Composite pipe

Abstract

A composite pipe is provided having a longitudinal axis comprising: a. a first annular composite layer comprising first polymer fibres embedded in a first polymer matrix; and b. a second annular composite layer comprising continuous fibres embedded in a second polymer matrix, wherein the continuous fibres are all oriented at the same angle, which is an angle from ±10º to less than ±45º to the longitudinal axis, the longitudinal axis being defined as 0º, and wherein the continuous fibres are selected from carbon fibres, glass fibres, fibres made of iron-nickel alloy with a face-centred cubic crystal structure, aramid fibres, basalt fibres and mixtures thereof.

Description

[0001] Composite Pipe

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a composite pipe, to the use of the composite pipe for transporting cryogenic fluid and to a method of manufacturing the composite pipe.

[0004] DESCRIPTION OF THE RELATED ART

[0005] A large amount of natural gas (mainly methane) is present in remote locations around the world. This gas is of significant value if it can be economically marketed. If the stored gas is reasonably close to the places where it is to be consumed and the terrain between the locations allows, then the gas is generally extracted and transported in gaseous form to those end locations. Transportation is achieved via underwater and / or onshore pipelines. However, if gas is produced where it is not economically feasible or where it is not permitted to lay a pipeline, then other techniques to transport the gas need to be employed.

[0006] A commonly used technique for transporting gas without a pipeline is to liquefy the gas at or near the production site and then to transfer the liquefied gas into a specially designed storage tank on a carrier, such as a ship. Liquefying the gas significantly reduces its volume and increases the mass of gas that can be stored and transported. In order to achieve this, the natural gas is cooled and condensed to a liquid state to produce liquefied natural gas (LNG). LNG is typically (but not always) stored and transported at substantially atmospheric pressure and at a temperature of about -162 ° C. When an LNG carrier arrives at a destination, typically the LNG is unloaded into other storage tanks. A regassification processes is then performed, as needed, to convert the LNG back into gaseous form, after which it may be transported, for example via pipelines, to end locations to be used. LNG is an increasingly popular transportation method for supplying natural gas to major energy consuming countries.

[0007] The piping used to transport liquefied gases, such as LNG or the liquefied components of air, must be capable of withstanding very low temperatures, typically below -150°C. At such temperatures, steels tend to crack, because they undergo a brittle-ductile transition which causes them to shatter, rather than deform. Typically, where metal piping is required, steel combined with 9% Nickel is used (commercialised as ‘Inconel’ or ‘Invar’), because it has a much lower brittle-ductile transition temperature, so remains ductile at the cryogenic temperatures in question.

[0008] Another application for a long cryogenic pipe is as the ‘cryostat’ component in superconducting electrical cables. As is known to the skilled person, these cables may be used for efficient transmission of electrical power over distances of 1 km or more. The cryostat component is in effect a pipe containing cryogenic fluids to cool the wire to the necessary temperatures at which super-conduction may occur. Liquid nitrogen at a temperature of around -190' C is one such common fluid.

[0009] Polymer pipe for transporting cryogenic fluids is also known. WO 2016 / 102618 A1 describes a process for making a polymer composite pipe comprising wound layers of polymer composite tape. Composite polymer piping has a number of advantages over metal piping. These include the fact that it does not corrode; that it is flexible, so that it may, for example, be wound onto a spool for storage and transport, or easily accommodate bends; that it can be made in continuous lengths which may be several kilometres long avoiding the need for welds and that it may be relatively low in weight. ‘618 is concerned with ensuring that the wound polymer composite tapes provide an adequate barrier to the cryogenic fluids. To that end, the tapes are wound so as to overlap one another and ensure that the tape edges of the preceding tape layer are overlapped by the next tape layer.

