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Thickness mapping by guided wave tomography

Wall thickness mapping is very important for quantifying corrosion within the petrochemical industry. One approach is guided wave tomography, where Lamb-type waves, which travel at different speeds depending on the thickness due to dispersion, are passed through the region of interest. Wave speed is then reconstructed by a tomographic inversion approach, and is converted to thickness by the known dispersion relationship. Here, the accuracy of three approaches to thickness mapping is evaluated: ray tomography, diffraction tomography, and a hybrid method combining the strengths of each. It is demonstrated that the hybrid method generates the best results, but that there is a fundamental resolution limit of around 2 λ introduced by the thickness to velocity mapping, since the varying velocity map cannot accurately capture the guided wave scattering that occurs from small scale features. To achieve better resolution it is therefore necessary to use inversion models which more accurately capture the guided wave scattering from such features.

Author(s):

Peter Huthwaite    
Imperial College London
United Kingdom