The piping systems used in nuclear power plants have a large amount of safety margin up to the point of the boundary failure, even when the input seismic load exceeds the allowable design level. This is attributed to the large strength capacity of the piping systems in the plastic region. A task group activity under the Japan Society of Mechanical Engineers (JSME) is conducted to establish an evaluation procedure, in which the inelastic behavior of piping systems is considered in a rational manner. A Code Case in the framework of the JSME Nuclear Codes and Standards has been developed as a deliverable of this activity.

For developing the Code Case, inelastic benchmark and parametric analyses on the tests of a pipe elbow and a piping system model made of carbon steel were conducted to investigate the variation of the elastic-plastic results. Based on these analytical results, we assume that setting the yield stress has a significant influence on the inelastic analytical results, while the work hardening modulus in the bilinear approximation of the stress-strain curve has little influence. The parametric analysis results confirmed that the variation in the analytical results among different analysts would be reduced by having a unifying analytical procedure.

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