Investigation of flexural creep for high-density polyethylene pipe

It is important to evaluate the viscoelastic behavior of high-density polyethylene pipe in service. Ring specimens of the same type, exposed at the same temperature, gave similar results for two types of pipes after used in service. No cracking/damage have been observed during the experiment. Arrhenius Equation and the Bi-directional Shift method are the appropriate methods to predict the long-term flexural modulus of the HDPE pipe. The long-term master curve, based on the William-Landel-Ferry (WLF) method showed more scattering of data than those, based on the Arrhenius and Bi-directional Shifting method due to temperature dependency of the crystalline in HDPE. Based on the most conservative Bi-directional Shifting method, the flexural modulus reductions after 100 years of service, are 40% and 46% of the initial modulus for un-notched specimens. Also, close results for notched specimens. Therefore, the HDPE pipe made with the new cell classification, 335420C, has a stiffness level good enough to meet the current specifications, after 100 years of service.