WO2013033305A1

WO2013033305A1 - Cable and umbilical

Info

Publication number: WO2013033305A1
Application number: PCT/US2012/053000
Authority: WO
Inventors: Siu Kit Joe Wong; Stephen Owen MAST; Brett KLINE
Original assignee: Oceaneering International Services Limited; Oceaneering International, Inc.
Priority date: 2011-08-31
Filing date: 2012-08-30
Publication date: 2013-03-07
Also published as: GB201114993D0; GB201309582D0; GB2499348A

Abstract

A multicore electrical cable (38) includes a plurality of insulated electrical conductors (46), each including at least one conductor wire strand (28,28a) forming the conductor core (42). A plurality of conductor wire strands (28,28a) are helically twisted together to form the conductor core (42) and the interstices between strands are filled with a conductive sealant (40) or one conductor wire strand forms the conductor core. The conductor cores (42) are over sheathed by a polymeric insulation layer (30), with a layer of an adhesive (44) provided between the polymeric insulation layer (30) and the conductor core (42) to fill interstices therebetween. The insulated electrical conductors (46) are bundled together, and over sheathed by an outer polymeric insulation layer (50), with a layer of adhesive filler (48) provided between the outer polymeric insulation layer (50) and the insulated electrical conductors (46). A subsea umbilical is also provided.

Description

Cable and Umbilical

Field of the invention

The present invention reiates to the provision of improved electrical cable with enhanced resistance to ingress of water or gas. The cable is suitable for use in subsea electric power and/or signal transmission and may be used in umbilical conduits such as are used in offshore drilling environments.

Background of the invention

in subsea working, such as offshore drilling environments it is necessary to supply electrical power, electrical signals, hydraulic signals and fluids to the wellhead.

An umbilical is a conduit that can contain a number of functional elements for subsea work. Typically an umbilical comprises a group of functional elements such as electric cables, optical fibre cables, thermoplastic hoses or steel tubes. Hoses and cables carried within an umbilical are generally of multilayer reinforced structures, such as are known in the art so that they have appropriate pressure containment, burst and compression resistance for the usage envisaged. The umbilical provides a convenient single conduit to carry the fluid, electrical and signalling requirements of the task in hand.

Typically the electric cables are low voltage cables, usually rated at less than 3000V and have a conductor size in the range of 1 to 35 mm².

Figure 1 shows a prior art subsea umbilical in cross section, The umbilical (1) contains a group of functional elements, including twelve thermoplastic hoses (2,4,6,8) and four muiticore low voltage electric cables (10,12), Others elements that may be present such as steel tubes and fibre optic cables are not shown in figure 1. The functional elements are bundled together with fillers (14,16,18,20), rods of solid or hollow plastics material to provide packing and bundle stability. The bundle is provided with an inner-sheath (22), two layers of armouring (24) and an outer-sheath (28) to form the umbilical.

Figure 2 shows in cross section a typical prior art muiticore low voltage cable (12). Each core (conductor core) in this example has seven circular, in cross section, strands of conductor material (28). A muiticore cable typically comprises two to four electric conductors; four are shown in the example. The conductor wires (strands) are generally made of copper. The conductor wires are twisted together helically and a layer of insulation (30) polymer material is extruded around each stranded conductor. The insulated conductors are then assembled helically (or oscillatory) together with fillers of a polymer material (32) as desired. A polymeric belting (34) fills the space between the insulation (30) and the outer polymeric jacket (36) and optionally a metal screen (36) is applied to the assembled insulated conductors. In an offshore subsea environment, sometimes an electrical cable, often within an umbi!icai as described above may develop an electrical fault or be damaged by e.g. fishing gear or heavy objects dropped from the surface, The cable or the umbilical carrying the cabie may be severed; cut underwater for repair or cut and dropped subsea for abandonment of the installation process.

When the eiectrical cabling and/or umbilical carrying the cabling are cut any spaces (interstices) within the umbiiicai and the cable will be flooded with sea water. This is undesirable as it effects cable performance and reduces design life.

In general, over a long period of time, water and gas (predominantly small molecule gases, typically hydrogen) tend to permeate into subsea electric cabling and can travel longitudinally along the cable and conductor interstices to the cabie ends where subsea terminations/connectors are located; internal pressures may increase which can compromise the performance of the connectors and may lead to low insulation resistance values and eventually electric failure.

WO2008/032019 describes using hydrogen absorbent materia! between insulated electric conductors and a tubular metallic layer, in order to prevent water and gas ingress by permeation. However, this cable design does not totally eliminate permeation over very long periods 10 plus years as the absorbing process reduces and saturation occurs and does not prevent water and gas longitudinal transmission along the length of the cable. When such a cable is cut or damaged in the subsea environment, the cable and insulated conductor interstices will be flooded with sea water.

