Air has been found to be present in circulating water lines at electric power generating stations. Macroscopic air pockets of interest are on the
order of inches to feet in size and have been found to lie along the top of the pipe. We have developed a technique to detect air pockets using
ultrasonic nondestructive evaluation. Specifically, we use pulse-echo ultrasonic techniques on concrete (the pipe material) and aluminun (as a
reference) samples. A peak-amplitude method is shown to be appropriate for aluminum samples. The same technique could not be used on
concrete because of the relatively thin samples required to overcome the high attenuation in concrete. A plexiglass delay-line and difference
signal are introduced to overcome this problem. The peaks of the difference signals for concrete resulted in a 217% change from water to air
backings. SSP was then investigated as a possible alternative, with a 121% change from water to air backings. At this point, using the peaks
from the difference signal is more reliable and requires far less signal processing.