ASTM A966/A966M-08(2012)
(Practice)Standard Practice for Magnetic Particle Examination of Steel Forgings Using Alternating Current
Standard Practice for Magnetic Particle Examination of Steel Forgings Using Alternating Current
SIGNIFICANCE AND USE
For ferromagnetic materials, magnetic particle examination is widely specified for the detection of surface and near-surface flaws such as cracks, laps, seams, and linearly oriented nonmetallic inclusions. Such examinations are included as mandatory requirements in some forging standards such as Specifications A508/A508M and .
Use of alternating current as the power source for magnetic particle examination imposes a significant restriction on the detection of subsurface indications, so that the procedure is essentially limited to the finding of flaws that are open to the surface. Attention therefore is drawn to the need to have the component in the finish-machined condition before conducting the magnetic particle examination.
The presence of residual magnetic fields in a component may be undesirable, and an advantage of the use of an AC power source for magnetic particle examination is that an acceptable level of demagnetization can be readily achieved.
SCOPE
1.1 This practice covers a procedure for the magnetic particle examination of steel forgings using alternating current as the power source. The procedure will produce consistent results upon which acceptance standards can be based. This practice does not contain acceptance limits or recommended quality levels.
1.2 Only alternating 50–60 cycle current shall be used as the electric power source for 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 units are to be regarded separately as standard. Within the text, the SI units are shown in brackets. The values stated in each system are not exact equivalents; therefore each system shall be used independently of the other. Combining values from the two systems may result in nonconformance with the specification. Unless the order specifies the applicable “M” specification designation [SI units], the inch-pound units shall be used.
1.5 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 regulatory limitations prior to use.
General Information
Relations
Standards Content (Sample)
NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.
Contact ASTM International (www.astm.org) for the latest information
Designation: A966/A966M − 08(Reapproved 2012)
Standard Practice for
Magnetic Particle Examination of Steel Forgings Using
Alternating Current
This standard is issued under the fixed designationA966/A966M; 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.
1. Scope A508/A508M Specification for Quenched and Tempered
Vacuum-Treated Carbon and Alloy Steel Forgings for
1.1 This practice covers a procedure for the magnetic
Pressure Vessels
particle examination of steel forgings using alternating current
A963/A963M Specification for Deep Drawing Steel (DDS),
as the power source. The procedure will produce consistent
Sheet, Carbon, Cold-Rolled (Withdrawn 2000)
results upon which acceptance standards can be based. This
2.2 Other Document:
practice does not contain acceptance limits or recommended
Practice No. SNT-TC-1A, Supplement B—Magnetic Par-
quality levels.
ticle Method
1.2 Onlyalternating50–60cyclecurrentshallbeusedasthe
3. Terminology
electric power source for any of the magnetizing methods.
3.1 Definitions:
1.3 When subsurface indications are sought in forgings,
3.1.1 (ac) magnetic particle method of examination, n—a
then dc magnetization in accordance with Practice A275/
method for detecting discontinuities on the surface in suitably
A275M should be used.
magnetized materials, which employs finely divided magnetic
1.4 The values stated in either inch-pound units or SI units
particles that tend to congregate in regions of leakage fields.
are to be regarded separately as standard. Within the text, the
3.1.2 indication, n—the visual magnetic particle buildup
SI units are shown in brackets. The values stated in each
resulting from leakage fields in the magnetic field.
system are not exact equivalents; therefore each system shall
3.1.3 linear indication, n—an indication in which the length
be used independently of the other. Combining values from the
is at least three times the width. The minimum length of
two systems may result in nonconformance with the specifi-
indications to be considered linear shall be ⁄16 in. [1.5 mm].
cation. Unless the order specifies the applicable “M” specifi-
cation designation [SI units], the inch-pound units shall be
3.1.4 magnetic flux, n—the product of the magnetic induc-
used.
tion and the area of a surface (or cross section) when the
magnetic induction is uniformly distributed and normal to the
1.5 This standard does not purport to address all of the
plane of the surface.
safety concerns, if any, associated with its use. It is the
3.1.4.1 Discussion—The concept that the magnetic field is
responsibility of the user of this standard to establish appro-
flowing along the lines of force suggests that these lines are
priate safety and health practices and determine the applica-
therefore “flux” lines, and they are called magnetic flux.
bility of regulatory limitations prior to use.
3.1.5 nonrelevant indications, n—indications produced by
2. Referenced Documents
leakagefieldswheretheconditionscausingthemarepresentby
accident or part design, or other features of the part having no
2.1 ASTM Standards:
relation to the damaging flaws being sought.
