GB2314597A

GB2314597A - Electrofusion fitting for a plastics pipe with gripping means

Info

Publication number: GB2314597A
Application number: GB9624073A
Authority: GB
Inventors: Alan John Dickinson; Jyri Jaakko Jarvenkyla; Franz-Josef Riesselmann
Original assignee: UPONOR BV
Current assignee: UPONOR BV
Priority date: 1996-06-25
Filing date: 1996-11-20
Publication date: 1998-01-07
Also published as: DE69709872D1; GB9624073D0; DE69709872T2

Abstract

An electrofusion fitting 1 for a plastics pipe 9,10 comprises a hollow, tubular enclosure with a body 2 to which an end 14 of the plastics pipe 9, 10 can be connected. The body 2 comprises at least one circumferential inner wall 4 and as least one circumferential outer wall 3 concentric therewith, the walls 3, 4 forming an annular space 5 for receiving the end of pipe 9, 10 and comprise thermoplastic material at least in their regions adjacent the annular space 5. At least one heating element 7, 8 for heating the thermoplastic material of the inner and outer walls 3, 4 located adjacent to, or embedded in, each of walls 3, 4 in their regions adjacent the annular space 5, and either: (i) the heating elements 7,8 are off-set with respect to each other in an axial direction (figure 9), or (ii) means are provided for gripping and/or for applying lateral pressure on the end 14 of the plastics pipe 9, 10 received in the annular space 5 during fusion, or (iii) both.

Description

ELECTROFUSION FITTING This invention relates to electrofusion fittings, and more particularly to an electrofusion fitting suitable for use with a wide range of plastics pipes.

Plastics pipes are becoming increasingly used for the conveying of fluids, in particular gases and liquids, through pipe-lines. Examples of commonly used plastics materials for such pipes include polyethylene and polyvinylchloride. The properties of these materials can be improved somewhat by, for example, orientation and/or cross-linking, but it is technically and practically difficult to raise the pressure resistance of the pipe higher than around 15 to 20 bars. Thus, although such thermoplastic materials are suitable for low pressure, ambient temperature applications, where higher pressures and temperatures are used, it has been necessary to develop, for example, multi-layer composite pipes wherein the plastics materials are reinforced, for example, with a metal or glass fibre layer, or other layer of high axial strength, or wherein a layer of foamed plastics material is provided for thermal insulation purposes.

The coupling of plastics pipes using electrofusion fittings is well known, and, for example, typical electrofusion fittings are described in DE 20 15 682 Al, 25 DE 32 26 575 C1, DE 3307 161 Al, DE 94 01 401 U1, EP 0 076 460 B1 and EP 0 115 623 B1. The entire disclosures of each of the abovementioned prior patents are incorporated herein by reference for all purposes.

Problems have been encountered in attempts to use conventional in-line electrofusion fittings for the coupling of multi-layer composite pipes. For example, because the conventional electrofusion fitting only fuses to the outer surface of a plastics pipe, the cut end face of the pipe is left unprotected. Whilst this is not normally a problem with simple homogeneous plastics pipes, with multi-layer composite pipes the reinforcing and/or thermal insulation layers can become exposed to the fluid in the pipe at the pipe end, leading to delamination, corrosion of metal layers and/or destruction of the foam insulation. Further, if multilayer composite pipes are only linked together at the outside with a weld joint, only this layer will take over the bearing function. Since the outer layer normally is relatively thin and the adhesion to the other layers is limited, such a connection cannot withstand higher strains over a longer period.

For example, certain multi-layer composite pipes which are designed to have great axial strength performance, due to the presence of reinforcing layers or cross-linked and/or oriented thermoplastic layers of high axial strength, cannot be joined by electrofusion methods to give a joint of comparable axial strength performance.

This is because the materials used for the outer layers of these pipes are often of lesser quality in this respect, as only tear strength, crack propagation properties and W stabilisation are normally taken into consideration in the choice of materials. The outer layer of such pipes is also often very thin, which also contributes to a lower axial strength. A special problem is also created by multi-layer pipes in which the layer underlying the outer layer of the pipe is foam, for example, as described in International Patent Application No PCT/FI96/00359, the entire disclosure of which is incorporated herein by reference for all purposes. This structure has very bad tear strength properties.

