GB2560732A

GB2560732A - High pressure fitting

Info

Publication number: GB2560732A
Application number: GB1704521.2A
Authority: GB
Inventors: John Muckle Derek
Original assignee: Radius Systems Ltd
Current assignee: Radius Systems Ltd
Priority date: 2017-03-22
Filing date: 2017-03-22
Publication date: 2018-09-26
Anticipated expiration: 2037-03-22
Also published as: GB2560732B; RU2752226C2; RU2019129708A; WO2018172751A1; RU2019129708A3; CN110691939A; GB201704521D0

Abstract

A fitting suitable for attaching low carbon steel pipes 3 with polyolefin liners 5 together comprises a first diameter D1 at a first end, a second diameter D2 at a second end and a tapered surface 27 therebetween. An attachment feature, which may comprise castellations and grooves 25, lies on an inner surface of the fitting. A compression ring 6 has an outer diameter D4, and inner diameter D3 and a tapered end 31. In use, the compression ring 6 is inserted into the liner 5 such that the Liner 5 is expanded and compressed against the attachment feature 25. The bore D3 of the compression ring is substantially equal in diameter to the bore of the liner such that the bore of the commissioned pipeline remains constant through the fitting. The interface between the liner 5 and the attachment feature 25 may form a labyrinth seal.

Description

(54) Title of the Invention: High pressure fitting

Abstract Title: High pressure fitting for lined pipe (57) A fitting suitable for attaching low carbon steel pipes 3 with polyolefin liners 5 together comprises a first diameter D1 at a first end, a second diameter D2 at a second end and a tapered surface 27 therebetween. An attachment feature, which may comprise castellations and grooves 25, lies on an inner surface of the fitting. A compression ring 6 has an outer diameter D4, and inner diameter D3 and a tapered end 31. In use, the compression ring 6 is inserted into the liner 5 such that the Liner 5 is expanded and compressed against the attachment feature 25. The bore D3 of the compression ring is substantially equal in diameter to the bore of the liner such that the bore of the commissioned pipeline remains constant through the fitting. The interface between the liner 5 and the attachment feature 25 may form a labyrinth seal.

High Pressure Fitting [0001] This invention relates to a fitting suitable for use in pressurised pipelines such as those used in oil and gas exploration, gas transmission and water networks.

BACKGROUND [0002] Pipelines for the transport of fluids at high pressure, for example pressures above 20bar, are often made from steel or other metal to provide high mechanical strength and containment of the fluid. In certain applications, for example where the fluid to be transported is corrosive, it is necessary to use materials that are either corrosion resistant, have an active corrosion protection system, or have a barrier liner or coating between the metal and the transported fluid. Metals that are corrosion resistant tend to have a high capital cost, whilst the use of active corrosion prevention systems leads to higher annual operating costs over the lifetime of the pipeline. In order to reduce total expenditure, solutions involving the use of coatings or liners to separate the metal from the corrosive fluid are increasingly employed.

[0003] To provide a lower cost solution it is known to specify plain carbon steel pipes with corrosion resistant alloy (CRA) inlays or liners made from a stainless steel and nickel alloy to provide corrosion resistance. Such liners whilst effective are known to present issues with handling during installation that risk damage to the alloy itself. Alternatives to this have been developed for certain applications whereby it is known to use a plastic liner instead, the choice of plastic dependent on the fluid conveyed and the operating temperature, with known liner materials including but not limited to polyethylene (PE), polyamide (PA), polyvinylidene fluoride (PVDF) and polyether ether ketone (PEEK). Plastic lined plain carbon steel tends to offer the most economically attractive solutions and their range of applications is growing.

[0004] The conventional approach to installing plastic liners into pipes is to first reduce the diameter of the liner and, whilst holding the liner at the reduced diameter, insert it into the steel pipe string. The liner is allowed to recover to its original dimensions after insertion to form a tight fit against the steel host pipe. It is known to install such liners in lengths in excess of 1000 metres in a single operation. The methods are well known and include processes such as Rolldown™ which is described in EP0834034 and Subline™ which is described in EP0514142.

[0005] Once a length of steel pipe has been provided with a plastic liner it is necessary to attach the end of the inserted plastic liner to the end of the steel pipeline itself. The attachment must fulfil two primary functions in service, that the plastic liner shall not move or pull away from the end connection by virtue of operating conditions such as fluid pressure or temperature, and that the connection shall form a seal to prevent the conveyed fluid from seeping into the area between the liner and the metal pipe.

