Periscope infrared thermography for local wall thinning in tubes

In this paper, a novel way to inspect local wall thinning in metal tubes with infrared thermography has been demonstrated. The first of its kind method utilizes a periscope-like reflector located deep inside a tube to mirror the radiated heat that flows across the tube thickness to an IR camera positioned outside the tube. Localized wall thinning was represented by partially drilled holes of different depths on a tube, of inner diameter 82 mm and outer diameter 91 mm. Feasibility studies were carried out through simulations using a finite element model. Experiments were performed to determine the thermal diffusivity of the material. Remaining thicknesses of the tubes in wall-thinned sections were found to be estimated reasonably well using measured time–temperature profiles obtained by flash method [Parker WJ, Jenkins RJ, Butler CP, Abbott GL. Flash method of determining thermal diffusivity, heat capacity, and thermal conductivity. J Appl Phys 1961;32:1679–84]. The good correlation found between model calculations and measurements vindicated the utility of a model-based approach to applications of pulsed IR thermography.