Composite and metal pipe assembly

Abstract

A pipe assembly 20 comprising: a pipe 30 comprising a composite body 32 and a plurality of coaxial nested composite collars 34 which protrude from an end of the composite body 32, wherein the composit

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a pipe assembly, an aircraft, and a method of manufacturing a pipe assembly. BACKGROUND OF THE INVENTION

[0002] Transporting fluid, in particular cryogenic fluid, through pipe assemblies and fluid lines is challenging due to the changes in temperature experienced by the pipe assemblies as the fluid travels through them. The issue is most keenly felt for pipe assemblies comprising a lightweight composite pipe bonded to a metal end fitting, where the thermal effects of fluid within the pipe can cause bonding issues between the components. This can in turn increase the likelihood of fluid leaking from the pipe assembly via the connection between the composite pipe and the metal end fitting. SUMMARY OF THE INVENTION

[0003] A first aspect of the invention provides a pipe assembly comprising: a pipe comprising a composite body and a plurality of coaxial nested composite collars which protrude from an end of the composite body, wherein the composite body and the composite collars comprise fibre-reinforced composite material; a fitting comprising a metal body and a plurality of coaxial nested metal collars which protrude from the metal body, wherein the metal body and the metal collars comprise metallic material; and a joint connecting the pipe to the fitting, wherein the composite collars are interleaved with and bonded to the metal collars at the joint.

[0004] A pipe assembly comprising a composite pipe connected to a metal fitting may provide a lightweight pipe assembly that is readily connectible to adjacent metal components using common joining techniques. The composite material may further be selected to achieve required component characteristics such as thermal insulation. Utilising interleaved collars at the joint between the pipe and the fitting provides an increased contact area of each component, similar to a finger joint or comb joint, which may result in a stronger connection when the components are bonded together. The interleaving also provides a transition region between the fitting and the pipe, where the radial thickness of the pipe assembly comprises both composite and metallic material. This transition region may have material properties that are between the relative material properties of the metal and composite components. As such, the transition region may help to reduce the step change in material properties of the pipe assembly along its length.

[0005] The composite body may comprise a plurality of composite core layers which are interleaved with a plurality of composite connection layers. The composite core layers and the composite connection layers may comprise a fibre-reinforced composite material. The composite connection layers may extend beyond the composite core layers to form the composite collars.

[0006] Providing composite collars formed of composite connection layers within the composite body may allow the composite collars to be formed integral to the composite body. This may provide a strong connection between the composite collars and the composite body, since the composite connection layers forming the composite collars may be bonded to the composite core layers along substantially the entire length of the pipe. Providing each core and connection section as a layer also provides a convenient method of manufacture using known composite manufacture techniques such as for example filament finding.

[0007] The composite core layers may abut the metal collars.

[0008] Providing composite core layers abutting the metal collars increases the surface area of the composite body in contact with the fitting. This may allow the ends of the composite core layers to be bonded to the metal collars, thus increasing the strength of the connection between the pipe and the fitting.

[0009] The metal body may comprise a plurality of metal core layers which are interleaved with a plurality of metal connection layers. The metal core layers and the metal connection layers may comprise metallic material. The metal connection layers may extend beyond the metal core layers to form the metal collars.

[0010] Providing metal collars formed of metal connection layers within the metal body may allow the metal collars to be formed integral to the metal body. This may provide a strong connection between the metal collars and the metal body, since the metal connection layers forming the metal collars may be bonded to the metal core layers along substantially the entire length of the fitting.

[0011] The metal core layers may abut the composite collars.

[0012] Providing metal core layers abutting the composite collars increases the surface area of the metal body in contact with the pipe. This may allow the ends of the metal core layers to be bonded to the composite collars, thus increasing the strength of the connection between the pipe and the fitting.

[0013] The metal core layers may be welded to the metal connection layers.

[0014] Welding may provide a convenient method of strongly and permanently bonding the metal core layers and the metal connection layers. Once welded, the distinct metal core layers and metal connection layers may be combined to form a single unitary metal body.