[0010] Cryogenic pipe, for instance for LNG transport or for use with super-conducting electrical cables, may undergo temperature decreases of the order of 200' C when cooled after installation from ambient temperature to the operating temperature. The temperature decrease may lead to a significant length contraction along the axis of the cryogenic pipe. Although the pipe’s length may typically contract by much less than one percent, for a pipe of a kilometer in length, that may amount to a length contraction of several meters for a temperature reduction of about 200°C. These changes in pipe length may, in turn, cause undesirable effects, such as a change in the contact location between pipe and the supporting structure, ground or sea bed, and the creation of stresses at rigid external interfaces such as pipe end terminations. To accommodate such a contraction, bellows and / or expansion / contraction bends may be employed, but these can be unreliable, bulky and / or expensive.

[0011] Moreover, non-cryogenic coaxial components within the complete pipe architecture, for example pipe insulation or protective sheaths, may be at a higher temperature closer to ambient and typically will be constructed from different materials having different coefficients of thermal expansion from the pipe material. Consequently these non-cryogenic components will contract in the axial direction by a different, usually lower, amount than the cryogenic pipe. This effect may also lead to high stresses and even to failure of the interface with the cryogenic pipe.

[0012] It is against this background that the present invention has been devised.

[0013] SUMMARY OF THE INVENTION

[0014] According to a first aspect of the invention a composite pipe is provided comprising: a. a first annular composite layer comprising first polymer fibres embedded in a first polymer matrix; and b. a second annular composite layer comprising continuous fibres embedded in a second polymer matrix, wherein the continuous fibres are all oriented at the same angle, which is an angle from ±10° to less than ±45° to the longitudinal axis, the longitudinal axis being defined as 0°, and wherein the continuous fibres are selected from carbon fibres, glass fibres, fibres made of iron-nickel alloy with a face-centred cubic crystal structure, aramid fibres, basalt fibres and mixtures thereof.

[0015] As used herein, the term “fibre” may refer to a single filament or may refer to a bundle or mesh of filaments associated with one another, such as by twisting them together.

[0016] As used herein, the continuous fibres, all oriented at the same angle, may be referred to as “unidirectional” continuous fibres.

[0017] In one example of the first aspect of the invention, the second annular composite layer is attached to the first annular composite layer. According to this example, the second annular composite layer may be attached to the first annular composite layer by fusion, such as by laser welding. In another example, the first annular composite layer and the second annular composite layer are not attached to one another and may be located separately from one another.

[0018] In another example of the first aspect of the invention, the second annular composite layer is disposed around the first annular composite layer. In another example the first annular composite layer is disposed around the second annular composite layer. Typically, the second annular composite layer is disposed around the first annular composite layer.

[0019] The technical challenge of accommodating a length contraction of less than two metres per kilometre over a temperature reduction of about 200°C is significantly more manageable than the larger length contractions experienced by currently available piping. Such a length contraction translates into a composite pipe having a coefficient of thermal expansion (CTE) of less than 10 x 10’6 / °C (the length contraction is the CTE x temperature drop x the pipe length). According to one example, the length contraction is less than 1 m per kilometre, corresponding to a CTE of less than 5 x 10-6 / °C.

[0020] In order to achieve this, a layer comprising continuous fibres is provided, the fibres being oriented at the same angle, which is an angle from ±10° to less than ±45° to the longitudinal axis, the fibres themselves having a low CTE. Typically, the CTE of the fibres themselves is less than 3 x 10’6 / °C.

[0021] The invention may therefore provide a composite pipe having a longitudinal axis comprising: a. a first annular composite layer comprising first polymer fibres embedded in a first polymer matrix; and b. a second annular composite layer comprising continuous fibres embedded in a second polymer matrix, wherein the continuous fibres are all oriented at the same angle, which is an angle from ±10° to less than ±45° to the longitudinal axis, the longitudinal axis being defined as 0°, and wherein continuous fibres have a coefficient of thermal expansion (CTE) of less than 3 x 10’6 / °C over a temperature range of 20°C to -190°C.

