WO2021141500A1

WO2021141500A1 - Leaks in pipes

Info

Publication number: WO2021141500A1
Application number: PCT/NO2021/050006
Authority: WO
Inventors: Morten TALGØ; John Helvik
Original assignee: Leak Detector As
Priority date: 2020-01-09
Filing date: 2021-01-11
Publication date: 2021-07-15
Also published as: NO20200027A1; NO347183B1

Abstract

There is described a method of surveying at least one section of pipeline for determining an existence or a location of a leak aperture in a wall of the pipeline, and related apparatus. In various examples, an optical sensing fibre is provided which is arranged inside and extends along the section of pipeline; a heat source fluid is advanced in a flow along the pipeline; temperature detection data are obtained from a plurality of detection locations along the optical sensing fibre, wherein in respect of each of at least some of the detection locations of said plurality, the data are obtained at a plurality of detection times to allow detecting a temporal development in temperature associated with the heat source fluid arriving in proximity to the detection location, and arrival times of the heat source fluid from different detection locations of the fibre are used to determine the existence or the location of the leak aperture.

Description

LEAKS IN PIPES

Technical field

The present invention relates in particular to the detection of leak apertures in pipes.

Background and prior art

Pipeline leakages have received attention in a wide range of industries due to the various problems they may cause. Water loss from leaking pipelines buried underground, for ex ample in water pipeline networks that supply water to users, can cause operational difficul ties for water companies. Today, significant efforts are made by water companies to detect and repair leaks that have occurred.

When inspecting water pipes that are buried underground, various techniques have previ ously been applied. These techniques include for instance acoustics. Techniques for sur veying pipes for detecting leaks can suffer from lack of precision, low energy transmission, environmental noise due to impacts, data noise, lack of sensitivity to large leakages, and human error and inconvenience in the positioning and operation of equipment during sur veys. Acoustic techniques may not be effective in plastics pipes where plastics material may not carry the acoustic energy effectively as compared with for example metal pipes. Water supply pipes are increasingly plastics material.

An aim of the invention is to provide an effective solution for leak detection that better meets the needs of water companies today. Another aim is to obviate or mitigate one or more drawbacks of prior art.

Summary of the invention

According to a first aspect of the invention, there is provided a method of surveying at least one section of pipeline for determining an existence or a location of a leak aperture in a wall of the pipeline, the method comprising the steps of: providing an optical sensing fibre which is arranged inside and extends along the section of pipeline; advancing a heat source fluid in a flow along the pipeline; obtaining temperature detection data from a plu rality of detection locations along the optical sensing fibre; wherein in respect of each of at least some of the detection locations of said plurality, the data is obtained at a plurality of detection times to allow detecting a temporal development in temperature associated with the heat source fluid arriving in proximity to the detection location; and using arrival times of the heat source fluid from different detection locations of the fibre to determine the ex istence or the location of the leak aperture.

The method may include inserting a batch of the heat source fluid into the pipeline. The inserted heat source fluid preferably fills a cross sectional flow section of the pipeline. The insertion step may comprise inserting the batch of heat source fluid into the flow of fluid. The fluid of the flow may be or comprise water. The heat source fluid may be or comprise water, e.g. hot water.

The batch of heat source fluid may typically be inserted into the pipeline through a passage way which extends through a wall of the pipeline. An interior of the pipeline may be acces sible through a manhole or other hole in the ground, which may include or provide access to the pipeline and/or passageway which extends through the wall of the pipeline.

The method may include heating the heat source fluid by transferring thermal energy to the fluid prior to inserting the heat source fluid into the pipeline. The heat source fluid may be stored in a tank or other receptacle. The heat source fluid may be heated in the tank. The method may include releasing the heat source fluid from the tank or other receptacle, e.g. by operating a valve. The heat source fluid may thus flow from the tank into the pipeline. The heat source fluid may be heated to have a temperature greater than the fluid of the flow.

Using the arrival times may comprise using a first arrival time at a first detection location and a second arrival time at a second detection location. The method may include deter mining, e.g. calculating or computing, at least one speed of advancement of the heat source fluid between different detection locations, e.g. the first and second detection locations. The method may include using the times of arrival at respective locations, determining a speed of advancement between first and second locations of a first pair of detection loca tions and determining the speed of advancement between first and second locations of a second pair of detection locations, and based on the determined speeds, e.g. by detecting a reduction in speed, determining the existence or location of the leak aperture. The speed may be determined or calculated using the elapsed time between the arrival times of the first and second locations and distance between locations, e.g. by dividing the elapsed time by the distance. The distance between detection locations may be known or predeter mined.

