Valve Selection and Installation for Oxygen Pipelines

In oxygen pipeline systems, oxygen is a highly reactive gas, and its flow and handling must be approached with extreme caution. Due to oxygen's high reactivity, interactions with metals, non-metallic particles, static electricity, and other elements can lead to temperature increases, potentially triggering ignition mechanisms and causing serious accidents like fires or explosions. Therefore, the selection, installation, and maintenance of valves in oxygen pipelines require strict technical standards and comprehensive protection against factors that might pose safety hazards. Proper valve design and precise installation are crucial to ensuring the safe and stable operation of oxygen pipeline systems.

Working Principle and Flow Channel Design of Oxygen Valves

In typical valves, the medium flows into the valve body from below the valve disc and exits above the valve disc after passing through the seat. However, oxygen valves are designed differently under high-temperature and high-pressure conditions. The flow direction is reversed: oxygen enters the valve above the disc and exits below it after passing through the seat. This design not only accommodates high-temperature and high-pressure working conditions but also ensures stable gas flow.
The interior of the valve's flow channel must be smooth and free of impurities, with no irregular corners. When machining the flow channel, any grooves must be rounded to avoid sharp edges that could cause airflow instability or friction. Sharp angles inside the valve parts must be rounded off to avoid edges or points that might cause sudden pressure or directional changes, reducing the risk of friction-related hazards.

Anti-Static Structure and Protective Devices

Since oxygen is highly flammable, anti-static measures are critical in the design of oxygen valves. The valve should have an effective anti-static structure, with grounding resistance no greater than 10Ω and flange-to-flange resistance no greater than 0.03Ω. This ensures that static electricity buildup does not lead to sparks that could ignite the oxygen.
Additionally, the valve stem and its threads should be equipped with protective devices to prevent dust from entering the stem, which could reduce static spark formation. These protective devices ensure that the exposed part of the valve stem is isolated from the atmosphere, preventing dust from entering through the threads and contaminating the oxygen medium.

Oil-Free and Degreasing Treatment and Installation Requirements

Oil-free and degreasing treatment is a crucial step in preventing fire and explosion risks during valve manufacturing and installation. The valve body and internal components must undergo strict degreasing treatment before and after assembly to ensure that no metal shavings, grease, dust, or solid particles remain inside the valve. Such impurities could cause friction during oxygen flow, leading to combustion or explosions.
Before installing the valve, the pipeline should be thoroughly cleaned to remove all impurities and contaminants. The valve should be installed in the closed position to ensure that no impurities get trapped in the sealing seat. If the valve has already undergone degreasing before leaving the factory and remains uncontaminated, it can be installed directly. It is recommended to inspect all parts that come into contact with oxygen, using methods like ultraviolet light or filter paper tests.
For valves that have been repaired, degreasing treatment must be redone, and the valve should be blown clean with oil-free dry air or nitrogen before installation. During installation, the valve should be wrapped in clean cloth to avoid recontamination.

Installation and Welding Requirements

Welding of oxygen pipeline valves to the pipes is highly stringent. Argon arc welding or electric arc welding is typically used to ensure the quality of the welds. After welding large-diameter valves, the welds should undergo flaw detection to ensure there are no cracks or defects. For welding flanges with concave-convex designs, it is recommended to use copper welding wire as the O-ring material, as it effectively improves the pipeline's fire resistance and sealing properties.

Grounding of Pipelines and Flange Gasket Selection

Oxygen pipeline systems must have good grounding capabilities to ensure all metal connections are electrically conductive, preventing dangerous static electricity accumulation. The pipeline's grounding resistance should be less than 10Ω, and metal wires should be used to bridge the flange and threaded connections, ensuring the resistance is no greater than 0.03Ω.
The selection of flange gaskets depends on the system's operating pressure. For pressures below 3MPa, PTFE gaskets or flexible graphite composite gaskets are suitable; for pressures between 3MPa and 10MPa, spiral-wound gaskets, annealed copper gaskets, and nickel or nickel alloy gaskets are recommended; for pressures exceeding 10MPa, annealed copper gaskets or nickel and nickel alloy gaskets should be used to ensure both sealing and fire resistance.

Special Considerations and Maintenance

During the installation and operation of oxygen valves, for heavier valves, support devices should be installed before and after the valve to prevent the pipe from bending or deforming under the valve's weight. Oxygen regulating valve groups should be placed in independent valve rooms or protective enclosures to ensure the safety of operators and to prevent external conditions from affecting the valves.
Throughout the operation of the oxygen pipeline system, all valves and their connecting components should be regularly inspected to ensure their sealing, stability, and the effectiveness of protective devices. Regular checks and maintenance help identify potential safety risks and allow for timely repairs, ensuring the system's long-term safe operation.

Conclusion

The valve selection and installation requirements for oxygen pipeline systems are stringent and involve several technical and safety considerations. By choosing the appropriate valve materials, designing efficient flow channels, incorporating anti-static structures, performing thorough oil-free and degreasing treatments, and following strict installation standards, safety hazards caused by static electricity, friction, and contamination can be effectively prevented. With these measures in place, oxygen pipeline systems can operate safely and reliably in high-temperature, high-pressure environments, ensuring smooth production and operation processes.