Manufacture of Pipe-in-Pipe Assemblies

Abstract

A pipe-in-pipe assembly comprises a bundled infill structure occupying an annulus between inner and outer pipes (12, 26) of the assembly. The infill structure is formed of a plurality of elongate elements laid along the inner pipe comprising a mixture of reinforcing elements (16B) and insulating elements (16A). The reinforcing elements have greater mechanical resistance than the insulating elements to radial compression whereas the insulating elements provide greater thermal insulation than the reinforcing elements. Pluralities of the reinforcing elements are positioned together within the infill structure to form reinforcing formations, such as spacer formations, embedded between insulating regions of the infill structure that are defined by pluralities of the insulating elements.

Claims

1. A pipe-in-pipe assembly, comprising: a bundled infill structure occupying an annulus between inner and outer pipes of the assembly, the infill structure being formed of a plurality of elongate elements laid along the inner pipe; wherein the elongate elements of the infill structure comprise a mixture of reinforcing elements and insulating elements, the reinforcing elements having greater mechanical resistance than the insulating elements to radial compression whereas the insulating elements provide greater thermal insulation than the reinforcing elements; and pluralities of the reinforcing elements are positioned together within the infill structure to form reinforcing formations that are circumferentially embedded between insulating regions of the infill structure defined by pluralities of the insulating elements.

2. The assembly of claim 1, wherein the infill structure comprises layers of the elongate elements laid on the inner pipe in radially-outward succession.

3. The assembly of claim 2, wherein the elongate elements of each layer are angularly staggered relative to the elongate elements of each neighbouring layer.

4. The assembly of claim 2 or claim 3, wherein the reinforcing formations incorporate fewer reinforcing elements in successive layers to taper in a radially outward direction.

5. The assembly of any preceding claim, wherein the reinforcing formations are spacer formations that are angularly spaced around the inner pipe and that extend radially from the inner pipe toward the outer pipe.

6. The assembly of claim 5, wherein the spacer formations each comprise a combination of the reinforcing elements and the insulating elements.

7. The assembly of any preceding claim, wherein the elongate elements of the infill structure further comprise one or more auxiliary elements whose primary purpose is to heat the inner pipe or to convey electrical current or data along the assembly.

8. The assembly of claim 7, wherein one or more of the auxiliary elements is a heating element that is in thermal contact with the inner pipe and is surrounded by insulating elements of the infill structure.

9. The assembly of claim 7 or claim 8, wherein one or more of the auxiliary elements is a data cable that is separated from the inner pipe and from any heating element by at least one insulating element or reinforcing element of the infill structure.

10. The assembly of any preceding claim, wherein the elongate elements lie on mutually parallel paths.

11. The assembly of any preceding claim, wherein the elongate elements lie on helical paths.

12. The assembly of any preceding claim, wherein the elongate elements comprise groups of elements braided, knitted, wrapped, twisted, bonded or fused together.

13. The assembly of any preceding claim, wherein the reinforcing elements comprise tubes or rods.

14. The assembly of any preceding claim, wherein the insulating elements comprise: hollow tubes; tubes filled with thermally insulating material; solid rods of thermally insulating material; or elements of a fibrous thermally insulating material.

15. The assembly of claim 14, wherein the reinforcing elements and the insulating elements are both tubular and the tubes of the insulating elements have thinner walls than the tubes of the reinforcing elements.

16. The assembly of any preceding claim, wherein the elongate elements of the infill structure are all of substantially the same diameter.

17. The assembly of any of claims 1 to 15, wherein the elongate elements of the infill structure increase in diameter in a radially-outward direction.

18. The assembly of any preceding claim, wherein the reinforcing formations extend through a full radial thickness of the infill structure.

19. The assembly of any preceding claim, comprising a circumferentially-continuous radial gap between the infill structure and the outer pipe.

20. A method of manufacturing a pipe-in-pipe assembly, the method comprising: forming a bundled infill structure around an inner pipe of the assembly by laying a plurality of elongate elements along the inner pipe; and inserting the inner pipe and the infill structure into an outer pipe of the assembly, the infill structure then occupying an annulus defined between the inner and outer pipes; wherein the elongate elements of the infill structure comprise a mixture of reinforcing elements and insulating elements, the reinforcing elements having greater mechanical resistance than the insulating elements to radial compression whereas the insulating elements provide greater thermal insulation than the reinforcing elements; and the reinforcing elements are placed together within the infill structure to form reinforcing formations, each of those formations comprising a plurality of the reinforcing elements and being circumferentially embedded between insulating regions of the infill structure defined by pluralities of the insulating elements.

