Note: Descriptions are shown in the official language in which they were submitted.
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PIPELINE INSPECTION TOOL
10
Field of Invention
This invention relates generally to inspection tools designed to detect
anomalies in
tubing, piping and pipelines and, more particularly, to inline inspection
tools employing
magnetic flux leakage detection techniques.
Background of the Invention
Many installed pipelines may be inspected using the Magnetic Flux Leakage
(MFL)
technique, primarily for the purpose of identifying metal loss anomalies.
Magnetic flux
leakage has been shown to respond in predictable ways to anomalies in the wall
of the
pipeline as the principal axis of the metal loss anomaly and field angle are
varied. Both
experimental and modeling results have been used to confirm this effect, which
is also
widely described in the literature.
Due in part to limitations imposed by data acquisition, data storage and
magnetic
circuit designs, most in-line inspection tools have employed axially oriented
magnetizers (see
CA 02708387 2016-09-02
e.g., U.S. Pat. No. 6,820,653 to Schempf et al.). However, the present axial
field magnetizer
designs make identification and quantification of extremely narrow axial
features difficult, or
in some cases, impossible. For these feature classes, a solution using a
magnetic field in the
circumferential or transverse direction, have been marketed and placed in
service over the
past decade by pipeline inspection providers. However, due to the constraints
of physics, the
performance and accuracy of these transverse magnetic flux inspection (TFI)
tools in general
is less than that of axial field tools for general metal loss anomalies.
Additionally, these TFI tools typically require a minimum of two magnetizer
assemblies in order to achieve adequate coverage, making it impractical or
difficult to
incorporate these into an existing axial MFL tool.
For those pipelines that may have extremely narrow metal loss features, or
certain
classes of seam weld anomalies, standard axial field tools do not provide
adequate detection
and quantification capabilities. In these cases, for MFL based tools, either
the initial or
supplemental surveys are performed using a TFI tool. While TFI tools may be
capable of
detecting extremely narrow anomalies and certain seam weld anomalies, they
also detect all
of the remaining volumetric metal loss features typically found in pipelines,
complicating the
process of identifying the targeted anomaly classes.
One of the earliest TFI arrangements is described in U.S. Pat. No. 3,483,466
to
Crouch et al. Crouch discloses a pair of electromagnets arranged perpendicular
to each other
with detectors such as magnetometers or search coils positioned on each side
of the magnets.
Other than the use of permanent magnets and hall device-type sensors, Crouch's
arrangement
remains as the basis for most modem implementations. Additionally, some
designs involve
segmented or individual discrete magnets that, in most cases, retain the
transverse or
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circumferential field direction. For example, U.S. Pat. No. 3,786,684 to Wiers
et al.
discloses individual magnets arranged in arrays oblique to the pipe axis with
the fields of
each array perpendicular the others. However, this arrangement limits the
field to sections
and areas between the poles of each individual magnet. Furthermore, the short
pole spacing
required for a Wiers-type implementation decreases the length of the magnetic
circuit,
thereby causing the tool to suffer from velocity effects, and also masks,
distorts or degrades
data quality at welds, dents, or other anomalies.
Other designs involve elaborate complex geometries, multiple magnetizer
sections,
and elaborate mechanical arrangements such as helical drives, gears and wheels
designed to
induce spiral or helical motion of the magnetizer section. For example, U.S.
Pat. No.
5,565,633 to Wernicke discloses a mechanically complicated device for use with
magnetizer
sections having two or more magnetic circuits and a plethora of sensing units.
In one
embodiment, the magnet blocks are arranged with spirally situated parallel
poles. In another
embodiment, the magnet blocks are twisted pole pairs displaced axially. Both
embodiments
require mechanically induced rotation in order to achieve full coverage of the
inner pipe
surface. Similar to Wernicke, U.S. Pat. No. 6,100,684 to Ramuat discloses a
substantially
transverse field magnetization arrangement that involves multiple magnetizer
sections and a
complex arrangement of wheels to induce helical motion of the sections and
achieve
overlapping or full coverage of the pipe wall. U.S. Pat. No. 7,548,059 to
Thompson et al.
includes two skids (poles) that incorporate fixed magnets arranged in closely
spaced pairs to
create a nominally transverse field spiraling around the pipe. This tool¨which
includes a
variety of moving parts such as supporting tendons, pulleys, and
springs¨requires much
added complexity in order to be flexible enough to accommodate bends in the
pipeline.
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Furthermore, the magnets in this arrangement induce a field between two
parallel poles,
forming a single closed loop circuit between the poles of the individual
discrete magnet
blocks.
Similar to Thompson et al., the magnets used in the prior art are described as
being
blocks, with no reference to a supple or conformable upper surface used for
the magnet
block. Use of a rigid contact arrangement for the magnetic circuit degrades
data quality by
introducing air gaps or variable reluctance zones in the magnetic field path
at dents or along
welds and other upsets that may be present within the pipeline. For certain
classes of
features, disturbances created in the ambient field mask or otherwise distort
the flux leakage
signals present because of the features of interest. Any magnetic anomalies
existing within
dents and weld zones are of greater significance due to their presence within
these zones and,
as such, represent areas in which data quality is critical.
