
4、g (full or half wave) current 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 ar
5、e outside the scope of this 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 E144
6、4/E1444M. If the requirements 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 spe
7、cifies the applicable “M” 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 syst
8、em shall be used independently 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 establi
9、sh appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:3A508/A508M Specification for Quenched and Tempered Vacuum-Treated Carbon andAlloy Steel Forgings for Pressure VesselsA788/A788M Specification fo
10、r Steel Forgings, General RequirementsE709 Guide for Magnetic Particle TestingE1444/E1444M Practice for Magnetic Particle Testing2.2 Other Document:Recommended Practice No. SNT-TC-1A, Supplement B-Magnetic Particle Method43. Terminology3.1 Definitions:3.1.1 indicationthe visual magnetic particle bui
11、ldup resulting from leakage fields in the magnetic field.1 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 April 1, 2013May 1, 2015
12、. Published April 2013May 2015. Originally approved in 1944. Last previous edition approved in 20082013 asA275/A275M 08.A275/A275M 08 (2013). DOI: 10.1520/A0275_A0275M-08R13.10.1520/A0275_A0275M-15.2 For ASME Boiler and Pressure Vessel Code applications see related Method SA-275/SA-275M in Section I
13、I of that Code.3 For referencedASTM standards, visit theASTM 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.4 Available from American Society for Nondestr
14、uctive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http:/www.asnt.org.This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technic
15、ally 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 considered the official document.*A Summary of Changes section appears at the end of this st
16、andardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.2 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 in. 1.6 mm.3.1.3 m
17、agnetic 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 lines are therefore “f
18、lux” 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 fields.3.1.5 nonrele
19、vant 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 discontinuities that mi
20、ght 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 examinations are included asma
21、ndatory 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 Application5.1 When in accord
22、ance 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 subjected to magnetic pa
23、rticle 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 forgings are to be
24、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 the magnetic parti
25、cle examination to this practice shall be qualified and certified in accordance witha written procedure conforming to Recommended Practice No. SNT-TC-1A or another national standard that is acceptable to boththe purchaser and the supplier.7. Stage of Inspection7.1 Unless otherwise specified by the p
26、urchaser, 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 half wave) or dire
27、ct-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 being examined.8.2 P
28、ortable 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 yokes are not included
29、 in the scope of this practice.9. Magnetic Particles9.1 The inspection medium shall consist of finely divided ferromagnetic 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 individual
30、ly and collectively, are important (seeSection 12).10. Surface Preparation10.1 The sensitivity of the magnetic particle 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 s
31、urfaces, or on surfaces havingA275/A275M 152small amounts of heat-treating scale without any special surface preparation; however, loose 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.finish where the definitio
32、nfor surface finish is as per Specification A788/A788M.10.2 The surfaces shall be free of grease, oils, or other substances to which the particles may adhere.10.3 Rough surfaces hamper the mobility of magnetic powders due to mechanical trapping which in turn produces falseindications. Such areas sho
33、uld be surface ground. If grinding is impractical, a paper tape overlay (as described in 15.1.1.2) mayeliminate the problem.11. Methods of Magnetization11.1 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
34、coils.11.1.1 Continuous MethodIn the continuous method, the inspection medium is applied to the surface under inspection whilethe current is 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 o
35、f 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 MethodIn the surge method a high-magnetizing force is applied and then reduced to a lower continuous value,which is maintained during application of the inspecti
36、on medium.11.2 At least two separate examinations shall be carried out on each area. The second examination shall be with the lines ofmagnetic flux approximately perpendicular to those used for the first examination in that area. A different means of magnetizingmay be used for the second examination
37、. Magnetizing in more than one direction cannot be accomplished simultaneously.NOTE 2An exception to the above rule is overall sequential multivector magnetization whereby several magnetizing circuits are provided forsequentially magnetizing a part in multiple directions depending upon the locations
38、 of the current connectors. By this technique, flaws of any orientationcan be detected with a single application of magnetic particles.11.3 The two general types of magnetization with regard to direction are longitudinal and circular, as follows:11.3.1 LongitudinalWhen a forging is magnetized longit
39、udinally, the magnetic flux lines are usually parallel to the axis of thepiece. A longitudinally magnetized piece always has definite poles readily detectable by compass or magnetometer. Longitudinalmagnetization is usually accomplished by placing the forging within a solenoid, often formed by wrapp
40、ing 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 CircularCircular magnetization is obtained by passing a current directly through the piece (Fig. 3), or induced througha conductor (Fig. 4), or conductors threade
41、d (Fig. 5) through an opening in the piece. Localized circular magentization may beobtained by passing current through the local areas by use of prod-type contacts (Fig. 6).11.4 The magnetic field is confined almost entirely to the piece and there may be no external manifestation of the magnetizedco
42、ndition. Indications will appear strongest in the direction perpendicular to the direction of 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
43、 below the point at which excessive adherence of the particles beginsto occur over the surface 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 propo
44、rtional to the thickness of the section being inspected.FIG. 1 Longitudinal MagnetizationA275/A275M 15311.5.1.1 Longitudinal MagnetizationFor encircling coils (Fig. 1), the turns of the coil shall be kept closely together. The fieldstrength decreases as distance from the coil increases and long part
45、s 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 fieldindicators (see 11.5.6).(1) Small ForgingsMagnetizing force shall be 35 000 ampere-turns divided by the sum of 2 pl
46、us 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) = 5000 ampere-turns; if a 5-turn coil is used, the current required is 5000/5 or 1000 A. This formula provides anadequate fiel
47、d strength on small parts having an L/D ratio of 4 or greater. For parts having a smaller L/D ratio, adequate fieldFIG. 2 Longitudinal Magnetization, with YokeFIG. 3 Circular Magnetization, Current Directly Through ForgingFIG. 4 Circular Magnetization, Current Through a ConductorFIG. 5 Circular Magn
48、etization, Current Through Conductors Threaded Through ForgingA275/A275M 154strengths 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 magnetizi
49、ng force shall be in the range from 1200 to 4500 ampere-turns. A fieldindicator (see 11.5.6) shall be used to demonstrate the presence of an adequate field strength over the area to be inspected.11.5.1.2 Circular Magnetization (Fig. 5)For circular magnetization with through coils, use the current with amperage asspecified in 11.5.2 divided by the number of turns in the coil.11.5.2 Direct MagnetizationWhen current is passed directly through the part to be examined, the current shall be between 100and 900 A per inch 4 and 35 A per millime
