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ToFD for Small Diameter Tube and Pipe Inspection

Wed, 26 August, 2020

The major advantages of Time of Flight Diffraction (ToFD) inspections are sizing accuracy in terms of height measurement and ease of determining real defects from geometric indications. This is due to a highly damped probe, as used in ToFD inspections, that provides a wide range of frequencies for better sensitivity and resolution.

ToFD transducers are positioned on each side of the weld in respect to PCS as per thickness and the refracted angle being used. The transmitter sends the ultrasonic signal into the material and a receiver receives reflected and diffracted ultrasound from discontinuities and geometric reflectors.

These ToFD transducers are small in physical size, so provide a wide area of coverage due to the wide beam spread in the inspection material. When the ultrasound signal comes in contact with the tip of a flaw or crack, diffracted energy is emanated in 360°. Measuring the time of flight of the diffracted beams enables accurate and reliable flaw detection and sizing, even if the crack is not oriented to the initial beam direction.

Typically used as an NDT method for inspecting small bore piping and tubular joints, ToFD provides better detection and sizing of volume indications in comparison with other ultrasonic based inspection techniques, as well as offering fast scanning for a prompt interpretation result when compared with RT-based techniques.

The current development of ToFD with improved probe characteristics, including a high frequency (15 MHz) and high refracted angle wedge (80°) enables further capabilities for the inspection of small bore pipes and tubes. The ToFD A-scan and B-scan image (below) shows how the ToFD can determine volume indications in a precise manner with respect to sizing and measurements.

The cobra scanner with ToFD technology provides a cost-effective, efficient, and reliable testing method capable of meeting the challenges associated with inspecting small diameter tubes and pipes.

TWI India offer level 2 training and CSWIP examination in Time of Flight Diffraction (ToFD) - Welds.


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