GB2389154A

GB2389154A - A seal assembly for dividing an annular space defined between the inner and outer pipes of a double-walled pipeline

Info

Publication number: GB2389154A
Application number: GB0305719A
Authority: GB
Inventors: Michael Antoine Joseph Ca Bell
Original assignee: Coflexip SA; Coflexip Stena Offshore Ltd
Current assignee: Technip Energies France SAS; Technip UK Ltd
Priority date: 2002-05-31
Filing date: 2003-03-13
Publication date: 2003-12-03
Anticipated expiration: 2023-03-13
Also published as: DK1509719T3; GB0305719D0; FR2840383B1; ATE463695T1; DE60332014D1; FR2840383A1; GB2389154B

Abstract

A seal assembly for dividing an annular space defined between an inner and an outer pipe in a double-walled pipeline, the seal assembly comprises an annular member 1 which fits in the annular space; and at least one longitudinal conveying means 6 passing through the annular member 1. The longitudinal conveying means 6 communicates with the annular space on either side of the seal assembly. The longitudinal conveying means may typically comprise electrical or heat conducting means or an optical fibre.

Description

2389 1 54

Seal Assembly 1 The present invention relates to double-walled 2 pipelines used for transporting fluids such as oil 3 and gas. In particular it relates to a seal 4 assembly (also referred to as a water stop) for use 5 in sealing an annular space between an inner pipe 6 and an outer pipe in such a double-walled pipeline.

8 Pipelines carrying heavy or crude oil need to be 9 thermally insulated as heavy oil tends to solidify 10 during transport from a subsea production well to 11 the surface due to heat losses in the submerged 12 pipeline. Thermal insulation is also required to 13 avoid the formation of hydrates which can occur for 14 certain crude oil compositions when the crude oil 15 cools down, for example, when there is a breakdown 16 in production flow rate.

18 Production lines which require a high level of 19 thermal insulation typically use a double-walled 20 pipe structure, for example a pipe-inpipe system.

21 A pipe-in-pipe system comprises an internal pipe

/ 1 within an external pipe separated by an annulus 2 volume. In such a structure, the annular space can 3 be filled with thermal insulation material. This 4 structure has the advantage that the external pipe 5 keeps the annular space dry and so, for example, in 6 subsea pipelines, the thermal insulation material is 7 protected from water. A further advantage of this 8 structure is that the pressure in the annulus can be g different from that outside the external pipe and 10 that inside the internal pipe. This is important if 11 the insulating material has a particular pressure 12 requirement or if a vacuum or partial vacuum is to 13 be used for insulating purposes. For example, the 14 annulus can be at atmospheric pressure while the 15 hydrostatic pressure experienced by the external (or 16 carrier) pipe and the internal pressure of the fluid.

17 in the internal pipe (flowline) are different.

18 Furthermore it is interesting to lower the pressure 19 in the annulus in order to increase the thermal 20 insulation performance.

22 One of the problems associated with such pipelines 23 is that of safeguarding the annular space against 24 the ingress of water, for example due to leaks in 25 the external or carrier pipe. Water in the annular 26 space will conduct heat from the inner flowline to 27 the carrier pipe thus destroying the effectiveness 28 of the insulation. This problem has been approached 29 in prior art pipe-in-pipe systems by

30 compartmentalizing the annular space by means of

( 1 permanent seals (GB 2 317 934, US 2 930 407, WO 2 00/09926).

4 Such prior art seals or waterstops are useful for

5 compartmentalisation of the annulus in the 6 longitudinal direction so that it can remain 7 partially dry in case of a leak in the carrier pipe.

8 However, such an arrangement has a major drawback 9 when it is desired to combine passive thermal 10 insulation with an active heating system which may 11 require the use of electrical cabling or hoses with 12 heat transfer fluid. Waterstops create 13 discontinuities and block passage of any equipment 14 running along the length of the production line, 15 such as that which may be required for an active 16 heating system.

18 The above problem is addressed by the seal assembly 19 of the present invention.

21 In accordance with the invention there is provided a 22 seal assembly for sealing an annular space defined 23 between an inner and an outer pipe in a double 24 walled pipeline comprising an annular member and at 25 least one longitudinal conveying means passing 26 through the annular member, wherein said 27 longitudinal conveying means communicate with the 28 annular space on either side of the seal assembly.

