Lined pipelines

Abstract

A liner for a host pipe comprises inner 14 and outer 16 polymer liner layers sandwiching a barrier layer 12. The liner is inserted into the host pipe (46, fig. 3a) in a radially contracted state, and

Description

LO CXI CO This invention relates to lined pipelines such as subsea flowlines and risers. In particular, the invention aims to simplify installation of a barrier liner into a host steel 5 pipe to protect the host pipe from internal corrosion, especially for use in pipelines that will convey corrosive fluids with high gas content. The invention also contemplates the use of a barrier liner to protect a host pipe from embrittlement where a pipeline will be used to transport hydrogen. 10 Corrosion protection is a key issue for pipelines used in the oil and gas industry, which are usually made of carbon steel to reduce their cost over often great lengths. Liners of polymers or composites, for example of high density polyethylene (HDPE), are commonly used to mitigate internal corrosion of pipelines as an alternative to more expensive liners of corrosion-resistant alloys. For brevity, polymer and composite liners 15 will be referred to collectively in this specification as polymer liners unless the context requires otherwise. In a lining process described in WO 2020 / 225532 and known in the art by the registered trade mark ‘Swagelining’, a polymer liner pipe is inserted into a steel host 20 pipe joint with the assistance of die-drawing. Specifically, the liner pipe initially has an outer diameter that is greater than the inner diameter of the host pipe but is then pulled through a distally-tapering annular swage die, exemplified by GB 2221741, to fit into the host pipe. By effecting radially-inward elastic contraction, the swage die reduces the outer diameter of the liner pipe to less than the inner diameter of the host pipe. In 25 this narrowed state, the liner pipe is pulled telescopically through the host pipe while longitudinal tension is maintained in the liner pipe between the swage die and a draw line. When the liner pipe is in an appropriate longitudinal position with respect to the host 30 pipe, tension applied by the draw line is released. This starts a reversion process in which the liner pipe contracts longitudinally and expands radially outwardly to press against the interior of the host pipe. The elastic radial expansion achieves an exceptionally tight fit and a strong mechanical connection between the liner pipe and the host pipe. When reversion is complete, the ends of the liner pipe are machined back into the corresponding ends of the host pipe to create sockets. When fabricating a pipeline by girth-welding the host pipe joint to a similarly lined pipe joint, their mutually-opposed sockets can receive a tubular polymer liner bridge to maintain continuity of the polymer 5 lining across the interface between the pipe joints. Whilst they are generally effective to resist aggressively corrosive fluids, polymer liners suffer from problems in practice. One such problem is permeation of fluids through the liner material. During operation, liquids and especially gases or vapours present in the 10 fluid flowing through the pipeline tend to migrate through the liner wall to enter the micro-annulus between the liner and the surrounding host pipe. There can also be leakage of fluid into the micro-annulus along leakage paths extending around the liner, for example through any gaps at joints between lined pipeline sections. 15 Over time, fluid accumulating in the micro-annulus may jeopardise bonding or LO engagement between the liner and the host pipe and promote corrosion of the host CXI PiPe- Also, transfer of fluid into the micro-annulus will continue until the pressure of fluid co in the micro-annulus matches that of the fluid flowing through the bore of the pipeline. Thereafter, any rapid reduction of pressure in the bore will lead to an overpressure in 20 the micro-annulus that will not equalise as quickly and could therefore cause the liner -j— to collapse inwardly. In enhanced hydrocarbon recovery techniques, polymer-lined pipelines can be used to inject fluids such as water or gas into a well producing hydrocarbons. In pipelines used 25 for water injection, the risk of liner collapse due to migration of gaseous species into the micro-annulus between the liner and the host pipe can be managed simply by specifying a wall thickness for the liner that is sufficient to resist collapse in all operating scenarios. In that case, the pressure of dissolved gas in the service fluid is assumed to be no greater than two bar and a further one bar is added to account for 30 atmospheric pressure during installation. The liner wall thickness required to prevent collapse at this critical pressure is calculated using an industry-accepted model known as the Frost equation. Substantial quantities of gas can also be conveyed along pipelines in combination with 35 liquids, either dissolved in liquids or separately from liquids, for example for injection into subterranean reservoirs as part of enhanced recovery or carbon capture techniques. In one such example, alternating slugs of gas and water can be injected into a well in a process known as water alternating gas (WAG) injection to recover more hydrocarbons from a reservoir, more efficiently than using gas or water alone. In another such example known as carbon capture utilisation and storage (CCLIS), 5 carbon dioxide can be conveyed along