WO2023031219A1

WO2023031219A1 - Subsea activated protection system

Info

Publication number: WO2023031219A1
Application number: PCT/EP2022/074113
Authority: WO
Inventors: Shambu Jayakumar
Original assignee: Nederlandse Organisatie Voor Toegepast-Natuurwetenschappelijk Onderzoek Tno
Priority date: 2021-08-30
Filing date: 2022-08-30
Publication date: 2023-03-09

Abstract

A protection assembly (2) and a method for protecting a subsea conduit using a protection assembly. The method includes arranging a protection assembly (2) around an outer surface of a free-laying longitudinal section of the subsea conduit (1), the protection assembly (2) being made of flexible material, and comprising an inflatable part (3) having a predetermined inflation length, and inflating the inflatable part (3) of the protection assembly (2). Furthermore, the protection assembly (2) may further comprise a side opening (4) extending in a longitudinal direction of the protection assembly (2).

Description

Subsea Activated Protection System

Field of the invention

The present invention relates to a method for protecting a subsea conduit, such as a cable or pipe. In a further aspect, the present invention relates to a protection assembly for protecting a part of a subsea conduit, the protection assembly being made of a flexible material.

Background art

British patent publication GB-A-22 69 274 discloses a bend restrictor for flexible cabling which is arranged to resist tensile forces and allowing an acceptable diameter bend of the cabling. Two or more relatively moving housing members and link means are provided, in effect providing a hard-shell protective arrangement.

International patent publication WO2015/071684 discloses a bend restrictor for an (underwater) cable, having first and second end sections and a plurality of intermediate sections in between.

European patent publication EP-A-2 721 700 describes a cable-pull in device for connecting an underwater cable to an offshore structure, using an inflatable bladder in an inflatable sealing section of a flexible outer conduit assembly.

Summary of the invention

The present invention seeks to provide an improved protection during handling and use of subsea conduits, such as (electrical) cables and pipes.

According to the present invention, a method as defined above is provided, comprising arranging a protection assembly around an outer surface of a free-laying longitudinal section of the subsea conduit, wherein the protection assembly is made of flexible material, and comprises an inflatable part having a predetermined inflation length and a predetermined inflation volume, connecting the subsea conduit to an installation above sea level via a J-tube connection, wherein the subsea conduit is sealed to the J-tube connection using a J-tube seal, providing the inflatable part of the protection assembly, surrounding the subsea conduit, over a predetermined length measured from the J-tube seal towards the seabed, connecting the inflatable part of the protection assembly to the J-tube seal via a connection element, and inflating the inflatable part of the protection assembly, wherein a side opening extends in a longitudinal direction of the protection assembly.

This method allows to guide a conduit from above sea-level to a subsea connection with a structure on the seabed and to provide a bending restriction functionality to the subsea conduit, i.e., the subsea part of the conduit, and a protection around the subsea conduit using a single protection assembly. In this manner the subsea conduit at the location is supported where the subsea conduit is connected to the J-tube and is thus provided with improved structural integrity to the connection. Additionally, the J-tube seal provides a coupling of the protection assembly to the J-tube while isolating the internals of the J-tube from the subsea environment.

In a further aspect, a protection assembly is provided as defined above, comprising an inflatable part having a predetermined inflation length and a predetermined inflation volume, and a connection element for connection of the inflatable part to a J-tube seal, wherein the J-tube seal connects the subsea conduit to an installation above sea level via a J-tube connection and a side opening extending in a longitudinal direction of the protection assembly, wherein the protection assembly surrounds the subsea conduit over a predetermined length measured from the J-tube seal towards the seabed.

In this configuration, the protection assembly can be attached to a subsea conduit very easily and cost-effectively, both above sea level (e.g. on a deck of a ship) and below sea level, and again can provide bending restriction and protection functionality.

