U.S. patent application number 13/509779 was filed with the patent office on 2013-09-12 for electromagnet inspection apparatus and method.
This patent application is currently assigned to INNOSPECTION GROUP LIMITED. The applicant listed for this patent is Andreas Boenisch. Invention is credited to Andreas Boenisch.
Application Number | 20130234701 13/509779 |
Document ID | / |
Family ID | 41509417 |
Filed Date | 2013-09-12 |
United States Patent
Application |
20130234701 |
Kind Code |
A2 |
Boenisch; Andreas |
September 12, 2013 |
ELECTROMAGNET INSPECTION APPARATUS AND METHOD
Abstract
A method and apparatus for the inspection of electrically
conductive components is described. The described apparatus
comprises a sensor module having a magnetiser unit suitable for
generating a variable DC magnetic field within the test component
and an eddy current probe. The variable DC magnetic field and eddy
current probe are configured to perform a partial saturation eddy
current test upon the test component. The eddy current probe
further comprises a magnetic field sensor that provides a means for
measuring the permeability within the test component. Employing the
magnetic field sensor provides apparatus that is more accurate and
flexible in its modes of operation since such sensors provide a
means for the actual permeability of a material being tested to be
measured. The described methods and apparatus find particular
application in the inspection of tubular components used in the oil
and gas exploration and production industries.
Inventors: |
Boenisch; Andreas;
(Schwarmstedt, DE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Boenisch; Andreas |
Schwarmstedt |
|
DE |
|
|
Assignee: |
INNOSPECTION GROUP LIMITED
Aberdeen
GB
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20120306483 A1 |
December 6, 2012 |
|
|
Family ID: |
41509417 |
Appl. No.: |
13/509779 |
Filed: |
November 12, 2010 |
PCT Filed: |
November 12, 2010 |
PCT NO: |
PCT/GB10/51892 PCKC 00 |
371 Date: |
August 21, 2012 |
Current U.S.
Class: |
324/239 |
Current CPC
Class: |
G01N 27/82 20130101;
G01N 27/9033 20130101 |
Class at
Publication: |
324/239 |
International
Class: |
G01R 33/18 20060101
G01R033/18 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 16, 2009 |
GB |
0920005.6 |
Claims
1. A sensor module for the non-destructive testing of a component
made of an electrically conductive material, the sensor module
comprising a magnetiser unit suitable for generating a variable DC
magnetic field within the test component and at least one eddy
current probe wherein the sensor module is configured to perform a
partial saturation eddy current test upon the test component and
wherein the at least one eddy current probe comprises a magnetic
field sensor that provides a means for measuring the permeability
within the test component.
2. A sensor module as claimed in claim 1 wherein the magnetic field
sensor is arranged to provide a feedback signal to the magnetiser
unit.
3. A sensor module as claimed in claim 1 wherein the magnetiser
unit comprises a variable DC magnet source.
4. A sensor module as claimed in claim 1 wherein the at least one
eddy current probe is positioned within the sensor module such that
an air gap is provided between the eddy current probe and the test
component when the sensor module is deployed.
5. A sensor module as claimed in claim 4 wherein the magnetic field
sensor is integrated within the eddy current probe.
6. A sensor module as claimed in claim 3 wherein the variable DC
magnet source is mounted between poles of a magnetic yoke.
7. A sensor module as claimed in claim 6 wherein the at least one
eddy current probe is located substantially centrally between the
poles of the magnetic yoke.
8. A sensor module as claimed in claim 1 wherein at least one of
the eddy current probes is flexibly supported within the sensor
module in order to allow them to locate as close as possible to the
test component.
9. A sensor module as claimed in claim 3 wherein the variable DC
magnetic source comprises a rotatably mounted permanent magnet.
10. A sensor module as claimed in claim 9 wherein the rotatably
mounted permanent magnet is rotatably mounted with respect to the
poles of the magnetic yoke.
11. A sensor module as claimed in claim 10 wherein the permanent
magnet is rotatably mounted between the poles of the magnetic yoke
so as to allow the permanent magnet to be moved to a deactivated
position.
12. A sensor module as claimed in claim 10 wherein the magnetiser
unit further comprise pole shoes attached to the poles of the
magnetic yoke.
13. A sensor module as claimed in claim 12 wherein the pole shoes
are shaped so as to assist location of the sensor module with the
component to be tested.
14. A sensor module as claimed in claim 1 wherein the magnetiser
unit comprises an electromagnet.
15. A sensor module as claimed in claim 1 wherein the sensor module
further comprises a suspension mechanism that provides a means for
varying the distance between the eddy current probes and the test
component.
16. A sensor module as claimed in claim 1 wherein the sensor module
further comprises one or more distance sensors that provide a means
for measuring the distance from the sensor module to a first
electrically conductive layer of the test component.
17. A sensor module as claimed in claim 1 wherein the eddy current
probes comprise eddy current coils arranged to operate in a
differential configuration
18. A sensor module as claimed in claim 1 wherein the eddy current
probes comprise eddy current coils arranged to operate in an
absolute configuration.
19. A sensor module as claimed in claim 1 wherein the magnetic
field sensor comprises a Hall sensor.
20. A sensor module as claimed in claim 1 wherein the sensor module
further comprises a data acquisition computer that provides a means
for collating and analysing the signals detected by the at least
one eddy current probe.
