U.S. patent application number 11/778256 was filed with the patent office on 2009-01-22 for method and device for long-range guided-wave inspection of fire side of waterwall tubes in boilers.
This patent application is currently assigned to Southwest Research Institute. Invention is credited to James F. Crane, Hegeon KWUN, Hirotoshi Matsumoto.
Application Number | 20090021253 11/778256 |
Document ID | / |
Family ID | 40174957 |
Filed Date | 2009-01-22 |
United States Patent
Application |
20090021253 |
Kind Code |
A1 |
KWUN; Hegeon ; et
al. |
January 22, 2009 |
METHOD AND DEVICE FOR LONG-RANGE GUIDED-WAVE INSPECTION OF FIRE
SIDE OF WATERWALL TUBES IN BOILERS
Abstract
Methods and devices for inspecting waterwall tubes for the
detection of fire side damage over a long length of the tube are
described. The system of the invention uses a magnetostrictive
strip and a flat coil-type plate magnetostrictive sensor (MsS) that
are held in place on the waterwall using a specially designed frame
and an electromagnetic circuit. The magnetostrictive strip and
plate type MsS are positioned against a tube in the waterwall using
an elastomeric pad or a fluid filled bladder to achieve close
contact and good mechanical coupling between the magnetostrictive
strip and the tube surface. When current activated, the
electromagnet holds the entire assembly in place and provides a DC
bias magnetic field required for plate magnetostrictive sensor
probe operation. Long-range guided-waves are pulsed into the tube
and reflected signals are detected within the same sensor
structure. The received signal data representative of a long
section of the tube under investigation is then analyzed for the
presence of anomalies and defects. When data acquisition for a
particular tube or tube section is completed the electromagnet is
turned off and the entire device is moved to the next tube in the
waterwall.
Inventors: |
KWUN; Hegeon; (San Antonio,
TX) ; Matsumoto; Hirotoshi; (Nagasaki, JP) ;
Crane; James F.; (San Antonio, TX) |
Correspondence
Address: |
KAMMER BROWNING PLLC
7700 BROADWAY, SUITE 202
SAN ANTONIO
TX
78209
US
|
Assignee: |
Southwest Research
Institute
|
Family ID: |
40174957 |
Appl. No.: |
11/778256 |
Filed: |
July 16, 2007 |
Current U.S.
Class: |
324/238 |
Current CPC
Class: |
G01N 2291/2634 20130101;
G01N 29/226 20130101; G01N 29/265 20130101; G01N 2291/0422
20130101; G01N 2291/044 20130101; G01N 29/28 20130101; G01N 29/2412
20130101; G01N 2291/2695 20130101; G01R 33/18 20130101; G01N 29/043
20130101 |
Class at
Publication: |
324/238 |
International
Class: |
G01N 27/83 20060101
G01N027/83 |
Claims
1. An apparatus for long-range torsional guided-wave inspection of
the fire side of a waterwall tube, the apparatus comprising: a
plate magnetostrictive sensor probe; a frame for positioning the
plate magnetostrictive sensor probe against an external surface of
the waterwall tube; a compressible/expandable bladder positioned
between the frame and the plate magnetostrictive sensor probe in a
manner that directs the magnetostrictive sensor probe against the
external surface of the waterwall tube; and an electromagnet
positioned across the frame in a manner that pulls the frame and
the associated bladder and plate magnetostrictive sensor probe
against the external surface of the waterwall tube.
2. The apparatus of claim 1 wherein the plate magnetostrictive
sensor probe is curved to approximate the outer diameter curvature
of the waterwall tube.
3. The apparatus of claim 1 further comprising a strip of
magnetostrictive material positioned between the plate
magnetostrictive sensor probe and the external surface of the
waterwall tube.
4. The apparatus of claim 1 wherein the electromagnet comprises an
inverted U-shaped core structure having a plurality of extended
feet, wherein the extended feet are structured for direct contact
with the external surface of the waterwall tube under inspection
and at least one adjacent waterwall tube to facilitate the
direction of the magnetic force towards the waterwall tubes.
5. The apparatus of claim 4 wherein the electromagnet core
comprises first and second extended feet directed orthogonal to an
axis of the waterwall tube under inspection so as to extend to make
contact with first and second waterwall tubes adjacent the
waterwall tube under inspection.
