Seamless Duplex Steel UNS S31803 Pipe
Our S31803 duplex pipes offer a strategic combination of high yield strength—nearly double that of conventional 300-series stainless steels—and outstanding resistance to chloride-induced stress corrosion cracking (SCC) and pitting. While UNS S31803 is the foundational duplex grade, GZH ensures every pipe meets the most rigorous industrial requirements through hydrostatic and ultrasonic testing. Through advanced cold-drawing and precision solution annealing, we guarantee optimal phase balance and a high-integrity surface finish for long-term reliability in petrochemical, marine, and energy infrastructure.
"Our S31803 pipes are often dual-certified to meet S32205 standards, ensuring a Pitting Resistance Equivalent Number (PREN) ≥ 35 for superior performance."
Seamless Duplex Steel UNS S31803 Pipe – Engineering Performance & Technical Specifications
What is Seamless Duplex Steel UNS S31803 Pipe?
Seamless Duplex Stainless Steel UNS S31803 Pipe is a high-performance, corrosion-resistant piping product manufactured from a solid billet of duplex stainless steel through a seamless hot-forming process. Unlike welded pipes, seamless pipes contain no weld seams, ensuring superior structural integrity, uniform mechanical properties, and enhanced reliability in high-pressure, high-temperature, and corrosive service environments.
Duplex stainless steel derives its name from its dual-phase microstructure, consisting of approximately 50% austenite and 50% ferrite. This balanced metallurgical structure provides an optimal combination of:
Theexcellent toughness and pitting corrosion resistance of austenitic stainless steels
Thehigh yield strength and stress corrosion cracking (SCC) resistance of ferritic stainless steels
The alloy designation UNS S31803, commonly known as Duplex Stainless Steel 2205, is defined under the Unified Numbering System (UNS) and is widely standardized under ASTM A790 / ASTM A789 specifications for seamless duplex stainless steel pipes and tubes.
Key Advantages of Seamless Duplex Stainless Steel Pipes
Superior Corrosion Resistance
UNS S31803 duplex stainless steel pipes provide exceptional resistance to chloride-induced stress corrosion cracking, pitting corrosion, and crevice corrosion, significantly outperforming conventional austenitic stainless steels such as 304 and 316 stainless steel.
High Mechanical Strength
Duplex 2205 pipes offer nearly twice the yield strength of standard austenitic stainless steels, allowing engineers to design thinner wall thicknesses while maintaining structural performance, reducing overall system weight and material costs.
Excellent Pressure & Temperature Performance
Theseamless manufacturing process eliminates weld defects, making these pipes highly suitable for high-pressure pipelines, offshore platforms, and critical industrial systems exposed to cyclic thermal conditions.
Optimized Cost Efficiency
Due to their higher strength-to-weight ratio and reduced nickel content, Duplex UNS S31803 pipes provide lower lifecycle costs compared with high-alloy stainless steels and nickel-based alloys.
Technical Specifications of Duplex Stainless Steel UNS S31803
All pipes are manufactured in accordance with ASTM A790 / ASTM A999 standards, ensuring strict control over chemical composition, mechanical properties, and dimensional tolerances.
Table 1: Chemical Composition of Duplex Steel UNS S31803
The composition of Duplex Steel UNS S31803 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 | … |
Table2:Mechanical Properties
| Tensile Strength | Yield Strength | Elongation | Hardness |
| ≥ 620 MPa | ≥ 450 MPa | ≥ 25% | ≤ 293 HBW |
Table 3: Typical Physical Properties
| Density | Melting Point | Thermal Expansion | Thermal Conductivity |
| 7.82 g/cm³ | 1385-1440 ℃ | 13.0 µm/m·℃ | 14.6 W/m·K |
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.
Industrial Applications of UNS S31803 Seamless Pipes
Thanks to their excellent corrosion resistance and high mechanical strength, Duplex Stainless Steel 2205 Seamless Pipes are widely used in demanding industries.
Oil and Gas Industry
Offshore platforms
Subsea pipelines
Manifolds, risers, and flowlines
Chemical Processing Industry
Heat exchangers
Pressure vessels
Chloride-rich processing equipment
Marine and Desalination Systems
Seawater piping systems
Reverse osmosis (RO) desalination plants
Cooling water pipelines
Pulp and Paper Industry
Digesters
Bleaching systems
Chemical storage tanks
Quality Assurance and Certified Testing
EverySeamless Duplex Stainless Steel Pipe undergoes comprehensive inspection and testing to ensure compliance with international quality standards, including EN 10204 3.1 / 3.2 certification.
Non-Destructive Testing (NDT)
Ultrasonic Testing (UT)
Eddy Current Testing (ET)
Hydrostatic Pressure Testing
Corrosion Resistance Testing
Intergranular Corrosion Testing
Pitting Corrosion Testing according to ASTM G48
Material Verification
100% Positive Material Identification (PMI)
Mechanical Testing
Impact Testing
Flattening and Flare Tests
Hardness Testing
These strict quality control procedures ensure that each pipe meets the highest standards required for critical industrial piping systems.