[0022] CTE, as used herein, is measured according to ASTM E228. A temperature range is provided, because the CTE-value of a material varies with temperature.

[0023] CTE values for suitable materials having a coefficient of thermal expansion (CTE) of less than 3 x 10’6 / °C over the temperature ranges in question are known to the skilled person. Low CTE materials include, but are not limited to, carbon, glass, aramid, basalt and iron-nickel alloys with a face-centred cubic crystal structure. Ironnickel alloys having this crystal structure are found to have a low CTE and include Invar alloys, such as Invar 36 (also known as FeNi36, since it contains 36% nickel and 64% iron). Accordingly, the continuous fibres may be selected from carbon fibres, glass fibres, fibres made of iron-nickel alloy with a face-centred cubic crystal structure, aramid fibres, basalt fibres and mixtures thereof. A skilled person may include a mixture of these continuous fibres in the composite pipe to achieve the desired CTE of the pipe.

[0024] In one example of the first aspect of the invention, continuous fibres may typically have a diameter from 5pm to 100pm.

[0025] In one example of the first aspect of the invention, the composite pipe of the first aspect of the invention comprises from 10%vol to 50%vol of continuous fibres. In another example, the composite pipe of the first aspect of the invention comprises from 15%vol to 40%vol of continuous fibres.

[0026] In another example of the first aspect of the invention, the continuous fibres are oriented at an angle from ±15° to ±30° to the longitudinal axis.

[0027] In a further example of the first aspect of the invention, the composite pipe according to the first aspect of the invention additionally comprises an internal layer and the first annular composite layer is disposed around and attached to an internal layer. The internal layer provides a surface onto which the polymer composite pipe body may be disposed. If a layer, such as the internal layer is not provided, then it may be complex and challenging to make the pipe body, especially in the case in which the pipe body is made of layers of wound tape. The internal layer typically comprises the same material as the first annular composite layer, although it may alternatively comprise a different material. The material of the internal layer may additionally be rolled to compact it. Typically, the internal layer comprises a sheet of material which has been formed into the shape of an annular cylinder.

[0028] In to one example of the first aspect of the invention, the internal layer has a thickness of 0.1 -1 mm, or a thickness of 0.2-0.7mm.

[0029] In another example of the first aspect of the invention, the first annular composite layer is attached to the internal layer by fusion, such as by laser welding.

[0030] In a further example of the first aspect of the invention, the first annular composite layer comprises, or may consist of, first polymer fibres embedded in a first polymer matrix. The first polymer fibres and the first polymer matrix comprise the same polymer or a different polymer.

[0031] In one example of the first aspect of the invention, the first polymer fibres and the first polymer matrix may comprise or consist of the same homopolymer, or one of them may comprise or consist of a copolymer thereof, or both of them may comprise or consist of a mixture of copolymer and homopolymer. In a further example, the homopolymer and / or the copolymer is a thermoplastic polymer.

[0032] In another example of the first aspect of the invention, the first polymer fibres and the first polymer matrix comprise or consist of the same polyolefin homopolymer, or one of them may comprise or consist of a copolymer of the polyolefin, or both of them may comprise or consist of a mixture of the polyolefin homopolymer and a polyolefin copolymer. In one example, the polyolefin is polyethylene or polypropylene. In a further example, the first polymer fibres consist of polypropylene or a copolymer thereof or mixtures thereof and the first polymer matrix consists of polypropylene or a copolymer thereof or mixtures thereof.

[0033] In one example of the first aspect of the invention, the first polymer fibres have a softening point which is higher than the softening point of the first polymer matrix. This may ensure that, if heat is applied to the polymer composite, for example during a heat compaction process or during welding and fusion processes, the matrix softens or melts, but the first polymer fibres do not soften or melt. The person skilled in polymer technology is aware of pairs of polymers which allow such a tailored softening point difference to be achieved.

