Radiography is one of the oldest and most widely used methods of non-destructive testing. Radiography uses radiation energy to penetrate solid objects in
order to assess variations in thickness or density that represent cracks or other internal imperfections. The test object is placed between the radiation source and a detector – either film or a digital detector. The thickness and density of the material that x-rays must penetrate affects the amount of radiation reaching the detector. This variation in radiation produces an image on the detector, which can show the internal features of the test object.
Conventional 2D radiography is a 2D shadowgraph of a 3D object, and as such is limited in providing exact depths and locations of the inside features. Computerized Tomography (CT) improves upon conventional 2D radiography by producing 3D cross-sectional images of an object from flat x-ray images. In a CT system, the test component is placed upon a turntable stage that is between the radiation source and an imaging system. The turntable and the imaging system are connected to a computer. The sample is rotated during the examination, and the digital detector registers hundreds of individual cross-sectional x-ray images from all angles, and the computer reconstructs the inner-structural image processing the data into a complete 3D representation. The characteristics of the internal structure of an object including dimensions, shape, defects, and density are readily available from CT images.
Radiography can be used to inspect almost any material for defects, and can also be used to locate internal features, confirm the location of hidden parts in an assembly and to measure thickness of materials. It has been used for decades as a non-destructive inspection technique in a wide variety of industries. It has relatively few limitations or negative considerations. Orientation of the sample to be inspected is key to successful inspection. Radiography is not as effective at detecting flaws that are oriented in a planar direction with respect to the radiation source, and is not effective at detecting delamination. Thick inspection samples are problematic for radiography as the analysis can be extremely time consuming. Finally, radiation can pose health and safety risks not present in other NDT methods.