Apparatus and Method to Locate an Object in a Pipeline
This invention relates to apparatus and a method to locate an
object in a pipeline. Particularly, it relates to apparatus and a
method for locating a moveable object which has been
introduced into the pipeline. In its preferred embodiments, it
relates to locating the position of a detector unit for the
detection of anomalies in pipelines that cany liquids, such as for
example oil or water, or gases, such as for example natural gas.
Discussion of the Prior Art
It is frequently useful to know the position of an object which has
been introduced into a pipeline, for example for maintenance or
leak detection purposes. For example, it is sometimes
necessary to know the position to a pipeline pig which has been
introduced to clean a pipeline. Knowing the position enables the
operator to predict when the pig will arrive at a pigging station,
or to take steps to free it if it has become jammed.
A particular type of object, of which it would be useful to know
the location within the pipeline at a particular time, is a detector
unit which senses conditions in the pipeline.
Untethered detector units which move through a pipeline,
sensing conditions as they go, have been known for many
years. For example, the oil industry has long used untethered
"pigs" which fill the cross-section of the pipeline and which are
pushed through by the flowing oil. In both oil and water
pipelines, untethered ball-like detector units have been used,
such as the one shown in PCT Published application WO
2006/081671 of Pure Technologies Ltd. In the currently
preferred form of the detector unit of that published application,
the unit rolls along the bottom of a fluid-filled pipeline, pushed
along by the fluid flow. There are also untethered powered
detector units, which pass though the pipeline by means of their
own motive power.
The detector unit is typically placed in the pipeline to detect
anomalous conditions such as leaks, corrosion or pipe wall
defects, using suitable known sensors to sense the particular
anomalous condition. Obviously, it is necessary to determine as
accurately as possible the location of the anomalous condition,
so that it can be remedied or monitored further. To determine
this location, it is usually important to know the location of the
detector unit at the time the anomalous condition is noted. In
most cases, methods using satellites (for example a GPS
locating device) are not useable, because the pipeline is buried
too far underground for such methods to work.
Various methods have been used to determine the location of
detector units within pipelines. A crude determination can be
made for detector units that are carried along by the fluid flow by
knowing the average speed of flow of the liquid within the
pipeline, and recording the elapsed time from when the unit was
released to pass through the pipeline until it comes to the
anomaly. This method is sometimes refined by having beacons
which emit particular sound signatures at intervals along the
pipeline (for example, at inspection ports) and using the times at
which the detector unit passes the beacons to help calibrate the
average flow rate for particular sections of the pipeline. If the
detector is designed to roll along the bottom of the pipeline, the
number of revolutions can be counted to provide an indication of
distance travelled. If the detector unit is equipped with a
magnetometer, this can sense elements of the pipe architecture
such as welds in a metal pipeline or bell and spigot joints in a
pipeline made of wire-wrapped concrete. Similarly, pressure
and temperature sensors on the detector unit can often sense
elements of pipe architecture such as places where other lines
join or leave the pipeline being monitored, because liquid
leaving or joining the pipeline being monitored affects the
pressure or temperature in that pipeline.
Although these methods of determining the location of detector
units are useful, they do not give a precise location for the
detector unit. Fluid flow within a pipeline may not be constant,
especially if the pipeline is partially filled with liquid or if it goes
up or downhill. The measurement of the number of revolutions
made by a rolling detector unit can sometimes be incorrect if the
unit is entrained in the fluid in the pipeline and loses contact with
the bottom of the pipeline. The sensing of pipe architecture may
not be feasible if only incomplete or imprecise records exist of
the locations of the architectural features.
It would therefore be useful to have an accurate and precise
method of determining the location of an object which has been
introduced into a pipeline, particularly a detector unit within the
pipeline, and to have apparatus to perform that method.
Brief description of the Invention
It has now been discovered that an acoustic emission at high
frequency is transmitted through pipelines with little loss in
amplitude. This permits the emission to be received at a remote
location, for example several kilometres away, without undue
attenuation.
If the precise time of sending of the acoustic emission through
the pipeline from a first location is determined, and the precise
time of that the emission is received at a second remote location
is determined, it is possible according to the invention to obtain
a very precise measurement of the length of the pipeline
between the location of sending and the location of receipt. T o
obtain the distance between the two locations, one determines
the time taken by the acoustic emission to travel between the
two locations, and multiplies this by the speed of sound of the
particular frequency in the type of liquid within the pipeline.
Where one of the first and second locations is a moveable
object within the pipeline and the other is a known position along
the pipeline, this provides a method for finding the location of the
moveable object.
Drawings
The invention will be described with reference to the drawings,
in which:
Figure 1 is a representation (not to scale) of a detector unit
equipped with a transmitting station according to the invention,
and located within a pipeline, where the detector unit is an
untethered ball rolling along the bottom of the pipeline. The
pipeline is shown in section in order to show the detector unit.
Figure 2 is a representation (not to scale) of a detector unit
equipped with a transmitting station according to the invention,
and located within a pipeline, where the detector unit is a
pipeline pig. The pipeline is shown in section in order to show
the detector unit.
