To understand the properties of the shape of the actual tee pipe and the effect of shape modeling on finite element method (FEM) analysis results, the authors measured the 3D shape of a 150A equal tee pipe and conducted inelastic static and modal analysis on a specimen including the equal tee pipe. The tee pipe joint used in this investigation was a “steel butt-welding type” carbon steel. In the inelastic analysis, the material property was modeled using bi-linear kinematic hardening. The data for two kinds of shapes were prepared for the FEM analysis: based on the measured configuration; based on the nominal dimension.

The 3D shape measurement showed that the actual wall thickness of the tee pipe joint was greater than the nominal value, and it was unevenly distributed in the pipe. The maximum measured wall thickness of the pipe was up to 47% thicker than the nominal value. The analysis showed that the model based on the nominal dimension reduces the collapse load by 25%–30% compared to that based on the actual shape. The distribution of cumulative equivalent plastic strain was also affected by the shape modeling; the model based on the nominal dimension predicts the point of strain concentration to be closer to the center of the tee. Though the natural frequencies of these models were different, which is attributed to the difference of elastic stiffness of each model, the mode shapes were similar.

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