WO2017098327A1

WO2017098327A1 - Improvements relating to polymer lined pipes

Info

Publication number: WO2017098327A1
Application number: PCT/IB2016/001884
Authority: WO
Inventors: Jitender Kumar RAI; Tomasz Tkaczyk
Original assignee: Technip France
Priority date: 2015-12-08
Filing date: 2016-12-07
Publication date: 2017-06-15
Also published as: GB2545183A; GB201521569D0; GB2545183B

Abstract

A polymer lined pipe (PLP) assembly comprising: a first PLP section comprising an first outer metal pipe and a first inner polymer liner, a second PLP section comprising a second outer metal pipe and a second inner polymer liner, at least one of the first and second inner polymer liners comprising a final portion having an internal female threaded portion extending inwardly; and a connection between the first and second PLP sections comprising a plastic screw-connection between the inner polymer liners.

Description

IMPROVEMENTS RELATING TO POLYMER LINED PIPES

The present invention relates to a polymer lined pipe (PLP) assembly, methods of forming PLP pipe sections and, and polymer lined pipelines formed therefrom.

Background to the Invention

One type of pipeline in the subsea and offshore field generally comprises an outer metal pipe made of for example, steel, in particular carbon steel, and a protective inner liner or sleeve. Such pipelines are well known in the art, and are generally termed 'polymer lined pipelines', sometimes abbreviated to "PLP" or "PLP pipeline", which can be formed from a series of joined polymer lined pipes, or pipe sections or pipe stalks, often also abbreviated to "PLP". The inner liner is generally formed of a polymer material such as a plastic, for example high density polyethylene, for the protection of the outer metal pipe against hydrocarbons and other corrosive fluids being transported by the pipeline, although they may also be used to transport non- corrosive fluids such as water.

One possibility is to provide a continuous liner along the full length of the pipeline, but this can be difficult to form. More commonly, the pipeline is formed of PLP sections or stalks, with each outer metal pipe being welded to its neighbour, most conventionally using butt or girth welding. Meanwhile, it is required to achieve an internal continuation of the lining across each join of the PLP sections.

The use of liner junction sleeves for this purpose is well known, and US7722085 shows a metallic junction sleeve having terminal portions with notched surfaces enabling it to be inserted in and anchored against the inside surface of the terminal portions of inner liners of two pipe elements.

W095/22713A1 shows a more complex lining sleeve intended to achieve the same purpose of continuation of the lining material between two PLP pipes, but which uses metallic inserts welded to CRA clad interior surfaces of two pup pieces.

However, where PLP pipelines are commonly intended to be bent or curved during forming, transportation, and/or laying, for example when being spooled and unspooled from a reel. A common stress point is any junction along the PIP pipeline, for example between liner sections. Any bending or curving causes the problem of ovality of the pipes, which can lead to a point of potential weakness where the parts may no longer be so securely aligned together as expected (compared with a perfect circular join), even possibly leading to a gap between the outer surface of a connector and the inner surface of a pipe.

This is especially so where at least part of the join is metallic, which will only undergo plastic deformation, and part is plastic, which is able to undergo elastic deformation. The different deformations are an obvious area of concern, especially after unspooling a PLP pipeline and its required 're-straightening'. Under the types of pressure that PLP pipelines are typically required to contain, any weakness or even gap can lead to a leak, which can become catastrophic once the pipeline is laid. A leak from the liner connection will become over-pressurised within the thin residual annular space between the liner and the outer metal pipe, which can lead to subsequently collapse of the liner when the bore pressure is released, for example in any stop in production, or for any reason to drop the bore pressure, such as needing to solve the problems of hydrates inside the pipeline. A leak will also lead to corrosive fluids entering into contact with the outer metal pipe, which will deteriorate the outer metal pipe, creating an undesired weak point.

It is an object of the present invention to provide a PLP assembly that avoids the provision of any such weakness in the joins of PLP pipelines.

