EP2164695A2

EP2164695A2 - Electrofusion fitting for a composite pipe

Info

Publication number: EP2164695A2
Application number: EP08762624A
Authority: EP
Inventors: Jeremy Archibald Bowman; Gordon Harrison
Original assignee: Radius Systems Ltd
Current assignee: Radius Systems Ltd
Priority date: 2007-07-05
Filing date: 2008-06-30
Publication date: 2010-03-24
Also published as: WO2009004377A3; GB0712969D0; WO2009004377A2; WO2009004377A8

Abstract

The present invention relates to fittings for macro-composite pipes (2), and more particularly to electrofusion fittings for composite plastic pipes having an internal barrier or strengthening layer (6). The electrofusion fitting has a constant internal diameter in the region of overlap with a cut pipe, so that it is not necessary to peel any material from the pipe to be joined during the jointing process.

Description

ELECTROFUSION FITTING FOR A COMPOSITE PIPE

The present invention relates to fittings for macro-composite pipes, and more particularly to electrofusion fittings for macro-composite plastic pipes having an internal barrier or strengthening layer. In this context, macro-composite pipes are laminated structures containing more than one layer in the pipe wall.

Multi-layer macro-composite pipes, including an internal barrier or strengthening layer are well known in the art. Multi-layer pipes are used in a number of different situations such as, for example, when a pipe having improved long-term strength at elevated temperatures is required. Alternatively, or in addition, multi-layer macro-composite pipes including a barrier layer may be used to protect against fluid permeation or the ingress of contaminants. By the same token, pipes of this type may be used when the egress of contaminated fluid flowing in the pipes needs to be eliminated.

In certain plastics pipes, an oxygen diffusion barrier layer may be provided. This barrier layer serves to prevent gas, and in particular oxygen, diffusion through the pipe wall. In other versions, the diffusion barrier can be an impermeable metallic layer, which provides both a strengthening function and functions to prevent permeation or diffusion of gases through the pipe wall. The present invention is concerned particularly with multi-layer pipes having an aluminium or aluminium-based barrier layer sandwiched between the layers of plastics material forming the pipe wall.

Multi-layer pipes of this construction have three particular advantages. Firs%, when the pipe is bent into a different shape, such as introducing a bend or curve into the pipe, the pipe retains its new configuration. The reason for this is that plastic deformation of the aluminium or aluminium-based layer occurs as the aluminium layer is bent beyond its yield stress. The recovery forces exerted by the plastics material, usually polyethylene, comprising the pipe walls are not sufficient to overcome the yield stress of the aluminium barrier layer with the consequence that the pipe retains its new shape. A second advantage is that the metallic barrier layer acts to inhibit oxygen diffusion through the plastics pipe. This not only improves the integrity of the pipe material itself but also avoids the penetration of oxygen into the fluid being transported. This feature is particularly important in systems where the permeation of oxygen into the transported fluid may result in corrosion or degradation of parts within the system. A third benefit of multi-layer pipes including a metallic layer is that they are able to prevent ultraviolet light from reaching the inner plastics layer or layers which reside on the inside of the barrier layer. This protects these internal layers from degradation due to radical formation etc. Consequently, it is not necessary to incorporate UV stabilisers in the plastics materials of the inner layer or layers. This has the further advantage of avoiding any potential leaching of chemical stabilisers into the fluid stream being transported.

A number of plastics pipes having metallic barrier layers and methods for their manufacture are disclosed in patents EP 0353977, EP 0581208 and EP 0644031 . In the interests of brevity, the structural features and methods of producing such pipes are not disclosed here but the reader's attention is drawn specifically to those patents. It is intended that the structural details and processing features disclosed in those patents form part of the present disclosure and these details are intended to be incorporated as part of the disclosure of this invention.

One problem when joining plastics pipes having a barrier layer is that the two exposed ends of the barrier layers may provide a conduit for water or other fluid to track along. The prior art seeks to address this problem in a number of ways. For example, WO2006/1 1 1738 uses an electrofusion coupling in which there is a stepped internal bore against which the exposed ends of the pipe can butt and seal. WO2006/1 1 1738 acknowledges that the use of a metallic barrier layer does, however, give rise to certain complications. For example, non- polar polymeric materials such as polyethylene do not bond to aluminium, giving rise to potential delamination issues. Thus, in manufacturing processes wherein the inner plastics layer is directly extruded into a freshly formed and welded aluminium tube comprising the barrier layer, the thermal shrinkage of the hot extruded inner plastics layer tends to cause delamination, requiring the use of a high strength adhesive between the inner plastics layer and the aluminium tube. Similarly with the outer plastics layer, the adhesion of the extruded plastics material to the surface of the aluminium usually needs to be enhanced by the provision of an intermediate adhesive layer.