a pipeline in a highly compressed, supercritical state to be injected into a formation deep underground, for example a depleted hydrocarbon reservoir. The high gas content of fluid conveyed by WAG and CCLIS pipelines makes the design 10 of liners challenging. For example, the high gas pressure in the micro-annulus resulting from permeation through the liner wall could require an impractically thick liner to resist collapse when the pipeline is depressurised. WAG and CCLIS environments also contain corrosive gases that can cause corrosion of the host steel pipe after permeating through the liner wall. 15 LO Lined pipelines are also used to convey hydrogen gas, which may for example be CXI manufactured offshore using renewable energy and then transported across the co seabed for storage or consumption. Transport of hydrogen through lined pipelines under high pressure presents challenges of permeation of hydrogen not only through 20 the liner wall but also into the wall of the steel host pipe. Thus, in the case of hydrogen, -j— the risk of liner collapse is accompanied by a risk of embrittlement of the steel that forms the host pipe. WO 02 / 33298 discloses a conventional solution to equalise pressure between the 25 micro-annulus and the bore of a lined pipe to avoid liner collapse, in which vents penetrate the liner wall. The vents may, for example, comprise porous sintered frit elements. Similarly, WO 2004 / 011840 discloses a liner bridge whose tubular sleeve is penetrated by vents for fluid communication between the micro-annulus and the bore of conjoined lined pipe sections. However, the inner surface of the host pipe remains 30 exposed to the potentially damaging effect of any fluid that enters the micro-annulus by permeation through the liner wall, or via the vents or another leakage path. Some lined pipelines require a gas-tight barrier layer that will resist permeation of gases such as hydrogen and corrosive fluids through the liner and into contact with the 35 inner surface of the surrounding host pipe. In this respect, pipe liners comprising gastight barrier layers are known but such liners cannot be installed into host pipes by the Swagelining® process that is required to provide a tight-fitting liner. This is because the stresses and extensions imposed on the liner pipe during the deformation of die drawing would result in delamination and failure of the barrier layer. 5 As an example, some existing barrier pipe solutions are manufactured with an overlapped barrier layer, typically of aluminium. This poses a problem of permeation where the overlap region of the barrier layer fails to act as a fully impermeable barrier. WO 2006 / 111738 describes a barrier pipe in which an intermediate barrier layer is 10 sandwiched between two polymer layers. The polymer layers prevent ingress of liquid and contact of liquid with the barrier layer and the barrier layer blocks gas that can permeate through the polymer layers. CN 115264189 discloses an example of a barrier pipe in which aluminium foils are 15 wound around a polymer core pipe. A drawback of this type of barrier pipe is the LO presence of a leak path for gas at the interfaces between successive turns of the foil. CM co Other barrier variants are known. For example, CN 111117041 discloses a graphene barrier. In EP 1716202, a food wrap polymer is modified for deposition of an aluminium 20 film. CN 104290365 discloses electroplating metal onto a polymer pipe. US 9234610 -j— describes welding a barrier layer over a polymer, although the heat of welding could risk melting the polymer. Against this background, the invention resides in a method of providing a host pipe with 25 a tubular laminated liner, which liner comprises a polymer radially inner liner and a polymer radially outer liner sandwiching a substantially impermeable barrier layer between them. The method comprises: inserting the outer liner into the host pipe in a radially contracted state; spraying, depositing, plating, or otherwise applying the barrier layer to the inner liner; radially expanding the outer liner within the host pipe; inserting 30 the inner liner into the host pipe in a radially contracted state with the barrier layer sprayed, deposited, plated or otherwise applied thereto; and radially expanding the inner liner within the host pipe to bring the inner and outer liners together with the barrier layer between them to form the laminated liner. The inner liner and / or the outer liner may be deformed elastically into the radially contracted state by die drawing. Radial expansion of the inner liner and / or the outer liner within the host pipe can be effected by elastic reversion. 5 The barrier layer, for example of graphene or metal, can be deposited onto the inner liner, for example by spraying or plating. The barrier layer can instead be wrapped around the inner liner, for example by wrapping an impermeable strip around the inner liner in a succession of turns and joining together adjoining edges of the successive turns of the strip to form the barrier layer as a continuous tube. The successive turns of 10 the strip can be overlapped and joined together along their adjoining edges where they overlap, for example by laser welding. The inner liner and / or the outer liner may be extruded. 15 Whilst a wall of the inner liner can be penetrated with vent holes, continuity of the barrier layer can be maintained across the vent holes. The host pipe is apt to be terminated with a compression ring that is disposed radially within and acts radially outwardly against the barrier layer. 