Lifetime of PE 100 pipes and the use of OIT test

The service life of PE (polyethylene) pressure pipes PE 80, PE 100, PE 100-RC is influenced by different factors. The ultimate end of life of a PE 100 material will be determined by full brittle failure caused by stress, oxidation and ageing. In order to protect PE 100 against oxidation, PE materials produced in accordance with the EN and ISO pressure pipe standards are equipped with different types of additives. The effectiveness of some additives can be determined by the OIT (Oxidation Induction Time ISO 11357-6). However, other additives that help to protect against ageing are not detected by the OIT. Thus, the OIT test result of a material does not provide a full picture of the additive package protection provided to the PE pressure pipe material[1]. Hence the test result does not give a true indication of the expected service life of a pipe system[2]. The best prediction tool for the determination of the expected service life for PE80, PE 100 and PE100-RC materials in pipe form is the evaluation of the long-term hydrostatic strength according to ISO 9080 done at 20°C, 60°C and 80°C. These data sets allow an extrapolation to longer service times at different temperatures and stress levels. Based on analysis of long term hydrostatic test results and on the practical experience gathered on PE water and gas networks over the last 40+ years, the TEPPFA and PE100+ associations published the statement regarding the expected 100 years lifetime of PE pressure pipe systems buried in the ground for water and natural gas supply (www.pe100plus.com). [1] Huszar, W.; McCarthy, Dr. M.; McGoldrick; Rothoeft, .W.; in Brömstrup, H: “Rohrsysteme aus PE 100”, 3rd. Edition, p. 36 [2] Schmutz, Th.; Kramer, E.; Zweifel, H.: “Oxidation Induction Time (OIT) – A tool to Characterize the Thermo-Oxidative Degradation of e PE-MD Pipe Resin?” Ciba-Geigy,