Subsea Connection of Pipeline Sections

Abstract

A method of assembling a pipeline at a seabed location comprises landing a connection tool (10) on the seabed over a free end portion of a first pipeline section (12) already placed on the seabed. The connection tool is locked to the free end portion of the first pipeline section, a lower end of a second pipeline section (26) is connected to the connection tool via an initiation line (68). While applying tension to the initiation line against reaction force of the connection tool, at least a lower end portion of the second pipeline section is landed on the seabed with the lower end facing a free end of the first pipeline section. The lower end of the second pipeline section is then pulled into mechanical engagement with the free end of the first pipeline section.

Claims

1. A method of assembling a pipeline at a seabed location, the method comprising: landing a connection tool on the seabed over a free end portion of a first pipeline section already placed on the seabed; locking the connection tool to the free end portion of the first pipeline section; connecting a lower end of a second pipeline section to the connection tool via an initiation line; while applying tension to the initiation line against reaction force of the connection tool, landing at least a lower end portion of the second pipeline section on the seabed with the lower end facing a free end of the first pipeline section; and pulling the lower end of the second pipeline section into mechanical engagement with the free end of the first pipeline section.

2. The method of claim 1, comprising locking the connection tool to the free end portion of the first pipeline section before connecting the initiation line to the connection tool.

3. The method of claim 1 or claim 2, comprising fixing the connection tool to the seabed.

4. The method of claim 3, comprising embedding a foundation of the connection tool in the seabed.

5. The method of claim 4, comprising pumping water from within a suction pile foundation of the connection tool.

6. The method of any preceding claim, comprising suspending an upper end portion of the second pipeline section above the seabed while pulling the lower end of the second pipeline section into engagement with the free end of the first pipeline section.

7. The method of claim 6, wherein the suspended upper end portion is a major portion of the second pipeline section.

8. The method of claim 6 or claim 7, comprising landing the upper end portion of the second pipeline section on the seabed after engaging the lower end of the second pipeline section with the free end of the first pipeline section.

9. The method of any preceding claim, comprising pulling the lower end of the second pipeline section by tension in at least one wire that extends from the connection tool toward the second pipeline section.

10. The method of any preceding claim, comprising pulling the lower end of the second pipeline section by interengaging at least one pair of complementary coupling parts and then advancing one of those coupling parts relative to the other.

11. The method of claim 10 when depending from claim 9, wherein the at least one wire pulls one coupling part into engagement with the other coupling part.

12. The method of claim 11, wherein one coupling part is a male formation and the other coupling part is a female formation, and the at least one wire extends through the female formation to the male formation before the female formation receives the male formation.

13. The method of any of claims 10 to 12, comprising attaching one of the coupling parts to the lower end portion of the second pipeline section before engaging the lower end of the second pipeline section with the free end of the first pipeline section.

14. The method of claim 13, comprising attaching said coupling part to the lower end portion of the second pipeline section after landing that lower end portion on the seabed.

15. The method of any preceding claim, comprising lifting the free end portion of the first pipeline section from the seabed before engaging the lower end of the second pipeline section with the free end of the first pipeline section.

16. A connection tool for assembling a pipeline at a seabed location, the tool comprising: a frame defining a downwardly-opening longitudinal passageway; a foundation arranged to fix the frame to the seabed; a clamp and a porch supported by the frame, the clamp and the porch being arranged to lock a first pipeline section extending along the passageway, in use, against movement relative to the frame; an attachment point for an initiation line of a second pipeline section to be landed on the seabed in use; and a pull-in system arranged to pull the second pipeline section into end-to-end engagement with the first pipeline section locked by the clamp and the porch.

17. The tool of claim 16, wherein the attachment point is substantially aligned with the clamp and porch in an upright central longitudinal plane.

8. The tool of claim 16 or claim 17, in combination with a second pipeline section having an initiation line, when anchoring the initiation line of the second pipeline section via the attachment point.

19. The tool of any of claims 16 to 18, wherein the clamp is mounted to the frame for vertical movement relative to the frame.

20. The tool of any of claims 16 to 19, wherein the porch is mounted to the frame for vertical movement relative to the frame.

