Reduction in Fm factor of UG-44(b) for sustained primary piping loads and / or gasket creep.

[Some Curious Guy]

UG-44(b) or code case 2901 has increased the design margin of standard flanges. Now we can increase the flange rated pressure by a factor ( 1 + Fm ) before we compare it with equivalent Pressure.
However the note (b) of Table UG-44-1 suggests an appropriate reduction in Moment factor (Fm) before using it for primary sustained piping loads or when there is a possibility of significant gasket creep.
A lot of time has passed since the introduction of code case 2901 / UG-44(b) and I hope people have become comfortable with it. Has anyone came across a method / procedure to calculate the Fm factor when standard flange are subjected to sustained primary piping loads or there is a possibility of gasket creep? As far as I know the softwares are issuing a warning for possible gasket creep when design temperature is high. They leave the task of appropriately reducing the Fm factor to the user.
Can people share their opinion and experience here regarding this issue ?
Is there non FEA method for this or FEA the only option ?

Thanks
Yaseer

 

[TGS4]

Have you read the paper that the method in UG-44(b) is based on? It is PVP2013-97814, by Dr. Warren Brown.

The paper has some recommendations for how to handle F_M

 

[Some Curious Guy]

Thanks @TGS4 for directing me to that paper. I could get a copy of the paper PVP2013-97814. I am just summarizing my findings for benefit of others.

The paper recommends to divide the FM factor by 2 if there is concern of sustained piping loads on the joint.

Flange rating per B16.5 / B16.47 considers the effect of high temperature creep. Since the method relies on flange rating it somehow automatically considers high temperature effect but in a very raw and crude fashion.

The paper directs us to the following references for more rigorous calculation of flange joint when assumptions of UG-44(b) are not met.