AN OFFSHORE PIPE SYSTEM AND A METHOD OF HEATING UNBONDED FLEXIBLE PIPES IN AN OFFSHORE PIPE SYSTEM

Abstract

The present invention relates to an offshore pipe system comprising a first unbonded flexible pipe and a second unbonded flexible pipe for transportation of fluids such as oil or gas. Each of the unbonded flexible pipes comprises a sealing sheath and an electrically conductive armor layer, and, moreover, the system comprises a first end fitting connected to the first end of the first unbonded flexible pipe and a second end fitting connected to the first end of the second unbonded flexible pipe. In the offshore pipe system the electrically conductive armor layer of the first unbonded flexible pipe is electrically connected with the electrically conductive armor layer of the second unbonded flexible pipe via a first electrical connection and a second electrical connection. To obtain an electrical circuit the first and second electrical connections are applied with a distance along the length of the first unbonded flexible pipe and the second unbonded flexible pipe, respectively. The invention also relates to a method for heating pipes by forming an electrical circuit between the pipes.

Claims

1. An offshore pipe system comprising a first unbonded flexible pipe and a second unbonded flexible pipe for transportation of fluids, each of said unbonded flexible pipes has a length along a longitudinal center axis, and a first and a second end, each of said unbonded flexible pipes comprises a sealing sheath and an electrically conductive armor layer, the system further comprises a first end fitting connected to the first end of the first unbonded flexible pipe and a second end fitting connected to the first end of the second unbonded flexible pipe wherein the electrically conductive armor layer of the first unbonded flexible pipe is electrically connected with the electrically conductive armor layer of the second unbonded flexible pipe via a first electrical connection and a second electrical connection, the first and second electrical connections are applied with a distance along the length of the first unbonded flexible pipe and the second unbonded flexible pipe, respectively.

2. The offshore pipe system according to claim 1, wherein the electrically conductive layer of the first unbonded flexible pipe is impressed with an electrical potential via its first electrical connection and the electrically conductive layer of the second unbonded flexible pipe is impressed with an electrical potential via its second electrical connection such that the summarized charge flowing through the first and the second unbonded flexible pipe is substantially zero (zero net charge).

3. The offshore pipe system according to claim 1, wherein the first end of the first unbonded flexible pipe is connected to a master potential and the potential of the second end of the second unbonded flexible pipe is actively adjusted to provide substantially zero net flow of current through the system.

4. The offshore pipe system according to claim 1, wherein the first end of the first unbonded flexible pipe and the second end of the second unbonded flexible pipe are connected to the two terminals of a power supply which is electrically floating.

5. (canceled)

6. (canceled)

7. The offshore pipe system according to claim 1, wherein the electrically conductive armor layer is arranged on the inside of the sealing sheath.

8. (canceled)

9. The offshore pipe system according to claim 1, wherein the electrically conductive armor layer is arranged on the outside of the sealing sheath.

10. (canceled)

11. (canceled)

12. The offshore pipe system according to claim 1, wherein the first electrical connection is applied between the first and the second end fitting.

13. The offshore pipe system according to claim 1, wherein the second electrical connection is applied between the second end of the first unbonded flexible pipe and the second end of the second unbonded flexible pipe.

14. The offshore pipe system according to claim 1, wherein the electrically conductive armor layer of the first unbonded flexible pipe is connected with ground.

15. The offshore pipe system according to claim 1, wherein the electrically conductive armor layer of the second unbonded flexible pipe is connected with ground.

16. (canceled)

17. (canceled)

18. The offshore pipe system according to claim 1, wherein the system comprises at least a third unbonded flexible pipe, said unbonded flexible pipe has a length along a longitudinal center axis, and a first and a second end, said unbonded flexible pipe comprises a sealing sheath and an electrically conductive armor layer.

19. The offshore pipe system according to claim 1, wherein, the system further comprises at least a third end fitting connected to the first end of the at least third unbonded pipe.

20. The offshore pipe system according to claim 1, wherein the third unbonded pipe is electrically connected with the first and the second unbonded pipe.

