L51648 Fitness-For-Purpose Assessment Procedures for Sleeve and Branch Welds in Pipelines

 One of the major problems associated with developing fitness-for-purpose procedures for sleeve and branch welds is the prediction of the local stress distribution at the welds. Since the presence of a sleeve or branch will increase the local stiffness of the pipe and give rise to local stress concentration effects, the stress distribution at sleeve or branch welds cannot be readily estimated using simple stress analysis.

This project studied the structural behavior of sleeve and branch connections in pipelines. Because these connections create local stress concentration effects, where several potential crack orientations need to be considered, the stress distribution at these points cannot be estimated using simple stress analysis. In this research, finite element analyses were performed to determine: (1) the local stress distribution resulting from internal pressure and remotely-applied tensile and bending loads at sleeve and branch welds; (2) the effects of sleeve thickness and length; (3) the effect of poor fits (i.e., gaps between the pipe and sleeve); and (4) the effect of a through-wall crack at sleeve and branch welds in pressurized pipe.