1、Designation: A966/A966M 08 (Reapproved 2012)Standard 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 adoption or, in the
2、 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. Scope1.1 This practice covers a procedure for the magneticparticle examination of steel forgings
3、 using alternating 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
4、 any of the magnetizing methods.1.3 When subsurface indications are sought in forgings,then dc magnetization in accordance with Practice A275/A275M 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 s
5、hown in brackets. 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 designat
6、ion SI units, 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 reg
7、ulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A275/A275M Practice for Magnetic Particle Examinationof Steel ForgingsA508/A508M Specification for Quenched and TemperedVacuum-Treated Carbon and Alloy Steel Forgings forPressure VesselsA963/A963M Specification for Deep Draw
8、ing 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 e
9、mploys 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 mi
10、nimum 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
11、that 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 fe
12、atures 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, orde
13、r, or specifications, forgings are to beexamined by the magnetic particle method using alternatingcurrent; the manufacturer and the supplier shall be in agree-ment concerning the following:1This practice is under the jurisdiction of ASTM Committee A01 on Steel,Stainless Steel and Related Alloys and
14、is the direct responsibility of SubcommitteeA01.06 on Steel Forgings and Billets.Current edition approved May 1, 2012. Published May 2012. Originallyapproved in 1996. Last previous edition approved in 2008 as A966/A966M 08.DOI: 10.1520/A0966_A0966M-08R12.2For referenced ASTM standards, visit the AST
15、M website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Withdrawn. The last approved version of this historical standard is referencedon www.astm.org.4Available
16、from American Society for NonDestructive Testing, 1711 ArlingateLane, P.O. Box 28518, Columbus, OH 43228-0518.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.1 The locations on the forging that are to be subjected tomagnetic part
17、icle examination.4.1.2 The type, size, number, location, 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 Fo
18、r ferromagnetic materials, magnetic particle examina-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 Specif
19、ications A508/A508M and A963/A963M.5.2 Use of 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. Atten
20、tion therefore is drawn to the need to havethe 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 examina
21、tion is that anacceptable level of demagnetization 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 nation
22、al standard that is acceptable to boththe purchaser 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
23、 be used. Whencurrent is passed through the 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
24、current yokes maybe used as a magnetizing apparatus.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
25、 sensitivity of the magnetic particle examinationwill 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
26、scale must be removed. However, to reveal fine 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 Magneti
27、zation11.1 The forging may be magnetized either 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
28、is still flowing. The alternating current sourcegenerates 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.
29、1.2 The surge and residual methods are not applicable 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
30、means ofmagnetization may be used for the second 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 magnetiz
31、inga part in multiple directions depending on 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 f
32、ollows:11.3.1 LongitudinalWhen a forging is 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 b
33、y placingthe forging within a solenoid, frequently 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
34、a conductor or conductors threadedthrough an 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).11.4 The magnetic field is confined almost
35、 entirely to thepiece and there may be no external manifestation of themagnetized condition. Indications will appear strongest in thedirection perpendicular to the direction of the magnetic field.A966/A966M 08 (2012)211.5 Field StrengthThe minimum field strength that willreveal and permit classifica
36、tion of all objectionable defectsshall be used. The 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
37、 directly proportional to thecurrent (ampere-turns 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 decrease
38、s as distance from the coil increases andlong parts 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
39、be 35 000ampere-turns divided by the sum of 2 plus 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 o
40、r 1000 A.This formula provides an adequate field 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 r
41、equired for each L/Drelationship.(2) Large ForgingsFor 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 Magneti
42、zation (Fig. 5)For circular mag-netization 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 di-rectly through the part to be examined, the current shall beFIG. 1 Longitudinal Magnetiza
43、tionFIG. 2 Longitudinal Magnetization, with YokeFIG. 3 Circular Magnetization, Current Directly Through ForgingFIG. 4 Circular Magnetization, Current Through a ConductorFIG. 5 Circular Magnetization, Current Through ConductorsThreaded Through ForgingFIG. 6 Circular Magnetization with “Prod” Type Con
44、tactElectrodesA966/A966M 08 (2012)3between 100 and 900 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 cur
45、rent for diameters or sections up to 5 in.125 mm are 600 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.
46、250 mm. If it is not practicalto obtain these current 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 1
47、1.5.6). When large parts havebeen examined by clamping 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 inspect
48、ion isintended to be performed on finished surfaces, the 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 m
49、agneticleaches should be permitted, then the following 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 pr