Summary of the Invention

There is provided a polymer lined pipe (PLP) assembly comprising:

a first PLP section comprising a first outer metal pipe and a first inner polymer liner,

a second PLP section comprising a second outer metal pipe and a second inner polymer liner,

at least one of the first and second inner polymer liners comprising a final portion having an internal female threaded portion extending inwardly;

and a connection between the first and second PLP sections comprising a plastic screw-connection between the inner polymer liners. A plastic screw connection is elastically deformable during spooling, unspooling and any straightening, etc. of the PLP, so that the parts of the connection do not damage each other during any such deformation of the PLP shape.

Optionally, one end of the first inner polymer liner comprises a male threaded portion, and the end of the second polymer inner liner comprises a final portion having an internal female threaded portion extending inwardly, to provide the plastic screw-connection between the inner polymer liners.

Optionally, one end of each of the first and second inner polymer liners comprises a final portion having an internal female threaded portion extending inwardly, and the PLP assembly further comprises a polymer connector having opposing complementary male threaded portion to provide the plastic screw-connection between the inner polymer liners.

Optionally, the polymer lined pipe (PLP) assembly as claimed in any one of claims 1 to 3 further comprising an elastic seal in the screw-connection between the polymer liners. Optionally, the elastic seal is in a groove next to the end of a male threaded portion of the plastic screw-connection.

Optionally, the elastic seal is an O-ring.

The present invention provides a polymer lined pipeline comprising a plurality of polymer lined pipe (PLP) sections comprising an outer metal pipe and an inner polymer liner, connected together by at least one PLP assembly as defined herein.

There is provided a method of forming a polymer lined pipe (PLP) section comprising an outer metal pipe and an inner polymer liner for use in forming the PLP assembly as defined herein, comprising at least the steps of:

providing a polymer liner former;

providing the part of one end portion of the polymer liner former with an internal female threaded portion extending inwardly.

Optionally, the method comprises at least the steps of:

providing a polymer liner former having a central portion of a first thickness and at least one end portion of a second thickness greater than the first thickness; locating the polymer liner former within the outer metal pipe such that at least a part of one the at least one end portion of the polymer liner former having the second thickness is within one end of the outer metal pipe;

providing the part of one end portion of the polymer liner former in the outer metal pipe with an internal female threaded portion extending inwardly.

Optionally, the method further comprises providing a polymer liner former having a central portion of a first thickness and portions at each end of a second thickness greater than the first thickness.

Optionally, the method further comprises providing each end of the polymer liner former in the outer metal pipe with an internal female threaded portion extending inwardly.

Optionally, the method further comprises providing a polymer liner former longer than the outer metal pipe, locating said polymer liner former within the outer metal pipe such that both ends of the polymer liner former extend beyond the ends of the outer metal pipe, and cutting the ends of the polymer liner former such that both ends of the polymer liner former having the second thickness are within the ends of the outer metal pipe.

Optionally, the method comprises at least the steps of:

providing a polymer liner having a male threaded portion from one end and an internal female threaded portion extending inwardly from the other end, locating the polymer liner within the outer metal pipe.

Optionally, the method comprises at least the steps of:

locating a polymer liner former within the outer metal pipe; and

providing the polymer liner former with a male threaded portion from one end and an internal female threaded portion extending inwardly from the other end,

Description of the Drawings

The invention can be better understood with reference to the following detailed description together with the appended illustrative drawings in which: Figure 1 is a longitudinal cross sectional view of PLP sections for forming a PLP assembly according to an embodiment of the present invention, and an end of a PLP pipeline;

Figure 2 is a view of the combination of the elements shown in figure 1 to provide the PLP assembly;

Figure 3 is an enlarged and disconnected longitudinal cross sectional view of the

PLP section and connector shown in Figure 1 ;

Figure 3A is a further enlarged view of portion A of figure 3;

Figure 4 is a perspective view of the connector shown in figure 3;

Figure 5 is a longitudinal cross sectional view of a first step in a method according to another embodiment of the present invention for forming a PLP section;

Figure 6 is a second step in the method of figure 5;

Figure 7 is a third step in the method of figure 5;

Figure 8 is a longitudinal cross sectional view of a PLP section former for use in forming another PLP assembly embodiment of the present invention;

Figure 9 is a longitudinal cross sectional view of an end piece to be attached to the PLP section former of Figure 8;

Figure 10 is the completed PLP section from Figures 8 and 9; and

Figure 1 1 is a longitudinal cross sectional view of a combination of several PLP sections shown in Figure 10 to provide another PLP assembly according to an embodiment of the present invention.

