Ultrasonic testing is a volumetric nondestructive technique. It is based on sound waves propagation into the product to be tested and on the related analysis and interpretation of the signals reflected or diffracted by the presence of internal defects. An ultrasound probe connected to the test equipment transmits short pulses of high-frequency sound waves into the item being inspected while passing over its surface by the mean of a couplant. Discontinuities and other defects cause some of the energy to be reflected according to the laws regulating the waves propagation. Sound pulses are viewed on a screen and technicians evaluate them to determine the presence and kind of the defects. Ultrasonic testing is also used to measure the residual thickness of industrial equipment, like boilers, piping and tanks.