GB2603196A

GB2603196A - Leak Detection

Info

Publication number: GB2603196A
Application number: GB2101380.0A
Authority: GB
Inventors: John Parker Michael; James Harris Andrew
Original assignee: CRALEY GROUP Ltd
Current assignee: CRALEY GROUP Ltd
Priority date: 2021-02-01
Filing date: 2021-02-01
Publication date: 2022-08-03
Also published as: GB202101380D0

Abstract

A leak detection apparatus 1 for a pipe comprises a distributed acoustic sensing(DAS) fibre 2 provided along a central conduit 4 of an elongate push rod 3. The push rod 3 is semi-rigid so as to enable it to be pushed along a pipe and sufficiently flexible so as to allow it to follow bends in the pipe. The apparatus 1 is provided with an antireflection device (25, figure 2) affixed to the insertion end (6) and provided with an optical coupler (7) at the other end for introducing optical pulses to DAS fibre 2 and for extracting backscattered pulses from DAS fibre 2. Vibrations propagating through the pipe cause variation in the backscattering that occurs within the DAS fibre 2 which enables identification of characteristic pipe events.

Description

LEAK DETECTION

Technical Field of the Invention

The present invention relates to leak detection in pipes. In particular, the present invention relates to apparatus and methods for leak detection in relatively small diameter water pipes such as those serving a property or distributing within a district metered area.

Background to the Invention

Water supply is a vital utility for homes and businesses. Potable water is distributed over larger distances via larger diameter trunk mains pipes at relatively high pressure. Typically, water is distributed from the trunk mains to multiple different district metered areas (DMA). A DMA is local region of a water supply network that services a defined set of properties. The set of properties may vary in size but might typically cover 1,000 homes or so. Within the DMA distribution is carried out via smaller diameter DMA distribution and access mains pipes and a pressure reduction valve (PRV) is frequently provided to provide a suitable water pressure within the DMA. From the DMA pipes, further very small diameter service pipes will branch off to individual properties.

A key aspect of managing water distribution is the detection of leaks. As pipes typically run underground, optimal leak detection requires access to the interior of the pipe in order to accurately locate the leak with maximum sensitivity, and such that.

disruption associated with uncovering the pipe for repair is minimised. Leaks in trunk mains are particularly serious in view of the potentially large impact on the wider network as such, there are numerous techniques for monitoring such trunk mains pipes and detecting such leaks.

For smaller diameter pipes leak detection can be more difficult. For instance, smaller pipes limit the size of sensors that can be inserted and the lower flow rates may mean that sensors relying on flow to travel along the pipe are of limited effectiveness. Additionally, multiple bends and curves in such smaller diameter pipes are typically tighter and sharper further impeding sensor insertion. A further problem is that the specific route of smaller pipes may not be well mapped for their entire length, in the case of domestic service pipes the route is in fact generally unknown.

Known techniques for leak detection and location in such pipes rely upon inserting a microphone or hydrophone mounted on an end of a push rod into the pipe.

Typically, the push rod is semi-rigid. This means that the push rod is sufficiently rigid so as to enable the microphone to be pushed along the pipe and sufficiently flexible so as to allow the rod to bend and therefore be pushed around bends in the pipe. Suitable rods may be formed from fibreglass or other plastic materials and may be provided as an extended continuous length. A cable is connected to the microphone to transmit captured acoustic signals to a user outside the pipe. As the microphone is pushed along the pipe there is a change in the acoustic signal as the microphone passes a leak. By listening for a change in the acoustic signal, a user can identify a leak as the microphone passes the leak. The leak location can then be estimated from the length of rod inserted into the tube. The estimated location can be difficult to establish if the route of the pipe is not well known. The method also suffers from reliance upon the skill of the user in interpreting the audio signal to identify a leak.

A more recent proposal is to insert a linear hydrophone array, in some cases 10 to 20 metres in length, pulled along a pipe by a suitable draw line and provided with an optical fibre for transmitting captured acoustic signals back from the hydrophones for processing outside the pipe. This arrangement can potentially enable computer processing of captured acoustic data over the length of the array, to identify potential leaks without reliance on operator skill. The linear array can additionally help identify leak location relative to the array, albeit that accurate location may still require knowledge of the pipe route. A drawback of this method is that the hydrophone array will still only be able to analyse over a relatively short distance at any one time, may be relatively rigid, may have a significant diameter, and may be susceptible to damage if it repeatedly impacts the pipe walls during insertion. As such this method may only be practically implemented on relatively straight pipe sections or larger diameter pipes.

