Unbonded flexible pipe and an offshore system comprising an unbonded flexible pipe

Abstract

An unbonded flexible pipe for offshore transportation of fluids from a subsea facility. The unbonded flexible pipe has a length along a longitudinal center axis, and a first and a second end, and a first end fitting connected to the first end. The unbonded flexible pipe comprises from inside and out an electrically conductive carcass, an electrically insulating innermost sealing sheath, at least one electrically conductive armor layer comprising at least one helically wound electrically conductive wire and an electrically insulating outer sealing sheath. At least the electrically conductive layers are mechanically terminated in the first end fitting and the pipe comprises electrical connections arranged to apply a voltage over the electrically conductive layers which electrically conductive layers are electrically connected at a distance along the length of the unbonded flexible pipe from the first end fitting of the unbonded flexible pipe to provide an electric circuit.

Claims

1. An unbonded flexible pipe for transportation of fluids, the unbonded flexible pipe has a length along a longitudinal center axis, and a first and a second end, and a first end fitting connected to the first end, the unbonded flexible pipe comprises from inside and out an electrically conductive carcass, an electrically insulating innermost sealing sheath, at least one electrically conductive armor layer comprising at least one helically wound electrically conductive wire and an electrically insulating outer sealing sheath, at least the electrically conductive layers are mechanically terminated in the first end fitting and the pipe comprises electrical connections in the first end fitting arranged to apply a voltage over the electrically conductive layers which electrically conductive layers are electrically connected at a far position of the unbonded flexible pipe at a distance from the first end fitting of the unbonded flexible pipe to provide an electric circuit and wherein the electrically conductive carcass and the electrically conductive armor layer are selected such that a voltage drop V.sub.c over the electrically conductive carcass is larger than a voltage drop V.sub.a over the electrically conductive armor layer.

2. The unbonded flexible pipe of claim 1, wherein V.sub.c>1.5 times V.sub.a.

3. The unbonded flexible pipe of claim 1, wherein the first end fitting comprises a bore extending through a front end in which the electrically conductive layers are mechanically terminated, and through a rear end of the first end fitting, the rear end of the first end fitting comprises a flange for being connected to a production site structure in fluid connection with a flow path thereof, the rear end of the first end fitting comprises an annular wall surface defining the rear end of the bore of the first end fitting, wherein at least a part of the annular wall surface is electrically insulated from the electrically conductive carcass.

4. The unbonded flexible pipe of claim 1, wherein an electric power blocking is arranged in the rear end of the bore of the end fitting.

5. The unbonded flexible pipe of claim 4, wherein the electric power blocking is a valve.

6. The unbonded flexible pipe of claim 4, wherein the electric power blocking is a sacrificial anode comprising a metal or a metal alloy which is less noble than the annular wall surface of the first end fitting.

7. The unbonded flexible pipe of claim 1, wherein the electrical connections arranged to apply a voltage over the electrically conductive layers are arranged to be connected to a main power supply for applying the voltage over the electrically conductive layers in said first end fitting, the main power supply is a dual power supply wherein one sub-power supply is connected over one of the electrically conductive layers and a zero potential and it adds a high potential to said one of the electrically conductive layers and another sub-power supply is connected over the other one of the electrically conductive layers and the zero potential and it adds a low potential to said other one of the electrically conductive layers.

8. The unbonded flexible pipe of claim 1, wherein the unbonded flexible pipe comprises electrical connections for applying a support power supply in the electric circuit at a distance from the main power supply.

9. The unbonded flexible pipe of claim 1, wherein the unbonded flexible pipe comprises two or more pipe length sections which are mechanically and electrically connected via respective intermediate end fittings, each pipe length section comprises from inside and out an electrically conductive carcass length section, an electrically insulating innermost sealing sheath length section, at least one armor layer length section comprising a length section of the at least one helically would electrically conductive wire and an electrically insulating outer sealing sheath length section, wherein the respective length sections of the conductive layers are electrically interconnected to provide the electric circuit.

