Abstract: An apparatus for manufacturing molecularly oriented plastics pipes includes a tubular mould of transverse dimensions equal to those of the pipe to be produced and equipped with a device for admitting a fluid under pressure into a region intended to receive the pipe section to be expanded, a member for closing and grasping one end of the pipe section of a tubular sleeve which opens into the mould by an end away from the closing and grasping member and the transverse dimensions of which correspond to those of the pipe section and a means for causing a controlled relative axial displacement of the sleeve in relation to the closing and grasping member in which the open end of the sleeve is equipped with an annular plunger incorporating a surface of a frustoconical shape extending towards the inner wall of the mould and widened out in a direction away from the closing and grasping member.