FABRICATING PIPE-IN-PIPE (PIP) PIPELINES

Abstract

Apparatus for assembling a pipe-in-pipe pipeline comprises a primary support system, such as an array of rollers, for supporting an outer pipe section and a secondary support system, such as a set of rails, for supporting an inner pipe section. The primary support system supports the outer pipe section centred on a longitudinal axis in common with a trailing end of a partially-completed pipeline. The secondary support system is deployed to support the inner pipe section also centred on that common axis, enabling the inner pipe section to be advanced and welded to an inner pipe of the partially-completed pipeline. The secondary support system is then retracted to advance the outer pipe section, supported by the primary support system, around the inner pipe section. This enables the outer pipe section to be welded to an outer pipe of the partially-completed pipeline.

Claims

1. A method of assembling a pipe-in-pipe pipeline by adding a succession of inner and outer pipe sections to a trailing end of the partially-completed pipeline, the method comprising: welding a leading end of a first inner pipe section to a trailing end of an inner pipe of the partially-completed pipeline; advancing a leading end of a second inner pipe section to a trailing end of the first inner pipe section; advancing an outer pipe section downstream from the second inner pipe section along and around the first inner pipe section and into abutment with a trailing end of an outer pipe of the partially-completed pipeline; and welding a leading end of the outer pipe section to the trailing end of the outer pipe.

2. The method of claim 1, comprising welding the leading end of the second inner pipe section to the trailing end of the first inner pipe section before advancing the outer pipe section onto the first inner pipe section.

3. The method of claim 2, comprising simultaneously welding the first inner pipe section to the inner pipe of the partially-completed pipeline and to the second inner pipe section.

4. The method of any preceding claim, comprising providing the outer pipe section and the second inner pipe section in concentric relation as a pipe-in-pipe pipe joint.

5. The method of any preceding claim, comprising supporting the advancing pipe sections when centred on a longitudinal axis in common with that of the trailing end of the partially-completed pipeline.

6. The method of claim 5, comprising deploying a secondary support system to support the first inner pipe section centred on said axis while advancing and welding the first inner pipe section to the inner pipe.

7. The method of claim 6, comprising retracting the secondary support system before advancing the outer pipe section, supported by a primary support system, around the first inner pipe section.

8. A method of assembling a pipe-in-pipe pipeline by adding inner and outer pipe sections to a trailing end of the partially-completed pipeline, the method comprising: using a primary support system to support an outer pipe section centred on a longitudinal axis in common with the trailing end of the partially-completed pipeline; deploying a secondary support system to support a first inner pipe section centred on said axis; while supported by the deployed secondary support system, advancing and welding the first inner pipe section to an inner pipe of the partially-completed pipeline; retracting the secondary support system; and while supported by the primary support system, advancing the outer pipe section around the first inner pipe section and welding the outer pipe section to an outer pipe of the partially-completed pipeline.

9. The method of claim 8, wherein after the secondary support system has been retracted, the outer pipe section supports the first inner pipe section centred on said axis.

10. The method of claim 8 or claim 9, further comprising redeploying the secondary support system behind the advanced outer pipe section and supporting a second inner pipe section on the deployed secondary support system, also centred on said axis.

11. The method of claim 10, comprising advancing the second inner pipe section, while supported by the deployed secondary support system, into abutment with the first inner pipe section.

12. The method of claim 10 or claim 11, comprising advancing the outer pipe section from around the second inner pipe section and onto the first inner pipe section.

13. The method of any of claims 7 to 12, wherein the primary support system contacts the outer pipe section at a first level and, when deployed, the secondary support system contacts the first inner pipe section at a second level above the first level.

14. The method of any of claims 7 to 13, wherein retraction of the secondary support system away from the first inner pipe section provides access for the outer pipe section to contact and be supported by the primary support system.

15. The method of claim 14, wherein the secondary support system comprises support formations that, during retraction, splay apart from each other in opposed lateral directions to define a gap that accommodates the outer pipe section between them.

