ASTM E426-98(2007)

NOTICE: This standard has either been superseded and replaced by a new version or withdrawn.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:E426–98 (Reapproved 2007)
Standard Practice for
Electromagnetic (Eddy-Current) Examination of Seamless
and Welded Tubular Products, Austenitic Stainless Steel
and Similar Alloys
This standard is issued under the fixed designation E426; 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 specification has been approved for use by agencies of the Department of Defense.
1. Scope 2. Referenced Documents
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1.1 This practice covers procedures that may be followed 2.1 ASTM Standards:
for eddy-current examination of seamless and welded tubular E543 Specification for Agencies Performing Nondestruc-
products made of stainless steel and similar alloys such as tive Testing
nickel alloys. Austenitic chromium-nickel stainless steels, E1316 Terminology for Nondestructive Examinations
which are generally considered to be nonmagnetic, are specifi- 2.2 Other Documents:
cally covered as distinguished from the martensitic and ferritic SNT-TC-1A Recommended Practice for Personnel Qualifi-
straight chromium stainless steels which are magnetic. cation and Certification in Nondestructive Testing
1.2 This practice is intended as a guide for eddy-current ANSI/ASNT CP-189 ASNT Standard for Qualification and
examination of both seamless and welded tubular products Certification of Nondestructive Testing Personnel
using either an encircling coil or a probe-coil technique. Coils NAS-410 NAS Certification and Qualification of Nonde-
and probes are available that can be used inside the tubular structive Personnel (Quality Assurance Committee)
product; however, their use is not specifically covered in this
3. Terminology
document. This type of examination is usually employed only
3.1 Standard terminology relating to electromagnetic ex-
to examine tubing which has been installed such as in a heat
exchanger. amination may be found in Terminology E1316, Section C,
1.3 This practice covers the examination of tubular products Electromagnetic Testing.
ranging in diameter from 0.125 to 5 in. (3.2 to 127.0 mm) and
4. Summary of Practice
wall thicknesses from 0.005 to 0.250 in. (0.127 to 6.4 mm).
4.1 The examination is conducted using one of two general
1.4 The values stated in inch-pound units are to be regarded
techniques shown in Fig. 1. One of these techniques employs
as the standard.
one or more exciter and sensor coils which encircle the pipe or
1.5 This standard does not purport to address all of the
tube and through which the tubular product to be examined is
safety problems, if any, associated with its use. It is the
passed. Some circuit configurations employ separate exciter
responsibility of the user of this standard to establish appro-
and sensor coils; whereas other configurations employ one or
priate safety and health practices and determine the applica-
more coils that concurrently function as both exciters and
bility of regulatory limitations prior to use.
sensors. Alternating current passes through the exciting coil
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This practice is under the jurisdiction of ASTM Committee E07 on Nonde- For referenced ASTM standards, visit the ASTM website, www.astm.org, or
structive Testing and is the direct responsibility of Subcommittee E07.07 on contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Electromagnetic Method. Standards volume information, refer to the standard’s Document Summary page on
Current edition approved Dec. 1, 2007. Published January 2008. Originally the ASTM website.
´1 4
approved in 1971. Last previous edition approved in 2003 as E426 - 98(2003) . AvailablefromAmericanSocietyforNondestructiveTesting(ASNT),P.O.Box
DOI: 10.1520/E0426-98R07. 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
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For ASME Boiler and Pressure Vessel Code applications see related Practice Available fromAerospace IndustriesAssociation ofAmerica, Inc. (AIA), 1000
SE-426 in Section II of that Code. WilsonBlvd.,Suite1700,Arlington,VA22209-3928,http://www.aia-aerospace.org.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E426–98 (2007)
inner surface, or subsurface discontinuities. The eddy-current
examination is sensitive to many factors that occur as a result
of processing (such as variations in conductivity, chemical
composition, permeability, and geometry) as well as other
factors not related to the tubing. Thus, all received indications
are not necessarily indicative of defective tubing.
