Material compatibility is the first and most critical step in valve selection for chemical service. A valve may be correctly sized, correctly rated, and correctly actuated — but if the body, trim, or seat material is incompatible with the process fluid, it will fail. This guide covers the most common chemical services encountered in process plants and the corresponding material recommendations.
Compatibility Matrix — Common Chemicals
| Chemical | Carbon Steel (WCB) | SS316L | Hastelloy C-276 | PTFE Seats | EPDM Seats |
|---|---|---|---|---|---|
| Hydrochloric acid (HCl) | No | No (>5%) | Yes | Yes | No |
| Sulphuric acid H₂SO₄ (>70%) | Yes (concentrated) | Limited | Yes | Yes | No |
| Nitric acid HNO₃ | No | Yes (<65%, cold) | Limited | Yes | No |
| Caustic NaOH (<70%) | Yes (<65°C) | Yes | Yes | Yes | Yes |
| Hydrogen Peroxide H₂O₂ | No | Limited (<30%) | Yes | Yes | Limited |
| Chlorine gas (wet) | No | No | Limited | N/A | No — FKM only |
| Acetic acid (<50%) | No | Yes | Yes | Yes | Yes |
| Seawater (Cl⁻ 19,000 ppm) | No (bare) | No (SCC risk) | Yes | Yes | Yes |
| Ammonia (NH₃) | Yes (dry) | Yes | Yes | Yes | Yes (not Neoprene) |
| Acetone / Ketones | Yes | Yes | Yes | Yes | No (swells EPDM) |
| Toluene / Xylene | Yes | Yes | Yes | Yes | No — FKM only |
| Methanol / Ethanol | Yes | Yes | Yes | Yes | Yes |
Key Material Selection Rules
- SS316L vs SS304: Use SS316L (not SS304) whenever chlorides are present — molybdenum content in 316L resists pitting; SS304 lacks Mo and pits in seawater and HCl
- Hastelloy C-276 (N10276) is the broadest-spectrum corrosion-resistant alloy — resists HCl, H₂SO₄, HF, oxidising and reducing acids, and seawater; use where no other material works
- PTFE seats are chemically compatible with almost all chemicals except fluorine gas and molten alkali metals — they are the universal seat material for chemical service
- EPDM seats resist alkalis, acids (pH 2–12), steam, and hot water — NOT suitable for hydrocarbons, oils, or solvents (swell and fail)
- FKM (Viton) seats resist hydrocarbons, aromatic solvents, and chlorinated solvents — NOT suitable for hot water, steam, or ketones
- Never use copper, brass, or bronze in ammonia service — ammonia forms copper-ammonia complexes, corroding the alloy
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