When joining two or more macro-composite plastics pipes, or when connecting a macro- composite plastics pipe to a fitting, it is important in certain applications, for instance the transport of hot (> 3O⁰C) water, that the exposed barrier layer and any adhesive layers at the cut end of the pipe should not be exposed to the environment. Atmospheric moisture, or fluid from the pipe, can track along the barrier layer surfaces or diffuse through the adhesive layers causing delamination and structural failure of the pipe. Hitherto this has necessitated the use of special mechanical metal fittings having protective means for the cut end of the pipe.

A popular means of joining polyolefin pipes, or of connecting a polyolefin pipe to a fitting, is electrofusion, in which adjacent polyolefin surfaces are heated and fused together using an electric resistance or induction heating element. Typically, in joining polyolefin pipes, the cut pipe ends are received within an electrofusion coupler comprising an injection moulded tubular polyolefin body having an embedded electric heating element and terminals for connection to an electric power supply. When the electric heating element is energized the outer surfaces of the pipes are fused to the inner surface of the polyolefin body. This conventional coupler has, however, no means to protect the exposed barrier layers at the cut pipe ends and thus cannot be used for composite plastics pipes. In JP10220676 there is described an electrically fused joint for synthetic resin pipes, which is provided with a cylindrical joint body made of the same material as the pipes, and which is mounted over the abutting pipe ends. The joint body has a current carrying heater body buried therein, and the inner diameter of the joint body increases continuously from the centre to the outside in the axial direction. The problem of joining composite pipes is not addressed and indeed the joint of JP10220676 could not be used with a composite pipe having a metallic barrier layer because the heater body would be expected to be "shorted out" by the metallic barrier layer.

WO 2006/1 1 1738 discloses an electrofusion fitting for joining two adjacent pipes of the type described previously. In this electrofusion fitting, two pipe ends are brought into proximity with one another on site, the outer polyethylene layer, the adhesive layers and the aluminium barrier layer are then peeled away from the inner polyethylene layer over a predetermined length starting from the end of each pipe. This operation is achieved in the trench in which the pipes sit using a purpose designed peeling tool for multi-layer macro-composite pipes. Once the operation has been completed it can be seen that a step is produced in the outer diameter of each pipe. An electrofusion connector having a correspondingly stepped inner diameter is then introduced over each end of the two pipes and brought into position. The two ends of the outer polyethylene layer, the adhesive layers and the aluminium barrier layer exposed by peeling away a region of the outer layers butt against a corresponding internal step sited within the internal diameter of the electrofusion fitting, at a distance from the end of the fitting corresponding to the width of the peeled away region of each pipe end. The internal diameter of the electrofusion fitting is sized at this point to provide a snug fitting with the outer diameter of the outer polyethylene layer of the pipe. The same is true at the other end of the electrofusion fitting. The remaining middle portion of the electrofusion fitting has an inner diameter which is less than that of the surrounding portions i.e. the wall thickness is greater. At least part of the inner surface of the fitting in this middle region forms a snug fitting with the two outer surfaces of the exposed inner polyethylene layers of each pipe. Viewed in cross-section along the length of the fitting from one end, the diameter can be seen to be stepped from a larger internal diameter to receive the end of a pipe to a smaller diameter and then back to the same larger internal diameter at the other end. Both the larger and smaller diameter regions contain electrofusion elements for bonding so that the outer and inner polyethylene layers bond to the fitting.

The above arrangement has a number of disadvantages. Firstly, the pipe ends to be electrofusion jointed cannot be peeled in a workshop and has to be peeled in situ, frequently in a trench or other dirty and awkward space. This leads to a risk of contamination by dirt etc which may reduce the quality of the bonding inside the fitting. Secondly, the fitting has a complicated internal shape which must be produced to correspond with the pipes to be joined. It is also necessary for effective joining of the pipes to ensure that both the larger and smaller internal diameter sections of the fitting have electrofusion elements present. If this is not the case it is not possible to ensure bonding of both the inner and outer polyethylene layers of the pipe. This creates manufacturing difficulties in producing an electrofusion fitting.

