GB2391255A - Buoyancy clamp and method of application - Google Patents

Abstract

A clamp for securing to a pipe or flowline for mounting buoyancy thereon, the clamp comprising <SL> <LI>i) a clamp body having surfaces against which buoyancy may abut <LI>ii) means for urging the clamp towards the pipe, and <LI>iii) a radially resilient member capable of expanding or contracting to conform to changes in diameter of the pipe. </SL>

Description

Buoyancy Clamp and Method of Application lately of the Invention This

invention relates to a clamp for clamping buoyancy to an object.

5 More espy eciall) I ut not exclusively the invention relates to clamps for clamp distributed buoyancy to subsea risers and umbilical lines.

Hereinafter the word "flowline" will be used to embrace risers and umbilical lines.

In order to extract hydrocarbons from underwater it is often necessary to provide Bowlines extending from the seabed to the surface. If the flowline severely depended from a surface mounting the weight of the dependent flowline would unless the flowline was made 15 uneconomically strong be likely to part. In order to prevent this buoyancy is mounted around the flowline along its length. It is not however possibly to merely bolt the buoyancy to the flowline.

All Bowlines are made to a manufacturing tolerance on diameter which so means that the actual diameter of the flowline will probably differ from a nominal size. Buoyancy or clamps machined to fit the nominal size flowline will be too small for a flowline larger Man nominal and too small for a flowline larger than nominal. In either case the buoyancy will not be secured to the flowline with optimal efficiency and it may not be 25 able to resist the upthrust up on causing it to shift. In some cases

ó sc,cu, Wig liSiatc11 siz.] L31V t' in tic 1, cause Lla'llagL: try the flC,A'lile.

Not all floulines al e of constant diameter in any event. Some flo,lines 5 such as flexible risers arL: maL1e of material which expands or contracts in response to changes in internal pressure of the contents, the load, ambient temperature or the temperature of the Bowline contents.

-; Additionally some Bowlines are not in a straight line and bending of the 0 Bowline requires the buoyancy to be of larger diameter than when the Bowline is linear.

Furthermore some Bowline materials creep. Creep is long term dimensional change in response to load.

To overcome these problems the present applicants devised a so-called riser clamp which is described in GB 2 286 649. This product since, much unitated, comprises a flexible clamp which is clamped around the riser or Bowline. Because the clamp is flexible it can conform closely to the 20 flow line. A buoyancy member can be provided with a pocket which has surfaces engaging the clamp. Buoyancy load is therefore transferred from the buoyancy to the Bowline.

While this invention went a considerable way towards overcoming the 25 problem of installing buoyancy onto flowlines the solution was not

pe fact cllLt llc, calf ?r,lle'1 c,laiilecl. I;tllati is [ill1L' CtlilSUllill will ilivOl\,6S a large luL of loose. ts. \7lle is attempting to irstall tle riser clangs On an exposed deck of a pi?elay vessel in extol eme conditions the desiral ility of quick instL..lation Faith 5 fey, arts to get lost quick!,' echoes apparent.

In installing the bolts fastening the clamp together there is a danger of cross-threading the bolts with the risk of heat build-up and degradation of physical properties.

While the clamp described in GB 2 286 649 goes some way towards providing an even pressure distribution about the flop line and succeeds to much greater extent than rigid clamps as described for example in GB 2 288 205 still more even pressure distribution would be desirable.

The invention seeks to reduce at least some of the problems with the prior art devices.

(! Summary of the Invention

20 According to the invention there is provided a clamp for securing to a pipe for mounting buoyancy thereon, the clamp comprising i) a clamp body having surfaces against which buoyancy may abut ii) means for urging the clamp towards the pipe, and

iii), racliallv esiililt lenlcr cabal le calf cxpaniing of Ct1ltrtlCtiil to coforn to CllDIlgeS in diameter of the pipe.

Brief Vescl iption of Drawings EmLoLiimcnts Off tile invention will be descriled bit way of non-linuting example bit reference to the accompanying figures of which Figure l is a perspective view of a first embodiment of the invention -- lo mounted on a pipe Figure 2 is a partially sectioned end elevation of a clamp having buoyancy mounted thereon, 5 Figure 3 is a view of a further embodiment of the invention.

Description of Preferred Embodiments

Prior art clamps have relied on the resilient properties of materials such

as Kevlar ( 3) and titanium which have low stiffness to strength ratios.

