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.