Classic NDT is more established technique and applied in new construction and to limited extent for inservice inspection. These methods are more skill based and procedures are well defined by standards.
Magnetic particle testing and Penetrant Testing are supportive test to visual inspection with typical application on ferromagnetic materials. MT is accomplished by inducing a magnetic field in a ferromagnetic material and then dusting the surface with iron particles. The surface will produce magnetic poles and distort the magnetic field in such a way that the iron particles are attracted and concentrated making defects on the surface of the material visible.
This supplementary method can be used on ferromagnetic and non-ferromagnetic material too. The dye penetrant testing can be used to locate discontinuities on material surfaces. A highly penetrating dye on the surface will enter discontinuities after a sufficient penetration time, and after removing the excess dye with a developing agent, the defects on the surface will be visible.
This test is a volumetric method and very sensitive in detecting internal flaws. Ultrasonic testing uses high frequency sound energy to conduct examinations and make measurements. Ultrasonic inspection can be used for flaw detection/evaluation, dimensional measurements, material characterization, and more. With present innovations in electronics there are many variants in UT starting with recordable UT, full auto Phased Array UT, Time of Flight Diffraction (TOFD), Long Range UT (LRUT), Short Range UT and many more.
Radiographic testing can be used to detect internal defects in castings, welds or forgings by exposure the construction to x-ray or gamma ray radiation. Defects are detected by differences in radiation absorption in the material as seen on a shadow graph displayed on photographic film or a fluorescent screen. RT technology has also undergone many changes film less and digital images are being used reduce use of chemicals and prevent waste generation. Direct Radiography (DR) provides immediate digital image on computer with shortest exposure time and this is fast catching up.