Abstract
A method for forming a subsea cable or a joint for a subsea cable is provided including providing a cable assembly that has at least a first conductor and a first insulation system surrounding the first conductor and forming a water barrier layer surrounding a length of the cable assembly. The water barrier layer has at least one coating of a metal material applied using a thermal spraying technique. A joint and a subsea cable obtainable by the above method is also provided.
Claims
1. A method for forming a subsea cable or a joint for a subsea cable, the method comprising: providing a cable assembly that comprises at least a first conductor and a first insulation system surrounding the first conductor; and forming a water barrier layer that surrounds a length of the cable assembly, wherein the water barrier layer comprises at least one coating of a metal material applied using a thermal spraying technique.
2. The method of claim 1, wherein the cable assembly is a first cable assembly and wherein the method comprises: providing a second cable assembly that comprises a second conductor and a second insulation system surrounding the second conductor; forming an electrical connection between the first conductor and the second conductor; and forming the water barrier layer to surround the electrical connection and a length of the second cable assembly.
3. The method of claim 2, wherein the first cable assembly comprises a first water barrier layer surrounding the first insulation system and the second cable assembly comprises a second water barrier layer surrounding the second insulation system, and wherein forming the water barrier layer comprises: forming a joint between the first cable assembly and the second cable assembly, wherein the joint comprises the coating and connects the first water barrier layer and the second water barrier layer.
4. The method of claim 3, wherein the joint comprises a joint element, and wherein forming the joint comprises: positioning the joint element to surround a further length of the first conductor and a further length of the second conductor; applying a first coating of the metal material using the thermal spraying technique to join the joint element to the first water barrier layer; and applying a second coating of the metal material using the thermal spraying technique to join the joint element to the second water barrier layer.
5. The method of claim 3, wherein the joint includes the coating.
6. The method of claim 1, wherein the cable assembly comprises a first water barrier layer surrounding the first insulation system and wherein forming the water barrier layer comprises repairing the first water barrier layer using the coating.
7. The method of claim 1, wherein the water barrier layer is formed to surround the first insulation system along its full length.
8. The method of claim 1, comprising: applying a protective layer surrounding at least part of the first insulation system, wherein the coating is applied to the protective layer.
9. The method of claim 1, comprising, prior to forming the water barrier layer, cleaning a surface of the first cable assembly to which the coating is to be applied.
10. The method of claim 9, wherein cleaning the surface uses atmospheric plasma cleaning.
11. The method of claim 1, wherein the thermal spraying technique comprises one of: flame spraying; arc spraying; plasma spraying; high velocity oxygen fuel spraying; or detonation gun spraying.
12. The method of claim 1, wherein the metal material comprises one of: a copper material; a copper nickel alloy material; a titanium material; or a lead material.
13. A joint between a first cable assembly and a second cable assembly obtainable according to the method of claim 1.
14. A subsea cable obtainable according to the method of claim 1.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] In the following description this invention will be further explained by way of exemplary embodiments shown in the drawings:
[0055] FIG. 1 is a schematic diagram of a cross-section of a single-conductor subsea power cable;
[0056] FIG. 2 is a schematic diagram of a cross-section of a three-conductor subsea power cable;
[0057] FIG. 3 is a flow chart of a process for forming a subsea power cable;
[0058] FIGS. 4A to 4D are schematic diagrams illustrating a process for joining two subsea power cables;
[0059] FIGS. 5A to 5C are schematic diagrams illustrating an alternative process for joining two subsea power cables;
[0060] FIGS. 6A and 6B are schematic diagrams illustrating a process for repairing an existing subsea power cable; and
[0061] FIGS. 7A and 7B are schematic diagrams illustrating a process for preparing a new subsea power cables.
