LNG Tanks Welding Construction And Roof Air Raising

LNG (Liquefied Natural Gas) is the abbreviation for liquefied natural gas. Natural gas is a combustible gas mined in the field gas, the main component of which is the methane. LNG is condensed liquid that natural gas under atmospheric pressure cooled to -162℃. With the rapid development of world economy, people pay more attention for energy growing. Natural gas has high calorific value, little pollution, low price and many other advantages. Natural gas becomes more and more popular as a clean energy. Many countries treat LNG as the preferred fuel and LNG becomes one of the world's most rapidly growing energy industries.LNG is usually stored in tanks at -162℃and about 0.1MPa. Tank has inside and outside structure. Outside tank is made of prestressed concrete structure and inside tank is made of 9%Ni steel. Therefore, welding construction of LNG storage tank is mainly welding technology of 9%Ni steel of inside tank. The main welding processes of inside tank are SMAW and SAW. SMAW is used in vertical welding and horizontal position for rooting, SAW is commonly used for the filling and cosmetic welding of horizontal welding.The design temperature of LNG storage tank is -162℃, and 9%Ni steel of inside tank plays the role of colling liquid and sealing the base metal. The mechanical performance for welding materials is very high. Therefore, the welding procedure qualification of 9%Ni steel was carried on and the mechanical properties of welded joints, microstructure and fracture morphology of two welding processes for 9%Ni steel were tested.Roof air raising is a key work for building large LNG storage tanks. Too heavy lifting pieces, high sealing requirements between lifting pieces and the tank wall and complex balanced series are main problems. Roof air raising procedure of a large-scale 160000m3 LNG cryogenic storage tanks is studied and the results show that: reasonable choice blowers under the weight of the tank top, design balance and sealing structure in the pre-construction is the key to ensure that roof air raising smoothly and safely.