GB2428080A

GB2428080A - Laying of elongate flexible articles

Info

Publication number: GB2428080A
Application number: GB0604081A
Authority: GB
Inventors: Matthew Trevor Snowdon; Michael William Shea
Original assignee: Acergy UK Ltd
Current assignee: Acergy UK Ltd
Priority date: 2005-07-07
Filing date: 2006-03-01
Publication date: 2007-01-17
Anticipated expiration: 2026-03-01
Also published as: BRPI0504783A; GB0513923D0; BRPI0504783B1; GB0604081D0; GB2428080B

Abstract

Apparatus for the laying of elongate flexible articles 95 from a vessel, comprising main tensioning means attached to a pivotable frame 100; main diverter means for diverting the flexible article to a vertical angle; auxiliary tensioning means for transferring the pipe to the top of the frame when the pipe is not being handled by the main tensioning means, the upper part of the frame being movable over the top of the main diverting means when supporting the pipe; and upper diverter means for diverting pipe into alignment with the main tensioning means. When the main tensioning axis is between 5 and 15 degrees to the vertical, the main tensioning means can preferably guide the flexible article without supporting it, the load being taken by the auxiliary tensioning means. When the main tensioning axis is at an angle less than 5 degrees however, the main tensioning means can open sufficiently wide to allow a rigid accessory (200, fig. 3a) to pass through.

Description

65093FF - 2006-02-24 Apparatus and Method for the Laying of Elongate

Articles This invention relates to apparatus and a method for the laying of elongate articles, and in particular, to a method and apparatus for sub-sea laying of elongate articles such as flexible pipes, umbilical pipes and cables.

It is known to lay flexible pipe, umbilical or other conduit from a vessel at sea. This pipe is conventionally stored upon, for example, a drum and is supported by tensioning means such as a track tensioner fixed in an horizontal orientation on the deck. This ensures that the considerable weight of the pipe between seabed and vessel is taken by the tensioner and not the drum. The pipe then passes over a diverter such as a wheel or a gutter placed, for example, at the back of the ship. This ensures that the pipe is overboarded and is deflected from the substantially horizontal orientation it has on the deck, to an orientation close to the vertical (an angle up to 20 degrees) required for laying the pipe on the seabed. A known vessel of this type is Seaway Condor.

An A-frame or similar supporting structure, in combination with a winch, is generally provided to support the passing over the diverter of connections and other accessories mounted on the pipe, such as collars, stiffeners, buoys and anodes. These accessories are relatively rigid and tend to be larger in width than the outer diameter of the pipe.

The tensioner can be opened to allow these accessories to pass through, but they would not pass directly over the diverter without damage.

When laying large diameter pipes in deep water, the suspended weight of the article imposes crushing loads where the pipe passes over the diverter. To keep those loads within acceptable limits, the tensioning means and diverter required become large and expensive, and take up a lot of space on the vessel. It is also known to lay flexible pipe using the storage drum as a winch to store both the pipe to be laid and to support the weight of the suspended pipe as it is laid. However such winch systems still require a large diverter to lay the pipe. Again, the size of this diverter and of the winch itself may become large and expensive as pipe diameter and depth increases. Again an A-frame is provided for overboarding accessories as shown for example in GB 2173760 65093FF 2006-02-24 Another drawback with krown horizontal lay systems is that the system occupies a great length and amount of space on the deck of the vessel. In practice, this means that deployment of the pipe is over the stem of the vessel where movement of the vessel is at its most and so the risk of damage to the article or the end connection is at its greatest. Even in the best conditions, additional crushing type loads are inevitably applied to the pipe as it bends over the stern of the vessel. This effectively limits the depth to which the pipe and the pipeline can be laid. To reduce crushing loads under conditions of heave and pitching, an even larger radius wheel or gutter is required, this taking up yet more space and increasing weight on the vessel. As a result of this, pipelaying at depths greater than 500 metres has not been possible using these known systems.

FR 2580267 discloses an alternative apparatus for manoeuvring a pipe over a direction changer (such as a wheel), by providing a retainer for retaining accessories attached to the pipe, the retainer manoeuvring the accessory on a path outside the surface of the wheel. However, this apparatus still becomes unwieldy when pipe diameter or water depth increases.

