Today the term normally refers to the radiography of components, welds or castings to check their integrity and assure their safety in use.

X-rays have been used for this purpose almost from the time of their discovery in 1896. Equipment became more powerful and flexible and smaller as time went on and the techniques became of vital importance during the Second World War.

Since then, in spite of other, newer methods of inspection now taking over from radiography, the medium is still the best and somtimes the only technique for many applications.