ASTM E1312-99

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Designation: E 1312 – 99
Standard Practice for
Electromagnetic (Eddy-Current) Examination of
Ferromagnetic Cylindrical Bar Product Above the Curie
Temperature
This standard is issued under the fixed designation E 1312; 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.
1. Scope cation and Certification in Nondestructive Testing
ANSI/ASNT-CP-189 Standard for Qualification and Certi-
1.1 This practice covers procedures for eddy-current exami-
fication of NDT Personnel
nation of hot ferromagnetic bars above the Curie temperature
2.3 AIA Standard:
where the product is essentially nonmagnetic, but below
NAS 410 Certification and Qualification of Nondestructive
2100°F (1149°C).
Testing Personnel
1.2 This practice is intended for use on bar products having
diameters of ⁄2 in. (12.7 mm) to 8 in. (203 mm) at linear
3. Terminology
throughput speeds up to 1200 FPM (366 MPM). Larger or
3.1 Definitions—Terminology E 1316 shall apply to the
smaller diameters may be examined by agreement between the
terms used in this practice.
using parties.
1.3 The purpose of this document is to provide a procedure
4. Summary of Practice
for in-line eddy-current inspection of bars during processing
4.1 Principle—The major advantage of examining ferro-
for the detection of major or gross surface discontinuities.
magnetic bar product above the Curie temperature with eddy
1.3.1 The types of discontinuities capable of being detected
currents is the enhanced signal-to-noise ratio obtained without
are commonly referred to as: slivers, laps, seams, roll-ins
the need for magnetic saturation.
(scale, dross, etc.), and mechanical damage such as scratches,
4.2 Sensors—This examination may be performed with
scores, or indentations.
various types or designs of encircling coils or with probe coils
1.4 This practice does not establish acceptance criteria.
that are fixed or rotating.
They must be specified by agreement between the using
4.2.1 One or more exciter or sensor coils is used to encircle
parties.
the bar through which the product to be examined is passed.
1.5 This standard does not purport to address all of the
When the hot bar is in close proximity to the sensing and
safety concerns, if any, associated with its use. It is the
exciting coils, eddy currents are induced in the hot product by
responsibility of the user of this standard to establish appro-
an alternating current. The sensing coil detects the electromag-
priate safety and health practices and determine the applica-
netic flux related to these currents. Changes or disruptions in
bility of regulatory limitations prior to use.
the normal flux pattern indicate the presence of discontinuities.
This technique is capable of examining the entire circumfer-
2. Referenced Documents
ence without contacting the product.
2.1 ASTM Standards:
4.2.2 The surface can also be examined with probe coils
E 543 Practice for Evaluating Agencies that Perform Non-
2 having one or more exciters and sensors which are spaced in
destructive Testing
2 close proximity to the product surface. The probe is usually
E 1316 Terminology for Nondestructive Examinations
small and does not encircle the product, making it necessary to
2.2 Other Documents:
rotate either the probes or the product to obtain 100 % coverage
SNT-TC-1A Recommended Practice for Personnel Qualifi-
of the circumference. This is essentially a contact technique
because the coil is fixtured in a device that rides on the
circumference to maintain a fixed distance between the coil and
This practice is under the jurisdiction of ASTM Committee E-7 on Nonde-
product surface.
structive Testing and is the direct responsibility of Subcommittee E7.07 on
Electromagnetic Method.
Current edition approved Sept. 10, 1999. Published November 1999. Originally
published as E 1312 – 89. Last previous edition E 1312 – 94. Available from American Society for Nondestructive Testing, 1711 Arlingate
Annual Book of ASTM Standards, Vol 03.03. Plaza, P.O. Box 28518, Columbus, OH 43228-0518.
Available from the Aerospace Industries Association of America, Inc., 1250
Eye Street, N.W., Washington, DC 20005.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E1312–99
4.2.3 Discontinuities cause either a change in phase or 6.3 Acceptance Criteria—Since acceptance criteria are not
signal amplitude when detected by the sensing coil. These specified in this practice, they shall be specified in the
signals are amplified and processed to activate marking or contractural agreement.
recording devices, or both. Relative severity of the imperfec-
tion can be indicated by the signal amplitude generated by the
7. Apparatus
flux change or the degree of change in phase.
7.1 Electronic Apparatus, should be capable of energizing
4.2.4 Caution must be exercised in establishing reference
the test coils or probes with alternating current at selectable
standards because flux changes caused by natural discontinui-
frequencies from 400 Hz to 100 kHz. Either manual or
ties might differ significantly from those generated by artificial
remotely operated switches can be used for frequency selec-
discontinuities.
tion. The equipment should include a detector display (CRT,
meters), phase discriminator, filters, modulators, recorders, and
5. Significance and Use
alarming/marking devices required for particular applications.
7.2 Sensors, whether probe or encircling coils, should op-
5.1 The purpose of this practice is to describe a procedure
erate through a frequency range from 400 Hz to 100 kHz.
for in-line-eddy-current examination of hot cylindrical bars in
7.2.1 The sensor windings must be cooled (such as water
the range of diameters listed in 1.2 for large and repetitive
jackets) to control the sensor operating temperature and pre-
discontinuities that may form during processing.
vent thermal damage to the sensors.
5.2 The discontinuities in bar product capable of being
7.2.2 Magnetic or electrostatic shields might be necessary to
detected by the electromagnetic method are listed in 1.3.1. The
suppress extraneous electrical transient noise. Electrostatic
method is capable of detecting surface and some subsurface
shields usually float above ground at the sensor and are
discontinuities that are typically in the order of 0.030 in. (0.75
connected to a cable and then to the preamplifier shield.
mm) and deeper, but some shallower discontinuities might also
1 1
be found. 7.2.3 Constant spacing, ranging from ⁄16 in. (1.6 mm) to ⁄4
in. (6.4 mm) between the sensors and product surface is
5.3 Discontinuities that are narrow and deep, but short in
obtained with positioning mechanisms usually equipped with
length, are readily detectable by both probe and encircling coils
product guiding devices to prevent mechanical damage to the
because they cause abrupt flux changes. Surface and subsur-
sensors.
face discontinuities (if the electromagnetic frequency provides
7.3 Transport Mechanism—A conveyor or other type of
sufficient effective depth of penetration) can be detected by this
mechanical device should be employed to pass the product
method.
through or past the sensors. It should operate at production (or
5.3.1 Discontinuities such as scratches or seams that are
system) speeds with a minimum vibration of the sensors or
continuous and uniform for the full length of cut length bars or
product, and should maintain alignment of the sensors and
extend for extensive linear distances in coiled product may not
product within the specified tolerances. Some systems may
always be detected when encircling coils are used. These are
require the transport to rotate either the bar, the sensors, or
more detectable with probe coils by intercepting the disconti-
both.
nuity in their rotation around the circumference.
7.3.1 The mechanical tolerances for restraining the longitu-
5.3.2 The orientation and type of coil are important param-
dinal centerline of the product relative
...