What are the special requirements for LNG storage tanks?

Natural gas is recognized as a clean, environmentally friendly, and safe high-quality energy source. The volume of liquefied natural gas is reduced by about 600 times, which brings great benefits to storage. The storage of liquefied natural gas uses atmospheric cryogenic storage tanks.
1. Low temperature resistance
The boiling point of LNG at normal pressure is -160℃. LNG chooses low-temperature and normal-pressure storage method to reduce the temperature of natural gas below the boiling point, so that the operating pressure of the storage tank is slightly higher than normal pressure. Compared with the high-pressure and normal temperature storage method, it can greatly reduce the thickness of the tank wall and improve safety performance.
Therefore, LNG requires that the liquid storage tank has good low temperature resistance and excellent cold insulation performance.
2. High safety requirements
Since the storage tank is a cryogenic liquid, once an accident occurs in the storage tank, the refrigerated liquid will evaporate in a large amount, and the amount of vaporization is about 300 times that of the original refrigerated state, forming an air mass that will automatically detonate in the atmosphere.
Therefore, the API, BS and other specifications require the storage tank to adopt a double-wall structure and use the blocking concept. When the first layer of tank leaks, the second layer of tank can completely block the leaked liquid and evaporated gas to ensure storage Safety. 3. Strict insulation measures
Since the temperature difference between the inside and outside of the tank can be up to 200°C, to maintain the temperature inside the tank at -160°C, the tank body must have good cold insulation performance, and high-performance cold insulation materials are filled between the inner and outer tanks. The cold storage material at the bottom of the tank must also have sufficient pressure bearing performance.
4. Good seismic performance
The seismic requirements of general buildings are to crack without falling under the prescribed seismic load. To ensure the safety of the storage tank under unexpected loads, the storage tank must have good seismic performance. For LNG storage tanks, it is required not to fall or crack under the prescribed seismic load.
Because of this, the selected construction site should generally avoid the seismic fault zone. Before construction, seismic testing of the storage tank should be conducted to analyze the structural performance of the storage tank under dynamic conditions to ensure that the tank body is not damaged under a given seismic intensity.
5. Strict construction requirements
Cryogenic storage tank welds must undergo 100% magnetic particle testing (MT) and 100% vacuum tightness testing (VBT). To strictly select cold-keeping materials, the prescribed procedures should be followed during construction. To prevent cracks in the concrete, post-tensioned prestressed construction is adopted, and the verticality of the tank wall is strictly controlled.