21. The method of claim 20, wherein the infill structure comprises layers of the elongate elements laid on the inner pipe in radially-outward succession.

22. The method of claim 21, wherein the reinforcing formations are tapered in a radially outward direction by incorporating fewer reinforcing elements in successive layers.

23. The method of any of claims 20 to 22, wherein the reinforcing formations are spacer formations that are angularly spaced around the inner pipe and that extend radially from the inner pipe toward the outer pipe.

24. The method of any of claims 20 to 23, wherein the elongate elements of the infill structure further comprise one or more auxiliary elements whose primary purpose is to heat the inner pipe or to convey electrical current or data along the assembly.

25. The method of claim 24, comprising laying at least one heating element in thermal contact with the inner pipe and laying insulating elements over and surrounding the at least one heating element.

26. The method of claim 24 or claim 25, comprising laying at least one data cable on at least one inner layer of elongate elements disposed between the data cable and the inner pipe.

27. The method of any of claims 20 to 26, comprising laying the elongate elements on parallel paths.

28. The method of any of claims 20 to 27, comprising laying the elongate elements on helical paths.

29. The method of any of claims 20 to 28, comprising laying the elongate elements on the inner pipe dispensed from at least one reel of a winding machine.

30. The method of claim 29, comprising laying the elongate elements successively on the inner pipe at positions spaced longitudinally along the inner pipe.

31. The method of claim 29, comprising laying a plurality of the elongate elements grouped together at a common longitudinal position on the inner pipe.

32. The method of claim 31, wherein the elongate elements are grouped by convergence from respective reels to the common longitudinal position on the inner pipe.

33. The method of claim 31, wherein the elongate elements are grouped before being conveyed together to the inner pipe as a group.

34. The method of any preceding claim, comprising compacting the infill structure by heating and/or radially-inward compression before inserting the inner pipe and the infill structure into the outer pipe.

Description

[0047] In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings in which:

[0048] FIG. 1 is a schematic side view of a pipeline production facility operating in accordance with the invention, showing winding modules on a first rotating support of a winding machine placing a first layer of elongate elements onto an inner pipeline of a PiP assembly;

[0049] FIG. 2 corresponds to FIG. 1 but shows winding modules on a second rotating support placing a second layer of elongate elements onto the inner pipeline, around the first layer, before the inner pipeline is inserted into an outer pipeline of the PiP assembly;

[0050] FIG. 3 is a schematic side view showing multiple winding modules on the same rotating support placing a corresponding number of layers of elongate elements onto an inner pipeline simultaneously;

[0051] FIG. 4 is a schematic side view showing elongate elements being grouped before a winding module on a rotating support places the group of elongate elements onto an inner pipeline;

[0052] FIG. 5 is a schematic side view showing winding modules on multiple longitudinally-spaced rotating supports placing respective elongate elements onto an inner pipeline in successive layers, followed by compaction of the layers;

[0053] FIGS. 6a and 6b are schematic cross-sectional detail views through layered elements before and after compaction;

[0054] FIG. 7 is a schematic partial cross-sectional view through a PiP assembly of the invention; and

[0055] FIG. 8 is a schematic cross-sectional detail view showing various layered elements that may be placed on the inner pipe of a PiP assembly of the invention.

[0056] FIGS. 1 and 2, in which like numerals are used for like features, show a pipeline manufacturing facility 10, such as a coastal spoolbase, in which an inner pipeline 12 of a PiP assembly is shown advancing longitudinally from left to right through a winding machine 14. The pipeline 12 is typically fabricated by welding together a succession of steel pipe joints at an upstream location within the facility 10, not shown.

[0057] When the pipeline 12 reaches the winding machine 14 shown in FIGS. 1 and 2, elongate elements 16 are unspooled from reels 18 of respective winding modules and then are guided by respective guides 20 onto the outer surface of the pipeline 12 as the pipeline 12 continues to advance. There, the elements 16 may optionally be fixed in place by circumferential straps or other conventional fixings, not shown.