Attempts to deal with these problems have been largely unsuccessful. In DE 44 44 914 there is shown an electrofusion coupler for a multi-layer composite pipe, wherein an annular end protector is provided for the adjoining pipe ends. This, however, does not seal against the pipe end and there is still a danger of fluid ingress giving rise to the problems outlined above. In DE 44 47 237 there is described an electrofusion coupler for high density polyethylene pipes wherein the pipe ends are inserted into annular spaces provided with electrofusion coils on their inner and outer surfaces.

However, with such a coupler, it is difficult to prevent fused material from extruding out of the annular space, leaving a void, and the high temperatures generated could easily lead to collapse of the foam insulation of some types of multi-layer composite pipe, for example, of the types described in Finnish Patent Application No 955960 (case 90135).

In German patent application number 19 625 439.6 there is described and claimed a welding fitting for a plastic tube, comprising: A connecting body to which an end of a plastic tube is connectable and which comprises at least one circumferential internal wall and at least one circumferential external wall concentric therewith, said walls forming a unilaterally open annular space therebetween to receive the end of the plastic tube and comprising plastic at least in their regions adjacent the annular space, at least one electrical heating element for heating the material of the internal and. external walls being embedded in each of said at least one internal wall and said at least one external wall in their regions near the annular space.

The welding fitting of this proposal is preferably provided with a reinforcement in the region of its at least one internal wall, and can have serpentine electrical heating conductors, which can move to accommodate fused plastics flow thereby substantially preventing the formation of voids during fusion.

Whilst the welding fitting of German patent application No 19 625 439.6 works well in practice with certain pipes, a further improvement in the prevention of void formation and improved sealing at the end of a multi-layer composite pipe would still be desirable.

According to the present invention there is provided an electrofusion fitting for a plastics pipe, which comprises a hollow, tubular enclosure comprising a body to which an end of the plastics pipe can be connected, the body comprising at least one circumferential inner wall and at least one circumferential outer wall concentric therewith, the inner and outer walls forming an annular space for receiving the end of the plastics pipe, and comprising thermoplastic material at least in their regions adjacent the annular space, at least one heating element for heating the thermoplastic material of the inner and outer walls being located adjacent to, or embedded in, each of said at least one inner wall and said at least one outer wall in their regions adjacent the annular space, and either: (i) the heating elements are off-set with respect to each other in an axial direction, or (ii) means are provided for gripping and/or for applying lateral pressure on the end of the plastics pipe received in the annular space during fusion, or both.

In a further aspect, the invention provides a method for connecting a plastics pipe using an electrofusion fitting, wherein there is used an electrofusion fitting comprising a hollow, tubular enclosure comprising a body to which an end of the plastics pipe can be connected, the body comprising at least one circumferential inner wall and at least one circumferential outer wall concentric therewith, the inner and outer walls forming an annular space for receiving the end of the plastics pipe, and comprising thermoplastic material in their regions adjacent the annular space, at least one heating element for heating the thermoplastic material of the inner and outer walls being located adjacent to or embedded in, each of said at least one inner wall and said at least one outer wall in their regions adjacent the annular space, and wherein the heating elements are energised to fuse the thermoplastic material and form a fusion bond to the plastics pipe, and either: (i) the heating elements are off-set with respect to each other in an axial direction, or (ii) a gripping force and/or lateral pressure is applied to the end of the plastics pipe during fusion, or (iii) both.

The hollow, tubular enclosure can comprise a plastics or a metal body, or may be of a composite construction, with plastics and reinforcing layers. The reinforcement can, for example, comprise a sleeve or grid formed from metallic materials, or it can comprise reinforcing fibres. In manufacturing a hollow, tubular enclosure reinforced with fibres, the reinforcing fibres can be wound on a preform and later provided with a plastics outer skin. Alternatively, the fibre reinforcement can comprise a three dimensional preform, which maintains its shape, and comprises fused plastics coated fibres. The preform can be set into a mould cavity and the spaces or interstices in the preform filled with a plastics matrix material by, for example, injection moulding, to give an oriented hollow, tubular enclosure, as described in PCT/EP96/02801.

The tubular enclosure can comprise an integral body, or can comprise two or more hollow body members which can be separately installed and connected. The hollow body members can be threaded, in order that they can be screwed together, or can have co-operating annular projections or depressions enabling them to be a push-fit or snap-fit together. In a preferred embodiment according to the invention, the enclosure comprises a first hollow body member comprising the at least one circumferential inner wall of the body, and a second hollow body member comprising the at least one circumferential outer wall of the body. On assembly, the first (inner) hollow member can be placed inside the second (outer) hollow member and an appropriate connection made in order to link the two hollow members together and create the annular space for receiving the end of the plastics pipe. Alternatively, the hollow members can be sequentially installed on the pipe, usually with the inner hollow member installed first.

