Floating Head: Spherically bolted head - Gasket

Dear All,

I am in trouble with a Spherically bolted head Calculation... Autopipe reports this 2 errors :

"356 FLANGE 14.02: gasket width insufficient ( minimum=31.104 mm ), the permissible gasket load is exceeded, use of a compression ring is recommended.
356 FLANGE 14.02: gasket width insufficient ( minimum=37.772 mm ), the permissible gasket load is exceeded, use of a compression ring is recommended."
regarding the same non-maintained calculus condition.

I found it strange because these minimum widths are too big for this heat exchanger....

Does anyone knows where i can find this method of calculation ? I already searched in ASME Section VIII, Division 1 and Divion 2 but i did not find anything...
It is strange that autopipe shows 2 errors with 2 different minimum gasket width, when on report only appear 1 condition not maintained. (see picture bellow)
This error only occurs at "[in operation, Ext.P.]" condition ... And the values only differ in "(Hext)max" variable... Does anyone knows what it is "(Hext)max" ? I know what it is "Hext" and how calculate it, but i dont know the diference to "(Hext)max" ... 

Can anyone help?

Thanks,