The loads in beam element programs such as CII will be distributed based on the stiffness of the system. Typically a more rigid system will yield conservative overall results but the results may not match the actual installed system out in the field.

All the components have some kind of stiffness and loads will be distributed throughout the system accordingly. From basic Statics the loads will distribute more to the stiff items. If you want more realistic results you should include Branch connection, Nozzle and Support stiffness if these can be obtained without excessive manhours being expended.

If you have the SIfs from an FEA, then you may already have the flexibitities also if you used PRG software products. Just go ahead and input this data. All you need is a little patience and the work will be done.

Granted for the "average" moderate size and mild operating condition systems there may not be much benefit or change in results for this extra work. BUT for more critical systems the NEW TREND should be to obtain the correct answers (within reason) and then evaluate how much real margin we have in the design. Also a more accurate analysis tends to help troubleshoot issues that arise from the Job Site.
Bob Zimmerman, P.E.
Vice President of The Piping Stress International Association (The PSI)