GB2391597A

GB2391597A - Method of and Apparatus for Interconnecting Lined Pipes

Info

Publication number: GB2391597A
Application number: GB0217940A
Authority: GB
Inventors: Vincent Alliot; Jean Louis Hoss
Original assignee: Stolt Offshore SA
Current assignee: Stolt Offshore SA
Priority date: 2002-08-02
Filing date: 2002-08-02
Publication date: 2004-02-11
Also published as: GB0217940D0

Abstract

There are disclosed methods of and apparatus for interconnecting lined metal pipes (18, 20), applying in particular to the offshore oil and gas industry. Corrosion is a common problem in the industry. Lining pipes overcomes the problem, but welding sections of pipe together can be a complicated and time-consuming task, requiring dedicated and sophisticated tooling. More desirable is the ability to use conventional pipe-laying equipment (3, 4, 5, 6, 7, 8, 9, 10) with little additional tooling. As such, there are disclosed methods and apparatus compatible with known offshore connection methods, particularly where the spacing of joints on the pipe is less than 100m. The chosen technique will not significantly impact the laying rate of the lined pipe, compared with unlined pipe. The method includes connecting lined pipes (18, 20) using a corrosion-resistant bridging member (12) that bridges both pipes (18, 20) and is located along its length between the liner (30) and the wall of the pipe, protecting the liners from the effects of welding (80), and further includes expanding rings (50) located within the liners to provide a seal between the liners and the bridging member (12), in a controlled sequence. There is also disclosed a bridging member (12), tooling (70) and pipelay apparatus suitable for use with this method.

Description

23g1 597 METHOD OF AND APPARATUS FOR INTERCONNECTING LINED PIPES

This invention relates to methods and apparatus for interconnecting metal pipes lined 5 with plastic or other deformable corrosion-resistant lining material. The invention finds particular application in the offshore oil and gas industry, but is not limited to such applications. 10 Steel pipes are commonly used for the transport of fluids of different types in the offshore industry. When conveying oil and gas, corrosion is a limited problem.

Offshore field operators also need to transport more corrosive fluids, in particular

seawater for pumping water into a water injection well head. Experience shows that water injection pipe suffers from rapid degradation due to corrosion of the steel pipe. In 15 order to provide a suitable service life when using unprotected steel pipe, the wall thickness would have to be significantly increased, making it heavier, more expensive and more difficult to install, especially in deep water. A very expensive solution would be to use corrosion-resistant metal, such as Inconel_ or stainless steel. Alternatively, steel pipe with internal thermoplastic liner can be used, satisfying both weight and cost 20 budgets. When using lined pipe for offshore applications, the lined pipe is typically fabricated on shore using the Swagelining_ technique, as described for example in United Kingdom patent GB 2186340. A slightly oversized liner pipe made of thermal plastic material is 25 pulled through the pipe using a reducing die. Once the pulling operation is completed and the pulling tension released, the liner over a period of time progressively returns to its original shape, locking itself inside the steel pipe. Single lengths of pipe over 1000m in length can be pre-fabricated and lined by this technique. If longer pipes are required, sections of lined pipe are then interconnected using the patented Weldlink_ welding 30 process, as disclosed in GB 2298256. This process consists of swaying a corrosion resistant sleeve to terminate each pipe section and welding both the sleeves and pipe materials using dedicated welding procedures and welding equipment. Multiple

welding operations are required for each pipe section being joined. The time taken for these operations is best measured in hours, but this is not prohibitive when joints are being made only once every kilometre or more.

5 Using these known techniques to produce offshore pipe requires setting up a dedicated fabrication, assembling and reeling base. A reel laying spread is also required to transport and lay the pipe offshore. In some circumstances this technique is not commercially attractive due to the costs associated with setting up the base and the limitation of the reel lay vessel (storage capacity, laying tension). As an alternative the 10 pipe could also be bottom-towed to the offshore field after being assembled and

fabricated. However this technique also has severe limitations such as crossing of existing pipe and complications caused by the nature and profile of seabed.

To construct a continuous pipeline it would, ideally, be possible to use existing offshore 15 pipe laying techniques, such as S-Lay or J-Lay, which fabricate a continuous pipeline from a large number of shorter steel pipe sections, on board a pipe laying vessel. The pipe sections then would be pre-lined with lengths of thermoplastic liner. US 5975802 (Willis) and US 6213686 (Baugh) describe two different pipelaying systems of this kind. In US 02, a series of welding and test stations, spaced along the deck of a pipe 20 laying vessel, operate in parallel to build the pipe rapidly from single sections. The welded pipe is then bent upwardly and then downwardly to be launched into the sea at the desired angle. In more conventional J-Lay processes, such as that described in US'686, double or quadruple pipe sections are pre-fabricated, and then up- ended in a special tower structure, to be welded onto the end of the pipe as it is paid out. Such 25 systems are highly developed and each section can be aligned, welded, tested and paid out in a matter of minutes.

