ESTIMATION OF LONG-TERM CREEP RUPTURE LIFE OF T91 ALLOY SUPERHEATER TUBE IN THE PRESENCE OF STEAM-SIDE OXIDE SCALES

摘要

Taking into account the effects that steam-side oxidation has on the effective load-bearing thickness and temperature of tube wall, a systematic probabilistic estimation method for the long-term creep rupture life of T91 alloy superheater tube is proposed in this work. The new creep strength assessment results of T91 alloy are utilized. Considering the influence of uncertain factors including the geometry dimensions and operational conditions, instead of usual deterministic methods, probabilistic life estimation is performed. A concept referred to as survival probability which reflects the possibility for the long-term creep rupture life to be longer than a given time is defined, and the effects of initial inner tube diameter, steam temperature and steam flow on the survival probability are analyzed. The results reveal that the increase of initial inner tube diameter or the steam temperature will decrease the survival probability, while the steam flow has an opposite effect. Measures that can be adopted to improve survival probability are also introduced. This work can provide reference for the design of high temperature steam generation components in coal-fired power plants. Besides, it is also expected that this work can guide the determination of metallographic inspection and replacement schedule of these components.