Accelerated ageing of plastic jacket pipes for district heating

The axial shear strength of plastic jacket pipes consisting of a steel medium pipe surrounded by polyurethane insulation and a casing of polyethylene was determined after service life. Recalculation of the physical life to equivalent life at 120 °C with the respective Arrhenius equation showed the envelope of lifetime ends much earlier than stated as minimum requirement in EN253. A method to determine an apparent activation energy considering additionally the oxidative degradation of PUR in plastic jacket pipes is presented. Enabled gas exchange within accelerated ageing similar to 30 years of life time resulted in an apparent activation energy of 95 kJ/mol, and additionally a further degradation, obviously due to corrosion, was found.