20 Kevlar A) being superior in these properties to titanium. However the available elasticity in these systems is often marginal or insufficient for service requirements. In accordance with the invention a radial spring comprising a resilient materials such as resilient polyxneric material for example elastomers such as compounded natural or synthetic rubbers 25 are interposed between the pipe and the means for exerting a clamping force on the pipe.

l l Referring to l;iu e 1 clam} 1 comprises clam Lotte 2. I)esi al b, the, stiffness of clamp body 2 is anisotropic. Prefer at ly clamp Rocky 2 is flexible in the sense of confoung to the pit e but rigid in a direction 5, arallel with the axis of the pipe 3.

Clamp b ody 2 could for example be tnade of a fibre for example glass, metal carbon or mixtures thereof' reinforced plastics (ERP) material. The plastics matrix may comprise for example epoxy, polyester, vinyl ester 1 O or other thernosetting resins. Appropriate lay-up of the fibres can assist in achieving the desired anisotopy in stiffness. Those skilled in the art will be able to devise other suitable materials.

FRP is particularly suitable because it has other properties useful in a 15 cramp body.

First FRP allows the clamp body to be of low weight. While FRP is of greater density Man water (typical values may be in the range 1 600 to 2 600 kgm-3) the damp can be made of relatively thin section material and 20 thus the clamp body can be lightweight. This is desirable because it means that the clamp body can be handled more easily than a heavier clamp body. Dense and heavy cleanups can have negative buoyancy which must be offset by the positive buoyancy clamped to the pipe. This buoyancy is expensive and bulky.

. Ail , I 1

(] l. A; i::: 4: 841)' bL'CtitI.t' tllL' 14ll' iS [1Oxilt' it Ct]ll(-ll.S \N't'11 tat tllL' t?ipC' CSpOCiOll)! '11011 slitted lay' tllC I8clill St Lillian tO 1 L1-il10] 11CillOftL'l-.

Allis r esults in gco1 ressure distril: lotion ar cund the Blip e and thus reducing the likelilcod of Leigh local loading and pit e damage which 5 call occur Title stiff clips.

Because FRP is tough and resilient L r ittle fracture which can occur with other materials such as thick syntactic foam during installation or subsequently is much less likely.

HydrocarL on or other material passing through the pipe can be learns or hot. Some of the heat will be transferred to the pipe's surroundings.

Syntactic foam is a good thermal insulator and so heat transferred to it will be retained resulting in local heating of the clang or pipe. Since 15 physical properties are often strongly dependent on temperature and local heating can degrade performance. FRP being of relatively high thermal conductivity and used in relatively thin section in contrast dissipates heat fairly well preventing local overheating. Heat dissipation is however unlikely to be sufficiently great as to cause problems with 20 hydrate formation, waxing or large increases in viscosity of the hydrocarbon contained in the pipe.

Clamp body 2 may comprise a single C shaped member or it may comprise a plurality of sectors. In the illustrated embodiment five 25 sectors are provided to give good, even transfer of load.

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(:IC\111}1 lc,1) 2 is}?IO\'IL11 Vito cl 1-alit\! calf t'psta1i' finest aaiil.st which in use tle l uoyanc,' call aI ut. U}pOrtilig rib s 5 are} rovided to revent breakage of the fins. Care 1las to be taken that the ills dc, clot 5 stiffen excessive!,' the Clip. In the L'lill3ldimOnt of figrrc 1 Sue}rotting rib s 5 are yrovic1ec1 on only one side of each fin 4. Additionally tile flat faces of the ribs 5 form surfaces against whirls in use the buoyancy may abut thereby transferring load to the flov, line.

10 Fins 4 have a slot provided therein through which passes a strap 6. Shap 6 is intended in use to be tightened sc' as to urge the clamp body 2 against the pipe 3 thereby causing the clamp 1 to be mounted firmly to the pipe and able to transfer buoyancy load to the pipe. In the illustrated embodiment strap 6 comprises titanium. GB 2 288 205 15 describes a titaniun, strapped riser clamp but in this clamp the titanium strap functions in a different way from that of the strap of the invention.

In the strap of GB 2 288 205 titanium is employed principally for its elasticity which allows the pipe and associated clamp to differ in size for a nominal dimension. In the present invention titanium is used 20 principally for other reasons notably to control the relative orientation and position of the individual sections of the assembly since it is less flexible than Kevlar(. Titanium is well known in the art for its lightweight and resistance to corrosion by seawater which properties are useful in the present invention.