[0034] In one example of the first aspect of the invention, the second polymer matrix comprises or consists of a polyolefin homopolymer, or a copolymer of a polyolefin. In one example, the polyolefin is polyethylene, polypropylene or mixtures thereof. In a further example, the second polymer matrix consists of polypropylene, or a copolymer thereof or mixtures thereof.

[0035] In one example of the first aspect of the invention, the first polymer matrix and the second polymer matrix comprise the same polymer or a different polymer.

[0036] In another example of the first aspect of the invention, the first polymer matrix and the second polymer matrix may comprise or consist of the same homopolymer, or one of them may comprise or consist of a copolymer thereof, or both of them may comprise or consist of a mixture of copolymer and homopolymer. In a further example, the homopolymer and / or the copolymer is a thermoplastic polymer.

[0037] In a further example of the first aspect of the invention, the first polymer matrix and the second polymer matrix comprise or consist of the same polyolefin homopolymer, or one of them may comprise or consist of a copolymer of the polyolefin, or both of them may comprise or consist of a mixture of the polyolefin homopolymer and a polyolefin copolymer. In one example, the polyolefin is polyethylene or polypropylene. In a further example, the first polymer matrix consists of polypropylene or a copolymer thereof or mixtures thereof and the second polymer matrix consists of polypropylene or a copolymer thereof or mixtures thereof.

[0038] In one example of the first aspect of the invention the first annular composite layer is formed of one or more plies of first composite tape wound at the same angle, the first composite tape comprising the first polymer fibres embedded in the first polymer matrix.

[0039] As used herein, the term “ply” refers to a sub-layer for the case in which a layer comprises more than one ply of wound composite tape. In the exceptional case in which a layer comprises just a single ply of wound composite tape, then the term “ply” is synonymous with the term “layer”.

[0040] According to this example, if there is more than one ply of first composite tape, then each ply of first composite tape is attached to the preceding ply of first composite tape, if there is a preceding ply of first composite tape, and each ply of first composite tape is attached to the succeeding ply of first composite tape, if there is a succeeding ply of first composite tape. According to one example, the tapes are attached to one another by fusion, such as by laser welding.

[0041] According to one example of the first aspect of the invention, the second annular composite layer is formed of one or more plies of wound second composite tape wound at the same angle, the second composite tape comprising the continuous fibres embedded in the second polymer matrix. According to this example, if there is more than one ply of second composite tape, each ply of second composite tape is attached to the preceding ply of second composite tape, if there is a preceding ply of first composite tape, and each ply of first composite tape is attached to the succeeding ply of second composite tape, if there is a succeeding ply of second composite tape. According to one example, the tapes are attached to one another by fusion, such as by laser welding.

[0042] According to one example of the first aspect of the invention, the second composite tape extends longitudinally and the continuous fibres are also aligned unidirectionally and longitudinally within the second polymer matrix of the second composite tape. In this way, when the tape is wound at the angles defined, the longitudinal fibres will also be wound at those angles.

[0043] According to another example of the first aspect of the invention, the second composite tape is cut from a planar sheet comprising woven continuous fibres embedded in the second polymer matrix, the cut being parallel to the direction of the warp fibres or parallel to the direction of the weft fibres, such that either the warp fibres or the weft fibres extend continuously, longitudinally along the longitudinal extent of the second composite tape. In such a case, the other of the cut warp fibres or the cut weft fibres are also present, but these are short fibres which extend orthogonally to the longitudinal extent of the second composite tape.

[0044] According to a further example of the first aspect of the invention, the second composite tape is cut from a planar sheet comprising a mesh of continuous fibres embedded in the second polymer matrix. In such a case, a proportion of the fibres extends continuously, longitudinally along the longitudinal extent of the second composite tape and a proportion is short fibres which have been cut and extend in other directions, such as orthogonally to the longitudinal extent of the second composite tape.

