Investigation of phased array UT procedure for crack depth sizing on nickel based alloy weld

Recently, it is reported that the primary water stress corrosion cracking (PWSCC) has been occurred at the nickel based alloy weld components such as steam generator safe end weld, reactor vessel safe end weld, and so on, in PWR. Defect detection and sizing is important in order to ensure the reliable operation and life extension of nuclear power plants. In the reactor vessel safe end weld, it was impossible to measure crack depth of PWSCC. The crack was detected in the axial direction of the safe end weld. Furthermore, the crack had some features such as shallow, large aspect ratio (ratio of crack depth and length), sharp geometry of crack tip, and so on. Therefore, development end improvement of defect detection and sizing capabilities for ultrasonic inspection technique have been required. Phased array UT technique was applied to nickel based alloy weld specimen with EDM notches and standard block with SDHs. From the experimental results, performance of phased array linear array probe and dual matrix array probe was investigated. In the basis of the results, UT procedure for crack depth sizing was manufactured. Furthermore, good accuracy of defect depth sizing by phased array UT for the inside inspection was shown. (author)