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Allowable 10% reduction in design temp. for flange per ASME SEC.VIII, DIV.1, B31.3, or B31.1 ???

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timsch

Mechanical
Oct 27, 2009
181
I recall seeing in either ASME SEC.VIII_DIV.1, B31.3, or B31.1, if I recall correctly, an allowance for a 10% reduction in design temperature for flanges that are on nozzles. I've read through the sections where I'd expect to find that in each, but cannot find it. If anyone could point me in the right direction, I'd appreciate it.

The product I'm designing now is a pipewell (thermowell made from pipe) which will has a flange that will mate to a nozzle flange on the pressure vessel. I design to the specs of the pressure vessel, which is Sec. VIII, Div.1. The pipewell mating flange will certainly be at a lower temperature than the pressure vessel, but I don't have the actual temperature it would be at, so was hoping to take the 10% allowance if I could.
 
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True only in the piping code for uninsulated flanges and fluid temperatures above 150°F. See ASME B31.3 301.3.2(b)(2). Interestingly this rule is based on degrees Fahrenheit, not on the absolute temperature (degrees Rankine) which to me would make more sense.

ASME Section VIII Div 1 doesn't have any similar derating equation for flange design temperatures, but you can design a vessel with multiple design temperatures for different components if needed.


-Christine
 
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