[0045] In one example of the first aspect of the invention, the second annular composite layer is attached to the first annular composite layer, the two layers together forming a composite layer pair, and the composite pipe comprises a plurality of composite layer pairs. Two or more composite layer pairs may be disposed around and attached to one another. In this example, a composite layer pair may attached to another composite layer pair by fusion, such as by laser welding. In another example, two or more composite layer pairs may be disposed separately from one another, dispersed throughout the composite pipe.

[0046] In another example of the first aspect of the invention, the composite pipe additionally comprises a third annular composite layer disposed around and attached to the second annular composite layer, wherein the third annular composite layer comprises third polymer fibres embedded in a third polymer matrix, the second annular composite layer being disposed between the first annular composite layer and the third annular composite layer to form a three-layer sandwich arrangement.

[0047] According to this example, the composite pipe may comprise a plurality of three- layer sandwiches. Two or more three-layer sandwiches may be attached to one another and a three-layer sandwich may be attached to another three-layer sandwich by fusion, such as by laser welding. Alternatively, two or more three-layer sandwiches may be disposed separately from one another, dispersed throughout the composite pipe.

[0048] In one example, the third polymer fibres may be the same as the first polymer fibres. Alternatively, the third polymer fibres may be different from the first polymer fibres. In one example the third polymer matrix may be the same as the first polymer matrix. Alternatively, the third polymer matrix may be different from the first polymer matrix.

[0049] The composite pipe according to the first aspect of the invention may be manufactured in continuous long lengths, such as greater than 1000m, greater than 2000m or greater than 3000m.

[0050] According to a second aspect of the invention, the use of a composite pipe of the first aspect of the invention is provided for conveying a fluid having a temperature below -30°C.

[0051] According to a third aspect of the invention, a method is provided of manufacturing a composite pipe having a longitudinal axis comprising: a. providing a first annular composite layer by winding at least one ply of a first composite tape comprising first polymer fibres embedded in a first polymer matrix, the ply or each ply of first composite tape comprising a plurality of adjacent windings all applied at the same angle to the longitudinal axis; and b. providing a second annular composite layer by winding at least one ply of a second composite tape, the second composite tape comprising continuous fibres embedded in a second polymer matrix, the ply or each ply of second composite tape comprising a plurality of windings all applied at the same angle to the longitudinal axis, which is an angle from ±10° to less than ±45°, and wherein the continuous fibres are selected from carbon fibres, glass fibres, fibres made of iron-nickel alloy with a face-centred cubic crystal structure, aramid fibres, basalt fibres and mixtures thereof.

[0052] In one example of the third aspect of the invention, the second annular composite layer is provided by winding the at least one ply of second composite tape around and attaching it to the first annular composite layer.

[0053] In one example of the third aspect of the invention, if the first annular composite layer comprises more than one ply of first composite tape, then the plies are bonded to one another by fusion.

[0054] In another example of the third aspect of the invention, if the second annular composite layer comprises more than one ply of second composite tape, then the plies are bonded to one another by fusion.

[0055] In a further example of the third aspect of the invention, the second annular composite layer is attached to the first annular composite layer by fusion.

[0056] In one example of the third aspect of the invention, the method is configured as a continuous method.

[0057] BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The invention will now be further described, by way of example only, and with reference to the accompanying drawings, of which:

[0059] Figure 1 a and Figure 1 b are exemplary composite pipes in accordance with embodiments of the invention;

[0060] Figure 2 shows a further structure of composite pipe according to an embodiment of the invention; and

[0061] Figure 3 is a graph of simulated composite pipe CTE (10’6 / °C) versus continuous fibre volume fraction for the structure of Figure 2 for three different materials, the three materials being: unidirectional, continuous carbon fibres in a polypropylene (PP) matrix; carbon fabric comprising continuous carbon fibres in a PP matrix; and unidirectional, continuous aramid fibres in a PP matrix.

[0062] DETAILED DESCRIPTION

[0063] A detailed description of the invention will now be provided.