10. The unbonded flexible pipe of claim 1, wherein the unbonded flexible pipe comprises a temperature sensor.

11. An offshore system comprising a production site structure and an unbonded flexible pipe suitable for transporting fluids from a subsea facility to the production site structure, the unbonded flexible pipe has a length along a longitudinal center axis, and a first and a second end, and a first end fitting connected to the first end, wherein the unbonded flexible pipe is connected to said production site structure via said first end fitting, the unbonded flexible pipe comprises from inside and out an electrically conductive carcass, an electrically insulating innermost sealing sheath, at least one electrically conductive armor layer comprising at least one helically wound electrically conductive wire and an electrically insulating outer sealing sheath, at least the electrically conductive layers are mechanically terminated in the first end fitting and the pipe comprises electrical connections in the first end fitting arranged to apply a voltage over the electrically conductive layers which electrically conductive layers are electrically connected at a far position of the unbounded flexible pipe at a distance from the first end fitting of the unbonded flexible pipe to provide an electric circuit and wherein the electrically conductive carcass and the electrically conductive armor layer are selected such that a voltage drop V.sub.c over the electrically conductive carcass is larger than a voltage drop V.sub.a over the electrically conductive armor layer.

12. The offshore system of claim 11, wherein the flow path of the production site structure comprises an inflow flow path section surrounded by an inflow flow path wall surface which in at least a length section is electrically insulated.

13. The offshore system as claimed in claim 11, wherein the system further comprises a main power supply for applying the voltage over the electrically conductive layers, the main power supply is electrically connected to at least one of the electrical connections to the electrically conductive layers in said first end fitting.

14. The offshore system as claimed in claim 11, wherein the system further comprises a main power supply for applying the voltage over the electrically conductive layers, the main power supply is electrically connected to both of the electrical connections to the electrically conductive layers in said first end fitting.

15. The offshore system as claimed in claim 11, wherein the system further comprises a main power supply for applying the voltage over the electrically conductive layers, the main power supply is a dual power supply wherein one sub-power supply is connected over one of the electrically conductive layers and a zero potential and it adds a high potential to said one of the electrically conductive layers and another sub-power supply is connected over the other one of the electrically conductive layers and the zero potential and it adds a low potential to said other one of the electrically conductive layers.

16. The offshore system as claimed in claim 11, wherein the system comprises a support power supply in the electric circuit arranged at a distance from the main power supply, the support power supply is arranged to impress an electrical potential difference between the electrically conductive layers at the far position of the unbounded flexible pipe such that the impressed electrical potential at the far position of each of the respective electrically conductive layers is negative where the electrical potential impressed by the main power supply at the first end of the unbounded flexible pipe to each of said respective electrically conductive layers is positive and positive where the electrical potential impressed by the main power supply at the first end of the unbounded flexible pipe to each of said respective electrically conductive layers is negative.

17. The offshore system as claimed in claim 11, wherein the electrically conductive armor layer and/or the electrically conductive carcass layer is grounded.

18. The offshore system as claimed in claim 11, wherein the inflow flow path comprises an inflow path section comprising an electric power blocking.

19. The offshore system as claimed in claim 18, wherein the electric power blocking is at least one bend of the inflow path section.

20. The unbonded flexible pipe of claim 2, wherein V.sub.c>2 times V.sub.a.

21. The unbonded flexible pipe of claim 5, wherein the valve is a ball valve.

22. The unbonded flexible pipe of claim 5, wherein the valve is a gate valve.

23. The unbonded flexible pipe of claim 6, wherein the anode comprises magnesium, brass, aluminum, zinc or titanium.

Description

DESCRIPTION OF DRAWINGS

(1) The invention will be explained more fully below in connection with a preferred embodiment and with reference to the drawings in which:

(2) FIG. 1 is a schematic side view of an offshore system comprising an unbonded flexible pipe and a top site structure.

(3) FIG. 2 is a schematic side view of another offshore system comprising an unbonded flexible pipe and a top site structure.

(4) FIG. 3 is a schematic side view of an unbonded flexible pipe where the individually layers of the unbonded flexible pipe are shown.

(5) FIG. 4 is a schematic cross-sectional side view of an unbonded flexible pipe comprising an intermediate end fitting.

(6) FIG. 5 is a schematic cross-sectional side view of an unbonded flexible pipe comprising a carcass and an armor layer and a first end fitting with electrical connections for applying a voltage over the carcass and the armor layers.