6. The apparatus of claim 5 wherein the electromagnet core further
comprises a third extended foot directed parallel to an axis of the
waterwall tube under inspection so as to extend to make contact
with the waterwall tube under inspection at a spaced distance from
a position of the plate magnetostrictive sensor probe, wherein the
three extended feet of the electromagnet core provide a stable
tripod support for the sensor probe against the waterwall
tubes.
7. The apparatus of claim 6 wherein the third extended foot extends
a distance from the electromagnet sufficient to provide a hand grip
to permit the manipulation of the apparatus in its placement on and
removal from the waterwall tubes.
8. The apparatus of claim 4 wherein the extended feet each comprise
curved base surfaces contoured to follow the curvature of the
external surface of the waterwall tubes.
9. The apparatus of claim 1 wherein the compressible/expandable
bladder comprises a closed cell having a flexible wall and
containing a partially compressible material.
10. The apparatus of claim 1 wherein the compressible/expandable
bladder comprises a closed cell having at least one port for
introducing a fluid into, or removing a fluid from the cell, so as
to increase or decrease a fluid pressure within the cell and
thereby increase or decrease a force against the plate
magnetostrictive sensor probe against the external surface of the
waterwall tube.
11. The apparatus of claim 1 further comprising control
instrumentation for activating and de-activating the electromagnet
so as to alternately draw the plate magnetostrictive sensor probe
against the external surface of the waterwall tube or release the
probe from the waterwall tubes.
12. The apparatus of claim 1 further comprising data analysis
instrumentation for directing an interrogation signal from the
plate magnetostrictive sensor probe into the waterwall tube under
inspection and analyzing a reflected signal received back from the
tube.
13. A method for long-range torsional guided-wave inspection of the
fire side of a waterwall tube, the method comprising the steps of:
providing and positioning a plate magnetostrictive sensor probe
over an external surface of the waterwall tube along a portion of a
circumference of the tube; providing and activating an
electromagnet across the plate magnetostrictive sensor probe to
draw and maintain the sensor probe into contact with the external
surface of the waterwall tube; and connecting the magnetostrictive
sensor probe to magnetostrictive sensor instrumentation and
generating and receiving interrogation signals into and from the
waterwall tube under inspection.
14. The method of claim 13 further comprising the step of providing
a strip of magnetostrictive material between the plate
magnetostrictive sensor probe and the external surface of the
waterwall tube.
15. The method of claim 13 further comprising the step of preparing
the external surface of the waterwall tube to provide mechanical
compliance between the plate magnetostrictive sensor probe and the
waterwall tube.
16. The method of claim 14 further comprising the step of
establishing a bias magnetic field within the magnetostrictive
strip to optimize torsional wave magnetostrictive sensor operation
using the activated electromagnet.
17. The method of claim 13 further comprising the steps of:
providing and positioning a compressible/expandable bladder over
the plate magnetostrictive sensor probe; and providing and
positioning a rigid inverted U-shaped frame over the compressible/
expandable bladder and plate magnetostrictive sensor probe.
18. A method for long-range torsional guided-wave inspection of the
fire side of a waterwall tube, the method comprising the steps of:
preparing the external surface of the waterwall tube to provide
mechanical compliance between the waterwall tube and a sensor probe
to be placed in contact therewith; providing and positioning a
plate magnetostrictive sensor probe over the prepared external
surface of the waterwall tube along a portion of a circumference of
the tube; providing a strip of magnetostrictive material between
the plate magnetostrictive sensor probe and the prepared external
surface of the waterwall tube; providing and positioning a
compressible/expandable bladder over the plate magnetostrictive
sensor probe; providing and positioning a rigid inverted U-shaped
frame over the compressible/ expandable bladder and plate
magnetostrictive sensor probe; providing and activating an
electromagnet across the plate magnetostrictive sensor probe to
draw and maintain the sensor probe into contact with the external
surface of the waterwall tube; establishing a bias magnetic field
within the magnetostrictive strip to optimize torsional wave
magnetostrictive sensor operation using the activated
electromagnet; and connecting the magnetostrictive sensor probe to
magnetostrictive sensor instrumentation and generating and
receiving interrogation signals into and from the waterwall tube
under inspection.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to methods and
systems for non-destructive testing and inspection of pipes, tubes,
and other longitudinal cylindrical structures. The present
invention relates more specifically to methods and systems for
accurately positioning long-range torsional guided-wave inspection
sensors on waterwall tubes in boiler structures and the like.
