Abstract: Liquefied Natural Gas (LNG) storage tanks are the most critical equipment in LNG receiving terminal. LNG storage tanks are normally full-containment storage tanks which are complex in structure, consisting of an outer tank and a 9% Ni steel inner tank. Welding of the shell plates of the inner tank is the key to the construction of LNG storage tanks. Single-sided automatic submerged arc welding is adopted for circumferential seams. However, this brings a huge amount of back gouging work and the shapes of grooves after back gouging are not standardized. Aiming at such problems, the original welding machine is renovated; back welding frame and back flux protection system are added to improve the shape of the seams at the back side and reduce the amount of back gouging work. The welding quality and efficiency is improved effectively.

Key words: LNG storage tank, automatic transverse welding of circumferential seam, back protection system