GB2388641A

GB2388641A - A thermally insulated rigid pipe in pipe system and method

Info

Publication number: GB2388641A
Application number: GB0211299A
Authority: GB
Inventors: Michael Antoine Bell; Sylvain Denniel
Original assignee: Coflexip SA; Coflexip Stena Offshore Ltd
Current assignee: Technip Energies France SAS; Technip UK Ltd
Priority date: 2002-05-17
Filing date: 2002-05-17
Publication date: 2003-11-19
Anticipated expiration: 2022-05-17
Also published as: WO2003098093A1; GB0211299D0; AU2003224273A8; AU2003224273A1; GB2388641B

Abstract

A rigid thermally insulated pipe-in-pipe assembly comprising at least one thermal insulation layer disposed between an inner pipe and outer pipe and comprised of elongate bars wound along the length of an inner pipe, the elongate bars comprising a plurality of bars formed of a first type of material with a first lambda value and a first compressive strength and a plurality of bars formed of a second type of material which has a second lambda value which is greater than the first and having a second compressive strength greater than the first compressive strength. Also disclosed is a method of forming the rigid, thermally insulated pipe-in-pipe assembly.

Description

i 1 238864 1

1 Thermally Insulated, Riaid Pine-in-Pie Systems and 2 Methods 4 The present invention relates to pipe-in-pipe 5 systems of the type comprising a rigid inner pipe 6 surrounded by a rigid outer pipe and having 7 thermally insulating material provided in the 8 annulus between the inner and outer pipes. The 9 invention relates especially to such systems and 10 associated methods particularly for subsea pipelines 11 laid from a pipelaying vessel by the reel pipelay 12 method.

14 Pipe-in-pipe systems are double walled pipe 15 structures typically used in subsea production lines 16 (particularly for the transport of hydrocarbon 17 products) that require the high level of thermal 18 insulation which can be provided by filling the 19 annulus of the pipe-inpipe structure with thermally 20 insulating material. Furthermore, the interior of 21 the annulus of the pipe-in-pipe structure is dry, so 22 that the thermal insulation material is protected

1 from water. Also, the interior of the annulus may 2 be maintained at atmospheric pressure, so that the 3 insulating material may not be subject to the 4 hydrostatic pressure that is supported by the 5 external pipe ("carrier pipe"), or to the internal 6 pressure of the fluid in the internal pipe 7 ("flowline"). For these reasons, the rigid pipe-in 8 pipe structure provides an arrangement that allows 9 the use of a wide variety of thermal insulation 10 materials with good insulation properties (low 11 lambdaj. 13 It is necessary to insulate subsea production lines 14 because of the tendency of heavy oils and the like 15 to solidify while being transported between the 16 subsea production well and the surface, as a result 17 of heat losses from the submerged pipeline.

18 Insulation is also necessary to avoid the formation 19 of hydrates that can occur when there is a cooling 20 of certain types of crude oil; e.g. during 21 interruptions to production.

23 Hitherto, two types of thermal insulation means have 24 been used in pipe-in-pipe systems. US-A-3547161 25 discloses an arrangement whereby the annulus is 26 completely filled with injected insulation material.

27 Another method employs half shells of insulating 28 material that are assembled longitudinally on the 29 flowline, with spacers between longitudinally 30 adjacent pairs of half shells.

( 3 1 Conventionally, two main techniques are used to lay 2 subsea pipelines from pipelaying vessels: the J-lay 3 (or S--lay) method and the reeling method. In the J 4 lay (or S-lay) method, the pipeline is assembled on 5 the vessel by welding together lengths of pipe 6 before laying them in the sea. This technique is 7 slow and expensive, requiring a crew of welders on 8 board the vessel. The reeling technique comprises 9 assembling the pipeline on shore and spooling the lO pipeline onto a reel which is subsequently 11 transported to the production site where it is 12 unreeled along the required pipeline path. This 13 allows the pipeline to be laid much more quickly, so 14 that the vessel is not required for as long a period 15 as in the case of J-lay/S-lay.

17 In the reeling technique, the rigid pipeline is 18 subjected to plastic deformation while being spooled 19 onto the reel, and the plastic deformation is 20 removed by straightening mechanisms while the 21 pipeline is being unreeled. During spooling of a 22 pipe-in-pipe assembly, tension is applied to the 23 pipeline to conform the carrier pipe to the reel.

24 The carrier pipe is bent through direct contact with 25 the reel drum, or with previously spooled layers of 26 the pipeline.

