L51737 Development of Modeling 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 modelling technologies, finite element modeling of branch connections using three-dimensional (3-D) solid elements is the only way to accurately determine the stress distributions local to the weld toes of branch connections.

This report describes work to access the applicability of linear elastic fracture mechanics (LEFM) principles to a saddle-pad reinforced branch connection modelled using 3-D elements, The effort concentrated on determining the amount and location of plastic zones resulting from different combinations of service loadings. Loadings considered include pressurization to 72% of the specified minimum yield strength with the addition of main pipe end tension or compression. The effect of contact and different material models were also quantified.