A novel method of ultrasonic tomographic imaging of defects in the coating layer by image fusion and binarization techniques

Protective coating materials are applied in a thin layer to the offshore metallic structure against corrosion. Delamination of the coating material is the main limitation and is one of the main issues encountered during operation which leads to localized corrosion. Ultrasonic non-destructive testing methods are widely used for inspection of coating. However, using conventional point-wise bulk wave methods can be time-consuming. In this research work, we implemented an ultrasonic tomographic imaging algorithm to inspect the delaminated zone of the coating materials using Lamb waves. The most sensitive Lamb wave mode was selected considering wave structure. Additionally, image processing techniques such as fusion and binarization were used to eliminate the blurred zones of the ultrasonic tomographic images. As a result of our investigation, the accuracy of the tomographic images was improved by eliminating blurred zones in the tomographic images of the delaminated zones. Graphical abstract