20 In summary, the invention proposes a novel and advantageous barrier solution that involves a multi-layered polymer barrier pipe system. A tight-fitting barrier liner results, being substantially impervious to migration of fluids into the outer micro-annulus between the barrier liner and the host pipe. 25 The barrier system of the invention comprises a barrier layer sandwiched between an outer liner and a collapse-resistant inner liner. The outer and inner liners may be of high-density polyethylene such as PE100. 30 Resistance to collapse of the inner liner may be achieved by including vents at longitudinal intervals to allow gas accumulations in the inner micro-annulus between the inner liner and the barrier layer to be vented back into the bore of the pipeline during cyclic depressurisation events. The size of the vents and the frequency of the vent locations are determined by the anticipated flow rate through the vents. The wall thickness of the inner liner is determined by the maximum transient pressure differential that is expected between the bore of the pipe and the inner micro-annulus in service, having regard to the pressure-equalising effect of any vents provided in the internal liner. 5 A continuous liner pipe of the invention may be installed into a host pipe using a reducing die and allowed to revert against the internal surface of the host pipe in accordance with the aforementioned Swagelining® technique. After a suitable reversion period during which a tight fit will be established for all liner layers, the barrier lined 10 pipeline can be terminated using compression rings of a corrosion resistant alloy. The outer liner and the inner liner are installed into the host pipe in separate operations, either or both of which may be performed using the Swagelining® technique. Before the inner liner is installed into the host pipe, the barrier layer is 15 applied thereto, so that the barrier layer is installed with the inner liner. LO CXI The impervious, gas-tight barrier layer is thick enough to prevent gas permeation co through the wall of the tubular liner but can be thin, flexible and yet strong enough to survive installation by the Swagelining® technique. For example, the barrier layer can 20 be fabricated from an elongate flat metallic sheet or strip that is wound helically around -j— a tubular inner liner. This brings together side edges of successive turns or coils of the strip, whereupon the side edges can be joined by helical seam welds to form a tube. The side edges of the strip can be joined by a butt joint or preferably by an overlap 25 joint. Welding methods may include resistance seam welding, HF welding or laser welding; of these, laser welding may be preferred with an overlap joint geometry. The welds should be substantially impermeable to migration of gas, providing hermetic seals along the entire length of the tube to complete a gas-tight structure. 30 The barrier layer can instead be a layer of graphene or metal that is sprayed, deposited, plated or otherwise applied to an outer side of the inner liner and / or an inner side of the outer liner. The barrier liner may have a laminated structure comprising a corrosion-resistant 35 barrier layer and at least one polymer layer that protects the barrier layer. The barrier liner may comprise an inner polymer layer defined by a tube to which the barrier layer is applied as an outer tubular layer, for example by wrapping, spraying, deposition or plating. In service, the barrier layer provides primary corrosion protection for the steel pipeline 5 whereas the outer and inner polymer layers protect the barrier layer from damage and erosion. In addition to mitigating corrosion of the host steel pipeline and the risk of liner collapse due to migration of gas through the liner, the construction methods of the invention 10 benefit from reduced installation cost compared to alternative technologies that are currently available. There is a significant cost reduction in personnel time and material cost, especially when compared to existing solutions involving corrosion-resistant alloys and metallurgically- or mechanically-lined pipes. 15 Secondary advantages may include reduced flow friction at the wall of the liner, less LO need for maintenance and inspection pigging and a reduced requirement for inhibitor CXI injection, hydrate mediation and biocide injection. 00 20 In order that the invention may be more readily understood, reference will now be -j— made, by way of example, to the accompanying drawings in which: Figures 1 and 2 are schematic side views showing the creation of a laminated tube to produce a barrier liner of the invention comprising an impermeable 25 barrier layer sandwiched between outer and inner polymer layers; Figures 3a and 3b are a sequence of schematic sectional side views showing a barrier liner produced as shown in Figure 1 or Figure 2 being inserted into a steel host pipe with the assistance of die drawing and then expanding within the 30 host pipe by elastic reversion; Figures 4a to 4e are a sequence of schematic sectional side views showing a tubular outer liner being inserted into a steel host pipe, a barrier layer being deposited within the outer liner and a tubular inner liner being inserted into the 35 host pipe within the outer liner to complete a barrier liner in which the barrier layer is sandwiched between the outer and inner liners; Figures 5a to 5e are a sequence of schematic sectional side views showing a barrier layer being deposited around a tubular inner liner, a tubular outer liner being inserted into a steel host pipe, and the inner liner being inserted into the 5 host pipe within the outer liner to complete a barrier liner in which the barrier layer is sandwiched between the outer and inner liners; and Figure 6 is a schematic sectional detail side view of a termination arrangement of a pipeline constructed in accordance with the invention. 