Limit load evaluation for healthy elbows and elbows with notch at intrados under in-plane bending moment

Abstract

Elbows are critical parts of any piping system used in nuclear power plant industry. These elbows experience internal pressure and also undergoes in-plane bending due to external loading. In the present study, limit load for two types of elbows, viz., healthy elbow and elbow having circumferential through-wall notch at intrados, with and without internal pressure subjected to in-plane bending moment is determined. Limit load is dependent on the parameters, namely, thickness, mean radius, bent radius, internal pressure, yield stress, notch size and deformed diameter of the elbow. Based on the experimental and numerical studies, the expressions for limit load evaluation were proposed by various researchers. In the present study, the limit load evaluation expressions proposed by Chattopadhyay and Tomar (2006), Chang-Sik and Kim (2006) and Hong et al. (2010) are considered. The general approach followed is to arrive at a weakening factor for considering the effects of bend geometry, internal pressure and presence of notch. Limit load obtained by using the above expressions have been compared with the twice elastic slope (TES) method and experimental measured maximum load (EMML) values. For elbows without any defect, limit load of TES method are about one-third approximately compared to EMML values. But for elbows with defect, it is lesser than EMML values by 20%. Predicted limit load for healthy elbows with and without internal pressure using the different expressions, found to vary less than 10% compared to TES method. For the elbows with circumferential through-wall crack at intrados without internal pressure, limit load obtained using TES method is around 15% more compared to the values obtained using the expressions.