2205 Seamless Duplex Steel Tube (UNS S31803)

UNS S31803 | 1.4462 | ASTM A789

2205 Seamless Duplex Steel Tube (UNS S31803) (S31803 / 1.4462) is manufactured to ASTM A789 from duplex steel (uns s31803) billet, cold-drawn to the required outside diameter and wall thickness. Supplied from our Wenzhou mill with EN 10204 3.1 mill test certificate, PMI and dimensional inspection on request.

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What Is a Seamless Duplex Steel S31803 Tube?

UNS S31803 is the original 2205 duplex composition and the direct predecessor of S32205. It shares the balanced austenite-ferrite structure and the characteristic combination of high strength and chloride resistance, and remains widely specified for oil and gas, chemical processing, desalination and marine engineering.

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 304Land316L, 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 produced without a longitudinal weld, ensuring uniform grain structure, enhanced mechanical integrity, and superior performance in high-pressure and corrosive service conditions.

2205 Key Features and Technical Advantages

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.

Duplex S31803 stainless steel exhibits outstanding resistance to:

These properties make it particularly suitable for seawater, offshore, and chemical processing environments.

Feature	Description
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:
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:
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.

2205 Product Specifications and Data

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	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	…

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.

Tensile Strength	Yield Strength	Elongation	Hardness
≥ 620 MPa	≥ 450 MPa	≥ 25%	≤ 293 HBW

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

2205 Dimensional Standards and Tolerances

S31803 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.

2205 Common Industrial Applications

Industry	Typical Applications
Oil and Gas Industry	Flowlines and manifolds Process and utility piping Sour service equipment
Chemical Processing Industry	Reactors and heat exchangers Chloride-bearing process lines Storage vessels
Desalination and Water Treatment	RO high-pressure piping Brine handling lines Water transport systems
Marine Engineering	Seawater cooling systems Shipboard piping Offshore platform equipment

2205 Quality Assurance and Production Process

Process Step	Description
Certification	All Duplex S31803 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.

S31803 vs S32205 (2205) – Technical Comparison

S31803 is the original duplex 2205 composition, while S32205 is its tighter-controlled successor. Both are balanced austenite-ferrite grades.

Chemical Composition

S31803: Cr 21.0–23.0%, Mo 2.5–3.5%, N 0.08–0.20%
S32205: Cr 22.0–23.0%, Mo 3.0–3.5%, N 0.14–0.20%
S32205 guarantees a higher minimum PREN

Corrosion Resistance

The tighter minimums in S32205 give more reliable resistance to pitting and crevice corrosion. For most process and marine duty the two perform comparably, but S32205 reduces the risk of a heat falling near the bottom of the compositional range.

Mechanical Properties

Yield strength around 450 MPa minimum, roughly double that of 316L, with good toughness to −50 °C and low thermal expansion compared with austenitic grades.

Selection Guide

Choose S32205 for new specifications and for chloride service where consistent PREN matters
S31803 remains valid where already specified, and is common in older oil and gas projects
Both resist chloride stress-corrosion cracking that would fail 304 or 316

Frequently Asked Questions About 2205 Seamless Duplex Steel Tube (UNS S31803)s

What is S31803 duplex tube?

UNS S31803 is the original 2205 duplex stainless steel composition, with a balanced austenite-ferrite microstructure. It combines high mechanical strength with good resistance to chloride stress-corrosion cracking.

Should I specify S31803 or S32205?

For new projects S32205 is preferable because its tighter compositional minimums guarantee a more consistent PREN. S31803 remains valid where an existing specification or drawing calls for it, and is common in older oil and gas projects.

What standard covers S31803 tube?

S31803 seamless tube is supplied to ASTM A789 / ASME SA789 and ASTM A790 / ASME SA790, with dimensional tolerances per ASTM A1016 / A1016M.

What is S31803 tube used for?

S31803 is used for oil and gas flowlines and manifolds, chemical processing equipment, desalination and water treatment piping, and marine engineering applications.

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Send your Seamless Duplex Steel S31803 Tube enquiry with grade, application, size (OD and wall thickness or schedule), quantity, length, end finish and inspection requirements. Our technical team will confirm availability, testing scope and lead time.

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