First, cause analysis of valve leakage
(1) Valve leakage caused by improper switch limit
Improper adjustment of the switch limit is one of the main reasons for current valve leakage. In actual work, you must first check whether the valve switch is adjusted accurately, especially to ensure that the switch can be fully closed. When most 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, it can cause leakage of the medium. But usually because the neck of the plug valve is constricted, the ball closing member and the valve body 10 to 15 degrees away will cause the medium to leak . There are many factors that cause improper adjustment of the switch limit. For example, during the assembly of the valve in the factory or during the transportation and loading and unloading process, the assembly angle of the accessories connected to the valve stem and the drive sleeve of the valve stem are misaligned. Leaking. With long-term use, impurities such as rust, dust, sand, and paint in the valve stem cover fall between the valve stem and the valve limit block, resulting in the valve switch cannot be fully closed and the valve leaks. In addition, the valve has not been drained for a long time, and a large amount of debris accumulated in the valve cavity causes the valve to not be fully closed, the interference of impurity gases, etc., can also cause the valve to leak inside.
(Two) valve leakage caused by the presence of valve impurities
The presence of impurities in the valve is another cause of valve leakage. These impurities can be sand, stones, rust, dust, etc., or tools such as welding rods, wood rods, and plastic products. Valve manufacturers in the process of valve production, if the water pressure test is not done after drainage, drying, anti-corrosion and application of grease, etc., it is easy to cause rust inside the valve, resulting in the production of pipeline valves with internal leakage phenomenon. In the process of installing oil and gas pipelines, if the protection of the pipeline is not done well, sediment, sewage, and impurities may enter the pipeline, and the phenomenon of valve leakage may occur. In addition, irregular operations during pipeline operation, long-term unused valves, and long-term maintenance of oil and gas pipelines may cause internal leakage of pipeline valves.
(Three) valve leakage caused by damage to the sealing surface
With the progress of pipeline work, oil and gas scours the pipeline for a long time. If there is a small area of damage to the pipeline during transportation, it will cause small damage to become large damage, which will cause oil and gas leakage. In actual pipeline work, if the violent loading and unloading or lifting methods are unreasonable, the integrity of the valve will be damaged, resulting in the occurrence of valve leakage. In the process of welding the valve, if welding spatter splashed on the closing part, the closing part would be damaged, and the sealing surface of the valve seat would be damaged when the valve was running, which further caused the internal leakage of the pipeline valve . In addition, the internal specifications of the valve are not up to standard, the valve works for a long time with a small opening, the sealing material is not qualified, the welding slag, hard particles and other impurities are mixed in the welding process, the cleaning of the pipeline is not complete, and the pressure on both sides of the valve Excessive conditions may cause damage to the valve, which will cause internal leakage of the oil and gas pipeline valve, which will bring huge economic losses to the oil and gas transportation project.
(IV) Valve leakage caused by improper maintenance
Pipeline maintenance is also a key link to ensure the normal work of the oil and gas pipeline industry. In the process of pipeline maintenance, some managers may reduce the frequency of pipeline maintenance due to the excessively high cost of regular pipeline maintenance, which will cause the valve closing parts and valve seats to be tightly locked, causing valve switching difficulties and re-activation. Seal damage occurred during the valve, which eventually caused internal leakage of the pipeline valve. If the plumber fails to maintain the pipeline in accordance with the correct maintenance methods and fails to supplement the sealing grease with the valve sealed with sealing grease in a timely manner, the internal leakage of the oil and gas pipeline valve can also be caused.
Judgment measures for valve leakage
(1) Formula for judging the magnitude of the internal leakage
When the valve is closed, there is no pressure on the rear pipeline or pressure vessel. At this time, it can be determined whether the valve has internal leakage through the pressure change of the pipeline or pressure vessel. In general, 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 and the pressure of the pressure vessel during the inspection, V0 represents the volume of the pressure vessel, T represents the time of detection, D Represents the nominal diameter of the pipeline. If the value of the calculated result V is greater than 0.04, we can judge that the valve has an internal leakage problem.
(2) Detect whether the oil and gas pipeline valve is leaking inside
When it is impossible to judge whether the valve has internal leakage through the rear pipeline or pressure vessel, we can use venting method to determine whether the valve has internal leakage. First, we need to adjust the switch of the valve to the fully closed position, especially the ball valve with a balance ball must be placed in the fully closed position, and then slowly open the valve's drain valve for drainage, provided that the oil and gas in the valve cavity can be completely exhausted , It means that the valve has no internal leakage. If the oil and gas in the valve cavity is not completely drained, it means that the valve has internal leakage. In addition, the leakage of oil and gas can be roughly calculated by venting the flow of oil and gas .
(3) Flowmeter leak detection method to detect internal leakage of oil and gas pipeline valves
Flowmeter leak detection method is a very simple method to determine whether the oil and gas pipeline valve has internal leakage. You need to prepare an adapter in advance, and then install a direct reading float precision flow meter or panel type gas flow meter with a measuring range of about 0.2 liters / minute on the drain plug or drain valve of the valve. The corresponding leakage amount can be read directly, and it can be directly determined whether there is an internal leakage in the oil and gas pipeline valve.
(IV) Valve Leakage Test Tool Method for Detecting Leakage of Oil and Gas Pipeline Valves
Before carrying out the inspection work, use a pipe fitting and a precision pressure gauge to make a valve leak detection tool. At the beginning of the testing work, first install the valve drain plug or the drain valve, and do a good job of detecting the valve leakage in advance. During the installation process, the shut-off valve can be placed in the fully open position, and the shut-off valve should be fully closed after installation. position. Slowly open the valve to be tested to ensure that the pressure in the valve cavity and the pressure in the pipeline are in a balanced state. Next, place the test valve in the fully closed position and do a good job of reading the pressure gauge. At this time, the measured pressure belongs to the pressure in the valve cavity. Open the shut-off valve, wait for the pressure in the valve cavity to drop by about 10% -15%, close the shut-off valve, and record the reading of the pressure gauge again. The measured pressure at this time belongs to the valve cavity detection pressure. During the measurement, do not neglect to record the recovery time of the valve cavity pressure. If the pressure in the valve cavity does not rise after discharge, we can conclude that there is no internal leakage in the oil and gas pipeline valve, otherwise the valve has internal leakage.
to sum up
In recent years, the internal leakage phenomenon of oil and gas pipeline valves has frequently occurred, which is difficult to fundamentally solve, which seriously affects the safe production and 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 the occurrence of internal leakage of valves in oil and gas pipelines as much as possible. Through the analysis of the causes of valve internal leakage and related measures to determine whether there is an internal leakage in the valve, continuously strengthen the management of valve operation, maintenance, and repair, and actively seek new technologies for pipeline equipment maintenance, so as to avoid internal leakage of oil and gas pipeline valves The occurrence of this phenomenon further improves the management level of pipeline valves.