Additionally, the prior art requires the use of a large number of poles or
surfaces in an
intimate contact arrangement to the pipe wall surface. This arrangement can
result in
extremely high frictional forces or resistance to motion being experienced by
the magnetizer
assembly, thereby inhibiting or preventing its use in applications requiring
lower friction.
As already discussed, pipeline operators are currently able to inspect many
installed
pipelines using the magnetic flux leakage (MFL) technique, primarily for the
purpose of
identifying metal loss anomalies. However, for certain classes of anomalies,
the current axial
field magnetizer designs used in the MFL technique make detection and
quantification of
extremely narrow, crack or crack-like axial features difficult or, in some
cases, impossible.
To enable detection and quantification of these features, alternative
techniques utilizing
acoustic (ultrasonic) waves have been studied or employed. These acoustic
waves are
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typically generated by external piezoelectric transducers or electro-magnetic
acoustic
transducers (EMAT).
EMAT implementations are usually one of two basic types: Lorentz and
magnetostrictive. Both types require an external magnetic bias field to be
present. In
Lorentz-type EMAT, the magnetic bias field is perpendicular to the pipe wall
and interacts
with Eddy current-induced paths or strains in the pipe wall. The
magnetostrictive-type
EMAT uses a magnetic bias field that is in the pipe wall plane, axial or
circumferential, and
interacts with magnetically induced strains.
It is well known in the nondestructive testing industry that magnetostriction
in steel is
much more efficient in generating shear horizontal (SH) acoustic waves when
the magnetic
bias field is at an angle with respect to the sensor coil conductors of the
EMAT. This result
has been verified by the inventors during initial development of an EMAT
sensor array
according to the invention disclosed herein. During the study it was
discovered that several
of the notches machined into test plates were not detectable using an axially
oriented
magnetic bias field. Rotating the magnetic bias field angle relative to the
axis of travel and
the EMAT sensor provided an increase of approximately 20 decibels in measured
signal.
This arrangement produced a much greater signal response compared to the
electronic noise,
resulting in distinct crack indications above a relatively uniform baseline.
Consequently SR wave applications using EMAT sensor coils that are set at an
angle
to the magnetic field, are usually superior to applications where the field
plane lines are
parallel to the sensor coil conductors (see e.g. DE Pat. App. Pub. No.
10/2007/0058043
assigned to Rosen Swiss AG). Detection and quantification of stress corrosion
cracking
(SCC) is one of the main types of anomalies targeted by this technique. In
addition to SCC,
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which is typically axially oriented, girth welds, which are circumferentially
oriented, have
been known to exhibit crack-like features. Therefore, for an EMAT system to be
globally
effective, a method is needed that is readily adaptable for detection of both
axially and
circumferentially oriented features.
Prior art in-line inspection tools use annular arrays of permanent magnets to
magnetize the pipe in a direction that is parallel to the axis of the pipe. To
obtain the
beneficial angle between the magnetic bias field and the sensor coils, the
sensor coils are
rotated toward the pipe axis (see e.g., Canadian Pat. Appl. No. CA 2,592,094
of Alers et al.).
The SH waves impinge on the plane of the axially oriented SCC at this same
angle.
Therefore, SH wave reflections from SCC are detected efficiently only by
receiver sensor
coils that are positioned lateral to and rotated toward the transmitter coil.
Also, the
attenuation measurements used for detection of coating disbond use receiver
coils that are
positioned diagonally to and rotated toward the transmitter coils. These
attenuation receiver
coils are shifted circumferentially so that they are in-line with the
transmitted wave. An
appreciable increase in received signal amplitude is an indication a coating
disbond.
There is a need for an EMAT tool that provides full coverage of the inner pipe
wall
surface without the need for mechanically complicated structures and produces
a field that
may be used with EMAT sensors to detect axially- or circumferentially-oriented
volumetric
features and coating disbonds.
There is a further need for a MFL tool that provides full coverage of the
inner pipe
wall surface without the need for mechanically complicated structures;
produces a field that
detects axially-oriented, circumferentially-oriented and volumetric features;
generates similar
responses from features regardless of whether the features are axially or
circumferentially
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oriented; eliminates or reduces velocity effects as well as signal masking,
disruptions and
distortion at welds, dents and other upsets; navigates pipeline obstructions,
bends and
reductions; and allows pipeline surveys to be accomplished in a single pass.
Summary of the Invention
A pipeline inspection tool made according to this invention includes at least
two pole
magnets arranged about an external surface of the tool body and oriented
oblique to the
central longitudinal axis of the tool body. A sensor array is provided between
the opposing
edges of the two pole magnets. The sensor array includes a line or set of
sensor coils that are
oriented at a different angle than the pole magnets relative to the
longitudinal axis of the tool
body. Therefore, the sensor array is at an angle with respect to the magnetic
bias field
generated by the pole magnets. The pole magnets and the sensor array may each
extend the
length of the tool body and have a general helical-shape. Preferably, the
sensor coil sets are
perpendicular to the longitudinal axis of the tool body but, depending on the
type of anomaly
to be detected, may be arranged parallel to the longitudinal axis of the tool
body.