The method may further comprise repeating the step of inserting at least one batch of heat source fluid into the pipeline, the heat source fluid advancing along the pipeline and the optical sensing fibre. After inserting the one batch, the method may include waiting until a temperature of contents of the pipeline has reduced or returned to a predefined value, e.g. to obtain a temperature sufficiently contrasting with the temperature of the fluid of the next batch to be inserted, before repeating the insertion step to insert a next batch.

The method may further comprise combining first response data associated with the inser tion of one batch and second response data associated with the insertion of another repeat batch. The method may further comprise correlating arrival events of the first and second response data. The method may further comprise obtaining the rate of advancement based on correlated arrival event times at the different locations.

The method may further comprise running the optical fibre into the pipeline through an ac cess passageway through a wall of the pipeline. The pipeline may be buried under ground and may extend horizontally.

According to a second aspect of the invention, there is provided a method of surveying at least one section of pipeline for determining an existence or a location of a leak aperture in a wall of the pipeline, the method comprising the steps of: providing an optical sensing fibre which is arranged inside and extends along the section of pipeline; advancing a heat sink fluid in a flow along the pipeline; obtaining temperature detection data from a plurality of detection locations along the optical sensing fibre; wherein in respect of each of at least some of the detection locations of said plurality, the data is obtained at a plurality of detec tion times to allow detecting a temporal development in temperature associated with the heat sink fluid arriving in proximity to the detection location; and using arrival times of the heat sink fluid from different detection locations of the fibre to determine the existence or the location of the leak aperture.

According to a third aspect of the invention, there is provided apparatus for performing the method of any preceding claim. According to a fourth aspect of the invention, there is provided a computer device for deter mining the presence or location of the leak.

Any of the above aspects of the invention may comprise one or more further features as described in relation to any other aspect, wherever described herein.

Embodiments of the invention are advantageous as will be apparent from the present de scription.

Drawings and specific description

These aspects will now be described further, by way of example only, with reference to the accompanying drawing, in which:

Figure 1 is a representation of apparatus for performing a survey of a pipeline; Figure 2 is a representation of a computer device for the apparatus of Figure 1; Figure 3 is a representation in close up of a section of pipeline with an optical sensing fibre arranged inside the section of the pipeline;

Figure 4 is a graph showing data obtained from the optical sensing fibre of Figure 3; and

Figure 5 is a plot against time of data obtained from the fibre for different locations the optical sensing fibre.

With reference to Figure 1, apparatus 1 for performing a survey of a pipeline is generally depicted, including in this example an underground pipeline 2. The pipeline 2 is an under ground water pipeline used for containing water. Water is normally communicated down stream through the pipeline 2 as indicated by arrow F, driven by a pressure differential, the pressure P1 being greater than the pressure P2. The pipeline 2 has a leak aperture 3 in the wall of the pipeline 2 through which water or other contents escapes out of the pipeline. The apparatus 1 provides for detecting or determining the leak aperture location 3.

The apparatus includes an optical temperature sensing fibre 4 which is disposed inside the pipeline 2 and extends along the pipeline 2. The optical sensing fibre 4, in respective de tection locations along the fibre, permits detecting at least one temperature or temperature change of pipeline contents in proximity to each said detection location. In use, a heat source fluid in the form of hot water is advanced along the pipeline 2 in a flow, the front of this fluid indicated by numeral 11. The optical sensing fibre 4 is used to detect the temperature or temperature change associated with the heat source fluid, at different detection locations of the optical sensing fibre. As may be appreciated, upon advancement in the flow, the hot fluid arrives first in proximity to one detection location of the optical sensing fibre and then another. Temperature detection data is obtained using the fibre from a plurality of detection locations along the optical sensing fibre 4. For each detection loca tion, the data is obtained at a plurality of detection times, e.g. as time series data recorded relative to a reference time, to allow a temporal development in temperature associated with the heat source fluid arriving in proximity to the detection location to be detected. Arrivals of the heat source fluid at different locations along the pipeline can then be detected from obtained detection data. The data are indicative of the temperature or temperature change at different detection locations, i.e. at different positions, along the fibre. Arrival times of the heat source fluid from different detection locations of the fibre are used to determine the existence or the location of the leak aperture.

More specifically, the arrival times for different detection locations can be used to determine or indicate whether the speed of advancement of the hot water has decreased along the pipeline and where that decrease takes place. Typically, the distance between detection locations along the fibre is known, or the detection locations have equal spacings along the fibre, and the speed can then be calculated. If there has been a decrease, the existence of the leak can be inferred. The leak aperture location corresponds to where the decrease in speed is identified.

