1、Designation: A 275/A 275M 07Standard Practice forMagnetic Particle Examination of Steel Forgings1This standard is issued under the fixed designationA 275/A 275M; the number immediately following the designation indicates the yearof original adoption or, in the case of revision, the year of last revi
2、sion. A number in parentheses indicates the year of last reapproval.A superscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.1. Scope*1.1 This practice2covers a procedure for magneti
3、c particleexamination of steel forgings. The procedure will produceconsistent results upon which acceptance standards can bebased. This standard does not contain acceptance standards orrecommended quality levels.1.2 Only direct current or rectified alternating (full or halfwave) current shall be use
4、d as the electric power source for anyof the magnetizing methods. Alternating current is not permit-ted because its capability to detect subsurface discontinuities isvery limited and therefore unsuitable.1.2.1 Portable battery powered electromagnetic yokes areoutside the scope of this practice.NOTE
5、1Guide E 709 may be utilized for magnetic particle examina-tion in the field for machinery components originally manufactured fromsteel forgings.1.3 The minimum requirements for magnetic particle ex-amination shall conform to practice standards of PracticeE 1444. If the requirements of this practice
6、 are in conflict withthe requirements of Practice E 1444, the requirements of thispractice shall prevail.1.4 This specification and the applicable material specifica-tions are expressed in both inch-pound units and SI units.However, unless the order specifies the applicable “M” speci-fication design
7、ation SI units, the material shall be furnishedto inch-pound units.1.5 The values stated in either SI units or inch-pound unitsare to be regarded separately as standard. The values stated ineach system may not be exact equivalents; therefore, eachsystem shall be used independently of the other. Comb
8、iningvalues from the two systems may result in non-conformancewith the standard.1.6 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 det
9、ermine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3E 709 Guide for Magnetic Particle ExaminationE 1444 Practice for Magnetic Particle Testing2.2 Other Document:Recommended Practice No. SNT-TC-1A, SupplementB-Magnetic Particle Method43. Termino
10、logy3.1 Definitions:3.1.1 indicationthe visual magnetic particle buildup re-sulting from leakage fields in the magnetic field.3.1.2 linear indicationan indication in which the length isat least three times the width. The minimum length ofindications to be considered linear shall be116 in. 1.6 mm.3.1
11、.3 magnetic fluxthe product of the magnetic inductionand the area of a surface (or cross section) when the magneticinduction is uniformly distributed and normal to the plane ofthe surface. The concept that the magnetic field is flowingalong the lines of force suggests that these lines are therefore“
12、flux” lines, and they are called magnetic flux.3.1.4 magnetic particle method of examinationa methodfor detecting discontinuities on or near the surface in suitablymagnetized materials, which employs finely divided magneticparticles that tend to congregate in regions of leakage fields.3.1.5 nonrelev
13、ant indicationsindications produced byleakage fields. However, the conditions causing them arepresent by design or accident, or other features of the parthaving no relation to the damaging flaws being sought. Theterm signifies that such an indication has no relation to thediscontinuities that might
14、constitute defects.1This 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 edition approved Sept. 1, 2007. Published September 2007. Originallyapproved in 1
15、944. Last previous edition approved in 2006 as A 275/A 275M 06.2For ASME Boiler and Pressure Vessel Code applications see related MethodSA-275/SA-275M in Section II of that Code.3For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serviceastm.org.
16、For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.4Available from American Society for Nondestructive Testing, 4153 ArlingatePlaza, Caller #28515, Columbus, OH 43228-0518.1*A Summary of Changes section appears at the end of this stan
17、dard.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.4. Basis of Application4.1 When in accordance with the requirements of theinquiry, contract, order, or specifications, forgings are fur-nished subject to magnetic particle examinati
18、on, the manufac-turer and the purchaser shall be in agreement concerning thefollowing:4.1.1 The locations on the forgings that are to be subjectedto magnetic particle examination.4.1.2 The type, size, number, location, and orientation ofindications that are to be considered injurious.4.1.3 The metho
19、d of application of magnetic particles,demagnetization requirements and magnetic field strengths.4.2 In cases where large undercuts in the forgings are to betaken by the purchaser, the manufacturer shall be given theprivilege (when the design permits) of machining slots orgrooves in the rough-machin
20、ed forging to explore the internalconditions prior to shipping.4.3 Acceptance standards.5. Personnel Requirements5.1 Personnel performing the magnetic particle examinationto this practice shall be qualified and certified in accordancewith a written procedure conforming to Recommended Prac-tice No. S
21、NT-TC-1A or another national standard that isacceptable to both the purchaser and the supplier.6. Stage of Inspection6.1 Unless otherwise specified by the purchaser, acceptanceinspection shall be performed on a forging in the finalmachined surface condition and final thermally treated condi-tion (in
22、cluding stress relief) or within 0.030 in. 0.8 mm of thefinal machined surface.7. Magnetizing Apparatus7.1 Rectified alternating (full or half wave) or direct-currentelectric power sources may be used. When current is passedthrough the part itself, the equipment shall consist of contact-ing or clamp
23、ing elements with sufficient surface area andclamping pressure to allow the required current to flow withoutdamaging (burning) the part being examined.7.2 Portable electromagnetic (ac-dc) yokes may be used inthe dc mode as a magnetizing apparatus, provided the sensi-tivity to detect crack-like defec
