It is particularly advantageous to line pipes with a plastic liner ; such liners provide corrosion protection and chemical protection, allowing carbon steel pipe to be used where expensive corrosion resistant alloys would otherwise be required. The liner typically is a thin wall semi-rigid polymer or fibre-reinforced polymer, whose OD is smaller than the ID of the outer steel pipe. It is conventional to line pipes with a liner by injecting a grout composition into a space between the liner and the pipe. The function of the grout is to enable pressure loads to be transferred directly to the outer pipe which carries the main structural loads. The thickness of the liner is normally as small as is practical for manufacture, transportation, handling and installation in the pipe and for it to be fluid-tight. Typically, the liner thickness is 1.5 to 3 mm for pipe diameters 2"to 10".

There are problems with grouting plastic liners in large diameter pipes, because liners are very weak against collapse, and the injection of the grout between the liner and the pipe imposes considerable external forces that can cause the liner to collapse. Table 1 gives a theoretical estimate of the external pressure causing collapse, in kPa, for a filament wound, glass reinforced epoxy liner in a range of pipe diameters and liner thicknesses.

Table 1 Pipe Diameter Liner Thickness t=2 mm t=4mm t=8mm 4" (10 cm) 260 2100 16800 8" (20 cm) 33 260 2100 16" (41 cm) 33 260 32" (81 cm) 1 4 33 The effect of the high pressure on the liner during injection of the grout can be catastrophic when the liner collapses or buckles. There also can be less obvious problems, such as ovalisation of the liner and micro-cracking. Ovalisation is

undesirable because of the reduction in the through-bore of the pipe. Micro-cracking causes the liner to lose its fluid-tightness.

The restriction on injection pressure in prior art methods of lining a pipe leads to a number of limitations: 1. The use of high viscosity grouts is restricted, because they require higher injection pressures. US-A-3482007 describes the use of a high water content cementitious grout to line a pipe. High water content cementitious grouts have a number of disadvantages such as the likelihood of pockets of unreacted water, a reduction in strength and load carrying capacity of the cement, and the likelihood that the cement will crack under bending loads.

2. The use of the liner in larger diameter pipes is restricted. It can be seen from Table 1 that for larger diameters, either the injection pressure must be reduced, or a thicker liner must be used to prevent collapse. The disadvantages of increasing the liner thickness are the increased cost of the liner, and the reduction in the effective bore provided within the pipe.

3. The length of pipe that can be lined in a single operation is restricted. The external pressure on the liner during injection of the grout is a back pressure caused by friction between the grout and the inside surface of the pipe and the outside surface of the liner. Thus, the injection pressure needs to be higher for longer lengths of pipe. The cost of the mechanical pipe connector is a significant portion of the cost of lined pipe : if a longer length can be lined, then the cost of the connectors per metre length of pipe is reduced proportionately.

4. The minimum size of the space between the liner and the pipe is restricted. The injection pressure needs to be higher when the space between the liner and the pipe is reduced. The advantages of reducing this space are that less grout is required, the bore of the liner is larger, and there is a possible improvement in the bond

strength of the grout.

5. The speed at which the grout can be injected is restricted. One way of reducing the injection pressure is to slow the rate of injection. However, if the injection time is too long, some polymer- based grouts will start to gel or cure before they reach the end of the pipe. In addition, restricting the injection rate restricts the manufacturing output or demands additional equipment.

Another major problem with lining pipe is the possibility of air pockets due to air entrapment during grout injection and of voids due to shrinking and cracking of the grout during curing. Large voids do not provide adequate support for the liner when the pipe is pressurised. Even small voids can cause problems when the pipe is used to transport gas. Gas can permeate through the liner and grout to build up pressure in the voids. When the pressure in the pipeline is released, which can happen over a period of only a few minutes, the gas in the voids does not have sufficient time to permeate back into the bore, and will expand and damage the liner. The damage to the liner can be severe enough to block the pipe, or in lesser cases can crack the liner sufficiently to allow the ingress of fluid.

We have now found a way to line pipe which overcomes these problems.

One aspect of our invention involves supporting the inside of the liner at the same time as the grout is injected between the liner and the pipe. This helps to prevent collapse of the liner during injection. Another aspect of our invention involves using sub-atmospheric pressure in the space between the liner and the pipe in order to minimise the risk of voids and air pockets. Another aspect of our invention is the use of a polymer based grout which adheres to the pipe and liner and which is flexible.

Another aspect of our invention involves coating the external surface of a liner for a pipe with a plurality of solid particles, in order to improve adhesion of the liner to a grout composition. There are other aspects of our invention, which will become clear from the following description.

According to one aspect of the invention there is provided a method of lining a pipe, comprising placing a liner within a bore of the pipe, injecting a grout composition into a space between an external surface of the liner and an internal

surface of the pipe, and simultaneously supporting an internal surface of the liner against the pressure applied to the external surface by the injection of the grout.

In one embodiment the internal surface of the liner is supported by pressurising the space within the liner such that the difference between the pressure within the liner and the pressure in the space between the liner and the pipe is less than the collapse pressure of the liner.

In another embodiment the internal surface of the liner is supported by expanding an inflatable bladder within the liner to bear against the internal surface of the liner such that the difference between the pressure within the bladder and the pressure in the space between the liner and the pipe is less than the collapse pressure of the liner.

In a further embodiment the internal surface of the liner is supported by a mandrel that bears against the internal surface of the liner to prevent the pressure in the space between the liner and the pipe from collapsing the liner. Preferably the mandrel can be collapsed in order to remove it from the pipe after the pipe has been lined.

According to another aspect of the invention there is provided apparatus for lining a pipe with a liner, comprising injection means for injecting a grout composition into a space between an external surface of the liner and an internal surface of the pipe, and support means for supporting an internal surface of the liner against the pressure applied to the external surface by the injection of the grout.

In one embodiment the support means includes a pump adapted to pressurise the space within the liner such that the difference between the pressure within the liner and the pressure in the space between the liner and the pipe is less than the collapse pressure of the liner.

In another embodiment the support means comprises an inflatable bladder disposed within the liner, and a pump adapted to pressurise the inflatable bladder to cause the bladder to bear against the internal surface of the liner such that the difference between the pressure within the bladder and the pressure in the space between the liner and the pipe is less than the collapse pressure of the liner.

In another embodiment the support means comprises a mandrel adapted

to bear against the internal surface of the liner to prevent the pressure in the space between the liner and the pipe from collapsing the liner. Preferably the mandrel is collapsible to facilitate removal from the pipe after the pipe has been lined.

