Recent industrial applications of laser-ultrasonic testing in Toshiba

M Ochiai 

A non-destructive testing system based on a non-contacting and remote laser ultrasonic technique was developed in Toshiba and successfully applied in some industrial practical inspections. Ultrasonic waves generated by intense laser pulse irradiation onto material and detected by another laser coupled with an optical interferometer are used to detect and size the cracks/defects in the material. The first industrial application of laser-ultrasonic testing in Toshiba was the detection of surface-breaking micro-cracks, such as stress corrosion cracking (SCC) on nuclear reactor internals. Newly developed signal processing allows crack depth measurement to be performed with an accuracy of 0.2 mm when the depth exceeds 0.5 mm. A particular laser ultrasonic testing system for inner surface of small diameter tube under water in nuclear reactor was developed and applied to the inspection of industrial light water reactors in Japan. The second application was the detection of weld defects during welding of turbine rotor, having a thickness for inspection of 150 mm. In this application, the higher sensitivity was required to detect defects in such a thick structure using laser-generated bulk waves because the travel distance of ultrasonic waves is long and the defect signal is attenuated. Combining the laser-ultrasonic testing system with the synthetic aperture focusing technique (SAFT), the authors realised detection, visualisation and sizing volumetric defects having a diameter of more than 1.5 mm. In-process volumetric inspection system for welded turbine rotors having a temperature of more than 200°C was established and applied to the practical manufacturing field in Toshiba. Finally, recent activities to improve the laser-ultrasonic testing system in Toshiba will be introduced.