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

5.1: Normal Beam Inspection
Pulse-echo ultrasonic measurements can determine the location of a
discontinuity in a part or structure by accurately measuring the time required
for a short ultrasonic pulse generated by a transducer to travel through a
thickness of material, reflect from the back or the surface of a discontinuity,
and be returned to the transducer. In most applications, this time interval is a
few microseconds or less. The two-way transit time measured is divided by
two to account for the down-and-back travel path and multiplied by the
velocity of sound in the test material. The result is expressed in the wellknown
relationship:
where d is the distance from the surface to the discontinuity in the test piece,
v is the velocity of sound waves in the material, and t is the measured
round-trip transit time.
d = vt/2 or v = 2d/t