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

It is evident that numerical methods have a useful role in the assessment o f welding conditions for the safe in-service welding of high-pressure gas p ipelines. No published work has considered the direct calculation of bum-th rough using a combination of thermal and stress analysis. Using empirical r elationships between welding process parameters and weld bead size and shap e is an appropriate way of defining the weldment geometry and the heat-sour ce coordinates. With this approach, adequate agreement between predicted we ld penetration, weld cooling times and heat-affected zone hardness has been made. Following the prediction of a thermal field a full thermo-elastic pl astic model can be used to predict the conditions likely to cause bum-throu gh. In this paper two significant research aspects of in-service welding have b een 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 m etal arc welding with hydrogen controlled electrodes has been formed and ha s given good correlation with experiment and field welds. 2. Preliminary bum-through modelling of in-service welding using non-linear thermal-stress numerical methods has given encouraging results.