(7) FIG. 6 is a schematic cross-sectional side view of another unbonded flexible pipe comprising a carcass and an armor layer and a first end fitting with electrical connections for applying a voltage over the carcass and the armor layers.

(8) FIG. 7 is a schematic cross-sectional side view of a part of an offshore system comprising an unbonded flexible pipe connected to a production site structure.

(9) FIG. 8 is a schematic cross-sectional side view of a part of another offshore system comprising an unbonded flexible pipe connected to a production site structure.

(10) FIG. 9 is a schematic side view of an embodiment of the unbounded flexible pipe of the invention connected to a main power supply.

(11) FIG. 10 is a schematic side view of an embodiment of the unbounded flexible pipe of the invention connected to a main power supply and a support power supply.

(12) FIG. 11 is a schematic illustration of a voltage diagram of an embodiment of the offshore system of the invention.

(13) The offshore system of FIG. 1 which is an embodiment of the invention comprises an unbonded flexible pipe 1 and a top site structure 2. The unbonded flexible pipe is arranged for transportation of fluids from a not shown subsea facility to the top site structure 2 which is arranged at the sea surface 9. The top site structure 2 is advantageously a vessel or a platform or an intermediate structure with fluid connection to a vessel or a platform. The unbonded flexible pipe has a first end 3, and a not shown first end fitting connected to the first end 3. The unbonded flexible pipe 1 comprises from inside and out a number of not shown layers comprising an electrically conductive carcass, an electrically insulating innermost sealing sheath, an electrically conductive armor layer comprising a helically wound electrically conductive wire and an electrically insulating outer sealing sheath. The layers of the unbonded flexible pipe 1 are mechanically terminated in the first end fitting and the pipe comprises not shown electrical connections arranged to apply a voltage over the electrically conductive layers which electrically conductive layers are electrically connected at a distance along the length of the unbonded flexible pipe from the first end fitting of the unbonded flexible pipe to provide an electric circuit. The unbonded flexible pipe 1 comprises three pipe length sections 1a, 1b, 1c mechanically interconnected with respective intermediate end fittings 5a, 5b, which intermediate end fittings 5a, 5b advantageously also provide electric interconnections. Preferably the electrically conductive layers are electrically connected in the pipe length section 1c farther from the first end fitting such as in a not shown second end fitting terminating a second end of the unbonded flexible pipe 1.

(14) The embodiment of the offshore system shown in FIG. 2 comprises an unbonded flexible pipe 11 and a top site structure 12a. The unbonded flexible pipe 11 is arranged for transportation of fluids from a subsea facility 16 to the top site structure 12a from where the fluids are transported via a top site pipe 4 e.g. a rigid or a flexible jumper, to a vessel 12b floating at the sea surface 19. The unbonded flexible pipe has a first end 13, and a not shown first end fitting connected to the first end 13. The unbonded flexible pipe 11 comprises from inside and out a number of not shown layers comprising an electrically conductive carcass, an electrically insulating innermost sealing sheath, an electrically conductive armor layer comprising a helically wound electrically conductive wire and an electrically insulating outer sealing sheath. The layers of the unbonded flexible pipe 11 are mechanically terminated in the first end fitting and the pipe comprises not shown electrical connections arranged to apply a voltage over the electrically conductive layers which electrically conductive layers are electrically connected at a distance along the length of the unbonded flexible pipe from the first end fitting of the unbonded flexible pipe to provide an electric circuit. The unbonded flexible pipe 11 comprises three pipe length sections 11a, 11b, 11c mechanically interconnected with respective intermediate end fittings 15a, 15b, which intermediate end fittings 15a, 15b advantageously also provide electric interconnections. Preferably the electrically conductive layers are electrically connected in the pipe length section 11c farther from the first end fitting such as in a not shown second end fitting connecting the unbonded flexible pipe 11 to the subsea facility 16.

(15) The unbonded flexible pipe shown in FIG. 3 comprises an innermost sealing sheath 25, e.g. of high density poly ethylene (HDPE), cross linked polyethylene (PEX), Polyvinyldifluorid (PVDF) or polyamide (PA). The innermost sealing sheath 25 is electrically insulating and further has the purpose of preventing outflow of the fluid transferred in the bore of the pipe, indicated by the arrow. Inside the innermost sealing sheath 25 the pipe comprises an electrically conductive carcass 26 which further serves the purpose of reinforcing the pipe against collapse. The carcass 26 is not liquid tight.

