Why Radiographic examination and how it is performed ?

Radiographic examination is often employed to measure tube wall thickness and identify the presence and thickness of internal coke deposits. Radiography can show a variation in thickness of a minimum of 2% of total thickness. Thickness is determined by directing the rays tangentially to the tube wall and recording the radiation on a film behind the tube. By comparing with some geometric standard projected on the film, the wall thickness can be determined. Performing radiography at various angles to the tube will allow wall thickness measurements in other planes. Additionally, localized thin areas can often be identified by radiography that could be missed by other techniques, like spot ultrasonic readings. For example, radiography is often employed to identify wall loss on return bends in erosive service.