US7285726 describes a subsea medium high voltage cabie wherein the gaps in the conductor wires are filled with a hydrophobic water-biocking compound to seek to minimise longitudinal water penetration and facilitate repair. However, water and gas ingress is still possible between the conductor and the inner insulator of semiconducting cross-linked polyethylene.

With the increasing need for operation in deeper water, cabling and umbilicals have become longer and are subject to harsher conditions in use. The need for increased performance and reduced failure rate, because of the costs and difficulties of repair and replacement, leads to a need for improved cabling and umbi!icals to provide satisfactory performance under harsher conditions.

Description of the invention

According to a first aspect the present invention provides a multicore electrical cable comprising: a piurahty of insulated electrical conductors, each comprising at least one conductor wire strand forming the conductor core;

wherein a plurality of conductor wire strands are helically twisted together to form the conductor core and the interstices between strands are filled with a conductive sealant; or

one conductor wire strand forms the conductor core;

wherein the conductor cores are each independently over sheathed by a polymeric insulation layer, with a layer of an adhesive provided between the polymeric insulation layer and the conductor cores to fill interstices therebetween; and

wherein the plurality of insulated electrical conductors are bundled together, and over sheathed by an outer polymeric insulation layer, with a layer of adhesive filter provided between the outer polymeric jacket insulation layer and the insulated electrical conductors to fill the interstices therebetween,

TypicaHy the insulated electrical conductors are laid helically or oscillatory (S/Z) when bundled together as is usual for muiticore cable.

Advantageously the bundle of insulated electrical conductors will further comprise solid filter, typically in the form of rods of polymer, typicaHy polyethylene and/or nylons. The filler such as filler rods adds crush strength and roundness to the bundle, and acts to partially fill and reduce the spaces or interstices between the bundle and the outer polymeric insulation layer. The layer of adhesive filler fills the remaining interstices.

The cable of the first aspect of the invention presents several advantages. Where a plurality of conductor wire strands are employed the conductive sealant fills all or substantially all the interstices between the wire strands preventing the ingress of gas or water but without loss of conductive connection between the strands which would affect the electrical properties of the cable.

The use of an adhesive between the conductor cores and the corresponding polymeric sheathing also serves to prevent gas or water ingress, by filling the interstices that would otherwise be present between the sheathing and the wire strands and/or conductive sealant. At the same time, as the adhesive bonds the insulation layer to the conductor cores, it acts to prevent separation between them. Such separation can occur with prior art arrangements due to internal pressures from permeation, leaving a path for gas and/or water ingress.

The use of the layer of adhesive filler between the outer jacket polymeric insulation layer and the bundle of insulated eiectrical conductors, (optionally including solid filler components), fills all or substantially ail the remaining interstices in the cable assembly, bonding the bundle of conductors to the outer insulation layer. This provides the same benefits in terms of prevention of ingress of water and gas as the adhesive layer employed with the conductor cores and corresponding insuiation layers. Preferably the filling medium chosen is sufficiently stiff so that it does not flow due to internal pressures (when cold, under operating conditions) in the conduit. Preferably the adhesive selected is such that it faciiitates stripabiiity of the insulated conductors so that electrical connections may be readily made.

According to a second aspect the present invention provides an insulated electrical conductor, suitable for use in the cable of the first aspect of the invention and comprising: a plurality of conductor wire strands helically twisted together to form a conductor core wherein the interstices between strands are fiiled with a conductive sealant;

wherein the conductor core is over sheathed by a polymeric insulation layer, with a layer of an adhesive provided between the poiymeric insulation layer and the conductor core to fill interstices therebetween.

Conveniently and typically seven conductor wire strands are employed, a central strand with six further strands arranged around it as shown hereafter and with reference to specific embodiments,

Advantageously the core of the insulated electrical conductor used for the second aspect of the invention is prepared by a process that includes a compacting step, wherein the p!uraiity of conductor wire strands and conductive sealant are drawn through a die after they are twisted together to produce a compacted conductor core. The effect of the compaction step is to minimise interstitial volume and to ensure that the conductive sealant is forced to completely fill the interstices between the wire strands, displacing any air or other gas present. The compacting step is typically carried out with sufficient force to distort the shape of the wire strands, to ensure sufficient pressure is applied, as discussed further hereafter and with reference to a specific embodiment.

According to a third aspect the present invention provides an insulated electrical conductor, suitable for use in the cable of the first aspect of the invention comprising: one conductor wire strand as the conductor core;

wherein the conductor core is over sheathed by a polymeric insulation layer, with a layer of an adhesive fliler provided between the polymeric insulation layer and the conductor core to fill interstices therebetween.