Short description of drawings

The present invention will be discussed in more detail below, with reference to the attached drawings, in which

Fig. 1 shows a cross sectional view of a protection assembly according to an embodiment of the present invention surrounding a subsea conduit;

Fig. 2 shows a perspective side view of a protection assembly according to a further embodiment of the present invention;

Fig. 3 shows a schematic view of a protection assembly in an actual application according to a further embodiment of the present invention; and

Fig. 4 shows a schematic view of a protection assembly in a further actual application according to a further embodiment of the present invention.

Description of embodiments

Electricity is transported from wind turbines to the mainland via subsea cables. Such cables need to be protected against fatigue and abrasion, for which in the art so-called ‘bend restrictors’ are used for this purpose (also known as ‘bend stiffeners’ or ‘bend protectors’). Usually, multiple bend restrictors are needed to protect a cable. According to the present invention embodiments, examples of which are described below, a protection assembly is provided that is easier to install, and also provides sufficient protection during and after installation of subsea conduits. The protection assembly and method embodiments described herein are applicable to various types of subsea conduits, such as (electrical) cables and pipes.

In general, the present invention embodiments of the protection assembly comprise an inflatable and flexible sleeve that fits around the cable or pipe. The inflatable sleeve can be installed on the deck (either water filled or air-filled, or even deflated e.g. with vacuum). This provides the cable with support e.g. during installation. After installation the sleeve can be either removed or filled with resin to form a permanent protective cover.

The present invention embodiments provide an arrangement for coupling a cable from an installation above sea-level, such as a wind turbine, to a subsea conduits via a J-tube connection which guides the cable below sea level or on the seabed to a structure on the seabed, such as an entry point of a power grid. In such applications, the subsea conduit is arranged with a protection assembly that comprises an inflatable sleeve coupling to the J-tube and surrounding the subsea conduit over a predetermined length measured from the connection with the J-tube. The inflatable part can be inflated, e.g. using air or another fluid, to provide stiffness and bending restriction to the respective part of the subsea conduit.

Fig. 1 shows a cross sectional view of a protection assembly 2 according to an exemplary embodiment of the present invention surrounding a subsea conduit 1. In this group of embodiments, a protection assembly 2 is provided for protecting a part of a subsea conduit 1 (e.g. a cable or a pipe), the protection assembly 2 being made of a flexible material, and comprising an inflatable part

3 having a predetermined inflation length and a predetermined inflation volume, and a side opening

4 extending in a longitudinal direction of the protection assembly 2. The side opening 4 allows to easy position the protection assembly 2 around the subsea conduit 1 .

In Fig. 1 , a diameter d of the subsea conduit 1 is shown, as well as a side opening 4. The side opening 4 extends at least 10 degrees (or generically with an angle a is shown in Fig, 1) of a cross sectional circumference of the subsea conduit 1 , when the inflation part 4 is inflated. This will provide both a protection of the subsea conduit 1 , and a certain amount of buoyancy of the combination, e.g. when the inflatable part 3 is filled with air. It is noted that these effects may also be present if the angle a is larger than 10 degrees, e.g. 90 degrees, or even up to 180 degrees.

Similarly, the combined effect of protection of the subsea conduit 1 and the buoyancy may also be provided in a further group of embodiments, wherein the inflatable part 3 has a C-shaped cross section when inflated (as also shown in the exemplary embodiment of Fig. 1 .

Fig. 2 shows a perspective side view of a protection assembly 2 according to a further embodiment of the present invention. In this view, the subsea conduit 1 is left out, but it will be clear that during actual use the subsea conduit is present in the inner hollow space provided by the inflatable part 3 of the protection assembly 2, which is equal to or larger than the diameter d of the subsea conduit 1 .

