First of all, thanks a lot for your prompt response Richard.

I would like to share my values just in case any help could arise:

A358 316
Elastic Modulus E(MPa)195100
Exp coef (mm/mmm/C) 0.0000156
Diameter: 323.8mm
Thickness= 21.44mm
T1= 25C
T2= 55C
Pressure = 152bar
Yield Stress= 207MPa

Results obtained in a RESTRAINED section UG B31.4:

SThermal (MPa) SE = E*ALPHA*(T1-T2) Formula: -91.3; Caesar II output: -96.0
SHoop (MPa ) SH=Pi(D-t)/20t Formula: 107.2; Caesar II output: 107.2
Long (MPa) SL=SE+vSH+M/Z+Fa/A Formula: -59.2; Caesar II output: -64.7
Seq=sqrt(SHsqr2-SHSL+SLsqr2+3Stsqr2) Formula: 146.0; Caesar II output: 171.9

Comb. Allow. (MPa) Formula: 186.3; Caesar II output: 186.3

So we do not understand how Caesar II calculates de Stress Equivalent values (Comb & Code) for this particular case. The difference is about 15% for the hot case.

Thanks again.