APPLICABILITY AND LIMITATIONS OF CURRENT LIFETIME PREDICTION MODELS FOR THERMOPLASTICS PIPES UNDER INTERNAL-PRESSURE

Engineering thermoplastics, in particular polyolefins such as special grades of poly(ethylene), are gaining importance in pipe applications such as gas and water supply systems. To ensure proper performance of such pipes over the required lifetime, polymer physics and mechanics c oncepts are needed to adequately account for the effects of time, temp erature, and environmental conditions as well as the occurrence of pip e defects and imperfections on relevant polymer properties and pipe pe rformance. This article provides a critical overview of the scientific background of current methodologies to describe the long-term behavio r of thermoplastic pressure pipes. in particular, the merits and limit ations of two different approaches - namely, the standard extrapolatio n method (SEM) described in ISO/TR 9080 and the linear elastic fractur e mechanics (LEFM) approach - are compared. Special attention is given to effects associated with material ageing and degradation.