Flexible pipe including thermal insulation

Abstract

Apparatus for providing a thermal insulation layer in a flexible pipe comprises hollow fibres disposed in a layer 307 of a flexible pipe body 300. A flexible pipe body comprising this apparatus can have the layer radially inside an armour layer 303, 305, 306 of the pipe body, and it can be radially outside a carcass layer and an extruded layer 310. The hollow fibres each can have a first and second end and a central bore, or a plurality of central bores, that extend between the ends. The hollow fibres can be encapsulated in a matrix or secured to a matrix. The apparatus can comprise at least 20% and less than 95% by volume of the hollow fibres. To manufacture the pipe body, a plurality of hollow fibres are disposed in a thermal insulation layer of a flexible pipe body, and the fibres can be bonded together with a matrix to form the thermal insulation layer. A tape for providing a layer in a flexible pipe body comprises an elongate tape body portion and hollow fibres disposed on the tape body, and it can comprise a matrix which bonds the hollow fibres together.

Description

The present invention relates to a method and apparatus for providing one or more thermally insulating layers in a flexible pipe. In particular, but not exclusively, the present invention relates to the use of an insulating tape including a plurality of hollow fibres disposed in one or more layers of flexible pipe body. Traditionally flexible pipe is utilised to transport production fluids, such as oil and / or gas and / or water, from one location to another. Flexible pipe is particularly useful in connecting a sub-sea location (which may be deep underwater) to a sea level location. The pipe may have an internal diameter of typically up to around 0.6 metres (e.g. diameters may range from 0.05 m up to 0.6 m). Flexible pipe is generally formed as an assembly of a flexible pipe body and one or more end fittings. The pipe body is typically formed as a combination of layered materials that form a pressure-containing conduit. The pipe structure allows large deflections without causing bending stresses that impair the pipe’s functionality over its lifetime. The pipe body is generally built up as a combined structure including polymer, and / or metallic, and / or composite layers. For example, a pipe body may include polymer and metal layers, or polymer and composite layers, or polymer, metal and composite layers. API Recommended Practice 17B provides guidelines for the design, analysis, manufacture, testing, installation, and operation of flexible pipes and flexible pipe systems for onshore, subsea and marine applications. API Specification 17J titled “Specification for Unbonded Flexible Pipe” defines the technical requirements for safe, dimensionally and functionally interchangeable flexible pipes that are designed and manufactured to uniform standards and criteria. Unbonded flexible pipe has been used for deep water (less than 3,300 feet (1,005.84 metres)) and ultra deep water (greater than 3,300 feet) developments. It is the increasing demand for oil which is causing exploration to occur at greater and greater depths where environmental factors are more extreme. For example in such deep and ultra-deep water environments ocean floor temperature increases the risk of production fluids cooling to a temperature that may lead to pipe blockage. When transporting crude oil, for example, blockage of the internal bore of the flexible pipe can occur due to paraffin formation. As a method to overcome such problems it has in the past been suggested that a layer of thermal insulation could be provided outside the armour layers of a flexible pipe, or as a replacement for a carcass layer. Thermal insulation has been somewhat effective in insulating the inner bore of the pipe from external low temperature thus helping prevent blockage. Nevertheless the insulating effects provided to date have been limited. Occasionally as an alternative a cold fluid is transported along the bore of the flexible pipe. Again it is helpful to thermally insulate such fluids to prevent undesired heating from the surrounding relatively warm environment. A known prior art technique for providing a thermal insulation layer is to wind tape manufactured from a thermally insulating material helically around an underlying layer during manufacture of flexible pipe body. Sometimes a tape formed from a polypropylene matrix with hollow glass spheres has been used which provides a low thermal conductivity (k) value and which is able to withstand reasonably high hydrostatic pressures. However, the hollow glass spheres in the tape are prone to crushing and internal and external pressures operate to squeeze the tape layer thereby reducing thickness and thus thermal insulation effects. Likewise these insulating tape layers are positioned radially outside the armour wires in the pipe so that inter-layer pressure from those armours does not act on the insulation tape and crush it. A further prior art technique for providing a thermal insulation layer is to extrude a layer of thermally insulating material over an underlying layer during manufacturing of flexible pipe body. Commonly a polymer matrix containing air bubbles and / or glass spheres has been used. However, this includes an additional and complicated manufacturing step which can be a complex process involving careful alignment, heating and cooling steps during manufacture. Also geometric tolerances are difficult to control during an extrusion process and this can have a knock-on effect to subsequent layers formed radially outside such an extruded layer. A still further prior art technique for providing a thermal insulation layer is to provide an interlocked profile, containing aerogel material, which is helically wound into a layer of a flexible pipe, for example as described in European patent EP2513539B1. With either the tape or the extruded layer technique mentioned above the materials used have until now demonstrated