Description of the Drawings

The various aspects of the present invention described herein can be practiced alone or in combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one example can typically be combined alone or together with other features in different examples of the invention.

Various examples and aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary embodiments and aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or "containing" for applicable legal purposes.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of", "consisting", "selected from the group of consisting of", "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa.

Referring to the drawings, figures 1 -4 show a first example of the present invention. Figures 1 and 3 in particular show a first polymer lined pipe (PLP) section 4 for use in forming a first PLP assembly.

Each first PLP section 4 comprises an outer metal pipe 30 and a fitted inner polymer liner 32. Each PLP section 4 may be any length, including typical stalk lengths of either 12m or 24m, but possibly up to 1 km or longer. The present invention is not limited by the length of each PLP section 4.

The outer metal pipe 30 may be any suitable metal, and may have any suitable thickness or dimension, typically intended to achieve a certain degree of flexibility in the formed pipeline, especially reelability to assist with reel-laying. Such outer metal pipes 30 are typically formed of steel, in particular carbon steel, and include without limitation corrosion resistant alloys. The outer metal pipe 30 may be any length, including typical stalk lengths of either 12m or 24m, but possibly up to 1 km or longer.

The outer metal pipe 30 may be any internal diameter from 10cm to 50cm or bigger. The outer metal pipe 30 may be any thickness from 5mm to 100mm or bigger. The outer metal pipe 30 may be formed from the assembly of a series of metal pipe stalk welded together. The person skilled in the art is aware how to form outer metal pipe 30 in general.

The inner polymer liner 32 may be formed of any suitable material, generally being a plastic material. Suitable materials include PE such as PE100, PERT (polyethylene raised temperature), PVDF, polyamide, and other polyolefin grades. The inner polymer liner 32 may be any thickness from 1 mm to 50mm, or greater. The inner polymer liner 32 is preferably extruded.

The inner polymer liner 32 may be able to be fitted within the outer metal pipe 30 so as to be wholly or substantially pressed against the inside face of the outer metal pipe 30 and fitted thereto, generally by compression or interference fit. Optionally, the external diameter of the liner is 'oversized' relative to the internal diameter of the outer metal pipe by at least 1 %, and optionally in the range >3% and <10%. The degree of 'tightness' between the liner and outer metal pipe to avoid any slippage during connector installation will vary, partly based on the nature of the PLP, and possibly on the method of installation.

Optionally, the inner polymer liner 32 terminates before one end 34 of each outer metal pipe 30, more optionally before both ends 34 of the outer metal pipe. Optionally, the inner polymer liner 32 is formed from a preformer of a longer length relative to the outer metal pipe 30, and then 'cut back' to terminate before the end 34 of the outer metal pipe 30.

In the example shown in Figures 1 -4, the final portion 36 of each end of the inner polymer liner 32 has an internal female threaded portion 38 extending inwardly in relation to the longitudinal axis of the inner polymer liner 32 or outer metal pipe 30 or PLP section 4. For that purpose, the final portion 36 can, but not necessarily, have a greater thickness than the rest of the inner polymer liner 32. The final portion 36 may be any thickness from 5 mm to 50mm, or greater.

Having a female thread in a polymer liner is known in the art, but an improved method of forming a female thread by machining the inside of the final portion 36 of the inner polymer liner 32 using suitable cutting apparatus is discussed further hereinafter.

In the example shown in Figures 1 -4, the PLP assembly includes a polymer connector 2 having at least one end having a complementary male threaded portion 10 extending outwardly, and adapted to mate with the female threaded portion 38 of the inner polymer liner 32 to connect the connector 2 with the inner polymer liner 32 of a PLP section 4. The cross-sectional shape of the threads of the male threaded portion 10 may be any suitable shape including triangular, trapezoidal, etc.: optionally a rectangular or square shape.