Another way of addressing these disadvantages is by using clamps to lay the pipe vertically such as disclosed in EP-A-0 054 332. The device comprises a mobile clamp beneath the vessel and a fixed clamp, each of which takes the load of the pipe alternately by gripping rigid accessories on the pipe. These rigid accessories are regularly spaced along the pipe and spaced sufficiently close to each other so that, when the mobile clasp holds an accessory and passes it to the fixed clamp, the length of its travel is sufficient such that the next accessory can be gripped by the moving clamp.

With such a device it is not possible to install a pipe not comprising rigid accessories or for which there is a too great a gap between two consecutive accessories.

It would be advantageous to reduce the deck area required by horizontal lay systems and increase their range of depth/diameter capability for a given overall size and 65093FF - 2006-02-24 weight. It would also be advantageous for such a vessel to be able to retain a reasonably low centre of gravity for stability, when laying pipe and when in transit.

In a first aspect of the invention there is provided an apparatus for the laying of elongate flexible articles from a vessel, the apparatus comprising: - storage means for an elongate flexible article; - main tensioning means for supporting the load of the suspended elongate flexible article; - main diverter means for diverting the elongate flexible article from an angle aligned with an axis of the main tensioning means to a substantially vertical angle for departure into the sea; and auxiliary tensioning means, including a frame structure mounted pivotably to said vessel, for transferring the load of said elongate flexible article to an upper part of said frame structure when said load is not taken by the main tensioning means, the pivoting of the frame structure permitting said upper part of the frame structure to move over the top of said main diverting means while supporting said load; wherein said main tensioning means are mounted on the pivotable frame structure so as to be operable with its axis tilted at a range of angles above horizontal and wherein there is further provided upper diverter means mounted on the frame structure for diverting the elongate flexible article from said storage means into alignment with the tensioning means axis.

By elevating the main tensioning means on the pivotable frame structure, valuable deck space can be freed for other uses. Furthermore, the ability to incline the axis of the main tensioning means and so reduce the angle imposed on the elongate flexible article by the main diverter means, allows the apparatus to be used in a wider range of diameter and depth situations than the known systems, without increasing so much its size and weight. Laying at 15 to 20 degrees in particular, the risk of crushing of the pipe is not so dependent on load and therefore the main diverter means in particular can be relatively small. A further advantage of this apparatus is that the frame structure has several functions, supporting both the main tensioning means and upper diverter means 65093FF 2006-02-24 while being useful in overboarding any rigid accessory over the main diverter means without damaging the elongate flexible article.

With the frame structure vertical and the tensioning means open, the structure can serve as an A-frame for the overboarding of accessories. In one embodiment, when the pivotable frame structure is at an angle between 15 degrees and 5 degrees from vertical, the main tensioning means are operable to guide the elongate flexible article without supporting it, the load of the suspended elongate flexible article being taken by the auxiliary tensioning means and when the tiltable frame structure is at an angle lower than 5 degrees, the main tensioning means are operable to open sufficiently wide to allow the passing of a rigid accessory mounted on said elongate flexible article.

In a further aspect of the invention there is provided a method of laying an elongate flexible article from a vessel, using the apparatus of the first aspect of the invention, 1 5 comprising the steps of: with the frame structure tilted at an angle greater than 15 degrees from vertical, laying said elongate flexible article, said elongate flexible article being suspended by and paid out with said main tensioning means, said main diverter means diverting said flexible elongate article to a more vertical orientation after it has passed through said main tensioning means; when a rigid accessory is encountered, suspending the paying out and attaching a line from said auxiliary tensioning means to said elongate flexible article, tilting the frame structure to bring the main tensioning means axis to an angle less than 5 degrees from vertical, the main tensioning means no longer supporting the elongate flexible article, said elongate flexible article now being supported by said auxiliary tensioning means; using said auxiliary tensioning means to pay out said elongate flexible article until said rigid accessory is passed to a level below that of said main diverter means; tilting said structure to an angle beyond 15 degrees and gripping said elongate flexible article with said main tensioning means; and disconnecting said line from said elongate flexible article and recommencing laying using said main tensioning means.

65093FF - 2006-02-24 Further optional features and refinements are as disclosed in the appended claims and in the description of exemplary embodiments which follows.

