In vessel design, is it possible for the calculated pressure to be higher than the design pressure?

The test pressure is 1.25 times the design pressure, multiplied by the ratio of the allowable stresses at the test temperature and the design temperature. (Refer to GB150) The calculated pressure can be greater than or less than the design pressure.

The test pressure and design pressure, the maximum allowable working pressure (if applicable), the permissible pressure at the design temperature, and the permissible stress at the test temperature are all interrelated. According to the provisions of the new pressure vessel code, the hydrostatic pressure of the liquid column must be added to the calculated pressure; this calculated pressure must be greater than or equal to the design pressure

The new pressure vessel code does not stipulate that all hydrostatic pressures exerted by liquid columns must be included in the calculated pressure. Whether or not they need to be included is determined according to the requirements of GB150; only when the hydrostatic pressure is equal to or greater than 5% of the design pressure is it included

Reply to 5# Zìyóuzìzài￥: I checked the so-called internal materials for the GB150 training course, and it shows that the mention of a 5% design pressure has been removed. When there are differences, we adopt a conservative approach by including the hydrostatic pressure of the liquid column

For the OP’s device, this phenomenon is normal; there’s no contradiction. Since the strength calculation of the equipment is based on the “calculated pressure” for determining its strength, as long as the equipment undergoes a pressure test while in a vertical position (this equipment can probably only be pressure-tested in a vertical orientation :), the test pressure specified in the standards should be used.

These two are different concepts. Please, OP, carefully study the definitions of design pressure and calculated pressure

According to the definitions in clauses 3.4.3 and 3.4.4 of GB150-1998, the design pressure applies to the entire equipment, whereas the calculated pressure applies to each individual pressure-bearing component. A single-chamber vessel has only one design pressure, but each pressure-bearing component may have its own calculated pressure. If the static pressure of the liquid column is taken into account, the calculated pressure on each pressurized component will, of course, be greater than the design pressure of the equipment. The test pressure applies to the entire equipment; therefore, in the formula given in Clause 3.8.1 of GB150-1998, the design pressure is used instead of the calculated pressure of individual components. Similar to the design pressure, the test pressure also refers to the pressure at the top of the equipment.

It is normal for the calculated pressure to be higher than the design pressure. Design pressure refers to the maximum pressure at the top of the vessel. The calculated pressure refers to the pressure borne by the container walls ； It could be local pressure or overall pressure. For example, in the case of tall vertical vessels, if the contents are gas, the design pressure is equal to the calculated pressure ； If the interior is a gas-liquid mixture, the pressure at the bottom equals the pressure at the top plus the hydrostatic pressure of the liquid. At this point, the calculation of the bottom wall thickness should be based on the calculated bottom pressure. The hydrostatic test pressures for vertical vessels are divided into two types: horizontal and vertical. The test pressure for vertical vessels is lower, as the static pressure of the water column must be taken into account; whereas for horizontal vessels, this water column pressure does not need to be considered.

I just looked up the draft for comments on GB150. Indeed, in the section regarding calculated pressure, the provision stating that liquid column static pressure should be taken into account only when it is 5% or more of the design pressure has been removed. Now, it simply states that liquid column static pressure must be considered. As a result, the safety factor has decreased and the wall thickness has been reduced; factors that could previously be ignored now cannot be neglected anymore. However, in several versions of the promotional materials related to the new pressure vessel regulations I found, there’s no mention whatsoever of this change in calculated pressure. This is indeed something we need to pay attention to

This post was last edited by Pinocchio on 2011-2-13 at 20:26. In Article 3.9.1 of the new regulations, it is also clearly stated that additional loads such as the static pressure of a liquid column should be taken into account when calculating the pressure. However, aside from the hydrostatic pressure of the liquid column, what other additional loads might need to be included in the calculated pressure? The valid version of GB150 is still the 1998 edition, and the strength calculation software is also based on GB150-1998. How should the discrepancy in the definitions of calculation pressures between the new regulations and GB150-1998 be addressed at present? Incidentally, in the owner’s example, both the working pressure and the design pressure are less than 0.1 MPa, so it should be designed as a pressure vessel at normal pressure. According to clause 3.3.4 of JBT 4735-1997 for steel welded atmospheric pressure vessels, the calculated pressure for common vessels also includes the hydrostatic pressure of the liquid column.