We developed a method to evaluate fatigue damage prior to crack initiation in aluminum alloy by measuring cell wall thickness (CWT method) as a result of intensive investigation on how dislocation structure changes during fatigue. The results were presented in LNG12. This CWT method was applied to the heat transfer tubes of a 15 year old ORV, Higashi-Ohgishima Power Plant, Tokyo Electric Power Company. Since the aim of evaluation was satisfied, the results will be presented here. For evaluation, several heat transfer tubes were selected mainly from the both end of panels where thermal stress due to temperature change during operation is known to be high. The samples were taken from the region near weld between these tubes and lower header. Dislocation structure was observed by Transmission Electron Microscopy. When developed cell structure was observed, cell wall thickness (CWT value) was measured. Fatigue damage index for each sample was evaluated by comparing the measured CWT value and the relationship obtained previously in the laboratory between the CWT values and fatigue damage index. It was found that only medium fatigue damage was observed even in the most heavily damaged sample. Further, remaining life was estimated by corn-paring the measured CWT values and how the diameter of the heat transfer tubes has changed with years. As a result, it was concluded that the usage of this ORV is safe for the foreseeing future from the standpoint of fatigue. Since the fatigue damage was generally heavier for the tubes with smaller diameter, it was confirmed that measuring diameter of the tubs is an effective screening method to CWT measurement. Based on these results, it can be concluded that CWT is a useful method to evaluate fatigue damage in actual ORVs.
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