AU2003235014A1

AU2003235014A1 - Device for stabilising the position of a pipeline installed on a seabed or riverbed

Info

Publication number: AU2003235014A1
Application number: AU2003235014A
Authority: AU
Original assignee: Van Oord Acz BV
Current assignee: VAN OORD ACZ BV
Priority date: 2002-08-14
Filing date: 2003-08-14
Publication date: 2004-03-04
Also published as: NL1021278C2

Description

I

Our Ref:78258543 P/00/011 Regulation 3:2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION STANDARD PATENT Applicant(s): Address for Service: Invention Title: Van Oord ACZ B.V.

Jan Blankenweg 2 4207 HN Gorinchem The Netherlands DAVIES COLLISON CAVE Patent Trade Mark Attorneys Level 10, 10 Barrack Street SYDNEY NSW 2000 Device for stabilising the position of a pipeline installed on a seabed or riverbed The following statement is a full description of this invention, including the best method of performing it known to me:- 5020 Device for stabilising the position of a pipeline installed on a seabed or riverbed.

DESCRIPTION

The invention relates to a device for stabilising the position of a pipeline laid on a seabed or riverbed Pipelines that are laid on a seabed or riverbed may be moved over the bottom by wave or current action, to such an extent that stresses are built up in the pipeline material, which stresses shorten the life of the pipeline considerably and, in some extreme situations, may even damage the pipeline or cause it to collapse.

In order to prevent the pipeline being exposed to such inadmissible loads or deformations, it is known to weight or stabilize the pipeline at regular intervals by placing concrete weights or block mattresses on the pipeline.

An example of such a block mattress, in which linkedtogether block elements are laid over the pipeline by means of cables or ropes, is known, for example from European patent application No. 0 152 232.

One drawback of using such weighting materials is the fact that the placement of blocks suspended from a long hoisting cable takes place in an uncontrolled and inaccurate manner, due to oscillations thereof caused by tidal currents. Furthermore, the pipeline may be damaged by the weighting materials falling down on the pipeline from some height. In addition to that, pressure points may form on the outer wall of the pipeline after the placement of the weighting material, such as the concrete block elements and/or block mattresses described in EP 0 152 232, as a result of the forces exerted by waves and/or water currents or the irregular shapes of the weighting materials, which pressure points may lead to damage or pipe fracture.

Furthermore, trawl nets from fishing boats can easily interfere with the known irregularly shaped weighting materials.

2 The present invention aims to provide a device for stabilising or weighting pipelines on a seabed and/or riverbed which prevents the pipeline from being damaged unnecessarily upon placement of such weighting materials, and wherein the occurrence of undesirable pressure points that may weaken and/or damage the wall of the pipeline after placement is prevented.

In accordance with the invention, the device comprises at least one elongated envelope, which envelope is filled with a granular material. The advantage of such an envelope filled with granular material is that it cannot damage the wall of the pipeline upon placement of the weighting material on the pipeline and that, also after placement of the device, the action of waves and water currents cannot lead to the formation of undesirable pressure points and thus to damage being caused to the pipeline wall.

Furthermore, the risk of trawl nets from fishing boats interfering with the weighting device is reduced, due to the limited constructional height of the device.

An improved weighting or stabilisation of the pipeline can be obtained in that, in accordance with the invention, the elongated envelope can be placed on the pipeline in a direction more or less perpendicular to the longitudinal direction of the pipeline.

According to an improved embodiment of the device according to the invention, the elongated envelope is attached to an underlay mat to be placed on the pipeline. It is the underlay mat that provides the strength, whilst the envelope filled with the granular material provides the weight. In order to increase the strength of the device as a whole, an overlay mat may be attached to the elongated envelope, which overlay mat likewise has a protective function once the envelope has been placed on the pipeline.

In a specific embodiment, the device comprises several parallel, linked-together elongated envelopes, more in particular the device comprises three elongated envelopes. The envelopes may be linked together so as to enhance the stability of the weighting device.

More specifically, the elongated envelopes, the overlay mat and the underlay mat may be made of the same material, which material is preferably flexible, thus enabling easy placement without the risk of the envelope being damaged or torn open, whilst the device can adapt its shape and orientation to the shape of the pipeline and the relief of the seabed or riverbed so as to provide an adequate stabilising function.

More in particular, the fill ratio of the envelope with granular material is up to 90%. This enables the envelope to adapt its shape and orientation to the shape of the pipeline and the seabed or riverbed, and it has been found by experiment that the granular material is compacted in the envelope in this way, thus realising an improved fixation or stabilisation of the pipeline on the seabed or riverbed.

It has been found that sand, gravel, stones or a combination thereof are suitable granular materials.

The invention furthermore relates to a construction for placing a stabilisation device according to the invention, which stabilisation device can be moved to a position just above the pipeline to be stabilised by means of a hoisting device present on a vessel. In accordance with the invention, the construction is characterized by a frame of bars provided with clamping means, between which the cross sides of a stabilisation device can be received.

