Valves for Carbon Monoxide (CO) Service
Carbon monoxide is a colourless, odourless, highly toxic gas encountered in syngas (CO + H₂), steel plant blast furnace gas (BFG), coke oven gas (COG), methanol synthesis, Oxo alcohols production, and as a combustion product. Its key hazard is that it is lethal at low concentrations (TLV-TWA 25 ppm; IDLH 1,200 ppm) without sensory warning. At high partial pressures and temperatures above 150°C, CO reacts with nickel to form nickel carbonyl [Ni(CO)₄] — an even more toxic compound — making nickel-containing alloys unsuitable for certain CO services.
Pressure Range
0.1–350 barg
Temperature
Ambient to +900°C (blast furnace/reformer)
Industries
Steel plant (blast furnace gas, coke oven gas), Syngas and ammonia plants, Methanol production
Key Properties — Carbon Monoxide (CO)
- TLV-TWA 25 ppm; IDLH 1,200 ppm — toxic at very low concentrations, no odour
- Flammable: 12.5–74% in air
- Nickel carbonyl formation above 50°C and high CO partial pressure — avoid nickel alloys
- Nelson curves do not directly apply to CO, but co-present H₂ governs HTHA risk
- Pyrophoric risk on venting to air — CO ignites spontaneously under some conditions
Material Compatibility — Carbon Monoxide (CO)
Ratings are indicative. Actual compatibility depends on concentration, temperature, velocity, and presence of contaminants. Always consult corrosion tables or a materials engineer.
| Material | Rating | Notes |
|---|---|---|
| Carbon Steel (WCB, PWHT) | Excellent | Standard for most CO service. PWHT required for weld-end valves. |
| SS 316L | Good | Acceptable for CO service; avoid where nickel content is a concern for Ni(CO)₄ formation. |
| Nickel alloys (Inconel, Monel) | Poor | Nickel carbonyl formation above 150°C — avoid in high-CO partial pressure service. |
| Hastelloy C-276 | Fair | High nickel content — same Ni(CO)₄ risk as above. Verify with process chemist. |
Recommended Valves
Gate Valve (carbon steel, pressure-seal bonnet)
High-pressure CO gas line isolation in syngas and blast furnace circuits
Ball Valve (WCB, PTFE seat)
Isolation and block service for CO lines in methanol and Oxo plants
Globe Valve (WCB, Stellite trim)
Control service in CO synthesis circuits
Safety Relief Valve
Mandatory overpressure protection — CO must vent to safe location (flare)
Check Valve
Compressor protection on CO discharge lines
Valves to Avoid
Nickel-base alloy valves in high CO partial pressure above 150°C
Non-PWHT welded valves in CO service
Special Considerations
Applicable Standards
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