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[Key words] pipeline valve, internal leakage, cause, judgment CLC number: G711 Document code: A Article ID:1009-914X(2019)02-0029-01
I. Analysis of the causes of leakage inside the valve (1) Improper adjustment of the internal leakage switch of the valve caused by improper switch limit is one of the most important reasons for the internal leakage of the valve. In actual work, it is first necessary to check whether the switch adjustment of the valve is accurate, especially to ensure that the switch can be fully closed. When most of the ball valves are in the fully closed position, even if the distance between the ball closing member and the valve body is 2 to 3 degrees, the leakage of the medium can be caused. However, usually because of the constriction inside the plug valve, the ball closing member and the valve body are 10 to 15 degrees apart to cause leakage of the medium [1]. There are many factors that cause improper adjustment of the switch limit. For example, during the process of assembling the valve in the factory or during the process of loading and unloading, the attachment of the valve stem and the valve stem drive set are misaligned, so that the limit deviation is further caused by the valve. Internal leakage. With long-term use, impurities such as rust, dust, sand, and paint generated in the stem sleeve fall between the valve stem and the valve stopper, resulting in the valve switch not being fully closed and the valve leaking. In addition, the valve is not inspected for a long time, and a large amount of impurities are accumulated in the valve cavity, which may result in the valve not being fully closed, interference of impurity gases, etc., and may also cause leakage of the valve.
(2) The presence of impurities in the valve caused by the presence of valve impurities is another cause of leakage inside the valve. These impurities may be sand, stones, rust, dust, etc., and may also be tools such as welding rods, wooden sticks, and plastic products. In the process of producing valves, if the valve manufacturer does not do the drainage, drying, anti-corrosion and grease application after the water pressure test, it will easily cause the internal rust of the valve, which will cause the leakage of the produced pipeline valve. phenomenon. In the process of installing oil and gas pipelines, if the pipeline protection is not done well, sediment, sewage and impurities may enter the pipeline, and there will be a large possibility of valve leakage. In addition, irregular operation during pipeline operation, long-term use of the valve, and maintenance work on the oil and gas pipeline for a long time may cause leakage of the pipeline valve.
(3) The internal leakage of the valve caused by the damage of the sealing surface. As the pipeline works, the oil and gas will wash the pipeline for a long time. If there is a small area damage in the pipeline during transportation, it will cause small damage to become large damage, resulting in Leakage of oil and gas. In the actual pipeline work, if the violent handling or lifting method is unreasonable, the integrity of the valve will be damaged, which will cause the valve leakage to occur. In the process of welding the valve, if the welding spatter is splashed on the closing member, the closing member will be damaged, and when the valve is operated, the sealing surface of the valve seat will be damaged, thereby further causing leakage in the pipeline valve [2]. In addition, the specifications of the valve trim are not up to standard, the valve works under a small opening for a long time, the sealing material is unqualified, the welding slag, hard particles and other impurities are mixed in the welding process, the cleaning pipeline is not working well, and the pressure on both sides of the valve Excessive conditions can lead to damage to the valve, which leads to internal leakage of the oil and gas pipeline valve, which brings huge economic losses to the oil and gas transmission project.
(4) The maintenance of the internal leakage pipeline of the valve caused by improper maintenance is also a key link to ensure the normal operation of the oil and gas pipeline industry. In the process of pipeline maintenance, some managers may reduce the number of pipeline maintenance due to the high cost of regular maintenance of the pipeline, so that the valve closing member and the valve seat are tightly locked, causing the valve to be difficult to switch. Sealing damage occurs in the valve, eventually causing internal leakage of the pipeline valve. If the plumber does not follow the correct maintenance method to maintain the pipeline, and does not timely replenish the sealant with the sealant seal, it can also be used to drain the internal leakage of the oil and gas pipeline valve.
Second, the judgment of the internal leakage of the valve (a) the internal leakage amount formula judgment method When the valve is closed, the rear pipeline or pressure vessel does not have pressure, then the pressure change of the pipeline or pressure vessel can be used to determine whether the valve exists Leakage phenomenon. Normally, we can use the following formula to calculate the size of the internal measurement: , where P1 and P2 represent the initial pressure of the pressure vessel, the pressure of the pressure vessel at the time of inspection, V0 represents the volume of the pressure vessel, and T represents the time of detection, D Indicates the nominal diameter of the pipeline. If the value of the calculated result V is greater than 0.04, we can judge the problem of internal leakage of the valve.
