Seawater duty is a materials question wearing a low-pressure disguise. The pressures and temperatures are mild; the chloride is not. The body-material rating table does the heavy lifting here, and the difference between a stainless grade that survives and one that pits is exactly what a knowledge base is for.
Intake, screening and RO feed lines are the common runs. The reference duty below is a mid-size isolation point on an intake header.
Typical duties
| Seawater intake and screening | Seawater · 6–16 bar · ambient · DN200–600 |
|---|---|
| RO feed and process headers | Seawater/brine · 16–25 bar · ambient · DN100–300 |
| Discharge and outfall | Seawater · ≤10 bar · ambient · DN300–800 |
16 bar · 35 °C · DN300 on Seawater / Brine (liquid): Butterfly Valve (concentric / double-offset / triple-offset) · body Stainless steel 316 (ASTM A351 CF8M) · Class 150.
at DN300 and Class 150 a butterfly valve is a fraction of the weight and cost of the alternatives
/* r11 P3-6 (user-approved): the duty-specific caution (e.g. class utilisation) belongs ON the page, not only in the unlocked report — the last boilerplate line stays report-only */Watch: Your duty uses 84% of the Class 150 rating at this temperature (16 bar of 19 bar) — inside the published rating, but with little room for pressure surges. Ask the manufacturer to confirm, or consider the next class up.
What to watch
- The ratings table, not habit, picks the body: read what the KB says about each cast material in seawater before defaulting to 316.
- Large sizes favour butterfly and check valves; the envelope notes say where each type's range stops.
- If the line sees throttling duty, say so — isolation answers do not transfer to regulation.
Where this connects on this site
- Seawater as a medium — the compatibility table
- Butterfly valves — the large-DN default
- Check valves — pump-discharge protection
Boundary rule: this page states single-point conclusions from the site's knowledge base — no supplier names, no matrices. The full 40-medium library lives in the selector.