Abstract
Provided is a method of laying empty pipes on the seabed, which method includes arranging a plurality of empty pipes in a bundle; arranging a bundle-strengthening element in a cavity defined by the pipes of the bundle; binding the bundle; and lowering the bundle to the seabed.
Claims
1. A method of laying empty pipes on the seabed, the method comprising: arranging a plurality of empty pipes in a bundle, wherein the plurality of empty pipes includes at least three pipes; arranging at least one bundle-strengthening element in a cavity defined by the plurality of empty pipes of the bundle, wherein the cavity is entirely surrounded or substantially surrounded by the plurality of empty pipes of the bundle; binding the bundle; and lowering the bundle to a seabed, wherein the weight of the at least one bundle-strengthening element is chosen to counteract the buoyancy of the plurality of empty pipes prior to or during lowering of the bundle to the seabed and ensure that the bundle remains submerged.
2. The method according to claim 1, wherein the radius of the bundle-strengthening element is chosen such that the bundle-strengthening element touches all empty pipes of the bundle.
3. The method according to claim 1, wherein the step of binding the bundle comprises wrapping tape around the bundle.
4. The method according to claim 1, wherein the empty pipes have the same diameter.
5. The method according to claim 1, wherein an empty pipe of the plurality of empty pipes is an unarmoured pipe.
6. The method according to claim 1, wherein the step of lowering the bundle to the seabed is followed by a horizontal directional drilling procedure to bury the bundle into the seabed.
7. A method according to claim 1, wherein the step of lowering the bundle to the seabed is followed by a step of installing a transmission cable arrangement into a pipe of the plurality of empty pipes.
8. The method according to claim 1, wherein the step of lowering the bundle to the seabed is followed by a step of pumping water into the plurality of empty pipes.
9. A bundling system, the bundling system comprising: a plurality of drums, each drum carrying a coiled empty pipe; at least one further drum carrying a coiled bundle-strengthening element; and a bundling unit adapted to arrange a plurality of the coiled empty pipes in a bundle and to arrange the coiled bundle-strengthening element in a cavity in the interior of the bundle, wherein the plurality of the coiled empty pipes includes at least three pipes, wherein the cavity is entirely surrounded or substantially surrounded by the plurality of empty pipes of the bundle, and wherein the weight of the at least one coiled bundle-strengthening element is chosen to counteract the buoyancy of the coiled empty pipes prior to or during lowering of the bundle to a seabed and ensure that the bundle remains submerged.
10. The bundling system according to claim 9, further comprising a binding unit adapted to bind the bundle.
11. The bundling system according to claim 9, further comprising a feeding unit adapted to feed the bundle onto or into the seabed.
12. The bundling system according to claim 9, wherein the bundle-strengthening element comprises a communications cable or an empty tube configured to accommodate a communications cable.
13. The bundling system according to claim 9, wherein the bundle-strengthening element comprises a wire rope.
14. The bundling system according to claim 13, wherein the bundling system is installed on a marine vessel.
Description
BRIEF DESCRIPTION
(1) Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein:
(2) FIG. 1 shows a first bundle that can be formed using embodiments of the inventive method as described herein;
(3) FIG. 2 shows a second bundle that can be formed using embodiments of the inventive method as described herein;
(4) FIG. 3 shows a third bundle that can be formed using embodiments of the inventive method as described herein;
(5) FIG. 4 shows a fourth bundle that can be formed using embodiments of the inventive method as described herein;
(6) FIG. 5 shows a fifth bundle that can be formed using embodiments of the inventive method as described herein;
(7) FIG. 6 shows an export line formed as a bundle using the inventive method;
(8) FIG. 7 indicates groups of wind turbines connected to an onshore substation by the bundle described in FIG. 6;
(9) FIG. 8 shows a prior art approach to installation;
(10) FIG. 9 shows an embodiment of the inventive bundling system; and
(11) FIG. 10 shows a step of loading an empty pipe with a transmission cable.
DETAILED DESCRIPTION
(12) FIGS. 1-5 show various different bundles B, B.sub.3, B.sub.6, B.sub.9 that can be formed using the inventive method. In FIG. 1, the bundle B is made of three empty pipes P, each with the same diameter. These empty tubes P or pipes P may be used to accommodate transmission cables to an offshore installation such as a wind turbine, for instance. Alternatively, they may be used to transport gas or oil from an offshore drilling facility to an onshore depot. A cavity C is formed by the triangular configuration of the three empty pipes P, and a bundle-strengthening element E is arranged in this cavity C during the bundling procedure. The inner bundle-strengthening element can be a communications cable E. Alternatively, the bundle-strengthening element E can be hollow and large enough to later accommodate a communications cable. The diameter of the bundle-strengthening element E is chosen so that it just fits inside the cavity C and touches each of the surrounding pipes P.
