ASTM A275/A275M-08(2013)
(Practice)Standard Practice for Magnetic Particle Examination of Steel Forgings
Standard Practice for Magnetic Particle Examination of Steel Forgings
ABSTRACT
This test method covers the procedures for the standard practice of performing magnetic particle examination on steel forgings. The inspection medium shall consist of finely divided ferromagnetic particles, whose size, shape and magnetic properties, both individually and collectively, shall be taken into account. Forgings may be magnetized in the longitudinal or circular direction by employing the surge or continuous current flow methods. Magnetization may be applied by passing current through the piece or by inducing a magnetic field by means of a central conductor, such as a prod or yoke, or by coils. While the material is properly magnetized, the magnetic particles may be applied by either the dry method, wet method, or fluorescent method. The parts shall also be sufficiently demagnetized after inspection so that residual or leakage fields will not interfere with future operations to which the steel forgings shall be used for. Indications to be evaluated are grouped into three broad classes, namely: surface defects, which include laminar defects, forging laps and folds, flakes (thermal ruptures caused by entrapped hydrogen), heat-treating cracks, shrinkage cracks, grinding cracks, and etching or plating cracks; subsurface defects, which include stringers of nonmetallic inclusions, large nonmetallics, cracks in underbeads of welds, and forging bursts; and nonrelevant or false indications, which include magnetic writing, changes in section, edge of weld, and flow lines.
SIGNIFICANCE AND USE
4.1 For ferromagnetic materials, magnetic particle examination is widely specified for the detection of surface and near surface discontinuities such as cracks, laps, seams, and linearly oriented nonmetallic inclusions. Such examinations are included as mandatory requirements in some forging standards such as Specification A508/A508M.
4.2 Use of direct current or rectified alternating (full or half wave) current as the power source for magnetic particle examination allows detection of subsurface discontinuities.
SCOPE
1.1 This practice2 covers a procedure for magnetic particle examination of steel forgings. The procedure will produce consistent results upon which acceptance standards can be based. This practice does not contain acceptance standards or recommended quality levels.
1.2 Only direct current or rectified alternating (full or half wave) current shall be used as the electric power source for any of the magnetizing methods. Alternating current is not permitted because its capability to detect subsurface discontinuities is very limited and therefore unsuitable.
1.2.1 Portable battery powered electromagnetic yokes are outside the scope of this practice.Note 1—Guide E709 may be utilized for magnetic particle examination in the field for machinery components originally manufactured from steel forgings.
1.3 The minimum requirements for magnetic particle examination shall conform to practice standards of Practice E1444/E1444M. If the requirements of this practice are in conflict with the requirements of Practice E1444/E1444M, the requirements of this practice shall prevail.
1.4 This practice and the applicable material specifications are expressed in both inch-pound units and SI units. However, unless the order specifies the applicable “M” specification designation [SI units], the material shall be furnished to inch-pound units.
1.5 The values stated in either SI units or inch-pound units are to be regarded separately as standard. The values stated in each system may not be exact equivalents; therefore, each system shall be used independently of the other. Combining values from the two systems may result in non-conformance with the standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of reg...
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Designation: A275/A275M − 08(Reapproved 2013)
Standard Practice for
Magnetic Particle Examination of Steel Forgings
This standard is issued under the fixed designationA275/A275M; the number immediately following the designation indicates the year
of original adoption or, in the 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.
This standard has been approved for use by agencies of the U.S. Department of Defense.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This practice covers a procedure for magnetic particle
responsibility of the user of this standard to establish appro-
examination of steel forgings. The procedure will produce
priate safety and health practices and determine the applica-
consistent results upon which acceptance standards can be
bility of regulatory limitations prior to use.
based. This practice does not contain acceptance standards or
recommended quality levels.
2. Referenced Documents
1.2 Only direct current or rectified alternating (full or half
2.1 ASTM Standards:
wave)currentshallbeusedastheelectricpowersourceforany
A508/A508M Specification for Quenched and Tempered
of the magnetizing methods.Alternating current is not permit-
Vacuum-Treated Carbon and Alloy Steel Forgings for
ted because its capability to detect subsurface discontinuities is
Pressure Vessels
very limited and therefore unsuitable.
E709 Guide for Magnetic Particle Testing
1.2.1 Portable battery powered electromagnetic yokes are
E1444/E1444M Practice for Magnetic Particle Testing
outside the scope of this practice.
2.2 Other Document:
NOTE1—GuideE709maybeutilizedformagneticparticleexamination
Recommended Practice No. SNT-TC-1A, Supplement
in the field for machinery components originally manufactured from steel
B-Magnetic Particle Method
forgings.
1.3 The minimum requirements for magnetic particle ex-
3. Terminology
amination shall conform to practice standards of Practice
3.1 Definitions:
E1444/E1444M. If the requirements of this practice are in
3.1.1 indication—the visual magnetic particle buildup re-
conflict with the requirements of Practice E1444/E1444M, the
sulting from leakage fields in the magnetic field.
requirements of this practice shall prevail.