21. The tool of any of claims 16 to 20, wherein the foundation comprises at least one suction pile.

22. The tool of any of claims 16 to 21, wherein the pull-in system comprises at least one winch wire extending from a winch mounted on the frame.

23. The tool of any of claims 16 to 22, wherein the pull-in system comprises at least one female coupling formation extending through the porch and at least one pull-in mechanism mounted on the porch in alignment with the female coupling formation.

24. The tool of claim 23 when depending from claim 22, wherein the or each winch wire extends through a respective female coupling formation of the porch.

25. The tool of claim 23 or claim 24, in combination with a reaction clamp arranged to be fixed to the second pipeline section in use, wherein the reaction clamp has at least one male coupling formation that is complementary to the female coupling formation of the porch and that is engageable with the pull-in mechanism mounted on the porch.

26. The tool of claim 25, wherein the at least one male coupling formation of the reaction clamp has a longitudinally-toothed profile for ratchet engagement with the pull-in mechanism.

Description

[0046] 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:

[0047] FIG. 1 is a side view of a connection tool of the invention suspended from a surface vessel at an installation site;

[0048] FIG. 2 is a perspective view of be connection tool shown in FIG. 1;

[0049] FIG. 3 is a perspective view of the connection tool, landed on the seabed around an end portion of a previously-laid first pipe stalk and lifting that end portion off the seabed;

[0050] FIG. 4 is a side view of the connection tool being used as an anchor for initiating laying of a second pipe stalk to be connected to the first pipe stalk;

[0051] FIG. 5 is a side view of the second pipe stalk being laid on the seabed, substantially in alignment with the first pipe stalk held by the connection tool;

[0052] FIG. 6 is a perspective view of an ROV installing a reaction clamp around the second pipe stalk, close to the end of the second pipe stalk that faces the first pipe stalk;

[0053] FIG. 7 is a perspective view of the connection tool pulling the reaction clamp attached to the second pipe stalk toward a lifting porch that supports the end portion of the first pipe stalk;

[0054] FIG. 8 is a perspective view the reaction clamp now engaged with a stroking mechanism of the lifting porch in readiness for final tie-in; and

[0055] FIG. 9 is an enlarged perspective view of the reaction clamp pulled by the stroking mechanism toward the lifting porch to effect final tie-in and interconnection of the first and second pipe stalks.

[0056] FIG. 1 of the drawings shows a connection tool 10 of the invention being moved toward a free end of a first pipeline section 12 that was previously laid or abandoned on the seabed 14. The connection tool 10 is shown suspended on a wire 16 from a vessel 18 at the surface 20 above the installation site, and is about to be landed on the seabed 14 over a free end portion of the first pipeline section 12. The free end portion terminates in the free end of the first pipeline section 12.

[0057] Advantageously, the vessel 18 need not be a specialised pipelaying vessel and so can be a relatively inexpensive and common offshore construction vessel. In this example, the wire 16 hangs from a crane 22 of the vessel 18 but the wire 16 could instead hang from a winch of the vessel 18.

[0058] The connection tool 10 may be transported to the installation site either suspended on the wire 16 underwater or lifted onto a working deck of the vessel 18, to be lowered into the water when required.

[0059] FIG. 1 also shows a work-class ROV 24 tethered to the vessel 18. The ROV 24 monitors the position, orientation and alignment of the connection tool 10 relative to the first pipeline section 12. The ROV 24 will also detach the wire 16 from the connection tool 10 once the connection tool 10 has been landed on the seabed 14. The ROV 24 may also couple itself to the connection tool 10 to apply propulsive or guiding thrust to the connection tool 10 when suspended in the water column.

[0060] As will be explained later with reference to FIG. 6, the same ROV 24, or a different ROV, is also involved with connecting a second pipeline section 26 to the first pipeline section 12.

[0061] FIG. 2 shows the connection tool 10 in isolation. FIG. 3 shows the connection tool 10 landed on, and partially embedded in, the seabed 14 astride the first pipeline section 12.

[0062] The connection tool 10 is generally symmetrical about an upright, substantially vertical central longitudinal plane. The tool 10 comprises a frame 28 that is arched in cross-section, defined by laterally-spaced pairs of legs 30 in a rectangular array and an upper bridge structure 32 that connects and extends between the pairs of legs 30.

