What Is a Pressure Tank?
Pressure tanks are tanks that hold pressure above atmospheric pressure.
However, pressure tanks store not only gases but also liquids. Liquids are not ordinary water, but ultra-low temperature fluids, such as liquid oxygen and liquid nitrogen.
Since these are gases at room temperature, they must withstand internal pressure to be stored in a liquid state.
Also, the fact that the pressure of a gas is higher than atmospheric pressure means that if a pressure tank is destroyed, the tank will be destroyed in an instant due to the release of the pressure.
For this reason, pressure tanks with pressure or capacity above a certain level are regulated as Class II or Class I pressure vessels.
Uses of Pressure Tanks
Pressure tanks are used in many places, from general factories to chemical plants. For example, a receiver tank for compressed air from a compressor is also a pressure tank. By temporarily holding pressure, pressure fluctuations caused by air usage can be reduced.
In addition, the steel industry, which uses large amounts of nitrogen and oxygen gases, has tanks that store liquid oxygen and liquid nitrogen.
These tanks contain liquid inside, but since liquid nitrogen and liquid oxygen are gases at room temperature, they must withstand pressure tanks to store them in a liquid state. They also have a double-layered outer layer for thermal insulation.
Principle of Pressure Tanks
Most pressure tanks are made of metals such as SS400 and SUS304, although some are made of resins, such as FRP.
Pressure tanks are made up of a body plate and a mirror plate, the thickness of which is calculated based on specifications.
What we have to be careful about here is that the strength concept of the welding part will change depending on the specifications and inspection of the welding joint. For example, if the weld is 100% radiation tested, the strength of the weld will be 1.0, which is the same as the original metal, but if not, the strength will be lower.
This means that the thickness of the plate will be thicker, but it is necessary to consider the cost and time required carefully for testing and how much to do.
In addition, attention should also be paid to the concept of internal pressure and external pressure. There is a difference in the calculation method between internal pressure and external pressure, and the thickness of the plate becomes thicker with external pressure.
If a mistake is made in the calculation of either, it will lead to rupture in the case of internal pressure, and to destruction by crushing in the case of external pressure.
To prevent such accidents, safety valves, and vacuum brake valves may be installed.