Numerical models of in-service welding of gas pipelines

It is accepted that numerical methods have a useful role in the assessment of welding conditions for the safe in-service welding of high-pressure gas pipelines. Only limited 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 co-ordinates. With this approach adequate agreement between predicted weld penetration, weld cooling times and HAZ hardness, has been made. The prediction of burn-through can be made using a full thermo-elastic–plastic model, but this leads lengthy calculations. Here, an approximate method of predicting burn-through has been developed and shown to give reasonable results. Therefore, in this paper, two significant research aspects of in-service welding have been addressed, as follows: • 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 (MMAW) with hydrogen controlled electrodes has been formed and has given good correlation with experiment and field welds. • An approximate method of predicting bursting pressure during in-service welding by translating the temperature field into an effective cavity in the pipe-wall.