This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles

for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

Designation: E2928/E2928M − 17

Standard Practice for

Examination of Drillstring Threads Using the Alternating
Current Field Measurement Technique1
This standard is issued under the fixed designation E2928/E2928M; 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.

1. Scope 2. Referenced Documents

1.1 This practice describes procedures to be followed during 2.1 ASTM Standards:2
alternating current field measurement examination of drill- E543 Specification for Agencies Performing Nondestructive
string threads on tubulars used for oil and gas exploration and Testing
production for detection and, if required, sizing of service- E1316 Terminology for Nondestructive Examinations
induced surface breaking discontinuities transverse to the pipe. E2261 Practice for Examination of Welds Using the Alter-
nating Current Field Measurement Technique
1.2 This practice is intended for use on threads in any
metallic material. 2.2 ASNT Standards3
SNT-TC-1A Personnel Qualification and Certification in
1.3 This practice does not establish acceptance criteria. Nondestructive Testing
Typical industry practice is to reject these connections on ANSI/ASNT-CP-189 Standard for Qualification and Certifi-
detection of a confirmed crack. cation of Nondestructive Testing Personnel
1.4 While the alternating current field measurement tech- 2.3 ISO Standard:4
nique is capable of detecting discontinuities in these ISO 9712 Non-Destructive Testing: Qualification and Certi-
connections, supplemental surface NDT methods such as fication of NDT Personnel
magnetic particle testing for ferrous metals and penetrant
testing for non-ferrous metals may detect more discontinuities. 3. Terminology
1.5 Units—The values stated in either inch-pound units or 3.1 For definitions of terms relating to this practice refer to
SI units are to be regarded separately as standard. The values Terminology E1316, Section A, Common NDT terms, and
stated in each system might not be exact equivalents; therefore, Section C, Electromagnetic testing. The following definitions
each system shall be used independently of the other. Combin- are specific to the alternating current field measurement tech-
ing values from the two systems may result in nonconformance nique:
with the standard. 3.2 Definitions:
1.6 This standard does not purport to address all of the 3.2.1 detector—one or more coils or elements used to sense
safety concerns, if any, associated with its use. It is the or measure a magnetic field; also known as a receiver.
responsibility of the user of this standard to establish appro- 3.2.2 exciter—a device that generates a time varying elec-
priate safety and health practices and determine the applica- tromagnetic field, usually a coil energized with alternating
bility of regulatory limitations prior to use. current (AC); also known as a transmitter.
1.7 This international standard was developed in accor- 3.2.3 uniform field—as applied to nondestructive testing
dance with internationally recognized principles on standard- with magnetic fields, the area of uniform magnetic field over
ization established in the Decision on Principles for the the surface of the material under examination produced by a
Development of International Standards, Guides and Recom- parallel induced alternating current, which has been passed
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
2
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on
1
This practice is under the jurisdiction of ASTM Committee E07 on Nonde- the ASTM website.
3
structive Testing and is the direct responsibility of Subcommittee E07.07 on Available from American Society for Nondestructive Testing (ASNT), P.O. Box
Electromagnetic Method. 28518, 1711 Arlingate Ln., Columbus, OH 43228-0518, http://www.asnt.org.
4
Current edition approved June 1, 2017. Published June 2017. Originally Available from International Organization for Standardization (ISO), ISO
approved in 2013. Last previous edition approved in 2013 as D2928/D2928M–13. Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
DOI: 10.1520/E2928_E2928M–17. Geneva, Switzerland, http://www.iso.org.