(16) On the outer side of the innermost sealing sheath 25, the flexible pipe comprises a pressure armor layer 23, which is e.g. of helically wound armor element(s) of metal or composite material or combinations, which is wound with an angle to the axis of the pipe of about 65 degrees or more e. g. about 85 degrees. The pressure armor layer 23 is not liquid tight.

(17) Outside the pressure armor layer 23, the pipe comprises two cross wound tensile armor layers 22a, 22b wound from elongate armor elements of metal or composite material or combinations. The elongate armor elements on the innermost tensile armor layer 22a are advantageously wound with a winding degree of about 55 degrees or less to the axis of the pipe in a first winding direction and the outermost tensile armor layer 22b is advantageously wound with a winding degree of about 60 degrees or less, such as between about 20 and about 55 degrees to the axis of the pipe in a second winding direction, which is the opposite direction to the first winding direction. The two armor layers with such opposite winding directions are normally referred to as being cross wound. The pipe further comprises an outer sealing sheath 21 protecting the armor layer mechanically and against ingress of sea water and further provides an electrical insulation. At least one of the pressure armor 23 or the tensile armor layers comprising at least one helically wound electrically conductive wire 22a, 22b. As indicated with the reference number 24, the unbonded flexible pipe preferably comprises anti-friction layers between armor layers 23, 22a, 22b. The anti-friction layers are usually not liquid tight and may for example be in the form of a wound film. In an embodiment the unbonded flexible pipe comprises not shown electrical insulation layer(s) between two or more of the armor layers 23, 22a, 22b.

(18) In the embodiment shown in FIG. 4 the unbonded flexible pipe comprising an intermediate end fitting between a first and a second length section 31a, 31b of the unbonded flexible pipe in which only some of the layers of the unbonded flexible pipe are terminated. The first and a second length section 31a, 31b of the unbonded flexible pipe comprise a number of not terminated layers 36 comprising from inside and out electrically conductive carcass, an electrically insulating innermost sealing sheath and a pressure armor layer. The first and the second length section 31a, 31b of the unbonded flexible pipe comprise each a number of terminated layers comprising from inside and out a pair of cross wound electrically conductive tensile armor layers and an electrically insulating outer sealing sheath 34a, 34b. An electrical insulation intermediate sheath is advantageously arranged to provide an electrical insulation between the pressure armor layer and the tensile armor layers. The electrical insulation intermediate sheath may be a terminated layer or a non-terminated layer provided that it provides the desired electrical insulation. The first and the second length section 31a, 31b can independently of each other comprise one or more additional layers, such as an insulation layer, an additional reinforcing layer etc.

(19) The tensile armor layer 32a of the first length section 31a is electrically connected to the tensile armor layer 32b of the second length section 31b for example as indicated by the wires 37a, 37b which electrically connect the tensile armor layers 32a, 32b to a connecting element 38 which in an embodiment is in the form of a voltage controller and/or a conductor controlling the voltage drop over the tensile armor layers 32a, 32b along the length of the respective length sections.

(20) In the embodiment of the invention shown in FIG. 5 only a section of the pipe 41a comprising the first end fitting 43 is shown. The unbonded flexible pipe comprises an electrically conductive carcass 46, an electrically insulating innermost sealing sheath 45, a pair of cross wound electrically conductive tensile armor layers 42 comprising at least one helically wound electrically conductive wire and an electrically insulating outer sealing sheath 41. The unbonded flexible pipe further comprises a pressure armor layer 43a which may also be electrically conductive. In a variation the pressure armor layer 43a is omitted. In another variation an electrically insulating layer is arranged between the pressure armor layer 43a and the pair of cross wound electrically conductive tensile armor layers 42. All of the layers of the unbonded flexible pipe are terminated in the first end fitting 43. The carcass 46, the electrically insulating innermost sealing sheath 45, and the pressure armor layer 43a are securely fixed as indicated with the fixing arrangement 47. The fixing arrangement is preferably arranged to fix each of the layers 46, 45, 43a individually e.g. as known in the art. An electrical connection 48a is arranged to connect the carcass 46 to a conductor 48b, such as a single voltage conductor. In the shown embodiment the connection to the carcass 46 is via the fixing arrangement 47. In a variation the electrical connection 48a is a direct connection to the carcass.