Optical fibre technology is available commercially for detecting temperature in multiple de tection locations along an optical fibre. The optical sensing fibre can be configured and operated in different ways for temperature detection data at multiple locations or sections. The optical fibre typically has multiple sensor elements or sensor sections along the fibre.

For present purposes, the exemplified optical sensing fibre 4 is a Fibre Bragg Grating (FBG) sensor fibre. The optical sensing fibre 4 is provided with gratings which are situated in discrete locations along the fibre. Data is then obtained from the different gratings using e.g. multiplexed temperature sensing. The grating has a response depending upon the temperature to which it is subjected, e.g. by the contents of the pipeline. A light source 8 is provided at surface and is arranged to transmit light through the fibre. Light is reflected from the gratings. The reflected light has different characteristic wavelengths from different gratings. Thus, light reflected from one grating has a power peak around at one wavelength or band, and light reflected from another grating has a power peak at another wavelength or band. The reflected wavelength from the grating is temperature dependent. A change in temperature produces a temperature dependent shift in wavelength and magnitude from the relevant grating. The reflected light is returned from the gratings through the fibre as a multiplexed signal. The light signal is received by the surface unit 10 and can then be pro cessed to obtain the power against wavelength spectral responses and/or temperature re sponse with time for the different wavelengths, in the different locations along the fibre. The optical fibre arranged in this way using gratings can be advantageous as it allows for very accurate measurements when the heat source fluid is moving quickly along the pipe. It can also provide measurements with high spatial accuracy as the gratings can in principle be arranged closely spaced along the fibre. However, it is envisaged to arrange the gratings typically with a i m spacing.

Figure 3 shows in further detail how the optical sensing fibre 4 is arranged. The optical sensing fibre 4 has distributed temperature gratings 44a-44c. The gratings 44a-44c are spaced apart at equal spacings 45a, 45b. They define thereby multiple “sensing” locations along the length of the fibre. As seen in Figure 4, the gratings 44a, 45b have peaks in power against wavelength overtime associated with the change in temperature arising in proximity to the gratings by the hot water advancing along the pipe. As the hot water has not yet reached the grating 44c, the resulting temperature change has not yet taken place, and therefore the power associated with grating 44c in Figure 4 is still low.

Sensor data from the optical fibre 4 is processed to allow responses as time series from the different locations along the fibre to be distinguished. The times of the response relative to each other or relative to a reference time can indicate the speed of hot fluid along the pipe line.

The speed of travel or advancement of the hot fluid between detection locations can also be calculated, providing the distance between detection locations is known or determined. This can be calculated by dividing the time of travel between locations with the distance therebetween. The travel time between locations can be obtained by forming the difference between the arrival times at different locations.

For example, the data from one detection location has a first anomaly, e.g. peak or trough, when the hot fluid has reached that first section. Similarly, the data from another location has a second anomaly, e.g. peak or trough, when the hot fluid has reached that second section. The second section is spaced some distance away and therefore the hot fluid arrives first at the first section, and then later at the second section. The anomalies occur at different times relative to a time of reference, e.g. the time of insertion of the hot fluid. The elapsed time between the appearance of the first and second anomalies at the first and second sections, corresponds to the elapsed time of travel along the pipeline between those sections. By dividing the distance by the elapsed time, the speed of advancement is calcu lated.

The distance between detection locations in the fibre is known in advance, and the relative position of the detection locations relative to the pipeline can be determined, e.g. by record ing the distance the fibre has been spooled out. The speed of advancement can be ob tained from the detected times of arrival or presence of the hot water at the different loca tions along the pipeline.

The calculation of the speed of advancement can be carried out for sections of the optical fibre progressively further downstream. A “profile” of speed measurements for the flow inside the pipe can be obtained along the fibre. It can then be seen at what location, if any, the speed falls. If the speed has decreased from one level at an upstream location to a lower level downstream, then this indicates the existence of the leak between those up stream and downstream locations.

The flow rate Q can be similarly calculated by the formula Q = v x a where v is flow velocity as obtained by calculation of flow speed from the arrival times, and a is the cross-sectional flow area of the pipe. The change in flow rate where the area a is remains the same is indicative of the presence of a leak.

