P1H-5 Application of Phased Array Ultrasonic Technique to Straddle Mount Type Low Pressure Turbine

Since the discovery of SCC (stress corrosion cracking) in the blade attachment region of nuclear power plant low pressure steam turbine disks, industry concern with regard to this problem has increased significantly around the world and also in Korea. Reliable ultrasonic inspection methods for the detection of SCC in steam turbine blade attachment area are essential to the rotor run/repair/retire decision making process. The broad beam conventional ultrasonic inspection technique was characterized to have inadequate resolution for flaw sizing and a tendency for false calls. Both of these characteristics necessitated blade removal for flaw confirmation. But the phased array technique by improved detection capability and resolution could decrease blade removal and also increase coverage of the examination areas with less scanning required. Application of phased array ultrasonic technique to straddle mount type low pressure turbine disk and blade in Korean standard nuclear power plant (KSNP) was studied in this paper