As noted above, due to the complexity of the pipe fabrication and welding procedure, the time for interconnecting each new section of lined pipe by the known Weldlink_ 30 technique can be measured in hours, rather than minutes. As a consequence, the method is not commercially compatible with the known techniques for laying steel offshore

pipe, which involve welding in relatively rapid succession much shorter pipe sections at the field, thus forming a continuous pipe.

5 Considering the foregoing matters, it is an object of the invention to provide a method of and apparatus for interconnecting lined pipes that is compatible with known offshore connection methods, particularly where the spacing of joints on the pipe is less than lOOm. Ideally, the chosen technique will not involve any reduction in the laying rate of the lined pipe, compared with unlined pipe.

In accordance with a first aspect of the present invention, there is provided a method of joining plastic-lined fluid conduits comprising the steps of: - providing a first conduit and a second conduit, each conduit comprising a wall of 15 metal defining a bore, said bore substantially lined by a plastic liner, said conduits having open ends for connection; providing a tubular bridging member having a first end and a second end; introducing said first end of said bridging member into said first conduit so as to provide a first portion of overlap between said liner and said bridging member; 20 - forming a first seal between said liner and said bridging member; - introducing said second end of said bridging member into said second lined conduit between the bore of the conduit and its liner so as to provide a second portion of overlap between said liner and said bridging member, the length of the bridging member and said overlap portions being such as to bring said first and second 25 conduits' ends substantially abutting, and - at a time after said ends are brought together welding said ends together, - at a time after said second overlap is formed, providing a ring portion of plastically deformable material dimensioned to fit within the bore of said liner, introducing said ring into the liner until it aligns with said second overlap, and expanding said 30 ring radially so as to press the liner against the bridging member to form a second seal between the liner and bridging member; the liner, the first and second seals and

the bridging member thus forming a continuous barrier between the interior bore of the lined conduits and the metal of the conduit walls.

The first end of said bridging member may be introduced into the first conduit between 5 the bore of the conduit and its liner, and a time after the conduit ends are brought together, providing as said means for forming said first seal a ring of plastically deformable material dimensioned to fit within the bore of said first conduit liner, introducing said ring into the liner until it aligns with said first overlap, and expanding said ring so as to press the liner against the bridging member.

Alternatively, the first end of said bridging member may be introduced within the bore of said first conduit liner, and a time after said ends are brought together, expanding said first end radially so as to press the bridging member against the liner to form said first seal.

The method may further comprise the additional step of expanding the bridging member radially in the region of the welded pipe ends so as to substantially displace any fluid trapped within the confines of the bridging member, the liners and the conduit walls in said region. Doing so protects the inner region of the weld from corrosive 20 fluid, such as air or sea water, maximising the life of the weld.

The expanding the bridging member radially in the region of the welded pipe ends may be performed concurrently with subsequent passes of welding.

25 The bridging member may be fabricated out of corrosion-resistant metal, for example Inconel_. At least one formation may be provided on each sealing portion to improve grip between the bridging member and the liner. In a preferred embodiment, each sealing 30 portion is provided with a series of circumferential formations. Alternatively, adhesive may be used.

At each end to be joined the end face of the plastic lining member may be longitudinally spaced from the end of said conduit. It may also be chamfered to reduce its cross-sectional area. This can aid the process of introducing the bridging member into the liner, and also reduces stress in the material of the bridging member in 5 embodiments where it is expanded over the end of the liner.

Alternatively, or in addition, the internal diameter of at least the first conduit may be increased at its end, so as to facilitate insertion of said bridging member between the liner and the wall of the first conduit.

One or both of said plastically deformable rings may provided as an annular ring portion, integral with said bridging member, whereby introducing the bridging member to the lined conduit also introduces said ring portion into the liner, in alignment with said overlap portion. Alternatively, the first ring may be introduced separately.

To minimise the number of steps performed offshore, the bridging member may be pre-

fitted to a section of conduit.

The conduit lining may be rigid plastic, or compressible. Also, it may be a loose fit 20 within the conduit, or an interference fit.

The bridging member may be constructed from metal, or from a non-metallic material.

It may further comprise a weldable portion located to align with the pipe ends being joined, in use. The step of welding the conduits together may also weld the bridging 25 member to the conduits.

The first and second conduits may be joined as part of an offshore pipe fabrication and laying process, each conduit being a section of pipeline added in turn to the pipeline being laid by repeating the steps of the method as set forth above. The sections may be 30 less than l00m long, requiring a relatively large number of joining operations, but overcoming the disadvantages associated with handling lengthy pipe sections, hundreds or even thousands of metres long.

The first conduit may be either the pipe section joined already to the pipeline, or may be the one being added. In the first case, the second conduit becomes the first conduit after the second conduit has been interconnected with the first conduit. In the second 5 case, the second conduit becomes the first conduit after interconnection.

The joining method may be performed while the first and second conduits are substantially horizontal, the assembled pipeline being bent first upwardly and then downwardly for entry into the sea.

