Ground facilities and equipment of daqing oil field under pressure valves due to abrasion, corrosion, or other reason there has been a leak. Due to internal leakage may be difficult to find, partial failure valve has not been timely change, affects the production and pose a safety hazard. online detection technology, therefore, more and more get the attention of people, the core technology is the use of acoustic emission technology on-line detection of petroleum, petrochemical, power plants and other industries of various valves leakage. 1, the basic principle of the acoustic emission leak detection ( 1) Acoustic emission signal and characterization parameters of any metal materials and components under the action of external force or internal friction, crack, or plastic deformation, the release of strain energy in the form of elastic wave phenomenon, called acoustic emission. When ae wave in the limited transmission medium, the refraction and reflection interface will happen, and on the solid surface into surface wave propagation along the surface with high speed. These come from acoustic emission source ( The point of failure) Source of acoustic emission wave has the characteristics of information, this information can be used to reflect the component faults and defects. Characterization of the parameters of acoustic emission signal sound emission rate, amplitude and amplitude distribution and energy. ( 2) leakage occurs the characteristics of acoustic emission signal when the valve less rigor, there is always a small amount of fluid flow through the valve of the gap jet and produce high-speed jet, the high velocity impact on pipe wall and inspire elastic wave, acoustic emission. It belongs to continuous acoustic emission signal, similar to white noise, the frequency in 30 ~ 50 KHZ. leakage when the acoustic emission signal features: 1 sparked by the leakage of acoustic emission wave is continuous; 2 leakage acoustic emission signal is stronger, and size of the amplitude is proportional to the flow rate, is proportional to the mean square root value of the signal. According to the characteristics of the acoustic emission signal generated by the leakage, the characterization parameters using acoustic emission rate and energy, it can obtain more abundant acoustic emission signal data, provide more sufficient basis for fault identification. Field application of the ultrasonic detector (2 1) Detector profile when leakage of acoustic emission wave to the sensor, the sensor converts acoustic emission wave voltage signals along a wire transfer to the detector, preamplifier is amplified signals from sensors, the role of the filter is to improve the signal-to-noise ratio and threshold is used to eliminate background noise of the circuit. Microprocessor for calculation, analysis, judgement, signal when the valve without leakage, display reading to zero; If there is leakage, the display value changes according to the degree of leakage, leakage, the greater the value. Leakage of audio components in acoustic emission signals produced after processing to the headphones, headphones to listen to the sound leakage. When the valve leakage, the headset can hear the sound of the sound intensity is different, according to the sound intensity can also assess the extent of the leak. ( 2) rigor test by ultrasonic detector to detect the high pressure system, usually adopt comparative reading to determine if leakage: the first step, contact the upstream side, reduce the sensitivity, the other voice fell to a minimum; The second step, the contact seat and downstream side; The third step, compare the difference of sound, if the valve leakage, seat or downstream of the acoustic intensity is equal to or greater than the upstream side of the intensity of the sound. In detecting low noise system, contact downstream of the Industrial Valves, the frequency selective way to clearly hear liquid LiuSheng, determine if leakage and the leakage situation according to the volume of reading. Using comparison method to detect the downstream interference at four o 'clock, sometimes these interference is very big, can spread to the area to check, led to the incorrect instructions of the valve leakage. Four-point methods include: choose the upper two equidistance point point A and point B, then select the downstream of equidistant points C and D two points. Will point A and point B signal strength and C and D points of signal strength, if C higher than that of point A and point B, shows that the valve is leaking; If D points higher than C, voice coming from other point of the downstream. When gas and liquid in the pipeline leakage, ultrasonic due to friction. SONAPHONEE can receive ultrasonic signals, and the ultrasonic signal into electrical signal display on the LCD screen. At the same time, the acoustic emission signal processing for the headset can hear the sound, and can be transmitted infrared interface to the PC. Epilogue (3 1) Application of acoustic emission technique (the valve Such as water valve, by-pass valve valve group) Detection of rigor, can guarantee the accuracy of the safe production and energy consumption control. ( 2) In the replacement of valve for the modification of the old, can provide the basis for project decision-making, and reduce the cost. ( 3) Ultrasonic testing technology can achieve valve on-line detection, the operation is simple, rapid, dynamic data directly. At present the test equipment can only be qualitatively determine whether there is leakage in Industrial Valves.
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