What is the difference between PAUT and TOFD?

Both PAUT (Phased Array Ultrasonic Testing) and TOFD (Time of Flight Diffraction) are forms of ultrasonic testing (UT) that are used by NDT inspection services to evaluate assets for flaws and defects.

Like PAUT, TOFD uses sound waves to detect flaws by measuring the time that it takes for the sound wave to be emitted and returned. However, the difference between PAUT and TOFD is that TOFD measures both high and low amplitude waves. That is, PAUT records only high amplitude waves that are returning from the back of the asset, while TOFD records both high amplitude waves and low amplitude waves that deflect off of the tips of flaws and defects.