limited ability to minimise the thermal conductivity (k) value in situ, and / or are very costly to implement. It is an aim of the present invention to at least partially mitigate the above-mentioned problems. It is an aim of certain embodiments of the present invention to provide flexible pipe body which can be used to form a flexible pipe of a type able to transport production fluids and which includes at least one thermal insulation layer offering a much reduced path for thermal conduction relative to prior art flexible pipe body. It is an aim of embodiments of the present invention to provide a riser assembly, jumper, flow line and / or method of manufacturing a flexible pipe able to operate in deep and ultradeep water environments. According to a first aspect of the present invention there is provided an apparatus for providing a thermal insulation layer in a flexible pipe. The apparatus may comprise a plurality of hollow fibres. The plurality of hollow fibres may be disposed in a layer of flexible pipe body. According to another aspect of the invention there is provided an apparatus for providing a thermal insulation layer in a flexible pipe, the apparatus comprising a plurality of hollow fibres disposed in a layer of flexible pipe body. The plurality of hollow fibres may each have a first end, a second opposing end, and at least one central bore that extends between the first end and the second end. Each of the hollow fibres may be cylindrical hollow fibres. A longitudinal axis may be defined between the first end and the second end of each of the hollow fibres. The plurality of hollow fibres may each include a plurality of central bores. The plurality of central bores may extend between the first end and the second end of each of the hollow fibres. Each of the hollow fibres may be microporous. Each of the hollow fibres may be nanoporous. The plurality of hollow fibres may each have an outer diameter that is less than 150 micrometres, for example less than 100 micrometres or less than 50 micrometres or less than 10 micrometres. The outer diameter of each of the hollow fibres may be at least 0.5 micrometre, for example at least 1 micrometre. The outer diameter of each of the hollow fibres may be between 0.5 micrometre and 150 micrometres. The outer diameter of each of the hollow fibres may be between 0.5 micrometre and 100 micrometres. The outer diameter of each of the hollow fibres may be between 0.5 micrometre and 50 micrometres. The outer diameter of each of the hollow fibres may be between 0.5 micrometre and 10 micrometres. The outer diameter of each of the hollow fibres may be between 1 micrometre and 150 micrometres. The outer diameter of each of the hollow fibres may be between 1 micrometre and 100 micrometres. The outer diameter of each of the hollow fibres may be between 1 micrometre and 50 micrometres. The outer diameter of each of the hollow fibres may be between 1 micrometre and 10 micrometres. The plurality of hollow fibres may each comprise a polymeric material, for example a crosslinked polymeric material. The plurality of hollow fibres may each comprise non-cross linked, high temperature polymeric materials or fluoropolymers, for example polyvinylidene fluoride (PVDF). The plurality of hollow fibres may each comprise a non-polymeric material, for example glass or carbon nanotubes. The plurality of hollow fibres may be encapsulated in a matrix. The plurality of hollow fibres may be embedded in a matrix. The plurality of hollow fibres may be secured, for example adhered, to a matrix. The matrix may comprise any material which can be produced as a tape. The matrix may comprise any material which can be wound around other components of a flexible pipe body. The matrix material may comprise any material which can be consolidated or adhered to an underlying layer of the pipe body. The matrix material may comprise any material which can be consolidated or adhered to a sub-layer of the thermal insulation layer, for example a sub-layer comprising helically wrapped windings of insulation tape comprising hollow fibres. The matrix may comprise a polymeric material. The matrix may comprise a thermoplastic material or a thermoset material. The matrix material may comprise one or more of, for example, polyvinylidene fluoride (PVDF), polyamide 11 (Nylon 11) or polyamide 12 (Nylon 12), polypropylene (PP), polyethylene (PE), polyether ether ketone (PEEK) or poly(methyl acrylate) (PMA), polyurethane (Pll), a perfluoroalkoxy alkane, e.g. PFA or MFA, polyphenylene sulfide (PPS), or any other suitable polymer. The matrix may be attached, for example adhered or bonded, to a carrier tape. The apparatus may comprise at least 20 % by volume of the plurality of hollow fibres. The apparatus may comprise less than 95% by volume of the plurality of hollow fibres. The apparatus may comprise between approximately 20% by volume and approximately 95% by volume of the plurality of hollow fibres. The apparatus may be a tape. The layer of flexible pipe body may be an elongate tape body portion. The hollow fibres may be disposed on the elongate tape body. According to another aspect of the invention there is provided a tape for providing a thermal insulation layer in a flexible pipe, the tape comprising a plurality of hollow fibres disposed in an elongate body portion of the tape. According to another aspect of the invention there is provided a flexible pipe body comprising the apparatus according to the preceding aspects of the invention. The apparatus may comprise a thermal insulation layer of the flexible pipe body. The flexible pipe body may include at least one armour layer. The at least one armour layer may comprise a metal or a composite material. The thermal insulation layer of the flexible pipe body may be radially inside the at least one armour layer of the flexible pipe body. The thermal insulation layer may comprise a tape. The tape may be helically wrapped around an underlying layer of flexible pipe body. The thermal insulation layer may comprise