GB2609262A

GB2609262A - Subsea electric cable

Info

Publication number: GB2609262A
Application number: GB2110848.5A
Authority: GB
Inventors: Deighton Alan; Smith Lindsay
Original assignee: Technip N Power SAS
Current assignee: TechnipFMC Subsea France SAS
Priority date: 2021-07-28
Filing date: 2021-07-28
Publication date: 2023-02-01
Also published as: GB202110848D0; WO2023007240A1

Abstract

The cable comprises at least one conductor 50, the conductor comprising a plurality of strands 52 having interstices 30 between them. The method comprises at least the steps of: (a) inserting a curable material 46 into the interstices from one end of the cable; and (b) allowing the curable material to cure and form a seal between the strands. The curable material may be a silicone gel or an addition-curing silicone rubber composition. Heat may be applied during the curing process. A sealing rig 32 includes a cable clamp 36, 38t o locate one end of the cable within the curable material 46. The curable material is forced into the cable interstices by gas pressure applied through a passage 49 in an end plug 42. A boot seal or sheath 44 is applied to the cable end to prevent unwanted insertion of the curable material into other regions of the cable. The cable may extend through a subsea umbilical (fig 1).

Description

SUBSEA ELETRIC CABLE

The invention relates to a method of forming a seal in an end of a subsea electric cable, optionally an electric cable extending through a subsea umbilical. The present invention also extends to a subsea electric cable and subsea umbilical with a so-formed sealed end, and a sealing kit.

Background

A subsea umbilical typically comprises a group of one or more types of elongated functional elements, such as electric cables, optical fibre cables, and hoses for fluid transportation of, for example, gas, water or chemical products such as methanol. The functional elements can be assembled together in a helical or S/Z manner and oversheathed and/or over-armoured for mechanical strength and ballast.

It is desirable for a single umbilical to be able to contain as many functional elements as are required for a particular application, for example, as are required for a particular oil field where the umbilical is intended for use.

Umbilicals are typically used for transmitting power, signals and fluids (for example for fluid injection, hydraulic power, gas release, etc.) to and from a subsea installation.

API Specification 17E / ISO 13628-5 "Specification for Subsea Umbilicals" provides standards for the design and manufacture of such umbilicals.

Subsea umbilicals are installed at increasing water depths, commonly deeper than 2000m. Such umbilicals have to be able to withstand severe loading conditions during their installation and their service life. Thus, subsea umbilicals usually also include one or more load bearing elements or components. The main components in charge of withstanding axial loads (due to the weight and to the movements of the umbilical) are steels tubes (see US6472614, W093/17176 and GB2316990), steel rods (see US 6472614), composite rods (see W02005/124213), or tensile armour layers (see Figure 1 of US6472614).

Electric cables used in subsea umbilicals fall into two distinct categories respectively known as power cables and signal cables. A typical subsea umbilical is illustrated in the accompanying Figure 1. Figure 1 shows an umbilical 1 comprising a number of hoses 2, 3, 4, 5 and four multicore low voltage electric cables or signal cables 6, 7, 8, 9 of different sizes. These functional elements are assembled in a S/Z manner together with fillers 10, before being oversheathed with a number of armoured layers 12 and an outer polymeric external sheath 11 in a manner known in the art, to form the umbilical 1.

Signal cables are generally used for transmitting signals, and/or for transmitting low power (<1 kW) to electrical devices on the seabed. Signal cables are generally rated at a voltage smaller than 3000V, and typically smaller than 1000V. Signal cables generally consist of small section insulated conductors bundled together as pairs (2), quads (4) or, very rarely, any other number, said bundle being further over-sheathed.

An example of quad signal cable is illustrated in the accompanying Figure 2. The electric cable comprises four small size stranded copper conductors 14, which are individually over sheathed by polymeric insulation layers 26 and helically bundled together. A polymeric filler material 24 is added to fill the voids in the bundle and achieve a cylindrical shape. This arrangement is optionally surrounded by an electromagnetic shielding 22 made from a wrapped copper or aluminium foil. A polymeric external sheath 27 protects the electric cable against mechanical damage and water ingress.

