WO2017182782A1

WO2017182782A1 - Junction box

Info

Publication number: WO2017182782A1
Application number: PCT/GB2017/051061
Authority: WO
Inventors: Stephen Craig BEECH; Peter Leslie CHRISTIAN
Original assignee: Global Marine Systems Limited
Priority date: 2016-04-18
Filing date: 2017-04-18
Publication date: 2017-10-26

Abstract

A junction box for joining a plurality of cable elements of an underwater cable is provided. The junction box comprises a sleeve having a major axis, the sleeve defining an internal region for accommodating joins between the cable elements. First and second sleeve retainers each comprise a bore for receiving a part of the cable which extends into the internal region. The first and second sleeve retainers are each detachably attached to a respective opposing end of the sleeve by an outer set of fasteners extending into the sleeve. A first sealing member provided at the interface between each said sleeve retainer and the sleeve. The first sealing member is configured to prevent ingress of hydrogen into the internal region from along the interface.

Description

JUNCTION BOX

The invention relates to a junction box for joining cables. The invention finds particular benefit for the installation of a sub-oceanic fibre optic cable or cable network.

Junction boxes, also referred to as 'joints' for sub-oceanic (or 'subsea') cables are known. These junction boxes may be provided at regular intervals along a cable to facilitate the connection of contiguous lengths of cabling. An assembly is typically provided inside the housing of the junction box to enable a technician to connect the ends of a plurality of exposed cables together. The housing is designed to sustain the high pressures which are present along the ocean floor, as well as the tensions applied to the subsea cable during installation and recovery of the cable. Junction boxes such as these are typically required to be water-tight and prevent the ingress of hydrogen, which could otherwise damage the internal components, particularly optical ones.

The 'Universal Joint', provided by Global Marine Systems Ltd, www.globalmarinesystems.com, is an example of a prior art junction box. A sleeve defines an internal region for accommodating joins between cable elements. Long 'through' bolts extend across the inner chamber to hold two opposing end pieces onto the sleeve. A first through bolt extends from a first end piece to an opposing end piece, whilst a second through bolt extends in the opposite sense from the opposing end piece to the first end piece. Each through bolt is sealed using a hydrogen seal in the form of an o-ring. Assembling the Universal Joint and disassembling it whilst at sea, for example to enable inspection of the joined cable elements upon detection of a fault, is typically a time-consuming and therefore expensive process. There is a need to simplify this process. It would also be desirable to increase the space which is available within the junction box to accommodate joins between cable elements.

A first aspect of the invention provides a junction box for joining a plurality of cable elements of an underwater cable, the junction box comprising: a sleeve having a major axis, the sleeve defining an internal region for accommodating joins between the cable elements;

first and second sleeve retainers each comprising a bore for receiving a part of the cable which extends into the internal region, wherein the first and second sleeve retainers are each detachably attached to a respective opposing end of the sleeve by an outer set of fasteners extending into the sleeve;

a first sealing member provided at the interface between each said sleeve retainer and the sleeve, wherein the first sealing member is configured to prevent ingress of hydrogen into the internal region from along the interface.

Unlike the Universal Joint, the junction box of the present invention comprises fasteners that extend into the sleeve itself so as to couple each sleeve retainer to a respective opposing end of the sleeve. This increases the space which is available within the internal region for fitting cable element joins. Furthermore, a plurality of fasteners is provided within the outer set of fasteners at each end for attaching the respective sleeve retainers to the sleeve. This simplifies the method of assembly as the 'net securing force' is shared between more fasteners. Although more fasteners are provided, time savings are achieved as a jig is no longer required to tighten the fasteners.

Hydrogen naturally diffuses within sea water and, if present within the junction box, can degrade cable elements of the junction box through a process known as hydrogen darkening. Special seals are typically required in order to prevent the ingress of hydrogen into an underwater junction box. Advantageously therefore, the first sealing members may form hydrogen seals preventing hydrogen gas travelling from outside of the junction box, along the interface between the sleeve retainers and the sleeve, past the outer set of fasteners, and into the internal region. At each end, the first sealing members are preferably arranged radially inside the outer set of fasteners with respect to the major axis. Advantageously, the first sealing members are therefore arranged to block a hydrogen pathway extending from a distal face of the sleeve retainers, along the outer sets of fasteners, across the interface between a proximal face of the sleeve retainers and the sleeve, and into the internal region.

