Radiographic testing is a non-destructive testing of components and assemblies that is based on differential absorption of penetrating radiation- either electromagnetic radiation of very short wave-lengths or particulate radiation by the part or test piece being tested. Because of differences in density and variations in thickness of the part, or differences in absorption characteristics caused by variation in composition, different portions of a test piece absorb different amounts of penetrating radiation. Unabsorbed radiation passing through the part can be recorded on film or photosensitive paper, viewed on a florescent screen or monitored by various types of electronic radiation detectors.
The term radiography testing usually implies a radiographic process that produces a permanent image on film or paper. Although in a broad sense it refers to all forms of radiographic testing. Neutron radiography refers to radiographic testing using a stream of neutrons rather than electromagnetic radiation.
Uses
Industrial Radiography inspection is used to detect features of a component or assembly that exhibit a difference in thickness or physical density as compared to surrounding material. Large differences are more easily detected than small ones. In general, radiography can detect only those features that have an appreciable thickness in direction parallel to the radiation beam. This means that the ability of the process to detect planar discontinuities such as cracks depends on proper orientation of the test piece during testing. Discontinuities such as voids and inclusions, which have measurable thickness in all directions, can be detected as long as they are not too small in relation to section thickness. In general, features that exhibit a 2% or more difference in absorption compared to the surrounding material can be detected. Radiography is more effective when the flaws are not planar.
Applicability
Radiographic testing is used extensively on castings and weldments. Radiography is well suited to the testing of semiconductor devices for cracks, broken wires, unsoldered connections, foreign material and misplaced components. Sensitivity of radiography to various types of flaws depends on many factors, including type of material, type of flaw and product form. Both ferrous alloys can be radio graphed, as can non-metallic materials and composites.