A study on assessment of creep life fraction for in-service high-temperature components

摘要

The grain boundary etching method for assessment of material degradation has received much attention because it is simple, inexpensive and easy to apply to in-service high-temperature components. Effectiveness of the method is verified in this paper by successful application of in-service components of aged fossil power plants, such as super-heater and reheater headers in this paper. A degradation parameter is employed by intersecting a point ratio. The intersecting point rati (N_i /N_0) is defined as the ratio of intersecting point (N_j) obtained from 5-minute picric acid etched surface to the point (N_0) obtained from a nital etched surface. Material degradation for in-service high-temperature components is estimated by an aging Larson-Miller parameter, aging LMP = T (20 + log t_r), which is calculated from aging temperature and aging time. The creep test is performed to characterize the correlation between intersecting point ratio and life fraction of serviced material. It confirms the possibility to apply the grain boundary etching method to creep life assessment of in-service high-temperature components.