(21) The electrically conductive tensile armor layers 42 are terminated and fixed in a fixing material 42a e.g. epoxy and an electrical connection 49 is arranged to connect the electrically conductive tensile armor layers 42 to ground.

(22) The first end fitting 43 comprises a front end 53a in which the electrically conductive layers are mechanically terminated, and a rear end 53b. The first end fitting 43 has a bore 50 extending through the front end 53a and the rear end 53b.

(23) The rear end 53b of the first end fitting 43 comprises a flange 52 with mounting holes 52a for being connected to a not shown production site structure in fluid connection with a flow path thereof.

(24) The rear end 53b of the first end fitting 43 comprises an annular wall surface 54 defining the rear end of the bore of the first end fitting, wherein at least a part 54a of the annular wall surface rear end 53b of the first end fitting 43 is electrically insulated from the electrically conductive carcass for example by being coated with a non-conducting polymer layer e.g. the part 54a of the annular wall surface rear end 53b is in the form of a wall section at the rear end comprising a rear end insulating layer in the form of an extension of the innermost sealing sheath.

(25) An electric power blocking 55 in the form of a valve 55 is arranged in the rear end of the bore 50 of the end fitting. The valve 55 is arranged immediately adjacent to the insulated part 54a of the annular wall surface rear end 53b.

(26) FIG. 6 shows another embodiment of an unbonded flexible pipe of the invention. The embodiment of FIG. 6 is similar to the embodiment of FIG. 5 where it is marked with same reference numbers. In the embodiment of FIG. 6 electrical connection 48a is arranged to connect the carcass 46 to an main power supply 58 and the electrical connection 49 is arranged to connect the electrically conductive tensile armor layers 42 to the main power supply 58. Thereby a voltage can be applied by the main power supply 58.

(27) An electric power blocking 55a in the form of an annular sacrificial anode 55a is arranged in the rear end of the bore 50 of the end fitting. Advantageously the cross wound electrically conductive tensile armor layers 42 are grounded at a position along the length of the unbonded flexible pipe e.g. in a distance of for example at least 10 m from the first end fitting 43.

(28) In the embodiment of the offshore system of the invention shown in FIG. 7 the offshore system comprises an unbonded flexible pipe 61 comprising a first end fitting 63 connected to a production site structure 72 by connecting elements 62a. The first end fitting 63 comprises a bore and the production site structure 72 comprises an inflow flow path section 70 arranged in fluid connection with the bore 60.

(29) The unbonded flexible pipe comprises from inside and out an electrically conductive carcass 66, an electrically insulating innermost sealing sheath 65, and a pair of cross wound electrically conductive tensile armor layers 62 comprising at least one helically would electrically conductive wire and an electrically insulating outer sealing sheath 61a. The layers are terminated as described in FIG. 5. The electrically conductive carcass 66 is connected to a conductor 68 and the tensile armor layers are grounded 69.

(30) The first end fitting 63 comprises a rear end 63b comprising an annular wall surface 64 defining the rear end of the bore 60 of the first end fitting 63. The entire annular wall surface 64 comprises an electrically insulating coating e.g. in the form of an extension of the electrically insulating innermost sealing sheath 65.

(31) The inflow path section 70 of the production site structure 72 is surrounded by an inflow flow path wall surface 74 which in a length section 74a immediately adjacent to the first end fitting 63 is electrically insulated e.g. by comprising an extension of the innermost sealing sheath 65 of the unbonded flexible pipe 61.

(32) The inflow path section 70 comprises an electric power blocking in the form of a sacrificial anode 75b and a valve 75a.

(33) In the embodiment of the offshore system of the invention shown in FIG. 8 the production site system comprises an unbonded flexible pipe 81 comprising a first end fitting 83 connected to a production site structure 92 by connecting elements 82a. The first end fitting 83 comprises a bore 80 and the production site structure 92 comprises a flow path 90 with an inflow flow path section 90a arranged in fluid connection with the bore 80.

