Abstract
The beam theory has been used for the limit load evaluation for straight pipes with surface flaws. In case of elbow pipe, however, the beam theory gives just an approximated solution because of the three-dimensional defomiation combining the beam bending and plate bending. In this study, we searched for the boundary, within which the approximation based on the beam theory was applicable. To determine the boundary, the bend radius and wall thickness was systematically changed, and the reasonable solutions were obtained by the fmite element analysis using the solid element with the reduced integration to avoid the numerical locking. The variation of error in the extrados and intrados surface stress with respect to the pipe dimensions was numerically clarified and 10%-error bound was fixed as the applicability boundary. The explicit formulation of the boundary was found to judge the applicability of beam theory to the elbow pipes.
