It is known that underwater wet welding shows inferior properties of joints to the open air welding due to hardening by rapid cooling and weld defects from difficult welding conditions. This study was performed to understand mechanical behavior of welded connections in steel pipe repaired with cover plate by underwater wet weld. The weld shape and hardness distribution in the weld were measured, and strength tests of front fillet and side fillet welded connections were performed. Experimental results show that weld shape and hardness affect the mechanical behavior of fillet welds. Finite element analysis shows a different concentration of strain in the yield zone affects the ductility of the connection.