[0064] Basic embodiments of the invention are shown in Figures 1 a and 1 b. In each of these embodiments, two annular layers are provided, a first annular composite layer 11 comprising first polymer fibres embedded in a first polymer matrix, and a second annular composite layer 12 layer comprising continuous fibres embedded in a second polymer matrix. These continuous fibres are all oriented at the same angle, which is an angle from ±10° to less than ±45° to the longitudinal axis, the longitudinal axis being defined as 0°. In embodiments, the continuous fibres may be selected from carbon fibres, glass fibres, fibres made of iron-nickel alloy with a face-centred cubic crystal structure, aramid fibres, basalt fibres and mixtures thereof.

[0065] Figure 1a shows an arrangement in which the first annular composite layer 11 is disposed around the second annular composite layer 12, whereas Figure 1 b shows an arrangement in which the second annular composite layer 12 is disposed around the first annular composite layer 11 - as stated previously, this is likely to be the favoured arrangement in many use cases.

[0066] The benefit of this approach is shown by a set of examples. The following examples were simulated using a program called LAP (Laminate Analysis Program) supplied by Anaglyph Limited. The simulation considers a flat planar section of laminate, rather than an axi-symmetric pipe. The skilled person understands that this is a reasonable simplification for a relatively thin-walled pipe as commonly found in industrial applications. The software predicts the overall CTE of the complete composite pipe wall. Secant CTEs were calculated for the constituent materials for the temperature range from 20°C to -196°C and again, the skilled person understands that using secant CTEs represents an acceptable approximation.

[0067] Pipe construction

[0068] A pipe having an internal diameter of 50.8mm (2 inches) was provided having 15 layers in which Layer 1 was innermost and Layer 15 outermost and each successive layer (moving radially outwards from the pipe’s longitudinal axis) was fused to the preceding layer. The arrangement of the layers was as follows: Layer 1 : 0.40mm thickness internal layer, comprising a rolled sheet of polypropylene fibres embedded in a polypropylene matrix (referred to herein as a PP SPC (single polymer composite)).

[0069] Layer 2: a 0.57mm thickness PP SPC layer comprising plies of SPC tape laid at +85° to the longitudinal axis.

[0070] Layer 3: a 0.57mm thickness PP SPC layer comprising plies of SPC tape laid at +85° to the longitudinal axis.

[0071] Layer 4: a layer comprising plies of tapes made of continuous unidirectional fibres embedded in a polypropylene matrix laid at +25° to the longitudinal axis.

[0072] Layer 5: a layer comprising plies of tapes made of continuous unidirectional fibres embedded in a polypropylene matrix laid at -25° to the longitudinal axis.

[0073] Layer 6: a 0.57mm thickness SPC layer comprising plies of PP SPC tape laid at - 85° to the longitudinal axis.

[0074] Layer 7: a 0.57mm thickness PP SPC layer comprising plies of SPC tape laid at - 85° to the longitudinal axis.

[0075] Layer 8: a layer comprising plies of tapes made of continuous unidirectional fibres embedded in a polypropylene matrix laid at +25° to the longitudinal axis.

[0076] Layer 9: a layer comprising plies of tapes made of continuous unidirectional fibres embedded in a polypropylene matrix laid at -25° to the longitudinal axis.

[0077] Layer 10: a 0.57mm thickness SPC layer comprising plies of PP SPC tape laid at - 25° to the longitudinal axis.

[0078] Layer 11 : a 0.57mm thickness SPC layer comprising plies of PP SPC tape laid at +25° to the longitudinal axis. Layer 12: a layer comprising plies of tapes made of continuous unidirectional fibres embedded in a polypropylene matrix laid at +25° to the longitudinal axis.

[0079] Layer 13: a layer comprising plies of tapes made of continuous unidirectional fibres embedded in a polypropylene matrix laid at -25° to the longitudinal axis.

[0080] Layer 14: a 0.57mm thickness SPC layer comprising plies of PP SPC tape laid at - 25° to the longitudinal axis.