According to another aspect of the invention there is provided a method of lining a pipe, comprising placing a liner within a bore of the pipe, injecting a grout composition into a space between an external surface of the liner and an internal surface of the pipe, and simultaneously reducing the pressure within said space. The reduction of the pressure helps to prevent the entrapment of air pockets and the formation of voids in the grout composition. It also pulls the grout composition through the annular space, and thus lowers the injection pressure required.

Preferably the pressure within the space is reduced to below 20 kPa, more preferably to below 10 kPa. It is preferred that the grout composition is injected at one end of the liner, while the air present in the space between the liner and pipe is removed downstream of the point of injection of the grout composition. Preferably the air present in the space between the liner and the pipe is removed from the opposite end of the liner to the point of injection of the grout composition.

According to another aspect of the invention there is provided apparatus for lining a pipe with a liner, comprising injection means for injecting a grout composition within a space between an external surface of the liner and an internal surface of the pipe, and means for reducing the pressure within said space.

Preferably the means for reducing the pressure within said space is a vacuum pump.

According to another aspect of the invention there is provided a method of lining a pipe, comprising placing a liner within a bore of the pipe and injecting a grout composition into a space between an external surface of the liner and an internal surface of the pipe, wherein the external surface of the liner and/or the internal surface of the pipe are pre-treated with a low viscosity material prior to injection of the grout composition.

The purpose of this pre-treatment is to wet the surface of the liner and/or pipe in order to reduce friction when the grout composition is injected; this reduction in friction enables the grout composition to be injected at lower injection pressures.

The low viscosity material may be a resin or glycol or water. The viscosity of this material is preferably below 1000 cPs at 20 °C. The low viscosity material may be drained from the space prior to injection of the grout composition, or may be displaced as the grout composition is injected.

According to another aspect of the invention there is provided a method of lining a pipe comprising placing a liner within a bore of the pipe, placing an injection head at each end of the liner, injecting a grout composition through at least one injection head into a space between an external surface of the liner and an internal surface of the pipe, wherein each injection head is moved into contact with the liner in order to provide a seal between each injection head and the liner, and wherein the movement of the injection heads is carried out in a direction along a longitudinal axis of the liner.

This enables the injection heads to be pushed onto the liner without relative rotational movement between the liner and the injection heads. This has a number of advantages : the damage to the sealing part of the injection heads during assembly is minimised; the damage to the cured grout composition during removal of the injection heads is also minimised; and, in the case of long lengths of pipe where the liners have been bonded end to end, torsion on the liners during the fitting of the heads (which could break the bonded joints) is eliminated.

According to another aspect of the invention there is provided apparatus for lining a pipe, comprising injection means for injecting a grout composition into a space between an external surface of a liner and an internal surface of the pipe, and an injection head adapted to be disposed at each end of the liner, each injection head being adapted to sealingly engage a respective end of the liner, wherein each injection head is moveable between a retracted position in which it does not sealingly engage the liner, and a sealing position in which it sealingly engages the liner, and wherein the movement of the injection heads between the retracted position and the sealing position takes place in a direction along a longitudinal axis of the liner.

Preferably each injection head comprises a body member adapted to sealingly engage the liner, and securing means for releasably securing the head member to the pipe to be lined. When the securing means has been secured to the

pipe, the body member can be brought into sealing engagement with the liner by moving it relative to the securing means in a direction extending axially of the liner.

There are a number of ways in which the body member can be secured to the securing means. One way is to provide a bolt which extends through an aperture in the body member and into an aperture in the securing means, so that screwing the bolt into the aperture of the securing means moves the body member towards the securing means. Preferably at least two of said bolts are provided, each of which extends through respective apertures in the body member and the securing means.

Jacking bolts may also be provided so that, after the grout composition has cured, the body member can be withdrawn from the securing means with minimum effort and damage to the ends of the liner and the cured grout. Preferably at least two such bolts are provided. The bolts screw through either the body member or the securing means and bear axially on the other.

The securing means preferably comprises a sleeve adapted to receive the pipe to be lined, and a fixing member, such as a bolt, provided on the sleeve and adapted to engage the pipe in order to secure the sleeve to the pipe.

The lined pipe can be joined by connectors which may be welded onto the pipe or threaded directly on the pipe. Continuity of corrosion protection across the joint between the lined pipe is normally provided by a"corrosion barrier ring"normally made of a material such as PTFE, which is axially compressed when the pipe is assembled together and which prevents the exposure of the connector to the fluid.

A plastic end cap (which is usually called a"flare") is conventionally used to protect the ends of the liner from exposure to fluid and from impact damage. Such flares are normally adhesive bonded to the end of the liner. The flare has an"L" shape in section.

According to a further aspect of the invention there is provided a method of lining a pipe, comprising placing a liner within a bore of the pipe, injecting a grout composition into a space between an external surface of the liner and an internal surface of the pipe, severing the ends of the liner after injection of the grout has been completed, and placing a corrosion barrier ring in contact with at least one end of the liner, in order to protect said end from direct exposure to fluid.

This technique avoids the need for the use of a flare. The flare conventionally used has the disadvantage that it protrudes into the bore of the liner, and thereby reduces the size of the bore. In addition, flares can cause localised erosion damage, and can be damaged by the passage of downhole tools or pipeline pigs.

The liner is preferably severed using an oscillating saw. It is very important, particularly when a flare is not used, that a clean cut is obtained without damage to the end of the liner. A filament wound liner contains thousands of filaments and is difficult to cut with a hacksaw or machine tool, without causing some damage to the ends of the liner. Because of the nature of the filament winding, damage during cutting often extends several inches from the end of the liner.

The corrosion barrier ring is preferably a gasket type PTFE ring. The thickness of the corrosion barrier ring is preferably less than or equal to substantially 50% of the outer diameter of the ring, and in some embodiments may be may be less than or equal to substantially 25% of the outer diameter of the ring. In an embodiment, the corrosion barrier ring has a thickness of substantially 1.5 mm and an outer diameter of substantially 5 mm. Preferably the thickness of the corrosion barrier ring is in the range 1 to 1.5 mm; a thickness of 0.05 inch (1.3) mm is very suitable. The corrosion barrier ring, per se, is a feature of the present invention.

It is preferred that the cut ends of the liner are sealed prior to engagement with the corrosion barrier ring, in order to reduce absorption of fluids at the cut fibres.

