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Time of Flight Diffraction (ToFD)
Time of Flight Diffraction (ToFD) is an advanced method of Ultrasonic inspection. It is a very sensitive and accurate method for non-destructive testing of discontinuities in welded joints.ToFD ultrasonic test method can perform crack sizing very precisely and allow the owner to run the equipments or plants until the critical crack depth and length is not reached with a minimal risk of failure. Conventional ultrasonic test method employs measuring of the amplitude of reflected signal which is relatively less reliable method of sizing defects because the amplitude strongly depends on the orientation of the crack. ToFD ultrasonic test method uses the time of flight of an ultrasonic pulse to determine the position of a discontinuity of interest.
ToFD ultrasonic test system consists of a pair of probes placed on opposite sides of a weld. One of the probes emits an ultrasonic pulse that is collected by the probe on the other side. In undamaged pipe, the signals picked up by the receiver probe are from two waves, one that travels along the surface and one that reflects off the far wall. These ultrasonic waves are diffracted from the tip of the discontinuities, if present. The size of the discontinuity is calculated by measuring time of flight of the ultrasonic pulse. Compared to conventional ultrasonic testing, ToFD ultrasonic testing instruments and probes are complex and expensive and requires highly trained, skilled and experienced technicians.