Evaluation of Applicability of Noncontact Analysis Methods to Detect Rust Regions in Coated Steel Plates

The applicability of noncontact analysis methods to the detection of rust in coated steel plates used for outdoor equipment has been examined. Reflection intensity measurements from a sample coated with epoxy resin show that optical coherence tomography using near-infrared (IR) light and THz waves can detect the hidden rust region, since near-IR light and THz waves can pass through the coating. This region can be reproduced by so-called THz imaging without contact. In contrast, neither X-ray fluorescence nor Fourier transform infrared spectroscopy can detect the rust, because of the strong X-ray and IR absorption peaks of the coating.