Modelling and numerical simulation of surface active species transport ‐ reaction in welding processes

Abstract

This paper deals with the modelling of steel melting process during TIG welding operations on the nuclear power plants. The issue of the quality assurance of welding operations on some components is of great importance for the nuclear safety management. However, there are many parameters involved in the process which makes the uncertainty of the whole operation important. Moreover, some repair operations make impossible the quality control of the final weld bead. This is the case of one such a weld this study focus on. A way to ensure the quality of such weld beads could be based on the weld pool shape prediction by the numerical simulation. Thus, giving the operating parameters such as arc energy distribution, the flow simulation inside the weld pool could provide the information on the final weld pool dimensions. The model describing the metal flow during the welding process developed in this work is based on the classical MHD and the enthalpy equations. Yet, the flow in the weld pool is mainly governed by variable surface tension force, the phenomenon known as Marangoni effect. The surface tension variation is in this case highly dependent on the thermal and the surfactant concentration gradients. In order to better evaluate this force, in this work, we present a new formulation of transport-reaction equations for surfactant and relative species in the molten steel. Moreover, this model takes into account species chemical reaction and evaporation. This allows mass fractions and gradients computation at the weld pool surface, and by this mean a better prediction of the surface tension force in case of variable chemical composition. The results of the simulations are compared to experimental data on the weld pool dimensions.