[0015] The pipe assembly may further comprise a continuous barrier which lines an interior of the composite body and an interior of the metal body.

[0016] Providing a barrier lining the full length of the pipe assembly covers the joint between the pipe and the fitting. This may reduce the likelihood of fluid within the pipe escaping by leaking through the walls of the pipe assembly, by covering a potential leak path for the fluid through the walls of the pipe.

[0017] The barrier may comprise a metallic material, which is optionally the same as the metallic material of the metal body and optionally the same as the metallic material of the metal collars.

[0018] Providing a metallic barrier may reduce the likelihood of fluid in the pipe assembly leaking from the pipe assembly via permeation through the pipe walls. Providing a barrier comprising the same metallic material as the metal body and / or metal collars may allow the metal body to be more easily bonded to the fitting, for example via welding.

[0019] The barrier may contact the interior of the composite body, and optionally the barrier is bonded to the interior of the composite body.

[0020] The barrier may contact the interior of the metal body, and optionally the barrier is bonded to the interior of the metal body.

[0021] Bonding the barrier to the interior of the metal body and / or the composite body may reduce the likelihood of fluid in the pipe assembly leaking from the pipe assembly through a leak path between the layers of the pipe wall.

[0022] The pipe assembly may further comprise liquid hydrogen contained within the pipe assembly.

[0023] The composite body of the pipe may provide a well-insulated fluid line through which cryogenic liquid (such as liquid hydrogen) may be transported. Optionally the composite body is further insulated by a foam covering or vacuum jacket.

[0024] The composite body and the composite collars may comprise the same fibre-reinforced composite material.

[0025] Providing the composite collars and the composite body as comprising the same fibre-reinforced composite material may improve ease of manufacture of the pipe.

[0026] The metal body and the metal collars may comprise the same metallic material.

[0027] Providing the metal collars and the metal body as comprising the same metallic material may improve ease of manufacture of the fitting.

[0028] The pipe assembly may further comprise a flange fitting comprising a body and a flange extending outwardly from the body, wherein the metal body is coupled to the body of the flange fitting.

[0029] A flange may provide a convenient method of coupling the pipe assembly to an external component. In particular, the fitting may provide a convenient portion for strongly coupling the pipe assembly to an external component via the flange fitting.

[0030] An axial end surface of the body may be welded to a radially inner surface of the metal body. An axial end surface of the metal body may be welded to a radial outer surface of the body.

[0031] The body may extend into and be bonded to the fitting. Providing a welded joint at both the radially inner surface of the fitting and the radially outer surface of the body may provide a strong connection between the fitting and the flange fitting.

[0032] The barrier may line an interior of the body.

[0033] Providing a barrier lining the interior of the body may cover the joint between the flange fitting and the pipe assembly. This may reduce the likelihood of fluid in the pipe assembly leaking from the pipe assembly through a leak path between the flange fitting and the fitting.

[0034] Optionally the composite collars and the metal collars are cylindrical.

[0035] Optionally the plurality of coaxial nested composite collars comprises three or more coaxial nested composite collars.

[0036] Optionally the plurality of coaxial nested metal collars comprises three or more coaxial nested metal collars.

[0037] A second aspect of the invention provides an aircraft comprising the pipe assembly of any preceding claim.

[0038] A third aspect of the invention provides a method of manufacturing the pipe assembly of the first aspect of the invention, the method comprising alternately adding the composite collars and the metal collars to interleave them at the joint, and curing the composite collars to co-bond them to the metal collars.

[0039] By alternately adding the composite and metal collars, each new collar may be supported by those radially inwards to hold the interleaved joint in place.

[0040] Each composite collar may be added by winding. For example the composite collars may be added by winding fibre-reinforced composite material onto a mandrel, or by winding dry-fibre material onto a mandrel and then infusing the dry-fibre material with a matrix (such as a resin) after all of the dry-fibre material has been added.

[0041] Winding may provide a convenient method for adding the fibre-reinforced material, for example by winding fibrous material about a removable mandrel. Alternatively the fibre-reinforced material may be added by wrapping a sheet of fibrous material and joining the edges at an axial seam.