[0003] 2. Description of the Related Art
[0004] Most fossil fuel based power generating systems utilize the
heat released from burning the fuel to convert water to high
pressure steam that is then used to turn a steam turbine connected
to an electrical generator. One of the most efficient ways of
heating water to convert it to steam involves the use of a
waterwall boiler wherein the fuel is burned within a confined
furnace space defined by walls made up of an array of water tubes.
As relatively cool water passes through the tubes it absorbs the
heat from the burning fossil fuel and eventually exits the array of
tubes as steam.
[0005] The most common cause of forced outage of fossil fuel
powered generating units is boiler tube failure. The majority of
these failures occur within the furnace waterwall tubes. Various
damage mechanisms are known to occur that lead to tube failures
through wall loss and cracking. Most of the damage to waterwall
tubes occurs on the fire side of the tube by way of wall thinning
due to corrosion and/or erosion that results from the furnace
exposure and the presence of corrosive gases in the fuel burning
process.
[0006] To prevent or reduce such boiler tube failures during plant
operation, the tubes within such waterwalls are inspected
nondestructively during normal outages, typically using ultrasonic
wall-thickness measurements. Since the boiler waterwall is a very
large structure and ultrasonic wall-thickness measurements are time
consuming, thickness measurements are typically taken at several
points along the height of the wall. Maintenance decisions
regarding the overall condition of the boiler are therefore made
based upon a statistical analysis of the very limited measurement
data. As a result, the reliability of the current decision making
process is less than desired and carries a substantial risk of
error. The reliability of the boiler would be significantly
improved if the condition of the boiler were determined based on
the inspection results of a large portion of the boiler wall, if
not the total boiler wall, rather than results from very limited
measurement points.
[0007] Long-range guided-wave inspection technology is an emerging
technology that has the capability of quickly surveying a large
volume of a structure for defects and providing comprehensive
condition information on the integrity of the structure. Using
relatively low frequency (typically under 200 kHz) guided-waves in
the pulse echo testing mode, this technology performs a 100%
volumetric examination of a large area of a structure and detects
and locates internal and external defects in the area around a
given test position. In exposed, single tube pipelines, for
example, a test range of more than five hundred feet can be
achieved in one direction for detecting 2% to 3% defects from a
given test position. Percent in such examples refers to the
circumferential cross-sectional area of the defect relative to the
total pipe or tube cross-section. The guided-wave inspection
technology, including the magnetostrictive sensor technology
developed at Southwest Research Institute in San Antonio, Tex., is
now widely used for testing piping networks in processing plants
such as refineries, chemical plants, and power generating stations.
The preferred guided-wave mode for pipe or tube inspection is
torsional (T) wave mode.
[0008] For generalized piping inspection, guided-wave probes that
encircle the entire pipe circumference are presently in use. To
install a guided-wave probe for piping inspection, the basic
systems and methodologies require full access around the pipe
circumference with about three to five inches of spacing. When
access is limited to only a portion of the piping circumference,
the long-range guided-wave inspection method is difficult to apply.
Waterwall tubes constructed in boiler furnaces present just such an
environment where access to the full circumference of an individual
tube is not possible. A typical firewall tube might be constructed
from metal components that appear on the outside surface to be an
array of closely spaced parallel pipes when; in fact, they most
often comprise a unitary structure where no space exists between
the pipes forming the wall. An example of a cross-section of a
typical firewall tube structure can be seen in FIG. 1 of the
present application.
[0009] Some efforts have been made in the past to provide sensor
structures and methodologies for their use directed to waterwall
boiler tubes. As indicated above, such inspections are typically
carried out using ultrasonic sensors and methodologies, although
the limited range of such sensors requires sampling techniques to
be utilized during testing. Other efforts in the field have
included those described in the following U.S. Patents:
[0010] U.S. Pat. No. 5,526,691 issued to Latimer et al. on Jun. 18,
1996 entitled Detection of Corrosion Fatigue Cracks in Membrane
Boiler Tubes describes a method for detecting defects and anomalies
in boiler tubes arranged in a panel and associated with a
waterwall. The system utilizes at least one EMAT (Electromagnetic
Acoustic Transducer) coil that generates ultrasonic shear waves at
a predetermined beam angle. The method is alleged to provide a
better signal-to-noise ratio than conventional ultrasonic
techniques and to further eliminate the need for a couplant between
the sensor and the boiler tube.
