Size Matching Criterion of High Temperature Waveguide Transducer for Quasi-Fundamental Shear Horizontal Wave

Structural health monitoring is potentially useful to improve the safety of critical pressure equipment serving in high-temperature environments, which is increasingly important in the process industry. A waveguide transducer enables the long-term monitoring of these equipment using reliable ultrasonic technology. For waveguide transducers used in specially engineered projects, the matching mechanism between the piezoelectric wafer and the waveguide unit proves crucial to excite the pure quasi-fundamental shear horizontal (shorten for SH0*) wave. In the present research, the piezoelectric wafer is mounted on the end surface of the waveguide unit, and the matching criterion of the piezoelectric wafer and the waveguide unit is investigated by numerical modeling and experiments. Both experimental and simulation results show that the non-dispersive and pure SH0* wave can be generated successfully when the ratio of the wafer length to the strip width lies within the range of 0.8 to 1 and the piezoelectric wafer width is equal to the waveguide unit thickness. Moreover, waveguide transducers have been designed and applied to measure the thickness of plates in high-temperature environments according to the derived matching criterion. The results show that the transducers can measure the plate thickness with great precision that the measurement error is less than 0.05 mm. This measurement accuracy can satisfy the needs of industrial thickness measurement. Therefore, the reliability of the matching criterion has been verified, which provides a reliable theoretical guideline for the design of waveguide transducers to generate and receive quasi-fundamental shear horizontal waves.

I. Introduction

There exist a large number of pipelines and pressure vessels in petrochemical, nuclear power, and other energy industries, holding high-temperature, high-pressure and corrosive media. If accidents happen to these critical engineering infrastructures, the operators and equipment in the plant would be put in a severely dangerous situation, and the surrounding environment could be polluted seriously as well [1], [2]. During the operation of pressurized equipment, localized wall thickness reduction turns out to be the major cause of accidents [3], [4]. The mechanism of localized wall-thinning could be complex and diverse: flowing accelerated corrosion, hydro-chemical erosion, thermal fatigue, vibration and shock, and interaction with each other can all cause wall-thinning. To ensure the safe operation of high-temperature pressurized equipment, it is necessary to introduce on-line monitoring techniques to evaluate the wall-thinning level in a real-time manner [5], [6].