24、ts is demonstrated to be at leastequivalent to that of the direct-magnetization method.7.2.1 Portable battery powered electromagnetic yokes arenot included in the scope of this standard.8. Magnetic Particles8.1 The inspection medium shall consist of finely dividedferromagnetic particles, which may b
25、e suspended in a suitableliquid medium, or used in dry powder form.8.2 The size and shape of the particles, and their magneticproperties, both individually and collectively, are important(see Section 11).9. Surface Preparation9.1 The sensitivity of the magnetic particle examination willdepend to a c
26、onsiderable extent upon the condition of thesurface being tested. Defects may be satisfactorily revealed onshot-blasted or otherwise cleaned forged surfaces, or onsurfaces having small amounts of heat-treating scale withoutany special surface preparation; however, loose scale must beremoved. To reve
27、al fine defects, the surfaces to be inspectedshould be smooth machined to at least a 250-in. 6.35-mfinish.9.2 The surfaces shall be free of grease, oils, or othersubstances to which the particles may adhere.9.3 Rough surfaces hamper the mobility of magnetic pow-ders due to mechanical trapping which
28、in turn produces falseindications. Such areas should be surface ground. If grinding isimpractical, a paper tape overlay (as described in 14.1.1.2) mayeliminate the problem.10. Methods of Magnetization10.1 The forging may be magnetized either by passingcurrent through the piece or by inducing a magne
29、tic field bymeans of a central conductor or by coils.10.1.1 Continuous MethodIn the continuous method, theinspection medium is applied to the surface under inspectionwhile the current is still flowing. The current source generateshigh amperage current in pulses of up to 1-s duration. Theduration of
30、this flow shall allow at least three pulses of currentor in the case where machines supply continuous current flowa minimum shot of15 to12-s duration should be applied.10.1.2 Surge MethodIn the surge method a high-magnetizing force is applied and then reduced to a lowercontinuous value, which is mai
31、ntained during application ofthe inspection medium.10.2 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 ofmagnetizing
32、 may be used for the second examination. Magne-tizing in more than one direction cannot be accomplishedsimultaneously.NOTE 2An exception to the above rule is overall sequential multi-vector magnetization whereby several magnetizing circuits are providedfor sequentially magnetizing a part in multiple
33、 directions depending uponthe locations of the current connectors. By this technique, flaws of anyorientation can be detected with a single application of magnetic particles.10.3 The two general types of magnetization with regard todirection are longitudinal and circular, as follows:10.3.1 Longitudi
34、nalWhen 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 by placingthe forging wit
35、hin a solenoid, often formed by wrapping cablearound the piece (Fig. 1). For special applications, magneticyokes can be used (Fig. 2) when requirements of 7.2 are met.10.3.2 CircularCircular magnetization is obtained bypassing a current directly through the piece (Fig. 3), or inducedthrough a conduc
36、tor (Fig. 4), or conductors threaded (Fig. 5)through an opening in the piece. Localized circular magenti-zation may be obtained by passing current through the localareas by use of prod-type contacts (Fig. 6).A 275/A 275M 07210.4 The magnetic field is confined almost entirely to thepiece and there ma
37、y be no external manifestation of themagnetized condition. Indications will appear strongest in thedirection perpendicular 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 max
38、imum field strengths practical are theones just below the point at which excessive adherence of theparticles begins to occur over the surface being inspected.10.5.1 Coil MagnetizationWhen coil magnetization isused, the magnetic field strength is directly proportional to thecurrent (ampere-turns if a
39、 coil or solenoid is used) andinversely proportional to the thickness 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 mus
40、t 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 10.5.6).(1) Small ForgingsMagnetizing force shall be 35 000ampere-turns divided by the sum of 2 plus the
41、“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 streng
42、th 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 10.5.6). The graph in Fig. 7 may beused to determine the ampere-turns required for each L/Drelationship.(2) Large ForgingsFor
43、large forgings the magnetizingforce shall be in the range from 1200 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 c
44、oils, use the current with amper-age as specified in 10.5.2 divided by the number of turns in thecoil.FIG. 1 Longitudinal MagnetizationFIG. 2 Longitudinal Magnetization, with YokeFIG. 3 Circular Magnetization, Current Directly Through ForgingFIG. 4 Circular Magnetization, Current Through a Conductor
45、FIG. 5 Circular Magnetization, Current Through ConductorsThreaded Through ForgingFIG. 6 Circular Magnetization with “Prod” Type ContactElectrodesA 275/A 275M 07310.5.2 Direct MagnetizationWhen current is passed di-rectly through the part to be examined, the current shall bebetween 100 and 900 A per
46、inch 4 and 35 A per millimetre 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 600 to 9
47、00Aper inch 25 to 35Aper millimetre;for diameters or sections between 5 and 10 in. 125 to250 mm, 400 to 600 A per inch 15 to 25 A per millimetre;and 100 to 400Aper inch 4 to 15Aper millimetre for outsidediameters or sections over 10 in. 250 mm. If it is not practicalto obtain these current levels fo
48、r diameters over 10 in.250 mm, 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 10.5.6). When large parts havebeen examined by clamping contacts
49、 to the wall thickness theadequacy of the field in the circumferential direction shall alsobe determined by the field indicator.10.5.3 Prod MagnetizationWhen prods are used to circu-larly magnetize a local area, the field strength is directlyproportional to the amperage used but also varies with the prodspacing and thickness of section being inspected.10.5.3.1 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 linear