DETAILED DESCRIPTION
[0062] FIG. 1 shows a cross section of a first cable 100. The first cable 100 is a subsea power cable. The first cable 100 has a cable core comprising a cable conductor 111, made of a highly conductive material such as copper, and an insulation system 112. The first cable 100 is a single conductor cable, meaning it only has one conductor. The insulation system 112 comprises one or more layers that circumferentially surround the cable core 111. The first cable 100 comprises a water barrier layer 113. The insulation system 112 is circumferentially surrounded by the water barrier layer 113. The water barrier layer 113 is formed of a metal material. The metal material is typically lead, although other metals may be used. The water barrier layer 113 is configured to prevent water ingress into the cable core, which may cause damage to the insulation system 112.
[0063] FIG. 2 shows a cross section of a second cable 200. The second cable 200 is a subsea power cable having three cable cores 215. The cable cores 215 each have a conductor 211 of a high conductive material, such as copper. The conductors 211 are surrounded by respective insulation systems 212. The respective insulation systems 212 are surrounded by respective water barrier layers 213. The three cable cores 215 are embedded in a filling material 214, which may be a filling compound. A sheath 217 formed of a polymer circumferentially surrounds the filling material 216.
[0064] The structures of the cables 100, 200 are exemplary structures for the purpose of explanation.
[0065] These cables 100, 200 may include other known elements. For example these cables may comprise an armouring layer, one or more bend restrictors or bend stiffeners, or, in the case of a three-core cable, such as cable 200, a water barrier layer that surrounds the complete structure in addition to the water barrier layers of the cable cores. The techniques described herein may also be used with other cable structures that include a water barrier layer. These cable structures may have any combination of the elements described in relation to the above cables 100, 200 as well as any other known elements.
[0066] The cables 100, 200 of FIG. 1 and FIG. 2 have water barrier layers 113, 213. These water barrier layers 113, 213 and the water barrier layers of any other cable structures may be formed using the techniques described herein. For ease of explanation, FIGS. 4A to 7B show cable assemblies having a single conductor, and therefore having a structure similar to the cable 100 of FIG. 1.
[0067] Cables such as the cables 100, 200 shown in FIGS. 1 and 2 may be formed from a single cable assembly, or more than one cable assembly joined together. A cable assembly comprises at least a cable core, including a conductor and an insulation system. A water barrier layer may be formed to surround the cable core to form the subsea cable from the cable assembly. Forming the water barrier layer may include creating an entirely new water barrier layer, reinstating or repairing an existing water barrier layer of the cable assembly, or joining two cable assemblies together.
[0068] FIG. 3 shows a flow chart of a method 300 for forming a subsea cable or for forming a joint between two cable assemblies. The method 300 includes the steps of providing 301 at least one cable assembly comprising a conductor and an insulation system. The method 300 also includes forming 302 a water barrier layer for the cable assembly using thermal spraying.
[0069] FIG. 3 indicates three ways 303A-C in which the water barrier layer can be formed. A first way 303A, which is explained in more detail below in relation to FIGS. 4A to 4D and FIGS. 5A to 5C, is that the water barrier layer may be formed as part of a joint between two cable assemblies. Each cable assembly may have an existing water barrier layer, and a join may be formed between the two existing water barrier layers, thereby forming a longer, comprehensive water barrier layer across both cable assemblies. In a second way 303B, described below in more detail in relation to FIGS. 6A and 6B, the water barrier layer can be formed by reinstating an existing water barrier layer. An existing water barrier layer of the cable assembly may be damaged, and repairing the damage using the thermal spraying technique may result in the water barrier layer being reinstated, and therefore formed. A third way 303C, which is described below in more detail in relation to FIGS. 7A and 7B, is that part or all of a new water barrier for a cable assembly may be formed using the method 300.
[0070] Turning to FIGS. 4A to 4D, a process for forming a joint between two cable assemblies is shown. As shown in FIG. 4A, a first cable assembly 401 and a second cable assembly 402 are provided. The first cable assembly 401 includes a first conductor 411, a first insulation system 412 surrounding the first conductor 411, and a first water barrier layer 413 surrounding the first insulation system 412. The first water barrier layer 413 has been stripped back to reveal a portion of the first insulation system 412 and the first insulation system 412 has been stripped back to reveal a portion of the first conductor 411. The second cable assembly 402 includes a second conductor 421, a second insulation system 422 surrounding the second conductor 421, and a second water barrier layer 423 surrounding the second insulation system 422. The second water barrier layer 423 has been stripped back to reveal a portion of the second insulation system 422 and the second insulation system 422 has been stripped back to reveal a portion of the second conductor 421.
