The issue of the maximum allowable operating pressure for pressure vessels that require airtightness. . .
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Gentlemen, I’ve been quite confused lately regarding the maximum allowable operating pressure. Nowadays, spherical tanks are required to be airtight and equipped with safety valves. Is it necessary to calculate the shell wall thickness using the maximum allowable operating pressure and then round it off? ?
It is not the maximum allowable operating pressure that is used to calculate the shell wall thickness; rather, it is the shell wall thickness that is used to determine what the maximum allowable operating pressure is.
Let’s first figure out what the “maximum allowable operating pressure” means
The maximum value refers to the fact that, due to secondary rounding, an extra amount of metal is used in the casing to withstand a pressure slightly higher than the designed pressure; the core principle here is to avoid wasting material
It is to determine the maximum allowable operating pressure that a spherical tank can withstand, by using the effective thickness of the shell plates. Generally, as is required for pressure vessels, a gas-tightness test must be conducted, and if the equipment is equipped with a safety valve, the maximum allowable operating pressure must be indicated on the drawings. Generally, the maximum allowable operating pressure can be set slightly higher than the design pressure; this way, during the airtightness test, the opening pressure of the safety valve can be set within the range that is greater than the design pressure but less than or equal to the maximum allowable operating pressure.
The maximum allowable operating pressure is generally taken as the minimum value of the pressure values calculated for each pressure-bearing component based on its effective thickness. The maximum allowable operating pressure can be determined by reversing calculation based on the effective thickness of the spherical shell; the maximum allowable operating pressure for the flange is selected according to flange standards. The smaller of these two values can be used as the maximum allowable operating pressure for this equipment. Subsequently, stress calculations are carried out on all components and stress points of the spherical tank, and approval is granted once these calculations show satisfactory results.
In the workplace, many people consider the 【maximum allowable working pressure】 to be the 【working pressure】 or the 【highest working pressure】; therefore, it is recommended to give the 【maximum allowable working pressure】 a different name.
I saw someone go to the special inspection agency to have the safety valves adjusted; they used the maximum allowable operating pressure as the rated pressure of the boiler when setting those valves, so it’s no wonder an accident might occur.