Alternatively, the joining method may be performed while the first and second conduits are inclined at an angle for entry into the sea. In a JLay vessel, where the pipe sections are paid out using a travelling clamp in an inclined tower, the expanding may be performed by a swaying device mounted in the head of the tower.

The bridging member may be introduced to the first conduit, and the first sealing portion expanded prior to elevation of the first conduit to said angle. This saves time at the welding station, and may also prevent the bridging member falling into or out of the pipe during elevation. Alternatively, the bridging member may be held in position 20 initially by some sort of gripping device until it is held in place after swaying.

Bridging members may be introduced to a plurality of lined conduit sections, prior to joining any two of the conduits together. The associated sealing portion may also be swayed at the same time. This can be performed for all pipe sections at a yard onshore 25 if desired, and will save time at the welding station. Protective caps or collars can be applied, to prevent damage to the projecting parts of the bridging member, for storage and transit.

The invention yet further provides in combination a plurality of lined metal pipe 30 sections and a corresponding plurality of bridging members suitable for use in assembling a pipeline by a method according to the invention as set forth above.

The invention in a second aspect provides in combination a tubular bridging member and said first ring portion adapted for use in the connecting method of the first aspect of the invention as set forth above, wherein said first end of said bridging member is introduced into the first conduit between the bore of the conduit and its liner.

The invention in a third aspect provides a tubular bridging member adapted for use in the connecting method of the first aspect of the invention as set forth above, wherein said first end of said bridging member is introduced within the bore of said first conduit liner. BRIEF DESCRIPI ION OF THE DRAWINGS

15 Embodiments of the invention will now be described, by way of example only, by reference to the accompanying drawings, in which: Figure 1 shows a pipe laying vessel suitable for adapting to the existing pipe joining methods of the present invention.

Figure 2 is a cut-away diagram of a tubular bridging sleeve of a first embodiment of the present invention, used to bridge internally between two sections of lined pipe being interconnected; 25 Figure 3a is a schematic cross-sectional diagram showing initial steps of a method of pipe joining of the first embodiment of the present invention, employing the bridging member of Fig. 2; Figure 3b shows the final steps involved in joining the two pipes together using the 30 apparatus described with reference to Figs. 2 and 3;

Figure 4 is a close-up, rotated view of the weld region where two pipes are joined, showing a void region, incorporated into the intermediate portion of the bridging sleeve. 5 Figures Sa, 5b and Sc are schematic cross-sectional diagrams showing steps of a method of pipe joining of a second embodiment of the present invention; Figure 6 is a schematic crosssectional diagram of pipe joining apparatus of a fourth embodiment of the present invention, combining features of other embodiments, as two 10 sections of pipe are brought together for assembly.

DETAILED DESCRIPTION OF THE EMBODIMENTS

15 The system according to the present invention facilitates the offshore assembly of prefabricated field joints with internal liners, using the field proven techniques of S-Lay

or J-Lay. The interconnection system is designed in such a way that it would not impact the laying rate of S-Lay or J-Lay spread. It also does not necessitate the establishment of a fabrication base on shore. In addition, using pipe reeling often requires an increase 20 in wall thickness of the pipe to accommodate the anticipated strain requirements. The technique of the present invention, however, allows using thinner pipe, substantially reducing procurement costs.

The interconnection process of the present invention to be described is an adaptation of 25 the existing welding process developed for welding pipe field joints in S lay or J lay

mode. Single, double or multiple pipe sections with the internal liner already fitted are pre-fabricated onshore, or on-deck. The sections may be pre-installed with components used during the assembly process, or the components may be provided separately. The sections and other required components are then shipped out to the offshore site, where 30 they are assembled to form a continuous pipeline.

Figure 1 shows schematically the arrangement of a pipe laying vessel l having a deck 2, on which is mounted a pipe line assembly arrangement 3, comprising the pipe interconnection system of the present invention, and various coating and testing stations, for assembling a continuous pipeline from a stock of pipe segments. Pipe 4 5 formed in this way progresses in the direction of the arrow, over first and second radius controllers 5, 6. A tillable ramp 7 is provided for launching the pipe over the stern of vessel 1. In solid lines, ramp 7 and other equipment are shown in a near-horizontal orientation, appropriate to lower water depths. In chain-dotted lines, the same components are shown in a steeply elevated orientation. The radius controllers 5 and 6 10 guide the pipe and restrict bending within set limits, according to the angle of the ramp 7. On ramp 7 there are mounted various pipe handling devices, such as straightener 8, tensioning and paying-out device 9 and fixed clamp 10. Sections of pipe for joining are stored in the hold of the vessel. Continuous lined pipe is formed by joining sections of pipe using the novel apparatus and method of interconnection.

The apparatus and method to facilitate interconnecting lined pipes are described in detail in the following sections, with reference to the accompanying diagrams.

