Source Influence for Focusing Potential of Guided Waves in Hollow Cylinders by Using a Circumferential Phased Array

The phased array focusing technique is being developed with the intent to inspect hundreds of feet of pipeline from a single array position. The single array position is beneficial if access to a pipe is limited, e.g. steam pipes onboard U.S. Naval ships, nuclear power plant pipes, oil and natural gas pipelines. The steam pipes have a protective coating which would ordinarily be removed and replaced for an inspection. From a single array position, ultrasonic guided waves propagate under the coating, down the length of the pipe and return information about potential defects. Focusing the ultrasonic energy at a predetermined location along the length of the pipe enhances the ability to detect defects that current state of the art inspection systems cannot. Focusing is achieved by applying excitation time delays to a multi-channel signal generation system. The excitation sources are equally spaced about the circumference of the pipe. Time delays are calculated using theoretically generated angular displacement profiles in a hollow cylinder. These theoretical displacement profiles are dependent upon excitation source influences. In this paper, the excitation source influence on focusing potential in pipe was studied. Further, focusing potential contour plots for different frequencies and distances from the excitation source were created. Based on the contour plots, sample focusing experiments were carried out.Copyright © 2004 by ASME