Abstract:
A clamp for a flexible pipe is provided that provide a load bearing flange on the flexible pipe permitting buoyancy jackets to be joined thereto. The clamp has a longitudinal axis arranged to extend along the length of the flexible pipe and a radial axis being perpendicular to the longitudinal axis. The clamp includes: a plurality of separate clamp elements being supported together in a radial array extending at least partially around the longitudinal axis; engagement means located between neighboring clamp elements to movably interconnect the clamp elements; and a strap being adapted to surround the clamp elements, in use for exerting a compressive force thereon. Also provided is a clamp element for use in the aforementioned clamp.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a national stage entry of International Application No. PCT/AU2015/000480 filed Aug. 12, 2015, which claims the benefit of Australian Application No. 2014903243 filed Aug. 19, 2014, the entire contents of both of which are incorporated by reference herein. 
     
    
     BACKGROUND 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a clamp for a flexible pipe. 
         [0004]    More particularly, the present invention relates to a clamp for a flexible pipe to provide a load bearing flange on the flexible pipe permitting buoyancy jackets to be joined thereto. 
         [0005]    2. Description of Related Art 
         [0006]    In operations involving subsea gas and oil production, there is provided a flexible pipe or umbilical, referred to as a riser, which is used to convey product, power and communications between seabed assets and the surface. The risers require a certain strength and rigidity but must also remain flexible to offset the effects of currents in the sea. As such, the risers are normally provided in the form of a multilayered product including an outer thermoplastic sleeve surrounding an internal webbing of armor steel wire. One resultant drawback is that the risers are rather heavy and place a large amount of tension on its support. 
         [0007]    The weight of the riser can be offset by joining buoyancy jackets to the riser at selected locations. In order to prevent the buoyancy jackets from sliding upwards along the riser, clamps are attached to the riser at selected locations and the buoyancy jackets are wrapped around the clamps. It is further preferable that the clamps are able to exert sufficient force onto the riser to frictionally prevent slippage of the riser&#39;s thermoplastic sleeve over its internal webbing. 
         [0008]    Known types of clamps consist of a few bulky C-shaped bodies forming a cylindrical aperture having an internal diameter corresponding to the external diameter of the riser, and which may be joined to each other along one side by a hinge. In use, the C-shaped bodies are positioned to encircle the riser and then clamped to the riser, either by bolting the free ends of the clamp together or by surrounding the C-shaped bodies with a compression band that is tightened. 
         [0009]    One disadvantage of using such bulky C-shaped bodies in a clamp is that the clamp is not easily adaptable for use on risers having different diameters. Also, the clamps are relatively heavy and difficult to manufacture due to the bulkiness of the C-shaped bodies. 
         [0010]    These above-mentioned disadvantages have been at least partially overcome by forming the clamp from a plurality of relatively small elements, which are arranged in a radial array surrounding the riser and are supported and joined together by the compression band. However, it has been found that such an array clamp can be difficult to handle due to a lack of structural definition when it is in a rest, i.e. before being mounted onto the riser, resulting from the inherent flexibility within the compression band. 
         [0011]    It is an object of the invention to suggest a clamp for a flexible pipe, which will assist in at least partially overcoming these problems. 
       SUMMARY OF THE INVENTION 
       [0012]    According to one aspect of the present invention, there is provided a clamp for a flexible pipe, the clamp having a longitudinal axis arranged to extend along the length of the flexible pipe and a radial axis being perpendicular to the longitudinal axis, the clamp comprising: a plurality of separate clamp elements being supported together in a radial array extending at least partially around the longitudinal axis; engagement means located between neighboring clamp elements to movably interconnect the clamp elements; and a strap being adapted to surround the clamp elements, in use for exerting a compressive force thereon. 
         [0013]    Each clamp element may be wedge shaped in end view. 
         [0014]    The wedge shape may extend through a radial arc of between 5° to 20°. 
