The purpose of this research is to investigate the effect of fatigue, in the presence of cracks in sigma phased Type 304H stainless steel materials that were analytically tested and to integrate that into a probabilistic physics of failure-based model that could be used to predict crack growth and by extension remaining useful life. Fatigue experiments were performed at different loading conditions on samples of SA-240 Type 304H steel obtained from the failed cracked shell walls of two reactor vessels, metallurgical analysis determined that the material exhibited sigma phase precipitates. The fatigue testing was conducted to generate the data needed for the probabilistic fatigue life prediction model development. A fatigue crack growth rate model will be developed and its parameters including their uncertainties will be estimated. A Bayesian approach will be adopted to perform uncertainty characterization and model validation.