WO1998037355A1

WO1998037355A1 - Clamping devices for pipelines and other tubular members

Info

Publication number: WO1998037355A1
Application number: PCT/GB1998/000347
Authority: WO
Inventors: Robert George Martin; Philippe Marie Yron Paul Secher
Original assignee: Coflexip Stena Offshore Limited
Priority date: 1997-02-20
Filing date: 1998-02-04
Publication date: 1998-08-27
Also published as: AU5995798A

Abstract

Clamping devices for attachment to the external surfaces of tubular members, such as conduits and pipes used in the offshore oil industry, and particularly applicable to tubulars having compressible coatings such as thermal insulation layers. Various embodiments of the invention are disclosed, all of which employ elastic elements which regulate the clamping force applied to the tubular in response to variations in the external diameter of the tubular, such as may result from creep of compressible coatings. Embodiments are disclosed in which the elastic elements operate in compression, in flexion and in torsion, or in combinations of these. In the preferred embodiment, the clamping forces are transmitted to the tubular via a series of flexion beams arranged around the circumference of the tubular. The invention finds particular application in securing flotation modules to flexible marine risers.

Description

"Clamping Devices for Pipelines and other Tubular Members"

The present invention relates to clamping devices intended to be attached to the external surfaces of tubular members. The invention is particularly, but not exclusively, applicable to pipelines, risers and the like for use in the offshore oil industry. Most particularly, the invention is intended for use with tubular members having compressible outer layers or coatings such as thick thermal insulation layers and protective sheaths of elastomeric and/or thermoplastic materials . The invention finds specific application in securing flotation modules to flexible risers . However, the invention is also useful as a general purpose clamp for pipelines, risers etc.

Flexible risers of the type of greatest interest for the purposes of the present invention are described in detail in API 17B (Recommended Practice) and API 17J (Specifications).

Examples of the type of thermal insulation layers most relevant to the present invention are described, for example, in EP-0162760-A and EP-0400689-A. Conventional clamps for use in locating flotation modules and the like to pipelines are of generally massive and rigid construction. Such clamps are secured to the pipe by friction created between the bearing surfaces of the clamps and the external surface of the pipe by the applied clamping force. A typical clamp arrangement might comprise two or more segments having part cylindrical bearing surfaces, the segments being secured together around the pipe by bolts extending in a tangential direction relative to the transverse cross-section of the pipe, with the clamping force being created by tensioning of the bolts.

The strength of the clamping force and of the resulting frictional forces will vary to some extent with differential variations in the outer diameter of the pipe and the inner diameter of the clamp; e.g. as a result of temperature variations or creep of the pipe and/or clamp materials . This is not generally a problem when the clamp is applied directly to a pipe formed from rigid materials (typically steel) or to a flexible pipe not having any compressible outer layers. There will normally be sufficient elasticity in the longitudinally tensioned bolts to accommodate the relatively small variations in diameter which occur with such pipes. The elasticity of conventional clamps is typically of the order of 0.1% to 0.5% of the diameter of the pipe.

Problems arise, however, when conventional clamps are applied on top of relatively flexible or deformable layers on the external surface of the pipe, such as thermally insulating layers and protective sheaths. These types of layers are typically formed from layers of elastomeric and/or thermoplastic materials, including relatively thick layers of foamed material. Such materials are liable to creep (deform radially inwardly) under the pressure of the applied clamping force, with the result that the clamping force and resulting frictional force decreases progressively over time. There is insufficient elasticity in the tensioning bolts of conventional clamps to follow the relatively large diameter variations which occur in these circumstances (typically of the order of 1% to 5% of the outer pipe diameter) . In the case of a vertical riser having flotation modules secured thereto, this means that the buoyancy force of the flotation module may cause it to move upwards along the riser as the friction between the clamp and the riser decreases.

It is an object of the present invention to provide an improved clamping assembly which will maintain a substantially constant clamping force on a pipe, even in the event of relatively large variations in the diameter of the pipe, such as may arise from creep of elastomeric and/or thermoplastic layers, coatings, sheaths or the like.

In accordance with a first aspect of the present invention there is provided a clamp assembly configured to be secured around the circumference of a tubular member, comprising: bearing means adapted to engage the surface of the tubular member, in use of the clamping assembly; clamping means adapted to generate a clamping force to be transmitted to the tubular member via said bearing means; and elastic means adapted to regulate the clamping force applied to said tubular member in response to variations in the external diameter of said tubular member. The elastic means may comprise elastic flexion members or elastic compression members or elastic torsion members, or combinations of elastic flexion members, elastic compression members and elastic torsion members .

