Fatigue-Ratcheting Study of Pressurized Piping System under Seismic Load

It has been observed that nuclear power plant piping systems may be loaded into the plastic range due to large amplitude reversible cyclic loading like seismic excitation. During such events, fatigue-ratcheting causes failure of pressurized piping systems. To understand the phenomenon, analytical and experimental studies are carried out on a typical pressurized piping system. The piping system is pressurized with water and subjected to continuous base excitation through shake table. Free vibration characteristics of the piping system are evaluated by sine sweep test. Analysis is performed using equivalent inertial forces. Chaboche nonlinear kinematic hardening model is used for ratcheting simulation. Fatigue life evaluation also carried out for the tested piping system as per ASME Boiler and Pressure Vessel Code, Section-III, Div-I, NB-3000. Experimental and analytical results are presented in the paper.