[0011] U.S. Pat. No. 6,125,703 issued to Mac Lauchlan et al. on
Oct. 3, 2000 entitled Detection of Corrosion Fatigue in Boiler
Tubes Using a Spike EMAT Pulsar describes a further EMAT based
method for detecting damage in ferromagnetic boiler tube structures
using a pair of EMAT coils adjacent the work piece at a non-zero
angle with respect to one another. A spike pulse is applied to one
of the EMAT coils to generate a horizontally polarized shear wave
which is reflected by flaws and defects in the work piece and
subsequently received by the second EMAT coil.
[0012] U.S. Pat. No. 6,497,151 issued to Watts et al. on Dec. 24,
2002 entitled Non-Destructive Testing Method and Apparatus to
Determine Micro Structure of Ferrous Metal Objects describes a
method and apparatus for non-destructively investigating structures
such as cast iron pipes. A sonic wave in induced in the object and
a sensor assembly captures the acoustic signal from the object. The
data analysis system calculates the energy of the acoustic wave or
calculates the time from its initial induction to determine a
nodularity measurement of the metal object.
[0013] U.S. Pat. No. 5,359,898 issued to Latimer on Nov. 1, 1994
entitled Hydrogen Damage Confirmation with EMATs describes a method
and apparatus for confirming hydrogen damage in boiler tubes that
comprises a pair of electromagnetic acoustic transducer coils
(EMATS) that are mounted for movement toward and away from each
other. An electromagnet produces pulses that generate acoustic
waves across a chord and within the wall thickness of the boiler
tube. The sensor is designed to adapt to boiler tubes of different
diameters by mounting the transducer coils in such a manner that
the coils can be pressed against the outer surface of the tubes. In
concert, the angle of the acoustic beam between the coils is
adjusted by changing the frequency of energy applied to the
coils.
[0014] In general, the prior efforts in the field have been
directed to the use of acoustic sensors or EMAT sensors. Very
little effort has been made to create sensor structures appropriate
for directing long-range guided-waves into such pipe walls,
primarily because of the inability to fully encircle the
circumference of the individual pipes. That is, none of the
previous efforts that utilize partial circumferential orientation
have provided suitable sensor adherence structures for long-range
guided-wave inspection purposes. No sensor structures have been
designed that can take advantage of the volumetric inspection
capabilities of long-range guided-waves where access to the entire
circumference of the pipe or tube is restricted. EMAT sensors, such
as described in the above U.S. Patents, are limited in that they
fail to achieve the volumetric inspection capabilities of
long-range guided-waves.
[0015] It would be desirable, therefore, to have a sensor structure
and a method for its implementation, that overcomes many of the
problems of existing sensor structures and the requirement that
they either fully encircle the pipe or tube under inspection or
that they utilize only local point inspection techniques such as
ultrasonics or EMAT technologies.
[0016] In the present invention, systems and methods for inspecting
the fire side of waterwall tubes in boilers, wherein limited access
to the entire circumference of the tube is found, are described.
The systems and methods are built upon existing magnetostrictive
sensor (MsS) methods and devices, particularly the thin
magnetostrictive strip approach (described in U.S. Pat. No.
6,396,262, entitled Method and Apparatus for Short Term Inspection
or Long Term Structural Health Monitoring; U.S. Pat. No. 6,429,650,
entitled Method and Apparatus Generating and Detecting Torsional
Wave Inspection of Pipes and Tubes; and U.S. Pat. No. 6,917,196,
also entitled Method and Apparatus Generating and Detecting
Torsional Wave Inspection of Pipes and Tubes, the disclosures of
which are each incorporated herein in their entirety by reference)
and a flat coil-type plate magnetostrictive sensor (MsS) (described
in U.S. Pat. No. 6,294,912, entitled Method and Apparatus for
Non-Destructive Inspection of Plate Type Ferromagnetic Structures
Using Magnetostrictive Techniques, the disclosure of which is
incorporated herein in its entirety by reference), the structures
of which are held in place on the waterwall tubes under the
influence of an activatable electromagnetic circuit.
