Effect of the Hydrostatic Pressure in the Diffusible Hydrogen at the Underwater Wet Welding

Abstract

The underwater wet welding using SMAW is widely used in maintenance and repairs of submerged structures. In this process, water can dissociate, providing substantial quantities of ions H+ and O2− at the molten pool. Hydrogen and oxygen may constitute gas bubbles in the molten weld metal which may result in formation of pores. The hydrogen can diffuse by the weld metal and heat-affected zone or be trapped in the structure of the weld metal in the form of residual hydrogen. The diffusible hydrogen in the weld metal and heat-affected zone might have a deleterious effect in the mechanical properties of welded joint. The diffusible hydrogen plus susceptible microstructure, such as martensite, presence of tensile residual tension and temperatures lower than 200°C can lead the arising of cracks in the weld metal and heat-affected zone. All these conditions are satisfied in underwater wet welding. The amount of diffusible hydrogen in the weld metal can be influenced by several factors. However, it is not yet known whether the depth of welding (pressure) affects the amount of diffusible hydrogen in weld metal. In this work, several measurements of diffusible hydrogen were made at following depth: 0.30m, 10m, 20m and 30m at wet welding. The electrode used was commercial waterproofed E6013. The diffusible hydrogen measurements were made through the gas chromatography method following the AWS D3.6M procedure. The porosity was measured using the macrographic method and a software called Quantikov. The weld bead reinforcement and width were also measured. The residual hydrogen also was measured. The results showed that diffusible hydrogen reduced substantially as the hydrostatic pressure increased. The porosity, as it was related previously, increased as the hydrostatic pressure increased. Changes in the residual hydrogen of the weld metal were not observed. So, it was possible to conclude that the welding depth affects directly the diffusible hydrogen and porosity levels of underwater wet welds.