16. The method of any of claims 7 to 15, comprising operating a longitudinal series of secondary support systems independently of each other for individual deployment and retraction in response to longitudinal movement of any of the pipe sections.

17. The method of any preceding claim, comprising advancing the outer pipe section along at least a full length of the first inner pipe section.

18. The method of any preceding claim, wherein: the outer pipe section is welded to the outer pipe at a downstream workstation; and the second inner pipe section is welded to the first inner pipe section at an upstream workstation.

19. The method of claim 18, wherein the first inner pipe section is welded to the inner pipe at an intermediate workstation.

20. The method of any preceding claim, comprising advancing the first inner pipe section when unsupported by the outer pipe section.

21. The method of any preceding claim, wherein the outer pipe section supports the first inner pipe section via at least one spacer in an annulus between those pipe sections.

22. The method of claim 21, comprising mounting the or each spacer to the first inner pipe section before advancing the outer pipe section over the or each spacer.

23. The method of any of claims 1 to 21, comprising advancing the outer pipe section as the or each spacer, disposed within and moving with the outer pipe section, slides over the first inner pipe section.

24. The method of any preceding claim, when performed aboard a pipelaying vessel during an S-lay operation.

25. Apparatus for assembling a pipe-in-pipe pipeline, the apparatus comprising a primary support system for supporting an outer pipe section and a secondary support system for supporting an inner pipe section, wherein: the primary support system is arranged to support the outer pipe section centred on a longitudinal axis in common with a trailing end of a partially-completed pipeline; the secondary support system is deployable to support the inner pipe section also centred on said axis, to enable the inner pipe section to be advanced and welded to an inner pipe of the partially-completed pipeline; and the secondary support system is retractable to advance the outer pipe section around the inner pipe section to enable the outer pipe section, when supported by the primary support system, to be welded to an outer pipe of the partially-completed pipeline.

26. The apparatus of claim 25, wherein the primary support system comprises at least one roller box or support table.

27. The apparatus of claim 25 or claim 26, wherein the secondary support system is mounted on the primary pipe support system.

28. The apparatus of any of claims 25 to 27, wherein the primary support system is configured to contact the outer pipe section at a first level and the secondary support system is configured, when deployed, to contact the first inner pipe section at a second level above the first level.

29. The apparatus of any of claims 25 to 28, wherein the secondary support system comprises laterally-displaceable support formations that, when deployed to respective inward positions, together define an axial path for guiding the advance of the inner pipe section.

30. The apparatus of claim 29, wherein the support formations are longitudinally-extending parallel rails.

31. The apparatus of claim 29 or claim 30, wherein the support formations, when retracted in opposite lateral directions to respective outward positions, define a gap between them to provide access for the outer pipe section to contact and be supported by the primary support system.

32. The apparatus of any of claims 29 to 31, wherein the support formations are pivotable about respective axes extending substantially parallel to the common longitudinal axis.

33. The apparatus of any of claims 25 to 32 and comprising a longitudinal series of secondary support systems, each of those systems being operable independently for individual deployment and retraction.

34. The apparatus of any of claims 25 to 33, wherein the primary support system is retractable away from the common axis to permit deployment of the secondary support system.

35. A pipelaying vessel configured for S-lay operation, comprising the apparatus of any of claims 25 to 34.

Description

[0052] In order that the invention may be more readily understood, reference will now be made, by way of example, to the remainder of the accompanying drawings, in which:

[0053] FIG. 2 is a schematic cross-sectional view of a PiP assembly;

[0054] FIGS. 3a and 3b are schematic cross-sectional views that, respectively, show the outer and inner pipes of the PiP assembly of FIG. 2 being supported in accordance with the invention;

[0055] FIGS. 4a to 4c are schematic cross-sectional views that show options for relative movement between outer and inner pipe supports and the PiP assembly of FIG. 2;

[0056] FIGS. 5a to 5h are a sequence of schematic side views of the firing line of an S-lay vessel when fabricating a PiP pipeline in accordance with the invention;

[0057] FIGS. 6a and 6b are a sequence of schematic side views that show a variant of the technique shown in FIGS. 5a to 5h;

