PROCESS FOR PRODUCING POLYETHYLENE PIPES WITH HIGH PRESSURE RESISTANCE AND POLYETHYLENE PIPES OBTAINED THEREBY

The present invention relates to a process for producing polyethylene pipes with high pressure resistance and polyethylene pipes obtained thereby. The pipes obtained by the process of the invention show increased pressure resistance and more consistent polymer properties. The process for producing a pipe comprises the steps of a) providing polyethylene pellets, b) extruding the polyethylene pellets into a pipe, wherein the extrusion step is conducted at an extrusion melt temperature of at least 225 °C, when the extrusion bath temperature is at least 15 °C, or at an extrusion melt temperature of at least 190 °C, when the extrusion bath temperature is at least 30 °C, extrusion melt temperature and extrusion bath temperature, and wherein the polyethylene pellets provided in step a) comprise a polyethylene composition comprising a copolymer of ethylene and hexene, and the polyethylene composition having a density of from 935 to 955 kg/m3 and a melt flow rate MFR5, determined according to ISO 1133, condition T at a load of 5.0 kg at 190 °C, of from 0.1 to 1.0 g/10 min., and the pipe obtained in step b) has a failure time in the accelerated point loading test (PLT+) of at least 400 h.