Seamless Super Duplex Steel UNS S32550 Pipe
Featuring a high Pitting Resistance Equivalent Number (PREN ≥ 40), our S32550 super duplex pipes provide exceptional durability in aggressive media, including sulfuric acid, phosphoric acid, and chloride-rich seawater. The addition of copper enhances its resistance to non-oxidizing acids, making it a superior choice for chemical processing, desalination, and offshore systems. Through advanced cold-drawing and precise solution annealing, GZH ensures every pipe maintains optimal phase balance and maximum mechanical strength for mission-critical industrial applications.
PREN = %Cr + 3.3X%Mo + 16 X%N ≥ 40
What Is a Seamless Super Duplex Steel UNS S32550 Pipe?
Seamless Super Duplex Steel S32550 Pipe is a high-performance, large-diameter cylindrical conduit crafted from a single, solid billet of a super duplex stainless steel alloy. Unlike welded pipes, it has no longitudinal weld joint, ensuring superior structural integrity and reliability, especially under high-pressure, high-temperature, and severely corrosive conditions.
The"UNS S32550" designation refers to a specific, highly-alloyed grade, also commercially known as Ferralium 255. This alloy is meticulously balanced with a high content of chromium, molybdenum, and nitrogen, which develops a unique two-phase microstructure of roughly equal parts austenite and ferrite. This structure provides an exceptional combination of high tensile strength, excellent resistance to stress corrosion cracking (SCC), and superior resistance to pitting and crevice corrosion, making it a premier choice for demanding, critical infrastructure applications in harsh environments.
Key Features and Advantages
Seamless S32550 Pipe offer a unique combination of benefits that make them invaluable in the most demanding industries:
Exceptional Corrosion Resistance: It provides outstanding resistance to pitting, crevice corrosion, and stress corrosion cracking in chloride-containing environments. This is a direct result of its high PREN (Pitting Resistance Equivalent Number) value (PREN≥40).
High Strength: The duplex (austenite-ferrite) microstructure delivers a high tensile and yield strength, approximately double that of standard austenitic stainless steels, allowing for thinner walls and lighter weight.
Excellent Toughness: It maintains good toughness and ductility at both low and ambient temperatures, making it suitable for a wide range of operational conditions, including cryogenic and elevated temperatures.
High Pressure and Stress Tolerance: The seamless construction eliminates a potential weak point, allowing the pipe to safely handle extremely high internal and external pressures, which is critical in major fluid transfer and structural applications.
Cost-Effectiveness: It provides a great balance of performance and cost, offering a high-performance, long-lasting alternative to more expensive pure nickel or high-nickel alloys.
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.
Table 1: Chemical Composition of 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 | Ohters |
| 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 | 4.20-5.20 | 18.00-19.00 | 2.50-3.00 | 0.15-0.10 | 1.50-2.50 | … |
| 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 | … | … |
| 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 | ≤0.05 | ≤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 | ≤0.08 | ≤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 | … |
Table 2: Typical Mechanical Properties of UNS S32550
UNS S32550 is specifically designed to maintain its strength and shape in high-stress, corrosive environments.
| Property | Value |
| Tensile Strength | ≥850 MPa |
| Yield Strength | ≥580 MPa |
| Elongation | ≥25% |
| Hardness | ≤320 HBW |
Table 3: Typical Physical Properties of UNS S32550
These physical properties highlight the material's ability to perform reliably under a wide range of conditions.