Power cables are used for transmitting high or higher electrical power (typically a few MW) to powerful subsea equipment such as pumps. Power cables are generally rated as 'low', 'medium' or 'high' voltage. A typical power cable is illustrated in the accompanying Figure 3. From inside to outside, it comprises a central copper conductor 16, semi-conductor and electrical insulation layers 18, a metallic foil screen 28 and an external polymeric sheath 29. The central conductor 16 has generally a stranded construction and a large section typically comprised between 50mm2 and 400mm2. Three phase power is provided by three such cables bundled together within the umbilical structure.

A problem with known electric cables is the presence and migration of water and gas along the electric cable conductor. Water and gas can permeate through polymer sheaths and insulation layers and then migrate along the cable conductor to subsea terminations and potentially lead to premature failure. Gas can also migrate to the topside junction boxes potentially creating hazards if not vented away.

In particular, hydrogen formation can occur where there are components comprising zinc within the cable or umbilical, for example zinc coated steel armours. If hydrogen forms within the umbilical, then the hydrogen gas will try to find a way to exit the cable or umbilical. Sometimes it finds a way through the external sheath of the cable or umbilical. However, it has also been observed the hydrogen could permeate through the electric cables' outer sheath and insulation layers to reach the electric conductors, and then propagate along the conductors towards the end of the cable or umbilical. At the end of the cable or umbilical, the hydrogen may become backed-up and may begin to build pressure Of the termination is not vented). This may lead to an explosion and/or a loss of electrical insulation (short circuit).

W02012/042189A1 describes an umbilical for use in the offshore production of hydrocarbons, the umbilical comprising at least one electric cable, the electric cable comprising at least one electric conductor, and at least one electric conductor comprising a plurality of electric strands having interstices, wherein the interstices are filled with the same metal-based material as the outer surface of the electric strands. But this solution requires including a further step in the manufacturing process of the cables, and thus increases their cost. Moreover, to be efficient, this additional layer need to be impermeable to gas/water, and flexible enough to withstand bending loads.

US7285726 describes a subsea power cable comprising a stranded copper conductor. The voids between the strands are filled with a hydrophobic water-blocking compound in order to prevent longitudinal water penetration and facilitate repair (col. 3, lines 20-23). However, this arrangement may lead to manufacturing complexity or problems as the jelly compound may gas out during the insulation extrusion process.

Cables filled with a gel can be bought. Such type of products are named "jelly-filled cables". However, sometimes the gel filling is not carried out accurately and the final performance of the cable is not as expected. Besides, jelly-filled cables are filled on all their length, thus increasing their overall cost.

One object of the present invention is to minimise or overcome these problems.

Summary of the Invention

According to one aspect of the present invention, there is provided a method of sealing a subsea electric cable, the electric cable comprising at least one electric conductor, the at least one electric conductor comprising a plurality of electric strands having interstices, comprising at least the steps of: (a) inserting a curable material into the interstices from one end of the electric cable; and (b) allowing the curable material to cure and form a seal between the electric strands.

According to another aspect of the present invention, there is also provided a subsea electric cable comprising at least one electric conductor, the at least one electric conductor comprising a plurality of electric strands having interstices, characterised in that the interstices are filled from one end with a curable material.

Optionally, there is provided a subsea electric cable whenever formed by a method as described herein.

According to another aspect of the present invention, there is provided a subsea umbilical comprising at least one electric cable as defined herein extending through the umbilical.

According to another aspect of the present invention, there is provided a sealing rig comprising an umbilical clamp, an end cap, and an intermediate curable material chamber, able to fill the interstices of a subsea electric cable comprising at least one electric conductor, and at least one electric conductor comprising a plurality of electric strands having interstices, from one end with a curable material.

Description of the invention

The present invention will now be described, by way of example only, and with reference to the accompanying drawings, in which:-Figure 1 is a cross-section of a prior art subsea umbilical; Figure 2 is a perspective cross-section of a prior art signal cable for use in a subsea umbilical; Figure 3 is a perspective cross-section of a prior art power cable for use in a subsea umbilical; Figure 4 is a side view of an electric conductor in preparation for a first embodiment of the present invention; Figure 5 is a cross-section of a sealing rig according to another embodiment of the present invention; and Figure 6 is a cross-section of the electric conductor of Figure 4 after providing allowing a curable material to cure and form a seal around the electric strands

Detailed description of the invention

As described above, a problem with known subsea electric cables is the presence and migration of water and gas along the electric cable conductor, in particular hydrogen formation. To prevent water or gas migration through cables, it is known to use a fillable material, such as a hydrogen absorbent or hydrophobic water-blocking material, around the core cable or in the cable strands or both. These types of products are known in the art as "jelly-filled cables". However, sometimes the gel filling is not carried out accurately, and the final performance of the cable is not as expected. However, as the cable is already laid, finding the problem, and repairing or replacing the cable is not simple. Furthermore, jelly-filled cables are filled throughout their complete length, thus increasing the cost.

