Valves for Ammonia (NH₃) Service
Ammonia is handled as a refrigerant (R-717), in fertiliser production, and as a chemical feedstock. It attacks copper alloys and zinc. For refrigeration systems, IIAR standards apply. Toxic (IDLH: 300 ppm) — requires leak-tight valve design.
Pressure Range
Up to 25 bar (refrigerant); up to 200 bar (synthesis gas)
Temperature
-33°C (liquid refrigerant) to 300°C (synthesis service)
Industries
Fertiliser / urea production, Cold storage / refrigeration, Chemical production
Key Properties — Ammonia (NH₃)
- IDLH: 300 ppm — toxic, requires gas detection
- Carbon steel is the primary material for liquid and gas ammonia
- Attacks copper, zinc, and their alloys
- Cryogenic liquid service: -33°C at atmospheric pressure
- Stress corrosion cracking of brass and copper alloys
Material Compatibility — Ammonia (NH₃)
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/A105/A333 Gr.6) | Excellent | Standard for ammonia — both refrigerant and process service. |
| SS 304/316 | Good | Acceptable but not normally required. Used where contamination is a concern. |
| Copper alloys (brass, bronze) | Not Recommended | SCC and corrosion — strictly prohibited in ammonia service. |
| Zinc alloys / Die-cast zinc | Not Recommended | Attacked by ammonia — all zinc must be absent. |
| PTFE | Good | Acceptable for seats and seals. |
| Nylon | Not Recommended | Degraded by ammonia. |
| EPDM | Good | Acceptable for refrigerant ammonia seals. |
Recommended Valves
Carbon steel globe valve (IIAR-rated)
IIAR standard for NH₃ refrigeration systems
Carbon steel ball valve (low-temp rated A333)
Process ammonia isolation and control
Cryogenic gate valve (extended bonnet)
Liquid ammonia -33°C storage — extended bonnet keeps packing at ambient
Pressure relief valve (spring-loaded)
Critical safety device on all pressurised ammonia vessels
Valves to Avoid
Any valve with copper, brass, or bronze wetted parts or body
Valves with zinc die-cast components
Nylon or polyamide-seated valves
Globe valves not rated for cryogenic temperatures in liquid NH₃ service
Special Considerations
Applicable Standards
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