[0063] The upper bridge structure 32 spans a downwardly-opening, longitudinally-extending, open-ended passageway 34 between the legs 30. This passageway 34 allows the tool 10 to be landed on the seabed 14 with the legs 30 straddling the first pipeline section 12 between them. Then, the first pipeline section 12 extends centrally along the passageway 34 between the legs 30 as shown in FIG. 3.

[0064] A foundation attached to the frame 28 comprises four suction piles 36 in a rectangular array, one on each leg 30. Each suction pile 36 has a port 38 for pumping seawater into or out from the hollow interior of the pile 36. For example, the ports 38 may be arranged for coupling to a pump supported by an ROV 24.

[0065] The suction piles 36 engage the soft seabed 14 when the connection tool 10 is ended and embed more deeply into the seabed 14 when water is pumped out through the ports 38. Conversely, when water is pumped in through the ports 38, the piles 36 rise relative to the seabed 14 and so are more easily lifted and disengaged from the seabed 14 when moving or removing the tool 10 after use.

[0066] A central longitudinally-extending beam 40 is cantilevered from one end of the bridge structure 32. The beam 40 supports a lifting clamp 42 that hangs from the beam 40. The lifting clamp 42 can be moved vertically relative to the beam 40 between lower and upper positions.

[0067] Jaws 44 of the lifting clamp 42 define a downwardly-facing opening to embrace and clamp around the first pipeline section 12 that extends along the passageway 34 as shown in FIG. 2. Once clamped in the jaws 44, the first pipeline section 12 can be lifted away from the seabed 14 by raising the lifting clamp 42 into the upper position.

[0068] A lifting porch 46 hangs centrally under an outrigger 48 at the end of the bridge structure 32 opposed to the beam 40, in alignment with the lifting clamp 42 in the central longitudinal plane. Jaws 50 of the porch 46 define a downwardly-facing opening to embrace and clamp around the first pipeline section 12 as shown in FIG. 3. This locks the connection tool 10 to the free end portion of the first pipeline section 12. For this purpose, the porch 46 can also be moved vertically relative to the outrigger 48 between lower and upper positions. Alternatively, the porch 46 could be fixed relative to the frame 28, in which case the lifting clamp 42 may lift the first pipeline section 12 into engagement with the porch 46.

[0069] The jaws 50 of the porch 46 are disposed between a pair of parallel bores or apertures 52 that extend longitudinally through the porch 46 from an outer face 54 to an inner face 56 of the porch 46. Each aperture 52 is aligned with a respective stroking mechanism 58 on the inner face 56 of the porch 46. Each stroking mechanism 58 may comprise a longitudinally-reciprocable hydraulic jack.

[0070] A winch system 60 is mounted on top of the bridge structure 32. Sheaves 62 are slung under the bridge structure 32 to guide winch wires 64 from the winch system 60, as seen in FIG. 7.

[0071] The bridge structure 32 also supports fixing formation 66 at its end above the porch 46. The fixing formation 66 provides an attachment point for an initiation wire 68 fixed to the lower end of the second pipeline section 26 as shown in FIG. 4. The ROV 24 shown in FIG. 1 can be used to make that connection.

[0072] Via the initiation wire 68, the second pipeline section 26 initially hangs as a catenary between the fixing formation 66 and an installation vessel (not shown) on the surface 20. Again, the installation vessel does not have to be a specialised pipelaying vessel as it needs only to tow, upend, lower and apply hold-back tension to the second pipeline section 26. In principle, the installation vessel could be the same vessel 18 as is used to transport and lower the connection tool 10 as shown in FIG. 1.

[0073] With the connection tool 10 anchored to the seabed 14 to provide a stable reaction point via the fixing formation 66, the second pipeline section 26 is lowered through the positions shown in dashed lines in FIG. 4 until its lower end portion touches down on the seabed 14 as shown in solid lines. The ROV 24 shown in FIG. 1 can monitor the position of the touch-down point if required.

[0074] It will be apparent that as the initiation wire 68 is attached to the connection tool 10 in substantially the same vertical plane as the porch 46 and the lifting clamp 42, this ensures correct positioning and orientation of the lower end of the second pipeline section 26 on the seabed 14 relative to the first pipeline section 12.

