Non-destructive evaluation of corrosion in steel liner plates embedded in concrete using nonlinear ultrasonics

Nuclear containment structures employ a leak-tight steel liner to avoid any unwanted particle release into the exterior environment. The steel liner can be embedded in concrete which creates large continuous areas where the steel plate is in direct contact with surrounding concrete. The impact of the aging of concrete structures due to the presence of structural discontinuities, such as the presence of foreign matter and a delamination gap at the embedded steel-concrete interface, is investigated for small laboratory-scale specimens manufactured with a novel inlay technique by nonlinear ultrasonic evaluation. A Total Damage Index (TDI) which combines several parameters related to acoustic wave distortion into a single damage index to rank the specimens is introduced. The findings in this work indicate that severe corrosion, the presence of foreign matter, and delamination gap in the steel-concrete interface can be detected using nonlinear ultrasonic techniques based on higher-harmonic analysis and modulation intensity using continuous ultrasonic probe excitation and an impactor to modulate the signal. The results obtained using the TDI are consistent with attenuation, a conventional parameter used in corrosion detection.