The dimensions of the enclosure will, of course, be largely determined by the outer diameter and wall thickness of the pipe or pipes to be connected, and the length of the fusion joint required, but preferably the annular space is arranged to give a tight fit and conform closely to the dimensions of the pipe end, and, as will be more particularly described hereinafter, it can in some embodiments even be slightly smaller in width than the thickness of the pipe wall.

Although it is not usually necessary to do so, it is possible to use the electrofusion fitting of the invention with pipes whose ends have been expanded in diameter, for example, as shown in European Patent Application No 95 10 4955 (case 90131), the entire disclosure of which is incorporated herein by reference for all purposes.

The electrofusion fitting can comprise a connector whereby a pipe is fused or "welded" to another component by the action of an electrical heating element which may be a resistance or an induction heating element. The electrofusion fitting can, for example, comprise electrical conductor elements, for example, metal coils, rings, metal mesh, or other suitably shaped electrically conductive members, which are located adjacent to, or embedded in, a layer of fusible thermoplastic polymeric material in the regions of the inner and outer walls forming the annular space. The electrical conductor elements may be energised, for example, by passage of an electric current therethrough, or by inductive heating, in order to melt the adjacent thermoplastic material and form a fusion bond with the inner and outer surfaces of the plastics pipe.

Preferably the heating elements of the electrofusion fitting are formed from serpentine coils of electrical resistance wire, or some similar construction which permits the heating elements readily to change diameter in order to take up any gaps between the walls of the annular space and the outer surfaces of the plastics pipe, to minimise any void formation.

In certain embodiments it is possible to use both electrical resistance heating elements and inductive heating elements. In such cases, for example, the heating element located adjacent to, or embedded in, the outer wall can be an electrical resistance heating element, and the heating element adjacent to, or embedded in, the inner wall can be an inductive heating element, or vice versa. Where the inductive heating element is embedded in the inner wall this can also provide a reinforcing layer, as more particularly described hereinafter. Where both electrical resistance heating elements and inductive heating elements are used, these do not necessarily need to be energised simultaneously.

The term "inductive heating element" includes the Curie Point heating elements described in EP-A-0480 053 the entire disclosure of which is incorporated herein by reference for all purposes.

The fusible thermoplastic polymeric material of the electrofusion fitting can comprise, for example, a polyolefin, for example, polyethylene, polypropylene, polybutylene and higher olefinic polymers; co-polymers of ethylene, propylene and butylene with each other and with other olefinically unsaturated monomers; olefinically unsaturated aromatic polymers such as polystyrene and styrene co-polymers; and polymers and co-polymers of vinyl monomers such as ethylene vinyl acetate copolymers, polycarbonates, and like materials.

Polyethylene is the preferred fusible polymeric material, particularly where multi-layer composite pipes having outer and inner polyethylene surfaces are to be joined.

If desired, the fusible thermoplastic polymeric material can comprise a modified polyolefin material, for example, an anhydride modified polyethylene, or the material can comprise a cross-linking agent which reacts during or after the fusion bonding step to cross-link the polymeric material and possibly the adjacent surface of the pipe. Modified polyolefins are particularly useful in joining polyolefin surfaces of dissimilar composition.

Suitable modified polyolefin materials include, for example, alpha olefin polymers and co-polymers comprising up to 10% by weight of an olefinically unsaturated carboxylic acid or an anhydride thereof, such as, for example, acrylic acid, maleic acid, itaconic acid, and succinic acid, or their anhydrides, as copolymer or graft copolymer components.

If desired, the fusible thermoplastic polymeric material can comprise one or more fillers, and, for example, it can comprise fillers which react and can reach high temperatures when exposed to infra-red radiation or electromagnetic radiation, for example, stainless steel fibres, as described in PCT/EP96/02801.

The use of such fillers to assist, or instead of, the fusion means described above is included as a further aspect within the invention.

