For operating components in nuclear power plant, in-service inspections (ISI) are carried out periodically and ASME Code Section XI provides some guidelines for the ISI. A detected flaw that exceeds the size of allowable flaws in components may be evaluation by analytical procedures such as ASME Code Section XI Appendix A. Flaw evaluation is important for structural integrity of nuclear power plant components. For analytical evaluations, the Appendix A provides methods of calculating crack tip stress intensity factors for flaws. Recently, there have been some changes in stress intensity factor calculation methods. This study reviews the recent changes in the methods to calculate stress intensity factors.