Coupling for tubular plastic pipes with liner of socket and liner of pipes being heat weldable

A pipe coupling assembly comprising

• first and second compound pipes having ends facing each other, each of said pipes having an inner layer (4) and an outer layer (3);
• a socket member (2) having an inner liner (10) and an outer sleeve (5) for joining said pipes,
• said inner liner of said socket assembly and said inner layers of said compound pipes being made of polymeric materials which are heat-weldable to each other, and
• said outer sleeve of said socket assembly and said outer layers of said compound pipes being made of high-strength, rigid polymeric materials which are frictionally joinable to each other;
• means (12, 13) forming a fluid-tight, continuous welded connection of said inner liner of said socket assembly to said inner layers (4) of said pipes;
• and
• means at opposite ends of said sleeve for forming frictional connections (7) between said sleeve and said outer layers of said pipes.

A method of forming a pipe coupling comprising the steps of

• forming first and second compound pipes each having an end to be joined to the other pipe, each of the pipes having an inner layer (4) and an outer layer (3) with the inner layer protruding beyond the end of the outer layer,
• forming a socket assembly (2) having an inner liner (10) and an outer sleeve (5) for joining the pipes, the socket assembly having opposite ends with the outer sleeve protruding beyond the inner liner, the sleeve and liner being dimensioned to receive the outer layer and liner, respectively, in concentric, mating relationships,
• the inner liner of the socket assembly and the inner layers of the compound pipes being selected from materials which are substantially chemically inert and are heat-weldable to each other, and
• the outer sleeve of the socket assembly and the outer layers of the compound pipes being selected from substantially rigid, high-strength materials which are frictionally joinable to each other;
• inserting the inner layers of side pipes into the opposite ends of the socket assembly,
• heating the ends of the inner layers and the inner liner to form a welded connection of the inner liner of the socket assembly to the inner layers (4) of the pipes;
• and
• adhering opposite ends of said sleeve to said outer layers of said pipes for forming frictional connections (7) between the sleeve and the outer layers of the pipes.