TOFD



How does it work?

Time of Flight Diffration Technique (TOFD) is a sophisticated way of non destructive testing dedicated for welds. It uses two probes arranged symmetrically to the weld joint, facing each other. One of them acts as a transmitter and sends an ultrasonic beam that, for easier understanding, can be divided into 3 signals:

  1. Lateral wave signal, which propagates just under the surface of examined object
  2. Back wall signal, which reflects from the opposite surface of examined object (root of the weld)
  3. Internal signal, that propagates through the volume between 1 & 2. If it encounters a flaw, the diffraction effect on the flaw edges will appear and part of the signal will be reflected in the direction of the second probe – the receiver.

As the sound path of those 3 signals differs, they will be received sequentially at increasing time, that will bring an information about location and sizing of the spotted flaw.

If the weld has no flaws, the second probe will receive signals 1 & 2 as they will hit it “geometrically”. The 3 signal will not appear because it will “miss” the receiver transducer.

If there is an internal flaw, the signal 3 will appear between signals 1 & 2.

If there is a surface crack, there will be lack of signal 1 or 2 depends on which side the flaw is. Additionally, signal 3 will appear and will indicate the end point of the crack.

What can be detected?

All kinds of internal flaws. This technique is extremely accurate in finding the cracks – the most dangerous defects of weld joints.

What can be achieved?

TOFD is one of the quickest and most accurate method of detecting, localizing and evaluating the internal flaws in weld joints. TOFD defect detection does not depend on the defect orientation, in contrast to the conventional UT, or the RT. The inspection results are immediately available, as is a permanent record. TOFD is superseding the X-ray from technical uses of non destructive testing, with Classification Societies admittance.



Polish version
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English version