According to one aspect of the present invention, the heating elements of the inner and outer walls of the body of the fitting are offset in an axial direction, in order to ensure that there is adequate material available to flow and fill the fusion areas around the heating elements. Where the heating elements of the electrofusion fitting of the invention are axially offset, they are preferably arranged such that the inner heating element is disposed adjacent to the closed end of the annular space, and the outer heating element is disposed at a distance from the closed and such that it does not axially overlap the inner heating element. This provides an opportunity for the end of the plastics pipe adjacent the inner heating element to "buckle" slightly on electrofusion, such that the fused material to support the inner fusion can sink from the outside of the pipe near the end of the pipe, whilst the fused material to support the outer fusion can be drawn in from the bore of the pipe to the region of the outer heating element.

In certain embodiments, the body of the electrofusion member can be so shaped that the walls bounding the annular space are slightly conical, and of a diameter increasing with distance away from the open end thereof. This feature may be particularly useful in combination with the offset heating elements described earlier, creating a profile to counteract the "buckling" of the end of the plastics pipe, and limiting any diameter reduction of the pipe.

In another aspect of the invention, at least during the electrofusion process, a gripping force and/or lateral pressure is applied to the end of the plastics pipe. Without wishing to be bound by any particular theory, it is believed that the action of gripping the end of the plastics pipe prevents any internal pressure generated by expansion of fused material within the annular space from extruding molten thermoplastic material from the end of the electrofusion fitting, thereby leaving voids and adversely affecting the quality of the joint. In a similar fashion, lateral pressure applied to the pipe surfaces at the end of the pipe serves to keep the pipe surfaces in close contact with the inner and outer walls forming the annular space in the fitting, thereby reducing the risk of void formation.

Where the electrofusion fitting is provided with gripping means, this can, for example, comprise a series of two or more teeth which are radially disposed around the annular space and protrude slightly into the annular space so that, in use, they are capable of contacting and gripping the outer and/or inner surfaces of the plastics pipe. The teeth of the gripping means can, if desired, be sharp enough to penetrate an outer surface layer of the plastics pipe, and, where a multi-layer composite pipe is to be connected, the teeth can penetrate to contact the reinforcing layer of the composite pipe, in order to improve the connection thereto.

Other forms of gripping means can be envisaged, for example, the teeth could be replaced by roughened surfaces on the walls of the annular space, or the gripping means could comprise a resilient split ring, or similar component.

In those embodiments of the invention in which lateral pressure is applied to the pipe surfaces at the end of the plastics pipe during fusion, this can be accomplished in a variety of ways. In a first method according to the invention, the width of the annular space is slightly less than the thickness of the plastics pipe wall, and the plastics pipe wall is compressed, or the annular space is expanded, in order to permit the plastics pipe end to be received in the annular space.

The width of the annular space can be, for example, from 100% to 95% of the thickness of the plastics pipe wall. When the compression, or expansion, forces are removed, the plastics pipe will be a tight interference fit in the annular space and the circumferential inner and outer walls of the body of the fitting will apply lateral pressure on the plastics pipe.

In a further embodiment, the body of the electrofusion fitting comprises an inner and an outer member which are assembled to form the annular space for receiving the end of the plastics pipe. The relative dimensions of the inner and outer body members can be so arranged that on assembly of the body of the electrofusion fitting around the end of the plastics pipe the circumferential inner and outer walls of the annular space exert lateral pressure on an end region of the plastics pipe. This embodiment has the advantage that pipes of different thickness, but the same outside diameter, or pipes of different thickness but the same inner diameter, can be connected by replacing only one of the inner or outer body members, as appropriate. This can reduce inventory and save costs.

In a further embodiment, the body of the electrofusion fitting can be provided with an annular spreading member which projects into the annular space from the closed end thereof, such that, when the plastics pipe is pushed into the annular space, the annular spreading member penetrates into the end wall of the plastics pipe exerting a spreading action thereon. The spreading member thereby forces the inner and outer surfaces of the plastics pipe into contact with the inner and outer walls surrounding the annular space of the fitting, which in turn apply lateral pressure on the end of the plastics pipe.

In a still further embodiment, it is possible for the material of the hollow, tubular enclosure comprising the circumferential outer wall of the annular space to be formed from a heat recoverable material, for example, an expanded, cross-linked thermoplastic material, such that, on heating, the expanded circumferential outer wall recovers to a smaller diameter, reducing the width of the annular space and exerting lateral pressure on the end region of the plastics pipe received therein.

