THRESHOLD HELIUM CONCENTRATION REQUIRED TO INITIATE CRACKING DURING WELDING OF IRRADIATED STAINLESS-STEEL

Results of this study show that severe HAZ cracking occurs in type 316 stainless steel containing 1.5, 5.2 and 10 appm He. Macrocracks, visible to the naked eye, were found to occur in 3 to 66% of total weld length. Fusion zone cracking was also observed in steels with He concentrations as low as 2.5 appm. No cracking was found in either the fusion zone or HAZ in the welds with 0.7 appm helium. Studies were also conducted to develop repair welding techniques which minimize the effects of helium-induced cracking in the heat-affected zone. The most promising of these repair welding techniques uses the application of a compressive stress during welding to overcome heat-affected zone cracking. The application of a compressive stress during welding was found to suppress the previously observed catastrophic cracking. The results of this work suggest that stress modified welding techniques may be used to suppress and control helium-induced cracking during repair welding of irradiated materials.