Can HG/T20592 flanges be used as substitutes for higher-grade ones?
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There is an socket weld flange DN25 PN16, and according to the pressure and temperature rating table, it does not meet the required maximum allowable operating pressure. The flange of DN25 PN40 has exactly the same dimensions as the PN16 flange, and it meets the maximum allowable operating pressure. Is it possible to upgrade from a lower generation to a higher one? I earnestly ask all the experts for their guidance
You’re using a higher generation for a lower generation task; that’s okay, but it’s not acceptable to use a lower generation for a higher generation task
I just don’t understand why it’s not allowed; the size and material are the same
Read my previous reply again
This post was last edited by wingfj on 2019-6-28 at 11:11 :o I know that you can’t use a lower grade to replace a higher one… but in this case, the size and material are the same, there’s no steel stamp either, and the processing method is identical as well. These two flanges are exactly identical
Since there is no steel stamp (which is itself a violation of the regulations), and the dimensions are exactly the same, who knows what the pressure rating is? Is it still necessary to use a substitute? Isn’t substituting something just creating trouble for no reason?
According to the regulations, the nominal pressure of a pipe flange should be one grade higher than the design pressure. If it’s Pn16, why choose a 40 rating? Shouldn’t it be 25 instead?
This post was last edited by zjq1962 on 2019-6-29 at 10:35. I’m not sure which standard specifies that the pressure rating of the flanges mentioned by Haiyou should be one grade higher than the design pressure At high design temperatures, one higher grade is not sufficient. It is necessary to ensure that the maximum allowable operating pressure of the selected flange is not less than the design pressure. It is also necessary to meet the design requirements specified by the user
First of all, I didn’t say it must be one rank higher; this member can check the relevant regulations. Please avoid playing word games. Yes, the maximum allowable operating pressure of the flange is not lower than the design pressure, and that’s correct.
This post was last edited by wanlirn on 2019-7-1 at 11:40. The socket flanges for DN25 PN16 and DN25 PN40 are exactly the same; what you mean is that the maximum allowable operating pressure for DN25 PN16 does not meet the requirements, while DN25 PN40 has the same dimensions as DN25 PN16, and its maximum allowable operating pressure can meet the requirements – this creates a contradiction! This isn’t replacing a higher-grade material with a lower one; you can definitely use DN25 PN40 in the diagram. What’s there to worry about? . . For the **standard**, just smile and be aware that it can be used in this way.
As you mentioned, this situation occurs only in a small portion of the flanges and is not representative of the whole; you can simply have the designers modify the technical documents.