Typically one or both of the first sealing members are provided in the form of an o-ring. The first sealing members may therefore conveniently provide a seal for the surrounding outer set of fasteners, without the need to provide separate seals for each individual fastener. The axis of each of the o-rings is typically coaxial with a major axis of the junction box and the sleeve. Preferably still, the first sealing members are formed of copper. Copper sealing members are particularly effective, in part due to their malleability. Furthermore, the first sealing members are preferably physically spaced apart from the outer sets of fasteners. This can help to prevent damage to the sealing members from occurring when the fasteners are fitted. Alternatively, the first sealing members may form plates.

In order to provide an approximately even securing force around the major axis, it is preferable that the outer sets of fasteners each comprise a plurality of fasteners circumferentially disposed about the major axis. For example, the outer sets of fasteners may each comprise at least four, preferably five, more preferably six fasteners. A higher number of fasteners reduces the torque required to sufficiently tighten each fastener, as the net securing force is split between more fasteners. This may also improve the effectiveness of the seal provided between the sleeve and each sleeve retainer. Preferably the junction box is configured such that the attachment between the first sleeve retainer and the sleeve can be performed independently of the attachment between the second sleeve retainer and the sleeve. This allows for convenient assembly and disassembly of the junction box. The junction box preferably further comprises first and second ferrule members configured to engage with the bore of the first and second sleeve retainers respectively. Each said ferrule member may comprise a port for receiving the part of the cable extending into the internal region. These ports typically extend along the major axis of the sleeve. The junction box may further comprise one or more cable sealing members arranged inside said ports to prevent hydrogen entering the internal region from along the cable. These cable sealing members may be formed of copper and may each form a hydrogen seal to protect any joined cable elements within the internal region from hydrogen damage.

Preferably, a first portion of each of the first and second ferrule members is arranged inside the sleeve, and a second portion of each of the first and second ferrule members protrudes from the sleeve, the first portions having a diameter greater than the second portions with respect to the major axis. The first portion may also hence have a diameter that is larger than the bore of the surrounding sleeve retainer. The ferrule members may therefore be configured such that each sleeve retainer fits over a respective second portion until they abut onto the first portion of the respective ferrule member. The internal region preferably comprises a cradle assembly for enabling the cable elements to be joined. This cradle assembly may be coupled to the first portion of one or both of the ferrule members. The cradle assembly provides a structure onto which cable elements, such as optical fibres, can be wound and joined. The cradle assembly may be removed from the junction box together with the coupled ferrule member for inspection of the cable element joins.

Preferably, the junction box further comprises first and second end caps configured to releaseably engage with the second portion of the first and second ferrule members. For example, the end caps may be configured to couple with a threaded outer surface of the second portion of the ferrule members. The first and second end caps are preferably further configured to engage with the first and second sleeve retainers respectively. For example, the end caps may be conveniently screwed onto the threaded outer surface of the second portions until they abut onto a distal face of the sleeve retainers. The end caps may help to seal the junction box and can provide a tapered surface extending from the sleeve retainers towards a cable protruding from either end of the junction box.

The junction box is preferably configured such that the attachment between the first sleeve retainer and the first ferrule member may be performed independently of the attachment between the second sleeve retainer and the second ferrule member. For example, the first and second sleeve retainers may each be attached to the respective first and second ferrule member by an inner set of fasteners, wherein the inner set of fasteners is disposed radially inward of the outer set of fasteners with respect to the major axis. In this case the junction box may further comprise a second sealing member provided at the interface between each sleeve retainer and the respective attached ferrule member so as to prevent ingress of hydrogen into the internal region. For example, the second sealing members may each be arranged outside the respective inner set of fasteners. Advantageously, the second sealing members may therefore be arranged to block a hydrogen pathway extending from a distal face of the sleeve retainers, along the inner sets of fasteners, across the interface between a proximal face of the sleeve retainers and a distal face of the first portion of the ferrule members, and into the internal region.

