Application of Microwaves for Nondestructive and High-Efficiency Detection of Wall Thinning Locations in a Long-Distance Metal Pipe

Abstract

This research aims to find an efficient and nondestructive way of detecting the locations of the pipe wall thinning (PWT) in a long-distance metal pipe at open-end condition. Time domain measurement of microwave signals is adopted in the method since microwaves can propagate a long distance with low attenuation in the pipe and reflection occurs at the PWT section. To carry out the measurement, a vector network analyzer and a self-designed coaxial-line sensor were used to generate microwave signals propagating in the pipe. By analyzing the time domain response of the signals and extracting the time of flight (TOF) that corresponds to the PWT location, the locations are quantitatively evaluated after the group velocity of the signals propagating in the pipe was calibrated. In order to approach a pipe with different PWT degrees and locations, three brass pipes with an inner diameter of 17.0 mm and lengths of 453 mm, 455 mm, and 2000 mm, respectively, were used in the experiment. In addition, five joints, which have the length of 17.0 mm and inner diameters from 17.10 to 18.20 mm were also used. The arithmetical mean error of the evaluation for PWT locations is found to be less than 1.7 mm, i.e. less than 0.068% of the length of the corresponding pipe. It indicates that a quite efficient and precise method to remotely and quantitatively evaluate PWT locations in a long-distance pipe has been established.