10 The following description includes various examples that do not fall within the scope of the claims. However, the skilled person will appreciate that elements of the descriptions of those examples have relevance to embodiments falling within the scope of the claims. 15 LO Referring firstly to Figures 1 and 2, these drawings show ways by which a laminated CXI tubular barrier liner 10 can be manufactured. In these examples, the barrier liner 10 co comprises a tubular impermeable barrier layer 12 that is sandwiched between tubular polymer layers, namely an inner layer 14 and an outer layer 16, disposed on its radially 20 inner and radially outer sides. Thus, the barrier liner 10 comprises three layers 14, 12, -j— 16 in concentric relation and in radially outward succession. In these examples, the inner layer 14 is defined by an extruded inner tube 18 of a thermoplastic polymer 20 such as HDPE. The inner tube 18 emerges from an extruder 25 22 and passes through a cooling bath 24 that solidifies the polymer 20 before entering an application station 26 at which the barrier layer 12 is applied to the radially outer side of the inner tube 18. The outer layer 16 is then applied to the radially outer side of the barrier layer 12 to 30 complete the barrier liner 10. In this example, the outer layer 16 is an extruded outer tube 28 of a thermoplastic polymer 20 such as HDPE. Thus, the inner tube 18 carrying the barrier layer 12 passes through a cross-head extruder 30 that extrudes the outer tube 28 concentrically around the barrier layer 12. 35 Optionally, before entering the application station 26 as shown in Figure 1, the inner tube 18 passes through a vent installation station 32 at which the otherwise continuous wall of the inner tube 18 is penetrated by longitudinally-spaced holes 34. The holes 34 serve as, or accommodate, vents to relieve overpressure arising in operation in the micro-annulus between the inner tube 18 and the barrier layer 12. The vents may, for example, be as described in WO 2023 / 041917. The barrier layer 12 can extend 5 continuously across the holes 34 or across vents disposed in the holes 34. Figures 1 and 2 also differ in how the barrier layer 12 is created. In Figure 1, the barrier layer 12 is fabricated from an elongate flat metallic sheet or strip 36 that is unwound from a spool 38 and wound helically around the inner tube 18. This brings together 10 parallel side edges of successive turns or coils of the strip 36 in abutting relation or preferably in overlapping relation as shown by the inclined dashed line in Figure 1. One or more welding heads 40 can then join the abutting or overlapping side edges of the strip 36 with a helical seam weld 42 to form a continuous gas-impermeable metallic tubular wall. 15 LO The side edges of the strip 36 can be joined by a butt joint or preferably by an overlap CXI joint. Welding methods may include resistance seam welding, HF welding or laser co welding; of these, laser welding may be preferred with an overlap joint geometry. The welds should be substantially impermeable to migration of gas, providing hermetic 20 seals along the entire length of the tubular barrier layer 12 to complete a gas-tight i— structure. In Figure 2, the barrier layer 12 is instead a layer of graphene or metal that is sprayed, deposited, plated or otherwise applied to the radially outer side of the inner tube 18. In 25 this example, a spray head 44 at the application station 26 is shown spraying the graphene or metal of the barrier layer 12. An immersion technique could also be used to deposit the barrier layer 12 onto the inner tube 18. Where graphene is used to form the barrier layer 12 of the invention, the graphene is suitably a ‘few-layer graphene’ (FLG) which may be defined as having two to ten well-defined stacked graphene 30 layers. Moving on now to Figures 3a and 3b, these drawings show the tubular barrier liner 10 being installed into a host pipe 46 using the Swagelining® technique. The barrier liner 10 and the host pipe 46 are in substantially concentric relation about a common central 35 longitudinal axis 48. The barrier liner 10 is pulled, from left to right as illustrated in Figure 3a, by a draw line 50 that is attached to a tapered distal end of the barrier liner 10. The draw line 50 is tensioned by a conventional jack system, which is not shown. As shown to the left side of Figure 3a, the barrier liner 10 initially has an outer diameter 5 that is greater than the inner diameter of the host pipe 46. Then, the barrier liner 10 is pulled through an annular swage die 52 that is spaced longitudinally or upstream from a proximal end of the host pipe 46 and that tapers in the downstream or pulling direction. By causing radially-inward elastic deformation or contraction of the barrier liner 10, the swage die 52 reduces the outer diameter of the barrier liner 10 to less than 10 the inner diameter of the host pipe 46. The barrier liner 10 