Valves are one of the main leakage sources in the pipeline system of the petrochemical industry, so it’s critical to the leakage of valves. Valve leakage rates are actually the valve sealing level, valve sealing performance is referred to as the valve sealing parts to prevent the ability of media leakage.
The main sealing parts of the valve including the contact surface between the opening and closing parts and the seat, the fitting of packing and stem and packing box, the connection between the valve body and the bonnets. The former belongs to internal leakage, which directly affects the ability of the valve to cut off the medium and the normal operation of the equipment. The last two are external leakage, that is, media leakage from the inner valve. The loss and environmental pollution caused by external leakage are often more serious than that caused by internal leakage. Then do you know what caused the valve leakage?
Casting and forging valve body
The quality defects formed in the casting process such as sand holes, sand, slag holes and pores, and the forging quality defects like cracks and folds, both can cause leakage in the valve body.
The sealing of the stem part is the packing in the valve, that is designed to prevent gas, liquid and other media leakage. valve leakage will be caused by the deflection of gland fastening, improper packing bolt fastening, too little packing, wrong packing material and improper packing installation method in the installation process of packing.
Incorrect or inappropriate seal ring material, poor surfacing welding quality with body; loose thread, screw and pressure ring; seal ring mounting, or use of a defective seal ring that was not found in the pressure test, resulting in valve leakage.
Rough grinding of sealing surface, deviation of assembly of valve stem and closing part, improper quality selection of sealing surface material will cause leakage of the contact part between the sealing surface and valve stem.
In general, external leakage of valves is mainly caused by the poor quality or improper installation of the cast body, flange, and packing. Internal leakage often occurs in three parts: open and close parts and seat sealing surface of the joint, valve body and bonnet joint, valve closed position.
In addition, improper valve types, medium temperature, flow, pressure, or valve switch can not be fully closed, which will also cause valve leakage. Valve leakage is not allowed especially for high temperature and pressure condition, flammable, explosive, toxic or corrosive media, so the valve must provide reliable sealing performance to meet the requirements of its use conditions on the leakage.