Applicability of Stress Intensity Factor Solution for Flat Plate to Nozzle Crotch Corner Flaw

Abstract

The applicability of a stress intensity factor (SIF) solution for a flat plate with a surface flaw (flat plate model) to nozzle crotch corner flaw is investigated by using a 3-D finite element method (FEM). Flaws due to stress corrosion cracking (SCC), fatigue, etc. are frequently postulated or detected at discontinuity regions. To evaluate the structural integrity of flawed components, it is important to calculate fracture mechanics parameters rationally and appropriately. SIF is one of the key fracture mechanics parameters for linear elastic fracture mechanics evaluation. Therefore, almost all fitness-for-service codes, e.g. ASEM BPVC Section XI, JSME FFS Code and R6 provide SIF solutions. However, they essentially provide SIF solutions only for flat plates or cylinders with flaws. Since nozzle crotch corner suffers from stress concentration and there are a lot of nozzle geometry parameters, there is no direct SIF solution for arbitrary nozzle geometries. To estimate SIFs for nozzle crotch corner flaws rationally and appropriately, the applicability of the SIF solution for the flat plate model needs to be verified. SIFs were calculated by using 3-D FEM for a flawed nozzle, and the results were compared with those calculated by equations and coefficients in the code solution. Our comparison showed that the flat plate model is applicable to nozzle crotch corner flaws rationally and conservatively.