[0075] Lowering of the second pipeline section 26 onto the seabed 14 continues after the initial touchdown, as shown in FIG. 5. Lowering is paused when a minor lower end portion of the second pipeline section 26 lies on the seabed 14 and a major upper end portion remains suspended in the water column between the surface 20 and the seabed 14.

[0076] Suspending the upper end portion in this way reduces the apparent weight of the second pipeline section 26 on the seabed 14. This makes it easier to pull the lower end of the second pipeline section 26 into engagement with the first pipeline section 12. Yet, the static lower end portion landed on the seabed 14 stabilises the lower end of the second pipeline section 26 against unwanted movement across the seabed 14, which could otherwise be driven by the effect of sea dynamics on the suspended upper end portion.

[0077] Turning next to FIG. 6 of the drawings, this shows an ROV 24 attaching a reaction clamp 70 to the end portion of the second pipeline section 26 that lies on the seabed 14. The ROV 24 has detached the initiation wire 68 from the end of the second pipeline section 26.

[0078] Features of the lifting porch 46 have counterparts in corresponding features of the reaction clamp 70. Specifically, jaws 72 of the reaction clamp 70 define a downwardly-facing opening to be lowered onto and to embrace and clamp around the second pipeline section 28. Also, the jaws 72 of the reaction clamp 70 are disposed between a pair of parallel prongs or stabs 74 that extend longitudinally toward the end of the second pipeline section 26. The stabs 74 are spaced and dimensioned to align with and to fit into the apertures 52 in the porch 46 of the connecting tool 10. The stabs 74 also have a ridged or sawtooth profile to engage as a ratchet with the stroking mechanism 58 on the inner face 56 of the porch 46.

[0079] FIG. 7 shows the operation of a pull-in system in which the winch wires 64 extend from the sheaves 62 of the connecting tool 10 through the apertures 52 in the porch 46. The ROV 24 couples each winch wire 64 to a free end of a respective one of the stabs 74. The winch system 60 of the connecting tool 10 is then activated to pull the stabs 74, and hence the second pipeline section 28 attached to the reaction clamp 70, toward the porch 46 and so toward the end of the first pipeline section 12. Tension in the winch wires 64 also corrects any minor misalignment between the second pipeline section 26 and the first pipeline section 12.

[0080] Eventually the stabs 74 enter the apertures 52 and extend through to the inner face 56 of the porch 46, where they are engaged by the stroking mechanism 58 as shown in FIG. 9. Reciprocal operation of the jacks of the stroking mechanism 58 then pulls the stabs 74 further into the apertures 52. This completes mechanical coupling between the first and second pipeline sections 12, 26 as the reaction clamp 70 attached to the second pipeline section 26 is pulled toward the porch 46 that supports the first pipeline section 12. For this purpose, the ends of the first and second pipeline sections 12, 26 are equipped with complementary fittings 76, such as pin and box fittings, to effect end-to-end mechanical coupling by relative axial movement.

[0081] The remainder of the second pipeline section 28 can then be laid on the seabed 14, hence elongating the first pipeline section 12 by the length of the second pipeline section 26. Third and subsequent pipeline sections can then added to the free end of the second pipeline section 26 by repeating the process as many times as is necessary to lengthen the emergent pipeline.

[0082] After the first and second pipeline sections 12, 26 have been coupled together, their interface is lowered back to the seabed 14 by lowering the lifting clamp 42 and the lifting porch 46 relative to the frame 28 of the connecting tool 10. The connecting tool 10 and the reaction clamp 70 can then be detached from the first and second pipeline sections 12, 26 and, in a reversal of the installation process, lifted from the seabed 14 for reuse.

[0083] Many variations are possible within the inventive concept. For example, the connection tool could have an on-board propulsion system and could, in principle, support itself with variable buoyancy like a submarine. Thus, the connection tool could itself be an underwater vehicle.

[0084] The first and second pipeline sections need not both be discrete pipe stalks or indeed of the same construction or dimensions, or laid by the same technique. For example, the first pipeline section could be a pipeline bundle and the second pipeline section could be a reel-lay pipe.