CREEP DAMAGE EVALUATION BY INTRA-GRANULAR DISTORTION ANALYSIS

A method of determining the deformation amount by examining the distor tion of grains in transmission electron microscope (TEM) called IGD (I ntra-granular Distortion) analysis was developed. In this paper, we qu antitatively evaluated creep and tensile strain by the shift vector of Kikuchi pattern. Good correlations between average distortion in grai ns and macro deformation amount were obtained for two heats of 2.25Cr- 1Mo steel after tensile and creep deformation. Based on the results, t he creep damage of a 2.25Cr-1Mo heat exchanger tube, used for 220 000 hours of service in a fossil power plant, was assessed. Creep strain o f the heat exchangeer tube was estimated to be 2% by IGD analysis, whi ch corresponded to life consumption of 70%, reasonable for the materia l used for 220 000 hours in service.