AU642965B2 - Stabilisation means - Google Patents

Description

642965 COMMONWEALTH OF AUSTRALIA Patents Act 1952 COMPLETE SPECIFICATION (Original) FOR OFFICE USE Application Number: PJ8797 Class Lodged: 23 February, 9-f9qf Int. Class Complete Specification Lodged: Accepted: Published: 21st February, 1991 0

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SOSs Priority: Related Art: TO BE COMPLETED BY APPLICANT Name of Applicants: Address of Applicants: SPUNCON PTY LTD and MARECON PTY LTD of 75 Canning Highway, Victoria Park, and 15 Rawson Street, Subiaco, respectively, both in the State of Western Australia, Commonwealth of Australia.

s 4SSO 0 Actual Inventor: Address for Service:- PIETER JAN de GEETER Wray Associates Primary Industry House 239 Adelaide Terrace Perth Western Australia 6000.

Complete Specification for the invention entitled: "Stabilisation Means" The following statement is a full description of this invention, including the best method of performing it known to me:- 1 THIS INVENTION relates to a means for providing gravity stabilisation of an object such as an underwater pipeline, and to a method of installing such means.

It is usually necessary to stabilise an underwater pipeline both during installation of the pipeline and once the pipeline is in position on the floor of the body of water. During installation of the pipeline, the gravity stabilisation is required to overcome any buoyancy effects of the pipeline. Once the pipeline is in position, 66 1 ,0 gravity stabilisation is required to prevent the pipeline from shifting under the effects of wave motion and water currents.

*0 0 In some situations gravity stabilisation is achieved by providing a coating of concrete on the pipeline so as to increase its weight; this procedure is known as weight-coating. It is not altogether satisfactory as some of the increased weight of the pipeline is utilised in offsetting the buoyancy effect of the increase in diameter of the pipeline.

0* go 20 In other situations, gravity stabilisation is achieved by use of a massive mat tructure comprising concrete elements flexibly linked together to allow the mat structure to be draped over the pipeline with the outer .00: edges of the mat structure resting on the floor of the *o body of water. While such mat structures perform satisfactorily once in position on a pipeline, they are designed to be installed on a section of the pipeline only after the pipeline section has been laid and so they do not satisfy the need for stabilisation of the pipeline section during laying. Furthermore the pipeline remains in a vulnerable state on the floor of the body of water until the mat structures have been laid. This can be a problem particularly if the site has to be evacuated owing to adverse weather conditions before all of the mat structures have been installed. Additionally, installation of the mat structures presents some difficulty as they have to be supported in a deployment frame while they are lowered into position above the appropriate section of the pipeline and then carefully located in position.

There is also a proposal in SU-594-390 (Kulygin et al) to provide a ballast weight assembly for a pipeline laid on lo marshy ground or underwater. The ballast weight assembly is adapted to clampingly engage the pipeline and comprises a pair of clamps pivotally connected togethex at their upper ends by a massive saddle comprising two sections which are pivcotally interconnected. The lower or free ,ends of the clamps are interconnected by a flexible band.

The ballast weight assembly is installed onto a pipeline using a detachable support beam to lower it onto the pipeline with the clamps located one on each side of the pipeline. As the ballast weight assembly is lowered onto 20 the pipeline, the flexible band deflects as it comes into contact with the upper section of the pipeline and so causes the clamps to pivot inwardly and clampingly engage the pipeline to secure the assembly in position. Because of the massive nature of the saddle, the ballast weight assembly would appear to provide the desired anchoring function.

9* There are, however, several deficiencies which appear to exist with the ballast weight assembly. One such deficiency is that the clamping action on the pipeline is very much reliant on vertical loadings applied to the clamps by the massive saddle. It therefore follows that the saddle should not rest on the pipeline for otherwise the vertical loadings on the clamps would be reduced with the result that the clamping action on the pipeline would 4 diminish. A further deficiency is that massive saddle produces a high centre of gravity in the ballast weight assembly with the result that the centre of gravity is above the centre of the pipeline when the assembly is in position. This is detrimental to the rotational stability of the ballast weight assembly when on the pipeline and means that it is most unlikely that the ballast weight assembly could be installed on a pipeline being lowered onto the seabed under normal operational conditions at sea. The rotational instability created by the ballast weight assembly may also create problems for a pipeline installed underwater owing to wave and current action. A Sstill further deficiency arising from the massive saddle Sis the large profile that the ballast weight assembly presents when in position on a pipeline. As a result of the large profile, there is a substantial surface area of the ballast weight assembly exposed to the influences of underwater currents and other water motion. The forces which are imparted to the ballast weight assembly as a 0 -~lt of the influences of such water motion can cause the assembly to dislodge from the pipelili or the pipeline to shift laterally underwater.

