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Key words: natural gas station; valve leakage; cause; detection method Introduction Valve is an important part of long-distance oil and gas pipelines. The barrier-free operation of valves plays an important role in the transportation of oil and gas. There is a possibility of damage to the valve, so leak detection of the valve has become an increasingly concerned issue. At present, there is no effective detection method for the internal leakage of valves in the petroleum and petrochemical industry. Therefore, it is particularly important to study accidents caused by internal leakage of valves and to reduce energy loss.
1 Types and characteristics of valves According to the form of seals, valves can usually be divided into contact seals and non-contact seals. The contact seal is to make the sealing surfaces contact, press and embed by external force, thereby eliminating the internal gap. The non-contact seal allows the valve to be sealed without the need for external forces. According to the material properties of the sealing surface, the valve sealing can be divided into plastic sealing, elastic sealing, grinding sealing and controlled film sealing. The plastic seal is a seal realized by the plastic sealing faces being pressed and pressed with each other. The sealing method has the advantages of large contact surface, uniform specific pressure distribution, easy processing, etc., but the reliability is slightly poor; the elastic seal generally adopts linear contact. The method requires that the shape of the contact surface has a relatively precise processing size, and the elastic seal has the advantages of high temperature and high pressure resistance, but the deformation amount of the elastic deformation is not large, so that it does not have sufficient compensation capability; the research sealing is precision ground The surface is sealed. Although the amount of deformation of the grinding surface is small, the grinding precision is extremely high, and only a small external force can be used to achieve a reliable sealing, so it is very suitable for high-parameter sealing applications; the controlled film sealing is sealed. The balance between force and liquid pressure is used to adjust the seal gap. The controlled membrane can be controlled by the electronic system or by the natural conditions of thermal expansion and contraction. The controlled membrane sealing method is mainly used for high speed and high pressure applications.
2 Causes of valve leakage 2.1 Sealing substructure Because the sealing pair works under a certain external pressure, the general sealing material is not an absolute rigid body, and slight deformation will occur under the action of force, and these tiny The deformation is a serious leak path for media such as liquid or gas. Different sealing substructures have different sealing properties, for example, the face seal and the line seal display are different.
2.2 The quality of the seal pair The quality of the seal pair is mainly reflected in the selection of materials, the matching of the surface shape and the precision of the processing. For example, under the same surface matching and processing accuracy conditions, when the material is plastically good, the sealing performance will be better. If the surface types do not match, even if the processing accuracy is good, it is difficult to compensate for the adverse effects of the surface mismatch.
2.3 The specific pressure of the sealing surface than the pressure sealing surface may improve or may damage the sealing performance. First of all, too large specific pressure is easy to cause valve damage, and too small specific pressure will make the sealing reliability worse. The choice of specific pressure directly affects the sealing performance. It is necessary to find the best sealing surface ratio through parameter calculation or a large number of experiments. Pressure parameters.
2.4 Physical properties of the medium Physical properties such as temperature, viscosity and hydrophilicity of the medium are important factors affecting the sealing performance of the valve. For precision valves, the temperature has a small effect on the size of the material, and at the same time causes a change in viscosity, which has a complex and unpredictable effect on the sealing performance. Therefore, the valve sealing performance with temperature compensation function is greatly improved.
3 Ways to detect valve leakage At present, there is no over-system detection method for valve leakage. Now there are generally two types: direct detection method and indirect detection method. The direct detection method mainly includes gas detection method, oil film detection method, cable detection method and optical fiber detection method. The principle is that the leaked transport organization is directly detected by a detector fixed on the outside of the valve to achieve the function of detecting and warning. Indirect detection methods include conservation law, flow balance detection method, operating pressure detection method, and ultrasonic detection method.
3.1 Negative pressure wave method When a leak occurs, there will be an instantaneous pressure difference and a speed difference. At this time, the pressure wave is generally called a negative pressure wave, and the difference between the upstream and downstream measurement time of the negative pressure wave is Time difference. The specific leak location can be determined by the speed at which the negative pressure wave propagates through the pipe. The principle of this pressure difference is that the loss of liquid material at the time of leakage causes a decrease in local liquid density, and a transient pressure drop and a speed difference occur. This method has good sensitivity and positioning accuracy, small construction and low cost, so it is convenient to install and maintain.
3.2 Operational pressure method This method is more convenient and quicker to use. The principle is similar to the communication device. It is mainly used for the detection of transport materials with slow flow rate and the leakage problem when it is serious.
3.3 Conservation Law This method is based on the application of the law of conservation of energy. Its shortcomings are serious and cannot be prevented in advance, and can only be detected after the leakage problem occurs. As long as the mass of the transported substance is detected, the mass flow of the substance is obviously obvious. When it changes, it can be detected. Therefore, it is rarely used for the detection of oil spills.
3.4 patrol observation method This is a commonly used detection method for general companies. It is necessary to send staff to conduct regular inspections. This method requires high demands on staff, requires carefulness and experience, and must have relative Knowledge needs to follow the pipeline to patrol and check it little by little. Its disadvantages are equally obvious, the patrol cycle is long, and employees need to be highly focused to detect, etc., and this method is relatively cost-effective compared to other methods, so companies generally adopt this method.
3.5 The principle of acoustic emission detection is to use acoustics to detect the leakage of the door valve. It is the rapid release of the endogenous energy, which generates transient elastic waves. Then the sensor contacts the elastic wave on the outer wall of the valve, and automatically transports the material when it leaks. Turning into an electrical signal, and finally by amplifying the received signal to monitor, can achieve the goal of detecting valve leakage online. The advantages are obvious: firstly, the operation method is more convenient, the requirements for the staff are not high, and only the task needs to be done seriously and responsibly, the requirement for proximity is not high; secondly, it is not necessary to disassemble the valve to detect whether the internal is A leak occurs; the other is that it does not affect the normal production of the company.
Conclusion In the industrial context, valve sealing has an important role in ensuring the safety of production. Future valves will be more complicated in structure, and even the traditional idea can not be used to analyze the sealing principle. Therefore, only the specific conditions can be used to analyze the sealing performance of the valve, and the level of protection can be improved in a targeted manner to achieve good results.
references:
[1]Zhang Caixia. Fault Analysis and Solution of Valve Transmission Device in Gas Transmission Station[J].Petrochemical Technology, 2018, 25(01): 226.
[2] Zhang Pingcun, Yin Gang, Yang Guangliang, Wang Zhaojun. A method for online repair of large valve stems [J]. Equipment Management and Maintenance, 2018 (01): 33-34.
[3] Li Wei, Ma Yundong, Jiang Peng, Huang Yuanhang, Ma Yunxiu. Analysis of the problem of internal leakage of oil pipeline valve based on acoustic detection system theory[J]. Pressure Vessel, 2017, 34(12): 55-62.
[4]Chen Qun. Application Research of Valve On-line Detection Technology in Petrochemical Plants[J]. Tax, 2017(33): 194.
Research on the Causes of Valve Leakage and Detection Methods in Natural Gas Field Stations
Abstract: The improvement of the industrial level has led to a sharp increase in the use of various valves, and energy companies have put forward higher requirements for the sealing performance of valves. In actual work, the event of valve leakage has occurred, and it is obvious that research on the cause of the valve leakage and the detection method are necessary. The reasons for valve leakage are various, and the degree of influence varies. According to different application conditions, different measures can be taken to prevent valve leakage.