Flexible pipe assembly comprising a built-in power cable

Abstract

The invention relates to a flexible pipe assembly (1) for use in a subsea installation (26). It comprises an unbonded flexible pipe (7) comprising a pressure sheath (10), at least one tensile armor layer (11) comprising a plurality of helically wound elongate elements (12), an outer sheath (13), and a first end fitting (8) and a second end fitting (9) located at respective ends of the flexible pipe. At least two of the elongate elements are arranged separated by a gap (15) forming a helical path along which at least one electric power cable (4) is arranged. Opposite ends of the at least one power cable are configured to be electrically connected to an associated first external device (2) and an associated second external device (5), thereby enabling transfer of electric power from the first external device to the second external device via the at least one power cable during use.

Description

[0001] FLEXIBLE PIPE ASSEMBLY COMPRISING A BUILT-IN POWER CABLE

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to a flexible pipe assembly for use in a subsea installation, wherein the flexible pipe assembly comprises an unbonded flexible pipe. In particular, it relates to a flexible pipe assembly comprising at least one power cable. Thereby, in addition to its use for transferring fluid, the flexible pipe assembly can also be used for transferring electric power via the at least one power cable from a first external device to a second external device connected at respective ends of the flexible pipe assembly. The invention further relates to a subsea installation comprising such flexible pipe assembly, the use thereof, and a method of manufacturing.

[0004] BACKGROUND OF THE INVENTION

[0005] Unbonded flexible pipes of the present type are for example described in the standard "Recommended Practice for Flexible Pipe", ANSI / API 17B, fifth edition, May 2014, and the standard "Specification for Unbonded Flexible Pipe", ANSI / API 17J, fourth edition, May 2014. Such pipes usually comprise an inner liner, also often called a pressure sheath or an inner sheath, which forms a barrier against the outflow of the fluid which is conveyed in the bore of the pipe, and one or more armoring layers. Often the pipe further comprises an outer protection layer, referred to as an outer sheath in the following, which provides mechanical protection of the armor layers. The outer sheath may be a sealing layer sealing against ingress of seawater. In certain unbonded flexible pipes, one or more intermediate sealing layers are arranged between the armor layers. The sheaths are typically made from polymer material.

[0006] In general, flexible pipes are expected to have a lifetime of at least 20 years in operation. Examples of unbonded flexible pipes are e.g. disclosed in US 6,978,806; US 7,124,780; US 6,769,454 and US 6,363,974.

[0007] In this text, the term "unbonded" means that at least two of the layers including the armoring layers and polymer layers are not bonded to each other. In practice, the known pipe normally comprises at least two armoring layers located outside the pressure sheath and optionally an armor structure located inside the pressure sheath; this armor structure is normally referred to as a carcass. These armoring layers comprise or consist of multiple elongated armoring elements that are not bonded to each other directly or indirectly via other layers along the pipe. Thereby the pipe becomes bendable and sufficiently flexible to roll up for transportation.

[0008] In addition to the unbonded flexible pipes, external umbilical cables are typically installed close thereto for transferring electric power between external devices arranged at opposite ends of the flexible pipes when they form part of a subsea installation. Such external umbilical cables can combine communication and electrical power distribution between the external devices, but they are expensive to produce and costly to install offshore.

[0009] OBJECT OF THE INVENTION

[0010] It is an object of the present invention to provide a flexible pipe assembly with which it is possible to overcome the need for using external umbilical cables for the transfer of electric power between external devices arranged at opposite ends of the flexible pipe assembly when it forms part of a subsea installation.

[0011] It is another object of the present invention to provide a flexible pipe assembly that is easier to install as part of a subsea installation than prior art solutions comprising the use of external umbilical cables.

[0012] It is an object of at least some embodiments of the present invention to provide a flexible pipe assembly with which both electric power and communication signals can be transferred between opposite ends of the flexible pipe assembly.

[0013] It is another object of at least some embodiments of the present invention to provide a flexible pipe assembly with which at least one power cable can be built into a flexible pipe by use of the same machinery as traditionally used for the arrangement of the tensile armor layer of the flexible pipe of the flexible pipe assembly. It is a further object of the present invention to provide an alternative to the prior art.

[0014] In particular, it may be seen as an object of the present invention to provide a flexible pipe assembly that solves the above mentioned problems of the prior art.