21. An inspection tool system for the non-destructive testing of
test components made of an electrically conductive material the
inspection tool system comprising at least one sensor module as
claimed in claim 1.
22. A method for the non-destructive testing of an electrically
conductive test component, the method comprising: measuring a
permeability within the electrically conductive test component;
varying the strength of a DC magnetic field generated within the
electrically conductive test component until the measured
permeability corresponds to a predetermined value; and performing a
Partial Saturation Eddy Current test upon the test component to
evaluate a condition of the test component.
23. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 22 wherein the method
further comprises the step of automatically varying the strength of
the DC magnetic field generated in response to a feedback signal
from the measured permeability within the electrically conductive
component.
24. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 23 wherein the
feedback signal is employed to control the orientation of a
permanent magnet with respect to poles of a permanent magnetic
yoke.
25. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 23 wherein the
feedback signal is employed to control the current provided to an
electromagnet.
26. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 22 wherein the step
of performing the Partial Saturation Eddy Current test upon the
component comprises performing an absolute mode Partial Saturation
Eddy Current test.
27. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 26 wherein the method
further comprises the step of performing a cross reference check
with the measured permeability within the test component when a
defect is detected.
28. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 22 wherein the step
of performing the Partial Saturation Eddy Current test upon the
component comprises performing a differential mode Partial
Saturation Eddy Current test.
29. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 22 wherein the method
further comprises the step of selecting or rejecting the test
component for further use according to the evaluated damage
condition.
30. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 22 wherein the method
further comprises the step of classifying the test component
according to the evaluated damage condition.
31. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 29 wherein the test
component is rejected if a predetermined measured value is exceeded
in the Partial Saturation Eddy Current test.
32. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 22 wherein the method
further comprises the step of generating a report on the condition
of a test component.
33. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 22 wherein the method
further comprises the step of using the evaluation of the condition
of a test component to generate a display to a user.
34. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 22 wherein the method
further comprises the step of using the evaluation of the condition
to create an image of the condition of the test component and
displaying the image to a user.
35. A method for the non-destructive testing of an electrically
conductive test component, the method comprising: measuring a
permeability within the electrically conductive test component;
performing a Partial Saturation Eddy Current test upon the test
component to evaluate a condition of the test component; and
automatically varying the strength of a DC magnetic field generated
for performing the Partial Saturation Eddy Current test in response
to a feedback signal from the measured permeability within the
electrically conductive component.
36. A method for the non-destructive testing of an electrically
conductive test component as claimed in claim 35 wherein the method
further comprises the step of initially varying the strength of the
DC magnetic field generated within the electrically conductive test
component until the measured permeability corresponds to a
predetermined value.
Description
[0001] The present invention relates to non-destructive testing,
and in particular to a method and apparatus for the inspection of
electrically conductive components. Applications of the invention
include the inspection of tubular components used in the oil and
gas exploration and production industries.
[0002] Non-destructive testing techniques are known for the
detection and identification of defects and/or fatigue in the
external wall of tubular components used in the oil and gas
industry, such as casings, production tubing, and pipelines.
[0003] One such non-destructive testing technique known in the art
is eddy current testing (ECT). ECT is based on the principle of
measuring the absolute or relative impedance Z of a probe or sensor
that comprises a conducting coil to which an alternating current is
applied. When the alternating current is applied to the probe a
magnetic field develops in and around the coil. This magnetic field
expands as the alternating current rises to a maximum and collapses
as the current is reduced to zero. If another electrical conductor
(the apparatus to be tested) is brought into close proximity to
this changing magnetic field, electromagnetic induction takes place
and eddy currents (swirling or closed loops of currents that exist
in metallic materials) are induced within the apparatus to be
tested. The eddy Currents flowing in the test material generate
their own secondary magnetic fields which oppose the primary
magnetic field of the coil and thus change the impedance detected
by the probe. This entire process can occur from several hundred
times to several million times each second depending on the
frequency of the applied alternating current.
[0004] In general, the probe is initially balanced on a defect free
area of the apparatus to be tested. The probe is then moved
relative to the apparatus and variations in the probe impedance Z
are recorded. At regions of discontinuities (defects, material
property variations, surface characteristics etc.) the flow of the
eddy currents is distorted and hence a change of the impedance Z is
measured by the probe.
[0005] For ECT techniques the probes can be configured in two
different operational modes referred to as absolute and
differential modes. Absolute probes generally have a single test
coil that is used to generate the eddy currents and sense changes
in the eddy current field as the probe moves over the apparatus
being tested. Absolute coils are generally suited for measuring
slowly varying proprieties of a material. In particular they can be
used for conductivity analysis, liftoff measurements material
property changes and thickness measurements.
[0006] Differential probes have two active coils usually wound in
opposition. When the two coils are over a flaw-free area of test
sample, there is no differential signal developed between The coils
since they are both inspecting identical material. However, when
one coil is over a defect and the other is over good material, a
differential signal is produced. Differential probes therefore have
the advantage of being very sensitive to localised defects yet
relatively insensitive to slowly varying properties such as gradual
dimensional or temperature variations.
[0007] ECT is an excellent method for detecting surface and near
surface defects when the probable defect location and orientation
is well known. However, ECT does have some inherent limitations.
For example the techniques are only applicable to conductive
materials, they require the surface to be tested to be accessible
to the probe, and they are limited in the depth of penetration into
the material being tested that can be achieved.
