Causes of internal leakage of ball valves
1) Reasons for internal leakage of the valve during the construction period:
① Improper transportation and hoisting cause the overall damage of the valve, resulting in internal leakage of the valve; ② When leaving the factory, the valve was not dried and treated with anti-corrosion after the water pressure was applied, causing the sealing surface to corrode and form internal leakage; ③ The construction site protection was not in place, and the valve There are no blind plates installed at both ends, and impurities such as rainwater and sand enter the valve seat, causing leakage; ④ During installation, no grease is injected into the valve seat, causing impurities to enter the back of the valve seat, or internal leakage caused by burns during welding; ⑤ Valve It is not installed in the fully open position, which will cause damage to the ball. During welding, if the valve is not in the fully open position, the welding spatter will cause damage to the ball. When the ball with welding spatter is turned on and off, the valve seat will be further damaged, thus Cause internal leakage; ⑥ Welding slag and other construction residues cause scratches on the sealing surface; ⑦ Inaccurate limit position during delivery or installation causes leakage, if the valve stem drive sleeve or other accessories are assembled at a wrong angle, the valve will leak.
2) Reasons for internal leakage of the valve during operation:
① The most common reason is that the operation manager does not maintain the valve considering the relatively expensive maintenance costs, or lacks scientific valve management and maintenance methods to prevent preventive maintenance of the valve, resulting in early failure of the equipment; ② Improper operation or lack of Carry out maintenance according to maintenance procedures to cause internal leakage; ③ During normal operation, construction residues scratch the sealing surface, resulting in internal leakage; ④ Improper pigging causes damage to the sealing surface and causes internal leakage; The seat and the ball are locked, causing seal damage and internal leakage when the valve is opened and closed; ⑥ The valve switch is not in place, causing internal leakage. Any ball valve, regardless of the open or closed position, generally tilts 2° to 3°, which may cause leakage; ⑦ Many large-diameter valves may cause leakage. Most ball valves have valve stem stoppers. If they are used for a long time, rust, dust, paint and other debris will accumulate between the valve stem and the valve stem stopper due to rust and other reasons. These debris will prevent the valve from rotating in place. Cause leakage – if the valve is buried, the lengthening of the valve stem will produce and drop more rust and impurities to prevent the valve ball from rotating in place, causing the valve to leak. Hardening or loosening of the limit bolt will make the limit inaccurate, resulting in internal leakage; ⑨ The valve position of the electric actuator is set to the front, and it is not closed in place, resulting in internal leakage; ⑩ The lack of periodic maintenance and maintenance will cause the sealing grease to dry out , Hardened and dried sealing grease accumulates behind the elastic valve seat, hindering the movement of the valve seat and causing the seal to fail.
The fixed shaft ball valve is commonly used in natural gas pipelines. The general inspection method is: turn the valve to the fully open or fully closed position, and check whether there is leakage through the discharge of the valve body drain nozzle. If it can be drained cleanly, the seal is good. If there is always pressure discharge, it can be considered that the valve is leaking, and the valve should be treated accordingly.
Treatment procedure for internal leakage of natural gas ball valve
① First check the limit of the valve to see if the internal leakage of the valve can be solved by adjusting the limit. ②Inject a certain amount of grease first to see if it can stop the leakage. At this time, the injection speed must be slow. At the same time, observe the change of the pointer of the pressure gauge at the outlet of the grease injection gun to determine the internal leakage of the valve. ③ If the leakage cannot be stopped, the internal leakage may be caused by the hardening of the sealing grease injected in the early stage or the damage of the sealing surface. It is recommended to inject valve cleaning fluid at this time to clean the sealing surface and valve seat of the valve. Generally, it is soaked for at least half an hour, if necessary, it can be soaked for several hours or even a few days. It is best to open and close the active valve several times during this process. ④ Re-inject the grease, open and close the valve intermittently, and discharge the impurities out of the back cavity of the valve seat and the sealing surface. ⑤ Check at the fully closed position. If there is still leakage, inject reinforced sealing grease, and open the valve cavity to vent, which can generate a large pressure difference and help seal. In general, by injecting reinforced sealing grease Endoleak can be eliminated. ⑥ If there is still internal leakage, repair or replace the valve.
Post time: Jul-09-2022