Each sensor coil set may lie 180 opposite a corresponding sensor coil set,
with a
portion of the opposing sensor coil sets contained within a common
circumferential band of
the tool. Sensor coil sets lying on a same side of the tool body are offset
from one another,
being generally evenly spaced apart and equidistant from the opposing edges of
the oblique-
oriented pole magnets. Each set of sensor coils includes at least one
transmitter coil and at
least two opposing pairs of receiver coils. One receiver coil in each pair may
be a RD
receiver coil and the other receiver coil may be a RA receiver coil. Because
the sensor coil
sets are rotated relative to the magnetic bias field, the receiver coils are
in-line with, and have
the same angular orientation as, the transmitter coil. In other words, the
receiver coils are
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oriented parallel to the transmitter coil and do not need to be shifted
diagonally or rotated
with respect to the transmitter coil.
The transmitter coil transmits a tone burst or signal that impinges upon the
wall of the
tubular member being inspected and travels back to the receivers. The receiver
coils are
spaced relative to the transmitter coil so that the signal transmitted by the
transmitter coil
does not mask detection of the reflected signal by the receiver coils. Each
receiver coil is
gated to receive these reflected signals¨which may be normalized¨within a
targeted
sampling zone and detect anomalies in the tubular member. The transmitter may
then
transmit a second signal after the first signal has travelled a predetermined
number of times
around the circumference of the tubular member. Depending on the orientation
of the sensor
coil sets relative to the oblique-oriented magnets, the sensor array is
capable of detecting wall
anomalies in both the axial and circumferential direction.
It is an object of this invention to provide a magnetic flux leakage (MFL)
tool that
responds to a broad range of anomalies capable of generating magnetic flux
leakage signals.
Another object of this invention is to provide a MFL tool capable of 360
coverage of the
internal pipe wall using a single magnetizer without the need for multiple
magnetizer
sections, magnetizers, or relative motion between the sensors or sections to
achieve detection
of nominally axially oriented features. It is another object of this invention
to provide a MFL
tool with an EMAT array that reduces the probability of missing cracks in the
pipe wall and
has improved sensitivity to small defects, i.e., up to 20 db increase in
signal amplitude. Yet
another object of this invention is to provide an EMAT array that requires a
substantial
decrease in RF pulser power requirements. Still yet another object of this
invention is to
provide an EMAT array that includes self-calibration of the transmitted
signals using the
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receiver coils closest to transmitter coils. A further object of this
invention is to provide an
EMAT array that experiences less interference between transmitters caused by
acoustic ring
around.
In a further embodiment, a pipeline inspection tool made according to this
invention
includes a magnetizer assembly having a cylindrical tool body, at least two
radial discs, and
an even number "n" of pole magnets arranged about an external surface of the
cylindrical
tool body. Each pole magnet¨which preferably has a conformable upper surface,
such as a
brush-like surface, between the magnet and the internal wall surface of the
pipe¨extends the
length of the cylindrical body located between the two radial discs. The
spacing between
adjacent pole magnets is about 360 /n, "n" being the number of pole magnets
employed. The
magnetic flux paths radiate from the magnet poles, diverging in opposite
directions and
returning to an opposing pole in similar fashion.
The pole magnets are rotated or spiraled about the cylindrical tool body so
that a
second end of each pole magnet is offset a predetermined amount "a" relative
to a first end of
that same pole magnet. The amount of rotation a applied to each of the pole
magnets
produces a magnetic field oblique to the central longitudinal axis of the tool
body (and
therefore the pipe). The amount of rotation a, which may range from 30 to 150
, is
preferably an amount of rotation that is effective for producing a magnetic
field that covers
360 of the internal wall surface of a pipe lying opposite the tool body.
A helical-shaped array of magnetic flux sensors may be arranged about the
cylindrical
tool body and substantially equidistant between adjacent pairs of pole
magnets. Preferably, a
degree of overlap in the sensor array is provided, with a first end of the
array of magnetic
flux sensors extending a distance "A" past a line containing a second end of
the array.
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It is an object of this invention to provide a magnetic flux leakage (MFL)
tool that
responds to a broad range of anomalies capable of generating magnetic flux
leakage signals.
Another object of this invention is to provide a MFL tool capable of 3600
coverage of the
internal pipe wall using a single magnetizer without the need for multiple
magnetizer
sections, magnetizers, or relative motion between the sensors or sections to
achieve detection
of nominally axially oriented features. Another object of this invention is to
provide a MFL
tool capable of detecting volumetric-type metal loss features in conjunction
with ultrasonic,
electro-magnetic acoustic transducer, or magnetostrictive detection methods.
Yet another
object of this invention is to provide a MFL tool that produces a magnetic
field which
generates a substantially similar response from axially-oriented or
transversely-oriented
features as well as generating detectable responses from volumetric-type metal
loss features.
Still yet another object of this invention is to provide a MFL tool that
eliminates or reduces
the mechanical motion effects upon flux leakage signals at welds, dents and
other upsets.
