Experimental Evaluation of the Bending Load Effect on the Failure Pressure of Wall-Thinned Elbows

Abstract

During normal operating conditions, piping systems in nuclear power plants are subject to internal pressure and bending loads induced by deadweight, thermal expansion, and internal pressure. Thus, understanding the effect of bending load on the failure of wall-thinned elbows is important to understand failure behavior and to evaluate the failure pressure reliably. This study includes a series of burst tests using full-scale 4-in. schedule 80 elbow specimens with local wall-thinning under combined internal pressure and in-plane bending load. The results are compared with those tested under simple internal pressure only. In the tests, various circumferential thinning angles (θ/π=0.125, 0.25, 0.5, 1.0) and thinning locations (intrados, extrados, and full-circumference) were considered. Each specimen was initially subjected to a displacement controlled in-plane bending load, closing mode for extrados wall-thinned elbows, and opening mode for intrados wall-thinned elbows, and then internal pressure was applied up to the point of final failure. The results showed that the effect of in-plane bending on the failure pressure and failure mode was minor under all wall-thinning conditions. In addition, the dependence of failure pressure on the circumferential thinning angle and thinning locations was identical to that observed under simple internal pressure.