Special requirements for LNG storage tanks

Special requirements for LNG storage tanks
1, low temperature resistance
The boiling point of liquefied natural gas at normal pressure is -160 °C. LNG selects the low-temperature and normal-pressure storage mode to lower the temperature of the natural gas below the boiling point, so that the operating pressure of the liquid storage tank is slightly higher than the normal pressure. Compared with the high-pressure normal temperature storage mode, the thickness of the tank wall can be greatly reduced and the safety performance can be improved. Therefore, LNG requires the liquid storage tank to have good low temperature resistance and excellent cold retention properties.

2, high security requirements
Since the tank stores low-temperature liquid, once the tank is accidentally, the refrigerated liquid will be volatilized in a large amount, and the gasification amount is about 300 times that of the original refrigerating state, and an air mass which will automatically detonate is formed in the atmosphere. Therefore, API, BS and other specifications require the tank to adopt a double-wall structure, using the sealing concept. When the first layer of tank is leaked, the second layer of tank can completely block the leakage liquid and vaporized gas to ensure storage. Safety.

3, the material is special
The tank wall of LNG cryogenic storage tanks is required to withstand low temperature. Generally, materials such as 9Ni steel or aluminum alloy are used, and the outer tank wall is prestressed reinforced concrete. 4, strict insulation measures
Since the temperature difference between the inside and the outside of the tank is up to 200 ° C, the tank body should have good cold-keeping performance and the high-performance cold-keeping material between the inner tank and the outer tank should be maintained at -160 ° C. The bottom insulation material must have sufficient pressure bearing properties.

5 good seismic performance
The seismic requirements of a typical building are cracked under the specified seismic load without falling. To ensure the safety of the tank under unintended loads, cryogenic liquid storage tanks must have good seismic performance. For LNG storage tanks, it is required to not fall or crack under the specified seismic load. Therefore, the selected construction site should generally avoid the earthquake fault zone. Before the construction, the LNG liquid storage tank should be subjected to seismic test to analyze the structural performance of the tank under dynamic conditions to ensure that the tank is not damaged under the given seismic intensity.

6, construction requirements are strict
Tank welds must be 100% magnetic powder (MT) and 100% vacuum tightness (VBT). To strictly select the cold insulation material, the prescribed procedures should be followed during construction. In order to prevent cracks in concrete, post-tensioned prestressing construction is adopted, and the verticality control of the tank wall is very strict. The outer tank top should have high compression and tensile strength and can withstand the impact of general falling objects. Due to the thick concrete at the bottom of the tank, the hydration temperature should be controlled during casting to prevent cracking due to temperature stress.