Improvements in or relating to monitoring of fluid pipes

Abstract

A messenger pipe for use in a fluid pipe comprises a tubular pipe wall which defines a cavity extending along the messenger pipe suitable for receiving a fibre optic cable. The pipe wall comprises one or more sensing fibres provided within the pipe wall. Each sensing fibre may be provided in a protective tube. Each sensing fibre may be provided in a helical formation. The messenger pipe may be provided with armour. The armour may comprise multiple elongate armour wires provided within the pipe wall. The armour wires may be provided on either side of the sensing fibres. The messenger pipe may have co-axially arranged layers. There is also provided a sensing apparatus comprising the messenger pipe, and a method of monitoring a fluid pipe using the messenger pipe.

Description

[0001] IMPROVEMENTS IN OR RELATING TO MONITORING OF FLUID PIPES

[0002] Technical Field of the Invention

[0003] The present invention relates to improvements in or relating to the monitoring of fluid pipes using a messenger pipe comprising one or more sensing fibres. In particular, the invention relates to a messenger pipe comprising a sensing fibre provided within a wall of the messenger pipe and a cavity for receiving a fibre optic cable. Furthermore, the present invention relates to monitoring fluid pipe networks within which a data communication cable network is provided. Preferably, the fluid pipe is a water pipe.

[0004] Background to the Invention

[0005] Many modern services rely upon pipes to carry or distribute fluids. Examples of fluids that can be distributed in this manner include fresh water, waste water and sewage, and fuels such as oil or gas or associated distillates, additionally in industrial uses which may include mining and similar. It is known to monitor the operation of the fluid system and the condition of pipes by using distributed acoustic sensing (DAS) and / or distributed strain sensing (DSS) and / or distributed temperature sensing (DTS). In these techniques an optical sensing fibre is provided along the fluid pipe and light pulses are optically coupled into the sensing fibre. Backscattered light pulses are then detected from the sensing fibre and can be used to make measurements along, or in the vicinity of, the fluid pipe. In this manner, blockages, leaks or other issues can be identified and scheduled for repair. The technique is further described in WO2019 / 166809A1.

[0006] It is also known to provide data communications fibres inside such fluid pipes as they provide a convenient way for cables to be routed using existing infrastructure. As such, there is an ongoing need to provide both sensing fibres and data communications fibres / data cables inside fluid pipes.

[0007] The data communication industry considers that it is optimal for a hollow duct, or messenger pipe, to be provided, and fibre optic micro-cables then blown down the duct, using well known techniques. This provides the advantage that the internal fibre optic micro-cable may be removed and replaced at any stage. Examples include where a lower fibre count is initially deployed and a larger fibre count is subsequently required, where a next generation cable with a higher fibre count within a given microcable outer diameter may be required, or otherwise where fibres within an installed duct have failed and a micro-cable may need to be replaced. This can provide advantages including protecting the sensitive optical fibres and cables, reducing the likelihood of fluid contamination and enabling easier replacement of the optical fibres. More details on messenger pipes such as these are described in WO2010 / 029365 A2.

[0008] Nevertheless, when using a sensing fibre to make measurements, use of a messenger pipe can cause some problems. The sensing fibre generally may rely on acoustic and / or mechanical and / or thermal coupling to the fluid / fluid pipe to enable detection of changes in these properties. As the messenger pipe is a barrier between the sensing fibre and the fluid / fluid pipe this can impact on the absolute and / or relative sensitivity of measurements using the sensing fibre.

[0009] In addition, as the messenger pipe generally has an internal cavity that is larger than the sensing fibre to facilitate easy installation, the sensing fibre may only have a relatively small number of points of contact with a pipe wall of the messenger pipe. As such, much of the sensing fibre may have minimal direct contact with the messenger pipe, further reducing the signal-to-noise ratios for any measurements.

[0010] Furthermore, the position of the sensing fibre within the messenger pipe is unknown. This can lead to uncertainty in the measurements as the sensing fibre may produce different measurements depending on if it is on a side of the messenger pipe adjacent the fluid pipe itself or adjacent the fluid.

[0011] Finally, as data communications companies develop ever more advanced optical data communications cables, they replace redundant or obsolete cabling with newer technologies. As the sensing fibre is often incorporated into a cable bundle with the data fibres, then the sensing fibre must also be replaced at the same time. This can lead to periods where no sensing is possible as there is no sensing fibre in the messenger pipe. Increased costs also arise from the production of a new sensing fibre and the recalibration of the sensing system to account for the properties of the new sensing fibre and its position within the messenger pipe, which may be different compared to the fibre it replaced. It is therefore an object of embodiments of the present invention to at least partially address the above issues.

[0012] Summary of the Invention

[0013] In a broad sense, the invention relates to a messenger pipe for use in a fluid pipe. The messenger pipe may comprise a pipe wall. The pipe wall may be tubular. The pipe wall may define a cavity. The cavity may extend along the messenger pipe. The cavity may be suitable for receiving a fibre optic cable. The pipe wall may comprise one or more sensing fibres. The one or more sensing fibres may be provided within the pipe wall.

[0014] Accordingly, in a first aspect of the present invention, there is provided a messenger pipe for use in a fluid pipe, the messenger pipe comprising a tubular pipe wall which defines a cavity extending along the messenger pipe suitable for receiving a fibre optic cable, wherein the pipe wall comprises one or more sensing fibres provided within the pipe wall.

[0015] Advantageously, the messenger pipe itself carries sensing fibres for monitoring the fluid and / or fluid pipe properties. The one or more sensing fibres are therefore a part of the pipe wall. As such, the one or more sensing fibres are in contact with the pipe wall along the length of the sensing fibre where monitoring is required. This allows the sensing fibres to be provided closer to, and in intimate contact with the fluid and fluid pipe. Additionally, direct mechanical and thermal coupling of each sensing fibre to the pipe wall is provided at all points along the sensing fibre. So, there is no air gap between the sensing fibre and pipe wall at points where monitoring is required. This improves both the sensitivity and the signal-to-noise ratio for measurements.

[0016] The one or more sensing fibres of the messenger pipe are therefore not a part of the cable provided inside the messenger pipe in use. As such, the cable that is installed inside the messenger pipe no longer needs to carry sensing fibres for sensing to be achieved. Accordingly, the present invention facilitates replacement or upgrade of cables, such as fibre optic data cables for data communication networks with no loss of sensing capacity during or after this operation. This could be particularly advantageous as it is envisaged that some variants of next generation data fibres may not actually be suitable for the purpose of sensing (e.g. hollow fibre).

[0017] There is also a reduction in recalibration requirements of the sensing system after the cable is replaced, possibly no recalibration is needed, and lower cost of manufacturing the cable as sensing fibres do not need to be integrated within it. The skilled person will however appreciate that a fibre optic cable comprising sensing fibres could still be used with the messenger pipe of the present invention and further that fibres provided for data connectivity may additionally be used for sensing. In such cases, the sensing fibre or data fibre used for sensing may be deactivated or simply not used for the cable section within the messenger pipe. Alternatively, the sensing fibre in the cable may be used for additional or alternative sensing, such as lower sensitivity sensing to the sensing fibre within the pipe wall.

[0018] Additionally, as the one or more sensing fibres are provided within the pipe wall, the one or more sensing fibres do not protrude from an outside surface of the messenger pipe. As such, they are well protected from damage during installation and use of the messenger pipe.

[0019] In the context of the present application, the term ‘fluid’ in relation to a fluid pipe may refer to any material, liquid or gaseous, including and fuels such as oil or gas or associated distillates, additionally in industrial uses which may include mining and similar, the invention may more specifically refer to a primarily water-based fluid, such as potable water, pre-treatment water, wastewater or water-based slurries.

[0020] Similarly, in the context of the present application, the term ‘pipe’ or ‘conduit’ may refer to any fluid conduit used to convey a fluid (gas, liquid or a mixture including a slurry) between two points, spaced apart at or below local ground level. In particular, the ‘pipe’ or ‘conduit’ may traverse at a relatively regular displacement from local ground level, without requiring the ‘pipe’ or ‘conduit’ to be horizontal.

[0021] The messenger pipe may have an axis defined by the tubular pipe walls. The axis may be provided centrally with respect to a cross-section of the pipe wall, for example at a centre of mass of the cross-section of the pipe wall, or placed at the invert or crown of the pipe wall. The messenger pipe may have a length defined along its axis. A radial direction may extend in a plane defined perpendicular to the axis of the messenger pipe and away from the axis of the messenger pipe.

