Abstract
It is often happened that dovetail of the low-pressure-turbine rotor cracks by stress corrosion crack (SCC) or corrosion fatigue (CF). For purpose of inspection of cracks, we have used ultrasonic testing method (UT) through periodical inspection of the plant. But this usual ultrasonic testing method is not adequate accurate, because this conventional method is affected by scale on the dovetail. Therefore, when the signal is detected by UT, we have to remove blades from a rotor and estimate the signal which is caused by cracks or scale on the dovetail. For this reason, we did research in order to develop ultrasonic testing method which has high accuracy and developed ultrasonic flaw detector equipment. By using this equipment, we can detect a flaw which is 1mm deep without affection of scale and we will have no necessity of removal of blades from a rotor.
