ULTRASONIC INSPECTION OF LONG STEEL PIPES USING LAMB WAVES

An ultrasonic inspection technique using Lamb waves was evaluated to d etect and determine the exact location of flaws present in long steel pipes. Since multiple modes of Lamb waves are generated due to their d ispersive characteristics in the inspected pipes, the selection of a s pecific Lamb wave mode is very important for inspection of flaws. Expe rimental 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 s howed that the A(0) mode is the most effective for detection and exact determination of the location flaws. A lucite wedge containing a wate r column that generates the A(0) Lamb wave mode was developed and used in the present inspection study. It was found that the ultrasonic bea m 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 stu dy showed feasibilities of ultrasonic inspection with the use of Lamb waves for detection of flaws in insulated or inaccessible steel pipes.