[0015] SUMMARY OF THE INVENTION

[0016] Thus, the above-described object and several other objects are intended to be obtained in a first aspect of the invention by providing a flexible pipe assembly for use in a subsea installation, wherein the flexible pipe assembly comprises an unbonded flexible pipe comprising:

[0017] - a pressure sheath extending in a longitudinal direction of the flexible pipe and being configured to carry a flow of fluid there-through during use,

[0018] - at least one tensile armor layer comprising a plurality of helically wound elongate elements surrounding the pressure sheath,

[0019] - an outer sheath surrounding the at least one tensile armor layer, and

[0020] - a first end fitting and a second end fitting located at respective ends of the flexible pipe, wherein:

[0021] - at least two of the elongate elements are arranged separated by a gap forming a helical path,

[0022] - at least one electric power cable is arranged along the helical path and extending at least from the first end fitting to the second end fitting,

[0023] - a first end of the at least one power cable is configured to be electrically connected to an associated first external device during use, and

[0024] - a second end of the at least one power cable is configured to be electrically connected to an associated second external device during use, thereby enabling transfer of electric power from the first external device to the second external device via the at least one power cable during use.

[0025] By "subsea installation" is preferably meant that at least a part of the installation is located under sea level, such as at the seabed. The invention has been developed for use in installations where the flexible pipe assembly can be used down to depths of above 500m, such as above 1000m, such as above 2000, such as between 3000m and 6000m. However, the same flexible pipe assembly may also be used at lower depths, such as solely on ground, close to sea level, or at sea level. Examples of fluids that can be transported through the flexible pipe are hydrocarbons, methanol, ethanol, CO2, water and ammonia. The flexible pipe assembly may e.g. be used for the transportation of fuel stored in a sub-sea storage unit to ships so that the ships can be fuelled at sea. It may also be used in Carbon Capture Storage (CCS) projects, where CO2 gas is pumped back into an undersea reservoir for permanent storage.

[0026] The elongate elements of the tensile armor layer may e.g. be in the form of metal wires and / or composite strips. However, any kind of material that is suitable for the use as helically wound tensile armor in an unbonded flexible pipe is covered by the scope of the present invention. The overall design of an unbonded flexible pipe is described in the API standard API 17J.

[0027] By "electric power cable" is preferably meant an electric conductor provided with an electrically isolating coating or layer on the outer surface thereof. The at least one electric power cable preferably extends un-interrupted from the first end fitting to the second end fitting.

[0028] An end fitting is a part or an assembly of parts that is configured to connect two unbonded flexible pipes by attaching an end of each unbonded flexible pipe to the end fitting. The end fitting may further be configured to connect a unbonded flexible pipe to a structure, such as an onshore structure, a subsea structure, a marine vessel, an offshore structure such as an oil rig or an offshore wind turbine, etc., by connecting an end of the unbonded flexible pipe to the end fitting, and connecting the end fitting to the structure, for example by connecting the end fitting to a flange or the structure.

[0029] The end fitting is further configured to provide a sealing of an end of a unbonded flexible pipe to prevent seawater from entering the unbonded flexible pipe and prevent release of fluid inside the unbonded flexible pipe to the surroundings, such as seawater. By "external device" is preferably meant a device located at a distance from the unbonded flexible pipe.

[0030] The first external device may e.g. be a power source for supplying electrical power into the power cable thereby enabling powering a second external device arranged at the opposite end of the flexible pipe. The power requirement for a second external device may e.g. be in the range of 1-10 kW. Such low levels of power consumption can be delivered from a single-phase AC power system of 50 / 60 Hz. The invention may also be used in a DC power system, which may e.g. be in the range of 1-10 kW. The technical performance of a flexible pipe assembly will have to be determined as a part of the design process for a given application, and it may vary from the measures mentioned.

[0031] The second external device may e.g. a measurement instrument, a valve, an actuator e.g. for valve control, or a battery. The electric power may e.g. be used for charging a battery that can subsequently be used for powering an actuator or a measurement instrument. However, any external devices configured for use in a subsea installation in accordance with the intended use of the present invention are covered by the scope of protection.

[0032] In some embodiments of the invention, the at least one power cable is electrically connected or connectable to a first connector at the first end and electrically connected or connectable to a second connector at the second end. However, the scope of protection also covers embodiment, wherein the power cable is configured to be connected directly with the first external device and / or the second external device without the need for such connectors. In embodiments having more than one power cable, these power cables may be connected or connectable to individual connectors for each cable. Alternatively, two or more power cables may be connected or connectable to a shared connector. The connectors should preferably be designed to have a liquid-tight design at the pressure they are to experience during use in order to ensure safe and wellfunctioning connectors.

