Investigation of long-term rupture pressure in PEX-AL-PEX composite pipes

Abstract

One of the most vital parameters in PE-X/Al/PE-X composite pipe production is the tolerated internal long-term hydrostatic pressure. Composite pipes rupture pressure depends not only on operating temperature and time but also on the layer's dimensions (inner polymer, outer polymer, and Aluminum layer), mechanical properties of layers, and welding types of the aluminum layer. In this research, the long-term life behavior of PEX multi-layer pipes until 1000 h was experimentally measured for different diameters and welding types. The hoop and radial stress of the pipe layers are calculated analytically, based on the classical elasticity theory. Also, by presented equations, the tolerable pressure of each layer can be defined as a function of long-term hydrostatic pressure, size, and mechanical properties of the Aluminum and Cross-linked Polyethylene layers in the pipe. The results show that the pressure bearing by the Aluminum layer is 84%–91% of pipe hydrostatic pressure. Meanwhile, the PE-X outer layer pressure bears less than 3% of the hydrostatic pressure, and the rest bears by the PE-X inner layer. The K coefficient is introduced as a pipe design parameter to show the relationship between the Aluminum tensile stress and the Aluminum layer hoop stress. In addition, by employing the Artificial Neural Network (ANN), the rupture pressure-time diagram for geometrical pipe parameters was predicted accurately with an acceptable fitting parameter R-squared more than 0.99.