65093FF - 2006-02-24

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which: Figure 1 shows a prior art horizontal pipelaying arrangement as installed on Seaway Condor.

Figure 2a shows, schematically, apparatus according to an embodiment of the invention in a pipelaying configuration with its tensioner axis inclincd at about 45 degrees from vertical; Figure 2b shows, schematically, the apparatus of Figure 1 in an alternative pipelaying configuration with its tensioner axis inclined at about 15 degrees from vertical; Figures 3a - 3f shows the apparatus of Figure 1 in different stages of the pipelaying operation when an accessory is encountered; and

DETAILED DESCRIPTION OF THE EMBODIMENTS

Figure 1 shows a side view of the vessel Seaway Condor with horizontal pipelaying equipment installed. This comprises a storage drum 10, a diverting chute 20, track tensioners 30, main diverter in the form of a drum 40, A-frame 50 (in positions a-d), draw-works 60, a working platform 70 and various sheaves 75, 80 and 90.

During pipelaying operations, flexible pipe stored upon the drum 10 is led through the track tensioner 30 which is fixed in an horizontal orientation on a raised deck. The diverting chute 20 supports the pipe between the drum 10 and the tensioner 30. The pipe then passes from the tensioner over the main diverting drum 40, through or by the working table 70 and into the sea. The working table allows particularly large accessories to be added to the pipe subsequent to it passing through the tensioner 30 and over drum 40. The considerable weight of the pipe between seabed and vessel is 65093FF - 2006-02-24 taken by the tensioner 30, gripping the pipe and not the drum 40. The drum 40 ensures that the pipe is deflected from the substantially horizontal orientation it has on the deck, to an orientation close to the vertical (an angle up to 20 degrees) required for laying the pipe on the seabed. Since the pipe at this point is under high tension, a large radius diverter is required to avoid excessive crushing of the pipe as it bends. Using a drum 40 allows several pipes to be laid in parallel. Alternative forms of diverter would be a simple wheel or arched track. Each line is provided with its own tensioner.

The A-frame 50, in combination with draw-works 60 allows the passing over the drum 40 of connections and other accessories mounted on the pipe, such as collars, stiffeners, buoys and anodes. To do this, a line (shown in broken form in illustration) from the draw-works 60 is led over sheaves 75, 80, 90, and is attached to the accessory. The tensioner 30 are then opened to allow the accessories to pass through. Once it has passed through, the A-frame 50 is moved from position a to position d (via positions b and c), thus lifting the accessory up and over the drum 40 and overboard. The line is then paid out until the pipeline again rests on the drum and, with the tensioner 30 re- engaged, the line can be released and normal pipelaying resumed.

Figs. 2a and 2b both shows pipelaying apparatus in alternative normal pipelaying, configurations, tilted at an angle a from vertical. In Figure 2a said angle a is approximately 45 degrees from vertical, and in Figure 2b said angle a is approximately degrees from vertical. The apparatus is suitable for the laying of flexible elongated elements such as flexible pipes or umbilical. The apparatus is preferably located at the stern of a vessel, although it could be positioned above a moon pooi located about mid ship, or located at either the port or starboard side of the vessel.

The apparatus is shown laying flexible pipe 95. The pipe may he stored on a reel located on the vessel deck 105. The options for such storage are well-known and not illustrated here. The apparatus comprises a tilting frame structure on the form of an A- frame 100 mounted to deck 105 via pivot 110. Supporting the A-frame 100 is a tilting system such as an auto-locking rack and pinion arrangement 115. Alternatively an hydraulic ram could be used). The A-frame also supports a track tensioner 120 (a four- 65093FF - 2006-02-24 track tensioner is illustrated here), a radius controller in the form of a gutter 125 (or endless belt conveyor system) at its top for directing the pipe over the frame, and a sheave arrangement 135 for passing the cable of an A&R winch 210 (Fig. 3) mounted on the deck 105 to a position above the tensioner. Below the A- frame 100 at deck level there is mounted a wheel 130 (or any other suitable diverting means such as a gutter) to divert the pipe 95 into the natural catenary configuration to the seabed.

