U.S. patent application number 09/815099 was filed with the patent office on 2002-09-26 for leak locator for pipe systems.
Invention is credited to Baumoel, Joseph.
Application Number | 20020134140 09/815099 |
Document ID | / |
Family ID | 25216849 |
Filed Date | 2002-09-26 |
United States Patent
Application |
20020134140 |
Kind Code |
A1 |
Baumoel, Joseph |
September 26, 2002 |
LEAK LOCATOR FOR PIPE SYSTEMS
Abstract
A system and method for determining a time of occurrence of a
pressure wave in a pipe provides a first sonic transducer and a
second sonic transducer at each of a plurality of site locations
along a pipe. Sonic waves are generated through a pipewall at a
rate. At each of the plurality of site locations, the sonic waves
travel from the first sonic transducer to the second sonic
transducer through a liquid flow in the pipe. A measure of travel
time is set for the sonic waves. The measure is compared to each of
the successive travel times for the sonic waves as the sonic waves
arrive at the respective second transducers. A string of counts is
output at each second transducer. Each count includes a first count
value if a present sonic wave has a travel time that is late as
compared to the measure. A time of occurrence of the pressure wave
is determined based on a reference clock when the string of counts
includes a string of first count values longer than a threshold
value. The time of occurrence of a pressure transient is indicated
by a first count in the string of first count values.
Inventors: |
Baumoel, Joseph; (Commack,
NY) |
Correspondence
Address: |
Frank Chau, Esq.
F. CHAU & ASSOCIATES, LLP
Suite 501
1900 Hempstead Turnpike
East Meadow
NY
11554
US
|
Family ID: |
25216849 |
Appl. No.: |
09/815099 |
Filed: |
March 22, 2001 |
Current U.S.
Class: |
73/40.5A ;
73/592 |
Current CPC
Class: |
G01F 1/66 20130101; G01M
3/243 20130101; G01N 2291/02836 20130101 |
Class at
Publication: |
73/40.50A ;
73/592 |
International
Class: |
G01H 003/00 |
Claims
What is claimed is:
1. A method for determining a time of occurrence of a pressure wave
in a pipe, comprising the steps of: providing a first sonic
transducer and a second sonic transducer at each of a plurality of
site locations along a pipe; generating sonic waves through a
pipewall at a rate, the sonic waves traveling from the first sonic
transducer to the second sonic transducer through a liquid flow in
the pipe at each of the plurality of locations; setting a measure
of travel time for the sonic waves; comparing the measure to each
of the successive travel times for the sonic waves as the sonic
waves arrive at the respective second transducers; outputting a
string of counts at each second transducer, each count including a
first count value if a present sonic wave has a travel time that is
late as compared to the measure; and determining a time of
occurrence of the pressure wave based on a reference clock such
that when the string of counts includes a string of first count
values longer than a threshold value, the time of occurrence of a
pressure transient is indicated by a first count in the string of
first count values.
2. The method as recited in claim 1, wherein the first sonic
transducer and the second sonic transducer are included in a
clamp-on flowmeter.
3. The method as recited in claim 1, wherein the step of generating
sonic waves through a pipewall at a rate includes generating sonic
waves through the pipewall at a repetition rate of between about
1000 pulses per second to about 1500 pulses per second.
4. The method as recited in claim 1, further comprising the step of
determining a location of a leak by computing a distance to the
leak from nearby site locations based on the time occurrence, a
sonic velocity of the liquid in the pipe and a measured flow rate
of the liquid in the pipe.
5. The method as recited in claim 1, wherein the step of setting a
measure of travel time includes setting the measure by employing
the travel time of the previously received sonic wave.
6. The method as recited in claim 1, wherein the step of outputting
a string of counts includes outputting a first digital value for
the first count value and outputting a second digital value for
travel times which are earlier than the measure.
7. The method as recited in claim 1, further comprising the steps
of computing a location of the leak by: determining a direction of
travel of the pressure wave in accordance with an arrival of the
pressure wave at adjacent site locations along the pipe; and
calculating a distance from the adjacent site locations to the leak
location.
8. A method for determining a time of occurrence of a leak in a gas
pipe, comprising the steps of: providing a first sonic transducer
and a second sonic transducer at each of a plurality of site
locations along a pipe; generating sonic waves through a pipewall
at a rate, the sonic waves traveling from the first sonic
transducer to the second sonic transducer through a liquid flow in
the pipe at each of the plurality of locations; setting a measure
of sonic conductivity for the sonic waves; comparing the measure to
each of the successive sonic waves for the sonic waves as the sonic
waves arrive at the respective second transducers; outputting a
string of counts at each second transducer, each count including a
first count value if a present sonic conductivity is above the
measure; and determining a time of occurrence of the pressure wave
based on a reference clock such that when the string of counts
includes a string of first count values longer than a threshold
value, the time of occurrence of the leak is indicated by a first
count in the string of first count values.
