Investigation of Residual Stresses in Extruded Thermoplastic PE-RT Pipes

Polyethylene of Raised Temperature resistance (PE-RT) is a versatile polymer with an enhanced ability to withstand higher temperatures than other standard polyethylene-derived materials. The application scope of PE-RT pipes extends across a broad range of residential and industrial uses. However, the inherent residual stresses developed during the fabrication processes of these pipes pose a significant challenge to their service performance. Moreover, the technical literature on residual stresses in PE-RT pipes is scarce. The investigations presented in this paper address this scientific and technical gap by experimentally quantifying the residual stresses present in different sizes of PE-RT pipes manufactured at the same plant. The slitting method was employed as the primary experimental procedure in these investigations. In addition to establishing experimental processes, this study aims to mitigate residual stresses in PE-RT pipes by investigating their sensitivity to varying annealing temperatures for one selected pipe size. Subsequently, the optimal annealing temperature (115 °C) was applied to the remaining pipe sizes to determine its efficacy in residual stress mitigation. Through the implementation of these procedures, the circumferential residual stresses in PE-RT pipes subjected to annealing at 115 °C were significantly reduced, with a minimum decrease of 78%. Furthermore, the longitudinal residual stresses were substantially diminished, reaching a state of near-complete elimination.