Selection of pressure class for the takeover flange
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I’m a complete beginner when it comes to pressure vessels. For connection flanges, should the pressure rating be one or two grades higher than the design pressure? Is there any specific standard that outlines this? I would appreciate guidance from those with more experience.
For the takeover flanges, flanges specified in HG/T20592–HG/T20635-2009 are generally used (in industries other than the petrochemical sector); these flanges are equipped with temperature-pressure gauges, allowing one to determine the maximum operating pressure for the flange at specific temperatures. The nominal grade of the flange is determined based on this. Therefore, some people choose a nominal grade for the flange that is one level higher for carbon steel and two levels higher for stainless steel, in order to avoid having to consult these specifications frequently.
For the takeover flanges, flanges specified in HG/T20592–HG/T20635-2009 are generally used (in industries other than the petrochemical sector); these flanges are equipped with temperature-pressure gauges, allowing one to determine the maximum operating pressure for the flange at specific temperatures. The nominal grade of the flange is determined based on this. Therefore, some people choose a nominal grade for the flange that is one level higher for carbon steel and two levels higher for stainless steel, in order to avoid having to consult these specifications frequently.
It also depends on the toxicity of the medium and its flammability
The PN and DN values of the flanges on the equipment are used for connecting pipes and instruments; they are primarily determined by the piping and automatic control teams. The equipment team needs to confirm these values based on the rated temperature and pressure
Learn the standards first! They’re all included in the standards!
It’s just to refer to the pressure-temperature ratings; when checking, should one consider the design pressure and design temperature or the operating pressure and operating temperature?
It refers to the operating temperature, also based on the maximum operating temperature. Generally, I choose according to the design temperature, to be more conservative: lol
According to the standards, factors such as operating pressure and operating temperature are taken into consideration; as the temperature rises, the allowable pressure decreases. There are tables available for reference on this. Another principle is to try to keep the flange grade standards as simple as possible, as this will significantly reduce the number of valves and other spare parts needed in the future!
Check the table. https://bbs.hcbbs.com/thread-2959259-1-1.html
It is selected based on the design temperature and the maximum allowable operating pressure. For details, see Chapter 7 of HG/T20592-2009 (starting from page 23).