ASTM E2261-03

Standard Practice for Examination of Welds Using the Alternating Current Field Measurement Technique

SIGNIFICANCE AND USE
The purpose of the alternating current field measurement method is to evaluate welds in the area of the toe for surface breaking discontinuities such as fatigue cracks. The examination results may then be used by qualified organizations to assess weld service life or other engineering characteristics (beyond the scope of this practice).
Comparison with Conventional Eddy Current Examination—conventional eddy current coils are typically configured to sense the field from the weld in the immediate vicinity of the emitting element, whereas alternating current field measurement probes are typically designed to sense the magnetic field from the weld distant from the exciter.
SCOPE
1.1 This practice describes procedures to be followed during alternating current field measurement examination of welds for baseline and service-induced surface breaking discontinuities.
1.2 This practice is intended for use on welds in any metallic material.
1.3 This practice does not establish weld acceptance criteria.
1.4 The values stated in either inch-pound units or SI units are to be regarded separately as standard. The values stated in each system might not be exact equivalents; therefore, each system shall be used independently of the other.
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

• Status: Historical
• Publication Date: 09-Feb-2003
• ICS: 25.160.40 - Welded joints and welds
• Technical Committee: E07 - Nondestructive Testing
• Drafting Committee: E07.07 - Electromagnetic Method

Relations

• Replaced By: ASTM E2261-07 - Standard Practice for Examination of Welds Using the Alternating Current Field Measurement Technique
• Effective Date: 01-Dec-2007
• Referred By: ASTM E2928/E2928M-23 - Standard Practice for Examination of Drillstring Threads Using the Alternating Current Field Measurement Technique
• Effective Date: 10-Feb-2003
• Referred By: ASTM E2905/E2905M-20 - Standard Practice for Examination of Mill and Kiln Girth Gear Teeth—Electromagnetic Methods
• Effective Date: 10-Feb-2003
• Referred By: ASTM E543-21 - Standard Specification for Agencies Performing Nondestructive Testing
• Effective Date: 10-Feb-2003