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States

1
 E2928/E2928M − 17
through the testpiece and is observable beyond the direct within a short distance of either side of the scan line at this
coupling of the exciting coil. location will interrupt or disturb the flow of the alternating
3.3 Definitions of Terms Specific to This Standard: current. Measurement of the absolute quantities of the two
3.3.1 alternating current field measurement system—the major components of the surface magnetic fields (Bx and Bz)
electronic instrumentation, software, probes, and all associated determines the severity of the disturbance (see Fig. 1) and thus
components and cables required for performing an examination the severity of the discontinuity. Discontinuity sizes, such as
using the alternating current field measurement technique. crack length and depth, can be estimated from the values of
these quantities or the physical locations of key points, or both,
3.3.2 box—the female thread in a drillstring connection. selected from the Bx and Bz traces along with the standardiza-
3.3.3 Bx—the x component of the magnetic field, parallel to tion data and instrument settings from each individual probe.
the thread root, the magnitude of which is proportional to the This discontinuity sizing can be performed automatically using
current density set up by the electric field. system software. Discontinuities essentially perpendicular to
3.3.4 Bz—the z component of the magnetic field normal to the thread may be detected (in ferritic metals only) by the flux
the examined pipe surface, the magnitude of which is propor- leakage effect.
tional to the lateral deflection of the induced currents in the 4.2 Configuration data is loaded at the start of the exami-
plane of that surface. nation. System sensitivity and operation is verified using an
3.3.5 configuration data—standardization data and instru- operation standardization block. System operation is checked
mentation settings for a particular probe stored in a computer and recorded prior to and at regular intervals during the
file. examination. This can be accomplished using discontinuity-
3.3.6 data sample rate—the rate at which data is digitized sizing tables in the system software. Data is recorded in a
for display and recording, in data points per second. manner that allows archiving and subsequent recall for each
thread. Evaluation of examination results may be conducted at
3.3.7 longitudinal—following from the above definition, a the time of examination or at a later date. The examiner
longitudinal discontinuity is parallel to the pipe axis and generates an examination report detailing complete results of
therefore perpendicular to the scan direction. the examination.
3.3.8 operational standardization block—a reference stan-
dard with specified artificial notches, used to confirm the 5. Significance and Use
operation of the system. 5.1 The purpose of the alternating current field measure-
3.3.9 pin—the male thread in a drillstring connection. ment method is to evaluate threads for surface breaking
3.3.10 satellite signals—Bx and Bz signals observed when discontinuities such as fatigue cracks running along the thread
the probe passes a discontinuity in an adjacent thread root. root. The examination results may then be used to determine
the fate of the tool. This may involve re-examination by an
3.3.11 surface plot—for use with array probes. This type of
alternative technique, immediate scrapping of the tool, or
plot has one component of the magnetic field plotted over an
reworking to remove discontinuities (beyond the scope of this
area, typically as a color contour plot or 3-D wire frame plot.
3.3.12 time base plots—these plot the relationship between
Bx or Bz values with time.
3.3.13 transverse—as is normal in drilling, the terms trans-
verse and longitudinal are defined in reference to the pipe axis.
Therefore, a transverse discontinuity is parallel to the thread
and hence to the scan direction. This is different to the situation
for weld inspection, covered in Guide E2261.
3.3.14 X-Y Plot—an X-Y graph with two orthogonal com-
ponents of magnetic field plotted against each other.
NOTE 1—Different equipment manufacturers may use slightly different
terminology. Reference should be made to the equipment manufacturer’s
documentation for clarification.

4. Summary of Practices
4.1 In a basic alternating current field measurement system,
a small probe is moved around the thread root. The probe
contains an exciter coil, which induces an AC magnetic field in
the material surface aligned to the direction of the thread root.
This, in turn, causes alternating current to flow across the
threads. The depth of penetration of this current varies with
material type and frequency but is typically 0.004 in. [0.1 mm] FIG. 1 Example Bx and Bz Traces as a Probe Passes Over a
deep in magnetic materials and 0.08 to 0.3 in. [2 to 7 mm] deep Crack (The orientation of the traces may differ depending upon
in non-ferrous materials. Any surface breaking discontinuities the instrumentation.)

