Radiographic tests are non-destructive tests of components and assemblies that rely on the differential absorption of penetrating radiation, either electromagnetic radiation of very short wavelengths or particle radiation by the test piece or test piece. Due to differences in density and variations in the thickness of the piece, or differences in absorption characteristics caused by the variation in composition, different portions of a test piece absorb different amounts of penetrating radiation. The non-absorbed radiation passing through the piece can be recorded on a photosensitive film or paper, viewed on a fluorescent screen or monitored by various types of electronic radiation detectors.
The term x-ray usually involves an x-ray process that produces a permanent image on film or paper. Although in a broad sense it refers to all forms of radiographic tests. Neutron radiography refers to radiographic tests using a stream of neutrons instead of electromagnetic radiation.
Applications
Industrial X-ray inspection is used to detect features of a component or assembly that exhibit a difference in thickness or physical density compared to the surrounding material. Big differences are easier to detect than small ones. In general, the radiograph can only detect those features which have an appreciable thickness in the direction parallel to the radiation beam. This means that the ability of the process to detect flat discontinuities such as cracks depends on the proper orientation of the test piece during the test. Discontinuities such as voids and inclusions, which have measurable thickness in all directions, can be detected as long as they are not too small relative to the thickness of the section. In general, features exhibiting a difference of 2% or more in absorption compared to the surrounding material can be detected. Radiography is most effective when defects are not planar.
Applicability
Radiographic tests are widely used in foundries and welding. The X-ray is well suited for testing cracked semiconductor devices, broken wires, unalloyed connections, foreign material and stray components. The sensitivity of radiography to various types of defects depends on many factors, including the type of material, the type of failure and the shape of the product. Both ferrous alloys can be plotted by radius, as can non-metallic and composite materials.
Limitations
Compared with other NDT methods, radiography is costly. Relatively large capital costs and fast allocations are required for a radiology laboratory. Field testing of thick sections is a time-consuming process. High activity sources require heavy armor protection for personnel protection. Cracks tightened in thick sections usually can not be detected at all, even when properly oriented. Minimal discontinuities such as inclusions in forged material, flakes, microporosity and microcracks can not be detected unless they are sufficiently secreted to produce a detectable gross effect. The laminations are impossible to detect with the radiography, due to its unfavorable orientation. The laminations do not produce differences of absorption that allow to distinguish laminated areas from areas free of limitation.
It is well known that large doses of x-rays or gamma rays can damage the skin and blood cells, can produce blindness and sterility, and in massive doses can cause serious disability or death. The protection of the personnel, not only of those who perform radiographic works, but also of those who are in the vicinity or of the radiographic tests, is of great importance. Safety requirements impose economic and operational restrictions on the use of radiography for testing.