In a further embodiment, the inflation volume of the inflatable part 3 is sufficiently large to provide buoyancy to the part of the subsea conduit 1. This can be effectuated in many ways, e.g. using air to fill the inflatable volume of the inflatable part 3, or in alternative manners, which will be discussed further below. A further possible feature to combine the buoyancy effect with the protection function of the protection assembly 2 is that the predetermined length of the inflatable part 3 is at least 10 times the diameter d of the subsea conduit 1 . The inflated protection assembly 2 is then long enough to provide a proper bending restriction function, and depending on the filling material of the inflatable part 3, provide a buoyancy effect. In an even further group of embodiments, the inflatable part 3 comprises at least one inflation compartment, with three inflation compartments 3a, 3b, 3c shown in the exemplary embodiment shown in Fig. 2. The multiple compartments 3a-3c may be inflated with different intent, e.g. sealing or attaching to subsea conduit 1 , providing a high degree of buoyancy, etc. depending on the respective volume and filling material used. As an additional or alternative application, the multiple compartments 3a-3c may be utilized to form channels around the subsea conduit 1 for heat exchange.

The protection assembly 2 may be provided with further components allowing easy and effective handling. In one embodiment, the protection assembly 2 further comprises one or more attachment elements 5, which are arranged to span across the side opening 4 during operation. This will allow for holding the protection assembly 2 to the subsea conduit 1 in a secure manner and in the desired (longitudinal) position. Note that the weight of such attachment elements 5 is not relevant as long as sufficient buoyancy and stiffness by the inflatable part 3 is obtained.

In a further embodiment, the protection assembly 2 further comprises intervention ports 6 in communication with the inflatable part 3. Such intervention ports 6 (one shown for each inflation compartment 3a, 3b, 3c in the exemplary embodiment of Fig. 2) may e.g. be used as filling ports accessible both during installation, and after installation, e.g. to implement one of the present invention method embodiments as discussed below. As indicated in the embodiment of Fig .2, even further ports may be provided, e.g. in the form of a venting port 6a.

In an even further embodiment, the protection assembly 2 further comprises handling elements 7, e.g. in the form of lashes, fasteners or other connection components. E.g. after installation of the protection assembly 2 to the subsea conduit 1 , the combination can be manipulated using a crane, e.g. on deck of a ship, or using a remotely operated vehicle (ROV), e.g. under sea level or on the sea bed.

A wide variety of plastics or rubber type of material may be used for the protection assembly 2, even including recycled materials.

In a further aspect, the present invention relates to a method for protecting a subsea conduit 1 (cable or pipe), comprising arranging a protection assembly 2 around an outer surface of a free- laying longitudinal section of the subsea conduit 1 , the protection assembly 2 being made of flexible material, and comprising an inflatable part 3 having a predetermined inflation length, and inflating the inflatable part 3 of the protection assembly 2. This allows to provide a bending restriction function to the subsea conduit 1 as well as protection around the subsea conduit 1 . The protection assembly 2 may be used on a single, electrical cable, as example of a subsea conduit 1 , but could also be applied to bundles of cables, and flexible or rigid pipes. The protection assembly 2 may also be installed across connections between two or more cables. It is noted that the present method embodiments allow to use more continuous support to a subsea conduit 1 , helping to even prevent very localised bending. After installation also continued protection against fatigue loading due to (sea) currents is provided. Furthermore, also the number of operations on deck during installation are reduced. The protection assembly 2 in some of the present method embodiments could be arranged to fully enclose the subsea conduit 1 , or alternatively may be provided with a side opening 4 as described in the protection assembly embodiments above. This side opening 4 would to allow the protection assembly 2 to be removed, applied to the subsea conduit 1 as a retrofit or to support the subsea conduit 1 , e.g. if it needs to be lifted. In an even further exemplary embodiment, the protection assembly 2 comprises an overlap, e.g. in the form of an extension flap, which may be used to more easily apply the protection assembly 2 to the subsea conduit 1 above or below sea level.

More in general, the present invention embodiments relate to using an inflatable and flexible sleeve (protection assembly 2) that fits around the cable or pipe (subsea conduit 1). The protection assembly 2 can be installed on deck of a ship (either water filled, air-filled, or deflated using e.g. a vacuum). This would provide the subsea conduit 1 with support during installation. It is noted that after positioning of the subsea conduit 1 it is possible to again remove the protection assembly 2.

Inflating comprises filling the inflatable part 3 with a fluid, i.e. a liquid such as water, or a gel, or a gas such as air, or another gas. This can be performed either above the sea level or below sea level, depending on the actual application wherein this method is applied.