[0022] The pipe wall may provide a self-supporting tubular shape to the messenger pipe. The pipe wall may be self-supporting when immersed in the fluid provided inside the fluid pipe. The pipe wall may be self-supporting irrespective of if the fibre optic cable is provided in the cavity or not. The messenger pipe may be configured to control the position of the fibre optic cable, preferably the position within the fluid pipe. The messenger pipe may be configured to protect the fibre optic cable. The cavity may be suitable for receiving the fibre optic cable by blowing of the fibre optic cable down the cavity. The messenger pipe and fibre optic cable may be separate. The fibre optic cable may be free to move, preferably in radial directions, within the messenger pipe. The messenger pipe and fibre optic cable may not be integrally formed. Thus, the messenger pipe is able to ensure quick and reliable installation of the fibre optic cable within the fluid pipe and protects the fibre optic cable both during installation and use.

[0023] Each sensing fibre may be provided inside a protective tube. The protective tube may be provided in the pipe wall. The protective tube may comprise a material that is more resilient and / or durable than the pipe wall. The protective tube may comprise a corrosion resistant material. Thus, the protective tube provides an additional layer of protection to reduce the likelihood of damage to the sensing fibre during manufacturing, installation and use of the messenger pipe.

[0024] The protective tube may provide a seal around the sensing fibre. The protective tube may be impervious to fluids. The protective tube may provide a hermetic seal around the sensing fibre. This can additionally reduce the likelihood of water or other material ingress to the sensing fibre which may reduce sensing capabilities or necessitate more frequent re-calibration of the sensing system.

[0025] The protective tube may comprise a tube cavity. The sensing fibre may be provided in the tube cavity. The tube cavity may be unfilled, for example it may comprise air. The tube cavity may be filled, for example it may be filled with a liquid or gel. By filling the cavity, the mechanical / acoustic and thermal coupling of the sensing fibre to the pipe wall is improved and signal-to-noise ratios are enhanced. In addition, by filling the cavity, the sensing fibre may be less sensitive to vibrations and mechanical stresses during installation of the messenger pipe which may otherwise damage the sensing fibre.

[0026] The protective tube may comprise a metal material, preferably a corrosion resistant metal. A metal may beneficially provide a more resilient seal around the sensing fibre. The protective tube may be formed from stainless steel, for example stainless steel 304 or 316. The protective tube may be formed from Incoloy (RTM) 825 or Inconel (RTM) 625. The protective tube and sensing fibre may together be commonly referred to in the art as a fibre in metal tube (FIMT). In an alternative embodiment the sensing fibres may be provided within a resilient polymer tube. The protective tube may be formed from a resilient polymer.

[0027] The protective tube may comprise an electrically conductive material, for example a metal as referred to above. The protective tube may be continuously conductive along its length. The protective tube may be suitable for transmission of electromagnetic signals along the protective tube. Preferably, the protective tube may be suitable for transmission of radio frequency electromagnetic signals along the protective tube. Advantageously, this can facilitate detection of the messenger pipe by radio frequency detection, for example, using a “cable avoidance tool” or “CAT scanner” as is known in the art. This is particularly useful where the fluid pipe is buried. An electrically conductive tube material may optionally be used, where the pipe wall also contains conductive elements for delivery of electrical power. In such an embodiment, the protective tube may act as a return path, for example in a protective earth leakage circuit breaker (ELCB) or residual current circuit breaker (RCCD) isolating system.

[0028] The protective tube may comprise any suitable outer diameter depending on the materials, dimensions and required characteristics of the other components of the messenger pipe, protective tube and sensing fibres. The protective tube may comprise an outer diameter of at least 1 mm, or at least 1.1 mm, or at least 1.2 mm, or at least 1.3 mm. The protective tube may comprise an outer diameter of no more than 5 mm, or no more than 3 mm, or no more than 2 mm. Preferably, the protective tube may comprise an outer diameter of about 1.3 mm. This ensures that the protective tube is compact and able to fit within the pipe wall easily. The protective tube may have any suitable thickness. In one example, the thickness is about 1 mm, or about 0.5 mm, or about 0.3 mm. Consequently, the inner diameter may be about 0.9 mm. Of course, any suitable thickness and diameters may be selected depending on the application and desired size / properties of the protective tube.

[0029] The protective tube may be provided within the pipe wall. As such, the protective tube may not protrude from an outside surface of the messenger pipe. This ensures that the pipe wall also protects the protective tube from unnecessary contact / stress and further reduces the likelihood of damage to the sensing fibres.

[0030] In other embodiments, the protective tube may be provided on the outside surface of the messenger pipe, or partially embedded in the pipe wall. This may be preferred where the risk of damage due to contact with other objects is low, the protective tube is very strong, or high sensitivity is required for the sensing fibres. It is conceivable that a single messenger pipe may be provided with two or more sensing fibres at different depths within the pipe wall. Those on the outside may be provided with higher strength / resilience protective tubes and may be partially embedded in the pipe wall. Those deeper in the pipe wall, or on an inside of the pipe wall, may require less protection and provide a reduced sensitivity.

[0031] Each sensing fibre may be formed of one or more optical fibre units, for example two or more optical fibre units, or at least four optical fibre units. Each optical fibre unit may comprise one or more single mode optical fibres. Each optical fibre unit may be provided with an individual sheath. Each individual sheath may be opaque. Each single mode optical fibre may be standard or bend insensitive, for example of the G657.X style. The fibres may have sensing properties modified by either mechanical surface formation or chemical means, for example as described further below. As such, the sensing fibre is optimally suited for sensing the properties of the fluid and / or fluid pipe.

[0032] Each sensing fibre may extend along the length of the messenger pipe. Each sensing fibre may extend at least 1 m, or at least 10 m, or at least 50 m, or at least 100 m, or at least 500 m, or may extend to 1,000 m or more along the length of the messenger pipe. Each sensing fibre may extend along the majority of the length of the messenger pipe. Each sensing fibre may extend along the entire length of the messenger pipe. This ensures that measurements can be taken along the length of the fluid pipe. Each sensing fibre may extend around a circumference of the messenger pipe. Each sensing fibre may extend all the way around the circumference of the messenger pipe. This ensures measurements are less dependent on the orientation / twisting of the messenger pipe in the fluid pipe. Preferably, the one or more sensing fibres are provided in a helical formation. The helical formation may be arranged around the axis of the messenger pipe. A helical formation can improve the structural stability of the messenger pipe. A helical formation will ensure flexing of the messenger pipe without undue stress on the sensing fibre. Furthermore, a helical formation beneficially ensures that individual sensing fibres have exposure to detectable events in all directions around the messenger pipe over the length of the messenger pipe. Where there are two or more sensing fibres, which may each be within a protective tube, this can ensure that a failure in a single sensing fibre or protective tube does not unduly hamper sensing operations.

[0033] The helical formation of the sensing fibres may have a pitch. The pitch may be in the region of 5 to 30 times greater than the messenger pipe diameter. In some embodiments suitable for use in water pipes, the messenger pipe may have a diameter in the range of 10-16 mm. In such embodiments, the pitch might be in the region of 50-500 mm, or more preferably 50-100 mm. This pitch is preferred as it provides increased flexibility of the messenger pipe to allow easier installation. The skilled person will appreciate that other ranges of messenger pipe diameters may be desirable depending on the fibre optic cable intended to be carried within it, in these circumstances, the pitch may change accordingly. In addition, the pitch may be determined based on the radial distance of the sensing fibres from the axis of the messenger pipe.

[0034] The messenger pipe may be provided with armour. The armour may be configured to strengthen and / or stiffen the messenger pipe. The armour may comprise multiple elongate armour wires. Alternatively the armour wires may comprise polymer rods, such as a polymer rod formed from a fibre reinforced polymer. The armour wires may be provided within and / or on the pipe wall. Preferably, the armour wires are provided within the pipe wall. This helps further protect them from damage. The armour wires may be provided on either side of one of the sensing fibres. Thus, the armour provides additional structural support to the messenger pipe and reduces risk of damage during installation and use, such as damage from rodents.

[0035] The armour may be formed from a suitable metal or a suitable polymer. A suitable metal may be steel or stainless steel, alternatively a more electrically conductive material, such as copper. A suitable polymer may be aramid or Kevlar (RTM). The armour may preferably comprise a single layer of armour wires. However, it may also comprise multiple layers where additional protection / strength is required.

[0036] The armour wires may be provided on either side of one of the sensing fibres around a circumference of the pipe wall. The armour wires may extend along the length of the messenger pipe. The armour wires may extend the same length as the sensing fibres. The armour wires may extend around the circumference of the messenger pipe. The armour wires may extend the same amount around the circumference as the sensing fibres. The armour wires of the armour may extend parallel to the one or more sensing fibres. The armour wires of the armour may be provided in a helical formation. The helical formation may match that of the one or more sensing fibres. As such, the sensing fibres may be flanked by the armour. This ensures that the armour does not block signals from the fluid pipe / fluid from reaching the sensing fibres as well as minimising increases in the pipe wall thickness due to the addition of armour to the pipe wall.

