Your system may not be supported at the proper/balanced locations. Look at supports offset from long risers or heavy valves. "Teeter-totter" (see-saw) effects will be more pronounced in a hydro case, in particular for large diameter piping. If you attach a CII iso plot showing supports and springs, unstable systems may be obvious to experienced stress personnel.
_________________________
Bob Zimmerman, P.E.
Vice President of The Piping Stress International Association (The PSI)