In W02019/166809 the use of distributed acoustic sensing (DAS) for monitoring pipes is disclosed. DAS involves the detection of backscattering of light.

pulses introduced into an optical fibre. The time of arrival and intensity of the backscattercd light is measured for each pulse, the time at which the backscattcred light is detected being related to the distance along the fibre the light has travelled before being scattered. Subsequent changes in the reflected intensity of successive pulses from a common region of the fibre correspond to variations in the strain applied to the fibre at that region, for instance due to vibrations experienced by the region of fibre. In this manner, the DAS fibre can act as a plurality of virtual microphones along the entire length of the fibre and can locate events causing acoustic signals down to an accuracy of around I meter. In such methods, the DAS fibre may be installed temporarily or permanently. Temporary installation is facilitated by introducing the fibre via a valve or other opening and allowing the fibre to be transported along the pipe by the fluid follow. Accordingly, this method of pipe monitoring is more readily used on larger diameter and/or relatively straight pipes than on smaller diameter pipes and those with more significant bends and curves.

It is therefore an object of the present invention to provide an apparatus and method that at least partially overcomes or alleviates the above issues.

Summary of the Invention

According to a first aspect of the present invention there is provided a leak detection apparatus for a pipe, the apparatus comprising: a push rod, a distributed acoustic sensing (DAS) fibre provided along the push rod; and an optical coupler operable to enable the introduction of light pulses into the DAS fibre and the extraction of backscattered light pulses from the DAS fibre for detection.

The DAS fibre can be operated as an array of a very large number of separate virtual hydrophones. As such it can more accurately detect and localise leaks along the entire length of any section of pipe where the apparatus is inserted, compared with a single hydrophone or conventional linear arrays of hydrophones. The DAS fibre does not impact adversely on the flexibility of the rod, thus ensuring that the apparatus can be readily inserted through small diameter or non-straight pipes.

The DAS fibre may be provided along substantially the full length of the push rod. In other embodiments, the DAS fibre is provided along at least one elongate section of the push rod. The DAS fibre may be substantially coaxial to the push rod or have a substantially parallel axis to the push rod. In further embodiments, the DAS fibre may have another relation to the push rod. For instance, the DAS fibre may run helically about the push rod axis.

The push rod may be a semi-rigid push rod. In this context, a push rod is semi-rigid where it is sufficiently rigid so as to enable the rod to be pushed along the pipe and sufficiently flexible so as to allow the rod to bend to enable the rod to be pushed around bends in the pipe.

The maximum axial extent of the push rod, the rigidity of the material and/or the cross-sectional profile dimensions of the rod may be selected such that the push rod is effectively semi-rigid when inserted into a pipe to be monitored. For instance, a push rod with a cross-sectional profile diameter in the range 4mm to 12mm might be suitable for use in a pipe of diameter 25mm to 150mm Smaller and large profiler diameter push rods may be suitable for use in larger diameter and smaller diameter pipes respectively.

The push rod may be provided as an extended continuous length. In such embodiments, the push rod may be deployed from a reel or spindle.

hi some embodiments, the push rod is formed from a single material or from a composite material. In such embodiments, push rods may be formed from any suitable materials including but not limited to: fibreglass, fibre reinforced plastic, FIDPE, polypropylene, or the like.

The push rod may have a substantially constant cross-sectional profile. In preferred embodiments, the cross-sectional profile may be substantially circular. In alternative embodiments, alterative cross-sectional profiles may be utilised.

In some preferred embodiments, the cross-sectional profile of the push rod may comprise a conduit. The DAS fibre may be provided within the conduit. The conduit may be coaxial with the push rod, may have a parallel axis to the push rod or may have another relation to the push rod axis For instance, the conduit may run helically about the push rod axis.

The conduit may have a cross-sectional profile corresponding to the cross-sectional profile of the push rod. For instance, a push rod with a circular cross-sectional profile may have a conduit with a circular cross-sectional profile.

In embodiments where the push rod has a conduit the DAS fibre may run along the conduit. The push rod can thus provide a protective barrier around the DAS fibre. This can prevent damage to the DAS fibre during storage, transport, insertion into a pipe and/or from debris within the pipe in use. In the event that there is a gap between the DAS fibre and the edges of the conduit, the gap may be filled with gel. This can improve acoustic coupling between the DAS fibre and the pipe or fluid within the pipe.