Another solution consists in applying a metallic layer, for example made of copper, between the insulation layer and the outer sheath of the electric cable. However, this solution also requires including a further step in the manufacturing process of the cable, thus again increasing its cost. Moreover, to be efficient, this additional layer needs to be impermeable to the gas or water, but still be flexible enough to withstand bending loads during spooling and laying.

The present invention provides a method of sealing only the end, or each end, of a subsea electric cable, optionally as a stand-alone cable, or extending through a subsea umbilical.

The electric cable comprises at least one electric conductor, and the at least one electric conductor comprises a plurality of electric strands having interstices. The method comprises at least the steps of: (a) inserting a curable material into the interstices from one end of the umbilical; and (b) allowing the curable material to cure and form a seal around the electric strands.

Subsea electric cables are typically used for transmitting power, signals and fluids (for example for fluid injection, hydraulic power, gas release, etc.) to and from a subsea installation.

A common use for such electric cables is as a functional element or elements in a subsea umbilical. API Specification 17E / ISO 13628-5 entitled "Specification for Subsea Umbilicals", provides specific standards for the design and manufacture of subsea umbilicals. The usual features of a subsea umbilical are known in the art, and can be as described herein. A subsea umbilical typically comprises a group of one or more types of elongated functional elements, such as electric cables, optical fibre cables, and hoses for fluid transportation of, for example, gas, water or chemical products such as methanol. The functional elements can be assembled together in a helical or S/Z manner and over-sheathed and/or over-armoured for mechanical strength and ballast.

It is desirable for a single subsea umbilical to be able to contain as many functional elements as are required for a particular application, for example, as are required for a particular oil field where the umbilical is intended for use.

Subsea umbilicals usually include one or more load bearing elements or components. The main components in charge of withstanding axial loads (due to the weight and to the movements of the umbilical) are steels tubes, steel rods, composite rods, or tensile armour layers.

A typical subsea umbilical is shown in the accompanying Figure 1 as described hereinabove, but the skilled man is aware that such umbilicals can comprise a range of components or elements, and the present invention is not limited thereto.

A subsea electric cable of the present invention comprises at least one electric conductor. The or each electric conductor is a stranded electric conductor comprising a plurality of electrically conducting strands, generally being circular in cross section, brought together in the form of a 'bundle'. In the present application, the terms "strand" and "wire" have the same meaning, with a stranded conductor being an assembly of wires or strands twisted together. The strands may be annealed such as with tin. Thus the present invention includes using tinned annealed stranded copper wire-based conductors (TASC).

An electric stranded conductor may comprise a plurality of electric strands of different size, designs, material, shape, etc. although commonly it is desired to use a number of similar strands when forming an electric conductor, optionally with a larger core wire or strand.

Electric cables of the present invention include those generally defined as 'power cables' and 'signal cables' as described above. Power cables are generally rated as low' voltage (LV), 'medium' voltage (MV) or 'high' voltage (HV).

Optionally, the present invention is particularly suitable to an electric cable being a low voltage cable, generally being for transmitting power up to 2 kV.

Methods of assembly, or otherwise bringing a number of electric strands together, to form an electric conductor are well known in the art, and include forming them in a helical or S/Z manner. Such methods are not further discussed herein.

In the bringing together of such strands, interstices are formed between the abutting outer surfaces of the strands. In another way, the abutting outer surfaces of the electric strands define the interstices. The number, nature, design, size or arrangement of the interstices can vary depending upon the number, nature, design, size, or arrangement of the electric strands.

The electric strands may be formed of any suitable material, generally being copper, optionally one or more other metals such as aluminium, and optionally a combination of metals including alloys.

The curable material usable in the present invention may be any single component or multiple component substance or material, provided either in a one-part or multiple-part formulation. The formulation may be useable directly, or require pre-mixing of its components before use. The final form of the curable material must be able to be inserted as required, and to subsequently cure and form a seal.