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:E2261–03
Standard Practice for
Examination of Welds Using the Alternating Current Field
Measurement Technique
This standard is issued under the fixed designation E 2261; 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 3.2 Definitions:
3.2.1 exciter—a device that generates a time varying elec-
1.1 Thispracticedescribesprocedurestobefollowedduring
tromagnetic field, usually a coil energized with alternating
alternating current field measurement examination of welds for
current (AC); also known as a transmitter.
baseline and service-induced surface breaking discontinuities.
3.2.2 detector—one or more coils or elements used to sense
1.2 This practice is intended for use on welds in any
or measure a magnetic field; also known as a receiver.
metallic material.
3.2.3 uniform field—as applied to nondestructive testing,
1.3 This practice does not establish weld acceptance crite-
the area of uniform magnetic field over the surface of the
ria.
material under examination produced by a parallel induced
1.4 The values stated in either inch-pound units or SI units
alternating current, which has been passed through the weld
are to be regarded separately as standard. The values stated in
and is observable beyond the direct coupling of the exciting
each system might not be exact equivalents; therefore, each
coil.The field is uniform on the surface but the strength decays
system shall be used independently of the other.
exponentially with depth.
1.5 This standard does not purport to address all of the
3.2.4 alternating current field measurement—a nondestruc-
safety concerns, if any, associated with its use. It is the
tiveexaminationtechniquethatmeasureschangesinanapplied
responsibility of the user of this standard to establish appro-
AC uniform magnetic field to detect and characterize discon-
priate safety and health practices and determine the applica-
tinuities.
bility of regulatory limitations prior to use.
3.3 Definitions of Terms Specific to This Standard:
2. Referenced Documents
3.3.1 alternating current field measurement system—the
electronic instrumentation, software, probes, and all associated
2.1 ASTM Standards:
components and cables required for performing weld exami-
E 543 Practice for Agencies Performing Nondestructive
nation using the alternating current field measurement tech-
Testing
nique.
E 1316 Terminology for Nondestructive Examinations
3.3.2 operational standardization block—a reference stan-
2.2 ASNT Standard:
dard with specified artificial slots, used to confirm the opera-
SNT-TC-1A Personnel Qualification in Nondestructive
tional parameters and to indicate discontinuity detection sen-
Testing
sitivity.
ANSI/ASNT-CP-189 Standard for Qualification and Certi-
3.3.3 Bx—the x component of the magnetic field, parallel to
fication of Nondestructive Testing Personnel
the weld toe, the magnitude of which is proportional to the
3. Terminology
current density set up by the electric field.
3.3.4 Bz—the z component of the magnetic field normal to
3.1 General definitions of terms used in this practice can be
the weld toe, the magnitude of which is proportional to the
found in Terminology E 1316, Section A, Common NDT
curvature of the current in the x-y plane.
terms, and Section C, Electromagnetic testing.
3.3.5 X-Y Plot—an X-Y graph with two orthogonal compo-
nents of magnetic field plotted against each other.
This practice is under the jurisdiction of ASTM Committee E07 on Nonde-
3.3.6 time base plots—these plot the relationship between
structive Testing and is the direct responsibility of Subcommittee E07.07 on
Bx or Bz values with time.
Electromagnetic Methods.
Current edition approved February 10, 2003. Published April 2003.
3.3.7 surface plot—for use with array probes. These plot
Annual Book of ASTM Standards,Vol 03.03.
one component of magnetic field over an area, typically as a
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
color contour plot or 3-D wire frame plot.
4th Floor, New York, NY 10036.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E2261–03
3.3.8 data sample rate—the rate at which data is digitized sizepredictionmustcompensateforthecoatingthickness.This
for display and recording, in data points per second. can be accomplished using discontinuity-sizing tables in the
system software. Using the wrong coating thickness would
4. Summary of Practice
have a negative effect on depth sizing accuracy if the discrep-
ancy was 0.04 in. [1 mm] or more. As the current flow is
4.1 In a basic alternating current field measurement system,
arranged normal to the weld toe there is no perturbation in that
a small probe is moved along the toe of a weld. The probe
direction so that no indication occurs at the interface due to
contains an exciter coil, which induces anAC magnetic field in
changes in permeability. Data is recorded in a manner that
the material surface aligned to the direction of the weld. This,
allows archiving and subsequent recall for each weld location.
in turn, causes uniform alternating current to flow across the
Evaluationofexaminationresultsmaybeconductedatthetime
weld, orthogonal to the toe. The depth of penetration of this
of examination or at a later date. The examiner generates an
current varies with material type and frequency but is typically
examination report detailing complete results of the examina-
0.004in.[0.1mm]deepinmagneticmaterialsand0.08-0.3in.
tion.
[2-7mm]deepinnon-ferrousmaterials.Anysurfacebreaking
discontinuities within 0.4 in. [10 mm] of either side of the scan
5. Significance and Use
line at this location will interrupt or disturb the flow of the
5.1 The purpose of the alternating current field measure-
otherwise uniform electromagnetic field. Measurement of the
ment method is to evaluate welds in the area of the toe for
absolute quantities of the two major components of the surface
surface breaking discontinuities such as fatigue cracks. The
magnetic fields (Bx and Bz) determines the severity of the
examination results may then be used by qualified organiza-
disturbance (see Fig. 1) and thus the severity of the disconti-
tions to assess weld service life or other engineering charac-
nuity. Discontinuity sizes, such as crack length and depth, can
teristics (beyond the scope of this practice).
be predicted from key points selected from the Bx and Bz
5.2 Comparison with Conventional Eddy Current
traces along with the standardization data and instrument
Examination—conventional eddy current coils are typically
settings from each individual probe. This discontinuity sizing
configured to sense the field from the weld in the immediate
can be performed automatically using system software.
vicinity of the emitting element, whereas alternating current
4.2 Standardization data and instrument settings for each
field measurement probes are typically designed to sense the
individual probe are determined at the factory and stored in a
magnetic field from the weld distant from the exciter.
computer file, which is loaded at the start of the examination.
System sensitivity is verified using an operation standardiza-
6. Basis of Application
tion block. System sensitivity is checked and recorded prior to