From the foregoing discussion it is evident that the means for gravity ,.tabilisation which have been described have o not performed altogether satisfactorily in the situations outlined.

The present invention seeks to provide a novel and useful means for gravity stabilisation which when applied to stabilisation of underwater pipelines can be utilised to provide gravity stabilisation both during laying of the pipeline and once the pipeline is in position on the floor of the body of water.

5 In one form the invention resides in a stabilisation means for providing gravity stabilisation of an object comprising a pair of weights having upper and lower surface portions and means interconnectably linking said weights for swinging movement towards and away from each other wherein said weights are adapted to be positioned on opposed sides of said object with said linking means resting on and across the top of said object such that said weights are caused to swing into engagement with said object so as to exert compressive forces against said opposed sides of said object, each of said weights having an inner surface portion through which the compressive force is applied to said object, said linking means comprising upper and lower connections, said upper connection interconnecting the upper surface portions of said weights and said lower connection interconnecting the lower surface portions of said weights, said weights and said linking means being so shaped and dimensioned that the centre of gravity of said stabilisation means is below the geometric centre of said object when said stabilisation means is in use.

V'64 With this arrangement, said stabilisation means can .0 clampingly engage against the object by virtue of the friction which arises as a result of the compressive force which exists between said weights and the object when said 449449 weights are not resting on a support surface such as the floor of a body of water.

*S .9 Said upper connection may be of any suitable construction such as a cable or like flexible member, a rod or like .9 element which is stiff yet capable of lateral deflection, 30 or a rigid member onto which the weights are hingedly mounted. For preference, however, said upper connection comprises a strap of flexible material which has the benefit that it can conform generally to the profile of the 6 upper section of the object and so not present a substantial surface which would be exposed to external influences.

Preferably, said lower connection is formed of a flexible material. For preference, said lower connection comprises a sheet of such flexible material onto which said weights are mounted.

Preferably, said upper connection is anchored to the upper surface portion of each weight.

Preferably, said lower connection is anchored to the lower surface portion of each weight.

Preferably, the arrangement between the upper connection and the weights is such that the compressive force which exists between each weight and said object exceeds the weight of said weight.

In another form the invention resides a stabilising means for stabilising an elongated object, said stabilisation means comprising a flexible base, at least one pair of weights mounted on the base and defining a locating space 20 therebetween for receiving a portion of said elongated object with said base overlying and engaging a top of said portion of said object, and an upper connection interconnecting said weights, said flexible base and said upper connection co-operating to permit movement ot the weights towards and away from each other whereby said weights can apply compressive forces against opposite sides S* of said elongated object, said weights and connection being so shaped and dimensioned that the centre of gravity of said stabilisation means is below the geometric centre of said object when said stabilising means is in use.

7 Preferably, said upper connection comprises a flexible strap the ends of which are connected to said weights along the top portions thereof.

In another form the invention resides in a method for stabilising an elongated object comprising the steps of locating and clampingly engaging a stabilisation means as set forth hereinbefore on a section of said elongated object and lowering said section of said elongated object and the stabilisation means engaged thereon onto a support surface.

In still another form the invention resides in a method for stabilising an elongated object such as a pipeline in a body of water comprising the steps of introducing the elongated object into the body of water and attaching a stabilisation means as set forth hereinbefore on the elongated object at intervals along the length thereof as the elongated object descends towards the floor of the body of water.

In still another form the invention resides in a method of 20 stabilising an underwater pipeline during the laying and use thereof comprising applying to said pipeline during S' laying thereof on underwater pipeline stabilising means as set forth hereinbefore and lowering said pipeline and I associated stabilising means into a body of water to rest on the bed thereof, said stabilising means gripping said pipeline during lowering thereof and holding said pipeline onto said bed after laying of said pipeline thereon.