Typically one or both of the second sealing members are provided in the form of an o-ring. Advantageously, this prevents the need to seal each of the fasteners of the inner set individually. Alternatively the sealing members may take the form of plates comprising apertures for receiving the first portion of the ferrule member, as well as the inner set of fasteners. The second sealing members are preferably formed of copper and may be physically spaced apart from the inner sets of fasteners.

The inner sets of fasteners preferably each comprise a plurality of fasteners circumferentially disposed about the major axis. For example, the inner sets of fasteners may each comprise at least four, preferably five, more preferably six fasteners. This helps to provide a uniform securing force across the junction box. Typically the fasteners of the first and/or second sets of fasteners are bolts. Advantageously, by providing a plurality of fasteners at each end, the junction box may be configured such that the torque required to place each fastener into a tightened state is less than 20 Nm. This is significantly less than the 160 Nm required to tighten the through bolts of the Universal Joint. The need for a jig to remove and tighten the fasteners is therefore avoided, thereby improving the speed with which a junction box may be taken apart and inspected. The inner region is typically sealed from hydrogen. This may be in part at least due to the presence of the sealing members. For example each first sealing member may be arranged such that no hydrogen gas path exists between the respective outer set of fasteners and the internal region along the interface between the sleeve retainer and the sleeve without encountering the first sealing member. Exposed cable elements that may be contained within the internal region may therefore be protected from degradation due to exposure to hydrogen.

A second aspect of the invention provides a cable and a junction box according to first aspect, wherein said cable comprises a plurality of cable elements that are joined within the internal region. Advantageously, the construction of the junction box may allow for a greater number of cable elements to be joined within the internal region than in the prior art. For example, at least 96, 150, or even 192 cable elements may be provided within the internal region. Typically the cable elements are optical fibres.

Optical fibres are often laid alongside power cables within subsea cable networks. The junction box of the first aspect may be formed with a sufficiently small volume so as to be housed within a power cable joint. Therefore, in a third aspect of the invention provides a power cable joint comprising housing, the housing containing a cable joint according to the second aspect. In a fourth aspect of the invention there is provided a marine cable installation comprising an underwater cable having one or more junction boxes according to the first aspect disposed thereon.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is an illustration of a perspective view of a cable joint according to an embodiment;

Figure 2 is an illustration of side view of the cable joint according to the embodiment; Figure 3 is an illustration of an end view of the cable joint according to the embodiment;

Figure 4 is a first illustration of a section side view of a junction box according to an embodiment;

Figure 5 is a second illustration of a section side view of a junction box according to the embodiment;

Figure 6 is an illustration of a sleeve retainer of a junction box according to the embodiment; and

Figure 7 is an illustration of a sectional perspective view of a power cable joint according to an embodiment.

Three different outer views of an embodiment of a cable joint comprising a junction box 20 are shown by Figures 1-3. The junction box 20 is substantially cylindrical and comprises first and second ports 18, 19 provided at distal opposing ends of the box 20. A first cable bundle 21 extends through the first port 18 and a second cable bundle 22 extends through the second port 19. The first and second cable bundles 21 , 22 each comprise a plurality of cable elements in the form of optical fibres which are insulated and protected by an outer jacket of the respective bundles 21 , 22. The optical fibres from the first bundle 21 are connected to the optical fibres from the second bundle 22 inside the junction box 20.

Figure 4 illustrates a first section view of the junction box 20 taken through the A- A plane of Figure 3. A second cross sectional view through the same plane is shown in Figure 5 in which different features have been emphasised from the illustration of Figure 4.

The junction box 20 comprises housing, referred to in the industry as a "pressure housing", which comprises a sleeve 1 , first and second sleeve retainers 1 1 , 15, and first and second ferrules 16, 17. The sleeve 1 extends along the centre of the box 20 and has an elongate, substantially annular shape which, in combination with the ferrules 16, 17, defines a substantially cylindrical inner chamber (also referred to herein as the splicing region) that accommodates a fibre tray 8. The junction box 20 and sleeve 1 have a common central major axis that extends along the cable bundles 21 , 22. The plurality of optical fibres of the first and second cable bundles 21 , 22 may be spliced on the fibre tray 8 using techniques known in the art. The fibre tray 8 is provided as part of a cradle assembly is supported inside the sleeve 1 using guides 2, 3.