The thread of the male threaded portion 10 is generally single start. However for some laying methods such as the 'S-lay', the thread is optionally a double start, to ease the alignment process.

Optional values for the dimensions and parameters of the thread of the male threaded portion 10 include;

Pitch: in the range >4.5mm to <10mm, can be any other value

Lead: I xpitch (single start), 2xpitch for double start

Depth: in the range >3.5mm to <10mm, can be any other value

Length of threaded portion (10): in the range >50mm <200mm.

The present invention is not limited to these dimensions and parameters.

The connector 2 may be formed from any suitable material, including any suitable plastic or polymer material, and including composite materials. Optionally, the connector 2 is formed from a polyolefin grade material such as PE-100 or PVDF. One possible connector 2 material is the same material used to form the inner polymer liner 32 of the PLP section 4. The appropriate material for the connector 2 can be selected to take account of the method of pipeline laying, and the nature of the fluid being transported by the pipeline.

Figures 3 and 4 in particular show the connector 2 having a cylindrical central section 6 between opposing cylindrical ends 8. The thickness of the cylindrical central section will vary depending on the other pipeline dimensions, but optionally can be in the range >20mm to <65mm.

Each connector end 8 has a complementary male threaded portion 10 extending outwardly along the longitudinal axis of the connector 2, and external of the end surface.

Optionally, the plastic screw-connection of the present invention includes one or more elastic seals, and at least one elastic sealable to abut the end of the female threaded portion of the inner polymer liner when connected to the PLP section.

Figure 3A is an expanded view of the portion A of figure 3, and better shows the connector 2 further comprising a shoulder 12 at the start of the male threaded portion 10. The shoulder 12 has a greater diameter than the male threaded portion 10 (optionally in the range 25% to 35% greater), and a circular groove 14 at least partially housing an elastic seal 16. The width and the depth of the groove 14 may vary. Optionally the width of the groove 14 is in the range >1.5mm <14mm, and optionally the depth of the groove 14 is in the range >0,8mm to < 7mm.

The elastic seal 16 serves to increase the integrity of the connection between the connector 2 and the PLP section 4, whilst being held in position by the circular groove 14.

The elastic seal 16 may be any suitable seal, typically an O-ring. O-rings may be made of any suitable elastic material, such as ethylene propylene or AFLAS, or indeed other elastomers with similar thermo-mechanical characteristics, including high resistance to heat, tear, abrasion and high tensile strength. Suitable O-rings may have a diameter between 1 -10mm, with a nominal compression range between 10% and 40%. Optionally, the majority, such as greater than 60% or more, of the elastic seal 16 is accommodated within the circular groove 14 to avoid displacing the elastic seal 16 during the male-female connecting, and in order to achieve a compression ratio of approximately 30-35%.

As the PLP section 4 is mated with the connector 2, the end of the female threaded portion 38 will abut 22 the elastic seal 16 to increase the integrity of the connector, and in particular to help prevent any leakage of content passing along the PLP section (and indeed subsequent PLP pipeline) if any irregularity ever occurs between the male and female threaded portions 10, 38. In use, there will be significant internal pressure within the PLP section 4, and a pressurised liquid can often find one or more irregularities, especially at or near any connection such as between the male and female threaded portions 10, 38. Such irregularities may have been formed or caused during the reeling or unreeling of the PLP section 4 onto and from a reel (not shown) to effect reel-laying of a PLP pipeline, and the position and arrangement of the elastic seal 16 ensures a greater degree of sealing integrity at the connection of the connector 2 and the PLP section 4 than conventionally expected. The abutment 22 maybe any thickness between 4mm to 45mm or bigger.

The elastic seal 16 is preferably located so as to achieve compression directly from or against the end 34 of the PLP section 4 as it reaches the end of its mating with the connector 2, to maximise its elastic sealing effect, and avoid any slippage during the mating. Optionally, the elastic seal 16 is 9% pre-strained in the circular groove 14 to prevent it from slipping or moving during the mating of the connector 2 and the PLP section 4.

