The issue regarding the operating temperature range of standard pressure vessel flanges
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When Type A flanges are selected in accordance with the pressure vessel flange standard NB/T 47021, the maximum operating temperature shall not exceed 300°C. According to Table 2 of standard NB/T 47020, which specifies the classification and technical requirements for pressure vessel flanges, if the flange material is Q345R, along with corresponding gasket and stud-nut materials, then the maximum allowable operating temperature is 350°C. So why is the upper operating temperature limit for flanges in NB/T47021 set at 300 degrees?
As specified in Table 2 of standard NB/T47020, if the flange material is Q345R, along with corresponding gasket and stud-nut materials, the maximum allowable operating temperature is 350°C. This value of 350°C is determined based on the applicable range of the materials. Similarly, flat welding flanges are divided into Type A (operating temperature range: -20 to 300°C) and Type B (operating temperature range: -20 to 350°C); the structural strength of Type B flanges is greater than that of Type A flanges. The allowable stress of materials decreases as temperature rises, and perhaps out of caution, Type B flanges should be used when the temperature is between 300°C and 350°C. In short, the specified operating temperature for type A being no more than 300 is likely due to conservatism, as well as to distinguish it from type B.
Type B flanges and Type A flanges are listed separately in Table 2
Have you considered why Table 2 groups Type B and long-flanged flanges together? It seems you didn’t understand what I meant. . . What I’m really trying to say is this: when using Q345R material, type A flanges can withstand temperatures up to 350 degrees. However, the reason why type A flanges are specified to only handle temperatures up to 300 degrees is to encourage the use of type B flanges in situations where the operating temperature lies between 300 and 350 degrees. After all, as temperature rises, the allowable stress of materials decreases, and Type B has a better pressure-bearing capacity than Type A. This is my understanding. . .
Thanks for the reminder. The original poster really paid close attention...
The 2nd floor is correct, agree agree. It is related to the structure of the flange.
I also agree that there are reasons for this, but the question is why, based solely on Table 2 of the standards, type A flanges can be used at 350 degrees.