Valves for Seawater Service
Seawater is highly corrosive due to dissolved chlorides (~3.5% NaCl), dissolved oxygen, biological activity (MIC), and temperature. Carbon steel corrodes rapidly; copper alloys, duplex stainless, and super-duplex are preferred for seawater service.
Pressure Range
0.5–25 bar — seawater lift to process system
Temperature
0–40°C (ambient seawater); up to 120°C in desalination brine
Industries
Offshore oil & gas, Desalination, Aquaculture
Key Properties — Seawater
- ~35,000 ppm chloride — aggressive to austenitic SS
- Oxygen content drives corrosion at ambient temperature
- Microbiologically influenced corrosion (MIC) from sulfate-reducing bacteria
- Biofouling blocks valve internals over time
- Velocity-accelerated corrosion in copper alloys above 3 m/s
Material Compatibility — Seawater
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. Acceptable only with cathodic protection and coating. |
| SS 316L | Fair | Pitting and crevice corrosion risk. Not recommended for seawater service. PREN must be verified. |
| Duplex 2205 | Good | PREN ~35 — acceptable for most seawater applications at ambient temperature. |
| Super-Duplex 2507 | Excellent | PREN ~43 — preferred for offshore seawater. Standard for North Sea applications. |
| Cupro-Nickel 90/10 | Good | Excellent for seawater up to 3 m/s velocity. Used in offshore fire water systems. |
| Naval Brass (HT Brass) | Good | Good for seawater at lower velocities. Not for high velocity or hot seawater. |
| Titanium Grade 2 | Excellent | Completely immune to seawater corrosion. Used in desalination. |
| Rubber-lined (EPDM) | Good | Good for seawater service at low pressure. |
Recommended Valves
Super-duplex butterfly valve
PREN >40, handles high chloride seawater — offshore standard
Cupro-nickel ball valve
Excellent for fire water and cooling water seawater systems
Titanium ball valve
Zero corrosion — used in desalination and highly critical seawater
Rubber-seated butterfly valve (EPDM)
Cost-effective for large diameter, low-pressure seawater service
Duplex 2205 gate valve
Seawater isolation in subsea and offshore process systems
Valves to Avoid
Carbon steel without cathodic protection and coating
Standard 304 or 316 stainless steel valves
Valves with aluminium bronze trim in high-velocity seawater
Cast iron valves
Special Considerations
Applicable Standards
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