an extruded thermal insulation layer. The extruded thermal insulation layer may be extruded over an underlying layer of flexible pipe body. The thermal insulation layer may be radially outside a carcass layer of the flexible pipe body. The thermal insulation layer is sandwiched between a first sacrificial layer and / or a second sacrificial layer of the flexible pipe body. The first sacrificial layer may comprise a polymeric material. The second sacrificial layer may comprise a polymeric material. Each of the first sacrificial layer and the second sacrificial layer may comprise a polymeric material. The thermal insulation layer may be radially outward of an extruded layer of the flexible pipe body. The thermal insulation layer may be bonded to the extruded layer. The extruded layer may be a first extruded layer. The flexible pipe body may comprise a second extruded layer. The second extruded layer may be radially outward of the thermal insulation layer. The flexible pipe body may comprise an armour layer. The armour layer may comprise a metal or composite material. According to another aspect of the invention there is provided a flexible pipe comprising the flexible pipe body according to the preceding aspect of the invention and one or more end fittings. According to another aspect of the invention there is provided a jumper, riser or flowline comprising a flexible pipe according to the preceding aspect of the invention. According to another aspect of the invention there is provided a method of manufacturing flexible pipe body. The method may comprise disposing a plurality of hollow fibres in a thermal insulation layer of a flexible pipe body. The method may comprise bonding the plurality of hollow fibres together with a matrix to form the thermal insulation layer of flexible pipe body. The method may comprise attaching the hollow fibre layer to a carrier layer. The method may comprise sandwiching the hollow fibre layer between two polymeric layers. The method may comprise applying an extrusion layer over the hollow fibre layer. The method may comprise locating the hollow fibre layer between a first sacrificial layer and a second sacrificial layer. According to another aspect of the invention there is provided a tape for providing a layer in a flexible pipe body. The tape may comprise an elongate tape body portion. The tape may comprise a plurality of hollow fibres disposed on the elongate tape body. According to another aspect of the invention there is provided a tape for providing a layer in a flexible pipe body, the tape comprising an elongate tape body portion and a plurality of hollow fibres disposed on the elongate tape body. The tape body portion may comprises a matrix. The matrix may be configured to bond the plurality of hollow fibres together. The tape may comprise a carrier layer. The tape may be sandwiched between a first polymeric layer and a second polymeric layer. Certain embodiments of the invention provide the advantage that they improve the thermal insulation properties of thermal insulation layers for flexible pipes. Air trapped within the hollow fibres of the thermal insulation acts as a thermal buffer, preventing conduction and convection of heat through the thermal insulation layer. The hollow fibres also beneficially resist the ingress of water. This prevents the air within hollow fibres being displaced by water, which would reduce the thermal insulation performance. Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which: Figure 1 illustrates a flexible pipe body according to an embodiment of the present invention; Figure 2 illustrates an example of a riser assembly suitable for transporting production fluid such as oil and / or gas and / or water from a sub-sea location to a floating facility; Figure 3 is a schematic representation of layers of a flexible pipe body according to an embodiment of the present invention; Figure 4 is a schematic representation of an insulation layer for the flexible pipe body of Figure 3; Figure 5 is a schematic representation of a hollow fibre for the insulation layer of Figure 4; Figures 6A is a schematic representation of a cross section view of the hollow fibre of Figure 5; Figures 6B to 6E show schematic representations of cross section views of alternative hollow fibres for the insulation layer of Figure 4; Figures 7A to 7C show schematic representation showing different arrangements of the insulation layer of Figure 4 in a flexible pipe body; Figure 8 is a schematic representation of layers of a flexible pipe body according to another embodiment of the present invention; and Figure 9 is an alternative schematic representation of the layers of a flexible pipe body as shown in Figures 3 and 8. In the drawings like reference numerals refer to like parts. Throughout this description, reference will be made to a flexible pipe. It will be understood that a flexible pipe is an assembly of a portion of pipe body and one or more end fittings in each of which a respective end of the pipe body is terminated. Figure 1 illustrates how pipe body 100 is formed in accordance with an embodiment from a combination of layered materials that form a pressure-containing conduit. Although a number of particular layers are illustrated in Figure 1, it is to be understood that the pipe body is broadly applicable to coaxial structures including two or more layers manufactured from a variety of possible materials. For example, the pipe body may be formed from polymer layers, metallic layers, composite layers, or a combination of different materials. It is to be further noted that the layer thicknesses are shown for illustrative purposes only. While some layers of the flexible pipe body may be described as bonded or consolidated, the flexible pipe may generally be considered an unbonded flexible pipe. That is, unless otherwise specified the various layers of the flexible pipe body are unbonded and thereby have the capacity to move longitudinally in relation to the adjacent layers during the bending or flexion