Sealing of the cut ends of the liner can be done using an adhesive, using the grout composition, or using the same resin as in the liner. Preferably the sealant has thermal and chemical resistance properties matching those of the liner.

An alternative to protecting the cut end of the liner with a corrosion barrier ring is to provide an insert between the end of the liner and the corrosion barrier ring, wherein an internal surface of the insert is flush with the internal surface of the liner.

The insert may be a corrosion resistant alloy, such as a stainless steel, or may be plastic. This insert also provides protection to the liner from damage due to wirelining operations which are carried out on downhole tubing. The space for the insert is cut in the liner and grout and the insert is fitted. The OD of the insert may be flush with the

ID of the connector, or the OD of the insert may be larger than the ID of the connector in which case the connector has a machined recess to hold the insert. This allows the insert to be thicker and provides a metal shoulder to prevent the insert from moving axially. The insert material may be bonded to the connector, and to the ends of the liner and grout, with an adhesive or with the grout composition. The main function of this material is as a sealant to prevent the ingress of fluid into the cut fibres in the liner, so the adhesive strength required is low. A sealant material such as liquid PTFE may therefore be used. It is desirable that the material be flexible because of the differential thermal expansion of the connector, liner, grout and insert at the interface.

It is preferred that all the features of the invention described above are used in the lining of the pipe, but it will be appreciated that any one of these features of the invention will provide advantages over the prior art, and that one or more of these features of the invention may be used in combination.

In all the above apparatus and methods of the invention, after the grout composition has been injected into the liner, it can be allowed to cure. Curing causes the grout composition to harden, and to adhere to the liner and the pipe, thereby providing a secure bond between the liner and the pipe.

The pipe can be preheated in order to reduce the viscosity of the grout composition, thereby allowing it to be injected at lower pressure. Preferably the pipe is preheated to a temperature between 20°C and 40°C. It is not usually advisable to heat the pipe to more than about 40°C, because this may cause the grout composition to cure before it has been fully injected (in general grout compositions cure faster at higher temperatures). The onset of curing causes an increase in the viscosity of the grout composition, which therefore requires the injection pressure to be increased.

In addition, or as an alternative, it is possible to pre-heating the grout composition prior to injection, in order to reduce the viscosity of the grout composition.

After the grout composition has been injected, it is preferred to heat the pipe in order to reduce the cure time. It is preferred that the temperature of the pipe is increased to at least 50°C, preferably at least 80°C. Typically this heating would be carried out for a minimum of 2 hours.

Either or both the heating steps may be carried out by placing the pipe

in a bath of hot water. Heating may also be done using an oven. The post-heating can be done by circulating hot water through the bore of the liner. Pre-heating cannot be efficiently done by circulating hot water through the bore of the liner, since the space between the liner and the pipe reduces heat transfer from the bore into the pipe.

It is preferred to maintain the injection pressure during curing of the grout composition to minimise voidage and the separation of the components of the grout composition and the byproducts of the curing process.

The methods and apparatus according to the invention allow the use of special grout compositions that are more flexible than cementitious grouts, and are of higher viscosity than cementitious grouts. To this end, we provide a new grout composition comprising or consisting of a curable phenolic polymer, which is advantageously cashew nut shell liquid (CNSL). In a preferred embodiment, the grout composition comprises a blend of first and second components, wherein the first component is a curable phenolic polymer, and the second component is a curable polymer and/or a curable cementitious material.

Most preferably the first component is a curable phenolic polymer containing unsaturated alkyl groups.

It is preferred that the first component is a natural resin, and the second component is a synthetic resin. We have obtained particularly good results when the first component is CNSL. The addition of CNSL greatly improves the flexibility of the cured grout composition and allows lower levels of acid catalyst to be used. The latter reduces the reaction of the acid catalyst with the steel pipe. Flexibility is highly desirable for lined pipe used in offshore pipeline which are subjected to high bending loads during installation and for downhole tubing in deviated wells. The flexibility (low elastic modulus) of the grout also helps to reduce stresses in the grout due to the differential thermal expansion of the liner and pipe. In addition, CNSL has a natural organic molecular structure which repels water, and as a component in the grout composition therefore adds a second level of corrosion protection. CNSL also has the advantage that it costs less than synthetic phenolic polymers, and is of relatively low viscosity compared to many synthetic phenolic polymers. Furthermore, the grout compositions containing CNSL have shown good bond strength both to the liner and

to the pipe.

Typically, CNSL contains about 90% anacardic acid, with the remaining 10% being a mixture of substituted resorcinols known as cardol. These compounds contain a linear alkyl side chain which contains an average of nearly two olefinic bonds.

CNSL has a dual functionality in resin-forming reactions, because it is both phenolic and olefinic in character. CNSL and its derivatives can therefore be (a) condensed with formaldehyde through the phenolic nuclei, and (b) polymerised through unsaturated side chains.

The CNSL-based polymer grout has a strongly hydrophobic nature because of the presence of a C, 5 hydrocarbon side chain on the CNSL molecule. As a result, the material is highly resistant to moisture.

The second component is preferably a synthetic phenolic polymer or an epoxy resin. When the second component is a phenolic polymer, it is preferably a low water phenolic polymer (with a water content after curing of less than 5%).

When the first component is CNSL, the purpose of the second component is to add strength to the cured grout composition and to accelerate the cure. CNSL on its own hardens slowly over many weeks. A function of the second component is therefore to achieve a hardened grout within a shorter period, typically 2-4 weeks.

The second component may alternatively be a blend of Portland cement with a phenolic polymer. In this case, the hydration reaction of the cement uses up water produced by the condensation reaction of the phenolic resin, resulting in a low water content in the cured grout.

Preferably the grout composition comprises 10 to 90 wt% of the first component, more preferably substantially 50% wot.

A curing agent would normally be added to the grout composition, prior to its use. For example, the curing agent for the CNSL may be formaldehyde, while the curing agent for the second component, when the second component is a phenolic polymer, may be ortho-phosphoric acid and/or xylene sulphonic acid.

The grout composition may include a component to aid the adhesion of the grout to the liner and pipe, such as a silane or siloxane. This component would also aid the adhesion of the grout to any grit provided on the external surface of the

liner, and to the a material in the grout composition.

A further material may be added to inhibit the curing of the first component until the curing agent for the second component has reacted with the second component. This allows the first and second components to be pre-mixed by the resin supplier before delivery, requiring only the addition of a single component to initiate the curing reaction.