Various materials are known in the art that are useable in the present invention, commonly based on involving one or more rubber substances or on one or more silicones, in particular the range of materials known as 'silicone rubbers'. A large range of silicone rubbers are commercially available, with a range of varying properties, such as viscosity, curing time and curing temperature, etc. Optionally, the curable material is a two-component material, intended to be mixed prior to use, optionally with appropriate time or time delay to allow some initial reaction.

The method of curing can be addition-curing or the like, and may also involve some element of heat addition, to achieve curing, in particular to achieve the required crosslinking and possibly vulcanization, to produce a final cured and formed material. The form and processing of the curable material is not limiting on the present invention.

In one embodiment, the curable material has a viscosity to allow insertion and curing in a number of hours, and at an ambient or room or close temperature, to produce a more solid material, typically a gel, which achieves a seal.

Curable materials are also known in the art which involve the use of a raised temperature and raised pressure to assist curing and forming.

Suitable curable materials include those commonly known in the art as "SilGels". A range of such materials are available from the company Wacker GmbH in Germany. The suitability of such materials can be determined as being suitable based on their viscosity, typically their viscosity at ambient or room temperature, followed by cured product data such as their final density, strength, resistivity and dielectric strength.

The insertion of the curable material into the interstices can be achieved in any suitable manner or steps, generally including the use of pressure or an increased pressure or pressurisation in order to assist or force the curable material into the interstices from one end of the umbilical, in particular from one end of the electric cable. With pressure or pressurisation, optionally, step (a) of the present invention comprises injecting a curable material into the interstices from one end of the umbilical, optionally under pressure.

The pressure could be provided by any suitable pressure means, including the use of a fluid, including a gas or mixture of gases, in particular using gaseous pressure, as well as physical means including a press or presses.

Optionally, inserting the curable material into the interstices from one end of the umbilical is carried out in a suitable environment, typically a closed environment. Apparatus or devices can be used to provide a closed environment around the end of the umbilical and/or end of a cable, including using a suitable rig, including a sealing rig.

Apparatus, devices or rigs are known in the art, generally comprising one or more clamps, containers or chambers, and ends or heads.

According to one embodiment of the present invention, there is provided a sealing rig comprising an umbilical clamp, an end cap, and an intermediate curable material chamber. The rig is able to assist filling the interstices of an electric cable comprising at least one electric conductor, and at least one electric conductor comprising a plurality of electric strands having interstices, from one end with a curable material.

Typically, a suitable apparatus, device or rig provides a controlled environment in which pressure can be applied to the curable material to assist its insertion into the interstices between the electric strands extending from one end of the umbilical. In particular, using gaseous pressure may require a sealed form of apparatus or rig, optionally formed of a number of parts which can come together to form a sealed environment.

The apparatus, device or rig may include providing an open or openable end, into which a curable material can be located to, towards or otherwise around the plurality of electric strands of an electric conductor having interstices. A suitable head or plug or cap can then be provided over the open or openable end, to provide a closed environment. Typically, pressure can then be applied through a suitable port or portal to assist insertion of the curable material into the interstices.

Optionally, the sealing rig of the present invention further comprises an inner core locatable between the umbilical clamp and the intermediate curable material chamber.

Thus, as part of the method of the present invention, the method can further comprise the step of locating a sealing rig around the one end of the electric cable involved in step (a). Optionally, the sealing rig comprises an umbilical clamp, an end cap, and an intermediate curable material chamber, further comprising the steps of: locating the umbilical clamp around the electric cable; and filing the intermediate curable material chamber with curable material; In this way, step (a) of the method of the present invention can comprise injecting a curable material under gaseous pressure into the interstices from one end of the electric cable, further comprising the step of; pressurising the curable material in the intermediate curable material chamber with a gas supplied through the end cap.

Optionally, the method of the present invention further comprises the step of exposing the electric strands from the electric conductor prior to step (a). Exposing can include working at enlarging, creating or extending the size, shape or design of the existing interstices between the electric strands, to assist the insertion of the curable material thereinbetween.

Thus, the present invention can include a method wherein the subsea electric cable comprises at least an outer sheath and one or more inner layers, further comprising the step of; exposing an inner layer; locating one or more seals, such as sheaths, sealing rings, sealing grease and/or sealing tape, around the inner layer to seal the one or more inner layers from the curable material.

