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

Despite these drawbacks, ultrasonic thickness measurements are widely
used to determine corrosion rates. To obtain a corrosion rate, a series of
thickness measurements is made over an interval of time, and the metal loss
per unit time is determined from the measurement samples. Hand-held
ultrasonic thickness gages are suitable for these measurements and are
relatively easy to use.
However, depending on the type of transducer used, the ultrasonic thickness
method can overestimate metal thicknesses when the remaining thickness is
under approximately 1.3 mm (0.05 in.). Another corrosion inspection method
consists of monitoring back-surface roughness with ultrasonic techniques.
The following example describes an application of this method in the
monitoring of nuclear waste containers.