The use of a metallic barrier layer gives rise to certain complications when peeling the pipe in situ. Since non- polar polymeric materials such as polyethylene do not bond to aluminium, giving rise to potential delamination issues, it is necessary to use a high strength adhesive between the inner plastics layer and the aluminium tube. Similarly with the outer plastics layer, the adhesion of the extruded plastics material to the surface of the aluminium usually needs to be enhanced by the provision of an intermediate adhesive layer. This leads to potential difficulties when peeling the pipe in a trench.

It is apparent that there are several problems associated with the production of fusion joints for composite plastics pipes. In particular, it would be desirable to provide an improved electrofusion fitting which avoids the need to peel away any of the outer layer and barrier layer.

It would also be desirable to produce a pipe fitting which can itself be formed directly from a piece of barrier pipe without needing to machine steps into the internal diameter. The present invention satisfies the above aims and overcomes some or all of the disadvantages of the prior art.

Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of the words, for example "comprising" and "comprises", means "including but not limited to", and is not intended to (and does 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. 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.

In a first aspect the present invention provides an electrofusion fitting for a macro- composite plastics pipe, the pipe comprising at least one inner plastics layer, at least one outer plastics layer and at least one barrier layer therebetween, the fitting comprising a tubular body formed at least in part from a thermoplastic polymer material and optionally comprising at least one barrier layer and adapted to receive a cut end of the pipe into each end of its internal bore and a plurality of electric heating elements disposed within the body, the body having a constant internal diameter in the region of overlap with a cut end of pipe, which corresponds with the outer diameter of the as- extruded macro-composite pipe to be joined, provided with a discrete heating element adapted, and wherein a heating element is disposed around the internal bore of the body at least in each of the regions which receive a pipe so that when energized, the elements are operative to make a fusion joint between the body and its adjacent pipe.

In a second aspect the invention provides a method of forming a joint for a macro- composite pipe, the pipe comprising at least one inner plastics layer, at least one outer plastics layer and at least one barrier layer therebetween, wherein there is used an electrofusion fitting, the fitting comprising a tubular body formed at least in part from a thermoplastic polymer material and optionally comprising at least one barrier layer and adapted to receive a cut end of the pipe into each end of its internal bore and a plurality of electric heating elements disposed within the body, the body having a constant internal diameter in the region of overlap with a cut end of pipe, which corresponds with the outer diameter of the as-extruded macro-composite pipe to be joined, provided with a discrete heating element adapted, and wherein a heating element is disposed around the internal bore of the body at least in each of the regions which receive a pipe so that when energized, the elements are operative to make a fusion joint between the body and its adjacent pipe, inserting the cut pipe end into the tubular body and energizing the electric heating elements to fuse the body to the adjacent pipe thereby forming a fluid- tight seal.

In a third aspect the invention provides a joint for a composite pipe formed using an electrofusion fitting or method according to the first and second aspects of the invention.

In a fourth aspect the invention provides the use of an electrofusion fitting to form a joint in a macro-composite pipe, the pipe comprising at least one inner plastics layer, at least one outer plastics layer and at least one barrier layer therebetween, wherein the fitting comprises a tubular body formed at least in part from a thermoplastic polymer material and optionally comprising at least one barrier layer and adapted to receive a cut end of the pipe into each end of its internal bore and a plurality of electric heating elements disposed within the body, the body having a constant internal diameter in the region of overlap with a cut end of pipe, which corresponds with the outer diameter of the pipe to be joined, provided with a discrete heating element adapted, and wherein a heating element is disposed around the internal bore of the body at least in each of the regions which receive a pipe so that when energized, the elements are operative to make a fusion joint between the body and its adjacent pipe.

We have found that an electrofusion fitting according to the invention, and a pipe coupling made using the same, do not suffer problems of leakage or of tracking of fluid along the barrier layer when transporting fluids at ambient temperatures or temperatures not exceeding 30⁰C. This means that the simplified fitting of the invention can be used in a wide variety of applications such as distribution of a mains water supply.