Preferably the grout contains a filler. Typical fillers include ceramic microspheres and fly ash. Preferably the grout composition comprises 20-80% filler by volume, more preferably 40% filler, by volume. The main function of the filler is to reduce the overall cost of the grout composition. In the case of hollow microspheres, the filler provides increased thermal insulation which for some applications is highly desirable (it reduces the temperature of the pipe wall). In this case, the space between the external surface of the liner and the internal surface of the pipe may be deliberately enlarged to provide greater thermal insulation.

In another aspect of the invention we provide a liner comprising a tubular material, preferably a flexible plastics material, with a plurality of solid particles bonded to the external surface thereof. In the case of a filament wound liner, the solid particles can conveniently be applied after the liner is wound and before the liner is cured. The solid particles are preferably provided in the form of a grit. The liner according to this aspect of the invention is capable of making an extremely good bond with a grout composition. A secondary benefit of gritting the external surface of the liner is that the grit"dries"off the surface, reducing resin undulations and peaks on the outside of the liner, and giving a tighter tolerance on the as-produced OD of the liner. The undulations on the OD of the liner due to the overlapping of the bands of fibre are controlled by the selection of appropriate filament sizes and bandwidth.

It is preferred that the solid particles have a size distribution with 99 per cent below 100 microns, but the size can be between 20 and 1000 microns. Preferably the solid particles comprise ceramic microspheres, most preferably hollow microspheres of aluminium silicate. Hollow microspheres have reduced impact on the viscosity of the grout composition.

According to another aspect of the invention, we provide a liner for a pipe,

comprising a tubular material containing fibres within a matrix comprising or consisting of a synthetic phenolic resin.

In one embodiment, said matrix comprises a blend of a poly-siloxane polymer with said synthetic phenolic resin. In another embodiment, said matrix comprises a blend of CNSL with said synthetic phenolic polymer. The synthetic phenolic polymer is preferably a low water phenolic polymer.

A resin rich layer is preferably provided on the bore of the tubular material. The resin rich layer preferably comprises a furane resin or another resin different to the resin of the liner. The resin rich layer may include a plurality of solid particles ; the solid particles may be the same as the solid particles described above.

The fibres may be, for example, glass and/or aramid fibres.

The methods and apparatus according to the present invention allow the use of higher viscosity, flexible grout compositions (such as the grout composition according to the invention), which do not crack when the pipe is bent up to the yield strength of the pipe (as occurs during offshore pipe lay). The methods and apparatus also allow the use of thin wall liners (typically 2-3 mm thick) in large diameter pipe (e. g.

80 cm or more). The methods and apparatus also allow longer lengths of pipe to be lined in a single operation, for example 25m lengths can be lined. The methods and apparatus also allow grouting to take place within the cure cycle of the grout composition, even for large diameter, long length pipes.

The methods and apparatus of the present invention are particularly useful for lining pipe to be used in offshore applications.

The grout composition according to the invention is chemically stable at the maximum operating temperate of the liner (typically up to 200 °C), and is flexible at ambient temperature and at the maximum operating temperature of the liner. The grout composition is almost incompressible, has low viscosity during filling, has low shrinkage during curing, and is water-repellent. The grout composition has a good bond strength to both the liner and the pipe.

Reference is now made to the accompanying drawings in which : FIG. 1 shows a pipe before a liner has been placed therein; FIG. 2 shows the pipe of FIG. 1, with a liner placed therein, with inlet and

outlet injection heads placed at each end of the liner ; FIG. 3A shows the inlet injection head of FIG. 2 in greater detail ; FIG. 3B shows the outlet injection head of FIG. 2 in greater detail ; FIG. 3C shows an alternative form of the inlet injection head; FIG. 3D shows a view of the outer seal ring of FIG. 3C; FIG. 4 shows schematically the equipment used to inject a grout composition into the space between the liner and pipe; FIG. 5A shows one embodiment of a method to seal the end of the liner ; FIG. 5B shows another embodiment of a method to seal the end of the liner, with a part thereof shown on an enlarged scale ; and FIG. 5C shows another embodiment of a method to seal the end of the liner ; FIG. 5D shows another embodiment of a method to seal the end of the liner ; FIG. 6 shows a lined pipe after assembly; FIG. 7A shows a conventional method of joining lined pipe using a threaded and coupled connection; FIG. 7B shows the use of a corrosion barrier ring bonded to the coupling ; FIG. 7C shows a variation of FIG. 7B, where a flush insert is used to terminate the end of the lined pipe ; FIG. 7D shows another variation of FIG. 7B, where a non-flush insert is used to terminate the end of the lined pipe; FIG. 8A shows alternative apparatus for grouting the pipe, where grout is injected through a plurality of openings in an end cap ; FIG. 8B shows a modification of FIG 8A, where a flush insert is used instead of an end cap; FIG 9A shows an alternative design of flush insert which improves the strength of the joint between the insert and the liner ; and FIG 9B shows an insert which is not flush with the bore of the liner.

Referring to FIG. 1, a length of pipe 1 to be lined is provided with snap-together pin and box connectors 4 and 5 welded onto the ends of the pipe by

welds 4a and 5a respectively. The pipe 1, with the connectors 4 and 5, is particularly suitable for pipelines and risers due to its high strength, metal to metal sealing, non-rotational assembly and break-out, and ease and speed of assembly. Each of the connectors 4 and 5 includes clamp grooves 6, seal grooves 7, seal nib 8 and circumferential teeth 9. A small recess 10 is machined in the box connector 5 to hold in place a corrosion barrier ring 36 (see FIGS. 5A to 5D). The connector 5 has a hydraulic injection port 40 through which hydraulic oil is injected during assembly and break-out to separate the teeth 9. In practice, identical lengths of the pipe 1 can be secured together by inserting the free end of the pin connector 4 of one pipe 1 into the free end of the box connector 5 of another pipe 1.

FIG. 2 shows the pipe 1 with a liner 2 and inlet and outlet injection heads 11 and 12 respectively, fitted to the pipe. An annular space 3 is provided between the liner 2 and the pipe 1, which receives a grout composition. The injection heads 11 and 12 each include a body member 11 a and 12a respectively. Each injection head 11 and 12 further includes securing means in the form of a sleeve 18 and locking bolts 13, by means of which the injection heads 11 and 12 are fitted to the pipe. The securing means for each of the injection heads 11 and 12 may be identical. The head members 11 a and 12a are each provided with a bolt 14 which is adapted to be secured to the sleeves 18 by means of a suitably shaped recess in the sleeves 18.

