UNS S32550|1.4507|S32550 Seamless Super Duplex Steel Tube
Featuring a high Pitting Resistance Equivalent Number (PREN ≥ 40), our S32550 super duplex tubes provide exceptional durability in sulfuric acid, phosphoric acid, and aggressive marine environments. The addition of copper enhances its resistance to non-oxidizing acids, making it a superior choice over standard super duplex grades for chemical processing and offshore systems. Through advanced cold-drawing and precise solution annealing, XinZhe ensures every tube maintains optimal phase balance and maximum mechanical strength for mission-critical industrial applications.
What Is a Seamless Super Duplex UNS S32550 Tube?
UNS S32550, commonly known as Ferralium 255, is a high-alloy super duplex stainless steel engineered for extremely aggressive, high-chloride environments. With roughly 25% chromium plus molybdenum, nitrogen and copper, it achieves a Pitting Resistance Equivalent Number (PREN) above 40 — enough to resist pitting, crevice attack and chloride stress-corrosion cracking in seawater and sour service alike.
Key Features and Technical Advantages
UNS S32550, commonly known as Ferralium 255, is a high-alloy super duplex stainless steel engineered for extremely aggressive and high-chloride environments.
With a high chromium content (~25%) and alloying elements such as molybdenum (Mo), nitrogen (N), and copper (Cu), S32550 achieves a Pitting Resistance Equivalent Number (PREN) > 40, delivering exceptional resistance to localized corrosion.
ASTM A789 S32550 seamless tubes are manufactured from solid billets using cold drawing or hot finishing processes, ensuring:
1. Exceptional Corrosion Resistance
- Pitting corrosion
- Crevice corrosion
- Chloride-induced Stress Corrosion Cracking (SCC)
2. Superior Mechanical Strength
- Duplex S31803 / S32205
- Austenitic grades such as 316L
3. Enhanced Erosion-Corrosion Resistance
- High-velocity seawater
- Abrasive slurries
4. Excellent Impact Toughness
- Maintains ductility at sub-zero temperatures
- Ideal for offshore, deepwater, and Arctic environments
5. Cost-Effective Alternative to Nickel Alloys
- Comparable corrosion performance in many environments
- Lower material and fabrication cost vs Ni-based alloys
Product Specifications and Data
- ASTM A789 / ASME SA789
- ASTM A1016
- EN 10216-5
- NORSOK / offshore specifications available upon request
To provide a comprehensive overview of this high-performance material, here are the detailed technical specifications and performance data for Super Duplex UNS S32550.
The composition of UNS S32550 is carefully balanced to achieve its superior corrosion resistance and high strength.
| Grade | C | Mn | P | S | Si | Ni | Cr | Mo | N | Cu | Others |
| 31803 | ≤0.03 | ≤2.00 | ≤0.03 | ≤0.02 | ≤1.00 | 4.50-6.50 | 21.00-23.00 | 2.50-3.50 | 0.08-0.20 | … | … |
| 32205 | ≤0.03 | ≤2.00 | ≤0.03 | ≤0.02 | ≤1.00 | 4.50-6.50 | 22.00-23.00 | 3.00-3.50 | 0.14-0.20 | … | … |
