| ABSTRACT: | MEASUREMENT AND GENERATION OF TORSIONAL WAVES FOR PIPE DAMAGE
DETECTION BY MEANS OF A NEW OBLIQUELY-ORIENTED MAGNETOSTRICTIVE STRIP
CONFIGURATION
Y.Y. Kim, C.I. Park, S.W. Han, and S.H. Cho
Seoul National University, Seoul, South Korea.
The objective of this investigation is to develop an efficient method to generate and measure torsional waves
in non-ferromagnetic pipes by using magnetostrictive transducers. In the conventional method to generate
torsional waves in pipes, a nickel strip is bonded circumferentially to the test specimen and pre-magnetized
along the circumferential direction by permanent magnets. Then, the application of the alternating current
onto the solenoid coils encompassing generates tensile waves at some angle relative to the pipe axis. If the
applied current is appropriate, the generated tensile wave is converted into the desired torsional waves.
Though this method is very useful, it has some disadvantages. Among others, it requires the pre-
magnetization of the strip, which is not desirable for long-term on-line inspection. To overcome this
problem, we propose a new strip configuration; several pieces of nickel strips are bonded at 45 degrees with
respect to the pipe axis. Because the strip is so oriented that the applied current onto the surrounding
solenoid coils can generate torsional waves without the pre-magnetization of the nickel strips. The validity
of the proposed transducer configuration as well as its good performance is verified through a series of
experiments.
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