Abstract: An improved ram extruder for the production of plastic pipe, especially plastic pipe of high molecular weight low pressure polyethylene, which comprises an extrusion die, heating means for heating polymer to be extruded, a ram which is reciprocated in the extrusion die, means for reciprocating said extrusion die and a mandrel which determines the inside diameter of plastic pipe to be extruded, the mandrel being rigidly connected with the ram. Also disclosed is a process for ram extruding plastic pipe by the use of such a ram extruder, especially a process for the formation of plastic pipe of high molecular weight low pressure polyethylene of molecular weight of more than 500,000. A pipe or tube of high molecular weight low pressure polyethylene of molecular weight more than 500,000 is also disclosed together with its use as a liner for a steel pipe.