Ultrasonic Testing (UT)

What is Ultrasonic Testing?

Ultrasonic testing using the pulse-echo method can be simply described as a type of material radar. A short pulse of very high-frequency mechanical vibrations is transmitted into the material. These vibrations are of the same nature as sound waves but are inaudible, hence they are called ultrasonic vibrations.

The pulses propagate through the material in a relatively narrow beam until they reach an interface, such as the opposite surface of the test object or an internal defect. From there, they are completely or partially reflected back to the transmitter, which now acts as a receiver. The time between transmitting a pulse depends on the distance traveled, as the propagation speed is constant for a given material type.

If a pulse is sent perpendicularly through a plate and the transit time is measured, the plate thickness can be calculated. Ultrasonic thickness gauges operate based on this principle.

If you want to locate internal defects in a test piece, you must know both the traveled distance and the point from which the ultrasonic pulse originates, as well as the direction it has traveled. Larger defects are mapped by moving the transducer, which emits and receives the ultrasonic pulses, across the surface of the object.