9. The method as recited in claim 8, wherein the step of
determining includes the step of computing the distance to the leak
from nearby site locations based on the time occurrence, a sonic
velocity of the liquid in the pipe and a measured flow rate of the
liquid in the pipe.
10. The method as recited in claim 8, wherein the step of setting a
measure includes setting the measure by employing an average based
on previously received sonic waves.
11. The method as recited in claim 8, further comprising the step
of providing a synchronization device, which provides
synchronization between the site locations to provide a time
reference for the step of determining a time of occurrence.
12. The method as recited in claim 8, further comprising the steps
of computing a location of the leak by: calculating a distance from
adjacent site locations to the leak location.
13. The method as recited in claim 8, further comprising the step
of correlating distance along the pipe to a map position.
14. A system for detecting pressure transients or sonic
conductivity changes in a length of pipe, comprising: a plurality
of site locations disposed along a pipe, each site location being
disposed a predetermined distance from adjacent site stations along
the pipe; an ultrasonic transducer system coupled to the pipe at
each site location, the ultrasonic transducer system including a
first sonic transducer which generates sonic waves at a rate and a
second sonic transducer which receives the sonic waves; the
ultrasonic transducer system adapted to measure travel times of the
sonic waves between the first and second sonic transducers and
compare the travel times to a measure such that a report of each
sonic wave is determined as late or early as compared to the
measure; and a monitor which records the reports and determines if
a string of late reports greater than a threshold size has occurred
wherein a time of the first report of the string of late reports
greater than the threshold size indicates a time of occurrence of a
leak in the pipe.
15. The system as recited in claim 14, wherein the ultrasonic
transducer system includes a clamp-on ultrasonic transducer system,
which is detachable, coupled to a pipewall of the pipe.
16. The system as recited in claim 14, wherein the rate includes a
repetition rate of between about 1000 pulses per second to about
1500 pulses per second.
17. The system as recited in claim 14, wherein a distance from the
site locations to the leak location is determined based on the time
occurrence and a sonic velocity of liquid in the pipe.
18. The system as recited in claim 14, wherein the measure is set
by the travel time of a previously received sonic wave.
19. The system as recited in claim 14, further comprising a
synchronization device, which provides synchronization between the
site locations to provide a time reference for calculating a
location of the leak.
20. The system as recited in claim 14, wherein a distance from the
site locations to the leak location is determined based on the time
occurrence and a sonic conductivity of a gas in the pipe.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] This disclosure relates to sensing systems and more
particularly, to a system for sensing a location of a leak in a
pipeline system.
[0003] 2. Description of the Related Art
[0004] It is common practice to install liquid and gas pipelines
underground or underwater, both to defeat the possibility of
tampering, and as may be necessary for regulatory or logistical
reasons (e.g., passing under a river). In such cases, when a leak
occurs, the actual source of the leak may not be visible. Under
such a circumstance, remediation of the leak, once detected by
other means, will not be possible until the actual source is
located.
[0005] Since time is of the essence when remediation is required,
to limit the amount of the spill, a system that identifies the
location is essential. Since pipelines can run through difficult
terrain, such as underwater or in jungle areas, knowing the exact
location is a significant factor in permitting fast remediation.
High precision avoids the need for time consuming digging of
substantial amounts of territory to find the leak.
[0006] It is well known that pipelines are under some degree of
pressure, either from the pumping of the gas or liquid, or by the
effect of gravity. Accordingly, when a pipeline ruptures, it is
generally accompanied by the reduction of pressure at the point of
the leak. This generates a low-pressure wave that travels in both
directions, at the speed of sound in the medium, plus or minus the
effect of actual flow rate in the downstream and upstream
directions respectively.
[0007] In pipeline systems, which may extend over many miles or
just a few hundred feet, it is necessary and often imperative to be
able to accurately detect the location of a leak. Leaking pipes may
cause dangerous conditions, or environmental issues if not properly
addressed in an expedient manner.
[0008] In the transport of hydrocarbons, such as oil, leaks may be
detected at monitoring stations, which are distributed at intervals
along the pipeline. Changes in pressure or flow rate are detected
and anomalies are determined to determine leaks in the pipeline.