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 E2928/E2928M − 17
practice). This practice is not intended for the examination of 8.2 Material Properties:
threads for non-surface breaking discontinuities. 8.2.1 Although there are unlikely to be permeability differ-
ences in a ferromagnetic material between different parts of a
6. Basis of Application
thread, if a probe is scanned across a permeability change such
6.1 Personnel Qualification—if specified in the contractual as an area of residual magnetism, this may produce indications
agreement, personnel performing examinations to this practice which could be similar to those from a discontinuity. Differ-
shall be qualified in accordance with a nationally or interna- entiation between a discontinuity signal and a permeability
tionally recognized NDT personnel qualification practice or change signal can be achieved by comparing scans from
standard such as ANSI/ASNT-CP-189, SNT-TC-1A, ISO neighboring threads. The signal from a discontinuity will die
9712, or a similar document and certified by the employer or away quickly. If there is no significant change in indication
certifying agent, as applicable. The practice or standard used amplitude two or more threads away along the pipe axis then
and its applicable revision shall be identified in the contractual the indication is likely due to the permeability changes in the
agreement between the using parties component.
6.2 Qualification of Nondestructive Evaluation Agencies—if 8.3 Magnetic State:
specified in the contractual agreement, NDT agencies shall be 8.3.1 Demagnetization—It must be ensured that the surface
qualified and evaluated as described in Specification E543, being examined is in a low magnetization state, or that any
with reference to sections on electromagnetic examination. The magnetization is uniform over the surface. Therefore the
applicable edition of Specification E543 shall be specified in procedure followed with any previous magnetic technique
the contractual agreement. deployed must include demagnetization of the surface, or
7. Job Scope and Requirements ensuring that connections are magnetically saturated. This is
because areas of remnant magnetization, particularly where the
7.1 The following items may require agreement by the leg of a magnetic particle examination yoke was sited, can
examining party and their client and should be specified in the produce loops in the X-Y plot, which may sometimes be
purchase document or elsewhere: confused with a discontinuity indication.
7.1.1 Location and type of threaded component to be
examined, design specifications, degradation history, previous 8.4 Thread Geometry:
nondestructive examination results, maintenance history, pro- 8.4.1 When a probe scans away from the shoulder of a pin
cess conditions, and specific types of discontinuities that are connection, the Bx indication value will decrease with little
required to be detected, if known. change in the Bz value. In the representative plot of Fig. 2, this
7.1.2 The maximum recommended probe scan speed is to appears as a drop in the X-Y plot. The Bx indication value will
be stated by the manufacturer. However, detection of smaller also decrease as a probe approaches the open end of a thread
discontinuities requires a slower probe scan speed or cleaning (pin or box).
of surface, or both.
7.1.3 Size, material grade and type, and configuration of
threads to be examined.
7.1.4 A thread numbering or identification system.
7.1.5 Extent of examination, for example: complete or
partial coverage, which threads and to what extent.
7.1.6 Type of alternating current field measurement instru-
ment and probe; and description of operations standardization
block used, including such details as dimensions and material.
7.1.7 Required thread cleanliness.
7.1.8 Environmental conditions, equipment and prepara-
tions that are the responsibility of the client; common sources
of noise that may interfere with the examination, such as motor
drive for rotary table.
7.1.9 Complementary methods or techniques may be used
to obtain additional information.
7.1.10 Acceptance criteria to be used in evaluating discon-
tinuities.
7.1.11 Disposition of examination records and reference
standards.
7.1.12 Format and outline contents of the examination
report.
8. Interferences
8.1 This section describes items and conditions, which may FIG. 2 Example X-Y Plot Produced by Plotting the Bx (vertical)
compromise the alternating current field measurement tech- and Bz (horizontal) Together (The orientation of the plot may dif-
nique. fer depending upon the instrumentation.)