The present invention may further comprise adhesive between one or more sets of the male threaded portions and the female threaded portions. The adhesive may be applied either on the male threaded portions, or the female threaded portions or both, by any method known in the art, including coating, spraying or painting, etc., to provide additional securement and/or sealing between the mating surfaces. The adhesive can be any suitable resin including epoxy / acrylic resins.

Optionally, the outer diameter of at least a portion of the central section of the connector is less than the inner diameter of the outer metal pipes, to form an annulus between the central section and the outer metal pipes. Any such annulus may have a depth of a few millimetres, such as in the range between 1 .5mm and 3mm, and a length to suit the desired connection, which may be <1000mm or >100mm. Optionally, the annulus includes a thermal insulation such as a fire blanket, intended to be located below the ends of the PLP outer metal pipes where they are to be welded together, such that during welding, the heat does not affect the nature of the connectors. The insulation material could be an aerogel (having a thickness of >3mm). To assist root/hot pass welding, a thin layer (>0.5mm thickness) of copper strip may added on top of any thermal insulation layer or wrapping.

Figures 3 and 3A also show the central section 6 of the connector 2 having two end walls 18 and an intermediate section 20 having a smaller radius than the end walls 18 so as to form an annulus between the central section 6 and the inner surface of an outer metal pipe once assembled. The width for the walls 18 is optionally >5mm.

Figure 4 is a perspective view of the connector 2 of figures 3 and 3A.

Figure 1 also shows a clamp or lay tensioner 42 holding a PLP pipeline 44 previously formed from two PLP sections 46, optionally being the same as PLP section 4, and another connector 48, optionally being the same as the connector 2. Figure 1 shows the bringing together of the male threaded portions 10 of the connector 2 at the end of the PLP section 4, and the female threaded portions 38 at the free end 50 of a second PLP section 46. The male and female threaded portions 10, 38 can be rotated together to mate and form a first PLP assembly using any suitable apparatus, device or unit, such as a hydraulic tong unit. The bringing together of the male and female threaded portions 10, 38 could be aligned on or along the firing line of a vessel, using guide rings.

Thus, and as shown in figure 2, a longer polymer lined pipeline 52 is formed from a plurality of PLP sections 46, 4, each comprising an outer metal pipe and an inner polymer liner, connected together by two connectors 48, 2.

The PLP pipeline 52 is ready to be extended further by the addition of one or more further such connectors and PLP sections to the free end 54 of the pipeline 52. The outer metal pipes of the pipeline 52 will be welded together (not shown) to finish the forming of the pipeline 52 ready for reeling or spooling onto a reel (not shown) in a manner known in the art. As the pipeline 52 is spooled, its curvature will create stresses at the PLP section joins, and the plastic nature of the screw-connections between the inner liners 32 assists compensating for any irregularities created thereby.

Figure 5 shows a first step in a method of forming a polymer lined pipe (PLP) section 60, optionally for use as the PLP section 4 shown in figures 1 -4.

The PLP section 60 comprises an outer metal pipe 62 and a polymer liner former 64. Figure 5 shows a polymer liner former 64 having a central section 66 of a first thickness, and end portions 68 having a second thickness greater than the first thickness of the central portion 66. The additional thickness of the second thickness over the first thickness is optionally >10%, >20%, >30%, or >40%.

The polymer liner former 64 could be formed from a section of liner material of the first thickness simply butt welded to two sections of liner material of the second thickness prior to use in the method of the present invention. Such a method of manufacture, especially prior to fitting to the outer metal pipe 62, avoids any stress or stretching on the liner material, maintaining its full integrity compared with methods of forming a liner involving stretching.

The polymer liner former 64 is located within the outer metal pipe 62 such that the central section 66 of the polymer liner former 64 is within the outer metal pipe 62 length, and the end portions 68 extend beyond at least one end, preferably both ends as shown in figure 5, of the outer metal pipe 62.

Figure 6 shows each end portion 68 of the polymer liner former 64 cut to a length so as to be within the ends of the outer metal pipe 60, such that the polymer liner former 64 now comprises a central section 66 and shortened end portions 68 still having the second thickness.

