Aging of Polyethylene Pipes Transporting Drinking Water Disinfected by Chlorine Dioxide. Part II-Lifetime Prediction

This article deals with the failure of polyethylene pipes transporting chlorine dioxide (DOC) disinfected water under pressures of few bars. Accelerated aging tries made at 20 or 40 degrees C show that the antioxidant is rapidly consumed in a superficial layer until a depth of about 1.2 mm. Carbonyl groups appear in a sharper layer of few hundreds micrometers. Natural aging results at various places, for various times up to about 30 years, reveal also a superficial attack with a depth of the order of 1.2 mm. An antioxidant loss by migration, in the whole sample thickness, is also observable. The shape of antioxidant concentration profiles indicates that the crossing of interfaces controls partially the whole migration kinetics. Failures, with brittle cracking, were observed in natural aging, after exposure times of the order of 515 years, i.e., far before the expected lifetime (50 years). A kinetic model has been elaborated to predict the time to failure. It is based on a chemical unit, which models the radical processes induced by DOC, and a mechanical unit based on an empirical creep law and a failure criterion depending of the molar mass calculated by the chemical unit. POLYM. ENG. SCI., 49:1642-1652,2009. (C) 2009 Society of Plastics Engineers