The injection heads 11 and 12 further include seals 20 which grip the ends of the liner 2. A gap 42 between the head 11 and sleeve 18, and the head 12 and sleeve 18, allows the seals 20 to be axially compressed against the connectors 4 and 5 by the action of the bolts 14. Once the seals 20 are tightly compressed, the size of the gap 42 is typically 0.1"-0.5" (2. 5-12.5 mm). The gap 42 also provides a convenient way of withdrawing the injection heads 11 and 12 after the grout has cured (by levers inserted into this gap). An annular space 3 is provided between the liner 2 and pipe 1.

It is clear from the FIG. 2 that the liner 2 extends beyond the free end of the connector 4. The seals 20 bear axially on the connector 4, or the connector 5, to keep the grout composition within the annular gap 3 during injection and curing. To ensure that the seals 20 bear on the connector, the liner 2 is cut to length so that it

cannot contact the seals 20 on both ends of the pipe.

FIG. 3A shows the inlet head 11 and FIG. 3B shows the outlet head 12 in greater detail.

For convenience of manufacture the seals 20 comprise two seal rings 15 and 16. The inner seal ring 16 bears radially on the smooth and dimensionally tightly controlled bore of the liner, and prevents the grout composition from escaping inwards.

The outer seal ring 15 bears axially on the end of the connector (it may also bear radially on the outside of the connector), and thus prevents the grout composition from escaping outwards. The outer seal ring 15 also provides support for the inner seal ring 16, allowing this to seal even if the bore of the liner is pressurised. The preferred material for seal rings 15 and 16 is PTFE, since this material resists the adhesion of the grout composition.

For convenience of manufacture, the outlet head 12 may be made up of two sub-assemblies.

All metal parts in contact with the grout composition are preferably PTFE or PTFE-Nickel coated to prevent adhesion. This also provides corrosion protection.

The injection head 11 has one or more inlet ports 21, and the injection head 12 has one or more outlet ports 22. The seal ring 15 has drilled holes 17 typically 1-5 mm diameter for the passage of the grout composition. When the grout composition cures in the pipe and injection heads, sprues of cured grout are formed in the holes 17.

When the injection head is removed, the grout will tear or break at the thinnest section which is these sprues, preventing damage to the cured grout in the annular space 3.

Holes 17 may be tapered or angled to the axis of the liner, to facilitate the breakage of these sprues with minimum damage to the cured grout at the end of the pipe.

There is also a port 23, in both head 11 and head 12, for pressurising the bore of the liner 2. Port 23 can be used to circulate hot water through the lined pipe after grouting, to accelerate the cure of the grout. This is a convenient alternative to using a hot water bath.

Through-holes 43 are provided for the assembly of the heads 11 and 12 to the sleeves 18, by means of the bolts 14 shown in Fig. 2. A tapped, counter-bored hole 19 can be provided to assist in the smooth, axial withdrawal of the seals from the

ends of the liner 2 after the grout has cured, by means of jacking bolts (not shown) bearing on the sleeve 18.

FIG. 3C shows an alternative design of the inlet injection head 11'. Many of the parts of the injection head 11'are the same as the injection head 11, and like parts have been designated with like reference numerals. An outer seal ring 15'is retained by a member 11 a', and an inner seal ring 16'is retained by a member 45. A space 46 is provided between members 11 a'and 45. A projection 47 on the member 45 ensures that the space 46 is not closed, and retains'O'-ring 56. Preferably the'0' rings 56 are made of PTFE or are PTFE coated to reduce the adhesion of the grout.

The member 11 a'is secured to the member 45 by means of pin 50 inserted in the through-holes 48 and 49. Each head usually has two pins 50. The pin 50 is tightened with nuts 51,54 and has washers 52,55. There is a step in the diameter of the through-holes 48 and 49, and corresponding step in the diameter of pin 50, allows part 45 to be separated from part 11 after the injection head has been removed from the pipe. This separation is done by removing nuts 51 and hammering or pushing on the ends of the pins 50. A close fit between the pins 50 and through-holes 48 and 49 ensures that part 45 is concentric with part 11.

FIG. 3D shows a plurality of grooves 15a, for the passage of the grout composition, provided on the outer seal ring 15'. The number of the grooves 15a is typically from 12 and 48 and their size is typically from 1-5 mm. The grooves 15a avoid a restriction on the flow of the grout composition. The number and size of the grooves 15a is set so as to match the size of an inlet hose for the grout composition.

The provision of the small grooves 15a, rather than wider openings, minimises the damage to the cured grout when the injection head is removed. To encourage shear in the grout sprues when the injection head 11'is removed, the grooves 15a are preferably rifled at an angle of around 30 degrees to the longitudinal axis of the pipe.

The grooves 15a can readily be produced with a file, using a metal ring to control the depth of cut, and their profile may be circular, semi-circular, rectangular or irregular.

Preferably the grooves 15a taper so that the thinnest end is towards the liner.

The major part of the outer seal ring 15 lands on the ends of the liner 2, pressing the liner against the inner seal ring 16. Since the OD of a filament wound

liner is rough, and the bore is smooth, the liner is sealed on its bore and not on its OD.

Since the liner bore is pressurised, the support from the outer seal ring 15 is very important for sealing.

The grout composition is injected through the or each inlet port 21, located on the periphery of the space 46, and distributes radially, entering the space 3 between liner and pipe through the grooves 17. Port (s) 21 can be placed either on the face of the head 11 (as shown) or on the outside diameter of the head.

A port 23'is provided in the member 11a'for the introduction of air or heating water into the bore of the liner through a through-hole 53 in the member 45.

For convenience of alignment, the port 23'is often located centrally on the injection head 11'.

A projection 57 on the member 45 is dimensioned so that it prevents the liner from moving into the space 46 (and thus blocking the flow of grout into the annular space 3), when the injection head is fitted. The projection 57 also prevents the outer seal ring 16 from being pushed into the space 46 when the injection head 11 is fitted.

A similar arrangement (not shown) to FIG. 3C may be used on the outlet injection head 12.

The modular construction of the injection heads 11 and 12, and the seal rings 15 and 16, allows the equipment to be adapted to suit different thicknesses of pipe (i. e. different liner diameters) at minimum cost.

Additional means, such as location dowels (not shown) and appropriate manufacturing tolerances on parts which engage, are used to ensure that the heads 11 and 12 hold the liner centrally within the connectors 4 and 5. The concentricity of the ends of the liner with the connectors is very important as it ensures that when the lined pipe is assembled, there is optimal alignment between the ends of the liner and the corrosion barrier ring 36, which is described below with respect to FIGS. 5A to 5D.

