ASTM E570-97(2004)e1
(Practice)Standard Practice for Flux Leakage Examination of Ferromagnetic Steel Tubular Products
Standard Practice for Flux Leakage Examination of Ferromagnetic Steel Tubular Products
SIGNIFICANCE AND USE
This practice outlines a procedure for examining ferromagnetic tubular products using the flux leakage method. If properly applied, this method is capable of detecting the presence and location of significant longitudinally or transversely oriented discontinuities such as pits, scabs, slivers, gouges, roll-ins, laps, seams, cracks, holes, and improper welds in ferromagnetic tubes under inspection. In addition, the severity of a discontinuity may be estimated and a rejection level set with respect to the magnitude of the electromagnetic indication produced by the discontinuity.
The response from natural discontinuities can be significantly different from the response for artificial discontinuities such as drilled holes or notches of equivalent depth. For this reason, sufficient work should be done to determine the conditions necessary to detect and mark natural discontinuities whose characteristics will adversely affect the serviceability of the tube, in order to establish acceptance criteria between the supplier and purchaser.
SCOPE
1.1 This practice covers the application and calibration of equipment using the flux leakage test method for detection of outer surface, inner surface, and subsurface discontinuities in ferromagnetic steel tubular products (Note 1) of uniform cross section such as seamless and welded tubing.
Note 1-The term "tube" or "tubular product" will be used to refer to both pipe and tubing.
1.2 This practice is intended for use on tubular products having outside diameters from approximately 1/2 to 24 in. (12.7 to 610 mm) with wall thicknesses to 1/2 in. These techniques have been used for other sizes, however, and may be so specified upon contractual agreement between the purchaser and the supplier.
1.3 This practice does not establish acceptance criteria; they must be specified by the using parties.
1.4 This standard does not purport to address 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.
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Designation:E570–97 (Reapproved 2004)
Standard Practice for
Flux Leakage Examination of Ferromagnetic Steel Tubular
Products
This standard is issued under the fixed designation E 570; 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 (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.
e NOTE—Editorial changes were made throughout the standard in January 2004.
1. Scope E 543 Practice for Evaluating Agencies that Perform Non-
destructive Testing
1.1 This practice covers the application and standardization
E 1316 Terminology for Nondestructive Examinations
of equipment using the flux leakage test method for detection
2.2 Other Documents:
of outer surface, inner surface, and subsurface discontinuities
SNT-TC-1A Recommended for Personnel Qualification and
in ferromagnetic steel tubular products (Note 1) of uniform
Certification of Nondestructive Testing Personnel
cross section such as seamless and welded tubing.
ANSI/ASNT CP-189 ASNT Standard for Qualification and
NOTE 1—The term “tube” or “tubular product” will be used to refer to 3
Certification of Nondestructive Testing Personnel
both pipe and tubing.
NAS-410 NAS Certification and Qualification of Nonde-
1.2 This practice is intended for use on tubular products
structive Personnel (Quality Assurance Committee)
having outside diameters from approximately ⁄2 to 24 in. (12.7
3. Terminology
to 610 mm) with wall thicknesses to ⁄2 in (12.7 mm). These
techniques have been used for other sizes, however, and may
3.1 Definitionsoftermsrelatingtofluxleakageexamination
be so specified upon contractual agreement between the
are provided in Terminology E 1316.
purchaser and the supplier.
4. Summary of Practice
1.3 This practice does not establish acceptance criteria; they
must be specified by the using parties.
4.1 This method consists of the following steps:
1.4 This standard does not purport to address the safety
4.1.1 The tube wall is magnetized at the area under exami-
concerns, if any, associated with its use. It is the responsibility nation to a proper level approaching magnetic saturation.
of the user of this standard to establish appropriate safety and
NOTE 2—Tubes subjected to magnetic inspections can retain various
health practices and determine the applicability of regulatory
strengthsandconfigurationofresidualmagneticfieldsdependinguponthe
limitations prior to use.
magnetization technique. If the residual field resulting from a given
technique can interfere with subsequent applications of the tube, then a
2. Referenced Documents
supplemental demagnetization process may be required.
2.1 ASTM Standards:
4.1.2 A flux sensor containing magnetic transducers is
placed on or above the outside surface of the tube in the
magnetized area.
1 4.1.3 Either the tube or the flux sensor is moved at a
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
structive Testing and is the direct responsibility of Subcommittee E07.07 on constant speed in the direction of the magnetic field so that the
Electromagnetic Method.
sensor scans the entire surface of the tube.
Current edition approved January 1, 2004. Published February 2004. Originally
approved in 1976. Last previous edition approved in 1997 as E 570 - 97.
2 3
For referenced ASTM standards, visit the ASTM website, www.astm.org, or Available fromTheAmerican Society for NondestructiveTesting (ASNT), P.O.
