Nondestructive thickness mapping of corroded plate structures using guided lamb wave propagation

Nondestructive evaluation (NDE) of thickness loss in plate structures is an important monitoring task. A two-step NDE method for rapid and reliable corrosion mapping of plate structures using the Lamb wave propagation is proposed in this study. The analytical model for thickness mapping via the Lamb wave propagation was presented. One strip and one plate specimen with varying thickness profiles were fabricated from steel and then tested. The A</em>0</sub> Lamb wave mode was propagated in the fabricated specimens with an excitation frequency of 60 kHz. The Lamb wave velocity and thus the Lamb wavenumber were first measured experimentally, which were used to estimate the thickness of the specimens for each measurement span from the numerical solution of the presented Lamb wave propagation model. The approximate mean thickness of the specimens within the corrosion zone was estimated in the first measurement step, while the mapping of the thickness profile of the corrosion zone was performed in the second measurement step. The mean thickness and the thickness profile of the corrosion zone estimated from the proposed method were found to be in good agreement with the actual mean thickness and thickness profile for both of the strip and plate specimens. Thus, it was concluded that the proposed Lamb wave propagation method can be utilized as a strong nondestructive evaluation tool for rapid thickness mapping of corroded plate structures.