SUMMARY OF THE INVENTION
[0017] The present invention therefore describes methods and
devices for inspecting waterwall tubes for the detection of fire
side damage (wall loss due to erosion and/or corrosion as well as
circumferential cracking) over a long length of the tube, in order
to rapidly obtain comprehensive condition information about the
tube without scanning along the entire tube length. The present
invention is a variation of the companion invention disclosure
(entitled Method and Device for Long-Range Torsional Guided-Wave
Inspection of Piping with a Partial Excitation and Detection around
the Pipe Circumference, the subject of co-pending U.S. patent
application Ser. No. (TBA), filed Jun. 25, 2007) but specifically
tailored for waterwall tube applications.
[0018] The system of the present invention uses a magnetostrictive
strip and a flat coil-type plate magnetostrictive sensor (MsS) that
are held in place on the waterwall using a specially designed frame
and an electromagnetic circuit. The magnetostrictive strip and
plate type MsS are positioned against a tube in the waterwall using
an elastomeric pad or a fluid (air or liquid) filled bladder to
achieve close contact and good mechanical coupling between the
magnetostrictive strip and the tube surface. When current
activated, the electromagnet holds the entire assembly in place and
provides a DC bias magnetic field required for plate
magnetostrictive sensor probe operation. Long-range guided-waves
are pulsed into the tube and reflected signals are detected within
the same sensor structure. The received signal data representative
of a long section of the tube under investigation is then analyzed
for the presence of anomalies and defects. When data acquisition
for a particular tube or tube section is completed the
electromagnet is turned off and the entire device is moved to the
next tube in the waterwall. In this manner, a large area of
waterwall may be rapidly investigated in its entirety, rather than
relying on a statistical sample for predicting the overall
condition of the waterwall. Further features of both the system of
the present invention and its method of use will become apparent
from the following detailed description with reference to the
appended drawing figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The accompanying figures will give a fuller description and
better understanding of the details and advantages of the present
invention. The drawing figures appended may be briefly described as
follows:
[0020] FIG. 1 is a perspective view of the sensor assembly of the
present invention positioned in conjunction with the firewall
surface of an array of waterwall tubes.
[0021] FIG. 2 is a perspective view from a reverse viewpoint (from
that of FIG. 1) showing the sensor assembly of the present
invention removed from its placement on the firewall to expose the
various contact components of the assembly.
[0022] FIG. 3 is a signal plot showing torsional wave data obtained
from a tube in a waterwall panel sample using the sensor assembly
and methodology of the present invention.
[0023] FIG. 4 is schematic block diagram showing the basic
mechanical, electronic, and electromagnetic components of the
complete system of the present invention.
[0024] FIG. 5 is a flow chart showing the basic process steps
associated with the methodology of implementing the system of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0025] In general, a preferred method and apparatus for inspecting
waterwall tubes for fire side damage according to the present
invention, may be summarized as follows:
[0026] (a) The placement of a plate type magnetostrictive sensor
(MsS) guided-wave probe on the fire side of a waterwall tube, that
operates in shear-horizontal (SH) wave mode or, equivalently,
torsional (T) wave mode within the tube.
[0027] (b) The mechanical coupling of the probe to the tube and the
launching of a pulse of guided-waves to one side of the probe (such
as upward) along the tube length and the detection of signals
reflected from that side. The process is then repeated to launch
waves to the other side of the probe (such as downward) and detect
the signals reflected from that side.
[0028] (c) The analysis of the received signal data for anomalies
and defects (cracks, fractures, wall-thinning, etc.).
[0029] The various drawing figures briefly described above
illustrate schematically a device for inspecting waterwall tubes
according to the basic features summarized above. The device is
specifically designed to be installed on a waterwall tube and to be
supported thereon by the waterwall tubes adjoining the tube under
inspection. The device uses a magnetostrictive strip (such as
described in U.S. Pat. Nos. 6,396,262, 6,429,650, and 6,917,196
referenced above and incorporated herein) and a flat-coil type
plate MsS (such as described in U.S. Pat. No. 6,294,912 also
referenced above and incorporated herein) that are held in place
under magnetic force from an electromagnetic circuit.
