When?
A piping flange is subject to pressure load. It is supposed this pressure is less than the pressure rating, so it’s no need to calculate the pressure effects alone. But the piping flange belongs to a piping system, so it is also subject of forces and moments due to the piping system behavior under the loads (sustain, thermal, occasional, etc).
We must try to evaluate the flange stress and the leakage danger under all loads.
But...how? No simple answer here!
First, here the "beam theory" is not applicable. The flange is rather a circular plate, so the calculation cannot be integrated directly in software.
One effective but rather conservative method is to transform the forces and moments in equivalent pressure and to compare the total pressure with the rating pressure.
There are modern Codes methods –see ASME VIII Div2 or EN 1591, trying to count directly the effect of all flange loads with the target to predict the flange stress, the flange rotation and the leakage danger. Unfortunately, ASME VIII Div2 method is specifically written for flanges design. And EN 1591 seems to neglect the radial stress and strain, and this may be a method limitation; anyway, prior to apply, the method should be qualified as valid for ASME flanges case.
In my opinion, a realistic approach would be:
- to model the piping system with more accurate rigidity of the flanges joints (based on a structural model analysis able to take into account the behavior of flange, bolts, gasket compression, etc)
- to evaluate the forces and moments that are loading the flange joint in the piping system
- to calculate the flange stress, bolt stress, flange rotation, gasket compression with a method valid for piping flange checking.
Looking to what we have today, we have a long way ahead!
Edited by mariog (11/01/08 07:30 AM)
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