Seamless Duplex Steel S31803 Tube
Our S31803 duplex tubes offer a strategic combination of high yield strength—nearly double that of conventional 316L—and outstanding resistance to chloride-induced stress corrosion cracking (SCC) and pitting. These properties make them indispensable for heat exchangers, chemical processing, and marine engineering. Through advanced cold-drawing and precision solution annealing, GZH ensures every tube maintains optimal phase balance and a high-integrity surface finish for long-term industrial reliability.
"Our S31803 tubes are often dual-certified to meet S32205 standards, ensuring higher nitrogen and chromium content for even better corrosion resistance."
Seamless Duplex Steel S31803 Tube (UNS S31803)
Overview of UNS S31803 Duplex Stainless Steel
UNS S31803 (ASTM F51) is a high-performance duplex stainless steel featuring a balanced microstructure composed of approximately 50% ferrite and 50% austenite. This dual-phase structure combines the excellent corrosion resistance of austenitic stainless steels with the high strength and durability of ferritic stainless steels.
Compared with conventional grades such as 304L and 316L,Duplex Stainless Steel S31803 offers significantly higher mechanical strength and improved resistance to localized corrosion, making it an ideal material for demanding industrial environments.
Seamless Duplex Steel S31803 tubes are manufactured without a longitudinal weld, ensuring uniform grain structure, enhanced mechanical integrity, and superior performance in high-pressure and corrosive service conditions.
Key Advantages of S31803 Duplex Stainless Steel Tubing
High Mechanical Strength
UNS S31803 provides a minimum yield strength of 450 MPa, which is nearly twice that of standard austenitic stainless steels. This allows engineers to design piping systems with thinner wall thickness, reducing both weight and overall project costs.
Excellent Resistance to Chloride Corrosion
Duplex S31803 stainless steel exhibits outstanding resistance to:
- Chloride-induced stress corrosion cracking (SCC)
- Pitting corrosion
- Crevice corrosion
These properties make it particularly suitable for seawater, offshore, and chemical processing environments.
Improved Fatigue Resistance
The duplex microstructure offers improved fatigue strength and higher resistance to cyclic loading compared with conventional stainless steels.
Superior Thermal Properties
S31803 has:
- Higher thermal conductivity
- Lower thermal expansion coefficient
These characteristics improve stability and efficiency in heat exchangers and high-temperature systems.
Cost-Effective Material Solution
Due to its high strength and excellent corrosion resistance, S31803 can replace thicker austenitic stainless steel components, resulting in material savings and improved lifecycle performance.
International Standards and Manufacturing Specifications
Seamless Duplex Steel S31803 tubes are produced according to internationally recognized standards to ensure reliability and safety in critical applications.
Common production standards include:
- ASTM A789 / ASME SA789
Seamless and welded ferritic/austenitic stainless steel tubing for general service. - NACE MR0175 / ISO 15156
Materials suitable for use in hydrogen sulfide (H₂S) environments in the oil and gas industry.
These standards define strict requirements for chemical composition, mechanical properties, dimensional tolerances, and quality inspection procedures.
Table 1: Chemical Composition
The composition of UNS S31803 (as specified by standards like ASTM A790) defines its properties:
| 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 | … |
Role of Key Alloying Elements
Chromium (Cr)
Provides strong corrosion resistance by forming a stable passive oxide layer.
Nickel (Ni)
Stabilizes the austenitic phase and enhances resistance to stress corrosion cracking.
Molybdenum (Mo)
Improves resistance to pitting and crevice corrosion, especially in chloride-containing environments.
Nitrogen (N)
Increases both mechanical strength and localized corrosion resistance, contributing to the superior performance of duplex stainless steel.
Industrial Applications of S31803 Duplex Steel Tubes
Due to its outstanding strength and corrosion resistance, UNS S31803 seamless duplex stainless steel tubing is widely used across several critical industries.
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 |
| 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
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.
Oil and Gas Industry
- Subsea pipelines
- Flowlines and risers
- Downhole tubing
- Offshore platform piping systems
Chemical Processing Industry
- Heat exchangers
- Pressure vessels
- Acid handling systems
- Chloride-containing process media
Desalination and Water Treatment
- Reverse osmosis (RO) high-pressure piping
- Evaporator tubing
- Seawater intake and distribution systems
Marine Engineering
- Seawater cooling systems
- Shipbuilding equipment
- Offshore structural components
Conclusion
Seamless Duplex Steel S31803 tubing (UNS S31803) offers an optimal balance of high strength, excellent corrosion resistance, and cost efficiency. Its dual-phase microstructure provides superior mechanical performance and outstanding durability in chloride-rich and high-pressure environments.
For industries such as offshore oil and gas, chemical processing, desalination, and marine engineering, S31803 remains one of the most reliable and widely specified duplex stainless steel grades.
By combining structural reliability, corrosion resistance, and economic advantages, S31803 seamless duplex tubing continues to be a preferred material for critical industrial piping systems.
