Time of Flight Diffraction (TOFD)


Time of Flight Diffraction (TOFD) is an ultrasonic NDE method used to examine welds, along with the heat affected zones in piping, pressure vessels, storage tanks, and structural steel.

The process makes use of a pair of ultrasonic probes, a transmitter, and a receiver, on each side of the area of interest. The transmitter emits an ultrasonic pulse which is then caught by the receiver on the opposite side; the quality of the received signal will differ depending on the status of the component. In an undamaged component the pulse will have split into two waves, a lateral wave that travels along the surface, and one known as a back wall reflection which, unsurprisingly, reflects off the back wall. In a component that has a crack on the other hand the wave becomes diffracted from the top and bottom edges of the crack. By measuring the time of flight of the pulse, the depth of the crack edges can be calculated using trigonometry.

TOFD inspection has several advantages that make it a worthwhile procedure to use. It has a high degree of repeatability and the growth of cracks can be tracked over time using multiple scans. It is especially sensitive to mid-wall flaws that may be missed by reflection based ultrasonics. It is one of the fastest NDE methods available and is able to detect many different types of damage with an incredible degree of accuracy.

Hi-Tech Testing has a dedicated staff of experts that are proficient in TOFD inspection, as well as the equipment to get the job done. Contact us to learn more about TOFD or to learn how Hi-Tech Testing’s experts can assist you. 

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