For seawater or high-chloride service, should valve material be duplex stainless steel or 316 stainless steel?
• Conclusion: duplex 2205 is preferred for seawater; 316 stainless is prone to pitting and crevice corrosion.
• 316 pitting risk rises sharply when chloride >200 ppm and temperature >60°C.
• Duplex 2205 has PREN ≥34, much higher chloride resistance than 316 with PREN ≈25.
• Body, stem and ball should all be duplex to avoid galvanic corrosion.
• For mildly corrosive fresh water, 316 is acceptable with CF8M material certificate specified.
• 316 pitting risk rises sharply when chloride >200 ppm and temperature >60°C.
• Duplex 2205 has PREN ≥34, much higher chloride resistance than 316 with PREN ≈25.
• Body, stem and ball should all be duplex to avoid galvanic corrosion.
• For mildly corrosive fresh water, 316 is acceptable with CF8M material certificate specified.