1、Designation: A 966/A 966M 08Standard Practice forMagnetic Particle Examination of Steel Forgings UsingAlternating Current1This standard is issued under the fixed designation A 966/A 966M; the number immediately following the designation indicates the yearof original adoption or, in the case of revis
2、ion, the year of last revision. A number in parentheses indicates the year of last reapproval.A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.1. Scope*1.1 This practice covers a procedure for the magneticparticle examination of steel forgings using alter
3、nating currentas the power source. The procedure will produce consistentresults upon which acceptance standards can be based. Thispractice does not contain acceptance limits or recommendedquality levels.1.2 Only alternating 5060 cycle current shall be used as theelectric power source for any of the
4、magnetizing methods.1.3 When subsurface indications are sought in forgings,then dc magnetization in accordance with Practice A 275/A 275M should be used.1.4 The values stated in either inch-pound units or SI unitsare to be regarded separately as standard. Within the text, theSI units are shown in br
5、ackets. The values stated in eachsystem are not exact equivalents; therefore each system shallbe used independently of the other. Combining values from thetwo systems may result in nonconformance with the specifi-cation. Unless the order specifies the applicable “M” specifi-cation designation SI uni
6、ts, the inch-pound units shall beused.1.5 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory li
7、mitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 275/A 275M Practice for Magnetic Particle Examinationof Steel ForgingsA 508/A 508M Specification for Quenched and TemperedVacuum-Treated Carbon and Alloy Steel Forgings forPressure VesselsA 963/A 963M Specification for Deep Drawing
8、Steel(DDS), Sheet, Carbon, Cold-Rolled32.2 Other Document:Practice No. SNT-TC-1A, Supplement BMagnetic Par-ticle Method43. Terminology3.1 Definitions:3.1.1 (ac) magnetic particle method of examination, namethod for detecting discontinuities on the surface in suitablymagnetized materials, which emplo
9、ys finely divided magneticparticles that tend to congregate in regions of leakage fields.3.1.2 indication, nthe visual magnetic particle buildupresulting from leakage fields in the magnetic field.3.1.3 linear indication, nan indication in which the lengthis at least three times the width. The minimu
10、m length ofindications to be considered linear shall be116 in. 1.5 mm.3.1.4 magnetic flux, nthe product of the magnetic induc-tion and the area of a surface (or cross section) when themagnetic induction is uniformly distributed and normal to theplane of the surface.3.1.4.1 DiscussionThe concept that
11、 the magnetic field isflowing along the lines of force suggests that these lines aretherefore “flux” lines, and they are called magnetic flux.3.1.5 nonrelevant indications, nindications produced byleakage fields where the conditions causing them are present byaccident or part design, or other featur
12、es of the part having norelation to the damaging flaws being sought.3.1.5.1 DiscussionThis term signifies that such an indica-tion has no relation to the discontinuities that might constitutedefects.4. Basis of Application4.1 When in accordance with the requirements of theinquiry, contract, order, o
13、r specifications, forgings are to beexamined by the magnetic particle method using alternating1This practice is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys and is the direct responsibility of SubcommitteeA01.06 on Steel Forgings and Billets.Current editio
14、n approved March 1, 2008. Published March 2008. Originallyapproved in 1996. Last previous edition approved in 2007 as A 966/A 966M 07.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume info
15、rmation, refer to the standards Document Summary page onthe ASTM website.3Withdrawn.4Available from American Society for NonDestructive Testing, 1711 ArlingateLane, P.O. Box 28518, Columbus, OH 43228-0518.1*A Summary of Changes section appears at the end of this standard.Copyright ASTM International
16、, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.current; the manufacturer and the supplier shall be in agree-ment concerning the following:4.1.1 The locations on the forging that are to be subjected tomagnetic particle examination.4.1.2 The type, size, number, l
17、ocation, and orientation ofindications that are to be considered injurious.4.1.3 The method of application and type of magneticparticles, demagnetization requirements, and magnetic fieldstrengths.4.1.4 Acceptance standards.5. Significance and Use5.1 For ferromagnetic materials, magnetic particle exa