In the present invention, step (b) of the method comprises allowing the curable material to cure and form a seal inbetween, and possibly also around, the electric strands. As mentioned herein, the curable material may be assisted by providing an enhanced or increased ambient temperature and/or pressure to assist its curing and forming of a seal.

Suitable injection pressures can be at least 10 bar, such as 20 bar, or higher, including 25 bar, or more.

Typically, the curing and forming may take a time period longer than insertion, such as several hours, to achieve the required curing and forming to form a seal. Thus, step (b) may involve an element of time, such as hours, as well as an enhanced or altered temperature and/or pressure to achieve the required curing and forming to form a seal around the electric strands.

The skilled person can see that a combination of time, a suitable temperature and pressure regime can be arranged to achieve suitable insertion of the curable material into the interstices that is variable. For example, an increased pressure for insertion may require less time than a lower insertion pressure. Similarly, an increased ambient temperature may require less time to achieve insertion of the curable material than a lower or ambient temperature.

Optionally, the method of the present invention is suitable for an electric cable being a low-voltage cable.

Optionally, the method of the present invention is suitable for an electric cable extending through a subsea umbilical. Subsea umbilicals are described herein, and the skilled man can see the application of an electric cable provided by the present invention in a subsea umbilical, particularly as a signal cable or a power cable.

Optionally, the method of the present invention is suitable for an electric cable oversheathed by one or more armour layers. The oversheathing may be closely or directly around one or more of the insulation layers of the electric cable per se, or around the electric cable and a number of other functional elements, especially in relation to a subsea umbilical.

Thus, the present invention extends to sealing an end of an electric cable extending through an armoured subsea umbilical.

The present invention also extends to a subsea electric cable comprising at least one electric conductor, the at least one electric conductor comprising a plurality of electric strands having interstices, characterised in that the interstices are filled from one end with a curable material.

The subsea electric cable can be formed by a method as described herein.

The present invention also extends to a subsea umbilical comprising a subsea electric cable whenever formed by a method of sealing as described herein Optionally, the curable material in the subsea umbilical is a silicone gel.

Optionally, the silicone gel is an addition-curing silicone rubber composition.

Optionally, the umbilical comprises an outer sheath and one or more inner layers.

Optionally, the electric cable of the umbilical of the present invention is a low-voltage cable.

Optionally, the electric cable is oversheathed by one or more armour layers.

The present invention also extends to a subsea umbilical comprising at least one electric cable as defined herein extending through the umbilical, including an armoured subsea umbilical.

Referring to the drawings, Figure 1 shows a typical subsea umbilical as described hereinabove, and Figures 2 and 3 show typical signal cables and power cables as described hereinabove.

Figure 3 shows a typical power cable, starting from the inside and going outside, comprising a central copper conductor 16, semi-conductor and electrical insulation layers 18, a metallic foil screen 28, and an external polymeric sheath 29. The conducting part of a power cable may comprise any number of strands, which may be uniform as shown in Figure 3, or may include one or more different diameter strands, including a core strand typically of a greater diameter than surrounding strands. The present invention is not limited by the nature or number of electric strands forming the electric conductor, as long as there are interstices thereinbetween.

The voltage rating for a low voltage (LV) electric conductor is typically up to 2kV and is designed to work at a large temperature range including up to 90°C, and below 0°C. Such power cables can be many metres long, including many thousands of metres, including at least 2000 metres, and possibly up to or above 3000 metres or 4000 metres long. It can be recognised that where a power cable is long, in particular thousands of metres long, seeking to accurately fill all the interstices between all the strands throughout the entire length of the power cable can be an expensive and an extensive job.

The present invention seeks to provide a solution to the problem of water and gas migration along the core of the electric cable, by providing a superior seal from at least one end of the electric cable.

Figure 4 of the accompanying drawings shows a low voltage cable 6, comprising a polymeric outer or external sheath 23 surrounding a polymeric filler material 24, surrounding a number of individual polymeric insulation layers 26, each insulation layer 26 surrounding an electric conductor 6b. The electric conductor 6b can be formed from a number of electric copper strands 6a, like the strands of the stranded copper conductors 14 in Figure 2 and of the stranded central copper conductor 16 in Figure 3, described above.

In Figure 4, it can be seen that the strands 6a have been deliberately pulled apart as they extend from the end of the insulation layer 26, to expand the nature of the interstices thereinbetween at the one end of the overall umbilical, and in particular at one end of the electric cable as shown in Figure 4.