[0008] Partial Saturation Eddy Current Testing (PSET) is a
particular type of eddy current test. PSET techniques employ
conventional eddy current coils to monitor the impedance levels
within a ferromagnetic material that is being tested. The eddy
current coils are however located between two poles of an
electromagnet and the electromagnet is arranged to apply a DC
magnetic field to the material in the region being monitored by the
eddy current coils. The principle behind the PSET technique is that
when the ferromagnetic material is magnetised by the DC
electromagnet the permeability within the material is changed. When
a defect is present the magnetic field generated by the
electromagnet experiences a higher flux density, analogous to the
situation where a stone is placed in a river causing the water flow
to divert around it. This higher flux density causes a change in
the localised relative permeability and so distorts the induced
eddy current fields in the material which is then detected as a
change of the impedance Z measured by the probe.
[0009] PSET effectively monitors the relative change in the
permeability of a material and so this technique is inherently less
sensitive to gradual material property changes. It is therefore
particularly effective when operated in a differential mode for the
detection of localised discontinuities, such as those caused by
cracks, pits and defects.
[0010] Since PSET is a relative or comparative technique, the
system must be calibrated on reference samples with artificial
damage and defects so as to identify the type and severity of
defect. However, in practice the material of the reference sample
and the test sample may be different. For example, the reference
sample may have a relative permeability of 2,500 H m.sup.-1.
However the inspection pipe may have a relative permeability of
2,000 H m.sup.-1. As a result with conventional PSET techniques the
identified defect often needs to be determined or corroborated by
an alternative NDT technique, for example by ultrasound testing,
since the relative permeability of the pipe is usually not known.
Often this is not a viable option and even when available it is
time consuming and expensive.
[0011] Theoretically, PSET can also be operated within an absolute
mode. However there is a known inherent problem associated with
such tests. When carrying out an absolute mode PSET false hits are
known to occur; i.e. a defect can be indicated when one does not
truly exist. The reason for these false hits is the fact that PSET
readings can be influenced by material property changes. These may
include changes in electrical conductivity or changes in the grain
structure, for example due to the effects of fatigue within the
material. These material property changes affect the relative
permeability of the material which in turn is then detected during
the absolute mode PSET. The absolute mode PSET cannot however
distinguish inherent material property changes from genuine
problems such as wall loss. This is because the PSET does not
directly measure changes in permeability, it only obtains an
apparent change in permeability due the effect this has on the
induced eddy currents. Thus, this apparent change could equally
well be a result of a material property change or a wall loss, or
indeed a combination of the two.
[0012] Theoretically, similar false readings can occur during PSET
operated in a differential mode if the material property change
occurs within a very localised area. However, in reality the
frequency of such false readings is much lower than those described
in relation to an absolute mode of operation.
[0013] One aim and object of aspects of the present invention is to
provide a method and apparatus which overcomes or mitigates the
drawbacks of prior art non-destructive testing techniques. A
further aim and object of aspects of the invention is to provide an
alternative method and apparatus to those proposed in the prior
art. Additional aims and objects will become apparent from reading
the following description.
SUMMARY OF INVENTION
[0014] According to a first aspect of the present invention there
is provided a sensor module for the non-destructive testing of a
component made of an electrically conductive material, the sensor
module comprising a magnetiser unit suitable for generating a
variable DC magnetic field within the test component and at least
one eddy current probe wherein the sensor module is configured to
perform a partial saturation eddy current test upon the test
component and wherein the at least one eddy current probe comprises
a magnetic field sensor that provides a means for measuring the
permeability within the test component.
[0015] In the context of this description, the term partial
saturation eddy current refers to an eddy current testing technique
in which applied magnetic field lines are used in combination with
an eddy current signal. This terminology is known in the art, but
may also be referred to as magnetic biased or DC field biased eddy
current testing.
[0016] The incorporation of the magnetic field sensor allows the
actual permeability of a material being tested to be measured and
so when used in conjunction with the magnetiser unit ensures that
the permeability in the test component matches that of a calibrated
standard. This reduces the reliance on alternative NDT techniques
to be employed to determine or corroborate the test results
obtained by the sensor module so saving on the time and costs
incurred when employing the sensor module. The sensor module also
offers greater flexibility in its modes of operation when compared
with other apparatus known in the art. For example the
incorporation of the magnetic field sensor provides a means for
reducing the occurrence of false readings when the sensor module is
operated within an absolute mode.
[0017] The magnetic field sensor may be integrated within the eddy
current probe. With this arrangement an air gap is provided between
the magnetic field sensor and the test component when the sensor
module is deployed.
[0018] Most preferably the magnetic field sensor is arranged to
provide a feedback signal to the magnetiser unit.
[0019] Employing the magnetic field sensor within a feedback loop
to the magnetiser unit allows for the magnetic field line density
within the test component to be maintained even when the distance
between the sensor module and the test component varies. This
provides for accurate and reproducible results to be achieved on
tests performed on the components, even when they exhibit a variety
of physical dimensions.
[0020] Preferably the magnetiser unit comprises a variable DC
magnet source, which may be mounted between poles of a magnetic
yoke.
[0021] It is preferable for the at least one eddy current probe to
be positioned within the sensor module such that an air gap is
provided between the eddy current probe and the test component when
the sensor module is deployed.