[0037] The armour wires may be provided at substantially the same radial distance from the axis of the messenger pipe as one another. An inner edge of the armour wires may be provided at substantially the same radial distance from the axis of the messenger pipe as one another. One or more armour wires may be provided at substantially the same radial distance from the axis of the messenger pipe as the one or more sensing fibres and / or protective tubes. An inner edge of the armour wires may be provided at substantially the same radial distance from the axis of the messenger pipe as an inner edge of the one or more sensing fibres and / or protective tubes. An outer edge of the armour wires may extend substantially the same radial distance from the axis of the messenger pipe as one another. An outer edge of the armour wires may extend radially further than an outer edge of the one or more sensing fibres and / or protective tubes from the axis of the messenger pipe. The armour wires may have an outer diameter greater than the outer diameter of the sensing fibres and, if provided, the protective tube provided around the sensing fibres. The armour wires may have an outer diameter of no more than 2 mm, or no more than 1.8 mm, or no more than 1.6 mm, or no more than 1.4 mm. The armour wires may have an outer diameter of no less than 1 mm, or no less than 1.1 mm, or no less than 1.2 mm, or no less than 1.3 mm. Preferably, the armour wires have an outer diameter of about 1.4 mm. Thus, if the messenger pipe is contacted and / or pierced, the armour wires are more likely to protect the sensing fibres from damage as they extend out further than them from the axis of the messenger pipe. Additionally armour wires of a diameter somewhat greater than that of sensing fibres and / or protective tubes will protect sensing tubes during messenger pipe sheath stripping operations.

[0038] A sensing fibre and adjacent armour wires of the armour may be spaced apart from one another by buffer zones. The buffer zones may comprise an electrically insulating material. The buffer zones may be provided between a wire of the armour and an adjacent sensing fibre. The buffer zone may be provided in a gap around the circumference of the pipe wall between a sensing fibre and wire of the armour. The buffer zone may comprise a resiliently deformable material that is softer than the armour. This can help protect the sensing fibre from the armour itself.

[0039] A buffer zone may be provided by a buffer wire. The buffer wire may extend parallel to the sensing fibre and armour wires. The buffer zone / buffer wire may be formed from a polymer, for example a plastics material such as nylon, polyethylene, polyvinyl chloride or the like. Thus, the buffer zone can be conveniently formed by a buffer wire that is arranged in parallel with the sensing fibre and armour wires.

[0040] Each buffer zone may extend about 1 mm between the sensing fibre / protective tube and a wire of the armour, for example about 1.1 mm. Each buffer zone may extend about 1 mm through the thickness of the pipe wall. Each buffer wire may have an outer diameter of about 1 mm, for example about 1.1 mm. The armour wires may extend radially further than the buffer zones from the axis of the messenger pipe. Thus, the buffer zones are also protected by the armour wire.

[0041] The one or more sensing fibres, armour and buffer zones may extend around substantially the entire circumference of the messenger pipe. As such, the messenger pipe strength is improved, the overall specific gravity may be increased and manufacture may be simplified, especially where the sensing fibres and armour are arranged in a helical formation.

[0042] The messenger pipe may comprise two or more sensing fibres. Each of the two or more sensing fibres may be spaced apart around a circumference of the pipe wall. Each of the two or more sensing fibres may be spaced apart equally around the circumference of the pipe wall. Successive adjacent sensing fibres of the two or more sensing fibres may be spaced apart by the same arc length around the circumference of the pipe wall. This can help ensure that measurement reliability is enhanced as damage or poor measurement conditions on one side of the messenger pipe is less likely to affect all sensing fibres. It also may provide a structure which is rotationally symmetric. Preferably, the cross-sectional structure of the pipe wall has a rotational symmetry of order at least 2. This reduces potential structural weak points around the circumference of the pipe wall.

[0043] The armour wires may be provided between adjacent sensing fibres of the two or more sensing fibres. The two or more sensing fibres may define two or more wire groups. Each wire group may be separated from one another by a sensing fibre, and preferably buffer zones. Each armour wire may be electrically conductive. Each armour wire may be formed of metal, for example highly conductive metal such as copper. Armour wires in each wire group may be electrically connected to one another. In the messenger pipe, each wire group may be electrically isolated from the other wire groups, for example by the insulating buffer zones / buffer wires. As such, the sensing fibres and buffer zones split the armour into groups of armour wires that are each electrically conductive. Each wire group may comprise an electrical resistance of no more than 100 Ohms per kilometre of messenger pipe length, or no more than 50 Ohms per kilometre of messenger pipe length, or no more than 25 Ohms per kilometre of messenger pipe length, or no more than 10 Ohms per kilometre of messenger pipe length, or no more than 5 Ohms per kilometre of messenger pipe length, or no more than 3 Ohms per kilometre of messenger pipe length. The resistance may be selected by control of the materials, resistivity, number and size of armour wires in each wire group. This allows for efficient electrical power transmission along the messenger pipe. One of the wire groups may therefore be denoted an electrically positive wire group. One of the wire groups may be denoted an electrically negative wire group. At the ends of the messenger pipe, the wire groups may be configured to be connected to an electrical power source and / or electrical load. This enables the wire groups to be easily used in practice.

[0044] The benefits of armour and the armour wires include mitigation to rodent damage in sections of the messenger pipe which are exposed to such potential damage. Additionally, where the messenger pipe comprises polyethylene, or a polyethylene derivative, or other material that has a high thermal expansion coefficient, the presence of the armour can mitigate expansion / contraction of the messenger pipe due to prevailing temperature variations.

[0045] The pipe wall may comprise an even number of sensing fibres, for example, 2 or 4 or 6 or 8 sensing fibres, or more. The sensing fibres may be spaced apart equally around the circumference of the pipe wall. The pipe wall may comprise an even number of wire groups. The wire groups may be defined by the sensing fibres. The wire groups may be split into positive and negative pairs of wire groups. Thus, parallel electrical connections may be achieved along the messenger pipe.

[0046] Each of the sensing fibres may have a sensitivity. The sensitivity may define the strength of backscattered light pulses generated by the sensing fibre in response to a property to be measured. The sensitivity may be dependent on the wavelength of the light pulses. The sensitivity may define a frequency response of a sensing fibre. The sensitivity may comprise an acoustic sensitivity, a sensitivity to strain induced vibrations and / or sensitivity to temperature variations.

[0047] The sensitivity of a specific sensing fibre may depend on the position of the sensing fibre in the pipe wall and proximity to the outside of the messenger pipe. The shorter the distance between the sensing fibre and the fluid or fluid pipe, the less attenuated signals will be and the sensing fibre will have a higher sensitivity. The sensitivity of a specific sensing fibre may depend on its inherent structural properties, for example any one or more of: material composition, chemical composition, and / or fibre structure. For example, for a sensing fibre comprising a doped silica material, varying the levels of impurity within the silica material may enhance or reduce the fibre’s sensitivity. In another example, a specific coating may be applied to a sensing fibre to alter its sensitivity. The sensitivity of a specific sensing fibre may depend on a surface morphology of the sensing fibre. The surface morphology may comprise scores or etches on the outside of the sensing fibre. For example, scores with specific patterns may create localized points that enhance the sensing fibre’s response to vibrations or acoustic signals. As such, the sensitivity can be tuned to provide enhanced measurement performance.

[0048] At least two of the two or more sensing fibres may have different sensitivities. This can allow the messenger pipe and two or more sensing fibres to collectively make more advanced measurements as measurements from specific sensing fibres can be combined or used in isolation to make a measurement of a certain property.

[0049] At an end of the messenger pipe, first and second sensing fibres of the two or more sensing fibres may be optically coupled together to provide an optical path extending along the first sensing fibre in a first direction and then along the second sensing fibre in a second direction. The first and second directions may be different directions to one another. The first and second directions may be opposite directions. Where the messenger pipe comprises more than two sensing fibres, three or more of the sensing fibres may be optically coupled together. The first and second sensing fibres, and any others optically coupled thereto, may form a continuous looped arrangement. In addition, the continuous looped arrangement may comprise sensing fibres that are not part of the messenger pipe, for example sensing fibres provided in the fibre optic cable. This enables comparative and / or aggregate analysis of backscattered light pulses from some or all of the sensing fibres in the looped arrangement. Through this analysis, more precise and accurate measurements are enabled. Additional performance gains can also be realised when the first and second sensing fibres have different sensitivity. This analysis and use of sensing fibres of different sensitivities to enhance measurement performance is described in more detail in PCT / GB2024 / 052286.

[0050] The messenger pipe may comprise four sensing fibres. The four sensing fibres may each be spaced apart by 90 degrees around the circumference of the pipe wall. The messenger pipe may comprise four wire groups. The four sensing fibres may define the four wire groups. This can provide a preferred amount of sensing fibres and wire groups considering the typical size and strength requirements for a messenger pipe.