18、mina-tion is widely specified for the detection of surface andnear-surface flaws such as cracks, laps, seams, and linearlyoriented nonmetallic inclusions. Such examinations are in-cluded as mandatory requirements in some forging standardssuch as Specifications A 508/A 508M and A 963/A 963M.5.2 Use o
19、f alternating current as the power source formagnetic particle examination imposes a significant restrictionon the detection of subsurface indications, so that the proce-dure is essentially limited to the finding of flaws that are opento the surface. Attention therefore is drawn to the need to havet
20、he component in the finish-machined condition before con-ducting the magnetic particle examination.5.3 The presence of residual magnetic fields in a componentmay be undesirable, and an advantage of the use of an ACpower source for magnetic particle examination is that anacceptable level of demagneti
21、zation can be readily achieved.6. Personnel Requirements6.1 Personnel performing the magnetic particle examinationin this practice shall be qualified and certified in accordancewith a written procedure conforming to Practice No. SNT-TC-1A or another national standard that is acceptable to boththe pu
22、rchaser and supplier.7. Stage of Examination7.1 Unless otherwise specified by the purchaser, acceptanceexamination shall be performed on a forging in the finalmachined surface condition.8. Magnetizing Apparatus8.1 A 50 or 60 cycle alternating current shall be used. Whencurrent is passed through the
23、forging itself, the equipment shallconsist of contacting or clamping elements with sufficientsurface area and clamping pressure to allow the requiredcurrent to flow without damaging (burning) the part beingexamined.8.2 Portable electromagnetic alternating current yokes maybe used as a magnetizing ap
24、paratus.9. Magnetic Particles9.1 The inspection medium shall consist of finely dividedferromagnetic particles (which may be coated with a fluores-cent material) suspended in a suitable liquid medium or used indry powder form.10. Surface Preparation10.1 The sensitivity of the magnetic particle examin
25、ationwill depend to a considerable extent upon the condition of thesurface being examined. While defects may be satisfactorilyrevealed on shot-blasted or otherwise cleaned forged surfaces,without any further surface treatment, all heat treatment orforging scale must be removed. However, to reveal fi
26、ne defectsof18 in. 3 mm or less in length, the surfaces to be examinedshall be smooth machined to at least a 250-in. 6.35-mfinish.10.2 The surfaces shall be free from grease, oils, or othersubstances to which the particles may adhere.11. Methods of Magnetization11.1 The forging may be magnetized eit
27、her by passingcurrent through the piece or by inducing a magnetic field bymeans of a central conductor, by coils, or by yoke.11.1.1 Continuous MethodIn the continuous method theinspection medium is applied to the surface under examinationwhile the current is still flowing. The alternating current so
28、urcegenerates high amperage current in pulses of up to 1 s duration.The duration of this flow shall allow at least three pulses ofcurrent, or in the case where machines supply continuouscurrent flow, a minimum shot of15 to12 s duration should beapplied.11.1.2 The surge and residual methods are not a
29、pplicable tothis practice.11.2 At least two separate examinations shall be carried outon each area. The second examination shall be with the lines ofmagnetic flux approximately perpendicular to those used forthe first examination in that area. A different means ofmagnetization may be used for the se
30、cond examination. Mag-netizing in more than one direction cannot normally beaccomplished simultaneously.An exception to the above rule isoverall sequential multivector magnetization whereby severalmagnetizing circuits are provided for sequentially magnetizinga part in multiple directions depending o
31、n the locations of thecurrent connectors. By this technique, indications of anyorientation can be detected with a single application ofmagnetic particles.11.3 The two general types of magnetization with regard todirection are longitudinal and circular as follows:11.3.1 LongitudinalWhen a forging is
32、magnetized longi-tudinally, the magnetic flux lines are usually parallel to the axisof the piece. A longitudinally magnetized piece always hasdefinite poles, readily detectable by compass or magnetometer.Longitudinal magnetization is usually accomplished by placingthe forging within a solenoid, freq
33、uently formed by wrappingcable around the piece (Fig. 1). For special applications,magnetic yokes can be used (Fig. 2).11.3.2 CircularCircular magnetization is obtained bypassing a current through the piece (Fig. 3) or by induced bypassing current through a conductor or conductors threadedthrough an
