As we learnt from PRG Webinar 044(Part 2), large thermal expansion load can be treated as primary load on equipment nozzle, similarly piping made too stiff by rigid strut to raise natural frequency to min 16 Hz, it is possible for thermal expansion load to cause crack in weld due to primary stress from expansion load.

For eg, for SS pipe, if we have temp drop of 100C between two anchors in straight length configuration, stress will be E*alpha*DT i.e. 2E6*0.018/1000*100 = 3600 kg/cm^2 .. which can cause primary failures in weld.

Maybe in our case, we have caused failure at welds to avoid imaginary two phase vibration by making the piping too stiff!

reg,
sam