[0081] Layer 15: a 0.57mm thickness SPC layer comprising plies of PP SPC tape laid at +25° to the longitudinal axis.

[0082] This is illustrated in Figure 2, which shows the internal layer 31 surrounded successively by first annular composite layers 11 comprising Layers 2, 3, 6, 7, 10,11 ,14 and 15 comprising first polymer fibres embedded in a first polymer matrix, and second annular composite layers 12 comprising Layers 4,5,8,9,12 and 13 comprising continuous fibres embedded in a second polymer matrix.

[0083] Example 1 : the continuous fibres in Layers 4,5,8,9,12 and 13 were high modulus, unidirectional carbon fibres (“Carbon HM UD”). They were embedded in a polypropylene matrix at a volume fraction of 60%. In the simulation, the continuous fibre volume fraction of the composite pipe was varied up to 30%, by increasing the layer thickness t from 0.05mm to 0.4mm and corresponding CTEs of the composite pipe were generated.

[0084] Example 2: the continuous fibres in Layers 4,5,8,9,12 and 13 were incorporated within a high modulus, woven carbon fibre fabric (“Carbon HM Fabric”). The fabric was embedded in a polypropylene matrix; the volume fraction of the continuous fibres only was 50%. In the simulation, the continuous fibre volume fraction of the composite pipe was varied up to 30%, by increasing the layer thickness from 0.05mm to 0.4mm, and corresponding CTEs of the composite pipe were generated. For the avoidance of doubt, fibres in the woven carbon fibre fabric, other than the continuous fibres in question are not included in the continuous fibre volume fraction of the composite pipe.

[0085] Example 3: the continuous fibres in Layers 4,5,8,9,12 and 13 were unidirectional aramid fibres (“Aramid UD”). They were embedded in a polypropylene matrix at a volume fraction of 60%. In the simulation, the continuous fibre volume fraction of the composite pipe was varied up to 30%, by increasing the layer thickness from 0.05mm to 0.4mm and corresponding CTEs of the composite pipe were generated.

[0086] Figure 3 shows a graph of composite pipe CTE (10’6 / °C) versus continuous fibre volume fraction for the three different continuous fibre types of Examples 1 , 2 and 3. The graph shows that increasing the continuous fibre volume fraction in the composite pipe reduces the composite pipe CTE to a level far below that for a pure SPC pipe (the CTE of pure SPC pipe is about 28 x 10’6 / °C). These data demonstrate that composite pipes as described herein will contract to a much lower degree when subjected to cryogenic temperatures.

Claims

CLAIMS1 . A composite pipe having a longitudinal axis and comprising: a. a first annular composite layer comprising first polymer fibres embedded in a first polymer matrix; and b. a second annular composite layer comprising continuous fibres embedded in a second polymer matrix, wherein the continuous fibres are all oriented at the same angle, which is an angle from ±10° to less than ±45° to the longitudinal axis, the longitudinal axis being defined as 0°, and wherein the continuous fibres are selected from carbon fibres, glass fibres, fibres made of iron-nickel alloy with a face-centred cubic crystal structure, aramid fibres, basalt fibres and mixtures thereof.

2. The composite pipe of claim 1 , wherein the second annular composite layer is disposed around and attached to the first annular composite layer.

3. The composite pipe of claim 1 or 2, comprising from 15%vol to 40%vol of continuous fibres.

4. The composite pipe of any preceding claim wherein the continuous fibres are oriented at an angle from ±15° to ±30° to the longitudinal axis.

5. The composite pipe of any preceding claim, wherein the fibres made of ironnickel alloy with a face-centred cubic crystal structure comprise Invar alloy fibres.

6. The composite pipe of any of claims 2 to 5, additionally comprising an internal layer, wherein the first annular composite layer is disposed around and attached to an internal layer.

7. The composite pipe of any preceding claim, wherein the first polymer fibres and the first polymer matrix comprise the same polymer or a different polymer.

