Studies on the propagation of surface cracks in a piping elbow subjected to an in-plane bending moment

Analysis and estimation of fracture parameters in flawed nuclear piping systems are of great importance in developing appropriate methodologies for ensuring structural integrity of these systems. The understanding of the response of surface-cracked piping components such as elbows under operating conditions is vital for the development of appropriate flaw acceptance criteria. The propagation of a semi-elliptical surface crack in a thick-walled elbow when subjected to an in-plane bending moment was studied. In the analysis, four different cases, namely a crack at one crown, at both crowns, at the intrados, and at the extrados, were considered. A three-dimensional finite element code using ANSYS was developed to evaluate the mode I stress intensity factor (SIF) based on the displacement extrapolation method. Making use of data from the finite element method (FEM) results, correlations were evolved using regression analysis to evaluate the SIF range in the depth and surface directions. The number of cycles to failure was predicted by applying the Paris law. The number of cycles to failure predicted through the FEM and correlation deviates from the experimental results available in the published literature by a maximum of about 13 per cent. The number of cycles to failure has also been predicted using closed-form solutions available in the literature and is compared with the FEM results.