| Property | Value |
| Density | 7.8 g/cm³ |
| Melting Point | 1420 - 1460 °C approx. |
| Thermal Expansion | 13.5 µm/m·°C (20-100°C) |
| Thermal Conductivity | 15.0 W/m·K (20°C) |
| Modulus of Elasticity | 200 GPa |
| Electrical Resistivity | 0.82 x 10⁻⁶ Ω·m (20°C) |
Table 4: The Standard of ASTM A790 Size Tolerance Size Chart :
| NPS Designator (Inches) | Permissible Variations in Outside Diameter (Inches) |
| 1⁄8 to 1 1⁄2, inclusive | Over: 1⁄64 in. (0.015 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 1 1⁄2 to 4, inclusive | Over: 1⁄32 in. (0.031 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 4 to 8, inclusive | Over: 1⁄16 in. (0.062 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 8 to 18, inclusive | Over: 3⁄32 in. (0.093 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 18 to 26, inclusive | Over: 1⁄8 in. (0.125 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 26 to 34, inclusive | Over: 5⁄32 in. (0.156 in.) |
| Under: 1⁄32 in. (0.031 in.) | |
| Over 34 to 48, inclusive | Over: 3⁄16 in. (0.187 in.) |
| Under: 1⁄32 in. (0.031 in.) |
Wall Thickness (WT) Tolerance
The wall thickness tolerances are defined by the nominal wall thickness (t) and the outside diameter (D).
1. Minimum Wall Thickness
The minimum wall thickness at any point on the pipe shall not be more than {12.5%} under the nominal (specified) wall thickness.
2. Maximum Wall Thickness (Percentage Over Nominal)
The maximum allowable wall thickness variation depends on the size and the t/D ratio (ratio of nominal wall thickness to ordered outside diameter):
| NPS Designator (Inches) | t/D Ratio | Permissible Variation (Over Nominal WT) |
| 1/8 to 2, inclusive | All ratios | +20.0% |
| 3 to 18, inclusive | t/D ≤ 5% | +22.5% |
| 3 to 18, inclusive | t/D >5% | +15.0% |
| 20 and larger (Seamless) | t/D ≤ 5% | +22.5% |
| 20 and larger (Seamless) | t/D >5% | +15.0% |
| 20 and larger (Welded) | All ratios | +17.5% |
Length Tolerance
For pipe ordered to a Specific Cut Length, the standard tolerance is +1⁄8 in. [3.2 mm], -0 in. [0 mm].
Pipe is typically supplied in Single Random Lengths (17 to 24 ft) or Double Random Lengths (38 to 40 ft), unless otherwise specified.
Disclaimer: These tolerances are based on the common requirements found in ASTM A790, primarily through its reference to ASTM A999. The full and most current specification document must always be consulted for official design and procurement purposes.
Common Applications
The combination of high strength and exceptional corrosion resistance of Seamless Super Duplex Steel UNS S32550 Pipe makes them a preferred choice for large-scale, critical infrastructure projects:
Oil and Gas Industry: Used extensively in offshore platforms, riser systems, deep-sea pipelines, and process piping where resistance to high-pressure, high-chloride, and sour gas (H2S) corrosion is paramount.
Chemical and Petrochemical Processing: Ideal for use in large heat exchangers, pressure vessels, reactors, and bulk fluid transfer piping operating in aggressive chemical media.
Desalination Plants: For main piping, vessels, and high-pressure feed lines where components must handle highly concentrated, high-temperature saline water.
Pulp and Paper Industry: In bleaching areas and other corrosive process sections.
Power Generation: Used in scrubbers and flue-gas desulfurization (FGD) systems where high-chloride and acidic conditions are present.
Manufacturing Process
The manufacturing of a Seamless Super Duplex Steel Pipe is a precise, multi-step process that ensures the material's unique properties are fully realized in the final product:
- Heating: A solid, round billet of UNS S32550 alloy is heated uniformly to a specific hot-working temperature.
- Piercing: The heated billet is then passed through a piercing mill, which forces a mandrel through its center, creating a thick-walled hollow shell. This is the stage that ensures the pipe's seamless nature.
- Rolling and Sizing: The hollow shell is then further processed, often through a mandrel mill or pilger mill, to progressively reduce its diameter and wall thickness to the precise dimensions required by industry standards (e.g., ASME/ANSI).
- Finishing and Inspection: The pipe is cut to length, followed by mandatory solution annealing and water quenching to establish the optimal duplex microstructure. Finally, it undergoes non-destructive testing (NDT), such as hydrostatic testing and ultrasonic inspection, to ensure the highest standards for performance, reliability, and structural integrity in the most demanding applications.