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 E2928/E2928M − 17
8.5 Crack Geometry Effects: 9.1.1 The electronic instrumentation shall be capable of
8.5.1 Since the effect of a discontinuity on the signals can be energizing the exciter at one or more frequencies appropriate to
detected some distance away, “satellite” signals are observed the thread material. The apparatus shall be capable of measur-
as the probe passes one thread (or two threads) away from a ing the Bx and Bz magnetic field amplitudes at each frequency.
sufficiently-large discontinuity. The satellite signals will be The instrument will be supplied with a processor, either
smaller than the main discontinuity signal, and symmetrically internally, or in the form of a portable personal computer (PC)
spaced one thread revolution either side. Care should be taken that has sufficient system capabilities to support the alternating
not to classify these signals as additional discontinuities. current field measurement software, which will be suitable for
8.5.2 A large discontinuity may jump across a thread crown the instrument and probes in use and the examination require-
from one root to the neighboring one. This causes a sudden rise
ments. The software provides control of the instrumentation
in Bx signal where the discontinuity leaves the root, and a
including set-up, data acquisition, data display, data analysis
sudden decrease in Bx signal at the same place in the
and data storage. The software provides algorithms for sizing
neighboring thread where the discontinuity enters the root.
8.5.3 Line Contact—when contacts occur across a disconti- the discontinuities (see Section 14). The software runs on the
nuity then minor loops occur within the main X-Y plot loop processor and, on start up, all communications between the
produced by the discontinuity. This can be differentiated from processor and the instrument are automatically checked. When
adjacent multiple discontinuities when there will be a number the software starts up, it automatically sets up the instrument
of separate loops, each returning to the background level. connected in the correct mode for alternating current field
8.5.4 Longitudinal Discontinuities—in the unlikely event measurement examination. Configuration data for each probe
that a discontinuity exists parallel to the pipe axis then the Bx is stored either on the processor or on the probe and is
may rise instead of fall and the Bz signal will remain the same transmitted to the instrument whenever a probe is selected or
as for a short transverse discontinuity. The X-Y plot will then changed. This configuration data may include different settings
go upwards instead of down in the representative plot of Fig. 2. dependent on the thread type and size being examined. For
The extent of this flux leakage signal above the surface is non-magnetic materials, if configuration data is not available
related to the opening of the discontinuity, so it may not be from the equipment manufacturer, a standardization may be
seen for tightly closed discontinuities. performed on reference blocks prior to the material examina-
8.6 Instrumentation: tion. Equipment operation is also checked by scanning over a
8.6.1 The operator should be aware of indicators of noise, standardization block (see 11.2.2). Once the instrumentation is
saturation or signal distortion particular to the instrument being set up for a particular probe, the software can be used to start
used. Special consideration should be given to the following and stop data acquisition. During data acquisition at least two
concerns: presentations of the data are presented on the display screen in
8.6.1.1 The excitation frequency of operation should be real time (see 4.1). Data from the probe is displayed against
chosen to maximize discontinuity sensitivity whilst maintain- time (with Fig. 1 as an example) and also as an X-Y plot (with
ing acceptable noise levels. Fig. 2 as an example). The data from the probe can also be
8.6.1.2 Saturation of electronic components is a potential displayed against position (see Fig. 1) if an encoder is used
problem in alternating current field measurement because with the probe. Depending upon equipment type, manual or
signal amplitude can increase rapidly as a probe is scanned into automatic position markers may be incorporated with the data.
tight angle geometry, such as a shoulder on a pin. This could Once collected the data can be further analyzed offline using
cause the Bx indication to rise above the top of the range of the the software to allow, for example, discontinuity sizing (see
A/D converter in the instrument. Data acquired under satura- Section 14) or annotation for transfer to examination reports.
tion conditions are not acceptable and appear as a flattening of The software also provides facilities for all data collected to be
the Bx response in the representative plots of Fig. 1 at the electronically stored for subsequent review or reanalysis,
maximum possible signal value. If saturation conditions are
printing or archiving.
observed, the equipment gain should be reduced until the Bx
value no longer appears to saturate and the examination 9.2 Driving Mechanicsm:
repeated. After adjusting the equipment gain, an equipment 9.2.1 Ideally, the pipe is placed on a rotary rig such that the
operation check as described in 11.2 is recommended, except pipe can be rotated about its own axis, allowing the probe to
that the loop size will be smaller. Note that this gain adjustment move down the axis. In this way, the complete thread can be
does not affect the discontinuity sizing capability. examined without having to move the probe around the pipe,
8.6.2 Instrument Induced Phase-Offset—The measurements thus avoiding twisting of the probe cable. Alternatively, if the
of magnetic field are at a chosen and fixed phase so that unlike
pipe cannot be rotated, an array probe can be used to examine
during conventional eddy current examination the phase angle
the complete thread in one turn of the probe.
does not need to be considered. The phase is selected at
manufacture of the probes and is stored in the probe file and is 9.3 Probes:
automatically configured by the instrument. 9.3.1 The probes selected should be appropriate for the form
of examination to be carried out dependent on thread size,
9. Alternating Current Field Measurement System geometry, size of detectable discontinuity and component
9.1 Instrumentation material.