| 31500 | ≤0.03 | 1.20-2.00 | ≤0.03 | ≤0.03 | 1.40-2.00 | 4.3-5.2 | 18.00-19.00 | 2.50-3.00 | 0.05-0.10 | … | … |
| 32550 | ≤0.04 | ≤1.50 | ≤0.04 | ≤0.03 | ≤1.00 | 4.50-6.50 | 24.00-27.00 | 2.90-3.90 | 0.10-0.25 | 1.50-2.50 | … |
| 32750 | ≤0.03 | ≤1.20 | ≤0.035 | ≤0.02 | ≤0.80 | 6.00-8.00 | 24.00-26.00 | 3.00-5.00 | 0.24-0.32 | ≤0.50 | … |
| 32760 | ≤0.03 | ≤1.00 | ≤0.030 | ≤0.01 | ≤1.00 | 6.00-8.00 | 24.00-26.00 | 3.00-4.00 | 0.20-0.30 | 0.50-1.00 | W 0.50 -1.00 |
| 32950 | ≤0.03 | ≤2.00 | ≤0.035 | ≤0.01 | ≤0.60 | 3.50-5.20 | 26.00-29.00 | 1.00-2.50 | 0.15-0.35 | … | … |
| 32906 | ≤0.03 | 0.80-1.50 | ≤0.030 | ≤0.03 | ≤0.50 | 5.80-7.50 | 28.00-30.00 | 1.50-2.60 | 0.30-0.40 | ≤0.80 | … |
| Tensile Strength | Yield Strength | Elongation | Hardness |
|---|---|---|---|
| ≥850 MPa | ≥580 MPa | ≥25% | ≤320 HBW |
| Density | Melting Point | Thermal Expansion | Thermal Conductivity | Modulus of Elasticity | Electrical Resistivity |
|---|---|---|---|---|---|
| 7.8 g/cm³ | 1420 - 1460 °C approx. | 13.5 µm/m·°C (20-100°C) | 15.0 W/m·K (20°C) | 200 GPa | 0.82 x 10⁻⁶ Ω·m (20°C) |
| Specified Outside Diameter (OD) (Inches) | Permissible Variations in OD (± Inches) |
| 1⁄2 to 1 | ±0.005 |
| Over 1 to 1-1⁄2 | ±0.008 |
| Over 1-1⁄2 to 2 | ±0.010 |
| Over 2 to 2-1⁄2 | ±0.012 |
| Over 2-1⁄2 to 3-1⁄2 | ±0.014 |
| Over 3-1⁄2 to 5 | ±0.020 |
| Specified Outside Diameter (OD) (Inches) | Specified Wall Thickness (WT) (Inches) | Permissible Variation (± Inches) |
| 1⁄2 to 1 (Inclusive) | 0.025 to 0.065(Inclusive) | ±0.010 |
| Over 0.065to 0.134 (Inclusive) | ±0.012 | |
| Over 1 to 1-1⁄2 (Inclusive) | 0.025 to 0.065 (Inclusive) | ±0.010 |
| Over 0.065 to 0.134 (Inclusive) | ±0.012 | |
| Over 1-1⁄2 to 2 (Inclusive) | 0.025 to 0.049 (Inclusive) | ±0.011 |
| Over 0.049 to 0.083 (Inclusive) | ±0.012 | |
| Over 0.083 to 0.148 (Inclusive) | ±0.014 | |
| Over 2 to 2-1⁄2 (Inclusive) | 0.032 to 0.065 (Inclusive) | ±0.013 |
| Over 0.065 to 0.109 (Inclusive) | ±0.015 | |
| Over 0.109 to 0.165 (Inclusive) | ±0.017 | |
| Over 2-1⁄2 to 3-1⁄2 (Inclusive) | 0.032 to 0.165 (Inclusive) | ±0.020 |
| Over 0.165 to 0.220 (Inclusive) | ±0.025 | |
| Over 3-1⁄2 to 5 (Inclusive) | 0.083 to 0.165 (Inclusive) | ±0.025 |
| Over 0.165 to 0.220 (Inclusive) | ±0.030 |
Dimensional Standards and Tolerances
S32550 super duplex seamless tubes are supplied to the dimensional tolerances of ASTM A789 / A1016 unless a tighter project specification applies.
- For Specific Cut Lengths, the standard tolerance is +1⁄8 in. [3 mm], -0 in. [0 mm].
Important Note: The values presented here are based on the common tables in the ASTM A789 standard. The full specification, particularly the referenced ASTM A1016/A1016M (General Requirements for Ferritic Alloy Steel, Austenitic Alloy Steel, and Stainless Steel Tubes), contains other essential requirements like straightness and details for tubes with ODs outside of this range. Always consult the latest official standard for design and procurement.
