RT
is a volumetric examination method used for examining the entire
specimen rather than just the
surface. It is the historical approach to examine completed welds for surface and subsurface
discontinuities. The change in absorption of radiation by solid metal and in areas of a discontinuity is used in this method. The radiation transmitted reacts with the film, a latent image is captured, and when the film is processed (developed) creates a permanent image (radiograph) of the weld. Some methods also use electronics to create a digital image and are referred to as “filmless.” Due to the hazard of radiation, and the licensing requirements, the cost can be higher and at the same time, the number of trained personnel is limited, than with other NDE methods. An NDT examiner interprets and evaluates the radiographs for differences in absorption and transmission results. Radiographic results display is different as compared with the normal background image of the weld or part being inspected. The radiographer also makes sure that the film is exposed by the primary source of the radiation and not backscatter radiation. The NDT examiner that performs the film interpretation, evaluation and reporting should be certified as a minimum to ASNT Level II requirements. However, all personnel performing radiography are required to attend radiation safety training and comply with the applicable regulatory requirements. There are very specific requirements with regard to the quality of the produced radiograph, including the sharpness of the image, the ability to prove adequate film density in the area of interest and sensitivity to the size and type of expected flaws. Requirements listed in Article 2 include:
surface. It is the historical approach to examine completed welds for surface and subsurface
discontinuities. The change in absorption of radiation by solid metal and in areas of a discontinuity is used in this method. The radiation transmitted reacts with the film, a latent image is captured, and when the film is processed (developed) creates a permanent image (radiograph) of the weld. Some methods also use electronics to create a digital image and are referred to as “filmless.” Due to the hazard of radiation, and the licensing requirements, the cost can be higher and at the same time, the number of trained personnel is limited, than with other NDE methods. An NDT examiner interprets and evaluates the radiographs for differences in absorption and transmission results. Radiographic results display is different as compared with the normal background image of the weld or part being inspected. The radiographer also makes sure that the film is exposed by the primary source of the radiation and not backscatter radiation. The NDT examiner that performs the film interpretation, evaluation and reporting should be certified as a minimum to ASNT Level II requirements. However, all personnel performing radiography are required to attend radiation safety training and comply with the applicable regulatory requirements. There are very specific requirements with regard to the quality of the produced radiograph, including the sharpness of the image, the ability to prove adequate film density in the area of interest and sensitivity to the size and type of expected flaws. Requirements listed in Article 2 include:
a.
Method to determine if backscatter is present.
b. Permanent
identification, traceable to the component.
c. Film selection in
accordance with SE-1815.
d. Designations for a hole or wire-type image
quality indicators.
e. Suggested radiographic techniques.
f.
Facilities for viewing radiographs
g. Calibration (certification of
source size).
The exposure and processing of a radiograph are
considered acceptable when it meets the required quality features in
terms of sensitivity and density. These factors are designed to
ensure that imperfections of a dimension relative to section the thickness will be revealed.
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