Thus, a minimum area of the end of the liner is unprotected from abrasion/erosion and a maximum area of the end of the liner is protected from direct exposure to the fluid.

FIG. 4 shows the equipment used to inject the grouting composition into the annular space 3.

The grout composition may comprises a resin contained in reservoirs 25

and a catalyst contained in reservoir 26. These materials are pumped by a positive displacement metering/mixing/dispensing pump 28, of the type often used in a field of manufacturing known as Resin Transfer Moulding. The components are mixed at the mixing nozzle 24. A pressure gauge 30 is provided to monitor the injection pressure at the inlet 21. The most suitable types of pump have minimal pulsation, and are preferably provided with a pressure guard, so in the event that the injection pressure reaches a preset level the pump will automatically slow down. The pump may be pressure controlled or flow controlled. The injection speed will preferably be in the range 0.1 to 1.0 litres/minute. The maximum injection pressure will preferably be below 1000 kPa. Pump 28 is preferably provided with a counter which displays the amount of resin which has been injected. The pumping equipment is provided with means 90 to recirculate the resin. This is done to remove air from the circuit and to avoid sedimentation. There is also provided means 92 to degas the resin by vacuum prior to injection.

An air supply 35, with a pressure gauge 34, is provided to pressurise the bore within the liner 2, via the port 23. This pressure will typically be in the range 300 to 600 kPa, and may be varied as the injection pressure is raised during filling.

A vacuum pump 33, with a pressure gauge 32, serves to remove air from the annular space 3 prior to injection of the grout composition, and from the inlet hoses.

This also maintains a low pressure within the annular space 3 during injection of the grout composition, helping to draw the grout composition. An interceptor vessel 31 prevents the grout composition from reaching the vacuum gauge 32 and pump 33.

Clear plastic hosing is used on both the inlet and outlet tubing to provide a visual indication of flow rates and the progress of the grout injection. This also serves to detect air which may inadvertently enter the grout during or after injection, for example at a faulty seal or connection. To reduce the pressure loss in the hoses, hoses are kept as short as practical and their diameter as large as practical, typically 3/8"-1" (9.5 mm-25.4 mm).

A solvent vat 27 is provided, and contains solvent. The solvent can be pumped by a pump 29 through the mixing nozzle 24 after injection of the grout composition is complete. The purpose of the solvent is to flush mixed resin from the

mixing nozzle 24.

FIG. 5A shows the connector 5 after the injection of the grout composition is complete, and the injection head 12 has been removed. The grout composition is designated 37 in FIG. 5A. One end of the liner 2 has been trimmed flush with the connector 4 and the other end of the liner has been trimmed flush with a projection 80 on the connector 5. The corrosion barrier ring 36 has been fitted in engagement with one cut end of the liner 2. The corrosion barrier ring 36 has a projection 20 that is retained in the recess 10 of the connector 5, to prevent it from displacement either during transportation or during the assembly of the pin and box connectors 4 and 5.

FIG. 5B shows an alternative embodiment to the embodiment shown in FIG. 5A. In FIG. 5B a protective insert 38 has been placed at one end of the liner 2.

The liner 2 and the grout 37 has been cut back and the insert 3 has been bonded into place. The advantage of the arrangement shown in FIG. 5B is that it is less likely that the cut ends of the liner 2 will be exposed to fluid, and the insert 38 can be made of a material that is particularly resistant to impact and abrasion. The insert may be made of an impact resistant plastic material or stainless steel.

FIG. 5C shows a liner terminated with an end cap or"flare"44. The corrosion barrier ring 36 has been bonded to the end cap prior to the end cap being fitted to the pipe.

FIG. 5D shows a liner termination where the corrosion barrier ring 36 is adhesively bonded directly to the end of the liner/grout/connector.

Where the corrosion barrier ring material is PTFE, good results have been obtained using a copolymer of PTFE as the bonding agent. Good results have also been obtained by using an epoxy adhesive with a PTFE corrosion barrier ring whose surface has been chemically pre-treated.

FIG. 6 shows two pipes 1 connected by the connectors 4 and 5. The corrosion barrier ring 36 is compressed between the connectors 4 and 5. The connectors 4 and 5 have a metal-to-metal abutment face 37 on the outside diameter thereof, which produces a preload in the connectors.

FIG. 7A shows the conventional method of joining lined pipe, using a threaded and coupled connection system. The pipe 1 is typically threaded with a

helical threadform 72, and the coupling 70 is screwed onto the pipe 1 to make up the connection. Sealing of the connector against internal pressure may be provided by any or all of the following means: a metal to metal seal 70 ;'O'ring seals (not shown) ; entrapment of lubricating dope within the teeth; or compression of a central corrosion barrier ring 71. The end of the liner 2 and the end 37 of the grout composition are protected by an end cap or"flare"44. The corrosion barrier ring 71 provides continuity of corrosion protection across the joint is mechanically trapped in a recess 75 in the coupling 70. It should be noted this type of connector is assembled to a visual indicator mark painted on the OD of the pipe 1.

FIG. 7B shows a threaded and coupled connection system, where the corrosion barrier ring 36, according to the present invention, is bonded to a coupling register 74. Many established connection systems, known as premium threaded connectors, use a register which provides a positive torque stop shoulder. Thus when the coupling is screwed onto the pipe, the load increases sharply when the end of the screwed pipe abuts the register on the coupling. The torque is monitored and screwing is stopped when the torque comes within a set range. Couplings with registers provide improved metal-to-metal sealing and are widely used in applications such as offshore wells and gas wells. However, they are not easily amenable to the use of lined pipe.

The relevance of the present invention is that by bonding the corrosion barrier ring 36 to the coupling register 74, rather than trapping the corrosion barrier ring within the coupling as in Fig 7A, a number of widely used connections can be readily modified for use with lined tubing. The corrosion barrier ring is preferably virgin PTFE. Bonding of the PTFE ring to the steel register can be done by pre-treating the surface of the PTFE, for example by chemical etching, and then using an epoxy adhesive. Preferably the bonding is done by hot melting or solvent melting a PTFE co-polymer film between the PTFE ring and the steel register.

FIG. 7C shows a threaded and coupled connection system where, according to our invention, inserts 38 are fitted at the ends of the lined pipe. These inserts may be metal or plastic. The corrosion barrier ring 36 bears and seals against the end of the inserts 38, rather than against the end of the liner and cured grout as in FIG. 7B. This reduces the possibility of fluid uptake by the liner and grout material.