In one embodiment, arranging the protection assembly 2 and inflating the inflatable part 3 is executed above sea level (e.g. on deck of a ship), followed by subsea positioning of the combination of subsea conduit 1 and protection assembly 2.

In a further embodiment, arranging the protection assembly 2 and inflating the inflatable part 3 is executed below sea level, followed by subsea handling of the combination of subsea conduit 1 and protection assembly 2. This allows e.g. repositioning of the subsea conduit 1 during operational life thereof, e.g. for repairs of requirement for additional support or protection.

In an even further embodiment, the method further comprises deflating the protection assembly 2 above sea level, wherein arranging the protection assembly 2 is executed above sea level and inflating the inflatable part 3 is executed below sea level. Deflating the inflatable part 3 can be accomplished e.g. using vacuum, for easier and more efficient handling before inflation of the protection assembly 2 at a desired location.

In addition, or alternatively, the method may further comprise replacing a fluid in the inflatable part 3 with a substance which solidifies over time. The substance is e.g. a resin, or a thermosetting plastic, and allows to transform the protection assembly 2 into a permanent protective cover for the subsea conduit 1.

Fig. 3 and 4 show schematic views of protection assemblies 2 used in two actual applications. The subsea conduit 1 may be protected using one protection assembly 2 (Fig. 3) or using two or more protection assemblies 2 (Fig. 4). Furthermore, a plurality of protection assemblies 2 of smaller dimensions may be used, which may be interconnected as a group to provide a sufficient degree of protection and/or buoyancy.

In Fig. 3, a partial view is shown of a subsea conduit 1 in the form of an electrical cable connected to an installation above sea level via a J-tube connection 10. The J-tube connection 10 allows to guide an electrical cable 1 into and up to further connectors present in a structure 11 positioned on seabed 12. Usually, the cable 1 is sealed to the J-tube 10 using a J-tube seal 10a. In this exemplary application, the subsea conduit 1 is provided with an inflatable part 3 ofthe protection assembly 2 surrounding the subsea conduit 1 over a predetermined length measured from the J- tube seal 10a. In this case, the inflatable part 3 is provided with a vent port 6a near the J-tube seal 10a, and ROV intervention ports 6 on various locations along the outside of the inflatable part 3. Depending on the stage of installation of the subsea conduit 1 into the J-tube 10, the inflatable part can be inflated, e.g. using air, to provide stiffness and bending restriction to the respective part of the subsea conduit 1 . Furthermore, once installed, the intervention ports 6 and vent port 6a may be used to replace the air with a resin, which, once hardened will transfer the inflatable part of the protection assembly 2 into a hard shell providing long time protection to that part of the subsea conduit 1 . In addition, or alternatively, a separate connection element may be provided on the end of the protection assembly closest to the J-tube seal 10a during operation. This may provide additional structural integrity to the protection assembly 2.

In Fig. 4 a subsea conduit 1 is shown used to connect a first wind turbine 15 installed on the seabed and a second wind turbine 16 with a floating structure 17. The subsea conduit 1 is connected to each wind turbine 15, 16 using a hang-off connection point 15a, 16a. In the fixed wind turbine 15, a cable pull-in opening 15b is provided, and the subsea conduit 1 leaves the tower construction of the wind turbine 15 in a rather small acute angle, necessitating a bend of the subsea conduit 1 towards the seabed. At that position, a protection assembly 2 is used to provide the proper bend restriction and stiffness to the undersea cable 1 . The connection of the undersea conduit 1 to the floating wind turbine 16 is usually accomplished using an opening in the bottom part, necessitating as well a proper guidance of the subsea conduit 1 , e.g. using a ballast weight 18 attached to the subsea conduit 1. Near to the floating wind turbine 16, the subsea conduit 1 is guided in a buoyant configuration, in a so-called lazy-loop or camelback configuration, to allow some movement of the floating wind turbine 16. By applying two protection assemblies 2 in accordance with the present invention embodiments, sufficient buoyancy can be provided to the subsea conduit 1 to have the proper position to make a secure and long lasting connection to the floating wind turbine 16. It is noted that the present invention protection assemblies 2 are used for various functions in this application, illustrating the flexibility and cost-efficiency of the present invention embodiments.