[0058] FIG. 7 is a perspective view of an S-lay firing line apparatus of the invention;

[0059] FIG. 8 is a perspective view of a roller box of the invention, being part of the firing line apparatus shown in FIG. 7, when in a first operating mode configured to support the inner pipe of a PiP assembly;

[0060] FIG. 9 is a top plan view of the roller box of FIG. 8 when in the first operating mode;

[0061] FIG. 10 is an end view of the roller box of FIG. 8 when in the first operating mode;

[0062] FIG. 11 is a top plan view of the roller box of FIG. 8 when in a second operating mode configured to support the outer pipe of a PiP assembly; and

[0063] FIG. 12 is an end view of the roller box of FIG. 8 when in the second operating mode.

[0064] Where appropriate, like numerals are used for like features in the description that follows.

[0065] Referring firstly to FIGS. 2 to 4c, FIG. 2 shows a pipe joint 14 comprising concentric inner and outer pipes 18, 20 of substantially the same length as each other. The inner and outer pipes 18, 20 are coaxial, being rotationally symmetrical about a common central longitudinal axis 36.

[0066] The inner pipe 18 has an external diameter that is substantially smaller than the internal diameter of the outer pipe 20. Thus, the inner and outer pipes 18, 20 are separated by an annulus 22 and, in particular, by a spacer 24 that is disposed in the annulus 22.

[0067] FIG. 3a shows a primary support system comprising paired cylindrical rollers 38 that are arranged to support the outer pipe 20. A longitudinal succession of such paired rollers 38 extends along and under the outer pipe 20. The rollers 38 turn about respective axes of rotation 40 that lie in a plane orthogonal to the central longitudinal axis 36, such that there is rolling contact between the rollers 38 and the outer pipe 20 in the longitudinal direction. As is conventional, the axes 40 of the rollers 38 converge downwardly so that the oppositely-inclined rollers 38 cradle the underside of the outer pipe 20. This keeps the outer pipe 20 correctly aligned as it travels along the firing line parallel to the central longitudinal axis 36.

[0068] FIG. 3b shows a secondary support system comprising paired rails 42 that are arranged to support the inner pipe 18 in accordance with the invention. The rails 42 extend parallel to each other and to the central longitudinal axis 36, such that there is sliding contact between the rails 42 and the inner pipe 20. The rails 42 are spaced apart laterally in a horizontal plane to cradle the underside of the inner pipe 18 in the gap between them. This keeps the inner pipe 18 correctly aligned as it travels along the firing line parallel to the central longitudinal axis 36.

[0069] As a comparison between FIGS. 3a and 3b makes clear, the rails 42 contact the inner pipe 18 at a level above the level at which the rollers 38 contact the outer pipe 20. The difference in height between those levels is sufficient for the rails 42 to support the inner pipe 18 in concentric alignment with the outer pipe 20 on their common central longitudinal axis 36, despite the much smaller external diameter of the inner pipe 18. Put another way, the closest point of the rails 42 is nearer, radially and vertically, to the central longitudinal axis 36 than the closest point of the rollers 38.

[0070] The rollers 38 may be part of a roller box or a support table. As will be explained, the rails 42 are apt to be fitted to a roller box or support table that is modified in accordance with the invention. The rails 42 could be replaced by a longitudinal array of rollers or could support such an array of rollers that effect rolling contact with, and axial alignment of, the inner pipe 18. More generally, additional rollers, rails or other guides could bear against the outside of the inner pipe 18 and/or against the outside of the outer pipe 20 to keep those pipes 18, 20 correctly aligned as they travel along the firing line parallel to the central longitudinal axis 36.

[0071] FIG. 3b shows the rails 42 that exemplify the secondary support system deployed in a first operating mode in which the rails 42 are positioned to support the inner pipe 18. However, it will be apparent that the rails 42 lie within the radius of the outer pipe 20 and so have to be moved laterally out of the way to allow clearance for longitudinal movement of the outer pipe 20. In this respect, FIG. 4a shows the outer pipe 20 supported by the rollers 38 in a second operating mode as also shown in FIG. 3a. Here, the rails 42 have been retracted and displaced outwardly relative to the central longitudinal axis 36 to positions outside the external circumference or envelope of the outer pipe 20. Optionally, but conveniently, the retracted rails 42 are also displaced upwardly and outwardly relative to their positions in the first operating mode shown in FIG. 3b.