Preferably the tubular body comprises an inner fusible plastics layer and an outer plastics layer with the at least one barrier layer disposed between the inner fusible plastics layer and the outer plastics layer.

More preferably, the tubular body is made from a plastics barrier pipe of larger diameter than the pipes being joined. The inner plasties layer and the outer plasties layer of the composite plasties pipe can comprise any suitable thermoplastic polymeric materials, consistent with the maintenance of the required properties. Thus the inner layer is required to be compatible with the fluid flowing through the pipe and substantially impervious thereto. Suitable polymeric materials include, for example, olefinically-unsaturated polymers and copolymers, for example, polyolefins such as polyethylene, polypropylene, and polybutylene; ethylene and propylene co-polymers, for example, and propylene-vinyl acetate polymers. Block copolymers and blends of any of the above polymers can also be used. The polymeric materials of the inner and outer layers can also be cross-linked as required. Suitable cross-linked polymeric materials include, for example, cross-linked polyolefins, for example, cross-linked polyethylene (PEX) and oriented cross-linked polyethylene PEXO). For many applications polyethylene is the preferred material for the inner and outer plastics layers of the pipe. The grade of polyethylene chosen, that is to say, high density, medium density, low density, or linear low density, will depend upon the particular application.

The barrier layer of the pipe is preferably a metallic layer, although pipes with barrier layers formed from plastics or other materials are not excluded. The barrier layer can comprise, for example, aluminium, aluminium alloys, stainless steel, copper, copper alloys, or any other suitable metal or metal alloy. The metal can comprise a welded sheet, for example, a welded aluminium sheet. In other embodiments the metal layer can be sputtered, or electro-deposited, or can comprise a wound and/or corrugated metal sheet. Usually the barrier layer will be bonded to the inner and outer plastics layers of the pipe through adhesive layers disposed on each side of the barrier layer. Aluminium or aluminium alloy is preferred as a barrier layer.

The inner fusible layer and the outer layer of the body of the electrofusion fitting of the present invention can comprise any suitable thermoplastic polymeric materials, consistent with the maintenance of the required properties. Thus the inner layer is required to be fusible and to be able to form a fusion joint with the plastics layers of the composite pipe. Suitable polymeric materials include, for example, olefinically- unsaturated polymers and co-polymers, for example, polyolefins such as polyethylene, polypropylene and polybutylene; ethylene and propylene copolymers, for example, propylene-vinyl acetate polymers. Block co-polymers and blends of any of the above polymers can also be used. The polymeric material of the outer layer can also be cross- linked as required. Suitable cross-linked polymeric materials include, for example, cross- linked polyolefins, for example, cross- linked polyethylene (PEX) and oriented .cross- linked polyethylene (PEXO). For many applications polyethylene is the preferred material for the inner fusible layer of the body. The grade of polyethylene chosen, that is to say, high density, medium density, low density, or linear low density, will depend upon the particular application.

In order to be able to receive the cut end of a composite pipe, and to be fused thereto in the simplest and most convenient manner, the internal diameter of the tubular body is constant throughout the fitting in an axial direction. This avoids many of the disadvantages of the prior art. Furthermore, we have found that a pipe joint can be established without, for example, the problem of "shorting out" the electrofusion element as might be expected from the prior art. It is also possible to form a good seal with a fitting of this type despite suggestions in the prior art that it is necessary to seal the exposed ends of a barrier pipe. Frequently, the pipe is scraped to remove a thin outer protective layer or to provide a clean surface on the outside of the pipe so that the pipe is ready for introduction into the electrofusion fitting. The fitting thus receives a cut end of the correctly scraped pipe into each end of its internal bore ready for joining.

The electric heating elements can be resistance elements or can be heated by induction, for example, as described in WO80/02124. The heating elements can comprise, for example, an electrical conductor element, for example, a metal coil, ring, serpentine ring, expanded mesh, or other suitably shaped member, which is preferably located adjacent to, or embedded in a section of the tubular body. There may be one or more heating elements. Preferably, the fitting utilises a single heating element. Preferably the electric or each heating element comprises a helically wound resistance wire. When more than one heating element is present, the heating elements may be connected in series or in parallel. The electrical conductor element may be energised, for example, by passage of an electric current there through, or by inductive heating, to form a fusion bond between the section of the tubular body and the adjacent layer of the composite pipe.

