Scanning inductive pulse phase thermography with changing scanning speed for non-destructive testing

This work aims at non-destructive detection of surface and subsurface defects in metallic specimens (e.g. railway track components) via pulsed inductive thermography in a moving setup. A new approach for scanning with changing speed has been developed to enable manual scanning of components in track. A steel specimen is heated with an inductor, and the surface temperature, including its variation over time, is recorded with an infrared camera. The infrared sequence is evaluated by Fourier transform to phase image, in order to increase the image quality. The proposed method uses a referencing object with AprilTags visible in each frame, allowing an adjustment by image registration. Changes in velocity during the scanning process are possible, as demonstrated by a manually performed scan of the specimen and the corresponding evaluation. Results obtained with different infrared cameras and scanning speeds were condensed into an estimation of the maximum scanning speed for a given camera specification.