of the flexible pipe body. As used herein, layers may optionally include sub-layers. A plurality of sub-layers cooperate to form a layer with a specific purpose. For example, a pressure armour layer may be formed of one or more pressure armour sub-layers. As used herein, the term “composite” is used to broadly refer to a material that is formed from two or more different materials, for example a material formed from a matrix material and reinforcement fibres. In some examples, a composite may be a composite tape layer. In other examples a composite may include an extruded layer. Fibres within a composite material may include any of carbon fibres, glass fibres, aramid fibres, basalt fibres, tensilized polymer fibres, metal wires, or any combination thereof. As used herein, a tape is to be broadly construed as encompassing any elongate structure having a preformed cross section that can be wound in a helical manner around an underlying structure. Thus, a tape refers to an elongate material provided in a wrapable or windable form, so as to form a layer by wrapping or winding around a radially inward layer of the flexible pipe body. For example, a composite tape is a wrapable or windable elongate composite material which is used to form a composite tape layer. As used herein, the term lay angle refers to the angle at which a tape or later is applied to, that is wrapped around, an underlying structure of the flexible pipe body. The lay angle is thereby an angle relative to the longitudinal axis of the flexible pipe body. A tape with a lay angle of 90° is a tape wrapped around a radius of a cross section of the flexible pipe body. It will be understood that the term radially issued to refer to a position in relation to the radius of the flexible pipe body. For example, the term radially inward is intended to refer to a position which is relatively closer to the centre, or central longitudinal axis, of the flexible pipe body. Radially outward is intended to refer to a position which is relatively more distant from the centre, or central longitudinal axis, of the flexible pipe body. As illustrated in Figure 1, a flexible pipe body includes an optional innermost carcass layer 101. The carcass provides an interlocked construction that can be used as the innermost layer to prevent, totally or partially, collapse of an internal pressure sheath 102 due to pipe decompression, external pressure, and tensile armour pressure and mechanical crushing loads. The carcass layer is often a metallic layer, formed from stainless steel, for example. The carcass layer could also be formed from composite, polymer, or other material, or a combination of materials. It will be appreciated that certain embodiments are applicable to ‘smooth bore’ operations (i.e. without a carcass layer) as well as such ‘rough bore’ applications (with a carcass layer). The internal pressure sheath 102 acts as a fluid retaining layer and comprises a polymer layer that ensures internal fluid integrity. It is to be understood that this layer may itself comprise a number of sub-layers. It will be appreciated that when the optional carcass layer is utilised the internal pressure sheath is often referred to by those skilled in the art as a barrier layer. In operation without such a carcass (so-called smooth bore operation) the internal pressure sheath may be referred to as a liner. An optional sacrificial or wear layer (not shown) may be included, as an extruded layer or helically wound tape layer, either or both radially inwardly or radially outwardly of the internal pressure sheath. These layers respectively provide a relatively smooth (compared to the outside surface of the carcass layer) surface over which to extrude the internal pressure sheath, or provide a sacrificial layer of material which may, under pressure, creep into gaps between wraps of an overlying metallic armour layer, particularly a pressure armour layer. An optional pressure armour layer 103 is a structural layer that increases the resistance of the flexible pipe to internal and external pressure and mechanical crushing loads. The layer also structurally supports the internal pressure sheath, and typically may be formed from an interlocked construction of wires wound with a lay angle close to 90°. The pressure armour layer is often a metallic layer, formed from carbon steel, for example. The pressure armour layer could also be formed from composite, polymer, or other material, or a combination of materials. The flexible pipe body also includes an optional first tensile armour layer 105 and optional second tensile armour layer 106. Each tensile armour layer is used to sustain tensile loads and internal pressure. The tensile armour layer is often formed from a plurality of wires (to impart strength to the layer) that are located over an inner layer and are helically wound along the length of the pipe at a lay angle typically between about 10° to 55°. The tensile armour layers are often counter-wound in pairs. The tensile armour layers are often metallic layers, formed from carbon steel, for example. The tensile armour layers could also be formed from composite, polymer, or other material, or a combination of materials. The flexible pipe body shown also includes optional layers of tape 104 which help contain underlying layers and to some extent prevent abrasion between adjacent layers. The tape layer may be a polymer or composite or a combination of materials. An example of such tapes may be found outside the tensile armour layer 106 where the incorporation of high strength fibres, aligned along the axial length of the tape, helps to stop the tensile armour wires from what is known as birdcaging (radially displacing under axial compression loading in the pipe). These anti-birdcaging or bandaging tapes are wrapped at an angle close to 90 degrees from the axis of the pipe. The flexible pipe body may also include layers of insulation 107 and will typically include an outer sheath 108, which comprises a polymer layer used to protect the