Where elastic flexion members are employed, these may be incorporated in the bearing means or in the clamping means or both.

Where elastic compression means are employed, these may be incorporated in the bearing means or in the clamping means or both, and/or may be interposed between said inner bearing means and said clamping means.

In preferred embodiments of the invention, the clamping means comprises a plurality of outer beam members arranged around the circumference of the tubular member, in use, and connected end to end by tensioning means, and the bearing means comprises a plurality of bearing units located inwardly of and aligned with said outer beam members, means being provided for transmitting forces generated by tensioning of said tensioning means via said outer beam members to said bearing units. In these embodiments, the beam members may comprise elastic flexion members, and/or the inner bearing units may incorporate elastic flexion members.

Preferably, in these preferred embodiments, said forces are transmitted to the bearing units via a line contact between said outer beams and said bearing units.

Said inner bearing units preferably each comprises a pair of bearing shoes connected together by a beam member, which beam member may comprise a flexion member . Said line contact preferably extends in an axial direction parallel to the longitudinal axis of the tubular member at the mid-point between the pair of bearing shoes which are connected by said beam member.

Preferably, said bearing shoes comprise generally elongate members extending in said axial direction. Most preferably, said bearing shoes are connected to said beam member by means of generally elongate, planar leg members extending substantially at right angles to said bearing shoes, the bearing shoes and leg members together having a T-section configuration.

Where the beam members of the bearing units or the outer beam members of the clamping means comprise elastic flexion members, these preferably comprise planar flexion members.

In the preferred embodiments of the invention, said planar flexion members comprise plate-like spring elements. Said spring elements preferably also have a tapered configuration, such that said flexion members will bend with a substantially uniform bend radius in response to an applied load.

Said flexion members of the bearing units preferably comprise first and second spring elements extending side by side in a direction perpendicular to said axial direction and disposed so as to apply a substantially evenly distributed load to said bearing shoes extending in the axial direction.

Said outer beam members preferably have end portions at their outermost ends in the direction perpendicular to said axial direction, said end portions being angled outwardly and being adapted for connection to said tensioning means.

In an alternative embodiment of the invention, the bearing means comprises a plurality of part-cylindrical segments adapted to be arranged around the circumference of the tubular member, in use, said segments being connected together by tensioning means extending between elongate elastic flexion members extending along the lengths of said part-cylindrical segments and being mechanically coupled to said segments at or adjacent to the ends thereof.

In a further embodiment of the invention, elastic torsion means are incorporated in the bearing means or in the clamping means or both, and/or interposed between said bearing means and said clamping means.

In this case, the bearing means preferably comprises a plurality of bearing units arranged around the circumference of the tubular member, in use, each of said bearing units comprising a bearing shoe, at least one strut extending outwardly from the bearing shoe and a lever arm extending at an angle to said at least one strut from an outer end thereof; said elastic torsion means comprises a plurality of torsion members extending parallel to the longitudinal axis of said tubular member, in use, a free end of the at least one lever arm of each of said bearing units being fixedly connected to a respective one of said torsion members; and said clamping means comprises means for applying torsional forces to each of said torsion members such that said torsional forces are transmitted to said bearing shoes via said lever arms and struts.

Preferably also, said bearing units and said torsion members are arranged in pairs, and said clamping means comprises a plurality of clamping assemblies, one of which is associated with each pair of torsion members and is adapted to apply an equal and opposite torsional force to each the associated pair of torsion members.

Preferably also, said torsion members are supported between a pair of parallel, annular support members, each of which surrounds the tubular member, in use of the apparatus .

In accordance with a second aspect of the invention there is provided a pipe assembly comprising a pipe, at least one clamp assembly in accordance with the first aspect of the invention, and at least one flotation means secured around the circumference of said pipe and anchored at at least one fixed axial location thereon by means of said at least one clamp assembly.

