Marine Grade 316 Stainless Steel Rectangular Hollow Section Welded ASTM A554
Marine grade rectangular hollow section (RHS) refers to 316 stainless steel rectangular tubing specifically designed for applications in coastal, offshore, and marine environments where standard 304 stainless steel would be susceptible to pitting and corrosion from chloride exposure. The addition of 2-3% molybdenum to the 316 grade provides significantly enhanced resistance to pitting, crevice corrosion, and stress corrosion cracking in seawater, salt spray, and chloride-rich atmospheres.
Rectangular hollow sections are manufactured by forming flat stainless steel strip into a rectangular shape and welding the seam longitudinally, followed by solution annealing and pickling or bright annealing to restore corrosion resistance. The result is a structural tube with sharp or rounded corners, available in a wide range of widths, heights, and wall thicknesses to suit various engineering and architectural applications.
| Parameter | Details |
|---|---|
| Product Name | Marine Grade Rectangular Hollow Section |
| Standard | ASTM A554 (MT-316 / MT-316L) |
| Equivalent Standards | EN 10219 (1.4401/1.4404), JIS G3446 (SUS316), GB/T 12770 |
| Construction | Welded (ERW – Electric Resistance Welded) |
| Outer Dimensions (A * B) | 10mm * 5mm to 200mm * 100mm (0.39″ * 0.20″ to 7.87″ * 3.94″) |
| Wall Thickness | 0.5mm – 5.0mm (0.020″ – 0.197″) |
| Length | 3m – 6m (standard); up to 12m (custom) |
| Surface Finish | Mill Finish, Pickled, No.4 Brushed, No.8 Mirror Polished |
| Corner Radius | 1.5 * WT maximum |
| Element | MT-316 (%) | MT-316L (%) | Requirement |
|---|---|---|---|
| Carbon (C) | ≤0.08 | ≤0.030 | Low carbon for better weldability |
| Manganese (Mn) | ≤2.00 | ≤2.00 | – |
| Silicon (Si) | ≤1.00 | ≤1.00 | – |
| Chromium (Cr) | 16.0 – 18.0 | 16.0 – 18.0 | Provides corrosion resistance |
| Nickel (Ni) | 10.0 – 14.0 | 10.0 – 14.0 | Enhances ductility and toughness |
| Molybdenum (Mo) | 2.0 – 3.0 | 2.0 – 3.0 | Key element for chloride resistance |
| Phosphorus (P) | ≤0.045 | ≤0.045 | – |
| Sulfur (S) | ≤0.030 | ≤0.030 | – |
| Iron (Fe) | Balance | Balance | – |
Key Difference Between 316 and 304:
- 316 contains 2-3% Molybdenum
- 304 contains 0% Molybdenum
- This single element dramatically improves chloride resistance
| Property | MT-316 | MT-316L |
|---|---|---|
| Tensile Strength | ≥515 MPa (75 KSI) | ≥485 MPa (70 KSI) |
| Yield Strength (0.2%) | ≥205 MPa (30 KSI) | ≥170 MPa (25 KSI) |
| Elongation | ≥35% | ≥35% |
| Hardness (HRB) | ≤95 | ≤95 |
| Hardness (HB) | ≤217 | ≤217 |
Typical Values (Annealed Condition):
- Elastic Modulus: 193 GPa (28,000 KSI)
- Shear Modulus: 77 GPa (11,200 KSI)
- Poisson's Ratio: 0.30
- Density: 7.98 g/cm³ (0.288 lb/in³)
| Property | Value |
|---|---|
| Density | 7.98 g/cm³ |
| Melting Range | 1370 – 1400°C (2500 – 2550°F) |
| Specific Heat (0-100°C) | 500 J/kg·K |
| Thermal Conductivity (100°C) | 16.3 W/m·K |
| Thermal Expansion (20-100°C) | 17.2 * 10⁻⁶ /°C |
| Electrical Resistivity (20°C) | 74 μΩ·cm |
| Magnetic Permeability | 1.02 (annealed, essentially non-magnetic) |
| Environment | 304 Performance | 316 Performance |
|---|---|---|
| Coastal / Salt Spray | Moderate (pitting possible) | Excellent |
| Marine (Seawater) | Poor (rapid pitting) | Good to Excellent |
| Chloride Solutions | Poor (SCC risk) | Good |
| Acids (Sulfuric, dilute) | Poor | Fair to Good |
| Acids (Phosphoric) | Fair | Good |
| Food / Beverage | Excellent | Excellent |
| Pharmaceutical | Excellent | Excellent |
| Outdoor (Industrial) | Good | Excellent |
Key Corrosion Metrics:
| Metric | 304 | 316 |
|---|---|---|
| PREN Value* | 18-20 | 24-26 |
| Critical Pitting Temperature | ~20°C | ~35°C |
| SCC Resistance in Chlorides | Low | High |
*PREN = Pitting Resistance Equivalent Number (Cr + 3.3Mo + 16N)*
Bottom Line: If your application involves saltwater, coastal exposure, de-icing salts, or chemical contact — choose 316.