Figure 3 is a representation (not to scale) of a receiving station
according to the invention, located at a known location on the
pipeline, and other equipment associated with it. The pipeline
and surrounding earth are shown in section in order to show the
receiving station.
Figure 4 is a representation (not to scale) of an alternate
embodiment of the invention, showing a transmitting station on a
pipeline and a detector unit equipped with a receiving station.
The pipeline and surrounding earth are shown in section in order
to show the receiving station and detector unit.
Detailed Description of the Invention
According to the invention, a transmitting station has a precise
clock, and a means for emitting a high-frequency acoustic
emission. At least one receiving station has an acoustic
receiver positioned to receive sounds occurring within the
pipeline, a precise clock and a recording device. The difference
(if any) between the readings of the two clocks at the same
absolute time is known, so that a correction can be made when
calculating the time taken for an emission to travel between
them. Preferably, the transmitting station is in a moveable
detector unit and the receiving device is at a fixed location in or
attached to the pipeline. The reason for this is that electric
power is usually more readily available at a fixed location (where
it can be supplied from a grid) than in a moveable device
dependent on batteries or the like. Abundant electric power
supply to the receiving station permits such station to be
provided with amplifiers to boost the signal received.
In the preferred embodiment, the transmitting station is located
aboard an untethered detector unit and the receiving station is
located at a known fixed point in the pipeline, such as, for
example, the point where the detector unit was launched in the
pipeline or a point where the pipeline is accessible through an
inspection port.
In a less preferred embodiment, the transmitting station is at a
known fixed point in the pipeline and the receiving station is
aboard the untethered detector unit.
In another embodiment useful when charting a pipeline of
unknown configuration where the speed of sound in the fluid in
the pipeline is known, the transmitting and receiving stations are
located at fixed points along the pipeline, and the invention is
used to determine the precise distance between the fixed points.
In another embodiment, useful when calibrating the system,
both stations are fixed points along the pipeline at a known
distance from one another, and the invention is used to
determine the precise speed of sound of the frequency used in
the type of fluid within the pipeline.
When the transmitting station is located aboard a moveable
detector unit, it is particularly preferred to have several receiving
stations in use at different locations along the pipeline. The
transmitting unit on the moveable detector device transmits its
high frequency acoustic emission. Depending where the
moveable detector unit is at any particular time, the emission
may be received at different receiving stations, or at several
receiving stations at once. Emissions received at any one
station are used to calculate the distance of the moveable
detector unit from that station.
From time to time the clocks in the transmitting and receiving
stations are synchronized, so that compensation can be made
for any error in their readings.. Conveniently, this is done by
determining the difference in readings of the clocks at the same
absolute time, so that the difference (the error) between their
readings is known. This can be done, for example, by comparing
each clock with a GPS time signal (which is taken for this
purpose as the absolute "correct" time), and noting the
difference between the GPS time reading and he reading of the
clock. This can be done either before or after the moveable
sensor unit travels down the pipe and emits the acoustic
emissions which are received at the receiving units. If high
precision commercially available clocks are used, there will be
little drift, and the synchronization need not be done each time
the moveable sensor unit is caused to travel down the pipe. A
person skilled in the art will know how often to synchronize,
having regard to the precision of the clocks being used and the
accuracy required.
In operation according to the invention, a high frequency
acoustic emission is created at the transmitting station at a
precisely known time. The acoustic emission is received at the
receiving station and the time of receipt is noted. From these
observations, the length of time taken for the acoustic emission
to pass through the liquid in the pipeline from the transmitting
station to the receiving station is determined. If the speed of
sound of the frequency used in the type of liquid within the
pipeline is not already known, this is determined. Then the
distance between the two stations at the time of the emission is
determined by multiplying the length of time taken for the
acoustic emission to pass through the liquid in the pipeline by
the speed of sound of the frequency used in the type of liquid
within the pipeline.
The means for emitting the acoustic emission at a precisely
known time is preferably a timer which causes emissions at
precisely-timed intervals. If the timer is present, it is not
absolutely necessary to have an associated recording device,
provided that the clock reading is known for any one emission,
as the clock readings for other emissions can be derived from
this. However, it is preferred to have a recording device which
shows the time of each emission as recorded by the associated
clock.
Alternately, if the transmitting station is on the detector unit,
means for emitting the acoustic emission can be an alarm which
causes an emission when a sensor on the detector unit senses
a reading beyond a pre-set limit or other predetermined alarm
condition, together with a recording device which records the
precise time at which the acoustic emission is emitted, as
recorded by the associated clock..
As stated above, the invention makes use of a high frequency
acoustic emission. The useable frequencies are dependent on
the nature of the fluid in the pipeline and the diameter of the
pipeline. Generally, low frequencies (below about 500 Hz.)
transmit for fairly long distances along the pipeline, but they are
not used in this invention because they transmit both through
the liquid and the walls of the pipeline, so the signal received at
the receiving station is a combination of the emission travelling
through the liquid and the walls.