It will be understood by the skilled person that the fillings (conductive sealant, adhesive and adhesive filler) provided between various components of the cables and insulated electrical conductors as described herein are provided so as to completely fill the interstices that would otheavise be present. However, such fillings may contain occasional defects, for example resulting from variations in the manufacturing process.

Therefore the fillings will fill all or substantially all of the interstices. According to a fourth aspect the present invention provides an umbilical for subsea use comprising at least one insulated conductor according to the second and/or according to the third aspect of the invention. The at least one insulated conductor may be a component of a multicore electrical cable according to the first aspect of the invention, Thus the umbilical may include both one or more insulated conductors as separate components and/ or one or more multicore electrical cables.

The insulated electrical conductors described above are typically of low voltage (i.e. rated less than 3000V) when used in subsea operations.

The conductor wire strands are usually of copper, aluminium or aluminium alloy. Suitable conductive sealant (conductive filler) materials are known in the art.

These are malleable mastic type solids that include conductive components, for example the Solarite KM-273Q strand seal material available from Solar Compounds Corporation of Linden NJ 07038 USA.

The polymeric insulation !ayer that sheaths the conductor cores may be of any type such as known in the art, for example they may be of a polyethylene polymer or ethylene propropylene copolymer.

The adhesive used between the conductor cores and their insulation layer is selected for the ability to bond to metal and/or the conductive sealant; and to the polymer of the insulation layer. For example an ethylene acrylic acid copolymer may be employed. Suitable adhesives include Pnmacor™ 5980I an ethylene acrylic acid copolymer resin, available from The Dow Chemical Company.

The adhesive filler employed for filling the interstices between the bundle of insulated electrical conductors and the outer polymeric insulation layer can be selected for bonding to the insulation layers. Typically both insulation layers are of a polyethylene. Conveniently a hot melt adhesive may be employed. For example ethylene vinyl acetate (EVA) based adhesive such as Bostik® EM 1000 hot melt adhesive available from Bostik, Inc. Wauwatosa, Wl 53226-3434 USA.

Methods of manufacture of the insulated electrical conductors, multicore cables and umbilicals discussed above constitute further aspects of the present invention.

When making an insulated electrical conductor according to the second aspect of the invention, manufacture may be by the following method:

One or more of the conductor wire strands is coated with conductive sealant. For example by dipping through a bath of the same. The plurality of conductor wire strands are helically twisted together in the known fashion to form the conductor core and to partially distribute the sealant in the interstices between strands. The conductor core is completed by passing the core through a die to compact the strands and force the sealant into ail the interstices between strands. The conductor core is then coated with adhesive, for exampie extruding or by dipping through a bath of warm adhesive resin and then the polymeric insu!ation layer is extruded onto the conductor core and its adhesive coating.

When making an insulated eiectricai conductor according to the third aspect of the invention, manufacture may be by the same method as described above for the conductor according to the second aspect except thai as a singie conductor wire strand is employed the twisting compacting step is not carried out and conductive sealant is not employed.

When making a multicore electrical cable according to the first aspect of the invention the plurality of insulated eiectricai conductors is laid helical or oscillatory in the known manner, together with any solid fi!iers such as polyethylene rods. The second layer of adhesive is applied to the bundle. Conveniently a thin insulating tape, for example a polyethylene tape may optionally be wound round the bundle and adhesive to contain both, ensuring the adhesive fil!s all interstices. The outer polymeric insulation layer is then extruded onto the bundle. If a thin instating tape has been employed it fuses to the outer polymeric layer as it is extruded onto the bundle.

Brief Description of the Drawings

Figures 1 and 2 show respectively a prior art subsea umbilical and a prior art low voltage multicore cable;

Figure 3 shows a low voltage multicore electric cable of the invention in schematic cross section; and

Figure 4 is an enlarged view of the schematic cross section of an insulated electrical conductor of the multicore cable shown in figure 3.

Description of the invention With Reference to Some Embodiments

A preferred embodiment of the invention is shown in figure 3, a cross section of a low voltage rnuiticore electric cable (38), suitable for use in an umbilical is illustrated. The low voltage multicore cable is rated smaller than 3000 volts and typically comprises two to four insulated eiectricai conductors, with four shown in this exampie. The conductor wire strands (28) are made of copper or aluminum or aluminum alloy.

Before the conductor wire strands (28,28a) were compacted they were ail of circular cross-section as for the prior art arrangement shown in figure 2 (parts 28 in that figure). In manufacture the central wire strand (28a) was coated with conductive sealant (40) which has been forced into the interstices between all the wire strands (28,28a) by the procedure of first twisting the strands together and then compacting the arrangement by passing it through a die. It will be understood that the distortion from the circular cross section shown in the outer six wire strands (28) may not be as great as depicted, depending on the degree of compaction applied, if no or relatively light compaction is applied the strands (28) will remain generally circular in cross section. The interstices in the conductor wire strands (28,28a) are fully filled with the conductive sealant compound (40).