[0042] Each metal collar may be added by being slid into place, for instance by translation in an axial direction.

[0043] Adding metal collars by translation in an axial direction of the pipe assembly provides a convenient method for assembling the fitting at an axial end of the pipe assembly. Each subsequent metal collar may increase in diameter to fit over the collar assembled prior. Alternatively each metal collar may be added by wrapping a metallic sheet and joining the edges at an axial seam. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

[0045] Figure 1 shows an aircraft;

[0046] Figure 2 shows an end of a pipe assembly;

[0047] Figure 3 shows a cross-sectional view of a first example of a pipe assembly;

[0048] Figure 4 shows a cross-sectional view of a second example of a pipe assembly;

[0049] Figure 5 shows a cross-sectional view of a third example of a pipe assembly;

[0050] Figure 6 shows a cross-sectional view of a fourth example of a pipe assembly;

[0051] Figure 7 shows a cross-sectional view of a fifth example of a pipe assembly;

[0052] Figure 8 shows a cross-sectional view of a sixth example of a pipe assembly;

[0053] Figure 9 shows a cross-sectional view of a seventh example of a pipe assembly; and

[0054] Figures 10A to 10G show a method of manufacturing a pipe assembly. DETAILED DESCRIPTION OF EMBODIMENT(S)

[0055] Figure 1 shows an aircraft 10. The aircraft 10 has a fuselage 12, and starboard and port fixed wings 13, 14. An engine 15 is mounted to each wing 13, 14. The aircraft 10 is a typical jet passenger transport aircraft but the invention is applicable to a wide variety of fixed wing aircraft types, including commercial, military, passenger, cargo, jet, propeller, general aviation, etc. with any number of engines attached to the wings or fuselage. The aircraft is a fixed wing aircraft with cantilever wings.

[0056] Fluid lines are provided within the aircraft 10 to transport liquid and / or gas about the aircraft 10. In particular, fuel lines are provided for transporting fuel from one or more storage tanks to the engines 15. Such fuel lines may comprise a pipe assembly 20 (shown in Figure 2) which can be connected to further pipe assemblies 20 or other structural components within the aircraft 10. Although described with reference to aircraft and aircraft fuel lines, it will be appreciated that the pipe assembly 20 may be used in a variety of applications.

[0057] Each of Figures 3 to 7 show a cross-sectional view of a pipe assembly 20 taken through a longitudinal axis Al of the pipe assembly 20. Each view shows only one end of the pipe assembly 20.

[0058] The pipe assembly 20 comprises a pipe 30, a fitting 40 and a joint 50 connecting the pipe 30 to the fitting 40. The pipe 30 comprises a composite body 32 and a plurality of composite collars 34 (only some of which are labelled for clarity) which protrude from an end of the composite body 32. The composite body 32 and each of the composite collars 34 are manufactured from a composite material, such as for example glass fibre reinforced polymer or carbon fibre reinforced polymer. The composite collars 34 extend around the full circumference or perimeter of the pipe 30 and are coaxial and nested. That is, they are centred on the axis Al of the pipe and are nested so that each composite collar 34 has a different diameter. In this example the composite collars 34 are cylindrical and circular in cross-section, but it will be appreciated that the pipe 30 and the collars 34 may be non-circular in cross-section. The composite collars 34 define concentric rings about the longitudinal axis Al.

[0059] Although shown as comprising five composite collars, it will be appreciated that the pipe 30 may comprise any number of composite collars 34, for example two, three, or more than three.

[0060] The pipe 30 extends over a majority of the length of the pipe assembly 20. This helps to reduce the weight of the pipe assembly 20 whilst still maintaining the required mechanical and / or thermal insulation properties of the pipe assembly 20.

[0061] The pipe 30 may extend much further than indicated in Figures 2-9, and may have a second fitting similar to the fitting 40 at the other end (not shown),

[0062] The fitting 40 comprises a metal body 42 and a plurality of metal collars 44 (only some of which are labelled for clarity) which protrude from an end of the metal body 42. The metal body 42 and each of the metal collars 44 comprise a metallic material and allow the pipe assembly 20 to be connected to adjacent components. For example, the fitting 40 may be welded to an adjacent metallic component which may not be possible for an entirely composite pipe.