[0006] An example of a fitting that terminates a plastic liner to a length of steel pipe is described in GB2298256. A hub piece is welded to the end of the steel pipe which comprises a CRA inlay and a series of circumferential grooves or teeth. The liner is installed and trimmed such that the liner covers the circumferential grooves after which a CRA insert is inserted into the plastic liner to place it in compression against the said grooves. This system has been widely used, for example, in the construction of water injection pipelines for the oil exploration industry and its limitations are understood. A first concern is that the preferred embodiment has circumferential teeth which protrude into the bore of the metallic pipeline, rather than use grooves cut into the body of the metal. This means that the bore of the pipe is reduced further at the entry point for insertion of the liner meaning a greater diameter reduction is required. A greater reduction can hinder the later recovery of the plastic which may not achieve a tight fit. In service, the placement of the insert causes a localised reduction in diameter of the lined pipe which restricts which applications the solution can be employed in. It can be used for example in water injection pipelines but not in hydrocarbon producing pipelines. The latter require inspection by pipe inspection ‘pigs’ that cannot pass through the localised reduction in diameter and also, hydrocarbon fluids tend to deposit waxy substances at disturbances in the pipe structure which could lead to blockages or increased pump energy requirements in service.

[0007] It is an object of the present invention to address at least some of the problems mentioned above.

BRIEF SUMMARY OF THE DISCLOSURE [0008] According to a first aspect of the invention there is provided a pipe connection apparatus for connection to a pipe comprising:

a pipe fitting comprising a hollow body having a bore with a first internal diameter at a first end, a second internal diameter greater than said first internal diameter at a second end, and a taper between the first end and the second end;

a compression ring having an internal diameter and a taper at one end; and an attachment feature on an inner surface of the fitting;

whereby a generally cylindrical polyolefin liner which, where it is expanded against an inner surface of said pipe, has an internal diameter substantially equal to the internal diameter of the compression ring and may be attached to the pipe fitting by inserting said liner into the bore and subsequently inserting the compression ring into said liner, thereby compressing a portion of said liner into engagement with the attachment feature.

[0009] In this way, once installed, the liner and the compression ring have substantially the same internal diameter which means that there is no localised reduction in diameter of the bore which might impede the passage of inspection pigs, swabs or other elements which may need to pass through the lined pipe.

[0010] The liner has a thickness which, when compressed into engagement with the attachment feature by the compression ring, may be locally reduced by 10%-30%. Preferably, the liner thickness is locally reduced by 20%.

[0011] Preferably, the attachment feature has a shape which enables cold flow shaping of said polyolefin liner therein to provide both a labyrinth seal and a mechanical anchor. The compression of the liner by the compression ring may cause part of the liner to plastically deform into the grooves, thereby firmly securing the liner in the fitting.

[0012] The angle of the taper on the pipe fitting may be substantially equal to the angle of the taper on the compression ring. This may help to provide relatively uniform compression of the liner between the taper on the compression ring and the taper on the pipe fitting that avoids localised wall damage to the liner resulting in a reduced thickness. Such a feature is desirable to avoid weakening of the liner in the immediate vicinity of the fitting where it is likely to experience axial loading when the pipeline first enters service.

[0013] In an embodiment, the attachment feature comprises one or more circumferential grooves recessed into the inner surface of the fitting. Alternatively, the attachment feature comprises two or more adjacent annular castellations protruding radially inwardly from the inner surface of the fitting, with grooves defined therebetween.

[0014] In either case, the attachment feature may include between three and five of said grooves.

[0015] In an embodiment, the attachment feature is disposed on said inner surface of said fitting between the second end and the taper of said fitting.

[0016] Preferably, said first internal diameter of the pipe fitting is equal to the internal diameter of the pipe to which the apparatus is to be connected.

[0017] In an embodiment, the bore of the pipe fitting has a third internal diameter at said second end, with said second internal diameter intermediate said first internal diameter and said third internal diameter, the third inner diameter being less than said second inner diameter and being greater or equal to the external diameter of the compression ring. Preferably, said third internal diameter defines an end face of the pipe fitting suitable for abutment sealing to another pipe or pipe fitting.

