WO2005078325A1

WO2005078325A1 - Device for protection of elongate element on a seabed and method for the installation of same

Info

Publication number: WO2005078325A1
Application number: PCT/NO2005/000057
Authority: WO
Inventors: Sverre Meisingset
Original assignee: Sverre Meisingset
Priority date: 2004-02-18
Filing date: 2005-02-17
Publication date: 2005-08-25
Also published as: NO20040705L; NO20040705D0; NO320257B1

Abstract

A device for the protection of an elongate element (22; 22') on the bottom (B) under a body of water including a body (10; 10') with a concavity about a first axis (X) and having a plurality of perforations (12) between the concave and convex sides of the body; whereby the body (10; 10'), when placed on the bottom, can form a hollow space (42) defined by said bottom (B) and the concave side of the body, the hollow space having an extent essentially along said axis (X) and designed to accommodate said elongate body (22). The device may include a plurality of suspension devices (18) for support of respective portions of said elongate element (22; 22') on the concave side of the body, and a plurality of suspension devices (26) on the convex side of the body for suspension of said body (10; 10') from a cable (24) or the like. The invention also includes a method for the installation, lifting or moving of a plurality of bodies (10; 10') connected to the elongate element (22; 22').

Description

Device for protection of elongate element on a seabed and method for the installation of same

The present invention relates to devices for the protection of pipelines, cables and other elongate elements on the seabed, and methods for the installation of same.

More specifically, the invention relates to a device for the protection of an elongate element on the bottom under a body of water. The mvention also relates to a method for the installation of a device for protecting an elongate element on the bottom under a body of water, using a lay vessel, barge or the like, wherein the device includes a plurality of bodies according to the mvention, and an installation cable for controlling the laying of the elongate element. The invention also relates to a method for lifting or moving an elongate element on the bottom under a body of water via a cable which at its two ends is fastened between two respective vessels, the elongate element being suspended from a plurality of bodies according to the invention, placed one after another.

A number of devices for the protection of cables, pipelines and the like on the seabed, and the installation (laying) thereof, are known. In addition to the known methods which include trenching, laying and backfilling, it is also known to use different devices which are placed on or over the cable, pipeline or the like, without the use of prior trenching.

US 5 193 937 describes a "mattress" of concrete or the like that is laid over a pipe or a cable on the seabed. The mattress is assembled on the seabed from a plurality of elements that joined together on site.

GB 2 084 286 relates to a flexible "mattress-like" element that is used as ballast and for protecting pipelines on the seabed. The element is preferably made of a non-woven fabric.

NO 14 13 46 also describes a "mattress" formed of two flexible plates that are joined together to form a chain. The mattress is so flexible that it adapts itself to the shape of the seabed and the installation that is to be protected.

NO 15 45 34 relates to a method and installation means for covering a cable, pipeline or the like on the seabed. There is therefore a need for a device for the protection of cables, conduits, pipes and the like that is easier to install than the known devices.

The present invention meets this need, inasmuch as it offers a device for the protection of an elongate element on the bottom under a body of water, characterised in that the device includes a body with a concavity about a first axis and having a plurality of perforations between the concave and convex sides of the body; wherein the body further comprises a first and a second end, each equipped with a plurality of buffers; whereby the body, when placed on the bottom, can form a hollow space defined by said bottom and the concave side of the body, the hollow space having an extent essentially along said axis and designed to accommodate said elongate body.

Preferred features of the device according to the invention are set forth in dependent claims 2 - 11.

