A method of molding a sleeve on a corrugated pipe consisting of an inner wall and fusion-bond ridges. Two clamps can close to engage several of the ridges. One to three of the ridges project into a molding space between the clamps. A core is inserted into pipe and closes the molding space. Hot pressurized resin softens and collapses the projected ridges and fusion bonds the pipe to the sleeve portion of the molding space.