Figure 2 is a cut-away diagram of a tubular bridging sleeve 12, used to bridge internally 20 between two sections of lined pipe being interconnected, the liner fitting within the bore of the sleeve. It comprises a hollow cylindrical tube with a smooth exterior surface of substantially equal bore, and a modified interior surface, modified to enhance the seal between the sleeve and a liner, when fitted. Such modifications comprise a number of circumferential channels 14, grouped at each end. The recesses are used to maximise 25 the efficiency of the seal and to enhance the grip between liner and sleeve. The sleeve therefore has three definable regions, these being a) at a first end, a first sealing portion 15 having multiple circumferential channels, b) at the other end, a second sealing portion 16 having multiple circumferential channels and c) an elongate intermediate portion 17, interconnecting the two sealing portions. The sealing portions and their 30 channels are described in detail, later in the document.

As part of the sleeve will be exposed to the fluid being transported, it needs to be fabricated from a corrosion-resistant material. A typical choice of material might be InconellM or stainless steel, however the skilled reader will appreciate that the choice of material is not limited to metals, but to any material providing the required physical 5 attributes.

Figure 3a is a schematic cross-sectional diagram of two prepared lined pipe sections 18, 20 being brought together for assembly with the bridging sleeve 12. Preparation involves operations that can effectively be performed on-shore, such as lining, end 10 bevelling and finishing sections of pipe.

The pipes 18, 20 are typically 6" (150mm) or greater in diameter, having a grade range of XS2 to X65 and a wall thickness of at least %" (-12mm). The liner material is a plastic material, such as polyethylene or polyvinylidene flouride, of HDPE/PE100 IS quality, of a thickness of at least 8mm. The liner 30 exhibits a thermal expansion of approximately 0. 18mm/m/ C and maximum operational temperature of approximately 80 C. Service conditions for the lined pipe are a maximum external pressure of approximately 200 bars and maximum internal pressure of approximately 345 bars. A typical fluid conveyed by the pipe would be deoxygenated seawater o2 < 5ppb plus 20 biocides batch injections.

A section 18 of pipe is mid-way through the process of being connected to a continuous pipeline 20, formed out of previously assembled sections of the same. As can be seen in the section 18 being fitted, the outer, steel pipe 22 includes a widened region 24, where 25 the bore of the pipe is enlarged. Both ends of the pipe section are shaped in the same way, unless items other than pipe sections are being fitted, such as pipe ends or flanges.

The pipe section 18, 20 has been pre-lined with a plastic liner 30. The lining is dimensioned when fitted to contact the inner surfaces of the pipe, with the exception of the widened region 24, approximately 300mm deep, where the liner makes no contact 30 with the pipe. The skilled reader will appreciate that this depth may vary, depending upon the size of the sections being interconnected. Furthermore, the liner is not the same length as the pipe to which it is fitted, the liner ends stopping approximately

120mm short 32, distancing the liner from the region where high weld temperatures would permanently and detrimentally modify the characteristics of the liner. The unlined distance 32 can be reduced where a quicker welding time is used, as less heat is put into the weld region. The converse applies.

The two sections of pipe 18, 20 are interconnected by insertion of a single additional sleeve 12 bridging between the cylindrical voids 34 of both pipe sections.

The ends of the bridging sleeve 12 and/or liner 30 may be bevelled to ease insertion of 10 the bridging sleeve into the bore of the liner. The sleeve, liners and widened portions of the pipe are dimensioned such that the sealing portions IS, 16 are adjacent the external surfaces of both liners, when fitted.

As part of the sleeve will be exposed to the fluid being transported, it needs to be 15 fabricated from a corrosion-resistant material. A typical choice of material might be Inconel_ or stainless steel, however the skilled reader will appreciate that the choice of material is not limited to metals, but to any material providing the required physical attributes. The sleeve may incorporate a ring of metal located in the mid-region and compatible with the welding process used to connect the pipe sections together. The 20 metal ring would form a back plate for the welding process, where required.

In order to keep the fluid being transported from contacting any of the susceptible steel pipe there is required a fluid-tight seal between the contacting surfaces of the plastic liner and the sleeve. This is achieved by swaying a cylindrical metal band 50, located 25 on the inside of the plastic liner but adjacent to a region where both liner and sleeve are colocated, which upon expansion by deformation forces the surfaces of the plastic pipe and sleeve together, thus forming a fluid-tight seal and ensuring that the liner is locked in its intended location. The liner is unable to move with respect to the steel pipe because it is gripped at both ends. To maximise the efficiency of the seal and to 30 enhance the grip between liner and sleeve, a number of circumferential channels 14 have been machined into the inner surface of the sleeve. When the liner is compressed by the swaying process the plastic deforms some way into the channels. Doing so

hinders any longitudinal movement of the pipe liner with respect to the sleeve, firmly capturing the liner in its intended location. The detailed form of the grooves may be the same, for example, as that described in GB 2298256, mentioned in the introduction.

The skilled person will appreciate that different methods may be equally effective for S adhering the contacting surfaces to each other, such as adhesives, or protrusions upon the inner surface of the sleeve.

It is possible to have a lined section of pipe pre-fitted with a sleeve of the first embodiment. In this instance each section of pipe is provided pre-fitted with the liner 10 30 and bonded sleeve 12, thereby minimising the number of operations per section performed offshore. This preferred approach is adopted for the following illustration.

