Development of fitness-for-purpose assessment procedures for branch welds

One major difficulty in developing fitness-for-purpose based flaw acceptance criteria for pipeline branch connections is the calculation of the stress distributions in the vicinity of the welds. Even with the latest computer aided modeling technologies, direct finite element modeling of branch connections using 3-D solid elements can be time consuming and cost prohibitive. Therefore, it is necessary to investigate the possibility of using more computationally-efficient finite element approaches to determine the stress distributions local to branch connections. This report describes work to develop flaw acceptance criteria based on fitness-for-purpose principles for branch connections in pipelines. The effort concentrated on investigating finite element modeling methodologies to predict accurately the stress distributions local to branch connections. These stress distributions can be used to develop fitness-for-purpose based flaw acceptance criteria that are consistent with those already developed for girth welds in Appendix A of API 1104.