Effect of Nickel on Toughness of Underwater Wet Welds

Underwater wet welding has been used as an option for the repair of offshore platforms. Rutile-grade electrodes are typically used to carry out the underwater repairs because of their good arc stability, bead appearance, and bead morphology. However, the main problems to overcome are porosity and reduction of toughness and strength as the water depth increases. During wet welding, the welding arc decomposes water into hydrogen and oxygen, which results in the formation of oxides and pores in the weld metal. The loss of alloying elements in the oxidation process and the fast cooling rate due to the quenching effect of water surrounding the weld are responsible for the deterioration in mechanical properties. This paper presents evidence of toughness improvements on wet welds made with experimental rutile-grade electrodes. Experimental electrodes with nickel added to the flux covering (0, 1.2, 2.3, and 3.0 wt. pct.) were extruded. A commercial rutile electrode was used for comparison. Bead-on-plate and multipass V-groove wet welds were made at 1 ft. water depth in fresh water. Charpy impact test specimens were machined from the V-groove welds and tested at four temperatures. The toughness measured at −50°C of wet welds with 3.0 wt pct. nickel was improved by a factor of four over the wet welds without nickel content. Smaller improvements were obtained with 2.3 wt. pct. nickel at −50°C. At higher temperatures, the toughness did not increase with nickel additions. All-weld-metal reduced-size tensile specimens made from the wet welds deposited with the commercial and experimental electrodes presented similar yield and tensile strength. The tensile specimen with 3.0 wt. pct. nickel presented lower ductility.