All of the components necessary for joining two pipe sections together have now been described. Pipe interconnection is consequently achieved in accordance with the Is following procedure and with reference to Figures 3 and 4, on the basis that the first sections of pipe have already been laid, forming a continuous section 20 extending into the sea from the pipe laying vessel, and using the pipe sections pre-fitted with sleeves as described in the previous paragraph: 1) Lower continuous section 20 of pipe (further) into the sea to allow the next pipe 20 section 18 to be fitted; 2) Clean the mating surfaces of the protruding sleeve 34 and plastic liner using, for example, compressed air; 3) Lower the next pipe section 18, with cylindrical metal band SO pre-fitted within the bore of the liner, onto the protruding sleeve until the two ends of the steel 25 pipes abut; 4) Weld 80 (Figure 2) the two pipes and sleeve together in a single operation (at this time, or after the final swaying operation); 5) Lower a swaying tool 70 into the sleeve until adjacent the sealing portion to be swayed, then radially expand the band 50 onto the liner, to form a seal between 30 sleeve and liner; 6) Perform any validation steps, such as non-destructive testing; 7) To continue laying further pipe, repeat the process from step 1.

Figure 3b shows steps 7 & 8 of the aforementioned pipe interconnection steps.

The welding process not only bonds the pipe sections together, but also bonds the 5 sleeve 12 to both pipes, resulting in a very strong and resilient connection. The skilled person will appreciate that certain sleeve materials will not be compatible with the chosen process for fusion welding, and as a consequence will not form the aforementioned bond between sleeve and pipe. Flexion of the pipe joint is resisted by not only the pipe-pipe (and pipe-sleeve bonds, where relevant), but also by the two 10 swayed regions. Consequently, relatively thin pipe walls can be used whilst still achieving the required pipe strength.

Note that the weld surfaces are maintained in alignment with respect to each other during this process by the field proven interconnection equipment, rather than by using

15 internal clamps. Furthermore, the welding process used is typical for S-lay and J-lay pipe laying methods currently in use, allowing plastic lined pipes to be used commercially for subsea pipe laying. In J-Lay Systems, where the pipe is suspended almost vertically during the jointing process, the pre-fitting of the bridging sleeve 12 ensures that the sleeve will not slide down the bore of the pipeline. The skilled reader 20 will appreciate that the alternative means can be employed, if pre-fitting is not convenient. For example, a removable plastic collar could be provided around the intermediate portion of each bridging sleeve, holding it in the mouth of the suspended pipe, until it has been sealed to the liner.

25 The skilled person will appreciate that the steps of swaying can be deferred until the most appropriate stage in the process, and as such are not rigidly bound to the order provided above.

Finally, note that the internal diameter of the join between pipes is not significantly 30 reduced by the method, allowing pigs, for example, to travel the pipeline relatively unhindered. The internal diameter of at least the conduit may be increased at its end, so

( as to substantially maintain the bore of the liner at the joints, after expansion of the bridging sleeve.

The choice of welding process for joining the two pipe sections together may dictate S that the bridging sleeve and conduits should be physically separated.

Figure 4b is a close-up, rotated view of the weld region, showing a void region 90, incorporated into the intermediate portion of the bridging sleeve in the vicinity of the weld point, where the two ends of the conduits 18, 20 being joined meet. This void 10 region ensures that the bridging sleeve is not involved in the conduit welding operation, ensuring integrity of the joint which a backing material would otherwise compromise.

In order to protect the newly formed joint from corrosion, any fluid trapped in the void region then needs to be substantially eliminated. This is achieved by performing an 15 additional swaying operation around the region of the void (but before both sealing portions are swayed, to provide the fluid an exit), deforming the bridging sleeve by expanding it radially outwards, substantially eliminating the void and thus any fluid within it. As a consequence there is considerably less corrosive fluid in proximity to the weld joint, maximising the life of the joint. The skilled person will appreciate that in 20 order to facilitate this the intermediate portion will have been designed to ensure that optimumdeformation occurs during the swaying process, and that the design may vary according to the selected sleeve material.

The weld on the outer surface of the pipe is protected in the usual manner, such as by 25 paint.

A further embodiment is hereafter described.

Figures Sa, 5b and 5c are detailed cross-sectional diagrams of the pipe joining 30 apparatus using a further type of corrosion-resistant sleeve 120. Either straight walled pipe 122, or conduit with widened ends (not shown) can be used, into which is fitted a plastic liner 124 with chamfered ends 130, stopping short of each end of the pipe.

The two sections of pipe 18, 20 are interconnected by insertion of the additional sleeve 120 bridging between the liners of both pipe sections. Like before, the sleeve is fabricated from a corrosion-resistant material and, depending upon the choice of sleeve 5 and pipe materials, may incorporate a ring of metal 1001ocated in the mid-region and operating as a back plate when welding the pipe sections together. The sleeve is fabricated from two relatively thin-walled cylinders concentrically joined at their centres. The outer cylinder 132 is unformed, but the inner 134 is shaped so that when fused together they form a single sleeve with a circumferential void region 136 at each 10 end. The end surfaces 138, 140 are chamfered to minimise cross-sectional area at the initial point of contact between sleeve and liner 124 and to guide the liner into the void 136 between the two cylinders. The ends of the liners are also chamfered 130 for the same reasons, but it is not essential that both bridging sleeve and liner are chamfered.