As mentioned in the introduction, the deck space below the tilting structure is usable in a way not achieved in known horizontal lay systems. The system is particularly flexible in that it allows pipelaying in a number of different configurations according to, for example, weather conditions, pipe diameter/specification, water depth etc. For instance the system can be used with the frame 100 horizontal, particularly if laying small diameter pipe able to withstand the greater stresses put on it by the wheel 130 at this angle. This may be useful should there be adverse weather and vessel stability is crucial. The structure can also be put at its lowest position to lower the centre of gravity of the vessel when in transit between operations.

During pipelay operations the crushing loads on pipe 95 can be reduced by tilting up the structure such that the angle of diversion around wheel 130 is less than 90 degrees. In particular, it is found that the crushing loads are markedly reduced when the tensioner is inclined in the range 1520 degrees off vertical (as in Fig. 2b) which is particularly relevant for large diameter pipe. Alternatively a tensioner angle of 45 degrees (as in Fig. 2a) results in a good compromise between stability, freed deck space and load on the pipe 95. This versatility allows the novel apparatus to handle combinations of pipe diameter and depth which in conventional designs would require and apparatus of increased size and weight. Other modes of operation are possible with the apparatus, beyond the straightforward laying operations described. In particular, operations to pass accessories over the diverter using the A-frame 100 will be described below.

Figs. 3a-3f show the same apparatus in various stages of operation to allow the passing of rigid accessories 200 such as pipe connections, when encountered. In figure 3a the accessory 200 is encountered, and a line 210 from the winch is securely attached to the 65093FF - 2006-02-24 accessory. While this is done the A- frame 100 remains tilted at 15 degrees or more and the track tensioner 120 still supports the load.

In Fig. 3b the frame 100 is tilted towards the vertical under action of the rack and pinion mechanism 115 but kept at an angle of between 5 and 15 degrees from the vertical. As the frame 100 is tilted the towards the vertical the track tensioner 120 opens so that the load is no longer taken by it. The load is now taken solely by the winch via line 210 attached to accessory 200. At this angle, the tensioner 120 only opens part way and is still operable to guide the pipe 95.

In Fig 3c the tower is tilted further towards the vertical such that it is now substantially vertical (at an angle less than 5 degrees). The track tensioner 120 now opens fully to allow the passing of the accessory. The A-frame 100 is designed with a dog leg 205 at its bottom with the guiding wheel 130 attached to the deck below this dog-leg.

Consequently, when the apparatus is in this vertical configuration, the wheel 130 is in a position clear of the path of the rigid accessory 200 and consequently there is no need for offsetting the wheel 130. Conversely when the frame is returned to its tilted configuration depicted in Fig. 1, the wheel's position is such that the pipe 95 falls onto it and is guided by it into the water at the desired angle. Alternatively there may be provided means for moving the guide out of the way as required (controlled by the pipelay controller), or attached to the frame 100 itself so that it moves out of the way automatically when the frame is moved to its vertical configuration.

In Fig. 3d the winch pays out the line 210 thus lowering the accessory 200 through the track tensioner 120 and below the wheel 130.

In Fig. 3e the A-frame 100 is tilted again to an angle of between 5 and 15 degrees. The track tensioner is partially closed to guide the pipe without supporting it.

In Fig. 3f the A-frame 100 is tilted back to its pipelaying configuration, similar to that shown in Fig. 1 but this time at an angle closer to 1 5 degrees. The track tensioner 120 is now fully closed and gripping the pipe 95. The line 210 can now be removed from the 65093FF - 2006-02 -24 accessory 200 such that the tensioner 120 supports the pipe 95 fully. Normal pipelaying can then recommence, paying out the pipe 95 using the track tensioner 120.

If a rigid accessory needs to be attached to the pipe which is larger than is possible to pass through the open tensioner then it may be added after passing. This may be facilitated by the addition of a working table at a position below the lower guiding means. A hold-off clamp may also be provided. In this case the wheel may be moveable clear of this working table when the working table is in use.

To support the above operations, control systems are provided whereby the tensioner is operable to grip the pipe 95 when in the Fig. 1 configuration, that is when the A- frame 100 is in an inclined position of an angle equal to or greater than 15 degrees from the vertical. When the frame is tilted at an angle between 5 degrees and 15 degrees the track tensioner 120 is arranged to release the pipe 95 by opening a distance less than its full travel. This means that the tensioner no longer takes the load but still guides the pipe in this position to ensure that the pipe does not clash with any of the surrounding equipment. When the frame is then tilted further, between vertical and 5 degrees, the track tensioner opens its full travel (or at least sufficiently wide) to allow the passing of a rigid accessory through it.

