Effect of location of crack in dent on burst pressure of pipeline with combined dent and crack defects

Abstract

Burst pressure of pipelines with longitudinal cracks located at the centre of rectangular dents varies with defect size and recent reports indicate that it could be very high for shallow cracks inside shallow dents and for cracks inside restrained dents. However, it is not clear whether cracks located in the flank of dents would have the same impact on burst pressure of pipelines with dent-crack defects. In addition, studies show that the location of maximum strain in circular dents shifts away from the centre towards the flank when dented pipes are pressurised, but the implication on the propagation of longitudinal cracks located in various parts of a dent has not yet been widely investigated. In this paper, models of pipelines with longitudinal cracks inside rectangular dents were created using the Finite Element Methods software Abaqus to analyse crack propagation and predict the associated burst pressure. The in-built Extended Finite Element procedure in Abaqus was used to model crack propagation through the pipe. The models were calibrated and validated using previously published results of burst tests and tests of material properties. The effect of longitudinal cracks in both the flank and centre of the dents on the burst pressure was analysed by varying the crack length, the crack depth, the dent depth, the internal pressure during dent formation and the dent constraint condition. The results show that longitudinal cracks in the flank of rectangular dents are more severe for pipeline integrity than cracks located in the centre of dents. Crack depth and crack location inside the dents are the most influential parameters when assessing dent-crack defects in pipelines. Their effects on burst pressure are magnified by crack length, dent depth and denting pressure.

Keywords

• Combined defect
• Pipeline
• Surface crack
• Through-wall crack
• Burst pressure
• Flank of dent