Evaluation of Atmospheric Corrosion on Coated Steel Using $K$ -Band Sweep Frequency Microwave Imaging

This paper investigated a K-band sweep frequency microwave imaging for the evaluation of coated atmospheric corrosion on mild steel. After theory analysis, the experimental system has been built by using a K-band open-ended rectangular waveguide, a vector network analyser, a scanning system, and a signal processing algorithm. Exposed and coated steel samples with different exposure periods (one, six, and ten months) have been prepared by International Paint. The height and roughness of these exposed corrosion samples have been measured by laser profilometry for comparison with microwave results. In experimental studies, the averaged magnitude of sweep frequency microwave signals describing the interaction of microwave signals with a corrosion layer has been used to image and map the corrosion under coating. These results show that the proposed sweep frequency microwave non-destructive testing technique can be used to identify, detect, and evaluate the coated corrosion in different exposure periods without selecting operation frequency, which is a potential solution for remote corrosion evaluation. These results also show that the power function is also suitable for demonstrating the development of short-term stage (in six months) atmospheric corrosion, such as long-term corrosion. With the exposure period increasing, the height of the corrosion layer quickly increases during first six months but has a little decrease at ten months.