Detection of Leakages of Valves

Detection of Leakages of Valves


Compared with other industries, there is serious environmental pollution in the chemical industry and the petroleum industry, so relevant departments and personnel must pay more attention to them. At present, China has stipulated the discharge standards of waste residue, waste gas and wastewater and adopted relevant measures to intervene, but there is currently a lack of attention to pollution sources, such as valve leakage. Valves are the most critical components used in petrochemical smelting equipment. Most of them use flammable, explosive, toxic and corrosive substances as the main medium in petrochemical production due to the large number of valves. In its practical application, the probability of valve failure is high, which will lead to serious waste of products, energy and raw materials, and aggravate the adverse impact on the environment. Therefore, the detection methods of valve leakage are discussed and analyzed in this article.
 
2.1 Visual observation
According to the inspection of the device by experienced operators, the method of smelling, listening and seeing is used to analyze whether there is leakage. This form cannot carry out continuous leak detection, so it has poor detection real-time performance.
 
2.2 Mass balance
Analyze whether there is a leakage from the difference between the mass value and the volume value of the medium flowing into and out of the valve. The application advantage is that it has good reliability and can test the leakage of small flow rate, but there are also defects in its application, which has poor timeliness for applications and can only detect the leakage of the valve.
 
2.3 Analysis of pressure points
The pressure point analysis method is the most important method for the application of valve leakage detection. The leakage generated above the operating valve will increase the upstream flow rate, and at the same time, the pressure value in the downstream and upstream will also decrease. Leakage will cause the pressure drop to be the greatest at the leak point, and it will gradually decrease towards the head and tail of the leak section. If the inlet flow or pressure value changes greatly, it indicates that there may be a leakage of the valve. This method can detect serious leakage.
 
2.4 Acoustic emission
In materials, after the partial source energy is released rapidly, a transient elastic wave will be formed, which refers to acoustic emission, also known as stress wave emission. In the valve inspection process, if the leakage occurs due to the poor sealing of the valve, the material inside the valve body will be ejected from the gap of the sealing surface, resulting in the formation of turbulent flow. This turbulence forms an impact on the surface of the sealing surface, causing elastic waves to be excited, which is the signal of leakage. The strength of the signal is related to the flow velocity, flow rate, physical properties of the fluid, pipeline layout, valve pressure drop and pre-valve pressure. The elastic wave will propagate from the valve body to the position of the material surface, which will induce a change in the detection surface position of the acoustic emission sensor. The detector will be affected by the piezoelectric effect, and the material will vibrate and transform to form an electrical signal, and then the electrical signal will be amplified, processed and recorded. Relying on record analysis and identification of the acoustic emission signal form, the leakage of the valve can be effectively controlled.
 
2.5 Negative pressure wave
If leakage occurs, the leakage location will cause a partial decrease in liquid density due to the loss of fluids, resulting in an instantaneous pressure drop. As a decompression wave source, it can rely on the fluid and pipeline to propagate by applying a certain speed to the upstream and downstream of the leakage point. If the pressure value before the leak is used as a reference, the decompression wave generated during the leak is also called a negative pressure wave. Set the sensors at both ends of the leak point. The position of the leak can be clarified based on the change in the pressure signal and the time difference between the upstream and downstream transmission of the negative pressure wave generated in the leak. This method has good sensitivity in detection, and does not need to build a mathematical model. The application principle is simple and has good applicability. Since the most critical issue in the application of the negative pressure wave is the setting of the number of pressure transmitters, a large number will cause resource waste, and a small number will cause false alarms of leakages; it can be combined with the current foreign advanced RBF neural grid. Carry out self-learning functions and sample selection to optimize the number of pressure transmitters.
 
3. Conclusion
To sum up, in the production and operation of petrochemical enterprises, the problem of valve leakage will induce major accidents. It is an important issue that must be paid attention to in oil production, which will reduce the economic benefits of enterprises, affect the safety of enterprise operations, and affect the effect of energy conservation and environmental protection. Analyzing the current valve management methods of petrochemical enterprises, simple inspections are the main form of valve management, which must be regularly inspected and repaired in the enterprise, and seriously affects the service life of valves and the safety of equipment operation. Therefore, to eliminate the valve leakage, it is necessary to optimize its structural design, select a reasonable type, gradually optimize the online leakage detection technology, carry out predictive maintenance, and use the negative pressure wave and RBF neural network to carry out valve leakage detection. In this way, the safety of valve application can be improved.