[0018] In an embodiment, the pipe fitting has a formation on an outer surface thereof capable of retaining an assembly tool.

[0019] According to a second aspect of the invention there is provided a kit of parts including at least one of the pipe connection apparatus of any preceding claim and at least one hollow cylindrical polyolefin liner which, where it is expanded against an inner surface of said pipe, has an internal diameter substantially equal to the internal diameter of the compression ring.

[0020] The kit may further comprise an assembly tool including a ram having an external diameter equal to or less than the internal diameter of the compression ring, a tapered leading edge and a substantially horizontal land on which said compression ring can be temporarily mounted.

[0021] According to a third aspect of the invention there is provided a method of lining a pipe comprising the steps of:

a. providing a kit of parts as described above;

b. attaching the first end of the fitting to the pipe;

c. inserting the liner into the pipe and the fitting and expanding the liner against an inner surface of the pipe; and

d. inserting the compression ring into the liner and the fitting such that the liner is compressed into the attachment feature.

[0022] According to a fourth aspect of the invention there is provided a method of lining a pipe comprising the steps of:

a. providing a kit as described above;

b. attaching the first end of the fitting to the pipe;

c. inserting the liner into the pipe and the fitting and expanding the liner against an inner surface of the pipe;

d. attaching said assembly tool to said formation on the outer surface of the pipe fitting;

e. attaching said ram with said compression ring mounted thereon to the assembly tool;

f. using the assembly tool to insert the ram and compression ring into the liner and the fitting such that the liner is compressed into the attachment feature, wherein said formation retains the assembly tool while it presses the leading edge of the ram against the end of the liner causing it to radially expand and in turn force the compression ring into the liner; and

g. removing the assembly tool and ram, leaving the compression ring in the liner and fitting.

[0023] In the method as described above, the fitting may be attached to the pipe by welding.

[0024] The method as described above may include the step of trimming the liner to a desired length after it has been inserted into the pipe and fitting.

BRIEF DESCRIPTION OF THE DRAWINGS [0025] Embodiments of the invention are further described hereinafter with reference to the accompanying drawings, in which:

Figure 1 (PRIOR ART) shows a cross section of an assembled prior art pipe connection apparatus;

Figure 2 shows a cross section of an assembled pipe connection apparatus in an embodiment of the present invention;

Figure 3 shows the insertion of a compression ring into a lined fitting in an embodiment of the present invention;

Figure 4 shows the insertion of a compression ring into a lined fitting wherein the entry diameter is constricted to permit the use of end face sealing means

DETAILED DESCRIPTION [0026] Figure 1 shows a cross section of pipe 3 made from a material that is not corrosion resistant but which is lined with a corrosion resistant polyolefin liner 5 in a prior art configuration. Pipe 3 is attached to fitting 1 by a welded joint 4. Fitting 1 includes a region on its inner surface having castellations 25 with grooves 2 defined therebetween. Once the fitting 1 is attached to the pipe 3, liner 5 is inserted into the pipe 3 and fitting 1 using a known process such as Rolldown™ or Subline™. A compression ring 6 having an outer diameter slightly larger than the inner diameter of the liner 5 is then forced into the fitting 1 to approximately the same axial location as grooves 2 and castellations 25 so that the liner is compressed in that region. This compression of liner 5 against castellations 25, causes the liner to plastically deform and “flow” into grooves 2, conforming to the shape of the castellations and attaching the liner 5 to the fitting 1. The grooves 2 and castellations 25 must provide a sufficiently strong attachment between the fitting 1 and the liner 5 to withstand the shear forces between the liner and the grooves. Typically between three and five grooves, which may be defined between four to six castellations may be sufficient to ensure adequate attachment between the grooves and the pipe 3. Once the pipe and fitting are lined they are welded to a similarly prepared pipe and fitting on end surface 7.

[0027] The above prior art arrangement provides an effective liner for preventing corrosion of a pipe. It also avoids the use of flanged connections which are not suitable for the usual installation technique which is to join a number of lined pipe sections using welding without melting the internal liner. Welding is preferred as it does not cause a localised increase in the outside diameter of the pipe. This means that a complete pipeline can be readily coiled onto a reeling barge from which a subsea deployment can be completed.

