Crack initiation and propagation paths for brittle failures in aligned and misaligned pipe butt fusion joints

Abstract

AbstractMedium density polyethylene pipes of 63, 90, and 125mm outside diameter, together with 63mm high density polyethylene pipes, were butt fusion joined to give aligned and controlled misaligned joints. These fabricated systems were tested at elevated temperatures under constant and fluctuating internal pressure loading. For brittle failures at the butt fusion joint, a thorough examination has been made of the points of crack initiation and the crack propagation path in relation to weld microstructure, It has been observed that the butt fusion process induces the presence of a long sharp notch formed when the internal weld bead rolls towards the pipe. This notch initiates circumferential joint failures, particularly in misaligned butt joints. Points of disturbance on the inner weld bead appear capable of inducing axial cracks at the butt fusion joint but only for aligned joints. The microstructure at the butt fusion joint was seen to have little influence on the crack propagation path.