It is noted that (part of) the protection assembly 2 may be buried in sand or small stones after installation (e.g. on a sea bed), or covered by additional protection measures. Then, the subsea cable 1 with one or more protection assemblies 2 attached will have additional protection as compared to a free-laying arrangement.

The present invention has been described above with reference to a number of exemplary embodiments as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.

Claims

7 Claims

1 . A method for protecting a subsea conduit, comprising arranging a protection assembly (2) around an outer surface of a free-laying longitudinal section of the subsea conduit (1), wherein the protection assembly (2) is made of flexible material, and comprises an inflatable part (3) having a predetermined inflation length and a predetermined inflation volume, connecting the subsea conduit (1) to an installation above sea level via a J-tube connection (10), wherein the subsea conduit (1) is sealed to the J-tube connection using a J-tube seal (10a), providing the inflatable part (3) of the protection assembly (2), surrounding the subsea conduit (1), over a predetermined length measured from the J-tube seal (10a) towards the seabed, connecting the inflatable part (3) of the protection assembly (2) to the J-tube seal (10a) via a connection element, and inflating the inflatable part (3) of the protection assembly (2), wherein a side opening (4) extends in a longitudinal direction of the protection assembly (2).

2. The method according to claim 1 , wherein inflating comprises filling the inflatable part (3) with a fluid.

3. The method according to claim 1 or 2, wherein arranging the protection assembly (2) and inflating the inflatable part (3) is executed above sea level [e.g. on deck of ship], followed by subsea of the combination of subsea conduit (1) and protection assembly (2).

4. The method according to claim 1 or 2, wherein arranging the protection assembly (2) and inflating the inflatable part (3) is executed below sea level, followed by subsea handling of the combination of subsea conduit (1) and protection assembly (2).

5. The method according to claim 1 or 2, further comprising deflating the protection assembly (2) above sea level, wherein arranging the protection assembly (2) is executed above sea level and inflating the inflatable part (3) is executed below sea level. 8

6. The method according to claim any one of claims 1-5, further comprising replacing a fluid in the inflatable part (3) with a substance which solidifies over time.

7. A protection assembly for protecting a part of a subsea conduit (1), the protection assembly (2) being made of a flexible material, and comprising an inflatable part (3) having a predetermined inflation length (I) and a predetermined inflation volume, a connection element for connection of the inflatable part (3) to a J-tube seal (10a), wherein the J-tube seal (10a) connects the subsea conduit (1) to an installation above sea level via a J-tube connection and a side opening (4) extending in a longitudinal direction of the protection assembly (2), wherein the protection assembly (2) surrounds the subsea conduit (1) over a predetermined length measured from the J-tube seal (10a) towards the seabed.

8. The protection assembly according to claim 7, wherein the side opening (4) extends at least 10 degrees of a cross sectional circumference of the subsea conduit (1), when the inflation part (4) is inflated.

9. The protection assembly according to claim 7 or 8, wherein the inflatable part (3) has a C- shaped cross section when inflated.

10. The protection assembly according to any one of claims 7-9, wherein the inflatable part (3) comprises at least one inflation compartment (3a, 3b, 3c).

11 . The protection assembly according to any one of claims 7-10, further comprising one or more attachment elements (5), which are arranged to span across the side opening (4) during operation.

12. The protection assembly according to any one of claims 7-11 , wherein the inflation volume is sufficiently large to provide buoyancy to the part of the subsea conduit (1).

13. The protection assembly according to any one of claims 7-12, wherein the predetermined length (I) is at least 10 times a diameter (d) of the subsea conduit (1). 9

14. The protection assembly according to any one of claims 7-13, further comprising intervention ports (6) in communication with the inflatable part (3).

15. The protection assembly according to any one of claims 7-14, further comprising handling elements (7).