Finite Element Simulation of Dynamic Behavior of Pressurized Piping System Under Large Seismic Load

The nuclear power plant piping systems are often subjected to the cyclic loading conditions due to transients, seismic or other unexpected events. During these events, the probable mode of failure for piping component is fatigue-ratcheting. Earlier the design of piping subjected to seismic excitation was based on the principle of static collapse. Later on, it was postulated that the cause of failure of piping components is fatigue ratcheting and not plastic collapse. The 1995 ASME Boiler & Pressure Vessel code, Section-III, has incorporated the reverse dynamic loading and ratcheting into the code. An Analytical study is carried out to investigate the behavior of the pressurized piping system under large seismic loading. The analysis is performed using equivalent inertial forces. Chaboche nonlinear kinematic hardening model is used for ratcheting simulation. The capability of the model to simulate the ratcheting response of the piping system is of particular interest. Comparison of analysis results against test results are presented in the paper.