Time-dependent strength of large diameter PE100 low sag pipe

Abstract

The qualification of large diameter polyethylene pipes in PE100-LS, a specially developed ‘low sag' pipe grade of polyethylene, is described, taking into account long term creep. The extrapolated long term strain under hydrostatic pressure was 2·9% at 50 years which is lower than the 3·5% observed for more conventional PE100 polyethylenes. For gravity pipes of PE100-LS, a strain value of 5% at 50 years is recommended, which is the same as for common PE pipe materials subjected to stress relaxation. The present study also resulted in quality control recommendations for large diameter PE pipe, based on a 1000 h hydrostatic pressure test in which there is assumed to be a linear strain versus log pressure relationship. When the main load is due to external soil loading, a 1000 h ring test is proposed, at a deflection of 15%, focusing on stress relaxation measurements rather than pressure testing.