Above about 500 Hz, within a range of frequencies which varies
with the type of fluid within the pipeline, the emissions are
absorbed or damped by the fluid within the pipeline. This
damping or absorption decreases as the frequency increases,
and varies with the type of fluid. For most liquids, the damping
is significant at frequencies in the range of about 500 - 18000
Hz., so these frequencies should be avoided. For gases,
damping depends on the pressure of the gas as well as its
composition, but generally frequencies below 18000 Hz may
encounter damping, especially when the gas is pressurized.
Frequencies above those at which the damping or absorption is
significant for the particular fluid are useable.
To avoid any likely damping or absorption, it is preferred to use
a frequency above 20 KHz, preferably in the range 20-100 KHz.
and more preferably in the range 30-80 KHz. Generally,
frequencies in the range 40 KHz.- 80 KHz are particularly
preferred in pipelines which contain water, and frequencies in
the range 30 KHz.-80 KHz. are particularly preferred in
pipelines which contain oil. Frequencies above 100 KHz, up to
for example 200 KHz, can also be used, but are generally not
preferred, because the high sampling rate required to receive
these frequencies usually requires more complicated equipment
than that needed for lower frequencies.
Depending on the size and construction of the transmission
station, when the detector unit carries the transmission station,
some frequencies within these ranges may resonate in the
detector unit It is preferred to use a resonant frequency when
possible when the detector unit has the transmission station, as
it is easier to create a high amplitude sound at a resonant
frequency than at other nearby frequencies.
Suitably, the acoustic emission should have a duration of at
least 1 ms. However, to distinguish it from possible evanescent
high frequency noises within the pipeline, a longer emission, of
20 ms. to 200 ms, is preferred. Longer emissions can also be
used if desired.
The emissions are spaced from each other by a time much
longer than the duration of the emission, so that successive
emissions do not overlap or interfere with one another at the
receiving station. However, they are frequent enough so that, at
the speed that the moving object is travelling, they serve to
locate the object to the desired degree of accuracy. For objects
travelling by entrainment in the flow of fluid in the pipeline, at
typical pipeline flow rates, sufficient accuracy of location is
obtained for most purposes if the emissions are repeated every
1 second to 15 seconds.
Although it is suitable in most situations to use an emission at
one particular frequency, it is also possible to send a
predetermined set of tones comprising several frequencies in a
predetermined order. Thus, for example, a set of tones could be
a sequence of four emissions of 6 ms. each in length at 42 KHz,
40.5 KHz., 39.0 KHz and 38 KHz. A set of tones like this can be
used where transient high frequency noises in the pipeline from
other sources are expected. The receiving station can be
designed to recognize only signals having these frequencies in
this order. Over distances of several kilometres, there may be
some overlapping of the signals at different frequencies, caused
by reflection of the signals from pipeline walls or architecture
such as valves, but the sequence of signals is still recognizable.
It is surprising that high frequencies propagate for long
distances through a pipeline, even though such frequencies
would normally be expected to attenuate rapidly in a liquid
medium. While the inventor does not wish to be bound by any
theoretical explanation, it is thought that the walls of the pipeline
act in a manner analogous to a waveguide to propagate high
frequency acoustic emissions.
The invention is operable at all conventional pipeline pressures,
from subatmospheric pressure to high pressures. The invention
will also operate in gas-filled pipelines and liquid filled pipelines.
In pipelines where there is liquid with gas above it (as for
example in a pipeline having water with air above it), there
should be a continuous path in at least one single phase (the
liquid or the gas) from the transmitting station to the receiving
station. A continuous path through the liquid is preferred.
In a particularly preferred embodiment, the transmitting station is
aboard a detector unit and a receiving station is at the point of
launch of the detector unit into the pipeline or at an inspection
port along the pipeline or at the intended location of recovery of
the detector unit from the pipeline. There can be several
receiving stations if desired. In one method of using this
apparatus, the transmitting unit transmits an acoustic emission
at fixed intervals. The intervals are chosen depending on the
expected speed of travel of the detector unit through the
pipeline, so that an acoustic emission will occur when the
detector unit is expected to have travelled approximately a
desired distance. The detector unit is provided with sufficient
battery capacity so that the emissions can be generated at the
desired time intervals during travel along the entire length of the
pipeline which the detector unit is to inspect. Also, the emissions
are spaced sufficiently so that there is a sufficient interval to
avoid overlap at the receiving station. For example, it is suitable
in most cases to set the acoustic emissions to occur at intervals
of from about 1/2 second to 2 minutes or even longer. Preferred
intervals ranges are from 1 second to 10 seconds.
The detector unit is launched and is allowed to proceed down
the pipeline to a retrieval point, with the length of pipeline to be
inspected being between the launch point and the retrieval point.
The detector unit is provided with conventional sensors such as
for example a hydrophone, magnetometer, temperature sensor
and the like for detecting anomalies. While passing through the
area to be inspected, the detection unit emits the acoustic
emissions at the predetermined intervals, and simultaneously
the sensors aboard it collect data on the condition of the
pipeline.
In a less preferred embodiment, instead of having acoustic
emissions emitted at set time intervals, an emission occur
whenever a sensor senses some anomaly, such as a result
outside a predetermined range or when a particular condition.