A further advantage of the fitting is that the electric heating element(s) do not come into contact with the exposed edge of the barrier layer which may be the case at the cut end of the composite pipe when used in conjunction with a conventional fitting. This avoids any potential problem of shorting out. For additional protection against the possibility of the electric heating element shorting out against the exposed edge of the barrier layer it would be possible to cover the exposed edge of the barrier layer with a protective insulating film or coating, or an insulating filler material before coupling the pipes in the fitting. In one preferred embodiment of the invention, the tubular body of the electrofusion fitting is manufactured from an extruded pipe. The heating elements can be introduced by "wire ploughing", or any other suitable technique. In the wire ploughing technique, a helical groove is disposed in or on the inner wall of an electrofusion fitting, from an outer part to an inner part thereof, and an electrical heating wire is located within the groove and connected at each end to an input/output terminal. Methods of wire ploughing are described in US4622087 and EP07301 18 and a suitable cutting tool is described in US4643057. The entire disclosures of these prior patents are specifically incorporated herein by reference and these techniques for introducing heating elements are intended to form part of the disclosure of the present invention insofar as they are applicable to the fitting of the present invention. In regions adjacent the barrier layer(s), the wire is preferably wholly surrounded by, or embedded in, the fusible inner layer of the body of the fitting. In another preferred embodiment, the wire is coated with an insulating varnish or similar coating, which can also assist in preventing shorting out between adjacent turns of wire. In addition, by using a barrier pipe to create the fitting of the present invention a barrier fitting is provided, which is needed in many applications.

In another embodiment of the invention, the electrofusion fitting is manufactured by injection moulding the tubular body over a mould core upon which an electrical heating wire has been helical wound.

The tubular body of the electrofusion fitting is preferably also provided with a barrier layer, which can be the same or different from the barrier layer of the composite pipe. The barrier layer is preferably a metallic layer and can also be a strengthening layer, producing a substantially stronger fitting. The barrier layer can comprise, for example, aluminium, stainless steel, copper, or any other suitable metal or metal alloy. The metal can comprise a welded sheet, for example, a welded aluminium sheet. In other embodiments the metal layer can be sputtered, or electro-deposited, or can comprise a wound and/or corrugated metal sheet. Preferably the barrier layer is directly bonded to the inner and outer layers of the tubular body, although it will often be necessary for the barrier layer to be bonded to the inner and outer layers of the tubular body through adhesive layers.

In embodiments where the tubular body of the electrofusion fitting is manufactured from an extruded composite pipe the exposed edge of the barrier layer at the cut ends of the fitting will need to be protected, for example, by means of annular aluminium foil protective layers.

The electrofusion fitting of the present invention can, for example, be an in-line coupler, for connecting two composite pipes in line, a bend, for connecting two composite pipes at an angle, a transition coupler, for connecting composite pipes of different diameters, or a fitting with other connecting means, for example, a screw-threaded end, a butt fusion end, a flanged end, or similar connecting means. The important feature is that the fitting of the invention obviates the need to modify the pipes being joined by peeling away the outer polyethylene layer and barrier layer. Where the fitting comprises a bend, this can be made by first bending a composite plastics pipe and then wire ploughing the heating elements therein. Alternatively, the wire may be ploughed-in first, then the pipe bent to form the bend.

The invention may find application in the electrofusion joining and connecting of a wide range of composite pipes. It is especially suitable for the connection of polyolefin composite pipes, and particularly polyethylene (PE and PEX) composite pipes. One important parameter to consider when selecting polyethylene (PE) based and metallic pipe systems is their ability to stop contaminants such as petrol migrating through the pipe wall, fitting or joint and into water contained within the pipe.

In many countries of the world, there is pressure to build more houses and flats. To supply land for new dwellings some countries, such as the United Kingdom (UK), are using old industrial land (so-called brownfield sites) for these new dwellings. The problem with such land is that contaminants may be found in the soil and, when potable water pipe networks are installed, there is concern that these contaminants may migrate into the drinking water supply.