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 E2928/E2928M − 17
9.3.1.1 Universal Thread Probe—used with interchangeable
shoes that are each designed to fit a particular thread size and
type. It is important to select the correct shoe for the thread to
be examined to avoid excessive lift-off or probe rock, and
probe wear.
9.3.1.2 Array Probe—made up of a number of elements;
each element is sensitive to a discrete section of the thread
(typically a single root, but may be part of a root for large
threads). The array probe is generally used for scanning a
complete thread in one full rotation. The probe may have
interchangeable scrapers to fit a particular thread size. In this
case, it is important to select the correct scrapers for the thread FIG. 3 Pin Thread Sample Serial Number XXX Showing Size and
to be examined to avoid excessive lift-off or probe rock, and Location of Reference Notch (Plan View and Side View. Not to
probe wear. Scale)

9.4 Data Displays:

9.4.1 The data display should include Bx and Bz indications
as well as an X-Y plot.
9.4.2 When multi-element array probes are being used, the
facility to produce color contour maps or 3-D wire frame plots
representing peaks and troughs should be available.
9.5 Excitation Mechanism:
9.5.1 The degree of uniformity of the magnetic field applied
to the material under examination is determined by the
equipment manufacturer. The geometry of the notches used in FIG. 4 Flat Plate Sample Serial Number XXX Showing Size and
the operation standardization block and the discontinuity sizing Location of Reference Notch (Plan View and Side View. Not to
model must be consistent with the excitation field. Scale)

10. Alternating Current Field Measurement

Standardization Blocks shall be accurate to within 610 % of the depth specified,
10.1 Artificial Notches for the Operation Standardization measured, and documented. The discontinuity length shall be
Block: accurate to within 60.040 in. [61.00 mm] of the dimension
10.1.1 The operation standardization block has specific specified.
artificial discontinuities. It is used to check that the instrument 10.2 Materials Other than Ferritic Steel:
and probe combination is functioning correctly. It may also be 10.2.1 If the technique is to be used on materials other than
used for standardization of the equipment for nonmagnetic ferritic steel, then it may be necessary to standardize the probes
materials. Unless otherwise specified by the client or equip- on this material. If configuration data are not available from the
ment manufacturer, the artificial discontinuities for the opera- equipment manufacturer, refer to manufacturer’s instructions.
tion standardization block are elliptical notches. The notch
geometry will be specified by the equipment manufacturer to NOTE 2—If this is not done then the sizes of the indications may be too
be consistent with the crack size estimation model. Typical small (so that small discontinuities may be missed) or too large (so that
spurious indications may be called), or the Bx indication may saturate
notch dimensions are as follows: making the examination invalid. This standardization is done using a
10.1.1.1 Notch in Thread Sample—An elliptical notch notch of reasonable size located at a thread root of a representative
placed in a thread root, near to the pin shoulder, with sample. The gain settings are altered, either automatically or manually
dimensions of at least 0.6 by 0.06 in. [15 by 1.5 mm] to give according to equipment type, until a loop of reasonable size is produced
in the X-Y plot while background noise indications are kept low. When the
a suitably large signal for comparison with that expected. (Fig. technique is to be used to size the depths of discontinuities detected in
3) material for which configuration data is unavailable, then a standardiza-
10.1.1.2 Notch in plate with a groove to mimic a thread root, tion block should be manufactured from the material with at least two
if no thread sample is available—An elliptical notch placed in notches of differing depth. This provides an adjustment coefficient that
the groove, at least 4 in. [100 mm] from an edge, with modifies the estimated depth from the sizing model.
dimensions of at least 0.6 by 0.06 in. [15 by 1.5 mm]. (Fig. 4) 10.3 Standardization blocks having artificial or simulated
10.1.2 These notches shall be less than 0.020 in. [0.50 mm] discontinuities for threads in materials other than carbon steel
wide. shall not be used for discontinuity characterization unless the
10.1.3 The standardization block may contain additional signals from the artificial discontinuities can be demonstrated
notches, for example smaller notches to indicate sensitivity. In to be similar to the signals for discontinuities detected. To be
this case, they shall be at least 0.75 in. [19 mm] from any other considered similar, a direct comparison should be performed
notch in both longitudinal and transverse directions. between responses to the simulated discontinuities and real
10.1.4 Artificial discontinuity depths are specified by giving cracks. This comparison should involve at least one limited
the deepest point of the discontinuity. Discontinuity depths sizing trial or a probability of detection (POD) study.

