Stainless application
Stainless Steel for Marine & Offshore
Seawater is the harshest chloride environment stainless steel ever meets. The grade ladder is set by it: 316L for splash and atmospheric duty, 2205 duplex where the part is submerged and stressed, 2507 super duplex where seawater is warm, stagnant or chlorinated. Crevices, not the open surface, are what fail first.
Specification
What Marine & Offshore Specifies
| Grades normally used | 316L · 2205 · 2507 |
|---|---|
| Product forms | Seamless tube · Plate · Fittings · Flanges · Bar |
| Standards & approvals | ASTM A790 (duplex pipe) · ASTM A789 (tube) · ASTM A240 (plate) · NORSOK M-001 · NACE MR0175 (where sour) |
Grade by grade
What Each Grade Does in Marine & Offshore
A stainless application page that lists grades without saying what each one is for is a catalogue, not a specification. These are the roles they actually play here.
| Grade | The job it does here | Detail |
|---|---|---|
| 2507 | The ceiling of the duplex family for seawater. PREN above 42 and roughly twice the yield of 316L let it survive warm, stagnant or chlorinated seawater — intakes, brine lines, desalination and subsea hardware that would pit 2205. | On request |
| 2205 | The submerged-and-stressed workhorse. Half the wall thickness of 316L for the same pressure, and it resists the chloride stress-corrosion cracking that cracks austenitic grades in seawater. | Specs → |
| 316L | The economical call for splash zone, deck equipment and atmospheric marine duty. Fine where the part is rinsed and ventilated; wrong once it is continuously immersed or trapped in a crevice. | Specs → |
Before you send the enquiry
Specification Mistakes That Cost Money Here
None of this is exotic. All of it arrives on real enquiries, and each one adds a round trip before a price can be issued.
1. Specifying 316L for an immersed or stagnant-seawater part. 316L pits and crevice-corrodes in warm or stagnant seawater; 2205 or 2507 is the honest grade for continuous immersion.
2. Ignoring crevice geometry. The bolt hole, the gasket seat and the weld gap corrode before the open surface — a crevice-free design is part of the material decision, not an afterthought.
3. Welding duplex without a nitrogen-bearing filler. A 2205 or 2507 weld that loses its austenite-ferrite balance loses its corrosion resistance with it.
4. Quoting duplex by the austenitic price reflex. 2205 and 2507 cost more per kilogram but carry the same pressure in a thinner wall — the installed cost can be lower, not higher.
Categories that serve it
What We Supply Into Marine & Offshore
Stainless Steel Coil
Cold-rolled and hot-rolled coil in 200 / 300 / 400 series.
Stainless Steel Sheet & Plate
Cold-rolled sheet and hot-rolled plate for structural and decorative use.
Stainless Steel Tube & Pipe
Seamless and welded round, square and rectangular tube.
Stainless Steel Bar & Rod
Round, flat, square and hexagonal bar, cold drawn or hot rolled.
Verification
What We Put in Writing for This Application
- Mill test certificate to the class your file requires — 2.2 or 3.1 — carrying the actual composition and mechanical values for the heat, so the grade is checkable against the order.
- Surface finish and gauge recorded before packing; photos of the sealed container.
- Where the market requires it, the food-contact, 3-A or coating test report with the issuing body named.
Before you ask
Marine & Offshore — Questions That Come Up
When does marine duty need 2507 instead of 2205?
When the seawater is warm, stagnant or chlorinated, or when the part is a high-value subsea or desalination component. 2507 raises PREN from about 35 to above 42 and roughly doubles the yield strength, so it survives conditions that pit 2205. For cooler, flowing seawater, 2205 is usually enough.
Why does 316L fail in seawater when it works fine in the splash zone?
Immersion changes the game. Open, rinsed 316L survives the splash zone; once it is continuously immersed in warm or stagnant seawater, chloride pitting and crevice corrosion attack it. The duplex grades 2205 and 2507 are built for that duty.
What standard governs duplex pipe for offshore?
Duplex and super duplex pipe follow ASTM A790, tube follows ASTM A789, and plate follows ASTM A240. Offshore projects usually add NORSOK M-001 material-selection requirements on top — name the standard and the project spec together.