AU734646B3

AU734646B3 - Stabilisation of submarine elongate structures

Info

Publication number: AU734646B3
Application number: AU72137/00A
Authority: AU
Inventors: Barry Errol Ellis; Antonino John Fogliani
Original assignee: JP Kenny Pty Ltd
Current assignee: JP Kenny Pty Ltd
Priority date: 1999-06-25
Filing date: 2000-12-07
Publication date: 2001-06-21
Anticipated expiration: 2006-06-26

Description

P/00/012 28/5/91 Regulation 3.2

AUSTRALIA

Patents Act 1990

ORIGINAL

COMPLETE SPECIFICATION PETTY PATENT Invention Title: Name of Applicant: Actual Inventor(s): Address for service: "Stabilisation of Submarine Elongate Structures" J P KENNY PTY LIMITED ANTONINO JOHN FOGLIANI and BARRY ERROL ELLIS WRAY ASSOCIATES 239 Adelaide Terrace Perth, WA 6000 Attorney code: WR The following statement is a full description of this invention, including the best method of performing it known to me:- "Stabilisation of Submarine Elongate Structures" Field of the Invention This invention relates to stabilisation of submarine elongate structures, such as pipelines including single and multiple pipelines (bundled and unbundled), umbilicals, cables, and other service conduits.

Background Art Submarine elongate structures, and in particular submarine pipelines, can become unstable through exposure to environmental influences, particularly hydrodynamic loads arising from underwater currents and wave action. These hydrodynamic loads typically increase in regions of shallow water. The combination of extreme environmental loads and shallow water are present in Australian waters, typically on the North West Shelf off the West Australian coast.

Various systems are currently utilised for submarine pipeline stabilisation, including weight .coatings on pipelines, coverings on pipelines, installation of pipelines in trenches in the seabed, and securing pipelines to the seabed by way of mechanical anchors. Various deficiencies and problems can be associated with each of these stabilisation systems. For example, weight coating requirements for pipelines can be very high or impracticable. Trenching of pipelines is required to be deep in the seabed. Coverings over the pipeline need to be thick and of adequate weight, and in some cases the covering material may itself be unstable. Mechanical anchors of high capacity are required at close intervals to secure the pipelines to the seabed.

While the abovementioned systems can be utilised in many situations, there are locations where the cost involved can be very high or indeed prohibitive, and the installation procedure can be time-consuming.

-3- It is against this background, and the deficiencies and problems associated therewith, that the present invention has been developed.

Disclosure of the Invention The present invention provides a stabilisation system for a section of a submarine elongate structure, comprising an end restraint at each end of the section of the elongate structure, each end restraint being adapted to be secured to the elongate structure to transfer axial tension generated by lateral movement of the elongate structure to the seabed or ground on which the end restraint is installed, each restraint comprising a pair of restraint faces spaced apart to define a gap along which the elongate structure can extend, the faces being configured such that the gap therebetween is of varying width for controlling curvature of the elongate structure during lateral movement thereof.

At least one intermediate restraint may be provided between the two end restraints for limiting lateral movement of the structure at the- location of the intermediate restraint.

The restraint locations provided by the end restraints and any intermediate restraint therebetween are spaced sufficiently to allow the elongate structure to move laterally and develop axial tension until an equilibrium position is achieved.

The restraint locations are selected so as to maintain axial tensions (and associated axial stresses) within allowable limits and to ensure that the extent of lateral movement of the elongate structure between the restraint locations is within an allowable range.

The configuration of the two restraint faces of each restraint allows the elongate structure to curve to one side or the other at the restraint location (depending on the direction of lateral movement) while limiting the maximum extent of curvature.

Preferably, each restraint face is curved.

Each restraint face can be either a continuous face, or a discontinuous face in the sense that it comprises a plurality of restraint zones disposed in the required configuration. Each restraint zone may be defined by a restraint column embedded in the seabed or ground. The columns may be connected one to the other to provide an integral restraint structure.

Brief Description of the Drawings The invention will be better understood by reference to the following description of one specific embodiment thereof as shown in the accompanying drawings in which: Figure 1 is a schematic plan view of a section of a pipeline fitted with a stabilisation system according the embodiment; Figure 2 is an elevational view of Figure 1; Figure 3 is a fragmentary plan view of the pipeline, showing a pair of intermediate restraint devices; Figure 4 is a side elevational view of Figure 3; Figure 5 is a sectional view on line 5-5 of Figure 3; Figure 6 is a fragmentary plan view of the pipeline showing an end restraint; Figure 7 is a fragmentary plan view of part of the end restraint, Figure 8 is a side view of Figure 7; Figure 9 is an end view of the collar structure; and Figure 10 is a sectional view on line 10-10 of Figure 6.

Best Mode(s) for Carrying Out the Invention The embodiment shown in the drawings is directed to a stabilisation system for stabilising a submarine pipeline 11 supported on a seabed 13 below water level 14.

The stabilisation system 10 includes two end restraints 15, one at each end of the section of the pipeline requiring stabilisation (only one of the restraints being shown in the drawings). The pipeline stabilisation system 10 further includes a plurality of intermediate restraints 17 positioned at intervals along the length of the pipeline 11. The intermediate restraints comprise restraint devices 20 are positioned in pairs, as will be explained in detail later.