28 The bending forces are transferred from the carrier 29 pipe to the flowline by spacers or annular walls 30 disposed along the length of the pipeline in the 31 annulus. When unreeling, the pipeline is 32 straightened by the carrier pipe being passed

1 through straightening means, such as opposed rollers 2 or roller track assemblies (as are well known in the 3 art). The straightening forces are applied to the 4 exterior of the carrier pipe, and are only 5 transferred to the flowline at the locations of the 6 spacers or annular walls inside the annulus.

7 Accordingly, the carrier pipe can be fully 8 straightened but it is not possible to fully 9 straighten the flowline inside the carrier pipe.

10 The flowline therefore retains some residual 11 curvature after the straightening process, depending 12 on the pitch of the spacers in the annulus. The 13 resulting relative displacement of the flowline 14 inside the carrier pipe results in local reductions 15 in the annulus gap between the two pipes, leading to 16 potential compression of the insulating material.

18 If reeling techniques are applied to pipe-in-pipe 19 structures of the type with injected thermal 20 insulation, continuous longitudinal lengths of the 21 insulation material have to be separated by annular 22 walls, and the pitch of the walls must be 23 sufficiently small (the walls must be sufficiently 24 closely spaced) to effectively transmit the bending 25 forces from the carrier to the flowline and so avoid 26 local reductions in the annulus gap between the two 27 pipes.

29 If reeling techniques are applied to pipe-in-pipe 30 structures of the type with "half shell" thermal 31 insulation, local compression of the insulating 32 material leads to a reduction in insulating

( 1 properties and so to a global reduction in the 2 thermal properties of the pipeline. In order to 3 counter such losses, it is necessary to add more 4 spacers (reducing the spacer pitch to reduce the 5 compression) or to modify the pipeline design so as 6 to increase the amount of insulating material (by 7 increasing the internal diameter of the carrier 8 and/or reducing the external diameter of the 9 flowline), but such solutions create many additional lo problems. Adding spacers reduces the total amount 11 of insulating material, and changing the pipe 12 diameters is usually unacceptable because it leads 13 to excessive costs and/or reduces the flow capacity 14 of the pipeline.

16 The problem of providing adequate thermal insulation 17 becomes more severe for long lengths of pipeline 18 laid in very deep water. The use of high 19 performance insulating materials (with low lambda 20 values) is the best solution, but such materials 21 tend to have low density and hence low mechanical 22 strength. Furthermore, the installation of spacers 23 or other accessories (such as waterstops or 24 bulkheads) is expensive and time-consuming, 25 offsetting the savings obtained by use of the 26 reeling technique.

28 The present invention seeks to provide improved 23 thermally insulated rigid pipe-in-pipe systems that 30 are suitable for spooling onto a reel and for 31 subsequent straightening in reel-type pipelaying 32 operations.

2 In accordance with a first aspect of the invention, 3 there is provided a rigid, thermally insulated pipe 4 in-pipe assembly comprising: a rigid inner pipe; a 5 rigid outer pipe; an annulus defined between the 6 inner and outer pipes; and at least one thermal 7 insulation layer located in said annulus; wherein: 8 said at least one thermal insulation layer comprises 9 a plurality of elongate bars wound along the length 10 of said inner pipe, said bars including a first 11 plurality of bars formed from a first material 12 having a first lambda value and a first compressive 13 strength and at least one additional bar formed from 14 a second material having a second lambda value 15 greater than said first lambda value and having a 16 second compressive strength greater than said first 17 compressive strength.

19 A rigid, thermally insulated pipe-in-pipe assembly 20 in accordance with the first aspect of the invention 21 may be laid using the reel pipelaying method by 22 spooling the pipe-in-pipe assembly onto a reel by 23 plastically bending the pipe-in-pipe assembly around 24 the reel, and subsequently unreeling the pipe-in 25 pipe assembly from the reel along a pipeline path 26 while straightening the plastically bent pipe-in 27 pipe assembly.

29 In accordance with a second aspect of the invention 30 there is provided a method of forming a rigid, 31 thermally insulated pipe-in-pipe assembly 32 comprising: providing a length of rigid inner pipe;

( 1 applying at least one thermal insulation layer to 2 the external surface of said inner pipe by winding a 3 plurality of elongate bars along the length of said 4 inner pipe, said bars including a first plurality of 5 bars formed from a first material having a first 6 lambda value and a first compressive strength and at 7 least one additional bar formed from a second 8 material having a second lambda value greater than 9 said first lambda value and having a second 10 compressive strength greater than said first 11 compressive strength; and inserting said inner pipe 12 with said at least one thermal insulation layer into 13 a rigid outer pipe.