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 E2928/E2928M − 17
10.4 Manufacture and Care of the Operation Standardiza- The probe is then scanned across the operation standardization
tion Blocks: block and over a reference notch as specified by the equipment
10.4.1 Drawings—for each operation standardization block manufacturer, producing a standardized data plot. Discontinu-
and standard, there shall be a drawing that includes the as-built ity indications are created when (1) the background level Bx
measured notch dimensions, material type and grade, and the value is reduced and then returns to the nominal background
serial number of the actual operation standardization block. level (see Fig. 1), and this is associated with (2) a peak or
10.4.2 Serial Number—each operation standardization positive (+ve) indication followed by a trough or negative (-ve)
block shall be identified with a unique serial number and stored indication (or a trough followed by a peak, depending on
so that it can be obtained and used for reference when required. direction of scan) in the Bz values. The resultant effect of the
10.4.3 Notch Spacing—the notches should be positioned to changes in Bx and Bz is a loop in the X-Y plot shown, for
avoid overlapping of indications and interference from end example, as the downward loop of Fig. 2. The presence of a
effects. discontinuity is confirmed when all three of these indications
10.4.4 Proper machining practices shall be used to avoid are present, that is, changes in the Bx and the Bz values and a
excessive cold-working, over-heating, and undue stress and loop in the X-Y plot. The loop should fill approximately 50 %
permeability variations. of the Bx direction and 175 % of the Bz direction of the X-Y
10.4.5 Blocks should be stored and shipped so as to prevent plot (that is, the loop is larger than the display in the Bz
mechanical damage. direction).
11.2.2.1 If the loop signal size differs from that expected
11. Equipment Operation Check from the operation standardization block, then the instrument
and probe settings should be checked. Each probe should have
11.1 Instrument Settings:
a unique probe file, the validity of which has been checked
11.1.1 Operating Frequency—The standard operating fre-
against the discontinuity sizing tables. The instrument settings
quency depends upon the equipment to be used and typically is
can be checked using the software package.
in the range of 5 to 50 kHz. The operating frequency should be
11.2.3 Each alternating current field measurement unit and
chosen according to manufacturers’ recommendations. Gener-
probe to be used during the examination should be checked
ally a lower frequency is best for ferritic steel or higher
with the operation standardization block. If the correct loop
conductivity non-ferritic metals, a higher frequency is best for
signal sizes cannot be obtained within a specified margin (for
lower conductivity non-ferritic metals. A higher operating
example 10 %), then there is a fault with the system, which will
frequency will also give better sensitivity on good surfaces. If
have to be determined. Do not use for examination unless
the system available is not capable of operating at the fre-
standardization validity is confirmed within the specified
quency described by this practice, the inspector shall declare to
margin.
the client that conditions of reduced sensitivity may exist.
11.1.2 Standardization—The configuration data, especially 11.3 Frequency of System Checks:
for magnetic materials, may be supplied by the manufacturer. 11.3.1 The system should be checked with all of the probes
If not, the equipment may need to be standardized. Standard- to be used during the examination prior to examining the first
ization is performed by loading manufacturer supplied configu- thread.
ration data for the nearest equivalent material, performing 11.3.2 System operation should be checked at least every
standardization measurements, and saving the resulting data four hours with the probe in use or at the end of the
and instrument settings as user configuration data. The stan- examination shift. If the discontinuity responses from the
dardization measurements are performed using the appropriate operation standardization block have changed by a specified
operation standardization block (see 10.1). The probe is placed margin (for example, 10 %), the threads examined since the
so the sensors lie at the bottom of the thread root, with the nose last operations standardization block check shall be re-
of the probe parallel to the thread. The probe is then scanned examined after following the procedure in 11.2.
across the operation standardization block and over a reference
notch as specified by the equipment manufacturer. The signal 12. Procedure
for the scanned notch is then selected and the gain is adjusted 12.1 Clean the thread surface to remove all grease, drilling
manually or automatically based on the measured signal and a mud and other deposits. Visually examine the thread for signs
reference signal for the discontinuity. Care must be used to of damage that may impede or damage the probe, and for
ensure that the reference notch is the same as the discontinuity corrosion pitting that may affect the signals.
for the reference signal. This information can then be saved as 12.2 Following the guidelines in 9.3, select a suitable probe
user configuration data. for the examination task, then, using the installed software,
11.2 Test System Check and Procedure: select a data file and a probe file. For a universal thread probe,
11.2.1 The test system shall consist of an alternating current fit the shoe appropriate for the thread to be examined.
field measurement instrument, a PC (if required), the probe and 12.2.1 For the box end, the probe is placed at the start of the
the operation standardization block. thread with the sensors located in the root as close as possible
11.2.2 The equipment operation check will be performed to the thread start (farthest away from open end of pipe) at a
using the appropriate operation standardization block (see suitable datum. This would typically be the thread run-out. A
10.1). The probe is placed so the sensors lie at the bottom of the datum line is marked on the outside of the pipe adjacent to the
thread root, with the nose of the probe parallel to the thread. center-line of the probe.

