Ultrasonic Flaw Detection in welds.
Ultrasound is used to check the integrity of full penetration welds. The technique consists of scanning the weld mass and the Heat Affected Zone (HAZ) with ultrasonic beams. These are emitted by an angle probe that is moved manually along the lateral region of the weld.

Ultrasound hitting an air space or an interface with a different material density is reflected back and is shown on a display. The detection and sizing of discontinuities is performed by receiving and evaluating the beam reflected back from the discontinuity surface.

Ultrasonic Flaw Detection in material.
This method uses the high frequency sound waves which pass through materials. A probe sends a sound wave into a test material. There are two indications, one from the initial pulse of the probe and the second due to the back wall echo on the other side of the material.

A defect creates a third indication and simultaneously reduces the amplitude of the back wall indication which is then shown up on the screen.