15 Other aspects and preferred features of the 16 invention are defined in the appended claims.

18 Embodiments of the invention will now be described, 19 by way of example only, with reference to the 20 accompanying drawings, in which: 22 Fig. 1 is a partially cut away perspective view of a 23 first embodiment of a pipe-in-pipe assembly in 24 accordance with the present invention; 26 Fig. 2 is a partial cross sectional view of a pipe 27 in- pipe assembly illustrating further preferred 28 features of embodiments of the invention; 30 Fig. 3 is a partial cross sectional view of a pipe 31 in-pipe assembly illustrating a further embodiment 32 of the invention;

( 2 Figs. 4a - 4e are schematic illustrations of 3 alternative cross sections of insulating strip 4 materials employed in the present invention; and 6 Fig. 5 is a partially cut away perspective view of a 7 further embodiment of a pipe-in-pipe assembly in 8 accordance with the present invention.

10 Referring now to the drawings, Fig. 1 shows a 11 thermally insulated pipe-in-pipe structure 12 comprising a rigid inner pipe or flowline lo, a 13 rigid outer pipe or carrier 12, and thermally 14 insulating material disposed in the annulus between 15 the flowline 10 and carrier 12. The thermally 16 insulating material comprises a plurality of bars or 17 strips of a first material 14 and at least one bar 18 or strip of a second material 16.

20 The bars 14 and 16 are wound upon the flowline so as 21 to extend along its longitudinal axis in a 22 serpentine manner. The bars 14, 16 may be wound 23 helically upon the flowline. However, the apparatus 24 required for continuous helical winding is 25 relatively complex and expensive. It is preferred 26 that, as illustrated, the bars 14, 16 are wound in a 27 so-called "S/Z" or "reversing lays, ("pseudo 28 helical'') configuration (as described, for example, 29 in GB-A-2219O63, in relation to forming flexible, 30 multi-conductor lines), in which the direction of 31 winding is reversed periodically. This technique 32 does not require the flowline 10 to be rotated

( 9 1 continuously relative to the bars 14, 16, 2 simplifying the required apparatus. As used herein, 3 the term "helical winding'' means either genuine, 4 continuous helical winding or pseudo-helical winding 5 such as S/Z winding. In Fig. l, for the sake of 6 clarity, the direction of winding is shown as being 7 reversed about every 90 degrees. In other 8 embodiments, the direction of winding is reversed 9 after approximately a complete turn of the bars 14, 10 16 about the flowline 10.

12 The machine used for winding the insulated bars 14, 13 16 in continuous helical winding or pseudo-helical 14 winding can be any one of a variety of many 15 different types. It may be a classical helical lay 16 or spiralling machine using a rotating device 17 sharing the reels that supply the insulated bars to 18 be wound. It can also be a winding machine where 19 the bars are provided to a rotating twist head 20 through a plurality of rotating plates which hold 21 the insulated bars around the flowline and in 22 parallel relationship. The plates are co- ordinated 23 in rotation and in certain cases are able to advance 24 simultaneously, the bars being assembled by 25 predetermined length. In this type of machine, the 26 insulated bars could be assembled step by step (by a 27 predetermined length) as the process of winding is 28 going on, contrary to the classical helical lay 29 machine where the insulated bars are stored on reels 30 shared on a rotating device (i.e. a continuous 31 process). In the case of S/Z winding of the bars, 32 the winding machine can use a plurality of spaced

1 rotating plates co-ordinated in rotation but with 2 fixed reels for supplying the insulated bars. This 3 kind of winding machine also avoids the need for a 4 rotating device sharing the supply reels of the 5 classical spiralling machine.

7 The first material 14 comprises a material having 8 relatively high thermal insulation properties (low 9 lambda) and, correspondingly, relatively low 10 mechanical (compressive) strength. The second 11 material 16 comprises a material having relatively 12 lower thermal insulation properties (higher lambda) 13 and, correspondingly, relatively higher mechanical 14 (compressive) strength. The first material 14 15 covers the majority of the surface area of the 16 flowline 10, providing good thermal insulation. The 17 second material covers the remainder of the surface 18 area of the flowline 10, and serves to transmit 19 bending forces applied to the carrier 12 to the 20 flowline 10 during spooling and subsequent 21 straightening of the pipe assembly. The second 22 material 16 is sufficiently strong to resist being 23 crushed during bending of the pipe assembly, and 24 protects the first material against excessive 25 compressive stresses. The second material should 26 occupy as little as possible of the annulus volume, 27 so as to maximise the thermal insulation properties, 28 whilst providing the required mechanical support 29 between the flowline 10 and carrier 12. In certain 30 embodiments, the second material may constitute 20\ 31 or more of the volume of the insulating layer.

