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.
Highlights
For the L-mode guide wave, the polarized electromagnetic ultrasonic transducer (EMAT), whose polarized direction is parallel to the axis direction, are placed on the surface of a pipe with the same interval in the circumferential direction of the pipe
For the T-mode guide wave, pieces of polarized EMATs, whose polarized direction is vertical to the axis direction, is placed on the surface of a pipe with the same interval to the circumferential direction
For the F-mode guide wave, the polarized EMAT, whose polarized direction is inclined in the axis direction, is placed on the surface of a pipe with the same interval in the circumferential direction
Summary
Murayama a heat exchanger such as a power plant Such pipes sometimes break in due to the corrosion or other damages during long range use. The guide wave propagates along the axis direction of a pipe without attenuation of the ultrasonic power. The guide wave inspection system using a polarized transverse wave with a PZT type transducer has already been developed and used in an application field. Such an ultrasonic sensor requires a couplant with a high viscosity. The inspection system, which can transmit and receive the guided wave using the electromagnetic ultrasonic acoustic wave transducer (EMAT) that injects the polarized traverse waves in the pipe thickness direction, was developed. We decided to develop a new pipe inspection system that can alternately use the 3 modes
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