lengthens as its outer diameter reduces. In this narrowed and elongated swaged condition, the barrier liner 10 is pulled telescopically through the host pipe 46 while longitudinal tension is maintained in the 15 barrier liner 10 between the draw line 50 and the swage die 52. Pulling continues until LO a distal end portion of the barrier liner 10 protrudes from a distal end of the host pipe 46 CXI as shown in Figure 3a. A proximal end portion of the barrier liner 10 is similarly left co protruding between the proximal end of the host pipe 46 and the swage die 52 as also shown in Figure 3a. The barrier liner 10 is eventually severed in planes orthogonal to 20 the central longitudinal axis 48, as shown by the dashed lines 54 in Figure 3a. 1— When the barrier liner 10 is in the correct longitudinal position with respect to the host pipe 46, tension in the draw line 50 is released. This initiates a reversion process that is shown completed in Figure 3b. During reversion, the elasticity of the polymer material 25 of the barrier liner 10 draws most of the protruding end portions of the barrier liner 10 into the host pipe 46 as the barrier liner 10 expands radially outwardly to press against the interior of the host pipe 46. The holes 34 in the inner pipe 18 of the barrier liner 10 effect fluid communication 30 between the bore of the barrier liner 10 and the inner micro-annulus defined at the interface between the inner pipe 18 and the barrier layer 12. Outer micro-annuli are also present at the interfaces between the barrier layer 10 and the outer pipe 28 and between the outer pipe 28 and the host pipe 46. However, no venting of those outer micro-annuli is required because the barrier layer 12 substantially prevents outward 35 migration of gas through the barrier liner 10. The outer pipe 28 provides continuous circumferential coverage of polymer on the radially outer side of the barrier layer 12 and so separates the barrier layer 12 from the internal surface of the host pipe 46. The polymer layer 18 therefore serves as a continuous spacer between the barrier layer 12 and the host pipe 46 that protects and 5 electrically isolates the barrier layer 12 to mitigate galvanic corrosion. Figures 4a to 4e and Figures 5a to 5e show further variants in which like numerals are used for like features. In these variants, die-drawing is used to install outer and inner polymer liners 56, 58 with an impermeable barrier layer 12 sandwiched between them 10 in concentric relation. The outer polymer liner 56 is installed first into a host pipe 46 of carbon steel and then the inner polymer liner 58 is installed within the outer liner 56. The barrier layer 12 is applied to the inner side of the outer liner 56 and / or to the outer side of the inner liner 58 before the inner liner 58 is installed within the outer liner 56. Longitudinally-spaced vents 60 penetrate the tubular wall of the inner liner 58 to relieve 15 overpressure in the micro-annulus between the inner liner 58 and the barrier layer 12 in LO operation. CM co Figures 4a, 4b, 5b and 5c show the tubular outer liner 56 being installed into the host pipe 46 using the Swagelining® technique. The outer liner 56 and the host pipe 46 are 20 in substantially concentric relation about the common central longitudinal axis 48. A -j— draw line 50 pulls the outer liner 56 through an annular swage die 52 that reduces the outer diameter of the outer liner 56 to less than the inner diameter of the host pipe 46. The outer liner 56 lengthens as its outer diameter reduces. 25 In this narrowed and elongated condition, the outer liner 56 is pulled telescopically through the host pipe 46 while longitudinal tension is maintained in the outer liner 56 between the draw line 50 and the swage die 52. Pulling continues until a distal end portion of the outer liner 56 protrudes from a distal end of the host pipe 46 as shown in Figures 4a and 5b. A proximal end portion of the outer liner 56 is similarly left 30 protruding between the proximal end of the host pipe 46 and the swage die 52 as also shown in Figures 4a and 5b. The outer liner 56 is eventually severed in planes orthogonal to the central longitudinal axis 48, as shown by the dashed lines 54 in Figures 4a and 5b. 35 When tension in the draw line 50 is released, this initiates a reversion process that is shown completed in Figures 4b and 5c. During reversion, the elasticity of the polymer material of the outer liner 56 draws most of the protruding end portions of the outer liner 56 into the host pipe 46 as the outer liner 56 expands radially outwardly to press against the interior of the host pipe 46. 5 Figure 4c shows the barrier layer 12 being sprayed, deposited, plated or otherwise applied to the interior of the outer liner 56. In this example, a spray head 44 is shown spraying graphene or metal of the barrier layer 12. Conversely, Figure 5a shows the barrier layer 12 being sprayed, deposited, plated or otherwise applied to the exterior of the inner liner 58. In this example, the tubular inner liner 58 emerges from an extruder 10 22 and passes through a cooling bath 24 that solidifies the polymer 20 of the inner liner 58 before entering an application station 26 at which the barrier layer 12 is applied to the radially outer side of the inner liner 58. In this respect, a spray head 44 is shown at the application station 26 spraying graphene or metal of the barrier layer 12. Again, a vent station 32 is shown installing the vents 60 in corresponding holes in the wall of the 15 inner liner 58. LO CXI With the barrier layer 12 thus created inside the outer liner 56 or outside the inner liner co 58, Figures 4d, 4e, 5d and 5e then show the inner liner 58 being installed into the host pipe 46 using the Swagelining® technique. The inner liner 58, the outer liner 56 and the 20 host pipe 46 are in substantially concentric relation about the common central -j— longitudinal axis 48. A draw line 50 pulls the inner liner 58 through an annular swage die 52 that reduces the outer diameter of the inner liner 58 to less than the inner diameter of the outer liner 56. The inner liner 58 lengthens as its outer diameter reduces. 