21. An offshore pipe system according to claim 1, wherein the offshore pipe system comprises at least one sacrificial anode.

22. (canceled)

23. A method for heating pipes in an offshore pipe system comprising at least a first unbonded flexible pipe and a second unbonded flexible pipe for transportation of fluids, each of said unbonded flexible pipes has a length along a longitudinal center axis, and a first and a second end, each of said unbonded flexible pipes comprises a sealing sheath and an electrically conductive armor layer, said method comprises the steps of: establishing an electrical connection between the electrically conductive armor layer of the first unbonded flexible pipe and the electrically conductive armor layer of the second unbonded flexible pipe to form an electrical circuit; and connecting the electrical circuit with a power supply capable of sending an electric current through the electrical circuit to heat the electrically conductive armor layers.

24. (canceled)

25. The method according to claim 23, wherein a first electrical connection is established between a first end fitting connected to the first end of the first unbonded flexible pipe and a second end fitting connected to the first end of the second unbonded flexible pipe.

26. The method according to claim 23, wherein a second electrical connection is established between the second end of the first unbonded flexible pipe and the second end of the second unbonded flexible pipe.

27. The method according to 23, wherein the first end of the electrically conductive layer of the first unbonded flexible pipe is impressed with a master potential and the second end of the electrically conductive layer of the second unbonded flexible pipe is impressed with a slave potential.

28. The method according to claim 23, wherein the master potential and the slave potential are adjusted such that the summarized current though the electrically conductive layer of the first unbonded flexible pipe and the electrically conductive layer of the second unbonded flexible pipe is substantially zero.

29. The method according to claim 23, wherein the offshore system comprises: a first end fitting connected to the first end of the first unbonded flexible pipe and a second end fitting connected to the first end of the second unbonded flexible pipe, and wherein the step of establishing an electrical connection is performed via a first electrical connection and a second electrical connection, the first and second electrical connections are applied with a distance along the length of the first unbonded flexible pipe and the second unbonded flexible pipe, respectively.

Description

DESCRIPTION OF DRAWINGS

[0105] The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

[0106] FIG. 1 shows an embodiment of a pipe system according to the invention;

[0107] FIG. 2 shows a schematically depiction of the electric circuit;

[0108] FIG. 3 shows an embodiment of a flexible pipe;

[0109] FIG. 4 shows an end fitting according to the invention;

[0110] FIG. 5 shows an alternative embodiment of the pipe system

[0111] The drawings are only schematically and only intended for showing the principles of the present invention and some details which do not form part of the invention have been omitted. The same reference numbers may be used for the same parts in the drawings.

[0112] FIG. 1 shows a floating production unit 1 which comprises an offshore pipe system 2 according to the invention. The floating production unit 1 is connected with a first unbonded flexible pipe 3 and a second unbonded flexible pipe 4. The pipes 3 and 4 are connected with the floating production unit 1 via a bearing structure 5 above the sea line 6.

[0113] At their second ends the pipes 3 and 4 are connected to subsea facilities 7 and 8 located at the seabed 9.

[0114] The unbonded flexible pipes 3 and 4 each comprise a layer which is electrically conductive. In this particular embodiment the electrically conductive layer is the inner armor layer, i.e. the carcass which is made from an electrically conductive stainless steel.

[0115] The pipes 3 and 4 are at their first ends connected to the bearing structure 5 via a first end fitting 10 and a second end fitting 11. At their second ends the unbonded flexible pipes 3 and 4 are connected with the subsea facilities 7 and 8 via second-end end fittings 12 and 13.

[0116] All the end fittings in the offshore pipe system 2 is equipped with electrical wiring and connection which allow the end fittings to transfer an electric current from a power supply to the carcasses of the pipes 3 and 4 and electrical connections between the carcasses. In FIG. 1 the power supply is not shown, however, the power supply is placed on the floating production unit 1 and the electric power is generated by an engine on the floating production unit.