Preferably, said pipe includes an outer layer of compressible material. Preferably also, said pipe is a flexible pipe.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

Fig. 1 is an end view of an embodiment of a clamp assembly in accordance with the invention located on a pipe;

Fig. 2 is an end view similar to that of Fig. 1, showing a flotation module located around the pipe and clamp assembly;

Fig. 3 is a sectional view on line A-A of Fig. 2; Fig. 4 is a plan view of an inner beam (or "shoe plate") and shoe assembly as seen in Fig. 3;

Fig. 5 is a plan view of an outer beam (or "bolt plate") as seen in Fig. 3;

Figs . 6 to 9 are schematic end view illustrations of further embodiments of clamp assemblies which are generally similar in configuration to the embodiment of Figs. 1 to 5;

Fig. 10 is a side view of a further embodiment of a clamp assembly in accordance with the present invention;

Fig. 11 is an end view of the embodiment of Fig. 10.

Fig. 12 is a plan view of still another embodiment of a clamp assembly in accordance with the present invention;

Fig. 13 a sectional view on line A-A of Fig. 12; and

Fig. 14 is an enlarged, sectional detail view on line B-B of Fig. 12.

Referring now to the drawings. Fig. 1 shows an end view of one example of a clamp assembly in accordance with the invention.

As seen in Fig. 1, the clamp assembly consists of a set of innermost components, or bearing means, which contact the pipe, and outer clamping means which secures the inner components to the pipe and which apply the clamping forces thereto.

The inner components, or bearing units, comprise a set of shoes 10 which bear upon the surface of the pipe 12. In this example, there are six shoes 10 equispaced around the circumference of the pipe, the shoes 10 being connected together in pairs by a first set of generally planar or plate-like beam members 14 , via radially extending legs 15. Each of the shoes 10 and legs 15 together comprise a T-section which extend in a direction parallel to the longitudinal axis of the pipe 12 (hereinafter referred to as "the axial direction").

The outer assembly comprises a second set of generally planar or plate-like beam members 16, each of which is aligned with one of the first, inner beam members 14. The ends 18 of the second, outer beam members 16 are angled outwardly from the pipe, and are connected together by bolts 20 extending through apertures (not shown) in the angled end portions and secured by nuts 22.

The outer assembly is mechanically coupled to the inner components by a single line contact 24 extending in the axial direction between each pair of respective first and second beam members 14 and 16. The line contacts (or "pivot points") 24 are located at the mid-points between the pairs of shoes 10 connected by each of the inner beam members 14. The required line contacts 24 may be provided by a length of small diameter (e.g. 5 mm) round bar. The round bar is preferably secured along its length to the inner beam member 14 with its ends projecting beyond the ends of the inner beam member 14 in the axial direction. The outer beam 16 also extends beyond the ends of the inner beam 14 in the axial direction and the ends of the round bar are secured thereto .

Accordingly, when the nuts 22 are tightened, the forces applied to the outer beams 16 are transferred to the inner beams, and thence to the shoes 10. The whole clamp assembly is thus secured to the pipe 12 by friction between the shoes and the pipe surface. Typically, such a clamp is used to provide an anchor for flotation modules (see Figs. 2 and 3) which are required to be secured to the pipe at fixed longitudinal locations.

Figs. 2 and 3 show the clamp assembly located on the pipe 12 in combination with a flotation module 26, typically comprising two semi-cylindrical components 28, 30, having internal recesses 32 dimensioned to accommodate the clamp assembly. The semi-cylindrical components 28, 30 are secured around the pipe 12 and clamp assembly by any suitable means, so that the flotation module 26 is retained at a fixed longitudinal position on the pipe 12 by its engagement with the clamp assembly.

In accordance with the present invention, the problems associated with applying clamps to pipes having coatings which are subject to creep are addressed by making the shoe plates (inner beams) 14 and bolt plates (outer beams) 16 relatively flexible and resilient. The inner and outer beams thereby act as flexion means which serve to regulate the clamping force applied to the pipe when the diameter thereof varies as a result of the coating creeping under the clamping pressure. In this example the flexion means can be regarded as leaf springs . The required characteristics of the flexion means can be obtained by adjusting the dimensions (particularly the thickness), and/or the configuration (particularly the shape when seen in plan view) and/or the materials of the shoe plates 14 and/or the bolt plates 16.