[0028] However, a disadvantage of the prior art arrangement is that the compression ring 6 causes a local narrowing of the bore of the pipe. This impedes the passage of inspection pigs, swabs or other elements which may need to pass through the lined pipe.

[0029] It is an aim of the present invention to provide a fitting connection, for example for plastic lined plain carbon steel pipe strings, that provides a secure anchoring of the liner, a seal to prevent fluid ingress to the interfacial area between the liner and the plain carbon steel pipe and to do this whilst providing a constant internal diameter along the length of the lined pipe with no localised constriction or narrowing resulting from the pipe fitting.

[0030] Figure 2 shows a pipe 3’ attached to a fitting T and lined with a liner 5’, which is attached to the fitting using a compression ring 6’ according to an embodiment of the present invention. The liner 5’ may comprise a corrosion resistant polyolefin. Fitting T includes a region having a first internal diameter D1 substantially equal to the internal diameter of pipe 3’ at a first end 21, allowing it to be attached to pipe 3’ via welded joint 4’. Fitting T also includes a region having a second internal diameter D2 which is larger than the first internal diameter D1. A plurality of annular castellations 25’ defining grooves 2’ therebetween are provided in the region of the fitting having the second internal diameter D2. The castellations 25’ may extend radially inwardly from the internal diameter D2 of the fitting 1’ (as illustrated in Figure

2). Alternatively, instead of castellations, grooves may extend radially outwardly away from internal diameter D2 of the fitting. Both possibilities are examples of an attachment feature for the liner which will be described in more detail below. The difference between the first internal diameter D1 and the second internal diameter D2 of the fitting is preferably substantially double the wall thickness of compression ring 6’.

[0031] The inner surface of fitting T has a tapered portion 27 disposed between the first and second ends whose internal diameter increases from said first internal diameter D1 to said second internal diameter D2 at a substantially uniform rate. The compression ring 6’ also has a tapered portion 31 adjacent to a first end 33. In the tapered portion 31, the outer diameter of the compression ring decreases at a substantially uniform rate from a maximum outer D4 diameter equal to the outer diameter of the compression ring to a minimum outer diameter D3 equal to the internal diameter of the compression ring. In this way a point 29 is formed at an end 33, and the outer wall of the compression ring 6’ has a generally wedge-shaped cross section in the tapered portion 31. The rate of decrease of the outer diameter in the tapered portion 31 of the compression ring 6’ is preferably substantially equal to the rate of increase of the internal diameter of the fitting T in the tapered portion 27 of fitting T.

[0032] The compression ring 6’ can be inserted into fitting T in a similar way to the compression ring 6 shown in figure 1, with the compression ring disposed at the same axial location as grooves 2’. Between three and five grooves are provided to ensure adequate attachment between the liner 5’ and the fitting T. However, unlike the Figure 1 arrangement, the configuration of the compression ring and the fitting shown in figure 2 allows the commissioned pipe to have a bore of constant diameter, because the compression ring 6’ does not protrude radially inwardly further than the liner 5’ into the bore of the pipe 3’. The relative sizes of the compression ring, the liner and the fitting that provide a commissioned pipe with a constant bore may be easily calculated. For example, the difference between the first D1 and second D2 internal diameters of the fitting may be approximately double the wall thickness of the compression ring 6’, and the internal diameter of the compression ring D3 may be approximately equal to the inner diameter of the liner. The thickness of the liner may be such that it is compressed when the compression ring is forced into place. The thickness may be locally reduced by 10-30%.

[0033] The embodiment shown in figure 2 provides a lined pipe and fitting having a generally uniform bore. The fitting may be attached to another, similar fitting using various conventional methods including for example flange to flange connection to the corresponding surface of another fitting. However, if the fitting is to be welded to another fitting then the liner 5’ cannot cover the entire surface of the fitting and must be trimmed inside fitting T. This is because the part of the liner disposed near end surface 7’ would be damaged when the fittings were welded together. A local increase in the bore in the region where the connection is made is therefore caused if the fittings are welded together.