FIG. 7D shows an alternative embodiment where the inserts 38 are not flush with the liner 2, and have a lip 76 which further reduces the possibility of direct exposure of fluid to the end of the liner.

FIG. 8A shows an another embodiment of injection head, designated 11".

The injection head 11"is similar to the injection head 11', and like parts have been designated with like reference numerals. In this embodiment, an end cap 44 is fitted to the liner 2 before the grout composition is injected. The end cap 44 has a plurality of openings 77 which match in position a plurality of openings 17'in injection head seals 20'. It should be clear that the non-rotational fitment of the injection heads is valuable to ensure alignment of the openings 17'in the seals 20'with the openings 77 in the end caps 44. When the grout composition is pumped through the injection head 11", the grout enters the annular space 3 via the openings 17'and 77. After the grout has cured, the end cap is removed. The cured grout fills the openings 77.

FIG. 8B shows a similar arrangement to 8A, and like parts have been designated with like reference numerals. The embodiment of FIG. 8A is employed when using an insert 38 rather than the end cap 44. In FIG. 8B the injection head is designated 11"'. The insert 38, with a plurality of openings 77', is bonded to the connector 4 before the pipe 1 is grouted. The connector 4 now bears directly on seal 20". Means, not shown, may readily be provided to prevent the end of the liner 2 from deflecting inwards under the action of the injection pressure.

Obtaining concentric alignment of the end of the liner 2 to the connector 4 is facilitated by the alternative designs of insert shown in FIGS. 9A and 9B.

FIG. 9A shows an insert with recess 78 into which the end of the liner locates. The insert is flush with the bore of the liner.

FIG. 9B shows an insert with lip 76. This lip provides a strong joint between the insert and liner, and protects the end of the liner from exposure to fluid.

This insert is not flush with the bore of the liner.

There will now be described an example of a method of lining a pipe using the apparatus described above. In this example the pipe to be lined is a 12m length pipe having an outer diameter of 10.75 inches (27.3 cm) and an inner diameter of 9.25 inches (23.5 cm), with the pin and box connectors 4 and 5 welded on each end of the

pipe 1. The bores of the pin and box connectors 4 and 5 are machined accurately to the nominal bore of the pipe, i. e. to 9.25 inches (23.5 cm).

The liner 2 is conventionally glass wound. A carbon or aramid tape or a hoop layer of glass or aramid fibre may be used on the bore of the liner to improve the abrasion resistance of a glass fibre liner. A preferred matrix material for the liner (ie a material to hold the fibres together) is a phenolic polymer, preferably a synthetic phenolic polymer. In one embodiment, the matrix material is a hybrid or blended resin of phenolic polymer with poly-siloxane polymer. In another embodiment, the matrix material is a low water synthetic phenolic polymer. In another embodiment the matrix material is a combination of a synthetic phenolic polymer with CNSL, similar to the grout previously described. This particular combination has advantages of reduced water uptake and improved flexibility compared to synthetic phenolic polymer on its own. Phenolic resins have been found to be very suitable for liners, because of their resistance to chemicals, including water, at elevated temperature.

A resin rich layer is preferably provided on the bore of the liner to improve the liner's erosion and chemical resistance. Optionally, this resin rich layer may be made of a different resin to the liner matrix material, for example a furane resin may be used for enhanced chemical resistance.

The liner is conventionally produced by filament winding on the OD of a mandrel.

An alternative method of producing the liner is by centrifugal casting (which is sometimes known as"fibre-casting") where a mix of resin and chopped fibre is spun and cast inside a mandrel. This has several advantages: the OD of the liner can be tightly controlled ; chopped fibre is cheaper than the yarn used in filament winding, especially for carbon fibre; fibre-casting produces a smooth, resin-rich inner surface; and the liner is easier to cut because of the absence of continuous fibres.

The dimensions liner 2 in this example has a bore of 8.80 inches (22.4 cm) and a wall thickness of 0.100 inches (0.254 cm). Thus, the annular gap between the liner 2 and the connectors 4 and 5 is 0.150 inches (0.381 cm). The size of the annular space 3 between the liner 2 and the pipe 1 will vary depending upon the manufacturing tolerance of the pipe 1.

The method of lining the pipe 1 is as follows. After the connectors 4 and 5 have been welded to the pipe 1, the internal weld beads are removed and the weld is non-destructively tested. The pipe 1 is then cleaned internally. This cleaning can be achieved by grit blasting, leaving a keyed dry surface for optimum adhesion of the grout. Preferably this cleaning is done not more than a few hours before the insertion of the liner, to avoid the rusting of the newly cleaned steel surface. Since the phenolic grout reacts with bare steel, affecting its cure, the steel pipe is preferably internally coated after grit blasting. This coating may typically be an epoxy or a phenolic resin.

Good results have been achieved by using a phenolic primer whose resistance to the environment and temperature is similar to that provided by the phenolic primer and the phenolic grout.

The outside surface of the liner 2 is preferably rough, clean and dry, for optimal adhesion of the grout composition. The usual method of improving adhesion of a grout composition to the liner is by grit blasting. However, grit blasting is expensive, and there is a risk of damaging the liner 2. An alternative method is to use a peel ply tape, removed shortly before inserting the liner 2 into the pipe 1. However, this tape is expensive, and its removal takes time. Thus, in accordance with the invention a grit is applied to the outside surface of the liner 2 when it is manufactured.

This technique increases the surface area of the external surface of the liner 2, thereby improving the mechanical keying of the grout composition to the liner 2; this technique also provides an alternative substrate for the grout composition to bond to. This latter feature is particularly important in the case of phenolic liners, which are more difficult to bond to than epoxy liners.

Prior to insertion of the liner into the pipe, the"dog-bone"ends of the filament wound liner are cut off and the liner is leak tested to ensure it is fluid-tight. A convenient way of carrying out this test is by fitting end caps on the liner and either immersing the liner in a water bath or covering it with"snoop" (soapy water). Typically the ends of the liner are stopped and the bore is pressurised to 50 kPa. Leaks can readily be detected by bubbles in the water.

The liner 2 is disposed within the pipe 1, and is then cut to a prescribed overhang of approximately 0.5 inches (1.3 cm)-the precise overhang is selected to suit

the seals 20 of the injection heads 11 and 12. Cutting to the required length is facilitated by cutting fixtures (not shown) that locate on the ends of the connectors 4 and 5. Cutting is done using an oscillating saw (not shown) to minimise damage to the liner 2. The edges of the ends of the liner are then chamfered using a suitable grinding tool for ease of fitment into seals 20.