[0051] Each sensing fibre may comprise a buffer zone provided either side of the sensing fibre. The buffer zone may separate the sensing fibre from an adjacent wire group. This ensures adequate electrical insulation and mechanical protection from the armour wires.

[0052] The messenger pipe may be configured to sink to the bottom of the fluid pipe when the fluid pipe is filled with a fluid. The messenger pipe may have a specific gravity of over 1. The messenger pipe may have specific gravity in the region of 1.252.5. Specific gravity may be defined as the relative density of the messenger pipe compared to the fluid in the fluid pipe.

[0053] The messenger pipe may have a stiffness in the region of 0.0775 - 0.2175 Nm2. The messenger pipe stiffness may be a beam stiffness which can be defined by measuring the drop between a supported messenger pipe end and an unsupported messenger pipe end of unit length due to an applied unit force N.

[0054] In particular embodiments, the messenger pipe may have the above specific gravity and stiffness combined with a diameter in the range of 10-20 mm. The pipe wall may have an annular cross-section. The annular cross-section is preferably a circular annulus, but other shapes are also possible and could be selected such as elliptical annulus, squared annulus, irregular annulus etc. The messenger pipe may have an outer diameter of at least 12 mm, or at least 14 mm, or at least 16 mm or at least 20 mm. In practice, there is no specific limit on the size of the messenger pipe, other than due to constraints of the fluid pipe it is intended to be provided within. However, in many circumstances, the messenger pipe may have an outer diameter of no more than 30 mm, or no more than 20 mm or no more than 16 mm. Preferably, the outer diameter of the messenger pipe may be 12 to 20 mm. The messenger pipe may have an inner diameter of more than 14 mm, or no more than 12 mm, or no more than 10 mm. The messenger pipe may have an inner diameter of at least 6 mm, or at least 8 mm, or at least 10 mm. The messenger pipe may optimally have an inner diameter of 6 to 14 mm. The pipe wall may therefore have a thickness defined in the radial direction from the cavity or inside of the pipe wall to the outside of the pipe wall. The pipe wall thickness may be at least 3 mm, at least 4 mm, or at least 5 mm. The pipe wall thickness may be no more than 8 mm, no more than 7 mm or no more than 6 mm. Preferably, the pipe wall thickness is about 3 or 8 mm. Such dimensions and properties may be well suited to pipes where the fluid comprises water and also provides sufficient space within the cavity of the messenger pipe for blowing of a fibre optic cable.

[0055] The fibre optic cable may have a diameter of less than the inner diameter of the messenger pipe. This allows for easy insertion into the messenger pipe. The fibre optic cable may have a diameter of 2 to 12 mm or more. The fibre optic cable may be a multi-core cable. The fibre optic cable may comprise any suitable number of cores as is known in the art, for example 12, 24, 48, 72, 96, 144, 288, 576 or 864 cores, greater fibre counts are also feasible. The fibre optic cable may comprise one or more data fibre bundles. Each data fibre bundle may comprise a plurality of optical fibres. The fibre optic cable may comprise single mode and / or multi-mode optical fibres. The fibre optic cable may comprise a sheath. Thus, the messenger pipe may be used with a variety of fibre optic cables. While a fibre optic “micro-cable” is mentioned in the background section above, the messenger pipe of the present invention may be changed in size to work with many different sizes of fibre optic cable, whether a “micro-cable” or not.

[0056] A messenger pipe having either or both of the above properties is adapted to reliably lie within the invert of a fluid pipe during fluid flow due to the density and stiffness of the messenger pipe. Nevertheless, the messenger pipe is sufficiently flexible to be readily stored on standard drums and readily introduced into the fluid pipe by pulling. Such a messenger pipe is also not unduly heavy for manual handling. Any sensing fibres within the messenger pipe may experience reduced noise due to reduction in movement of the messenger pipe within the fluid pipe. This may beneficially increase the effective signal-to-noise ratio of the sensing fibres.

[0057] In some embodiments, the messenger pipe specific gravity may be in any one of the ranges 1.25-1.5, 1.5-1.75, 1.75-2, 2-2.25, 2.25-2.5 or greater. The messenger pipe specific gravity may be selected to fall within a desired range by incorporating armour and / or by suitable selection of the layers forming the pipe wall, materials, or layer thicknesses, as described further below. In some embodiments, the messenger pipe stiffness may be in any one of the ranges 0.1-0.2 Nm2, 0.12-0.18 Nm2, 0.14-0.16 Nm2, 0.15-0.155 Nm20.0775-0.16 Nm2, 0.1-0.145 Nm2, 0.11-0.13 Nm2, 0.12-0.125 Nm20.14-0.2175 Nm2, 0.16-0.2 Nm2, 0.18- 0.19 Nm2, or 0.18-0.185 Nm2. The messenger pipe stiffness may be selected to fall within a desired range by incorporating armour and / or by suitable selection of the layers forming the pipe wall, materials, or layer thicknesses, as described further below.

[0058] The pipe wall may comprise a layered structure. The pipe wall may comprise two or more layers. The layers may be arranged co- axially. The layers may extend along the length of the pipe wall. Thus, the pipe wall has a simple structure that enables various configurations and different properties as described below and herein.

[0059] The pipe wall may comprise an inner layer. The inner layer may define an inside of the messenger pipe. The inner layer may be free of sensing fibres. The inner layer may be free of armour. The inner layer may have an inner diameter equal to the inner diameter of the messenger pipe. The inner layer may have a thickness of about 2 mm. The inner layer may be formed by extrusion. The inner layer may comprise a polymer, for example a plastics material, such as polyethylene, e.g. high density polyethylene, or the like. The inner layer may have an applied coating to reduce friction during blowing or insertion of an introduced fibre micro-cable, for example as described below.

[0060] The pipe wall may comprise a barrier layer. The barrier layer may be configured to resist fluid ingress into the cavity. The barrier layer may comprise a material resistant to fluid ingress. The barrier layer may comprise a foil, for example a metal foil. The foil may have a thickness of 50 pm, or 100 pm, or greater. The metal foil may comprise aluminium. The foil may be glued to an outside of the inner layer, for example by infrared heat source, such as a heat gun. The barrier layer may comprise an insulating film. The insulating film may be electrically insulating. The insulating film may comprise a polymer, for example a plastics material such as polyester, or Mylar (RTM). The insulating film may be provided around the foil. The barrier layer may be thin compared to the other layers. The barrier layer may be of a thickness of at least 50 pm, or at least 100 pm, or greater. The barrier layer thereby provides a line of defence against water ingress into the cavity as well as mechanical support to the messenger pipe. The insulating film assists in preventing potential electrical connections between any one or more of a metal protective tube, or FIMT, and the armour wire groups.

[0061] The pipe wall may comprise a sensing layer. The sensing layer may comprise the one or more sensing fibres. The sensing layer may be the only layer to comprise sensing fibres. The sensing layer may comprise the armour. Preferably, the sensing fibres, armour and / or buffer zones are arranged in the sensing layer as described above. The sensing layer may comprise a polymer, for example a plastics material, such as polyethylene, e.g. high density polyethylene, or the like. The sensing layer may be provided around the inner layer and / or barrier layer. The sensing fibres, armour and / or buffer zones may be laid around the inner layer and / or barrier layer. The polymer may be set around the sensing fibres, armour and / or buffer zones. The polymer may be extruded onto the sensing fibres, armour and / or buffer zones.

[0062] The sensing fibres may be embedded within the pipe wall. The sensing fibres may not protrude from the inside or outside surfaces of the pipe wall. The sensing fibres may be provided between the inner and outer diameters of the pipe wall. The sensing fibres may be provided beneath the outer layer. The sensing fibres may be provided around the inner layer. The sensing fibres may be provided between an inner layer and outer layer. The sensing fibres may be embedded in the sensing layer. These features are optimally combined with the features of the inner and / or outer layer being free of sensing fibres. This helps ensure the sensing fibres are in a controlled region of the pipe wall that is optimally suited for enhanced measurements and protection of the fibres from damage.

[0063] Preferably, a protective tube is used around each sensing fibre. This helps protect the sensing fibres during the manufacture process from heat stresses and / or changes in volume of the bulk material that is setting / extruded around the sensing fibres.