[0034] Figure 3 shows an embodiment in which fittings T can be attached together by a mechanical means such as a flange 12 which preferably includes a sealing component 8. In this embodiment a CRA (corrosion resistant alloy) inlay 9 can be provided with a reduction in the opening diameter D5 (the “third internal diameter”) of the fitting. Diameter D5 is larger than D4to permit the passage of the compression ring 6’ therethrough but is less than D2. The reduced opening diameter D5 defines an end face of the pipe fitting suitable for abutment sealing to another pipe or pipe fitting. The compression ring 6’ may have a length such that when the compression ring 6’ is fitted against the inlay 9, the compression ring 6’ extends to the end face, thereby maintaining a continuous bore diameter throughout the fitting T. The fitting to fitting abutment facilitates the use of optional sealing component 8. The sealing component 8 may be a face to face gasket or sealing ring. Pipe strings can be subsequently butted together and joined to form a complete pipeline which is desirable to minimise the overall outermost diameter of the fitting for space constricted applications.

[0035] Figure 4 shows the insertion of a compression ring into a lined fitting using another method of the present invention. The fitting T is provided with a formation on the external surface thereof which, in the illustrated embodiment, is a circumferential groove 11. The formation 11 is used to retain an assembly tool [0036] Fitting 1’ is first attached to pipe 3’ via welded joint 4’, and liner 5’ is then inserted into the fitting and pipe by conventional means and trimmed flush with end surface 7’ of fitting T. Once the liner is in place, an assembly tool 13 including a hydraulic ram or press 14, having the compression ring 6’ temporarily mounted thereupon, is attached to fitting 1’ using circumferential groove 11 as a temporary mounting point. The compression ring 6’ sits on a substantially horizontal land. Once the assembly tool 13 is attached to fitting T the hydraulic press 14 is advanced into the fitting, driving compression ring 6’ into fitting T and causing liner 5’ to be compressed against castellations 25’ so that the liner 5’ plastically deforms into grooves 2'. When the hydraulic press 14 is removed, compression ring 6’ detaches therefrom and remains in place within the fitting. In this way the lined pipe and fitting have a constant bore. Once hydraulic press 14 is removed from the fitting, groove 11 could optionally be used in the attachment of the fitting to another fitting.

[0037] In all the embodiments it can be seen that radial expansion of the liner to the diameter D2 is not accompanied by localised wall thinning of the plastic liner material which would occur if the plastic is subject to a substantially plastic strain affecting the whole wall thickness. Instead, the plastic liner material is locally compressed into the attachment feature.

[0038] Compression of the plastic material of the liner 5’ between D4 and D2 is preferably 20%, not less than 10% and no more than 30%.

[0039] Although the embodiments shown in figures 2-4 show an attachment feature in the form of grooves and/or castellations 25’ disposed on an inner surface of fitting T, it will be understood that other attachment features for example a plurality of studs or bores would also be possible.

[0040] The claimed invention does not include how one fitting could be joined to another to enable multiple lined pipe sections to be joined to form a continuous pipeline. Suitable methods for this are matters of routine engineering principles and would include but not be limited to such examples as flange to flange jointing, screwed connections, mechanical couplers and pipe to pipe welding [0041] In the context of the present invention it will be understood that the term “fitting” means a component for connecting a first pipe to a second, adjacent pipe. Such a fitting may be connectable to the first pipe, or it may be integrally formed with the first pipe.

[0042] Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of them mean “including but not limited to”, and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0043] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0044] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

1. A pipe connection apparatus for connection to a pipe comprising:

2. The pipe connection apparatus of claim 1 wherein said liner has a thickness which, when compressed into engagement with the attachment feature by the compression ring, is locally reduced by 10%-30%.

3. The pipe connection apparatus of claim 2 wherein the liner thickness is locally reduced by 20%.

4. The pipe connection apparatus of any of the preceding claims wherein the attachment feature has a shape which enables cold flow shaping of said polyolefin liner therein to provide both a labyrinth seal and a mechanical anchor.

5. The pipe connection apparatus of any of the preceding claims wherein the angle of the taper on the pipe fitting is substantially equal to the angle of the taper on the compression ring.

6. The pipe connection apparatus of any of the preceding claims wherein the attachment feature comprises one or more circumferential grooves recessed into the inner surface of the fitting.

7. The pipe connection apparatus any of claims 1-5 wherein the attachment feature comprises two or more adjacent annular castellations protruding radially inwardly from the inner surface of the fitting, with grooves defined therebetween.

8. The pipe connection apparatus of claim 6 or claim 7, wherein the attachment feature includes between three and five of said grooves.

9. The pipe connection apparatus of any of the preceding claims, wherein the attachment feature is disposed on said inner surface of said fitting between the second end and the taper of said fitting.