In certain embodiments, it may be preferred to manufacture the circumferential inner walls of the hollow, tubular enclosure from a relatively rigid material, or to provide it with a reinforcing layer, such that when the circumferential inner wall is pushed into the pipe it is a tight interference fit therein, and may even expand the bore of the plastics pipe slightly. This can ensure that an adequate supply of thermoplastic material is available to fill the fusion region around the inner heating element. Similarly, the material of the circumferential outer wall of the connecting body can be made from a material which is slightly flexible so that it can be expanded outwards over the pipe end, to be in close contact with the outer surface of the plastics pipe once the pipe has been pushed into the annular space.

In some cases it is desirable that the electrofusion fitting should provide electrical continuity across a connection, especially between the reinforcing metal layers of two composite pipes to be connected. Such pipes are described in PCT/FI96/00359 mentioned hitherto. The electrofusion fitting of the present invention provides a particularly simple way of maintaining electrical continuity, and this is a preferred and further aspect of the invention. Electrical continuity can be provided for example, by connecting the heating elements, either before or after fusion, to the adjacent ends of the electrically conductive layers of the pipes. Each electrofusion coil can, for example, be provided with terminal(s) which may be connected, either directly, or through mechanical gripping means, to the reinforcing metal layers. Electrical continuity is thereby provided through the terminals or through the mechanical gripping means which is capable of penetrating and piercing any oxide layer on the reinforcing metal layer, and thence through the electrofusion coils to the metal layer on the other composite pipe to be connected. Other methods of providing electrical continuity can also be provided, for example, mechanical gripping means could be provided which are directly connected or connected via the tubular enclosure if the enclosure is formed from a conductive material.

Certain embodiments of the invention will now be described, by way of example only, with reference to the accompanying Drawings in which: Figure 1 shows, in part sectional side elevation, a first electrofusion coupler and pipe joint of the invention wherein the plastics pipe ends are compressed before being received in the electrofusion fitting; Figure 2 shows, in part sectional side elevation, a second electrofusion fitting according to the invention in which the fitting is provided with spreading means for penetrating the end wall of the plastics pipe; Figure 3 shows, in sectional side elevation, a fragmentary view of a further electrofusion fitting according to the invention, and its application to the coupling of plastics pipes having a homogeneous wall; Figure 4 shows, in sectional side elevation, the coupler of figure 3 after electrofusion; Figure 5 shows, in sectional side elevation, a fragmentary view of a still further embodiment of an electrofusion coupler according to the invention wherein the body is in two parts which are connected together; Figure 7 shows in sectional view an electrofusion fitting according to the invention provided with gripping means; Figure 8 shows a fragmentary sectional view of a joint formed using an electrofusion coupler according to the invention with means for maintaining electrical continuity across the joint; and Figure 9 shows a fragmentary sectional view of a joint formed using a further electrofusion fitting according to the invention with gripping means and a conical inner wall.

Referring firstly to Figure 1, there is shown an electrofusion coupler illustrated generally at 1 comprising a body portion 2 having an outer circumferential wall 3 and an inner circumferential wall 4 defining an annular space 5. The inner and outer walls 3, 4 are connected and spaced apart by a mid-section 6.

Adjacent respectively the outer and inner surfaces of the annular space 5 are positioned electrical resistance heating coils 7 and 8 which are embedded respectively in the walls 3 and 4. The pipes 9 and 10 to be connected together are of multi-layer composite construction, comprising outer and inner plastics skin surfaces 11 and 12 and a foamed plastics core 13.

In use, the wall thicknesses of the pipes 9 and 10 at the ends thereof are reduced by compression means (not shown) so that the thickness at an end portion 14 is sufficient to enable the end portion to enter an annular space 5 in the electrofusion coupler 1. Once the plastic pipes 9, 10 have entered the annular spaces 5 of the electrofusion coupler 1, there will be a tendency for the pipe wall to expand resiliently towards its original thickness. In so doing, the inner and outer circumferential walls of the annular space 5 will constrain the expansion and thereby exert lateral pressure on the inner and outer surfaces of the thermoplastic pipes. This lateral pressure is maintained during electrofusion, and, after the heating elements 7, 8 have been energised, and the walls 3, 4 fused to the plastics pipe surfaces 11, 12, it is found that voids in the annular space 5, caused be insufficient contact between the fusion surfaces and lack of filling by fused material, are substantially minimised.

Referring now to Figure 2, there is shown a second embodiment of an electrofusion coupler according to the invention, illustrated generally at 20. The coupler is substantially similar to that shown in Figure 1, except that the coupler 20 is provided with annular spreading means 21, 22 which project into the annular spaces 23.

