Time-of-flight-diffraction Technique (TOFD) is considered as one of the fastest methods and high performance technique of Non-destructive testing (NDT) since a weld can be characterized to a certain degree with one single scan along its length with two probes.

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It is an improved version of the conventional ultrasonic testing method which provides a fully computerized system able to scan, store, and evaluate indicators in terms of height, length, and position. There is no other method currently available with similar grade of coverage, precision and speed.

The basic principle of TOFD:

  • An ultrasonic probe is positioned on either side of the weld, one acting as a transmitter and the other a receiver.
  • The longitudinal sound beam can encounter obstacles on its path, which cause reflected and diffracted signals.
  • When the probes are moved in a parallel motion along the weld, the resultant waveforms are digitized, stored on hard disk and displayed on the video-screen as a grey scale image.
  • The image build up is in effect a through sectional view of the weld examined and can be used for accurate sizing and monitoring of indications.