May I ask if it is non-compliant to have a design pressure that is higher than the operating pressure?
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I’m a newcomer and not a professional; I’ve just started working with pressure vessel design. Currently, I’m designing a natural gas storage tank with a volume of 2 m³ and operating pressures of 16 bar and 6 bar. My colleagues here have asked me to use a pressure value of 2.5 MPa for all calculations, citing safety reasons. Is this appropriate? I’m not from a chemical machinery field; I’m currently learning *pressure regulations*. Please forgive any mistakes I might make – even after I’ve finished calculating, I’ll still need to consult a professional. It’s just to help me get familiar with this subject. The medium is pure natural gas, and it’s a gas supply buffer tank. Is it necessary to install a drain port? The requirement that the inlets and outlets be located at the top and bottom was also set by others. Are there any specific considerations regarding the exact location of these openings, such as the distance from the axis to the upper and lower parts of the tank? And how should the length of the extensions inward and outward be determined? I also took a look at SW6 and found that there are many terms I’m not familiar with; I don’t know how to name them – things like hydrostatic column pressure, weld metal cross-sectional area, etc. Thank you to all the experienced colleagues for your guidance! ! ! !
That’s just the way things are in reality. There are several situations: 1) For many devices, during the design phase, the operating pressure is not provided by the customer; instead, a design pressure is assigned directly. 2) Many customers deliberately increase the design pressure for the so-called sake of greater safety. This situation is more common with smaller devices, as the cost does not increase much. In a word, do whatever your boss tells you to do, and do whatever the client asks you to do – that’s all there is to it.
The pressure in the buffer tank changes significantly; there may be temporary high pressures
It’s normal! Under normal operation, the chlorine buffer tank here operates at 0.15–0.20 MPa; the maximum pressure is 0.35 MPa when chlorine is being fed in. However, the design pressure is 2.50 MPa. A higher design pressure makes users feel safer, but it cannot be set arbitrarily. Otherwise, there will be a lot of trouble, and it’s not safe either. One is the pressure resistance test; if the operating pressure at which the device is used is 0.20 MPa, then the pressure applied during this test is usually set at 0.25–0.30 MPa. The calibration pressure for safety valves is 2.50 MPa or even higher. One is the leak test, which is conducted as a pressure resistance test at 0.25–0.30 MPa. Therefore, an excessive safety margin gives users an overly relaxed mindset, while neglecting the truly important safety tasks. In actual use, it is artificially reduced to a buffer tank with a pressure of 0.20 MPa, yet it is still used as if it were a buffer tank with a pressure of 2.50 MPa.
The operating pressure is often around 0.1 MPa, but the owner wants it to be changed to 1.6 MPa everywhere. If the owner does not give any instructions or if there are no specific requirements from the process engineering team, the set pressure of the safety valve is generally adopted, or a slightly higher value.
The selection of design pressure sometimes also requires considering the pressure of the entire system.
As long as there’s no problem with the process system, then everything will be fine. It’s also okay to do as your superiors instruct you to
2.5 is fine; those who don’t understand SW6 can press F1
For some fatigue-prone components, increasing the design pressure can eliminate the need for fatigue analysis; furthermore, taking into account accidents and other situations within the process system, it is possible to specify a design pressure.
What the customer needs to provide you are the operating pressure and the maximum pressure. If the maximum pressures are 16 bar and 6 bar, then a design pressure of 2.5 MPa for 16 bar and 1.6 MPa for 6 bar will be sufficient