[0063] Suitable metallic materials for the metal body 42 and the metal collars 44 are Invar, stainless steel (304L or 316L), gold, aluminium or copper.

[0064] The metal collars 44 extend around the full circumference or perimeter of the fitting 40 and are coaxial and nested. That is, they are centred on the axis Al of the pipe assembly and are nested so that each metal collar 44 has a different diameter. In this example the metal collars 44 are cylindrical and circular in cross-section, but it will be appreciated that the fitting 40 and the collars 44 may be non-circular in cross-section. The metal collars 44 define concentric rings about the longitudinal axis Al.

[0065] Although shown as comprising five metal collars 44, it will be appreciated that the pipe 30 may comprise any number of metal collars 44, for example two, three, or more than three.

[0066] The joint 50 provides a connection between the pipe 30 and the fitting 40. The composite collars 34 are interleaved with the metal collars 44 at the joint 50 to form alternating layers of material as shown in Figure 3. Each composite collar 34 is bonded to the adjacent metal collar(s) 44. By interleaving the collars 34, 44, the surface area of the pipe 30 in contact with the fitting 40 is increased. This may allow the strength of the joint 50 between the pipe 30 and the fitting 40 to be increased, since a greater total surface area of the composite collars 34 may be bonded to a greater total surface area of the metal collars 44. To form an interleaved joint 50, each of the pipe 30 and the fitting 40 are provided with at least two collars 34, 44 respectively. Optionally each of the pipe 30 and the fitting 40 have the same number of collars 34, 44.

[0067] Interleaving the collars 34, 44 at the joint 50 also provides a transition region between the pipe 30 and the fitting 40. This transition region may help to reduce the step change in local material properties along the length of the pipe assembly 20.

[0068] By way of non-limiting example, the pipe assembly 20 may be configured to contain or transport a cryogenic fluid such as liquid hydrogen.

[0069] Hydrogen gas can easily leak through any interface between a composite part and another part. The use of a metallic fitting 40 solves this leakage problem at the interface, because it can be machined with a flat face more easily.

[0070] The pipe 30 and the fitting 40 may be manufactured from materials having different coefficients of thermal expansion. This may result in the pipe 30 and the fitting 40 expanding and / or contracting by different amounts as the temperature within the pipe assembly 20 changes, for example as cryogenic fluid flows through the pipe assembly 20. This difference in expansion and / or contraction may result in stresses and / or deformation occurring at the joint 50, which may increase the likelihood of the cryogenic fluid leaking from the pipe assembly 20 or the pipe assembly 20 becoming damaged. The transition region has a coefficient of thermal expansion between that of the pipe 30 and fitting 40 respectively. As such the step change in local coefficient of thermal expansion along the pipe assembly 20 is reduced (i.e. spread over two smaller step changes rather than one larger step change). This may help to accommodate expansion and / or contraction of the pipe assembly 20.

[0071] Figure 4 shows a further example of a pipe assembly 20. Each composite collar 34 extends from the composite body 32 by a different length, with the radially innermost composite collar 34 being the longest, and the radially outermost composite collar 34 being the shortest. This may provide greater control over changes in local material coefficients along the pipe assembly 20, by providing multiple smaller step changes in local material properties between the pipe 30 and the fitting 40. Although shown as the length of adjacent composite collars 34 decreasing with increased radial distance from the axis Al, it will be appreciated that the arrangement and length of the composite collars 34 may be varied depending on the required local material properties of the pipe assembly 20.

[0072] The pipe 30 may be manufactured using known techniques, such as filament winding as will be discussed with reference to Figures 10A to 10F. As such, the pipe 30 may comprise distinct layers, which are bonded together (for instance by co-curing) to form the pipe 30. The distinct layers may for example be “prepreg” layers containing pre-impregnated fibres which are subsequently co-cured (i.e. multiple un-cured parts cured simultaneously) to bond them together. Figure 5 shows an example of a pipe assembly 20 comprising a pipe 30 formed of multiple bonded composite layers. It will be appreciated that Figure 5 is schematic and that (once bonded) the distinct composite layers may not be visible.