Still another object of this invention is to provide a MFL tool that detects
and quantifies the
extremely narrow axial classes of anomalies, with the added benefit of doing
so in
conjunction with an existing axial field magnetizer, providing greater overall
accuracy in
metal loss anomaly quantification. Another object of this invention is to
minimize the
number of moving parts and assemblies incorporated into the MFL tool. Still
yet another
object of this invention is to provide a means for the MFL tool to compress in
order to pass
by obstructions, bends and reductions in a pipe. A further object of this
invention is provide
a single tool in which the pipeline survey may be done in a single pass,
reducing the amount
of effort required by both the pipeline operator and inspection personnel for
onsite
operations, data handling, data analysis, and final report generation.
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Brief Description of the Drawings
FIG. IA is an isometric view of an axially oriented magnetizer design. The
direction
of the magnetic field is circumferential or transverse to the longitudinal
axis of the pipe.
FIG. 2A is an isometric view of an embodiment of an oblique magnetizer
assembly
according to this invention that utilizes a spiral magnet pole design. The
pole magnets are
rotated or spiraled about 300 and include a flexible or conformable upper
surface.
FIG. 3A is a view of another embodiment of the oblique magnetizer assembly in
which the pole magnets are rotated about 60 .
FIG. 4A is a view of yet another embodiment of the oblique magnetizer assembly
in
which the pole magnets are rotated about 90 .
FIG. 5A is a view of still yet another embodiment of the oblique magnetizer
assembly
in which the pole magnets are rotated about 120 .
FIG. 6A is a view of yet another embodiment of the oblique magnetizer assembly
in
which the pole magnets are rotated about 1500
.
FIG. 7A is an end view of another embodiment of the oblique magnetizer
assembly,
illustrating the relationship between the two ends of the spiraled or rotated
pole magnets. In
this example, the pole magnets are rotated about 135 . The conformable upper
surface of
each pole magnet includes a bristle or brush-type surface.
FIG. 8A illustrates field results from the oblique magnetizer arrangement. The
field
direction is diagonal, or oblique, to the longitudinal axis of the pipe.
FIG. 9A is a view of an embodiment of the oblique magnetizer assembly that
includes
a helical-shaped sensor array mounted from one end of the magnetizer to the
other, providing
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complete coverage of the internal pipe wall surface and incorporating a degree
of overlap to
accommodate any tool rotation that may take place.
FIG. 10A is a view of the oblique magnetizer assembly of FIG. 8A encased in a
pipe
section.
FIG. 11A is a view of an inline inspection tool that includes the oblique
magnetizer
assembly, an axial magnetizer and a deformation sensing section.
FIG. 12A is a schematic illustrating one side of a sensor array that includes
two lines
or sets of EMAT sensor coils located between two oblique-oriented pole
magnets. Each
sensor coil set includes two pairs of receiver coils and a transmitter coil
located in-between
the pairs of receiver coils. The sets are aligned perpendicular to the central
longitudinal axis
of the inline inspection tool (and, therefore, perpendicular to the central
longitudinal axis of
the tubular member being inspected) and each coil in the set shares a common
centerline with
the other coils in the set.
FIG. 13A is a view of one side of a sensor array having the EMAT sensor coil
arrangement of FIG. 12A as applied to a 24 inch diameter tubular member.
FIG. 1B is an isometric view of a transversed oriented magnetizer design. The
direction of the magnetic field is circumferential or transverse to the
longitudinal axis of the
pipe.
FIG. 2B is an isometric view of an embodiment of an oblique magnetizer
assembly
according to this invention that utilizes a spiral magnet pole design. The
pole magnets are
rotated or spiraled about 30 and include a flexible or conformable upper
surface.
FIG. 3B is a view of another embodiment of the oblique magnetizer assembly in
which the pole magnets are rotated about 60 .
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FIG. 4B is a view of yet another embodiment of the oblique magnetizer assembly
in
which the pole magnets are rotated about 90 .
FIG. 5B is a view of still yet another embodiment of the oblique magnetizer
assembly
in which the pole magnets are rotated about 1200
.
FIG. 6B is a view of yet another embodiment of the oblique magnetizer assembly
in
which the pole magnets are rotated about 150 .
FIG. 7B is an end view of another embodiment of the oblique magnetizer
assembly of
illustrating the relationship between the two ends of the spiraled or rotated
pole magnets. In
this example, the pole magnets are rotated about 135 . The conformable upper
surface of
each pole magnet includes a bristle or brush-type surface.
FIG. 8B illustrates field results from the oblique magnetizer arrangement. The
field
direction is diagonal, or oblique, to the longitudinal axis of the pipe.
FIG. 9B is a view of an embodiment of the oblique magnetizer assembly that
includes
a helical-shaped sensor array mounted from one end of the magnetizer to the
other, providing
complete coverage of the internal pipe wall surface and incorporating a degree
of overlap to
accommodate any tool rotation that may take place.
FIG. 10B is a view of the oblique magnetizer assembly of FIG. 8B encased in a
pipe
section.
