ASTM E426-98(2003)e1

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Designation:E426–98 (Reapproved 2003)
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 E 426; 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 specification has been approved for use by agencies of the Department of Defense.
e NOTE—Editorial changes made throughout the standard in July 2003.
1. Scope E 543 Practice for Agencies Performing Nondestructive
2 Testing
1.1 This practice covers procedures that may be followed
E 1316 Terminology for Nondestructive Examinations
for eddy-current examination of seamless and welded tubular
2.2 Other Documents:
products made of stainless steel and similar alloys such as
SNT-TC-1A Recommended Practice for Personnel Qualifi-
nickel alloys. Austenitic chromium-nickel stainless steels,
cation and Certification in Nondestructive Testing
which are generally considered to be nonmagnetic, are specifi-
ANSI/ASNT CP-189 ASNT Standard for Qualification and
cally covered as distinguished from the martensitic and ferritic
Certification of Nondestructive Testing Personnel
straight chromium stainless steels which are magnetic.
NAS-410 NAS Certification and Qualification of Nonde-
1.2 This practice is intended as a guide for eddy-current
structive Personnel (Quality Assurance Committee)
examination of both seamless and welded tubular products
using either an encircling coil or a probe-coil technique. Coils
3. Terminology
and probes are available that can be used inside the tubular
3.1 Standard terminology relating to electromagnetic ex-
product; however, their use is not specifically covered in this
amination may be found in Terminology E 1316, Section C,
document. This type of examination is usually employed only
Electromagnetic Testing.
to examine tubing which has been installed such as in a heat
exchanger.
4. Summary of Practice
1.3 This practice covers the examination of tubular products
4.1 The examination is conducted using one of two general
ranging in diameter from 0.125 to 5 in. (3.2 to 127.0 mm) and
techniques shown in Fig. 1. One of these techniques employs
wall thicknesses from 0.005 to 0.250 in. (0.127 to 6.4 mm).
one or more exciter and sensor coils which encircle the pipe or
1.4 The values stated in inch-pound units are to be regarded
tube and through which the tubular product to be examined is
as the standard.
passed. Some circuit configurations employ separate exciter
1.5 This standard does not purport to address all of the
and sensor coils; whereas other configurations employ one or
safety problems, if any, associated with its use. It is the
more coils that concurrently function as both exciters and
responsibility of the user of this standard to establish appro-
sensors. Alternating current passes through the exciting coil
priate safety and health practices and determine the applica-
which by reason of its proximity induces current in the tubular
bility of regulatory limitations prior to use.
product. The sensor coil detects the resultant electromagnetic
2. Referenced Documents flux related to these currents.The presence of discontinuities in
the tubular product will affect the normal flow of currents and
2.1 ASTM Standards:
this change is detected by the sensor. The encircling coil
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
structive Testing and is the direct responsibility of Subcommittee E07.07 on
Electromagnetic Methods. Annual Book of ASTM Standards, Vol 03.03.
Current edition approved July 10, 2003. Published September 2003. Originally Available fromTheAmerican Society for NondestructiveTesting (ASNT), P.O.
approved in 1971. Last previous edition approved in 1998 as E 426 - 98. Box 28518, 1711 Arlingate Lane, Columbus, OH 43228-0518.
2 5
For ASME Boiler and Pressure Vessel Code applications see related Practice Available from Aerospace Industries Association of America, Inc., 1250 Eye
SE-426 in Section II of that Code. Street, N.W., Washington, DC 20005.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
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E426–98 (2003)
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
E 543. The applicable edition of Practice E 543 shall be
specified 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-
tor, filter circuits, modulation circuits, magnetic-saturation
devices, recorders, and signaling devices as required for the
particular application.
7.2 Examination Coils—Examination coils shall be capable
FIG. 1 Sketch Showing Encircling-Coil and Probe-Coil of inducing current in the tube and sensing changes in the
Techniques for Electromagnetic Examination of Tubular Products
electrical characteristics of the tube.
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
7.3 Probe Coils—Probe coils shall be capable of inducing
of the tubular product.
current in the tube and sensing changes in the electrical
4.2 Another technique employs a probe coil with one or
characteristics of the tube (Note 3). Probes generally consist of
more exciters and sensors which is brought in close proximity
an exciting coil and sensing coil or Hall element mounted in a
of the surface of the tubular product to be examined. Since the
common holder. A Hall element is a semiconductor that by
probe is generally small and does not encircle the article being
reason of the Hall effect is capable of responding in a manner
examined, it examines only a limited area in the vicinity of the
directly proportional to magnetic-flux density. However, when
probe. If it is desired to examine the entire volume of the
used with an exciting coil, it should be remembered that
tubular product, it is common practice to either rotate the
eddy-current flow is influenced by the excitation frequency.
tubular product or the probe. In the case of welded tubular
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.
7.4 Driving Mechanism—A mechanical device capable of
5. Significance and Use
passingthetubethroughtheexaminationcoilorpasttheprobe.
5.1 Eddy-current examination is a nondestructive method of It shall operate at a uniform speed with minimum vibration of
locating discontinuities in a product. Changes in electromag- coil, probe, or tube and maintain the article being examined in
netic response caused by the presence of discontinuities are proper register or concentricity with the probe or examination
detected by the sensor, amplified and modified in order to coil. Where required, the mechanism shall be capable of
actuate audio or visual indicating devices, or both, or a uniformly rotating the tube or probe.
mechanical marker. Signals can be caused by outer surface, 7.5 Reference Standard—The standard used to adjust the
inner surface, or subsurface discontinuities. The eddy-current sensitivity setting of the apparatus shall be sound and of the
examination is sensitive to many factors that occur as a result same nominal alloy, temper, and nominal dimensions as the lot
of processing (such as variations in conductivity, chemical of tubes or pipes to be examined on a production basis. It shall
composition, permeability, and geometry) as well as other be of sufficient length to permit the required spacing of the
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E426–98 (2003)
artificial discontinuities (at least 4 ft, and preferably longer). using parties, or whenever improper functioning of the equip-
Artificial discontinuities made in the tube or pipe shall be ment is suspected. If improper functioning is found, restan-
centeredasne
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