Surface crack detection in welded stainless steel canisters using shear horizontal waves

Ultrasonic inspection methodologies for welded stainless steel canisters in spent nuclear fuel dry storage casks are investigated for detection of stress corrosion cracking (SCC) in the heat affected zone (HAZ) of a weld. Shear horizontal (SH) waves having 3D wave motion, which are actuated and received by periodic permanent magnet electromagnetic acoustic transducers (EMATs), are used to detect cracks perpendicular or parallel to the weld line. Due to the limited accessibility to the welds in the stainless steel canister, three different types of sensor layouts amenable to robotic delivery are proposed that use either through-transmission or pulse-echo sensor configuration. A stainless steel welded plate having artificial surface breaking notches near the weld is inspected to demonstrate the performance of the methods. Two dimensional ultrasonic images showing the notch locations are obtained by scanning a pair of EMATs in the direction parallel to the weld line. The feasibility of detecting cracks normal to, and along, the weld line using pulse-echo mode is demonstrated. Thus, robotically delivered SH-wave EMATs will be effective for inspecting the entirety of the weld lines in the stainless steel canister, even in the presence of guide channels.