Inspection of nuclear assets with limited access using feature guided waves

Resistance Seam Welding (RSW) is frequently used in many industries where low-cost mass manufacturing of gas/fluid-tight seals are required. One particular use case is in the fabrication of canisters to store nuclear material. Given the expected long lifetime and high replacement cost associated with nuclear infrastructure, it is common for an increase in the design life to be sought during operation. This leads to a need to integrate Non-Destructive Testing (NDT) techniques in a complex environment which frequently has accessibility issues. For the inspection of RSW nuclear canisters, one promising solution is to use Feature Guided Waves (FGWs) to rapidly screen the whole circumferential RSW joint from only partial circumferential access to ensure safe storage and targeted repackaging. FGWs can travel long distances while locally confining their energy to a topological feature such as a weld or stiffener. This paper explores such use of FGWs through both theoretical and practical experimental methods. To understand which FGW modes exist in the RSW joint, the Semi-Analytical Finite Element (SAFE) method was used, revealing four suitable wave modes. An anti-symmetric flexural RSW guided mode was down-selected due to its ease of excitation, intense energy concentration around the RSW, low dispersion and attenuation. Three-dimensional Finite Element (FE) simulations were conducted to explore the sensitivity of the flexural FGW to transverse cracks of differing dimensions. Experimental results on simplified and realistic geometries to transverse crack defects of ≥1 mm deep show the efficacy of using this method to efficiently screen nuclear canister RSW joints for such defects in-situ.