A Method For Measuring Pressure Of Thin-Walled Vessels Based On Surface Wave

Thin-walled vessel is a kind of equipment used widely in modem industry. In order to ensure that the manufacturing process works properly and safely, it is necessary to measure the pressure in vessels. Conventional methods for measuring pressure usually require drilling a hole in the wall of vessels, which not only induces local stress concentration but also brings many safety problems. It is known that the propagation velocity of Rayleigh wave has a relationship with the stress and the temperature of the propagation media. Based on this theory, a correlation model among the propagation time of ultrasonic and the surface temperature and the pressure of vessels was developed; According to this model, a reference method by the circumferential and that axis direction is proposed; The pilot study on surface temperature and pressure of vessel measured simultaneously has been done; The correlative time estimation method based on the Hilbert-Huang Transform is presented and a dual sing-around measurement system was developed. The main research achievements are showed as follows:1. A correlation model among the propagation time of ultrasonic and the surface temperature and the pressure of vessels was developed. The velocity of ultrasonic propagating in the medium is affected by the stresses, temperature, thermo-stress and curvature. The propagation distance of ultrasonic is influenced by strain and thermal deformation. We found the pressure and temperature was the greatest two influencing factors to propagation time and they have the same order of magnitude. Other factors could be omitted. So, the relationship among the propagation time of ultrasonic and the surface temperature and the pressure of vessels was developed.2. A dual sing-around measurement system based on TDC (Time -to-Digital Converter) was developed. The system has simple structure and low price. The system can realize on-line measurement. Moreover, using this system, not only the transit time of surface wave can be measured through sing-around method to improve the precision, but also the transit time difference between two surface waves can be detected. The system meets the requirement of the reference measurement method and the method of the surface temperature and the pressure of vessel measured simultaneously.3. Cross correlation methods based on Hilbert-Huang Transform are applied to improve the accuracy of time delay estimation. Because of the pulse high attenuation and distortion, signal processing method should be used to improve the accuracy of time delay estimation. The HHT's performance in denoising was compared with wavelet transform's performance through experiment and the HHT method was adopted in this paper. Experimental results shows that the denoising result using HHT is a better approximation to the ideal signal than the result using a wavelet transform. Furthermore, HHT has better computing efficiency and improve the precision of pressure measurement.4. A reference method for pressure measurement was proposed. The surface temperature and the pressure of vessel measured simultaneously were studied. To a low and middle pressure vessel which be made of steel, the magnitude orders of the relationship among the propagation time of ultrasonic and the surface temperature and the pressure were analyzed. Based on these analyses, the simplified model could be obtained and the reference method by the circumferential and that axis direction of the vessel was proposed. This method can decrease the time influences. The pilot study on surface temperature and the pressure of vessel measured simultaneously has been done. A water vessel and a air vessel have been chosen as specimen. The experimental results are in agreement with the simplified model. The results also show that the influence of temperature variation and thermo-stress could be decreased by reference method. So the method could gain high accuracy.