FIG. 11B is a view of an inline inspection tool that includes the oblique
magnetizer
assembly, an axial magnetizer and a deformation sensing section.
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Detailed Description of the Preferred Embodiments
Preferred embodiments of a magnetic flux leakage (MFL) tool made according to
this
invention will now be described by making reference to the drawings and the
following
elements illustrated in the drawings:
In-line inspection tool 65 Second end of 61
MFL tool / oblique magnetizer 67 Longitudinal centerline of 61
21 Cylindrical tool body 69 Conformable upper surface
23 First end of 21 71 Brushes
Second end of 21 80 Magnetic field
27 Longitudinal axis of 21 81 Magnetic flux path of field 80
31 Radial disc 90 Sensor array
40 Magnetic circuit 91 First end of 90
41 Pole magnet 93 Second end of 90
43 First end of 41 94 Sensor coil line or set of 95,
97 & 98
45 Second end of 41 95 Transmitter coil
47 Longitudinal centerline of 41 96 Shear horizontal wave
generated by 95
49 Conformable upper surface 97 RD receiver coil
51 Brushes 98 RA receiver coil
61 Pole magnet 99 Central axis of sensor coil set
94
63 First end of 61 100 Axial magnetizer
110 Deformation sensing section
310 In-line inspection tool 351 Brushes
320 MFL tool / oblique magnetizer 361 Pole magnet
321 Cylindrical tool body 363 First end of 61
323 First end of 21 365 Second end of 61
325 Second end of 21 367 Longitudinal centerline of 61
327 Longitudinal axis of 21 369 Conformable upper surface
331 Radial disc 371 Brushes
340 Magnetic circuit 380 Magnetic field
341 Pole magnet 381 Magnetic flux path of field 380
343 First end of 341 390 Sensor array
345 Second end of 341 391 First end of 390
347 Longitudinal centerline of 341 393 Second end of 390
349 Conformable upper surface 400 Axial magnetizer
410 Deformation sensing section
5
Figures IA through 13A show one embodiment of the invention. Referring first
to
FIG. 1A, a north pole magnet 41 and a south pole magnet 61 are arranged about
180
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opposite one another on a cylindrical tool body 21 so that the respective
longitudinal
centerline 47, 67 of each pole magnet 41, 61 is parallel to the longitudinal
centerline 27 of
the cylindrical tool body 21 (and therefore parallel to a central longitudinal
axis of the pipe
being inspected). Although pole magnets 41, 61 differ from prior art
implementations in
that, for example, each magnet 41, 61 extends along the entire length of the
cylindrical body
21, their axial orientation as illustrated here is typical of prior art
implementations. Arranged
in this way, pole magnets 41, 61 generate a circumferential or transverse
magnetic field
relative to the pipe wall¨as illustrated by magnetic flux paths 81¨and
multiple magnetizer
sections are required to provide complete coverage of the internal wall
surface of the pipe.
Referring now to FIGS. 2A to 6A, an oblique magnetizer assembly 20 according
to
this invention includes a magnetic circuit 40 that has two spiraled pole
magnets 41, 61
arranged about 1800 opposite one another on cylindrical tool body 21. Each
pole magnet 41,
61 extends between a first end 23 and second end 25 of the cylindrical tool
body 21.
Additional pairs of spiraled pole magnets 41, 61 may also be employed, with
each spiraled
pole magnet 41 or 61 extending between the ends 23, 25 of cylindrical tool
body 21 and
spaced 360 /n from its adjacent and opposite pole magnet 61, 41 ("n" being an
equal to the
number of pole magnets 41, 61 employed). The pole magnets 41, 61 preferably
have a
flexible or conformable upper surface 49, 69, respectively, that helps reduce
friction forces
and minimize velocity effects as the oblique magnetizer assembly 20 travels
through the
interior of a pipe. The conformable upper surface 49, 69 also allows the
magnetizer
assembly 20 to compress a sufficient amount in order to pass by internal
obstructions, bends,
and reductions in the pipe that might otherwise damage the magnetizer assembly
20 or slow
or prevent its passage.
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The rotation amount of the pole magnets 41, 61 depends on the amount of
rotation
required to achieve full coverage of the internal pipe wall surface. Going
through the
sequence from FIG. 2A to FIG. 6A, the pole magnets 41, 61 are each rotated or
spiraled in
incremental amounts, for a nominal rotation of about 150 degrees (as
illustrated in FIG. 6A).
When rotated, the second end 45, 65 of the pole magnet 41, 61 is offset by a
predetermined
angle or amount a relative to its respective first end 43, 63 (see FIG. 7A).
Because of this
rotation amount a, the respective longitudinal centerline 47, 67 of each
spiraled pole magnet
41, 61 is non-parallel to the central longitudinal axis 27 of the cylindrical
tool body 21. The
rotation of pole magnets 41, 61 also helps induce a sufficient amount of
rotation of
magnetizer assembly 20 as it travels through the interior of the pipe.