[0022] Preferably the at least one eddy current probe is located
substantially centrally between the poles of the magnetic yoke. The
at least one eddy current probe, or where a plurality of probes is
provided, a subset of the probes may also be flexibly supported
within the sensor module in order to allow them to locate as close
as possible to the test component.
[0023] Most preferably the variable DC magnetic source comprises a
permanent magnet rotatably mounted with respect to the poles of the
magnetic yoke. Relative rotation of the permanent magnet and the
magnetic yoke therefore provides a means for varying the DC
magnetic field generated within the test component.
[0024] The rotatable magnet will allow the magnetic field strength
to be changed. In particular it will also allow switching off of
the magnetisation such that there is no flux through the test
component. This will switch off the attractive force between the
sensor module and the test component. It is important for the
proper handling of the sensor module that the attractive magnetic
force can be switched off.
[0025] The permanent magnet may be rotatably mounted between the
poles of the magnetic yoke so as to allow the permanent magnet to
be moved to a deactivated position. In the deactivated position
there is no, or minimal, DC magnetic field generated by the
permanent magnetic within the test component.
[0026] Alternatively the variable DC magnetic source comprises an
electromagnet.
[0027] The magnetiser unit may further comprise pole shoes, which
may be attached to the poles of the magnetic yoke. Preferably the
pole shoes are shaped so as to assist location of the sensor module
with the component to be tested.
[0028] Preferably the sensor module further comprises a suspension
mechanism that provides a means for varying the distance between
the eddy current probes and the test component.
[0029] The sensor module may further comprise one or more distance
sensors that provide a means for measuring the distance from the
sensor module to a first electrically conductive layer of the test
component. The distance sensors therefore provide a means for
monitoring the thickness of an outer non-conductive material of the
component.
[0030] The eddy current probes may comprise eddy current coils
arranged to operate in a differential and/or an absolute
configuration. The operating frequency range for the eddy current
coils is preferably in the frequency range of 1 to 500 KHz.
[0031] Most preferably the magnetic field sensor comprises a Hall
sensor. The Hall sensors preferably provide a means for measuring
magnetic field strengths between about 0.1 and 0.5 Tesla.
[0032] Preferably the sensor module further comprises a data
acquisition computer that provides a means for collating and
analysing the signals detected by the at least one eddy current
probe.
[0033] According to a second aspect of the present invention, there
is provided an inspection tool system for the non-destructive
testing of components made of an electrically conductive material
the inspection tool system comprising at least one sensor module in
accordance with the first aspect of the present invention.
[0034] According to a third aspect of the present invention there
is provided a method for the non-destructive testing of an
electrically conductive test component, the method comprising:
[0035] measuring a permeability within the electrically conductive
test component; [0036] varying the strength of a DC magnetic field
generated within the electrically conductive test component until
the measured permeability corresponds to a predetermined value; and
[0037] performing a Partial Saturation Eddy Current test upon the
test component to evaluate a condition of the test component.
[0038] The incorporation of the step of measuring the permeability
within the electrically conductive component allows the strength of
the generated DC magnetic field within the electrically conductive
test component to be set so that the permeability within the test
component matches that of a calibrated standard. This reduces the
reliance on alternative NDT techniques to be employed to determine
or corroborate the test results obtained by the sensor module so
saving on the time and costs incurred when employing the described
method.
[0039] Most preferably the method for the non-destructive testing
of electrically conductive components further comprises the step of
automatically varying the strength of the DC magnetic field
generated in response to a feedback signal from the measured
permeability within the electrically conductive component.
[0040] Employing a feedback signal of the measured permeability to
the generated DC magnetic field allows for the magnetic field line
density and hence the permeability within the component to be
maintained throughout the duration of a test. This provides for
accurate and reproducible results to be achieved on tests performed
on the components, even when they exhibit a variety of physical
dimensions.
[0041] Optionally the feedback signal is employed to control the
orientation of a permanent magnet with respect to poles of a
permanent magnetic yoke. Alternatively the feedback signal is
employed to control the current provided to an electromagnet, which
may be located between poles of a permanent magnetic yoke.
[0042] Optionally the step of performing the Partial Saturation
Eddy Current test upon the component comprises performing an
absolute mode Partial Saturation Eddy Current test. In this
embodiment, when the Partial Saturation Eddy Current test detects a
defect a cross reference is made with the measured permeability
within the test component so as to determine whether the detected
defect is a result of a material change within the test component.
Employing this cross reference check reduces the occurrence of
false readings of defects being detected.
[0043] Alternatively the step of performing the Partial Saturation
Eddy Current test upon the component comprises performing a
differential mode Partial Saturation Eddy Current test.
[0044] The method may comprise the additional step of selecting or
rejecting the test component for further use according to the
evaluated damage condition. Alternatively, the method may comprise
classifying the test component according to the evaluated damage
condition.
[0045] The test component may be rejected if a predetermined
measured value is exceeded in the Partial Saturation Eddy Current
test.
[0046] Preferably, the method further comprises the additional step
of generating a report on the condition of a test component. The
method may comprise the additional step of using the evaluation of
the condition of a test component to generate a display to a user.
The method may comprise the additional step of using the evaluation
of the condition to create an image of the condition of the test
component and displaying the image to a user.