[0117] Thus, the electrical current from the power supply is sent via the first end fitting 10 through the carcass of the first pipe 3 to the end fitting 12. The end fitting 12 is connected with the subsea facility 7, which is electrically connected with the subsea facility 8 via the connection line 15. From the subsea facility the electrical current passes through the end fitting 12 and into the carcass of the second pipe 4, and to the second end fitting 11 from which it is returned to the power supply.

[0118] The above description basically describes how the system works with direct current. In case of alternating current the direction of the current will change in response to the frequency of the impressed voltage. However, sending a current through an electrically conductive layer in a flexible pipe is already known and a skilled person will be able to adapt the present invention to be operated with direct current (DC) or alternating current (AC) respectively.

[0119] Although the connection line 15 between the subsea facilities is shown as being below the seabed 9, the connection line 15 may also be placed directly on the seabed 9 or above the seabed if desired.

[0120] FIG. 2 is a schematically depiction of the electric circuit in the offshore pipe system shown in FIG. 1.

[0121] The electrical circuit 22 comprises a first electrical conduit 23 and a second electrical conduit 24. The first electrical conduit 23 extends between the connection points 25 and 27. In a similar manner the second electrical conduit 24 extends between the connection points 23 and 27. In this respect, the electrical conduits 23 and 24 illustrate the electrically conductive layers of the unbonded flexible pipes and the electrical connections points 25, 26, 27 and 28 correspond to end fittings in the offshore pipe system in FIG. 1.

[0122] The electrical circuit 22 also comprises a power source 29, which sends electric power through the electric conduits 23 and 24 via wires 30 and 31 and connection line 32. In FIG. 2 the electric power travels in the circuit 22 in one direction which is the case when direct current is applied. Due to the electrical resistance in the electrical conduits 23 and 24, the electric current passing though the conduits will cause the temperature to increase in the conduits and thus provide a heating effect.

[0123] FIG. 3 shows section of an unbonded flexible pipe 40 suitable for use in the offshore pipe system according to the invention. From the inside an out the pipe comprises an armor layer 41, a sealing sheath 42, a second armor layer 43 and a third armor layer 44, and finally a sealing sheath 45.

[0124] The inner armor layer 41 is normally known as the carcass and comprises an elongate strip wound to form a tube. The elongate strip is in most cases made from steel, in particular stainless steel. However, for some purposes the carcass may be made from other materials, such as polymer material or composite materials.

[0125] The sealing sheath 42 is referred to as the innermost sealing sheath and is covering the carcass or inner armor layer 41. The innermost sealing sheath is constituted by an extruded layer of polymer material, such as poly ethylene. Normally the sealing sheath 42 is substantially impermeable to liquid and also electrically insulating.

[0126] The armor layers 43 and 44 are normally known as tensile armors. The layers 43 and 44 may be made from metal wires or wires of polymer or composite material.

[0127] The sealing sheath 45 is normally referred to as the outer sealing sheath. The outer sealing sheath 45 is conveniently an extruded layer of polymer material, e.g. polyethylene.

[0128] When the unbonded flexible pipe 40 is used in the offshore pipe system according to the invention, the electrically conductive layer will usually be the inner armor layer 41. As mentioned the carcass or inner armor layer is in most cases made from metal, such as stainless steel which is electrically conductive and has a suitable electrical resistivity around 10.sup.8 (m).

[0129] Alternatively one of the layers 43 or 44 may be used as electrically conductive layer. These layers are often made from metal, e.g. from stainless steel.

[0130] FIG. 4 shows a schematical section of an end fitting 50 comprising electric wiring for connecting an electrical conductive layer in a flexible pipe with a power supply.

[0131] The unbonded flexible pipe 60 which is terminated in the end fitting 50 is only shown with the carcass 61 and the sealing sheath 62. In this embodiment the carcass 61 is the electrically conductive layer. In practice the unbonded flexible pipe may comprise more layers as shown in FIG. 3 and these layers may be terminated in the end fitting in a conventional manner.