FIG. 8A illustrates the magnetic field 80 generated from a prototype of
oblique
magnetizer assembly 20, which was configured similar to the magnetizer
assembly 20 shown
in the rotation sequence of FIGS. 2A to 6A. Unlike prior art in-line
inspection tools, the
direction of magnetic field 80 is diagonal or oblique to the pipe axis rather
than
circumferential or transverse, with magnetic flux paths 81 emanating from the
poles 41, 61
and traveling in opposite directions to reach a corresponding pole 61, 41. The
magnetic flux
lines 81 generated by each pole magnet 41, 61 are guided to the path of least
resistance: into
the pipe wall and toward the adjacent pole magnet 61, 41. The angle of the
magnetic field 80
is generally perpendicular to the flux lines 81 formed by the magnetic poles
41, 61 and
generally parallel to a line forming the shortest distance between the magnet
poles 41, 61.
The direction of magnetic field 80 within the extents of poles 41, 61 may
range from 30 to 60
degrees relative to the pipe axis.
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Referring now to FIGS. 9A & 10A oblique magnetizer assembly 20 may include a
helical-shaped sensor array 90 located substantially equidistant between
rotated pole magnets
41, 61 and arranged to provide complete coverage of the internal wall surface
W of pipe P
and accommodate any rotation of magnetizer assembly 20 that may take place.
The
individual sensors in sensor array 90 may be of a kind well-known in the art
for detecting
magnetic flux leakage signals. Sensor array 90 preferably extends between the
first end 23
and second end 25 of cylindrical body 21 (and therefore between the respective
ends 43, 45
and 63, 65 of pole magnets 41, 61) and incorporates a degree of overlap A
between a first end
91 and second end 93 of sensor array 90. The conformable upper surfaces 49, 69
of the pole
magnets 41, 61 (see e.g. FIG. 6A) may be in the form of brushes 51, 71. Radial
discs 31A &
B help propel and center magnetizer assembly 20 as it moves forward in pipe P
under
differential pressure.
The final configuration of oblique magnetizer assembly 20 may include any
current
combination of data sets, including but not limited to deformation, high level
axial MFL,
internal/external discrimination, inertial data for mapping, and low level or
residual MFL. In
one preferred embodiment of an inline inspection tool 10 incorporating oblique
magnetizer
assembly 20, the tool 10 includes an axial magnetizer 100 and a deformation
sensing section
110 (see FIG. 11A).
Referring now to FIGS. 12A & 13A, sensor array 90 includes electro-magnetic
acoustic transducers (EMAT) sensor coils 95, 97 & 98 located between the
opposing edges
42,62 of the oblique-oriented permanent pole magnets 41, 61. The sensor coils
95,97 & 98
are preferably arranged in sensor coil lines or sets 94a-e as defined by a
respective sensor coil
set central axis 99a¨e. Each central axis 99a¨e is generally parallel to the
other axes 99a¨e
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and oriented at a predetermined angle y relative to the central longitudinal
axis 27 of
cylindrical tool body 21. A substantially identical set of sensor coil sets
(not shown) to
sensor coil sets 94a¨e is arranged on the opposing external surface of
cylindrical tool body
21, about 1800 opposite sensor coil sets 94a¨e.
The oblique-oriented pole magnets 41, 61 are generally at an angle 13 relative
to
central longitudinal axis 27, with angle [I being different than angle y.
Because the flux lines
81 generated by pole magnets 41, 61 are generally perpendicular to the edges
42, 62 of the
pole magnets 41, 61, magnetic field 80 is rotated at an angle c relative to
the central
longitudinal axis 21 and, therefore, is at an angle with respect to sensor
coil sets 94a-e. In a
preferred embodiment, angle y is about 90 , angle 13 is about 45 , and angle E
is about 45 .
Arranging the sensor coil sets 94a¨e perpendicular to the central longitudinal
axis 27
of cylindrical tool body 21 (and therefore perpendicular to the pipe axis)
allows sensor array
90 to detect features in both the axial and circumferential directions.
Transmitter coils 95
generate SH waves 96 that travel circumferentially around the pipe and impinge
at a normal
angle (perpendicular) to axially oriented cracks. Arranging the sensor coil
sets 94a¨e parallel
to the central longitudinal axis 27 of the cylindrical tool body 21 (and
therefore parallel to the
pipe axis) allows sensor array 90 to detect features in the circumferential
direction. Shear
horizontal waves 96 are transmitted along the pipe wall in the axial direction
so that
reflections from transverse cracks, such as cracks in girth welds, are
detected. Unlike the
orientation of receivers in prior art EMAT tools, receiver coils 97, 98 do not
have to be
shifted diagonally with respect to, or rotated toward, the transmitter coil 95
in order to gain
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the benefits of having magnetic field 80 rotated with respect to the EMAT
sensor coils 95, 97
& 98.
Sensor coils 95, 97 & 98 may be mounted on a suitable mechanism such as a
spring
loaded pads (not shown) that keep the coils 95, 97 & 98 in close proximity to
the inside
diameter of the pipe. The transmitter coils 95 induce SH guided waves 96 in
two
circumferential directions around the pipe. The receiver coils 97 detect
reflections from
stress corrosion cracks (SCC) and serve as the calibration receivers. Receiver
coils 98 detect
the SH guided waves 96 that propagate from the transmitter coils 95 in the
circumferential
direction. The characteristic features of these detected signals, such as
amplitude and time of
arrival, can be used to detect features such as coating disbond, corrosion and
SCC.
