Abstract: The seismic design criteria in ASME code, edition 2002 was compared with that in ASME code, edition 1995, and the intention to derive a less severe design criteria was studied. A conservative factor was defined so that the margin of the design criteria was evaluated. The linear and nonlinear response of elbow under seismic loading was evaluated and the influence of the material nonlinearity, large deformation and pressure on the response of the elbow was investigated. Based on the results of the elbow under seismic loading, the margin of the seismic design criteria for the piping in ASME code was analyzed. The results show that the seismic design criteria for the piping are greatly conservative.