In the ordinary remnant life evaluation of boiler headers or other large-diameter pipes used in high temperature conditions, the damage can be inspected only from their outer surfaces. When a pipe is designed for high pressure conditions, theratio of its inner and outer diameters becomes also high. In that case, it is expected that the outside damage is different from the inside one.Therefore, this research has been carried out to inspect that such evaluation techniques can be applied to higher pressurized plants. Damages on superheater headers of two kinds of aged thermal power plants have been investigated. Internal pressure creeptests using pipe specimens have been also carried out to examine the damage distribution in high damaged state.The significant difference in the damaged state is not observed between the inside and the outside of aged plants. In the high damaged specimens, creep cavities are discovered only on their outside surfaces. These results show the applicability of thesetechniques to the higher pressurized plants.
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