[0058] FIG. 1 shows a first layer of elements 16 being placed onto the pipeline 12. FIG. 2 shows a second layer of elements 16 being placed onto the pipeline 12 around, or on top of, the first layer of elements 16.

[0059] FIG. 1 shows, schematically, a rotating support 22 of the winding machine 14 that turns about the central longitudinal axis 24 of the pipeline 12 as the pipeline 12 advances through the winding machine 14. The support 22 carries the reels 18 of the winding modules in a circumferential array, equi-angularly spaced around the central longitudinal axis 24.

[0060] In this example, each reel 18 is tilted relative to the central longitudinal axis 24 so that the elements 16 of the first layer are wound onto the pipeline 12 in a helical arrangement, spiralling around the central longitudinal axis 24. In other examples, as noted previously, the elements 16 could follow wavy paths such as an S-Z pattern, or straight paths that are parallel to the central longitudinal axis 24 and to each other.

[0061] For simplicity of illustration, only eight reels 18 and their associated elements 16 are shown in this example, three of which are hidden behind the pipeline 12 and behind the five reels 18 that are visible in this view. In practice, there will be several more reels 18 and elements 16 so that the angular spacing between neighbouring elements 16 of the first layer is substantially less than is shown here. Indeed, preferably, there is substantially no angular spacing between neighbouring elements 16 of the first layer when they are placed on the pipeline 12.

[0062] FIG. 2 shows a second rotating support 22 of the winding machine 14 that turns about the central longitudinal axis 24 in the same direction as the first support 22 as the pipeline 12 advances through the winding machine 14. The second support 22 carries the reels 18 of additional winding modules in a circumferential array, also equi-angularly spaced around the central longitudinal axis 24. The reels 18 and their associated guides 20 place the elements 16 of the second layer onto the previously-laid first layer of elements 16 in a corresponding helical arrangement.

[0063] In principle, it would be possible for the elements 16 unspooled from the reels 18 of the second rotating support 22 to be interleaved between, rather than placed on top of, elements 16 previously placed from the reels 18 of the first rotating support 22. Thus, the second rotating support 22 could be used to infill any circumferential gaps that may remain between elements 16 of the first layer previously dispensed from the reels 18 of the first rotating support 22. In other words, the second rotating support 22 could be used to complete the first layer of elements 16 rather than initiating or placing a second layer of elements 16.

[0064] More generally, a succession of rotating supports 22, each carrying reels 18 of elongate elements 16, may be used to complete or to place each layer of elements 16 on the pipeline 12 until the desired number of layers, each with the desired density of elements 16, has been achieved.

[0065] In FIG. 2, the pipeline 12 carrying layers of elements 16 is shown being inserted telescopically into the outer pipe 26 of a PiP assembly. The outer pipe 26 may, for example, be more than 1.5 km long as part of a pipe stalk that will form part of a reel-laid pipeline.

[0066] FIGS. 3 to 5 show other ways of placing layers or groups of elongate elements 16 onto a pipeline 12. For simplicity, the elements 16 are shown in these drawings as following a straight path that is parallel to the longitudinal direction in which the pipeline 12 is advanced. However, a helical or otherwise curved path is possible instead, as described and illustrated above. In these examples, three layers are shown but additional layers or other groupings would be possible.

[0067] FIG. 3 shows that it is possible to place layered elements 16 onto the pipeline 12 simultaneously. In this example, this is achieved by directing the elements 16 from respective reels 18 of a common support 22 on convergent paths to guides 20 that apply the elements 16 to the pipeline 12 at a common longitudinal position, stacked in a layered arrangement.

[0068] FIG. 4 shows that separate elements 16 can be aggregated to form a group before the grouped elements are spooled together onto a reel 18 of a support 22. The grouped elements 16 are then dispensed together from the reel 18 and placed onto the pipeline 12 together via a common guide 20. The group of elements 16 may be thick enough, or may contain enough layers of elements 16, substantially to fill the annulus of a PiP assembly that comprises the pipeline 12.