In other embodiments, the push rod may have a groove on an exterior surface and the DAS fibre may run within the groove. The DAS fibre may be retained in position by any suitable fixing means including but not limited to adhesive, adhesive tape, clips, brackets or the like. In further embodiments, the DAS fibre may be fixed to the exterior surface, without a groove or the like, and may be retained in position by any suitable fixing means including but not limited to adhesive, adhesive tape, clips, brackets or the like.

In other embodiments the DAS fibre may be integrally bonded within the push IS rod. This can be achieved by forming the push rod around the DAS fibre or by providing the DAS fibre within the conduit or groove and then filling the conduit or groove with packing material. The packing material may be the same as or the material forming the push rod and/or may be acoustically or thermally matched to the material forming the push rod. In such embodiments, the DAS fire essentially forms part of the structure of the push rod itself.

In some embodiments, the push rod may comprise a coil spring. The coil spiing may extend along the full length of the push rod. The coil spring may be provided around a central conduit. The DAS fibre may be provided within the central conduit. The coil spring may be substantially helical. The central conduit may be filled with gel.

This can improve acoustic coupling between the DAS fibre and the pipe or fluid within the pipe.

The cross-section of the coil spring is preferably substantially circular but may be oval, square or oblong in alternative embodiments, an oblong profile specifically providing enhanced linear stiffness while maintaining flexibility to transit curves and bends. The coil spring may be formed from any suitable material. In many embodiments, the coil spring is formed from metal such as stainless steel, or the like.

The coils may be provided with a coating. The coating may be applied directly to the external surface of each coil. Suitable coating materials include but are not limited to HDPE, polypropylene, polyurethane, or the like.

Additionally or alternatively, the coil spring may be provided with a sheathing cover. The sheathing cover may have a hollow cylindrical form so as to provide a central conduit or bonded to the spring material, in such a fashion the spring is rendered water tight and pressure proofed. Suitable cover materials include but are not limited to HDPE, polypropylene, polyurethane or the like. Where there is a gap between the coil spring and the cover, the gap may be filled with gel. This can improve acoustic coupling between the DAS fibre and the fluid within the pipe.

In such embodiments, a linear tensional support may be provided along the central spring conduit. The tensional support may comprise a flexible stainless steel multi-wire rope, rigidly affixed to die ends of the spring, or the like. Such a technique would prevent linear extension of the spring when being pulled back along the pipe and IS around bends and curves.

In such embodiments, the fibre may alternatively be integrally bonded within the central conduit. This can be achieved by providing the DAS fibre within the conduit and then filling the conduit with packing material. The packing material may be the same as or the material forming the push rod and/or may be acoustically or thermally matched to the material forming the push rod. In such embodiments, the DAS fibre essentially forms part of the structure itself.

The DAS fibre may be a single fibre. The DAS fibre may be a dedicated fibre within a bundle of fibres. The bundle of fibres may form a multicore fibre cable. The DAS monitoring preferably operates from one end only. As such the DAS fibre may have an optical coupler at one end only. In such instances, the DAS fibre may be a single ended fibre. The DAS fibre may be provided with an anti-reflection device. This provides enhanced operation and sensitivity of the DAS analyser unit. The anti-reflection device may be provided at the opposing end of the push rod to the optical coupler. The anti-reflection device may be provided within the push rod or provided in an end cap for the push rod. The anti-reflection device may be embodied by a number of tight loops in the end of the fibre. Such loops may be of a diameter of the order of, say, 6mm or so.

The DAS fibre may be provided with an exterior coating or cover. This can provide protection for the DAS fibre. In the event that the DAS fibre is provided within a multicore fibre, the coating or cover may be provided over the multicore fibre. In the event that there is a gap between the DAS fibre and the coating or cover, the gap may be filled with gel. This can improve acoustic coupling between the DAS fibre and the pipe or fluid within the pipe.

The apparatus may comprise a light emitter for introducing light pulses into the fibre via the optical coupler. Additionally, the apparatus may comprise a light detector for detecting backscattering of the said light pulses via the optical coupler. The light emitter may be a laser. The emitted light may any suitable wavelength for transmission along and backscattering within the DAS fibre. The light emitter and light detector may he integrated into a light transceiver unit.

