Ultrasonic Inspection of Long Steel Piping Using Lamb Waves

Abstract

An ultrasonic inspection technique using Lamb waves was evaluated to detect and determine the exact location of flaws present in long steel pipes. Since multiple modes of Lamb waves are generated due to their dispersive characteristics in the inspected pipes, the selection of a specific Lamb wave mode is very important for inspection of flaws. Experimental studies of flaw detectability with the use of each Lamb wave mode, namely, the A(0), S-0, A(1), and S-1 modes and their ultrasonic attenuation characteristics were conducted. The experimental results showed that the A(0) mode is the most effective for detection and exact determination of the location flaws. A lucite wedge containing a water column that generates the A(0) Lamb wave mode was developed and used in the present inspection study. It was found that the ultrasonic beam divergence after wrapping around the inspected pipe once interferes with exact determination of the location of flaws and that the maximum reflection signals are obtained when the transducer is offset axially from the straight line with the position of the flaw. The present study showed feasibilities of ultrasonic inspection with the use of Lamb waves for detection of flaws in insulated or inaccessible steel pipes.