The junction box 20 is substantially symmetric about a plane B-B (illustrated in Figure 2) that bisects the box 20 midway along the major axis, in a direction perpendicular to the major axis. In other words, corresponding features are generally provided at each distal end of the junction box 20. As shown in Figure 5 the first ferrule 16 is of a different type however to the second ferrule 17 such that two different types of cable bundles 21 , 22 may be joined together by the box 20. This enables improved versatility over the prior art. Alternatively the first and second ferrules 16, 17 may be of the same type. The first and second ports 18, 19 extend through the centre of the first and second ferrules 16, 17 respectively such that the cable bundles 21 , 22 are fed through the ports 18, 19 into the box 20. For sake of clarity, the cable bundles and fibres are not shown in Figures 4 and 5. The sleeve 1 extends over a first, proximal portion of the ferrules 16, 17 and abuts onto the first and second sleeve retainers 1 1 , 15. The sleeve retainers 1 1 , 15 are substantially disc shaped and comprise a central bore through which a second, distal portion of the ferrules 16, 17 protrude. The major axis of the junction box 20 extends through the bores of the sleeve retainers 11 , 15. The first portions have a larger diameter than the second portions and the bores with respect to the major axis of the junction box 20. The first portions abut against a proximal face of the sleeve retainers 1 1 , 15 facing towards the internal region.

The first and second sleeve retainers 1 1 , 15 are secured to the first and second ferrules 16, 17 respectively, as well as to the ends of the sleeve 1 by fasteners 6, 7 in the form of bolts. An inner set of bolts 6 and an outer set of bolts 7 are circumferentially arranged at each end of the sleeve 1 about the major axis. The inner sets of bolts 6 extend from the first and second sleeve retainers 1 1 , 15 into the first and second ferrules 16, 17 respectively so as to couple the sleeve retainers 1 1 , 15 to the ferrules 16, 17. The outer sets of bolts 7 are provided at a larger radial distance from the major axis than the first set 6 and extend from the respective sleeve retainers 11 , 15 into respective opposing end faces of the sleeve 1. The splicing region is sealed to prevent the ingress of hydrogen, which could otherwise degrade the internal fibres. In the present embodiment this is achieved by sealing members 25, 26 in the form of hydrogen seals formed of copper are provided at each end of the sleeve 1. The first sealing members 25 have the form of an o-ring, wherein a single o-ring is provided at each end of the box 20, between the ends of the sleeve 1 and an inner face of the respective sleeve retainer 11 , 15. The first sealing members 25 prevent the ingress of hydrogen through the interface between the end of the sleeve 1 and the abutting proximal face of the respective sleeve retainer 1 1 , 15. Advantageously, the outer set of bolts 7 is radially disposed outside of, and is separated from, the first sealing member 25 at each end relative to the major axis. A common seal is hence conveniently provided for each of the bolts of the outer sets 7. A more reliable hydrogen seal is therefore provided over the prior art as the need for the separate hydrogen seals around each respective through bolt is avoided. A second sealing member 26 in the form of a hydrogen seal formed of copper is provided between the inner face of the sleeve retainers 1 1 , 15 and a corresponding surface of the respective ferrules 16, 17. The second sealing members 26 are each o-rings and surround the respective inner set of bolts 6 that extend between the sleeve retainers and the respective ferrule. The second sealing members 26 assist in preventing the ingress of hydrogen through the inner bolts 6, along the ferrules and the sleeve 1 , into the splicing region. Additional sealing members may be provided to prevent the ingress of hydrogen from the cables into the splicing region. The present embodiment allows for more securing bolts 7 to be provided than the Universal Joint. This simplifies the method of assembly as the 'net securing force' may be shared between more bolts. In the Universal Joint a force of 160 Nm was required to secure each through bolt, whereas a force of only 10.5 Nm is required to secure each bolt 7 and produce an equivalent net force. Although more bolts 7 are provided, time savings are achieved as a jig is no longer required to secure the bolts.