[0073] The composite body 32 comprises a plurality of shorter composite core layers 32a and a plurality of longer composite connection layers 32b, the composite connection layers 32b extending beyond the composite core layers to form the composite collars 34. The composite core layers 32a are interleaved with the composite connection layers 32b to provide gaps into which the metal collars 44 extend. The composite core layers 32b may abut the metal collars 44 as shown in Figure 5. This allows both the composite core layers 32a and the composite connection layers 32b to be bonded to the fitting 40, which provides a stronger joint 50.

[0074] Both the composite core layers 32a and the composite connection layers 32b may extend over substantially the entire length of the composite body 32. Optionally the outermost composite collar 32b may extend over the full length of the metal fitting 40, rather than only extending over part of the length of the metal fitting 40 as shown.

[0075] The fitting 40 may be manufactured and / or assembled as a series of distinct metal layers subsequently bonded together, for example by stir welding. Each distinct layer may be a thin metal shell, with a plurality of nested metal shells increasing in diameter assembled to achieve a required thickness of the fitting 40. Once assembled, the distinct layers may be coalesced, for example by friction stir welding to form a unitary metal body 42. Figure 6 shows an example of a pipe assembly 20 comprising a fitting 40 formed of multiple metal layers. It will be appreciated that Figure 6 is schematic, and that the distinct metal layers may not be visible in the final part.

[0076] The metal body 42 comprises a plurality of shorter metal core layers 42a and a plurality of longer metal connection layers 42b, the metal connection layers 42b extending beyond the metal core layers to form the metal collars 44. The metal core layers 42a are interleaved with the metal connection layers 42b to provide gaps into which the composite collars 34 extend. The metal core layers 42a may abut the composite collars 34 as shown in Figure 6. This allows both the metal core layers 42a and the metal connection layers 42b to be bonded to the pipe 30, which provides a stronger joint 50.

[0077] The pipe assembly 20 may further comprise a continuous barrier 60 lining an interior of the pipe 30 and the fitting 40, as shown in Figure 7. It is preferable to bond the barrier 60 to the pipe 30 and to the fitting 40 to reduce the likelihood of fluid within the pipe assembly 20 leaking through the joint 50.

[0078] A problem with composite materials is that hydrogen gas can permeate easily through the body of the composite material. Metallic materials tend to have a lower diffusivity, hence the barrier 60 prevents such permeation through the composite pipe 30.

[0079] The continuous barrier 60 may comprise a tube around which the pipe 30 and / or the fitting 40 is assembled and / or manufactured. The barrier 60 may be a thin tube having a wall thickness of approximately 10% of the overall wall thickness of the pipe assembly 20. The barrier 60 extends over the full length of the pipe assembly 20 and in particular extends over the joint 50. Providing a barrier extending over the joint 50, in particular at the radially innermost interface between the pipe 30 and the fitting 40, may reduce the likelihood of fluid within the pipe assembly 20 leaking from the pipe assembly 20 through the joint 50. It is also preferable to provide a barrier 60 comprising a non-permeable material to reduce the likelihood of fluid within the pipe assembly 20 permeating through the barrier 60. The barrier 60 may therefore comprise a metallic material such as Invar, stainless steel (304L or 316L), gold, aluminium or copper. To improve ease of manufacture of the pipe assembly 20, the barrier 60 may be manufactured from the same metallic material as the fitting 40. This may allow the fitting 40 to be secured to the barrier 60 (for example by friction stir welding) more easily.