The receiver coils 97, 98 are placed at a predetermined distance from
transmitter coil
95 so that signal responses are detected by receiver coils 97, 98 but not
affected adversely by
the initial electronic excitation pulse. Each transmitter coil 95 in a set
94a¨e is grouped with
two receiver coils 97, 98 on each side. Sensor array 90 preferably includes
the requisite
number of transmitter coils 95 and receiver coils 97, 98 in order to provide
overlapping
coverage of SCC and coating disbond detection. In one preferred embodiment,
each of two
sensor arrays 90¨arranged opposite one another and for use in a 24-inch
diameter pipe¨
included five transmitter coils 95 and 20 total receiver coils 97, 98.
Each transmitter coil 95 when fired causes SH guided waves 96 to propagate to
both
to the left and to the right of the coil 95 and around the circumference of
the pipe. The
receiver coils 97, 98 closest to the active transmitter coil 95 are first
sampled in time (gated)
to receive the outgoing waves 96 and then gated at a longer predetermined time
delay,
preferably on the order of 50 and 90 microseconds for a 24-inch diameter pipe,
to detect
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CA 02708387 2016-09-02
reflections from SCC. These reflections are from targeted sampling zones "Z"
located
between the RD receiver coils 97 and a predetermined distance "D" past the RA
receiver
coils 98 so as to maximize coverage and minimize interference. The reflection
signals are
normalized, i.e., divided by the outgoing signals detected in the RD receivers
97 to provide
continuous calibration of the signal reflections.
By way of example, considering a 24-inch pipe and a target axial sample
spacing of 6
mm (0.24 in.), a pulse rate of 390 Hz will yield an axial resolution of 5.1 mm
(0.20 in.). This
pulse rate allows the SH wave 96 to travel approximately 4.25 times around the
pipe
circumference before the second pulse or tone burst is fired. Consequently,
the remnants of
the first pulse are between the receiver coils 97, 98 and therefore have no
affect on the
receiver coils 97, 98 located on the opposite side of tool body 21 within that
circumferential
ring at the sampling time interval (gate).
The SH waves 96 are still within the receiver gates during the third tone
burst, after
the wave 96 has traveled about 8.5 times around the pipe. Using an attenuation
factor of 0.8
in 2 feet of travel (a factor determined from lab experiments), a tone burst
transmitted at 100
percent full scale has an amplitude of less than 0.3 percent when it arrives
at the receiver
coils 97, 98 located on the opposite side of the cylindrical tool body 21.
This amount of
noise is usually negligible compared to other sources of noise, e.g., thermal
electronic noise,
which can be as much as 3 percent of full scale.
Coating disbond is detected in the targeted sampling zones Z between RD
receiver
coils 97 and RA receiver coils 98 which are located in-line with the
transmitter coils 95.
Coating disbond detection may be accomplished by computing the ratio of the
gated receiver
CA 02708387 2016-09-02
signals. Ratios that are above a set threshold indicate a lack of coating or
disbond on the pipe
in a particular zone 99.
In studies conducted by the inventors, a sensor array 90 made according to
this
invention has shown the following benefits over the prior art:
= improved sensitivity to small defects, i.e., up to 20 db increase in signal
amplitude;
= substantial decrease in RF pulser power requirements;
= full circumferential inspection coverage, reducing the probability of
missing
cracks;
= self-calibration of the transmitted signals using the receiver coils closest
to
transmitter coils; and
= less interference between transmitter coils caused by acoustic ring
around.
Additional configurations are possible, depending upon the pipe diameter, with
differing numbers of pole magnets 41, 61, sensor coils 95, 97 & 98 and sensor
arrays 90. For
circumferential detection, for example, the sensor array 90 would be rotated
at an oblique
angle i relative to the pipe axis, still being located within the angular
magnetic biasing field
80. In addition to SCC and crack-like features, these configurations could
respond to
features such as coating disbonds and metal loss. The resulting system may
also be used as
an EMAT-only system or combined with any of the various other technologies
available in
in-line inspection tools, including but not limited to MFL, Deformation,
Caliper, and
Mapping.
Figures 1B through 11B show a second embodiment of the invention. Referring
first
to FIG. 1B, a north pole magnet 341 and a south pole magnet 361 are arranged
about 180
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CA 02708387 2016-09-02
opposite one another on a cylindrical tool body 321 so that the respective
longitudinal
centerline 347, 367 of each pole magnet 341, 361 is parallel to the
longitudinal centerline 327
of the cylindrical tool body 321 (and therefore parallel to a central
longitudinal axis of the
pipe being inspected). Although pole magnets 341, 361 differ from prior art
implementations
in that, for example, each magnet 341, 361 extends along the entire length of
the cylindrical
body 321, their axial orientation as illustrated here is typical of prior art
implementations.
