A method for producing a biaxially oriented tube from thermoplastic material, wherein a tube in preform condition is extruded from thermoplastic material and is subjected to a temperature conditioning. Use is made of an expansion device and of a drawing device which is arranged downstream of the expansion device. The expansion device includes a non-deformable expansion part and a run-on part located upstream of the non-deformable expansion part and having an upstream sealing member. The expansion device further includes a first gas discharge duct having one or more first inlet ports in the exterior surface of the expansion device, a first inlet port being open or closed or partly closed dependent on whether or not the first inlet port is covered and closed, or partly closed, by the tube.

A sizer for cooling an extrudate, which includes a core and a housing. The core includes an extrusion channel which accommodates the extrudate, a core cooling channel, and a core vacuum channel in fluid communication with the extrusion channel. The housing includes a housing cooling channel and a housing vacuum channel. The core cooling channel is in fluid communication with the housing cooling channel, and the core vacuum channel is in fluid communication with the housing vacuum channel.