pipe against penetration of seawater and other external environments, corrosion, abrasion and mechanical damage. Each flexible pipe comprises at least one portion, sometimes referred to as a segment or section of pipe body 100 together with an end fitting located at at least one end of the flexible pipe. An end fitting provides a mechanical device which forms the transition between the flexible pipe body and a connector. The different pipe layers as shown, for example, in Figure 1 are terminated in the end fitting in such a way as to transfer the load between the flexible pipe and the connector. Figure 2 illustrates a riser assembly 200 suitable for transporting production fluid such as oil and / or gas and / or water from a sub-sea location 201 to a floating facility. For example, in Figure 2 the sub-sea location 201 includes a sub-sea flow line. The flexible flow line 205 comprises a flexible pipe, wholly or in part, resting on the sea floor 204 or buried below the sea floor and used in a static application. The floating facility may be provided by a platform and / or buoy or, as illustrated in Figure 2, a ship 202. The riser assembly 200 is provided as a flexible riser, that is to say a flexible pipe 203 connecting the ship to the sea floor installation. The flexible pipe may be in segments of flexible pipe body with connecting end fittings. It will be appreciated that there are different types of riser, as is well-known by those skilled in the art. Embodiments may be used with any type of riser, such as a freely suspended (free, catenary riser), a riser restrained to some extent (buoys, chains), totally restrained riser or enclosed in a tube (I or J tubes). Figure 2 also illustrates how portions of flexible pipe can be utilised as a flow line 205 or jumper 206. Referring now to Figure 3, there is shown a cross section of a flexible pipe body 300 according to an embodiment of the present invention. The flexible pipe body 300 includes an extruded layer 310. The extruded layer 310 is radially outward of a carcass layer (not shown). An insulation layer 307 is radially outward of the extruded layer 310. A pressure armour layer 303, which may be metallic or composite, is radially outward of the insulation layer 307 and two tensile armour layers 305, 306 are radially outward of the pressure armour layer 303. The insulation layer 307 optionally comprises a tape. As shown in Figure 4, the insulation layer 307 comprises a hollow fibre layer which includes a matrix material 311, which may be, for example, a polymeric matrix material, within which a plurality of hollow fibres 312, which may be, for example, polymeric or composite hollow fibres, are embedded. The hollow fibre layer includes between approximately 20 percent by volume and approximately 95 percent by volume of the hollow fibres. The dense packing of hollow fibres within the hollow fibre layer advantageously improves the insulation properties of the insulation layer. The hollow fibres 312 may be provided as long, medium or short lengths, however there are some advantages to limiting the length of fibres which will be discussed later. The matrix material 311 can be any material within which the hollow fibres 312 can be encapsulated or embedded and which can be produced as a tape which can be wound around other components of the flexible pipe body and optionally consolidated or adhered to an underlying layer of the pipe body or sub-layer of the thermal insulation layer, the sublayer comprising helically wrapped windings of insulation tape comprising hollow fibres. The matrix material may comprise one or more of, for example, polyvinylidene fluoride (PVDF), polyamide 11 (Nylon 11) or polyamide 12 (Nylon 12), polypropylene (PP), polyethylene (PE), polyether ether ketone (PEEK) or Poly(methyl acrylate) (PMA), polyurethane (Pll), PFA or MFA, PPS, or any other suitable polymer. The tape from which the insulation layer 307 may be formed may have a width of between 25 and 200 mm, and a thickness of between 0.1 and 5 mm. The hollow fibres 312 may be aligned across the width of the tape in order to maximise the density with which the hollow fibres 312 can be packed within the matrix material 311, however may be aligned in any direction, with respect to the axial length of the tape, within the matrix material without significantly compromising thermal insulation performance of the insulation layer (the hollow fibres do not have to be aligned with a strength direction of the tape as would be the case with, for instance an anti-birdcaging I bandaging tape, where the predominant strength is required in the axial length direction of the tape). The hollow fibres 312 may be adhered to the matrix material 311 and held in place with a carrier layer. In some examples, the hollow fibres 312 may be sandwiched between two layers of matrix material 311. The layers of matrix material 311 may then be heat sealed in order to encapsulate the hollow fibres 312 within the matrix material 311. Examples of hollow fibres 312 which may be used in the insulation layer 307 will now be described with particular reference to Figure 5 and Figures 6A to 6E. As shown in Figure 5, each of the hollow fibres 312 is generally cylindrical and hollow. The hollow fibre 312 has a first end 320, a second end 322 and a central bore 324. The hollow fibre 312 has a longitudinal axis A-A. As shown in Figure 6A, the hollow fibre 312 may have a single central bore 324 which has a generally circular cross section. The central bore 324 extends along the longitudinal axis A-A of the hollow fibre thereby providing a first opening at the first end 320 and a second opening at the second end 322. The hollow fibre 312 has an outer diameter OD. In other examples of the invention, for example as shown in Figures 6B, 6C, 6D and 6E, the hollow fibre may have a plurality of central bores which extend along the longitudinal axis A-A of the hollow fibre thereby providing a plurality of first openings at the first end 320 and a plurality of second openings at