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Box 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518.
Standards volume information, refer to the standard’s Document Summary page on Available from Aerospace Industries Association of America, Inc., 1250 Eye
the ASTM website. St., NW, Washington, DC 20005.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E570–97 (2004)
4.1.4 Each magnetic transducer in the flux sensor is con- described in Practice E 543. The applicable edition of Practice
nected to an electronic console which amplifies, filters, and E 543 shall be identified in the purchase specification or
electronically processes the signals such that significant dis- contractual agreement between the using parties.
continuities are indicated (visually, audibly), and marked with
7. Interferences
paint, or automatically removed from the production line, or
both. 7.1 There are some manufacturing processes that produce
4.1.5 Asuitablemeansforassuringnearmagneticsaturation
tubing with surface conditions that could interfere with or
oftheproduct(subjecttoperiodiccheckorcalibration)mustbe obscure signals related to inner surface discontinuities. In the
provided as part of the examination to verify the capability of
examination of heavy-walled tubing having these conditions,
detection of outside diameter and inside diameter discontinui- the ability to examine reliably for inner surface discontinuities
ties. may be affected.
7.2 When examining tubes with large rapid surface varia-
5. Significance and Use
tions, false signals may be caused by the sensors bouncing
along the surface of the tubes.
5.1 This practice outlines a procedure for examining ferro-
7.3 For active pole magnetizing systems, a small air gap
magnetic tubular products using the flux leakage method. If
between the magnetizing system and material under examina-
properly applied, this method is capable of detecting the
tion could cause a heavy accumulation of scale buildup on the
presence and location of significant longitudinally or trans-
pole pieces.
versely oriented discontinuities such as pits, scabs, slivers,
gouges,roll-ins,laps,seams,cracks,holes,andimproperwelds
DETECTION OF LONGITUDINAL
in ferromagnetic tubes under inspection. In addition, the
DISCONTINUITIES
severity of a discontinuity may be estimated and a rejection
level set with respect to the magnitude of the electromagnetic
8. Apparatus
indication produced by the discontinuity.
8.1 Rotary Mechanism—The rotary mechanism shall be
5.2 The response from natural discontinuities can be signifi-
capable of rotating a magnetizing system or flux leakage
cantly different from the response for artificial discontinuities
sensors, or both, in unison around tubing that is being
such as drilled holes or notches of equivalent depth. For this
translated axially through the mechanism, thereby producing a
reason, sufficient work should be done to determine the
helical scan over the surface. Good examination practices
conditions necessary to detect and marknatural discontinuities
require that the pole pieces of the magnetizing system rotate
whose characteristics will adversely affect the serviceability of
uniformly about the tube and that the flux sensor ride on the
the tube, in order to establish acceptance criteria between the
tube or be spaced uniformly above the surface of the tube
supplier and purchaser.
during rotation.
8.2 Spin Feed Mechanism—The spin feed mechanism shall
6. Basis of Application
be capable of positioning a magnetizing system or flux leakage
6.1 The following criteria may be specified in the purchase
sensors, or both, on or near the surface of a translating rotating
specification, contractual agreement, or elsewhere, and may
tube such that there is a uniform spacing between the pole
require agreement between the purchaser and supplier:
pieces of the magnetizing system and the tube. The flux
6.1.1 Acceptance criteria.
leakage sensors shall ride on the surface of the tube or be held
6.1.2 Type, dimensions, location, and number of artificial
uniformly from the surface of the tube during examination.
discontinuities to be placed on the reference standard.
8.3 Magnetizing System:
6.1.3 Size and type of tubing to be examined.
8.3.1 An active field magnetizing system consists of a
6.1.4 Extent of examination (that is, full length, weld zone
suitable means of applying a strong adjustable transverse
only if welded, etc.).
magnetic field to the region of the tube under the flux sensors
6.1.5 Disposition of material with discontinuity indications.
and shall be capable of bringing that region of the tube to near
6.1.6 Methods of verifying dimensions of artificial discon-
saturation. Typical systems employ either permanent magnets
tinuities and allowable tolerances.
or controllable electromagnets. If permanent magnets are used,
6.1.7 Time of inspection, that is, the point(s) in the manu-
a means shall be provided to adjust the spacing of the pole
facturing process at which the material will be inspected.
pieces in order to reach the proper magnetization level. Refer
6.1.8 Nondestructive testing (NDT) personnel shall be
to Section 13 for application of longitudinal magnetic fields.
