Method for joining high-pressure composite pipes

1. A method for joining high-pressure composite pipes each comprising a pipe-shaped inner layer made of a synthetic resin, a reinforcing layer made of a crosslinked stretched polyolefin resin sheet and wound on an external circumferential surface of the inner layer, and an outer layer made of a synthetic resin and laminated on the reinforcing layer, which method comprises the steps of:

heating and melting an end of each high-pressure composite pipe,

flaring the melted end of each high-pressure composite pipe, with a diameter thereof gradually enlarging toward an end face thereof,

butting the flared ends of both flared high- pressure composite pipes together and fusing internal circumferential surfaces of their inner layers, with their reinforcing layers being turned outwardly,

preparing an annular band which has an annular shape and one or more slits therein, in which band a groove runs circumferentially in the middle of an inner circumferential surface, and round-tipped ridges extend circumferentially along both side edges of the inner circumferential surface,

approximately centering the annular band over a fusion point of the high-pressure composite pipes,

mounting the annular band in such a manner that the groove can house a bulge which is formed by fusion and protrudes outwardly along the fusion point, and that tips of the ridges can contact, on both sides of the bulge, with external circumferential surfaces of the high-pressure composite pipes, and

fastening the annular band.

2. A method for joining high-pressure composite pipes according to claim 1 , which further comprises the steps of:

approximately centering a heat-shrinkable reinforcing material over the fusion point of the high-pressure composite pipes, and

shrinking the reinforcing material by heating.

3. A method for joining high-pressure composite pipes according to claim 1 , which further comprises the steps of:

removing a bulge formed along the fusion point of the high-pressure composite pipes, approximately centering a heat-shrinkable reinforcing material over an area from which the bulge is removed, and

shrinking the reinforcing material by heating.

4. A method for joining high-pressure composite pipes according to claim 2 or 3 , wherein the reinforcing material is a tube-shaped element obtained by integrally winding a crosslinked stretched polyolefin resin sheet into tubular form.

5. A method for joining high-pressure composite pipes according to claim 4 , wherein the tube-shaped element is obtained by spirally and integrally winding the crosslinked stretched polyolefin resin sheet on an external circumferential surface of a core, in a plurality of layers which are oriented in reverse inclination directions from each other; and then removing the core.

6. A method for joining high-pressure composite pipes according to claim 2 or 3 , wherein the reinforcing material is a tube-shaped element obtained by enlarging a diameter of a thermoplastic resin pipe, such that a resin for reinforcing a joint area of the high-pressure composite pipes and a vicinity thereof is oriented in a circumferential direction.

7. A method for joining high-pressure composite pipes according to claim 1 , wherein the polyolefin resin sheet is crosslinked to show a gel fraction of 20% by weight or higher.

8. A method for joining high-pressure composite pipes according to claim 1 , wherein the polyolefin resin sheet is crosslinked by adding a photopolymerization initiator and irradiating an electron ray or an ultraviolet ray.