Nondestructive Pressure Measurement in Vessels Using Rayleigh Waves and $L_{\rm CR}$ Waves

Abstract

A new nondestructive pressure-measurement method that can avoid potential safety problems caused by applying traditional pressure-measurement methods in vessels is presented. This method utilizes ultrasonic Rayleigh waves and critically refracted longitudinal waves (L CR waves). The change in pressure induces a change in the stresses in the vessel's wall. According to the acoustoelastic principle, variations in stress affect the wave velocity. Meanwhile, the velocity of ultrasonic waves can also be affected by the change in temperature. Considering the effect of the pressure and temperature of the vessel on both the wave velocity and propagation distance of the ultrasonic waves, the relationship between ultrasonic transit time delay and both the pressure and temperature change is established. Furthermore, a modified model of pressure measurement is deduced. With this model, a reference method for temperature compensation, without temperature measurement, is presented. The reference method utilizes Rayleigh waves and L CR waves. These two kinds of ultrasonic waves travel along the axial direction of the vessel's wall, bearing the same changes in pressure and temperature. The relationship between the reference transit time delay between two ultrasonic transducers and the pressure is established through theoretical analysis and calibration tests on an air vessel. To reduce the error caused by the unevenness of temperature distribution, which might occur in the vessel's and the transducer's material, a new kind of transducer is used in the experiment, which has two piezoelectric elements and can be used for the Rayleigh and L CR waves. A pair of such transducers is mounted along the axial direction of the air vessel. The penetration area of the Rayleigh wave is almost the same as that of the L CR wave with the use of the new transducers. Comparison tests between the new transducers and the custom-used transducers show that the new transducers have better repeatability. Finally, using the air vessel as a specimen, experimental results show that the reference method is effective and that the pressure values calculated using the reference method are close to the manometer-measured values.