Dear Mr. Richard Ay,
Thank you for the partial answers.

1. The "gasket seating" results and "operating condition" results must be practically the same for a very small pressure value as load.
Why?

Because in terms of mathematics, the forces, stress etc must be continuous functions against the variable "p". A discontinuity is possible but must show something very special.

In terms of physics. In your example for 1 psig load, the forces reported (in Plot) are HG=797 N, W=1371115 N.


Since for seating condition HG=W, what exactly is the physical phenomenon that is able to modify the HG to 0.058% of the initial value? For a very small pressure load, the gasket load must have a value near the bolts load, that’s my opinion.

2 I can see an axial force is not affecting the reported HG. Please, can you give some details: what reference is following this approach? To be clearer, the Kellogg results, very common referred, show exactly how the gasket load is affected by the external loads.
If I understand well the results, a pressure load is changing the gasket load while an external load no?

Best regards.