The compacted conductor cores (42), formed from the conductor wire strands

(28,28a) and the conductive sealant (40), have an uneven surface as a result of the twisting of the strands, and there would be micro voids between the compacted conductor and the insulation where they are not bonded together. These voids are filled with adhesive.

A layer of adhesive (44) and a polymeric insulation layer (30) are extruded around each conductor core (42), so that the adhesive is underneath the insulation. The adhesive materia! (44) must be flexible and should be bonded vvel! to the insulation (30) and to the compacted conductor core (42). The compacted conductor core (42), the adhesive (44) and the polymeric insulation layer (30) constitute an insulated electrical conductor (46).

The insulated conductors (48) are assembled helical together with solid polymer fillers (32). Since the insulated conductors are of round cross-section, there is space between the insulated conductors (46) where they are not bonded to one another; and this space contains the second layer of adhesive (48). It will be understood that the all the interstices in the assembled insulated conductors (48) are filled with the adhesive (48).

An outer polymeric insulation layer (50) is extruded around the assembled insulated conductors (48), solid filler rods (32) and adhesive (48). Not shown in this example is a thin layer of tape that may be employed outside the adhesive (48), to contain it, in advance of the application of the outer layer (50).

Figure 4 is a view of one of the insulated conductors (46) of figure 3 i.e. an insulated electrical conductor according to the second aspect of the invention. The figure shows more clearly the sealant (40) between the conductor wire strands (28.28a) and the layer of adhesive (44) between the conductor core (42) and the outer polymeric insulation layer (30).

Claims

CLAIMS:

1. A rnulticore electrical cable comprising:

a plurality of Insulated electrical conductors, each comprising at least one conductor wire strand forming the conductor core;

wherein a p!uraiity of conductor wire strands are he!ica!!y twisted together to form the conductor core and the interstices between strands are fi!ied with a conductive sealant; or

one conductor wire strand forms the conductor core;

wherein the conductor cores are each independently over sheathed by a polymeric insulation !ayer, with a iayer of an adhesive provided between the polymeric insulation iayer and the conductor cores to fill interstices therebetween; and

wherein the plurality of insulated electrical conductors are bundled together, and over sheathed by an outer poiymeric insulation !ayer, with a Iayer of adhesive filler provided between the outer polymeric insulation Iayer and the insulated eiectrical conductors to fill interstices therebetween.

2. A rnulticore eiectrical cable according to claim 1 wherein the plurality of insuiated electricai conductors are laid helically or are laid oscillatory when bundled together.

3. A rnulticore electrical cable according to claim 1 or claim 2 further comprising solid fiiier provided in the bundle of insulated electrical conductors.

4. A rnulticore electrical cable according to any preceding claim wherein the polymeric insulation layer that sheaths the conductor cores is of a polyethylene polymer.

5 A rnulticore eiectrical cable according to any preceding claim wherein the adhesive used between the conductor cores and their insulation layer is an ethylene acrylic acid copolymer.

6. A rnulticore eiectrical cable according to any preceding claim wherein the adhesive employed for filling the interstices between the bundle of insulated electrical conductors and the outer polymeric insulation layer is an ethylene vinyl acetate (EVA) based hot melt adhesive.

7. An insulated electrical conductor, for use in the cable of any one of claims 1 to 6 and comprising: a plurality of conductor wire strands helically twisted together to form a conductor core wherein the interstices between strands are filled with a conductive seaiant;

wherein the conductor core is over sheathed by a polymeric insulation layer, with a layer of an adhesive provided between the polymeric insulation layer and the conductor cores to fill interstices therebetween.

8, An insuiated electrical conductor according to claim 7 wherein seven conductor wire strands are employed, a central strand with six further strands arranged around it.

9 An insulated electrical conductor according to claim 7 or claim 8 wherein the conductor core is prepared by a process that includes a compacting step.

10. A process for the manufacture of an insulated electrical conductor according to claim 7, the process comprising:

coating one or more of a plurality of conductor wire strands with a conductive sealant;

helically twisting together the plurality of conductor wire strands to form a conductor core;

passing the conductor core through a die to compact the plurality of wire strands and force the sealant into interstices between strands, thereby forming a compacted conductor core;

coating the compacted conductor core with adhesive; and

extruding a polymeric insulation layer onto the conductor core and its adhesive coating.

11. An umbilical for subsea use comprising at least one of; a multicore cable according to any one of claims 1 to 6; or an insulated electrical conductor according to any one of claims 7 to 9,