Creep Strength Assessment and Review of Allowable Tensile Stress of Creep Strength Enhanced Ferritic Steels in Japan

A committee at Japan Power Engineering and Inspection Corporation was organized to evaluate long-term creep strength and to review current allowable tensile stress of creep strength enhanced ferritic steels. In FY2005, allowable tensile stresses of KA-STPA29 type steels (ASME Gr.92), KA-STPA24J1 type steels (ASME Gr.23) and KA-SUS410J2TB steel regulated in METI (Ministry of Economy, Trade and Industry) Thermal Power Standard Code has been reviewed. Creep rupture data of those materials have been analyzed by means of region splitting method in a similar way to that applied for a previous review on a modified 9Cr-1Mo steel (ASME Gr.91) and KA-SUS410J3 type steels (ASME Gr.122). It has been concluded that the allowable tensile stresses in a creep regime of KA-STPA29 type steels and KA-SUS410J2TB steel should be revised to the lower values.