[0030] The magnetostrictive strip and plate type MsS are pressed
against the tube with a bladder or elastomeric material to maintain
close contact and good mechanical coupling between the sensor and
the tube surface. To achieve an appropriate mechanical coupling,
the tube wall will typically require sandblasting or other abrasive
surface preparation in the local contact area. When activated by
the flow of current there through, the electromagnet holds the
entire assembly in place and further provides the DC bias
magnetization required for optimal plate MsS probe operation. When
data acquisition is complete, the electromagnet is turned off and
the whole device is moved to the next tube in the waterwall.
[0031] Reference is made to FIG. 1 for a detailed description of
the structure of the sensor assembly of the present invention and
the manner of its placement and implementation on a typical
waterwall panel. Sensor assembly 10 in FIG. 1 is shown in place on
waterwall panel 12. It is understood that the orientation of
waterwall panel 12 shown in FIG. 1 (i.e., in a horizontal
orientation) may not be typical of structures normally encountered
in place in operational facilities. Typically, a waterwall might be
a vertically oriented panel which provides a primary motivation for
the novel attachment features of the sensor assembly of the present
invention. That is, one of the primary features of the present
invention is the ability to attach the sensor assembly and remove
it easily from a vertical structure without requiring physical
attachment devices to prevent the sensor from falling off of the
vertically oriented wall. It will be understood, however, by those
skilled in the art, that the orientation of waterwall 12 is
irrelevant to the operation of sensor assembly 10 of the present
invention.
[0032] In the example shown in FIG. 1 waterwall panel 12 is
comprised of an array of parallel, closely spaced tubes. Waterwall
tube 14 is the tubular structure that is being subjected to
inspection in the example shown in FIG. 1. Adjacent waterwall tubes
16a and 16b each play a role in supporting the structure of sensor
assembly 10 as described in more detail below.
[0033] Sensor assembly 10 is comprised of a magnetostrictive sensor
assembly (described further below) and a larger electromagnet
assembly 24. Electromagnet assembly 24 is comprised of
electromagnetic coil 26 which surrounds electromagnetic core 28.
Extensions of electromagnetic core 28 comprise support feet 30a and
30b which extend at right angles from the core which passes through
electromagnetic coil 26. These core and support components
preferably comprise metallic or other ferromagnetic materials of
high magnetic permeability, that serve to guide the magnetic field
generated by electromagnetic coil 26 towards the waterwall, and in
particular towards attractive adherence to adjacent waterwall tubes
16a and 16b.
[0034] Also extending from electromagnetic core 28 is balance arm
34 which extends to and is supported by balance foot 32. Each of
the support feet 30a and 30b as well as balance foot 32 comprise
ferromagnetic material such that when electromagnet 24 is activated
an attractive magnetic force towards the waterwall is experienced
at each of the extensions. As shown in FIG. 1 the face of each of
these support structures that is directed toward waterwall panel 12
may have a concave surface that follows the curvature of the convex
surface of the outer wall of each of the tubes that make up
waterwall panel 12 so as to facilitate this stabile positioning of
the sensor assembly 10.
[0035] Positioned within a support frame 36 beneath electromagnet
assembly 24 are the components that make up the magnetostrictive
sensor (MsS) assembly. Support frame 36 is a solid structure that
positions a curved face towards waterwall panel 12 as shown. Within
this curved face is positioned bladder/elastomeric material 22 that
cushions and facilitates the maintenance of close contact between
the MsS and the waterwall panel. Bladder/elastomeric material 22 is
itself a curved structure, and supports a curved plate type
magnetostrictive sensor (MsS) (not seen in FIG. 1 but shown as 20
in FIG. 2) which in turn covers a magnetostrictive strip (also not
seen in FIG. 1 but shown as 18 in FIG. 2). Various electrical wires
and other conductors necessary for the operation of sensor assembly
10 are omitted from FIG. 1 for clarity. These would include wires
directed to electromagnetic coil 26 which may be remotely activated
as well as the sensor signal wires which connect to plate
magnetostrictive sensor 20. These wires would ultimately extend
from sensor assembly 10 and a wiring harness typically with an
intermediate releasable connector extends to control
instrumentation and data analysis instrumentation as described in
more detail below.
