A database to evaluate stress intensity factors of elbows with throughwall flaws under combined internal pressure and bending moment

Abstract

The advent of the leak-before-break (LBB) concept has widely replaced the traditional design basis event of a double-ended guillotine break (DEGB) in the design of primary heat transport (PHT) piping. The use of the LBB concept requires postulation of the largest credible cracks at highly stressed locations and demonstration of their stability under the maximum credible loading conditions. Stress analysis of PHT piping in nuclear power plants shows that the highly stressed piping components are normally elbows and branch tees. This necessitates detailed fracture mechanics evaluation of such piping connections by computing their stress intensity factors (SIF) and/or J-integral. Simple analytical solutions for evaluation of the SIF and J-integral for cracks in straight pipes are readily available in the literature. However the same type of solution for elbows and tees is limited in the open literature. In the present work a database is generated to evaluate the SIF for throughwall circumferential and longitudinal cracks under combined internal pressure and bending moment. Different parameters used to characterise a cracked elbow are pipe factor (h), pipe bore radius to thickness ratio (r/t) and crack length. Another parameter(ρ) is used to consider the relative magnitude of stresses due to internal pressure and remote bending moment. This database has been used to derive closed-form expressions to evaluate the SIF for elbows with cracks in terms of the aforementioned parameters.