My question is about gasket modulus used in Caesar II Flange Leakage Calculation (based on AMSE VIII Div 1). Caesar User Guide States gasket modulus lies in the range of 347000 psi to 437500 psi.
This value makes gasket very rigid and hence B16.20 (para 3.2.6) code requirement for spiral wound gasket compression will be not be achieved.
B16.20 (para 3.2.6)
"Spiral-wound gaskets NPS 1⁄2, NPS 3⁄4, and NPS 1 in Classes 150, 300, and 600 shall be designed so that a uniform bolt stress of 172 MPa (25,000 psi), based on the nominal bolt root diameter, will compress the gasket to a thickness of 3.30 mm ±0.13 mm (0.130 in. ± 0.005 in.). All other gasket sizes and classes shall be designed so that a uniform bolt stress of 207 MPa (30,000 psi) will compress the gasket to a thickness of 3.30mm± 0.13mm(0.130 in. ± 0.005 in.)."

Also, shouldn’t gasket modulus be same for same type of spiral wound gasket irrespective of pipe size and rating?
I have tried many calculations in Caesar II and required gasket compression during initial tightening is never achieved as required by B16.20.
Can you help where am I making a mistake?

We found those (estimated) modulus values in a book. This modulus value is used in the (FEA) leakage estimate - to compute the (spring) stiffness. If you have a better source or guide for this value - use it.