what is radiographic Test.

Radiographic Testing uses X’Ray and Gamma Radiation that penetrates through the part and produces an image on a film. Radiographic inspection is suitable for all types of metal (i.e Stainless, Carbon Steel, Inconel, Duplex , CuNi and other Steel Alloys). However the applicability of radiography for weld inspection depends a great deal upon the weld joint location, joint configuration, and material thickness. Almost any thickness of a weld in flat plate can be radio graphed, but lack of access to a joint may prevent best use of the method. Radiographic testing is commonly used for testing plates and Pipe Butt Welds in process piping, jacket legs and braces, conductors, piles, beam splices, deck plates, etc.

 Radiographic testing can detect the following discontinuities:

1. Surface discontinuities such as under-cut, inadequate joint penetration, and excessive reinforcement & burn-through-all of which may also be detected by the visual inspection

2. Surface discontinuities that would be detected by liquid penetrant and magnetic particle test method.

3. SubSurface discontinuities that cannot be detected by visual, liquid penetrant or magnetic particle methods and may not be detected by the ultrasonic test method. However, radiography is most sensitive to discontinuities aligned with radiation beam while ultrasonic inspection is most sensitive to discontinuities that are at right angles to the sound beam.

Test Limitations

The cost of radiography usually goes up as the joint becomes more complex, and the amount of information that can be obtained becomes more limited. Discontinuities must be more or less aligned with the radiation beam. This is no problem for detection of slag or porosity because these are usually round in cross section and are aligned with a beam from any direction. However, cracks, incomplete fusion and lamination must be aligned with the beam to be detected.

Radiation Hazard

The use of radiography has one aspect not associated with the other non-destructive methods and that is the radiation hazard. Excessive exposure to radiation from an x’ray machine or a radioactive isotope cannot be detected by any human senses (i. e smelling, touching, hearing, tasting) but may cause permanent injury or death. Almost all authorities required that radiographers be licensed or have special training or both. Radiography is, however, a safe operation when conducted in accordance with establishing procedure.

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