Note: Descriptions are shown in the official language in which they were submitted.
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A N~N-INVASIVE 8Y8TEM AND METHOD FOR IN8PECTION OF VALVES
Background of the Invantion
This invention relates to valves and more
particularly to a non-invasive system and method for the
inspection of valves.
It may be explained here that generally a
check-valve includes a housing and a movable element
mounted in the housing for movement between an open
position and a closed position and intermediate positions
between the open and closed positions. The check-valve
operates by allowing flow in one direction when the movable
element i5 in the open position while preventing flow in
the other when the movable element is in the closed
position. The check valve has no external moving parts and,
therefore, the position of the movable element and its
integrity cannot be evaluated with normal visual inspection
methods without valve disassembly.
Failures of a few check valves in applications
directly related to a safe shut down of a nuclear powered
electrical generating unit during nuclear power plant
operations led to a review of all check valve maintenance
actions and failures. INFO (Institute of Nuclear Power
Operations) published the results of the review in a
Significant Operating Experience Report (SOER) No. 86-03
entitled "check valve Failures or Degradation" in October,
1986. The conclusions of this report were that the major
causes of check valve failures were primarily due to
misapplication and inadequate preventative maintenance.
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As a result of INFO's SOER 86-03, the electric
industry worked with EPRI (the Electric Power Re~earch
Institute) and formed a program to address the needs of the
industry. In 1988, EPRI issued a report entitled
"Application Guidelines for Check Valves in Nuclear Power
Plants." The EPRI report provided guidelines recommending
the use of non-invasive inspection techniques to verify
proper operation of check valves.
Currently, inspection of check valves is
generally accomplished by the disassembly of the valve and
visually inspecting the internals. There is a very limited
use of non-invasive inspection techniques consisting of
ultrasonic, acoustic or, to a limited extent, magnetic
techni~ues. Acoustic techniques involve the detection of
structural-borne noise, i e. acoustic energy or -~ibrations,
emanating from the internal workings of the valve. The
acoustic technigue generally employs a piezoelectric
crystal sensor, such as an accelerometer, mounted on the
valve housing. All structural-borne acoustic energy waves
or vibrations are detected by the acoustic sensor and
converted by it to electric analog voltage signals or data
representative of acoustic energy. The data is recorded
and then analyzed in an attempt to diagnose which internal
valve condition the data is indicating.
Although the indications of various conditions
and/or "problems" within the valve can be detected as
vibrations by the acoustic sensor, the interpretation of
the data as to which problem the acoustic energy or
vibrations is indicating is difficult. For example, it is
difficult at times, to differentiate betweenvibrations
caused by impacts between worn parts and impacts which are
expected in normal operation of the valve, i.e., impacts
which occur upon the opening and closing of the valve.
Also vibrations created by impacts caused by worn parts as
the movable element fluctuates between open and closed
positions can be misinterpreted as vibrations created by
impacts caused by the movable member striking the valve
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housing or a valve stop in its fully opened position. It
is also possible for the entire movable member to be
missing with just the mounting arm which mounts the movable
member to the housing remaining and obtain vibrations and
resulting acoustic signatures in the data that might be
misinterpreted as vibrations of impacts caused by the
movable member striking the valve stop when, in fact, it is
the mounting arm which is striking some portion of the
valve's internal structure.
Magnetic techniques for the inspection of valves
currently relate to systems which provide information
regarding the position of the movable element of the valve.
The magnetic technique involves the use of a permanent
magnet mounted on the movable element to provide a varying
magnetic field as the position of the movable element
changes. A magnet field sensor is used to measure the
magnetic field strength from a point outside the valve. As
magnetic field strength changes, the sensor will indicate
the position of the movable element. knowing the position
of the movable element permits limited diagnostic
evaluation of check valves. For example, a fluctuating
movable element will be evident using the magnetic
technique. Proper seating of the movable element upon
closure, however, would not be evident using magnetic
techniques although the position of the movable element
would indicate closed. Also, and more importantly, worn
internal parts would not be evident using magnetic
techniques.
Because of these and other difficulties
associated with check valve inspection technigues presently
employed, there now exists a need and a strong demand for
an economical, viable means for the non-invasive inspection
of check valves to verify proper operation without the
disadvantages of the current inspection techniques.
