The Time of Flight Diffraction (TOFD) technique is rapidly gaining importance as a stand-alone inspection technique. Time of Flight Diffraction is an advanced ultrasonic inspection technique that fulfils a need for reliable inspections. It is a powerful technique because it can simultaneously detect and size defects. TOFD inspection employs two longitudinal wave (L-wave) angle beam transducers arranged symmetrically opposite facing each other, straddling the weld or base material under test. One probe acts like a transmitter of ultrasonic energy while the other probe receives the ultrasound energy. Time of Flight Diffraction is now routinely used in a wide range of applications such as inspection of piping and pressure vessels.
A routine TOFD inspection provides the operator with the following information:
Information on the type of defect is limited, similar to both manual and mechanized ultrasonic inspection. This is not necessarily a problem, because from a fracture mechanics point of view, many defects that are normally regarded as volumetric such as slag inclusions, may be sharp enough to be able to act as crack initiators. Also this aspect is compensated to a certain extent by the ability of TOFD to distinguish between “defects without measurable height” and “defects with measurable height”. This, in combination with the high probability of detection (POD) and a low false call rate (FCR), makes Time of Flight Diffraction a valuable tool for routine NDT.
We hold the following TOFD equipment: