Long-term creep strength and strength reduction factor for welded joints of ASME Grades 91, 92 and 122 type steels

摘要

Creep rupture data of base metal and welded joints of several creep strength enhanced ferritic (CSEF) steels was collected and long-term creep strength of those steels was evaluated by the SHC committee in Japan. The previous allowable tensile stress of those steels regulated in METI Thermal Power Standard Code was reviewed and weld strength reduction factor was investigated. The master creep life equations for not only base metal, but also welded joints were developed. According to the evaluated creep rupture strength, allowable tensile stress of ASME Grade 122 type steels was revised in December 2005 and those of ASME Grade 91 and 92 type steels was revised in August 2007. The creep strength reduction factor obtained from 100,000 hours creep rupture strength of welded joints and base metal was given as a function of temperature.