1、Designation: A966/A966M 08 (Reapproved 2012)A966/A966M 15Standard Practice forMagnetic Particle Examination of Steel Forgings UsingAlternating Current1This standard is issued under the fixed designation A966/A966M; the number immediately following the designation indicates the yearof original adopti
2、on or, in the case of revision, 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.1. Scope Scope*1.1 This practice covers a procedure for the magnetic particle examinat
3、ion of steel forgings using alternating current as thepower source. The procedure will produce consistent results upon which acceptance standards can be based. This practice does notcontain acceptance limits or recommended quality levels.1.2 Only alternating 5060 cycle current shall be used as the e
4、lectric power source for any of the magnetizing methods.1.3 When subsurface indications are sought in forgings, then dc magnetization in accordance with Practice A275/A275M shouldbe used.1.4 The values stated in either inch-pound units or SI units are to be regarded separately as standard. Within th
5、e text, the SI unitsare shown in brackets. The values stated in each system are not exact equivalents; therefore each system shall be usedindependently of the other. Combining values from the two systems may result in nonconformance with the specification. Unlessthe order specifies the applicable “M
6、” specification designation SI units, the inch-pound units shall be used.1.5 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 and health practices and determine
7、the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A275/A275M Practice for Magnetic Particle Examination of Steel ForgingsA508/A508M Specification for Quenched and Tempered Vacuum-Treated Carbon andAlloy Steel Forgings for Pressure VesselsA788/A788M Sp
8、ecification for Steel Forgings, General RequirementsA963/A963M Specification for Deep Drawing Steel (DDS), Sheet, Carbon, Cold-Rolled (Withdrawn 2000)32.2 Other Document:Practice No. SNT-TC-1A, Supplement BMagnetic Particle Method43. Terminology3.1 Definitions:3.1.1 (ac) magnetic particle method of
9、examination, na method for detecting discontinuities on the surface in suitablymagnetized materials, which employs finely divided magnetic particles that tend to congregate in regions of leakage fields.3.1.2 indication, nthe visual magnetic particle buildup resulting from leakage fields in the magne
10、tic field.3.1.3 linear indication, nan indication in which the length is at least three times the width. The minimum length of indicationsto be considered linear shall be 116 in. 1.5 mm.1 This practice is under the jurisdiction of ASTM Committee A01 on Steel, Stainless Steel and Related Alloys and i
11、s the direct responsibility of Subcommittee A01.06on Steel Forgings and Billets.Current edition approved May 1, 2012May 1, 2015. Published May 2012May 2015. Originally approved in 1996. Last previous edition approved in 20082012 asA966/A966M 08.A966/A966M 08 (2012). DOI: 10.1520/A0966_A0966M-08R12.1
12、0.1520/A0966_A0966M-15.2 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.3 The last approved version of this hi
13、storical standard is referenced on www.astm.org.4 Available from American Society for NonDestructive Testing, 1711 Arlingate Lane, Nondestructive Testing (ASNT), P.O. Box 28518, 1711 Arlingate Ln., Columbus,OH 43228-0518.43228-0518, http:/www.asnt.org.This document is not an ASTM standard and is int
14、ended 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 technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the curr
15、ent 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 standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States13.1.4 magnetic flux, nthe produ
16、ct 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.3.1.4.1 DiscussionThe concept that the magnetic field is flowing along the lines of force suggests that these lines are therefore “flux
17、” lines, and theyare called magnetic flux.3.1.5 nonrelevant indications, nindications produced by leakage fields where the conditions causing them are present byaccident or part design, or other features of the part having no relation to the damaging flaws being sought.3.1.5.1 DiscussionThis term si
18、gnifies that such an indication has no relation to the discontinuities that might constitute defects.4. Basis of Application4.1 When in accordance with the requirements of the inquiry, contract, order, or specifications, forgings are to be examined bythe magnetic particle method using alternating cu
19、rrent; the manufacturer and the supplier shall be in agreement concerning thefollowing:4.1.1 The locations on the forging that are to be subjected to magnetic particle examination.4.1.2 The type, size, number, location, and orientation of indications that are to be considered injurious.4.1.3 The met
20、hod of application and type of magnetic particles, demagnetization requirements, and magnetic field strengths.4.1.4 Acceptance standards.5. Significance and Use5.1 For ferromagnetic materials, magnetic particle examination is widely specified for the detection of surface and near-surfaceflaws such a
21、s cracks, laps, seams, and linearly oriented nonmetallic inclusions. Such examinations are included as mandatoryrequirements in some forging standards such as Specifications A508/A508M and A963/A963M.5.2 Use of alternating current as the power source for magnetic particle examination imposes a signi
22、ficant restriction on thedetection of subsurface indications, so that the procedure is essentially limited to the finding of flaws that are open to the surface.Attention therefore is drawn to the need to have the component in the finish-machined condition before conducting the magneticparticle exami
23、nation.5.3 The presence of residual magnetic fields in a component may be undesirable, and an advantage of the use of an AC powersource for magnetic particle examination is that an acceptable level of demagnetization can be readily achieved.6. Personnel Requirements6.1 Personnel performing the magne
24、tic particle examination in this practice shall be qualified and certified in accordance witha written procedure conforming to Practice No. SNT-TC-1A or another national standard that is acceptable to both the purchaserand supplier.7. Stage of Examination7.1 Unless otherwise specified by the purchas