34、 opening in the piece (Fig. 4 or Fig. 5). Byagreement with the purchaser (see 11.5.3) localized circularmagnetization may be obtained by passing current throughlocal areas by the use of prod-type contacts (Fig. 6).A 966/A 966M 08211.4 The magnetic field is confined almost entirely to thepiece and th
35、ere may be no external manifestation of themagnetized condition. Indications will appear strongest in thedirection perpendicular to the direction of the magnetic field.11.5 Field StrengthThe minimum field strength that willreveal and permit classification of all objectionable defectsshall be used. T
36、he maximum field strengths practical are theones just below the point at which excessive adherence of theparticles begins to occur over the surface being inspected.11.5.1 Coil MagnetizationWhen coil magnetization isused, the magnetic field strength is directly proportional to thecurrent (ampere-turn
37、s if a coil or solenoid is used) andinversely proportional to the thickness of the section beinginspected.11.5.1.1 Longitudinal MagnetizationFor encircling coils(Fig. 1), the turns of the coil shall be kept closely together. Thefield strength decreases as distance from the coil increases andlong par
38、ts must be magnetized in sections. If the area to beinspected extends beyond 6 in. 150 mm on either side of thecoils, the adequacy of the field shall be demonstrated by the useof field indicators (see 11.5.6).(1) Small ForgingsMagnetizing force shall be 35 000ampere-turns divided by the sum of 2 plu
39、s the “length overdiameter” 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/Dratio of 5. Therefore, 35 000/(2 + 5) = 5000 ampere-turns; if a5-turn coil is used, the current required is 5000/5 or 1000 A.This formula provides an adequate field
40、strength on small partshaving an L/D ratio of 4 or greater. For parts having a smallerL/D ratio, adequate field strengths shall be demonstrated by theuse of a field indicator (see 11.5.6). The graph in Fig. 7 may beused to determine the ampere-turns required for each L/Drelationship.(2) Large Forgin
41、gsFor large forgings the magnetizingforce shall be in the range from 1200 to 4500 ampere-turns. Afield indicator (see 11.5.6) shall be used to demonstrate thepresence of an adequate field strength over the area to beinspected.11.5.1.2 Circular Magnetization (Fig. 5)For circular mag-netization with t
42、hrough coils, use the current with amperage asspecified in 11.5.2 divided by the number of turns in the coil.FIG. 1 Longitudinal MagnetizationFIG. 2 Longitudinal Magnetization, with YokeFIG. 3 Circular Magnetization, Current Directly Through ForgingFIG. 4 Circular Magnetization, Current Through a Co
43、nductorFIG. 5 Circular Magnetization, Current Through ConductorsThreaded Through ForgingFIG. 6 Circular Magnetization with “Prod” Type ContactElectrodesA 966/A 966M 08311.5.2 Direct MagnetizationWhen current is passed di-rectly through the part to be examined, the current shall bebetween 100 and 900
44、 A 4 and 35 A per millimetre per inch ofdiameter or cross section (per inch or millimetre of greatestwidth in a plane at right angles to current flow). For hollowparts this would be wall thickness when cables are clamped tothe wall. Suggested current for diameters or sections up to 5 in.125 mm are 6
45、00 to 900 A/inches 25 to 35 A per millimetre;for diameters or sections between 5 and 10 in. 125 to250 mm, 400 to 600 A/inches 15 to 25 A per millimetre; and100 to 400 A/inches 4 to 15 A per millimetre for outsidediameters or sections over 10 in. 250 mm. If it is not practicalto obtain these current
46、levels for diameters over 10 in. 250mm, the presence of an adequate field strength shall bedemonstrated using a field indicator. In all other instances theadequacy of the magnetizing force shall be demonstrated bymeans of a field indicator (see 11.5.6). When large parts havebeen examined by clamping
47、 contacts to the wall thickness, theadequacy of the field in the circumferential direction shall alsobe determined by the field indicator.11.5.3 Prod MagnetizationSince this method may inducearcing or burning at the contact areas, and the inspection isintended to be performed on finished surfaces, t
48、he use of prodmagnetization is not permissible without the prior approval ofthe purchaser. For the same reason magnetic leaches may notbe used to introduce current into the part without the priorapproval of the purchaser. If the use of prods or magneticleaches should be permitted, then the following
49、 conditionsshall apply:11.5.3.1 A magnetizing force of 75 to 100 A per linear inch3 to 4 A per millimetre of prod spacing shall be used formaterial under34 in. 20 mm thick, and 100 to 125Aper linearinch 4 to 5 A per millimetre of prod spacing shall be used formaterial34 in. 20 mm and over in thickness.11.5.3.2 Prod spacing shall be a maximum of 8 in.200 mm. Prod spacing less than 3 in. 75 mm usually is notfeasible due to banding of the particles around the prods. Careshall be taken to prevent local overheating or