Pressure changes are determined between monitoring stations;
however, with conventional detection systems when the leak has
first occurred is not known. Accordingly, location of the leak is
difficult to determine with the accuracy needed for a quick
response. With conventional systems, a leak's location can be
determined in a region on the order of hundreds of meters (e.g.,
150 to 200 meters).
[0009] Therefore, a need exists for a system and method for
accurately determining the location and time of occurrence of a
leak in a pipeline system.
SUMMARY OF THE INVENTION
[0010] A system and method which defines the location in a
pipeline, at which a leak has occurred, with very high precision,
using the detection of the low-pressure wave resultant from the
leak is disclosed. The low-pressure wave travels at the speed of
sound in the liquid or gas in the pipeline in both upstream and
downstream directions. Site stations that can detect the arrival
time of the pressure wave are located at opposite ends of the
pipeline segment. The Site Stations detect the arrival time of the
low-pressure wave non-intrusively, and with great precision.
[0011] Transmission of the sensed data to a master station permits
the computation of the location to within the precision permitted
by the time resolution that the low-pressure wave is detected. A
global positioning system (GPS) mapping system is employed to
permit rapid access to the site of the leak by either helicopter,
truck or boat, as may be appropriate.
[0012] A system and method for determining a time of occurrence of
a pressure wave in a pipe provides a first sonic transducer and a
second sonic transducer at each of a plurality of site locations
along a pipe. Sonic waves are generated through a pipewall at a
rate. At each of the plurality of site locations, the sonic waves
travel from the first sonic transducer to the second sonic
transducer through a liquid flow in the pipe. A measure of travel
time is set for the sonic waves. The measure is compared to each of
the successive travel times for the sonic waves as the sonic waves
arrive at the respective second transducers. A string of counts is
output at each second transducer. Each count includes a first count
value if a present sonic wave has a travel time that is late as
compared to the measure.
[0013] A time of occurrence of the pressure wave is determined
based on a reference clock when the string of counts includes a
string of first count values longer than a threshold value. The
time of occurrence of a pressure transient is indicated by a first
count in the string of first count values. The time of occurrence
is employed in accurately calculating the position of a leak, hot
tap or malfunctioning valve, pump, etc.
[0014] These and other objects, features and advantages of the
present invention will become apparent from the following detailed
description of illustrative embodiments thereof, which is to be
read in connection with the accompanying drawings.
BRIEF DESCRIPTION OF DRAWINGS
[0015] This disclosure will present in detail the following
description of preferred embodiments with reference to the
following figures wherein:
[0016] FIG. 1 is a schematic diagram of a pipe system having a leak
detection system installed in accordance with the present
invention;
[0017] FIG. 2 is a cross-sectional view of the pipe system of FIG.
1 showing greater detail of sonic energy waves traveling in the
pipe at a site station in accordance with the present
invention;
[0018] FIG. 3 depicts a time line of signals generated by
transducers of FIG. 2 in accordance with the present invention.
[0019] FIG. 4 shows a plot in accordance with the present invention
indicating one and zero reports to establish when a leak has
occurred;
[0020] FIG. 5 shows a pipeline map which correlates distances with
positions on a pipeline system in accordance with the present
invention; and
[0021] FIG. 6 is a block/flow diagram for a system/method for
determining the time of occurrence of a pressure and/or detecting
leaks in the pipe system in accordance with the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] The present invention includes a system and method for
measuring pressure transients in a flow within a pipe. The present
invention provides a new and very precise way of locating the place
where a leak has occurred on a pipeline, which transports liquids,
such as hydrocarbons or other types of liquid. Advantageously, the
present invention provides a precision of less than several meters,
and preferably, under 1 meter is determining the location of a
leak.
[0023] Referring now in specific detail to the drawings in which
like reference numerals identify similar or identical elements
throughout the several views, and initially to FIG. 1, a pipeline
system 10 is shown in accordance with one embodiment of the present
invention. System 10 includes a plurality of monitoring or site
stations 12a-12d, generally referred to as site stations 12
hereinafter, which monitor occurrences within pipe system 10. In
the embodiment shown, site stations 12 each preferably include a
wide beam transit-time ultrasonic flow meter 14, as described in
U.S. Pat. No. 5,117,698, incorporated herein by reference. Flow
meter 14 may include a clamp-on type, which clamps to an exterior
wall of a pipe 16 to permit flow characteristics to be measured in
pipe 16. Flow meters 14 may be adapted to monitor flow
characteristics at site stations 12.
