ASTM A789 duplex tube is a standard specification for seamless and welded duplex stainless steel tubes intended for general corrosion-resistant and high-strength applications. Duplex stainless steel offers a balanced austenitic-ferritic microstructure (approximately 50% austenite / 50% ferrite), delivering approximately twice the yield strength of common austenitic grades like 304 or 316, combined with excellent resistance to chloride stress corrosion cracking (SCC), pitting, and crevice corrosion.
These tubes are widely used in heat exchangers, condensers, instrumentation lines, hydraulic systems, process piping, and oil & gas exploration, where both strength and corrosion resistance are critical.
Key Features
| Feature |
Description |
| Standard |
ASTM A789 / ASME SA789 |
| Construction Types |
Seamless and longitudinally welded |
| Microstructure |
Austenitic + Ferritic (≈50/50 dual-phase) |
| Yield Strength |
400 – 550 MPa (depending on grade) |
| PREN |
25 – 42 (depending on grade) |
| Corrosion Resistance |
Excellent against SCC, pitting, and crevice corrosion |
| Temperature Range |
-50°F to 600°F (-46°C to 316°C) |
| Magnetic |
Yes |
| Weldability |
Good with proper procedures |
Available Grades
| Grade |
UNS |
Type |
Yield Strength (min) |
PREN |
Key Application |
| 2304 |
S32304 |
Lean Duplex |
≥400 MPa |
~25 |
Cost-effective alternative to 304/316 |
| 2205 |
S32205 / S31803 |
Standard Duplex |
≥450 MPa |
≥35 |
Most widely used: heat exchangers, process lines |
| 2507 |
S32750 |
Super Duplex |
≥550 MPa |
≥42 |
Extreme environments; subsea, high chloride |
| S32760 |
S32760 |
Super Duplex (Z100) |
≥550 MPa |
≥40 |
Offshore, seawater, sour service |
Equivalent Designations
| Grade |
ASTM UNS |
EN |
JIS |
| 2304 |
S32304 |
1.4362 |
SUS329J3L |
| 2205 |
S32205 / S31803 |
1.4462 |
SUS329J3L |
| 2507 |
S32750 |
1.4410 |
SUS329J4L |
| S32760 |
S32760 |
1.4501 |
— |
Seamless vs. Welded Tube Comparison
| Feature |
Seamless Tube |
Welded Tube |
| Construction |
No weld seam |
Longitudinal weld |
| Pressure Rating |
Higher |
Slightly lower |
| Cost |
Higher |
Lower (10-20% less) |
| Lead Time |
Longer |
Shorter |
| Size Availability |
Limited in large diameters |
More flexible |
| Weld Integrity |
N/A |
100% NDT tested |
| Best For |
High pressure, sour service, critical applications |
General service, heat exchangers, cost-sensitive projects |
Corrosion Resistance Highlights
| Corrosion Type |
2205 Performance |
2507 Performance |
| Pitting / Crevice |
Excellent (PREN ≥35) |
Very High (PREN ≥42) |
| Stress Corrosion Cracking |
Highly resistant |
Very highly resistant |
| General Corrosion |
Superior to 316L |
Superior to 2205 |
| Seawater Resistance |
Good |
Excellent |
| H₂S Sour Service |
NACE MR0175 compliant |
NACE MR0175 compliant |
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