Line Laser Scanning Thermography System for Paint Thickness Estimation

Abstract

In this study, a novel paint-thickness visualizing (PTV) system is proposed using a line laser thermography and image processing algorithms for the paint thickness estimation. The prior paint-thickness techniques have a high accuracy for estimating paint-thickness on steel structures, but the
technical hurdles exist for using real structures such as contact type and single point inspection. The proposed PTV system offers advantage of non-contact and non-invasive paint-thickness inspection over the existing techniques. Once the proposed PTV system generates thermal waves on the
steel structure surface using line laser beam scanning, the corresponding thermal responses are measured using an infrared (IR) camera. According to the paint thickness, the thermal wave reflecting phenomena alters at the layer between paint and steel structure and the newly proposed image processing algorithm quantifies the amount of the altered thermal wave reflection with visualizing the paintthickness distribution. The performance of the proposed PTV system was verified through lab scale tests with painted steel structure. Six types of paints which are used for a real steelbox girder bridges were used for the verification and 40 μm of the paint thickness difference was successfully visualized.