[0033] The at least one power cable may have a length allowing for the first and / or second connector to be moved a distance from the respective end fitting to allow for connection to a first and / or second external device being located at a distance from the flexible pipe assembly. Such a length provides flexibility with respect to the use. For example, it allows for connecting the connector to a static structure outside of the end fittings, such as an oilrig, subsea rigid structure, offshore platform, vessel, etc.

[0034] In embodiments comprising first and second connectors, the first end fitting may comprise at least one first compartment accommodating the first connector, and the second end fitting may comprise at least one second compartment accommodating the second connector, and each end of the at least one power cable may be guided away from the gap and into the respective compartment in which it is connected to the respective connector. The first and / or second end fittings may also be provided with one or more further compartments e.g. for providing space for excessive length of the power cable.

[0035] Each of the at least one first compartment and the at least one second compartment is preferably closed by a pressure bearing cover configured to remain fluid-tightly closed during use. The actual requirements ensuring this will depend on actual maximum water depths for a given application. The fluidtightness must fulfil the requirements in the relevant standard, such as the API 17J standard.

[0036] In embodiments comprising first and second connectors, the flexible pipe assembly may further comprise a first connector holder configured for holding the first connector, and a second connector holder configured for holding the second connector, and the first and second connector holders may be arranged in close proximity of the respective end fittings, such as on outer surfaces of the respective end fittings.

[0037] The flexible pipe may comprise two or more power cables arranged in the same gap or in separate gaps, each gap being between two neighbouring elongate elements.

[0038] The flexible pipe may comprise at least two power cables forming a power cable pair of which one power cable carries a forward current and the other power cable carries a return current. There may also be enough power cables to form more than one power cable pairs. In embodiments comprising at least two power cables, they may be used for powering separate second external devices. Alternatively or in combination therewith, two or more power cables may be used for powering the same second external device. This will e.g. be relevant when more power than what can be supplied via one power cable is needed for a satisfactory functioning of a second external device.

[0039] In some embodiments of the invention, two or more power cables are arranged adjacent to each other in one gap. In some embodiments of the invention, free space in a gap caused by the width of a gap being larger than the width of a power cable is filled with filling material to prevent movement of the power cable. It may therefore be advantageous to arrange more than one power cable in a gap where there is sufficient space therefore.

[0040] Pairing of power cables will offer an additional advantage as it will hereby be possible to increase the amount of electrical power that can be transferred. If the two power cables in one gap between neighbouring elongate elements are configured in such a way that one cable is carrying the forward current, while the adjacent cable is carrying the return current, it is possible to form a bifilar wire configuration. Such a bifilar wire configuration of two power cables in one gap may be beneficial, when it comes to parameters like mutual and parasitic capacitance and inductance.

[0041] An outer diameter of the at least one power cable may be smaller than or equal to a thickness of the elongate elements. Hereby a subsequent layer of elongate elements, when present, can be arranged flat on top of the layer comprising the at least one power cable without any material protruding in the radial direction that could otherwise negatively influence the overall layout and the stresses in the flexible pipe. However, in embodiments wherein the outer sheath is made from a resilient polymer material, as is typically the case, it might be considered acceptable to have a larger outer diameter of the at least one power cable provided that it is arranged in an outermost tensile armor layer. The part of the at least one power cable would in that case just cause a corresponding deformation of the outer sheath, and this would typically not cause any problems for the use of the flexible pipe assembly. The outer diameter of the at least one power cable will be determined as part of a design process. Typically, it will be selected to be as large as possible in order to fill out as much as possible of the gap from the missing elongate element.

[0042] A power cable of a flexible pipe assembly according to the present invention typically comprises a conductor cable enclosed by at least three layers forming encapsulation, tubing, and insulation, respectively.

[0043] The at least one power cable may have one or more of the following properties: The encapsulation may be able to withstand a temperature of at least 150 degrees Celsius over prolonged periods. This layer may for example be made from or comprise fluorinated ethylene propylene (FEP). The tubing may be able to withstand a pressure of at least 600 bar (60 MPa) and a temperature of at least 150 degrees Celsius over prolonged periods. Furthermore, the tubing may have a yield strength of at least 650 kPa. The tubing may be made of a corrosion resistant material, such as 316L stainless steel or the commercially available alloy INCOLOY® 825 that provides increased corrosion resistance in a hydrogen sulphide-containing environment, such as in petroleum and gas. The conductor cable may be configured to withstand at least 1000 V. It may have a resistance of maximum 23 Ohm / Km at 20 degrees Celsius and of maximum 36 Ohm / Km at 150 degrees Celsius. The insulating material may typically be a polymer material.