This ensures that a precise distance from the receiving station
can be registered for an anomalous sensor reading, to permit
follow-up work at the location where the anomaly was noted. For
this embodiment to work properly, the precise time of sending
the emission must be recorded. This can be done by recording
the sensor results along with a time trace which shows the time
as recorded by the clock. The precise time of sending of the
emission can be determined by examining the trace to see the
time at which the sensor registered the anomalous result. For
convenience, the emission can also be recorded on the time
trace.
At the retrieval point, the detection unit is removed from the
pipeline in known fashion and the data downloaded from it. The
time of sending of each emission is compared with the records
of the receipt of that emission at the receiving station. The time
of sending and receipt are standardized by correcting for any
error between the clocks (as determined by synchronization,
which is done as necessary), and the speed of transmission of
sound of the emission frequency in the liquid is either known or
determined empirically. From this information, the distance
travelled by each emission is calculated by multiplying the time
taken for that emission to travel between the transmission
station and the receiving station. This provides a dataset
showing the location of the detector unit when each acoustic
emission was sent out (if the detector unit carries the
transmitting station) or received (if the detector unit carries the
receiving station). The records of observations made by the
sensors aboard the moveable detector unit and the times they
were made are correlated with this information This permits the
location of the detector unit at the time of any anomalous sensor
reading to be determined, to within the distance traveled by the
detector unit in the interval between the acoustic emissions
immediately before and after it. Even more precision can be
obtained by interpolating data to within the interval. Of course, in
the embodiment where the detector unit carries the transmitting
station, even more precision is possible if the sensor is arranged
to trigger an emission precisely when an anomalous sensor
reading occurs.
This information can also be used to determine the velocity of
the detector unit in the pipeline, by plotting the position of the
detector unit at the time of successive emissions at spaced time
intervals, and noting the distance travelled in the interval
between emissions. This information can be used to correct
distance measurements made by other conventional techniques
for measurement. Also, the velocity determined for the detector
unit as it approaches a receiving unit and then recedes from the
receiving unit can be interpolated to find out precisely the time
at which the detector unit passes the receiving unit.
If desired, emissions can be sent at predetermined time
intervals and additional emissions (using a frequency or a set of
tones different from the frequency or set of tones for the
emissions at the set time intervals) can be sent when a sensor
senses some anomalous result. This permits the tracing of the
distance traveled by the detector unit and the correlation of such
information with the results from sensors, while also giving
additional location information when an anomalous condition is
encountered.
In a less preferred embodiment, the acoustic emissions are sent
at predetermined time intervals from a transmitting station at the
launch point, the retrieval point, or some other point along the
pipeline, for example a location between the two where there is
access to the pipeline through an inspection port. The receiving
station is on the detector unit. The data retrieval and processing
are essentially the same. This arrangement does not permit
sending an emission when an anomalous sensor reading is
detected by the detector unit.
In general for liquids, sufficient accuracy for the speed of sound
is obtained by using handbook values for the speed of sound of
the frequency used through the type of liquid in the pipeline.
However, the speed does change with temperature and
pressure, so better accuracy can be obtained by doing a
calibration. For gases, handbook values are less reliable, as the
pressure in the pipeline fluctuates as the gas is pumped, so
calibration is recommended.
To do the calibration, the transmitting station is placed at a
known location in the pipeline, such as an inspection port or a
pig release station, as shown in Figure 4 at 500. The receiving
station is placed at a second location along the pipeline, such
as another inspection port or a pig receiving station as shown at
400 in Figure 4, which location is a known distance along the
pipeline from the transmitting station. The detector unit is not
used while doing the calibration. Preferably the two locations are
less than 1 km. from one another and there are no sharp bends
in the pipeline between them. A least one acoustic emission at
the desired frequency is then sent from the transmitting station
at a known time to the receiving station. The time at which it is
received is then noted. The elapsed time for the emission to
travel from the transmitting station to the receiving station is then
found by subtracting the time sent from the time received, with
any necessary calibration correction. As the distance travelled
between the two stations is known, the speed of sound in the
liquid or gas is found by dividing the distance by the elapsed
time.
The invention can also be used to measure the length an
unknown length of pipeline between two locations accessible
from ground level. The pipeline, being underground, may have
turns not evident from ground level, so its length may not be
ascertainable from ground level. To measure its length, a
transmitting station is set up as shown at 500 in Figure 4 at one
location, and a receiving unit as shown at 400 in Figure 3 is set
up at the second location. Preferably, the two locations are as
close as conveniently possible, having regard to available
ground locations, and the pipeline is filled with liquid which has a
known speed of sound at the frequency chosen. .A least one
acoustic emission at the chosen frequency is then sent from the
transmitting station at a known time to the receiving station. The
time at which it is received is then noted. The elapsed time for
the emission to travel from the transmitting station to the
receiving station is then found by subtracting the time sent from
the time received, with any necessary calibration correction. As
the speed of sound in the liquid is known, the distance is found
by is found by multiplying the speed of sound by the elapsed
time.
