Evaluation of Ultrasonic Examination Detectability for Cast Austenitic Stainless Steel Weld Flaw

Cast austenitic stainless-steel material is widely used in various industrial fields because it is easy to manufacture complex shapes and has excellent corrosion resistance. They are installed in the reactor coolant system piping, valve body, elbow, flange and safety end in Korea Nuclear Power Plant. However, the signal-to-noise ratio is low due to the scattering and attenuation effects of the ultrasonic beam inside the material, making it difficult to secure the reliability of the inspection. In this study, the round robin test was performed using specimens reflecting the shape of CASS piping and welds, and the detectable length and depth of flaws according to the ultrasonic inspection method were evaluated using a simple linear regression model and a probability of detection model. As a result of the test, the flaw length measurement showed a relatively high correlation in terms of accuracy than the depth measurement. In addition, it was experimently verified that the phased array ultrasonic testing method is capable of detecting flaws of a relatively smaller size than the manual conventional ultrasonic testing method.