In the present example, and as best seen in Figs. 4 and 5, the shoe plates 14 and the bolt plates 16 are configured so as to bend at the same rate along their lengths perpendicular to the axial direction. In this particular embodiment, the shoe plate 14 is configured in plan view with two "spring" elements 34, 36 which extend side-by-side between the shoe legs 15 and which are connected to one another mid-way between the legs 15. Each of the elements 34, 36 tapers outwardly in each direction from the middle towards the legs 15, the two elements being connected together by a neck 38 at their widest points. The spring elements 34, 36 are also configured to be coupled to the legs 15 at optimum locations, so that the force applied to the shoes is distributed substantially evenly in the axial direction.

The bolt plates 16 each comprise a single spring element 40 which tapers in each direction from the middle outwardly to the angled end portions 15, the end portions 15 having apertures 42 for receiving the ends of the bolts 20.

The bending moment applied to the spring elements attenuates linearly outwards from the line contacts 24. The tapering of the inner and outer spring elements means that the stiffness of the spring elements also varies linearly so that the bend radius of the spring elements is substantially constant for a given applied force.

When the clamping assembly of the invention is applied to a pipe and the clamping force is applied by tightening the nuts 22, a proportion of the energy generated is stored in the leaf spring arrangement provided by the inner and outer beams 14 and 16. This energy is released as the coating of the pipe 10 creeps (deforms radially inwardly) under the clamping pressure, so as to maintain a substantially constant clamping force. Conversely, if the pipe diameter increases (e.g. as a result of thermal expansion), this is also accommodated by the spring arrangement. It will be understood that additional "layers" of spring elements might be incorporated into the assembly between the outer clamping means and the inner bearing means if necessary or desirable.

In order to avoid any risk of the ends of the T- sections defined by the bearing shoes 10 and legs 15 punching through the material of the flotation module 26, plate-like elements might be attached to the ends of the T-sections or otherwise interposed between the T-sections and the annular faces of the recess 32.

The clamp assembly may be formed from any suitable materials having regard to the required mechanical characteristics of the device and the environment within which it is to be deployed, and should be as light in weight as possible so as not to negate the buoyancy of the flotation module. Typically, the clamp assembly might be formed from stainless steel. Lightweight metals or alloys such as titanium or the like might be employed if economically justifiable, and certain types of plastic may also be suitable.

Accordingly, the elastic means incorporated in the assembly serve to regulate the clamping force in response to variations in the pipe diameter. They also serve to avoid undesirably high forces being applied through the coating to the pipe itself. This is particularly important when the pipe is of the flexible type.

Improvements and modifications may be incorporated without departing from the scope of the invention. In particular, it will be understood that the "elastic means " of the invention may be implemented in any of a variety of ways other than the example provided by the detailed embodiment disclosed herein. The general configuration of the clamp assembly as a whole might also be varied. Figs. 6 to 14 are simplified schematic illustrations of a number of such possible variations.

Figs. 6 to 9 show examples of variations which are similar in their basic configuration to the detailed embodiment described above and having certain combinations of features in common therewith. In each of these cases the pipe is identified by numeral 100 and the tensioning means (e.g. bolts and nuts) by numeral 102. Outer elastic means, where present, are identified by numeral 104, inner elastic means and bearing shoe assemblies, where present, by numeral 106, and components providing line contact between outer and inner assemblies or components by numeral 108.

The clamp assemblies in these examples can be seen to consist of three "segments" arranged around the pipe 100. The number of segments employed can be varied as required. Additional constructional details not described below can be inferred from the embodiment of Figs. 1 to 5.

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The elastic means in this example comprises elastic flexion beams 134 extending along each side of each bearing member 130, between and supported by the two lugs 132 at each end of each side, (in Fig. 11, the flexion beams 134 have been omitted from the left hand side of the drawing) .

The clamping force is applied by tensioning means 136, typically nuts and bolts as in previous examples, connecting the adjacent flexion beams of the two bearing members 130. As in the other embodiments, the elasticity of the flexion bars serves to regulate the clamping force applied to the pipe 100 in the event of the diameter varying because of creep of coating materials or for any other reasons.

Figs. 12 to 14 illustrate still another variation, in which the "elastic means" of the clamp operate in torsion, rather than in flexion or compression. This embodiment again employs pairs of bearing shoes 140 which engage the surface of the pipe/tubular 100. Each of the bearing shoes 140 is supported by a generally cylindrical shaft 142 extending substantially parallel to the longitudinal axis of the pipe 100. Each of the shafts 142 is supported at either end by connection to respective annular plates 144, which have an internal diameter 146 (Fig. 13) providing a loose fit about the outer diameter of the pipe 100. The shafts 142 are mounted so as to be freely rotatable with respect to the annular plates 144, and are disposed in pairs, each pair of shafts 142 being associated with a pair of bearing shoes 140.

