non destructive services
radiographic testing
Radiographic Testing (RT), or industrial radiography, is a nondestructive testing (NDT) method of inspecting materials for hidden flaws by using the ability of short wavelength electromagnetic radiation to penetrate various materials.
Either an X-ray machine or a radioactive source (Ir-192, Co-60, and Se75) can be used as a source of radiation. At WIS only X-Ray machines, Ir-192 & Se75 are used. Since the amount of radiation emerging from the opposite side of the material can be detected and measured, variations in this amount of radiation are used to determine thickness or composition of material. Penetrating radiations are those restricted to that part of the electromagnetic spectrum of wavelength less than about 10 nanometers.
The beam of radiation must be directed to the middle of the section under examination and must be normal to the material surface at that point, except in special techniques where known defects are best revealed by a different alignment of the beam. The length of weld under examination for each exposure shall be such that the thickness of the material at the diagnostic extremities, measured in the direction of the incident beam, does not exceed the actual thickness at that point by more than 6%. The specimen to be inspected is placed between the source of radiation and the detecting device, usually the film in a light tight holder or cassette, and the radiation is allowed to penetrate the part for the required length of time to be adequately recorded.
The result is a two-dimensional projection of the part onto the film, producing a latent image of varying densities according to the amount of radiation reaching each area. It is known as a radiograph, as distinct from a photograph produced by light. Because film is cumulative in its response (the exposure increasing as it absorbs more radiation), relatively weak radiation can be detected by prolonging the exposure until the film can record an image that will be visible after development. The radiograph is examined as a negative, without printing as a positive as in photography. This is because, in printing, some of the detail is always lost and no useful purpose is served.
Before commencing a radiographic examination, it is always advisable to examine the component with one's own eyes, to eliminate any possible external defects. If the surface of a weld is too irregular, it may be desirable to grind it to obtain a smooth finish, but this is likely to be limited to those cases in which the surface irregularities (which will be visible on the radiograph) may make detecting internal defects difficult.
After this visual examination, the operator will have a clear idea of the possibilities of access to the two faces of the weld, which is important both for the setting up of the equipment and for the choice of the most appropriate technique.
Defects such as laminations and planar cracks are difficult to detect using radiography, which is why penetrants are often used to enhance the contrast in the detection of such defects. Choice of the penetrant is determined by the ease with which it can penetrate the cracks and also with which it can be removed.
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WIS have implemented and are now accredited to the following: EN ISO 9001:2015, EN ISO 14001:2015 and EN ISO 45001:2018.
WIS have attended courses and examinations at QSA-Global in Houston, Texas and now have technicians trained and qualified in Servicing & Maintenance of the QSA-Global equipment. WIS also have technicians trained and qualified in Source Retrieval, this entailed the actual retrieval of a live source, which other companies providing this service do not carry out. WIS intend to roll out these services to NDT Contractors nationwide.