[0072] In principle, it is possible to move the rails 42 of the secondary support system into the deployed positions of the first operating mode shown in FIG. 3b without moving the rollers 38 of the primary support system relative to the central longitudinal axis 36. However, if there is insufficient clearance for this, provision can be made to retract the primary support system out of the way when deploying the secondary support system. In this respect, FIGS. 4b and 4c show two ways in which the rollers 38 could be retracted to allow clearance for the rails 42 to move from the retracted position shown in FIG. 4a into the deployed position shown in FIG. 3b.

[0073] FIG. 4b shows the rollers 38 pivoted away in opposite directions from their positions in the second operating mode as shown in FIGS. 3a and 4a. Conveniently, each roller 38 could be mounted with a respective one of the rails 42 on a common pivotable chassis, such that swinging the roller 38 out of contact with the outer pipe 20 in the second operating mode also swings the rail 42 into contact with the inner pipe 18 in the first operating mode. The rollers 38 and the rails 42 could, for example, pivot about axes parallel to the central longitudinal axis 36.

[0074] FIG. 4c shows the rollers 38 lowered away from their positions in the second operating mode as shown in FIGS. 3a and 4a, following a downward translational movement of both rollers 38 in unison.

[0075] Whilst FIGS. 3b to 4c all show the rails 42 engaging the outer contour of the inner pipe 18, the rails 42 may, in practice, bear against spacers or centralisers that are mounted on the inner pipe 18. This keeps the rails 42 clear of fragile thermal insulation material that may be wrapped around the inner pipe 18. If there is no risk of damage to thermal insulation, the rails 42 may bear directly against the inner pipe 18 when in the second operating mode. The rails 42 may also be adjustable to different radii relative to the central longitudinal axis 36 when in the second operating mode, also to cater for the presence of spacers or centralisers.

[0076] Turning next to FIGS. 5a to 5h, these drawings illustrate a method of the invention for assembling a sliding PiP pipeline 10 on the firing line 12 of an S-lay vessel, using a secondary support system comprising rails 42 as illustrated in FIGS. 3b to 4c. In this instance, the firing line 12 comprises, in downstream succession, a first workstation 28A, a second workstation 28B and a third workstation 28C. The workstations 28A, 28B, 28C are spaced longitudinally from each other by the length of a pipe joint 14, this being either 12 m or 24 m depending upon whether the pipe joint 14 is a single or double joint.

[0077] Again, the pipeline 10 is assembled and launched in a downstream direction from right to left as the vessel advances from left to right. Thus, a PiP pipe joint 14 shown on the right of the drawings is added to the upper, trailing end of the pipeline 10 and a catenary of the assembled pipeline 10 is shown on the left of the drawings. The catenary is gripped by, and suspended from, tensioners downstream of the location shown in FIGS. 5a to 5h. In this case, however, the tensioners have been omitted from these drawings.

[0078] In FIGS. 5a to 5h, the rails 42 are shown in solid lines when lowered and deployed in the first operating mode as shown in FIGS. 3b, 4b and 4c and in dashed lines when raised and retracted in the second operating mode as shown in FIG. 4a.

[0079] In this example, the secondary support system exemplified by the rails 42 and the primary support system exemplified by the rollers 38 of the roller boxes 26 are structurally connected. In particular, the rails 42 are supported by, and movable relative to, the roller boxes 26. Also, when the rails 42 of neighbouring roller boxes 26 are deployed in the first operating mode, those rails 42 align and cooperate in series to form a substantially continuous track.