[0044] In addition to being configured to transfer electric power as described above, the at least one power cable may further be configured for transferring a superposed electric signal, such as a low frequency communication signal. This kind of communication may be referred to as power line communication, and the use thereof will be known on its own to a person skilled in the art. Such a superposed electric communication signal may e.g. be used for initiating an actuation of a valve so that it moves from a closed to an open configuration in order to allow for a flow of fluid from a subsea tank into the flexible pipe. In embodiments having more than one power cable, the configuration to transfer a superposed power signal in addition to the electric power may apply to all the power cables or to only one or some of them. Thus, by such embodiments of the present invention, in addition to providing the supply of power, the flexible pipe assembly can also provide the requested communication channel normally found in umbilical cables. Thereby a more compact solution is obtained which is advantageous especially during installation as less components are to be handled. Furthermore, the decrease in the number of components also lowers the risk of damage during use of the subsea installation.

[0045] In any of the embodiments as described above, the flexible pipe assembly may further comprise at least one optical fibre extending at least between the first and second end fittings thereby enabling transfer of communication signals along the flexible pipe assembly during use.

[0046] The overall idea leading to the present invention was based on a desire to introduce a power distribution system into a known flexible pipe in order to be able to offer an alternative technology to using external umbilical cables. Normally, such external umbilical cables combine communication and electrical power distribution. This type of external umbilical cable is expensive to produce and costly to install offshore. Thus, with a flexible pipe assembly according to at least some embodiments of the present invention, the functionality of an umbilical cable is integrated into the flexible pipe structure itself, and therefore there is no need for an external umbilical cable.

[0047] In some embodiments of the invention, the second end of the at least one power cable is configured to be connected to the second external device via a transformer. Such a transformer may e.g. be used to convert between AC and DC power, and / or it may be used to convert the power to another voltage. The power will typically be transferred from the first external device to the second external device as AC power, but it may also be as DC power.

[0048] In any of the embodiments as described above, the flexible pipe assembly may further comprise a carcass extending along the flexible pipe to provide structural, such as hydrostatic, support thereto. It will be well known to a person skilled in the art how to design a carcass and incorporate it in a flexible pipe. In addition, the flexible pipe may comprise at least one pressure armor layer that is configured to support the internal pressure from fluid flowing in the pipe. The carcass is typically arranged within the pressure sheath, and the pressure armor is typically arranged between the pressure sheath and the tensile armor layer.

[0049] Further details and specifications can be found in the API standard API 171

[0050] In a second aspect, the invention relates to a subsea installation comprising:

[0051] - a flexible pipe assembly according to the first aspect of the invention as described above,

[0052] - at least one first external device electrically connected to the first end of the at least one power cable, and

[0053] - at least one second external device electrically connected to the second end of the at least one power cable, thereby enabling transfer of electric power from the first external device to the second external device via the at least one power cable during use.

[0054] In a third aspect, the invention relates to the use of a flexible pipe assembly according to the first aspect of the invention as described above for supplying electric power and / or electric signals from a first external device in the form of a power source connected to the first end of the power cable to an associated second external device connected to the second end of the power cable.

[0055] Alternatively, the third aspect of the invention may be described as a method of supplying electric power and / or electric signals from a first external device in the form of a power source connected to the first end of the power cable to an associated second external device connected to the second end of the power cable by use of a flexible pipe assembly according to the first aspect of the invention as described above.

[0056] In a fourth aspect, the invention relates to a method of manufacturing a flexible pipe assembly according to the first aspect of the invention as described above, the method comprising a step of manufacturing the unbonded flexible pipe, the step comprising:

[0057] - providing the pressure sheath,

[0058] - winding the at least one power cable around the pressure sheath simultaneously with winding the elongate elements around the pressure sheath thereby forming the at least one tensile armor layer comprising the at least one power cable, and

[0059] - extruding the outer sheath so that it covers the at least one tensile armor layer. The first, second, third and fourth aspects of the present invention may each be combined with any of the other aspects. These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

[0060] BRIEF DESCRIPTION OF THE FIGURES

[0061] The flexible pipe assembly according to the invention as well as possible uses thereof will now be described in more detail with regard to the accompanying figures. The figures show one way of implementing the present invention and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0062] Figure 1 schematically shows the overall design of an embodiment of a flexible pipe assembly for use in a subsea installation.