(2) Venting method to detect whether the valve of the oil and gas pipeline is leaking. When the valve or the pressure vessel cannot be used to judge whether the valve has internal leakage, we can use the venting method to determine whether the valve is leaky. First, we adjust the switch that needs the valve to the fully closed position. In particular, the ball valve with the balance ball must be placed in the fully closed position, and then slowly open the drain valve of the valve for sewage discharge, if the oil and gas in the valve cavity can be completely drained. This indicates that the valve has no internal leakage. If the oil and gas in the valve chamber is not completely drained, it indicates that the valve has internal leakage. In addition, the leakage of oil and gas can be roughly calculated by the flow of venting oil and gas [3].
(3) Flowmeter leak detection method to detect whether the oil and gas pipeline valve is leaky. The flowmeter leak detection method is a very simple method to judge whether the oil and gas pipeline valve is leaky. An adapter must be prepared in advance, and then a direct-reading float precision flowmeter or panel gas flowmeter with a range of approximately 0.2 liters/min should be assembled on the drain plug or drain valve of the valve, and finally from the flowmeter. The corresponding leakage amount can be read directly, and it is directly judged whether there is an internal leakage in the oil and gas pipeline valve.
(4) Valve internal leakage test tool method to detect whether the oil and gas pipeline valve is leaking. Before the inspection work, the valve internal leak detection tool is made by pipe fittings and precision pressure gauge. At the beginning of the test work, first install the drain plug or drain valve of the valve, and check the tool for leaking inside the valve in advance. During the installation process, the cut-off valve can be placed in the fully open position, waiting for the installation to close the shut-off valve. position. Slowly open the valve to be tested to ensure that the pressure in the valve chamber and the pressure in the pipe are in equilibrium. Next, put the test valve in the fully closed position and do the reading of the pressure gauge. The measured pressure is the pressure in the valve cavity. Open the shut-off valve and wait for the pressure in the valve chamber to drop by about 10%-15%. Close the shut-off valve and record the pressure gauge reading again. The measured pressure is the valve chamber pressure. During the measurement process, do not ignore the time to record the recovery of the valve cavity pressure. If the pressure in the valve chamber does not rise after discharge, we can conclude that there is no internal leakage in the valve of the oil and gas pipeline, and vice versa.
Summary In recent years, the internal leakage of oil and gas pipeline valves has occurred frequently, which is difficult to solve fundamentally and seriously affects the safe production operation of the entire oil and gas pipeline. The importance of valves in oil and gas pipelines is irreplaceable. In actual pipeline transportation work, it is necessary to avoid leakage of oil and gas pipeline valves as much as possible. By combining the measures of internal leakage of the valve to analyze and judge the existence of internal leakage of the valve, the management of valve operation, maintenance and overhaul is continuously strengthened, and new technologies for maintenance of pipeline equipment are actively sought, so as to avoid leakage of valves of oil and gas pipelines. The occurrence of phenomena, thereby further improving the management level of pipeline valves.
References [1] Zhu Xiping. Maintenance and troubleshooting techniques for natural gas pipeline ball valves [J]. Natural Gas Industry. 2005(07)
[2]Liu Kai. Analysis of the causes of leakage inside the pipeline valve of Suininglan and recommended measures[J].China Petroleum and Chemical Industry Standards and Quality,2014,12(1)
[3]Wang Chenglong. Analysis of the causes of valve leakage and countermeasures [J].Petrochemical Safety and Environmental Protection Technology, 2007, 23.
[Abstract] As we all know, the importance of valves in oil and gas pipelines is irreplaceable. It can not only regulate the pressure of pipelines, but also distribute the flow direction of medium, which ensures the safe transportation of pipelines to a certain extent. With the development of society and the advancement of science and technology, the requirements for the safety, reliability and service life of valves for oil and gas pipelines are also increasing. If the problem of internal leakage of the pipeline valve is not discovered in time, it may bring serious safety hazards to the oil and gas industry, which will cause huge economic losses. This paper mainly starts from the cause of the leakage of the oil and gas pipeline valve, and judges the internal leakage of the valve.