[0047] According to a fourth aspect of the present invention there
is provided a method for the non-destructive testing of an
electrically conductive test component, the method comprising:
[0048] measuring a permeability within the electrically conductive
test component; [0049] performing a Partial Saturation Eddy Current
test upon the test component to evaluate a condition of the test
component; and [0050] automatically varying the strength of a DC
magnetic field generated for performing the Partial Saturation Eddy
Current test in response to a feedback signal from the measured
permeability within the electrically conductive component.
[0051] Employing a feedback signal of the measured permeability to
the generated DC magnetic field allows for the magnetic field line
density and hence the permeability within the component to be
maintained throughout the duration of a test. This provides for
accurate and reproducible results to be achieved on tests performed
on the components, even when they exhibit a variety of physical
dimensions.
[0052] Optionally the method further comprises the step of
initially varying the strength of the DC magnetic field generated
within the electrically conductive test component until the
measured permeability corresponds to a predetermined value.
[0053] Embodiments of the fourth aspect of the invention may
comprise preferable or optional steps of the method of the third
aspects of the invention or preferable or optional features of the
first or second aspects of the invention, or vice versa.
[0054] According to a fifth aspect of the present invention there
is provided a sensor module for the non-destructive testing of a
component made of an electrically conductive material, the sensor
module comprising a magnetiser unit suitable for generating a
variable DC magnetic field within the test component and at least
one eddy current probe wherein the variable DC magnetic field and
eddy current probe are configured to perform a partial saturation
eddy current test upon the test component and wherein the at least
one eddy current probe comprises a magnetic field sensor that
provides a means for measuring the permeability within the test
component.
[0055] Embodiments of the fifth aspect of the invention may
comprise preferable or optional steps of the method of the third or
fourth aspects of the invention or preferable or optional features
of the first or second aspects of the invention, or vice versa.
[0056] According to a sixth aspect of the present invention there
is provided a method for the non-destructive testing of an
electrically conductive test component, the method comprising:
[0057] measuring a permeability within the electrically conductive
test component; [0058] varying the strength of a DC magnetic field
generated within the electrically conductive test component until
the measured permeability corresponds to a predetermined value; and
[0059] employing the variable DC magnetic field to perfor a Partial
Saturation Eddy Current test upon the test component to evaluate a
condition of the test component.
[0060] Embodiments of the sixth aspect of the invention may
comprise preferable or optional steps of the method of the third or
fourth aspects of the invention or preferable or optional features
of the first, second or fifth aspects of the invention, or vice
versa.
BRIEF DESCRIPTION OF DRAWINGS
[0061] Aspects and advantages of the present invention will become
apparent upon reading the following detailed description and upon
reference to the following drawings in which:
[0062] FIG. 1 presents a perspective view of a sensor module in
accordance with an embodiment of the invention;
[0063] FIG. 2 presents a schematic representation of the sensor
module of FIG. 1;
[0064] FIG. 3 presents a second schematic representation of the
sensor module of FIG. 1 indicating the eddy currents and magnetic
field lines present during operation;
[0065] FIG. 4 presents a block diagram schematically showing the
interaction of components of the apparatus of FIG. 1 in
overview;
[0066] FIG. 5 is block diagram of a processing system in accordance
with an embodiment of the invention; and
[0067] FIG. 6 is block diagram of a processing system in accordance
with an alternative embodiment of the invention.
DETAILED DESCRIPTION
[0068] FIG. 1 presents a perspective view of a sensor module 1 in
accordance with an embodiment of the invention while FIG. 2
presents a schematic representation of the sensor module 1 located
with a component to be tested 2. The sensor module 1 can be seen to
comprise a DC magnetiser unit 3, an array of eddy current probes 4,
each eddy current probe 4 comprising an eddy current coil 5 with an
integrated magnetic field sensor 6 e.g. a Hall sensor, one distance
sensor 7 and two suspension wheel mechanisms 8. Electronic
connectors 9 are employed to provide power to the sensor module 1
e.g. for the DC magnetiser unit 3, the eddy current coils 5, the
Hall sensors 6 etc.
[0069] Signals detected by the sensor module 1 are transmitted to a
data acquisition computer 10 that is employed to record all of the
eddy current and Hall sensor data. The computer 10 may form an
integrated part of the sensor module 1 or be located remotely.
Transmission of the data may be via hardwiring e.g. via a fibre
optic line or by wireless transmission techniques. A multiplexer
board 11 may be incorporated within the sensor module 1 so as to
provide a means for multiplexing the data from all of the eddy
current coils 5 and the integrated Hall sensors 6 in the array to
respective channels of the data acquisition computer 10.
[0070] The magnetiser unit 3 comprises a permanent magnetic yoke 12
through which the magnetic flux strength can be adjusted. To
achieve this, the magnetiser unit 3 has a permanent magnet 13
located within a rotatable cylindrical barrel 14 that is positioned
between the poles 15 of the permanent magnetic yoke 12. Controlled
rotation of the cylindrical barrel 14 is provided by an electric
motor 16 which is itself preferably controlled by the data
acquisition computer 10.
[0071] By rotating the permanent magnet 13 in the cylindrical
barrel 14, the magnetic field lines can be arranged to be directed
through the poles 15 (when the permanent magnet 13 lies
perpendicular to the orientation of the poles 15) or to be directed
parallel to the poles 15 (when the permanent magnet lies parallel
to the orientation of the poles 15). Thus the magnetiser unit 3 can
be moved between a fully activated position and a deactivated
position, respectively.