1 The bars of the second material 16 thus act as 2 helical spacers, avoiding the need for conventional 3 annular spacers. The number and arrangement of the 4 helical spacers 16 is selected so as to limit any 5 deformation (crushing) of the first insulating 6 material 14 during bending and/or straightening to 7 an acceptable value. The spacers 16 may have a 8 radial depth substantially equal to that of the -

3 first material 14 or, as shown in Fig. 2, the radial -

10 depth he of the second bars 16 may be greater than ll that, hi, of the first bars 14, in order to better; 12 protect the first bars 14 from crushing during 13 bending/straightening. 15 Depending upon the winding pattern, the winding 16 pitch, and the degree of compression of the first 17 material 14 that is acceptable, there should be at 18 least one bar of the second material 16. For 19 example, where a particular pipeline design requires 20 the presence of a spacer every two meters along the 21 length of the flowline 10, a single high strength 22 bar 16 could be used with a winding pitch of two 23 meters, or two bars 16 could be used with a winding 24 pitch of four meters. Where more than one bar of 25 the second material 16 is employed, these will 26 generally be spaced equidistantly around the 27 circumference of the flowline 10, with a plurality 28 of bars of the first material 14 located 29 therebetween. In the illustrated embodiments, three 30 bars of the second material 16 are used.

1 During bending/straightening of the pipe assembly, 2 the thermally insulating, high strength bars 16 3 serve to maintain the flowline 10 in a concentric 4 position in the carrier pipe 12, limiting any 5 displacement of the flowline, and limiting any heat 6 loss through the spacers 16 themselves.

8 The invention has a number of other advantages 9 related to the manufacturing of the pipeline. The lo insulating materials may be applied in a; 11 substantially continuous process by means of a 12 winding machine, without the need of a step-by-step 13 process to apply discrete spacers and/or insulating 14 elements as in previous methods. As shown in Figs. 15 2 and 5, the method also makes it easy to 16 incorporate heating cables, or other secondary hoses 17 for active heating, conduits or electrical or 18 optical cables or the like 18 in the insulating 19 layers (e.g. disposed in recesses 20 formed in the 20 bars, preferably in the inner faces of the bars, and 21 most preferably in the bars of the second material 22 14).

24 The pipe-in-pipe structure of the invention may be 25 formed by winding the materials 14, 16 onto the 25 exterior surface of a length of the inner pipe 10 27 and the inner pipe 10 with the materials 14, 16 28 applied thereto may then be inserted into the outer 29 pipe 12. A plurality of inner pipe sections may be 30 assembled together prior to applying the materials 31 14, 16, and a plurality of outer pipe sections may

( 13 1 be assembled together prior to inserting the 2 insulated inner pipe therein.

4 The cross sectional size and shape of the first and 5 second bars 14 and 16 may be substantially 6 identical, although it may be desirable for the 7 second bars 16 to have a greater radial depth than 8 the first bars 14, as discussed above. As shown in 9 Fig. 4, the radially opposed faces of the bars 14, 10 16 may be curved to match the curvatures of the 11 flowline 10 and carrier pipe 12, and their lateral; 12 faces may have complementary curvatures and/or 13 overlapping features to reduce convection along the 14 radial gaps between adjacent bars.

16 As shown in Fig. 3, multiple (generally two or 17 three) layers of insulating materials 14 and 16 may 18 be applied. The high strength bars 16 of the 19 various layers should cross one another in order to j 20 transmit bending forces through the crossing points 21 from the outer layer to the flowline 10. For this 22 purpose, the bars of adjacent layers may be wound 23 out of phase and/or with differing pitches and/or in 24 opposite directions.

26 For most reel pipelaying applications, the second 27 material 16 will generally have to be capable of 28 supporting compressive forces up to about 300 kN.

29 The second material 16 might suitably have a shore 30 hardness (D) greater than 50 and a lambda value less 31 than 0.3 W/Km. For example, the second material 16

( l might suitably comprise a polyamide reinforced by 2 glass fibre.