At the same time as this demand for land exists, people are increasingly expecting the water piped to their dwellings to be of the highest standard. This requirement for clean water, and the requirement for brownfield land to be used for new dwellings may be contradictory. This is because it is known that certain materials may not stop the migration of contaminants through the pipe wall, this being particularly true of, for example, the components of petrol migrating through the walls of polyethylene (PE) pipes. We have developed a test to demonstrate that the pipe system of the type used in the present invention (PE-AI-PE pipe and the fitting of the present invention) acts as an effective barrier to the inward migration of petrol. The test involved filling a sample pipe and fitting under test with clean water, then surrounding the sample with sand saturated with un-leaded petrol for a period of 60 days. At the end of this period the water was drained carefully from the pipe and analysed by Gas Chromatography and Mass Spectrometry (GCMS). This allowed a quantitative measure to be gained of the inward migration of petrol components; the BTEX chemicals (benzene, toluene, ethyl benzene and xylene) were selected for analysis. The performance of the different pipe systems tested was then related to pipe system design.

Many barrier pipe systems currently use metallic fittings. The use of conventional all plastic bodied (not the barrier fittings of this present invention) electrofusion fittings allowed significantly more contamination to migrate through into the water in the pipe. This issue was discussed in the paper by Christodoulou et al, session 1 1 of Plastics Pipes XIII, October 2006, Washington DC USA. Thus conventionally for the supply of clean water, metal fittings significantly out-perform plastics bodied fittings. However, the electrofusion fittings of the present invention now allow the integrity of the barrier to be maintained along the entire run of a jointed pipe.

A further advantage of the pipe fittings of the present invention, which can be used without machining, is that they impart extra strength to the pipe and pipe joint. Thus pipe runs incorporating pipe fittings according to the invention are structurally more robust over their length than pipe runs that do not include barrier fittings to join sections of barrier pipe. This means on the one hand that the pipe run is more secure and, on the other hand, that fluids can be carried at higher internal pressures than is the case for conventional plastics fittings.

This high pressure advantage can also be used with conventional PE piping (i.e. piping without a metal barrier layer) in high pressure applications such as water distribution where pressures of over 20 or even 25 bar may be required. High pressure water distribution often uses thick walled conventional PE piping, which is able to withstand the required pressures. Conventional electrofusion joints are not, however, able to withstand pressures of over 20 bar, so instead relatively heavy and expensive metal fittings, able to withstand these high pressures, have been used to join PE piping for joints in high pressure applications. The electrofusion fittings of the present invention can now, however, be used to join conventional PE piping in these high pressure applications.

Embodiments of electrofusion fittings and joints in accordance with the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a fragmentary section through one end of an electrofusion coupler and joint according to the prior art and Figure 2 shows a fragmentary section through an electrofusion coupler and joint according to the invention.

Referring firstly to figure 1 , there is shown a prior art electrofusion joint, illustrated generally at 1 , comprising a composite pipe 2 and an electrofusion in-line coupler illustrated generally at 3. The composite pipe comprises an outer plastics layer 4, an inner plastics layer 5 and an aluminium barrier layer 6. The aluminium barrier layer 6 is bonded to the inner and outer plastics layers by adhesive layers 7 and 8 respectively. A portion of the cut end 9 of the pipe is cut back in order to provide a step or abutment 10, which includes the exposed edges 1 1 , 12 and 13 of the aluminium barrier layer 6, and the adhesive layers 7 and 8 respectively.

The electrofusion coupler 3 comprises a body 14 comprising an inner fusible plastics layer 15, an outer plastics layer 16 and an aluminium barrier layer 17. The aluminium barrier layer is bonded to the inner and outer plastics layers of the body 14 by adhesive layers 18 and 19 respectively. The body 14 of the electrofusion coupler has a first section 20 lying adjacent to a length 21 of the inner plastics layer 5 of the pipe and a second section 22 of larger diameter lying adjacent to a cut back length 23 of the outer layer 4 of the pipe. The first and second sections 20, 22 of the body 14 are provided with embedded electric heating elements 24 and 25 respectively. The elements 24 and 25 may be of the same or different electrical design. For example, where the diameters of the first and second sections 20, 22 differ considerably the elements 24, 25 may have different wire diameters or the wire coils may have a different pitch. The elements 24 and 25 are connected by a wire 26. An upstanding electrical connector 27 is provided on the outer surface of the electrofusion coupler 3 and has a terminal 28 connected by a wire 29 to the heating element 25. The electrofusion coupler 3 is symmetrical in shape and has a similar terminal and electrical heating elements at its opposed end (not shown), which are connected in series with the terminal 28, and elements 24 and 25 (as indicated by wire 30 and fragmentary electrical heating element 31 ), and adapted to connect with another composite pipe end (not shown).