30 Typically, the longitudinal conveying means 31 comprises one or more electrical conduction.

2 Preferably the longitudinal conveying means 3 comprises one or more heat transfer means and one or 4 more optical fibres housed within optical fibre 5 housing tubes.

7 Embodiments of the invention will now be described, 8 by way of example only, with reference to the 9 accompanying drawings in which: 11 Figure 1 is a cross-sectional view of a seal 12 assembly according to the present invention; 14 Figure 2 is a cross-sectional view, taken along the 15 line A - A' in Figure 3, of a seal according to the 16 invention, with internal and external pipes shown in 17 broken lines; 19 Figure 3 is a plan view of a seal assembly according 20 to the invention; 22 Figure 4 is a sectional view of the seal assembly 23 shown in Figure 3 taken along the line A-A'; 25 Figure 5 is a sectional view of the seal assembly 26 shown in Figure 3 taken along the line B-B'; 28 Figure 6 is a sectional view of the seal assembly 29 shown in Figure 3 taken along the line C-C';

( 1 Figure 6a is a view of the tie-straps shown in 2 Figure 6 from position E; and 4 Figure 7 is a perspective view of a seal assembly 5 according to the invention.

7 With reference to Figures 1 to 5, a seal assembly 8 comprises an annular member (1), having a body (2) 9 with inner and outer lips (3, 4), and longitudinal 10 conveying means (6) passing therethrough. The 11 annular member (1) may further comprise an insert 12 (5) of steel or the like for strengthening / 13 rigidity purposes.

15 The inner and outer lips (3, 4) preferably extend 16 beyond the inner and outer circumference of the body 17 (2) of the annular member (1). The inner and outer 18 lips (3, 4) are preferably made of a resilient 19 deformable material, typically a rubber or 20 elastomeric material such as polyurethane for 21 example. The body (2) of the annular member (1) is 22 preferably made of a more rigid material, such as a 23 harder polyurethane material, and may contain a 24 strengthening insert (5) typically made of nylon or 25 metal for example.

27 When the seal assembly (1) is inserted into the 28 annular space between the inner and outer pipes (9, 29 10) of a pipe-in-pipe system (as shown in Figure 2) 30 the inner and outer lips (3, 4) are deformed wedging 31 the annular member (l) in place. Thus the inner lip

l 1 (3) forms a liquid tight seal against the outer wall 2 (11) of the inner pipe (9) and the outer lip (4) 3 forms a liquid tight seal against the inner wall 4 (12) of the outer pipe (10), 6 Preferably said longitudinal conveying means (6) 7 comprises electrical conducting means traversing the 8 water stop. Typically the electrical conducting 9 means may be in the form of a cable or of a rod.

10 The electrical conducting means may comprise a rod 11 traversing the waterstop that is connected at either 12 end, via suitable connection means, to a cable 13 running along the inner pipe between waterstops.

14 The use of a rod with a relatively large cross 15 section inserted directly within the waterstop body 16 to convey electrical power alleviates the problem of! 17 overheating which could occur when using electrical 18 heating cables inserted directly in the waterstop 20 A sleeve (8) may be provided at the point between 21 the inner and outer lips (3, 4) where the 22 longitudinal conveying means exits the seal 23 assembly. The sleeve (8) surrounds the longitudinal 24 conveying means (6) and is moulded from the 25 waterstop body (2). When the longitudinal conveying 26 means (6) comprises a rod for conveying electrical 27 power, a heat shrink sleeve may be used to surround 28 the connection between the rod and the cable. In 29 this case the heat shrink sleeve surrounds the 30 sleeve (8)of the waterstop body (2) the connection i 31 and the cable end to ensure that the connection is

1 completely insulated and protected against any 2 ingress of water.

4 Typically the sleeve (8) will be formed via a 5 moulded node formed in the annular member during 6 manufacture. The longitudinal conveying means may 7 then be put in place by forcing it through the node.

8 Additional nodes (see 6a Figure 7) may be formed in 9 the annular member which facilitate incorporation of 10 additional longitudinal conveying means at a later 11 date.