The tensioner 120 may he controlled to open and close as required by configuring the pipelay control system accordingly. The control system can be arranged such that, should the angle of inclination become less than 15 degrees but greater than 5, the tensioner is disengaged under control of the control system and remain so until the angle of inclination is returned to 15 degrees. Furthermore the system can cause the tensioner to open further when the A-frame is tilted beyond 5 degrees from the vertical.

In such a case, safety features should be included to both prevent the tensioner being opened and prevent the inclination being increased closer to vertical when the tensioner is still carrying the load.

The embodiments mentioned above are for illustrative purposes only and other embodiments and variations can he envisaged with departing from the spirit and scope 65093FF - 2006-02-24 of the invention. It is envisaged, for instance, that the track tensioner be made to disengage with the pipe at less than 15 degrees mechanically without the intervention of a control system.

Claims

65093FF - 2006-02-24

I. An apparatus for the laying of elongate flexible articles from a vessel, the apparatus comprising: - storage means for an elongate flexible article; - main tensioning means for supporting the load of the suspended elongate flexible article; - main diverter means for diverting the elongate flexible article from an angle aligned with an axis of the main tensioning means to a substantially vertical angle for departure into the sea; and - auxiliary tensioning means, including a frame structure mounted pivotably to said vessel, for transferring the load of said elongate flexible article to an upper part of said frame structure when said load is not taken by the main tensioning means, the pivoting of the frame structure permitting said upper part of the frame structure to move over the top of said main diverting means while supporting said load; wherein said main tensioning means are mounted on the pivotable frame structure so as to be operable with its axis tilted at a range of angles above horizontal and wherein there is further provided upper diverter means mounted on the frame structure for diverting the elongate flexible article from said storage means into alignment with the tensioning means axis.
2. Apparatus according to claim I wherein, when the main tensioning means axis is at an angle between 15 degrees and 5 degrees from vertical, the main tensioning means are operable to guide the elongate flexible article without supporting it, the load of suspended elongate flexible article being taken by the auxiliary tensioning means.
3. Apparatus according to claim I or 2 wherein, when the main tensioning means axis is at an angle lower than 5 degrees, the main tensioning means are operable to open sufficiently wide to allow the passing of a rigid accessory mounted on said elongate flexible article.

65093FF - 2006-02-24
4. Apparatus according to any preceding claim further comprising electronic control means to control the opening and closing of said tensioning means depending on the angle of tilt of said frame structure.
5. Apparatus according to claim 4 wherein said control means is further arranged to prevent the tensioning means being opened or the frame structure being tilted to bring the axis beyond 15 degrees towards the vertical, when it is supporting the elongate flexible article.
6. Apparatus according to any preceding claim wherein said main diverter means comprises a wheel, drum or gutter sized to enable the normal laying of the pipe.
7. Apparatus according to any of claims I to 5 wherein said upper diverter means comprises a gutter or conveyor system.
8. Apparatus according to any preceding claim wherein said main diverter means is attached to the deck in a position whereby, when said tensioner means axis is tilted at degrees, said lower guiding means guides said flexible elongate article as the flexible elongate object is paid out, and when said frame structure is tilted towards the vertical said lower guiding means is clear of said flexible elongate article.
9. Apparatus according to claim 8 wherein said main diverter means is located at a place displaced horizontally and/or vertically from the pivot point of said tiltable frame structure.
10. Apparatus according to any of claims I to 7 wherein said main diverter means is moveable to and from an operational position.
11. Apparatus according to any preceding claim further comprising a work station located below said main diverter means.