[0080] The pipe assembly 20 may further comprise a flange fitting 70 as shown in Figures 8 and 9 to provide means for connecting the pipe assembly 20 to external components. Examples of external components may include further pipe assemblies 20 and aircraft structures such as ribs or spars. The flange fitting 70 comprises a body 72 connected to the fitting 40 and an annular flange 74 extending outwardly from the body 72. The flange 74 may have apertures or other features (not shown) for connecting the flange 74 to external components. The metal body 42 is coupled to the body 72 of the flange fitting, for example by weld beads 76a, 76b shown in Figures 8 and 9. It may be preferable to provide a flange fitting 70 comprising the same metallic material as the metal body 42.

[0081] Figure 8 shows a first example of a pipe assembly 20 comprising a barrier 60 and a flange fitting 70. The body 72 extends into the fitting 40, in contact with the inner surface of the barrier 60. In further examples (not shown) the pipe assembly 20 does not comprise a barrier 60 and the body 72 contacts an interior surface of the fitting 40. It is preferable to terminate the body 72 of the flange fitting prior to the joint 50 so that the body 72 can be connected to the fitting 40 (for example by welding) without affecting the joint 50 and / or the pipe 30.

[0082] In the example shown in Figure 8, an axial end surface of the body 72 is welded to an inner surface of the barrier 60 by a weld bead 76a, and an axial end surface of the fitting 40 is welded to an outer surface of the body 72 by a weld bead 76b. As well as increasing the strength of the connection, welding with two weld beads 76a,b may reduce the likelihood of fluid within the pipe assembly 20 leaking through the interface between the flange fitting 70 and the fitting 40 since each weld bead 76a,b provides a non-permeable barrier.

[0083] Figure 9 shows a further example of a pipe assembly 20 comprising a barrier 60 and a flange fitting 70. The barrier 60 extends continuously over substantially the entire length of the pipe assembly 20, and lines an interior of the pipe 30, the fitting 40 and the flange fitting 70. Covering each of the interfaces between the flange fitting 70, the fitting 40 and the pipe 30 may reduce the likelihood of fluid in the pipe assembly 20 leaking through these interfaces. In the example shown, the body 72 extends into and is secured to an end surface of the metal body 42 by a weld bead 76b.

[0084] Figures 10A to 10G show a method of manufacturing a pipe assembly 20 comprising a barrier 60. Each figure shows a cross-sectional view of one end of the pipe assembly 20 in a partially assembled state about a mandrel 100

[0085] Figure 10A shows a first step in the method, in which the barrier 60 is slid onto the mandrel 100. The barrier 60 forms the radially innermost portion of the pipe assembly 20 as described earlier, and hence subsequent layers of material are assembled over the barrier layer 60.

[0086] Figure 10B shows a second step in the method, where a first metal core layer 42a is positioned on the barrier 60. The metal core layer 42a is slid onto a first end of the barrier 60 in an axial direction indicated by the arrows.

[0087] Figure 10C shows a third step in the method, where a first composite connection layer 32b is added to the barrier 60. In the example shown, the composite connection layer 32b is deposited by winding a line 112 of fibre-reinforced material onto the mandrel 100 from a winding tool 110. The line 112 of fibre-reinforced material may comprise a filament, tow or tape of fibres pre-impregnated with a resin, which is then cured once all the composite layers are wound onto the mandrel to solidify the fibre-reinforced material and co-bond it to the metal parts.

[0088] Figure 10D shows a fourth step in the method, where a first metal connection layer 42b is assembled onto the first metal core layer 42a. The metal connection layer 42b has a greater diameter than the metal core layer 42a such that the metal connection layer 42b passes over and contacts the first metal core layer 42a. The metal connection layer 42b is slid onto the first end of the mandrel 100 in an axial direction indicated by the arrows.

[0089] Figure 10E shows a fifth step in the method, where a first composite core layer 32a is assembled onto the first composite connection layer 32b. The fourth step is similar to the third step (shown in Figure 10C) and comprises winding fibre-reinforced material onto the partially assembled pipe assembly.

[0090] In this way, the composite collars 34 and the metal collars 44 are alternately added to interleave them at the joint 50. These steps may be repeated as shown in Figures 10F and lOGto increase the number of interleaved collars 34, 44 until a required number of collars and / or pipe wall thickness is achieved.

