The Effect of the Pipe Material in the Behaviour of Longitudinal Cracks under Pressure

Longitudinal cracks in pipes exhibit expansion under pressure increases due to increased stresses in the pipe walls. The crack expansion increases the leak area and thus the flow rate from the crack. It has theoretically been shown that when tension is applied to a plate with centre crack edges running transversely, compressive stresses occur around the crack. As the stresses reach a certain level, they will cause local buckling of the crack walls, resulting in the opening of the crack. The aim of this investigation is to understand the structural behaviour of a longitudinal crack failure of pipe materials under pressure. This objective is achieved by investigating the structural behaviour of a plate material around the crack and determining the critical stress, thus deriving an equation for the crack opening as a function of pressure and material properties, and subsequently an equation for the leakage behaviour, and establishing a relationship between the crack behaviour of a flat plate and a circular pipe material. A rectangular steel plate with a centre crack is used to investigate the structural behaviour of a pipe material with a longitudinal crack. The results of this investigation will assist in predicting the appropriate leakage equation for pipes.