J-Resistance Properties of Narrow Gap GTAW Welds for Ferritic Primary Loop Piping

J-Resistance properties of automatic narrow gap gas tungsten arc welds (NGGTAW) for ferritic primary loop piping were investigated. The piping diameter is 1066 mm and its thickness is 76 mm. To do this, tensile, micro-hardness and J-R tests were performed and the microstructures of the welds were examined. Tensile and J-R tests were conducted at 316°C and 177°C for temperature effect and at 1 mm/min and 1000 mm/min for strain rate effect. The results were compared with the weld cases which are fabricated by the conventional SMAW process. NGGTAW welds investigated in this paper have lower J-R curves than the SMAW welds do. Fracture surfaces of the NGGTAW welds have an unusual appearance with deep ditches and holes due to the inclusions and pores. It is believed that the high density of the inclusion and the pore which exists in the NGGTAW welds is responsible for this low toughness and the cracked surface. Therefore, for an improvement of the NGGTAW weld toughness, it is recommended that sulfur content should be limited to a considerably low level and the pore should be eliminated by modifying the welding procedure specification.