6. Basis of Application
6.1 If specified in the contractual agreement, personnel
performing examinations to this practice shall be qualified in
accordance with a nationally recognized NDT personnel quali-
fication practice or standard such as ANSI/ASNT-CP-189,
SNT-TC-1A, NAS-410, ASNT-ACCP, or a similar document
and certified by the certifying agency, as applicable. The
practice or standard used and its applicable revision shall be
identified in the contractual agreement between the using
parties.
NOTE 1—MIL-STD-410 is canceled and has been replaced with NAS-
410, however, it may be used with agreement between contracting parties.
6.2 If specified in the contractual agreement, NDT agencies
shall be qualified and evaluated in accordance with Practice
E543. The applicable edition of Practice E543 shall be speci-
fied in the contractual agreement.
7. Apparatus
7.1 Electronic Apparatus—The electronic apparatus shall
be capable of energizing the examination coils or probes with
alternatingcurrentsofsuitablefrequenciesandshallbecapable
of sensing the changes in the electromagnetic response of the
sensors. Equipment may include a detector, phase discrimina-
FIG. 1 Sketch Showing Encircling-Coil and Probe-Coil
tor, filter circuits, modulation circuits, magnetic-saturation
Techniques for Electromagnetic Examination of Tubular Products
devices, recorders, and signaling devices as required for the
particular application.
which by reason of its proximity induces current in the tubular
7.2 Examination Coils—Examination coils shall be capable
product. The sensor coil detects the resultant electromagnetic
of inducing current in the tube and sensing changes in the
flux related to these currents.The presence of discontinuities in
electrical characteristics of the tube.
the tubular product will affect the normal flow of currents and
this change is detected by the sensor. The encircling coil NOTE 2—Fill factor effect is an important consideration since coupling
variations can affect the examination significantly.
technique is capable of examining the entire 360-deg expanse
of the tubular product.
7.3 Probe Coils—Probe coils shall be capable of inducing
4.2 Another technique employs a probe coil with one or
current in the tube and sensing changes in the electrical
more exciters and sensors which is brought in close proximity
characteristics of the tube (Note 3). Probes generally consist of
of the surface of the tubular product to be examined. Since the
an exciting coil and sensing coil or Hall element mounted in a
probe is generally small and does not encircle the article being
common holder. A Hall element is a semiconductor that by
examined, it examines only a limited area in the vicinity of the
reason of the Hall effect is capable of responding in a manner
probe. If it is desired to examine the entire volume of the
directly proportional to magnetic-flux density. However, when
tubular product, it is common practice to either rotate the
used with an exciting coil, it should be remembered that
tubular product or the probe. In the case of welded tubular
eddy-current flow is influenced by the excitation frequency.
products frequently only the weld is examined by scanning
NOTE 3—Lift-off effect is an important consideration since coupling
along the weld zone.
variations can affect the examination significantly.
5. Significance and Use
7.4 Driving Mechanism—A mechanical device capable of
5.1 Eddy-current examination is a nondestructive method of passingthetubethroughtheexaminationcoilorpasttheprobe.
locating discontinuities in a product. Changes in electromag- It shall operate at a uniform speed with minimum vibration of
netic response caused by the presence of discontinuities are coil, probe, or tube and maintain the article being examined in
detected by the sensor, amplified and modified in order to proper register or concentricity with the probe or examination
actuate audio or visual indicating devices, or both, or a coil. Where required, the mechanism shall be capable of
mechanical marker. Signals can be caused by outer surface, uniformly rotating the tube or probe.
E426–98 (2007)
7.5 Reference Standard—The standard used to adjust the 9. Procedure
sensitivity setting of the apparatus shall be sound and of the
9.1 Standardize the apparatus at the start of the examination
same nominal alloy, temper, and nominal dimensions as the lot
run using the reference standard. The recommended maximum
of tubes or pipes to be examined on a production basis. It shall
interval between restandardization is 4 h although more or less
be of sufficien
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