How does Caesar calculate the bolting seating stress in the flange leakage calculation module? I can't seem to get the same numbers.

Following ASMEVIII:

The minimum initial bolt load is given by
Wm2 = 3.14 x b x G x y
I have a 40NB flange where b=12.22mm, G=76.65mm, and y=24132.5kPa
So Wm2 = 70.977kN.

I have 4 bolts with 12.7mm diameter, so my total area is
Ab = pi x D^2 = 0.0005067 m^2

So my stress is Wm2/Ab = 140.1MPa, which I can compare against my bolt allowables. This is the same as comparing the actual bolt area Ab, to the required bolt area Am2 (Am2 = Wm2/Sa, where Sa is the bolt allowable stress) which is what ASME says to do.

The calculation module gives me a bolting seating stress of 537.3MPa.

Last time I posted I got flamed, so pls be gentle this time. I'm still green, which is why I ask questions! I'm getting a book to read from a friend which may help, but I thought I'd put this forward.

Cheers