Studies Into the Use of Non-linear Ultrasound to Detect Corroded Steel Plates Embedded in Concrete

In some nuclear power plants, the containment liners are embedded in concrete. The purpose of the containment liner is to minimize the risk of radioactive leakage by granting a leak-tight containment building. In the presence of flaws in the surrounding concrete, such as voids, or foreign objects embedded in the concrete, there is a risk that the liner plate might corrode. This could degrade the leak tightness of the containment building, leading to an increased risk of radioactive leakage. A project is being carried out at Lund University whose purpose is to assess the capability of non-linear ultrasound to detect corroded steel plates embedded in concrete. Second harmonic analysis has been used to determine if general corrosion induced an increase in acoustical non-linearity. This was done by inspecting a steel plate with varying grades of corrosion immersed in water. Results from this study indicated that severe corrosion increases the relative parameter of quadratic non-linearity ( Beta’). Beta' is given by the ratio between the second harmonic amplitude and the fundamental amplitude
squared. Building on this result, initial findings from modulation experiments on concrete cylinders with embedded steel plates with varying grades of corrosion are presented.