A Study on Quantitative Thickness Evaluation Using Film Density Variation in Film Radiography

Based on the assumption that film density increases exponentially with exposure in the industrial radiographic film. An equation representing the characteristic curves of industrial radiographic films and a new density-thickness relation are suggested. The accuracy and reliability of the suggested relation has been tested using radiographs of a carbon steel step wedge with known thickness variation by polychromatic X-ray and γ-ray (Ir192). The experimental results were well agreed to the proposed relation in the range of film densities from 1.0 to 3.5 and it was more accurate than the conventional relation. It is also found that γ-ray is more effective in this purpose than polychromatic X-ray, which results in variation of effective linear absorption coefficient due to beam hardening effect as thickness increases. Therefore using the equation and experimentally determined parameters the quantitative evaluation of thickness variation is possible and it can be used to evaluate the depth of local corrosion of pressure vessels in plants