The end restraints 15 are secured to the pipeline section to transfer axial tension, generated by lateral movement of the pipeline, to the seabed or the ground on which the end restraints 15 are installed. Typically, each end restraint 15 would be positioned on the seabed 13 as shown in the drawings, but it may be positioned on the ground (shoreline) at a'location where the pipeline enters or exits the water, As mentioned above, the intermediate restraint devices 20 are positioned in pairs, as best seen in Figures 3 and 4 of the drawings. The intermediate restraint devices 20 are positioned in pairs in order to facilitate installation. In the event that larger capacity installation equipment is used, a combined single unit may be used.

Each restraint device 20 comprises two opposed restraint faces 21 in spaced apart relationship to define a gap 23 therebetween through which the pipeline 11 extends. In this embodiment, each restraint face 21 is defined by a plurality of spaced apart columns 25, at least some of which are embedded in the seabed 13, as best seen in Figures 4 and 5. With this arrangement, each column defines a restraint zone for restraining lateral movement of the pipeline.

The columns 25 are arranged in a curved formation so that the restraint face 21 that they define is of a curved configuration, as best seen in Figure 3 of the drawings. The columns 25a at one end are furthest apart and the columns 25b at the other end are closest together, so that the gap 23 between the faces 21 progressively increases from one end to the other. The upper ends of the columns 25 are interconnected by longitudinal elements 27 and transverse elements 29. With this arrangement, the combination of the columns 25 together with the longitudinal elements 27 and transverse elements 29 form a unitary structure 31.

The two restraint devices 20 in each pair are positioned such that the end columns 25b are adjacent each other and the corresponding restraint faces 21 in alignment. With this arrangement, the two restraint devices 20 co-operate to control the extent to which the pipeline 11 can curve to one lateral side or the other at the location at which the two restraint devices 20 are installed. This control is achieved by the curvature of the restraint faces 21.

Each of the end restraints 15 comprise a restraint device 40 of similar construction to the restraint devices 20, and a restraining collar structure 43 secured to the. pipeline 11. As restraint device 40 is of similar construction to restraint device 20, similar reference numerals are used to identify like parts. The collar structure 43 presents an abutting face 45 which bears against the columns which are positioned closest together. Co-operation between each collar structure 43 and the restraint device 40 against which it bears serves to transfer axial tension generated by lateral movement of the pipeline 11 to the seabed 13 (or ground) in which the restraint device 40 is anchored. The curved restraint faces 21 control the extent to which the pipeline 11 can curve at the end restraint The collar structure 43 is of split construction comprising two parts which can be bolted or otherwise secured together around the pipeline to clampingly engage the pipeline. Such an arrangement is particularly suitable in cases when the stabilisation system 10 is fitted to an existing pipeline. In cases when the -7stabilisation system is fitted during installation of a new pipeline, the collar structure may be welded or otherwise secured to the pipeline.

The end restraints 15 are positioned at the ends of the pipeline section to be stabilised and the intermediate restraint devices 20 are positioned in pairs at appropriate intervals between the end restraints 15. Typically, the spacing between each end restraint 15 and the adjacent intermediate restraint 17, and the spacing between intermediate restraints 17, could be in the order of one kilometre or more. Associated lateral movements of the pipeline 11 between the restraint locations can be in the order of 20 metres or more. This compares with conventional restraint systems where restraint locations have spacings in the order of 20 metres and have negligible movement of the restrained pipeline between the restrained locations.

The fact that the restraint system according to the embodiment can have restraint locations at significantly greater spacings than conventional arrangements allows installation in considerably less time and at a considerably lower cost.

The feature whereby the restraint faces 21 in the end restraints 15 and in the intermediate restraints 17 control the extent to which the pipeline 11 can curve as it undergoes lateral movement, permits the use of restraint locations at significantly increased spacings in comparison to conventional arrangements.

In operation, the curved restraint faces 21 support the pipeline 11 as it undergoes lateral movement and control the extent to which the pipeline can bend, thereby restraining lateral movement of the pipeline and stabilising the pipeline by ensuring that the lateral movement and the associated pipeline stresses are within allowable limits.

From the foregoing, it is evident that the present invention provides a simple yet highly effective arrangement for stabilisation of submarine pipelines and other like structures It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described. There are, for example, instances where intermediate restraints would not be required between the end restraints. One such instance may be where a pipeline is relatively short (for example up to 1 km long). In such a case, the two end restraints are likely to work effectively without the need for any intermediate restraint.

Throughout the specification, 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 group of integers but not the exclusion of any other integer or group of integers.

Claims

1. A stabilisation system for a section of a submarine elongate structure, comprising an end restraint at each end of the section of the elongate structure, each end restraint being adapted to be secured to the elongate structure to transfer axial tension generated by lateral movement of the elongate structure to the seabed or ground on which the end restraint is installed, each restraint comprising a pair of restraint faces spaced apart to define a gap along which the elongate structure can extend, the faces being configured such that the gap therebetween is of varying width for controlling curvature of the elongate structure during lateral movement thereof.

2. A stabilisation system according to claim 1 wherein at least one intermediate restraint is provided between the two end restraints for limiting lateral movement of the structure at the location of the intermediate restraint.

3. A stabilisation system according to claim 1 or 2 wherein each restraint face is curved. Dated this sixteenth day of January 2001. J P KENNY PTY LIMITED Applicant Wray Associates Perth, Western Australia Patent Attorneys for the Applicant