A275/A275M Practice for Magnetic Particle Examination of
3.1.5.1 Discussion—This term signifies that such an indica-
Steel Forgings
tion has no relation to the discontinuities that might constitute
defects.
This practice is under the jurisdiction of ASTM Committee A01 on Steel,
4. Basis of Application
Stainless Steel and Related Alloys and is the direct responsibility of Subcommittee
A01.06 on Steel Forgings and Billets.
4.1 When in accordance with the requirements of the
Current edition approved May 1, 2012. Published May 2012. Originally
inquiry, contract, order, or specifications, forgings are to be
approved in 1996. Last previous edition approved in 2008 as A966/A966M – 08.
DOI: 10.1520/A0966_A0966M-08R12.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or The last approved version of this historical standard is referenced on
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM www.astm.org.
Standards volume information, refer to the standard’s Document Summary page on Available from American Society for NonDestructive Testing, 1711 Arlingate
the ASTM website. Lane, P.O. Box 28518, Columbus, OH 43228-0518.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
A966/A966M − 08 (2012)
examined by the magnetic particle method using alternating 10. Surface Preparation
current; the manufacturer and the supplier shall be in agree-
10.1 The sensitivity of the magnetic particle examination
ment concerning the following:
will depend to a considerable extent upon the condition of the
4.1.1 The locations on the forging that are to be subjected to
surface being examined. While defects may be satisfactorily
magnetic particle examination.
revealed on shot-blasted or otherwise cleaned forged surfaces,
4.1.2 The type, size, number, location, and orientation of
without any further surface treatment, all heat treatment or
indications that are to be considered injurious.
forging scale must be removed. However, to reveal fine defects
4.1.3 The method of application and type of magnetic
of ⁄8 in. [3 mm] or less in length, the surfaces to be examined
particles, demagnetization requirements, and magnetic field
shall be smooth machined to at least a 250-µin. [6.35-µm]
strengths.
finish.
4.1.4 Acceptance standards.
10.2 The surfaces shall be free from grease, oils, or other
5. Significance and Use
substances to which the particles may adhere.
5.1 For ferromagnetic materials, magnetic particle examina-
11. Methods of Magnetization
tion is widely specified for the detection of surface and
near-surface flaws such as cracks, laps, seams, and linearly
11.1 The forging may be magnetized either by passing
oriented nonmetallic inclusions. Such examinations are in-
current through the piece or by inducing a magnetic field by
cluded as mandatory requirements in some forging standards
means of a central conductor, by coils, or by yoke.
such as Specifications A508/A508M and A963/A963M.
11.1.1 Continuous Method—In the continuous method the
inspection medium is applied to the surface under examination
5.2 Use of alternating current as the power source for
while the current is still flowing.The alternating current source
magnetic particle examination imposes a significant restriction
generateshighamperagecurrentinpulsesofupto1sduration.
on the detection of subsurface indications, so that the proce-
The duration of this flow shall allow at least three pulses of
dure is essentially limited to the finding of flaws that are open
current, or in the case where machines supply continuous
to the surface.Attention therefore is drawn to the need to have
1 1
current flow, a minimum shot of ⁄5 to ⁄2 s duration should be
the component in the finish-machined condition before con-
applied.
ducting the magnetic particle examination.
11.1.2 The surge and residual methods are not applicable to
5.3 The presence of residual magnetic fields in a component
this practice.
may be undesirable, and an advantage of the use of an AC
11.2 At least two separate examinations shall be carried out
power source for magnetic particle examination is that an
on each area.The second examination shall be with the lines of
acceptable level of demagnetization can be readily achieved.
magnetic flux approximately perpendicular to those used for
6. Personnel Requirements
the first examination in that area. A different means of
magnetization may be used for the second examination. Mag-
6.1 Personnel performing the magnetic particle examination
netizing in more than one direction cannot normally be
in this practice shall be qualified and certified in accordance
accomplishedsimultaneously.Anexceptiontotheaboveruleis
with a written procedure conforming to Practice No. SNT-
overall sequential multivector magnetization whereby several
TC-1A or another national standard that is acceptable to both
magnetizing circuits are provided for sequentially magnetizing
the purchaser and supplier.
a part in multiple directions depending on the locations of the
7. Stage of Examination
current connectors. By this technique, indications of any
orientation can be detected with a single application of
7.1 Unless otherwise specified by the purchaser, acceptance
magnetic particles.
examination shall be performed on a forging in the final
machined surface condition.