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 E2928/E2928M − 17
12.2.2 For the pin end, the probe is placed at the start of the tinuity required to be found. A typical scan speed is 2 in./s [50
thread with the sensors located in the root as close as possible mm/s]. This will produce a regular scan on the display screen.
to the thread start (farthest away from the end of the pipe) at a If short discontinuity-like signals are found, then the area
suitable datum. This would typically be the thread run-out. A should be reexamined with a slower scan speed. The length and
datum line is marked on the shoulder adjacent to the center-line speed of scanning will govern the data-sampling rate selected.
of the probe. With the introduction of faster software or hardware, it is
12.2.3 The pipe is then rotated if possible (by motor or by possible to select respective data sampling rates to produce
hand), or the probe is moved, such that the probe moves around faster scanning rates.
the thread towards the open end of the pipe. A marker is placed 13.1.2 Acquire and record data from the operation standard-
in the data every rotation of the pipe, when the marked datum ization block at the selected examination speed.
line passes the probe center-line. Discontinuity indications are 13.1.3 Acquire and record data from the threads to be
created when the following three points are indicated: examined. Maintain as uniform a probe speed as possible
12.2.3.1 The background level Bx value is reduced and then throughout the examination to produce repeatable indications.
returns to the nominal background level, Fig. 1.
12.2.3.2 This is associated with a peak, or positive (+ve) 13.2 Scanning Direction:
indication followed by a trough, or negative (-ve) indication (or 13.2.1 The probe should always be scanned parallel to the
a trough followed by a peak, depending on direction of scan) in thread root and this will give recognizable indications from
the Bz values, Fig. 1. transverse discontinuities as shown in Figs. 1 and 2. Scanning
12.2.3.3 The resultant effect of the changes in Bx and Bz is in this direction will also give recognizable, but different,
a downward loop in the X-Y plot, which is shown as a indications in the unlikely event of longitudinal discontinuities
downward loop in the example plot of Fig. 2. parallel to the pipe axis. The operator should be familiar with
12.2.4 The presence of a discontinuity is confirmed when all these types of indications.
three of these indications are present, that is, the Bx, the Bz and
a loop in the X-Y plot. Note that discontinuities of significant 14. Discontinuity Sizing Procedure
size will produce satellite indications one or more revolutions 14.1 When requested by the client, the sizing of any
either side of the location of the discontinuity. confirmed service-related defects may be performed as de-
12.2.5 Analysis of data should be undertaken only after data scribed herein using measurements taken of the Bx signatures
is collected from the complete thread. To aid analysis, a plus the distance between terminal peak/trough of the Bz
restricted section of data should be selected by zooming in on signature, as measured on the component.
part of the time axis (for example, one revolution of the pipe),
14.2 Length:
then moving through the data in stages.
14.2.1 Once an area containing a discontinuity has been
12.3 Compensation for Material Differences: located, a repeat scan is taken through the discontinuity. The
12.3.1 To compensate for the small differences in readings amplitude of the signal shall be compared with that seen during
caused by variations in permeability, conductivity or geometry the initial detection scan to ensure it is the same. This is to
for a given material, the data may be centered on the display avoid mistakenly sizing from a smaller satellite signal in an
area. For larger differences, the equipment settings should be adjacent thread root, which would result in a large underesti-
adjusted or a more suitable probe configuration should be used, mate of depth. The length of the discontinuity is determined by
or both, in accordance with the manufacturer’s instructions. locating the extreme ends of the discontinuity using the peak
12.4 Size and record all discontinuity indications as de- (+ve) and trough (-ve) Bz locations. These positions are just
scribed in Section 14, as applicable. inside the actual ends of the discontinuity. Markers are placed
on the component at these two locations and the distance
12.5 Note areas of limited sensitivity, using indications from
between the markers measured by a tape or ruler. This Bz
the operation standardization block as an indicator of discon-
length is used with the discontinuity sizing tables to determine
tinuity detectability.
the true length and depth of the discontinuity. Alternatively, the
12.6 Using a discontinuity characterization standard, evalu- length of the detected discontinuity may be measured directly
ate relevant indications in accordance with acceptance criteria by the system software using a position encoder.
specified by the client, if applicable.
14.3 Depth:
12.7 If desired, examine selected areas using an appropriate 14.3.1 The depth of the discontinuity is calculated using the
complementary method or technique to obtain more Bx minimum and Bx background values and the Bz length of
information, adjusting results where appropriate. the discontinuity measured from the Bz data. Once these values
12.8 Compile and present a report to the client. have been put into the software, then the discontinuity depth
will be estimated using the discontinuity sizing table.
13. Examination Considerations
13.1 Scanning Speed: 15. Report
13.1.1 The scanning speed is chosen using the appropriate 15.1 Reporting Requirements—a list of reporting require-
data sampling rate to obtain reasonable fidelity with the details ments is given in Table 1. Reference should be made to the
of the scanned object given the length of the shortest discon- Client reporting requirements (7.1.4). The items listed below

