TOFD detection technology is the conversion of wave form at the tip of discontinuous defect. When it is converted, diffraction wave will be generated. This diffraction wave covers a large angle range, then diffraction wave will detect the existing defects. The over time of recorded signal can measure the height of defects, so defects can be quantified. Defect size is usually defined as diffraction signal The signal amplitude has nothing to do with defect quantification.

TOFD detection technology uses two pulse probes, one for sending and one for receiving, which are symmetrically arranged relative to the weld center line. When the acoustic pulse is transmitted to one end of the receiving probe, the first signal reaches one end of the receiving probe, which is the lateral wave. The lateral wave propagates under the surface of the inspected work-piece. If there is no defect, the second signal to the receiving probe will be the bottom echo. The receiving probe determines the position and height of the defect by receiving the diffraction signal of the defect tip and its time difference.