Abstract: A joint between pipes (12, 14) each having a liner (16, 18) of polyolefin such as polythene. The pipes are spaced apart and the liner protrudes from each and is joined to its neighbor by a fusion coupling (20). The pipes are interconnected by a shell (24, 26, 28) and epxoy cement grout (34) fills the space between the liner and the shell. The liner is inserted in the pipe after it has been reduced in diameter by passing it through a die. The pressure of gas or liquid within the liner in use is greater than the liner can withstand alone but the grout transfers pressure loading to the shell. In modifications the coupling is replaced by a PECAT coupling or by flanged couplings joined to the pipes by butt fusion or by electrofusion directly or using electrofusion couplers. The liner may be locked in position using electrofusion fittings to prevent change of dimensions by reversion.

Abstract: Large fittings or other structures are made by rotationally moulding a first component 18 of polyethylene and joining cylindrical pups 20, 22, 24 of polyethylene to the component by butt fusion joints 26, 28, 30. The structure within the boundary 50 is irradiated with gamma radiation followed by post-heating to remove free radicals. The extremities of the pups are shielded to prevent irradiation. Their capability to be joined to polyethylene pipes 12, 14, 16 by butt-fusion joints 32, 34, 36 is unimpaired. The irradiation introduces cross-linking to give improved properties such as impact resistance and stress crack resistance and to bring the fitting within the specification for polyethylene pipe for natural gas distribution. The joints 26, 28, 30 are made using differential heating of the ends to be joined to compensate for differences in melt flow index. Alternatively, the component 18 is slightly irradiated to lower its MFI before the pups are joined to it.

Abstract: A method for connecting a plastics pipe to a fitting incorporating an externally grooved insert. The insert, which is a tight fit in the pipe, is forced into the end of the pipe, and a sleeve, previously located on the pipe, is then forced to the end of the pipe so that the pipe end is tightly gripped between the insert and the sleeve. The insert is tubular and is provided with a plurality of circumferential grooves in its outer surface. Each groove has in axial section substantially straight sides and a straight base, the angle between the base and each side being obtuse. Insertion of the insert causes the external diameter of the pipe to increase so as to be greater than the internal diameter of the sleeve.