Ultrasonic testing is one of the most reliable non-destructive testing techniques in Predictive Maintenance. It is based on the propagation of ultrasonic waves in the object or material tested. UT is most commonly used on steel, metals and alloys in general, but can also perform on concrete, wood and composites.

In most common UT applications, very short ultrasonic pulse-waves with center frequencies ranging from 0.1-15 MHz, and occasionally up to 50 MHz, are transmitted into materials to detect internal flaws or to characterize materials. A common example is ultrasonic thickness measurement, which tests the thickness of the test object, for example, to monitor pipework corrosion