Which Grade Is Best for Marine Environments?
Stainless steel plates used in marine environments must resist saltwater corrosion, pitting, and stress corrosion cracking. Among all available grades, SS 316, SS 316L, and SS 904L stand out as the most effective for seawater exposure. These grades offer superior corrosion resistance, long-term durability, and low maintenance—making them ideal for shipbuilding, offshore structures, desalination plants, and coastal infrastructure.
What Is Marine-Grade Stainless Steel?
Marine-grade stainless steel is any stainless alloy specifically engineered to withstand chloride-induced corrosion caused by seawater and saline air. Grades like 316 and 904L are categorized as marine-grade because they contain molybdenum and higher nickel content, enhancing their resistance to pitting, crevice corrosion, and salt spray.
Applications of Marine-Grade Stainless Steel
- Ship hulls, decks & tanks
- Desalination systems & RO plants
- Oil & gas platforms
- Subsea pipelines & fasteners
- Coastal railings, stairs & gates
- Underwater fabrication & flanges
- Boat fittings & propeller shafts
Mechanical Properties That Matter in Marine Use
When choosing stainless steel for marine environments, buyers should prioritize the following properties:
- High Pitting Resistance Equivalent Number (PREN)
- Tensile Strength: Above 500 MPa for structural performance
- Elongation & Ductility: Required to withstand wave stress
- Weldability: Crucial for on-site marine fabrication
- Resistance to SCC: Especially in warm, high-chloride zones
Grades like SS 316L (PREN ~25) and SS 904L (PREN >34) outperform basic grades like 304, making them the trusted choice for salt-heavy atmospheres.
Comparison of SS 304 vs 316 vs 904L for Saltwater
| Grade | Molybdenum | Nickel | PREN Value | Chloride Resistance | Common Use |
|---|---|---|---|---|---|
| SS 304 | 0% | ~8% | ~18 | Not recommended | Coastal interiors |
| SS 316 / 316L | ~2-2.5% | ~10-12% | ~24–25 | Good | Marine fittings, hull parts |
| SS 904L | ~4.5% | ~24% | >34 | Excellent | Seawater piping, offshore rigs |
Conclusion: SS 316/316L is a strong baseline for most marine needs. For extreme salt, warm waters, or long-term exposure, SS 904L is the superior choice.
Seawater Resistance and Pitting Protection
In seawater, chloride ions aggressively attack unprotected stainless steel. Pitting and crevice corrosion occur rapidly unless the alloy has a high molybdenum and chromium content.
- SS 304 starts pitting in mild saline within days.
- SS 316 resists chlorides up to 1000 ppm.
- SS 904L resists over 3000 ppm chloride, ideal for submerged structures.
Fabrication, Welding & Maintenance in Marine Use
- SS 316L and SS 904L offer good weldability without post-weld treatment.
- Both resist intergranular corrosion after fabrication.
- 904L requires higher cutting force and special tools due to its toughness.
- Cleaning should include freshwater rinsing to reduce salt buildup on exposed parts.
Plate Thickness, Sizes & Availability for Marine Projects
Marine stainless steel plates are commonly available in:
- Thickness Range: 3 mm to 50 mm
- Standard Sizes: 1250 x 2500 mm, 1500 x 3000 mm, 2000 x 6000 mm
- Customization: CNC cut-to-size and radius edge cutting
At Hindustan Steel Corporation, we stock 316L and 904L marine plates ready for export and local delivery.
Certifications for Marine & Offshore Compliance
We supply marine-grade stainless steel plates with:
- Third-party inspection (TPI) from DNV, Lloyd’s, ABS
- IBR / CE / PED / ISO certifications
- Full traceability with Mill TC / EN 10204 3.1 / 3.2
- Compliant with ASTM A240 / ASME SA240 / NACE MR0175 where applicable
Why Choose Hindustan Steel for Marine-Grade SS Plates?
- Ready stock of SS 316L & SS 904L in multiple sizes
- Competitive marine steel prices and bulk discounts
- Export-ready supply chain with moisture-barrier packaging
- In-house cutting, shearing, and inspection
- Serving India’s top shipyards, oil platforms & coastal EPC projects
Export-Ready Marine Grade Plate Supply & Packaging
We export stainless steel marine plates to:
- Shipbuilding yards in UAE, Oman, Qatar, and Vietnam
- Offshore projects in the North Sea, Indian Ocean, and South Asia
- Desalination plants and chemical docks globally
Packaging Includes:
- PE-coated wrapping or waterproof tarpaulin
- Edge-protected bundles with fumigation certificate
- Markings: Heat number, batch, plate dimensions, grade, and origin
Buyer Tip – How to Select the Right Marine Grade?
Ask these before choosing a grade:
- Will the plate be submerged or coastal?
- Is the environment high-chloride (e.g., Gulf region)?
- What’s your budget per kg for corrosion resistance?
For short-term, semi-exposed use: SS 316L
For long-term or submerged/high salinity zones: SS 904L
For decorative/non-contact zones: SS 304 (non-recommended for saltwater)
Quality Approvals & Technical Dossier
- Mill TC + Lab Reports
- ASTM / ASME compliance
- ISO 9001 / PED / IBR certified
- NDT, PMI, IGC Test, and HIC report on request
You receive a complete documentation folder with every marine-grade steel supply from Hindustan Steel Corporation.
FAQs for Best Stainless Steel for Marine Use
What is the best grade for seawater resistance?
SS 904L is ideal due to its high molybdenum and nickel content, providing superior chloride resistance.
Can SS 316L plates be used underwater?
Yes, SS 316L performs well in submerged environments with up to 1000 ppm chloride levels.
What’s the difference between SS 316 and SS 316L?
316L has lower carbon, making it more weld-friendly and less prone to intergranular corrosion.
Is duplex steel better than 316 for marine?
In highly corrosive or high-pressure marine zones, duplex grades (like 2205) offer even higher strength and resistance than 316L.
Which tests confirm marine-grade plate quality?
Look for Mill TC, pitting corrosion test (ASTM G48), IGC, and third-party inspections.
Do I need to polish marine plates?
For aesthetic or anti-fouling purposes, plates may be supplied in No. 4 or 2B finish, but polishing doesn’t improve corrosion resistance.
What thickness is used for ship hulls and platforms?
Typically 6 mm to 25 mm depending on the project specification.
Is 904L costlier than 316L?
Yes, 904L is premium due to high nickel content but delivers better ROI in harsh saltwater environments.
Can I get marine steel plates delivered to the port?
Yes, we offer CIF and FOB delivery to major Indian and international ports.
Request a Price Quote or Marine Datasheet
Need 316L or 904L for shipbuilding or seawater processing?
Call us or email your BOQ. We’ll respond within 1 working day with:
- Competitive plate prices per kg
- Mill TC sample
- Lead time & export schedule
- Grade comparison PDF (316L vs 904L)