Stiffening Effects on Thin-Walled Piping Elbows of Adjacent Piping and Nozzle Constraints

Elbows, attached to component nozzles or adjacent piping, experience a stiffening effect due to the restraint of ovalization provided by the nozzle or pipe. Using the thin-shell, finite difference program STAGSC, a numerical study of two elbows of different geometry with varying degrees of ovalization restraint was performed. Attention was confined to small displacement, elastic analysis of pure in-plane and out-of-plane bending. The analysis shows that in all cases there is a significant decrease in elbow flexibility due to the constraints. There is also a corresponding decrease in the circumferential stress index which is approximately proportional to the reduction in flexibility. These results indicate that a simple, rational basis could be developed for modifying elbow flexibility factors to allow for flange and nozzle stiffening in overall piping flexibility analysis. Original data are presented which relate elbow flexibility factors and stress indices to the degree of nozzle constraint for two elbow geometries.