With regard to the high pressure(HP) feed water heater of thermal power plant at Tokyo Electric Power Company(TEPCO) sites, inspection of feed water(FW) tubes wall thickness are conducted whenever required such that frequent tube leak occurs. As a standard inspection methodology, FW heater is disassembled during planned outage, tube wall thickness is measured by the ultrasonic pulse techique(UT), then plugs are installed at the both ends of FW tube if its measured wall thickness is found below

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... alculated threshold.However, the root causes of wall thinning of FW tube are various such as erosion and corrosion, based on wall thinning condition, the above threshold is not applied but utilizing the other technically well-grounded evaluation method is sometimes more rational.Therefore, TEPCO classified wall-thinning condition based on inspection data and established technically well-grounded and rational evaluation methodologies of FW tube wall thickness to suite each wall thinning condition. Moreover, with recent improvement of inspection technique, technology enabled faster, larger amount, and more accurate data acquisition, TEPCO has developed the systematized evaluation methodology that can transact data acquisition and evaluation simultaneously.This article introduces the logic of evaluation methods and examined algorithms to make them systematized.