[0071] As shown in FIG. 4B, an electrical connection 415 is formed between the first cable assembly 401 and the second cable assembly 402, specifically between first conductor 411 and the second conductor 421. To achieve the electrical connection 415, the first cable assembly 401 and the second cable assembly 402 are brought close to one another so that the first conductor 411 and the second conductor 421 are close to one another or are in contact. An electrical connection 415 is then formed, which may be achieved by applying a conductor between the first conductor 411 and the second conductor 421 or by physically connecting the two conductors 411, 421.
[0072] FIG. 4C and FIG. 4D show a joint 450 being formed between the first cable assembly 401 and the second cable assembly 402. As shown in FIG. 4C, a joint element 432 is provided. The joint element 432 is positioned over a portion of the first conductor 411 and a portion of the second conductor 421. The joint element 432 extends across the joint formed between the first conductor 411 and the second conductor 421. The joint element 432 in this example is a metal sheath that has been shaped to conform to the first cable assembly 401 and second cable assembly 402 by rolling down its ends to have an angled profile. The joint element 432 may be a tape, sheet, or foil formed of metal in other examples. The joint element 432 extends to cover the exposed joint between the conductors 411, 421 and the exposed portions of the insulation systems 412, 422. The joint element 432 also extends to cover part of the first and second water barrier layers 413, 423.
[0073] In FIG. 4D, the joint element 432 is joined to the first cable assembly 401 and second cable assembly 402 to form the joint 450 and to form a full water barrier layer 430 between the cable assemblies 401, 402 and across the joint 450.
[0074] The joining is achieved by applying coatings of a metal material that join the joint element 432 to the first water barrier layer 413 and the second water barrier layer 423 respectively. A first coating 431 is applied to join the joint element 432 to the first water barrier layer 413. A second coating 433 is applied to join the joint element 432 to the second water barrier layer 423. The coatings 431, 433 are applied using a thermal spray technique 440. The coatings 431, 433 form a watertight connection between the joint element 432 and the water barrier layers 413, 423, thereby forming the full water barrier layer 430. The full water barrier layer 430 therefore includes the first water barrier layer 413, the first coating 431, the joint element 432, the second coating 433 and the second water barrier layer 423.
[0075] The coatings 431, 433 are formed by thermally spraying a metal material. The metal material may be the same metal material as the joint element 432 is formed from, and may be the same metal material that the first water barrier layer 413 and the second water barrier layer 423 are formed of.
[0076] Although not shown in FIGS. 4A to 4D, the process may also involve forming an insulation system between the first cable assembly 401 and the second cable assembly 402. Forming the insulation system may comprise reinstating an insulation system by connecting the first insulation system 412 to the second insulation system 422 with an intermediate insulation system.
[0077] FIGS. 5A to 5C show a different way of forming a joint using a thermal spraying technique. In FIG. 5A, a first cable assembly 501 and a second cable assembly 502 are provided. The first cable assembly 501 and the second cable assembly 502 have similar structures to the cable assemblies 401, 402 of FIGS. 4A to 4D, and include respective conductors 511, 521, insulation systems 512, 522, and water barrier layers 513, 523. The insulation systems 512, 522 surround their respective conductors 511, 521 and have been stripped back to reveal parts of the conductors 511, 521, while the water barrier layers 513, 523 surround the insulation systems 512, 522 and are stripped back to reveal parts of the insulation systems 512, 522.
[0078] In this way of joining the cables, as shown in FIG. 5B, an electrical connection 515 is formed between the first cable assembly 501 and the second cable assembly 502. This may be performed in the same way as the electrical connection 415 was formed between the cable assemblies 401 and 402 in relation to FIG. 4B.