[0064] The pipe wall may comprise an outer layer. The outer layer may define an outside of the messenger pipe. The outer layer may be free from sensing fibres. The outer layer may be free of armour. The outer layer may have an outer diameter that is equal to the outer diameter of the messenger pipe. The outer layer may have a thickness of about 1 mm or about 2 mm. The outer layer may be formed from a polymer. The outer layer may be formed from a plastics material, such as polyethylene, e.g. high density polyethylene, or the like. The polymer of the outer layer and the polymer of the sensing layer may be mutually polymerisable. The polymer of the outer layer and the polymer of the sensing layer may be suitable for forming a single interconnected polymer network between the outer layer and sensing layer. The polymer of the outer layer may be the same as the polymer of the sensing layer. The polymer of the outer layer may be formed simultaneously with the polymer of the sensing layer. The sensing layer and outer layer may be integrally formed. The outer layer may be extruded. Thus, the outer layer provides an additional layer that protects the sensing fibres and ensures adequate separation between them and the outside of the messenger pipe.

[0065] The messenger pipe may comprise a low friction coating. That is, a coating which provides a lower friction surface than an otherwise uncoated messenger pipe. An inner surface of the messenger pipe may comprise a low friction coating. This can help ensure installation of the fibre optic cable is easier. An outer surface of the messenger pipe may comprise a low friction coating. This can help provide easier installation of the messenger pipe within the fluid pipe. The low friction coating may be provided by a liner.

[0066] The messenger pipe may comprise surface formations provided on an outside surface of the pipe wall, for example on the outer layer. The surface formations may be configured to reduce fluid drag. The surface formations may reduce fluid drag as compared to an otherwise smooth outer surface of the pipe wall. Thus, by reducing fluid drag, forces experienced by the messenger pipe are reduced and noise generated by fluid passing over the pipe is also reduced, which reduces measurement error for the sensing fibres. The surface formations may comprise a repeating pattern of surface formations. The repeating pattern may run substantially parallel to or helically around the axis of the cable. The surface formations may comprise projecting features. The surface formations may comprise recessed features. The surface formations may comprise both projecting and recessed features. Projecting features may comprise pimples or ribs. Recessed features may comprise dimples or grooves.

[0067] In another broad aspect, there is provided a sensing apparatus for monitoring a fluid pipe. The sensing apparatus may comprise the messenger pipe as described above in a broad sense and / or as described in the first aspect. The sensing apparatus may comprise a light emitter for introducing light pulses into the sensing fibre. The sensing apparatus may comprise a light detector module configured to detect backscattering of the light pulses from the sensing fibre and output a detector output signal in response thereto.

[0068] Accordingly, in a second aspect of the invention, there is provided a sensing apparatus for monitoring a fluid pipe comprising the messenger pipe of the first aspect, a light emitter for introducing light pulses into the sensing fibre, and a light detector module configured to detect backscattering of the light pulses from the sensing fibre and output a detector output signal in response thereto.

[0069] As such, by connection to a suitable light detector module and light emitter, the messenger pipe can be used to monitor the fluid pipe.

[0070] The messenger pipe may of course include any one or more of the optional features as described in relation to the first aspect.

[0071] The sensing apparatus may comprise a processing unit for processing the detector output signal so as to obtain information about the condition of the fluid pipe. The processing unit may be provided locally to the sensing apparatus. Alternatively, the processing unit may be provided remotely, such as in a remote server. In such embodiments, the sensing apparatus may comprise a communications apparatus arranged to transmit the detector output signal to the processing unit.

[0072] The sensing apparatus may further comprise a fibre optic cable provided within the messenger pipe. In such embodiments, the fibre optic cable may comprise one or more sensing fibres. The sensing fibres of the fibre optic cable may be optically coupled to one another and / or the sensing fibres of the messenger pipe. The sensing fibres of the fibre optic cable and messenger pipe may form a looped arrangement as described above. This can provide for more advanced analysis and measurement procedures, preferably also leveraging the varying sensitivity of different fibres in the looped arrangement to optimise measurements.

[0073] According to another broad aspect of the invention, there is provided a fluid pipe comprising a messenger pipe. The messenger pipe may be a messenger pipe as described broadly herein and / or the messenger pipe of the first aspect. The fluid pipe may comprise the sensing apparatus of the second aspect. The messenger pipe may form part of the sensing apparatus.

[0074] Accordingly, in a third aspect, there is provided a fluid pipe comprising the messenger pipe of the first aspect.

[0075] The messenger pipe may be provided along a section of the fluid pipe to be monitored. The sensing fibre may extend along the entire section of the fluid pipe to be monitored. The section of the fluid pipe to be monitored may be the entire fluid pipe.

[0076] In another aspect, there is provided a fluid distribution system comprising one or more fluid pipes. The one or more fluid pipes may each be a fluid pipe according to the third aspect above.

[0077] Accordingly in a fourth aspect, there is provided a fluid distribution system comprising one or more fluid pipes according to the third aspect.

[0078] In another broad aspect, there is provided a data communication network comprising fibre optic cables configured to carry network data. At least some of the said fibre optic cables may be laid within messenger pipe according to the present invention.

[0079] Accordingly in a fifth aspect, there is provided a data communication network comprising fibre optic cables configured to carry network data, at least some of said data cables laid within messenger pipe according to the present invention.

[0080] The said messenger pipes may be laid for at least a part of their length within one or more fluid pipes. The said fluid pipes may comprise a part of a fluid distribution system. In such embodiments, said fluid pipes may comprise a branched network of pipes or part of a branched network of pipes. In such embodiments, the data cables may be configured to carry system data from said fluid distribution system alongside said network data. Said system data may be generated by one or more system sensors and / or one or more system devices. The data communication network may comprise a network data controller operable to manage data transmission across the network. The network data controller may be separate to or integrated with a fluid distribution system controller, as required or desired.

[0081] Each fibre optic cable may comprise multiple optical fibres. In some such embodiments, each fibre optic cable may comprise multiple bundles of optical fibres. In embodiments having multiple fibre bundles, each fibre bundle may be provided within an individual sheath.

[0082] In some embodiments, each optical fibre may be a single mode optical fibre. In other embodiments, optical fibres may be a multi-mode optical fibre. In further embodiments, the data cable may comprise a mixture of single mode and multi-mode optical fibres. In some such embodiments, only the optical fibres dedicated to sensor data may be single mode optical fibres.

[0083] In a sixth aspect of the invention, there is provided a method of manufacturing a messenger pipe of the first aspect, the method comprising providing a tubular pipe wall wherein one of more sensing fibres are provided within the pipe wall.

[0084] The method may comprise forming an inner layer of the pipe wall. The method may comprise extruding the inner layer.

[0085] The method may comprise forming a barrier layer around the inner layer. The method may comprise gluing a foil onto the inner layer. The method may comprise arranging an insulating film onto the foil.

[0086] The method may comprise forming a sensing layer around the inner layer and / or barrier layer. The method may comprise laying the one or more sensing fibres onto the inner layer and / or barrier layer. The method may comprise laying the armour, and preferably buffer zones, onto the inner layer and / or barrier layer, optionally between adjacent sensing fibres. The method may comprise providing a material around the sensing fibres. The method may comprise setting a material around the sensing fibres. The method may comprise extruding a material onto the sensing fibres. The sensing fibres may each be provided in a protective tube. The method may comprise forming an outer layer around the sensing fibres. The method may comprise extruding the outer layer. The outer layer may be formed simultaneously with the sensing layer.

[0087] Alternatively, the method may comprise forming an outer layer. Then, adhering the sensing fibres to an inner surface of the outer layer. This can provide an alternative means of construction where the sensing fibres are still within the pipe wall.

[0088] The invention also relates to methods of monitoring a fluid pipe. The method may comprise installing a messenger pipe, preferably the messenger pipe of the first aspect. The method may comprise introducing light pulses into a sensing fibre of the messenger pipe. The method may comprise detecting backscattered from the sensing fibre. The method may comprise processing the backscattered light so as to obtain information about the condition of the fluid pipe and / or events occurring within or in the vicinity of the fluid pipe.

[0089] Accordingly, according to a seventh aspect of the present invention, there is provided a method of monitoring a fluid pipe, the method comprising the steps of: installing a messenger pipe according to the first aspect within the fluid pipe; introducing light pulses into a sensing fibre of the messenger pipe; detecting backscattered light pulses from the sensing fibre; and processing the backscattered light pulses so as to obtain information about the condition of the fluid pipe and / or events occurring within or in the vicinity of the fluid pipe.

[0090] The method may comprise installing a fibre optic cable in the cavity of the messenger pipe. The method may comprise blowing the fibre optic cable down the cavity of the messenger pipe.

[0091] The messenger pipe, sensing apparatus, fluid pipe and fluid distribution systems, as well as methods of manufacture and monitoring described above in broad terms and in accordance with the first to seventh aspects, may all share any one or more features with one another optional or otherwise.