the second end 322. Referring now to Figure 6B, the hollow fibre 312B has a plurality of central bores 324B, 325B. In this example, the central bore 324B is in a central portion of the hollow fibre 312B and has a generally circular cross section. A plurality of inner conduits are arranged around an inner wall of the hollow fibre 312B. The inner conduits are open at each end and thus form the plurality of central bores 325B, which also have a generally circular cross section. Similarly, the hollow fibre 312C has a plurality of central bores 324C, 325C, 326C. In this example, the central bore 324C is in a central portion of the hollow fibre 312C and has a generally circular cross section. A plurality of inner conduits are arranged around an inner wall of the hollow fibre 312C. The inner conduits are open at each end and thus form the plurality of central bores 325C, which also have a generally circular cross section. Each of the plurality of inner conduits has an inner conduit which is open at each end and divides the central bore 325C into two passageways, central bore 325C and central bore 326C. The central bores 326C are also generally circular in cross section. Like the hollow fibre 312C, the hollow fibre 312D has a plurality of central bores 324D, 325D, 326D. In this example, the central bore 324D is in a central portion of the hollow fibre 312D and has a generally circular cross section. A plurality of inner conduits are arranged around an inner wall of the hollow fibre 312D. The inner conduits are open at each end and thus form the plurality of central bores 325D, which also have a generally circular cross section. Each of the plurality of inner conduits has an inner conduit which is open at each end and divides the central bore 325D into two passageways, central bore 325D and central bore 326D. The central bores 326D are also generally circular in cross section. In this example, adjacent inner conduits which form the plurality of central bores 325D are separated by a wall 327D. The walls 327D may be solid or hollow. If hollow, the walls 327D may form further channels through the hollow fibre 312D. The hollow fibre 312E similarly includes a central bore 324E which is generally circular in cross section. The hollow fibre 312E also includes a plurality of inner conduits which are open at each end and form a plurality of central bores 325E which are generally circular in cross section. The plurality of inner conduits which form the plurality of central bores 325E are in this embodiment arranged in a hexagonal shape within the hollow fibre 312E, however other configurations may be envisaged. The central bore 324E may also be completely replaced by the plurality of inner conduits which form the plurality of central bores 325E. In each of the examples described above, the hollow fibres have an outer diameter that is in the range 0.5 - 150 micrometres. The central bores 324, 324B, 324C have an inner diameter that is in the range 0.25 - 100 micrometres. The central bores 325B, 325C, 324D, 325D, 324D have an inner diameter that is in the range 25 nanometers to 25 micrometres. The hollow fibres 312, 312B, 312C, 312D may therefore be described as being microporous. In alternative examples of the invention the central bores of the hollow fibres may be smaller, and thus the hollow fibres may be described as being nanoporous. An example of the arrangement of the central bores in a nanoporous hollow fibre is shown in Figure 6E. The central bores 324, 324B, 324C, 324D, 324E, 325B, 325C, 325D, 325E, 326C, 326D in the hollow fibres may also advantageously be sectioned along their lengths to prevent or limit the length of ingress of water or other fluids as a result of capillary action at an end or break in the hollow fibre. The central bores within the hollow fibres trap air within the insulation layer, which advantageously improves the insulation properties of the insulation layer. The hollow fibres may also resist ingress of water into the fibres due to pressure effects of sealed lengths of hollow fibre resisting capillary action of water, which helps to protect them from having the air in them displaced with the water, which would reduce their insulation performance. In each of the examples described above, the process for obtaining suitable lengths of fibre to introduce to the matrix material 311 may include a chopping of lengths of fibre to a desired length, that process may optionally include a process which seals the central bores of the hollow fibres though a process of melting material proximate to the cut ends of the hollow fibres. The length of the hollow fibres included in the insulation layer may be long, medium or short, however medium or shorter lengths have an advantage in that they provide a limitation to which water can find ingress into the central bores of the hollow fibres (via capillary action) displacing air I gas from the central bores and thereby reducing the insulation layer effectiveness. Some degree of water ingress may be inevitable from exposed open ends of the central bores of hollow fibres however if the fibre length is short then the volume of water which can readily enter the insulation layer is minimised. For clarity, a short fibre may be in the order of millimetres long, a medium length fibre may be in the order of centimetres long, while long fibres may be in the order of metres in length. In each of the examples described above, the hollow fibres may be manufactured from a polymeric material, for example a cross-linked polymeric material. Such materials improve the strength and stability of the insulation layer, which may be in contact with carbon dioxide and / or hydrogen sulphide. It will be appreciated that other materials may also be suitable for the hollow fibres, including non-cross-linked, high temperature polymeric materials, fluoropolymers such as Polyvinylidene fluoride (PVDF), and non-polymeric materials such as glass, carbon nanotubes etc. The hollow fibres may be manufactured by any suitable method, for example