Reasons for internal leakage in ball valves:

1. Causes of internal leakage during the construction period:

① Improper transportation and lifting causing overall damage to the valve, thereby resulting in internal leakage;

② During factory production, if the water pressure test was not conducted followed by drying and anti-corrosion treatment of the valve, the sealing surface would be corroded and internal leakage would occur;

③ Insufficient protection at the construction site, without installing blind plates at both ends of the valve, and impurities such as rainwater and sand entered the valve seat, causing leakage;

④ During installation, if no lubricating grease was injected into the valve seat, impurities would enter the rear part of the valve seat, or welding would cause internal leakage due to burn injury;

⑤ If the valve was not installed in the fully open position, the ball would be damaged during welding. If the valve was not in the fully open position, the welding splashes would cause damage to the ball, and when the ball with the welding splashes was switched, it would further cause damage to the valve seat, thereby resulting in internal leakage;

⑥ Construction remnants such as welding slag would cause scratches on the sealing surface;

⑦ Inaccurate limit settings during factory or installation would cause leakage. If the valve stem drive sleeve or other accessories were assembled at an incorrect angle, the valve would leak.

The causes of internal leakage in the valve during operation:

① Common reasons are that the operation manager considers the relatively high maintenance costs and does not perform maintenance on the valve, or lacks scientific valve management and maintenance methods and does not perform preventive maintenance, resulting in the equipment prematurely failing;

② Improper operation or failure to follow the maintenance procedures would cause internal leakage;

③ During normal operation, construction remnants would scratch the sealing surface, causing internal leakage;

④ Improper pigging would cause damage to the sealing surface, resulting in internal leakage;

⑤ Long-term lack of maintenance or inactivity of the valve would cause the valve seat and ball to become stuck, resulting in damage to the seal during valve opening and closing, and internal leakage;

⑥ Inadequate valve opening or closing would cause internal leakage. For any ball valve, regardless of the open or closed position, a tilt of 2° to 3° would usually cause leakage;

⑦ Many large-diameter ball valves have valve stem stop blocks. If used for a long time, due to rust and other reasons, rust, dust, paint, and other debris would accumulate between the valve stem and the valve stem stop block, causing the valve to be unable to rotate to the proper position and resulting in leakage - if the valve is buried, the extended valve stem would generate more rust and impurities that would hinder the valve ball from rotating to the proper position, causing valve leakage;

⑧ Most actuators also have limiters. If they are corroded for a long time, the lubricating grease would harden or the limit screw would loosen, causing inaccurate limiters and internal leakage;

⑨ The valve position setting of the electric actuator is set too far forward, resulting in internal leakage;

⑩ Lack of periodic maintenance and upkeep would cause the sealing grease to dry and harden, with dried sealing grease accumulating behind the elastic valve seat, hindering the valve seat movement, resulting in sealing failure.

The method for judging internal leakage of natural gas ball valves:

The commonly used ball valves on natural gas pipelines are fixed-axis ball valves. The general inspection method is: rotate the valve to the fully open or fully closed position, and check for leakage through the discharge port of the valve body. If the discharge can be completely cleaned, it indicates good sealing. If there is always pressure discharge, it can be considered that the valve is leaking, and the valve should be dealt with accordingly.