3s ~ummary of the Invention
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It is a primary object of the present invention
to provide a non-invasive system and method for the
inspection of valves which comblnes acoustlc and magnetic
techniques in response to, and in satisfaction of, the
aforementioned need and strong demand experienced in actual
practice. For this purpose, the invention provides a
non-invasive inspection system for a valve of the type
including a housing and a movable element mounted in the
housing for movement between an open position and closed
position and intermediate positions between the open and
closed positions. First means are provided for both
detecting acoustic energy in the valve during an inspection
interval and generating data representative of the detected
acoustic energy. Second means are provided for both
detecting signals indicative of the position of the movable
element during an inspection interval and generating data
representative of the detected signals. Third means are
provided which are coupled to the first and second means
for simultaneously receiving the data generated by the
first and second means.
In accordance with another aspect of the present
invention, a non-invasive method of inspecting a valve of
the type having a housing and an internal element mounted
in the housing for movement between open and closed
positions and intermediate positions between the open and
closed positions is provided. The method comprises the
steps of: detecting acoustic energy in the valve during an
inspection interval and generating data representative of
the detected acoustic energy; detecting signals indicative
of the position of the movable element during an inspection
interval and generating data representative of the detected
signals; recording the data generated for subsequent
analysis and/or processing the data generated to place the
data generated in a form for analysis whereby to detect
various conditions within the valve.
Still another aspect of the invention is the
provision of a dual sensor. The dual sensor comprises in
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combination: a container; first m~ans disposed in the
container for both detecting acoustic energy and generating
data representative of the detected acoustic energy; and,
second means disposed in the container for both detecting
magnetic field strength signals and generating data
representative of the detected signals.
The above and other objects, features and
advantages of the present invention will be apparent from
the following detailed description of a preferred
embodiments thereof taken in conjunction with the
acco~panying drawings.
Brief Description of Drawina~
Figure 1 is a cross-sectional, schematic view of
a check valve illustrating its various parts and dual
sensor mounted thereon in accordance with the invention;
Figure 2(a) is an enlarged, fragmentary view of
the dual sensor in accordance with the invention;
Figure 2tb) is a washer assembly designed to
secure a permanent magnet;
Figure 3 is an overall block diagram of the
non-invasive inspection system in accordance with the
inventions;
Figures 4-10 are diagrammatic acoustic and
magnetic tracings useful to explain the system and method
in accordance with the invention;
Figure 11 is a block diagram of the computer
program structure; and
Figure 12 is a flow diagram useful to explain the
analysis of collected data from a check valve.
D~cription of the Preferred Embodiments
Referring now to the drawings and first to
Figure 1, a
so-called "swing check" valve is indicated generally at 10.
The swing check valve is the most common check valve in use
and the system and method in accordance with the invention
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will be described in association with the ~wing check
valve. It i8 to be understood, however, that the ~ystem
and method of the invention applies to all check valves
including the so-called "tilting disk" check valve and the
S ~o-called "lift check" valve.
The swing check valve 10 comprises a valve body
or housing 11 which has a chamber 14 therein and includes
an inlet opening 16 and an outlet 15 which respectively
communicate with
opposite ends of the chamber 14. A movable element or disk
20 is hingedly supported on the housing 12 by hinge arm 22
and hinge pin 24. The disk 20 is disposed in the path of
fluid flow from the inlet opening 16 to the outlet opening
18 and is mounted for pivotal movement about the hinge pin
24, generally toward the outlet opening 18, in response to
fluid flow through the housing 11. The disk 20 is mounted
on the hinge arm 22 by washer 26 and nut 28. Access to the
interior of the valve is provided by means of removable
valve bonnet 30 which is secured to valve housing Il by
bolts and nuts 32 and 34, respectively. Only one of such
bolts and nuts are shown in Figure 1. when the valve is
closed, disk 20 is in engagement with disk seat 36 and when
it is in its fully opened position, disk 20 contacts and
rests against disk stop 38.
From the foregoing, it will be understood that
disk 20 is movable between an open position with disk 20
resting against disk stop 38 and a closed position with
disk 20 in engagement with disk seat 36 and, intermediate
positions between the open and closed positions depending
upon the level of fluid flow from the inlet opening 16 to
the outlet opening 18.