Referring to the drawings, Figure 1 shows a pipeline 10,
containing fluid 11, which can be for example, oil, water or
natural gas. The pipeline is buried in the ground 12. There is a
leak 14 in the pipeline, and fluid 13 is escaping from the leak
into the ground as shown at 13..
The transmitting station, in this embodiment, is contained within
the detector unit 100, which in this illustrative example is a ball
sensor unit similar to that shown in PCT Published application
WO 2006/081671 of Pure Technologies Ltd., The detector unit
comprises ball-shaped sensor unit 101 within a protective outer
urethane foam cover 104. Arrow 19 shows the direction of the
fluid flow. As the detector unit is more dense than the fluid, it
rolls along the bottom of the pipeline, pushed along by the fluid
flow 19.
Within the sensor unit 101 are conventional sensors 203 and
204, for example a magnetometer 203 and a hydrophone
(acoustic sensor) 204. There is a hole 103 in the protective
foam cover 104 to permit the hydrophone 204 to be in direct
contact with the liquid 11.
Also within the sensor unit 101 is a precise clock 202. This is
connected to an acoustic emitter 201, which can emit acoustic
signals at a pre-chosen frequency within the range of 20 - 100
KHz, The acoustic emitter can be, for example, a %" diameter
x .1" thick piezo crystal. The acoustic emitter is arranged to emit
an acoustic signal at set time intervals, for example once every
3 seconds.
Alternately or in addition, acoustic emitter 201 can be a tone
generator which can emit a pre-chosen sequence of acoustic
signals at frequencies in the range 20-100 KHz. Preferably,
there is a hole 102 in the protective foam cover 104 so that the
acoustic emitter transmits directly into the fluid 11.
A memory device 205, which can be a conventional
commercially-available SD memory card or flash memory, is
linked by suitable circuitry 206 to record data generated by the
sensors 203 and 204. Suitably, the memory device 205 also
records a continuous time trace from the clock, so that the
precise time of each piece of data recorded by the sensors 203
and 204 is recorded. It is also possible for the memory device to
record on the same trace the time of each acoustic emission,
but this is not absolutely necessary, as the acoustic emissions
occur at set time intervals which are governed by the clock. In
some cases (as, for example, where one sensor is a
hydrophone which senses high frequencies), the data recorded
by the sensor will include the periodic acoustic emissions in its
recorded data.
In a preferred embodiment, the acoustic emitter 201 is a tone
generator, and is linked to one or more of the sensors 203 and
204, so that the acoustic emitter will send an acoustic emission
which is a specific set of tones when the sensor senses a value
outside a predetermined range.
Battery 207 provides power for the elements 201-205 through
circuitry 206.
In Figure 1, the detector unit is passing adjacent the leak 13.
The hydrophone 204 detects the sound of the fluid leaking from
the pipeline, and the record of this sound is recorded in the
memory device 205. Data showing the time of each acoustic
signal is also recorded in the memory device 205.
Figure 2 shows an alternate embodiment. In figure 2, similar
elements are labelled with the same numbers as in Figure 1.
In Figure 2, the detector unit is a pipeline pig 300, held in
position in the pipeline 10 by sealing flaps 301 and pushed
along the pipeline by the flow of the fluid in the pipeline as
indicated by arrow 19. in this embodiment, the fluid 11 can be
for example oil or a refined oil product, as pipelines for such
products commonly use pipeline pigs for inspection, and are
provided with pigging stations where pigs can be inserted into or
removed from the pipeline. . Within the pig are conventional
sensors 203 and 204, for example a magnetometer 203 and a
hydrophone (acoustic sensor) 204. Hydrophone 204 has its
sensing portion on an exterior surface of the pig so that it can
detect acoustic events in the surrounding fluid 11.
As in the embodiment of Figure 1, the detector unit of Figure 2
contains a precision clock 202 connected to an acoustic emitter
201, which can emit acoustic signals at a pre-chosen frequency
within the range of 20 - 100 KHz, or if desired can emit a pre-
chosen sequence of acoustic signals at frequencies within the
range 20-100 KHz. A memory device 205, which can be a
conventional flash memory or SD card, is linked by suitable
circuitry 206 to record data generated by the sensors 203 and
204. The memory device 205 records also a continuous time
trace from the clock, so that the precise time of each piece of
data recorded by the sensors 203 and 204 is recorded. Battery
207 provides power for the elements 201-205 through circuitry
206.The acoustic emitter is arranged to emit an acoustic signal
at set time intervals, for example once every 5 seconds.
The detector unit of Figure 2 is passing adjacent the leak 13.
The hydrophone 204 detects the sound of the fluid leaking from
the pipeline, and the record of this sound is recorded in the
memory device 205. Data showing the time of each acoustic
signal is also recorded in the memory device 205.
Figure 3 shows a receiving station 400. Again the same
numbers are used to identify the same things. Typically, the
receiving station is at the access port where the detector unit
has been inserted into the pipeline, or at the access port where
it will be removed, or at an inspection port intermediate between
the two. It is preferred to have several intermediate receiving
stations along the length of pipeline being examined, for
example at inspection ports, if possible at intervals of every
kilometre or so. In Figure 3, the receiving station is located at
inspection port 413, intermediate between the access port for
insertion and the access port for removal. The precise
geographical location of access port 13 is known, either by
locating it from pipeline drawings and maps or by locating it by a
GPS reading.
