The underwater welding of ferritic-austenitic duplex steels is arousing growing interest inspired by the urgent need for developing welding technologies used for repairing underwater pipelines transporting oil. The tests involved underwater welding using covered electrodes (process 111). The research also involved Tekken technological tests performed under water at a depth of 0.5 m and in air as well as macro and microscopic metallographic tests, ferrite content measurements and hardness measurements of joints. The test results obtained revealed that the underwater welding of duplex steels could lead to cold crack formation. In the case considered above, cold crack susceptibility was attributed to arc burning instability.