The invention also includes a method for the installation of a device for protecting an elongate element on the bottom under a body of water, using a lay vessel, barge or the like, wherein the device includes a plurality of bodies according to the invention, and an installation cable for controlling the laying of the elongate element, characterised by the following steps: a) fastening a first end of the elongate element on the concave side of a first of said bodies; b) fastening a first end of the installation cable on the convex side of a first of said bodies; c) in a controlled manner, running the installation cable, and the body and a part of the elongate body, down into the water by the lay vessel, barge or the like, the body and the elongate body being suspended via the cable from a supporting structure at the surface, until a second of said bodies can be mounted end to end to the first of the bodies; d) arranging a second of said bodies for support as indicated in step a), the second body being placed end to end with one of the ends of said first body, separated by buffers; e) arranging the second of said bodies for support as indicated in step b); f) repeating steps c), d) and e) until the desired number of bodies has been placed on the bottom, whereby said elongate body is protected by a row of said bodies. The invention also includes a method for lifting or moving an elongate element on the bottom under a body of water via a cable which at its two ends is fastened between two respective vessels, the elongate element being suspended from a plurality of bodies according to the invention, placed one after another, characterised by the following steps: a) fastening the cable on the convex side of a plurality of said bodies, via respective suspension devices; b) providing buoyancy at selected positions along the length of the cable so as to lift said plurality of bodies and respective parts of the elongate body off the bottom; c) moving said plurality of bodies and respective parts of the elongate body to the desired position by supplying a pulling force via the cable from the vessels; d) removing the buoyancy and said pulling force so that said plurality of bodies and respective parts of the elongate body are placed on the bottom.

Preferred features of the method according to the invention are set forth in dependent claims 14 - 15.

An embodiment of the invention will now be described in further detail with reference to the attached drawings.

Figure la is a perspective view of an embodiment of the element according to the invention.

Figure lb is a side view of the element in Figure la, without buffers.

Figure lc is an end view of the element in Figure la.

Figure Id shows the element in Figure la with buffers mounted thereon.

Figure 2 is an end view of the element in a further embodiment of the invention.

Figure 3 is an end view of the element in yet another embodiment of the invention.

Figure 4a shows a plurality of interconnected elements in a use of the invention for the laying of a cable, conduit, pipe or the like.

Figure 4b is an enlargement of a part of Figure 4a.

Figure 5 shows yet another embodiment of the invention.

Figure 6a illustrates the laying of a pipe, a cable, a conduit or the like, with the use of a plurality of elements according to the invention.

Figure 6b illustrates the start-up phase of the laying operation shown in Figure 6a. Figure 7 illustrates an alternative embodiment of the element according to the invention for connection to a seabed installation.

Figures 8a and 8b illustrate an alternative use of the element according to the invention, in connection with the lifting and moving of an installed cable, pipe, conduit or the like.

Figure la is a perspective view of the element according to the invention. The element 10 may be made of any material per se such as reinforced concrete, various synthetics or the like. The element 10 is curved with a concavity about the axis X-X, i.e., in this embodiment, a semi-circular cross-section. This can also be seen from Figure lc. Figures la, lb and Id all also show the holes or perforations 12 in the element 10. These may be of varying or identical size.

The element 10 is designed for emplacement against the seabed B. A hollow space 42 is then formed as shown in Figure lc. As the element is intended to be placed in a row of adjacent elements, it is advantageous to equip each element with detachable buffers 16.

Figure 2 is an end view of the element 10 showing the semi-circular cross-section. It should be noted that the cross-sectional shape per se is not important, but a semicircular cross-section may be suitable for production purposes. The crucial aspect, however, is the hollow space 42 (ref. Figure lc) that is formed when the element is placed on, for example, a seabed. A pipeline, cable or other conduit or elongate element 22 can be suspended in this space via a suspension device 18. This suspension device 18 may, for example, be a circular sling that is passed through respective perforations 12 and locked via, for example, shackles 20 on the outside of the element. The elongate element 22 will thus be suspended in the space 42 formed between the element 10 and the bottom B, and will therefore be protected from both the seabed and the surrounding ocean environment. The element is thus good protection against, for example, fishing gear and other objects. The skilled person will also understand that the device according to the invention makes lesser demands as regards the nature and gradient of the seabed. Even if the element 10 is placed in an inclined position relative to the horizontal plane, the elongate element 22 will still hang from the suspension 18.

