Affiliations: [a] Advanced Fusion Reactor Engineering Laboratory,
Department of Quantum Science and Energy Engineering, Graduate School of
Engineering, Tohoku University, Aramaki-Aza-Aoba 6-6-01-2, Aoba-ku, Sendai,
Miyagi, 980-8579, Japan
Abstract: This paper presents a technique using microwaves nondestructive
testing to detect circumferential crack and its location in stainless steels
pipe. This approach is based on the surface current flow in the inner surface
of the test pipe, when electromagnetic (EM) waves are propagating inside the
pipe. Since the conductive pipe is an excellent waveguide, EM-wave can be
propagated inside the pipe above the cutoff frequencies in large distances. To
detect circumferential crack in pipes, a suitable EM-wave mode is generated in
the inspected pipe with crack. For this purpose, a mode-converter is used to
convert rectangular TE_{10}-mode to the circular
TM_{01}-mode. This mode is controlled and resonated by a
moving a plunger mounted in the mode-converter. To show the crack existence
from experimental data, the background signal of a pipe without a crack is
subtracted from that one with a crack. The location of the crack is found by
knowing the time of flight (TOF) of the reflected waves and the group
velocities of the waves in each part of the waveguides used in this study. The
TOFs are obtained through an analysis based on the Inverse Fast Fourier
Transform (IFFT) of the signals in the frequency domain and a method of signal
cancellation. The obtained results show that this NDT method is suitable for
determining of crack locations in large pipes without point-by-point screening
since electromagnetic waves above their cutoff frequencies can propagate in
pipes without significant attenuation loss. Our study is of a fundamental
interest in nuclear power plants and piping systems.
Keywords: Non destructive testing (NDT), electromagnetic waves, time of flight (TOF), inspected pipe, Inverse Fast Fourier Transform (IFFT)