13 Longitudinal conveying means (6) facilitates I 14 communication through the seal assembly to the 15 annular space on either side. Said longitudinal 16 conveying means may optionally comprise heat 17 transfer means, such a tube to connect heat transfer 18 fluid hoses or information / data transfer means, 19 such as an optical fibre, for example.

21 A backing ring (15, see Figure 7) may be provided 22 for connecting adjacent seal assemblies. The back 23 ring (15) fixed to a shoulder on a waterstop body 24 (2) may be attached to the back ring (15) of an 25 adjacent seal assembly via a tie-strap (13) and 26 suitable fixing means (14). Typically the fixing = 27 means (14) may comprise rivets, nut and bolts -

28 arrangements or the like.

30 Two or more different types of longitudinal s 31 conveying means may be used in combination. For

1 example a seal assembly may comprise a plurality of 2 copper rods used to convey electrical power to 3 heating cables for heating the annular space in the 4 pipe-in-pipe system together with one or more 5 optical fibres for monitoring temperature within or 6 curvature of the system. Figure 3 is a plan view of 7 an annular member (1) comprising four groups of 8 three conductor rods (6a) and two optical fibres 9 (6b).

11 In the case where the longitudinal conveying means 12 comprises an optical fibre, the optical fibre may be 13 housed in a tube passing through the seal assembly.

14 A suitable sealant, such an an epoxy resin, may be 15 introduced within the tube in order to ensure the 16 sealing of the optical fibre within the seal 17 assembly.

19 Generally unidirectional seal assemblies such as 20 those shown in the Figure 1 are used in pairs as 21 illustrated in Figures 2 t 7, so that the combined 22 effect is to prevent water flow in either direction.

23 Between two unidirectional seal assemblies the 24 longitudinal conveying means may be covered, for 25 example a polyurethane sheath or coating (7) may be 26 used to provide insulation (for example in the case 27 where the longitudinal conveying means (6) comprises 28 electrical conducting means). Furthermore, in the 29 case where the longitudinal conveying means (6) 30 comprises an optical fibre for monitoring 31 temperature, the optical fibre may be in contact

1 with the flow line pipe or with a metal element 2 linked to the flow line pipe between two 3 unidirectional seal assemblies. Cold spots may 4 exist between two unidirectional waterstop 5 assemblies in a pipe system using active heating 6 since the heating cables do not contact the flow 7 line pipe between the seal assemblies. The optical 8 fibre arrangement described has the advantage that 9 it facilitates monitoring of such cold spots.

ll The present invention further relates to a method of 12 manufacturing a seal assembly comprising the steps 13 of moulding a body (1) from a suitable material, 14 moulding an end piece having inner and outer lips 15 (3, 4) from a suitable material, sealably attaching 16 said body (l) to said end piece and incorporating 17 longitudinal conveying means which traverses the 18 seal assembly.

20 Preferably, the method of the invention further 21 comprises the step of forming one or more nodes in 22 the end piece, said nodes are adapted to facilitate 23 incorporation of the longitudinal conveying means.

24 For example the nodes may be manufactured in such a 25 manner that the longitudinal conveying means can be 26 passed through the end piece in a heat shrink 27 operation which forms a heat shrink seal between the 28 end piece and the longitudinal conveying means (6).

30 Preferably, the nodes are in manufactured from a 31 resilient material in the form of tubes, the

1 diameter of which is less than that of the 2 longitudinal conveying means. The longitudinal -

3 conveying means, for example an electrically 4 conducting rod may then be forced through the 5 resilient tubular node thus ensuring a good fit and 6 seal between the end piece and the longitudinal; 7 conveying means.

One or more auxiliary or supplemental nodes (6c) may 10 be formed in the end piece in order to facilitate 11 later incorporation of additional longitudinal 12 conveying means. In an alternative manufacturing 13 method, the waterstop body (1) can be moulded with 14 the longitudinal conveying means (6) the mould.