15 Figure 5c shows how a fluid-tight seal between sleeve 120 and liner 124 is achieved.

The sleeve is fitted onto the liner, with the outer cylinder 132 of the sleeve remaining in contact with the inner wall of the steel pipe 122 whilst the inner cylinder 134 of the sleeve becomes the new inner surface of the pipe, bridging between liner sections. A seal is formed between liner and sleeve by using a swaying tool 70 to concentrically 20 deform the inner cylinder of the sleeve to grip the liner, thereby forming a fluid-tight seal and ensuring that the liner remains in its intended location.

As with an earlier embodiment, to maximise the efficiency of the seal and to further enhance the grip between liner and sleeve, a number of circumferential channels 14 25 may be additionally machined into the inner surface of the sleeve. When the liner is compressed by the swaying process the plastic deforms some way into the channels.

Doing so further hinders any longitudinal movement of the pipe liner with respect to the sleeve, firmly capturing the liner in its intended location. The skilled person will appreciate that different methods may be equally effective for adhering the contacting 30 surfaces to each other, such as adhesives, or protrusions upon the inner surface of the sleeve. Furthermore, as the outer cylinder of the sleeve will not in use come in contact with corrosive fluid, it can alternatively be fabricated from other materials, such as low

cost carbon steel, removing the need for a separate weldable insert 100 (where required) as the whole cylinder is weldable.

The liner is unable to move with respect to the steel pipe because it is firmly captured at 5 both ends.

It is possible to have a lined section of pipe pre-fitted with a sleeve of the second embodiment. In this instance each section of pipe is provided pre-fitted with the liner and bonded sleeve, thereby minimising the number of operations per section performed 10 offshore. This preferred approach is adopted for the following illustration.

All of the components necessary for joining two pipe sections together have now been described. Pipe interconnection is consequently achieved in accordance with the following procedure, on the basis, like before, that the first sections of pipe have 15 already been laid, forming a continuous section 20 extending into the sea from the pipe laying vessel and using the pipe sections pre-fitted with sleeves as described in the previous paragraph: 1) Lower continuous section 20 of pipe (further) into the sea to allow the next pipe section 18 to be fitted; 20 2) Clean the mating surfaces of the cylindrical void 136 of the protruding sleeve using, for example, compressed air; 3) Lower the next pipe section 18 onto the protruding sleeve, so that the pipe liner is guided into the cylindrical void of the sleeve and until the two ends of the pipes abut; 25 4) Weld 80 the two pipes and sleeve together (at this time, or after the final swaying operation); 5) Lower a swaying tool 70 into the sleeve until adjacent the sealing portion to be swayed, then radially expand the inner cylinder of the sleeve into the liner; 6) Perform any validation steps, such as non-destructive testing; 30 7) To continue laying further pipe, repeat the process from step 1.

As with the previous embodiment, the welding process not only bonds the pipe sections together, but also bonds the sleeve 120 to both pipes, resulting in a very strong and resilient connection. Flexion of the pipe joint is resisted by not only the pipe-pipe and pipe-sleeve bonds, but also by the two swayed regions. Consequently, relatively thin 5 pipe walls can be used whilst still achieving the required pipe strength.

internal clamps. Furthermore, the welding process used is typical for Slay and J-lay 10 pipe laying methods currently in use, allowing plastic lined pipes to be used commercially for subsea pipe laying.

This particular configuration of bridging sleeve 120 ensures that the sleeve is not capable of being lost by sliding down the bore of the pipeline, providing flexibility on 15 when the sleeve could be fitted to the pipe.

The skilled person will appreciate that the steps of swaying can be deferred until the most appropriate stage in the process, and as such are not rigidly bound to the order provided above.

Finally, note that due to the thin sleeve walls, the internal diameter of the join between pipes is not significantly reduced by the method, allowing pigs, for example, to travel the pipeline relatively unhindered. The internal diameter of at least the conduit may be increased at its end, so as to substantially maintain the bore of the liner at the joints, 25 after expansion of the bridging sleeve.

The choice of welding process for joining the two pipe sections together may dictate that the bridging sleeve and conduits should be physically separated. Correspondingly, a void region may be deliberately introduced into the bridging sleeve around the weld 30 point, where the two ends of the conduits being joined meet. This void region ensures that the bridging sleeve is not involved in the conduit welding operation, maintaining the integrity of the joint.