[0024] Distances of segments A, B, C, etc. as shown in FIG. 1 are
known. This information will be used to locate leaks as will
described below.
[0025] Referring to FIG. 2, clamp-on wide beam transit-time
ultrasonic flow meter 14 includes a set of ultrasonic transducers.
A transducer 20 is employed to transmit wide beam ultrasonic
signals into pipe 16 and flow 24. A transducer 22 is employed to
receive wide beam ultrasonic signals from pipe 16 and flow 24. The
transmitted sonic energy in the form of a wide beam 26 travels
across pipe 16 and is measured by transducer 22. A computer or data
acquisition device 25 may be employed with flow meter 14 to perform
computations to determine flow rates, proportions of the
constituents material of flow 24, storing lookup tables or other
parameters needed to determine characteristics of flow 24.
[0026] A natural mode of sonic energy transmission is excited in
pipe 16, in which a transverse wave 30 travels axially down the
pipe wall at the velocity characteristic of the pipe's material,
and at a frequency dependent on the pipe material and a wall
thickness "t". When such a wave 30 is generated, as it travels down
the pipe wall, wave 30 radiates a sonic wave 32 into the flow 24,
which ultimately reflects off the far wall and reenters the pipe
wall on the same side of the pipe from which is was originally
transmitted. The sonic energy then enters this receive transducer
22 and generates a receive signal.
[0027] Referring FIGS. 1 and 2, one principle of operation for the
present invention is the detection of the change in liquid density
associated with the lowering of pipeline pressure caused by a leak
at, e.g., location 40. This low-density transient wave 41
propagates both upstream and downstream from the point of the leak
at the velocity at which sound travels through the liquid(s). When
these transient waves arrive at an upstream measuring station 12b,
measuring station 12b records the transient with a time resolution
of, e.g., between 1 and 2 milliseconds for a transmission rate of
about 1000 pulses per second.
[0028] Clamp-on ultrasonic flowmeter 14 senses the sonic
propagation velocity of the medium in pipe 16. It does so by
measuring the time that it takes for a sonic pulse 32 to travel
over a known path length through the medium, generally a diagonal
path from the transmitting transducer 20 that reflects diagonally
from the opposite side of the pipe to be detected by the receive
transducer 22.
[0029] Since the sonic velocity of liquid media 24 is dependent on
the density of the liquid, and the density of the liquid is a
function of the pressure, it is seen that detection of a change in
sonic propagation velocity is a means of detecting relative
pressure itself. Accordingly, the clamp-On ultrasonic flowmeter 14
has the ability to sense the change in pressure caused by a leak,
as the pressure wave arrives from the point of the leak, traveling
at the speed of sound, to the location of the flowmeter site
station 12 (FIG. 1). Since it is not required that the site station
measure flow, a freestanding ultrasonic pressure wave detector may
be employed in an alternate embodiment.
[0030] The monitoring of the flow (density) is performed at each
measuring station 12a, 12b, 12c, etc.). Each measuring site station
12 is synchronized by a common clock or synchronization device 15.
For example, synchronization device 15 may include a zero latency
communication system, WWV or global positioning system (GPS)
technology. A synchronizing pulse is sent to or maintained at each
station 12. The common clock signal provides a frame of reference
for a leak detection position as will be described in detail
below.
[0031] It may be seen that any spurious high frequency transients,
whose wavelength is shorter than the sonic beam path length, will
have their effect integrated out of the detection range of the
ultrasonic pressure wave detector of the present invention. Since,
in a pipe of, say, 12 inches diameter, filled with, say, Crude Oil,
the path length is about one meter, and the sonic propagation
velocity can be, say, 1400 meters per second, any spurious wave
with a frequency of higher than about 1400 Hz will be filtered out.
But, since the low pressure wave caused by a pipe rupture will
generally have a rise time of more than 1 millisecond, (an
equivalent frequency of below 1000 Hz), the system described will
be able to detect the transient change of sonic propagation
velocity caused by a leak induced low pressure wave, and be free of
the disruptive effects of anomalous pressure waves endemic to a
pipeline.
[0032] Since the sonic propagation velocity of the liquids of
interest lie in the range of from about 700 to 1500 meters per
second, to locate the leak within one meter would provide that
sensing the arrival of the transient at each of the segment's site
stations 12 with a time resolution of about 1 millisecond.
Accordingly, a site station 12 includes a means of generating a
sonic interrogation pulse into the pipeline at least every
millisecond. On reception of the sonic pulse, it will be determined
how long it took for the pulse to arrive, from the time of its
transmittal.