Figure 5 shows a cross-section of a sealing rig 32 according to one embodiment of the present invention. The sealing rig 32 comprises an umbilical clamp 36 and associated inner core piece 38, an end cap 42, and an intermediate curable material chamber 40.

The umbilical clamp 36 and associated inner core piece 38 could be a single piece, or otherwise multiple or split and able to be formed around the electric cable 6, and to provide a defined grip therewith prior to the method and processing described herein after.

The material chamber 40 can be formed of any suitable material, including but not limited to ABS (acrylonitrile butadiene styrene). The end cap 42 serves to seal the other end of the material chamber 40 once one end of the chamber 40 is filled as discussed hereinafter. Optionally, the sealing rig is encapsulated by an outer shell 34, which can serve to assist closure of the sealing rig, in particular for health and safety reasons, between the end clamp umbilical clamp 36 and the end cap 42.

Figure 5 shows the addition of a boot seal or sheath 44 between the external sheath 23 of the electric cable 4 and the polymeric filler material 24, and optionally any electromagnetic shielding 22 of the electric cable 6. The sheath 44 is adapted to prevent the insertion of the curable material between two or more of the layers of the electric cable 6 not desired.

Once the electric cable 6 is located within the material chamber 40 as shown in Figure 5, a suitable curable material 46 can be loaded into the material chamber 40. Suitable curable materials are known in the art, and are generally multiple-component silicone rubbers, able to crosslink and cure at room temperature or there above in a manner known in the art. Typically materials include the range known as SilGel, which are two part curable silicone compositions intended to have a low viscosity to form a cured silicone rubber. One known material is 'SilGel 612', a pourable, addition curing RTV2 silicone rubber that vulcanizes at room temperature to a silicone gel.

Once the material chamber 40 is filled with the curable material 46, an end cap 42 can be secured at the open end, optionally using one or more seals such as 0-rings, to increase the sealing thereinbetween.

The end cap 42 includes a portal 49 to allow a flow of gas along arrow A from an external source, such as a gas cylinder under pressure, into the material chamber 40. This is to assist and best achieve the insertion of the curable material 46 into the interstices between the electric strands 6a of the electric cable 6. The gas pressure may be greater than 10 bar, such as 20 bar or 25 bar, able to inject the curable material 46 into the interstices along a suitable distance of the electric cable 6 to form a seal, in particular to form a high pressure seal, to prevent the migration of water and/or gas, in particular hydrogen gas, out from the end of the electric cable 6.

The skilled man can recognise that application of an enhanced temperature environment around the relevant end of the electric cable 4, typically a temperature above ambient temperature, such as >20°C, >30°C, >40°C, such as in the range 30-40°C, such as 35-40°C, can assist with the subsequent curing of the curable material, and so the forming of a seal around the electric strands 6a. The skilled man can recognise that a combination of suitable temperature, pressure and time, leads to optimal insertion of the curable material along and into the interstices.

Optionally, the curable material is inserted into the interstices by at least up to a metre, or at least greater than a metre, such as up to 2 metres, or more than 2 metres, such as up to 3 metres, or more than 3 metres, or more, over time. In trials, the use of a pressure of 20 bar for at least several minutes, has achieved insertion of a suitable SilGel silicone material for at least 2 metres along the interstices from one end of a 4mm2 or 6mm2 electric cable, and therefore from one end of a subsea umbilical, possibly more than 2.5 metres.

Figure 6 shows in cross-section an individual electric conductor 50, comprising seven electric strands 52 formed in a hexagonal-centred pattern to provide the electric conductor 50, within an insulation layer 26a. The strands 52 can be seen to have a number of interstices thereinbetween. The electric conductor 50 is characterised in that the interstices are filled from one end with a curable material 30. The curable material 30 could be inserted into the interstices from one end in a manner and using a method as described herein. The electric conductor 50 can form part of a subsea electric cable as a stand-alone cable, optionally with additional oversheathing, or be used as one element or part of a subsea umbilical as discussed herein.

The purpose of the present invention is to provide an electric cable without any voids between the electric strands of the conductor or conductors of the electric cable, from at least one end of the cable, optionally from both ends. Voids such as the interstices between electric strands can allow water and/or gas to permeate through the length of the electric cables, and to migrate to subsea terminations and potentially lead to premature failure.

