An engineer need some electromagnetic waves to find cracks in the joints of an oil pipline.?

What kind of electromagnetic wave would we use?An engineer need some electromagnetic waves to find cracks in the joints of an oil pipline.?
A process called radiography could be used effectively.





History


Radiography started in 1895 with the discovery of X-rays (later also called R枚ntgen rays after the man who first described their properties in rigorous detail), a type of electromagnetic radiation. Soon after the discovery of X-rays, radioactivity was discovered. By using radioactive sources such as radium, far higher photon energies could be obtained than those which can be obtained from normal X-ray machines. Soon these found various applications, from helping to find shoes that fit, more lasting medical uses and the examination of non-living objects. X-rays and gamma-rays were put to use very early, before the dangers of ionising radiation were discovered. After World War II new isotopes such as Cs-137, iridium-192 and cobalt-60 were made available for use in industrial radiography, hence the use of radium and radon decreased.








[edit] Uses





[edit] Inspection of welds


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.





X-ray sources


A high energy X-ray machine can be used. It is often important to use a high accelerating voltage to provide the electrons with a very high energy. This is because in a braking radiation source the maximum photon energy is determined by the energy of the charged particles. A recent development is the betatron, which is a device similar to a cyclotron that acts as a very intense photon source.





See. http://en.wikipedia.org/wiki/Industrial_鈥?/a>