[0033] In one embodiment, at a repetition rate of about, for
example, 1 to 2 milliseconds, each site station 12 transmits
ultrasonic pulses into the pipe wall by use of wide beam clamp-on
transducer 20. This pulse enters the liquid and travels in such a
way as to ultimately pass through the pipe wall and reflect back to
the side of transducer 22. The pipewall acts as a beam splitter,
splitting the ultrasonic beam between the pipewall and the flow.
Transducer 22 detects the ultrasound pulse and conveys a signal
(receive signal) at site stations 12. The arrival time of the
signal depends on the sonic propagation velocity of the liquid flow
24 in pipe 16. Sonic propagation velocities of sound in liquids are
a function of the liquid's density. Since the arrival of a
low-density wave will lower the sonic velocity measured at the
transducer location, the arrival time of the sonic pulses will be
suddenly extended. The extension of the sonic pulses is employed in
the present invention to accurately determine the time of
occurrence of the leak (or drop in pressure) and the location of
the leak.
[0034] Site station 12 amplifies the received transducer signal and
digitizes its arrival time, e.g., relative to the travel time of
the previously transmitted sonic pulse. A time reference or measure
(see FIG. 3) is established for the arrival time of the signal
prior to the arrival of a low-density (e.g., leak transient) wave.
The reference is created by setting a reference in normal or stable
flow conditions. Thus, when a low-pressure wave arrives, signifying
a leak, site stations 12 are in a position to notice the sudden
delay in arrival time of a received sonic signal.
[0035] The receive signal may have a "marker" embedded in the
receive signal or a portion of the receive signal may be employed
as a reference which is used as a discrete time location to be
compared to a measure value. If the liquid sonic velocity is
changing due to chemical or temperature causes, such density or
sonic velocity changes are much slower than pressure transient
causes, and so the alternate late or early outputs will
occasionally see an extra late or early output to move the window
so as to follow the slow time movement of the signal. The extra
signals can be averaged out over time.
[0036] When a low-pressure transient caused by a leak arrives, the
time of the signal is suddenly changed by an amount dependent on
the actual degree of the pressure of the density change. In such a
case, it will take a number of successive late counts before a new
average value is determined (before the Measure is stabilized)
[0037] Referring to FIG. 3, an example of a late count is shown.
The transmission of sonic wave 32 (FIG. 1) or signal 203 produces a
pipe wall signal 205 (wave 30 in FIG. 1). Envelope 202 breaks a
threshold line 206 at a point 207 beyond a threshold or measure
time (labeled "Measure" in FIG. 3). Site station 12 (FIG. 1)
records the successive late/early counts and divides the counts
into bit words. When a synchronizing pulse arrives at, e.g.,
one-minute intervals, site station 12 transmits these words
sequentially to a master station 44. If there are 1,000 transmit
pulses per second, in one minute there will have been 60,000
transmit pulses at the time that the next synchronizing pulse
arrives. This provides that, at a 16-bit word density, 3750 16-bit
bytes are be transmitted to master station 44.
[0038] A threshold line 206 in FIG. 3 or other reference may be
employed to define a position where signal 204 first arrived. The
beginning of this sloped line or "cusp" marks the arrival time of
the low-pressure wave in this example, however other references may
be selected.
[0039] Wide beam ultrasonic transducers 20 and 22 of FIG. 2 operate
as exciters of the pipe's sonic waveguide properties. These are
dependent on the pipe's wall thickness and material, which together
determine the desired frequency and phase velocity of the
transducer. In one embodiment, with a transmittal form transducer
20 of from 3 to 5 pulses shown as signal 203, a very large and "low
Q" (fast response) envelope 202 is preferably generated at
transducer 22. The signal 204 may be fully rectified or subjected
to other wave shaping processes. The arrival time T of the signal
204 is detected by digitally imaging the very sharp (low Q) shape
of the received signal, and then using digital computation to
analyzing the wave shape to identify the arrival time T of the very
first "cusp" of the received signal 204.
[0040] This arrival time T is digitally represented and fed into a
register or other storage device, after being averaged, for example
exponentially averaged. Exponential averaging, in one embodiment is
performed by subtracting the currently sensed arrival time
T(current) from the previously exponentially averaged arrival time
T(previous) and dividing the result by a large number, say from 3
to 10. The result of the division is then added or subtracted from
a result of a prior exponential average (or previously assigned
number) to establish a new average to be used for the next
transmission. This has the effect of establishing a relatively
stable value representing the arrival time for the current liquid
under nominal conditions.
