GB2624936A

GB2624936A - Pipe for transporting cryogenic fluids

Info

Publication number: GB2624936A
Application number: GB2218112.7A
Authority: GB
Inventors: Priddy James; Coles Johnathan
Original assignee: Enoflex Ltd
Current assignee: Enoflex Ltd
Priority date: 2022-12-01
Filing date: 2022-12-01
Publication date: 2024-06-05
Also published as: GB2624976A; GB202218112D0; WO2024115883A1

Abstract

A polymer composite pipe having a longitudinal axis comprises: an internal layer 7 having an exterior surface; and a polymer composite pipe body 9 disposed around and bonded to the exterior surface. The internal layer is formed from a longitudinal sheet of polymer composite 1 having a sheet width defined between first and second longitudinal side edges, the sheet having been wrapped around the longitudinal axis. In one embodiment, the sheet is wrapped such that first and second edges are contiguous and overlap. In a second embodiment, the circumference of the internal layer is greater than the sheet width such that a longitudinal gap is defined between the side edges. Preferably, the polymer composite comprises polymer fibres, such as polyethylene or polypropylene, in a matrix which may comprise the same polymer. The fibres of the internal layer are preferably aligned either parallel or orthogonal to the longitudinal axis and the pipe body comprises layers of wound composite tape 10. A method of making the polymer composite pipe comprises wrapping the longitudinal sheet of polymer composite around the longitudinal axis to form the internal layer and disposing the pipe body around the internal layer. The pipe may be particularly for transporting cryogenic fluid, such as liquefied natural gas (LNG).

Description

Pipe for Transporting Cryogenic Fluids

FIELD OF THE INVENTION

The present invention relates to a polymer composite pipe, to the use of the polymer composite pipe for transporting cryogenic fluid and to a method of making the polymer composite pipe

DESCRIPTION OF THE RELATED ART

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.

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.

The piping used to transport liquefied gases, such as LNG or the liquefied -2 -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.

Polymer pipe for transporting cryogenic fluids is also known. WO 2016/102618 Al 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. '618 explains that the tapes are wound directly onto a mandrel or that, alternatively, the tapes may be wound onto a tube liner. '618 suggests that the tube liner may comprise already consolidated tape layers. A mandrel or such layers of tape may be relatively rigid and inflexible at low temperatures. Moreover, the process to lay the tape layers and consolidate them to form a tube liner may be complex to perform.

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

SUMMARY OF THE INVENTION

According to a first alternative of the first aspect of the invention, a polymer composite pipe having a longitudinal axis is provided, comprising: a. an internal layer having an exterior surface; b. a polymer composite pipe body disposed around and bonded to the exterior surface; wherein the internal layer is formed from a longitudinal sheet of polymer composite -3 -having a sheet width defined between a first longitudinal side edge and a second longitudinal side edge, the longitudinal sheet of polymer composite having been wrapped around the longitudinal axis, such that the first longitudinal side edge and the second longitudinal side edge are contiguous or overlap one another and the internal layer has the form of an annular cylinder.

In one example, the polymer composite pipe body is bonded to the exterior surface by fusion.

In the case in which the first longitudinal side edge and the second longitudinal side edge are contiguous, they may or may not be connected together. If the first longitudinal side edge is connected to the second longitudinal side edge, then the connection may be formed by any suitable method, such as by bonding. In one example, bonding may be by fusion.

In the case in which the first longitudinal side edge and the second longitudinal side edge overlap one another, then the annular cylinder may or may not be sealed in the region of overlap. If there is a seal, then the seal may be formed by any suitable method, such as by bonding. In one example, bonding may be by fusion.

According to a second alternative of the first aspect of the invention, a polymer composite pipe having a longitudinal axis is provided, comprising: a. an internal layer having an exterior surface; b. a polymer composite pipe body disposed around and bonded to the exterior surface; wherein the internal layer is formed from a longitudinal sheet of polymer composite having a sheet width defined between a first longitudinal side edge and a second longitudinal side edge, the longitudinal sheet of polymer composite having been wrapped around the longitudinal axis, such that the internal layer has the form of a broken annular cylinder having a circumference which is greater than the sheet width, the internal layer comprising a longitudinally extending break defined between the first longitudinal side edge and the second longitudinal side edge.

