In a previous study [1], the seismic behavior of a piping system with local thinning elbow caused by liquid droplet impingement erosion (LDI) was evaluated using hybrid seismic testing method in Central Research Institute of Electric Power Industry (CRIEPI). In those studies, torsional buckling and wrinkles occurred at locally wall thinning elbow under large amplitude seismic motion of eight times the design basis earthquake based on the allowable stress level. It was concluded that buckling should be considered as a failure mode. In this study, the torsion buckling under out-of-plane bending of locally wall thinning elbows could be demonstrated by finite element analyses. Torsion buckling deformation agreed well with test result and the critical buckling deformation was clarified by comparing parameter analyses. The buckling formula was proposed to prevent the torsion buckling of locally wall thinning elbow.

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