Light emission may be controlled in order to vary any one or more of: pulse frequency, light wavelength, pulse length and pulse intensity of the emitted Detected backscattered light may be processed to determine vibration amplitudes and frequencies experienced by particular scattering points on the fibre and hence particular locations along the pipe. The method may include the step of filtering the received vibration signals. The filtering may be in respect of time of receipt (and hence location along the DAS fibre) or in respect of vibration frequency, vibration amplitude, or a combination thereof. In particular, the combination may include matching vibration frequency and amplitude against expected acoustic signatures of particular events, and by way of pattern recognition or artificial intelligence algorithms. This can enable the method to be focussed on detecting or excluding particular sources of vibration. In one example, this could be orifice noise caused by fluid leaking from the pipe. In other examples, this could be pressure waves within the pipe or including temperature variations within the pipe (such as may be experienced with the adiabatic decompression of a gaseous fluid at a leak location). In still further implementations, the processing unit may be operable to detect vibrations associated with activity outside the pipe. For instance, this may include the detection of traffic on roads overlying or close to a buried pipe, digging activity, or use of ground tamping for exact pipe leak determination.

The processing and/or filtering of detected light signals may be carried out by a processing unit. The processing unit may be in communication with the light detector.

The processing unit may be in communication with the light emitter. In such embodiments, the processing unit may be operable to control the light emitter. The processing unit may be provided locally to the light detector and the light emitter.

The push rod may additionally be provided with an electrical conductor along the push rod. The conductor may comprise a conductive cable or wire. The conductor may be provided along substantially the full length of the push rod. In other embodiments, the conductor cable is provided along at least one elongate section of the push rod. The conductor may be substantially coaxial to the push rod or have a substantially parallel axis to the push rod. In further embodiments, the conductor may have another relation to the push rod. For instance, the conductor may run helically IS about the push rod axis.

In some embodiments, the conductor may be integrated into another feature of the apparatus. In one such example, the conductor may comprise a cover over the DAS fibre. In some such embodiments, the DAS fibre may be formed as a FIMT (fibre in metal tube). Suitable metals for forming the tube of the FLMT include but are not limited to stainless steel or the like. In those embodiments where the push rod comprises a coil spring, the coil spring may itself be the conductor.

The conductor may be provided with an electrical coupler operable to introduce radio frequency electrical signals on to the conductor. The apparatus may be provided with a signal generator operable to introduce electrical signals on to the conductor. The signal generator may be connected to the conductor via a suitable electrical coupler. In suitable embodiments, the signal generator may be in communication with and/or controlled by the processing unit.

The signals introduced may have a characteristic frequency. This can enable the route of the push rod and hence the route of a below ground pipe to be traced from above ground by detecting the characteristic signal. Detection of the characteristic signal may be achieved using a utility CAT (cable avoidance tool) scanner, or the like. Detecting a leak in terms of the distance along the push rod from the DAS fibre and mapping the route of the pipe by detecting the characteristic signal, the location of a leak in a buried point can be accurately ascertained simply by inserting the apparatus of the present invention into a pipe. This allows leaks within buried pipes to be located accurately without uncovering the pipe and/or allows such leaks to be repaired with minimal focussed excavation of the pipe. Further this may allow the transit of the push rod to be monitored during insertion, tracking progression at any one moment in time.

hi such embodiments, the characteristic frequency may be constant.

Alternatively, the characteristic frequency may vary in a predetermined pattern. In further such embodiments, the characteristic frequency may be varied according to the depth of pipe. For instance, shallower pipes may be tracked with higher frequency signals and deeper pipes may be traced with lower frequency signals. Suitable frequencies for the characteristic frequency may fall in the range 512Hz to 33kHz. In one suitable example the characteristic frequency may be around 33kHz.

In some embodiments, the light emitter, light, detector, signal generator and processing unit may be integrated into a pipe assessment unit. The pipe assessment unit may be provided with a user interface. The user interface may enable a user to control operation of the pipe sensor unit and/or review indications relating to the condition of the monitored pipe. The pipe assessment unit may additionally or alternatively be provided with a communication operable to communicate with one or more external devices. This can allow data from thc apparatus to be transmitted to one or more external devices for analysis and/or for control signals from one or more external devices to be relayed to the apparatus. The communication unit may be operable to facilitate communication via any suitable wired or wireless communication protocols.

The apparatus may comprise a spindle upon which the push rod can be wound for storage. In such embodiments, the spindle may be provided on a free-standing frame such that the push rod may be introduced into a pipe directly from the spindle. In some such embodiments, the pipe assessment unit may be integrated into the free-standing frame.