4 The first material suitably has a lambda value less 5 than 0.1 W/Km and may comprise, for example, 6 polyurethane (PU) foam, rubber foam, PVC foam, 7 aerogel or syntactic foam.

9 The bars 14, 16 are preferably wound with a 10 relatively long pitch (i. e. with a winding angle; 11 less than about 35 degrees).

13 Improvements and modifications may be incorporated 14 without departing from the scope of the invention as 15 defined in the claims appended hereto.

Claims

l Claims

3 1. A rigid, thermally insulated pipe-in-pipe 4 assembly comprising: 5 a rigid inner pipe; 6 a rigid outer pipe; 7 an annulus defined between the inner and outer 8 pipes; and -

9 at least one thermal insulation layer located 10 in said annulus; wherein: 11 said at least one thermal insulation layer; 12 comprises a plurality of elongate bars wound along 13 the length of said inner pipe, said bars including a 14 first plurality of bars formed from a first material 15 having a first lambda value and a first compressive 16 strength and at least one additional bar formed from 17 a second material having a second lambda value 18 greater than said first lambda value and having a l9 second compressive strength greater than said first 20 compressive strength.

22 2. A rigid, thermally insulated pipe-in-pipe 23 assembly as claimed in claim 1, wherein said bars 24 are helically wound along said inner pipe.

26 3. A rigid, thermally insulated pipe-in-pipe 27 assembly as claimed in claim 1 or claim 2, wherein 28 said bars are wound in an S/Z configuration.

29: 30 4. A rigid, thermally insulated pipe-in-pipe 31 assembly as claimed in any preceding claim,

( 1 including a second plurality of bars of said second 2 material. 4 5. A rigid, thermally insulated pipe-in-pipe 5 assembly as claimed in any preceding claim, 6 including a plurality of thermal insulation layers, 7 each comprising a plurality of said elongate bars 8 wound along the length of said inner pipe.

10 6. A rigid, thermally insulated pipe-in-pipe 11 assembly as claimed in any preceding claim, wherein 12 said at least one bar of said second material has a 3 13 radial depth greater than said bars of said first 14 material. I 16 7. A rigid, thermally insulated pipe-in-pipe 17 assembly as claimed in any preceding claim, wherein 18 radially opposed faces of the bars are curved to 19 match the curvatures of the inner and outer pipes.

21 8. A rigid, thermally insulated pipe-in-pipe 22 assembly as claimed in any preceding claim, wherein 23 lateral faces of the bars have complementary, 24 mutually interlocking configurations.

26 9. A rigid, thermally insulated pipe-in-pipe 27 assembly as claimed in any preceding claim, 28 including at least one cable, hose or conduit 29 incorporated in said at least one thermal insulation 30 layer.

1 10. A rigid, thermally insulated pipe-in-pipe 2 assembly as claimed in any preceding claim, wherein 3 said second material has a shore hardness (D) 4 greater than 50. j 6 11. A rigid, thermally insulated pipe-in-pipe 7 assembly as claimed in any preceding claim, wherein 8 said first material has a lambda value less than 0.1 -

9 W/Km. 11 12. A rigid, thermally insulated pipe-inpipe 12 assembly as claimed in any preceding claim, wherein 13 said second material has a lambda value less than 14 0.3 W/Km.

16 13. A rigid, thermally insulated pipe-inpipe 17 assembly as claimed in any preceding claim, wherein 18 said second material costituces at least 20t of the 19 volume of the at least one thermal insulation layer.

21 14. A method of forming a rigid, thermally 22 insulated pipe-in-pipe assembly comprising: 23 providing a length of rigid inner pipe; 24 applying at least one thermal insulation layer 25 to the external surface of said inner pipe by 26 winding a plurality of elongate bars along the 27 length of said inner pipe, said bars including a -

28 first plurality of bars formed from a first material 29 having a first lambda value and a first compressive 30 strength and at least one additional bar formed from 31 a second material having a second lambda value 32 greater than said first lambda value and having a

1 second compressive strength greater than said first 2 compressive strength) and 3 inserting said inner pipe with said at least 4 one thermal insulation layer into a rigid outer 5 pipe. 7 15. A method as claimed in claim 14, further - 8 comprising: 9 assembling a plurality of inner pipe sections 10 to provide said length of rigid inner pipe prior to 11 applying said at least one thermal insulation layer 12 to the external surface thereof; and 13 assembling a plurality of outer pipe sections 14 to provide a length of said rigid outer pipe before 15 inserting said inner pipe with said at least one 16 thermal insulation layer therein.