Patent ID: 8632646

Claim:
A method for joining pipes in which a first pipe and a second pipe that is made of thermoplastic resin are joined together, comprising: a first step in which an end portion of the first pipe, which includes at least one portion to be engaged that is sunk toward an inner circumferential surface side at an outer circumferential surface of the end portion of the first pipe, is inserted into an end portion of the second pipe, in which at least one protruding portion is formed on an outer circumferential surface of the end portion of the second pipe, and the portion to be engaged is positioned at an inner circumferential surface side of the protruding portion of the second pipe; and a second step in which, as a result of a transmitting component that transmits ultrasonic waves being pressed against an outer circumferential surface of the protruding portion that is positioned corresponding to the portion to be engaged of the first pipe which is inserted into the second pipe, the second pipe is softened by the ultrasonic waves so that an engaging portion which is made to protrude from an inner circumferential surface of the second pipe into the portion to be engaged is formed, and becomes engaged with the portion to be engaged.