More particularly, the clamping means are provided between two respective corner points of the frame, with said clamping means more in particular being composed of at least one strip and a clamping element that can be placed into abutment with the strip.

The clamping element may be a second strip extending parallel to said first strip, or an element that can be inflated or expanded by means of a working fluid, for example an element such as a hose that can be pressurised.

More in particular, the clamping means can be actuated from the vessel, so as to place the stabilisation device on and over the pipeline in an effective and safe manner, i.e. without damaging the pipeline that is to be stabilised.

The invention will now be explained in more detail with reference to the drawing, wherein: Figures la-ld are views of an embodiment of a stabilisation device according to the invention, showing the device during various stages of the placement thereof over a pipeline by means of a construction according to the invention; Figure 2 shows the longitudinal view, a side view and a top plan view of the stabilisation device that is shown in Figures la-ld.

Figures la-ld show various stages of the placement of a stabilisation device according to the invention by means of a construction according to the invention.

The stabilisation device consists of at least one, three in the present embodiment, elongated envelopes 2a-2c. Said elongated envelopes 2a-2c extend parallel to each other, and they are linked together in such a manner that they form one strong unit. In order to give the stabilisation device 1 additional strength, the elongated envelopes 2a-2c are arranged on an underlay mat 3.

The underlay mat 3 has cross sides 3a and 3b, which cross sides are received in clamping means 12a and 12b, respectively, of a construction 10 for placing the stabilisation device on the pipeline present on the seabed 6.

The construction 10 is built up of a frame of bars lOe, which bars lOe form a more or less rectangular frame 10 having corner points lOa-lOd. Disposed between the corner points 10a-lOb and lOc-lOd are the clamping means 12a and 12b, respectively, for clamping down the cross sides 3a and 3b, respectively, of the underlay mat 3 of the stabilisation device 1.

In a more specific embodiment, the clamping means 12a and 12b are composed of two strips extending parallel to each other, which can be moved towards and away from each other by suitable means. The cross sides 3a and 3b can be received and clamped down between said two strips of the clamping means 12a and 12b, respectively.

On the other hand, the clamping means may be composed of at least one strip and a clamping element that can be placed into abutment with the strip, which may be an element which can be inflated or expanded by means of a working fluid, for example an element such as a hose that can be pressurised.

The frame 10 is provided with suitable stay ropes 11a-11d at the corner points lOa-lOd, which stay ropes 11a-11d are connected to a hoisting device present on the deck of a vessel (not shown) via a hoisting cable (not shown).

Upon placement of the stabilisation device 1 as shown in Figure la, the stabilisation device 1 is suspended from the construction with the cross sides 3a-3b thereof being clamped down in the clamping means 12a-12b of the construction 10, to a position just above the pipeline 5, which is present on the seabed, for example.

As is shown in Figure lb, the lowering of the construction and the stabilisation mat 1 being held therein can be monitored by an underwater robot 13. The placement of the stabilisation mat 1 on the pipeline 5 can thus take place in a simple and safe manner without unnecessary damage being caused to the wall of the pipeline 5. This in contrast to the situation wherein concrete blocks or block mattresses are used as weighting materials, in which case the risk of damage caused by the weighting materials falling down on the pipeline from some height cannot be entirely excluded, due to the fact that said blocks or mattresses cannot be placed as efficiently or accurately, whilst also their shape plays a part in this regard.

On the contrary, the stabilisation device 1 according to the invention is composed of at least one elongated envelope, three in the present embodiment, which is filled with a granular material. Said granular material may be sand, gravel, stones or a combination thereof, for example.

Since the elongated envelopes and the underlay mat are made of a flexible material, which may have an open structure, the stabilisation device 1 can adapt its shape or orientation to the shape (the dimension/diameter) of the pipeline as well as to the relief of the seabed 6. This ensures an optimum positioning of the stabilisation device with respect to the pipeline and thus an effective stabilisation thereof.

Furthermore, the formation of pressure points in the wall of the pipeline, which may cause the pipeline to weaken or fracture, during movement of the pipeline caused by the action of waves or currents is thus prevented.

The composite structure consisting of the underlay mat 3 and one or more elongated envelopes 2a-2c not only provides a strong stabilisation (as a result of the presence of the underlay mat but it also makes it possible to place a considerable weight (provided by the envelopes 2a-2c) on the pipeline.

As Figures la-ld show, the elongated envelope 2a-2c is preferably arranged perpendicularly to the longitudinal direction of the pipeline 5. This ensures the most optimum stabilisation of the pipeline.

Another advantage of the stabilisation device 1 compared with the use of conventional weighting materials, such as concrete blocks or block mattresses, is the fact that the stabilisation device 1 is characterized by a large weight, thus providing an adequate stabilisation or weighting effect, whilst furthermore the constructional height of the device is limited. This renders the stabilisation device 1 less sensitive to the action of the currents, whilst furthermore trawl nets from fishing boats interfere less with the device. This ensures a longer life of the stabilisation device according to the invention, whilst also the stabilisation of the pipeline on the seabed for the riverbed will be retained longer.

