WO2003095880A1

WO2003095880A1 - A method and a vessel for pipe-laying at sea

Info

Publication number: WO2003095880A1
Application number: PCT/NO2003/000152
Authority: WO
Inventors: Trond Kjetil Nodberg
Original assignee: Aker Marine Contractors AS
Current assignee: Aker Marine Contractors AS
Priority date: 2002-05-10
Filing date: 2003-05-09
Publication date: 2003-11-20
Anticipated expiration: 2004-11-10
Also published as: AU2003232690A1; NO20022243D0; NO317541B1; MXPA04011185A; AU2003232690B8; NO20022243L; AU2003232690B2

Abstract

A method for laying a pipeline (8), umbilical or other coilable device from a laying vessel (1, 2) at sea, where the pipeline is uncoiled from a pipe coil (3) arranged on the vessel (1) and is brought therefrom down to the sea floor. As laying vessel use is made of a composite vessel (1, 2) which comprises a first vessel in the form of a barge (1) or the like which is connected to a second vessel in the form of a dynamically positionable vessel (2), said pipe coil (3) being placed on the barge (1).

Description

A method and a vessel for pipe-laying at sea.

The present invention relates to a method for laying a pipeline, umbilical or other coilable device from a lay- barge at sea, where the pipeline is uncoiled from a pipe 5 coil arranged on the barge and is guided therefrom via a ramp at one side of the barge down to the sea floor while the lay-barge is moved along a predetermined track.

A lay-barge for such a purpose is disclosed in GB 1312592. During the laying operation the barge is supposed to be o moved along the laying track by means of tug boats . In order to have sufficient control of the direction and speed of the movement of the barge, three or four tug boats may be needed, for instance as shown in US 4117692. Nevertheless, it will be difficult to coordinate the pulling di- 5 rection and force in order to facilitate the necessary control of the tension of the pipe and its angle with respect to the bottom of the sea during the laying. This is very important in order for the pipe not becoming over- stressed and damaged. Concurrently, it is important to o have the necessary lateral control in order for the pipe to be laid exactly in the predetermined track even when considerable wind and current is prevailing transversely of the laying direction. A further drawback is of course the high cost of having to use that many tug boats.

5 Thus, it is the purpose of the invention to provide a method and a vessel which make the laying operation less costly and makes it easier to perform, while giving at the same time better control of the tension in the pipe and the advancing direction of the barge.

o This is obtained according to the invention by a method as defined in claim 1 and a vessel as defined in claim 6. Advantageous embodiments of the invention are defined in the dependent claims. According to the invention, by moving the lay-barge by means of a dynamically positionable ves- sel which is connected to the barge so that a composite vessel is formed, approximately the same manoeuvring properties are obtained as in a much more expensive conventional installation vessel.

s For better understanding of the invention it will be described more closely with reference to the two exemplifying embodiments of laying vessels according to the invention shown in the appended drawings where:

Figure 1 shows a plan view of a first vessel according to o the invention comprising a barge and a dynamically posi- tionable vessel arranged side by side,

Figure 2 shows a side view of the barge of Figure 1,

Figure 3 shows an end view at a larger scale of the composite vessel of Figure 1 without deck equipment,

s Figure 4 shows a side view of a composite vessel comprising a barge and a dynamically positionable heavy lift vessel , and

Figure 5 shows a plan view of the vessel of Figure 4.

The vessel shown in Figure 1 comprises a barge 1, for in- 0 stance a standard North Sea barge having a flat deck and dimensions of 90 x 27 metres. The barge is connected to a dynamically positionable (DP) vessel 2 by means of moorings 17. The DP-vessel is preferably of consequence class 2.

5 The barge 1 is provided with a forward carousel or reel 3 with a coiled pipe 8. When uncoiling the pipe during laying the pipe passes from the reel 3 via a pipe deflector 10 to a pipe straightener 7, and from there on to a forward and a rear pipe tensioner 5 and 6, respectively. The o pipe further passes over a pivotally supported pipe ramp 9, which may be raised and lowered by means of a crane 11. Furthermore, the barge has a rear reel 4 for pipe or umbilical .

On the deck between the reels 3 and 4 the barge is pro- vided with a power station 13, a control room 14, a crew room 15 and a workshop 16. In conjunction with the forward reel 3 a moveable winch 18 is arranged. A crane 19 having a capacity of 10-20 tons and good lifting heights is placed so that it can handle the pipe ends during coiling of a pipe. For this operation the barge also has a welding station and a station for non-distractive testing, and a gripping arrangement for fixation of the pipe for welding (not shown) . An A/R (abandonment/recovery) winch is designated 12.

The barge 1 alone is shown in side view in Figure 2. In this connection the reels 3 , 4 of the barge are loaded with pipe or umbilical at land-based fabrication facility. Thereupon the unmanned barge is towed to the installation site, e.g. by means of a standard tug boat, typically hav- ing 60-80 tons BP. At the installation site the barge 1 is coupled to the DP vessel 2. This may be an anchor handling vessel (AHV) of DP class 2. The AHV is moored along the barge using its usual mooring equipment, i.e. hawsers 17, with necessary fenders 20 therebetween. This will also ap- pear from Figure 3, where additionally the main propeller 21, the retractable bowtruster 22 and the rear tunnel truster 23 of the AHV are shown.

