Non-destructive evaluation has become an essential part of the quality assurance programs in many manufacturing industries providing information about engineering parameters, material quality, product reliability and safety right from the stage of raw material to fabrication, preservice and in-service inspection. Presently a wide variety of techniques are available.
In the early 20th century NDT started as a qualitative tool. Except for radiography which started as an imaging method practically all the other methods relied on signals and their interpretation. This made interpretations very subjective. Thus till the 1950s and 1960s radiography was the most popular and widely used method. With the advances in sensors instrumentation, information technology and availability of computational and processing techniques in the 1980's and 1990's there has been a paradigm shift. Many of the NDE methods transformed themselves into imaging methods and NDE became quantitative proving to be an aid not only for QA personnel but also designers by providing reliable engineering parameters. NDE methods which have made tremendous advances during the last ten years are radiography, ultrasonics and thermal imaging.