Probabilistic fracture mechanics analysis on a pipe with cracks under cyclic thermal loading

The integrity of piping system is a technically important issue for the safety of nuclear power plants, and the fatigue induced by cyclic dynamic loading plays a role in the assessment of the service time of down periods of the plant. The cyclic loading fatigue that occurs at pipes is one of the topics that should be addressed for the life management of light water reactor. In this study, a feed water nozzle of a steam generator was analyzed with postulated cracks under thermo-mechanical cyclic loading. The fatigue crack propagation in the complex geometry was estimated by using the J-integral vector theory, which was verified with numerical calculations for the investigated structure. The J-integrals for several cracks with different size were selected as interpolation points and the J-integral of cracks during fatigue propagation was calculated using mathematical interpolation. Considering uncertainties in the material properties and geometry parameters, the crack growth and probabilistic analysis methodology is practicable for a quantitative determination of failure probabilities based on fatigue crack propagation. (authors)