Preferably, the elongated envelopes 2a-2c and the underlay mat are made of a woven or stitched material. More in particular, the material is a geotextile.

It has been found that a fill ratio of the envelope with granular material up to 90% provides a strongly improved stabilisation of the pipeline 5. In particular if sand is used as the granular material in the envelope, this fill ratio makes it possible for the sand to be locally compacted near the pipeline 5 (indicated at A and B in Figure id) as a result of the flexible elongated envelope being bent, causing the sand to harden and thereby anchor the pipeline 5 in place. This latter aspect significantly reduces the effect of the waves and the currents on the pipeline, which in turn significantly reduces the occurrence of pressure points and thus of peak loads on the wall of the pipeline 5 that may damage or pierce the wall.

In a specific embodiment, the underlay mat 3 has a length L of 14 m and a width B of 5 m, whilst the length 1 of the elongated envelopes 2a-2c is about 12 m (see Figure Preferably, each elongated envelope has a cross-sectional dimension of 1.4 by 0.6 m when filled with the granular material to a fill ratio of up to It will be apparent that the stabilisation device according to the invention provides an improved stabilisation of pipelines on a seabed or a riverbed, wherein damage caused by weighting blocks, such as concrete blocks or block mattresses, falling down on the pipeline from a small height and, accordingly, damage caused to the pipeline by pressure points and/or peak loads will belong to the past.

In addition to that, the placement of the stabilisation mat can take place much more accurately, since it is not suspended from a long hoisting cable, as is the case with the known weighting blocks, which may be caused to oscillate by the tidal currents.

The placement of the stabilisation mat/envelopes can be monitored by means of an underwater camera via an underwater robot, which underwater robot can furthermore be used for correcting the position of the placement construction so as to obtain a correct placement of the stabilisation envelopes. To this end, the underwater robot may be connected to the placement construction, for example via a robot arm.

The number of elongated envelopes which are placed substantially perpendicular to the pipeline 5 can be varied in dependence on the purpose for which they are used and on the diameter of the pipeline.

An overlay mat (not shown) may be arranged over the elongated envelopes 2a-2c, which overlay mat may function as a protective layer for weighting material in the form of boulders and/or other weighting materials that may be used to cover the stabilisation device 1 after placement thereof.

Throughout this specification and the claims which follow, unless the context requires otherwise the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as an acknowledgment or any form of suggestion that, that prior art forms part of the common general knowledge of Australia.

Claims

1. A device for stabilising the position of a pipeline laid on a seabed or riverbed, comprising at least one elongated envelope, which envelope is filled with a granular material, characterized in that the elongated envelope is attached to an underlay mat to be placed on the pipel i ne.

2. A device according to claim 1, characterized in that the elongated envelope can be placed on the pipeline in a direction more or less perpendicular to the longitudinal direction of the pipeline.

3. A device according to any one or more of the preceding claims, characterized in that an overlay mat is attached to the elongated envelope.

4. A device according to any one or more of the preceding claims, characterized in that the device comprises several, for example three, parallel, linked-together elongated envelopes. A device according to any one or more of the preceding claims, characterized in that the elongated envelopes, the overlay mat and-the underlay mat are made of the same material.

6. A device according to claim 5. characterized in that said material is flexible.

7. A device according to claim 5 or 6, characterized in that said material has an open structure.

8. A device according to any one or more of the claims 5-7, characterized in that said material is a woven material.

9. A device according to any one or more of the claims 5-8, characterized in that said material is a stitched material. A device according to claim 8 or 9, characterized in that said material is a geotextile.

11. A device according to any one or more of the preceding claims, characterized in that the fill ratio of the envelope with granular material amounts up to

12. A device according to any one or more of the preceding claims, characterized in that sand, gravel, stones or a combination thereof form the granular material.

13. A construction for placing a stabilisation device according to any one or more of the preceding claims, which stabilisation device can be moved to a position just above the pipeline to be stabilised by means of a hoisting device present on a vessel, characterized by a frame of bars provided with clamping means, between which the cross sides of a stabilisation device can be received.

14. A construction according to claim 13, characterized in that said clamping means are provided between two respective corner points of the frame. A construction according to claim 13 or 14, characterized in that said clamping means are composed of at least one strip and a clamping element that can be placed into abutment with said strip.

16. A construction according to claim 15, characterized in that said clamping element is a second strip extending parallel to said first strip.

17. A construction according to claim 15, characterized in that said clamping element is an element that can be inflated or expanded by means of a working fluid, for example an element such as a hose that can be pressurised.

18. A construction according to claim 15, characterized in that said clamping means can be actuated from the vessel.

19. A construction according to any one or more of the claims 13-18, characterized in that the construction can be moved or positioned by means of an underwater robot. 11 A device for stabilising the position of a pipeline installation on a seabed or riverbed substantially as hereinbefore described with reference to the drawings.

21. A construction for use with a stabilising device substantially as hereinbefore described with reference to the drawings. DATED this 14 th day of August, 2003 Van Oord ACZ B.V. By Their Patent Attorneys DAVIES COLLISON CAVE