1、Designation: A 966/A 966M 07Standard 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. Theability to detect subsurface discontinuities is very limited whenusing an alternating power source, and therefore the testsurfaces should be in the final thermally treated and finishmachined condition.1.3 When subsurface indications are sought in forgings,then dc magnetizatio
5、n in accordance with Test Method 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 brackets. The values stated in eachsystem are not exact equivalents; therefore each system sha
6、llbe 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 units, the inch-pound units shall beused.1.5 This standard does not purport to address all of t
7、hesafety 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 limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2A 275/A 275M Test Method f
8、or Magnetic Particle Exami-nation of Steel Forgings2.2 Other Document:Practice No. SNT-TC-1A, Supplement BMagnetic Par-ticle Method33. Terminology3.1 Definitions:3.1.1 (ac) magnetic particle method of examination, namethod for detecting discontinuities on the surface in suitablymagnetized materials,
9、 which employs 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
10、. The minimum 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
11、concept 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
12、other features 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, contra
13、ct, order, 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:4.1.1 The locations on the forging that are to be subjected tomagnetic particle examination.1This pract
14、ice 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 edition approved May 1, 2007. Published June 2007. Originallyapproved in 1996. Last previous edition approved i
15、n 2006 as A 966/A 966M 96(2006).2For referenced ASTM standards, visit the ASTM 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.3Available from American Soci
16、ety 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, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4.1.2 The type, size, numbe
17、r, 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. Personnel Requirements5.1 Personnel performing the magnetic particle e
18、xaminationin 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 purchaser and supplier.6. Stage of Examination6.1 Unless otherwise specified by the purchaser, acceptancee
19、xamination shall be performed on a forging in the finalmachined surface condition.7. Magnetizing Apparatus7.1 A 50 or 60 cycle alternating current shall be used. Whencurrent is passed through the forging itself, the equipment shallconsist of contacting or clamping elements with sufficientsurface are
20、a and clamping pressure to allow the requiredcurrent to flow without damaging (burning) the part beingexamined.7.2 Portable electromagnetic alternating current yokes maybe used as a magnetizing apparatus.8. Magnetic Particles8.1 The inspection medium shall consist of finely dividedferromagnetic part
21、icles (which may be coated with a fluores-cent material) suspended in a suitable liquid medium or used indry powder form.9. Surface Preparation9.1 The sensitivity of the magnetic particle examination willdepend to a considerable extent upon the condition of thesurface being examined. While defects m
22、ay 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 fine defectsof18 in. 3 mm or less in length, the surfaces to be examinedshall be smooth machined to at least
23、 a 250-in. 6.35-mfinish.9.2 The surfaces shall be free from grease, oils, or othersubstances to which the particles may adhere.10. Methods of Magnetization10.1 The forging may be magnetized either by passingcurrent through the piece or by inducing a magnetic field bymeans of a central conductor, by
24、coils, or by yoke.10.1.1 Continuous MethodIn the continuous method theinspection medium is applied to the surface under examinationwhile the current 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 a
25、t least three pulses ofcurrent, or in the case where machines supply continuouscurrent flow, a minimum shot of15 to12 s duration should beapplied.10.1.2 The surge and residual methods are not applicable tothis practice.10.2 At least two separate examinations shall be carried outon each area. The sec
26、ond 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 second examination. Mag-netizing in more than one direction cannot normally beaccomplished simultaneously.An
27、exception to the above rule isoverall sequential multivector magnetization whereby severalmagnetizing circuits are provided for sequentially magnetizinga part in multiple directions depending on the locations of thecurrent connectors. By this technique, indications of anyorientation can be detected
28、with a single application ofmagnetic particles.10.3 The two general types of magnetization with regard todirection are longitudinal and circular as follows:10.3.1 LongitudinalWhen a forging is magnetized longi-tudinally, the magnetic flux lines are usually parallel to the axisof the piece. A longitu