When the check valve 10, as just described, is in
new or "good" condition in a properly designed use or
application, the disk 20 closes tightly against the disk
seat 36 preventing back leakage. when such a "good" valve
opens, tight clearances
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between internal parts prevents relative motion and
exce6sive wear cond~tions. Also, the valve dlsk assembly,
i.e., the hinge arm 22, disk 20, washer 26 and nut 28, will
contact the disk stop 38 during the opening and should come
to rest on the stop 38.
A valve in "poor" condition, i.e., with internal
damage or in an inadequate design application, may not
close tightly. That is, disk 20 may not close tightly
against the disk seat 36 and back leakage may occur. when
a "poor" valve opens, wear on the hinge pin 24 may cause
the hinge pin 24 to rattle; wear on the hinge arm 22 may
cause the arm 22 to rattle; and/or, wear on the disk nut 28
may cause the disk 20 to wobble. In addition, insufficient
flow of fluid through the valve 10 causes the disk 20 to
fluctuate to positions intermediate fully open and closed
positions continuously and results in excessive wear on the
hinge pin 24. If such fluctuations include the valve disk
assembly striking the valve stop 38, excessive wear will
occur on the disk nut 28 and hinge arm assembly, i.e., the
hinge arm 22, the hinge pin 24 and their respective
associated structures.
As alluded to above, because of recent industry
concerns related to operation of and failures of check
valves, it has become desireable to assure proper valve
performance through non-invasive valve inspection. An
effective inspection technique for check valves should be
able to detect the following conditions: disk position;
wear of internal parts; loose or missing internal parts;
and, disk/disk seat leakage.
With respect to disk position, an effective
inspection technique should be able to determine: stroke
time, i.e., the time for the disk to move from the closed
position to the open position; whether or not the disk is
in the fully opened, fully closed or intermediate position;
flutter of the disk including the magnitude and frequency
of the flutter; and, any contact with the disk seats/stops.
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With respect to wear of internal parts, an
effective inspection technique should be able to determine:
hinge pin/bushing wear; seat/disk facing sur~aces wear;
and, disk to hinge arm connection wear.
With respect to seat leakage, an effective
inspection technique should be able to determine: the
presence of leakage; and, the rate of such leakage.
With an acoustic inspection technique seat
leakage or back-leakage through the closed disk/disk seat
area can be detected because such leakage causes broadband
frequency acoustic energy waves, i.e., vibrations, to be
input to the valve structure as the fluid flows between the
disk/disk seat surfaces. These energy waves are detected by
the acoustic sensor as a continuous energy level higher
than the normal non-leaking condition. Therefore, back
leakage can be detected.
Worn internal parts can be detected by an
acoustic technique because worn internal parts create
abnormal clearances allowing relative motion between those
parts resulting in transient impact acoustic energy waves
being input to the valve structure. These relatively low
energy impacts are detected by the acoustic sensor as the
disk assembly moves. Therefore, worn hinge pins or hinge
arms, and loose, wobbling disks can be detected by acoustic
inspection techniques.
A fluctuating disk that does not contact the disk
stop or disk seat inputs no energy into the valve structure
and, therefore, is not detectable by the use of an acoustic
inspection technique. Once the disk makes contact with the
disk stop, energy waves are impacted into the valve
structure and can be detected by an acoustic inspection
technique. The continued impacting of the disk to disk
stop is discernible as discrete impact signatures with an
acoustic inspection technique. The valve disk closing
against the disk seat is also detectable as the disk
impacts the disk seat. Normal closure is seen as a single
discrete event while valves with worn parts and excessive
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clearance provide signatures that indicate multiple impacts
as the seat wobbles into a steady state condition.
As lndicated above, there are a number of
disadvantages to utilizing acoustic inspection techniques
alone for analyzing check valves. First, although various
indications of condit~ons
within the valve can be detected by the acoustic sensor,
the diagnosing as to which problem or condition the
acoustic signal is indicating is difficult. For instance,
impacts caused by worn hinge pins or hinge arm and several
impacts of the disk to disk stop may be difficult to
differentiate. Also impacts created by worn parts as the
disk fluctuates could be misinterpreted as disk to disk
stop impacting. Another disadvantage with acoustic
inspection techniques, is that no acoustic indication is
available when the disk is fluttering without contacting
the disk stop or disk seat. It is also possible for the
entire disk to be missing with just the hinge arm remaining
and get acoustic signatures that might be misinterpreted as
disk to stop impacting as the hinge arm fluctuates and
impacts the valve internal structure.