( a I ll-al? ( is ill lllL'cllllt)LlilllL'llt (l l'it.7tIl-t' I PI\'j(1L'L1 ^'itll OXi.S Ban te' Its, to Ill it is V!c'llLLl ctllL' isc, SC'CU] L'Li. t C311 Len' much easier tc, control the dimensions of this arrangement than to control to dimensions of a Ke\lar stray. l his allows the axis bars to 5 1 e joint lair shorter bolts to vehicle mCans that less time is r equireL1 to fastest tl,L, clamp to the pipe which can be imp or tent in off-shore installation. As will be apparent hereinafter the clamp of the inventions works in a different way from prior art clamps such as described in GB 2

288 205. In the present invention elasticity is not principally provided b 10 the strap 6 but by a resilient layer to be described hereinafter. Since the strap 6 is not functioning primarily as an elastic member it need not be strained as highly as in the prior art arrangements as described in GB 2

288 205. Since the sh ap is not subject to strain creep is much less of a problem than with the prior art titanium strapped clamp. Additionally

5 since the strap is subject to much less strain than in the prior art

arrangement there is less heating of screw-threaded fasteners 8 and hence a reduce likelihood of galling of the thread.

It will additionally be noted that the axis bars are inboard of the strap 20 edge reducing the bending moment of the strap ends and removing the maximum bending moment away from the strap edge. This reduces the prospect of damage or faults at the edge which can result in crack propagation.

- l ) $:. C:lcal< ill L1 jI11L'\1SI(] of- tile (1LSiL.111 l]]lil]C3l it is Ill the, present inVelltitn pr illei} all\1ccomI11odated not so nod by elasticity' of the strap as by a r cactial spring ilterposei Let wee the means exerting load on the p ipe and the pipe itself. In the embodiment of figure 1 the 5 radial spr ing comprises cl resilient layer 9 intermediate to strap and the clamp body 2. It will Lee ap F,arelt to the skilled worker and exemplified hereinafter that the r esilient layer 9 need not lie intermediate the clamp body and the pipe b ut could lie inboard of the clamp body.

10 Resilient layer 9 comprises an elastomeric layer for example of compounded natural or synthetic rubbers. This layer is able to take up differences in size frown a nominal value. The material should be resistant to stress relaxation which is long term change in load in response to fixed displacement.

Resilient layer 9 serves a number of purposes. As noted its principal Function is to accept changes in dimension from the nominal design value whether as a result of manufacturing tolerance or movement in service. To achieve this the resilient material conforms to changes due to 20 dimensional change in the pipe. Some resilient materials such as rubber have a high Poisson's ratio which means that while resilient they are almost incompressible. This means that spaces need to be provided into which the resilient material can move. This can conveniently be achieved by providing the resilient material in a plurality of spaced 25 apart sections or in a single section with a plurality of gaps. In the

l l 1). .. It >i l imp 1 lilt' t'silit'llt 10\'t'' to ball Lefty into tilt' same 1 () acljacclt tic the axis l:'ars.

Provicieci that the coefficient elf friction between the resilient layer and at 5 Iciest lisle of to ctlcr ccm}'onents atyRillSt \\rhiC]] it abuts is low r esilielt layer 9 has another acivantage Lamp ecially vat lien the resilient layer 9 lies intermediate tile strap and the clamp body. In the prior art arrangements

relative movement between the strap and the clamp body may not occur due to the "capstan effect" of the strap passing around touch of the lo clamp body. The resilient layer facilitates relative movement and hence allows mor e efficient transfer of load.

In the illush-ated embodiment a plurality of plastics rods 11 extend between ends of the clamp thereby keeping the strap and resilient layer IS captive and thus enhancing handleability of the clamp prior to and during fitting.

As can be seen from Figure 2 once installed around the pipe the clamp is jacketed by a buoyant body provide with a pocket which bears against Jo the fins thereby transferring buoyancy load to the pipe.

Those skilled in the art will have no difficulty in devising suitable buoyant materials. In an embodiment of the invention the buoyant material comprises glass reinforced epoxy macrospheres 1000 25 encapsulated in epoxy syntactic foam 1001. The buoyancy can have an

I l, f t t l l intL.t,rtil t7k] ill rt' einfrce1 plastic skin 1002 ^, IlicIl ma)' be pro\'idec vat ith alit a,tifulin coaling fair example as descril?e1 in GI3 01 3() 452.6 the cliscIsure of hick is incorporated herein by reference.

