TITLE:
A New Guide Wave Inspection System Using Three Polarized Transverse Wave EMATs without Any Couplant
AUTHORS:
Riichi Murayama
KEYWORDS:
Guide Wave, Transverse Wave, EMAT, Nondestructive Inspection, Pipe
JOURNAL NAME:
Journal of Sensor Technology,
Vol.6 No.4,
October
27,
2016
ABSTRACT: A guide wave is provided with the characteristic of long range propagation in the axis
direction of a pipe, so it is possible to detect many defects over a large pipe area at
once. At present, there is a technique to generate a guide wave using a piezoelectric
element (PZT). However, the transverse wave-transducer using PZT needs to require
a high viscosity couplant because the transverse wave cannot travel into typical liquid
like water or oil. A guide wave inspection system that uses an electromagnetic ultrasonic
transducer (EMAT) which does not require any couplant has then been developed
to solve this trouble. First, a guide wave into a pipe, L, T and F-mode, can be
transmitted and received by a polarized shear horizontal transverse wave propagating
to the thickness direction when the vibration direction has been adjusted to the
best direction. At next stage, the three EMATs for L, T and F-mode with different
polarized vibration directions were piled up to improve the performance at the same
position under the permanent magnet to inspect the pipe at the same condition.
Next, the system with the EMATs can be confirmed to be able to detect three guide
wave modes signal with enough intensity. Finally, the detection performance using
the test pipes with any artificial defects has been done by the developed pipe inspection
system, and any drilled holes and any notches can be detected. It is indicated
that the developed system could be useful in real industrial field.