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. In order to wind tape, a surface must be provided onto which it may be wound. WO 201 6/1 02618 Al discusses a steel mandrel for this purpose. A metal mandrel such as this may render the pipe stiff and inflexible. '618 suggests that, in some instances, the mandrel may be removed after manufacture of the pipe body. In order to wind tapes to a mandrel, the tapes must be attached to the mandrel and breaking that attachment to remove the mandrel afterwards may not be straightforward. '618 also suggests the possibility of using layers of already compacted tape as a liner, but the same technical challenge arises in making such a liner, because it must be manufactured over a mandrel which must then be removed.

Both the first and second alternatives of the first aspect of the invention provide a polymer composite pipe body disposed over an internal layer formed of a longitudinal sheet of polymer composite which has been wrapped into a cylinder or broken cylinder. In other words, the internal layer is formed of a single, unitary material which is simple to make and is of a homogenous, unitary construction, with fewer joins than other alternatives, such as already consolidated tape layers. Making the internal layer in this way also allows the skilled person easily to specify the alignment of fibres embedded in the polymer composite of the internal layer. Selecting the fibre alignment may allow properties of the internal layer, such as the stiffness, to be tailored to different end-uses. Finally, the longitudinally extending break provided in the second alternative of the first aspect of the invention may enhance the flexibility of the composite polymer pipe. The internal layer is not intended to function as a barrier layer, so the presence of a break is acceptable.

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

According to another example of the first aspect of the invention, the polymer -5 -composite may comprise or consist of polymer fibres embedded in a polymer matrix, that is, both the longitudinal sheet of polymer composite and the polymer composite pipe body comprise or consist of polymer fibres embedded in a polymer matrix.

The polymer fibres and the 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. Advantageously, the homopolymer and/or copolymer is a thermoplastic polymer.

The polymer fibres and the 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 another example, the polymer fibres consist of polypropylene or a copolymer thereof or mixtures thereof and the polymer matrix consists of polypropylene or a copolymer thereof or mixtures thereof.

According to one example, the polymer fibres have a softening point which is higher than the softening point of the 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 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.

According to this example, the polymer fibres of the internal layer are aligned either parallel to the longitudinal axis or orthogonal to the longitudinal axis.

According to another example, the composite pipe body comprises layers of wound polymer composite tape.

According to one particular example, the pipe body comprises: a. a first layer of polymer composite tape wound over the internal layer, the first layer of polymer composite tape comprising a plurality of adjacent windings all applied at the same angle, being an angle in the -6 -range from +750 to < +900; b. a second layer of polymer composite tape wound over the first layer, the second layer of polymer composite tape comprising a plurality of adjacent windings, all applied at the same angle as the windings of the first layer of polymer composite tape, the windings of the second layer being applied longitudinally offset with respect to the windings of the first layer, so as to overlap the interfaces of the adjacent windings in the first layer of polymer composite tape; c. a third layer of polymer composite tape wound the second layer, the third layer of polymer composite tape comprising a plurality of adjacent windings all applied at the same angle, being an angle in the range from -75° to < -900; d. a fourth layer of polymer composite tape wound over the third layer, the fourth layer of polymer composite tape comprising a plurality of adjacent windings, all applied at the same angle as the windings of the third layer of polymer composite tape, the windings of the fourth layer of polymer composite tape being applied longitudinally offset with respect to the windings of the third layer of polymer composite tape, so as to overlap the interfaces of the adjacent windings in the third layer of polymer composite tape; wherein the longitudinal axis is defined to be 0°.

These layers of wound polymer composite tape may provide the fluid containment barrier and the pressure boundary wall of the pipe.

In one example, the longitudinal offset in b and d is 30-70% of the tape width and, in another example, the longitudinal offset in b and d is about 50% of the tape width.

The pipe body may additionally comprise one or more further layer(s) of tape wound over the fourth layer, each tape layer being wound at an angle from ±15° to ±40°. Such additional layers may bestow axial and bending strength to the polymer composite pipe. -7 -

The polymer composite pipe according to the invention may be manufactured in continuous long lengths, such as greater than 1000m, greater than 2000m or greater than 3000m.

