What are the special requirements for LNG cryogenic storage tank- Doer equipment

1. Low temperature resistance

The boiling point of LNG under normal pressure is - 160 ℃. LNG is stored at low temperature and normal pressure to lower the temperature of 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, it can greatly reduce the tank wall thickness and improve the safety performance. Therefore, LNG requires the liquid storage tank to have good low temperature resistance and excellent cold insulation performance.

2. High safety requirements

As the cryogenic liquid is stored in the tanks, an accident occurs in the tanks one day, and the refrigerated liquid will volatilize in large quantities. The gasification amount is about 300 times that of the original refrigerated state, forming an air mass that will automatically detonate in the atmosphere. Therefore, API, BS and other specifications require the tank to adopt a double wall structure. With the concept of containment, when the first layer of tank leaks, the second layer of tank can completely block the leaked liquid and vapor to ensure safe storage.

3. Special materials

The inner tank wall is required to be low temperature resistant, generally made of 9Ni steel or aluminum alloy, and the outer tank wall is prestressed reinforced concrete.

4. Strict thermal insulation measures

As the maximum temperature difference between the inside and outside of the tank can reach 200 ℃, the tank body must have good cold insulation performance to keep the temperature inside the tank at - 160 ℃. High performance cold insulation materials shall be filled between the inner tank and the outer tank. The cold insulation materials at the tank bottom should also have sufficient pressure bearing performance.

5. Good seismic performance

The anti-seismic requirement of general buildings is to crack without collapse under the specified seismic load. In order to ensure the safety of the storage tank under accidental load, the storage tank must have good seismic performance. LNG tanks are required not to collapse or crack under the specified seismic load. For this reason, the selected construction site should generally avoid the earthquake fracture zone. Before construction, the seismic test should be conducted on the tank, and the structural performance of the tank under dynamic conditions should be analyzed to ensure that the tank is not damaged under a given seismic intensity.

6. Strict construction requirements

The tank welds must be subject to 100% magnetic particle testing (MT) and 100% vacuum airtight testing (VBT). Cold insulation materials shall be strictly selected and the specified procedures shall be followed during construction. In order to prevent cracks in concrete, post tensioning prestress construction is adopted, and the perpendicularity of tank wall is strictly controlled.

The concrete outer tank top shall have high compressive and tensile capacity, and be able to withstand the impact of general falling objects. As the tank bottom concrete is thick, the hydration temperature shall be controlled during pouring to prevent cracking caused by temperature stress.