Induction heating as practical preheating and post weld heat treatment to improve the quality in underwater wet welding of fi ne grain structural steels with high carbon equivalents

In this research project medium-frequency induction technology was used for preheating and post-weld heat treatment in underwater wet welding. After the induction heating was successfully characterised, both a reduction in the diffusible hydrogen content and a decrease in hardness in the heat-affected zone was demonstrated for wet welding application. In addition, safety issues relating to the use of induction technology in wet underwater welding were addressed for the first time. Induction preheating and post-weld heat treatment was successfully applied by divers. A T-joint of steel grade S460N with a carbon equivalent of 0.51% and thus causing a high susceptibility to hydrogen-assisted cracking, was successfully wet SMAW welded without cracks.