[0091] Once all the composite layers 32a, 32b are assembled, the pipe 30 is cured to cocure the composite layers together and co-bond them to the fitting 40 and the barrier 60. Once all the metal layers 42a, 42b are assembled, the metal layers may be welded together, for example by friction stir welding, so they coalesce to form a continuous part. This welding process may also be used to weld the fitting 40 to the barrier 60.

[0092] In this example the composite layers 32a, 32b are added by winding a line 112 of pre-impregnated fibre-reinforced composite material onto the mandrel 100. In other embodiments the composite layers 32a, 32b may be added by winding dry-fibre material onto the mandrel 100 and then infusing the dry-fibre material with a matrix (such as a resin) after all of the dry-fibre layers have been added.

[0093] The pipe assembly described above is intended for use in a hydrogen fuel application, but in other embodiments the pipe assembly may be configured to carry kerosene or any other fluid material.

[0094] Where the word 'or' appears this is to be construed to mean 'and / or' such that items referred to are not necessarily mutually exclusive and may be used in any appropriate combination.

[0095] Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.

Claims

1. A pipe assembly comprising: a pipe comprising a composite body and a plurality of coaxial nested composite collars which protrude from an end of the composite body, wherein the composite body and the composite collars comprise fibre-reinforced composite material; a fitting comprising a metal body and a plurality of coaxial nested metal collars which protrude from the metal body, wherein the metal body and the metal collars comprise metallic material; and a joint connecting the pipe to the fitting, wherein the composite collars are interleaved with and bonded to the metal collars at the joint.

2. A pipe assembly according to claim 1, wherein the composite body comprises a plurality of composite core layers which are interleaved with a plurality of composite connection layers; the composite core layers and the composite connection layers comprise a fibre-reinforced composite material; and the composite connection layers extend beyond the composite core layers to form the composite collars.

3. A pipe assembly according to claim 2, wherein the composite core layers abut the metal collars.

4. A pipe assembly according to any preceding claim, wherein the metal body comprises a plurality of metal core layers which are interleaved with a plurality of metal connection layers; the metal core layers and the metal connection layers comprise metallic material; and the metal connection layers extend beyond the metal core layers to form the metal collars.

5. A pipe assembly according to claim 4, wherein the metal core layers abut the composite collars.

6. A pipe assembly according to any preceding claim, further comprising a continuous barrier which lines an interior of the composite body and an interior of the metal body.

7. A pipe assembly according to claim 6, wherein the barrier comprises a metallic material.

8. A pipe assembly according to claim 6 or 7, wherein the barrier contacts an interior of the composite body.

9. A pipe assembly according to any of claims 6 to 8, wherein the barrier contacts an interior of the metal body.

10. A pipe assembly according to any preceding claim, further comprising liquid hydrogen contained within the pipe assembly.

11. A pipe assembly according to any preceding claim, wherein the composite body and the composite collars comprise the same fibre-reinforced composite material.

12. A pipe assembly according to any preceding claim, wherein the metal body and the metal collars comprise the same metallic material.

13. A pipe assembly according to any preceding claim, further comprising a flange fitting comprising a body and a flange extending outwardly from the body, wherein the metal body is coupled to the body of the flange fitting.

14. A pipe assembly according to claim 13, wherein an axial end surface of the body is welded to a radially inner surface of the metal body; and an axial end surface of the metal body is welded to a radial outer surface of the body.

15. A pipe assembly according to claim 14 when dependent on any of claims 6 to 9, wherein the barrier lines an interior of the body of the fitting.

16. A pipe assembly according to any preceding claim, wherein the composite collars and the metal collars are cylindrical.

17. An aircraft comprising the pipe assembly of any preceding claim.

18. A method of manufacturing a pipe assembly according to any of claims 1 to 16, the method comprising alternately adding the composite collars and the metal collars to interleave them at the joint, and curing the composite collars to co-bond them to the metal collars.

19. A method according to claim 18, wherein each composite collar is added by winding.

20. A method according to claim 17 or 18, wherein each metal collar is added by being slid into place.

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