Bend Angle Effect on B2 and C2 Stress Indices for Piping Elbows

Abstract

B2 and C2 stress indices are used for calculation of stress terms corresponding to moment loading in evaluation of nuclear piping components. The formulas given in the ASME Boiler & Pressure Vessel Code for calculating these indices for elbows and curved pipes are independent of the bend angle. The objective of this investigation was to study the effect of the bend angle on the values of B2 and C2. For this purpose, elbows with sizes ranging from 2.5 to 20 in. have been studied. The values of B2 and C2 have been calculated by detailed analysis using finite element models. Each elbow size has been analyzed for various bend angles (e.g., 15, 30,[[ellipsis]]90 deg and above). The results of this study show that the values of B2 and C2 based on the ASME Code formulas are conservative and more so if the bend angle is less than 90 deg. The values of B2 and C2 decrease as the bend angle is decreased. The reduction in the values is very significant for smaller bend angles. Simple relations have been established to express the dependence of B2 and C2 on the bend angle. Based on these results, a modified form of ASME Code formulas is proposed to account for the bend angle effect.