At inspection port 413, an acoustic receiver 401 which is
capable of receiving the frequencies generated by the acoustic
emitter 201 of Figure 1 or Figure 2 is located in contact with the
fluid 11 or else in contact with a portion of the pipe wall or other
appurtenance through which sound at the frequency of
operation can pass without significant attenuation. In figure 3, an
alternate position of acoustic receiver 401, on the outside of the
pipe, is shown at 401a, with circuitry 402a (shown as a dashed
line) connecting it to the other components. While better
reception of sound is obtained if the receiver 401 is in contact
with the liquid 11, it is often more convenient for servicing to
place the receiver in contact with the pipe as at 401a or an
attached appurtenance such as the inspection port, and this
generally provides adequate sound pickup. Of course, if an
acoustic receiver is positioned in contact with the fluid, as shown
at 401, no receiver is needed in the alternate position at 401a
and circuitry 402a is not needed.
Connected to the receiver 401 is an amplifier 402, memory
device 403 and a precise clock 404. Power for the clock,
memory device and receiver is supplied by a power source, here
shown as a battery 405, and all are connected by circuitry 406.
For ease of access, the clock, memory device and battery are
located at or above ground level 17. Clock 404 has been
synchronized with clock 202 before the detector unit is released
into the pipeline, so that the error between them when
measuring the same time is known.
In operation, the acoustic emitter 201 of either the ball sensor
unit of Figure 1 or the pipeline pig of Figure 2 emits signals at
predetermined intervals at a predetermined frequency. If
desired, instead of a signal at a predetermined frequency,
acoustic emitter 201 can emit groups of signals at
predetermined frequencies in a predetermined order at such
predetermined intervals. Events sensed by sensors 203 and
204, along with a continuous recording of the time displayed by
clock 202, are recorded in memory device 205. It is not
necessary to record the times of the acoustic emissions in the
memory device (although this can be done of desired), because
the emissions occur at predetermined intervals, and the time of
the first emission are known because the acoustic emitter 201 is
enabled at the known time when the detector unit is released
into the pipeline. Additionally, if the hydrophone 204 picks up the
frequency at which the signals are emitted, its recording will
provide a record of such signals.
The fluid 13 leaving the pipeline leak 14 emits noise as the fluid
leaves the pipeline. This noise, indicated as wavefronts 16, is
picked up by the hydrophone 204 and is recorded in the memory
device 205 along with the other events sensed by sensor 204.
Optionally, the memory device can have associated software
which recognizes that an anomalous piece of data has been
recorded and causes the acoustic emitter 201 to send out a
sequence of tones immediately. This sequence is different from
any tone or frequency sent out at the predetermined interval,
and is to provide information which will give an exact location at
which the anomalous data has been acquired. Normally,
however, it is not found necessary to do this, as sufficiently
precise location can be obtained by interpolating the anomalous
data between the signals sent out at the predetermined
intervals.
The acoustic emissions 215 pass through the fluid in the
pipeline, and are received by acoustic receiver 401 or 401a
(Figure 3). In a preferred embodiment, the acoustic receiver has
associated software which compares the known time of sending
of each acoustic emission (which is known because the clocks
of the receiving station and the transmission station are
synchronized) with the arrival time of that emission and
multiplies the difference by the speed of sound of that frequency
to provide in real time a position of the detector unit in the
pipeline. This is of particular utility when the receiving station is
at the location where the detector unit is to be retrieved from the
pipeline, as it permits an operator at that location to view the
real-time position of the detector unit and to make preparations
for its retrieval.
If this preferred embodiment is used, the real-time position of the
detector unit is recorded directly. Otherwise, the precise time of
receipt of each emission as shown by clock 404 is recorded in
memory device 403.
After the desired inspection has been made, the contents of
memory devices 403 and 205 are examined. Where anomalous
readings, or readings which indicate a condition of interest, have
been made by the sensors, the time that these are recorded in
the memory device as having been observed are noted. The
acoustic emissions issued at periodic intervals which are
nearest to the time of the observation (and any special acoustic
emission, if made, when the anomalous result was observed)
are then compared with the record of the receipt of those
emissions at the receiving station. The time lag between the
sending and the receipt of each emission, multiplied by the
speed of sound of that frequency in the liquid which is in the
pipeline, gives a very precise measurement of the distance
between the detector unit and the receiving station at the time
the emission was sent. This locates precisely the location of the
detector unit, and hence the sensor, when the anomalous
signals were sensed by the sensor, so that further testing or
pipeline repair can be carried out. The accuracy of the location
of course decreases with the distance of the detector unit from
the receiving unit where the results are received. Therefore, it is
preferred to have receiving stations spaced along the pipeline,
and to examine the relevant emissions as received by at least
two receiving stations.
