Time of Flight Diffraction (TOFD) is a reliable method of nondestructive ultrasonic testing (UT) used to look for flaws in welds. TOFD uses the time of flight of an ultrasonic pulse to deduct the defect. It can also be used for assessing the heat-affected zones of other components as well as piping, pressure vessels, clad material, storage tanks, and structural steel.

TOFD uses a pair of ultrasonic transducers emitting sound waves into a component and measuring the time of flight, one as a transmitter and the other as a receiver. The low frequency waves propagate at an angle and diffract back to the receiver on hitting any defect.