Valves for Nitric Acid (HNO₃) Service
Nitric acid is a strong oxidising acid used in fertiliser production, explosives manufacturing, stainless steel passivation, and pharmaceutical synthesis. Its strong oxidising nature means carbon steel passivates at high concentrations - but ordinary stainless steels generally perform well unlike with HCl or H₂SO₄.
Pressure Range
1–20 bar
Temperature
Ambient to 80°C
Industries
Fertiliser (ammonium nitrate), Explosives (TNT, RDX), Pharmaceutical synthesis
Key Properties - Nitric Acid (HNO₃)
- Strong oxidiser - passivates carbon steel above ~65% concentration
- SS 304L and 316L perform well in dilute and concentrated HNO₃
- Fuming HNO₃ (>85%) is a strong oxidiser - attacks organics, rubber
- Red fuming HNO₃ contains dissolved N₂O₄ - extreme oxidiser
- Does not cause chloride SCC (unlike HCl)
Material Compatibility - Nitric Acid (HNO₃)
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 |
|---|---|---|
| SS 304L | Excellent | Standard for all concentrations of HNO₃. More resistant than 316L due to lower Mo content. |
| SS 316L | Good | Slightly lower corrosion resistance than 304L for HNO₃ due to molybdenum - but still widely used. |
| Carbon Steel (passivated) | Fair | Only for >65% concentration at ambient temperature - passivation layer forms. |
| Aluminium alloys | Good | Good for dilute HNO₃ - used in food-grade applications. |
| PTFE | Good | Acceptable for dilute and concentrated HNO₃ at ambient temperature. Verify for fuming acid. |
| Rubber (natural/NBR) | Not Recommended | Nitric acid attacks most rubbers and organics rapidly. |
| Hastelloy C-276 | Fair | Not ideal for HNO₃ - SS 304L is preferred due to Mo susceptibility. |
Recommended Valves
SS 304L ball valve
Standard for all HNO₃ concentrations - best corrosion resistance
SS 304L butterfly valve
Large bore, low-pressure HNO₃ service
PTFE-seated ball valve
Prevents nitric acid contact with valve body - sealing reliability
SS 304L diaphragm valve
Pharmaceutical or food-grade dilute HNO₃ - no dead-legs
Valves to Avoid
Rubber-lined valves (nitric acid attacks all common rubbers)
Hastelloy C-276 for hot concentrated HNO₃ (Mo susceptibility)
Carbon steel for dilute HNO₃
Special Considerations
Applicable Standards
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