Radiography is the most commonly known non-destructive test method. Radiography can be used to obtain a permanent image of the surface and sub-surface (embedded) discontinuities. The same discontinuities can be radiographed again after a period of service life and the radiographs can be compared to measure the change in the size and shape of the discontinuity. There are numerous applications of radiography in engineering applications.
Some of the common uses are the detection of surface and subsurface features of interest in welded parts, castings, forgings, wall thickness measurement, corrosion mapping, detection of blockages inside sealed equipment, detection of reinforcing the material in concrete slabs, measuring bulk density of materials, measuring porosity in concrete, etc. The conventional film radiography is the most sensitive test method. On the contrary, digital or computed radiography have certain advantages over conventional film radiography.
This method of weld testing makes use of X-rays, produced by an X-ray tube, or gamma rays, produced by a radioactive isotope. The basic principle of radiographic inspection of welds is the same as that for medical radiography. Penetrating radiation is passed through a solid object, in this case, a weld rather that part of the human body, onto a photographic film, resulting in an image of the object’s internal structure being deposited on the film. The amount of energy absorbed by the object depends on its thickness and density. Energy not absorbed by the object will cause exposure of the radiographic film. These areas will be dark when the film is developed. Areas of the film exposed to less energy remain lighter. Therefore, areas of the object where the thickness has been changed by discontinuities, such as porosity or cracks, will appear as dark outlines on the film. Inclusions of low density, such as slag, will appear as dark areas on the film while inclusions of high density, such as tungsten, will appear as light areas. All discontinuities are detected by viewing shape and variation in density of the processed film.
Radiographic testing can provide a permanent film record of weld quality that is relatively easy to interpret by trained personnel. This testing method is usually suited to having access to both sides of the welded joint (with the exception of double wall signal image techniques used on some pipework). Although this is a slow and expensive method of nondestructive testing, it is a positive method for detecting porosity, inclusions, cracks, and voids in the interior of welds. It is essential that qualified personnel conduct radiographic interpretation since the false interpretation of radiographs can be expensive and interfere seriously with productivity. There are obvious safety considerations when conducting radiographic testing. X-ray and gamma radiation is invisible to the naked eye and can have serious health and safety implications. Only suitably trained and qualified personnel should practice this type of testing.
At Perceivestar, we manufacture & supply all accessories and consumables associated with Radiography Testing.
Recent Comments