Nonlinear ultrasonic characteristics of a corroded steel plate

Corrosion in leak-tight plate structures, such as the containment liner in Nuclear Power Plants ( NPPs), is detrimental to their operational state. To tackle this issue, the present work aims to assess the feasibility of using nonlinear ultrasound to detect corrosion. The corrosion product of main concern in the present study contains several microscopic and macroscopic cracks and delaminations. Three parameters based on nonlinear acoustics were studied by using two types of measurements on a uniformly corroded steel plate. The relative parameter of quadratic nonlinearity (ss(1)), given by the ratio between the second harmonic amplitude and the fundamental amplitude squared, was measured using indexed measurements with a pitch-catch setup while the specimen was immersed in water. The sideband peak count ( SPC), which is a measure of the number of sidebands generated from a wide band excitation, was extracted from through- transmission measurements. The third parameter studied is a measure of the energy distributed in the sidebands over the energy at the excitation frequencies (alpha). This parameter is determined for the same datasets used for SPC. All three parameters increased in the severely corroded region of the inspected steel plate, indicating the potential use of nonlinear ultrasonics to detect corrosion.