Residual life techniques for plant life extension

According to industry estimates, by the year 1990, 15% of the total capacity and 75% of the reserve capacity of the electric power in the U.S.A. will be supplied by units which are over 30 years old. Under current procedures for life assessment, which embody severely conservative assumptions, a large number of the boilers will probably be retired at the end of the 30 years. Development of more accurate life assessment procedures may enable extension of their life by 20-30 years and result in an improvement of their availability by at least 1%. The effects of environment, stress state and cyclic operation on creep damage need to be considered. The validity of the life fraction rule for life assessment needs to be verified. For heavy section components, creep crack growth data should be generated for typical boiler steels, and generalized methodologies which rationalize crack growth in terms of readily measurable parameters must be developed. Research projects directed by the Electric Power Research Institute have made significant advances in a number of these areas. This paper is a progress report of the results from the various projects relating to boiler pressure parts operating in the creep regime.