Review of PE Pipe Lifetime Prediction Based on PENT Test

A new method of evaluating polyethylene (PE) pipe brittle failure time has been recently proposed [1]. The method consists of an extrapolation of the failure time in standard PENT test to brittle failure time of PE pipes of arbitrary diameter and wall thickness at various loads and temperatures. The method is based on several assumptions that have not been adequately addressed in [1]. This paper presents a detailed review of the theoretical and experimental basis of the extrapolation proposed in [1] and reveals its limitations. A fracture mechanics analysis of the PENT test is presented. It requires evaluation of parameters in “power law” equation of the slow crack growth (SCG). Thus a specimen whose stress intensity factor (SIF) is independent of crack length has been used to serve this purpose. Such specimen allows an accurate determination of crack growth rate vs. SIF relationship and thus predicts the duration of SCG stage of brittle fracture process at various temperatures. The study indicates that the formula proposed in [1] can be used for materials ranking with respect to SCG resistance within a limited temperature range, but is inadequate for estimation of lifetime in brittle fracture.