10. The pipe connection apparatus of any of the preceding claims wherein said first internal diameter of the pipe fitting is equal to the internal diameter of the pipe to which the apparatus is to be connected.

11. The pipe connection apparatus of any of the preceding claims wherein the bore of the pipe fitting has a third internal diameter at said second end, with said second internal diameter intermediate said first internal diameter and said third internal diameter, the third inner diameter being less than said second inner diameter and being greater or equal to the external diameter of the compression ring.

12. The pipe connection apparatus of claim 11 wherein said third internal diameter defines an end face of the pipe fitting suitable for abutment sealing to another pipe or pipe fitting.

13. The pipe connection apparatus of any of the preceding claims wherein the pipe fitting has a formation on an outer surface thereof capable of retaining an assembly tool.

14. A kit of parts including at least one of the pipe connection apparatus of any preceding claim and at least one hollow cylindrical polyolefin liner which, where it is expanded against an inner surface of said pipe, has an internal diameter substantially equal to the internal diameter of the compression ring.

15. The kit of claim 14 further comprising an assembly tool including a ram having an external diameter equal to or less than the internal diameter of the compression ring, a tapered leading edge and a substantially horizontal land on which said compression ring can be temporarily mounted.

16. A method of lining a pipe comprising the steps of:

a. providing a kit of parts as claimed in claim 14;

b. attaching the first end of the fitting to the pipe;

17. A method of lining a pipe comprising the steps of:

a. providing a kit as claimed in claim 15 when dependent on claim 13;

b. attaching the first end of the fitting to the pipe;

d. attaching said assembly tool to said formation on the outer surface of the pipe

5 fitting;

f. using the assembly tool to insert the ram and compression ring into the liner and the fitting such that the liner is compressed into the attachment feature,

10 wherein said formation retains the assembly tool while it presses the leading edge of the ram against the end of the liner causing it to radially expand and in turn force the compression ring into the liner; and

18. The method of claim 16 or claim 17, wherein the fitting is attached to the pipe by welding.

19. The method of any of claims 16-18 including the step of trimming the liner to a desired length after it has been inserted into the pipe and fitting.

Intellectual

Property

Office

Application No: GB1704521.2 Examiner: Mr Philip Osman

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Amendment to the claims have been filed as follows

1. A pipe connection apparatus for connection to a polyolefin lined pipe comprising:

a pipe fitting comprising a hollow body having a bore with a first internal diameter at a first end, a second internal diameter greater than said first internal diameter proximate a

5 second end, and a taper between the first end and the second end;

a compression ring having an internal diameter and an external taper at one end;

and an attachment feature on an inner surface of the fitting;

whereby a generally cylindrical polyolefin liner which, where it is expanded against

10 an inner surface of said pipe, has an internal diameter substantially equal to the internal diameter of the compression ring may be attached to the pipe fitting by inserting said liner into the bore and subsequently inserting the compression ring into said liner, thereby compressing a portion of said liner into engagement with the attachment feature.

2. The pipe connection apparatus of claim 1 wherein said liner has a thickness which,

15 when compressed into engagement with the attachment feature by the compression ring, is locally reduced by 10%-30%.

4. The pipe connection apparatus of any of the preceding claims wherein the attachment

20 feature has a shape which enables cold flow shaping of said polyolefin liner therein to provide both a labyrinth seal and a mechanical anchor.

25 6. The pipe connection apparatus of any of the preceding claims wherein the attachment feature comprises one or more circumferential grooves recessed into the inner surface of the fitting.

7. The pipe connection apparatus any of claims 1-5 wherein the attachment feature comprises two or more adjacent annular castellations protruding radially inwardly from the

30 inner surface of the fitting, with grooves defined therebetween.

Ί— 20

CM

9. The pipe connection apparatus of any of the preceding claims, wherein the attachment feature is disposed on a parallel region, on said inner surface of said fitting between the second end and the taper of said fitting.

16. A method of lining a pipe comprising the steps of:

a. providing a kit of parts as claimed in claim 14;

b. attaching the first end of the fitting to the pipe;

17. A method of lining a pipe comprising the steps of:

a. providing a kit as claimed in claim 15 when dependent on claim 13;

b. attaching the first end of the fitting to the pipe;

5 fitting;

22 11 17