According to a second aspect of the invention, the use of a composite polymer pipe of the first aspect of the invention for conveying a fluid, especially a liquid, having a temperature below -150°C is provided.

According to the first alternative of a third aspect of the invention, a method of making a polymer composite pipe having a longitudinal axis is provided, the polymer composite pipe comprising a polymer composite pipe body and an internal layer, the method comprising: a. Providing a longitudinal sheet of polymer composite having a sheet width defined between a first longitudinal side edge and a second longitudinal side edge; b. Wrapping the longitudinal sheet of polymer composite around the longitudinal axis, such that the first longitudinal side edge and the second longitudinal side edge are contiguous or overlap one another to provide the internal layer which has the form of an annular cylinder having an exterior surface; c. Disposing the pipe body around the internal layer and bonding it to the exterior surface According to the second alternative of a third aspect of the invention, a method of making a polymer composite pipe having a longitudinal axis is provided, the polymer composite pipe comprising a polymer composite pipe body and an internal layer, the method comprising: a Providing a longitudinal sheet of polymer composite having a sheet width defined between a first longitudinal side edge and a second longitudinal side edge; b Wrapping the longitudinal sheet of polymer composite around the longitudinal axis to provide the internal layer in the form of a broken -8 -annular cylinder having a circumference which is greater than the sheet width, so that the internal layer comprises a longitudinally extending break defined between the first longitudinal side edge and the second longitudinal side edge, the internal layer having an exterior surface; c. Disposing the pipe body around the internal layer and bonding it to the exterior surface.

The method of the first or second alternatives of the third aspect of the invention provides a simpler process alternative to prior art processes. The internal layer is formed of a single longitudinal sheet of polymer composite which is bent into an annular cylinder or a broken annular cylinder around a mandrel. There is no need to remove the internal layer afterwards and the process for making it is simpler than a process for making an annular cylinder of already-compacted tape.

In one example of the method of the first or second alternatives of the third aspect of the invention, wrapping the longitudinal sheet of polymer composite in b. is achieved by: i. conveying the longitudinal sheet of polymer composite in a direction of travel over rollers which bend the longitudinal sheet of polymer composite into a U-shaped preform; ii. passing the U-shaped preform through a cone-shaped funnel which is configured to wrap the U-shaped preform around a mandrel to provide the internal layer.

The longitudinal sheet of polymer composite may additionally be heated sufficiently to render it compliant and reduce the degree of force needed to bend it into a U-shaped preform and wrap it around the mandrel.

According to another example, disposing the polymer composite pipe body around the internal layer in c. is achieved by winding one or more layer(s) of polymer composite tape around the internal layer formed in b. According to a first alternative, the one or more layer(s) of polymer composite tape are wound around the internal layer formed in b while it is still wrapped around the mandrel. According to a second -9 -alternative, the one or more layer(s) of polymer composite tape are wound around the internal layer formed in b after the internal layer has been conveyed beyond the mandrel in the direction of travel. The second alternative may be used if the internal layer is stiff enough and/or the tension in the tape is sufficiently low for the internal layer not to collapse when tape is wound onto the internal layer.

In one example, the polymer composite tape is bonded to the exterior surface of the internal layer by fusion. In one example, heat may be provided in the form of a laser beam to fuse the tape of the composite material to exterior surface of the internal layer. A laser beam may be capable of providing very localized melting and fusion at one or both of the surfaces to-be-combined, thereby ensuring that the remainder of the composite is not significantly heated and that, for example, the fibres do not soften or melt.

In one example, after the winding of a first layer of wound polymer composite tape, any second and further layer(s) of wound polymer composite tape are bonded to the preceding layer of wound polymer composite tape by fusion. More preferably, heat is provided in the form of a laser beam to fuse the tape of the composite material to the preceding layer of wound polymer composite tape. Laser fusion/welding may have the advantages discussed above.