[0092] 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:

[0093] Figure 1 is a schematic cross-sectional diagram of a first embodiment of a messenger pipe and fibre optic cable provided inside the messenger pipe;

[0094] Figure 2 is a schematic diagram of a fluid pipe containing the messenger pipe and fibre optic cable of Figure 1 ;

[0095] Figure 3 is a schematic cross-sectional diagram of a second embodiment of a messenger pipe;

[0096] Figure 4 is a schematic cross-sectional diagram of a third embodiment of a messenger pipe; and

[0097] Figure 5 is a schematic illustration of a data communication network comprising one or more cables laid within messenger pipes.

[0098] Referring to Figures 1 and 2, a first embodiment of a messenger pipe 20 is installed within a fluid pipe 1 to provide a conduit for a fibre optic cable 10 within the fluid pipe 1. In this embodiment, the fluid pipe 1 is part of a fluid distribution system (not shown) configured to distribute drinking water. As such, it is important that both the fibre optic cable 10 is protected by the messenger pipe 20, but also that the risk of contamination of the water by the messenger pipe 20 and / or fibre optic cable 10 is minimised. Further information about how this is achieved is provided below.

[0099] The fibre optic cable 10 comprises one or more data fibre bundles 11, in this embodiment, seven data fibre bundles are shown in this instance provided in a hexagonal close packed array. Each data fibre bundle 11 typically comprises a plurality of single mode optical fibres. The skilled person will appreciate that each bundle can alternatively contain multi-mode optical fibres and / or a mixture of single mode optical fibres and multi-mode optical fibres. The bundles may comprise 12, 24 or any other suitable number of individual fibres. Each bundle 11 may optionally be provided with an individual bundle sheath (not shown) to hold the bundle together, provide abrasion protection and / or, if opaque, block the capture or escape of stray light. The single mode fibres within the data bundle might typically match a known communications standard such as G.652x or G.657x.

[0100] The data fibre bundles 11 can be provided in a linear formation, each substantially parallel to the cable axis. More typically, the data fibre bundles 11 are in a helical formation centred on the cable axis. This improves the structural stability of the cable 10.

[0101] The fibre optic cable 10 further comprises a sheath 12 provided around the outside of the bundles 11. The sheath 12 protects the bundles 11 and holds the cable 10 together and may be any suitable sheath 12 as is known in the art.

[0102] The fibre optic cable 10 further comprises two sensing fibres 13 provided in spaces between the bundles 11 and the sheath 12, in this embodiment, the two sensing fibres 13 are provided on opposite sides of the cable 10. These are discussed further below.

[0103] Referring to Figure 1, the messenger pipe 20 comprises a tubular pipe wall 21 that is annular and defines a cavity 22 extending along the messenger pipe 20. The pipe wall 21 is sized such that the cavity 22 is suitable for receiving the fibre optic cable 10. As described below, the pipe wall 21 comprises one or more sensing fibres 23 provided within the pipe wall 21.

[0104] In this embodiment, the pipe wall 21 comprises a layered structure, with four co-axially arranged layers. An inner layer 24 defines an inside surface 25 of the pipe wall 21 and the shape of the cavity 22. In this embodiment, the inner layer 24 has an inner diameter of 8 mm, which is also the inner diameter of the messenger pipe 20 / pipe wall 21. The inner layer 24 has a thickness defined in a radial direction that is perpendicular to an axis of the pipe wall 21, the inner layer thickness being about 2 mm in this embodiment. In this embodiment, the inner layer 24 is formed from high density polyethylene.

[0105] In this embodiment, the inside surface 25 of the messenger pipe 20 comprises a low friction coating which is configured to provide a lower friction surface than the otherwise uncoated pipe 20. For example, in this embodiment, the low friction coating may provide a lower friction surface than bare high density polyethylene. This assists introduction of the fibre optic cable 10 into the cavity 22 as described below.

[0106] In this embodiment, provided around the inner layer 24 is a barrier layer comprising a metal foil 26 and insulating film 27. In this embodiment, the metal foil 26 comprises an aluminium foil that is glued onto the outside of the inner layer 24. The metal foil 26 is configured to provide a water-tight seal around the inner layer 24 and protect the cavity 22 from water ingress as well as provide structural support to the messenger pipe 20. In this embodiment, the barrier layer has a thickness of about 100 pm.

[0107] The insulating film 27 is shown in Figure 1 as a broken line, and in this embodiment, comprises an electrically insulating material such as polyester. The insulating film 27 is provided over the metal foil 26 and is configured to electrically insulate the metal foil 26 from other components of the messenger pipe 20 as described below.

[0108] In this embodiment, around the insulating film 27 is provided a sensing layer 28 and outer layer 29 respectively. In this embodiment, the sensing layer 28 and outer layer 29 are integrally formed, and in this example, this is achieved as both comprise a high density polyethylene (HDPE) material. The outer layer 29 defines the outside surface 30 of the messenger pipe 20 and is potable water compatible to ensure reduced risk of contamination of fluids in the fluid pipe 1. In this embodiment, the outer layer 29 has an outer diameter of about 14 mm, which is equal to the outer diameter of the messenger pipe 20 / pipe wall 21.

[0109] In this embodiment, the outside surface 30 may also comprise a low friction coating similar to the low friction coating on the inside surface 25 mentioned above. The outer surface may comprise surface formations which may act to minimise fluid drag and induced noise and lift forces. These may facilitate easier installation of the messenger pipe into the fluid pipe 1 and can also provide less hydrodynamic drag forces on the messenger pipe 20 once installed and subject to fluid flow inside the fluid pipe 1. The sensing layer 28 differs from the outer layer 29 in that the sensing layer 28 comprises two sensing fibres 23, buffer wires 31 and armour wires 32 embedded within the HDPE. In contrast, the outer layer 29 is free of sensing fibres 23 and other components, the provision of this outer layer 29 helps the pipe wall provide adequate protection to the sensing fibres and other parts of the pipe wall from damage. As such, the two layers can be separated by the broken line 33 shown in Figure 1, and the structure of the sensing layer 28 is described further below.

[0110] In this embodiment, each sensing fibre 23 is formed of four optical fibre units (not shown) and each optical fibre unit comprises one or more single mode optical fibres. Suitable single mode fibres could be for example of the G652.X or G657.X style. Of course, other types of fibre or fibre unit may also be used so long as they are suitable for generating the backscattered light pulses necessary for monitoring of the fluid pipe 2 as described below.

[0111] In this embodiment, each sensing fibre 23 is provided in a protective tube 34. The protective tube comprises a corrosion resistant and resilient material, and is configured to protect the sensing fibre 23 from both thermal and mechanical stresses during installation and manufacture. The protective tube 34 also hermetically seals the sensing fibre 23 to prevent liquid ingress into the sensing fibre 23, which may reduce sensitivity of the fibre or necessitate replacement / re-calibration.

[0112] In this embodiment, each protective tube 34 is formed from stainless steel, and the sensing fibre 23 and protective tube 34 are collectively termed a fibre in metal tube (FIMT) in the art.

[0113] As the protective tube 34 is formed from a metal, it advantageously also provides a continuous conductor that can be detected using radio frequency detection techniques, such as those employed by cable avoidance tools or CAT scanners. The protective tube 34 can also be used for transmission of radio frequency signals along the messenger pipe if desired as it is electrically isolated from the other components as described below. The protective tube 34 may additionally be used as a return loop for ELCB / RCCD protection where electrical power is to be carried. In this embodiment, the protective tube 34 has an outer diameter of about 1.3 mm and an inner diameter of about 0.9mm. The inside of the protective tube 34 comprises the sensing fibre 23 and any remaining space may be filled with a gel (not shown) to enhance thermal and mechanical coupling of the sensing fibre 23 to the protective tube 34.

[0114] In this embodiment, the two sensing fibres 23 are arranged at diametrically opposed positions around the circumference of the sensing layer 28 and at the same radial distance from the axis of the messenger pipe 20. Two buffer wires 31 are provided on either side of each sensing fibre 23 around the circumference of the sensing layer 28. A plurality of armour wires 32 are provided around the rest of the circumference of the sensing layer 28 and between the buffer wires 31. Consequently, substantially the entire circumference of the sensing layer 28 is occupied by the sensing fibres 23, buffer wires 31 and armour wires 32.

[0115] The sensing fibres 23, buffer wires 31 and armour wires 32 are all arranged substantially parallel to one another, extending both along the length of the messenger pipe 20 and around its circumference in a helical formation. In this embodiment, the helical formation has a pitch of about 50-100 mm. This helps to ensure that along the length of the messenger pipe 20, each sensing fibre 23 may make measurements in all directions around the messenger pipe 20. In addition, it reduces potential weak points in the messenger pipe 20, especially as the rotational symmetry of the pattern of sensing fibres 23, buffer wires 31 and armour wires 32 is of order two. In addition, it provides for flex of the messenger pipe without damage to the sensing fibres 23.