In order to reduce the interaction between the propeller stream of the AHV 2 and the barge 1 as much as possible, it is advantageous to leave the aft part of the AHV extending past the end of the barge. The slip stream from the main propellers 21 and any side trusters 23 aft will have little or no interaction with the barge hull. Tunnel trusters and/or asimut trusters 22 in the bow of the AHV will be located along the forward half of the barge 1, but due to the difference of the draft they will have little or no interaction with the barge. Typical drafts are 7,5 m for the AHV and 3 m for a 90 x 27 m barge carrying a load of 5000 tons. Furthermore, it is of advantage to place the 5 AHV on the same side of the barge as the pipe ramp 9 is located. The pull from the pipeline 8, which may be quite substantial, is thereby taken up as close as possible to the motive vessel in order to minimize the turning moment to which the composite vessel is subjected by the pull o from the pipeline.

In order for the DP system of the AHV to function with its "new" hull, i.e. the barge and AHV moored together, the hull model in the software of the DP system must be changed, i.e. a new geometry and new coefficients for s wing, current and waves must be introduced. This is an operation which can be performed easily for most DP systems in current use. When this is done, a common DP test must be performed before the laying operation starts. In order to have control of where the pipe is laid on the sea o floor, an ROV must be used for monitoring of "touchdown" . It would be natural and most economical to place the ROV on the AHV. Furthermore, an acoustic reference system may be used along the laying tract in order to provide continuous signals for the DP system on the composite vessel 5 in order to facilitate continuous correction of the laying operation.

The laying of the pipe 8 is thereafter performed as a usual laying operation from a single hull laying vessel. Model tests may be used in order to find the best hull and o geometric relationships for the composite vessel. When the laying operation has been performed, the barge is brought back to the coiling base by a common tug boat while the AHV is demobilised for other jobs if this is most expedient. If such jobs are not available at profitable rates, 5 the DP vessel may of course also be used for the towing operations. As an alternative to using anchor handling vessels for the DP vessel 2, particularly in waters with more inclement weather conditions like the North Sea, use may be made by a submergible DP-controlled heavy lift vessel. Such a constellation is illustrated in Figures 4 and 5, where the barge 1 is placed on the deck of a heavy lift vessel 24 such that a minor part of the barge with the pipe ramp 9 extends outside the edge of the deck. The heavy lift vessel 24 positions the pipe 8 as during a common laying operation from a conventional single hull lay- ing vessel . The heavy lift vessel may advantageously be of the type which can lift about 15000 tons.

When the laying operation is completed, the barge 1 may be brought back to the coiling base by a common towing vessel, while the heavy lift vessel is demobilised for other jobs. Also in this case the heavy lift vessel may be used for the transportation phase if this is indicated by the job situation.

The invention is not limited to the exemplifying embodiments described above, but may be varied and modified by the skilled person within the frame of the appended claims.

Claims

C l a i m s

1. A method for laying a pipeline (8), umbilical or other coilable device from a lay-barge (1) at sea, where the pipeline is uncoiled from a pipe coil (3) arranged on the barge (1) and is moved therefrom via a ramp (9) at one side of the barge down to the sea floor while the lay- barge (1) is moved along a predetermined track, c h a r a c t e r i s e d i n that for moving the lay- barge (1) use is made of a second vessel in the form of a dynamically positionable vessel (2) , either a vessel of the anchor handling type, preferably of consequence class

2, which is moored adjacent to the lay-barge (1) along the side thereof where the ramp (9) is located, or a semi- submergible heavy lift vessel (Fig. 3) upon which the lay- barge (1) is placed.

2. A method according to claim 1, c h a r a c t e r i s e d i n that a plurality of pipe coils (3) are arranged on the barge (1) .

3. A method according to claim 1 or 2 , c h a r a c t e r i s e d i n that the barge (1) is provided with the pipe coils (3) at the shore and thereafter is towed to the installation site at sea by means of a third vessel before it (1) is moored to said second vessel (2) .

4. A method according to claim 3, c h a r a c t e r i s e d i n that said second vessel (2) is also used as said third vessel.

5. A method according to a preceding claim, c h a r a c t e r i s e d i n that the dynamic posi- tioning system of said second vessel (2) , before the laying operation is started, is reprogra med for adaptation to the composite vessel (1, 2) , the reprogramming prefera- bly comprising hull geometry and coefficients for wind, current and waves .

6. A vessel for laying pipelines (8) at sea, comprising a first vessel in the form of a lay-barge (1) having at least one pipe coil (3) with pipe (8) to be laid, and auxiliary equipment (5, 19) for such operations, and means for moving said first vessel (1) along a predetermined track, c h a r a c t e r i s e d i n that said means comprises a second vessel (2) in the form of a dynamically position- able vessel, either a vessel of the anchor handling type which is moored fixedly adjacent that side of the first vessel (1) which is closest to the point where the pipeline (8) leaves said first vessel (1) during the laying, or a semi-submergible heavy lift vessel (Fig. 3) upon which the first vessel (1) is located.

7. A vessel according to claim 6, c h a r a c t e r i s e d i n that said second vessel (2) is located adjacent said first vessel (1) with its stern (Fig. 2) provided with thrusters (Fig. 1) extending beyond said first vessel (1) .

8. A vessel according to claim 6 or 7, c h a r a c t e r i s e d i n that said first vessel

(1) is a standard North Sea barge having a flat deck and a width less than 31 m.

9. A vessel according to claim 6, 7 or 8, c h a r a c t e r i s e d i n that said auxiliary equipment comprises an adjustable laying ramp (9) , a welding station, a testing station, a gripping station for holding the pipe during welding, and a 10-20 tons crane (19) .

10. A vessel according to claim 6, 7, 8 or 9, c h a r a c t e r i s e d i n that said second vessel (2) is an anchor handling vessel having dynamic positioning equipment of consequence class 2.