*:oThe invention will be better understood by reference to the following description of one specific embodiment thereof as 30 shown in the accompanying drawings in which:- 7a Fig. 1 is a schematic cross-sectional view of stabilisation means according to the embodiment positioned on a pipeline resting on the seabed; Fig. 2 is a side elevational view of the stabilisation means of Fig. 1; Fig. 3 is a plan view of the stabilisation means of Fig. 1; Fig. 4 is a schematic view showing the stabilisation means clampingly engaging a section of the pipeline as it is lowered into position on the seabed; Fig. 5 is a schematic side elevational view showing the stabilisation means located on the section of the pipeline being installed on the seabed; Fig. 6 is a schematic cross-sectional view illustrating certain forces which are established between the stabilisation means and the section of the pipeline being installed on the seabed; 0 o: 0# :l o 0 0 0 9

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00 9 0* 8 Fig. 7 is a force equilibrium diagram relating to the situation existing in Fig. 6; Fig. 8 is a schematic view illustrating one set of frictional forces which are established between the stabilisation means and the pipeline; Fig. 9 is a schematic view showing a longitudinal portion of the pipeline and illustrating a further set of frictional forces which are established between the stabilisation means and the pipeline; Fig. 10 is a schematic view illustrating the stabilisation means when it is occupying an unstable position on the pipeline and showing the resultant forces which act to return the stabilisation means S, to a central position; and Fig. 11 is a schematic view of a pipeline being laid S9* onto a seabed with several stabilisation means according to the embodiment spaced along the length of the pipeline.

The embodiment shown in the drawings is directed to a 2b means 10 for gravity stabilisation of an underwater pipeline 11 both during installation of the pipeline and once the pipeline is resting on the seabed. The stabilisation means 10 can be used to overcome any buoyancy effect on the pipeline and stabilise it against lateral movement when exposed to forces induced by water currents and wave action The stabilisation means also serves to afford some protection against undermining of the pipeline by water currents as it rests on the seabed.

The stabilisation means 10 is in the form of a mat structure which is draped over the pipeline, The mat structure 10 comprises a flexible base 13 and weights 19 mounted on the base 13. The base 13 is planar and of rectangular configuration, having a longitudinal extent with a pair of longitudinal sides 15 and a transverse extent with a pair of transverse sides 17. The base is pervious to water but impervious to fine sand and may be in the form of a sheet of robust woven mesh fabric formed from, for example, polypropylene or other high strength synthetic material which is resistant to degradation by water, sunlight and other harmful elements which may exist in the environment in which the stabilisation means is used.

Weights 19 are mounted on one face of the flexible base.

In this embodiment the weights 19 are in the form of concrete blocks and each block is secured to the flexible base by means of a plurality of pins (not shown) which extend through the base and are embedded in the block.

o The pins are formed of material resistant to degradation and shock loadings. In another arrangement, the concrete o blocks can be secured to the flexible base by way of loops which are woven into the base and embedded into the concrete of the blocks.

The concrete blocks are arranged in confronting 0 relationship in two rows 21, and a locating space 23 is defined between the two rows for receiving a section of the pipeline as will be explained later.

The concrete blocks are elongated, each having a Slongitudinal extent transverse to the inner face thereof.

The nner faces 2S of the concrete blocks are substantially normal to the plane of the flexible base when the latter is laid in flat condition. More particul.arly, the ien~ faCes 25 are shaped to conform to the profile of the pipeline. This has the effect of reducing the extent to which each inner face is exposed to hydrodynami forces.

10 The outer face 27 of each block is configured for the purpose of offering lower resistance to oncoming water flow thereby reducing the effect of water motion on the stabilisation means. This configuration of the blocks also serves to reduce the likelihood of the blocks being caught on obstacles at any stage such as during handling and installation or while in place underwater. In this embodiment, the outer face comprises two face sections, being a first face section 27a which is substantially norma), to the plane of the base 13 and a second face section 27b which is inclined inwardly, as best seen in S* Figs. 1 and 4 of the drawings.

£4 a The spacing between the inner faces of confronting blocks is such that the width of the section 13a of flexible base extending across the locating space 23 is sufficient to straddle the section of pipeline received in the locating space, as shown in Fig. 1.

,Lifting lugs 32 or other attachment means are embedded in the blocks to facilitate lifting of the stabilisation 1 20 means for transportation and instaliation purposes.

0 The mattress structure is adapted to clampingly engage the pipeline 13 when draped over the pipeline during installation. For this purpose an upper connection means in the form of flexible strap 29 is provided between confronting concrete blocks in the two rows. The ends of each flexible strap 29 are fixed to the top faces of the respective concrete blocks by way of fixing means 31 such as pins embedded in the block. The flexible strap 29 in combination with the flexible base 13 effectively provides a hinge between the two confronting blocks such that hen the mat is draped over the pipeline with a section of the pipeline received in the locating space 23, the confronting blocks are caused to swing inwardly with the 11 result that the inner faces 25 clampingly engage the pipeline, as best shown in Fig. 4 of the drawings. For this purpose, the portion of the flexible strap 29 bridging the locating space 23 is shorter in length than the width of the section 13a of the flexible base extending across the locating space 23.

