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

There could be a number of issues going on (pressure, corrosion, etc.) For this job, take a look at the "flange.msg" file (which will be in the data directory). This is a text file with the intermediate computations performed by the flange module. If you still can't determine where the number came from, e-mail me the .FLG file with your data.

Thanks for the tip Richard.

Also is there any way to get around the error message for the gasket ID being less than the flange ID? (in the case of lap joint flanges)

Not at the present time. If the gasket ID is less than the flange ID, then the gasket is hanging out into the flow area. Why would you want this?

In the case of lap joint flanges the 'stub' is the actual portion on which the gasket sits. The stub inner diameter (and the gasket ID) is smaller than the inner diameter of the 'loose' flange.

(The ASME code still defines the flange inner diameter as the inner diameter of the loose flange.)

The gasket reaction diameter for a lapjoint flange is the midpoint between the flange and the lap (stub). So my guess would be to use the stub OD as the gasket OD, and the flange ID as the gasket ID.

Is this right?