According to one aspect of this example, the method comprises: a. winding a first layer of polymer composite tape over the internal layer, the first layer of polymer composite tape comprising a plurality of adjacent windings all applied at the same angle, being an angle in the range from a. +75° to < b. winding a second layer of polymer composite tape over the first layer, the second layer of polymer composite tape comprising a plurality of adjacent windings, all applied at the same angle as the windings of the first layer of polymer composite tape, the windings of the second layer being applied longitudinally offset with respect to the windings of the first layer, so as to overlap the interfaces of the adjacent windings in the first player of polymer composite tape; c. winding a third layer of polymer composite tape over the second layer, the -10 -third layer of polymer composite tape comprising a plurality of adjacent windings all applied at the same angle, being an angle in the range from -75° to < -900; d. winding a fourth layer of polymer composite tape over the third layer, the fourth layer of polymer composite tape comprising a plurality of adjacent windings, all applied at the same angle as the windings of the third layer of polymer composite tape, the windings of the fourth layer of polymer composite tape being applied longitudinally offset with respect to the windings of the third layer of polymer composite tape, so as to overlap the interfaces of the adjacent windings in the third layer of polymer composite tape; wherein the longitudinal axis is defined to be 00.

According to another example, the method may additionally comprise winding one or more further layer(s) of tape wound over the fourth layer, each tape layer being wound at an angle from ±150 to ±40°.

According to another example, the method is configured as a continuous process, such that a continuous longitudinal sheet is conveyed in the processing direction, is continuously wrapped to form an internal layer in the form of an annular cylinder or a broken annular cylinder having an exterior surface and the pipe body is continuously disposed around and bonded to the exterior surface. The continuous process may allow polymer composite pipe to be manufactured in continuous long lengths, such as greater than 1000m, greater than 2000m or greater than 3000m.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be further described, by way of example only, and with reference to the accompanying drawings, in which: -11 -Figure 1 shows a schematic perspective view of an apparatus used in the method according to an example of the invention.

Figure 2 shows a schematic perspective view of part of the apparatus used in the method according to an example of the invention.

Figure 3 shows a further perspective view of part of the apparatus used in the method according to an example of the invention.

Figure 4 shows an end elevation of the polymer composite pipe according to an example of the invention.

Figure 5 shows detail 'A' of the polymer composite pipe of Figure 4.

DETAILED DESCRIPTION

A detailed description of the invention will now be provided with reference to the above figures. A given reference number is always used to denote the same feature in each of the accompanying drawings.

In one example, a polypropylene single polymer composite (SPC) sheet is prepared, comprising: - extruded and drawn polypropylene homopolymer fibres which have been plane woven into sheets (woven sheets) such that the fibres are aligned either along an axis or at 900 to the axis; - a polypropylene copolymer matrix in the form of thin film sheets (thin film sheet) having a softening point which is 20°C lower than the melting point of the polypropylene homopolymer fibres.

One or more woven sheets is encased between thin film sheets to form the SPC. If there is more than one woven sheet, then each woven sheet may be separated from the next woven sheet by a thin film sheet interposed between the woven sheets.

-12 -In one example, an SPC sheet is prepared which comprises three woven sheet layers, each having a thickness of 0.15mm. Each woven sheet layer is separated from the next woven sheet layer by an intermediate layer of thin film sheet, so that there are two intermediate layers of thin film sheet in total. Each intermediate layer of thin film sheet has a thickness of 0.02mm. The combination is sandwiched between two "skin" layers of thin film sheet, each skin layer having a thickness of 0.04mm. There are thus seven layers in total, being two "skin" layers, three woven sheet layers and two intermediate layers.

The seven sandwiched layers are hot-compacted into an SPC of 0.57mm thickness. During hot compaction, the thin film layers soften or melt to form the matrix. Softening or melting of the polypropylene homopolymer fibres is avoided or minimized, by careful application of heat and because of the higher softening point of the homopolymer fibres.

SPCs of the present type are strong and tough at cryogenic temperatures, they are flexible and relatively low cost to produce. Their good material properties are in part due to the good adhesion between the fibres and the matrix on account of their identical or very similar chemical properties. SPCs have the environmental advantage that they may be melted to recycle them.

In one example a 50.8mm (2 inch) internal diameter pipe is manufactured from the above-described SPC sheet in the following manner. For completeness, pipes having other dimensions, such as 15.24cm (6 inch), 20.32cm (8 inch) or 25.4cm (10 inch) internal diameter, etc. could also be made in this way: Both an internal layer and polymer composite tape are cut to width from a longitudinal sheet of SPC. The polymer composite tape is cut to have a width of 18mm (and has a thickness of 0.57mm, as mentioned above). The internal layer, cut to a width of 159.51mm, is additionally rolled to further compact it to a thickness of 0.4mm.