8. The composite pipe of any preceding claim, wherein the first polymer fibres and the first polymer matrix comprise the same polyolefin.

9. The composite pipe of claim 8, wherein the polyolefin is polyethylene or a copolymer thereof, polypropylene, or a copolymer thereof.

10. The composite pipe of any preceding claim, wherein both the first polymer fibres and the first polymer matrix consist of polypropylene or a copolymer thereof.11 . The composite pipe of any preceding claim, wherein the first polymer matrix and the second polymer matrix comprise the same polymer or a different polymer.

12. The composite pipe of claim 11 , wherein the first polymer matrix and the second polymer matrix comprise the same polyolefin.

13. The composite pipe of claim 12, wherein the polyolefin is polyethylene or a copolymer thereof, polypropylene or a copolymer thereof.

14. The composite pipe of any preceding claim, wherein both the first polymer matrix and the second polymer matrix consist of polypropylene or a copolymer thereof.

15. The composite pipe of any preceding claim, wherein the first annular composite layer is formed of one or more plies of wound first composite tape wound at the same angle, the first composite tape comprising the first polymer fibres embedded in the first polymer matrix, wherein, if there is more than one ply of first composite tape, each ply of first composite tape is attached to the preceding and / or succeeding ply of first composite tape.

16. The composite pipe of any preceding claim wherein the second annular composite layer is formed of one or more plies of wound second compositetape wound at the same angle, the second composite tape comprising the continuous fibres embedded in the second polymer matrix wherein, if there is more than one ply of second composite tape, each ply of second composite tape is attached to the preceding and / or succeeding ply of second composite tape.

17. The composite pipe of any preceding claim, wherein the second annular composite layer attached to the first annular composite layer together form a composite layer pair and the composite pipe comprises a plurality of composite layer pairs.

18. The composite pipe of any of claims 2 to 16, additionally comprising a third annular composite layer disposed around and attached to the second composite layer, wherein the third annular composite layer comprises third polymer fibres embedded in a third polymer matrix, the second annular composite layer being disposed between the first annular composite layer and the third annular composite layer to form a three-layer sandwich arrangement.

19. The composite pipe of claim 18, comprising a plurality of three-layer sandwiches.

20. The composite pipe according to claim 18 or 19, wherein the third polymer fibres are the same as the first polymer fibres and the third polymer matrix is the same as the first polymer matrix.21 . The use of a composite pipe of any preceding claim for conveying a fluid having a temperature below -30°C.

22. A method of manufacturing a composite pipe having a longitudinal axis comprising: a. providing a first annular composite layer by winding at least one ply of a first composite tape comprising first polymer fibres embedded in a first polymer matrix, the ply or each ply of first composite tapecomprising a plurality of adjacent windings all applied at the same angle to the longitudinal axis; and b. providing a second annular composite layer by winding at least one ply of a second composite tape, the second composite tape comprising continuous fibres embedded in a second polymer matrix, the ply or each ply of second composite tape comprising a plurality of windings all applied at the same angle to the longitudinal axis, which is an angle from ±10° to less than ±45°, and wherein the continuous fibres are selected from carbon fibres, glass fibres, fibres made of ironnickel alloy with a face-centred cubic crystal structure, aramid fibres, basalt fibres and mixtures thereof.

23. The method of claim 22, wherein the second annular composite layer is provided by winding the at least one ply of second composite tape around and attaching it to the first annular composite layer.

24. The method of claim 22 or 23, wherein, if the first annular composite layer comprises more than one ply of first composite tape, then the plies are bonded to one another by fusion.

25. The method of any of claims 22 to 24, wherein, if the second annular composite layer comprises more than one ply of second composite tape, then the plies are bonded to one another by fusion.

26. The method any of claims 22 to 25, wherein the second annular composite layer is attached to the first annular composite layer by fusion.

27. The method of any of claims 22 to 26 which is configured as a continuous method.

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