Figure 3 shows a further embodiment of the invention in which an additional suspension device 26 is locked to the element 10 via perforations 12. This suspension element 26 may also be a circular sling. To prevent the circular sling 26 from falling into the element 10, the sling, together with the locking device 20', may form a loop which runs through two perforations 12 in the longitudinal direction of the element 10, so that the loop 26 does not fall through the perforation. Figure 3 also shows how the suspension device 26 is fastened to an installation cable 24. The suspension device 26 may be fixedly or slidably fastened to the cable 24.

Figure 4a shows how the device 10 according to the invention, via the said suspension devices, can be suspended in a catenary and installed on the seabed.

Figure 4b is an enlarged section of a part of Figure 4a and also shows the buffers 16. It can also be seen from Figures 4a and 4b how the suspension device 26 uses two perforations for suspension of the cable 24. Figure 4a also shows how the element 10 according to the invention protects the elongate element 22 when the body 10 according to the invention is placed on the seabed.

Figure 5 shows a variant where two bodies 10 according to the invention, via connecting studs 28, are mounted against each other to completely encircle an elongate element 22'. The elongate element 22', which similarly may be a cable, pipeline, conduit or the like, is in this case fully protected by the two elements 10, received in the hollow space 42'. A configuration of this kind may be suitable in places where the bottom conditions are particularly difficult, or when the diameter of the elongate element calls for it.

As mentioned, the device 10 according to the invention may be used for both protection and installation of a pipeline, conduit, pipe or the like 22 on the seabed B.

Figure 6b shows the start of an installation sequence where the elongate element 22 is stored on a drum 32, and the installation cable 24 is stored on a drum 30. At the start of the installation operation, the first body 10 in the chain and the forward end of the elongate body 22 are secured to the cable 24 via the suspension devices 18, 20, 26, 20', as described above. The pay-out speed of the cable 24 determines the laying speed. The cable 24 also absorbs the forces that are exerted on the elements 10 and the elongate element 22.

Figure 6a shows the installation sequence when the forward end of the catenary has been placed on the seabed. Here, a subsea structure may be involved (connected) in a known way. Although the method is illustrated in this figure with the use of a barge 36 and an operating crane 38, in combination with a lay vessel 34, the invention should not be limited to such an arrangement. The main point is that the elements are run down vertically into the water, and that the installation cable 24 bears the forces of the catenary in the water.

In some uses it may be advantageous and necessary for the elongate element 22 to describe a curve. This aspect can be ensured by equipping the body 10' with chamfered ends as shown in Fig. 7. By placing the chamfered elements 10' in a row, the desired curve can be obtained.

The invention is further directed towards a method for lifting and moving an elongate element 22, 22'. This is illustrated in Figures 8a and 8b, where the two ends of the cable 24 are secured to respective vessels V, and a plurality of buoyancy elements A are connected to the cable 24 by a plurality of the elements 10, as shown in Figure 8a. Such buoyancy elements may be gas-filled cylinders or the like. In this way, the row of elements 10, together with the elongate element 22 mounted within, can be lifted off the seabed and moved to another position by the vessels V. Figure 8b is a variant of this, where the buoyancy elements A have been replaced by a plurality of secondary slings C connected to the necessary or practical number of vessels V.

Claims

P a t e n t c l a i m s

1.

A device for the protection of an elongate element (22; 22') on the bottom (B) under a body of water, including a body (10; 10') with a concavity about a first axis (X) whereby the body (10; 10'), when placed on the bottom, can form a hollow space (42) defined by said bottom (B) and the concave side of the body, the hollow space having an extent essentially along said axis (X) and designed to accommodate said elongate body (22), characterised in that the body (10; 10') is provided with a plurality of perforations (12) between the concave and convex sides of the body.

2.

A device according to claim 1, characterised in that the body (10; 10') includes a first and a second end, each provided with respective recesses (14) for receiving respective detachable affixed buffers (16).

3.

