Analysis of ductile and brittle failures from creep rupture testing of high-density polyethylene (HDPE) pipes

A comprehensive analysis of ductile and brittle failures from creep rupture testing of a wide spectrum of HDPE pipes was conducted. The analysis indicates that the ductile failure of such pipes is primarily driven by the yield stress of the polymer (or pipe). Examination of ductile failure data at multiple temperatures indicates a systematic improvement in performance with increasing temperature. It is proposed that testing at higher (above-ambient) temperatures leads to progressive relaxation of the residual stresses in the pipe; this causes the pipe to perform better as residual stresses are known to help accelerate the fracture process. Finally, our investigation indicates no correlation, whatsoever, between brittle failures in pressurized pipes and the PENT (Pennsylvania edge-notch tensile test; ASTM F1473) failure times. Therefore, one has to be extremely cautious in interpreting the true value of the PENT test when developing polymers and pipes for high-performance pressure pipe applications.