[0072] Rotation of the permanent magnet 13 between the fully
activated position and the deactivated position allows for the DC
magnetic field strength generated by the magnetiser unit 3 to be
varied. During operation the position of the permanent magnet 13,
and hence the strength of the magnetic field produced by the
magnetiser unit 3, is controlled automatically by the motor 16 in
conjunction with feedback from the Hall sensors 6 (as described in
further detail below)
[0073] It will be appreciated by those skilled in the art that the
magnetiser unit 3 may comprise a DC electromagnet instead of the
combination of the permanent magnet 13 mounted and the cylindrical
barrel 14.
[0074] Located underneath the poles 15, may be fitted pole shoes 17
that are preferably shaped to locate with the component 2 to be
tested. For example, the pole shoes 17 may exhibit a curved profile
that assists the location of the sensor module 1 upon the outer
surface of a pipe.
[0075] At either end of the magnetiser unit 3 are located the
suspension wheel mechanisms 8. Each suspension wheel mechanisms 8
comprise a pair of rollers 18 mounted upon an adjustable arm 19.
The suspension wheel mechanisms 8 therefore provide a means for
varying the distance between the eddy current probes 4 and the test
component 2. The positional adjustment is provided by means of two
lift-off adjustment mechanism 20. In the presently described
embodiment the lift-off adjustment mechanism comprises a screw
mechanism that allows the distance to be increased or decreased, as
appropriate.
[0076] The distance sensor 7, which may be inductive or capacitive
type sensors, are located on the adjustable arms 19. The distance
sensor 7 provides a means for measuring the distance to the first
metallic layer of the component 2 to be tested. Thus, if the
component 2 comprises an outer non-conductive material e.g.
polyethylene, then the distance sensor 7 provides a means for
monitoring its thickness. This information provides valuable
details of the outer plastic coatings e.g. polyethylene
incorporated within components used in the oil and gas exploration
and production industries. In addition, the measured distance to
the first outer ferromagnetic layer helps determine the actual
distance between the eddy current probes 4 and the test component
2. It will be appreciated by those skilled in the art that
alternative embodiments of the sensor module 1 may comprise a
single distance sensor 7.
[0077] The sensor module 1 is arranged such that the array of eddy
current probes 4 are located centrally between the poles 15, and if
present, the pole shoes 17 of the magnetiser unit 3. In a preferred
embodiment the Hall sensors 6 comprise chips embedded within the
eddy current probes 4. Alternatively the eddy current probes 4 may
be retracted from the plane defined by the poles 15 the permanent
magnetic yoke 12 and optionally flexibly supported in order to run
as close as possible to the surface of the component 2 to be
tested. With both of these arrangements an air gap 21 is provided
between the eddy current probes 4 and the component 2 when the
sensor module 1 is deployed. As a result the Hall sensors 6 provide
a means for measuring magnetic field strength within the air gap
21. Measuring the axial magnetic field component within the air gap
21 allows for the determination of the magnetisation levels within
the test component 2. This is because the parallel component of the
magnetic field is continuous. The larger the air gap 21 however the
more difficult it is to determine the magnetisation levels within
the test component 2. This unique relation is such that if the Hall
sensors 6 are calibrated for a certain magnetisation levels then
the Hall sensors 6 allow for an operator to determine when the same
level of magnetisation is reached within the test component 2.
[0078] The eddy current coils 5 may comprise a Bridge coil system
operated in a differential and/or an absolute configuration or a
send-receive coil system operated in a differential and/or an
absolute configuration. The operating frequency range for the eddy
current coils 5 is preferably in the frequency range of 1 to 500
KHz while the Hall sensors 6 preferably provide a means for
measuring magnetic field strengths between 0.1 and 0.5 Tesla. These
magnetic field strengths correspond to magnetisations levels of up
to 1.6 T within the test component itself.
Operation of the Sensor Module
[0079] The principles of operation of the sensor module 1 will now
be described with reference to FIG. 3. In particular, FIG. 3 shows
the magnetic field line density 22 of the magnetic field generated
by the magnetiser unit 3 and the eddy currents 23 generated in the
test component 2 by the alternating current flowing through the
eddy current coils 5. The basic steps in performing an inspection
with the sensor module 1 are as follows: [0080] employing the
sensor module 1 to measure the permeability within the electrically
conductive test component 2; [0081] varying the strength of a DC
magnetic field generated within the electrically conductive test
component 2 until the measured permeability corresponds to a
predetermined value; and [0082] performing a Partial Saturation
Eddy Current test upon the test component 2 to evaluate a condition
of the test component.
[0083] The first step generally employs the selecting a frequency
and strength for the AC current to drive the eddy current coils 5
so as to provide the most suitable combination for testing of the
component 2. The Hall sensors 6 are then employed to measure the
permeability within the electrically conductive test component
2
[0084] The Hall sensors 6 are again employed in the step of varying
the strength of the DC magnetic field generated within the
electrically conductive test component 2. Since the sensor module 1
is initially calibrated with a reference sample the Hall sensors 6
can be employed to measure the magnetic field line density 22 and,
as described above, effectively provides a measurement of the
permeability within this reference sample. Therefore, when the
sensor module 1 is located on a defect free area of the test
component 2 the DC magnetic field produced by the magnetiser unit 3
can be varied until the magnetic field line density 22, and hence
the permeability within the test component 2, mirrors that used
during calibration process. Since the permeability within the
calibration sample and the test component are now set to be one to
one, then the influence of a defect on the eddy currents 23 will be
the same. The employment of the Hall sensors 6 therefore provides a
means for consistently reproducing results between the calibration
sample and the test components 2. This removes the need for
alternative NDT techniques to be employed to determine or
corroborate the test results and so the time and costs incurred
when employing the sensor module 1 to carry out a NDT is
significantly reduced.
