It is known to join the ends of plastic pipes by the so called method of butt fusing.

This involves heating the ends of two plastic pipes and then forcing them together for a suitable period for them to fuse. However, it is expensive, burdensome and time consuming to provide and operate the machinery necessary to heat the ends of the plastic pipes, force them together and leave them in this condition for a sufficient period for them to fuse. Furthermore, beading is generally produced at the heated and fused portion of plastic pipe which extends into the bore of the joined pipes. This beading reduces the diameter of the bore of the joined pipes.

The present invention seeks to alleviate at least some of the problems discussed above.

According to a first aspect o f the p resent i nvention, there i s provided a method o f joining plastic pipes, the method comprising:- threading an annular flange onto an end portion of a plastic pipe; threading an annular electrofusion coupler onto the end portion of the plastic pipe; fusing the annular electrofusion coupler to the plastic pipe; if the end portion of the plastic pipe extends beyond the annular electrofusion coupler, trimming the plastic pipe to be substantially flush with the annular electrofusion coupler; performing the above steps on another plastic pipe; positioning the annular electrofusion couplers of both plastic pipes substantially adjacent to each other and substantially in axial alignment with each other; and securing the annular flanges to each other.

Such a method of joining plastic pipes overcomes the problems discussed above with butt fused plastic pipes. Furthermore, the above method of joining plastic pipes enables the plastic pipes to be subsequently separated if required, e. g. for maintenance, by releasing the annular flanges from each other.

The annular flanges are preferably releasably secured to each other, for example, using nuts and bolts. The annular flanges are preferably made from metal and may have a plurality of bolt holes through which bolts may be passed to secure the annular flanges to each other. The annular electrofusion coupler is preferably made from plastics material with suitable heating wires embedded within it. The joined plastic pipes may be provided within an outer pipe such as a cast iron main. According to a second aspect of the present invention, there is provided a connector for connecting two plastic pipes, the connector comprising:- an annular flange to be threaded onto each plastic pipe; an annular electrofusion coupler to be threaded onto each plastic pipe and fused to the plastic pipe; and means to secure the annular flanges to each other.

According to a third aspect of the present invention, there is provided a pipeline formed using the method of the first aspect of the present invention.

The various aspects of the invention may be embodied in many ways, but some specific embodiments will now be described by way of example with reference to the accompanying drawings, in which:- Figure 1 shows a plastic pipe to be joined to another plastic pipe; Figure 2 shows an annular flange to be threaded over a plastic pipe; Figure 3 shows a plastic pipe with an annular flange threaded over it; Figure 4 shows a rear view of the arrangement shown in Figure 3; Figure 5 shows the arrangement of Figure 3 with the addition of an electrofusion coupler; Figure 6 shows the arrangement of Figure 5 with the plastic pipe trimmed; Figure 7 shows a side view of two plastic pipes joined together; Figure 8 shows two joined plastic pipes inside a first outer surrounding pipe; and Figure 9 shows two joined plastic pipes inside a second outer surrounding pipe.

Figure 1 shows a plastic pipe 10, in this case made from polyethylene (PE). The pipe 10 could be used for any suitable application such as conveying fluids for example fuel gas, oil, slurries, sewerage etc.

Figure 2 shows an annular flange 20, in this case made from metal, provided with a central hole 21 to accommodate a pipe such as plastic pipe 10. The flange 20 has a plurality of equiangularly spaced bolt holes arranged around its periphery.

Figure 3 shows the plastic pipe 10 with the central hole 21 of the flange 20 threaded over it.

Figure 4 shows a rear view of the pipe 10 and flange 20 with an optional shim 23 arranged between the pipe 10 and flange 20 to spread the weight of the flange 20 on the pipe 10.

Figure 5 is a front view similar to that of Figure 3 with the addition of an annular plastic electrofusion member 30 threaded onto the end of pipe 10 after the flange 20.

The annular plastic electrofusion member 30 has connection wires 31 which can be connected to a power source. The annular plastic electrofusion member 30 has heating wires embedded inside, near its inner surface and connected to the connection wires 31 so that when energised by a power source connected to the connection wires 31, the heating wires embedded in the member 30 melt the surrounding plastic of the inside surface of the member 30 and the outside surface of the pipe 10 to fuse them together. Once the electrofusion member 30 is fused to the pipe 10, the connection wires 31 may be removed. The electro fusion member 30 may be positioned some distance from the end of pipe 10 when it is fused to the pipe 10, as shown in Figure 5, in which case the end portion of pipe 10 extending out from the electrofusion member 30 will be cut off to bring the end of pipe 10 flush with the exposed edge of electrofusion member 30 as shown in Figure 6. Alternatively, if the end of pipe 10 is sufficiently perpendicular to the axis of the pipe 10, the electrofusion member 30 can be fused to the end of pipe 10 without the need for cutting off an exposed section of pipe 10.

Figure 7 shows the securing together of two sections of pipe 10 prepared as in Figure 6. The ends of the pipes 10 and the exposed surfaces of electrofusion couplers 30 are brought into contact with each other and secured to each other by nuts 24 and bolts 25 secured between the flanges 20 using bolt holes 22. If desired a containment ring (not shown) may be secured around both electrofusion couplers 30 to reduce the likelihood of them being forced outwards by pressure from within the pipe.

If convenient or desired, the plastic pipes 10 may be provided as a loose fit inside an outer pipe 40 which may be an existing pipe, such as a cast iron main for example as shown in Figure 8 and Figure 9. In Figure 8, the plastic pipes 10 and flanges 20 are accommodated within outer pipe 40. The outer pipe 40 may not have a joint or may have a joint at or near to where the plastic pipes or joined. Alternatively, the plastic pipes 10 could be provided within outer pipes 40 with the flanges 20 extending out of outer pipes 40, for example, in the gap between two neighbouring outer pipes as shown in Figure 9.

Even though the annular flanges 20 are described as being joined by nuts 24 and bolts 25, any suitable method or apparatus for joining the flanges 20 may be used such as using clamps. However, the method or apparatus for joining the annular flanges 20 is preferably releasable.