Whilst filling of electric strand interstices during manufacture of electric cables during their 'bundling' is possible, this is an extensive and expensive process and operation, requiring a high degree of accuracy and control of the amount of filling material being applied, whilst avoiding any increase in the size of the overall electric conductor (as each conductor size is critically important to the overall design and forming of the electric cable and/or subsea umbilical).

The present invention provides a simple solution to still achieving the sealing of any water and/or gas within the electric conductor, either during manufacture of an electric conductor, or the electric cable, or once bundled with other components of a subsea umbilical. The present invention prevents such water and gas reaching or migrating to one end of the cable and into a further connection, in particular to a subsea termination, without affecting the flexibility of the overall electric cable and/or umbilical. This also prevents any change in the expected operation of the subsea cable, in particular any change to the possibility of fatigue damage during installation, and/or its dynamic positioning in service under water.

Claims

CLAIMS1. A method of sealing an end of a subsea electric cable, the electric cable comprising at least one electric conductor, the at least one electric conductor comprising a plurality of electric strands having interstices, comprising at least the steps of: (a) inserting a curable material into the interstices from one end of the electric cable; and (b) allowing the curable material to cure and form a seal between the electric strands.
2. A method as claimed in claim 1 wherein step (a) comprises injecting a curable material into the interstices from one end of the electric cable.
3. A method as claimed in claim 2 wherein step (a) comprises injecting a curable material under pressure into the interstices from one end of the electric cable.
4. A method as claimed in claim 2 wherein step (a) comprises injecting a curable material under gaseous pressure into the interstices from one end of the electric cable.
5. A method as claimed in any one of the preceding claims further comprising the step of locating a sealing rig around the one end of the electric cable.
6. A method as claimed in claim 5 wherein the sealing rig comprises an umbilical clamp, an end cap, and an intermediate curable material chamber, further comprising the steps of: pre-locating the umbilical clamp around the electric cable; and filing the intermediate curable material chamber with curable material.
7. A method as claimed in claim 6 wherein where step (a) comprises injecting a curable material under gaseous pressure into the interstices from one end of the electric cable, the method further comprising the step of; pressurising the curable material in the intermediate curable material chamber with a gas supplied through the end cap.
8. A method as claimed in any one of the preceding claims further comprising the step of: exposing the electric strands from the electric conductor prior to step (a)
9. A method as claimed in any one of the preceding claims wherein the electric cable comprises at least an outer sheath and at least one inner layers, further comprising the step of; exposing one or more of the inner layers; and; locating one or more seals around at least one inner layer to seal the one or more inner layers from the curable material.
10. A method as claimed in any one of the preceding claims further comprising the step of; applying heat to the curable material during step (b).
11. A method as claimed in any one of the preceding claims wherein the curable material is a silicone gel.
12. A method as claimed in claim 11 wherein the silicone gel is an addition-curing silicone rubber composition.
13. A method as claimed in any one of the preceding claims wherein the electric cable is a low-voltage cable.
14. A method as claimed in any one of the preceding claims wherein the electric cable extends through a subsea umbilical.
15. A method as claimed in any one of the preceding claims wherein the electric cable is oversheathed by one or more armour layers.
16. A subsea electric cable comprising at least one electric conductor, the at least one electric conductor comprising a plurality of electric strands having interstices, characterised in that the interstices are filled from one end with a curable material.
17. A subsea electric cable whenever formed by a method of any one of claims 1 to 15.
18. A subsea electric cable as claimed in claim 16 or claim 17 wherein the curable material is a silicone gel.
19. A subsea electric cable as claimed in claim 18 wherein the silicone gel is an addition-curing silicone rubber composition.
20. A subsea electric cable as claimed in any one of claims 16 to 19 wherein electric cable is a low-voltage cable.
21. A subsea electric cable as claimed in any one of claims 16 to 20 wherein the electric cable is oversheathed by one or more armour layers.
22. A subsea umbilical comprising at least one electric cable as defined in any one of claims 16 to 21 extending through the umbilical.
23. A sealing rig comprising an umbilical clamp, an end cap, and an intermediate curable material chamber, able to fill the interstices of a subsea electric cable, the electric cable comprising at least one electric conductor, and at least one electric conductor comprising a plurality of electric strands having interstices, from one end with a curable material.