Figure 6 shows a fourth embodiment, whereby features of a previous embodiment are combined with a new variant of sealing portion. Here, a section of pipe 20 is formed for use with a bridging sleeve that tapers, the plastic liner following the contours of the 5 pipe and the bridging sleeve sealing against the inner surface of the liner. The other end of the pipe, denoted by pipe 18, is fanned for use with a bridging sleeve of the first embodiment, the plastic liner traversing the pipe as an unformed sleeve, the liner sealed between the bridging sleeve and a swaying ring. Pipe section 20 can have the bridging sleeve pre-installed, to speed up pipe laying by halving the required quantity of fit-and 10 swage operations per section of pipe being joined.

The skilled reader will appreciate that numerous variations are possible within the principles of the apparatus described above. Accordingly it will be understood that the 15 embodiments illustrated herein are presented as examples to aid understanding, and are not intended to be limiting on the spirit or scope of the invention claimed.

Claims

CLAI M S

I A method of joining plastic-lined fluid conduits comprising the steps of: - providing a first conduit and a second conduit, each conduit comprising a wall 5 of metal defining a bore, said bore substantially lined by a plastic liner, said conduits having open ends for connection; providing a tubular bridging member having a first end and a second end; introducing said first end ot said bridging member into said first conduit so as to provide a first portion of overlap between said liner and said bridging member; 10 - forming a first seal bctwocn said liner and said bridging member; - introducing said second end of said bridging member info said second lined conduit between the bore of the conduit and its liner so as to provide a second portion of overlap between said liner and said bridging member, the lengtl1 of the bridging, member and said overlap portions being such as to bring said first I 5 and second conduits' ends substantially abutting. and - at a time after said ends arc brought together welding said ends together' - at a time after said secontl overlap is formed, providing a ring portion of plastically deformable material dimensioned to fit within the bore of said liner, introducing said ring into the liner until it aligns with said second overlap, and 2() expanding said ring radially so as to press the liner against the bridging member to form a second seal between the liner and bridging, member; the liner, the first and second seals and the bridging member thus forming a continuous barrier bctwccn the interior bore of tile lined conduits and the metal of the conduit lls. 2. A method of joining conduits as claimed h1 claim 1, wherein the first end of said bridging mcmbCr is introducotd into the first conduit between the bore of the conduit and its liner, anti a time after the conduit ends arc brought to=,cthcr' providing as said nicans for forming, said first seal u r in;, of plastically dcfLlrniabic material dUlcnsioncd 2() to fit within the bore of said first conduit liner, introducing, said ring into the liner until it aliens with said first overlap, and expanding said ring so as to press the liner against the br itiin nlCniher.

3. A method of joining conduits as claimed in claim I, wherein the first end of said hridin member is introduced within the bore of said first conduit liner, and a time after said ends are brought together, expanding said first end radially so as to press the 5 bridging member against the liner to form said first seal.

4. A method of joining conduits as claimed in any preceding claim, further comprising the additional step of expanding the bridging member radially in the region of the welded pipe ends so as to substantially displace any fluid trapped within the I () confines of the bridging member, the liners and the conduit wal Is in said region.

5. A method of joining conduits as claimed in claim 4, wherein said radial expansion h1 to region of the welded pipe ends is performed concurrently with subseLlueut passes of weldhig.

6. A method of joining conduits as claimed in any preceding claim, wherein said hricighg nenber is fabricated out of corrosion-resistant metal.

7. A melilod of joining conduits as claimed he any preceding claim, vvilerein at 9() least one formation is provided on at least one of said overlap portions to improve grip between to bridging member and the liner.

S. method of joining conduits as claimed in claim 7, wherein each sealing portion comprises a series of circumiercntial formations.

t). A metilotl of joining conduits as claimed in any of claims I to 7 wherein adLesivc is applied to at least one of said overlap portions to improve grip between the hridgina ncnher and the liner.

2() 1() A nctilotl of joining conduits as claimed in any prcccdbig, claim, wherein at each cold to tic joined, the end face of the plastic Ihlhg mcnlcr is lo'g,itufinally spaced front the end of said conduit.

I 1. A method of joining conduits as claimed in any preceding claim, wherein at each ent1 to be joined the end face of the plastic lining member is chamfered to reduce the cross-sectional area presented to said bridging member.

s 12. A method of joining conduits as claimed in any preceding claim, wherein the internal diameter of at least the first conduit is increased at its end, so as to facilitate insertion of said bridging member between the liner and the wall of the first conduit.

1() 13. A method of joining conduits as claimed in claim 12, wherein at least one of said plastically deformable rings is provided as an annular ring abortion, integral with said bridging member, whereby introducing the bridging member to the lined conduit also introduces said ring portion into the liner, in alignment with said overlap portion.

15 14. A method of joining conduits as claimed in any olclaims I to 12, whcreh first of said plastically deformable rheas is introduced separate to the bridging, mcmbcr.

15. A method of joining conduits as claimed in any preceding claim, wherein to ninimise the number of steps pcrfonned offshore, the bridging, member is pre-fittcd to 7() a section ot conduit.

1(. A method of joining conduits as claimed in any F,rcceding clahn, wherein saicl hridgig mcmhcr further comprises a wcidahic portion located to align with the pipe culls loci',= jowl, ill se.