With reference to Figures 1 to 3, the longitudinal sheet of SPC (1) is conveyed in a direction of travel (2) through a forming box (not shown) which heats the -13 -longitudinal sheet of SPC (1) to 50-70°C to make it more pliable. The fibres embedded in the longitudinal sheet of SPC are aligned parallel to the direction of travel (2) or are aligned at 90° to the direction of travel (2). The longitudinal sheet of SPC (1) is conveyed further in the direction of travel (2) over rollers (4) which bend it into a U-shaped preform (5). The forming box and rollers (4) are located in housing (3) in Figure 1. Housing (3) has been removed for the purposes of showing the internal workings in Figures 2 and 3. The U-shaped preform (5) is conveyed further in the direction of travel (2) through a cone-shaped funnel (6) and onto a static mandrel (8) to wrap it into an internal layer (7) in the form of a broken annular cylinder, such that the longitudinal break (11), shown in Figures 4 and 5, in the broken annular cylinder is 2mm wide.

While the internal layer (7) is conveyed along the static mandrel (8) in the direction of travel (2), layers (9) of SPC tape (10), prepared as described above, are wound onto the internal layer (7).

The windings of the first layer of SPC tape (10) are applied at an angle of about +85° to the longitudinal axis (the longitudinal axis is defined as 0°) and are fused to the internal layer (7) by laser welding using a laser welding device (not shown).

The windings of the second layer of SPC tape (10) are applied over the first layer of SPC tape and the windings are applied at the same angle as the windings of the first layer, but the windings of the second layer of SPC tape (10) are applied longitudinally offset with respect to the windings of the first layer of SPC tape (10), so as to overlap the interfaces of the adjacent SPC tape (10) windings in the first layer. The windings of the second layer of SPC tape (10) are fused to the windings of the first layer of SPC tape (10) by laser welding using a laser welding device (not shown).

The windings of the third layer of SPC tape (10) are applied at an angle of about -85° to the longitudinal axis and are fused to the windings of the second layer of SPC tape (10) by laser welding using a laser welding device (not shown).

-14 -The windings of the fourth layer of SPC tape (10) are applied over the third layer of SPC tape (10) and the windings are applied at the same angle as the windings of the third layer, but the windings of the fourth layer of SPC tape (10) are applied longitudinally offset with respect to the windings of the third layer of SPC tape (10), so as to overlap the interfaces of the adjacent SPC tape (10) windings in the third layer. The windings of the fourth layer of SPC tape (10) are fused to the windings of the third layer of SPC tape (10) by laser welding using a laser welding device.

The four layers (9) of windings at an angle of about +/-85° are essentially hoop windings which, together, form the pressure boundary wall.

Four additional wound tape layers (9) are provided as follows: * The windings of the fifth layer of SPC tape (10) are applied at an angle of +25° to the longitudinal axis and are fused to the fourth layer of SPC tape (10) by laser welding using a laser welding device (not shown).

* The windings of the sixth layer of SPC tape (10) are applied at an angle of -25° to the longitudinal axis and are fused to the fifth layer of SPC tape (10) by laser welding using a laser welding device (not shown).

* The windings of the seventh layer of SPC tape (10) are applied at an angle of +25° to the longitudinal axis and are fused to the sixth layer of SPC tape (10) by laser welding using a laser welding device (not shown).

* The windings of the eighth layer of SPC tape (9) are applied at an angle of -25° to the longitudinal axis and are fused to the seventh layer of SPC tape (10) by laser welding using a laser welding device (not shown).

Layers 5-8 bestow axial and bending strength to the pipe.

Figure 4 shows a cross-section of the finished polymer composite pipe and Figure 5 is a magnified detail 'A' from Figure 4. These figures show the internal layer (7) and the layers (9) of wound SPC tape (10). The longitudinal break (11) in the internal layer is also shown.

-15 -A polymer composite pipe manufactured according to this example has an internal diameter of 50.8mm (2 inch) and a length of 2000m. It is suitable for conveying LNG and may be operated at a pressure of up to 19 Barg (Bar gauge) and a temperature from -196°C to +50°C, with -163°C being a typical operating temperature.