The flexible strap 29, section 13a of the flexible base and the blocks 19 are suitably dimensioned and shaped such that the centre of gravity of the mat structure is below ,*10 the geometric centre of the pipeline when installed in 0* position.

The flexible strap 29 can be maintained permanently in plac: after installation of the pipeline on the seabed, ,retrieved for further use if so desired, or simply cut to allow the concrete blocks to further rotate downward to settle further into the seabed.

By connecting the flexible strap 29 to the top of each concrete block, the arrangement is such that the compressive force which i,s established between the block 20 and the pipeline would normally exceed the weight of the block. This can be seen with reference to Fig. 6 of the drawings which shows relevant forces involved. The compressive force existing between each block and the pipeline is identified by reference character C, the tensile force existing in the flexible strap is identified by reference character T and the weight of the block is identified by reference character W. The weight of the block is shown passing through the centre of gravity of the block which is identified by reference character Cg.

The resulting force squilibrium diagram shown in Fig. 7 reveals that the compressive force does exceed the weight of the block and this ensures that there is good frictional engagement between the riat structure and the 12 pipeline. This frictional engagement may be enhanced by provision of a coating of friction material at appropriate locations on the flexible base.

Frictional engagement between the mat structure and the pipeline serves two purposes, as can be seen from Fig. 8 and 9 of the drawings. Referring to Fig. 8 of the drawings it can be seen that the compressive force C generates a frictional force which resists rotation of the mat structure about the longitudinal axis of the pipeline.

00 410 Referring to Fig. 9 of the drawings, it can also be seen A 0 that the compressive force establishes a further *4 frictional force S1 which acts to resist sliding movement of the blocks along the pipeline when it is inclined in the downward direction. The frictional forces also cooperate to prevent tilting of the mat structure on the pipeline.

It is envisaged that the construction of the mat structure would provide a self-righting ability should the structure Sbe placed into, or otherwise assume, an unstable position o on the pipeline. This feature can be seen from Fig. 10 of the drawings in which the mat structure is shown in an unstable position. When the mat structure is in this unstable position, the moments of forces generated by the weights are unequal and the resultant moment has a 0 tendency to return the mat structure to an equilibrium condition on the pipeline.

In this embodiment, the pipeline 11 is assembled in sections and lowered onto the seabed from a barge 33 which is shown in Fiq, 11 of the drawings. The barge floats on the body of water 34 and is provided with a stinger which is hingedly supported on the barge at 37 and which is supported at its free end on a float 39. Roller assemblies 40 are mounted on the deck of the barge and on 13 the stinger 35 to support the pipeline as it advances into the water. The mat structures 10 are stacked on the barge and lifted into position on the pipeline 11 by way of a crane 41 which carries a lifting frame 43. The mat structures are positioned at intervals along the pipeline as it is lowered onto the seabed from the barge, the spacing between successive mats being determined according to the stabilisation requirements. Tension is maintained in the pipeline to prevent excessive sagging during the installation process. As each mat structure is positioned on the pipeline, it clampingly engages the pipeline in the manner described previously. This ensures that the mat S00.* structure does not slip along the pipeline and also 0 prevents tilting of the mat structure on tt'i" pipeline.

Furthermore it ensures that the mat structure does not dislodge from the pipeline as the latter moves with wave motion. The mat structures also provide the pipeline with rotational stability as it is lowered to the sea bed owing to the fact that the centre of gravity of the mat structure is below the centre of the pipeline.

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As the mat structure moves into contact with the seabed, it spreads outwardly to assume the position shown in Fig.

1 of the drawings where sections 13b of the base rest on the seabed and section 13a straddles the pipeline.

It should be appreciated that the scope of the invention 00 is not limited to the scope of the embodiment described.

For instance, there may be more than one row of concrete blocks on each side of the locating space 23 if desired.

Claims (17)

1. A stabilisation means for providing gravity stabilisation of an object comprising a pair of weights having upper and lower surface portions and means interconnectably linking said weights for swinging movement towards and away from each other wherein said weights are adapted to be positioned on opposed sides of said object with said linking means resting on and across the top of said object such that said weights are caused to swing into engagement with said object so as to exert compressive forces against said opposed sides of said object, each of said weights having an inner surface portion through which the compressive force is applied to said object, said linking means comprising upper and lower connections, said upper connection interconnecting the upper surface portions of said weights and said lower connection interconnecting the lower surface portions of said weights, said weights and said linking means being so shaped and dimensioned that the centre of gravity of said stabilisation means is below the geometric centre of said object when said stabilisation means is in use.