In accordance with the invention, acoustic
inspection techniques are coupled with magnetic inspection
techniques in a novel manner to form a non-invasive
inspection system and method that clearly diagnoses
deteriorated conditions within the check valve. Referring
again to Figure l, there is shown at 50 a sensor which
preferably, as shown in Figure 2, takes the form of a dual
sensor comprised of a first means or accelerometer 52 and a
second means or Hall effect generator 54 disposed in a
single container 56. Of course, the accelerometer 52 and
Hall effect generator 54 may be separate elements and be
positioned in spaced
apart relationship on the valve structure. The dual sensor
50 is attached to the valva bonnet 30 with mounting shoe 58
which is threadably received in the bottom of the container
56 of the dual sensor 50. The mounting shoe 58 may be
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attached to the bonnet 30 ~y bonding as, for example, by a
suitable epoxy.
Also shown in Figure 1 is a permanent magnet 60
mounted on the disk 20 for movement therewith with the
North/South axis of the magnet 60 being disposed (North to
South) perpendicular to the disk 20. A magnet with a
strong magnetic field in tçrms of magnetic moment is
preferred. The magnet field strength of the magnet 60
measured at either pole should be greater than 2 kilogauss.
The magnet 60 may be mounted on the disk 20 by, for
example, suitable epoxies, metal putties or welding. As
shown in Figure lb, the magnet 60 may be located in an
opening 62 provided in the washer 26. The magnet 60 may be
located anywhere on the hinge arm/disk assembly for
movement therewith. The placement of the permanent maqnet
60 on the disk 20 or hinge arm 22 will provide a varying
magnetic field as the position of the disk 20 changes. The
magnetic field strength (in Gauss) as measured from a
stationary point outside the valve is proportional to the
position of the disk 20.
The accelerometer 52 may, for example, comprise a
piezoelectric crystal accelerometer and functions to both
detect acoustic energy or vibrations in the valve during an
inspection
interval and generate data in the form of analog voltage
signals representative of the detected acoustic energy.
The Hall effect generator 54 may, for example,
comprise a ceramic crystal such as indium arsinide, which
has a transfer function of MV/Gauss. The Hall effect
generator 54 generates data in the form of analog voltage
signals representative of the detected signals, i.e., the
changing magnetic field strength as the disk 20 and magnet
60 are in motion. The actual millivolt reading obtainPd
from the sensor 54/electronic system (to be described
below) once calibrated would indicate the position of the
disk 20.
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Referring now to Figure 3, an overall block
diagram of the non-invasive inspection system in accordance
with the invention is illustrated. The system comprises
the dual sensor 50 which i8 coupled via leads 70 and 72 to
third means or receiving means shown generally at 74.
Essentially, the receiving means are shown to the right of
the dashed vertical line 73 in Figure 3. The leads 70 and
72 are coupled to the input of a signal conditioner 75.
Signal conditioner 75 comprises gauss meter circuitry which
converts the Hall effect generator output to an electrical
voltage through amplification and filtering, and charge
amplifier circuitry which converts the accelerometer output
to an electrical voltage through charge to voltage
conversion, amplification and filtering.
The signal conditioner 75 may be connected
directly to a recording means or tape recorder 76 or to an
analog to digital converter 78. when the system is used in
the field, the signal conditioner 75 and recorder 76 may be
brought to the location of the check-valve where the sensor
50 would be attached to the valve and the output signals
from the sensor 50 would be recorded for subsequent
analysis. The recorder 76 preferably includes an acoustic
channel having a frequency response of 500 Hz to 10 kHz and
a magnetic channel having a frequency response of 0 to 10
Hz.
At a permanent installation or in the event that
the whole receiving means would be brought to a remote
field location, the data from the dual sensor 50 could be
input directly to the analog to digital converter 78
without first recording the data from the sensor 50.