[0116] The inner edges of the sensing fibres 23, buffer wires 31 and armour wires 32 are all arranged against the insulating film 27 and so substantially the same radial distance from the axis of the messenger pipe 20. In this embodiment, the armour wires 32 have a greater diameter than the sensing fibres 23 and buffer wires 31 and so extend furthest from the axis of the messenger pipe 20. The armour wires 32 are, in this embodiment, 1.4 mm in diameter. The armour wires 32 are formed from a resilient material, such as a metal, which in this embodiment is copper. The armour wires 32 thereby provide an armour configured to strengthen the messenger pipe 20 and protect the sensing fibres 23 and buffer wires 31. In this embodiment, the buffer wires 31 comprise a resilient material that is softer than the armour wires 32, and are non-conductive, and are configured to provide a buffer zone each side of the sensing fibres 23 and protect the FIMT from the armour wires 32. In this embodiment, the buffer wires 31 comprise a plastics material such as nylon or polyethylene. In this embodiment, the buffer wires 31 have a diameter of about 1.1 mm.

[0117] As described above, the FIMT / sensing fibres 23 and buffer wires 31 split the armour wires 32 into two wire groups: wire group A and wire group B, as denoted by A and B in Figure 1. As the armour wires 32 comprise copper, they are electrically conductive. In the sensing layer 28, the armour wires 32 are closely packed and in contact with one another within their wire group, as such, the wires 32 of each wire group are all electrically connected to one another. However, the buffer wires 31 are electrically insulating, as is the insulating film 27, as such, wire group A is electrically insulated from wire group B. Consequently, electrical power and / or signals may be transmitted along each wire group.

[0118] In order to manufacture the messenger pipe 20, the inner layer 24 is first formed by extrusion. The metal foil 26 is then provided and glued to the outside of the inner layer 24. The insulating film 27 is provided over the metal foil 26 and then the FIMTs comprising sensing fibre 23, buffer wires 31 and armour wires 32 are arranged in a helical formation around the insulating film 27. Next, the HDPE forming the sensing layer 28 and outer layer 29 is extruded over and around the FIMTs / sensing fibres 23, buffer wires 31 and armour wires 32. While the HDPE sets to finalise the sensing layer 28, the protective tube 34 reduces the likelihood of damage to the more sensitive sensing fibres 23. The low friction coating may then be provided on the inside / outside surfaces as required.

[0119] In an alternative embodiment, the outer layer 29 may be formed first and then the sensing fibres 23 provided on and adhered to the inside of the outer layer 29.

[0120] The messenger pipe 20 as described above may then be installed into the fluid pipe 1, for example by known techniques for installation of cables in a fluid pipe 1 such as pulling. Then, the fibre optic cable 10 may be installed into the messenger pipe 20, for example by blowing of the fibre optic cable 10 down the cavity 22. The cross-sectional profile of the messenger pipe 20 and fibre optic cable 10 may then resemble the schematic diagram of Figure 1.

[0121] In this embodiment, the messenger pipe 20 is part of a sensing apparatus 35 comprising the messenger pipe 20, fibre optic cable 10, a light emitter 36, a light detector module 37 and processing unit 38. The light emitter 36 is optically coupled to the sensing fibres 23 and is configured to introduce light pulses into the sensing fibres 23. The light detector module 37 is also optically coupled to the sensing fibres 23 and is configured to detect backscattered light pulses from the sensing fibres 23 and output a detector output signal in response. The processing unit 38 is provided locally to the light detector module 37 and is configured to receive the detector output signal and obtain information about the condition of the fluid pipe. In other embodiments, the processing unit could be provided remotely, such as in a cloud-based server, and a communications apparatus may be provided to transmit the detector output signal to the remote processing unit.

[0122] In addition, in this embodiment, the two sensing fibres 23 of the messenger pipe 20 have different sensitivities or frequency responses. For example, they may have different structural properties or chemical compositions which means that they are each optimised for certain measurements or monitoring conditions. The two sensing fibres 23 may therefore be defined as a first sensing fibre 23 and a second sensing fibre 23, and in this embodiment, the first sensing fibre 23 is etched (not shown) to provide localised points that enhance the response of the sensing fibre 23 to vibrations or acoustic signals. Consequently, the first sensing fibre 23 has a higher sensitivity to vibrations than the second sensing fibre 23.

[0123] In this embodiment, the light emitter 36 and light detector module 37 are both optically coupled to the first sensing fibre 23. The sensing apparatus then further comprises a first splice 39 that optically couples an end of the first sensing fibre 23 distal from the light emitter 36 and light detector module 37 to the second sensing fibre 23. This provides an optical path extending along the first sensing fibre 23 in a first direction and then along the second sensing fibre 23 in a second direction, the second direction being opposite to the first direction.

[0124] In addition, a second splice 40 is provided that connects the end of the second sensing fibre 23 distal from the first splice 39 to one of the sensing fibres 13 in the fibre optic cable 10. Thus, the optical path extends from the second sensing fibre 23 into a sensing fibre 13 of the fibre optic cable 10.

[0125] As described above, a continuous looped arrangement is formed comprising the sensing fibres 13, 23. As the first and second sensing fibres 23 are provided within the messenger pipe wall, they have higher sensitivity than the sensing fibre 13 of the fibre optic cable 10 as it does not have continuous coupling to the fluid pipe / fluid. Consequently, the continuous looped arrangement provides an optical path with the higher sensitivity first sensing fibre 23 adjacent to the light emitter and light detector module, then a medium sensitivity second sensing fibre 23, then a lower sensitivity sensing fibre 13 of the fibre optic cable 10.

[0126] In this embodiment, there is also provided an electrical power source 41, for example a battery, generator or connection to a power grid and an electrical load 42. At one end of the messenger pipe 20, the positive and negative terminals of the power source 41 are electrically connected to wire group A and wire group B of the armour wires 32 respectively. Consequently, wire group A is a positive wire group and wire group B is a negative wire group.

[0127] At the other end of the messenger pipe 20, wire group A and B are electrically connected to the load 42 so that it may receive electrical power from the power source 42 via the messenger pipe 20. This is very useful in remote situations where no other electrical power source is available, for example, electrical power could be supplied to a sensor and communications apparatus provided on the fluid pipe to allow detection of a property and backhaul of the sensor data without the need for a battery or other local power source. Due to the size and materials of the armour wires, an electrical resistance of down to 2 to 3 Ohms / km of messenger pipe may be achieved. Consequently, efficient power transmission is realised. In order to monitor the fluid pipe 1, the light emitter 36 generates light pulses which are coupled into the first sensing fibre 23. These travel down the sensing fibres 23, 13 and backscattered light pulses are generated which travel back towards the light detector module 37. The light detector module 37 detects the backscattered light pulses and generates a detector output signal indicative of them. Then the processing unit 38 receives the detector output signal and processes it to obtain information about the condition of the fluid pipe.

[0128] By considering the time of detection for backscattered pulses, the processing unit 38 may determine which sensing fibre 13, 23 a pulse originated from, and its position along the fluid pipe 1. This allows selection and aggregation of measurements from the different sensitivity fibres to improve measurement uncertainty and increase the range of measurements that are possible for the sensing apparatus. In this embodiment in particular, the highest sensitivity fibre is adjacent the emitter and so receives potentially the highest power light pulses, which facilitates measurement of the weakest signals from the fluid pipe. In contrast, the sensing fibre 13 of the fibre optic cable has the lowest sensitivity and also receives the lowest power light pulses due to power losses as they travel through the first and second sensing fibres 23. This facilitates simultaneous sensing of stronger signals that may otherwise saturate the first and second sensing fibres 23.

[0129] Of course, in other embodiments, there may be no splice to a sensing fibre in the fibre optic cable. Additionally or alternatively, all fibres in the continuous looped arrangement may have the same sensitivity.

[0130] In other embodiments more or less sensing fibres may be provided in the messenger pipe.

[0131] Referring to Figures 3 and 4, second and third embodiments of a messenger pipe 20 are shown. These embodiments share many of the same features of the first embodiment above and so like numerals are used and only differences with respect to the first embodiment are described below. In both Figures, the messenger pipe 20 is shown without a fibre optic cable inside the cavity 22. However, both are of course suitable for receiving a cable, such as like that described in relation to the first embodiment. Referring to Figure 3, in the second embodiment, the messenger pipe 20 comprises only one sensing fibre 23. Consequently, as compared to the first embodiment, the armour wires 32 extend all the way around the rest of the circumference of the pipe wall 21 that is not occupied by the two buffer wires 31 either side of the only FIMT / sensing fibre 23 and protective tube 34.

[0132] In this embodiment, the armour wires 32 are therefore not divided into two wire groups. This embodiment may be advantageous where additional armour is required for a particularly harsh installation or use environment, or where reduced sensing capability or cost is required. To save further costs in a relatively low risk environment, the buffer wires 31 and armour wires 32 may also be omitted all together, in which case the sensing layer would just comprise a single sensing fibre.

