Investigating the effect of hydrostatic pressure on arc and bubble transport phenomenon in underwater wet self-shielded flux cored arc welding

A mathematical simulation model was established to describe arc and bubble transport phenomena during underwater wet self-shielded flux cored arc welding (UW-FCW-S) at various hydrostatic pressures. The mass density, specific enthalpy, specific heat, electrical conductivity, thermal conductivity, and viscosity of high- temperature arc plasma ionized by mixtures (60 %H-2 + 30 %CO2 + 10 %CO) were calculated and investigated under different hydrostatic pressures. The simulation results showed that the arc changed from a bell shape at atmospheric pressure to an "I" shape under high hydrostatic pressure. The mass density and specific heat increased with the water depth, which resulted in the contraction of the arc. The evolution of bubbles can be divided into growth, necking, and separation processes under different hydrostatic pressures. Specifically, the difference observed was that the bottom shape of the bubble near the workpiece became flat during the necking and separation processes as the water depth increased from approximately 0 to 110 m (0.1 to 1.2 MPa), and a double necking phenomenon appeared. Moreover, the evolution period of the bubble increased with hydrostatic pressure. The maximum fluctuation amplitude of the arc temperature indicated that the UW-FCW-S process became stable when the water depth reached 50 m, but the process stability was compromised at a depth of 110 m. Experiments were conducted to verify the numerical model, and the simulation results of the bubble evolution process agreed well with the experimental values. This study quantitatively analyzed the impact of hydrostatic pressure on the dynamic behavior of arc and bubble in UW-FCW-S, laying a crucial foundation for improving the application of UW-FCW-S in deep water.