         [0015]    The wedge shape may extend through a radial arc of substantially 8°. 
         [0016]    Each clamp element may have an inner face for engaging the flexible pipe, the inner face being concave, convex or planar. 
         [0017]    The inner face may comprise an interface for increasing the compliance of the clamp element and clamp with the flexible pipe. 
         [0018]    The interface may be a resiliently deformable strip disposed along a length of the inner face. 
         [0019]    Each clamp element may have an outer face for engaging the strap, the outer face having a groove for receiving the strap. 
         [0020]    The strap may be restrained against the outer face by projections extending from the outer face, under which projections opposed edges of the strap are slidably located. 
         [0021]    Each clamp element may include opposed lateral faces, wherein the engagement means includes corresponding plug and socket formations provided on each of the lateral faces. 
         [0022]    The plug and socket formations may be integrally formed on each of the lateral faces. 
         [0023]    The plug and socket formations may be arranged to permit pivoting movement between neighboring clamp elements around the longitudinal axis. 
         [0024]    The clamp may include spacer cushions provided between neighboring clamp elements. 
         [0025]    The cushions may be resiliently deformable. 
         [0026]    The cushions may be joined to or integrally formed with the clamp elements. 
         [0027]    A number of discrete cushions may be provided, wherein the cushions radially straddle the engagement means. 
         [0028]    The clamp elements may be supported together by being mounted on at least one filament. 
         [0029]    Each clamp element may include a transverse passage for receiving the filament. 
         [0030]    The passage may extend through the engagement means. 
         [0031]    According to a further aspect of the present invention, there is provided a clamp element for use in the clamp as described herein. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0032]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0033]      FIG. 1  is a perspective view of a clamp for a flexible pipe according to an embodiment of the invention; 
           [0034]      FIG. 2  is an enlarged perspective view of a clamp element of the clamp shown in  FIG. 1 ; 
           [0035]      FIG. 3  is a side view of the clamp element seen along arrow III in  FIG. 2 ; and 
           [0036]      FIG. 4  is an end view of the clamp element seen along arrow IV in  FIG. 2 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0037]    Referring to  FIG. 1  of the drawings, there is shown a clamp in accordance with the invention, being generally indicated by reference numeral  10 . The clamp  10  is adapted to be attached to a flexible pipe or riser  12  to form and provide a load bearing flange on the riser  12 , thereby enabling buoyancy jackets (not shown) to be joined to the riser  12 . Although only a short section of the riser  12  is shown, the riser  12  can have any suitable length and is conventionally in the form of a cylindrical tube. 
         [0038]    The clamp  10  is substantially ring shaped and is formed by a plurality of discrete wedge shaped clamp elements  14  that are joined together in a radial array as will be further described hereafter. Although the clamp  10  is shown as an incomplete ring extending only partially around the riser  12 , additional clamp elements  14  can be added to the clamp  10  to fully close and complete the ring. 
         [0039]    The clamp  10  has a longitudinal axis  16  arranged to extend, in use, along the length of the riser  12  and further has a radial axis  18  being perpendicular to the longitudinal axis and being arranged to coincide with a radial axis of the riser  12 . 
         [0040]    The clamp  10  includes a tension strap  20  surrounding the clamp elements  14 . The strap  20  has opposed looped ends  22 , through each of which extends a transverse tensioning bar  24 . The bars  24  project beyond the strap  20  and can be joined to each other via their projecting ends by bolts  26 . In use, the bars  24  are drawn towards each other to tighten the strap  20  around the clamp elements  14 , thereby to force a non-slip frictional engagement between the clamp elements  14  and the riser  12 , whereafter the bars  24  are secured together by the bolts  26  to maintain the tension within the strap  20 . 