[0041] The averaged number or stored register number is a measure
value (Measure in FIG. 3) against which the next arrival time T
will be compared. When each new pulse is received, along with
adjusting the exponential average, a determination is made whether
the latest pulse is later or earlier than the average previously
established. In one embodiment, a pulse with an arrival time (T)
later than the Measure is coded as a "1" in a FIFO, and earlier is
coded as a "0". Thus, a FIFO may empty its contents by transmitting
the contents to a master station 44 (FIG. 1) or other reporting
location, which will store the history of Early/Late results of the
transmissions.
[0042] If the sonic velocity of the liquid changes, say due to
changes in liquid chemistry, temperature or pressure not associated
with leaks, the history of ones and zeroes will register this
gradual change by a small excess of ones or zeroes until a new
stable average is established. However, this process is much slower
than the very fast change in sonic propagation velocity caused by a
leak. Accordingly, it should be possible to distinguish a true leak
from other causes for a change in sonic propagation velocity. These
other changes may be characterized and identified in the history of
late/early determinations at master station 44. Such changes may
include opening a valve, activating a pump, etc.
[0043] When a leak occurs, and the pressure wave arrives at site
station 12 (FIG. 1), the leading edge of that change from a higher
to a lower pressure is instantaneously effective in reducing the
sonic propagation velocity at that location. Accordingly, the first
report after its arrival will be a "1". In fact, since an
exponential average divider will be chosen so the Average will only
change slowly, all the transmissions following the arrival of the
pressure wave will be ones, until the exponential average has had
time to establish a new average, associated with the new lower
post-leak pressure.
[0044] The contents of the FIFO are periodically sent to master
station 44, in a time-synchronized fashion. They are preferably
grouped into digital words and then compressed, so that, for
example, the 60,000 ones or zeros collected in a one minute period,
assuming a 1 millisecond pulse transmit rate, can be represented in
about 500 bytes.
[0045] Referring to FIG. 4, master station 44 (FIG. 1) may include
a computer or other monitoring device which creates a display 70 in
which, for example, each site station's data is displayed as a
result of an integration or cumulative sum. Display 70 shows
integrated ones 71 and zeros 73 for a site station for a given
synchronized time (e.g., one minute or other set amount of time) as
a plot 72.
[0046] If a one is integrated as a height increase, and a zero as a
height decrease, on data plot 72, then when, on the average there
are as many ones as zeroes, plot 72 will be a relatively flat line
74, near zero. If there is a leak, starting at the display time 76
that site station first started to receive the continuous ones
caused by a leak, display 70 shows an integration of the ones,
forming a linearly rising line 78 until a new average 79 is
achieved. This permits identification of the exact time that the
low-pressure transient arrived, to the millisecond. This also
permits location of a leak to the order of magnitude of about 1
meter or better, dependent only on signal to noise ratio of the
signal. Rising line 78 indicates a leak. Master station 44 may
include characteristic curve data, which is compared to the sit
station data to determine a leak. The duration and sizes of the
plots can be compared to a reference value(s) or threshold to
determine the severity or type of leak.
[0047] The characteristic display of a leak transient, and
duration, may be employed as a leak detector. However, leak
detection may be performed by other means as well. In either case,
master station 44 will show the characteristic sign of a leak on
each of site stations bounding the segment on which the leak has
occurred. The time synchronized display 70 will show the relative
arrival time at each of the segment's site stations 12. The
operator or software for each site station will be capable of
determining when the first arrived "one" was received after a
pressure transient (display time 76).
[0048] Referring to FIG. 1 and FIG. 3, once the arrival times are
registered from each site station 12 to master station 44, master
station 44 computes the location of the leak by a formula. An
example of a formula which may be employed to compute the distance
to a leak is shown as EQ. 1, which is based on the difference in
absolute arrival times:
D.sub.u=D.sub.t(V.sub.s.sup.2-V.sub.f.sup.2)+D.sub.s((V.sub.s-V.sub.f)/2V.-
sub.s)
[0049] where:
[0050] D.sub.t=difference in absolute pressure wave site arrival
times;
[0051] D.sub.u=distance from upstream site station to the leak
location;
[0052] V.sub.s=liquid sonic propagation velocity;
[0053] V.sub.f=flow velocity;
[0054] D.sub.s=total pipeline segment length
[0055] It is possible to compute the leak location without
knowledge of flow rate, but only at reduced accuracy.
Advantageously, V.sub.s is employed in computing leak location.