3.1.2 linear indication—an indication in which the length is
1.4 This practice and the applicable material specifications
at least three times the width. The minimum length of
are expressed in both inch-pound units and SI units. However,
indications to be considered linear shall be ⁄16 in. [1.6 mm].
unless the order specifies the applicable “M” specification
3.1.3 magnetic flux—the product of the magnetic induction
designation [SI units], the material shall be furnished to
and the area of a surface (or cross section) when the magnetic
inch-pound units.
induction is uniformly distributed and normal to the plane of
1.5 The values stated in either SI units or inch-pound units
the surface. The concept that the magnetic field is flowing
are to be regarded separately as standard. The values stated in
along the lines of force suggests that these lines are therefore
each system may not be exact equivalents; therefore, each
“flux” lines, and they are called magnetic flux.
system shall be used independently of the other. Combining
3.1.4 magnetic particle method of examination—a method
values from the two systems may result in non-conformance
for detecting discontinuities on or near the surface in suitably
with the standard.
magnetized materials, which employs finely divided magnetic
particles that tend to congregate in regions of leakage fields.
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
A01.06 on Steel Forgings and Billets. For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Current edition approved April 1, 2013. Published April 2013. Originally contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
approved in 1944. Last previous edition approved in 2008 as A275/A275M – 08. Standards volume information, refer to the standard’s Document Summary page on
DOI: 10.1520/A0275_A0275M-08R13. the ASTM website.
2 4
For ASME Boiler and Pressure Vessel Code applications see related Method AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
SA-275/SA-275M in Section II of that Code. 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A275/A275M − 08 (2013)
3.1.5 nonrelevant indications—indications produced by clampingpressuretoallowtherequiredcurrenttoflowwithout
leakage fields. However, the conditions causing them are damaging (burning) the part being examined.
present by design or accident, or other features of the part
8.2 Portable electromagnetic (ac-dc) yokes may be used in
having no relation to the damaging flaws being sought. The
the dc mode as a magnetizing apparatus, provided the sensi-
term signifies that such an indication has no relation to the
tivity to detect crack-like defects is demonstrated to be at least
discontinuities that might constitute defects.
equivalent to that of the direct-magnetization method.
8.2.1 Portable battery powered electromagnetic yokes are
4. Significance and Use
not included in the scope of this practice.
4.1 For ferromagnetic materials, magnetic particle examina-
9. Magnetic Particles
tion is widely specified for the detection of surface and near
surface discontinuities such as cracks, laps, seams, and linearly
9.1 The inspection medium shall consist of finely divided
oriented nonmetallic inclusions. Such examinations are in- ferromagnetic particles, which may be suspended in a suitable
cluded as mandatory requirements in some forging standards
liquid medium, or used in dry powder form.
such as Specification A508/A508M.
9.2 The size and shape of the particles, and their magnetic
4.2 Use of direct current or rectified alternating (full or half properties, both individually and collectively, are important
wave) current as the power source for magnetic particle (see Section 12).
examination allows detection of subsurface discontinuities.
10. Surface Preparation
5. Basis of Application
10.1 The sensitivity of the magnetic particle examination
will depend to a considerable extent upon the condition of the
5.1 When in accordance with the requirements of the
surface being tested. Defects may be satisfactorily revealed on
inquiry, contract, order, or specifications, forgings are fur-
shot-blasted or otherwise cleaned forged surfaces, or on
nished subject to magnetic particle examination, the manufac-
surfaces having small amounts of heat-treating scale without
turer and the purchaser shall be in agreement concerning the
any special surface preparation; however, loose scale must be
following:
removed. To reveal fine defects, the surfaces to be inspected
5.1.1 The locations on the forgings that are to be subjected
should be smooth machined to at least a 250-µin. [6.35-µm]
to magnetic particle examination.
finish.
5.1.2 The type, size, number, location, and orientation of
indications that are to be considered injurious.
10.2 The surfaces shall be free of grease, oils, or other
5.1.3 The method of application of magnetic particles,
substances to which the particles may adhere.
demagnetization requirements and magnetic field strengths.
10.3 Rough surfaces hamper the mobility of magnetic
5.2 In cases where large undercuts in the forgings are to be powders due to mechanical trapping which in turn produces
taken by the purchaser, the manufacturer shall be given the
false indications. Such areas should be surface ground. If
privilege (when the design permits) of machining slots or grinding is impractical, a paper tape overlay (as described in
grooves in the rough-machined forging to explore the internal
15.1.1.2) may eliminate the problem.
conditions prior to shipping.
11. Methods of Magnetization
5.3 Acceptance standards.
11.1 The forging may be magnetized either by passing
current through the piece or by inducing a magnetic field by
6. Personnel Requirements
means of a central conductor or by coils.
6.1 Personnel performing the magnetic particle examination
11.1.1 Continuous Method—In the continuous method, the
to this practice shall be qualified and certified in accordance
inspection medium is applied to the surface under inspection
with a written procedure conforming to Recommended Prac-
while the current is still flowing. The current source generates
tice No. SNT-TC-1A or another national standard that is
high amperage current in pulses of up to 1-s duration. The
acceptable to both the purchaser and the supplier.
duration of this flow shall allow at least three pulses of current
or in the case where machines supply continuous current flow
7. Stage of Inspection
1 1
a minimum shot of ⁄5 to ⁄2-s duration should be applied.
