Numerical methods to predict failure during the in-service welding of gas pipelines

Abstract

It is evident that numerical methods have a useful role in the assessment of welding conditions for the safe in-service welding of high-pressure gas pipelines. No published work has considered the direct calculation of burn-through using a combination of thermal and stress analysis. Using empirical relationships between welding process parameters and weld bead size and shape is an appropriate way of defining the weldment geometry and the heat-source coordinates. With this approach, adequate agreement between predicted weld penetration, weld cooling times and heat-affected zone hardness has been made. Following the prediction of a thermal field a full thermo-elastic plastic model can be used to predict the conditions likely to cause burn-through. In this paper two significant research aspects of in-service welding have been addressed, as follows: 1 A new mathematical description of a heat source to represent the common in-service welding process, i.e. vertically up and vertically down manual metal arc welding with hydrogen controlled electrodes has been formed and has given good correlation with experiment and field welds. 2 Preliminary burn-through modelling of in-service welding using non-linear thermal-stress numerical methods has given encouraging results.