1、Designation: A 275/A 275M 08Standard 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 () 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 magnetic
3、 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 used
4、 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 1
5、Guide 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 designa
7、tion 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. Combi
8、ningvalues 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 dete
9、rmine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:3A 508/A 508M Specification for Quenched and TemperedVacuum-Treated Carbon and Alloy Steel Forgings forPressure VesselsE 709 Guide for Magnetic Particle TestingE 1444 Practice for Magnetic Parti
10、cle Testing2.2 Other Document:Recommended Practice No. SNT-TC-1A, SupplementB-Magnetic Particle Method43. Terminology3.1 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
11、 least three times the width. The minimum length ofindications to be considered linear shall be116 in. 1.6 mm.3.1.3 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
12、. The concept that the magnetic field is flowingalong the lines of force suggests that these lines are therefore“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, w
13、hich employs finely divided magneticparticles that tend to congregate in regions of leakage fields.3.1.5 nonrelevant indicationsindications produced byleakage fields. However, the conditions causing them arepresent by design or accident, or other features of the parthaving no relation to the damagin
14、g flaws being sought. Theterm signifies that such an indication has no relation to thediscontinuities that might 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 Ste
15、el Forgings and Billets.Current edition approved Nov. 1, 2008. Published November 2008. Originallyapproved in 1944. Last previous edition approved in 2007 as A 275/A 275M 07.2For ASME Boiler and Pressure Vessel Code applications see related MethodSA-275/SA-275M in Section II of that Code.3For refere
16、nced 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.4Available from American Society for Nondestructive Testing, 4153 Arling
17、atePlaza, Caller #28515, 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. Significance and Use4.1 For ferromagnetic materials, magnetic parti
18、cle examina-tion is widely specified for the detection of surface and nearsurface discontinuities such as cracks, laps, seams, and linearlyoriented nonmetallic inclusions. Such examinations are in-cluded as mandatory requirements in some forging standardssuch as Specification A 508/A 508M.4.2 Use of
19、 direct current or rectified alternating (full or halfwave) current as the power source for magnetic particleexamination allows detection of subsurface discontinuities.5. Basis of Application5.1 When in accordance with the requirements of theinquiry, contract, order, or specifications, forgings are
20、fur-nished subject to magnetic particle examination, the manufac-turer and the purchaser shall be in agreement concerning thefollowing:5.1.1 The locations on the forgings that are to be subjectedto magnetic particle examination.5.1.2 The type, size, number, location, and orientation ofindications th
21、at are to be considered injurious.5.1.3 The method of application of magnetic particles,demagnetization requirements and magnetic field strengths.5.2 In cases where large undercuts in the forgings are to betaken by the purchaser, the manufacturer shall be given theprivilege (when the design permits)
22、 of machining slots orgrooves in the rough-machined forging to explore the internalconditions prior to shipping.5.3 Acceptance standards.6. Personnel Requirements6.1 Personnel performing the magnetic particle examinationto this practice shall be qualified and certified in accordancewith a written pr
23、ocedure conforming to Recommended Prac-tice No. SNT-TC-1A or another national standard that isacceptable to both the purchaser and the supplier.7. Stage of Inspection7.1 Unless otherwise specified by the purchaser, acceptanceinspection shall be performed on a forging in the finalmachined surface con
24、dition and final thermally treated condi-tion (including stress relief) or within 0.030 in. 0.8 mm of thefinal machined surface.8. Magnetizing Apparatus8.1 Rectified alternating (full or half wave) or direct-currentelectric power sources may be used. When current is passedthrough the part itself, th
25、e equipment shall consist of contact-ing or clamping elements with sufficient surface area andclamping pressure to allow the required current to flow withoutdamaging (burning) the part being examined.8.2 Portable electromagnetic (ac-dc) yokes may be used inthe dc mode as a magnetizing apparatus, pro
26、vided the sensi-tivity to detect crack-like defects is demonstrated to be at leastequivalent to that of the direct-magnetization method.8.2.1 Portable battery powered electromagnetic yokes arenot included in the scope of this standard.9. Magnetic Particles9.1 The inspection medium shall consist of f
27、inely dividedferromagnetic particles, which may be suspended in a suitableliquid medium, or used in dry powder form.9.2 The size and shape of the particles, and their magneticproperties, both individually and collectively, are important(see Section 12).10. Surface Preparation10.1 The sensitivity of
28、the magnetic particle examinationwill depend to a considerable 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 prepar
29、ation; however, loose scale must beremoved. To reveal fine defects, the surfaces to be inspectedshould be smooth machined to at least a 250-in. 6.35-mfinish.10.2 The surfaces shall be free of grease, oils, or othersubstances to which the particles may adhere.10.3 Rough surfaces hamper the mobility o
30、f magneticpowders due to mechanical trapping which in turn producesfalse indications. Such areas should be surface ground. Ifgrinding is impractical, a paper tape overlay (as described in15.1.1.2) may eliminate the problem.11. Methods of Magnetization11.1 The forging may be magnetized either by pass
31、ingcurrent through the piece or by inducing a magnetic field bymeans of a central conductor or by coils.11.1.1 Continuous MethodIn the continuous method, theinspection medium is applied to the surface under inspectionwhile the current is still flowing. The current source generateshigh amperage curre
32、nt in pulses of up to 1-s duration. Theduration of 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.11.1.2 Surge MethodIn the surge method a high-magnetizing force is applied and th
33、en reduced to a lowercontinuous value, which is maintained during application ofthe inspection medium.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 examin
34、ation in that area. A different means ofmagnetizing 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 prov
35、idedfor sequentially magnetizing a part in multiple directions depending uponthe locations of the current connectors. By this technique, flaws of anyorientation can be detected with a single application of magnetic particles.11.3 The two general types of magnetization with regard todirection are lon
36、gitudinal and circular, as follows: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 hasA 275/A 275M 082definite poles readily detectable by compass or magnetometer.Longitudi
37、nal magnetization is usually accomplished by placingthe forging within a solenoid, often formed by wrapping cablearound the piece (Fig. 1). For special applications, magneticyokes can be used (Fig. 2) when requirements of 8.2 are met.11.3.2 CircularCircular magnetization is obtained bypassing a curr
38、ent directly through the piece (Fig. 3), or inducedthrough a conductor (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).11.4 The magnetic field i
39、s confined almost 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.11.5 Field StrengthThe minimum field strength that willreveal and permit classification
40、 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 dir
41、ectly 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 decreases as
42、 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 be 3
43、5 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 or 10
44、00 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 requi
45、red 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 Magnetizati
46、on (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.FIG. 1 Longitudinal MagnetizationFIG. 2 Longitudinal Magnetization, with YokeFIG. 3 Circular Magnetization, Current Directly Through ForgingFIG. 4
47、 Circular Magnetization, Current Through a ConductorFIG. 5 Circular Magnetization, Current Through ConductorsThreaded Through ForgingA 275/A 275M 08311.5.2 Direct MagnetizationWhen current is passed di-rectly through the part to be examined, the current shall bebetween 100 and 900 A per inch 4 and 3
48、5 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 900Aper inch
49、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 for 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 11.5.6). W