Each of the bearing shoes 140 is fixedly connected to the associated shaft 142 by first and second outwardly extending struts 148, spaced along the length of the shoe 140, the outer end of each strut being connected to an end of a lever arm 150, the other end of which is fixedly connected to the shaft 142. The lever arms 150 of each pair of shafts 142 extend away from each other, so that the associated bearing shoes 140 extend along the "outside" of the pair of shafts 142.

In this example, the clamping force is applied by means of a screw-threaded tensioning member 152 associated with each pair of shafts 142. Each shaft has a tensioning arm 154 located at the mid-point thereof and extending inwardly towards the pipe 100. The tensioning member 152 extends between and through the tensioning arms 154 adjacent the innermost ends thereof, away from the shafts 142, the clamping force being applied by means of nuts 156. As can be seen in Fig. 14, tightening the nuts 156 forces the lowermost ends of the tensioning arms towards each other in the direction of the arrows F. This transmits torsional forces to the shafts 142 in the direction of the arrows T. The torsional energy stored in the shafts 142 is in turn transmitted via the lever arms 150 and struts 148, pressing the bearing shoes 140 into contact with the pipe 100.

The shafts 142 thus act as elastic torsion members. Torsional energy can be stored in the shafts 142, enabling the clamp to accommodate variations in the diameter of the pipe as in the previous embodiments.

Further variations may be envisioned incorporating combinations of flexion and/or compression and/or torsion members to provide the required elastic properties .

It will be understood that certain design features of conventional clamps may be equally applicable to clamps in accordance with the present invention. With regard to the bearing contact between the clamp and the pipe surface, for example, the bearing surfaces or shoes or the like may be configured to provide substantially continuous contact over the area of bearing contact, or contact may be distributed among discrete portions of the total bearing area ("punctuated contact").

The advantages of the present invention may be appreciated by considering an example of a flotation module secured by a clamping assembly to a vertical riser formed from flexible pipe having a thermally insulating layer. A typical flotation module might have a buoyancy force of 300kg. Hydrodynamic effects in service might increase this to 500kg. By contrast, hydrodynamic and buoyancy effects during initial installation might be as high as 1000kg. A friction coefficient of 0.1 between clamp and pipe dictates a total clamping force of 10 tonnes for the installation phase. This can reduce to 5 tonnes in service.

With a conventional clamp, a reduction in diameter of the pipe of as little as 0.5% will result in the clamping force being reduced to zero. The elastic clamp assemblies provided by the present invention may be configured to provide sufficient opposition to the buoyancy force of the flotation module in long term use for pipe diameter reductions of the order encountered with thermally insulating layers and the like. It can be seen, therefore, that the invention provides a substantial improvement in the performance of the clamp over conventional practice in the art.

Claims

1. A clamp assembly configured to be secured around the circumference of a tubular member, comprising: _. bearing means adapted to engage the surface of the tubular member, in use of the clamping assembly; clamping means adapted to generate a clamping force to be transmitted to the tubular member via said bearing means ; and elastic means adapted to regulate the clamping force applied to said tubular member in response to variations in the external diameter of said tubular member.

2. A clamp assembly as claimed in Claim 1, wherein said elastic means comprise elastic flexion members or elastic compression members or elastic torsion members, or combinations of elastic flexion members and/or elastic compression members and/or elastic torsion members .

3. A clamp assembly as claimed in Claim 2, including elastic flexion members incorporated in the bearing means or in the clamping means or both.

4. A clamp assembly as claimed in Claim 2, including elastic compression means incorporated in the bearing means or in the clamping means or both, and/or interposed between said bearing means and said clamping means.

5. A clamp assembly as claimed in any preceding Claim, wherein the clamping means comprises a plurality of outer beam members arranged around the circumference of the tubular member, in use, and connected end to end by tensioning means, and the bearing means comprises a plurality of bearing units located inwardly of and aligned with said outer beam members, means being provided for transmitting forces generated by tensioning of said tensioning means via said outer beam members to said bearing units .

