It is a non-destructive testing (NDT) method in which beams of high frequency sound waves that are introduced into the material being tested are used to detect surface and sub-surface flaws. The sound waves travel through the materials with some attenuation of energy and are reflected at interfaces. The reflected beam is detected and analyzed to define the presence and location of flaws.
Ultrasonic waves are almost completely reflected at metal gas interfaces. Partial reflection occurs at metal liquid or metal solid interfaces, with the specific percentage of reflected energy depending mainly on the ratios of certain properties of the matter on opposite sides of the interface.
Cracks, laminations, shrinkage, cavities, bursts, flakes, pores, bonding faults and other discontinuities that can act as metal-gas interfaces can be easily detected. Inclusions and other inhomogenities in the metal being inspected can also detected by causing partial reflection or scattering of the ultrasonic waves, or by producing some other detectable effect on the ultrasonic waves.
Ultrasonic testing or inspection (UT) is used for quality control and materials testing in all major industries. This includes Ultrasonic testing of castings, forgings, plates, extruded components, weld joints, electrical and electronic component manufacturing, production of steel, aluminum and titanium, fabrication of structures such as air frames, pressure vessels, ships, bridges, motor vehicles, machinery and jet engines. In service ultrasonic testing for preventive maintenance is used for detecting impending failure of rail road rolling stock axles, press columns, earth-moving equipment, mill rolls, mining equipment and other machines and compo nets. The flaws to be detected include voids, cracks, inclusions, pipe, laminations, bursts and flakes. They may be inherent in the raw materials, may result from fabrication and heat treatment, or may occur in service from fatigue, corrosion or other causes. Ultrasonic testing can also be used to measure thickness of metal sections during manufacturing and maintenance inspections.