Daqing Oilfield ground facilities and equipment pressure valve due to wear and tear, corrosion or other reasons, there have been internal leakage. Due to the leakage is difficult to find, part of the fault valve has not been promptly replaced, affecting the production and the existence of security risks. Therefore, on-line valve detection technology has drawn more and more attention. At present, the core technology is the use of acoustic emission technology to detect the leakage of various valves in the petroleum, petrochemical and power plant industries online. 1 acoustic emission leak detection of the basic principles (1) acoustic emission signal and its characterization parameters Any metal materials, components under the action of external force or internal friction, cracking or plastic deformation, the elastic wave in the form of the release of the phenomenon of strain energy, Called acoustic emission. When an AE wave propagates in a finite medium, it encounters reflections and reflections at the interface and transforms from surface to surface at a very high velocity. These acoustic emission waves from acoustic emission sources (ie, points of failure) have source characteristic information, which can be used to reflect component failures and defects. The parameters characterizing the acoustic emission signal are acoustic emission rate, amplitude and amplitude distribution, and energy. (2) the characteristics of the acoustic emission signal when the valve leak occurs When the tightness of the valve is poor, there will always be a small amount of fluid injected through the valve gap, resulting in high-speed jet, the high-speed fluid on the wall to stimulate the elastic wave , That is, acoustic emission. It belongs to continuous acoustic emission signal, similar to white noise, the frequency of 30 ~ 50kHz. The characteristics of the acoustic emission signal generated when the valve is leaking are as follows: 1. The acoustic emission excited by the leakage is continuous; 2. The acoustic emission signal generated by the leakage is strong and its amplitude is proportional to the leakage rate and the root mean square The value is proportional. According to the characteristics of acoustic emission signals generated by the leakage, the parameters of acoustic emission and energy are used as the characterization parameters. It can obtain richer acoustic emission signal data and provide more sufficient evidences for fault identification. 2 ultrasonic detector on-site application (1) Detector Introduction When the leakage of acoustic emission waves transmitted to the sensor, the acoustic emission wave from the sensor into a voltage signal along the wire transmission to the detector, preamplifier role is to enlarge the sensor The signal sent, the role of the filter is to improve the signal to noise ratio, the threshold circuit is to eliminate the background noise. Microprocessor signal calculation, analysis, to determine, when the valve is leak-free, the display reads 0; if there is leakage, the display value changes with the degree of leakage, the greater the leakage, the greater the value. The acoustic components of the AE signal generated by the leak are processed and sent to the headset, which is used to listen to the sound of the leak. When the valve leaks, you can hear different sound intensity by the headphones, according to the strength of the sound heard can also determine the extent of the leak. (2) the valve tightness test Ultrasonic detector with a high pressure valve system, the relative readings are usually used to determine whether the leak: the first step, contact the upstream side, reducing the sensitivity to the rest of the sound to a minimum; the second step, the contact valve Seat and the downstream side; the third step, compare the sound differences, if the valve leaks, the seat or the downstream side of the vibration intensity equal to or greater than the sound intensity on the upstream side. In the detection of low-noise system, the downstream contact with the valve, the frequency selection method to clearly hear the flow of sound, according to the size of readings to determine whether the leak and leakage conditions. When using the four-point comparison method to detect downstream disturbances, these disturbances are sometimes large and can propagate to the area to be detected, resulting in erroneous indication of valve leakage. The four-point method includes: selecting two equidistant points A and B at the upstream and two points C and D at the equidistant downstream. Compare the signal intensities at point A and point B with the signal intensities at point C and point D. If point C is higher than point A and point B, there is a leak in the valve. If point D is higher than point C, the sound is heard downstream The other point came. When gas, liquid leakage in the pipeline, due to friction and ultrasonic waves. SONAPHONEE can receive ultrasonic signals, and ultrasonic signals into electrical signals displayed on the display. At the same time the acoustic emission signal is processed as audible sound to the headset, and can be transmitted to the PC through the infrared interface. 3 Conclusion (1) the use of acoustic emission technology on the valve (such as water valve, valve manifold by-pass valve) for tightness testing, to ensure safety in production and energy control accuracy. (2) The replacement of the valve in the old area for testing, can provide the basis for project decision-making, and reduce the cost of renovation. (3) ultrasonic detection technology can achieve online valve testing, simple operation, dynamic fast, intuitive data. At present, the testing equipment can only qualitatively determine whether there is leakage in the valve.
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