Automatic welding technology for vertical welds of 9%Ni steel plates for inner LNG storage tanks

Shielded Metal Arc Welding (SMAW) is always used for the vertical welding of inner wall of LNG storage tanks in China, and there has been no successful case for the application of automatic welding technology to vertical welding so far. In this paper, an automatic Flux Cored Arc Welding (FCAW) technology with multi-layer, filament, short arc, circumferential swing and short pause on both sides of the groove was proposed through the automatic welding test of vertical welds of 9%Ni steel plates. Then, tests on mechanical properties were conducted for the welds made with this technology. The results show that the tensile, bending and low-temperature impact properties of the specimens can meet the requirements of relevant standards. In particular, the low-temperature Charpy impact energy of the heat affected area is 17.6% higher than that of SMAW. In addition, the vertical FCAW was applied to a 16×10⁴ m³ LNG tank in a LNG receiving terminal of China, with the welding efficiency increased by 52% and the welding repair rate reduced by 2% in comparison to SMAW. In addition, the tank passed the hydrostatic test, kept stable in trial run, and was put into operation. So, the research results could provide some theoretical guidance and practical basis for the promotion of automatic welding for vertical welds of inner LNG storage tank in the future.