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, visi ble to the naked eye, were found to occur in 3 to 66% of total weld le ngth. Fusion zone cracking was also observed in steels with He concent rations 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 cond ucted to develop repair welding techniques which minimize the effects of helium-induced cracking in the heat-affected zone. The most promisi ng of these repair welding techniques uses the application of a compre ssive stress during welding to overcome heat-affected zone cracking. T he application of a compressive stress during welding was found to sup press the previously observed catastrophic cracking. The results of th is work suggest that stress modified welding techniques may be used to suppress and control helium-induced cracking during repair welding of irradiated materials.