Valves for Caustic Soda (NaOH) Service
Sodium hydroxide (caustic soda) is used extensively in the chlor-alkali industry, paper & pulp, alumina refining, and chemical manufacturing. Concentrated NaOH attacks aluminium and zinc. Hot caustic above 60°C attacks SS 304/316 via stress corrosion cracking (caustic SCC).
Pressure Range
1–25 bar
Temperature
Ambient to 130°C
Industries
Chlor-alkali production, Paper & pulp (kraft pulping), Alumina refining (Bayer process)
Key Properties — Caustic Soda (NaOH)
- Strong alkali — highly corrosive to aluminium, zinc, and tin
- Caustic SCC: SS 304/316 susceptible above 60°C
- Carbon steel generally acceptable at concentrations up to 50% at ambient temperature
- Exothermic dissolution — generates heat on dilution
- Solidifies below ~12°C at 50% concentration — freeze protection required
Material Compatibility — Caustic Soda (NaOH)
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) | Good | Acceptable up to 50% NaOH at ambient temperature. Not for hot concentrated caustic. |
| SS 316L | Fair | Risk of caustic SCC above 60°C. Cold dilute service only — verify. |
| Nickel 200/201 | Excellent | Best all-round material for hot concentrated NaOH. Industry standard. |
| Monel 400 | Good | Good for hot caustic service — preferred where Nickel 200 is cost-prohibitive. |
| PTFE-lined | Excellent | Chemically inert to all NaOH concentrations. |
| Rubber-lined (natural rubber/EPDM) | Good | Good up to 50% at ambient temperature. |
| Aluminium alloys | Not Recommended | Rapidly attacked at all concentrations. |
Recommended Valves
Nickel 200 globe valve
Hot concentrated NaOH — gold standard material, no SCC risk
PTFE-lined ball valve
All concentrations — inert lining, no metal contact
Carbon steel gate valve
Ambient dilute caustic process service
Rubber-lined butterfly valve
Large bore, low-pressure dilute NaOH systems
Valves to Avoid
Aluminium-bodied valves (any concentration)
Zinc die-cast components
SS 304/316 in hot caustic above 60°C
Bronze or brass valves
Special Considerations
Applicable Standards
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