Use of Elastic Follow-Up to Study the Effect of Displacement Controlled Loading on Plastic Collapse Pressures for Circumferentially Cracked Pipes

Abstract

General rightsThis document is made available in accordance with publisher policies. Please cite only the published version using the reference above. ABSTRACTStructural integrity assessments of pressurised pipes consider plastic collapse as a potential failure mode. This paper uses finite element analysis to explore the effect of the pipe end boundary conditions on the collapse pressure. Two end conditions are considered: a fixed axial load and a fixed axial displacement. The fixed axial displacement condition represents a long-range axial residual stress. In the R6 structural integrity assessment procedure long-range residual stress is associated with elastic follow-up. However, no guidance is given on whether the level of elastic follow-up is sufficient to justify treating long-range residual stress as a primary stress.In this paper, a method is proposed to estimate elastic follow-up of an internally pressurised pipe containing a fully circumferential crack. It is found that the elastic follow-up is related to the length of the pipe. A short pipe that contains a fully circumferential crack, subjected to a displacement induced axial stress, has a global collapse that is not modified by the fixed displacement condition. The short pipe corresponds to a small elastic follow-up factor, Z. However, as the elastic follow-up factor increases, the presence of long-range residual stress starts to make a contribution to global collapse. When elastic follow-up is significant, a long-range residual stress has the same effect on global collapse as does a mechanical stress.