The secret of high-pressure valves: the guardian of robustness and precision

‌Refinery Site Observation‌
In the hydrocracking unit area of ​​Zhenhai Refining and Chemical, engineer Chen Li is calibrating the bolts of a DN80 valve with a torque wrench. "This High Pressure Gate Valve is 1.8 times thicker than an ordinary gate valve," he tapped the shiny surface, "The A182 F22 material is normalized three times during forging, and the grain size can reach ASTM 7 level."

‌Structural hardcore configuration‌
▌Wedge gate: 7° bevel with built-in "pressure compensation", the system automatically increases the sealing pressure by 8.5MPa for every 10MPa increase in pressure
▌Valve stem protection: Nitrided 17-4PH stainless steel valve stem, surface hardness reaches HRC45, a natural gas project has undergone more than 8000 hours of sulfide stress cracking test
▌Flange reinforcement: The neck taper of the neck welding flange (WN type) is 12°, which is 40% higher than the bearing capacity of the flat welding flange

‌Limit verification moment‌
At the Dushanzi Petrochemical Test Site, a PN420 gate valve is undergoing severe tests:
•Instantaneous pressure: pressurized from normal pressure to 630MPa (1.5 times the design pressure), maintained for 30 minutes without deformation
•Hot and cold shock: after being immersed in liquid nitrogen at -196℃, 560℃ high-temperature oil and gas are immediately introduced, and there is no leakage after 50 cycles
• Particle wear: The medium containing 15% catalyst is continuously flushed at a flow rate of 25m/s, and only a shallow mark of 0.07mm is produced on the gate sealing surface

‌Maintenance Iron Rule‌

After each operation, it must be retracted 1/8 turn to prevent the gate from being over-pressurized and embedded in the valve seat (a factory thus avoids the gate from getting stuck during annual maintenance)
The packing gland bolts must be tightened diagonally twice and the final torque is locked, and the error is controlled within ±5N·m
When the spare valve is stored, the valve stem must be rotated 20° every month to prevent static friction oxidation of the sealing surface
This revision of GB/T 12234 adds special test clauses for high-pressure valves, requiring that the API 598 zero leakage standard can be achieved after 300 openings and closings under pressure. This "industrial dumbbell" guards the high-pressure lifeline of 23 industries from shale gas mining to coal chemical industry.