As the operation time of a power plant increases, the degradation and the cracks inside of the structure exposed to high temperature will increase gradually. Therefore, degradation rate, crack growth rate and fracture life of the structure can be evaluated according to the level of degradation and the growth of crack length. We performed creep rupture test and crack growth test with stress and temperature changes to evaluate the degradation rate, crack growth rate and fracture life. Degradation rate was evaluated using micro-cavities. The area fraction of the cavities increased with the increasing temperature and life fraction (t/t_f). da/dt, the crack growth rate against C_t estimated from the relationship between load line displacement rate and cavity increase rate, was in good agreement with the result of da/dt vs C_t acquired from the test. It shows that the creep crack growth rate can be evaluated by the increase of cavity area fraction. It was also found that the predicted life calculated with the cavity growth rate was in good agreement with experimental results.
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