Radiographic Testing (RT or X-ray) is an NDO in which an object is irradiated by means of radiation. This can be used to detect/demonstrate defects in the object. Performed with an X-ray tube or radiographic source, radiographic testing is known as a test method that can reliably detect defects. Within radiography, a distinction is made between the recording/exposure of the X-ray film and the interpretation of the X-ray film.
Before the start of radiographic testing, the surface condition of the object must be uniform in geometry (grooves and sharp transitions can influence the interpretation). No high demands on surface condition are made in order to perform the test properly.
Ionizing radiation is used to carry out the test. This radiation has the characteristic that it can cause ions in the medium it irradiates. It can be generated in an electrical device, such as an X-ray tube. Or it can be obtained by the decay of a radioactive source from an unstable state to a stable one.
In both cases, only the massless energy packets/photons are used for the test.
The radiation will be used to irradiate the object. Through ionisation within the object the radiation will be partially absorbed. Depending on the composition of the object, each section will show a different absorption. These absorption differences will be recorded by means of an X-ray film. The more radiation reaches an X-ray film, the darker it becomes. This is similar to the exposure time of a “normal” photo.
In order to assess the X-ray film, it will first have to be developed by hand or an automatic process. Through the impact of the radiation, the molecular composition within the light-sensitive layer of the X-ray film changes. During the development process this will be converted into a visible black and white image.
The quality of the X-ray film will have to be established by means of the used picture quality indicator. Assessing/Interpreting the captured image is complex, because a 3D object creates a projected 2D image. This obtained image will only consist of black and white and grayscale. Any imperfections in the object will show a different shade of grey (usually darker) in respects to the rest of the object, we call this an indication.
The identified indications are assessed by the inspector according to the required standard and/or specification. The indication shall be assessed in accordance with the required standard, resulting in acceptable or unacceptable.
Volume testing of materials where both surface and internal defects such as cracks, binding errors, insufficient weld fills gas and slag (inclusions) can be demonstrated.
Testing can be applied to all materials, as long as they are not affected by the radiation applied to them, but specifically to the following products:
- Casting parts of more complex geometry;
- Inspection of sandwich/honeycomb constructions in the aerospace industry;
- Inspection of composites in the aerospace industry ;
- Corrosion detection or wall thickness determination of conducts in the aerospace industry;
The inspectors are trained according to EN4179.
Tests may take place in accordance with all applicable standards and requirements of the principals and ASTM-E-1444.