Creep rupture life and design factors for high-strength ferritic steels

Creep-strength enhanced ferritic steels such as Gr.91, Gr.92 and Gr.122 have been introduced for power plant applications recently, and some have experienced creep failure in boiler tubes and thick wall components after several years of operation. In order to use these steels safely in power plants, establishment of creep life prediction and design factors for base metal and weldment is essential. In this paper, creep rupture strengths and lives obtained by means of uniaxial creep testing and internal pressure component testing for the above-mentioned high-strength ferritic steels are presented comparatively. Design life and weld reduction factors are discussed based on the data and on ASME criteria for establishing allowable stresses in the time-dependent temperature region.