The annular spreading means 21, 22 have a conical section and a sharp point 24 for penetrating the end walls 25 of the multi-layer composite pipes 26 and 27.

In use, the multi-layer composite pipes 26, 27 are pushed into the annular spaces 23 of the electrofusion coupler 20 until the sharp points of the spreading means 21, 22 contact the end walls 25. The pipes 26, 27 are then driven into the coupler 20 until the end walls 25 bottom on the closed ends of the annular spaces 23. At this point the spreading means 21, 22 have penetrated the end walls 25 of the pipes and by a wedging action have forced the pipes into pressure contact with the outer and inner walls 28, 29 of the annular spaces 23. The heating coils 30, 31 are then energised in order to fuse the coupler to the pipes 26, 27. Again, by maintaining pressure on the outer and inner surfaces of the pipes 26, 27, the appearance of voids during electrofusion is substantially minimised.

Referring now to Figure 3, there is shown a fragmentary view of an electrofusion coupler, illustrated generally at 40, wherein the electrofusion elements 41, 42 are offset, or staggered, in an axial direction, with respect to the plastics pipe 43 to be connected. As illustrated, the pipe 43 is of homogeneous construction, and, for example, the pipe wall can comprise extruded high density polyethylene. The coupler has outer and inner circumferential walls 44, 45 which, as illustrated, are of unequal length, although this is not essential.

The inner wall 45 is provided with a reinforcing layer 46 of metal mesh.

The heating elements 41, 42 can consist of electrical resistance heating wires in the form of helical coils or serpentine loops, as illustrated in the inset drawing.

The effect of electrofusion using the coupler of Figure 3 is shown in Figure 4, where the distortion of the pipe 43 has been greatly magnified to illustrate the principle involved. It can be seen that the portion 48 of the pipe end has sunk under the heat generated by the heating element 42, thereby filling the fusion area around the heating element 42 to give a broad area of fusion joint. In the portion 49 of the pipe 43, under the influence of the heat generated by the heating element 41 fused material has been drawn from the pipe bore to fill the fusion area around the heating element 41 to form another excellent fusion joint.

Referring now to Figures 5 and 6, there is shown a further embodiment of an electrofusion coupler according to the invention, illustrated generally at 50. The coupler comprises an outer body member 51 and an inner body member 52, which are spaced apart and connected together by a central connecting region 53. The connection is illustrated diagrammatically, but it could be either a threaded section or a push-fit or snap-fit coupling. If desired, the inner member 52 can be provided with a metal reinforcing member 59.

In use, the outer and inner members 51, 52 can be either pre-assembled and the multi-layer composite pipe 54 inserted therein, or the inner member 52 can first be inserted into the pipe 54 and the outer member 51 slid thereover. It is possible for the inner member 52 to be a tight fit in the pipe 54, thereby exerting pressure on the inner wall thereof, and for the outer member 51 to exert resilient pressure on the outer surface of the pipe 54, for example, if the inner diameter of the outer member 51 is slightly less than the outer diameter of the pipe 54.

The connection of the fusion coils 55, 56, 57 and 58 is shown diagrammatically in the inset drawing.

The assembled fusion joint is shown in Figure 6.

The construction provides good pressure contact between the outer and inner members 51, 52 and the multi-layer composite plastics pipe 54, so that a good fusion joint is obtained.

Referring now to Figure 7, the electrofusion fitting 60 has an inner wall 61 and an outer wall 62, defining an annular space 63. Projecting into the annular space from respectively the inner and the outer walls are annular teeth 64, 65. When a pipe end 66 is inserted into the annular space 63 the teeth 64, 65 grip the pipe and resist its removal from the fitting. As shown the teeth 64, 65 are formed by metal rings, but other materials could also be used. After insertion of the pipe end 66, the heating elements 67, 68 are energised and the fusion joint completed.

In Figure 8, the electrofusion coupler 70 has an inner wall 71 and an outer wall 72, defining an annular space 73. The inner wall has a step region 74 towards the closed end of the annular space 73. Adjacent the outer wall 72 there is positioned a heating element 75, which is electrically connected to an identical element 76 on the other side of the coupler.

The inner wall also has a heating element 77, which extends around the step region 74 and is connected to an electrical contact 78. The contact 78 is connected to an identical contact 79 on the other side of the coupler.

