Valves for Synthesis Gas (Syngas — CO + H₂) Service
Synthesis gas (syngas) is a mixture of carbon monoxide (CO) and hydrogen (H₂) produced by steam methane reforming (SMR), partial oxidation, or gasification of coal, biomass, or refinery residues. It is used as feedstock for ammonia synthesis, methanol production, Fischer-Tropsch GTL, and direct reduced iron (DRI). Syngas combines two highly hazardous components: CO is extremely toxic (TLV 25 ppm) and H₂ causes hydrogen embrittlement of high-strength steels. Both components are flammable, and syngas mixtures are pyrophoric at certain compositions.
Pressure Range
20–350 barg (SMR reformer to high-pressure synthesis loop)
Temperature
200–900°C (reformer outlet) down to ambient in downstream sections
Industries
Ammonia plants (SMR syngas), Methanol plants, GTL (Fischer-Tropsch)
Key Properties — Synthesis Gas (Syngas — CO + H₂)
- CO component: extremely toxic (TLV-TWA 25 ppm), colourless and odourless
- H₂ component: causes hydrogen embrittlement (HE) of high-strength ferritic steels
- Highly flammable mixture: flammability range 12–75% H₂, 12–74% CO in air
- Nelson curves applicable: high-temp, high-partial-pressure H₂ causes HTHA in carbon steel
- CO can cause nickel carbonyl formation with nickel-containing alloys at certain conditions
Material Compatibility — Synthesis Gas (Syngas — CO + H₂)
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 (PWHT per API 941 Nelson curves) | Good | Acceptable for lower partial pressure H₂ service per API 941 Nelson curves. PWHT mandatory. |
| SS 316L | Excellent | Excellent for syngas at all conditions; austenitic SS not susceptible to HE. |
| A217 WC6 / WC9 | Good | Low-alloy Cr-Mo steel per Nelson curves for high-temperature syngas. |
| Nickel alloys (Inconel 625) | Fair | Avoid in high CO partial pressure — risk of nickel carbonyl formation above 150°C. |
| Duplex 2205 | Fair | Not recommended for high-H₂-partial-pressure above 50 barg without NACE review. |
Recommended Valves
Gate Valve (PWHT Cr-Mo steel, pressure-seal bonnet)
Main isolation for high-pressure syngas headers in SMR and ammonia plants
Globe Valve (PWHT Cr-Mo, Stellite trim)
Control of syngas flow in reforming circuits — Stellite seat for erosion resistance
Ball Valve (SS 316L body, Class 600–1500)
Isolation in syngas synthesis loops where tight shutoff is required
Check Valve
Prevention of reverse syngas flow on compressor discharge
Safety Relief Valve
Mandatory overpressure protection in all syngas process sections
Valves to Avoid
High-strength steel valves (>90 ksi TS) not validated to NACE MR0103
Nickel-trim valves in high-CO partial pressure above 150°C
Special Considerations
Applicable Standards
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