[0063] Figure 2 schematically shows an embodiment wherein the flexible pipe comprises a carcass.

[0064] Figure 3 schematically shows a possible design of an end fitting of a flexible pipe assembly.

[0065] Figure 4 schematically shows the end fitting of figure 3, in which a compartment is closed by a pressure bearing cover.

[0066] Figure 5 schematically shows an embodiment of an end fitting comprising a connector holder configured for a respective connector.

[0067] Figures 6. a and 6.b schematically shows the arrangement of a power cable in a gap between elongate elements. Figure 6. a is a partial three-dimensional view and figure 6.b is a cross-sectional view.

[0068] Figure 7 schematically shows an example of how a power cable may be arranged in relation to an end fitting. Figure 8 schematically shows an embodiment of a subsea installation according to the present invention.

[0069] Figure 9 is a schematic circuit diagram of an exemplary power distribution system of a subsea installation according to the present invention.

[0070] Figure 10 shows a flowchart of a method of manufacturing a flexible pipe assembly according to the invention.

[0071] Figure 11 shows a photo of an exemplary winding process of step B of the method in figure 10.

[0072] DETAILED DESCRIPTION OF AN EMBODIMENT

[0073] Figure 1 schematically shows the overall design of an embodiment of a flexible pipe assembly 1 arranged ready for use in a subsea installation. In the figure, all the components are arranged at the same level, but in practise, they will typically be arranged at different heights and some of them several kilometres apart. The subsea installation comprises a flexible pipe assembly 1 as will be described in more details in the following. It further comprises a first external device 2 electrically connected to the first end 3 of the power cable 4, and a second external device 5 electrically connected to the second end 6 of the power cable 4. Thus, electric power can be transferred from the first external device 2 to the second external device 5 via the at least one power cable 4 during use of the subsea installation. The helically arranged power cable 4 is shown with just a few turns for illustrative purposes only. In the real flexible pipe, the power cable 4 will not be visible as it is covered by the outer sheath; see following figures.

[0074] The illustrated flexible pipe assembly in figure 1 comprises an unbonded flexible pipe 7 and a first end fitting 8 and a second end fitting 9 located at respective ends of the flexible pipe 7. The layers of the flexible pipe are illustrated in figure 2. A pressure sheath 10 extends in a longitudinal direction of the flexible pipe 7 and is configured to carry a flow of fluid there through during use. At least one tensile armor layer 11 comprising a plurality of helically wound elongate elements 12 surrounds the pressure sheath 10. An outer sheath 13 surrounds the at least one tensile armor layer 11. As mentioned above, the flexible pipe assembly 1 may further comprise a carcass 14 extending along the flexible pipe 7 to provide structural, such as hydrostatic, support thereto. Such a carcass 14 is shown in the embodiment in figure 2. At least two of the elongate elements 12 are arranged separated by a gap 15 forming a helical path. In the illustrated embodiment, one electric power cable 4 is arranged along the helical path and extending from the first end fitting 8 to the second end fitting 9. However, at described above, there may be more than one power cable 4 as will also be shown in the following. As shown in figure 1, a first end 3 of the power cable 4 is configured to be electrically connected to an associated first external device 2 during use, and a second end 6 of the at least one power cable 4 is configured to be electrically connected to an associated second external device 5 during use. In the illustrated embodiment, such connections are enabled by having the power cable 4 electrically connected to a first connector 16 at the first end 3 and electrically connected to a second connector 17 at the second end 6. The first and second connectors 16,17 are schematically shown as dots in the figure, but any suitable type of electrical connector is covered by the scope of protection. An example of a design is shown in figure 7. Thus, by such a flexible pipe assembly 1 it is possible to transfer electric power from the first external device 2 to the second external device 5 via the at least one power cable 4 during use. As described in more details above, the power cable 4 may further be configured for transferring a superposed electric signal. The flexible pipe 7 may comprise more layers as seen in figure 2.

