Creep damage simulation test and creep life assessment system for elevated temperature plant components.

Abstract

The creep damage experienced under the actual operating conditions, in many cases, occurs and progresses without observable strain. In order to reproduce such creep damage experienced in actual components of power plants a creep damage simulation test was developed. In this creep damage simulation test, large diameter and thick walled 21/4Cr-1Mo steel pipe was tightly fitted and constrained by the austenitic 18Cr-8Ni steel pipes with greater thermal expansion at the outside and inside diameter of tested 21/4Cr-1Mo steel pipe and subjected to thermal cycles of heating at 600°C and cooling down to 20°C.Resultantly, progress of creep damage such as generation of creep voids, their linking and occurrence of cracks were observed with the increase of cycles in the tempered martensite structure of heat affected zone but not in the ferrite and peartite structure of base metal. These observation results clarified the relationship between the progresses of creep damage and the creep life consumption rate and suggested that it was needed to distinguish between the heat affected zone of creep-brittle material and base metal of creep-ductile material in the creep damage analysis and life assessment of CrMo steel such as 21/4Cr-1Mo steel. Finally a creep life assessment system based on those findings was proposed and operating procedures of the system were indicated with its practical applicability.