The Effect of Flaw Shape on the Fracture Propensity of Nozzle Corner Flaws

Three-dimensional finite element models were formulated to evaluate the distribution of the elastic stress intensity factor around the periphery of cracklike flaws postulated to exist at the corners of nozzles intersecting cylindrical shells. The effect of the assumed shape of the nozzle corner flaw on the distribution of the stress intensity factor along the crack front was determined in order to indicate where initiation of crack growth is most likely to occur and what shape the crack is most likely to take subsequent to stable crack growth. This is important because of the uncertainty associated with the flaw shape and its effect on crack growth in the nozzle corner region. Stress intensity factors computed from the nozzle corner flaw models were also compared with solutions evaluated using 1) a simplified procedure similar to that given in Section XI of the ASME Boiler and Pressure Vessel Code that makes use of the stresses calculated in the absence of the flaw, 2) the method recommended specifically for nozzle corner flaws in Section III of the ASME Code, and 3) a previously published empirical formula. The results of this paper confirm the adequacy of the simplified procedure for the analysis of nozzle corner flaws of different shapes.