65093FF - 2006-02-24
12. Apparatus according to any preceding claim further comprising a hold- off clamp located below said main diverter means.
13. Apparatus according to any preceding claim arranged such that the main tensioning means cannot grip the pipe when its axis is at an angle less than 15 degrees.
14. Apparatus according to any preceding claim wherein there is provided said auxiliary tensioning means includes a sheave arrangement mounted on said upper part of the frame structure for transferring a line from another part of said auxiliary tensioning means to a point above said elongate flexible object.
Apparatus according to claim 14 wherein said other part of the auxiliary tensioning means comprises a winch mounted at deck level.
16. Apparatus according to any preceding claim wherein said main tensioning means comprise a track tensioner having a plurality of tracks.
17. Apparatus according to claim 1 6 wherein said track tensioner is a four track tensioner, comprising four tracks arranged symmetrically around said axis.
18. Apparatus according to any preceding claim wherein said main tensioning means is arranged to open sufficiently wide to allow a rigid accessory to pass when the said frame is tilted less than said predetennined angle from vertical.
19. Apparatus according to any preceding claim wherein said main tensioning means is arranged to engage and support said elongate flexible article automatically when the axis is tilted beyond 1 5 degrees.
20. Apparatus according to any of claims 1 to 18 wherein the apparatus is arranged such that said main tensioning means is engagable when the axis is tilted beyond said degrees, but requires positive engagement.

65093FF - 2006-02-24
21. Apparatus according to any preceding claim wherein tilting means is provided between the frame structure and the vessel.
22. Apparatus according to claim 21 wherein said tilting means comprises a rack and pinion arrangement.
23. Apparatus according to claim 21 wherein said tilting means comprises an hydraulic ram.
24. Apparatus according to any preceding claim wherein said frame structure is tiltable between substantially vertical and substantially horizontal.
25. Apparatus according to any preceding claim wherein said auxiliary tensioning means comprises a winch.
26. A pipe laying vessel including apparatus according to any preceding claim wherein said apparatus is located at the stern of a vessel.
27. A pipe laying vessel including apparatus according to any preceding claim wherein said apparatus located above a moon pool located about mid ship.
28. A pipe laying vessel including apparatus according to any preceding claim wherein said apparatus is adapted to be located at either the port or starboard side of the vessel.
29. A method of laying an elongate flexible article from a vessel, using the apparatus of any of claims I to 25, comprising the steps of: with the frame structure tilted at an angle greater than 15 degrees from vertical, laying said elongate flexible article, said elongate flexible article being suspended by and paid out with said main tensioning means, said main diverter means diverting said flexible elongate article to a more vertical orientation after it has passed through said main tensioning means; 65093FF - 2006-02-24 when a rigid accessory is encountered, suspending the paying out and attaching a line from said auxiliary tensioning means to said elongate flexible article, tilting the frame structure to bring the main tensioning means axis to an angle less than 5 degrees from vertical, the main tensioning means no longer supporting the elongate flexible article, said elongate flexible article now being supported by said auxiliary tensioning means; using said auxiliary tensioning means to pay out said elongate flexible article until said rigid accessory is passed to a level below that of said main diverter means; tilting said structure to an angle beyond 15 degrees and gripping said elongate flexible article with said main tensioning means; and disconnecting said line from said elongate flexible article and recommencing laying using said main tensioning means.
30. Method according to claim 29 wherein there is a further step of tilting said frame structure to put the axis at an angle between 15 degrees and 5 degrees from vertical, while supporting and/or paying out the flexible elongate article with the auxiliary tensioning means, the main tensioning means guiding the elongate flexible article without supporting it.
31. Method according to claim 29 or 30 wherein, when the axis is at an angle less than 5 degrees from vertical, the main tensioning means are opened sufficiently to allow the passage of a rigid accessory mounted on said elongate flexible article and said rigid accessory is passed therethrough and to a level below that of the main diverter means.
32. Method according to any of claims 29 to 31 further including passing said elongate flexible article over said upper diverter means, prior to passing it through said main tensioning means.
33. Method according to any of claims 29 to 32 wherein said main tensioning means engage and support said elongate flexible article automatically when said axis is tilted beyond 15 degrees from vertical.

65093FF - 2006-02-24
34. Method according to any of claims 29 to 32 wherein said main tensioning means are activated to engage and support said elongate flexible article once said tower is tilted beyond 15 degrees.
35. Method according to any of claims 29 to 34 wherein further accessories are attached to said elongate article subsequent to it passing through said main tensioning means.
36 Apparatus as hereinbefore described with reference to the accompanying drawings.
37. Method as hereinbefore described with reference to the accompanying drawings.