UNDERSTANDING ULTRASONIC THICKNESS GAUGES.

A quick, nondestructive method of detecting the presence of corrosion and monitoring its progress in pipes and tanks is to measure wall thicknesses with a portable ultrasonic gage. Accurate readings can be obtained through solid depths ranging from 0. 05 to 12 in. Most metals and some polymeric materials lend themselves to the ultrasonic technique. Two basic types of portable ultrasonic gages are available. The first device operates on the resonance principle; the other uses a pulsed echo technique similar to sonar (sound navigation ranging). Both instruments generate and transmit an ultrasonic signal through the wall of the material being tested. The signal is then reflected from the opposite wall and detected by a transducer. This article discusses types of gages, their operation, and instrument costs.