Radiography

Radiography (RT)

Many different techniques requiring a high level of technical skill are associated with this method of Nondestructive testing.

In Industry RT is used to reveal sub-surface flaws in materials and evaluate such things as weld quality, wall thickness of piping, etc. Technicians must be state licensed, skilled at safely producing high quality radiographs and experienced at radiographic interpretation.

A typical field technique for RT involves the use of penetrating X-Ray or Gamma ray radiation to expose radiographic film. Radiation is directed through a part and onto special film containing a radiation sensitive silver halide or other media leaving a latent image on the film. This image is then converted into a visible image by film processing. The resulting film negative shows the internal features and soundness of the part. Material thickness and density changes are indicated as lighter or darker areas on the film.

Interpretation of radiographs takes place in three basic steps which are detection, interpretation, and evaluation. All of these steps make use of the radiographer's visual acuity and depend on the technicians experience level and knowledge of the discontinuities associated with specific industries and components.

Image quality is determined by a combination of variables such as exposure time, distance from the source to the film, film type and material thickness. A good radiograph show lots of detail. Quality is described in terms of radiographic contrast (the degree of density difference between adjacent areas on a radiograph) and definition (the abruptness of change in going from one density to another)

Image quality indicators(IQI) are used to provide a means of visually informing the film interpreter of the contrast sensitivity and definition of the radiograph. The IQI indicates that a specified amount of material thickness change will be detectable in the radiograph, and that the radiograph has a certain level of definition.