11.3 The two general types of magnetization with regard to
direction are longitudinal and circular as follows:
8. Magnetizing Apparatus
11.3.1 Longitudinal—When a forging is magnetized
8.1 A50 or 60 cycle alternating current shall be used.When
longitudinally, the magnetic flux lines are usually parallel to
current is passed through the forging itself, the equipment shall
the axis of the piece.Alongitudinally magnetized piece always
consist of contacting or clamping elements with sufficient
has definite poles, readily detectable by compass or magne-
surface area and clamping pressure to allow the required
tometer. Longitudinal magnetization is usually accomplished
current to flow without damaging (burning) the part being
by placing the forging within a solenoid, frequently formed by
examined.
wrapping cable around the piece (Fig. 1). For special
8.2 Portable electromagnetic alternating current yokes may applications, magnetic yokes can be used (Fig. 2).
11.3.2 Circular—Circular magnetization is obtained by
be used as a magnetizing apparatus.
passing a current through the piece (Fig. 3) or by induced by
9. Magnetic Particles
passing current through a conductor or conductors threaded
9.1 The inspection medium shall consist of finely divided through an opening in the piece (Fig. 4 or Fig. 5). By
ferromagnetic particles (which may be coated with a fluores- agreement with the purchaser (see 11.5.3) localized circular
cent material) suspended in a suitable liquid medium or used in magnetization may be obtained by passing current through
dry powder form. local areas by the use of prod-type contacts (Fig. 6).
A966/A966M − 08 (2012)
FIG. 5 Circular Magnetization, Current Through Conductors
Threaded Through Forging
FIG. 1 Longitudinal Magnetization
FIG. 6 Circular Magnetization with “Prod” Type Contact Elec-
trodes
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.
FIG. 2 Longitudinal Magnetization, with Yoke
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.
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. 3 Circular Magnetization, Current Directly 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
having an L/D ratio of 4 or greater. For parts having a smaller
L/Dratio,adequatefieldstrengthsshallbedemonstratedbythe
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
FIG. 4 Circular Magnetization, Current Through a Conductor
relationship.
(2) Large Forgings—For large forgings the magnetizing
11.4 The magnetic field is confined almost entirely to the force shall be in the range from 1200 to 4500 ampere-turns.A
piece and there may be no external manifestation of the field indicator (see 11.5.6) shall be used to demonstrate the
magnetized condition. Indications will appear strongest in the presence of an adequate field strength over the area to be
direction perpendicular to the direction of the magnetic field. inspected.
A966/A966M − 08 (2012)
feasible due to banding of the particles around the prods. Care
shall be taken to prevent local overheating or burning of the
surface being examined. Steel- or aluminum-tipped prods or
copper-brush-type prods rather than solid copper-tipped prods
are recommended where the magnetizing voltage is over 25 V
open circuit (bad contact) in order to avoid copper penetration.
Permanent magnetic leeches may be used as a pair or in
conjunction with a prod. Leeches should not be used in excess
of 1500 A because loss of magnetization occurs.
11.5.3.3 A remote control switch, which may be built into
the prod handles, shall be provided to permit the current to be
turned on after the prods have been properly positioned and to
turn off before the prods are removed in order to prevent
arcing.
11.5.3.4 Examination Coverage—Examinations shall be
conducted with sufficient overlap to ensure 100 % coverage at
the established sensitivity.
11.5.3.5 Direction of Magnetization —At least two separate
FIG. 7 Longitudinal Magnetization
examinations shall be carried out on each area. The prods shall
be placed so that the lines of flux during one examination are
11.5.1.2 Circular Magnetization (Fig. 5)—For circular mag-
approximately perpendicular to the lines of flux during the
netization with through coils, use the current with amperage as
other.
specified in 11.5.2 divided by the number of turns in the coil.
11.5.4 Indirect circular magnetization of forgings may be
11.5.2 Direct Magnetization—When current is passed di-
accomplished by the use of a central conductor as shown in
rectly through the part to be examined, the current shall be
Fig.4.Therecommendedcurrentlevelis100to125Aperinch
between 100 and 900A[4 and 35Aper millimetre] per inch of
[4 to 5Aper millimetre] of bore diameter.Alternatively a field
diameter or cros
...
Questions, Comments and Discussion
Ask us and Technical Secretary will try to provide an answer. You can facilitate discussion about the standard in here.