Those skilled in the art would understand, based on the present
disclosure, how to perform an equivalent computation of leak
location even when there are several batches of different liquids
in the pipeline segment, each at different sonic propagation
velocity.
[0056] Small leaks, resulting in smaller changes in pressure, will
manifest their lower magnitude as compared to larger leaks, by the
reduced amount of time that it will take for the site stations to
establish a new exponential average (see, e.g., line 79 in FIG. 3).
If the leak is large enough to change the sonic propagation
velocity by a recognizable difference from the random "One/Zero"
behavior prior to the event of the leak itself, it will be possible
to identify its location accurately.
[0057] Since the sonic propagation of the liquid ranges on the
order of magnitude of 1,000 meters to 1,500 meters per second, a
time resolution of 1 millisecond or better in data collection
permits a precision of leak location in the range of, for example,
from 1 to 1.5 meters from the actual location 40 of the leak.
[0058] Master station 44 may continuously monitor pipeline 16 for
leaks. This may be performed by triggering an alarm when a
predetermined number of late counts are experienced. Alternately, a
conventional leak detection system may be employed, which then
instructs a remediation staff to determine the location of the
leak. By consulting data at master station 44, particularly
inspecting the data stored for the period of time at which the leak
is suspected of occurring, the leak's position can be accurately
determined in accordance with the present invention.
[0059] The resultant computation defines the distance, D.sub.u
between either of site stations 12b or 12c to the leak location 40.
Since pipelines are not always linear in their configuration, it
would be advantageous to translate the distance indication into a
particular longitude and latitude position.
[0060] Referring to FIG. 5, master station 44 or other location
includes a map 80 of a pipeline 82. Every point on pipeline 82 is
translated into geographical coordinates, e.g., latitude and
longitude. In the event of a leak, a location of the leak will be
calculated and indicated on that map by a suitable marker, with the
latitude and longitude displayed. Thus, an appropriate vehicle can
be used to quickly transport a remediation crew to the site, by
truck, helicopter, boat, etc. to remedy the leak.
[0061] By identifying the sonic propagation velocity at least at
one point in time, a sequence of ones and zeros may be employed to
identify the sonic propagation velocity at any time. This is useful
in determining the density of the product at each site station, as
would be used for interface detection or product type and quality
detection.
[0062] As opposed to the behavior of liquids, gases in general do
not change their sonic propagation velocity with pressure. However,
a change in pressure will affect the sonic conductivity to
ultrasonic pulses in gases. Since each site station can measure the
amplitude of each received sonic pulse, at the same time as it
measures its arrival time, the same method for leak location used
for liquid flows may be employed for gas pipelines. This may be
implemented by providing a one or zero output responsive to a
receive signal increase or decrease in amplitude control data. This
would replace the sonic propagation velocity one or zero data
employed for liquids. In all other respects, the operation of the
system is identical.
[0063] Referring to FIG. 6 with continued reference to FIGS. 1 and
2, a block/flow diagram for a system/method for locating a leak in
a pipeline is illustratively shown. It is to be understood that the
method of FIG. 6 applies equally for a gas pipeline, where sonic
conductivity is employed instead of sonic velocity. In block 100,
transducer 20 transmits sonic pulses 203 (FIG. 3) to transducer 22
at a predetermined rate. The transmission produces a pipe wall
signal 205 (FIG. 3). In one embodiment, the predetermined rate is
1,000 times per second. Other rates may be employed and have the
effect of increasing (higher rate) or decreasing (lower rate) the
precision of the system on the present invention. In block 102, a
reflected pipe wall signal 205 (wave 32 of FIG. 2) is received by
transducer 22 which processes signal 205 to generate a receive
signal 204 (FIG. 3). In one embodiment the signal 204 is full wave
rectified and filtered to obtain a signal representing an envelope
202 as illustratively shown in FIG. 3.
[0064] In block 104, an amount of time between transmission of a
sonic wave and the arrival time of the sonic wave at the receive
transducer is determined. In one embodiment, a threshold level 206
(FIG. 3) is set which is employed to indicate when the sonic wave
has arrived at transducer 22. The threshold level 206 can be set in
advance based on experience, based on amplification factors of the
sonic signals, based on previously received signals, or a
combination of factors. When the envelope 202, marker or reference
portion breaks the threshold level 206, a travel time is measured
represented by T in FIG. 3. This is the travel time of the sonic
waves between transducers 20 and 22.
