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 find the location of a reflector. It can also be used for weld overlays and the heat affected zones of other components as well such as piping, pressure vessels, clad material, storage tanks, and structural steel.
Like most UT methods, TOFD works by emitting sound waves into a component and measuring the time from them to return. What makes TOFD different from other UT methods is that, rather than measuring only for the high amplitude sound waves that reflects off of the back of the component, it instead measures the response time of low amplitude waves that are diffracted by the tips of cracks.