904L or 2205 Stainless steel membrane housing For handling concentrated phosphoric acid (H₃PO₄), the choice between 904L and 2205 stainless steel depends on the concentration, temperature, and presence of impurities (especially chlorides or fluorides). Here’s a direct comparison to guide your material selection:
| Property | 904L Stainless Steel | 2205 Duplex Stainless Steel |
|---|---|---|
| Composition | High Ni (25%), Mo (4.5%) | Balanced ferritic-austenitic, ~22% Cr, 5% Ni, 3% Mo |
| Phosphoric Acid Resistance | Excellent (especially pure acid) | Moderate to Good (risk of localized corrosion) |
| Chloride Stress Corrosion Cracking (SCC) | Very resistant | Less resistant (better than 316L but worse than 904L) |
| Cost | Higher | Lower |
| Mechanical Strength | Lower than 2205 | Higher (duplex strength) |
🧪 Material Performance in Phosphoric Acid
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904L is specifically designed for strong acid resistance, particularly in non-oxidizing acids like phosphoric acid.
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Performs well in all concentrations of H₃PO₄ up to boiling point.
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Particularly good in pure or fertilizer-grade phosphoric acid.
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2205 Duplex can be used in dilute to moderately concentrated phosphoric acid, but it is not ideal for highly concentrated or hot acid, especially if chlorides or fluorides are present.
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Risk of pitting and crevice corrosion increases with impurities or elevated temperatures.
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✅ Recommendation
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Use 904L stainless steel for concentrated phosphoric acid, especially above 50% concentration or if the acid is hot.
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Use 2205 only for diluted phosphoric acid under controlled conditions (low temp, low impurities).
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🧯 Important Note
If fluorides or chlorides are present in the phosphoric acid (as in “wet-process” acid used in fertilizers), even 904L may not suffice, and Hastelloy or plastic-lined systems might be needed.
Let me know your exact operating conditions (temperature, acid concentration, presence of impurities), and I can give a more precise material recommendation.
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