The optical density histogram behavior of the photogrammetry of the welding line in the radiography of steel with gamma ray

This paper tries to find a suitable probability distribution function for the optical density of the welding lines in the radiographic films. For this purpose, real gamma ray radiography films of the oil and gas pipelines were used in the operational areas of the National Oil Company. The number of the radiographic films was 4 and due to the unpredictability of the radiographic conditions and the existence of different regions on the surface of the films, histogram curves of the scattered data were selected to this investigation. More than 36 probability distribution functions were fitted on the histograms. 11 fitted probability functions with R-sq.≥0.95 were selected among the total functions. In addition, the final selected functions were fitted to 4 internal concavity (Suk Back) defects. Based on our obtained results, the best function was Pearson IV. Although a Gaussian function was also fitted and behaved quite well, but it was found that it is not perfect.