qualified in accordance with a nationally recognized NDT
8.3.2 A residual field magnetizing system consists of a
personnel qualification practice or standard such as ANSI/
meansofapplyingacircularresidualmagneticfieldtoanentire
ASNT CP-189, SNT-TC-1A, MIL-STD-410, NAS-410, or a
tube before the tube is inspected. Typical systems employ a
similar document. The practice or standard used and its
centrally positioned conducting rod through which a high
applicable revision shall be specified in the purchase specifi-
direct current is passed; alternatively, the current may be
cation or contractual agreement between the using parties.
conducted through the tube itself. The current produces a
NOTE 3—MIL-STD-410 is canceled and has been replaced with NAS-
circular active magnetic field which is concentric with the
410, however, it may be used with agreement between contracting parties.
current distribution. When the current ceases, there remains a
6.1.9 If specified in the purchase specification or contractual residual magnetic field which is circular, concentric with the
agreement, NDT agencies shall be evaluated and qualified as tube, and wholly contained within the tube wall.
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E570–97 (2004)
8.4 Flux Leakage Sensors: the tube (Fig. 2(a)). Rotation of the tube with the magnetizing
8.4.1 The flux sensor shall consist of magnetic field trans- poles held stationary will also produce the same effect (Fig.
ducers that respond to variations in magnetic flux density. 2(b)).
These sensors generally consist of one of the following types: 9.1.5 Relative motion between the flux sensor and the flux
electromagnetic coils, Hall probes, magneto diodes, magnis- leakagefieldcausedbythediscontinuityisgenerallyutilizedto
tors, or magnetoresistors. These sensors are normally used to generate a voltage in the flux sensor. The amplitude of the
detect the flux leakage directly from the discontinuity in the voltage generated by the sensor is generally indicative of the
tube; however, they may also be used to detect flux leakage severityofthediscontinuitywhenallotherfactorsareconstant.
patterns that have been transferred from the tube to a strip of The flux leakage field measured at the outside surface of the
magnetic tape. The flux sensors should be of sufficient number tube resulting from an inside surface discontinuity is much
and length so as to provide 100 % coverage while scanning the broader than the leakage field from a discontinuity of equal
tube surface to be examined at the desired examination speed. severity located on the outer surface of the tube, resulting in a
Theirlocation(withrespecttothemagneticpolepiecesandthe lower signal frequency for the inner surface discontinuity (Fig.
tubular product) should result in maximum response to the 3(a) and 3(b)). Several types of equipment utilize this infor-
leakage field caused by a discontinuity in the tubular product. mation to determine whether the discontinuity is located on the
8.4.2 The depth and orientation of a discontinuity below the inner or outer surface of the tube.
outside surface will affect the magnitude of the signal received 9.1.6 Near saturation is required to provide repeatable and
from it. Sensitivity decreases significantly as the distance reliable indications for the presence of outer surface, inner
between the flux leakage sensor and the tube under examina- surface, or subsurface discontinuities. A suitable measuring
tion is increased. Therefore, the sensors should remain clean means or reference samples or both are required to properly
and have uniform contact with the tube surface, or if air riding adjust the equipment for operation at the required sensitivity
the sensors should be held at a uniform distance above the and magnetization level.
surface of the tube. 9.2 The examination of tubular products for transverse
8.5 Electronic Instrumentation—The electronic apparatus discontinuities utilizing a longitudinal magnetic field is dis-
shallbecapableofamplifyingsignalsfromthefluxsensorsand cussed in Section 14.
processing them for the operation of alarms. Multiple probes
10. Reference Standard
may be used to increase the speed of examination. The signals
10.1 The tubes selected for reference standards should be
may be processed in two separate channels to result in a
first examined to ascertain that they are free of interfering
differentiation between inner and outer surface discontinuities.
natural discontinuities prior to the introduction of artificial
Each of the two sets of electronic channels should contain its
defects. The standard tube shall be of the same alloy, temper,
own sensitivity and threshold triggering controls for indepen-
and nominal dimensions as the tubes to be examined on a
dent setting of percentage of wall rejection levels.
production basis. The standard shall be of sufficient length to
8.6 Driving Mechanism—A mechanical drive mechanism
permit the required spacing of artificial discontinuities and to
shall be used which is capable of rigidly holding and passing
be mechanically stable while in the examining position in the
the tube through the inspection apparatus at constant speed and
apparatus. Artificial discontinuities placed in the tube shall be
concentric with the inspection apparatus. As required, the
of the following types:
driving mechanism shall be capable of rotating and advancing,
10.1.1 Notches—Longitudinal outside surface or inside sur-
or just advancing the tube with a constant speed.
facenotchesmaybeproducedeitherbyairabrasive,milling,or
9. Principles of Examination
EDM (Electric Discharge Machining). Notch depth is usually
9.1 Conduct the examination of tubular products for longi- specified as a percent of nominal wall thickness with typical
tudinal discontinuities employing a transverse magnetic field values being 5, 10, 12 ⁄2 , or 20 %. N
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