Acoustic on-line detection of valve internal leakage pressure valves for Daqing Field ground facilities and equipment have internal leakage due to wear, corrosion or other reasons. Because the inner leakage is very difficult to find, some faulty valves have not been replaced in time, which affects the production and the existence of potential safety problems. Therefore, the valve on-line detection technology has attracted more and more attention, the core technology is the use of acoustic emission technology on-line detection of oil, petrochemical, power plant and other industries valve leakage. The basic principle of acoustic emission leak detection (1) acoustic emission signal and its characterization parameters, when any metal material or component is subjected to friction, crack or plastic deformation under external or internal forces, the phenomenon of the release of strain energy in the form of elastic waves is called acoustic emission. When the acoustic emission wave propagates in the finite medium, it will refract and reflect when it meets the interface, and convert to the surface wave on the solid surface and propagate along the surface at a high speed. These AE waves from AE sources (failure points) have the characteristic information of the source, which can be used to reflect the faults and defects of the components. The parameters of acoustic emission signal are acoustic emission rate, amplitude and amplitude distribution and energy. (2) the characteristics of Acoustic emission signal when internal leakage occurs in the valve. When the tightness of the valve is poor, a small amount of fluid is always ejected through the gap of the valve, resulting in high-speed jet, the high-speed fluid impinges on the pipe wall and excites the elastic wave, I. E. Acoustic Emission. It is a continuous acoustic emission signal, similar to white noise, its frequency in 30 ~ 50 Khz. The characteristics of ACOUSTIC EMISSION SIGNAL PRODUCED BY VALVE LEAKAGE: 1 the Acoustic emission wave excited by leakage is continuous; 2 the Acoustic emission signal produced by leakage is strong, and its magnitude is proportional to the leakage rate, proportional to the root mean square of the signal. According to the characteristics of Acoustic emission signal produced by leakage, the acoustic emission rate and energy are used as the characterization parameters, which can obtain more abundant acoustic emission data and provide more sufficient basis for fault identification. Field application of ultrasonic detector (1) detector brief introduction, when the acoustic emission wave produced by the leakage is transmitted to the sensor, the acoustic emission wave is converted by the sensor into voltage signal and transmitted to the detector along the wire, the function of the preamplifier is to amplify the signal sent by the sensor, the function of the filter is to improve the signal to noise ratio, and the function of the threshold circuit is to eliminate the background noise. The microprocessor calculates, analyzes and judges the signal. When the valve has no leakage, the display screen reads 0. If there is leakage, the display value changes with the degree of leakage. The larger the leakage, the larger the value. The audio component of the acoustic emission signal generated by the leak is processed and sent to the headphones, which are used to listen for the sound of the leak. When the valve leaks, the headphones can hear different sound intensity, according to the heard sound intensity can also judge the degree of leakage. (2) valve tightness test. When testing a valve high pressure system with an ultrasonic detector, a comparative reading is usually used to determine whether there is a leak: Step 1, contact the upstream side, reduce sensitivity and minimize other sounds; step 2, contact seat and downstream side; step 3, compare the difference in sound, if the valve leaks, seat or downstream side of the sound vibration intensity equal to or greater than the upstream side of the sound intensity. In the detection of low-noise system, the contact valve downstream, the use of frequency selection to clearly hear the sound of liquid flow, according to the size of the reading to determine whether leakage and leakage. When the four-point comparison method is used to detect the downstream interference, the interference is sometimes very large and can spread to the area needed to be detected, leading to the wrong indication of valve leakage. The four-point method consists of choosing two equidistant points A and B in the upper reaches and two equidistant points C and D in the lower reaches. Compare the signal strength at points A and B with that at points C and D. if point C is higher than points a and B, the valve is leaking. If Point D is higher than point C, the sound is coming from other points downstream. When the gas, liquid leakage in the pipeline, due to friction and ultrasonic waves. SONAPHONEE can receive ultrasonic signals and convert the ultrasonic signals into electrical signals for display on a display screen. At the same time, the acoustic emission signal is processed into audible sound and transmitted to the headset, and can be transmitted to the PC through the infrared interface. Conclusion (1) the application of acoustic emission technology to check the tightness of valves (such as water-mixing valves and by-pass valves) can ensure the safety of production and the accuracy of energy consumption control. (2) the examination of the valve replacement in the old district reconstruction can provide the basis for the decision-making of the project and reduce the reconstruction cost. (3) ultrasonic testing technology can realize valve on-line testing, which is simple to operate, dynamic and fast, and data is intuitionistic. At present, the test equipment can only determine whether there is leakage in the valve qualitatively.