| A * B (mm) | Wall Thickness (mm) | Weight (kg/m) | Typical Use |
|---|---|---|---|
| 10 * 5 | 0.5, 0.8 | 0.22 – 0.35 | Small frames, marine hardware |
| 15 * 10 | 0.8, 1.0, 1.2 | 0.47 – 0.69 | Boat railings |
| 20 * 10 | 0.8, 1.0, 1.2, 1.5 | 0.55 – 0.99 | Coastal furniture |
| 20 * 15 | 1.0, 1.2, 1.5 | 0.69 – 1.03 | Marine frames |
| 25 * 15 | 1.0, 1.2, 1.5, 2.0 | 0.85 – 1.35 | Handrails (coastal) |
| 25 * 25 | 1.0, 1.2, 1.5, 2.0 | 1.03 – 1.59 | Square – marine structures |
| 30 * 20 | 1.2, 1.5, 2.0 | 1.29 – 2.07 | Boat frames |
| 40 * 20 | 1.5, 2.0, 2.5 | 1.83 – 2.98 | Marine equipment |
| 40 * 40 | 1.5, 2.0, 2.5 | 2.50 – 3.98 | Square – coastal structures |
| 50 * 25 | 1.5, 2.0, 2.5 | 2.18 – 3.50 | Trailer frames (coastal) |
| 50 * 50 | 1.5, 2.0, 2.5, 3.0 | 3.16 – 5.05 | Square – marine columns |
| A * B (mm) | Wall Thickness (mm) | Weight (kg/m) | Typical Use |
|---|---|---|---|
| 60 * 40 | 2.0, 2.5, 3.0 | 3.70 – 5.45 | Offshore structures |
| 60 * 60 | 2.0, 2.5, 3.0 | 4.31 – 6.32 | Square – marine frames |
| 80 * 40 | 2.0, 2.5, 3.0 | 4.15 – 6.11 | Chemical plant supports |
| 80 * 60 | 2.5, 3.0, 4.0 | 5.89 – 8.99 | Heavy marine |
| 80 * 80 | 2.5, 3.0, 4.0 | 7.08 – 10.74 | Square – offshore |
| 100 * 40 | 2.5, 3.0, 4.0 | 6.16 – 9.53 | Chemical piping supports |
| 100 * 50 | 2.5, 3.0, 4.0 | 6.52 – 10.08 | Marine platforms |
| 100 * 80 | 3.0, 4.0, 5.0 | 9.52 – 15.18 | Heavy marine structures |
| 100 * 100 | 3.0, 4.0, 5.0 | 10.75 – 16.98 | Square – offshore columns |
| 120 * 60 | 3.0, 4.0, 5.0 | 9.92 – 15.82 | Desalination plant frames |
| 150 * 100 | 4.0, 5.0 | 18.53 – 22.50 | Heavy chemical structures |
| 200 * 100 | 4.0, 5.0 | 22.82 – 28.05 | Large marine structures |
Custom dimensions available upon request
| Parameter | Tolerance |
|---|---|
| Outside Dimensions (A & B) | ±0.5% (min ±0.3mm, max ±1.5mm) |
| Wall Thickness | ±10% |
| Length (fixed) | +3mm / -0mm |
| Twist | ≤0.5mm per meter * width/100 |
| Concave/Convex | ≤0.4mm per side |
| Corner Radius | ≤1.5 * WT |
| Straightness | ≤1.0mm per meter |
| Finish | Code | Description | Ra (μm) | Best For |
|---|---|---|---|---|
| Mill Finish | – | As-welded, light scale | 2.0-3.0 | Industrial, hidden marine structures |
| Pickled | No.1 | Acid cleaned, matte | 1.5-2.5 | Chemical plants, welding prep |
| Brushed (Hairline) | No.4 | 150-180 grit brushed | 0.4-0.8 | Marine handrails, coastal railings |
| Mirror Polished | No.8 | Highly reflective | 0.1-0.2 | Architectural marine, luxury yachts |
| Satin | 320-400 grit | Fine matte | 0.3-0.5 | Food processing, pharmaceutical |
Recommendation for Marine Applications: No.4 Brushed finish provides the best balance of corrosion resistance and aesthetics. The brushed surface hides minor scratches and salt spray marks.
Why Choose Marine Grade Rectangular Hollow Section?
| Benefit | Explanation |
|---|---|
| Corrosion Resistance | Molybdenum (2-3%) provides chloride resistance for coastal/marine environments |
| Structural Strength | Rectangular shape offers high strength-to-weight ratio |
| Cost-Effective | More affordable than duplex grades for most marine applications |
| Wide Availability | Common sizes in stock |
| Easy Fabrication | Weldable and formable with standard equipment |
| Low Maintenance | No coating or painting required |
| Long Life | 15-25+ years in coastal atmospheres |
| Aesthetic Options | Available in multiple finishes (BA, polished) |
| Full Traceability | Mill test certificates with every shipment |
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For inquiries, technical data sheets, or a quotation for marine grade rectangular hollow section (316 stainless steel RHS / marine grade rectangular tubing), please contact our sales team.
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