Residual Stress Analysis of In-Service Welded Gas Pipelines

Abstract

Maintenance work and extension of gas pipelines have to be done mostly with the pipeline being in operation to ensure continuous network coverage. Therefore, in-service welding operations are inevitable for both situations. The present paper focuses on a circumferential fillet weld connecting a high-pressure gas pipeline with a T-fitting, which is suitable for stoppling and the construction of connection branches. Against the background of safety assessment and process optimization the welding procedure is investigated by means of experiment and simulation. The simulation is based on the finite element method and predicts the temperature field as well as the evolution of the microstructure and the residual stresses during welding and cooling. The heat input during welding is modeled using the double ellipsoid heat source by Goldak, which is adapted to multi-pass welding and implemented in the commercial software ABAQUS. The microstructure evolution is analyzed by a phase transformation model based on the Avrami equation. A subsequent stress analysis provides results regarding the residual stresses. The simulation is validated by welding experiments dealing with a three-pass fillet weld. The experimental and numerical results are presented and compared by means of macrosections and thermocouple measurements.