Fracture Mechanics Study of Cracked Pipe Bends Under Internal Pressure and Bending Moments

The present work attempts to investigate some aspects of the fracture behavior of cracked pipe bends under the action of in-plane bending moments, with and without internal pressure. The results of the elastic-plastic FE analysis of the defect free elbow under the action of in-plane opening and closing bending moments are presented with the emphasis on the hoop and axial stress distribution at various salient locations in the elbow. A severity matrix is outlined subsequently, correlating the various possible cracked configurations and the loading patterns. Parametric studies on the cracked elbows are carried out, in which the parameters, such as ratio of crack depth to elbow thickness (a/t), angle of the part-through wall crack, bend factor ‘h’ and the internal pressure ‘P’ are varied. The variations of the J-integral versus load and load versus load line displacement are presented. The crack initiation load is determined from the material specific critical value of the J-integral. A non-dimensional parameter is suggested as ratio of plastic collapse load to the crack initiation load, which increases with the increase in the internal pressure both in case of the throughwall flawed elbow as well as in the part-throughwall flawed elbow.