17. A method of joining conduits as claimed in claim 1(. wllCrein the step of welding the conduits together also wckis tlc bridhg mcmhcr to Alec conduits.

18. A metlotl ol joining conduits as elaimett ill any preceding, claim, whereh1 said 3() conduit lining comprises rigid plastic.

19 A method of joining conduits as claimed in claims 1 to 17, wherein said conduit linh,g, is compressitlc.

2() A method of joint conduits as claimed in any prcccding, claim, whcrch said 5 conduit lining is a loose fit within the conduit.

21 A method of joining conduits as claimed in claims I to 19, wherein said conduit lining is an interference fit within the conduit.

I () 22. A method of offshore pipeline fabrication and laying, conprising the joining of first and second conduits by the repetition of the sequence of steps as clahilcd hi any of claims I to 21 to produce a continuous pipeline, each conduit hcing a section of pipclhe added in turn to the pipeline hcing laid.

15 23. mcthoci of offshore pipeline fabrication and laying as clahnetl in claim 22, whcrch said first conduit is the pipe section joined already to tile pipelhe and the second conduit becomes the first conduit after the second conduit has been interconnected with the first conduit.

2(} 24. A method of offshore pipeline fabrication and laying as claimed in claim 23' wherein said first conduit is the one bchl added to said pipeline and the second conduit becomes the first conduit after interconnection.

25. A netiloci of offshore pipclhc fabrication and laying as claimed in any of 95 claims " to 24, whcrch, each said section is less than 1 ()()n, long,.

2(. A ncthod of offshore pipclhc fabrication and lays as clahilcd in any ol clains " to 25, wlcrcin talc joint of the conduits is pcrfon,cd while Alec first and accord conduits arc substantially horizontal, the asscmbicd pipclhc being bent first () upwardly anti then downwardly for entry into the sea.

\ 27. method of offshore pipeline fabrication and laying as claimed in any of claims 22 to 25 wherein the joining of the conduits is performed while the first and second conduits are inclined at an angle for entry into the sea.

5 28. A method of offshore pipeline fabrication and laying as claimed in claim 27 wherein the method is performed upon a J-l ay vessel and the expanding of the sealing portions of the bridging member is carried out by a swaying device mounted in the head of said tower.

1 () 29. A method of offshore pipeline fabrication and laying as claimed in claims 27 or 28 wherein the hrilging member is introduced to the first conduit and the first sealing portion expanded prior to elevation of the first conduit to said angle.

30. A method of offshore pipeline fabrication and laying as claimed in claims 27 or 15 28 wherein the bridging nemher is hcid in position initially by some SON of gripping device until it is held in place alter swaying.

31. A method of offshore pipeline fabrication and laying as claimed in any of claims 22 to 30 wherein bridging members are introduced to a plurality of lined 2() conduit sections prior to joining any two of the conduits together.

32. A method of offshore pipeline fabrication and laying as claimed in claim 31.

wlerein an associated sealing portions is also swayed at the same time.

25 33. A pipe laying apparatus speeipcally adapted lair Rosin th1Ctl conduits by a ncthod as claimcti ill any of claims I to 21 or for t:abricating and laying pipeline by a ctlod as claimed in any of clahns 22 to:12.

34. A plurality of lined natal pint sections and a corresponding plurality of 3() Ride mcmhcrs suitable for Disc in assembling a pipeline by a method as claimed in any ot claims 22 to 32 or rising talc metloti as claimed in ally of claims I to 21.

35. A tubular bridging member combined with said first ring portion adapted for use in tlc metilotl as claimed ill any of claims I to 32 wherein said first end of said bridging mcmhcr is introduced into the first conduit betwocn the bore of the conduit and its liner.

36. A tubular bridging men1bcr adapted for use in a method as claimed in any of claims I to 32 wherein said first end of said bridging member is introduced within the bore of said first conduit liner.

10 37. A tubular bridging mt miner as claimed in claim 36 wherein at least one coronation is provided on at Icast one sealing portion to improve the grip between the hritlgin metilLcr and the liner of the conduits.

38. A tubular bridging member as claimed in claim 37 wherein said fornication is coinpriscs a series of circumferential formations to improve the grip between the hridin mcmhcr and the liner otthc conduits.

39. A tubular bridging member as claimed in any of claims 37 or 38 wherein the cod of Bloc bridging member is chamfered to aid insertion of Saitl bridging tnember into 7() the lined conduit.

4(). An expansion tool for USC in the metl1otis as claimed in any of claims I to 32.

said tool pcrtorming the expansion of portions of said tubular bridging mcolher as claimed in claims 35 to 39.

41. An apparatus substantially as 1lcreinbclorc dcscriLcd with rCfcRcHcc to any of figures I to (' of tlc acconipanying drawings.

42. A ncthotl substantially as hcrcinbchorc IcscriLctl with reference to ally of 3() f;,urcs I to of talc accompanying, tirawings.

( 43. A tool substantially as hereinbcDore described with rcfcrcnce to any of figures I to 6 of the accon3,anying drawings.