A method for forming an integral socket to a pipe made from biaxially oriented thermoplastic material is described. The pipe has a pipe body and is provided, at one or both ends, with an integral socket. The biaxially oriented thermoplastic pipe is subjected to a socket-forming operation comprising the steps of fixing both axial ends of the unheated end part of the pipe, heating the fixed end part to a suitable socket-forming temperature in one or more steps, and expanding the axially fixed end part with the aid of a fluid pressure in the interior of the end part and/or a vacuum on the outer side of the end part, which expansion may begin as early as during the heating of the end part.