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Keywords: natural gas pipelines; valves; faults; maintenance techniques Introduction Valves are the most common equipment in natural gas pipelines, and their normal operation plays an important role in the safe use of natural gas. If the valve fails, it may lead to natural gas leaks, explosions, natural gas shutdowns, and other conditions that affect the use of natural gas and the safety of natural gas stations. Valves have the effect of controlling gas flow and flow in pipeline yards and are widely used in real life. There are many reasons for its failure and the consequences of the failure are serious. Under the circumstances of natural gas leakage, the personal safety and economic assets of the personnel are seriously threatened. Therefore, understanding the common faults of valves and their maintenance methods to ensure the normal operation of the valves is of great significance to the development of China's natural gas pipeline transportation.
1 Common Faults of Natural Gas Valves 1.1 Ball Valve Internal Leakage 1.1.1 General Performance of Faults Internal leakage of valves is a relatively common type of valve faults in natural gas pipelines. Therefore, fault analysis and solution measures must be implemented. In the failure analysis, the general method is: to make the valve fully open or fully closed, and to detect the discharge of the valve body drain to confirm whether there is a leak. If the gas can be eliminated, it is proved that the airtightness is good; if there is always a gas discharge, it is proved that the valve has internal leakage and should be dealt with accordingly. When checking a type of valve with a passage in the valve body, it can only be performed in the fully closed state. This is because when the valve is fully opened, the passage is also open, and it is impossible to judge the sealing condition of the valve. Valves belonging to this category include GROVEB-5, PBV ball valves, ROBERTCORT ball valves and B-7A ball valves.
1.1.2 Causes of Failure Analysis When analyzing the causes of failures, analyze them according to the time period of failure.
(1) The reasons for the internal leakage during the construction phase are as follows: 1 During the transportation and hoisting of the valve, improper operation practices are likely to cause the overall damage of the valve, resulting in internal leakage of the valve; 2 when the valve is shipped from the factory Without necessary drying and antiseptic treatment, the sealing surface of the valve is rusted and internal leakage occurs. 3 Foreign materials such as rain, sand, etc. do not enter the valve body due to protective measures in the construction process, causing internal leakage; 4 Installation process to the valve seat The lack of effectiveness of lubrication protection, so that debris into the valve seat, and then due to wear caused by internal leakage; 5 valve installation process requires welding process, if the valve is not fully open, welding spatter will cause damage to the ball, and attached Balls with welding spatter will accelerate damage to the valve seat during operation, resulting in internal leakage of the valve. For example, when there is a large misalignment in the mounting angle of the stem drive sleeve or other components, the seal of the valve may be affected.
(2) The internal leakage that occurs during the valve working operation has the following causes: 1 The improper operation or maintenance of the valve may cause internal leakage of the valve if it is not managed and maintained according to the corresponding procedures. 2 Maintenance of the pipeline or valve When the sealing surface is damaged due to improper cleaning measures, or the lack of regular maintenance or use, the valve seat and the ball solid to death, in the forced opening and closing of the valve damage the seal of the valve; 3 large diameter ball valve valve stem commonly has to stop Blocks, if used for a long time, cause a large amount of iron filings, dust, or impurities to accumulate between the valve stem and the stem stop block due to corrosion, so that the valve cannot be restored to its original position and cause internal leakage. For example, rust or impurities from the extended stem of a buried valve will fall on the ball valve, which will affect the rotation of the ball valve. The ball valve cannot be restored to its original position, causing internal leakage of the valve.
1.2 Abnormal valve switching operation Abnormal operation of the valve switch is also the most common type of valve failure. There are many reasons for this happening, and the situation is as follows: (1) As the ball valve is not maintained for a long time, the valve seat and the ball are locked, which makes the valve appear immobile or other abnormal conditions; (2) Most of the foreign matter that enters the natural gas pipeline accumulates around the valve seat, which affects the normal operation of the valve stem. Foreign matter includes sand, dust, and aging, hardened sealing grease, etc.; (3) If natural gas contains moisture, moisture will Liquefaction occurs in different transport environments. The resulting condensate flows to the lowermost lower pivot of the valve or to the lower end of the valve body. When the temperature is lower than 0°C, the retained moisture condenses into ice and affects the normal operation of the valve.