The electrofusion coupler can be used for jointing multilayer composite pipes of some complexity. As illustrated, the pipe 80 has, taken in order from outside to inside, an outer conductive layer 81, a thick foam layer 82, an aluminium layer 83, a thin foam layer 84 and a high axial strength PEX layer 85. The pipe is prepared by cutting back a section of the layers 84, 85 to expose a length 86 of the aluminium layer 83, corresponding to the step 74. When the pipe end 80 is inserted into the annular space 73 the conductive layer 81 contacts the heating element 75, and the length 86 of the aluminium layer contacts the electrical contact 78. In this way, electrical conductivity is maintained from the conductive layer 81 to the element 76 via the element 75, and from the aluminium layer 83 to the contact 79 via the contact 78. The element 76 and contact 79 can of course be connected to a further pipe end (not shown) prepared in the same way as pipe end 8b.

After insertion of the pipe end 80 into the annular space 73 the elements 75 and 77 are energised, either simultaneously or sequentially to fuse the coupler 70 to the pipe end 80.

Referring now to Figure 9, the electrofusion fitting 90 has an outer cylindrical wall 91 and an inner conical wall 92 defining an annular space 93. The inner and outer walls are provided with heating elements 94 and 95 respectively. The outer wall 91 is also provided, at its free end, with a gripper 96 which comprises a threaded nut 97 which can be tightened on a thread (not shown) on the outer wall 91 and bears on a compression O-ring 98.

The fitting 90 is particularly useful for connecting foam pipes, and, as shown, a foam pipe 100 can be inserted into the annual space 93 until it abuts against the conical inner wall 91. Further travel of the pipe 100 compresses its lower end section 101 until the pipe bottoms on the end wall 102 of the annular space 93. The gripper 96 is then tightened so that the threaded nut 97 compresses the O-ring 98 which in turn exerts a gripping force on the pipe outer surface 103. After the pipe has been fully inserted the heating elements 94 and 95 are energised, either sequentially or simultaneously, to fuse the electrofusion fitting 90 to the pipe 100.

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.

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.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings), may be replaced by alternative features serving the same, equivalent or similar purposes, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent of similar features.

The invention is not restricted to the details of the 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.

Claims

1. An electrofusion fitting for a plastics pipe, which comprises a hollow, tubular enclosure comprising a body to which an end of the plastics pipe can be connected, the body comprising at least one circumferential inner wall and at least one circumferential outer wall concentric therewith, the inner and outer walls forming an annular space for receiving the end of the plastics pipe, and comprising thermoplastic material at least in their regions adjacent to the annular space, at least one heating element for heating the thermoplastic material of the inner and outer walls being located adjacent to, or embedded in, each of the said at least one inner wall and said at least one outer wall in their regions adjacent the annular space, and either (i) the heating elements are off-set with respect to each other in an axial direction, or (ii) means are provided for gripping and/or for applying lateral pressure on the end of the plastics pipe received in the annular space during fusion, or (iii) both.

2. An electrofusion fitting according to Claim 1, wherein the tubular enclosure comprises an integral body.

3. An electrofusion fitting according to Claim 1, wherein the tubular enclosure comprises two or more hollow body members which can be separately installed and connected.

4. An electrofusion fitting according to Claim 3, wherein the enclosure comprises a first hollow body member comprising the at least one circumferential inner wall of the body, and a second hollow body member comprising the at least one circumferential outer wall of the body.

5. An electrofusion fitting according to any of the preceding claims, wherein the heating elements comprise electrical resistance heating elements or induction heating elements.

6. An electrofusion fitting according to any of the preceding claims, wherein the heating elements are formed from serpentine coils of electrical resistance wire.

7. An electrofusion fitting according to any of the preceding claims, wherein the thermoplastic material comprises polyethylene.

8. An electrofusion fitting according to Claim 5 or 6, wherein the heating elements of the inner and outer walls of the body of the fitting are offset in an axial direction.

9. An electrofusion fitting according to Claim 8, wherein the inner heating element is disposed adjacent to the closed end of the annular space, and the outer heating element is disposed at a distance from the closed end such that it does not axially overlap the inner heating element.

10. An electrofusion fitting according to any of the preceding claims, wherein the gripping means comprises a series of two or more teeth which are radially disposed around the annular space and protrude into the annular space so that, in use, they are capable of contacting and gripping the outer and/or inner surfaces of the plastics pipe.

11. An electrofusion fitting according to any of the preceding claims, wherein the width of the annular space is slightly less than the thickness of the plastics pipe wall.