16 The present invention also provides a pipe system 17 comprising an inner pipe and an outer pipe and a r 18 seal assembly described herein. For example the lo pipe system may comprise an inner pipe and an outer 20 pipe with electrical heating cables running along 21 the flow line or inner pipe, the electrical heating 22 cable being connected to one or more rods traversing 23 each seal assembly. Such a pipe system may further 24 comprise heat dissipation means close to the seal 25 assembly, at the point where the heating cable is 26 lifted from the flow line to be connected to the rod 27 of the seal assembly. Such heat dissipation means 28 may comprise a thin aluminium layer wrapped around 29 the external sheath of the cable and linked to the 30 flow line so as to prevent overheating of the cable.

1 The design of the waterstop or seal assembly and the 2 internal surface of the carrier pipe may provide for -

3 relative movement between the carrier pipe and the 4 waterstop fixed on the flow line pipe. Such 5 relative movement may be advantageous in that it 6 facilitates a reduction of the number of in-line 7 connections of the heating electrical cables 8 required during manufacture of the pipe system.

- 10 The annular space in the pipe system may also 11 comprise insulation material and/or one or more 12 elements chosen from bulkheads to transfer loads 13 (services or handling loads) between the carrier -

14 pipe and the flowline; spacers to centre the 15 flowline within the carrier pipe; buckle arrestors 16 to prevent the propagation of a buckle along the 17 carrier pipe. Preferably the seal assemblies are r 18 installed near to buckle arrestors so that when 19 buckle propagation is stopped, any water leak due to 20 the buckle will not be allowed to proceed through 21 the double walled pipeline annulus.

24 e

Claims

( 2 CLAIMS!

4 (1) A seal assembly for dividing an annular space 5 defined between an inner and an outer pipe in a 6 double-walled pipeline comprising an annular 7 member adapted to fit within the annular space 8 and at least one longitudinal conveying means 9 passing through the annular member, wherein 10 said longitudinal conveying means communicates 11 with the annular space on either side of the 12 seal assembly.

14 (2) A seal assembly according to Claim l wherein

15 the annular member comprise inner and outer 16 lips adapted to sealably engage the inner and 17 outer pipes 19 (3) A seal assembly according to either Claim 1 or 20 Claim 2 wherein the longitudinal conveying 21 means comprises electrical conducting means.

23 (4) A seal assembly according to Claim 3 where the 24 electrical conducting means comprises a rod or 25 a cable or a plurality thereof.

27 (5) A seal assembly according to any preceding 28 Claim wherein the longitudinal conveying means 29 comprises a rod traversing the annular member, 30 said rod being adapted at one or both ends for 31 connection to a cable.

( (6) A seal assembly according to Claim 5 wherein 3 the rod is connected at one or both ends to a 4 cable, the seal assembly further comprising one 5 or more sleeves covering the connections 6 between said rod and said cable.

8 (7) A seal assembly according to Claim 1 wherein 9 the longitudinal conveying means comprises one 10 of more optical fibres housed within optical 11 fibre housing tubes.

13 (8) A seal assembly according to Claim 1 wherein 14 the longitudinal conveying means comprises one 15 or more heat transfer means.

17 (9) A pipe system comprising an inner pipe and an 18 outer pipe and a seal assembly according to any 19 one of the preceding Claims.

21 (10) A pipe system according to Claim 9 comprising 22 at least one pair of unidirectional seal 23 assemblies. 25 (11) A pipe system according to Claim 10 wherein the 26 longitudinal conveying means is at least 27 partially insulated between each unidirectional 28 seal of each pair of seal assemblies.

30 (12) A method of manufacturing a seal assembly 31 comprising the steps of moulding a body from a

1 suitable material, moulding an end piece having 2 inner and outer lips from a suitable material, 3 sealably attaching said body (1) to said end 4 piece and incorporating longitudinal conveying -

5 means which traverses the seal assembly. -

7 (13) A method according to Claim 12 further 8 comprising the step of forming one or more 9 nodes in the end piece, said nodes being lo adapted to facilitate incorporation of the 11 longitudinal conveying means.

13 ( 14) A method according to Claim 13 wherein the 14 nodes are in manufactured from a resilient 15 material in the form of tubes, the diameter of 16 which is less than that of the longitudinal 17 conveying means. -

19 (15) A method according to either Claim 12 or Claim -

20 13 further comprising the step of forming one 21 or more auxiliary or supplemental nodes in the 3 22 end piece.