The arrangement calf I:ig 1 is by no means the only wait in urllich the 5 invention can 1 e eml odied.

Figure 3 illustrates a further embodiment of the invention. In this embodiment clamp body 102 comprises for example a fibre-reinforced material. Once again the body is desirable flexible in the sense of 0 confornung to the pipe but relatively rigid in the direction of the axis of the pipe.

Intermediate the clamp body 102 and the pipe lies radial spring member 109. In this embodiment rather than simply comprising a layer of 5 resilient material radial spring member or resilient layer 109 comprises a plurality of arcuate resilient leaves. Resilient layer 109 can then take up changes in dimension of the pipe from a nominal as described by reference to the embodiment of Figure 1. It will be apparent to the skilled worker that shapes other than resilient leaves can be adopted 20 example include waisted tubes.

The embodiment of Figure 3 does not require a discrete strap: body 102 provides the strapping functionality. Body 102 comprises a pair (or other number including one) of body members. The free edges 120 of body 102 25 arc urged together to exert a load on the pipe. In the illustrated

( I ? '. I l l c'lllclilL'llt tllt'L3)' IllOl11IS Ol-L' jclillOc1 fit OC CXtI-lit)' L3!' SClL'' tllRc3OtiCti fastOl1L'rs 108 and at the other lay pivot 110. Me clang may conveniently l c recounted Oil the pipe l: y mounting the screw thread fasteners in position lay hand or using a nut runner or other tool in the 5 al stance of significant load. The clamp is then placed around the p ipe and the ends 122 carrying the pivot hole 121 urged together with a temporary clamp until a pivot pin can lee inserted in the pivot holes. The temporary clamp can then be removed leaving the clamp positioned.

This fastening technique avoids the need to fasten screw-threaded 0 fasteners under heavy load.

Claims (11)

lS Claims

1. A clamp for securing to a pipe or flcwline for mounting buoyancy thereon, tle clamp comprising 5 ill) clamp body having surfaces against vehicle L uoyanc) mail abut v) recleans for urging the clamp towards the pipe, and vi) a radially resilient mender capable of expanding or contracting to conform to changes in diameter of the pipe.

2. A clamp as claimed in claim 1 wherein the radially resilient material lies intermediate the means for urging the clamp towards the pipe and the clamp body.

5

3. A damp as claimed in claim 1 or claim 2 wherein the radially resilient material comprises a polymeric material

4. A clamp as claimed in claim 3 wherein the polymeric material comprises compounded natural or synthetic rubber.

5. A clamp as claimed in any one of the preceding claims wherein the radially resilient material is spaced apart from adjacent material to which it is not bonded at a plurality of locations.

. A Cl'lli a,; cli',d ill Of])' <A f [I],[IL]UIl1, Lairs!|OjI) AL c1}? L Ate cc,llp ises a fir', cifo cod}elastics stub ial.

7. A clarity as clainletl in claim 6 A,lerei the fibre reinforced plastics 5 material comprises thermosetting resin come rising e} oxy, polyester, vinyl ester or mixtures thereof reinforced lay fibres of one or none of glass, carbon or metal.

8. A clamp as claimed in any one of the preceding claims wherein the l o means for urging the clamp body toward the pipe comprises titanium or Kevlar() (poly-paraphenylene terephthalamide).

9. A clamp for securing to a pipe or Bowline for securing buoyancy thereon substantially as described herein by reference to any one is or more of the figures.

10. The use of a clamp as claimed in any one of the preceding claims i in mounting buoyancy on a pipe or Bowline.

20

11. A method of mounting buoyancy on a pipe or Bowline the method comprising the steps of a) mounting a clamp comprising i) a clamp body having surfaces against which buoyancy may 25 abut,

ii) 111L)aI1S {] LI] \,i])h {I1L] L 111p L1OL], tt)l'Li tilt, tlipL', 01lL iii) a radially r esilient enltr capaL to of exit ancling or contracting Kit conform to changes in diameter of tint, p ipe about the pipe, 5 b) urging the clamp body towards the pipe and c) mounting buoyancy on the clamp body (..., it.