Time of Flight Diffraction

Advanced Inspection for Critical Asset Integrity

TOFD offers a reliable and efficient method of weld testing and defect sizing. A valuable complement to PAUT, TOFD is ideal for both pipeline integrity inspections and infrastructure inspections, delivering high accuracy and repeatability in assessing material and weld conditions.

The Time of Flight Diffraction (TOFD) method uses a pair of angle-beam L-wave ultrasonic probes that are used in a pitch-catch configuration with the sound beam passing through the area of interest. A transmitter probe emits an ultrasonic pulse which is picked up by the receiver probe on the opposite side.

In an undamaged part, the signals picked up by the receiver probe are the result of multiple different wave energies that were generated by the transmitted beam: one that travels along the surface (lateral wave) and another L-wave that reflects off the inside surface (back-wall reflection), and one S-wave that reflects off the inside surface. When a discontinuity such as a crack is present, there is a diffraction of the ultrasonic sound wave from the top and bottom tips of the crack.

Using the measured time of flight of the transmitted and diffracted energy responses, the height and depth of the flaw can be calculated.