Research On A Method For Pressure Measurement In Pressure Vessel Using Reflected Longitudinal Wave

Pressure vessels, as special equipment, are widely used in industry. Also pressure vessels as dangerous equipment often cause explosion and fire, killing and injuring many people. To ensure the safety in production and improve the production efficiency, the monitoring of pressure state in the pressure vessel is an important sector. However, traditional methods for pressure measurement generally require drilling holes in the vessel wall, which cause local stress concentration and lead to potential cracks and other safety problems. Therefore, there is an urgent need for non-intrusive pressure measurement in pressure vessels. Research on the new method for non-intrusive pressure measurement based on the ultrasonic wave is the purpose of this thesis. On the basis of previous research, a new method for pressure measurement using reflected longitudinal wave is proposed. Compared with the critically refracted longitudinal wave (LCR wave) that is widely used in the stress measurement field, the reflected longitudinal wave has higher amplitude and signal-to-noise ratio (SNR). Experimental results validate that the pressure measurement method based on the reflected longitudinal wave has higher sensitivity and measurement accuracy compared with the LCR wave. Considering the significant influence of temperature on the ultrasonic pressure measurement, a pressure measurement model with temperature compensation is proposed. The main contents and innovations of this thesis are summarized as follows:(1) The pressure measurement model based on the reflected longitudinal wave is developed. According to the acoustoelastic theory, the change of wave speed with stress is analyzed in detail. According to the shell theory, the relationship between the pressure and the stress inside the vessel wall is obtained. Combining the acoustoelastic theory and the shell theory, the pressure measurement model based on the reflected longitudinal wave is developed.(2) The cross-correlation method based on the FIR digital filter is applied to calculate the travel-time change. The pressure-induced travel-time change is very small, so the accurate measurement of the travel-time change is a key problem for the ultrasonic pressure measurement. The cross-correlation method for time delay estimation only requires that two sets of signals are similar in waveform and has no requirement for the signal amplitude. The cross-correlation method is different from the traditional timing methods that require the voltage triggering and cause the measurement errors when the signal amplitude changes. The FIR digital filter has strict linear phase and ensures that the filtered signals have the same group delay. The experimental results show that the cross-correlation method for time delay measurement based on the FIR digital filter is simple and reliable.(3) Water vessels are chosen as specimens. The experimental results validate the correctness of measurement model based on the reflected longitudinal wave from two aspects of different probe spacing and different pressure vessels. The contrast experiments of pressure measurement based on the reflected longitudinal wave and the LCR wave show that the pressure measurement method based on the reflected longitudinal wave has higher sensitivity and measurement accuracy compared with the LCR wave. Furthermore, the conclusion that pressure-induced travel-time change could be considered independent of the temperature within a wide temperature range is experimental validated and analyzed. On the basis, a measurement model with temperature compensation is proposed. Experimental results show that the temperature influence could be efficiently compensated and the pressure measurement could be made with high accuracy.