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 E2928/E2928M − 17
TABLE 1 Reporting Requirements 15.1.5 The names and qualifications of personnel perform-
NOTE 1—The data report sheets generated by the alternating current ing the examination.
field measurement examination will be specifically designed with the 15.1.6 Models, types, and serial numbers of the components
system and current examination requirements in mind. The essential of the alternating current field measurement system used,
information contained on a data sheet will include: including all probes.
General Information 15.1.7 For the initial data acquisition from the operation
Date standardization block, a complete list of all relevant instrument
Operator’s Name
Probe Operator settings and parameters used, such as operating frequencies,
Component ID Number and probe speed. The list shall enable settings to be referenced
File Number to each individual thread examined.
Equipment used
15.1.8 Serial numbers of all of the operations standardiza-
Scanning Data tion blocks used.
Filename 15.1.9 Brief outline of all techniques used during the
Page Number examination.
Position on Thread
Probe Number
15.1.10 A list of all areas not examinable or where limited
Probe Direction sensitivity was obtained. Where possible, indicate factors that
Tape Position may have limited sensitivity.
Examination Summary
NOTE 3—Factors that influence sensitivity to discontinuities include but
Detailed Record of Indications / Anomalies are not limited to: operating frequency, instrument noise, instrument
Filename
filtering, digital sample rate, probe speed, coil configuration, probe travel
Page Number noise and interference described in Section 8.
Position on Thread 15.1.11 If applicable, specific information about techniques
Start of Discontinuity (Tape reference)
End of Discontinuity (Tape reference)
and depth sizing for each discontinuity.
Length of Discontinuity (inches/millimetres) 15.1.12 Acceptance criteria used to evaluate discontinuities.
15.1.13 A list of discontinuities as specified in the purchas-
ing agreement.
Remarks
Diagram/Drawing of component under examination 15.1.14 Complementary examination results that influenced
interpretation and evaluation.
15.2 Record data and system settings in a manner that
allows archiving and later recall of all data and system settings
should be included in the examination report. All information for each thread. Throughout the examination, data shall be
below should be archived, whether or not it is required in the recorded and retained for later retrieval per customer
report. requirements, or in the absence of customer requirements, per
15.1.1 Owner, location, type and serial number of compo- company practice.
nent examined. 15.2.1 Report form. An example report form is shown in
15.1.2 Size, material type and grade, and configuration of Fig. 5.
threads examined.
15.1.3 Thread numbering system. 16. Keywords
15.1.4 Extent of examination, for example, areas of interest, 16.1 alternating current field measurement; drillstring; elec-
complete or partial coverage, which threads and other parts, tromagnetic examination; ferromagnetic material; non-
and to what length. magnetic material; root; thread

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 E2928/E2928M − 17

FIG. 5 Example Alternating Current Field Measurement Report

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 E2928/E2928M − 17
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