Injection heads 11 and 12 are then fitted to the connectors 4 and 5 respectively. For ease of assembly, sleeves 18 are fitted first, and then the injection head body members 11 a and 12a are bolted to sleeves 18. The arrangement of the injection heads is such that the injection head seals 20 can be pushed onto the liner 2 without rotation.

Prior to grout injection, the seals 20 are tested either by injecting air at low pressure into the annular space 3 or by measuring the vacuum that can be obtained in the annular space 3. It is important to test the seals 20, in order to ensure that a proper vacuum can be obtained in the annular space 3, to prevent air from getting into the grout composition, and to prevent the grout composition from entering the bore of the liner 2. This also acts as an additional check on the fluid tightness of the liner, in particular in view of any damage that may have occurred during handling and transportation from the facility where the liners are produced.

The pipe 1 is then preheated. The viscosity of the grout composition is highly temperature dependent, and heating the pipe before and during injection reduces the viscosity of the grout composition, allowing it to be injected at lower pressures. Preheating the grout composition is generally not worthwhile, because of the high surface area to volume ratio once the grout composition is in the pipe: an unheated pipe acts as a cold sink and rapidly draws any heat form the grout composition. Thus, it is much more effective to heat the pipe.

Preheating the grout in the pumping machine 28 only serves to reduce the pressure drop in the machine, and is normally necessary.

The grout composition cures faster with higher temperatures, so it is advisable to heat the pipe only to a moderate temperature. This temperature is preferably between 20°C and 40°C. It is important that the pipe 1 is heated uniformly to avoid local hot spots. Heating from the bore of the liner (for example using hot

water) is inefficient, since the annular space 3 reduces heat conduction into the steel pipe. Thus, it is preferred to heat the pipe by immersing it in heated water. The water is re-circulated to maintain its temperature. Where available, heating ovens are also a convenient means of pre-and post-heating the pipe.

The pipe is inclined such that the inlet head 11 is lower than the outlet head 12. The ideal angle is where the outlet head is vertically above the inlet head, however, for ease of manufacture, the angle to the horizontal is typically between 1°C and 5°. The inlet port 21 is orientated at the bottom azimuth and the outlet port 21 is at the top azimuth. Air is then drawn out of the annular space 3 by the vacuum pump 33 until a pressure below-90 kPa has been reached. At this point it may be desirable to wet the surfaces of the liner and pipe by pumping through a low viscosity material, to reduce friction, and thereby reduce the injection pressure needed to inject the grout composition.

After the surfaces of the liner 2 and the pipe 1 have been wetted, the bore of the liner 2 is pressurised and the grout composition is injected into the annular space 3, while monitoring the injection pressure at the inlet port 23 using the pressure gauge 34. The net external pressure on the liner 2 is maintained below the collapse pressure thereof by keeping the pressure within the bore of the liner 2 sufficiently high. Since the pressure within the bore of the liner 2 expands the liner 2, and therefore reduces the annular space 3, it is preferable not to pressurise the bore any more than necessary. It may be desirable only to pressurise the inlet end of the bore of the liner 2, rather than the full length-the external pressure on the liner 2 is a maximum at the inlet port 21 and reduces to zero ahead of the grout composition.

Another method of supporting the liner 2 is by using a collapsible mandrel (not shown) or an inflatable bladder (not shown). Once again, the mandrel, or the bladder, need not extend over the full length of the liner 2. The advantage of the collapsible mandrel is that it does not expand the liner 2 and therefore does not reduce the size of the annular space 3.

The vacuum pump is kept running while the grout composition is being injected, and helps to draw the grout through the pipe. The injection pressure is altered to maintain a steady flow of the grout composition, which helps to avoid

entrapment of any remaining air and the creation of voids. The pressure in the bore of the liner is adjusted if necessary as the required injection pressure rises during the injection.

The injection of the grout composition is stopped after the resin has exited the port 21 on the outlet head and before it reaches the interceptor vessel 31. At this time the inlet hose between the mixing nozzle 24 and the port 21 is clamped or valved closed. The outlet hose between the outlet port 22 and the vacuum gauge 31 is typically around 2m long, is elevated relative to the inlet end of the liner, and is not clamped ; this arrangement enables the pipe 1 to draw grout composition from the outlet hose during curing. The pressure in the bore of the liner 2 may be released either before or after curing.

In a modification, pressure is maintained on the grout composition, during the early stages of curing. This reduces shrinkage, prevents the agglomeration of air pockets, minimises voids, and minimises separation of grout components. It also helps to obtain the best possible bond strength. One convenient way of applying this pressure, while ensuring that the net pressure on the liner is below its collapse pressure, is to connect the outlet hose to the bore of the liner. If this is done, care must be taken to prevent the ingress of air into the grout composition.

The curing of the grout composition may be accelerated by temperature.

This may be carried out by using a hot water bath or a heating oven. Alternatively, hot water can be circulated through the bore of the liner. Typically, a temperature of 80 to 100 °C is maintained for a minimum of 2 hours.

After the grout composition has cured, the injection heads 11 and 12 are removed and cleaned. Jacking bolts on the injection heads 11 and 12 permit the seals 20 to be withdrawn in a smooth axial action, with minimal damage to the grout composition.

At this point the liner 2 and the cured grout composition 37 are inspected.

Cutting fixtures (not shown) are then used to cut the liner 2 to the edge of the connectors 4 and 5. The cutting is carried out with the oscillating saw (not shown) to prevent damage to the liner 2. Any excess grout composition on the connectors 4 and 5 is removed. The cut ends of filament wound liners are then sealed with a suitable

resin. The purpose of sealing the ends of the liner 2 is to minimise fluid uptake at the cut ends of the fibres; this sealing also improves the impact resistance of the liner ends.

The end of the liner may be cut back so that a flush inset ring 38 may be fitted, as shown in FIG. 5B. Alternatively an end cap or flare 44 may be bonded to the end of the liner, as shown in FIG. 5C.

Finally, the corrosion barrier 36 is fitted. In the embodiments shown in FIG. 5C and 5D, the corrosion barrier ring 36 is bonded to an end cap or to the end of the connector 4 and liner 2. The corrosion barrier ring 36 serves to reduce fluid uptake by the liner 2 and to prevent the exposure of the steel connectors 4 and 5 to the fluid transported in the pipe 1. Typically the material of the corrosion barrier ring is virgin (unfilled) PTFE.

It will be appreciated that further modifications may be made to the invention, other than those discussed above.