Development in Plastic Materials # 2004 Milan
There are three factors that can influence the service life of plastics pipes: mechanical overloading, environmental stress cracking and degradation caused by oxidation at high temperatures. This article deals primarily with the degradation that occurs during processing at high temperatures and also – as an autocatalytic process – during prolonged use of the pipes. Creep tests show that degradation through oxidation over an extremely long test duration ends in a brittle fracture, whereby the actual load is virtually of no consequence. The influence of stabilizers and pigments on the long-term performance of HDPE pipes have now been investigated – for the first time ever – in long-term failure tests under internal hydrostatic pressure. These tests show that blue pigmented pipes have a service life three times that of black pipes. This difference is explained by the fact that blue pipes are additionally equipped with a HALS type UV stabilizer which exercises an additional beneficial influence on long-term stability.