Claims

-16 -CLAIMS1 A polymer composite pipe having a longitudinal axis comprising: a. an internal layer having an exterior surface; b. a polymer composite pipe body disposed around and bonded to the exterior surface; wherein the internal layer is formed from a longitudinal sheet of polymer composite having a sheet width defined between a first longitudinal side edge and a second longitudinal side edge, the longitudinal sheet of polymer composite having been wrapped around the longitudinal axis, such that the first longitudinal side edge and the second longitudinal side edge are contiguous or overlap one another and the internal layer has the form of an annular cylinder.
2 A polymer composite pipe having a longitudinal axis comprising: a. an internal layer having an exterior surface; b. a polymer composite pipe body disposed around and bonded to the exterior surface; wherein the internal layer is formed from a longitudinal sheet of polymer composite having a sheet width defined between a first longitudinal side edge and a second longitudinal side edge, the longitudinal sheet of polymer composite having been wrapped around the longitudinal axis, such that the internal layer has the form of a broken annular cylinder having a circumference which is greater than the sheet width, the internal layer comprising a longitudinally extending break defined between the first longitudinal side edge and the second longitudinal side edge.
3. The polymer composite pipe of claim 1 or 2, wherein the internal layer has a thickness of 0.1-1mm.
4. The polymer composite pipe of claim 3, wherein the internal layer has a thickness of 0.2-0.7mm.
5. The polymer composite pipe of any preceding claim, wherein the polymer composite comprises polymer fibres embedded in a polymer matrix.
6. The polymer composite pipe of claim 5, wherein the polymer fibres and the polymer matrix comprise the same polymer or a copolymer thereof.
7. The polymer composite pipe of claim 5 or 6, wherein the polymer fibres and the polymer matrix comprise the same polyolefin or a copolymer thereof.
8. The polymer composite pipe of any of claims 5 to 7, wherein the polyolefin is polyethylene or polypropylene.
9 The polymer composite pipe of any of claims 5 to 8, wherein the polymer fibres consist of polypropylene or a copolymer thereof and the polymer matrix consists of polypropylene or a copolymer thereof.
10. The polymer composite pipe of any of claims 5 to 9, wherein the polymer fibres have a softening point which is higher than the softening point of the polymer matrix.
11. The polymer composite pipe of any of claims 5 to 10, wherein the polymer fibres of the internal layer are aligned either parallel to the longitudinal axis or orthogonal to the longitudinal axis.
12. The polymer composite pipe of any preceding claim, wherein the composite pipe body comprises layers of wound polymer composite tape.
13 The polymer composite pipe of claim 12, wherein the pipe body comprises: a. a first layer of polymer composite tape wound over the internal layer, the first layer of polymer composite tape comprising a plurality of adjacent windings all applied at the same angle, being an angle in the -18 -range from +750 to < +900; b. a second layer of polymer composite tape wound over the first layer, the second layer of polymer composite tape comprising a plurality of adjacent windings, all applied at the same angle as the windings of the first layer of polymer composite tape, the windings of the second layer being applied longitudinally offset with respect to the windings of the first layer, so as to overlap the interfaces of the adjacent windings in the first layer of polymer composite tape; c. a third layer of polymer composite tape wound the second layer, the third layer of polymer composite tape comprising a plurality of adjacent windings all applied at the same angle, being an angle in the range from -75° to < -900; d. a fourth layer of polymer composite tape wound over the third layer, the fourth layer of polymer composite tape comprising a plurality of adjacent windings, all applied at the same angle as the windings of the third layer of polymer composite tape, the windings of the fourth layer of polymer composite tape being applied longitudinally offset with respect to the windings of the third layer of polymer composite tape, so as to overlap the interfaces of the adjacent windings in the third layer of polymer composite tape; wherein the longitudinal axis is defined to be 0°.
14. The polymer composite pipe of claim 13, wherein the longitudinal offset in b and d is 40-70% of the tape width.
15. The polymer composite pipe of claim 13 or 14, additionally comprising one or more further layer(s) of tape wound over the fourth layer, each tape layer being wound at an angle from ±15° to ±40°.
16 The use of a polymer composite pipe of any preceding claim for conveying a fluid having a temperature below -150°C.