1.3 Other faults Natural gas pipeline valve types are different, so their respective faults also have certain differences. For example, the use of a ball valve operated with a turbine or worm to mesh with a drive, in the event of a failure during use, generally includes a situation where the gear is severely worn or broken resulting in an inability to properly mesh; the occurrence of an infrequent engagement occurs frequently; improper operation can make the worm The safety pin breaks during use; whether it is a worm or a bearing on a turbine, damage to the valve will result in normal operation of the valve; in the case of grease flooding, it is likely to be contaminated, which can also cause valve failure. The bolts connected between the wheel box and the valve body may loosen and break. If the power supply is missing or the connection of the wires is wrong, the power head is likely to fail. The general failure of the gas-liquid linkage ball valve is that the gas line and the oil line are blocked and the pipeline speed limit valve is always closed; the pressure of the gas source is too small to support the normal operation of the valve; the sealing performance of some hydraulic cylinders or rotating parts is subject to Loss caused by leakage and so on.
2 measures to reduce valve failure 2.1 Maintenance Technology 2.1.1 Stem leak repair technology In general, the ball valve stem is not set on the upper and lower seals, so no special maintenance, but the long-term use of the stem due to Wear or aging may cause leakage at the valve stem. If the valve stem has an injection port, seal leakage can be added to the injection port; if it is a valve stem of other structures, the leakage of the leak should be eliminated by injecting the seal packing or compressing the packing gland according to the structure of the valve stem. It should be noted that if you need to inject the sealing grease, you should use a manual grease gun to slowly inject.
2.1.2 Other repair techniques When the valve operation is abnormal, a certain amount of cleaning fluid can be injected. After soaking and then operating, the above failures can be eliminated. When handling the leakage of the valve stem, the tightness of the compression screw should be controlled. Affect the valve's ease of switching, too loose will affect the sealing; if the grease is polluted by water, you should disassemble the gear box to remove the pollution of grease, replace the new grease, in the lower temperature season, but also Low-temperature greases (such as ethanol-based greases) are used to reduce freezing plugging.
2.2 Increase Maintenance and Maintenance Management 2.2.1 Valve Maintenance and Management during Construction Phase In the construction phase, scientific and effective methods should be adopted to maintain the natural gas pipeline valves to ensure the safety of the valves. Strictly control the loading and unloading process of the valve to prevent it from being mechanically damaged. During lifting of the valve, it is forbidden to hang the suspending rope on the actuator or the valve stem, so as to avoid the bending of the valve stem and the sealing of the valve diameter and the destruction of the gear box. The situation occurs; in the process of shipment of the valve, easy blind plates are installed at both ends to avoid impurities during the transportation and installation of the valve; during the construction, the valve and its components are to be placed in accordance with requirements, so as to avoid Damaged discharge nozzles, grease injection nozzles and other parts; In addition, adequate lubrication of the valve before installation is also very important, and timely detection of smooth lubricating channels.
2.2.2 Maintenance and management of the use phase Periodically inspect the tightness of the valve and timely deal with the problem of internal leakage. According to the operation status of the valve, formulate a reasonable maintenance system. If the valve is acted once, it can inject proper amount (1/8 of the volume of the sealing system. Grease, to avoid foreign matter into the valve seat cavity, affect its sealing; activities less valve, should ensure that at least once a year action, action when the appropriate amount of grease injection, can reduce the ball when the dry grinding activities; before winter Full maintenance of the valve, in particular to exclude the water inside the valve chamber, to avoid freezing; grease inside the gear transmission should be replaced once a year.
3 Conclusion Valves are important gatekeepers of natural gas pipeline transportation systems, and the hazards caused by their faults are enormous. Therefore, the relevant scientific research workers should increase the research on various valve failures, and timely and scientifically and effectively prevent valve failure measures to ensure the normal transportation of natural gas in China.
At the same time, it is necessary to update the installation and maintenance technology of the valve in a timely manner, issue a valve maintenance and management manual, and ensure the safe operation of the natural gas station with scientific, advanced and standardized management methods.
References [1] Liu Jianyu, Qiao Linfeng, Ma Jian. Pre-installation management of natural gas pipeline valves [J]. Oil and gas storage and transportation, 2015,05:528-532.
[2] Zhang Fuyuan, Huang Yongshen. Analysis of Common Faults and Maintenance Strategies of Valves [J]. Science and Technology Innovation and Application, 2015, 23:142.
[3] Zhang Siyang, Wu Meng, Li Wang. Discussion on the analysis and detection method of inner leakage of large-diameter ball valve for long-distance natural gas pipelines [J]. Value Engineering, 2016, 25: 178-180.
Analysis of Natural Gas Pipeline Valve Troubleshooting
Abstract: Valves are important devices in natural gas transportation pipelines. Their role is to control the flow of natural gas in pipelines and prevent the leakage of natural gas. This article briefly describes the common faults of natural gas pipeline valves, that is, ball valve leakage and abnormal valve switching operation, analyzes the valve status under fault conditions, and proposes suggestions for preventing valve faults, hoping to provide theoretical references for related personnel.