6. A clamp assembly as claimed in Claim 5, wherein the beam members comprise elastic flexion members, and/or the inner bearing units incorporate elastic flexion members.

7. A clamp assembly as claimed in Claim 5 or Claim 6, wherein said forces are transmitted to the bearing units via a line contact between said outer beams and said bearing units .

8. A clamp assembly as claimed in any one of Claims 5 to 7, wherein said inner bearing units each comprises a pair of bearing shoes connected together by a beam member .

9. A clamp assembly as claimed in Claim 8, wherein said beam member comprises a flexion member.

10. A clamp assembly as claimed in Claim 8 or Claim 9 when dependent from Claim 7, wherein said line contact extends in an axial direction parallel to the longitudinal axis of the tubular member at the mid- point between the pair of bearing shoes which are connected by said beam member.

11. A clamp assembly as claimed in Claim 8, Claim 9 or Claim 10, wherein said bearing shoes comprise generally elongate members extending in said axial direction.

12. A clamp assembly as claimed in Claim 11, wherein said bearing shoes are connected to said beam member by means of generally elongate, planar leg members extending substantially at right angles to said bearing shoes , the bearing shoes and leg members together having a T-section configuration.

13. A clamp assembly as claimed in any one of Claims 8 to 12, wherein the beam members of the bearing units or the outer beam members of the clamping means comprise elastic flexion members .

14. A clamp assembly as claimed in Claim 13, wherein said flexion members comprise planar flexion members.

15. A clamp assembly as claimed in Claim 14, wherein said planar flexion members comprise plate-like spring elements .

16. A clamp assembly as claimed in Claim 15, wherein said spring elements have a tapered configuration, such that said flexion members will bend with a substantially uniform bend radius in response to an applied load.

17. A clamp assembly as claimed in Claim 15 or Claim 16, wherein said flexion members of the bearing units comprise first and second spring elements extending side by side in a direction perpendicular to said axial direction and disposed so as to apply a substantially evenly distributed load to said bearing shoes extending in the axial direction.

18. A clamp assembly as claimed in any one of Claims 5 to 17, wherein said outer beam members have end portions at their outermost ends in the direction perpendicular to said axial direction, said end portions being angled outwardly and being adapted for connection to said tensioning means.

19. A clamp assembly as claimed in any one of Claims 1 to 3, wherein said bearing means comprises a plurality of part-cylindrical segments adapted to be arranged around the circumference of the tubular member, in use, said segments being connected together by tensioning means extending between elongate elastic flexion members extending along the lengths of said part- cylindrical segments and being mechanically coupled to said segments at or adjacent to the ends thereof.

20. A clamp assembly as claimed in Claim 1 or Claim 2, including elastic torsion means incorporated in the bearing means or in the clamping means or both, and/or interposed between said bearing means and said clamping means.

21. A clamp assembly as claimed in Claim 20, wherein: said bearing means comprises a plurality of bearing units arranged around the circumference of the tubular member, in use, each of said bearing units comprising a bearing shoe, at least one strut extending outwardly from the bearing shoe and a lever arm extending at an angle to said at least one strut from an outer end thereof; said elastic torsion means comprises a plurality of torsion members extending parallel to the longitudinal axis of said tubular member, in use, a free end of the at least one lever arm of each of said bearing units being fixedly connected to a respective one of said torsion members; and said clamping means comprises means for applying torsional forces to each of said torsion members such that said torsional forces are transmitted to said bearing shoes via said lever arms and struts.

22. A clamp assembly as claimed in claim 21, wherein said bearing units and said torsion members are arranged in pairs, and said clamping means comprises a plurality of clamping assemblies, one of which is associated with each pair of torsion members and is adapted to apply an equal and opposite torsional force to each the associated pair of torsion members.

23. A clamp assembly as claimed in Claim 21 or Claim 22, wherein said torsion members are supported between a pair of parallel, annular support members, each of which surrounds the tubular member, in use of the apparatus .

24. A pipe assembly comprising a pipe, at least one clamp assembly as defined in any one of Claims 1 to 23, and at least one flotation means secured around the circumference of said pipe and anchored at at least one fixed axial location thereon by means of said at least one clamp assembly.

25. A pipe assembly as claimed in Claim 24, wherein said pipe includes an outer layer of compressible material.

26. A pipe assembly as claimed in Claim 24 or Claim 25, wherein said pipe is a flexible pipe.