[0075] In the embodiment shown in figure 1, the second end 6 of the power cable 4 is connected to the second external device 5 via a transformer 18. A transformer 18 may also be arranged at the other end of the power cable 4 or at both ends. Such a transformer may be substituted with a power converter for converting AC to DC and vice versa. There may also be a transformer and a converter at one end or at both ends. A converter can e.g. be for converting an AC power transferred via the power cable 4 to a DC power to be used for powering the second external device 5.

[0076] Figure 3 schematically shows a possible design of an end fitting 8,9 for use with an embodiment in which the at least one power cable 4 is provided with a first connector 16 at a first end 3 and a second connector 17 at a second end 6. The end fitting 8,9 comprises at least one compartment 18 accommodating the connector 16,17. The end 3,6 of the power cable 4 is guided away from the gap 15 and into the respective compartment 18 in which it is connected to the respective connector 16,17; see figure 7 for more details. Typically, the first and second end fittings 8,9 will have such a design, but the scope of protection also covers embodiments wherein only of the end fittings comprises a compartment 18. As shown schematically in figure 4, each compartment 18 is closed by a pressure bearing cover 19 configured to remain fluid-tightly closed during use.

[0077] Figure 5 schematically shows an embodiment of an end fitting 8,9 comprising a connector holder 20,21 configured for a respective connector. The figure shows only one of the connector holders. In the illustrated embodiment, the first and second connector holders 20,21 are arranged on outer surfaces 22 of the respective end fittings 8,9. They are schematically shown as boxes, but any technically suitable design is covered by the scope of protection.

[0078] Figure 6. a schematically shows a partial three-dimensional view of an embodiment in which the flexible pipe comprises a power cable 4 arranged in a gap 15 between two neighbouring elongate elements 12. As mentioned above, there may also be two power cables 4 forming a power cable pair of which one power cable carries a forward current and the other power cable carries a return current; this will be shown in figure 9. Figure 6.b schematically shows a cross- sectional view of the power cable 4 in figure 6. a. As seen, the power cable 4 is dimensioned so that an outer diameter thereof is smaller than or equal to a thickness of the elongate elements 12. Hereby a subsequent layer of elongate elements 12 can be arranged flat on top of the layer comprising the power cable 4 without any material protruding in the radial direction that could otherwise negatively influence the overall layout and the stresses in the flexible pipe 7. It may also be necessary to fill the remaining gap with e.g. strips 23 of composite material in order to ensure that the power cable remains in the desired position; this is shown in figure 6. a.

[0079] Figure 7 schematically shows an example of how a power cable 4 may be arranged in relation to an end fitting 8,9. The figure is a cross-sectional side view of a section of the region around an end fitting 8,9 of the invention, wherein only a section of the end fitting and part of the tensile armor layers 11 and a power cable 4 are shown. In this embodiment, after finishing the production of the flexible pipe 7 itself, the at least one power cable 4 will have to be terminated in the two end fittings 8,9. This means that the power cable 4 will have to be guided away from the tensile armor layer 11 and fed to a compartment 18 inside the end fitting 8,9, where the power cable 4 can be connected to the connector. As described above, the scope of protection also covers other embodiment, such as embodiments where the ends of the power cable are configured to extend to a distance from the end fittings where they can be connected to respective external devices. As shown in figure 7, the power cable 4 passes through a cavity 24 where it is fixed by securing material, such as epoxy. In the illustrated embodiment, the power cable 4 is applied with an excessive length 4a. It is mounted to a connector 16,17 which is temporally or permanently mounted to a lid 25 covering an exit opening 26 via which the power cable 4 can extend. In use, the connector 16,17 or the connector with the lid 25 can be removed, and the connector 16,17 connected to the power cable 4 can be withdrawn for establishing a connection to an external device 2,5 as described above.

[0080] Figure 8 schematically shows an embodiment of a subsea installation 26 according to the present invention. A first external device 2 is located above sea level 27. It comprises an external power cable 28 connected to a first end fitting 8 of the flexible pipe assembly 1 extending into the sea and comprising at least one electric power cable 4 in a manner as described above. At a depth below the sea level 27, such as at the seabed, the subsea installation 26 comprises at least two additional flexible pipe assemblies 1 connected via their respective end fittings 8,9 in a manner that will be well known to a person skilled in the art. At the subsea location where two end fittings 8,9 are connected, there will typically be a requirement for transfer of power. In the illustrated embodiment, suitable jumper cables 29 are connected from the two end fittings 8,9 to a breakout base 30, which is an external subsea structure. At this breakout base 30, it is also possible to have actual consumers of power and possible overlaid electric signals for transferring communication along the flexible pipe assembly 1. These consumers may e.g. be some of the types of external devices 2,5 mentioned above. The connections from the breakout base 30 and to the end fittings 8,9 and external devices 2,5, respectively, are schematically shown as lines in the figure. The connectors 16,17 are schematically shown as dots. The flexible pipe 7 extending from the first external device 2 above sea-level is typically referred to as a dynamic riser, and the flexible pipe 7 extending between the two external devices 2,5 arranged at the seabed are typically referred to as a static flow-line. Since the invention relates to one flexible pipe assembly 1, the left-hand external device at the seabed forms the second external device for the dynamic riser and forms the first external device for the static flow-line.