[0069] As one example, the separate elements 16 can be aggregated by being braided together in a braiding machine 28 upstream of the reel 18. Thus, a braiding machine 28 is an example of an aggregating apparatus for bringing together separate elements 16 and joining them to form a group. More generally, the elements 16 can be knitted or twisted together, bundled, bonded, fused or wrapped by an aggregating apparatus to form a layered or non-layered group. The group of elements 16 remains flexible enough to be bent or twisted along its length while being guided to the pipeline 12, optionally via intermediate storage such as the reel 18, without buckling, crushing or otherwise damaging the elements 16.

[0070] The arrangement shown in FIG. 5 is akin to that shown in FIG. 2 in that layers of elements 16, from respective reels 18 on respective supports 22, are built up sequentially. The elements 16 are applied to the pipeline 12 and then to previously-placed layers of elements 16 at locations spaced longitudinally along the pipeline 12. In this example, however, the pipeline 12 carrying the layered elements 16 then passes through a compacting apparatus 30.

[0071] The compacting apparatus 30 may comprise a die that narrows in the direction of travel of the pipeline 12 to deform the cross-section of the elements 16 plastically and/or a heater that softens or melts at least an outer part of each element 16.

[0072] The effect of the compacting apparatus 30 is shown schematically in the before-and-after drawings of FIGS. 6a and 6b. Its effect is to deform, radially compact and circumferentially spread the elements 16, hence packing them together closely into more intimate contact with each other to forming a thinner and denser agglomeration.

[0073] Compacting may of course be applied in other manufacturing arrangements, such as those described with reference to the preceding drawings.

[0074] An advantage of the invention is the ability to manufacture and install a complete infill structure for a PiP annulus in a continuous automated process, as exemplified above. The infill structure of the invention satisfies all functional requirements that would conventionally require separate thermal insulation and spacers, in particular, thermal management and resistance to radial compression. The infill structure of the invention also satisfies the requirement to locate auxiliary elements such as heating wires or fibre-optic cables within the annulus.

[0075] The invention achieves these objectives by selecting different types of elongate elements 16 to be laid in a mixed bundle of parallel elements 16 and combining and positioning those elements 16 within the infill structure appropriately. FIGS. 7 and 8 illustrate some of the possibilities of this approach.

[0076] In FIG. 7, a PiP assembly 32 of the invention comprises an inner pipe 12 spaced concentrically within an outer pipe 26, defining an annulus 34 between them. The annulus 34 contains an infill structure of the invention that comprises concentric layers, in this example four layers, containing various types of elongate elements 16.

[0077] Optionally, as shown, the outermost layer of elements 16 is spaced radially inwardly from the inner side of the outer pipe 26, leaving a radial, circumferentially-continuous gap 36 that interrupts conductive transmission of heat through the annulus 34. The inner side of the outer pipe 26 also has an optional low-friction coating 38 to ease insertion of the inner pipe 12 and the elements 16 into the outer pipe 26.

[0078] In this example, neighbouring layers of elements 16 are mutually staggered circumferentially, thus aligning or nesting each element 16 of one layer angularly between elements 16 of the next layer. This enables successive layers to interlock for increased rigidity. Also, the elements 16 increase slightly in diameter from layer to layer in radially outward sequence so that the elements 16 of all layers can bear against their neighbouring elements 16 in each layer without circumferential gaps between them.

[0079] Most of the elements 16 of the infill structure are primarily thermally insulating in their material(s) and/or their structure. Those insulating elements are designated 16A in FIG. 7. In several circumferential locations, the insulating elements 16A are stacked radially from the inner pipe 12 toward the outer pipe 26 through all layers of the infill structure. The stacked insulating elements 16A together form insulating regions 40 around the inner pipe 12.

[0080] Some of the elements 16 of the infill structure are primarily mechanically resistant in their material(s) and/or their structure, at least with respect to radial compression. Those mechanically resistant, reinforcing elements are designated 16B in FIG. 7.

[0081] It will be apparent from FIG. 7 that the reinforcing elements 16B are grouped together in circumferential alignment to form discrete reinforcing formations, specifically spacer formations 42, that extend radially from the inner pipe 12 toward the outer pipe 26 through all layers of the infill structure. The spacer formations 42 are angularly spaced around the annulus 34, in this example at 60 intervals. The spacer formations 42 are stabilised by the abutment of the reinforcing elements 16B with the adjoining insulating elements 16A, hence being embedded by or between the insulating regions 40.