An end cap 28, 29 is provided at each distal end of the junction box 20. The end caps are substantially cone shaped and extend from the sleeve retainers 11 , 15 to the respective cable bundles 21 , 22 in a flat tapered manner. The second portions of the ferrules 16, 17 protrude through the central bore of the sleeve retainers 1 1 , 15 and comprise a threaded outer surface (shown in Figure 5) onto which the end caps 28, 29 are secured. The end caps 28, 29 have a corresponding threaded inner surface (shown in Figure 4), for engaging with the second portion of the ferrules 16, 17. The end caps 28, 29 assist with the encapsulation of the junction box 20 by abutting onto the outer face of the sleeve retainers 1 1 , 15. The construction of the junction box 20 allows for a simpler and therefore quicker method of assembly (and conversely disassembly) than the prior art. When a fault in a subsea cable is detected a submersible may be used to retrieve a portion of the cable and bring it to a vessel on the surface. The junction box 20 may be taken apart such that connections between the fibres in the fibre tray 8 may be checked and tested using the following process. The first end cap 28 is unscrewed from the first ferrule 16 so as to expose the distal face of the first sleeve retainer 11. The outer set of bolts 7 is then removed, allowing the first sleeve retainer 1 1 to be uncoupled from the sleeve 1. The inner bolts 6 are also removed to uncouple the first sleeve retainer 11 from the first ferrule 16. This process may be repeated at the opposing end of the junction box 20, however each 'end' (comprising the end cap, sleeve retainer and ferrule) of the box 20 is independently separable from the other. The end caps 28, 29, sleeve retainers 1 1 , 15 and sleeve 1 may then be slid along the cable bundles 21 , 22 and the guides 2, 3, so as to expose the fibre tray 8. The fibres are then tested using conventional techniques until the fault is corrected. The process is reversed to reassemble the junction box 20.

The simpler construction of the junction box 20 allows for a larger inner chamber (or splicing region) to be provided than is available in prior art devices. This is achieved in part by the fact there is no longer a need for the securing bolts to extend between each of the ferrules and therefore occupy space within the inner chamber. This facilitates the connection of more fibres than has previously been possible. For example, 96 or even 192 fibres may be accommodated and spliced together in the present embodiment, for example using fusion spliced, micro splint splice encapsulations. Furthermore, this may be achieved within a junction box 20 having a smaller profile and volume. For example, the junction box 20 may have a length of 30 cm and an outside maximum diameter of 9 cm. Fibre optic cables may extend alongside power cables, provided to convey electricity, in large composite cables provided offshore. The relatively small volume of the fibre-optic junction box conveniently enables it to be provided inside the housing of a power cable joint 30, as illustrated by Figure 7.

The pressure housing is metallic and is configured to withstand water pressure in excess of 2 km water depth and a maximum tension within the cable of greater than 20 kN. This housing is insulated using either a heat shrink or polyurethane moulding. This provides additional water immersion integrity and allows for insulation of the electrical connector and toning of the cable for fault location.

Outside of export and array power cable rigid repair joints, joints made in accordance with embodiments of the invention can be made to telecoms cables bundled to other cables such as HVDC cables (single power core) where the weight of the telecoms cable is supported by the larger power cable. Embodiments of the invention may also find use in direct electrical heating (DEH) systems where oil and gas pipelines are heated to prevent the formation of hydrates.

As will be appreciated, an improved junction box is hereby provided enabling a simpler and quicker assembly than the prior art, as well as the potential for accommodating more cable element joints in a reduced volume.

Claims

1. A junction box for joining a plurality of cable elements of an underwater cable, the junction box comprising:

a sleeve having a major axis, the sleeve defining an internal region for accommodating joins between the cable elements;

2. A junction box according to claim 1 , wherein the first sealing members are each arranged radially inside of the respective outer set of fasteners with respect to a major axis of the junction box.

3. A junction box according to claims 1 or 2, wherein one or both of the first sealing members are provided in the form of an o-ring.

4. A junction box according to claim 3, wherein the axis of the o-rings are coaxial with the major axis.

5. A junction box according to any of the preceding claims, wherein the first sealing members are formed of copper.

6. A junction box according to any of the preceding claims, wherein the first sealing members are physically spaced apart from the outer sets of fasteners.

7. A junction box according to any of the preceding claims, wherein the outer sets of fasteners each comprise a plurality of fasteners circumferentially disposed about the major axis.

