A New Approach to Essential Welding Variables in Girth Welding of High Strength Pipe Steels

In the narrow groove joints typically used for mechanized GMAW girth welding of high strength pipe, weldment properties are controlled by a large number of variables. The groove geometry, the bevel offset distance, the pass sequence and number of passes, the heat input per pass, the preheat and interpass temperatures, single vs. dual torch configuration, and the chemical composition of the consumable and the base pipe can all have an effect on the weldment properties. Determining the primary and secondary variables that control mechanical properties is a daunting task. Use of an integrated thermal-microstructural model has allowed virtual experiments to be conducted by varying the aforementioned welding variables to identify the primary and secondary drivers that control thermal behavior, microstructural evolution and ultimately weld and HAZ mechanical behavior. Outputs from this model have been used to correlate the essential process variables with weld hardness.