         [0041]    Referring now to  FIGS. 2 to 4 , there is shown an individual clamp element  14 . The clamp element  14  has an inner face  28  for abutting against the riser  12  and an outer face  30  for receiving the strap  20 . The clamp element  14  is wedge shaped, when seen in end view (as in  FIG. 4 ), with the inner face  28  having a smaller width than the outer face  30 . The clamp element  14  further has two lateral faces  32 ,  34  that are rotationally symmetrical around the radial axis  18 . 
         [0042]    Depending on the diametrical size of the clamp  10  to be assembled, the wedge shape of the clamp element  14  can extend through an arc of between 5° to 20°. In the embodiment shown, the wedge shape of the clamp element  14  extends through an arc of about 8°, i.e. being the relative angle between the opposed lateral faces  32  and  34 . 
         [0043]    The inner face  28  can be shaped to be concave, convex or planar, the selection of the appropriate shape being dependent on the specific application for the clamp  10  and the amount of pressure required to be applied to the riser  12 . In accordance with a preferred embodiment of the present invention, the inner face  28  comprises an interface (not shown) disposed as an additional layer mounted on the inner face  28 . The interface comprises a deformably resilient material, preferably rubber, for increasing the compliance of the clamp element  14  and clamp  10  with the riser  12  as the riser  12  and/or underlying pipe structure, for example, bends and flexes beneath the clamp  10 . It is preferred that the interface is provided as a strip, comprising a quadrilateral cross-section, disposed along substantially the full length of the inner face  28 . 
         [0044]    With particular reference to  FIG. 3 , the outer face  30  has a central channel  36 , having opposed flanges  38  on either side of the channel  36 . When the clamp  10  is assembled, the respective channels  36  of neighboring clamp elements  14  cooperate to form a circumferential groove  40  (see  FIG. 1 ) being adapted to receive the strap  20 . On the opposed sides of the channel  36 , tabs  42  project from either flange  38  and extend into the channel  36 . The tabs  42  are spaced away from the channel floor  44  and each define a recess  46  into which the outer edges of the strap  20  can be located to assist in holding the strap  20  in place within the channel  36  and the circumferential groove  40 . 
         [0045]    The clamp element  14  further includes a plug  48  and socket  50  provided on and integrally formed with each of the lateral faces  32  and  34 . The plug  48  and socket  50  are shaped corresponding to each other and are equidistantly spaced from both the inner face  28  and the radial axis  18 . Thus the plug  48  on the lateral face  32  is aligned opposite to the socket  50  on the opposed lateral face  34 . 
         [0046]    In the embodiment illustrated, the plug  48  and socket  50  are centrally aligned with the flanges  38 . When the clamp  10  is assembled, the plug  48  of one clamp element  14  is received into and engages with the socket  50  of its neighboring clamp element  14 , and vice versa, so as to interconnect the neighboring clamp elements  14 . The plug  48  and socket  50  are preferably semi-cylindrical or arc-shaped to permit a slight pivoting movement between neighboring clamp elements  14  around one axis, i.e. only relative to the longitudinal axis  16  (as seen in  FIG. 1 ) but not relative to the radial axis  18 . 
         [0047]    In other embodiments, not illustrated in the drawings, it is envisaged that the plug  48  can be substituted for a further similar socket  50  and that an independent interconnecting member, e.g. a sphere or cylindrical disc/wheel, will be received into both the sockets  50  between the neighboring clamp elements  14 . Still further, it is also envisaged that the clamp element  14  can have only a single interconnecting plug  48  and socket  50 , for example lateral face  32  will have only a plug and the opposed lateral face  34  will have only a socket. In such an embodiment, the plug and socket will be aligned along the radial axis  18  (however, in such case there will no longer be rotational symmetry around the radial axis  18 ). 
         [0048]    The clamp element  14  includes two spacer cushions  52 ,  54  respectively on each of the lateral faces  32  and  34 , with the cushions standing proud of the lateral faces  32 ,  34 . The cushions  52 ,  54  space the neighboring clamp elements  14  slightly apart from each other. 