[0081] Figure 9 is a schematic circuit diagram of an exemplary power distribution system of a subsea installation 26 according to the present invention. The flexible pipe assembly in this embodiment has two power cables 4 forming a pair of a power distribution system of which one power cable carries a forward current and the other power cable carries a return current. To the left is a standard 400 V 3-phase topside power system 31. Two of the phases are connected to the pair of power cables 4. If necessary, the 400 V phase-to-phase voltage can be increased by a step-up transformer located topside as shown in the figure. This transformer can help increase the available subsea power, if required. If the subsea consumer side requires 230 V single-phase, a step-down transformer will be required as indicated in Figure 9. In an alternative embodiment (not shown), there is only one power cable carrying the forward current whereas the return current runs along one or more of the elongate elements 12 of the tensile armor layer 11. This is possible due to the elongate elements 12 having such a cross-sectional area that no significant resistance is present. Hereby one less power cable 4 is needed compared to the embodiment in figure 9.

[0082] Figure 10 shows a flowchart of a method of manufacturing a flexible pipe assembly 1 according to the invention. The method comprises a step of manufacturing the unbonded flexible pipe 7, the step comprising: A: Providing the pressure sheath 10.

[0083] B: Winding the at least one power cable 4 around the pressure sheath 10 simultaneously with winding the elongate elements 12 around the pressure sheath 10 thereby forming the at least one tensile armor layer 11 comprising the at least one power cable 4. C: Extruding the outer sheath 13 so that it covers the at least one tensile armor layer 11.

[0084] The flexible pipe 7 may comprise more layers, such as a carcass 14 as described above, and the manufacturing thereof will be well known to a person skilled in the art.

[0085] Figure 11 shows a photo of a section of an exemplary winding process of step B in the method in figure 10. As shown, one elongate element 12, in the form of a wire, of the tensile armor layer 11 is replaced by a power cable 4 during the winding of the tensile armor layer 11. If a tensile armor layer 11 consists of N wires, there will be N reels rotating around the flexible pipe 7 during the production of the tensile armor layer 11. Therefore, if one armor wire is replaced by a power cable 4, it means that one reel will have to carry the power cable 4 during the rotating process.

[0086] Although the present invention has been described in connection with the specified embodiments, it should not be construed as being in any way limited to the presented examples. The scope of the present invention is set out by the accompanying claim set. In the context of the claims, the terms "comprising" or "comprises" do not exclude other possible elements or steps. Also, the mentioning of references such as "a" or "an" etc. should not be construed as excluding a plurality. The use of reference signs in the claims with respect to elements indicated in the figures shall also not be construed as limiting the scope of the invention. Furthermore, individual features mentioned in different claims, may possibly be advantageously combined, and the mentioning of these features in different claims does not exclude that a combination of features is not possible and advantageous.

Claims

CLAIMS1. A flexible pipe assembly (1) for use in a subsea installation (26), wherein the flexible pipe assembly (1) comprises an unbonded flexible pipe (7) comprising:- a pressure sheath (10) extending in a longitudinal direction of the flexible pipe (7) and being configured to carry a flow of fluid there-through during use,- at least one tensile armor layer (11) comprising a plurality of helically wound elongate elements (12) surrounding the pressure sheath (10),- an outer sheath (13) surrounding the at least one tensile armor layer (11), and- a first end fitting (8) and a second end fitting (9) located at respective ends of the flexible pipe (7), wherein:- at least two of the elongate elements (12) are arranged separated by a gap (15) forming a helical path,- at least one electric power cable (4) is arranged along the helical path and extending at least from the first end fitting (8) to the second end fitting (9),- a first end (3) of the at least one power cable (4) is configured to be electrically connected to an associated first external device (2) during use, and- a second end (6) of the at least one power cable (4) is configured to be electrically connected to an associated second external device (5) during use, thereby enabling transfer of electric power from the first external device (2) to the second external device (5) via the at least one power cable (4) during use.

