I am working on a project where the steam turbine manufacturer has given nozzle displacements plus allowable forces and moments (which are very low). I have modelled the nozzles as displacements with the linear displacements DX, DY and DZ as given by the manufacturer but with rotational displacements RX, RY and RZ set to 0. In some of the operating cases the resulting moments exceed the manufacturers allowables. This is especially true in the OCC case for seismic loading. The piping system is largely suspended on spring hangers with appropriate seismic stops. Stresses in all cases are not a problem. My questions are as follows:

1. Is my modelling method correct with the nozzle rotations set to zero? Is there a better method so that the stiffness of the nozzles can be relaxed? Is the WRC method of modelling nozzles at vessels applicable here?

2. My operating case is (OPE)W+D1+T1+P1+F1
My sustatined case is(SUS)W+P1+F1
My occasional case is(OCC)UNI1 for seismic
My occasional case is(OCC)= SUS+UNI1
My thermal case is (EXP)= OPE-SUS
Are these cases correct for obtaining the forces and moments for the sustained case (turbine cold) and the operating case (turbine hot)?

3. The turbine manufacturers do not state if their allowable forces and moments are still applicable during a seismic event or do they allow some leeway here? What has been your experience?