Thermal‐oxidative aging performance and life prediction of polyethylene pipe under cyclic and constant internal pressure

Abstract

To study the aging characteristic of the polyethylene (PE) 100 pipe under constant and cyclic internal pressure, a new accelerated thermal-oxidative aging test equipment was developed. Thermal-oxidative aging behaviors of PE pipe under constant pressure and cyclic pressure were studied in various temperatures (80, 95, and 110 C) by accelerated aging tests. The tensile test result shows that the fracture strength of PE pipe decreases as the aging time prolongs. Meanwhile, the pipe aged in the higher temperature behaves faster decreasing rate. A faster decreasing rate is also observed under the condition of cyclic pressure, compared to that under constant pressure. The thermal stability of the pipe gradually reduces and the reducing rate under cyclic pressure is higher than that under constant pressure. The result of infrared spectroscopy test suggests that oxygen-containing groups (i.e., C O) are formed on the surface of PE pipes, indicating that oxidative degradation phenomenon of PE pipes occurs during the aging process. Furthermore, based on the measured result of fracture strength, lifetime prediction models of PE 100 pipe under constant pressure and cyclic pressure are proposed. The result shows that the lifetime of PE 100 pipes obviously decreased under cyclic pressure, and it is 27.96% shorter than that under constant pressure.

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