The error between the clocks on the receiving stations and the
transmitting station is preferably determined at the beginning or
end (or both) of a passage of a detector unit though the pipeline
by comparison with a common standard such as a GPS time
signal. If a detector unit is sent though a pipeline for an
inspection taking several hours, there may be some drift,
depending on the accuracy of the clocks used. Generally, the
clocks which are commercially available are accurate to within
about 1 millisecond per hour. More accurate clocks can be
obtained commercially but are more expensive. A drift of
several milliseconds an hour can be tolerated without unduly
affecting the accuracy of the results, because every time that the
detector unit passes a known location, such as a beacon or a
receiving station, a correction factor for drift can be applied.
Figure 4 shows an alternate embodiment in which the
transmitting station is located at an access port, and the
receiving station is located on a detector unit. The same
numbers are used as in previous figures to indicate the same
things as in those previous figures. The figure is not to scale and
jagged lines 600 indicate that there is a length of pipeline of
several hundred metres in length that has been omitted between
the parts shown on the two sides of the jagged line.
Figure 4 shows a transmitting station 500 located at an access
port 513. The transmitting station has a precise clock 502. This
is connected by circuitry 504 to an acoustic emitter 501, which
can emit acoustic signals at a pre-chosen frequency within the
range of 20 - 100 KHz, The acoustic emitter can be, for
example, a 3/4" diameter x .1" thick piezo crystal. The acoustic
emitter is arranged to emit an acoustic signal at set time
intervals, for example once every 3 seconds. Preferably, there is
a memory device 507 which records the acoustic signals and
the time of emission of each such signal.
Alternately or in addition, acoustic emitter 501 can be a tone
generator which can emit a pre-chosen sequence of acoustic
signals at frequencies in the range 20-100 KHz.
The acoustic emitter is shown as being in contact with fluid 11.
However, if desired, the acoustic emitter can be placed in
alternative position 501a in acoustic contact with the pipeline
(here shown as on the cover of access port 513) and be
connected to the clock 502 by circuitry 504a.
Power source 503 powers the clock and acoustic emitter
through power circuitry 505.
In this embodiment the receiving station is mounted on a
detector unit, here illustrated as a pig 540 similar to pig 300
shown in Figure 2. As in Figure 2, the detector unit 540 contains
a precision clock 202 and sensors 203 and 204. As discussed
previously, sensor 204 is a hydrophone. .A memory device 205,
which can be a conventional flash memory or SD card, is linked
by suitable circuitry 206 to record data generated by the sensors
203 and 204. The memory device 205 records also a continuous
time trace from the clock, so that the precise time of each piece
of data recorded by the sensors 203 and 204 is recorded.
Battery 207 provides power for these elements through circuitry
206.
Unlike the pig in Figure 2, however, pig 540 has no acoustic
emitter. Instead, there is an acoustic receiver 550 which is
capable of receiving the emissions generated by acoustic
emitter 501 of transmitting station 500. If necessary, the sound
received is amplified by an amplifier 551, and is recorded along
with the traces from clock 202 and sensors 203 and 204 in
memory device 205. If hydrophone 204 is designed so that it
can pick up the frequency or frequencies emitted by acoustic
emitter 501, then receiver 550 and amplifier 551 can be omitted,
and the hydrophone can function as both acoustic sensor for
leaks and the like and as the receiving station for the invention.
In operation, the acoustic emitter 501 or 501a emits signals at a
predetermined interval from one another at a predetermined
frequency. If desired, instead of a signal at a predetermined
frequency, acoustic emitter 501 or 501a can emit groups of
signals at predetermined frequencies in a predetermined order
at such predetermined interval.
At the pig, receiver 550 (or hydrophone 204, if it can pick up the
appropriate frequency) receives emissions sent out by acoustic
emitter 501 or 501a. The emissions (which are amplified if
necessary by amplifier 551), events sensed by sensor 203 and
hydrophone 204, along with a continuous recording of the time
displayed by clock 202, are all recorded in memory device 205.
The fluid 13 leaving the pipeline leak 14 emits noise as the fluid
leaves the pipeline. This noise, indicated as wavefronts 16, is
picked up by the hydrophone 204 and is recorded in the memory
device 205 along with the other events sensed by sensor 204.
After the desired inspection has been made, the contents of
memory device 205 and memory device 507 are examined, and
the clock traces are adjusted to compensate for error between
the clock readings, if any.. Where the sensors show anomalous
readings, or readings which indicate a condition of interest, the
time that these are recorded in the memory device 205 as
having been observed are noted. The acoustic emissions
received nearest to the time of the observation are then
compared with the record of when those emissions were sent
from the transmitting station. The matching of emissions sent
and emissions received by counting the number of emissions
sent by the transmitting station and the number of emissions
received by the receiving station since the pig's travel through
the pipeline began. The time lag between the sending and the
receipt of each emission, multiplied by the speed of sound of
that frequency in the liquid which is in the pipeline, gives the
measurement of the distance between the detector unit and the
receiving station at the time the emission was sent. This locates
precisely the location of the detector unit, and hence the sensor,
when the anomalous signals were sensed by the sensor, so that
further testing or pipeline repair can be carried out.
