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Design Temperature - Mean metal temperature

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notsocommonsense

Petroleum
Jul 2, 2008
10
Folks,

AME B31.3 has a table (301.3.2) that says you can use 90% of the process temp as your mean metal temperature conservatively for uninsulated flanges if your process temp exceeds 65 C (150 F). Is there a similar shortcut method for ASME Section VIII vessel nozzle flanges?

Other question. As I know it, max coincident temp/pressure refers to the condition which yields the value closest to the allowable stress curve dictated by the P/T curve outlined by the pressure temperature chart for a given material/flange rating. So if I have operating conditions that exceed the max coincident temperature but at lower pressures, is that allowable by code - to me it seems it should be. Just looking for a confirmation. I'm a process engineer trying to figure out what to do with a vessel that has exceeded design temps on numerous occasions but never to the point of having the max allowable pressure exceeded for that temperature coincidentally.

Thank you

Yearn fer it, Learn it, confirm it, earn from it!
 
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The answer to your first question is no, ASME Section VIII doesn't have any specific derating formula for lower uninsulated flange/bolt design temperatures, but you are permitted to design a vessel with multiple design temperatures for different components as needed.


-Christine
 
for your second question, I do that all the time when I want to design a fitting to a B16.5 flange rating. That way I only have to do one calculation that covers all the P/T's for a class.

on the attached page. If I want to check a Cl.150, I would run my calculations at 100°F, for a Cl.300 I would use 850°F, and so one. For me, I have to check all the materials I'm using, but if you are just worried about a flange, you checked it against the same material.



 
 https://files.engineering.com/getfile.aspx?folder=a7abfb2d-ed16-4b47-b88d-18767a72c5de&file=Ratios.pdf
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