The pipe may be a water pipe. In alternative embodiments the pipe may be a gas pipe. In particular the pipe may be a district metered area (DMA) distribution or access pipe or a service supply pipe for a particular property.

According to a second aspect of the present invention there is provided a leak detection apparatus for a pipe, the apparatus comprising: a push rod; a conductor provided along the push rod; a distributed acoustic sensing (DAS) fibre provided along the push rod; and an optical coupler operable to enable the introduction of light pulses into the DAS fibre and the extraction of backscattered light pulses from the DAS fibre for detection.

The apparatus of the second aspect of the present invention may incorporate any or all features of the first aspect of the present invention, as desired or as appropriate.

According to a third aspect of the present invention there is provided a leak detection apparatus for a pipe, the apparatus comprising: a push rod comprising a coil spring; a distributed acoustic sensing (DAS) fibre provided along the push rod; an optical coupler operable to enable the introduction of light pulses into the DAS fibre and the extraction of backscattered light pulses from the DAS fibre for detection; and wherein the coil spring comprises a conductor along the push rod.

The apparatus of the third aspect of the present invention may incorporate any or all features of the first and second aspects of the present invention, as desired or as appropriate.

According to a fourth aspect of the present invention there is provided a method of detecting a leak in a pipe, the method comprising the steps of: inserting an apparatus according to the first, second or third aspects of the present invention into the pipe; pushing the apparatus along the pipe; introducing coherent light pulses into the DAS fibre; detecting backscattered light from the DAS fibre; and processing the backscattered light so as to obtain information about the condition of the pipe.

I I

The method may include the step of installing the DAS fibre in the pipe. The fibre may be installed temporarily. In such instances the method may include the step of removing the DAS fibre from the pipe after use.

Inserting the DAS fibre may include the steps of providing an aperture in the pipe wall and introducing a DAS fibre through the aperture. The aperture may be an existing aperture, such as a valve, meter or other potential opening. In other embodiments, the method may include the step of forming a suitable aperture. The aperture may be provided with a fitting operable to provide a seal between the DAS fibre and the edges of the aperture. The fitting may be adapted to enable the formation of an aperture.

The method may comprise the steps of depressurising the fluid pipe before forming the aperture and installing a leak tight coupling around the fibre at each aperture. In other embodiments, the aperture may be formed and the DAS fibre introduced without depressurising the pipe. Numerous such 'hot tap' techniques are IS known in the art.

In embodiments where the method uses an apparatus according to the second or third aspects of the present invention, the method may include the additional steps of locating the route of an underground pipe. This may be achieved by introducing radio frequency electrical signals of a characteristic frequency on to the conductor; and detecting the characteristic signal above ground. By detecting the variation in intensity of the characteristic signal, the route of the pipe can be traced from above ground. The signals may be detected above ground using a utility CAT (cable avoidance tool) scanner, or the like.

According to a fifth aspect of the present invention there is provided a method of detecting and locating a leak in a pipe, the method comprising the steps of inserting an apparatus according to the second or third aspects of the present invention into the pipe; pushing the apparatus along the pipe; introducing coherent light pulses into the DAS fibre; detecting backscattered light from the DAS fibre; processing the backscattered light so as to obtain information about the condition of the pipe; and introducing a characteristic electrical signal on to the conductor; detecting the characteristic signal above ground so as to trace the route of the pipe.

The methods of the fourth and fifth aspects of the present invention may incorporate any or all of the features of the first three aspects of the present invention, as desired or as appropriate. The method of the fifth aspect of the present invention may incorporate any or all features of the method of the fourth aspect of the present invention, as desired or as appropriate.

Detailed Description of the Invention

In order that the invention may be more clearly understood one or more embodiments thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 shows a cutaway view of an apparatus for detecting a leak in a pipe according to an embodiment of the present invention; Figure 2 shows a schematic overview of the apparatus of figure 1; Figure 3 shows at (a) and (b) cutaway views of alternative apparatus for detecting a leak in a pipe and tracing the route of a pipe according to an embodiment of the present invention; Figure 4 shows a schematic overview of the apparatus of figure 3; Figure 5 shows (a) a cross-sectional view of an alternative apparatus for detecting a leak in a pipe and tracing the route of a pipe according to an embodiment of the present invention, (b) a spring incorporated into the embodiment of figure 5a and example alternative spring cross-sectional profiles (c) and (d); Figure 6 illustrates the use of suitable embodiments of the apparatus of the present invention in use for detecting a leak in a pipe; and Figure 7 schematically illustrates the use of suitable embodiments of the apparatus of the present invention for tracing the route of a pipe, alongside leak detection.