25 In this narrowed and elongated condition, the inner liner 58 is pulled telescopically through the host pipe 46 lined with the outer liner 56 while longitudinal tension is maintained in the inner liner 58 between the draw line 50 and the swage die 52. Pulling continues until a distal end portion of the inner liner 58 protrudes from a distal end of 30 the outer liner 56 as shown in Figures 4d and 5d. A proximal end portion of the inner liner 58 is similarly left protruding between the proximal end of the outer liner 56 and the swage die 52 as also shown in Figures 4d and 5d. The inner liner 58 is eventually severed in planes orthogonal to the central longitudinal axis 48, as shown by the dashed lines 54 in Figures 4d and 5d. When tension in the draw line 50 is released, this initiates a reversion process that is shown in progress in Figures 4e and 5e. During reversion, the elasticity of the polymer material of the inner liner 58 draws most of the protruding end portions of the inner liner 58 into the outer liner 56 as the inner liner 58 expands radially outwardly to press 5 against the interior of the outer liner 56 via the barrier layer 12 that is sandwiched between them. The host pipe 46 lined in accordance with the invention serves as a pipe joint that can be welded end-to-end with the host pipes of similar pipe joints to fabricate a lined 10 pipeline or pipe stalk of any desired length. Thus, when reversion is complete, the ends of the barrier liner 10 or the outer and inner liners 56, 58 are machined back to, or into, the corresponding ends of the host pipe 46. For example, the ends of the various liners 10, 56, 58 may be machined to create sockets to receive polymer liner bridges whose outer shape complements the sockets. 15 Finally, after a suitable reversion period, a termination arrangement like that shown in Figure 6 is apt to be provided at an end of a pipeline lined in accordance with the invention. In the example shown in Figure 6, a barrier liner 10 is defined by a three-layer laminated tube that comprises inner and outer tubes 18, 28 sandwiching a barrier 20 layer 12 between them. In the description of Figure 6 that follows, the outer liner 56 of Figures 4a and 5b could be substituted for the outer tube 28 and the inner liner 58 of Figures 4d and 5d could be substituted for the inner tube 18. Before installing the barrier liner 10, an end portion of the host pipe 46 is mechanically 25 or metallurgically lined with a short tubular inlay 62 of a corrosion-resistant alloy (CRA). An inboard ridged portion 64 of the CRA inlay 62 has a series of internal circumferential ridges that defines a castellated longitudinal section as shown. When installed into the host pipe 46, the barrier liner 10 extends into the inlay 62. After 30 installation, the barrier liner 10 is cut back into the host pipe 46 for part of the length of the inlay 62, leaving a chamfered end that lies outboard of the ridged portion 64. The barrier liner 10 is pressed into engagement with the ridged portion 64 of the inlay 62 by radially outward force applied by a CRA compression ring 66 that is received in a 35 circumferential recess 68 on the inner face of the barrier liner 10. The recess 68 extends partially through the thickness of the inner tube 18. Engagement of the outer 11 08 25 tube 28 with the ridged portion 64 of the inlay 62 locks the barrier liner 10 against longitudinal movement relative to the host pipe 46. The barrier layer 12 of the barrier liner 10 is sandwiched between the host pipe 46 and 5 the compression ring 66 via the outer tube 28 on the radially outer side of the barrier layer 12 and via the inner tube 18 on the radially inner side of the barrier layer 12. Many other variations are possible within the inventive concept. For example, the polymer tubes or layers could differ substantially from each other in thickness. Also, it 10 is not essential that the various polymer tubes or layers are extruded. Instead, the outer tube or layer could be defined by a flexible web that converges with and is applied to the barrier layer, for example after being unspooled from a reel. It would also be possible for at least one of the polymer tubes or layers to be sprayed onto or otherwise deposited onto the barrier layer. 15 The polymer of the tubes or layers has been exemplified by a thermoplastic such as polyethylene, but a thermoset polymer is also possible in principle. At least one of the tubes or layers could comprise a polymer matrix with embedded reinforcing elements to define a composite structure. 20 In principle, the side edges of a helical strip defining a barrier layer like that shown in Figure 1 could be joined by means other than a weld, such as an adhesive bond, provided that the resulting joint remains substantially impermeable to migration of gas.

