In the design phase of the components fatigue analysis is conducted considering the ASME Code Section III rules, with the cumulative usage factor based on the stress and number of cycles predicted for all operating events. Considering the implicit safety factors this ensures, in fact, that no crack will nucleate. But the inspection methods performed in the component before it enters in operation may not detect a small flaw such as a flaw below the threshold detection of the technique. Also, despite the fatigue analysis, flaw initiation may result from the cyclic operating loading. In this situation the analysis should be performed under the ASME Code Section XI Appendix A rules (for ferritic components). Attention should be done to the sequence of the cyclic events along the years of plant operation. The fatigue crack growth evaluation in the reactor vessel is compared with the results of a case from the industry. The final crack size should be lower than the critical one as was verified in the problem analyzed.