(34) The unbonded flexible pipe comprises from inside and out an electrically conductive carcass 86, an electrically insulating innermost sealing sheath 85, and a pair of cross wound electrically conductive tensile armor layers 82 comprising at least one helically would electrically conductive wire and an electrically insulating outer sealing sheath 81a. The layers are terminated as described in FIG. 5. An main power supply 88 is arranged to apply a voltage over the carcass 86 and the tensile armor layers 82. The tensile armor layers 82 are advantageously grounded 89 at a distance from the first end fitting 83 e.g. in a not shown second end fitting or in a not shown intermediate end fitting.

(35) The first end fitting 83 comprises a rear end comprising an annular wall surface 84 defining the rear end of the bore 80 of the first end fitting 83. The entire annular wall surface 84 comprises an electrically insulating coating e.g. in the form of an extension of the electrically insulating innermost sealing sheath 85.

(36) The inflow path section 90a of the production site structure 92 is surrounded by an inflow flow path wall surface which in a length section 794 immediately adjacent to the first end fitting 83 is electrically insulated e.g. by comprising an extension of the innermost sealing sheath 85 of the unbonded flexible pipe 81.

(37) The inflow path section 90a comprises an electric power blocking in the form of a bend 95a with a bending degree of about 90 degrees and a sacrificial anode 75b arranged in the bend 95a where turbulent flow can be expected.

(38) FIG. 9 show an embodiment of the unbounded flexible pipe of the invention connected to a main power supply 106. The unbounded flexible pipe has a plurality of layers, but only the carcass 101 and the electrically conducting armor later 102 are shown. The unbounded flexible pipe has a first end terminated in a first end-fitting indicated with the dotted lines 103 and a second end terminated in a second end-fitting indicated with the dotted lines 107. It should be understood that the unbounded flexible pipe generally has a length of from 20 m up to several hundred m or even 1, 2 or 3 km or longer. The distance between the two ends of the pipe can therefore be quite substantial. The unbounded flexible pipe comprises electrical connections 104, 105 arranged to apply a voltage over the electrically conductive layers 101, 102. The main power supply 106 is connected to the electrical connections 104, 105. It should be understood that the main power supply 106 advantageously can be turned on and of e.g. via a toggle switch optionally in dependence of the temperature of the fluid in the pipe and optionally automatic regulated by a not shown regulating unit. The electrically conductive layers 101, 102 are connected to each other in the second end-fitting 107 as indicated with the interconnection 108. This interconnection can for example be a toggle switch or a short circuiting arrangement.

(39) FIG. 10 show another embodiment of the unbounded flexible pipe of the invention connected to a main power supply 116. The unbounded flexible pipe has a plurality of layers, but only the carcass 111 and the electrically conducting armor later 112 are shown. The unbounded flexible pipe has a first end terminated in a first end-fitting indicated with the dotted lines 113 and a second end terminated in a second end-fitting indicated with the dotted lines 117. The unbounded flexible pipe comprises electrical connections 114, 115 arranged to apply a voltage over the electrically conductive layers 111, 112. The main power supply 116 is connected to the electrical connections 114, 115. At the second end of the pipe in the second end-fitting 117, the electrically conductive layers 111, 112 are connected to each other via a support power supply 120 connected to the respective electrically conductive layers 111, 112 via electrical connections 118, 119. The impressed potentials at the respective first and second end of the respective electrically conductive layer may for example be as described above.

(40) FIG. 11 shows the power drop over respectively the electrically conductive carcass 121 and the electrically conductive armor layer 122. At the first end fitting 123 the electrically conductive carcass 121 and the electrically conductive armor layer 122 are connected to a power supply 130, which impress a voltage over the layers. At the far positionhere the second end fitting 127 the electrically conductive carcass 121 and the electrically conductive armor layer 122 are interconnected and grounded such that the electrical potential at this position is zero. The electrical potential is shown in the diagram where the voltage is plotted in dependence of the position along the pipe. It can be seen that the voltage drop over the carcass 121 is much larger than the voltage drop over the armor layer 121, which means that most of the heat will be generated in the carcass.