Reasons for valve internal leakage during construction
Improper transportation and hoisting may cause overall damage to the valve, leading to internal leakage;
Failure to dry and anticorrosion treatment of the ball valve after water pressure test during factory delivery results in rust formation on the sealing surface, causing internal leakage;
Inadequate protection on construction site, without blind plates installed at both ends of the valve, rainwater, sand and other impurities enter the valve seat, causing leakage;
Failure to inject grease into the valve seat during installation results in impurities entering the rear of the valve seat, or welding burn causes internal leakage;
Failure to install the valve in the fully open position results in damage to the ball, if the valve is not in the fully open position during welding, the welding spatter will cause damage to the ball, and if the ball with welding spatter is further switched, it will cause damage to the seat, resulting in internal leakage;
Weld slag and other construction debris cause scratches on the sealing surface;
inaccurate limit position during factory delivery or installation causing leakage, if the stem driving sleeve or other accessories of the natural gas ball valve are not aligned, the valve will leak.
Reasons for valve internal leakage during operation
The most common reason is that maintenance costs are considered too high by the operator, and there is a lack of scientific valve management and maintenance methods, resulting in premature equipment failure;
Improper operation or failure to follow maintenance procedures causes internal leakage;
Scratches on the sealing surface caused by construction debris during normal operation result in internal leakage;
Improper pipeline cleaning causes damage to the sealing surface, resulting in internal leakage;
Long-term maintenance-free or inactive valves result in seizing of the seat and ball, causing sealing damage during valve switch;
Internal leakage is caused by improper opening/closing position of the ball valve. Regardless of the open/closed position of the ball valve, a tilt of 2° to 3° may cause leakage;
Most large-diameter ball valves have stem limit blocks. If used for a long time, rust, dust, and paint will accumulate between the stem and the stem limit block due to rust and other reasons. These impurities will cause the valve to be unable to rotate into place, resulting in leakage - if the valve is buried underground, an extended stem will cause more rust and impurities to hinder the ball from rotating into place, causing valve leakage;
General actuators also have limit positions. If corroded for a long time, lubricating grease hardens or limit bolts become loose, the limit position will be inaccurate, resulting in internal leakage;
The valve position setting of the electric actuator is too far forward, and it is not completely closed, causing internal leakage;
Lack of periodic maintenance and lubrication, causing the sealing grease to dry and harden. The dried sealing grease accumulates behind the elastic seat, blocking the movement of the seat and causing sealing failure.
The commonly used inspection method for fixed axis natural gas ball valves on natural gas pipelines is to rotate the valve to the fully open or fully closed position, and check for leaks through the valve body's vent valve. If clean discharge can be achieved, it indicates good sealing. If pressure is always being discharged, it indicates the valve is leaking, and appropriate measures should be taken accordingly.