29、dinally magnetized piece always hasdefinite poles, readily detectable by compass or magnetometer.Longitudinal magnetization is usually accomplished by placingthe forging within a solenoid, frequently formed by wrappingcable around the piece (Fig. 1). For special applications,magnetic yokes can be us
30、ed (Fig. 2).10.3.2 CircularCircular magnetization is obtained bypassing a current through the piece (Fig. 3) or by induced bypassing current through a conductor or conductors threadedthrough an opening in the piece (Fig. 4 or Fig. 5). Byagreement with the purchaser (see 10.5.3) localized circularmag
31、netization may be obtained by passing current throughlocal areas by the use of prod-type contacts (Fig. 6).10.4 The magnetic field is confined almost entirely to thepiece and there may be no external manifestation of themagnetized condition. Indications will appear strongest in thedirection perpendi
32、cular to the direction of the magnetic field.10.5 Field StrengthThe minimum field strength that willreveal and permit classification of all objectionable defectsshall be used. The maximum field strengths practical are theones just below the point at which excessive adherence of theparticles begins t
33、o occur over the surface being inspected.10.5.1 Coil MagnetizationWhen coil magnetization isused, the magnetic field strength is directly proportional to theFIG. 1 Longitudinal MagnetizationA 966/A 966M 072current (ampere-turns if a coil or solenoid is used) andinversely proportional to the thicknes
34、s of the section beinginspected.10.5.1.1 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 parts must be magnetized in sections. If the area to beinspected extends beyo
35、nd 6 in. 150 mm on either side of thecoils, the adequacy of the field shall be demonstrated by the useof field indicators (see 10.5.6).(1) Small ForgingsMagnetizing force shall be 35 000ampere-turns divided by the sum of 2 plus the “length overdiameter” ratio of the test part. For example, a part 10
36、 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 strength on small partshaving an L/D ratio of 4 or greater. For parts havi
37、ng a smallerL/D ratio, adequate field strengths shall be demonstrated by theuse of a field indicator (see 10.5.6). The graph in Fig. 7 may beused to determine the ampere-turns required for each L/Drelationship.(2) Large ForgingsFor large forgings the magnetizingforce shall be in the range from 1200
38、to 4500 ampere-turns. Afield indicator (see 10.5.6) shall be used to demonstrate thepresence of an adequate field strength over the area to beinspected.10.5.1.2 Circular Magnetization (Fig. 5)For circularmagnetization with through coils, use the current with amper-age as specified in 10.5.2 divided
39、by the number of turns in thecoil.10.5.2 Direct MagnetizationWhen current is passed di-rectly through the part to be examined, the current shall bebetween 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
40、to current flow). For hollowFIG. 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 Magnetizat
41、ion with “Prod” Type ContactElectrodesFIG. 7 Longitudinal MagnetizationA 966/A 966M 073parts this would be wall thickness when cables are clamped tothe wall. Suggested current 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 betw
42、een 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 levels for diameters over 10 in. 250mm, the presence of an adequate field s
43、trength shall bedemonstrated using a field indicator. In all other instances theadequacy of the magnetizing force shall be demonstrated bymeans of a field indicator (see 10.5.6). When large parts havebeen examined by clamping contacts to the wall thickness, theadequacy of the field in the circumfere
44、ntial direction shall alsobe determined by the field indicator.10.5.3 Prod MagnetizationSince this method may inducearcing or burning at the contact areas, and the inspection isintended to be performed on finished surfaces, the use of prodmagnetization is not permissible without the prior approval o
45、fthe 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 conditionsshall apply:10.5.3.1 A magnetizing force of 75 to 100 A per line
46、ar 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.10.5.3.2 Prod spacing shall be a maximum of 8 in.200 mm. Prod spacing le
47、ss 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 burning of thesurface being examined. Steel- or aluminum-tipped prods orcopper-brush-type prods rather than solid copper-tipped prodsare recommended where t
48、he magnetizing voltage is over 25 Vopen circuit (bad contact) in order to avoid copper penetration.Permanent magnetic leeches may be used as a pair or inconjunction with a prod. Leeches should not be used in excessof 1500 A because loss of magnetization occurs.10.5.3.3 A remote control switch, which
49、 may be built intothe prod handles, shall be provided to permit the current to beturned on after the prods have been properly positioned and toturn off before the prods are removed in order to preventarcing.10.5.3.4 Examination CoverageExaminations shall beconducted with sufficient overlap to ensure 100 % coverage atthe established sensitivity.10.5.3.5 Direction of MagnetizationAt least two separateexaminations shall be carried out on each area. The prods shallbe placed so that the lines of flux during one exam
