The inner tank wall of the lng storage tank is required to be resistant to low temperature, and materials such as 9Ni steel or aluminum alloy are generally used, and the outer tank wall is prestressed reinforced concrete. For liquefied natural gas tanks, there are also many special requirements, such as special requirements in terms of materials, insulation and construction. Next, I will tell you about the specific requirements for liquefied natural gas tanks.
(1)low temperature resistance
The boiling point of LNG under normal pressure is -160°C. LNG chooses a low temperature and normal pressure storage method to reduce 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. Therefore, LNG requires the liquefied natural gas tanks to have excellent low temperature resistance and excellent cold insulation.
(2)high safety requirements
Because the low temperature liquid is stored in the tank, in the event of an accident in the liquefied natural gas tanks, the refrigerated liquid will volatilize a lot, and the vaporization 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 standards all require the liquefied natural gas tanks to adopt a double-wall structure, and use the blocking concept. When the first layer of the tank leaks, the second layer of the tank can block the leaking liquid and evaporated gas to ensure storage safety. .
(3)special material
The inner tank wall requires low temperature resistance, generally 9Ni steel or aluminum alloy and other materials are used, and the outer tank wall is prestressed reinforced concrete.
(4)High thermal insulation requirements
Because the temperature difference between the inside and outside of the tank can reach up to 200°C, to keep the temperature inside the tank at -160°C, the tank body must have a good cold insulation function, and high-function cold insulation materials are filled between the inner tank and the outer tank. The cold insulation material at the bottom of the tank should also have sufficient pressure bearing function.
(5)Good anti-seismic function
The general seismic requirement of buildings is to crack without falling under the regular seismic load. In order to ensure the safety of storage tanks under unexpected loads, it is necessary for storage tanks to have good seismic performance. For liquefied natural gas tanks, it is required that they will not fall or crack under regular seismic loads.
For this reason, the selected production site should generally avoid the earthquake fault zone. Before construction, the seismic test should be performed on the storage tank to analyze the structural function of the liquefied natural gas tanks under dynamic conditions to ensure that the tank body is not damaged under a given seismic intensity.
(6)Strict construction requirements
It is necessary to carry out 100 magnetic particle testing (MT) and 100 vacuum air tightness testing (VBT) for tank welds. It is necessary to strictly select the cold insulation materials, and the rules and procedures should be followed in the construction. In order to prevent cracks in the concrete, post-tensioning prestressed construction is used, and the straightness of the tank wall is strictly controlled.
The concrete outer tank roof should have high compressive and tensile capacity, and can resist the blow of general falling objects. Because the concrete at the bottom of the tank is thick, the hydration temperature should be controlled during pouring to prevent cracking due to thermal stress.
Based on the above analysis, it is related to the relevant requirements of LNG cryogenic storage tanks, mainly involving the above six points, I hope to be helpful to everyone.
Post time: May-19-2022