[0132] Consequently, the end fitting 50 is shown in a simplified embodiment showing the housing 51 and mounting flange 52 with holes 53 for bolt.

[0133] The pipe 60 has a bore 63 defined by the carcass 61 for transporting fluids. The bore 63 corresponds with a bore 54 in the end fitting 50. The carcass 61 is terminated with a carcass end ring 64 which is in electric contact with an electrically conducting ring shaped member 55 mounted in the end fitting 50. The electrically conducting ring shaped member 55 is insulated from the end fitting 50 by the insulator 56.

[0134] The electrically conducting ring shaped member 55 is connected with a connection point or contact 57 in the mounting flange 52 via the electric wire 58. The bore 54 of the end fitting may be coated with an insulating material to reduce the risk of galvanic corrosion in the end fitting when an electric current is send through the carcass 61.

[0135] In the embodiment shown in FIG. 4, the electric contact 57 is mounted in the flange 52. However, it is also possible to place the contact 57 differently, e.g. in a side surface of the end fitting.

[0136] FIG. 5 shows an embodiment of the offshore pipe system comprising three pipes.

[0137] Basically the offshore pipe system 2 shown in FIG. 5 corresponds to the system shown in FIG. 1, in which a floating production unit 1 comprises an offshore pipe system 2 according to the invention. The floating production unit 1 is connected with a first unbonded flexible pipe 3, a second unbonded flexible pipe 4, and a third unbonded flexible pipe 16. The pipes 3, 4 and 16 are connected with the floating production unit 1 via a bearing structure 5 above the sea line 6.

[0138] At their second ends the pipes 3, 4 and 16 are connected to the subsea facilities 7, 8 and 17 located at the seabed 9.

[0139] The unbonded flexible pipes 3, 4 and 16 each comprise a layer which is electrically conductive.

[0140] The pipes 3, 4 and 16 are at their first ends connected to the bearing structure 5 via a first end fitting 10, a second end fitting 11, and a third end fitting 18. At their second ends the unbonded flexible pipes 3, 4 and 16 are connected with the subsea facilities 7, 8 and 17 via second-end end fittings 12, 13 and 19.

[0141] All the end fittings in the offshore pipe system 2 is equipped with electrical wiring and connection which allow the end fittings to transfer an electric current from a power supply to the electrically conductive layers of the pipes 3, 4, 16 via electrical connections between the electrical conductive layers. In FIG. 5 the power supply is not shown, however, the power supply is placed on the floating production unit 1 and the electric power is delivered from a generator on the floating production unit.

[0142] The electrical current from the power supply is sent via the first end fitting 10 through the carcass of the first pipe 3 to end fitting 12. The end fitting 12 is connected with the subsea facility 7, which is electrically connected with the subsea facility 8 via the connection line 15, which via connection line 15a is further connected with the subsea facility 17. From the subsea facilities the electrical current passes through the end fittings 13 and 19 into the electrically conductive layers of the second pipe 4 and the third pipe 16, and to the second end fitting 11 and the third end fitting 18 from which it is returned to the power supply to close the electrical circuit.

[0143] Thus, the electric current is sent to the seabed 9 via the pipe 3 and returned to the sea line 6 via the pipes 4 and 16. As it may be seen in FIG. 5 the unbonded flexible pipe 3 is significantly longer than the unbonded flexible pipes 4 and 16, and although the returning current is divided to run in two electrically conductive layers, the current will still be able to provide a heating effect in the two electrically conductive layers. Each of the electrically conductive layers of the pipes 4 and 16 will have a shorter length than the length of the electrically conductive layer in the pipe 3,

[0144] In respect of the direction of the current, this will only be true when applying direct current to the offshore pipe system. However, a skilled person will also know how to apply alternating current to the offshore pipe system.

[0145] A skilled person will also be able to adapt the offshore pipe system to other combinations of three or more pipes. Moreover, a skilled person will be able to select suitable electrically conductive material for the electrically conductive armor layer, e.g. among electrically conductive steel alloys.