The pores and cracks formations in weld bead during underwater wet welding are the main cause that prevent to reach the required mechanical properties of the weld metal. These defects are closely associated with the decomposition of the water molecule under conditions of electric arc. In this paper the thermodynamic calculations of the complex process of the water decomposition under the conditions of high temperatures of electric arc to a pressure of one atmosphere of steam is exposed. The values of the partial pressures of the five main products of the vaporizations and decomposition of the water (H2O(g), H2, O2, H and O) are calculated for temperatures among 1870 and 4000 K. Due to the fact that atomic hydrogen is the main responsible for the pore formation in the weld metal its partial pressure as function of partial pressures of atomic oxygen and steam (water vapor) is expressed. Values of hydrogen solubility in the liquid metal in conditions of underwater wet welding at 50 and 100 m of depth and, a comparison between the thermodynamic calculation and porosity measurement results are presented.
Underwater wet welding; pore formation; thermal water decomposition