Claims

1. A method of providing a host pipe with a tubular laminated liner, which liner comprises a polymer radially inner liner and a polymer radially outer liner sandwiching 5 a substantially impermeable barrier layer between them, the method comprising:inserting the outer liner into the host pipe in a radially contracted state,spraying, depositing, plating, or otherwise applying the barrier layer to the inner 10 liner;radially expanding the outer liner within the host pipe;inserting the inner liner into the host pipe in a radially contracted state with the 15 barrier layer sprayed, deposited, plated or otherwise applied thereto; andLOCXI radially expanding the inner liner within the host pipe to bring the inner andco outer liners together with the barrier layer between them to form the laminatedliner.__ 20-j— 2. The method of Claim 1, comprising radially contracting the inner liner and / or theouter liner into the radially contracted state by die drawing.

3. The method of Claim 1 or Claim 2, wherein radial expansion of the inner liner and / or 25 the outer liner within the host pipe is effected by elastic reversion.

4. The method of any preceding claim, comprising wrapping the barrier layer around the inner liner.30 5. The method of Claim 4, comprising wrapping an impermeable strip around the innerliner in a succession of turns and joining together adjoining edges of the successive turns of the strip to form the barrier layer.

6. The method of Claim 5, comprising overlapping the successive turns of the strip and 35 joining together their adjoining edges where they overlap.LO CXI007. The method of any of Claims 1 to 3, comprising depositing the barrier layer onto the inner liner.

8. The method of any preceding claim, comprising extruding the inner liner and / or the 5 outer liner.

9. The method of any preceding claim, comprising penetrating a wall of the inner liner with vent holes.10 10. The method of Claim 9, comprising maintaining continuity of the barrier layeracross the vent holes.

11. The method of any preceding claim, wherein the barrier layer is of graphene or metal.1512. The method of any preceding claim, comprising terminating the host pipe with a compression ring disposed radially within and acting radially outwardly against the barrier layer.

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