12. An electrofusion fitting according to Claim 11, wherein the body of the electrofusion fitting comprises an inner and an outer body member which are assembled to form the annular space for receiving the end of the plastics pipe, and wherein the relative dimensions of the inner and outer body members are so arranged that, on assembly of the body of the electrofusion fitting around the end of the plastics pipe, the circumferential inner and outer walls of the annular space exert lateral pressure on an end region of the plastics pipe.

13. An electrofusion fitting according to any of the preceding claims, wherein the body is provided with an annular spreading member which projects into the annular space from a closed end of the said space, such that, in use, when the plastics pipe is pushed into the annular space, the annular spreading member penetrates into the end wall of the plastics pipe exerting a spreading action thereon.

14. An electrofusion fitting according to any of the preceding claims, wherein the material of the hollow tubular enclosure comprising the circumferential outer wall of the annular space is formed from a heat recoverable material.

15. An electrofusion fitting according to any of the preceding claims, wherein the circumferential inner wall of the hollow, tubular enclosure is provided with a reinforcing layer.

16. An electrofusion fitting according to any of the preceding claims, which is adapted to connect multi layer composite pipes having electrically conductive layers, and which is adapted to provide electrical continuity across the connection.

17. An electrofusion fitting according to any of the preceding claims, substantially as hereinbefore described with reference to and as illustrated in the accompanying Drawings.

18. An electrofusion fitting substantially as hereinbefore described.

19. A method for connecting a plastics pipe wherein there is used an electrofusion fitting comprising a hollow, tubular enclosure comprising a body to which an end of the plastics pipe can be connected, the body comprising at least one circumferential inner wall and at least one circumferential outer wall concentric therewith, the inner and outer walls forming an annular space for receiving the end of the plastics pipe and comprising thermoplastic material in their regions adjacent the annular space, at least one heating element for heating the thermoplastic material of the inner and outer walls being located adjacent to, or embedded in, each of said at least one inner wall and said at least one outer wall in their regions adjacent the annular space, which comprises: disposing the end of the plastics pipe in the annular space and energising the heating elements to fuse the thermoplastic material and form a fusion bond to the plastics pipe, and wherein either: (i) the heating elements are off-set with respect to each other in an axial direction, or (ii) a gripping force and/or lateral pressure is applied to the end of the plastics pipe during fusion, or (iii) both.

20. A method according to Claim 19, wherein the hollow, tubular enclosure comprises a first hollow body member comprising the at least one circumferential inner wall of the body, and a second hollow body member comprising the at least one circumferential outer wall of the body, and wherein the hollow members are sequentially installed on the plastics pipe.

21. A method according to Claim 19 or 20, wherein the width of the annular space is slightly less than the thickness of the plastics pipe wall, and the plastics pipe wall is compressed, or the annular space is expanded, in order to permit the plastics pipe end to be received in the annular space.

22. A method according to any of Claims 19 to 21, which comprises assembling an inner and an outer body member to form the annular space for receiving the end of the plastics pipe, the relative dimensions of the inner and outer body members being arranged so that on assembly of the body of the electrofusion fitting around the end of the plastics pipe, the circumferential inner and outer walls of the annular space exert lateral pressure on an end region of the plastics pipe.

23. A method according to any of Claims 19 to 22, wherein the plastics pipe is pushed into the annular space of the hollow, tubular enclosure and wherein the body of the electrofusion fitting is provided with an annular spreading member which projects into the annular space from a closed end of the said space, such that, when the plastics pipe is pushed into the annular space, the annular spreading member penetrates into the end wall of the plastics pipe exerting a spreading action thereon.

24. A method according to any of Claims 19 to 23, wherein the material of the hollow, tubular enclosure comprising the circumferential outer wall of the annular space is formed from a heat recoverable material, and wherein the end of the plastics pipe is disposed in the annular space and the heat recoverable materials is heated in order to recover the circumferential outer wall to a smaller diameter, reducing the width of the annual space and exerting lateral pressure on the end region of the plastics pipe received therein.

25. A method according to any of Claims 19 to 24, wherein the circumferential inner wall of the hollow, tubular enclosure is pushed into the pipe to expand the bore of the plastics pipe.

26. A method according to any of Claims 19 to 25 substantially as hereinbefore described.

27. An electrofusion joint for a plastics pipe, formed from an electrofusion fitting according to any of Claims 1 to 18.

28. An electrofusion joint for a plastics pipe formed using a method according to any of Claims 19 to 26.

29. An electrofusion joint substantially as hereinbefore described.