What are the common faults of cryogenic valves

1. The failure occurs on every connection. Cryogenic valves belong to this type of failure: valve sealing and freezing, leakage of valve seat and pipe connection flange, leakage of tin-filled screws at both ends of the valve screw sleeve. Stem packing is usually located in the packing groove on the stem near the wall of the cold box. If the packing is uneven, not firm or the valve stem is not straight or round, the cryogenic liquid or gas will leak along the packing gap. External cold and heat transfer freezes the moisture in the air in the packing, which freezes the valve stem. In this case, only steam or hot water is used to heat the filler and open and close the valve. However, when the valve is opened or closed, the water that accumulates in the packing can freeze again. Because the valve switch is cumbersome, the fire valve often twists the valve stem, which damages the handwheel.
Therefore, after overhauling the valve, it is necessary to install and tighten the gasket evenly and tighten the compression nut. Leakage in the valve stem packing should also be checked during the overall leak test of the air separation unit and should be addressed prior to cold running. Common causes of flange leakage are rough, flat sealing surfaces, poor piping compensation, uneven bolt tightening, and improper bolt material. The end of the threaded sleeve on the outside of the stem is connected by a tin-filled thread, which is prone to cracking and leakage after long-term use. If the leak pressure test reveals a leak, the stem is best pulled out, refilled with tin and tightened, preferably with silver solder. Cryogenic valves are equipment that require frequent maintenance, high standards, strict requirements, and careful maintenance and use during the normal operation of the air separation plant.
2. The top of the valve is faulty. The valve crown (valve head) of this type of valve is movably attached to the valve stem so that the two sealing surfaces can “self-adjust” when the valve is closed. After long-term use, the non-return gasket will damage the titanium, nickel, zirconium, monel alloy valve, which will cause the locknut to loosen, and the valve top will fall off when the valve is opened. At this point, the valve loses its closing function. Lock nut damage may be due to improper material, use cold, brittle metal instead. Another common snag is that the top of the valve is not closing tightly, or the valve is leaking.
The common reason is that the top of the valve and the sealing surface of the valve seat are crushed by hard objects, such as silica gel, metal shavings, welding slag and other hard objects, resulting in dents. In this case, marine valves usually expend a lot of effort to close the valve, exacerbating the pressure loss. The centerline of the valve stem may not be perpendicular to the sealing surface (valve surface) of the valve seat, or the valve top surface and valve surface may wear out during long-term use, and the valve may leak.
3. Valve stem failure. A more common hindrance is thread wear on the valve stem and screw sleeve. This valve will not close due to the ceramic valve. In general, the threads on the stem are less likely to gall, while the internal threads on the threaded sleeve (brass) are more prone to damage. The reason may be that the force when opening the valve is too large, or the thread is difficult to twist even after opening and closing, and the thread is bitten.