The present invention relates to leak detection apparatus for pipes, in particular water pipes in district metered area (DMA) or water pipes for supplying particular properties. As is shown in figure 1 and figure 2, a first embodiment of a leak detection apparatus 1 for insertion into a pipe under inspection (not shown in figures 1 & 2) comprises a distributed acoustic sensing (DAS) fibre 2 provided along an elongate push rod 3. The DAS fibre is a suitable optical fibre and is provided in a central conduit 4 of push rod 3. The conduit 4 may be filled with a suitable acoustic gel to ensure good acoustic coupling between DAS fibre 2 and the exterior surface of the push rod 3.

Alternatively, the DAS fibre 2 may be bonded within the conduit by filling the conduit. with a suitable bonding material. The DAS fibre 2 is typically a single strand or multi-strand optical fibre and may be coated if desired.

The push rod 3 is semi-rigid. In this context, this means that the push rod 3 is sufficiently rigid so as to enable the push rod 3 to be pushed along a pipe and sufficiently flexible so as to allow the push rod 3 to bend to enable the rod to be pushed around bends in the pipe. In the present example, the push rod 3 may be formed from glass fibre, fibre reinforced plastic, HDPE, polypropylene, or the like and the specific dimensions of the push rod 3 can be selected to ensure the correct flexibility and rigidity bearing in mind the pipe to be inspected.

As is shown more clearly in figure 2, the apparatus 1 is typically supplied on a spindle 5. This allows the apparatus 1 to be readily stored and deployed. Typically, the spindle 5 is mounted on a suitable free-standing frame (not shown). One end 6 of the apparatus is adapted for insertion into a pipe to be inspected. The end 6 is typically provided with a protective cover or cap (not shown). This can prevent the ingress of water from the pipe, or debris, into the conduit 4 and protect the DAS fibre 2 from impact with the interior surfaces of the pipe during insertion. An anti-reflection device 25 is securely affixed to the insertion end of the push rod 3. The anti-reflection device is typically formed from typically a number of small diameter loops of DAS fibre 2, nevertheless the skilled man will be aware that other embodiments to achieve an anti-reflection fibre end may be provided in alternative embodiments.

The other end of the apparatus is provided with an optical coupler 7. The coupler is operable to enable optical pulses to be introduced to DAS fibre 2 and for backscattered pulses to be extracted from DAS fibre 2 for detection. In the embodiment of figure 2, an optical transceiver 8 is provided for generating pulses for introduction to the DAS fibre 2 and analysing backscattercd pulses. The optical transceiver 8 is connected to the coupler via a patch fibre 9.

Vibrations propagating through the water in the pipe result in corresponding vibration of the DAS fibre 2. Vibrations of the DAS fibre 2 cause variation in the backscattering that occurs from each backscattering site within the DAS fibre 2.

Accordingly, these variations can be used to provide an indication of the vibration experienced by each section of the DAS fibre 2. By suitable processing it is possible to identify vibrations as being characteristic of particular pipe events. This may be achieved by determining the frequencies or amplitudes of vibrations or by filtering selected frequencies of vibration. Common pipe events that might he detected beyond orifice noise and negative pressure waves indicative of leaks include flow noise, pressure waves indicative of operation of pipe machinery (valves, pumps or the like) or the change of fluid temperature. Where sensitivity permits, events external to the pipe may also be detected and monitored. By analysing the time of arrival of the backscattered light it is possible to determine the location of the identified events in terms of distance along the DAS fibre 2. This can then be readily related to the distance of insertion of the apparatus 1 into the pipe and hence the location of any detected leaks can be determined in terms of distance along the pipe. If the pipe route is known any leak locations can therefore be accurately identified. Where necessary, targeted excavation may be carried out at the leak locations to expose the pipe for inspection and/or repair.

Alternative embodiments of the leak detection apparatus are shown in figure 3a and figure 3b. These embodiments are adapted to enable the route of the pipe under inspection to be traced. This can aid leak location identification, especially if the pipe route below ground is not known.