7.1 Unless otherwise specified by the purchaser, acceptance 11.1.2 Surge Method—In the surge method a high-
inspection shall be performed on a forging in the final magnetizing force is applied and then reduced to a lower
machined surface condition and final thermally treated condi- continuous value, which is maintained during application of
tion (including stress relief) or within 0.030 in. [0.8 mm] of the the inspection medium.
final machined surface.
11.2 At least two separate examinations shall be carried out
on each area.The second examination shall be with the lines of
8. Magnetizing Apparatus
magnetic flux approximately perpendicular to those used for
8.1 Rectified alternating (full or half wave) or direct-current the first examination in that area. A different means of
electric power sources may be used. When current is passed magnetizing may be used for the second examination. Magne-
through the part itself, the equipment shall consist of contact- tizing in more than one direction cannot be accomplished
ing or clamping elements with sufficient surface area and simultaneously.
A275/A275M − 08 (2013)
NOTE 2—An exception to the above rule is overall sequential multi-
vector magnetization whereby several magnetizing circuits are provided
for sequentially magnetizing a part in multiple directions depending upon
the locations of the current connectors. By this technique, flaws of any
orientation can be detected with a single application of magnetic particles.
11.3 The two general types of magnetization with regard to
direction are longitudinal and circular, as follows:
11.3.1 Longitudinal—When a forging is magnetized
longitudinally, the magnetic flux lines are usually parallel to
the axis of the piece.Alongitudinally magnetized piece always
has definite poles readily detectable by compass or magnetom-
eter. Longitudinal magnetization is usually accomplished by
placing the forging within a solenoid, often formed by wrap-
ping cable around the piece (Fig. 1). For special applications,
FIG. 2 Longitudinal Magnetization, with Yoke
magnetic yokes can be used (Fig. 2) when requirements of 8.2
are met.
11.3.2 Circular—Circular magnetization is obtained by
passing a current directly through the piece (Fig. 3), or induced
through 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 local
areas by use of prod-type contacts (Fig. 6).
11.4 The magnetic field is confined almost entirely to the
piece and there may be no external manifestation of the
magnetized condition. Indications will appear strongest in the
FIG. 3 Circular Magnetization, Current Directly Through Forging
direction perpendicular to the direction of the magnetic field.
11.5 Field Strength—The minimum field strength that will
reveal and permit classification of all objectionable defects
shall be used. The maximum field strengths practical are the
ones just below the point at which excessive adherence of the
particles begins to occur over the surface being inspected.
11.5.1 Coil Magnetization—When coil magnetization is
used, the magnetic field strength is directly proportional to the
current (ampere-turns if a coil or solenoid is used) and
inversely proportional to the thickness of the section being
inspected. FIG. 4 Circular Magnetization, Current Through a Conductor
11.5.1.1 Longitudinal Magnetization—For encircling coils
(Fig. 1), the turns of the coil shall be kept closely together.The
field strength decreases as distance from the coil increases and
long parts must be magnetized in sections. If the area to be
inspected extends beyond 6 in. [150 mm] on either side of the
coils,theadequacyofthefieldshallbedemonstratedbytheuse
of field indicators (see 11.5.6).
FIG. 5 Circular Magnetization, Current Through Conductors
Threaded Through Forging
(1) Small Forgings—Magnetizing force shall be 35 000
ampere-turns divided by the sum of 2 plus the “length over
diameter” ratio of the test part. For example, a part 10 in.
[250 mm]longby2in.[50mm]inoutsidediameterhasanL/D
ratio of 5. Therefore, 35 000/(2 + 5) = 5000 ampere-turns; if a
5-turn coil is used, the current required is 5000/5 or 1000 A.
This formula provides an adequate field strength on small parts
FIG. 1 Longitudinal Magnetization having an L/D ratio of 4 or greater. For parts having a smaller
A275/A275M − 08 (2013)
means of a field indicator (see 11.5.6). When large parts have
been examined by clamping contacts to the wall thickness the
adequacy of the field in the circumferential direction shall also
be determined by the field indicator.
11.5.3 Prod Magnetization—When prods are used to circu-
larly magnetize a local area, the field strength is directly
proportional to the amperage used but also varies with the prod
spacing and thickness of section being inspected.
FIG. 6 Circular Magnetization with “Prod” Type Contact Elec-
11.5.3.1 Amagnetizing force of 75 to 100Aper linear inch
trodes
[3 to 4 A per millimetre] of prod spacing shall be used for
materialunder ⁄4in.[20mm]thick,and100to125Aperlinear
inch [4 to 5Aper millimetre] of prod spacing shall be used for
L/D ratio, adequate field strengths shall be demonstrated by the
material ⁄4 in. [20 mm] and over in thickness.
use of a field indicator (see 11.5.6).The graph in Fig. 7 may be
used to determine the ampere-turns required for each L/D
11.5.3.2 Prod spacing shall be a maximum of 8 in. [200
relationship. mm]. Prod spacing less than 3 in. [75 mm] usu
...
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