What is RT?

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 method uses the change in absorption of radiation by solid metal and areas of a discontinuity. 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 are available which 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 the trained and certified personnel more limited, than with other NDE methods. An NDT examiner interprets and evaluates the radiographs for differences in absorption and transmission results. Radiographic indications show a different density in comparison 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 about 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. The requirements include:

• Method to determine if backscatter is present.
• Permanent identification, traceable to the component.
• Film selection under SE-1815.
• Different designations for hole or wire-type image quality indicators (penetrameters).
• Suggested radiographic techniques.
• Facilities for viewing radiographs.

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 thickness will be revealed. Standards for industrial radiography require the use of one or more image quality indicators (IQIs) to determine the required sensitivity is achieved. The IQI that was previously known as penetrameter is no longer being used in most codes. To assess sensitivity the required hole or wire as specified by the governing code must be visible on the finished radiograph. Mistakes with IQIs (penetrameters) can have a much greater impact on thinner wall pipe where large root pass imperfections can significantly reduce the strength and integrity of a weld. IQIs (penetrameters) are tools used in industrial radiography to establish the quality level of the radiographic technique