Calculating the speed or velocity is not essential. As can be seen in Figure 5, one can plot the data for different detection location of the fibre against time. The times of the anomalies associated with the response of the fibre to the increase in temperature can be observed relative to one another. In Figure 5, the section numbers increase with distance down stream along the optical sensing fibre 4. There is a greater elapsed time between the oc currence of the temperature response between sections s4 and s5 than that elapsed be tween sections s2 and s3. This indicates that there has been a reduction in velocity from which it can be inferred that the leak 3 is located between the sections s3 and s4. Thus, in some examples, the data from the fibre can be processed and then analysed visually for each section to identify the whereabouts of the leak.

The apparatus 1 also includes means for inserting the heat source fluid, in this case hot water, into the pipeline 2 at selected times. The hot water is initially prepared and stored in a tank 6. When required, a valve 7 is operated to release an amount of the hot water into the pipeline. The hot water is supplied through a passageway through side of the pipeline, e.g. the same passageway 5 that is used to run the optical fibre into the pipeline 5. The valve 7 is located in a conduit between the tank and the pipeline. The conduit extends from the tank into and/or through the passageway. The hot water (T2) is hotter than the contents (T1) already in the pipeline, e.g. hotter than water or other fluid which may already be con tained in the pipeline when inserting the hot water.

The hot water fills the pipe, and due to the pressure differential P1 > P2, the hot water upon being inserted then advances through the pipeline 2. The temperature of the advancing water is detected at different locations by the fibre. In other words, the temperature of the hot water is detected when the hot water arrives in proximity to respective sensor elements in different locations along the fibre. Since the temperature increases when the hot water arrives adjacent to the sensing element, this temperature increase can be detected.

It can be useful to insert hot water into the pipeline, batch-wise, several times. The data associated with the insertion of one batch can then be compared or combined with the data associated with another batch to improve the basis for estimating the time of arrival of the hot water in different locations along the pipeline. For example, by correlating or combining data derived from insertion of different batches, a more distinctive anomaly, e.g. steeper slope or more defined peak, in the optical response for the particular detection location of fibre may be obtained.

Furthermore, the hot fluid in different batches can have different temperatures, and can differ from the temperature of the contents inside the pipeline prior to insertion of the batch by different amounts. This may also improve the data, signal to noise ratio, and quality of determination of the arrival times and speed. This can help to identify small leaks where the differences in speed upstream and downstream may be smaller.

It can be appreciated that since the optical fibre is sensitive to temperature, and an anomaly indicative of the arrival of the is obtained when the hot fluid arrives due to the increase in temperature that the hot fluid produces, the technique described above can correspondingly be applied in a pipeline initially containing hot fluid. In such an example, a batch of heat sink fluid, e.g. cold water, can be inserted into the pipeline. The cold water advances down stream producing a reduction in temperature which is detectable by optical response of the fibre in different detection locations of the fibre corresponding to the progress of the cold water along the pipeline.

With reference additionally to Figure 2, the apparatus 1 includes a computer device 100 which has an In/Out unit 101, a microprocessor 102, and memory 103. The In/Out unit 101 is used for communicating with, e.g. sending instructions, to the valve 7 for controlling the insertion of hot fluid. The In/Out unit 101 is also used for communicating with the optical unit 10 for transmitting light into the fibre and receiving light from the fibre, and sending data to or from the optical unit, e.g. transmission data or response data. The microprocessor 102 is used to execute at least one computer program, e.g. for processing and/or analysing the response data which may comprise combining data from different batches, determining the times of arrivals at different locations along the pipeline, determining the rates of ad vancement at different locations along the pipeline, determining a location of the leak. The computer program is stored in the memory 103. Data is stored in memory 103, including e.g. the time of insertion of hot fluid, the distance that the fibre extends along the pipeline, as may be used to determine the elapsed times and distances in the pipeline. The computer device 101 includes a display 104 which can be used for viewing the data, e.g. a plot such as that of Figure 5.

The optical sensing fibre 4 is contained in a rope which is spooled out from a drum 12. The optical sensing fibre for instance constitutes a core of the rope. Strands of synthetic or natural fibres are laid e.g. helically wound about the core, along the length of the rope. The rope can be wound with tight arc onto the drum 12. The apparatus 1 includes a vertical drum about which the rope is wound. The rope is spoolable in and out from the drum. The drum may be supported on a unit connected to the pipeline e.g. at the entrance to the pas sageway 5, e.g. in the manhole. The apparatus may include a feeder device to grip and urge the rope off the spool and through the passageway 5 into the pipeline 2. By way of construction, the rope may be buoyant so as to allow it to be drawn along the pipe by the flow of fluid in the pipeline.

