Analysis of painted steel by a hand-held X-ray fluorescence spectrometer

Steel with a paint layer was analyzed with a hand-held X-ray fluorescence spectrometer. When the 0.5 mm thick paint layer was composed mainly of light elements, alloying elements in steel such as Fe, Cr, Ni, W, and Mo were easily detected. 0.2% Mo in steel was detectable even if the paint contained Ti or Fe as a main element. The signal intensity of each element in steel decreased exponentially when the paint thickness increased, and the degree of decrease depended on the X-ray energy. Therefore the peak intensity for non-painted steel could be calculated from the paint thickness. The paint thickness was estimated from the intensity ratio Fe Kβ/Kα or W Lβ/Lα. When a paint of Ti (0.07–0.49 mm thick) was used, the peak intensities of the Fe Kα, Cr Kα, Ni Kα, and Mo Kα lines for non-painted steel were estimated by using the intensity ratio Fe Kβ/Kα, with errors of less than 30%. The content of each element in steel is estimated when the fluorescent X-rays are detectable by analysis of painted steel without removing the paint layer. On-site screening of painted steel can be performed on the basis of the alloy composition estimated by analysis with a hand-held XRF spectrometer.