In either event, the data generated by the sensor
50 is coupled to the analog to diqital converter 78 which
converts the analog voltage output signals generated by
sensor 50 to digital voltage signals suitable for input to
digital signal processing means or computer 80 which
includes a memory 82 for storing data. The computer 20 is
coupled to a display device 84 which provides a display 86
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of data generated by the sensor 50 in a form suitable ~or
analysis. The computer 20 is programmed to scan through
the data input to it and locate significant data according
to a predetermined algorithm. Most preferably the
computer would locate data corresponding to impacts
resulting from fluid flow through the valve or movement of
the movable element or disk 20 and corresponding to the
position of the disk 20 at the time of the internal
impacts.
Progr~m Description
Figure 11 shows a block diagram of the structure
of the program (software system) used for check valve
investigations. The Main Menu 200 is the overall control
mechanism for utilizing the software routines. The
Utilities 202 routine is used for maintenance on the
computer system. Within the Utilities 202 routine would be
system confiquration, backup, file transfer, and DOS
commands. The Display 204 routine contains a series of
software modules used to present data on the screen 86.
These modules include a preview of the data prior to data
storage, data scrolling allowing scanning of data over
relatively long periods of time, zooming capabilities about
a cursor, and a Fast Fourier Transform (FFT) The Data
collection 206 routines receives data from the Analog to
Digital converter 78 and enters it into a file format.
Through the use of previewing the data, storage onto disk
can be accomplished without any analysis of the data. The
Data Base 208 routines contain all valve data taken from
different plants, i.e., remote valve locations, along with
information from the nameplate and tags on the valve. The
Data
Base 205 allows data comparisons between different tests on
the same valve. The Data Analysis 210 routines contain the
methods and calculations required to analyze the data to
determine the condition of the va]ve. These calculations
include time at cursors Cl and C2, acoustic and magnetic
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values at cursors, RMS level between cur60rs, Peak level
between cursors, and FFT between cursors. The Analysis 210
routines also include standard reports that can be output
to a printer (not shown)
S In order to properly analyze check valves with
the acoustic signature, nearly ten seconds of data must be
viewed by the analyst to assure the valve is stable. The
acoustic channel must have an upper limit of frequency
response of 5KHz. The A/D converter 78 must collect 20,000
samples per second to achieve a 5KHz frequency response.
Therefore, 200,000 samples will be collected in the ten
second data collection period. The problem here is that
only 1,000 samples can be displayed at any time with
state-of-the-art computer equipment. Therefore, the
software routines must be able to quickly locate and
present data requiring analysis.
Figure 12 is a flow diagram used to analyze the
data collected from a check valve. Note in Figure 3 that
the screen is divided into two parts 300, the real time
part showing the magnetic and acoustic traces and an
envelop part 111. The ten second data sample is enveloped
to allow the entire ten seconds'
profile 214 to be presented within the envelop section 212
of the display. The first 1,000 samples or 1/200th of the
10 second data sample is presented 302. The real time
acoustic and magnetic traces are displayed (See Figure 3)
The analyst can scan all ten seconds of data by computer
command 302. where in the ten seconds of data the 1,000
samples on the real time display is located, is shown by a
marker 216 under the envelop trace (See Figure 3). This
enables the analyst to quickly focus on pertinent data.
Cursor operation 304 is the tool the analyst uses
to examine the data and determine the condition of the
check valve. With multiple cursors cl and C2, the following
can be accomplished.
Time between impacts
Acoustic RMS level for leak detection
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Peak value between cursors
Magnetic and Acoustic values at cursor
FFT of Acoustic signal between cursor
~ Correlate Acoustic Impacts with Magnetlc trace
Following the analysis, a report 306 can be
generated
to provide a hard copy record.
From the foregoing description and, in accordance
with the invention, it will be understood to those skilled
in the art that the output data of the Hall effect
generator 54 indicates
the position of the disk 20 coincident with the detection
of impacts within the valve or acoustic signatures, i e.,
output data of the accelerometer 52, indicating a valve
condition such as would result from fluid flow through the
valve or movement of the disk 20. As will be further
explained with reference to Figures 4-lO, the knowledge of
the position of the disk 20 at the time of the detection of
an acoustic event provides the necessary discernment
reguired to analyze the diagnostic meaning of the acoustic
events, i e. impacts or vibrations within the valve
structure.
