Insight into hydrostatic pressure effects on diffusible hydrogen content in wet welding joints using in-situ X-ray imaging method

In this study, a special phenomenon of gas evolution in the metal droplet and melt pool during underwater wet welding was investigated by in-situ imaging method in a simulated deep-water environment. In general, the dissolved hydrogen escaped from molten droplet and molten pool in the form of bubbles during molten metal solidification. As the increase of hydrostatic pressure, the gas cannot expand enough to burst the droplet and release gas, but instead of entering into molten pool again. The combinations of the internal pressure in the bubble and hydrogen-rich atmosphere induced by welding arc resulted in that the melt pool has been subjected to dual influences. The diffusible hydrogen content in the deposited metal significantly increased from 23.3 to 66.3 ml/100 g with increasing the water depth to 150 m, which was related to the high hydrogen partial pressure and the rapid solidification rate of molten metal.