NDE of Pipe Inner Corrosion With Delayed Echoes of SV Wave Propagated Circumferentially in Liquid-Filled Pipes

A new ultrasonic NDT method is proposed for detecting inner corrosion of pipes with circumferential vertical shear wave, SV wave, propagated within the pipe wall and longitudinal wave propagated in liquid for liquid-filled pipes. When SV wave excited at the outer surface of a pipe impinges the inner surface, a part of the wave energy leaks into the liquid. Longitudinal wave excited there propagates in liquid and reaches other points on the inner surface of the pipe. At there, longitudinal, Rayleigh and SV waves are excited and propagated again within/or along the pipe wall. With angle-beam SV wave transducer, we can detect delayed echoes caused by slow velocity in liquid. Using the simple ray theory, we estimated the propagation paths of the delayed echoes and confirmed them by experiments with a water-filled pipe of partial shielding on the inner surface. The results show that only limited propagation paths exist for given measurement configuration, i.e., geometry of a pipe, incident and receiving angles of the transducers, property of liquid in a pipe. Using this new method, we detected the degree of corrosion on the inner wall of pipes.