[0036] Balance arm 34 further provides a convenient mechanism for
manipulating sensor assembly 10 during its placement against and
removal from waterwall panel 12. A technician might conveniently
grasp balance arm 34 and hold sensor assembly 10 in place on the
appropriate waterwall tube while activating electromagnet assembly
24. The magnetic field created by electromagnet core 28 would
thereafter serve to adhere sensor assembly 10 to waterwall panel 12
while testing occurs. When testing is completed, the technician
could once again grasp balance arm 34 and de-activate electromagnet
assembly 24 to permit the easy removal of sensor assembly 10 from
waterwall panel 12 and the replacement of the same on an adjacent
waterwall tube.
[0037] Reference is now made to FIG. 2 for a brief description of a
view of sensor assembly 10 removed from its placement on a
waterwall panel. In this reverse view, the structure and placement
of magnetostrictive strip 18 in conjunction with plate
magnetostrictive sensor 20 is shown. These sensor components are
positioned on and supported by bladder/elastomeric material 22
which itself is supported by sensor support frame 36 which is a
rigid curved frame structure positioned beneath electromagnet
assembly 24. In this view, balance arm 34 is shown to extend from
electromagnetic core 28 to form a tripod assembly in conjunction
with support feet 30a and 30b which also extend from electromagnet
core 28. Once again, the appropriate electronic/electrical cabling
associated with operation of the sensor assembly is not shown in
the view in FIG. 2 for clarity.
[0038] Reference is now made to FIG. 3 for an example of typical
signal data acquired with the sensor apparatus and methodology of
the present invention. FIG. 3 represents a signal plot showing 150
kHz T-wave (torsional wave) data obtained from a tube in a
waterwall panel sample using the method of the present invention.
The data shown in FIG. 3 was obtained by placing a plate type
magnetostrictive sensor probe near one end of the tube that was
approximately 3 feet long and 2 inches in outside diameter. The
tube had a typical 0.28 inch wall thickness. The defect established
in the tube was a circumferential notch that was approximately 0.6
inches long and 0.11 inches deep at its maximum depth. FIG. 3 shows
the signal representative of the initial pulse 50 as well as a
return signal representative of the far end 52 of the tube. The
defect return signal 54 is seen in the signal plot in FIG. 3 as
clearly distinguishable from the balance of the intermediate signal
amplitude. The signal plot shown as amplitude versus distance
includes, as known in the art, a correlation between signal timing
and distance from the signal source based upon the velocity of the
signal within the material of the waterwall tube.
[0039] It has been observed experimentally that the generated
guided-waves, once launched, not only propagate along the tube on
the side on which the MsS probe is placed, but also spread out,
through the web between the tubes, into the backside of the tube as
well as into the adjacent tubes. However, the amount of wave energy
transmitted to the backside and the adjacent tubes through the web
is shown to be small relative to the wave energy in the probe side
of the tube under testing. Therefore, the invented method primarily
inspects the fire side of waterwall tubes and the return signal can
be identified as reflective of the condition of the tube to which
the sensor assembly is specifically fixed.
[0040] The inspection range over which defects can be detected
depends on the wave frequency and the actual condition of the tube
under testing. Generally, however, a 30 to 50 foot inspection range
may be achieved in one direction using 100 kHz waves. Since both
sides of the probe can be inspected from a given probe location,
the entire length of a tube in a waterwall may be inspected from a
single testing location.
[0041] Reference is now made to FIG. 4 for a brief description of
the overall system of the present invention and the functional
connections between the various components required to carry out
the methodology of the invention. In FIG. 4 waterwall panel 12 is
represented as the base structure onto which the sensor assembly 10
(dashed outline) is placed. Sensor assembly 10 is again made up of
magnetostrictive strip 18 that forms the contact surface with
waterwall panel 12. Plate magnetostrictive sensor 20 is positioned
in close proximity to magnetostrictive strip 18 and is supported by
bladder/elastomeric material 22. Electromagnet assembly 24 is
positioned over the balance of sensor assembly 10 and serves to
establish adherence of the sensor assembly to waterwall panel 12 as
well as providing the bias magnetic field for optimal sensor
operation. In the present application, electromagnet assembly 24 is
preferably a DC electromagnet so as to provide a static magnetic
field, both for purposes of adherence to the waterwall and the bias
magnetic field.
[0042] Connections between sensor assembly 10 and the balance of
the instrumentation associated with the present invention are also
disclosed in FIG. 4. Activation and de-activation of electromagnet
24 is carried out by directing current flow through the coils
therein by way of electrical conductors 60 which extend to control
instrumentation 70. Plate magnetostrictive sensor 20 is operable
through electrical conductor/signal line 64 which connect to data
analysis instrumentation 74 for the system.