Figure 7 shows a further step in the method, wherein a cutting tool, such as an internal boring tool 70 supported by a clamp ring 71 surrounding the PLP section 60, is able to cut by rotation an internal female threaded portion 72 in the end portions 68 of the inner liner former 64 having the second thickness. In this way, there is formed an inner polymer liner 74 having an internal female threaded portion 72 extending inwardly from each end, for use in forming a polymer lined pipe assembly and/or a polymer lined pipeline as described herein.

Figures 8-1 1 show a second example of the present invention.

Figure 8 shows a polymer lined pipe (PLP) section 80 similar to the PLP section 4 shown in Figures 1 -4, comprising an outer metal pipe 82, and now a fitted inner polymer liner preformer 84.

The inner polymer liner preformer 84 may again be formed of any suitable material, generally being a plastic material. The inner polymer liner preformer 84 may be any thickness from 1 mm to 50mm or greater. The inner polymer liner preformer 84 is preferably extruded.

The inner polymer liner preformer 84 may be able to be fitted within the outer metal pipe 82 so as to be wholly or substantially pressed against the inside face of the outer metal pipe 82 and fitted thereto, generally by compression or interference fit.

One end 85 of the inner polymer liner preformer 84 terminates before one end 86 of the outer metal pipe 82, and comprises an internal female threaded portion 88 extending inwardly in relation to the longitudinal axis of the PLP section 80. The female threaded portion 88 may be machined as discussed hereinabove.

Figure 9 shows a plastic hub 90 having a complementary male threaded portion 92 adapted to mate with the female threaded portion 88. The plastic hub 90 may be formed from any suitable material, including any suitable plastic or polymer material, and including composite materials. One possible hub material is the same material used to form the inner polymer liner former 84 of the PLP section 80. The appropriate material for the hub 90 can be selected to take account of the method of pipeline laying, and the nature of the fluid being transported by the pipeline.

Figure 9 also shows the hub 90 having a cylindrical end section 94 opposite to the end having the internal female threaded portion 88, and ending in a thickness corresponding to the thickness of the inner polymer liner preformer 84. Optionally, the hub 90 includes a shoulder 96 between the male threaded portion 92 and the end section 94, with a circular groove (not shown) in the shoulder 96 to at least partially house an elastic seal 98 in the form of an O-ring. As discussed hereinabove, the elastic seal 98 serves to increase the integrity of the connection between PLP sections, whilst being held in position by the circular groove.

Optionally, the outer diameter of at least a portion of the end section 94 of the hub 90 is less than the inner diameter of the outer metal pipe 82, to form an annulus 99 between the hub 90 and the outer metal pipes of two adjoining PLP sections. Any such annulus may have a depth of a few millimetres, such as in the range between 1 .5mm and 3mm. Optionally, the annulus includes a thermal insulation such as a fire blanket, intended to be located below the ends of the PLP outer metal pipes where they are to be welded together, such that during welding, the heat does not affect the nature of the connectors.

The hub 90 can be welded to the inner polymer liner former 84 to provide a PLP section 100 shown in Figure 10 having a now formed inner polymer liner 102. The inner polymer liner 102 has one end 85 comprising an internal female threaded portion 84 extending inwardly, and an opposing end with a complementary male threaded portion 92 provided by the hub 90, able to provide a plastic screw- connection between the inner polymer liners of a series of PLP sections 100, as shown in Figure 1 1 , in the form of a PLP pipeline 104.

The hub 90 can be welded to the inner polymer liner former 84 either after cutting the inner polymer liner former 84 back to a suitable length within the length of the outer metal pipe 82, or by stretching a pre-sized inner polymer liner former 84 beyond the length of the outer metal pipe 82, adding the hub 90, and then relaxing the inner polymer liner former 84 to its post-elastic length within the outer metal pipe 82, with the majority of the hub 90 extending therefrom.

As each PLP section 100 is mated with a successor PLP section 100 as shown in Figure 1 1 to create a second PLP assembly, the end of each female threaded portion 106 will abut 108 the elastic seal 98 of each hub 90 to increase the integrity of the connection. The position and arrangement of the elastic seal 98 ensures a greater degree of sealing integrity of each PLP connection than conventionally expected.

