Radiographic testing is capable of obtaining an image of internal volumetric discontinuities (in some cases it is possible to detect some advantageously orientated 2D defects). The most frequent use of RT is for examination of welds, castings (also with very complicated shapes), electrotechnical industry, civil engineering, ... Due to tradition and demonstrativeness of the method RT is one of the most important in NDT of the equipment with higher level of the inadvisability (e.g. pressure vessels), in the aerospace and petrochemical industry.

Physical background

During the passing of X-ray through the material radiation is attenuated. This attenuation depends (among others) on the thickness of penetrated material. In case when there is

an advantageously orientated defect in material, the radiation is in space of defect reduced less (or more - in dependence on material) compared to the reduction by base material. Behind the material it is possible to detect an invisible radiation profile of X-ray, which is necessary to convert to a visible picture by a suitable detector. In case of classical (film) radiography it is radiographic film. Each film has its own characteristic curve that determines final image contrast. Practically it is useful (and required by standards) to work in the linear part of the characteristic curve. It means to work with optical densities above D = 2 (up to D = 4). On the other hand characteristic curves of DR, CR and radioscopic systems are linear and therefore there is no limit in optical density. Image contrast changes due to different optical densities and the same difference between intensity of the primary and secondary radiation.