Time Of Flight Diffraction (TOFD)

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  9. Time of Flight Diffraction (TOFD)

Time of flight diffraction (TOFD) inspection is an ultrasonic inspection that can locate and size defects in welds and other components. This method is commonly performed on welds and weld overlays, piping, pressure vessels, clad material, storage tanks, and structural steel. Heavy wall vessels and piping can be thoroughly assessed for fabrication flaws with TOFD.

TOFD can be combined with pulse-echo (angle) techniques to improve data reliability, probability of detection, and accuracy of sizing. The TOFD and pulse echo probes are attached to a scanner simultaneously. Line scans are performed parallel to the weld direction.


  • Verifying compliance with fabrication requirements for piping and vessels in accordance to standards
  • In-service defect monitoring
  • Detecting defects during the manufacturing process


  • High degree of repeatability
  • Position and size data for every flaw can be compared to track flaw growth or corrosion rates; this can be done both generally and for individual pits
  • Not limited by defect orientation
  • Precise defect sizing capability
  • Sensitive to all kinds of defects
  • Portable, battery operated testing device
  • On-line, volumetric inspection
  • Very fast scanning
  • Set-up independent of weld configuration
  • Inspection setup independent of weld joint configuration.
  • Amplitude insensitive, acoustical coupling less critical


  • Weld must be accessible from both sides
  • There is a dead zone for detection near the surface of the material
  • Gathers large volumes of information which takes experienced technicians to interpret