2. A stabilisation means according to claim 1 wherein said upper connection comprises a strap of flexible material.

3. A stabilisation means according to claim 1 or 2 wherein said lower connection is formed oZ a flexible material. 2 4. A stabilisation means according to claim 3 wherein I said lower connection comprises a sheet of said flexible :o material onto which said weights are mounted. 9 f 9 0*0 15 A stabilisation means according to any one of the preceding claims wherein said upper connection is anchored to the upper surface portion of each weight.

6. A stabilisation means according to any one of the preceding claims wherein said lower connection is anchored t;o the lower surface portion of each weight.

7. A stabilisation means according to any one of the preceding claims wherein each of said weights is elongated, the longitudinal extent of said weight being transverse to the inner surface portion thereof.

8. A stabilisation means according to any one of the preceding claims wherein the inner surface portion of each of icaid weights is shaped to conform to the profile of the object.

9. A stabilisation means according to any one of the preceding claims wherein said object is received in a locating space defined between said pair of weights and wherein there is provided at least one further weight on each side of said locating space. A stabilisation means according to claim 9 wherein :said weights on eaci side of the locating space are arranged in a row fir applying compressive forces against said object. @00

11. A stabilisation eans according to any one of the preceding claims wherein each weight has an outer surface portion configured fa' reduced resistance to oncoming water flow. 0 0 000 0 40000 16

12. A stabilisation means for stabilising an elongated object, said stabilisation means comprising a flexible base, at least one pair of weights mounted on the base and defining a locating space therebetween for receiving a portion of said elongated object with said base overlying and engaging a top of said portion of said object, and an upper connection interconnecting said weights, said flexible base and said upper connection co-operating to permit movement of the weights towards and away from each other whereby said weights can apply compressive forces against opposite sides of said elongated object, said weights and connection being so shaped and dimensioned that the centre of gravity of said stabilisation means is below the geometric centre of said object when said stabilising means is in use.

13. Means according to claim 12 wherein said upper connection comprises a flexible strap the ends of which are connected to said weights along the top portions thereof.

14. An underwater pipeline stabilisation means comprising a flexible water pervious blanket adapted to cover a portion of said pipeline and having an outwardly extending portion on each side of said pipeline, a weight secured to said blanket on each outwardly extending portion thereof for holding said blanket in covering engagement with said pipeline, and a flexible connector secured to each of said weights and extending therebetween for hinging said weights together, said connection extending across said pipeline when said weights are positioned on either side thereof with said blanket overlying and stabilising said pipaline. a A pipeline stabilisation means as defined in claim 14, wherein the centre of gravity of said pair of weights and said blanket is below the centre of gravity of said N *^aijj 17 pipeline when said stabilising means is mounted on said pipeline.

16. A pipeline stabilisation means as defined in claim 14 or 15, wherein said weight and blanket clampingly engage said pipeline.

17. A pipeline stabilisation means as defined in claim 14, or 16, wherein said connector comprises a strap of flexible material.

18. A method for stabilising an elongated object comprising the steps of locating and clampingly engaging a stabilisation means according to any one of the preceding claims on a section of said elongated object and lowering said section of said elongated object and the stabilisation means engaged thereon onto a support surface.

19. A method for stabilising an elongated object such as a pipeline in a body of water comprising the steps of introducing the elongated object into the body of water and attaching a stabilisation means according to any one of claims 1 to 17 on the elongated object at intervals along the length thereof as the elongated object descends towards the floor of the body of water. 0 0 S J 20. A method of stabilising an underwater pipeline during the laying and use thereof comprising applying to said pipeline during laying thereof on underwater pipeline stabilising means according to any one of claims 14 to 17, and lowering said pipeline and associated stabilising means into a body of water to rest on the bed thereof, said stabilising means gripping said pipeline during lowering thereof and holding said pipeline onto said bed after laying of said pipeline thereon. 0 18

21. A stabilisation means substantially as herein described with reference to the accompanying drawings.

22. A method of stabilising an elongated object substantially as herein described. DATED this tenth day of August, 1993 SPUNCON PTY LTD and MARECON PTY LTD Applicants WRAY ASSOCIATES Perth, Western Australia ~Patent Attorneys for Applicant .4 C a C. C. C CC C C C, eq. CO CO C C C C C C CC C 04 C C C CC a *CCC 0 C C 0* C C