Burst Pressures of Pipes Containing Dents and Gouges

Abstract

Mechanical damage to pipelines may take the form of dents and gouges, which may also incorporate cracks. The combination of a gouge within a dent has long been recognized as the most severe form of damage, and can result in failure at very low internal pressures. Yet despite much expensive full-scale testing, predictions of subsequent burst pressures of such damaged pipes are unreliable, and assessment procedures are very conservative. This paper describes a series of burst tests on model aluminium pipes containing dents and smooth gouges, specifically excluding cracks. The results show that gouges located near the axial extremity of a dent cause low-pressure failure, and indicate the presence of two regions of high strain at the axial extremities of the initial dent. For gouges in other areas of the dent, the Battelle flow stress dependent model for ductile failure of plain gouges in undented pipes is shown to give reasonable predictions of burst pressures, which are independent of the dent depth. In all of the pipes tested, failure was ductile, and this is attributable to the absence of cracks. Pipes withstood pressures in excess of the corresponding normal operating pressures, except where gouges were located near the axial extremity of the dent. The results throw much light on the published results from tests on full-size steel pipes, and support earlier hypotheses that removal of cracks from a damaged pipe by light grinding may significantly increase the pipe burst pressure.