using the methods described in WO2007007051 and EP3925692. The performance of the hollow fibres may be improved further through the application of nano-thickness coatings such as of a metal using vapour deposition or chemical deposition. Coatings may also be applied to enhance whetting of the outer diameter surfaces of the fibres to improve adhesion with the matrix material 311. As shown in Figure 7A, the tape forming the insulation layer 307 includes a high proportion or density of hollow fibres 312 embedded within a polymeric matrix 311. The hollow fibres 312 are bonded together and preferably sealed at the ends by the matrix material. The tape is attached to a carrier layer 308 to enable the insulation layer 307 to be wound around the flexible pipe body 300. In some examples of the invention, for example as shown in Figure 7B, the insulation layer 307 and carrier tape 308 are sandwiched between polymer layers 309A, 309B. Such polymer layers may be bonded to adjacent polymer layers in the flexible pipe structure. Additional layers may also be incorporated into such tapes, for instance one or more thin foil layers either side of the insulation layer, between that and the polymer layers 309A and / or 309B to further help prevent water ingress through permeation and maintain the performance of the insulation layer over time (maximizing insulative capacity remaining at the end of the service life of a flexible pipe of around 25 years). An alternative to the arrangement of Figure 7B is shown in Figure 7C. In this example, an additional layer or extrusion 313 is applied over the insulation layer 307. Referring now to Figure 8, there is shown a cross section of a flexible pipe body 400 according to an embodiment of the present invention. The flexible pipe body 400 includes an extruded layer 410. The extruded layer 410 is radially outward of an internal carcass layer (not shown). An insulation layer 407, for example as described above in relation to Figures 3 to 7C, is radially outward of the extruded layer 410. A pressure armour layer 403, which may be metallic or composite, is radially outward of the insulation layer 407 and two tensile armour layers 405, 406 are radially outward of the pressure armour layer 403. In this embodiment, the insulation layer 407 is located between two sacrificial layers 408, 409. The sacrificial layers 408, 409 prevent direct contact between the insulation layer 407 and metallic layers, for example the metallic pressure armour layer 403. The sacrificial layers 408, 409 may be extruded layers or may be tape layers wound helically around the underlying pipe layer(s). With particular reference to Figure 9, the proposed configurations provide the synergic effects of the tortuous paths 500A, 500B, 500C generated by the hollow fibres 312 embedded in the polymeric matrix 311 of the insulation layer 307, 407, in conjunction with the shielding promoted by the contact pressure between the polymeric layers and the metallic pressure armour layer(s) of the flexible pipe 300, 400. This provides a second permeation restriction for the gases coming from the conveyed fluid which have to go through the hollow fibre insulation layer 307, 407, leading to a significantly less severe annulus environment by reducing both permeation and temperature in the annulus. This also provides the advantage of reducing the amount of insulation material that is required in the flexible pipe body 300, 400, since increased temperature may make corrosion worse, however if the environment is less severe a higher temperature may be tolerated, so less insulation is required. The crush resistance and tolerance of the hollow fibres is greater than that of the glass microspheres used in prior art systems and thus the insulation layer of the present invention can be positioned anywhere within the layered structure of the flexible pipe body, including radially inward of the pressure and tensile armour layers. This has the added advantage of enabling the use of lower cost materials and / or extending the life of reinforcement materials 403, 405, 406 by reducing the temperatures in those layers of the flexible pipe body. The improved thermal insulation properties provided by the inclusion of hollow fibres within the insulation layer enables the thickness of the insulation layer, and thus the amount of insulation material, to be reduced. Various modifications to the detailed arrangements as described above are possible. For example, the central bores of the hollow fibres are described as being generally circular in cross section. It will be understood that, in alternative embodiments of the invention, the central bores may be any shape in cross section. In the example described above, the insulation layer 307, 407 is described as a tape. It will be understood that, in embodiments of the invention, the insulation layer may include a single thickness of tape, or multiple layers or thicknesses of tape. The insulation layer may, for example, include a double thickness of tape. In other examples, the insulation layer may include partially overlapping layers of tape, such that the thickness of the insulation layer is 1.5 times the thickness of the tape. In some applications it is possible also that the insulation layer material of the current invention may be extruded directly onto the pipe as a layer, or even co-extruded with one or more polymer layers radially inside and / or outside of the insulation layer. It will be clear to a person skilled in the art that features described in relation to any of the embodiments described above can be applicable interchangeably between the different embodiments. The embodiments described above are examples to illustrate various features of the invention. Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise. Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. An apparatus for providing a thermal insulation layer in a flexible pipe, the apparatus comprising a plurality of hollow fibres disposed in a layer of flexible pipe body.