An optional annular insulating layer 32 can be disposed against the abutment 10 in order to provide further protection for the exposed edges 1 1 , 12 and 13 of the aluminium and adhesive layers of the pipe 2.

The electrofusion coupler 3 is manufactured from an extruded macro-composite pipe by machining the inner surface of the pipe to form an abutment 33, complementary to the step 10, and then wire ploughing the electric heating elements 24, 25 into the inner surface. The electrical connector is then mounted on the body 14, and the terminal 27 connected to the electric heating element 25, in a separate operation. In order to protect the cut edges of the aluminium barrier layer 17 from the environment an optional annular metallic layer 17a may be adhesively bonded to the end face of the body 14.

In forming the electrofusion joint, the composite pipe end is first cut back to produce the step or abutment 10 and then inserted into the coupler 3 until the surfaces of abutments 10 and 33 meet. A similarly prepared pipe (not shown) is inserted in the opposed end of the coupler. An electric current is then passed via the terminal 27 through the electric heating elements 24, 25 in order to fuse together the adjacent surfaces of the pipe and the coupler. Since there is little or no heating in the region of the abutments 10 and 33 these surfaces are not fused and there is no opportunity for the plastics material to flow away from the abutting surfaces. However, because the abutting surfaces are wholly surrounded by the fused regions 20, 21 and 22, 23, the exposed edges 1 1 , 12, 13 of the aluminium barrier layer and the adhesive layers are environmentally sealed.

Referring now to Figure 2, there is shown part of a section of an electrofusion coupler and joint according to the invention, wherein the same numerals refer to the same features as in Figure 1 . Embedded in the inner bore 40 are electric heating elements 41 and 42, which are disposed adjacent lengths of the pipes 2 and 47 respectively. The coupler is symmetrical in the embodiment shown and the electric heating elements 41 and 42 are connected to each other by a bridging wire 45, heating element 41 is connected to the terminal 28 by a wire 29, and heating element 42 is connected to its adjacent heating element by bridging wire 45. The purpose of bridging wire 45 is to leave a cold zone between the heating elements 41 and 42 adjacent to the exposed edges of the aluminium barrier layer 6 and the adhesive layers 7,8 at the cut back end of the pipe. This also helps to prevent molten plasties material from flowing into the interior of either of the pipes.

In use the terminals 28 are connected to a source of electric power and the heating elements, which are all connected in series, cause local fusion of the surfaces of the pipe and the coupler, effectively sealing the exposed edges of the aluminium barrier layer 6 and the adhesive layers 7, 8 from the outside by fused zones and forming a strong joint. By leaving cold zones adjacent to the exposed edges of the aluminium barrier layer 6 and the adhesive layers 7, 8 and the junction 48 between the pipes, flow of plastics material away from these critical regions is avoided.

Whilst the coupler illustrated in Figure 2 is symmetrical about the axis of symmetry shown by Line A-A in Figure 2, this need not always be the case, and it is envisaged within the invention that unsymmetrical couplers, having electrofusion elements at one end and a mechanical connection at the other, or combining different types of electrofusion connections, for example in reducer couplings, are also possible.

Thus, in another embodiment, the internal diameter of the fitting need not be constant throughout the entire length of the fitting, but it is essential that the internal diameter remains constant for the entire length of overlap with each pipe received into the fitting.

In the case of a reducer joint, for example, this means that the fitting will have a constant internal bore in the region of overlap with the first pipe of given diameter, so that the exterior of the pipe can be bonded to the corresponding inside surface of the bore without need for modification of the pipe. Similarly, in the region of overlap with a second smaller or larger pipe at the other end of the pipe fitting, the internal diameter of the bore will remain constant in the region of overlap. This means that bonding of the exterior surface of the second pipe can be effected with the inner surface of the bore of the fitting in the overlapping region.

