Sorry if I'm not giving much help here, but when I hear swivel, I don't look to CAESAR II. CAESAR II is a beam bending model. I think of a swivel as a geometrically constrained system - a linkage.
Our stiffness matrix is based on the original (input) layout of all these beam elements. They do not take large rotation well. If you swivel angulates more than a few degrees, CAESAR II will not properly predict the loads.
The expansion joint manufacturers deal with hinged piping systems. Perhaps they can help.