Floating head under external pressure

[Ehiman1]

Good evening to everyone,
Is there someone that use Autopipe Bentley to design heat exchangers?
In the calculation of bolts load of floating head under internal+external pressure I saw that Autopipe uses the following formula:
Wm2+Hext < 2*pi*N*G*Y
to check gasket stress, I suppose, but I have never seen this formula in ASME VIII div. 1.
Where:
Hext = Pext*D^2/4
Someone can explain me if this formula is correct and why?

Many Thanks

 

[SnTMan]

extragol1A, I am not an Autopipe user, and I have not seen that particular calculation before, but, it appears similar in form to the so-called "Nmin" calculation from Brownell & Young used for girth flanges and floating head internal pressure.

It is intended (or so I assume) to protect against crushing of the gasket due to the applied loads, namely, full bolt load for internal pressure, Ab*Sa, and for external pressure, gasket seating load Wm2 plus the load due to external pressure, Hext as above.

I'd guess Autopipe would check each condition (if present) and select the widest of the two.

Regards,

Mike

Added Nmin:

The problem with sloppy work is that the supply FAR EXCEEDS the demand