Valves for Phosphoric Acid (H₃PO₄) Service
Phosphoric acid is a moderate acid used in fertiliser production (wet process phosphoric acid), food processing, metal surface treatment, and semiconductor manufacturing. Wet process P₂O₅ contains fluoride and sulfate impurities that dramatically increase corrosivity over pure acid.
Pressure Range
1–16 bar
Temperature
Ambient to 100°C
Industries
Fertiliser (DAP, MAP, SSP), Food additives (cola, baking powder), Metal surface treatment (pickling)
Key Properties — Phosphoric Acid (H₃PO₄)
- Wet process phosphoric acid contains HF and H₂SO₄ impurities — far more corrosive
- Pure food-grade phosphoric acid is relatively mild
- SS 316L acceptable for food-grade and clean phosphoric acid
- Fluoride content in wet process acid attacks many metals and PTFE at elevated temperature
- Rubber lining is a primary defence for wet process acid
Material Compatibility — Phosphoric Acid (H₃PO₄)
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 | Poor | High corrosion rate in most phosphoric acid concentrations. |
| SS 316L | Good | Food-grade or pure H₃PO₄ up to 85% at ambient. Not for wet process acid with fluoride. |
| Hastelloy C-276 | Excellent | Best choice for wet process phosphoric acid with fluoride impurities. |
| Rubber-lined (natural rubber) | Good | Excellent for wet process acid — industry standard for large bore piping. |
| FRP / PVDF-lined | Good | PVDF good for clean phosphoric acid service. |
| PTFE-lined | Good | Excellent for clean phosphoric acid. Caution with fluoride-bearing wet process acid at elevated temperature. |
Recommended Valves
Hastelloy C-276 ball valve
Wet process phosphoric acid with fluoride/sulfate impurities
Rubber-lined butterfly valve
Large bore wet process acid service — industry standard
SS 316L ball valve
Food-grade and pure phosphoric acid service
PTFE-lined diaphragm valve
Clean phosphoric acid in pharmaceutical and food processing
Valves to Avoid
Carbon steel valves (high corrosion rate)
Copper alloys
Standard SS 304 in concentrated acid
Special Considerations
Applicable Standards
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