C95800 NAB vs SS316 vs Super Duplex for Seawater Valves
Technical guide · Supreme Valves India · Updated 2026-10-28
Direct answer: For seawater shutoff, SS316 alone is often the wrong default. Prefer nickel aluminium bronze (C95800) when the marine/desal BOQ names Al-bronze/NAB, or super duplex when the owner bans copper alloys or chloride duty exceeds NAB’s project envelope. Write the UNS number on the RFQ.
Material comparison (buyer view)
| Material | Seawater note | Typical valve types |
|---|---|---|
| SS316 / CF8M | Risky in stagnant chlorides; OK for many non-seawater chemicals | Process ball/gate inland |
| C95800 NAB | Proven seawater casting alloy on marine BOQs | Ball, butterfly, check Class 150 |
| Super duplex (e.g. F53/F55 family) | High chloride / high spec projects | Critical seawater isolation |
BOQ patterns we see
BODY MOC ALUMINIUM BRONZE ASTM B148 UNS C95500 / C95800BALL VALVE FULL BORE FLANGED RF NAB C95800 PTFE SEAT- Desal packages comparing NAB vs super duplex on the same P&ID
RFQ checklist
- UNS number (C95800 vs C95500)
- Seawater / desal / fire-water duty
- Ends RF or FF
- Seat material compatible with seawater
Start with the NAB ball RFQ and NAB hub.
Frequently asked questions
Why is SS316 often rejected for seawater?
Chloride pitting and crevice corrosion risk under deposits and stagnant seawater. Many marine and desal specs move to NAB or duplex/super duplex instead of relying on 316 alone.
When is C95800 NAB the right call?
Seawater ball, butterfly and check valves on fire-water, cooling and desal lines where aluminium bronze is named on the datasheet. Match UNS C95800 or C95500 exactly as written.
When is super duplex worth the cost?
High chloride, higher velocity, or owner specs that ban copper alloys. Confirm welding/NACE requirements and delivery — super duplex is not a drop-in NAB substitute without design review.