ASTM A789 UNS S32550 (Ferralium 255) | High-Performance Super Duplex Tubing for Extreme Environments
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:
- No weld seams (eliminating weld-related corrosion risks)
- Superior mechanical strength
- High reliability in high-pressure and subsea applications
Key Features & Performance Advantages
1. Exceptional Corrosion Resistance
- Outstanding resistance to:
- Pitting corrosion
- Crevice corrosion
- Chloride-induced Stress Corrosion Cracking (SCC)
- Ideal for seawater, sour gas (H₂S), and acidic environments
2. Superior Mechanical Strength
- Yield strength ≥ 580 MPa, significantly higher than:
- Duplex S31803 / S32205
- Austenitic grades such as 316L
- Enables reduced wall thickness and structural weight
3. Enhanced Erosion-Corrosion Resistance
- Copper (Cu) addition improves resistance to:
- High-velocity seawater
- Abrasive slurries
- Suitable for dynamic flow systems
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
Technical Specifications
Applicable Standards
- ASTM A789 / ASME SA789
- ASTM A1016
- EN 10216-5
- NORSOK / offshore specifications available upon request
Product Specifications and Data
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.
UNS S32550 is specifically designed to maintain its strength and shape in high-stress, corrosive environments.
These physical properties highlight the material’s ability to perform reliably under a wide range of conditions.
The Standard of ASTM A789 Size Tolerance Size Chart :
| 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 |
Length Tolerance
ForSpecific 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.
Typical Applications of S32550 Super Duplex Tubes
S32550 is widely used in extreme corrosive and high-load environments:
Offshore Oil & Gas
- Subsea manifolds
- Umbilical tubing
- Heat exchangers for sour service
Marine Engineering
- Seawater cooling systems
- Propeller shafts
- High-load structural components
Desalination Systems
- Reverse osmosis (RO) piping
- Brine concentrators
- High-pressure tubing
Environmental & Pollution Control
- Flue Gas Desulfurization (FGD) systems
- Industrial scrubbers
Manufacturing Process & Quality Assurance
Manufacturing Process
- Hot Piercing & Cold Drawing
- Solution Annealing with rapid quenching
- Strict phase balance control (duplex structure)
Inspection & Testing
Certification
- EN 10204 3.1 / 3.2 MTC
- Third-party inspection (DNV, BV, SGS)
Corrosion Testing
- Pitting Corrosion Test (ASTM G48)
- Intergranular Corrosion (ASTM A262 Practice E)
Mechanical Testing
- Tensile Testing
- Impact Testing
- Flattening & Flaring Tests
Non-Destructive Testing (NDT)
- 100% Ultrasonic Testing (UT)
- Eddy Current Testing (ET)
Material Verification
- 100% PMI (Positive Material Identification)