[0043] Bladder/elastomeric material 22 has been described
alternately as either a resilient material or an inflatable air or
fluid bladder, each of which would facilitate the maintenance of
close contact between the magnetostrictive sensor and the waterwall
panel. In the embodiment utilizing an air bladder (or fluid
bladder) it would be possible and advantageous in certain
environments to vary the force exerted by the bladder onto the
magnetostrictive sensor components. Reference to "fluid" herein in
connection with the bladder will be understood to include both air
(gas flow) and liquid. Control of this force could be carried out
through the use of a connected port in bladder 22, a connecting
pressure line 62, and an appropriate pressure control system 72
that would direct air or fluid into bladder 22 or allow such air or
fluid to be released from bladder 22 to vary the force. Control
over this functionality could likewise be integrated into control
instrumentation 70. As described above, all of the system
components associated with sensor assembly 10 are integrated into a
handheld device that adheres itself to the waterwall panel. A
connecting harness comprising the connecting lines shown in FIG. 4
would extend from the sensor assembly to the instrumentation of the
system.
[0044] Reference is finally made to FIG. 5 for a brief description
of the method steps associated with implementation of the system of
the present invention. As indicated above, some variations in the
methodology will result from structural variations in the
configuration of the waterwall panel and the tubes under
inspection. In general, however, the process involves preparing the
surface of the fire side of the waterwall and providing the
apparatus of the present invention to be placed into contact with
the tube surfaces within the waterwall.
[0045] The process as described in FIG. 5 therefore begins at Step
102 in which a tube surface on the fire side of the waterwall
section to be inspected is prepared as by sandblasting or otherwise
exposing a contact surface. Step 104, shown in FIG. 5 as being made
up of a sequence of steps, collectively defines the step of
providing the MsS probe assembly. This step of providing the probe
initially comprises, at Step 106, the provision of the Ms strip
that is ultimately positioned on the prepared surface of the tube
along an arc section of the outer circumference of the tube. Over
the Ms strip is positioned, at Step 108, a curved plate MsS probe
(flat coil type) and, at Step 110, a compressible/expandable
bladder.
[0046] At Step 112, a rigid U-shaped frame is positioned over the
compressible/expandable bladder and plate MsS probe. As the final
step in providing the sensor probe assembly, an electromagnet is
positioned over the MsS and frame at Step 114 to draw the probe
assembly against the tube surface. It is anticipated that the
radius of curvature associated with the individual boiler tubes
within a specific waterwall, would directly determine a similar
radius of curvature for the Ms strip, the MsS, and the U-shaped
frame holding the assembly. The bladder/elastomeric material serves
to compensate for modest variations in these curvatures to assure
optimal contact with the tube surface.
[0047] Once the provided MsS Probe Assembly has been magnetically
drawn against the tube surface, then at Step 116, the electromagnet
serves to establish a baseline magnetic field within the tube to
optimize signal sensitivity. Finally, at Step 118, the MsS probe
assembly is connected to appropriate MsS instrumentation (as shown
in FIG. 4) and interrogation signals (in the form of T-waves as
described above) are directed into the tube and reflected signals
are received back for analysis.
[0048] Although the present invention has been described in terms
of the foregoing preferred embodiments, this description has been
provided by way of explanation only and is not intended to be
construed as a limitation of the invention. Those skilled in the
art will recognize modifications of the present invention and its
methods of use that might accommodate specific cylindrical pipe or
tube waterwall structures and even specific boiler configurations.
Such modifications as to waterwall structures or sensor structures
where such modifications are merely incidental to the specific NDE
environment do not necessarily depart from the spirit and scope of
the underlying invention. As indicated above, it is anticipated
that variations in tube diameters would require corresponding
variations in the curvature of the contact components described
(although various standard sized waterwall tube diameters are known
in the art).
[0049] The methodology may also differ with variations in boiler
configuration. Some boilers may require no more than a single
placement of the apparatus of the present invention against a
specific tube while other larger boilers might benefit from
multiple placements at progressive locations along a single tube.
Here again, such variations in methodology do not depart from the
spirit and scope of the invention.
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