[0079] Next, as shown in FIG. 5C, a joint 550 is formed. The joint 550 is formed by applying a coating 531 across the electrical connection 515 to connect the first water barrier 513 with the second water barrier 523, to form a full water barrier 530. The coating 531 is applied using a thermal spraying technique 540. In the example shown, a protective layer 560 is provided around the first and second cable assemblies 501, 502 that surrounds the area on which the coating 531 is being applied. The protective layer 560 may comprise a metallic foil. The protective layer 560 may provide a surface for the coating 531 to bond or adhere to and/or may provide protection to the electrical connection 515 and the insulation layers 512, 522. The coating 531 may be applied over the protective layer 560 and so that it extends beyond the protective layer 560 and comes into contact with the water barrier layers 513, 523, so that a full, watertight water barrier layer 530 can be formed. In this case, therefore, the joint 550 may be said to consist of the coating 531 because the full water barrier layer 530 is formed between the water barrier layers 513, 523 using only the coating 531. The protective layer 560 is considered to be separate to the coating 531 and the joint 550.
[0080] FIGS. 6A and 6B show how a cable assembly 601 can be repaired using thermal spraying. In FIG. 6A, a cable assembly 601 is shown. The cable assembly 601, as with the cable assemblies 401, 402, 501, 502 of earlier Figs. has a single-conductor structure that is visible in FIGS. 6A and 6B. The cable assembly 601 has a conductor 611, an insulation system 612 that surrounds the conductor 611, and a water barrier layer 613 that surrounds the insulation system 612.
[0081] The water barrier layer 613 has been damaged in use, in handling, or in transit, and two areas of damage 670 are depicted in FIG. 6A. In this example, the damage 670 is to the water barrier layer 613 only, and the insulation system 612 and conductor 611 are intact.
[0082] FIG. 6B illustrates reinstating a full water barrier layer 630 by repairing the damage 670. To reinstate the water barrier 630, a coating 631 is applied to each area of damage to form a repaired portion 671. The coating 631 is applied by a thermal spraying technique 640.
[0083] In some examples, the insulation system of a cable may be damaged. It may be useful in such situations to cut the cable into two cable assemblies, remove the damaged parts, and to then use a technique for joining the cable assemblies as described above in relation to FIGS. 4A to 4D or FIGS. 5A to 5C to provide a repair and to reinstate the water barrier layer. Although not detailed here, in some examples the method may include removing a portion of the water barrier layer around the damaged area and repairing the layers underneath, using a conventional method.
[0084] FIGS. 7A and 7B show how a new water barrier layer 730 can be formed for a cable assembly 701. The cable assembly 701 is provided in FIG. 7A and comprises a conductor 711 and an insulation system 712. In FIG. 7A the cable assembly 701 lacks a water barrier layer.
[0085] FIG. 7B shows a water barrier layer 730 being applied using a thermal spraying technique 740. The water barrier layer 730 comprises a coating 731 formed by the thermal spraying. The coating 731 is being applied over a protective layer 760 that surrounds the insulation system 712. The water barrier layer 730 therefore surrounds the insulation system 712 and the protective layer 760.
[0086] Each of the thermal spraying techniques 440, 540, 640, 740 shown in the figs. above illustrate a spray gun connected to a reservoir of feedstock that is used to form the coatings. The feedstock may be solid and may be liquefied by the spray gun or other equipment as it is supplied to the spray gun. A spray gun may be used and may be handled by a technician who directs a spray of liquid onto the cable assembly to form the coating. The technician may vary the parameters of the spray to suit the purpose. The cable assembly may be moved relative to the gun or the gun may be moved relative to the cable assembly, depending on the application. Although metals are referred to above, the feedstock may be a polymer or composite material. The coatings applied by thermal spraying may comprise or may be formed from a polymer or composite material.
[0087] In each of the techniques described above, the surface to which the coating is being applied may be cleaned prior to applying the coating or initiating thermal spraying. The cleaning may be a form of plasma cleaning, preferably atmospheric plasma cleaning.
