The other NDT methods are used for detection of defects which are open to the surface nearer to the surface. To detect more deeply seated discontinuities, NDT methods with test medium capable of deeper penetration and system that senses even minute changes in the characteristics, behavior of the test medium is required. Radiographic inspection is one of the most widely used methods of NDT as this is applied to all metals and alloys, both ferrous and nonferrous, for detection of volumetric type of defects. The range of capabilities offered by the variety of sources and equipments has brought radiography to the forefront of NDT techniques.
Testing of multilayer vessels and welds is generally a difficult task due to in accessible inner layers. RT is the only NDT method to evaluate multilayered vessels during manufacturing stages and in-service. Development of micro focal X-ray units has made it possible to extend radiographic practice to meet the requirements of more stringent quality levels demanded for critical applications, besides a host of new applications. It is know that the sensitivity in radiography depends to a large extend on the focal spot size. In micro focal radiography, the focal spot size is less than 100microns and typically 15-50 micron as compared to a few mm or ½ a mm in conventional radiography. Using microfocal RT, intricate geometrical components such as tube to tube sheet. Welds can be tested with a sensitivity of even 1% of wall thickness 0-3mm. microfocal RT can be used for detection of micro cracks of around 25micron in size. Another application of microfocal RT is to check the integrity of micro-welds used electronic integrated circuits.
One of the advantages of RT is that no prior preparation of the surface of the component is necessary. The main disadvantage of the RT is the possible hazards due to exposure to radiation if proper care is not taken.