         [0049]    The cushions  52 ,  54  are shown being provided on the same side of the radial axis  18  as the socket  50 , however, they could also be provided on the plug side of the radial axis  18 . One cushion  52  is attached to a boss  53 , being located between the socket  50  and the outer face  30 . The other cushion  54  is attached to a boss  56  being located between the socket  50  and the inner face  28 . The cushions  52 ,  54  thus radially straddle the socket  50  when the clamp  10  is assembled. 
         [0050]    On the opposed side of the radial axis  18  to the cushions  52 ,  54  and equidistantly spaced therefrom, the clamp element  14  has abutments  58 ,  60  against which the cushions  52 ,  54  of a neighboring clamp element  1  will abut when the clamp  10  is assembled. 
         [0051]    The cushions  52 ,  54  are preferably made from a resiliently compressible material. Although the cushions  52 ,  54  are illustrated as toroids, any other shaped cushions could also be used, for example circular. 
         [0052]    It is envisaged that the clamp elements  14  will be made from a thermoplastics material by injection moulding. It is further envisaged that the cushions  52 ,  54  could be moulded together with the clamp elements  14  in a two-stage injection moulding process. 
         [0053]    To avoid warping of the plastics material during the manufacturing process, the clamp elements  14  should preferably have a body thickness of less than 10 mm. However, such a thin body thickness reduces the structural rigidity of the clamp elements  14  and limits the amount of compression force that they can withstand, in use, being applied by the strap  20  before being crushed. Thus, a number of strengthening ribs  62  are provided on each lateral face  32 ,  34 . 
         [0054]    The clamp element  14  has two passages  64 ,  66  (see  FIG. 3 ), one each extending centrally through the plug  48  and the socket  50  through which filaments (not shown) can be threaded to assemble the clamp  10 . The filaments are tied off onto the terminal clamp elements  14  at either end of the clamp  10 . Advantageously, buttresses  68  (see  FIG. 1 ) can be provided at the terminal ends of the clamp  10  to assist in preserving the radial alignment of clamp elements  4 . In this way, the clamp elements  14  can be retained in the C-shaped form of the assembled clamp  10  with their plugs  48  and sockets  50  loosely interconnecting even before mounting on the riser  12 . 
         [0055]    The filaments will be tied in such a manner permitting the clamp elements  14  to move relative to each other by rotation around the plugs  48  and by corresponding compression of the cushions  52 ,  54 . Thereby the terminal ends of the clamp  10  can be parted sufficiently to allow the clamp  10  to be mounted onto the riser  12 . By the clamp elements  14  pivoting around the interconnecting cylindrical plugs  48  and sockets  50 , the cushions  54  are compressed and cushions  52  allowed to expand to open the clamp  10  sufficiently to permit it to be mounted onto the riser  12 , but without the plugs  48  disengaging from the sockets  50 . 
         [0056]    The filaments may further be tied in such a manner that a tensile load is applied, reacted by a corresponding compressive load in the cushions  52 ,  54 . The compressive force provides an even spacing between the clamp elements  14 , and further assists with maintaining the C-shaped form of the clamp  10 . 
         [0057]    The combination of forces may be such that sufficient movement in either direction is permitted, to allow the clamp  10  to open for fitment to the riser  12 , or to allow contraction of the diameter upon tightening of the strap  20 . 
         [0058]    Following the mounting of the claim  10  onto the riser  12 , the strap  20  is attached and tightened, which reduces the radial size of the clamp  10  so that it immovably locks onto the riser  12 . The radial size of the clamp  10  is reduced both by pulling the terminal ends of the clamp  10  closer to each other and also by compressing the cushions  52 ,  54  to reduce the spacing between neighboring clamp elements  14 . 
         [0059]    In a further embodiment, it is envisaged that the cushions  52 ,  54  could be rigid members capable of being destructively crushed during tightening of the strap  20 . 
         [0060]    Modifications and variations as would be apparent to a skilled addressee are deemed to be within the scope of the present invention.