[0085] The step of performing the Partial Saturation Eddy Current
test generally involves the steps of scanning the sensor module 1
over the surface of the test component 2 so as to monitor the
impedance signal detected by the eddy current coils 5 and the
magnetic field strength signals detected by the Hall sensors 6. The
signal detected by the eddy current coils 5 indicated the presence
of defects and both signals can thereafter be analysed so as to
identify the type of defects detected.
[0086] A further advantage of employing the Hall sensors 6 within
the sensor module 1 is that they provide a means for maintaining
the appropriate magnetic field line density 22, and hence the
permeability, within the test component 2 for the duration of a
scan. In reality test components 2 often comprise bends exhibiting
various radii of curvature. As a result it can be difficult to
maintain the thickness of the air gap 21 as the module 1 is scanned
over the test component 2. Other factors which can alter the
distance between the sensor module 1 and the test component 2
include variations in the thicknesses of an outer non-conductive
material. If the distance between the sensor module 1 and the test
component 2 increases the magnetic field line density 22 within the
test component 2 will reduce. In a similar manner, if the distance
between the sensor module 1 and the test component 2 decreases then
the magnetic field line density 22 within the test component 2 will
be increased. In order to maintain the permeability within the test
component 2 the magnetic field strength needs to be increased or
decreased, as appropriate.
[0087] With normal PSET apparatus it is not possible to determine
the level by which the magnetic field strength should be increased
or decreased. However the Hall sensors 6 provide the means for
achieving this functionality since they provide a measurement of
the permeability within the test component 2 and so can be employed
as a feedback to the magnetiser unit 3. In this way the magnetic
field line density 22 can be automatically monitored and controlled
by the Hall sensors 6 and the magnetiser unit 3 so as to maintain
the required level permeability within the test component 2. Thus
the sensor modules 1 can be employed with test components 2 having
a variety of physical dimensions without any noticeable reduction
in the accuracy of the results obtained.
[0088] A further advantage of the incorporation of the Hall sensors
6 is in their ability to reduce the occurrence of false readings,
particularly within the embodiments of the sensor module 1 that
employ probes comprising absolute coils. For example, consider the
situation where the eddy current signal 23 detects an apparent
change in permeability. As discussed previously, this apparent
change in permeability may be due to wall loss or to a material
changes within the test component 2. The Hall sensors 6 provide an
alternative means for detecting permeability changes which result
from change in the material properties itself e.g. electrical
conductivity or changes in the grain structure, due to the effects
of fatigue within the material. By using the results obtained from
the Hall sensors 6 as a cross reference with those detected by the
eddy current coils 5 those permeability changes due to inherent
material changes can be eliminated during the analysis process.
[0089] It will be appreciated by those skilled in the art that one
or more of the above described sensor modules 1 may be incorporated
within an inspection tool system employed for the non-destructive
testing of components made of an electrically conductive
material.
[0090] FIG. 4 shows schematically the interaction 24 of different
components of such an inspection tool. At step 25, once the Hall
sensor 6 has been employed in conjunction with the magnetiser unit
3 to set the required permeability within the test component 2 the
partial saturation eddy current test is performed. Test are carried
out over a surface area of the test component 2 and the measured
data is combined at step 26 in the data acquisition computer 10. At
step 27, the data are analysed in the data acquisition computer 10
and are compared with calibration data held in database 28. The
results of this analysis may be used to directly classify (step 29)
the test component 2, for example indicating that it is suitable or
unsuitable for a particular application. Alternatively, the
classification step 29 may be based on a report at step 30. The
report may be written to a database at step 31. In addition, at
step 32, a display may be generated from the report, for display to
a user. The user, who may be an expert in non-destructive testing
and NDT test data interpretation, may then classify the test
component 2 based on their interpretation of the data.
Alternatively, the expert user may confirm or verify an automatic
classification performed by the inspection tool. The results of the
classification may be stored along with the report data and details
of the test component 2 or particular oil and gas installation
tested.
[0091] FIGS. 5 and 6 are flow charts which show the processing of
the measurement data according to example embodiments of the
invention. In these embodiments, the data processing module 33 is
located within the data acquisition computer 10 which is located
remotely from the sensor modules 1, and is configured to receive
the data transmitted by the sensor modules 1 via a fibre optic
interface 34.
[0092] In the example of FIG. 5, the measurement data are received
in the data processing module 33 from the fibre optic interface 34
and multiplexer board 11. In step C1 the partial saturation eddy
current measurement data are received in the data processing module
33, and the signal phase (step C1-2A) and the signal amplitude
(step C1-2B) are evaluated individually. The analysing algorithm
uses in step C1-2A the signal phase to characterise a type of event
which has been detected in the wall of the component 2, and uses in
step C1-2B signal amplitude as a representation of the order of
magnitude of a detected event. The results are indicated at
evaluation step E1.