25、er, acceptance examination shall be performed on a forging in the final machinedsurface condition.8. Magnetizing Apparatus8.1 A 50 or 60 cycle alternating current shall be used. When current is passed through the forging itself, the equipment shallconsist of contacting or clamping elements with suff
26、icient surface area and clamping pressure to allow the required current to flowwithout damaging (burning) the part being examined.8.2 Portable electromagnetic alternating current yokes may be used as a magnetizing apparatus.9. Magnetic Particles9.1 The inspection medium shall consist of finely divid
27、ed ferromagnetic particles (which may be coated with a fluorescentmaterial) suspended in a suitable liquid medium or used in dry powder form.10. Surface Preparation10.1 The sensitivity of the magnetic particle examination will depend to a considerable extent upon the condition of the surfacebeing ex
28、amined. While defects may be satisfactorily revealed on shot-blasted or otherwise cleaned forged surfaces, without anyA966/A966M 152further surface treatment, all heat treatment or forging scale must be removed. However, to reveal fine defects of 18 in. 3 mmor less in length, the surfaces to be exam
29、ined shall be smooth machined to at least a 250-in. 6.35-m finish.finish where thedefinition for surface finish is as per Specification A788/A788M.10.2 The surfaces shall be free from grease, oils, or other substances to which the particles may adhere.11. Methods of Magnetization11.1 The forging may
30、 be magnetized either by passing current through the piece or by inducing a magnetic field by means ofa central conductor, by coils, or by yoke.11.1.1 Continuous MethodIn the continuous method the inspection medium is applied to the surface under examination whilethe current is still flowing. The al
31、ternating current source generates high amperage current in pulses of up to 1 s duration. Theduration of this flow shall allow at least three pulses of current, or in the case where machines supply continuous current flow, aminimum shot of 15 to 12 s duration should be applied.11.1.2 The surge and r
32、esidual methods are not applicable to this practice.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 magneti
33、zationmay be used for the second examination. Magnetizing in more than one direction cannot normally be accomplished simultaneously.An exception to the above rule is overall sequential multivector magnetization whereby several magnetizing circuits are providedfor sequentially magnetizing a part in m
34、ultiple directions depending on the locations of the current connectors. By this technique,indications of any orientation can 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
35、.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, readily detectable by compass or magnetometer. Longitudinalmagnetization is usually accomplished by placing t
36、he forging within a solenoid, frequently formed by wrapping cable around thepiece (Fig. 1). For special applications, magnetic yokes can be used (Fig. 2).11.3.2 CircularCircular magnetization is obtained by passing a current through the piece (Fig. 3) or by induced by passingcurrent through a conduc
37、tor or conductors threaded through an opening in the piece (Fig. 4 or Fig. 5). By agreement with thepurchaser (see 11.5.3) localized circular magnetization may be obtained by passing current through local areas by the use ofprod-type contacts (Fig. 6).11.4 The magnetic field is confined almost entir
38、ely 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 the magnetic field.11.5 Field StrengthThe minimum field strength that will reveal and permit classification of all objectionabl
39、e 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 surface being inspected.11.5.1 Coil MagnetizationWhen coil magnetization is used, the magnetic field strength is directly proportional
40、 to the current(ampere-turns if a coil or solenoid is used) and inversely proportional to the thickness of the section being inspected.11.5.1.1 Longitudinal Magnetization MagnetizationFor encircling coils (Fig. 1), the turns of the coil shall be kept closelytogether. The field strength decreases as
41、distance from the coil increases and long parts must be magnetized in sections. If the areato be inspected extends beyond 6 in. 150 mm on either side of the coils, the adequacy of the field shall be demonstrated by theuse of field indicators (see 11.5.6).(1) Small ForgingsMagnetizing force shall be
42、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.FIG. 1 Longitudinal MagnetizationA966/A966M 153Therefore, 35 000(2 + 5) = 5000 ampere-turns; if a 5-turn
43、coil is used, the current required is 5000/5 or 1000 A. This formulaprovides an adequate field strength on small parts having an L/D ratio of 4 or greater. For parts having a smaller L/D ratio, adequatefield strengths shall be demonstrated by the use of a field indicator (see 11.5.6). The graph in F
44、ig. 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 11.5.6) shall be used to demonstrate the presence of an adequate field strength ove
45、r the area to be inspected.FIG. 2 Longitudinal Magnetization, with YokeFIG. 3 Circular Magnetization, Current Directly Through ForgingFIG. 4 Circular Magnetization, Current Through a ConductorFIG. 5 Circular Magnetization, Current Through Conductors Threaded Through ForgingA966/A966M 15411.5.1.2 Cir
46、cular 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 90
47、0 A 4 and 35 A per millimetre per inch of diameter or cross section (per inch or millimetre of greatest width in a planeat right angles to current flow). For hollow parts this would be wall thickness when cables are clamped to the wall. Suggestedcurrent for diameters or sections up to 5 in. 125 mm a
48、re 600 to 900A/inches 25 to 35Aper millimetre; for diameters or sectionsbetween 5 and 10 in. 125 to 250 mm, 400 to 600 A/inches 15 to 25 A per millimetre; and 100 to 400 A/inches 4 to 15 A permillimetre for outside diameters or sections over 10 in. 250 mm. If it is not practical to obtain these curr
49、ent levels for diametersover 10 in. 250 mm, the presence of an adequate field strength shall be demonstrated using a field indicator. In all other instancesthe adequacy of the magnetizing force shall be demonstrated by means of a field indicator (see 11.5.6). When large parts have beenexamined by clamping contacts to the wall thickness, the adequacy of the field in the circumferential direction shall also bedetermined by the field indicator.11.5.3 Prod MagnetizationSince this method may induce arcing or burning at th
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