Radiation passes through an object and is absorbed to a greater or lesser extent dependent on the thickness and type of material through which it passes thus forming an image which can be collected using either radiographic film or various electronic means.

Radiography can be used to detect defects in steel objects of up to 600 mm in thickness where very high energy radiation sources are used, but the thickness limit for conventional x-ray machines is around 60 mm of steel whilst that for the commonly used gamma ray source is 80 mm of steel.

Radiography is extremely sensitive to volumetric type defects but suffers from a low probability of detection where planar defects such as cracks are encountered. It has a major advantage over ultrasonic testing in that a permanent record is directly produced.