[0080] The rails 42 of neighbouring roller boxes 26 can be deployed and retracted independently as required. This allows deployed rails 42 of a roller box 26 to support part of an inner pipe 18 protruding from an outer pipe 20 while that outer pipe 20 is supported by the rollers 38 of a neighbouring roller box 26, whose rails 42 are retracted. When an advancing outer pipe 20 supported by the rollers 38 of one roller box 26 approaches deployed rails 42 of a neighbouring roller box 26, those rails 42 retract before collision to allow the outer pipe 20 to proceed unhindered.

[0081] FIG. 5a shows a discrete intermediate inner pipe 18A supported by deployed rails 42 and being advanced downstream while approaching the upper or upstream end of the pipeline 10, which is supported by roller boxes 26 and held at the second intermediate workstation 28B. FIG. 5a also shows a PiP pipe joint 14 being advanced downstream while approaching the upstream end of the intermediate inner pipe 18A.

[0082] When the downstream or leading end of the intermediate pipe section 18A has been brought into abutment with the trailing end of the inner pipe 18 of the pipeline 10 at the second workstation 28B as shown in FIG. 5b, a welding apparatus 30 forms a circumferential butt weld 32 between them. In this respect, as before, the inner pipe 18 of the pipeline 10 is displaced relative to the outer pipe 20 of the pipeline 10 in the upstream direction to protrude from the upper end of the outer pipe 20. By staggering the upper ends of the inner and outer pipes 18, 20 in this way, the upper end of the inner pipe 18 is accessible for welding.

[0083] Next, with the intermediate inner pipe 18A still supported by the rails 42, the pipe joint 14 is advanced to bring the downstream or leading end of its inner pipe 18 into abutment with the upstream or trailing end of the intermediate inner pipe 18A at the first workstation 28A. A welding apparatus 30 then forms a circumferential butt weld 32 between the intermediate inner pipe 18A and the inner pipe 18 of the pipe joint 14 as also shown in FIG. 5b.

[0084] In principle, it would be possible to form the welds 32 at the first and second workstations 28A, 28B simultaneously with each other and/or with the weld 34 at the third workstation 28C between successive outer pipe sections 20.

[0085] FIG. 5c shows the trailing end of the pipeline 10 now advanced to the third workstation 28C, hence advancing the intermediate inner pipe 18A and the pipe joint 14 with it. The weld 32 between the trailing end of the intermediate inner pipe 18A and the leading end of the pipe joint 14 is therefore now at the second workstation 28B. An additional PiP pipe joint 14A is shown approaching the trailing end of the pipe joint 14, which is now at the first workstation 28A.

[0086] FIG. 5d then shows the optional step of fixing spacers 24 around the intermediate pipe section 18A. Some of the rails 42 supporting the intermediate inner pipe 18A can be retracted, if required, to provide clearance for mounting the spacers 24. The rails 42 can then be deployed radially inwardly to the extent required to bear against the spacers 24. This step can be performed before the abovementioned steps if required; for example, the intermediate pipe section 18A could be provided with spacers 24 at the outset.

[0087] Next, as shown in FIG. 5e, the outer pipe 20 of the pipe joint 14 is advanced in the downstream direction along and around the intermediate inner pipe 18A. The outer pipe 20 of the pipe joint 14 slides over the spacers 24 of the intermediate inner pipe 18A as the rails 42 supporting the intermediate inner pipe 18A are retracted, allowing the rollers 38 of the roller boxes 26 to support the advancing outer pipe 20. FIG. 5f shows the outer pipe 20 of the pipe joint 14 now advanced fully along the intermediate inner pipe 18A into mutual abutment with the outer pipe 20 of the pipeline 10 at the third workstation 28C.

[0088] FIG. 5g shows the additional pipe joint 14A brought into mutual abutment with the trailing end of the pipe joint 14 at the first workstation 28A. A first welding apparatus 30 is shown forming a circumferential butt weld 32 between the inner pipes 18 of the pipe joint 14 and of the additional pipe joint 14A. A second welding apparatus 30 shown at the third workstation 28C forms a circumferential butt weld 34 between the trailing end of the outer pipe of the pipeline 10 and the leading end of the outer pipe 20 of the pipe joint 14. These two welding operations may be performed simultaneously at the workstations 28A, 28C as shown in FIG. 5g. However, in principle, either welding operation could be performed before the other, conveniently first at the third workstation 28C as soon as the outer pipe 20 of the pipe joint 14 has been advanced fully along the intermediate inner pipe 18A.