(13) In FIG. 2, the bundle B is made of four empty pipes P, each with the same diameter. In this exemplary embodiment, a hollow tube E is arranged in the cavity formed by the four empty pipes P, and the hollow tube E is loaded with a communications cable CC. The diagram also shows several further bundle-strengthening elements E arranged on the outside of the bundle B in the channels formed by adjacent pipes P. In this embodiment, these outer bundle-strengthening elements E are wire ropes or wire cables that have sufficient weight to ensure that the bundle B remains submerged, i.e. to counteract the buoyancy of the air in the empty pipes P.
(14) FIG. 3 shows a three-pipe bundle B.sub.3. The three pipes P have each been loaded with a transmission cable TC, and the remaining space has been filled with water for the purpose of cooling the transmission cables TC. The inner bundle-strengthening element CC is a communications cable such as a fibre-optic cable. In this exemplary embodiment, three more outer bundle-strengthening elements E are arranged in the channels formed by the three pipes P along the outside of the bundle B.sub.3. These outer bundle-strengthening elements E may be wire ropes or cables, for example. Of course, it may be sufficient to use only one or two such bundle-strengthening elements E, or none at all if the weight of the inner bundle-strengthening element is sufficient to give the bundle the desired stability. The diagram also indicates a wrapping tape W that serves to hold the bundle together. It may be assumed that all bundles described herein can be wrapped after the bundle is formed, using a wrapper machine as described above.
(15) Similarly to FIG. 3, FIG. 4 shows a six-pipe bundle B.sub.6. Here also, the six pipes P have each been loaded with a transmission cable TC. Two inner bundle-strengthening elements CC are provided in the form of communications cables. In this exemplary embodiment, six additional outer bundle-strengthening elements E are arranged in channels formed by adjacent pipes P along the outside of the bundle B.sub.6. This six-pipe bundle B.sub.6 can extend from an onshore location to the perimeter of a wind farm where it is divided into two three-pipe bundles B.sub.3 similar to that described in FIG. 3 above. Each three-pipe bundle can be formed to comprise three pipes, a communications cable CC in the centre, and three outer bundle-strengthening elements E arranged in the channels formed along the outside of the bundle. FIG. 5 shows a nine-pipe bundle B.sub.9, which can be divided into three three-pipe bundles B.sub.3 similar to that described in FIG. 3 above.
(16) Such a division is illustrated in FIG. 6, which shows an export line L with a length in the region of 50 km extending from an onshore substation 4 to an offshore windfarm 5. At the windfarm, the nine-pipe bundle B.sub.9 is divided into three smaller bundles B.sub.3, each with three pipes P, an inner communications cable CC acting as a bundle-strengthening element and a number of outer bundle-strengthening elements E. The pipes P can be loaded with the transmission cables TC after completion of the bundle-laying procedure.
(17) FIG. 7 indicates six groups of twelve wind turbines (indicated by the six strings of dots). Each wind turbine “string” is connected to the onshore substation by a three-pipe bundle B.sub.3, which in this exemplary embodiment has a capacity of 145 kV, and the three bundles B.sub.3 shown in the diagram originate from a nine-pipe bundle B.sub.9 described in FIG. 5 and FIG. 6 above.
(18) In a prior art approach as shown in FIG. 8, wind turbines of a windfarm 5 must be connected to an offshore substation 80 over transmission lines, each with a capacity of 33-66 kV. The offshore substation 80 is connected to an onshore substation 8 by means of a transmission line L.sub.8 with a capacity of 130-220 kV.
(19) FIG. 9 shows an embodiment of the inventive bundling system 1. In this embodiment, the bundling system is installed on a marine vessel 3. The bundling system 1 comprises a plurality of drums 10. Several drums have been loaded with coiled empty pipes P. At least one other drum has been loaded with coiled bundle-strengthening elements, e.g. a communications cable CC to be enclosed by the pipes of a bundle, and a number of further drums carrying wire cables E to provide additional weight to the bundle. A bundling machine 11 is fed with the desired number of empty pipes P and the desired bundle-strengthening elements E, CC, and arranges these in a bundle B, for example any bundle described in FIGS. 1-5 above. As the bundle B emerges from the bundling machine 11, it is wrapped in tape by a bundle wrapper 12, and pushed downwards into the sea so that it is lowered to the seabed. For the sake of clarity, such a feeding unit F is shown schematically in the diagram. The marine vessel 3 proceeds through the water at a rate that is matched to the speed of the bundling system 1.
(20) FIG. 10 shows a step in a later procedure in which an empty pipe P is loaded with a transmission cable TC. A “pig” 20 is connected to one end of a transmission cable TC and inserted into one end of a pipe P. The pipe P is provided with a water inlet 21 and a seal 22. When pressurized water is pumped into the pipe P, the pig 20 is propelled along the pipe P, pulling the transmission cable TC behind it. Friction rollers 23 can assist in pushing the transmission cable TC into the pipe P.
(21) Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.
(22) For the sake of clarity, it is to be understood that the use of “a” or “an” throughout this application does not exclude a plurality, and “comprising” does not exclude other steps or elements.