8. A junction box according to any of the preceding claims, wherein the outer sets of fasteners each comprise at least four, preferably five, more preferably six fasteners.

9. A junction box according to any of the preceding claims wherein the attachment between the first sleeve retainer and the sleeve may be performed independently of the attachment between the second sleeve retainer and the sleeve.

10. A junction box according to any of the preceding claims, further comprising first and second ferrule members configured to engage with the bore of the first and second sleeve retainers respectively.

1 1. A junction box according to claim 10, wherein the first and second ferrule members each comprise a port for receiving the part of the cable extending into the internal region.

12. A junction box according to claim 1 1 , further comprising one or more cable sealing members arranged inside said ports to prevent hydrogen entering the internal region from along the cable.

13. A junction box according to any of claims 10 to 12, wherein a first portion of each of the first and second ferrule members is arranged inside the sleeve, and wherein a second portion of each of the first and second ferrule members protrudes from the sleeve, the first portions having a diameter greater than the second portions with respect to the major axis.

14. A junction box according to claim 13, further comprising a cradle assembly configured to enable said cable elements to be joined, wherein the cradle assembly is coupled to the first portion of one or both of the ferrule members.

15. A junction box according to claims 13 or 14, further comprising first and second end caps configured to releaseably engage with the second portion of the first and second ferrule members respectively.

16. A junction box according to claim 15, wherein the first and second end caps are configured to couple with a threaded outer surface of the second portion of the first and second ferrule members respectively.

17. A junction box according to claims 15 or 16, wherein the first and second end caps are further configured to engage with the first and second sleeve retainers respectively.

18. A junction box according to any of claims 10 to 17, wherein the first and second sleeve retainers and the first and second ferrule members are configured such that the first sleeve retainer may be attached to the first ferrule member independently of the second sleeve retainer being attached to the second ferrule member.

19. A junction box according to any of claims 10 to 18, wherein the first and second sleeve retainers are attached to the first and second ferrule members respectively by an inner set of fasteners, wherein the inner set of fasteners is disposed radially inward of the outer set of fasteners with respect to the major axis.

20. A junction box according to claim 19, further comprising a second sealing member provided at the interface between each of the first and second sleeve retainers and the respective attached ferrule member so as to prevent an ingress of hydrogen into the internal region.

21. A junction box according to claim 20, wherein the second sealing members are arranged outside the respective inner set of fasteners.

22. A junction box according to claims 20 or 21 , wherein one or both of the second sealing members are provided in the form of an o-ring or a plate.

23. A junction box according to any of claims 20 to 22, wherein the second sealing members are formed of copper.

24. A junction box according to any of claims 19 to 23, wherein the second sealing members are physically spaced apart from the inner sets of fasteners.

25. A junction box according to any of claims 19 to 24, wherein the inner sets of fasteners each comprise a plurality of fasteners circumferentially disposed about the major axis.

26. A junction box according to any of claims 19 to 25, wherein the inner sets of fasteners each comprise at least four, preferably five, more preferably six fasteners.

27. A junction box according to any of the preceding claims, wherein said fasteners are bolts.

28. A junction box according to any of the preceding claims, wherein the torque required to place each fastener into a tightened state is less than 20 Nm.

29. A junction box according to any of the preceding claims, wherein the inner region is sealed from hydrogen.

30. A junction box according to any of the preceding claims, wherein each first sealing member is arranged such that no gas path exists between the respective outer set of fasteners and the internal region along the interface between the sleeve retainer and the sleeve without encountering the first sealing member.

31. A junction box according to any of the preceding claims, wherein the internal region comprises a cradle assembly configured to enable the cable elements to be joined.

32. A cable joint comprising a cable and a junction box according to any of the preceding claims, wherein said cable comprises a plurality of cable elements that are joined within the internal region.

33. A cable joint according to claim 32, wherein the cable elements comprise 96, preferably 150, more preferably 192 cable elements.

34. A cable joint according to claims 32 or 33, wherein the cable elements are optical fibres.

35. A power cable joint comprising housing, the housing containing a cable joint according to any of claims 32 to 34.

36. A marine cable installation comprising an underwater cable having one or more junction boxes according to any of claims 1 to 31 disposed thereon.