The PLP pipeline 100 is ready to be extended further by the addition of one or more further PLP sections 100. The outer metal pipes of the section 80 can then be welded together (not shown) to finish the forming of the pipeline 100 ready for reeling or spooling onto a reel (not shown) in a manner known in the art. As the pipeline 100 is spooled, its curvature will create stresses at the PLP section joins, and the plastic nature of the screw-connections between the inner liners 102 assist compensating for any irregularities created thereby.

The present invention provides a polymer lined pipe (PLP) assembly comprising a plastic screw-connection between the inner polymer liners. The connections between the PLP sections may be solely of one type as defined herein, or a combination of same, without limitations as to the number or positions of such combination.

In the present invention, any deformation on the connection between the inner polymer liners of adjoining PLP sections will be the same as the deformation to the polymer liners themselves, and will be wholly elastic deformation, reducing if not eliminating such connections as potential weak spots during reeling and unreeling of a PLP pipeline. The male threaded portions of the connector are adapted to mate by screw fit with the female threaded portions of the inner polymer liners of PLP pipe sections, to form a continuation of the liner along the PLP assembly, i.e. along the bore of the PLP assembly, and so-formed PLP pipeline where extended further.

Claims

1 . A polymer lined pipe (PLP) assembly comprising:

a first PLP section comprising an first outer metal pipe and a first inner polymer liner,

and a connection between the first and second PLP sections comprising a plastic screw-connection between the inner polymer liners.

2. A polymer lined pipe (PLP) assembly as claimed in claim 1 wherein one end of the first inner polymer liner comprises a male threaded portion, and the end of the second polymer inner liner comprises a final portion having an internal female threaded portion extending inwardly, to provide the plastic screw-connection between the inner polymer liners.

3. A polymer lined pipe (PLP) assembly as claimed in claim 1 wherein one end of each of the first and second inner polymer liners comprises a final portion having an internal female threaded portion extending inwardly, and the PLP assembly further comprises a polymer connector having opposing complementary male threaded portion to provide the plastic screw-connection between the inner polymer liners.

4. A polymer lined pipe (PLP) assembly as claimed in any one of claims 1 to 3 further comprising an elastic seal in the screw-connection between the polymer liners.

5. A polymer lined pipe (PLP) assembly as claimed in claim 4 comprising an elastic seal in a groove next to the end of a male threaded portion of the plastic screw-connection.

6. A polymer lined pipe (PLP) assembly as claimed in claim 4 or claim 5 wherein the elastic seal is an O-ring.

7. A polymer lined pipeline comprising a plurality of polymer lined pipe (PLP) sections comprising an outer metal pipe and an inner polymer liner, connected together by at least one PLP assembly as claimed in any one of claims 1 to 6.

8. A method of forming a polymer lined pipe (PLP) section comprising an outer metal pipe and an inner polymer liner for use in forming the PLP assembly as defined in any one of claims 1 to 7, comprising at least the steps of:

providing a polymer liner former;

9. A method of forming a polymer lined pipe (PLP) section as claimed in claim 8, comprising at least the steps of:

10. A method as claimed in claim 9 further comprising providing a polymer liner former having a central portion of a first thickness and portions at each end of a second thickness greater than the first thickness.

1 1 . A method as claimed in claim 10 further comprising providing each end of the polymer liner former in the outer metal pipe with an internal female threaded portion extending inwardly.

12. A method as claimed in any one of claims 9 to 1 1 further comprising providing a polymer liner former longer than the outer metal pipe, locating said polymer liner former within the outer metal pipe such that both ends of the polymer liner former extend beyond the ends of the outer metal pipe, and cutting the ends of the polymer liner former such that both ends of the polymer liner former having the second thickness are within the ends of the outer metal pipe.

13. A method of forming a polymer lined pipe (PLP) section as defined in claim 8, comprising at least the steps of:

14. A method of forming a polymer lined pipe (PLP) section as defined in claim 8, comprising at least the steps of:

locating a polymer liner former within the outer metal pipe; and