[0089] Thus extended, the pipeline 10 is advanced by the tensioners to bring the new trailing end of the pipeline 10 to the third workstation 28C as shown in FIG. 5h. The leading and trailing ends of the inner pipe 18 of the pipe joint 14 are now in line with the third and second workstations 28C, 28B respectively. The outer pipe 20 of the additional pipe joint 14A can then be advanced along the inner pipe 18 of the pipe joint 14, as in FIGS. 5e and 5f, to be welded to the outer pipe 20 at the new trailing end of the pipeline 10 as in FIG. 5g. Another PiP pipe joint 14B is shown in FIG. 5h ready for its inner pipe 18 to be welded at the first workstation 28A as in FIG. 5g. Similar steps are repeated until the pipeline 10 is complete.

[0090] FIGS. 6a and 6b show another way of handling the spacers 26. In this example, the spacers 26 move with the outer pipe 20 of the pipe joint 14. Consequently, there is no need to place spacers 26 onto the intermediate inner pipe 18A before advancing the outer pipe 20 of the pipe joint 14 downstream. This arrangement could be adopted where there is no thermal insulation material preinstalled around the intermediate inner pipe 18A or the inner pipe 18 of the pipe joint.

[0091] In FIGS. 6a and 6b, welds 32 have already been formed between the inner pipe 18 of the pipeline 10 and the intermediate inner pipe 18A and between the intermediate inner pipe 18A and the inner pipe 18 of the pipe joint 14. The outer pipe 20 of the pipe joint 14 is shown being advanced downstream, together with its spacers 24, along and around the intermediate inner pipe 18A. The spacers 24 within the outer pipe 20 of the pipe joint 14 slide over the intermediate inner pipe 18A as the rails 42 supporting the intermediate inner pipe 18A are retracted, allowing the rollers 38 of the roller boxes 26 to support the advancing outer pipe 20. Conversely, the rails 42 of the upstream roller boxes 26 are deployed to support the inner pipe 18 of the pipe joint 14.

[0092] FIGS. 7 to 12 show a practical implementation of the invention. The S-lay firing line arrangement 44 of FIG. 7 comprises two axially-aligned groups of three independently-operable roller boxes 26 of the invention, alternating with workstations 28 between the groups and at their ends. FIGS. 8 to 12 are enlarged views of one of the roller boxes 26 of that arrangement 44.

[0093] FIGS. 8, 9 and 10 show the roller box 26 in a first operating mode in which rails 42 are deployed to support the inner pipe 18 of a PiP assembly as described above. Conversely, FIGS. 11 and 12 show the roller box 26 in a second operating mode in which the rails 42 are retracted to allow rollers 38 beneath to support the outer pipe 20 of the PiP assembly. Driven by a tilt mechanism 46 and aided by counterweights 48, the rails 42 retract by swinging upwardly and outwardly into the raised, separated position shown in FIGS. 11 and 12.

[0094] As best seen in FIGS. 8, 9 and 10, arrays of guide rollers 50 cooperate with the rails 42 to define a path for the inner pipe 18. The guide rollers 50 overhang the rails 42, thus being positioned and oriented to prevent the inner pipe 18 from lifting away from the rails 42. This keeps the inner pipe 18 aligned with the central longitudinal axis 36 as illustrated in FIGS. 2 to 4c.

[0095] Many other variations are possible within the inventive concept. For example, the inventive concept could, in principle, also be applied to manufacturing a PiP pipeline in another context, for example at a coastal spoolbase in support of reel-lay operations. Thus, in this specification, references to pipelines or PiP assemblies include pipe stalks that are fabricated from a succession of pipe joints and that are then welded together, in turn, to form longer pipelines. However, the invention is particularly beneficial in the space-constrained environment of an S-lay firing line.