Alternatively, a cable or flexible rod may be used, these having greater stiffness than the rope, to facilitate “pushing” the rod or cable into and along the pipeline through the passageway 5. The passageway 5 may have section arranged at an angle with respect to the pipe axis to facilitate directing the fibre along the pipeline.

The apparatus includes a counter device 9 which can provide a read out of the length of rope spooled out from the drum 12. When a certain length has been spooled out, the dis tance along which it extends in the pipeline 2 may also be inferred.

Optionally, the survey is performed between two ground holes, e.g. manholes 16, each with an access passageway 5 through the wall of the pipeline. The manholes have a known distance between. The rope can be spooled out and extend along the pipeline in the length between the passageway of the first manhole and that of the second manhole. The second, downstream manhole can be used to verify the presence of the optical fibre.

By previous surveying, it may be already determined that a particular section of pipeline, e.g. between manholes, has a leak. The technique here described can be performed to detect the specific position of the leak within the section of pipeline.

The technique described can be convenient way of detecting leaks. In particular, it is not restricted by material of the pipeline, and is effective in arrangements where the pipeline e.g. comprises composites or plastics pipe. By arranging the fibre inside the pipeline, a direct sensing of the temperature of the contents of the pipeline is achieved, which can facilitate obtaining a good, low-noise signal from the advancing heat source/sink fluid. Measurements can be obtained repeatedly, by repeat insertion of the heat source/sink fluid, to enhance the signal to noise ratio. The technique can be deployed without producing environment impact noise, and conveniently the optical fibre and inserted fluid can be pro vided through existing access structure, such as manhole and entrance in the side of the pipe. The optical fibre is readily deployable by motorized spooling in or out from drum 12. As can be appreciated any of the drum 12, the surface unit 10, the computer device 100 and the tank 6 can be arranged at or above ground level.

Claims

1. A method of surveying at least one section of pipeline for determining an existence or a location of a leak aperture in a wall of the pipeline, the method comprising the steps of: providing an optical sensing fibre which is arranged inside and extends along the section of pipeline; advancing a heat source fluid in a flow along the pipeline; obtaining temperature detection data from a plurality of detection locations along the optical sensing fibre; wherein in respect of each of at least some of the detection locations of said plurality, the data are obtained at a plurality of detection times to allow detecting a temporal devel opment in temperature associated with the heat source fluid arriving in proximity to the de tection location; and using arrival times of the heat source fluid from different detection locations of the fibre to determine the existence or the location of the leak aperture.

2. A method as claimed in claim 1, wherein the heat source fluid fills a cross sectional flow section of the section of the pipeline.

3. A method as claimed in claim 1 or 2, which further comprises inserting a batch of the heat source fluid into pipeline, wherein heat source fluid comprises water.

4. A method as claimed in claim 3, wherein the batch of heat source fluid is inserted into the pipeline through a passageway which extends through a wall of the pipeline.

5. A method as claimed in claim 3 or 4, which includes heating the heat source fluid by transferring thermal energy to the fluid prior to inserting the heat source fluid into the pipe line.

6. A method as claimed in any of claims 3 to 5, which further comprises repeating the step of inserting at least one batch of heat source fluid into the pipeline, the heat source fluid advancing along the pipeline and the optical sensing fibre.

7. A method as claimed in claim 6, which further comprises: combining first response data associated with the insertion of one batch and second response data associated with the insertion of another repeat batch; correlating arrival events of the first and second response data; obtaining the rate of advancement based on correlated arrival event times at the different locations.

8. A method as claimed in any preceding claim, which further comprises running the optical fibre into the pipeline through an access passageway through a wall of the pipeline;

9. A method of surveying at least one section of pipeline for determining an existence or a location of a leak aperture in a wall of the pipeline, the method comprising the steps of: providing an optical sensing fibre which is arranged inside and extends along the section of pipeline; advancing a heat sink fluid in a flow along the pipeline; obtaining temperature detection data from a plurality of detection locations along the optical sensing fibre; wherein in respect of each of at least some of the detection locations of said plurality, the data are obtained at a plurality of detection times to allow detecting a temporal devel opment in temperature associated with the heat sink fluid arriving in proximity to the detec tion location; and using arrival times of the heat sink fluid from different detection locations of the fibre to determine the existence or the location of the leak aperture.

10. Apparatus for performing the method of any preceding claim.

11. A computer program which is computer-executable for performing at least one or more of the steps of the method of any preceding claim.

12. A computer device on which the computer program of claim 11 is stored so as to be executable by the computer device.