UNS S31803 Seamless Pipe ASTM A789 4" Schedule 40 Stainless Steel Pipe
UNS S31803 duplex stainless steel pipe is a widely used duplex grade that offers a balanced mix of good strength, excellent corrosion resistance, and cost-effectiveness. It is the original standard duplex stainless steel, commonly specified in ASTM A790 and ASTM A789 for both seamless and welded pipe applications.
With a dual-phase microstructure (austenite + ferrite), UNS S31803 provides approximately twice the yield strength of 304 or 316L austenitic stainless steels, while maintaining good weldability and fabricability.
| Parameter | Range | |
|---|---|---|
| Outer Diameter (OD) | 6.0 mm – 610 mm (1/4″ – 24″) | |
| Wall Thickness (WT) | 0.5 mm – 50 mm (Schedule 5S – XXS) | |
| Length | Customized (up to 12 meters or as required) | |
| Type | Seamless / Welded | |
| End Finish | Plain end, beveled end, threaded, or grooved |
| Feature | Description |
|---|---|
| High Yield Strength | Minimum 450 MPa (65 ksi) – 2x stronger than 316L |
| Good Corrosion Resistance | Resistant to pitting, crevice corrosion, and stress corrosion cracking (SCC) |
| Chloride Resistance | Suitable for brackish water, seawater, and high-chloride environments |
| Weldable | Can be welded using standard methods with proper filler (e.g., 2209) |
| Cost-Effective | Lower cost than super duplex grades (e.g., 2507) and nickel-based alloys |
| Wide Temperature Range | Serviceable from -50°C to 300°C depending on conditions |
| Element | UNS S31803 | UNS S32205 (Enhanced 2205) |
|---|---|---|
| Chromium (Cr) | 21.0 – 23.0 | 22.0 – 23.0 |
| Nickel (Ni) | 4.5 – 6.5 | 4.5 – 6.5 |
| Molybdenum (Mo) | 2.5 – 3.5 | 3.0 – 3.5 |
| Nitrogen (N) | 0.08 – 0.20 | 0.14 – 0.20 |
| PREN | 30 – 34 | 33 – 37 |
Which one to choose?
S31803 is suitable for most general duplex applications and is often more available and cost-effective.
S32205 is preferred for slightly more aggressive environments or when better weldability and higher pitting resistance are required.
Many ASTM A790 pipes today are dual-certified as S31803 / S32205, meeting both specifications.
| Element | UNS S31803 Requirements |
|---|---|
| Carbon (C) | ≤ 0.030 |
| Silicon (Si) | ≤ 1.00 |
| Manganese (Mn) | ≤ 2.00 |
| Chromium (Cr) | 21.0 – 23.0 |
| Nickel (Ni) | 4.5 – 6.5 |
| Molybdenum (Mo) | 2.5 – 3.5 |
| Nitrogen (N) | 0.08 – 0.20 |
| Phosphorus (P) | ≤ 0.030 |
| Sulfur (S) | ≤ 0.020 |
| Iron (Fe) | Balance |
| Property | Value |
|---|---|
| Tensile Strength | ≥ 620 MPa (90 ksi) |
| Yield Strength (0.2% offset) | ≥ 450 MPa (65 ksi) |
| Elongation | ≥ 25% |
| Hardness (HRC) | ≤ 30 |
| Density | 7.8 g/cm³ |
PREN = %Cr + 3.3 × %Mo + 16 × %N
UNS S31803 PREN Range: 30 – 34
| Standard | Description |
|---|---|
| ASTM A790 | Seamless and welded ferritic/austenitic stainless steel pipe |
| ASTM A789 | Seamless and welded ferritic/austenitic stainless steel tubing |
| ASME SA790 / SA789 | Boiler and pressure vessel code |
| EN 10216-5 | European standard for duplex steel tubes |
| EN 10217-7 | Welded duplex steel tubes |
| NACE MR0175 / ISO 15156 | Suitable for sour service (H₂S environments) |
| Industry | Typical Applications |
|---|---|
| Oil & Gas | Flowlines, gathering lines, process piping, and offshore platforms |
| Chemical Processing | Heat exchangers, pressure vessels, and reactor piping |
| Marine Engineering | Seawater cooling systems, ballast lines, and desalination plants |
| Pulp & Paper | Digesters and bleach plant equipment |
| Water Treatment | Reverse osmosis (RO) high-pressure piping |
| Construction | Structural components in coastal or de-icing salt environments |
Q: What is the difference between UNS S31803 and UNS S32205?
A: S32205 has tighter limits on Cr, Mo, and N, giving it slightly higher pitting resistance (PREN 33-37 vs 30-34). Many pipes today are dual-certified as both S31803 and S32205.
Q: Is UNS S31803 suitable for seawater applications?
A: Yes, S31803 offers good resistance to seawater and brackish water. For continuous immersion in aggressive seawater, super duplex (e.g., UNS S32750) may be recommended.
Q: Can UNS S31803 pipe be welded to 316L?
A: Yes, but proper filler metal (e.g., 309L or 2209) and welding procedure are required. Consult our technical team for specific cases.
Q: Is UNS S31803 magnetic?
A: Yes, due to its ferrite content, S31803 is slightly magnetic – unlike fully austenitic grades like 304 or 316.
Q: Do you provide cutting and threading services?
A: Yes, we offer custom cutting, beveling, threading, and grooving per your requirements.
Please provide your required size (OD × WT), quantity, standard, and delivery port. We will reply within 24 hours with a competitive price.
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