Research On Thermal-oxidative Ageing Behavior And Mechanism Of Polyethylene Pipe Under Pressure Loadings

Polyethylene(PE)gas pipeline has been extensively used in gas transportation.Once the leakage occurs,it will threaten people's property and life safety.Because of the working condition,withstanding the internal pressure and environment,the ageing phenomenon of PE pipe will inevitably occur.To study the aging behavior of PE pipes under thermal-oxidative environment,the aging performance and mechanism of PE 100 pipes under constant hydraulic pressure,constant internal pressure and cyclic internal pressure were investigated by means of experimental research and theoretical application.The main contents include:(1)Thermal-oxidative aging properties of PE pipes under constant hydraulic environment.The ageing performance of PE gas pipes in constant pressure water bath was studied from the point of view of degradation of PE pipes under constant liquid pressure at 80 C.The relationship between the performance and exposure time of PE pipes in pressure water bath environment was explored.The aging of PE pipes was examined by combining the macro and micro performance changes of mechanical properties,microstructure,antioxidant consumption and thermal properties.The thermal aging analysis model of PE pipes under constant hydraulic environment was established from the macro and micro aspects.(2)Thermo-oxidative aging performance of PE pipes under cyclic and constant pressure loadings.Taking the aging environment of PE gas pipeline under actual working conditions as a reference object,we independently designed and developed an experimental device for thermal oxygen aging of PE pipes under cyclic and constant pressure.Accelerated aging tests of PE pipes were carried out at 80,95 and 110 ?.Thermo-oxidative aging models of PE pipes under two pressure types(constant pressure 0.2 MPa and cyclic pressure 0.15-0.24 MPa)were established.The relationship between mechanical properties,thermal stability,surface microstructure and antioxidant content of PE pipes with time was analyzed from the perspective of macro-micro combination.The relationship between macro and micro properties of PE pipes under different pressure was studied,and the aging mechanism of PE pipes under different pressure was explored.The research above provided a theoretical basis for the study of thermal oxygen aging life prediction of PE pipes.(3)Thermal-oxidative aging lifetime prediction of PE pipes under cyclic and constant pressure.Based on the aging performance test of PE pipes under cyclic and constant pressure,the thermal-oxidative aging lifetime of PE gas pipe was evaluated.Based on statistical theory,using MATLAB program and dynamic curve linearization method,the thermo-oxidative aging life equation of PE pipes under two kinds of pressure was constructed.At the same time,Hoàng & Lowe method was introduced to establish the antioxidant depletion life equation of PE pipes under two types of pressure from the aspect of antioxidant consumption.The results demonstrate that the aging life of PE pipe under cyclic pressure is 27.6% and 16.02% shorter than that under constant pressure,based on the two aspects respectively.Based on different aging properties,the life of PE pipes under specific working conditions is evaluated,which provides a reference for the life evaluation of PE pipes under actual working conditions.