In the embodiment of figure 3a, as with figure I, the apparatus la comprises a DAS fibre 2 provided within an optionally 2e1 filed central conduit 4 of a semi rigid push rod 3, or an optionally integrally bonded fibre. In addition, a conductor 11 is provided in the conduit 4. Typically, the conductor 11 is an electrical cable, such as a copper wire, and may be coated with an insulating coating if required, it may be integrally bonded within the conduit. In figure 3b, the apparatus la differs from the apparatus 1 a of figure 3b in that the DAS fibre 2 is provided within a metal tube 12, which acts as the conductor. Such fibres in metal tubes (FIMT) readily available. As with the conductor 11, the metal tube 12 may be coated with an insulating coating if required.

Turning now to figure 4, apparatus la, lb is additionally provided with an electrical signal generator 10, electrically connected to conductor 11 or metal tube 12 as appropriate. The signal generator 10 applies a characteristic electrical signal to the conductor 11 or tube 12. Typically, this is a signal with a characteristic frequency.

Turing to figure 5, a further alternative embodiment of the apparatus 1 c is shown. In this embodiment, the push rod comprises a coil spring 13 with a central space 4 within which DAS fibre 2 is provided. As with the previous embodiments, space 4 can be filled with an acoustic gel. As is illustrated in figure 5b, the spring 13 is typically helical. The spring 13 typically has a substantially circular cross-section profile, as illustrated in figure 5a. The spring wire in figure Sc may have a substantially circular IS cross section, or an alternative cross-section, such as the oblong cross-section of spring 13d shown in figure 5d.

The spring 13 may be provided within a flexible sheathing cover 14, which provides some protection for the spring 13 and prevents water ingress into the central space 4 while providing pressure proofing. The cover 14 might typically be formed from a polymer such as I-IDPE, polypropylene, polyurethane or the like. The spring 13 can optionally be supplied with a linear tensional support 15, typically a wire. Both the spring 13 and support wire 15 are typically formed from metal and may be coated with a protective and/or insulating coating. The support wire is typically fixed rigidly to each end of the spring to prevent spring extension on withdrawal from a pipe.

/5 Optionally, the spring 13 may be used as the conductor or the linear tensional support wire 15 may be used as the conductor.

Turning now to figure 6, use of the apparatus 1, la, lb, lc is illustrated schematically in an underground pipe 20 containing water 18, or which may alternatively contain a gaseous fluid. Typically, the pipe 20 is a DMA access or distribution pipe or a property service supply pipe. The apparatus 1, I a, 1 b, lc is inserted into the pipe via a valve, meter, or other live access port 19. Typically, this is a pre-existing valve, meter, or access port 19, nevertheless, it may be possible to create a new aperture for introducing the apparatus 1, la, lb, lc to the pipe 20, if desired. Once inserted, the optical transceiver 8 introduces optical pulses into the DAS fibre 2, detects and analyses the backscattered signals to identify potential leaks. As above, the leak location in terms of the position along the fibre 2 and hence along pipe 20 can be readily identified Where an apparatus I a, lb or 1 c is used, the electrical signal generator 10 additionally applies a characteristic signal to the conductor 11, tube 12 or spring 13 as appropriate. A suitable detector (not shown) such as a utility CAT (cable avoidance tool) scanner, or the like can detect the characteristic signals above ground. In particular, the detector can detect the characteristic signal strength. Typically, this will he within a threshold value in a relatively narrow elongate strip 21 centred on the pipe route as illustrated in figure 7. Accordingly, the pipe route can be traced by detecting the characteristic signal above ground. By combining knowledge of the pipe route with knowledge of the position of leaks 22-24 along the DAS fibre, the location of such leaks can be readily identified even if the pipe route was not previously known. Excavation can thus take place at the leaks locations 22-24 if required for repair of the pipe 20.

The one or more embodiments are described above by way of example only. Many variations are possible without departing from the scope of protection afforded 20 by the appended claims.

