Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

TOFD provides a wide area of coverage with a single beam by exploiting
ultrasonic beam spread theory inside the wedge and the inspected material.
When the beam comes in contact with the tip of a flaw, or crack, diffracted
energy is cast in all directions. Measuring the time of flight of the diffracted
beams enables accurate and reliable flaw detection and sizing, even if the
crack is off-oriented to the initial beam direction.
During typical TOFD inspections, A-scans are collected and used to create B-
scan (side view) images of the weld. Analysis is done on the acquisition unit
or in post-analysis software, positioning cursors to measure the length and
through-wall height of flaws.
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Tip Diffraction
Off-oriented to the initial beam direction
Time of Flight
A-scan / B-scan
Post analysis software