[0065] In block 106, travel times for the sonic waves are compared
to a measure to determine early or later travel times. In one
embodiment, a travel time is expressed as a number of clock cycles
from transmission to receipt (e.g., the envelope 202 breaking
threshold line 206 in FIG. 3). Travel times can be adapted to
represent sonic conductivities when gas pipelines are employed. The
measure may be determined as an exponentially averaged quantity as
described above. A determination is made to see if the newly
arrived wave is later or early as compared to the measure.
[0066] If the sonic velocity of the liquid is stable, then it is
very probable that successive late/early counts will, on average,
alternate between being late and early. In other words, the counts
will average out over time to have an equal number of occurrences
of counts having a value less than the stored buffer value
(measure) and a value more than the stored buffer value (measure).
Each result is stored as a "1" (late) or a "0" (early) in, e.g., a
first-in-first-out device (FIFO). A string of early and late
reports is recorded and analyzed, in block 108.
[0067] If a leak has occurred, the pressure at that point usually
drops, lowering the liquid density and reducing liquid sonic
velocity. The low-pressure wave caused by the leak travels upstream
and downstream, being read, in block 110, first by the nearest site
stations 12a, and then by the further site stations 12b (FIG. 1).
This permits a determination of the direction in which the pressure
wave is traveling. When the wave arrives at each site station 12,
the lower density and lower sonic velocity of the wave causes the
receive signal to move "late." While the exponential buffer catches
up to a new position or average of the receive signal (the "new"
measure position), the FIFO will only receive "late" reports (e.g.,
a string of 1's). A string of late reports indicates the change in
flow, e.g., a transient pressure wave due to a leak in pipe 16.
[0068] In block 112, the location and time of occurrence of the
leak is computed by determining the difference in arrival time of a
first "1" for the string of late reports (from the FIFO) at each
site station, taking into account the length of each segment (e.g.,
distances A, B, C, etc.), the sonic velocity in the liquid and the
effect of actual liquid flow rate (e.g., add the flow rate to the
sonic velocity for a wave traveling with the flow, and subtracting
the flow rate from the sonic velocity for a wave traveling against
the flow). The digital 1's and 0's sequence or string is used to
identify the occurrence. EQ. 1, set forth above, may be
employed.
[0069] In one embodiment, since the sonic velocity of hydrocarbon
liquids is about 1 m/s, at least a 1 meter resolution is achievable
for the location of the leak. This is a significant improvement
over conventional systems, which have a precision of about 150
meter to 200 meters.
[0070] While the system of the present invention will determine the
linear distance from the segment's site stations where a leak has
occurred, acting on this information is not simple if the pipeline
is not linear. Especially on buried or underwater pipelines,
locating the leak relative to its terrain markers, or its absolute
location (GPS) may be needed. This is especially true if the
pipeline is convoluted.
[0071] Accordingly, in block 114, distances traveled by a pressure
wave along a pipeline may be correlated to map positions, e.g.,
latitude and longitude positions. Master station 44 (FIG. 1) may
include a "Map" of the pipeline, with an algorithm that converts
the distance from each surrounding Site Station to specific
position, e.g., a latitude and longitude of the leak location. This
may be combined with a Global Positioning System to mark the
location on a GPS Map system which could guide trucks, helicopters,
ships, etc. to the actual leak location.
[0072] The system and methods of the present invention may be
employed to quickly identify the locations of other anomalies,
which may occur in pipeline system. For example, the present
invention may be employed to determine a location where a theft of
product is being carried out, by, e.g., hot-tapping the pipeline.
In addition, the present invention will identify the location of
any pump or valve, which is being operated unsafely.
[0073] A significant advantage is provided by the use of clamp-on
ultrasonic transducers, in place of using pressure sensors to
determine the arrival of a low-pressure leak wave. There are many
pressure transients in a pipeline, caused by pump or valve
operations, and by other instruments or obstructions in the
pipeline. A small diameter pressure sensor will see all of these
transients, which can actually obscure the actual leak wave
transient. The sonic arrival time system of the present invention
integrates out all the transients that have a wavelength smaller
than the liquid path length of the sonic beam injected into the
pipe. Thus, the sonic system has a greater dynamic range, and is
more efficient in leak detection.
[0074] Having described preferred embodiments for a novel leak
locator for pipe systems (which are intended to be illustrative and
not limiting), it is noted that modifications and variations can be
made by persons skilled in the art in light of the above teachings.
It is therefore to be understood that changes may be made in the
particular embodiments of the invention disclosed which are within
the scope and spirit of the invention as outlined by the appended
claims. Having thus described the invention with the details and
particularity required by the patent laws, what is claimed and
desired protected by Letters Patent is set forth in the appended
claims.
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