Also from the foregoing, it will be understood
that the receiving means 74 may comprise the recorder 76
for recording the data generated by the dual sensor 50 or
the data processing means which comprises the analog to
digital converter 78, the digital processing means or
computer 80 and the display means 84. The data processing
means processes the data generated by the first means or
accelerometer 52 and second means or Hall effect generator
54 to place the data generated by the accelerometer 52 and
Hall effect generator 54 in a form for analysis.
Referring now to Figures 4-10, these figures are
diagrammatic, acoustic and maqnetic tracings as might
appear on the display 86. Each of the traces comprise or
represent approximately five milliseconds from ten seconds
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of recorded and processed data from the output of the
accelerometer 52 and/or
Hall effect generator 54. The computer 20 has scanned the
data and selected this data for display in accordance with
its program because, for example, the level of the signals
as at 80-96 in the trace 79 of Figure 4 i8 above a
predetermined level. The signals at 80-96 represent
multiple impacts occurring within the valve. Diagnosing
this acoustic signature would indicate several possible
conclusions. The trace of Figure 4 could be indicating
disk 20 to disk stop 38 impacting or disk 20 fluttering
with hinge pin 24 wear or looseness or disk 28 to disk seat
36 impacting or any combination of these. Figure 5 is an
acoustic trace with no apparent impacting. Diagnosing the
trace 98 of Figure 5 could lead to two conclusions. Either
the disk 28 is fluttering with no impacting or the valve
internal parts are not moving. Thus, reviewing the
acoustic-traces of Figures 4 and 5 alone will not provide
complete diagnostics of the internal workings of the valve.
Referring now to Figure 6, which shows the
response of both sensors 52 and 54 to a check valve
closure. On the acoustic trace 100, flow noise is seen to
decrease, as at 102, followed by an impact signature, as at
104, of the disk 20 making contact with the seat 36. This
analysis is confirmed by the magnetic trace 106. The
magnetic signature of the valve closing shows the magnetic
field strength decreasing, as at 108, to the seat or closed
position, as at 110.
Figure 7 shows the response of both sensors 52
and 54 to a check valve closing with several bounces of the
disk 20 and improper valve seating, i.e., closing. The
acoustic signature 112 shows flow noise, as at 114, up to
the point where the disk 20 impacts the seat 36 three
times, as at 116, 118, 120, followed by substantial leak
flow noise, as at 122, indicating either a degraded disk 20
or an improperly seated disk 20. The magnetic trace 124
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shows the disk closing, as at 126, with a bounce signature
present, as at 128 and 130.
Figure 8 shows the response of both sensors 52
and 54 for a check valve opening. The acoustic signature
S 132 begins to show flow noise, as at 134, followed by
impact with the disk stop 38, as at 136, and consequent
flow noise as at 138. The magnetic trace 140 shows the
valve opening, as at 142, with the disk 20 coming to a stop
at the impact with the disk stop 38, as at 144.
Figure 9 shows the response of both sensors 52
and 54 to a valve opening with possible hinge pin wear or
excessive looseness. The acoustic trace 146 shows several
small impact signatures, as at 148, 150 and 152, prior to
the disk 20-to-disk stop 38 impact as at 154. These
precursor impacts, 148, 150 and 152, are a result of
movement due to excessive clearances within the mechanical
assembly of the check valve. This indicates possible hinge
pin wear or excessive looseness. The magnetic
trace 156 shows the valve opening, as at 158, with the disk
20 coming to a stop at the impact with the disk stop 38, as
at 160.
Referring now to Figure 10 which shows the
response of both sensors 52 and 54 to a valve opening. The
magnetic trace 164 shows the disk is unstable causing
excessive fluttering with impacts between the disk 20 and
disk stop 38, as at 166-174. The acoustic trace 176 also
shows such multiple impacts as at 178-186 consistent with
the magnetic trace indicating fluttering.
From the foregoing, it will be understood that a
non-invasive system and method for the inspection of valves
has been provided which can be used to address INFO SOER
86-03 and ASME code In-Service Testing requirements.
Although I have described my invention by
reference to particular illustrative embodiments thereof,
many changes and modifications of the invention may become
apparent to those skilled in the art without departing from
the spirit and scope of my invention. I therefore intend
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to include, within the patent warranted hereon, all such
changes and modifications as may rea60nably and properly be
included within the scope o~ my contribution to the art.