Claims

I . An electrofusion fitting for a macro-composite plastics pipe, the pipe comprising at least one inner plastics layer, at least one outer plastics layer and at least one barrier layer therebetween, the fitting comprising a tubular body formed at least in part from a thermoplastic polymer material and optionally comprising at least one barrier layer and adapted to receive a cut end of the pipe into each end of its internal bore and a plurality of electric heating elements disposed within the body, the body having a constant internal diameter in the region of overlap with a cut end of pipe, which corresponds with the outer diameter of the as extruded macro-composite pipe to be joined, provided with a discrete heating element adapted, and wherein a heating element is disposed around the internal bore of the body at least in each of the regions which receive a pipe so that when energized, the elements are operative to make a fusion joint between the body and its adjacent pipe.

2. An electrofusion fitting according to claim 1 , wherein the tubular body comprises an inner fusible plastics layer and an outer plastics layer with the at least one barrier layer disposed between the inner fusible plastics layer and the outer plastics layer.

3. An electrofusion fitting according to claim 1 or claim 2, wherein the inner fusible layer and the outer layer of the body of the electrofusion fitting comprise a polyolefin polymer material.

4. An electrofusion fitting according to any one of the preceding claims, wherein the electric heating elements comprise a metal coil, ring, serpentine ring, or expanded mesh.

5. An electrofusion fitting according to any of the preceding claims, wherein the electric heating elements are embedded in a section of the tubular body.

6. An electrofusion fitting according to any one of the preceding claims, wherein the electric heating elements comprise helically wound resistance wires.

7. An electrofusion fitting according to any one of the preceding claims, wherein the electric heating elements are connected in series.

8. An electrofusion fitting according to claim 6, wherein the heating elements are spaced apart leaving a relatively cold region between them to accommodate an exposed region between the two ends of the pipes to be joined.

9. An electrofusion fitting according to any one of the preceding claims, wherein the tubular body of the electrofusion fitting is manufactured from an extruded pipe.

10. An electrofusion fitting according to any one of the preceding claims, wherein the tubular body of the electrofusion fitting is provided with a barrier layer.

I I . An electrofusion fitting according to claim 10, wherein the barrier layer is metallic.

12. An electrofusion fitting according to claim 1 1 , wherein the barrier layer comprises aluminium, aluminium alloy, stainless steel, copper or copper alloy.

13. An electrofusion fitting according to any one of the preceding claims, which is an in-line coupler, for connecting two composite pipes in line, a bend, for connecting two composite pipes at an angle, a transition coupler, for connecting composite pipes of different diameters, or a fitting with other connecting means.

14. A method of forming a joint for a macro-composite pipe, the pipe comprising at least one inner plastics layer, at least one outer plastics layer and at least one barrier layer therebetween, wherein there is used an electrofusion fitting, the fitting comprising a tubular body formed at least in part from a thermoplastic polymer material and optionally comprising at least one barrier layer and adapted to receive a cut end of the pipe into each end of its internal bore and a plurality of electric heating elements disposed within the body, the body having a constant internal diameter in the region of overlap with a cut end of pipe, which corresponds with the outer diameter of the as extruded macro- composite pipe to be joined, provided with a discrete heating element adapted, and wherein a heating element is disposed around the internal bore of the body at least in each of the regions which receive a pipe so that when energized, the elements are operative to make a fusion joint between the body and its adjacent pipe, inserting the cut pipe end into the tubular body and energizing the electric heating elements to fuse the body to the adjacent pipe thereby forming a fluid-tight seal.

15. A joint for a composite pipe formed using an electrofusion fitting or method according to any of claims 1 to 14.

16. The use of an electrofusion fitting to form a joint in a macro-composite pipe, the pipe comprising at least one inner plastics layer, at least one outer plastics layer and at least one barrier layer therebetween, wherein the fitting comprises a tubular body formed at least in part from a thermoplastic polymer material and optionally comprising at least one barrier layer and adapted to receive a cut end of the pipe into each end of its internal bore and a plurality of electric heating elements disposed within the body, the body having a constant internal diameter in the region of overlap with a cut end of pipe, which corresponds with the outer diameter of the as extruded macro-composite pipe to be joined, provided with a discrete heating element adapted, and wherein a heating element is disposed around the internal bore of the body at least in each of the regions which receive a pipe so that when energized, the elements are operative to make a fusion joint between the body and its adjacent pipe.