Arranged in this way, pole magnets 341, 361 generate a circumferential or
transverse
magnetic field relative to the pipe wall¨as illustrated by magnetic flux paths
381¨and
multiple magnetizer sections are required to provide complete coverage of the
internal wall
surface of the pipe.
Referring now to FIGS. 2B to 6B, an oblique magnetizer assembly 320 according
to
this invention includes a magnetic circuit 340 that has two spiraled pole
magnets 341, 361
arranged about 1800 opposite one another on cylindrical tool body 321. Each
pole magnet
341, 361 extends between a first end 323 and second end 325 of the cylindrical
tool body
321. Additional pairs of spiraled pole magnets 341, 361 may also be employed,
with each
spiraled pole magnet 341 or 361 extending between the ends 323, 325 of
cylindrical tool
body 321 and spaced 360 /n from its adjacent and opposite pole magnet 361, 341
("n" being
an equal to the number of pole magnets 341, 361 employed). The pole magnets
341, 361
preferably have a flexible or conformable upper surface 349, 369,
respectively, that helps
reduce friction forces and minimize velocity effects as the oblique magnetizer
assembly 320
travels through the interior of a pipe. The conformable upper surface 349, 369
also allows
the magnetizer assembly 320 to compress a sufficient amount in order to pass
by internal
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CA 02708387 2016-09-02
obstructions, bends, and reductions in the pipe that might otherwise damage
the magnetizer
assembly 320 or slow or prevent its passage.
The rotation amount of the pole magnets 341, 361 depends on the amount of
rotation
required to achieve full coverage of the internal pipe wall surface. Going
through the
sequence from FIG. 2B to FIG. 6B, the pole magnets 341, 361 are each rotated
or spiraled in
incremental amounts, for a nominal rotation of about 150 degrees (as
illustrated in FIG. 6B).
When rotated, the second end 345, 365 of the pole magnet 341, 361 is offset by
a
predetermined angle or amount a relative to its respective first end 343, 363
(see FIG. 7B).
Because of this rotation amount a, the respective longitudinal centerline 347,
367 of each
spiraled pole magnet 341, 361 is non-parallel to the central longitudinal axis
327 of the
cylindrical tool body 321. The rotation of pole magnets 341, 361 also helps
induce a
sufficient amount of rotation of magnetizer assembly 320 as it travels through
the interior of
the pipe.
FIG. 8B illustrates the magnetic field 380 generated from a prototype of
oblique
magnetizer assembly 320, which was configured similar to the magnetizer
assembly 320
shown in the rotation sequence of FIGS. 2B to 6B. Unlike prior art in-line
inspection tools,
the direction of magnetic field 380 is diagonal or oblique to the pipe axis
rather than
circumferential or transverse, with magnetic flux paths 381 emanating from the
poles 341,
361 and traveling in opposite directions to reach a corresponding pole 361,
341. The
magnetic flux lines 381 generated by each pole magnet 341, 361 are guided to
the path of
least resistance: into the pipe wall and toward the adjacent pole magnet 361,
341. The angle
of the magnetic field 380 is generally perpendicular to the flux lines 381
formed by the
magnetic poles 341, 361 and generally parallel to a line forming the shortest
distance
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between the magnet poles 341, 361. The direction of magnetic field 380 within
the extents of
poles 341, 361 may range from 330 to 360 degrees relative to the pipe axis.
Referring now to FIGS. 9B & 10B oblique magnetizer assembly 320 may include a
helical-shaped sensor array 390 located substantially equidistant between
rotated pole
magnets 341, 361 and arranged to provide complete coverage of the internal
wall surface W
of pipe P and accommodate any rotation of magnetizer assembly 320 that may
take place.
The individual sensors in sensor array 390 may be of a kind well-known in the
art for
detecting magnetic flux leakage signals. Sensor array 390 preferably extends
between the
first end 323 and second end 325 of cylindrical body 321 (and therefore
between the
respective ends 343, 345 and 363, 365 of pole magnets 341, 361) and
incorporates a degree
of overlap A between a first end 391 and second end 393 of sensor array 390.
The
conformable upper surfaces 349, 369 of the pole magnets 341, 361 (see e.g.
FIG. 6B) may be
in the form of brushes 351, 371. Radial discs 331A & B help propel and center
magnetizer
assembly 320 as it moves forward in pipe P under differential pressure.
The final configuration of oblique magnetizer assembly 320 may include any
current
combination of data sets, including but not limited to deformation, high level
axial MFL,
internal/external discrimination, inertial data for mapping, and low level or
residual MFL. In
one preferred embodiment of an inline inspection tool 310 incorporating
oblique magnetizer
assembly 320, the tool 310 includes an axial magnetizer 400 and a deformation
sensing
section 410 (see FIG. 11B).
While an EMAT tool and a MFL tool that includes an oblique magnetizer and
helical
sensor array has been described with a certain degree of particularity, many
changes may be
made in the details of construction and the arrangement of components. An EMAT
tool
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CA 02708387 2016-09-02
according to this disclosure, therefore, is limited only by the scope of the
attached claims,
including the full range of equivalency to which each element thereof is
entitled.