17.A method of making a polymer composite pipe having a longitudinal axis and comprising a polymer composite pipe body and an internal layer, the method -19 -comprising: a. Providing a longitudinal sheet of polymer composite having a sheet width defined between a first longitudinal side edge and a second longitudinal side edge; b. Wrapping the longitudinal sheet of polymer composite around the longitudinal axis, such that the first longitudinal side edge and the second longitudinal side edge are contiguous or overlap one another to provide the internal layer which has the form of an annular cylinder having an exterior surface; c. Disposing the pipe body around the internal layer and bonding it to the exterior surface.
18.A method of making a polymer composite pipe having a longitudinal axis and comprising a polymer composite pipe body and an internal layer, the method comprising: a. Providing a longitudinal sheet of polymer composite having a sheet width defined between a first longitudinal side edge and a second longitudinal side edge; b. Wrapping the longitudinal sheet of polymer composite around the longitudinal axis to provide the internal layer in the form of a broken annular cylinder having a circumference which is greater than the sheet width, so that the internal layer comprises a longitudinally extending break defined between the first longitudinal side edge and the second longitudinal side edge, the internal layer having an exterior surface; c. Disposing the pipe body around the internal layer and bonding it to the exterior surface.
19 The method of claim 17 or 18, wherein wrapping the longitudinal sheet of polymer composite in b. is achieved by: i. conveying the longitudinal sheet of polymer composite in a direction of travel over rollers which bend the longitudinal sheet of polymer -20 -composite into a U-shaped preform; ii. passing the U-shaped preform through a cone-shaped funnel which is configured to wrap the U-shaped preform around a mandrel to provide the internal layer.
20. The method of claim 19 additionally comprising heating the longitudinal sheet of polymer composite sufficiently to render it compliant and reduce the degree of force needed to bend it into a U-shaped preform and wrap it around the mandrel.
21 The method of any of claims 17 to 20, wherein disposing the polymer composite pipe body around the internal layer in c. is achieved by winding one or more layer(s) of polymer composite tape around the internal layer formed in b.
22. The method of claim 21, wherein the one or more layer(s) of polymer composite tape are wound around the internal layer formed in b while it is still wrapped around the mandrel.
23. The method of claim 22, wherein the one or more layer(s) of polymer composite tape are wound around the internal layer formed in b after the internal layer has been conveyed beyond the mandrel in the direction of travel.
24. The method of any of claims 21 to 23, wherein the polymer composite tape is bonded to the exterior surface by fusion.
25. The method of any of claims claim 21 to 24, wherein, after the winding of a first layer of wound polymer composite tape, any second and further layer(s) of wound polymer composite tape are bonded to the preceding layer of wound polymer composite tape by fusion.
26 The method of any of claims 21 to 25, comprising: -21 -a. winding a first layer of polymer composite tape over the internal layer, the first layer of polymer composite tape comprising a plurality of adjacent windings all applied at the same angle, being an angle in the range from a. +75° to < +900; b. winding a second layer of polymer composite tape over the first layer, the second layer of polymer composite tape comprising a plurality of adjacent windings, all applied at the same angle as the windings of the first layer of polymer composite tape, the windings of the second layer being applied longitudinally offset with respect to the windings of the first layer, so as to overlap the interfaces of the adjacent windings in the first player of polymer composite tape; c. winding a third layer of polymer composite tape over the second layer, the third layer of polymer composite tape comprising a plurality of adjacent windings all applied at the same angle, being an angle in the range from -75° to < -90°, d. winding a fourth layer of polymer composite tape over the third layer, the fourth layer of polymer composite tape comprising a plurality of adjacent windings, all applied at the same angle as the windings of the third layer of polymer composite tape, the windings of the fourth layer of polymer composite tape being applied longitudinally offset with respect to the windings of the third layer of polymer composite tape, so as to overlap the interfaces of the adjacent windings in the third layer of polymer composite tape; wherein the longitudinal axis is defined to be 0°.
27. The method of claim 26, wherein the longitudinal offset in b and d is 4070% of the tape width.
28. The method of claim 26 or 27, additionally comprising winding one or more further layer(s) of tape wound over the fourth layer, each tape layer being wound at an angle from ±150 to ±40°.
29 The method of any of claims 17 to 28 which is configured as a continuous process.