2. The apparatus as claimed in claim 1, wherein the plurality of hollow fibres each has a first end, a second opposing end, and at least one central bore that extends between the first end and the second end.

3. The apparatus as claimed in claim 2, wherein the plurality of hollow fibres each include a plurality of central bores that extend between the first end and the second end.4 The apparatus as claimed in any of claims 1 to 3, wherein the plurality of hollow fibres each have an outer diameter that is less than 150 micrometres.

5. The apparatus as claimed in claim 4, wherein the outer diameter is at least 0.5 micrometre.

6. The apparatus as claimed in any of claims 1 to 5, wherein the plurality of hollow fibres are encapsulated in a matrix or secured to a matrix.

7. The apparatus as claimed in any of claims 1 to 6, wherein the apparatus comprises at least 20 % by volume of the plurality of hollow fibres.

8. The apparatus as claimed in any of claims 1 to 7, wherein the apparatus comprises less than 95% by volume of the plurality of hollow fibres.

9. A flexible pipe body comprising the apparatus as claimed in any of claims 1 to 8.

10. The flexible pipe body as claimed in claim 9, wherein the apparatus comprises a thermal insulation layer of the flexible pipe body.

11. The flexible pipe body as claimed in claim 9 or claim 10, wherein the thermal insulation layer of the flexible pipe body is radially inside at least one of the armour layers of the flexible pipe body.

12. The flexible pipe body as claimed in claim 10 or claim 11 wherein the thermal insulation layer is radially outside a carcass layer of the flexible pipe body.

13. The flexible pipe body as claimed in any of claims 10 to 12, wherein the thermal insulation layer is radially outward of an extruded layer of the flexible pipe body.

14. The flexible pipe body as claimed in any of claims 9 to 13 further comprising an armour layer.

15. A flexible pipe comprising the flexible pipe body as claimed in any of claims 9 to 13 and one or more end fittings.

16. A jumper, riser or flowline comprising the flexible pipe as claimed in claim 15.

17. A method of manufacturing flexible pipe body, comprising the steps of disposing aplurality of hollow fibres in a thermal insulation layer of flexible pipe body.

18. The method as claimed in claim 17, further comprising the steps of bonding the plurality of hollow fibres together with a matrix to form the thermal insulation layer of flexible pipe body.

19. A tape for providing a layer in a flexible pipe body, the tape comprising an elongate tape body portion and a plurality of hollow fibres disposed on the elongate tape body.5   20. The tape as claimed in claim 19, wherein the tape body portion comprises a matrixthat is configured to bond the plurality of hollow fibres together.

Images