Examples
Example 1 - Water pipeline
In a 36 inch diameter pipeline, filled with potable water at a
pressure of approximately 200 psi, emissions from a transmitting
station on a detector unit were transmitted through the water in
the pipeline and successfully received at a receiving station at a
pipeline inspection port 800m. away. The detector unit was a
ball-type sensor unit of the type shown in PCT Published
application WO 2006/081671, rolling along the bottom of the
pipeline. The emissions were 25 ms. in length at a frequency of
40000 Hz.
Example 2 - Oil pipeline
In a 10 inch diameter pipeline, filled with crude oil at a pressure
of approximately 200 psi, emissions from a transmitting station
from a transmitting station on a detector unit were transmitted
through the oil in the pipeline and were successfully received at
a receiving station at a pig launching station 200 m. away. The
detector unit was a ball-type sensor unit of the type shown in
PCT Published application WO 2006/081671, rolling along the
bottom of the pipeline. The emissions were 25 ms. in length at a
frequency of 30000 Hz.
Example 3 - Natural gas Pipeline
In a 200 mm. diameter natural gas pipeline, with gas at pressure
varying between about 103 kPa and 270 kPa, emissions from a
transmitting station on a detector unit were transmitted through
the gas in the pipeline and were successfully received at a
receiving station at an inspection port 50 m. away. The detector
unit was a ball-type sensor unit of the type shown in PCT
Published application WO 2006/081671, rolling along the bottom
of the pipeline. The emissions were 25 ms. in length at a
frequency of 65000 Hz.
It is understood that the invention has been described with
respect to specific embodiments, and that other embodiments
will be evident to one skilled in the art. The full scope of the
invention is therefore not to be limited by the particular
embodiments, but the appended claims are to be construed to
give the invention the full protection to which it is entitled.
What is claimed is:
1. Apparatus for locating an object in a pipeline, comprising
a transmitting station having means for transmitting in the pipeline acoustic emissions
having a frequency in the range from 20 KHz to 200 KHz,
a receiving station having a receiver capable of receiving the acoustic emissions
transmitted by the transmitting station,
one of said receiving station and said transmitting station being located at a known
position on the pipeline and the other of said receiving station and said transmitting station
being located on said object; and
clock means to determine the time taken for said acoustic emissions to travel between
the transmitting station and the receiving station.
2. Apparatus for locating a moving object within a pipeline, comprising;
a transmitting station on such object having means for transmitting in the pipeline
acoustic emissions having a frequency in the range from 20 KHz to 200 KHz,
first clock means associated with said transmitting station for transmitting said acoustic
emissions at known times or at predetermined intervals,
a receiving station on the pipeline at a known location and having an acoustic receiver
capable of receiving the acoustic emissions transmitted by the transmitting station, and
second clock means associated with the receiving station to determine the times said
acoustic emissions are received by said receiving station.
3. Apparatus as claimed in claim 2, in which the error if any between the reading of the
clock means associated with the transmitting station and the reading of the clock means
associated with the receiving station is known.
4. Apparatus as claimed in any of claims 1-3 including recording means associated with
the transmitting station to record acoustic emissions sent by the transmitting station and
recording means associated with the receiving station to record acoustic emissions received
by the receiving station.
5. Apparatus as claimed in any preceding claim, in which the object is a detector unit
equipped with at least one sensor to detect at least one anomalous condition within the
pipeline.
6. Apparatus as claimed in claim 5, in which the sensor is equipped so that the detection
of an anomalous condition by the sensor causes the transmitting station to transmit an
acoustic emission.
7. Apparatus as claimed in any preceding claim, in which the means for transmitting
acoustic emissions transmits emissions having a frequency in the range from 20 KHz to 100
KHz.
8. A method for determining the position of an object in a pipeline which contains fluid,
comprising;
transmitting in the pipeline acoustic emissions having a frequency in the range from 20
KHz to 200 KHz from the object within the pipeline,
receiving the acoustic emissions at a known position on or in the pipeline,
determining the time taken for said acoustic emissions to travel between the object and
the known position, and
determining the speed of sound in the fluid in the pipeline.
9. A method for determining the position of an object in a pipeline which contains fluid,
comprising;
transmitting in the pipeline acoustic emissions having a frequency in the range from 20
KHz to 200 KHz from a known position on or in the pipeline,
receiving the acoustic emissions at the object,
determining the time taken for said acoustic emissions to travel between the known
position and the object, and
determining the speed of sound in the fluid in the pipeline.
10. A method as claimed in either of claims 8 or 9, in which the acoustic emissions have a
frequency in the range from 20 KHz to 100 Khz.
11. A method as claimed in any of claims 8-10, in which the acoustic emissions have a
duration in the range of from 1 millisecond to 200 milliseconds.

Apparatus for locating
an object in a pipeline, comprising a
transmitting station having means for
transmitting in the pipeline acoustic
emissions having a frequency in the
range from 20 KHz to 200 KHz; a receiving
station having a receiver capable
of receiving the acoustic emissions
transmitted by the transmitting station;
one of the receiving station and the
transmitting station being located at a
known position on the pipeline and the
other of the receiving station and the
transmitting station being located on the
object; and clock means to determine
the time taken for the acoustic emissions
to travel between the transmitting station
and the receiving station.