[0082] In the example shown in FIG. 7, the spacer formations 42 taper radially outwardly to form a stable structure that minimises the heat transmission path through the annulus 34. This taper can be achieved by reducing the number of reinforcing elements 16B moving outwardly through each spacer formation 38 from one layer to the next, here reducing from five such elements 16B in the innermost layer to two such elements 16B in the outermost layer.

[0083] The example shown in FIG. 7 also comprises auxiliary elements 16, in this case heating wires 16C and fibre-optic cables 16D.

[0084] The heating wires 16C are grouped at equi-spaced angular locations within the insulating regions 40, alternating with the spacer formations 42. The heating wires 16C are part of the innermost layer of elements 16, hence being in thermal contact with the inner pipe 12. They are buried under one or more surrounding outer layers of insulating elements 16A.

[0085] The fibre-optic cables 16D are positioned in an intermediate layer of the infill structure within the insulating regions 40, the better to sense conditions in the body of the annulus 34. To the benefit of thermal isolation, the fibre-optic cables 16D are also separated from the heating cables 16C, and from the heated inner pipe 12, by at least one insulating element 16A or by at least one layer of such elements 16A.

[0086] The fibre-optic cables 16D are also equi-angularly spaced around the infill structure within the annulus 34, although this spacing is not essential. Also, some or all of the fibre-optic cables 16D could be replaced with other auxiliary elements 16 such as power cables or even fluid conduits.

[0087] In a variant of the arrangement shown in FIG. 7, mechanically-reinforcing elements 16B could be positioned immediately adjacent to the heating wires 16C and/or the fibre-optic cables 16D to protect them and/or the thermally insulating elements 16A locally, depending on the materials and future operational utilisations of the PiP assembly 32 and the heating cables 16C.

[0088] Turning finally to FIG. 8, four mutually-staggered and hence interlocked layers of elements 16 are also shown in this example, like the arrangement in FIG. 7. However in this case, as in FIG. 6a, the elements 16 are all of substantially equal diameter. Consequently, there are increasing circumferential gaps between the elements 16 of the second to fourth layers in radially outward sequence. However, the elements 16 of the first, innermost layer abut their neighbouring elements 16 in that layer. Also, in arrangements where the neighbouring layers are not staggered, elements 16 of equal diameter could abut their neighbouring elements 16 in all layers if the number of elements in outer layers is increased to close circumferential gaps between them.

[0089] FIG. 8 exemplifies various possible configurations of the thermally insulating elements 16A and the mechanically-resistant reinforcing elements 16B. It does so in the context of a spacer formation 42. In this example, the spacer formation 38 is formed of two types of reinforcing elements 16B, namely thick-walled tubes 1661, which could be made of extruded polymer or metal, and solid rods 1662, which could be made of extruded polymer.

[0090] The insulating elements 16A shown in FIG. 8 are: hollow, gas-filled thin-walled tubes 16A1, which could be made of extruded polymer; thin-walled tubes 16A2, which could also be made of extruded polymer but are filled with thermal insulation material such as an aerogel; solid rods 16A3 of thermally insulating material such as a polymer foam; and elements 16A4 of a fibrous thermally insulating material such as a braid, a yarn or a rope.

[0091] FIG. 8 also shows the possibility that a spacer formation 42 could be formed of a hybrid or mixture of insulating elements 16A and reinforcing elements 16B. Here, a core of insulating elements 16A1 lies within an outer wall of reinforcing elements 16B1 and 16132, further to restrict heat transfer across the annulus 34.

[0092] Many other variations are possible within the inventive concept. For example, relative rotational movement between the pipeline 12 and the reels 18 of the winding machine 14 could instead, or additionally, be effected by turning the pipeline 12 about the central longitudinal axis 24.

[0093] Whilst, in the above examples, the pipeline 12 moves past stationary equipment comprising the reels 18, guides 20 and supports 22, it would be possible instead for that equipment to move past a stationary pipeline 12. Similarly, it would be possible for the outer pipe 26 of a PiP arrangement to be advanced over a stationary pipeline 12, or to be assembled around the pipeline 12.