[0093] This comparison with calibration data held in database 28
takes place at step V1, and may be used directly to provide an
assessment of the condition of the test component 2. The result of
the comparison is recorded in data storage means at step D1.
[0094] An alternative processing method is shown schematically in
FIG. 6 of the drawings, and is also carried out while using the
sensor module 1 in data processing module 33b. The embodiment of
FIG. 6 is similar to that of FIG. 5, with like steps indicated with
like reference numerals. However, the embodiment of FIG. 6 differs
in that provision is made for an additional evaluation of the test
component 2 by the use of predetermined quality criteria which are
preset into the system as analysis thresholds. An appropriate
number of analysis thresholds S1 to Sn are preset in the data
processing module 33b. At step H1 to Hn, the evaluation results E1
are compared with the analysis thresholds. A signal indication is
output at step K, for example if the analysis threshold has been
exceeded, and indicates that the test object should be rejected. In
step V1-Vn, a visual indication is presented to an operator, and
step D1 to Dn, the analysis results are recorded in the data
storage module 31. In this embodiment, the results of the
evaluation steps E1 may optionally be visually (and/or audibly)
presented to the operator at steps V1-Vn.
[0095] In the method of FIG. 6, the inspection tool is calibrated
before use, by using calibrating test objects. These calibrating
test objects are of substantially the same dimensions and materials
as the components to be inspected. The calibration test objects
comprise artificially-produced instances of damage to the material
with known dimensions. In a preferred embodiment, the calibration
defects are made according to international standards, such as the
specifications of the American Petroleum Institute (API). The test
defects may for example be produced by spark erosion, machining or
drilling. By using calibrated test objects, the sensitivity of the
tool system to the kind of defects which are typically encountered
can be verified. After calibration to the API standards, the
inspection tool may be used for the inspection of components,
including tubular components used in the oil and gas exploration
and production industries.
[0096] The described sensor module provides a number of significant
advantages over the apparatus and methods known in the art. In the
first instance the incorporation of the Hall sensors provides NDT
apparatus that is more accurate and flexible in its modes of
operation since their employment provide a means for the actual
permeability of a material being tested to be measured. As a result
the Hall sensors can be used in conjunction with the magnetiser
unit so as to ensure that the permeability in a test component
matches that of the calibrated standard. This removes the need for
alternative NDT techniques to be employed to determine or
corroborate the test results obtained by the sensor module so
saving on the time and costs incurred when employing the described
apparatus. Indeed there are often environments where such
alternative NDT apparatus cannot be deployed and so in these
circumstances determination or corroboration would simply not be
available.
[0097] Secondly the use of the Hall sensors within a feedback loop
to the magnetiser unit allows for the magnetic field line density
within a test component to be maintained even when the distance
between the sensor module and the test component is altered. This
provides for more accurate and reproducible results on the test
components, even when they exhibit a variety of physical
dimensions, when compared with results obtained from NDT apparatus
known in the art.
[0098] The described sensor module also offers greater flexibility
in its modes of operation when compared with other apparatus known
in the art. For example the incorporation of the Hall sensors
provides a means for reducing the occurrence of false readings,
particularly when the sensor module is operated within an absolute
mode. Thus the described apparatus and methods can be accurately
employed in both absolute and differential mode of operation. The
described apparatus and methods may therefore be readily deployed
for the non-destructive testing of ferromagnetic materials in the
form of single or multiple layer structures e.g. pipes, plates,
vessels (tank floors, vessel plating), steel bridge structures,
flexible risers and steel wire ropes (including power wires).
[0099] The invention provides a sensor module comprising a
magnetiser unit for generating a variable DC magnetic field and an
eddy current probe is described. The apparatus provides a means for
performing partial saturation eddy current tests upon a test
component. A magnetic field sensor is incorporated within the eddy
current probe thus allowing for the permeability within the test
component to be measured. The permeability within the test
component can therefore be matched to that of a calibrated standard
so reducing the reliance on alternative non-destructive testing
techniques to be employed to determine or corroborate the test
results. The magnetic field sensor may also be arranged to provide
a feedback signal to the magnetiser unit thus allowing the magnetic
field line density within the test component to be maintained
during a test. Accurate and reproducible results can therefore be
achieved on test components exhibiting a variety of physical
dimensions.
[0100] A method and apparatus for the inspection of electrically
conductive components is described. The described apparatus
comprises a sensor module having a magnetiser unit suitable for
generating a variable DC magnetic field within the test component
and an eddy current probe. The variable DC magnetic field and eddy
current probe are configured to perform a partial saturation eddy
current test upon the test component. The eddy current probe
further comprises a magnetic field sensor that provides a means for
measuring the permeability within the test component. Employing the
magnetic field sensor provides apparatus that is more accurate and
flexible in its modes of operation since such sensors provide a
means for the actual permeability of a material being tested to be
measured. The described methods and apparatus find particular
application in the inspection of tubular components used in the oil
and gas exploration and production industries.
[0101] The foregoing description of the invention has been
presented for purposes of illustration and description and is not
intended to be exhaustive or to limit the invention to the precise
form disclosed. The described embodiments were chosen and described
in order to best explain the principles of the invention and its
practical application to thereby enable others skilled in the art
to best utilise the invention in various embodiments and with
various modifications as are suited to the particular use
contemplated. Therefore, further modifications or improvements may
be incorporated without departing from the scope of the invention
as defined by the appended claims.
* * * * *