Claims

CLAIMS1. A leak detection apparatus for a pipe, the apparatus comprising: a push rod, a distributed acoustic sensing (DAS) fibre provided along the push rod; and an optical coupler operable to enable the introduction of light pulses into the DAS fibre and the extraction of backscattered light pulses from the DAS fibre for detection.
2. A leak detection apparatus as claimed in claim 1 wherein the DAS fibre is provided along substantially the full length of the push rod.
3. A leak detection apparatus as claimed in claim 1 or claim 2 wherein the push rod is formed from a single material or from a composite material.
4. A leak detection apparatus as claimed in any preceding claim wherein the push rod has a substantially constant cross-sectional profile.
5. A leak detection apparatus as claimed in any preceding claim wherein the cross-sectional profile of the push rod comprises a conduit and the DAS fibre is provided within the conduit.
6. A leak detection apparatus as claimed in claim 5 wherein if there is a gap between the DAS fibre and the edges of the conduit, the gap is filled with gel, or where the DAS fibre is integrally bonded within the conduit.
7. A leak detection apparatus as claimed in any preceding claim wherein the push rod comprises a coil spring extending along the full length of the push rod.
8. A leak detection apparatus as claimed in claim 7 wherein the coil spring is provided around a central conduit and the DAS fibre is provided within the conduit.
9. A leak detection apparatus as claimed in claim 8 wherein the conduit is filled with gel.
10. A leak detection apparatus as claimed in claim 8 or claim 9 wherein a linear tensional support is provided along the central conduit.
A leak detection apparatus as claimed in any one of claims 7 to 10 wherein the coil spring is provided with a sheathing cover and if there is a gap between the coil spiing and the cover, the gap is filled with gel.
12. A leak detection apparatus as claimed in any preceding claim wherein the DAS fibre is provided with an exterior coating or cover and any gap between the DAS fibre and the coating or cover is filled with gel.
13. A leak detection apparatus as claimed in any preceding claim wherein the apparatus comprises a light emitter for introducing light pulses into the fibre via the optical coupler and a light detector for detecting backscattering of the said light pulses via the optical coupler.
14. A leak detection apparatus as claimed in claim 13 wherein the processing and/or filtering of detected light signals is carried out by a processing unit in communication with the light detector and/or the light emitter.
15. A leak detection apparatus as claimed in any preceding claim wherein the push rod is provided with a conductor along substantially the full length of the push rod.
16. A leak detection apparatus as claimed in claim 15 wherein the conductor is a conductive cable
17. A leak detection apparatus as claimed in claim 15 wherein the conductor is a cover over the DAS fibre.
18. A leak detection apparatus as claimed in claim 15 when dependent directly or indirectly upon any one of claims 7 to 11 wherein the coil spring or linear tensional support is the conductor.
19. A leak detection apparatus as claimed in any one of claims 15 to 18 wherein the apparatus is provided with a signal generator operable to operable to introduce electrical signals on to the conductor.
20. A leak detection apparatus as claimed in claim 19 when dependent directly or indirectly upon claim 13 wherein the signal generator is in communication with and/or controlled by the processing unit.
21. A leak detection apparatus as claimed in any preceding claim wherein the DAS fibre is provided with an anti-reflection device at the opposing end of the push rod to the optical coupler.
22. A leak detection apparatus as claimed in any preceding claim wherein the apparatus comprises a spindle upon which the push rod can be wound for storage.
23. A method of detecting a leak in a pipe, the method comprising the steps of: inserting an apparatus comprising: a push rod, a distributed acoustic sensing (DAS) fibre provided along the push rod; and an optical coupler operable to enable the introduction of light pulses into the DAS fibre and the extraction of backscattered light pulses from the DAS fibre for detection into the pipe; pushing the apparatus along the pipe; introducing coherent light pulses into the DAS fibre; detecting backscattered light from the DAS fibre; and processing the backscattcred light so as to obtain information about the condition of the pipe.
24. A method as claimed in claim 23 wherein the method includes providing an existing aperture in the pipe wall or forming a suitable aperture in a pipe wall and introducing a DAS fibre through the aperture.
25. A method of detecting and locating a leak in a pipe, the method comprising the steps of: inserting an apparatus comprising: a push rod; a conductor provided along the push rod; a distributed acoustic sensing (DAS) fibre provided along the push rod; and an optical coupler operable to enable the introduction of light pulses into the DAS fibre and the extraction of backscattered light pulses from the DAS fibre for detection into the pipe; pushing the apparatus along the pipe; introducing coherent light pulses into the DAS fibre; detecting backscattered light from the DAS fibre; processing the backscattered light so as to obtain information about the condition of the pipe; introducing a characteristic electrical signal on to the conductor; and detecting the characteristic signal above ground so as to trace the route of the pipe.
26. A method as claimed in claim 25 wherein the method includes providing an existing aperture in the pipe wall or forming a suitable aperture in a pipe wall and introducing a DAS fibre through the aperture.