I don’t understand

Dude, your understanding is wrong. The design pressure is the highest pressure that a tank can withstand, and it has nothing to do with the location of the tank.

In the presence of a medium, isn’t the pressure at the top of the container lower than that at the bottom?

No, the pressure of a gaseous medium is definitely higher than that of a liquid one.

I see what you mean; I understand a bit of it. Does this make sense to you? Design pressure refers to the maximum operating pressure at the top of the container, as determined by the relevant regulations. However, gaseous media exert higher pressure than liquid media, and since the gas is located at the top of the container, the pressure there will be higher. This reasoning holds true； In the case of a liquid medium, the pressure at the bottom of the container is higher than that at the top. When determining the design pressure, it is necessary to take into account the pressure due to the liquid column; I think I’ve seen this somewhere before. So, the pressure at the top is still used as the design pressure

Definition of pressure in GB150.1-2011: Operating pressure: the highest pressure that may be reached at the top of the vessel under normal operating conditions; Design pressure: the maximum pressure specified for the top of the vessel, which, together with the corresponding design temperature, serves as the basic design load condition for the vessel, and its value is not lower than the operating pressure； Calculation pressure: The pressure used to determine the thickness of a component at the corresponding design temperature, including additional loads such as the hydrostatic pressure of liquid columns. 1. Although the pressure at the top is the lowest, when using this pressure as a value for calculating the thickness of pressure-bearing components, additional loads such as the hydrostatic pressure of the liquid column are taken into account; this does not reduce the strength of the pressure-bearing components ； 2. The design pressure is primarily used to determine the pressure rating of pressure vessels and to classify them into different categories. It must be a pressure in the gas phase; therefore, it is defined as \"the highest pressure at the top of the vessel\". If the pressure at the bottom of the container is considered, then a water tank filled with water to a certain height is also classified as a pressure vessel.

This post was last edited by Pinocchio on 2016-7-26 at 15:47. By understanding the meanings of design pressure and calculated pressure, it should become clear. The design pressure does not include the static pressure of the medium, and is not used directly in wall thickness calculations ； Calculated pressure = design pressure + static pressure of the medium, used for calculating the shell wall thickness. A device can have multiple operating pressures, but only one design pressure. Add a few more words to your post title :)

The design pressure is the maximum working pressure that may be reached at the top; the calculated pressure should be greater than or equal to this maximum working pressure, which is the design pressure. All types of loads are taken into account in the calculations for the shell, and the material is isotropic. So, regarding the issue of pressure at the top and bottom you mentioned: is there any static load present? , and do the top and bottom bear the same pressure? This is a conceptual issue; it has nothing to do with the calculation process

Great post; it cleared up my doubts