[0133] Referring to Figure 4, in the third embodiment four sensing fibres 23 are placed within the pipe wall 21, separated by 90 degrees from one another around the circumference of the pipe wall 21. Each sensing fibre 23 is provided within a protective tube 34 and flanked by buffer wires 31 as described in relation to the first embodiment.

[0134] In this embodiment, the armour wires 32 are consequently divided into four wire groups: A; B; C; and D. This may facilitate more advanced power delivery or other electrical signals to be delivered along the messenger pipe.

[0135] This embodiment may also be preferred where more advanced or sensitive sensing is required.

[0136] As described above, the number of sensing fibres may vary, to accommodate this the size and / or number of armour wires may be adjusted to provide space for additional sensing fibres or buffer zones.

[0137] The above described embodiment describes a messenger pipe with an inner diameter of about 8 mm. As such, the cavity formed within it is suitable for receiving anything up to a 144 core fibre optic cable suitable for data transmission. Of course, if larger fibre optic cables are used, the messenger pipe may be enlarged to accommodate this, or reduced in size if smaller cables are used. This may include a corresponding change in the size of each component, such as armour wires, buffer zones, sensing fibres, protective tubes, and / or layers of the messenger pipe, and / or a change in the number of armour wires used to ensure the circumference of the pipe wall is filled between adjacent sensing fibres.

[0138] In one other embodiment, one of the sensing fibres in the messenger pipe may be replaced with a bundle of multi-mode optical fibres. These fibres may be configured to receive high power light from an emission source and deliver the light to the other end of the messenger pipe. The light may then be incident on a photodiode in order to generate electrical power at the other end of the messenger pipe.

[0139] As indicated above, the messenger pipe is particularly suited for facilitating installation (and subsequent repair / replacement) of fibre optic cable 10 used for a data communication network. This is illustrated schematically in figure 5 wherein a network of fibre optic data cables 220, 240, 260 provides a link between end user nodes 270 and a network controller 210, which facilitates connection to external networks 290. The end user nodes can be provided within individual dwellings, businesses or the like or may comprise bases stations for cellular networks or local wireless networks.

[0140] Extending from the network controller 210 are one or more trunk data cables 220. Each said trunk data cable 220 typically comprises at least one bundle of single mode or multi-mode optical fibres.

[0141] Each trunk cable 220 is typically connected to at least one primary junction boxes 230. Within the primary junction box 230 the fibres within the trunk data cable 220 may be spliced together with corresponding fibres in one or more district data cables 240. As with the trunk data cables 220, each said district data cable 240 typically comprises at least one bundle of single mode or multi-mode optical fibres.

[0142] Each district data cable 240 may connect to one or more subsidiary junction boxes 250. Within the subsidiary junction box 250 the fibres within the district data cable 240 may be spliced together with corresponding fibres in one or more local data cables 260. As with the trunk data cables 220 and the district data cables 240, each said local data cable 260 may comprise at least one bundle of single mode or multi-mode optical fibres. More typically, a local data cable 260 may comprise a single bundle of single mode or multi-mode optical fibres or indeed only a one single mode or multimode optical fibre. From said subsidiary junction boxes 250 the local data cables 260 provide a connection to individual end user nodes 270. The end user nodes 270 may be provided in homes, business premises of the like.

[0143] The skilled person will appreciate that the described network topology and structure is by way of example only. In particular, the skilled person will appreciate that many variations of network topology and structure may be contemplated to fit the particular requirements of a given situation. In particular, the network may have more or fewer branches and may have more or fewer levels of junction and more or fewer end user nodes.

[0144] In the present invention, at least some of the cables 220, 240, 260 are provided within messenger pipes 20. Furthermore, at least some of the messenger pipes are provided within fluid pipes 1, for instance fluid pipes 1 forming part of a water distribution network. The skilled person will appreciate that trunk data cables 220, 240, 260 may additionally or alternatively be provided within any suitable fluid distribution system including, but not limited to drainage and / or sewage systems.

[0145] 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 by the appended claims, in particular dimensions and materials are exemplary and may be varied as appropriate.

Claims

CLAIMS1. A messenger pipe for use in a fluid pipe, the messenger pipe comprising a tubular pipe wall which defines a cavity extending along the messenger pipe suitable for receiving a fibre optic cable, wherein the pipe wall comprises one or more sensing fibres provided within the pipe wall.

2. The messenger pipe of claim 1 wherein each sensing fibre is provided inside a protective tube, the protective tube being provided in the pipe wall.

3. The messenger pipe of claim 2 wherein the protective tube is formed of metal.

4. The messenger pipe of any preceding claim wherein each sensing fibre extends along a length of the messenger pipe and preferably around a circumference of the messenger pipe in a helical formation.

5. The messenger pipe of any preceding claim wherein the messenger pipe is provided with armour comprising multiple elongate armour wires provided within the pipe wall and provided on either side of one of the sensing fibres.

6. The messenger pipe of claim 5 wherein the armour wires extend along the length of the messenger pipe and preferably around the circumference of the messenger pipe in a helical formation.

7. The messenger pipe of claim 5 or claim 6 wherein the sensing fibre and armour wires are spaced apart from one another by two buffer zones.

8. The messenger pipe of claim 7 wherein buffer zone is provided by a buffer wire extending parallel to the sensing fibre and armour wires, optionally wherein the buffer wire is formed from a polymer.

9. The messenger pipe of any preceding claim wherein the messenger pipe comprises two or more sensing fibres spaced apart around a circumference of the pipe wall.

10. The messenger pipe of claim 9 wherein the two or more sensing fibres are spaced apart equally around the circumference of the pipe wall.

11. The messenger pipe of claim 9 or claim 10 wherein at least two of the two or more sensing fibres have different sensitivities.

12. The messenger pipe of any of claims 9 to 11 wherein at an end of the messenger pipe, first and second sensing fibres of the two or more sensing fibres are optically coupled together to provide an optical path extending along the first sensing fibre in a first direction and then along the second sensing fibre in a second direction, the first and second directions being different directions to one another and preferably opposite directions.

13. The messenger pipe of any of claims 9 to 12 wherein the messenger pipe is provided with armour comprising multiple elongate armour wires provided within the pipe wall, wherein the armour wires are provided between adjacent sensing fibres of the two or more sensing fibres.

14. The messenger pipe of claim 13 wherein the two or more sensing fibres comprise an even number of sensing fibres, and the sensing fibres define an even number of wire groups, each wire group being electrically insulated from the other wire groups and comprising one or more of the armour wires.

15. The messenger pipe of claim 14 wherein the messenger pipe comprises four sensing fibres spaced apart by 90 degrees around the circumference of the pipe wall and four wire groups.

16. The messenger pipe of any of claims 13 to 15 wherein each sensing fibre comprises a buffer zone provided either side of the sensing fibre and separating the sensing fibre from an adjacent wire group.

17. The messenger pipe of any preceding claim wherein the pipe wall comprises a layered structure with two or more co-axially arranged layers.

18. The messenger pipe of claim 17 wherein the pipe wall comprises any one or more of: a. an outer layer defining an outside of the messenger pipe and free of sensing fibres; b. a sensing layer comprising the sensing fibres; c. a barrier layer comprising a material resistant to water ingress; andd. an inner layer defining an inside of the messenger pipe and free of sensing fibres.

19. The messenger pipe of claim 18 wherein an outer surface and / or an inner surface of the messenger pipe comprises a low friction coating.

20. The messenger pipe of claim 18 or claim 19 wherein the outer surface comprises surface formations for reducing fluid drag.

21. A sensing apparatus for monitoring a fluid pipe comprising the messenger pipe of any preceding claim, a light emitter for introducing light pulses into the sensing fibre, and a light detector module configured to detect backscattering of the light pulses from the sensing fibre and output a detector output signal in response thereto, and optionally a processing unit for processing the detector output signal so as to obtain information about the condition of the fluid pipe.

22. A fluid pipe comprising the messenger pipe of any one of claim 1 to 20 provided within the fluid pipe.

23. The fluid pipe of claim 22 wherein the messenger pipe forms part of the sensing apparatus of claim 21.

24. A fluid distribution system comprising one or more fluid pipes according to claim 22 or claim 23.

25. A data communication network comprising fibre optic cables configured to carry network data, wherein at least some of said fibre optic cables are laid within messenger pipe according to any one of claims 1 to 20.

26. A method of monitoring a fluid pipe, the method comprising the steps of: installing a messenger pipe according to claims 1 to 20 within the fluid pipe; introducing light pulses into a sensing fibre of the messenger pipe; detecting backscattered from the sensing fibre; and processing the backscattered light so as to obtain information about the condition of the fluid pipe and / or events occurring within or in the vicinity of the fluid pipe.

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