Pressure of pressure vessels
Thread Content
I would like to ask everyone: Why is the working pressure specified in GB/T 150 defined as the highest pressure that may be reached at the top of the container? If it is filled with a gaseous medium, the stress on all parts of the container should be the same, right? If there is a liquid medium, shouldn’t the pressure at the bottom of the container be higher? I’m not very familiar with the force analysis of pressure vessels; could the teachers please help me understand this? Thank you!
This is a bit complicated to explain; generally speaking, the top part experiences the highest pressure.
For the compressed elements in other areas, the pressure at the top combined with the hydrostatic pressure of the liquid column constitutes the calculated pressure, isn’t that right?
You are right; if there is a liquid medium, the pressure at the bottom is indeed higher than that at the top. For this reason, if there is a change in the liquid level, the pressure at the bottom also changes. Although the working pressure is the pressure at the top of the container, it is the calculated pressure that determines the thickness of the component, and this calculated pressure includes the hydrostatic pressure of the liquid column.
Using the pressure at the top of the container as the operating pressure may be based on the fact that the area at the top of the container is a gas phase space, unaffected by the liquid column, so its pressure remains constant, whereas the pressure at other points changes depending on the level of the liquid surface. Another point is that the gas phase space poses the greatest danger. Since the pressure at the top is not the highest throughout the container, standards stipulate that when the static pressure of the liquid column reaches a certain level, it must be taken into account in the calculated pressure to ensure strength.
The design of the original pressure gauges meant that when pressure was measured in other locations, these gauges tended to get damaged more frequently (due to reading errors, rust, etc.). Moreover, different manufacturers used varying design standards; once standardization was achieved, this parameter was adopted as the working pressure
Working pressure, design pressure, and calculated pressure are different concepts.
Since the net pressure of the liquid column varies, to ensure accuracy and avoid disputes, the pressure at the top is used.