J-resistance properties of automatic narrow gap gas tungsten arc welds (NGGTAWs) for ferritic primary loop piping were investigated. The piping diameter is 1066mm, and its thickness is 76mm. The tensile, microhardness, and J-R tests were performed, and microstructures of the welds were examined. Tensile and J-R tests were conducted at 316°C and 177°C for temperature effect, and at 1mmmin and 1000mmmin for strain rate effect. The results were compared with other welds, which are fabricated by the conventional shielded metal arc weld (SMAW) process. The NGGTAW welds investigated in this paper have lower J-R curves than the SMAW welds. Fracture surfaces of the NGGTAW welds showed deep ditches and holes due to inclusions and pores. It is believed that the high density of the inclusions and the pores, which exist in the NGGTAW welds, is responsible for this lower toughness and the fracture surface appearances. Therefore, to improve the NGGTAW weld toughness, it is recommended that sulfur content should be limited to a considerably low level, and the pores should be eliminated by modifying the welding procedure specification.

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