Common Industrial Applications
Offshore Oil and Gas
- Subsea manifolds and flowlines
- Riser and umbilical tubing
- High-pressure process piping
Marine Engineering
- Seawater cooling systems
- Propulsion and ballast piping
- Firewater and deluge systems
Desalination Systems
- Reverse osmosis (RO) high-pressure piping
- Brine handling and reject lines
- Multi-stage flash evaporator tubing
Environmental and Pollution Control
- Flue gas desulphurisation (FGD) systems
- Wastewater and effluent handling
- Scrubber and absorber internals
Quality Assurance and Manufacturing Process
Certification
All Super Duplex S32550 tubes are supplied to ASTM A789 / ASME SA789 and ASTM A790 / ASME SA790 with EN 10204 3.1 mill test certificates. Third-party inspection (SGS, BV, TUV, Lloyd's), PMI reports and full heat-number traceability can be provided on request.
Non-Destructive Testing (NDT)
Hydrostatic or eddy-current testing is performed on 100% of tubes. Ultrasonic testing (UT) and dye-penetrant inspection (PT) are available for critical service, with records retained for each production lot.
Material Verification
Positive Material Identification (PMI) and spectrometric analysis confirm that the chemical composition matches the ordered grade and that the ferrite/austenite balance is within the specified range.
Mechanical Testing
Tensile, yield, elongation and hardness tests are carried out per heat. Impact testing can be supplied at the project design temperature for subsea and low-temperature service.
Dimensional Inspection
Outside diameter, wall thickness, ovality and straightness are measured against ASTM A1016 / A1016M or ASTM A789 tolerances. Length, square-cut ends and end-finish conditions are verified before packing.
S32550 (Ferralium 255) vs S32750 (2507) – Technical Comparison
S32550 and S32750 are both super duplex grades with PREN above 40, but they differ in chemistry and in how that chemistry is used.
Chemical Composition
- S32550 (Ferralium 255): ~25% Cr, ~3% Mo, ~2% Cu, with nitrogen — the copper addition is the distinguishing feature
- S32750 (2507): ~25% Cr, ~4% Mo, ~0.3% N, no deliberate copper
- Both achieve a balanced austenite-ferrite microstructure
Corrosion Resistance
Both resist pitting, crevice corrosion and chloride stress-corrosion cracking in seawater. The copper addition in S32550 specifically improves resistance to erosion-corrosion in high-velocity seawater and abrasive slurries, which is why it is often selected for pump and valve components and for lines carrying solids.
Mechanical Strength
S32550 offers a yield strength of at least 580 MPa, comparable to or slightly above S32750, and both allow significant weight reduction against austenitic grades. Toughness at sub-zero temperature is good in both.
Selection Guide
- Choose S32550 where erosion-corrosion resistance in high-velocity or abrasive seawater service is the design driver
- Choose S32750 where maximum pitting and crevice resistance with the broadest established service record is preferred
- Both are cost-effective alternatives to nickel alloys in many chloride-bearing duties
Frequently Asked Questions
What is UNS S32550 super duplex tube?
UNS S32550, commonly known as Ferralium 255, is a high-alloy super duplex stainless steel tube with a balanced austenite-ferrite structure. Its approximately 25% chromium plus molybdenum, nitrogen and copper deliver a PREN above 40, giving exceptional resistance to pitting, crevice corrosion and chloride stress-corrosion cracking.
What is the difference between S32550 and S32750?
Both are super duplex grades with PREN above 40. S32550 contains copper, which specifically improves resistance to erosion-corrosion in high-velocity seawater and abrasive slurries. S32750 (2507) carries more molybdenum and no copper, favouring maximum pitting and crevice resistance.
What standard covers S32550 tube?
S32550 seamless tube is normally supplied to ASTM A789 / ASME SA789 for general seamless tubing, with ASTM A790 / ASME SA790 covering pipe dimensions. Dimensional tolerances follow ASTM A1016 / A1016M.
What is S32550 tube used for?
S32550 is used for subsea manifolds and flowlines, seawater cooling systems, reverse-osmosis high-pressure piping, and flue-gas desulphurisation equipment — anywhere high-chloride service combines with mechanical load.
Ready to Request a Quotation?
Send your Seamless Super Duplex UNS S32550 Tube enquiry with grade, application, size (OD and wall thickness or schedule), quantity, length, end finish and inspection requirements including any ferrite content limits or third-party witnessing.
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