6.1 Personnel Qualification:
andatregularintervalsduringtheexamination.Notethatwhen
6.1.1 If specified in the contractual agreement, personnel
a unidirectional input current is used, any decay in strength of
performing examinations to this practice shall be qualified in
the input field with probe lift-off or thin coating is relatively
accordance with a nationally recognized NDT personnel quali-
small so that variations of output signal (as may be associated
fication practice or standard such as ANSI/ASNT-CP-189 or
with a discontinuity) are reduced. If a thick coating, that is,
SNT-TC-1A or a similar document and certified by the em-
greater than 0.04 in. [1 mm] is present then the discontinuity
ployer or certifying agent, as applicable. The practice or
standard used and its applicable revision shall be identified in
the contractual agreement between the using parties.
6.2 Qualification of Nondestructive Evaluation
Agencies—if specified in the contractual agreement, NDT
agencies shall be qualified and evaluated as described in
Practice E 543, with reference to sections on electromagnetic
examination. The applicable edition of Practice E 543 shall be
specified in the contractual agreement.
7. Job Scope and Requirements
7.1 The following items may require agreement by the
examining party and their client and should be specified in the
purchase document or elsewhere:
7.1.1 Location and type of welded component to be exam-
ined, design specifications, degradation history, previous non-
destructive examination results, maintenance history, process
conditions, and specific types of discontinuities that are re-
quired to be detected, if known.
7.1.2 The maximum window of opportunity for work.
(Detection of small discontinuities may require a slower probe
scan speed, which will affect productivity.)
7.1.3 Size, material grade and type, and configuration of
FIG. 1 Typical Bx and Bz Traces as a Probe Passes Over a Crack welds to be examined.
E2261–03
7.1.4 A weld numbering or identification system. from a linear discontinuity will die away quickly away from
7.1.5 Extent of examination, for example: complete or the location of the discontinuity so that the scan away from the
partial coverage, which welds and to what length, whether weld toe will be flatter. If there is no significant change in
straight sections only and the minimum surface curvature. indication amplitude at 0.80 in. [20 mm] distance from the
7.1.6 Meansofaccesstowelds,andareaswhereaccessmay weld then the indication is likely due to the effect of the
be restricted. grinding.
7.1.7 Type of alternating current field measurement instru-
8.4 Residual stress, with accompanying permeability varia-
ment and probe; and description of operations standardization tions, may be present with similar, but much smaller, effects to
block used, including such details as dimensions and material.
grinding.
7.1.8 Required operator qualifications and certification.
8.5 Seam Welds:
7.1.9 Required weld cleanliness.
8.5.1 Seam welds running across the line of scanning also
7.1.10 Environmental conditions, equipment and prepara-
produce strong indications in the Bx and Bz, which can
tions that are the responsibility of the client; common sources
sometimes be confused, with a discontinuity indication. The
of noise that may interfere with the examination.
same procedure is used as for grinding marks with further
7.1.11 Complementary methods or techniques may be used
scans being taken away from the affected area. If the indication
to obtain additional information.
remains constant then it will not have been produced by a
7.1.12 Acceptance criteria to be used in evaluating discon-
linear discontinuity.
tinuities.
8.6 Ferromagnetic and Conductive Objects:
7.1.13 Disposition of examination records and reference
8.6.1 Problems may arise because of objects near the weld
standards.
that are ferromagnetic or conductive which may reduce the
7.1.14 Format and outline contents of the examination
sensitivity and accuracy of discontinuity characterization when
report.
they are in the immediate vicinity of the weld.
8.7 Neighboring Welds:
8. Interferences
8.7.1 In areas where welds cross each other, there are
8.1 This section describes items and conditions, which may
indications, which may be mistaken for discontinuities. (See
compromise the alternating current field measurement tech-
8.5.)
nique.
8.8 Weld Geometry:
8.2 Material Properties:
8.8.1 When a probe scans into a tight angle between two
8.2.1 Although there are permeability differences in a fer-
surfacestheBxindicationvaluewillincreasewithlittlechange
romagnetic material between weld metal, heat affected zone
in the Bz. This will cause the X-Y plot to rise.
material and parent plate, the probe is normally scanned along
8.9 Crack Geometry Effects:
a weld toe and so passes along a line of relatively constant
8.9.1 A discontinuity at an angle to the scan—a discontinu-
permeability. If a probe is scanned across a weld then the
ity at an angle to the scan will reduce either the peak or the
permeability changes may produce indications, which could be
trough of the Bz as the sensor probe only passes through the
similar to those from a discontinuity. Differentiation between a
edgeofoneendofthediscontinuity.Thisproducesanun-equal
transverse discontinuity signal and the weld signal can be
sided X-Y plot. Additional scans may be made along the weld
achieved by taking further scans parallel to the discontinuity.
or parent plate to determine the position of the other end of the
The signal from a discontinuity will die away quickly. If there
discontinuity.
is no significant change in indication amplitude at 0.8 in. [20
8.9.2 A discontinuity at an angle to the surface—the effect
mm] distance from the weld then the indication is likely due to
of a discontinuity at a non-vertical angle to the probe is
the permeability changes in the weld.
generally to reduce the value of the Bz signal. The value of the
8.3 Magnetic State:
Bx signal will not be reduced. This has the effect of reducing
8.3.1 Demagnetization—It must be ensured that the surface
the width of the X-Y plot.
being examined is in the non-magnetized state. Therefore the
8.9.3 Line contact or multiple discontinuities—when con-
procedure followed with any previous magnetic technique
tacts occur across a discontinuity then minor loops occur
deployed must include demagnetization of the surface. This is
withinthemainX-Yplotloopproducedbythediscontinuity.If
because areas of remnant magnetization, particularly where the
more than one discontinuity occurs in the scan then there will
leg of a magnetic particle examination yoke was sited, can
be a number of loops returning to the background.
produce loops in the X-Y plot, which may sometimes be
8.9.4 Transverse discontinuities—ifatransversediscontinu-
confused with a discontinuity indication.
8.3.2 Grinding marks—magnetic permeability can also be ity occurs during the scan for longitudinal discontinuities then
the Bx will rise instead of falling and the Bz signal will remain
affected by surface treatments such as grinding. These can
cause localized areas of altered permeability across the line of the same as for a short longitudinal discontinuity.
...