During a major overhaul of a large integrated refining and chemical enterprise, multiple API 600 gate valves used in the low-temperature unit of the ethylene plant were repaired and put back into use. Their sealing performance under ultra-low temperature conditions has attracted attention from peers.
The medium temperature of this unit is close to minus zero degrees Celsius and contains a small amount of hydrogen sulfide and moisture. Conventional gate valves are prone to material brittleness and sealing surface freezing problems in this environment. The gate valve selected by the enterprise is designed according to the API 600 standard, and the valve body material is made of alloy steel with qualified low-temperature impact toughness. The valve stem is treated with nitriding, and the packing is made of low temperature resistant graphite. The gate and valve seat are matched and ground to ensure compatibility.
During disassembly and inspection, maintenance personnel found that after continuous operation cycles, the internal sealing surface of the valve was slightly worn, there were no corrosion marks on the surface of the valve stem, and the packing box still maintained good elasticity. The opening and closing torque of the low-temperature gate valve has increased in the cold state, but the handwheel operation of this batch of valves is still relatively smooth without any jamming phenomenon. In recent years, refining enterprises have continuously extended maintenance intervals to improve production efficiency, and have put forward higher requirements for the long-term reliability of valves.
The API 600 standard covers low-temperature impact testing methods, providing a basis for material selection under low-temperature conditions. The results of this maintenance indicate that gate valves manufactured strictly according to standards can meet the demanding requirements of low-temperature refining environments, help reduce unplanned shutdowns, and ensure long-term operation of the equipment.