A device according to claim 1, characterised by a plurality of suspension devices (18) for support of respective portions of said elongate element (22; 22') on the concave side of the body, parts of the suspension devices (18) being passed through selected respective perforations (12) and fastened to respective locking devices (20) on the convex side of the body.

4.

A device according to claim 1, characterised by a plurality of suspension devices (26) on the convex side of the body for suspension of said body (10; 10') from a cable (24) or the like, parts of the suspension devices (26) being passed through selected respective perforations (12) and fastened to respective locking devices (20¹) on the concave side of the body.

5.

A device according to claim 4, characterised in that said parts of each suspension device

(26) are passed through a respective perforation (12).

6.

A device according to claim 4, characterised in that each suspension device (26), together with respective locking device (20'), forms a loop, and that each suspension device (26) uses two perforations (12), so that said loop does not fall through the perforation when the suspension device is detached from the cable (24).

7.

A device according to claim 4, characterised in that the suspension devices (26) are designed for suspension from buoyancy elements (A) or other lifting devices (C, V).

8.

A device according to claims 1-7, characterised by a plurality of fasteners (28) along the edges of the body (10; 10'), by means of which fasteners (28) the bodies may be fastened to each other in pairs to form a hollow space (42') defined by the concave sides of said pairs of bodies, the hollow space (42') having an extent essentially along said axis (X) and designed to accommodate said elongate body (22').

9.

A device according to claims 1-8, characterised in that said first and second ends of the body (10') are chamfered relative to each other, so that when a plurality of bodies are placed one after another in a row, the row describes a curved path.

10.

A device according to claims 1-9, characterised in that the suspension devices (18, 26) are circular slings and that the locking devices (20, 20') are shackles.

11.

A device according to claims 1-10, characterised in that the body (10; 10') has a semicircular cross-section.

12.

A method for the installation of a device for protecting an elongate element (22; 22') on the bottom (B) under a body of water, using a lay vessel (34), barge or the like (36), wherein the device includes a plurality of bodies (10; 10') as disclosed in claims 1-9, and an installation cable (24) for controlling the laying of the elongate element, characterised by the following steps: a) fastening (18, 20) a first end of the elongate element (22; 22') on the concave side of a first of said bodies (10; 10'); b) fastening (26, 20') a first end of the installation cable (24) on the convex side of a first of said bodies (10; 10'); c) in a controlled (32) manner, running the installation cable (24), and the body and a part of the elongate body, down into the water by the lay vessel, barge or the like, the body and the elongate body being suspended via the cable (24) from a supporting structure (34, 36) at the surface, until a second of said bodies can be mounted end to end to the first of the bodies; d) arranging a second of said bodies (10; 10') for support (18, 20) as indicated in step a), the second body being placed end to end with one of the ends of said first body, separated by buffers (16); e) arranging the second of said bodies for support (26, 20') as indicated in step b); f) repeating steps c), d) and e) until the desired number of bodies has been placed on the bottom (B), whereby said elongate body is protected by a row of said bodies.

13.

A method for lifting or moving an elongate element (22; 22') on the bottom (B) under a body of water via a cable (24) which at its two ends is fastened between two respective vessels (V), the elongate element being suspended (18; 20) from a plurality of bodies

(10; 10') as disclosed in claims 1-9, placed one after another, characterised by the following steps: a) fastening the cable (24) on the convex side of a plurality of said bodies ( 10; 10'), via respective suspension devices (26, 20'); b) providing buoyancy at selected positions along the length of the cable so as to lift said plurality of bodies (10; 10') and respective parts of the elongate body off the bottom; c) moving said plurality of bodies (10; 10') and respective parts of the elongate body to the desired position by supplying a pulling force via the cable (24) from the vessels (V); d) removing the buoyancy and said pulling force so that said plurality of bodies (10; 10') and respective parts of the elongate body are placed on the bottom.

14.

A method according to claim 13, characterised in that the buoyancy is provided via buoyancy elements (A).

15.

A method according to claim 13, characterised in that the buoyancy is provided via a plurality of secondary slings (C) connected to vessels (V).