2. Flexible pipe assembly (1) according to claim 1, wherein the at least one power cable (4) is electrically connected or connectable to a first connector (16) at the first end (3) and electrically connected or connectable to a second connector (17) at the second end (6).

3. Flexible pipe assembly (1) according to claim 2, wherein- the first end fitting (8) comprises at least one first compartment (18a) accommodating the first connector (16), and- the second end fitting (9) comprises at least one second compartment (18b) accommodating the second connector (17),wherein each end (3,6) of the at least one power cable (4) is guided away from the gap (15) and into the respective compartment (18a, 18b) in which it is connected to the respective connector (16,17).

4. Flexible pipe assembly (1) according to claim 3, wherein each of the at least one first compartment (18a) and the at least one second compartment (18b) is closed by a pressure bearing cover (19) configured to remain fluid-tightly closed during use.

5. Flexible pipe assembly (1) according to claim 2, further comprising:- a first connector holder (20) configured for holding the first connector (16), and- a second connector holder (21) configured for holding the second connector (17), wherein the first and second connector holders (20,21) are arranged in close proximity of the respective end fittings (8,9), such as on outer surfaces (22) of the respective end fittings (8,9).

6. Flexible pipe assembly (1) according to any of the preceding claims, wherein the flexible pipe (7) comprises two or more power cables (4) arranged in the same gap (15) or in separate gaps, each gap (15) being between two neighbouring elongate elements (12).

7. Flexible pipe assembly (1) according to claim 6, wherein the flexible pipe (7) comprises at least two power cables (4) forming a power cable pair of which one power cable carries a forward current and the other power cable carries a return current.

8. Flexible pipe assembly (1) according to claim 6 or 7, wherein two or more power cables (4) are arranged adjacent to each other in one gap (15).

9. Flexible pipe assembly (11) according to any of the preceding claims, wherein an outer diameter of the at least one power cable (4) is smaller than or equal to a thickness of the elongate elements (11).

10. Flexible pipe assembly (1) according to any of the preceding claims, wherein the at least one power cable (4) comprises a conductor cable which is configured to withstand at least 1000 V and which has a resistance of maximum 23 Ohm / Km at 20 degrees Celsius and of maximum 36 Ohm / Km at 150 degrees Celsius.

11. Flexible pipe assembly (1) according to any of the preceding claims, wherein the at least one power cable (4) is further configured for transferring a superposed electric signal.

12. Flexible pipe assembly (1) according to any of the preceding claims, wherein the second end (6) of the at least one power cable (4) is configured to be connected to the second external device (5) via a transformer (18).

13. Flexible pipe assembly (1) according to any of the preceding claims, further comprising a carcass (14) extending along the flexible pipe (7) to provide structural, such as hydrostatic, support thereto.

14. Subsea installation (26) comprising:- a flexible pipe assembly (1) according to any of the preceding claims,- at least one first external device (2) electrically connected to the first end (3) of the at least one power cable (4), and- at least one second external device (5) electrically connected to the second end (6) of the at least one power cable (4), thereby enabling transfer of electric power from the first external device (2) to the second external device (5) via the at least one power cable (4) during use.

15. Use of a flexible pipe assembly (1) according to any claims 1 to 13 for supplying electric power and / or electric signals from a first external device (2) in the form of a power source connected to the first end (3) of the power cable (4) to an associated second external device (5) connected to the second end (6) of the power cable (4).

16. Method of supplying electric power and / or electric signals from a first external device (2) in the form of a power source connected to the first end (3) of the power cable (4) to an associated second external device (5) connected to thesecond end (6) of the power cable (4) by use of a flexible pipe assembly (1) according to any claims 1 to 13.

17. Method of manufacturing a flexible pipe assembly (1) according to any of claim 1 to 13, the method comprising a step of manufacturing the unbonded flexible pipe (7), the step comprising:- providing the pressure sheath (10),- winding the at least one power cable (4) around the pressure sheath (10) simultaneously with winding the elongate elements (12) around the pressure sheath (10) thereby forming the at least one tensile armor layer (11) comprising the at least one power cable (4), and- extruding the outer sheath (13) so that it covers the at least one tensile armor layer (11).

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