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Built for extreme environments: high pressure, high chloride, high corrosion.
Duplex (22% Cr) and Super Duplex (25% Cr) stainless steels are the workhorses of modern offshore, subsea, desalination, chemical and power industries. These materials combine the best of two worlds:
Result:
For engineering teams designing pipelines, risers, manifolds and corrosion-critical components, ASTM A789/A790 duplex tubes offer unmatched dependability.
These are welded stainless-steel tubes manufactured from duplex alloys that contain a balanced austenite–ferrite microstructure. They provide:
Duplex Grades
Super Duplex Grades
These materials outperform 316/317 stainless steel in nearly all severe environments.
1. 2X Mechanical Strength
Duplex alloys deliver 2× the yield strength of 316. Meaning:
2. Extreme Resistance to Chlorides (Seawater, Brine, Desalination)
| Alloy | PREN (Pitting Resistance Equivalent Number) |
|---|---|
| 316L | ~25 |
| Duplex 2205 | ~35 |
| Super Duplex 2507 | >40–45 |
Higher PREN = higher pitting & crevice corrosion resistance.
3. Excellent SCC (Stress Corrosion Cracking) Resistance
Super Duplex tubes resist stress cracking in:
4. Superior Life-Cycle Cost
Although duplex and super duplex alloys cost more upfront than 316, their lifespan and performance reduce maintenance cost drastically—especially in offshore and chemical plants.
Duplex (UNS S31803 / S32205) | Super Duplex (UNS S32750 / S32760)
| Section | Parameter | Technical Specification — Duplex & Super Duplex Welded Tubes |
|---|---|---|
| Standard | Specifications | ASTM A789 (Seamless & welded duplex tubes) / ASTM A790 (Seamless & welded duplex pipe) |
| Product Type | Duplex & Super Duplex stainless steel tubes for high-pressure, corrosive & offshore applications | |
| Available Grades | Duplex | S31803, S32205, S32304 |
| Super Duplex | S32750 (2507), S32760 (Zeron 100) | |
| Finish Options | Mill Finish | Standard industrial |
| Pickled & Passivated | Descaled, corrosion-protected | |
| Polished (for instrumentation) | 180 / 240 / 320 grit (on request) | |
| Manufacturing Process | Welded (TIG / ERW / Plasma) | Weld bead removed or bead-rolled |
| Heat Treatment | Solution annealed + water quenched | |
| Straightening | Precision straightened for offshore tolerances | |
| Dimensional Range | OD | 6 mm – 168 mm |
| Wall Thickness | 0.8 – 10 mm | |
| Length | 6m / 12m / custom | |
| Mechanical Properties (Typical) | Tensile Strength | Duplex: 620–800 MPa • Super Duplex: 750–900 MPa |
| Yield Strength | Duplex: 450–550 MPa • Super Duplex: 550–650 MPa | |
| Hardness | ≤ 32 HRC (heat-treated) | |
| Corrosion Resistance | Chloride Stress Corrosion | Excellent (Super Duplex best) |
| Pitting Resistance Equivalent (PREN) | Duplex: 28–35 • Super Duplex: >40 | |
| Seawater resistance | Very high | |
| Chemical Composition | Duplex | 22% Cr, 5–6% Ni, 3% Mo, N enhanced |
| Super Duplex | 25% Cr, 7% Ni, 4% Mo, W added (for Zeron 100) | |
| Testing Requirements | Mandatory | Hydro, Eddy Current, Flattening, Flaring, NDT |
| Advanced | PMI, IGC, Impact test at –46°C, RT (welds), UT | |
| End Finishing | Tube Ends | Plain / Beveled / Deburred |
| Cleaning | Passivation for high corrosion resistance | |
| Key Advantages | Duplex | High strength + corrosion resistance at lower cost than 316 |
| Super Duplex | For extreme chloride, seawater, offshore & chemical environments | |
| Industry Applications | Oil & Gas | Subsea manifolds, umbilicals, heat exchangers, offshore platforms |
| Chemical Processing | Chlorides, acidic media, phosphoric & sulfuric environments | |
| Desalination Plants | Brine circulation lines, high-pressure piping | |
| Pulp & Paper | Bleach plant lines | |
| Power Generation | Condensers, cooling water systems | |
| HSN Code | Stainless Tubes | 73064000 |
| Standard | Covers | Use Case |
|---|---|---|
| ASTM A789 | Seamless & welded duplex tubes | Heat exchangers, condensers, instrumentation |
| ASTM A790 | Seamless & welded duplex pipe | Process piping, offshore risers, manifolds |
Both standards cover Duplex & Super Duplex materials but differ in dimensional & mechanical requirements.
Oil & Gas (Onshore + Offshore)
Desalination Plants
Chemical & Petrochemical
Power & Energy
Marine Engineering
Pulp & Paper
| Outside Diameter (OD) | Wall Thickness (WT) | Typical Applications |
|---|---|---|
| 6 – 19.05 mm | 0.8 – 2.0 mm | Instrumentation, chemical injection, control lines |
| 19.05 – 38.1 mm | 1.0 – 3.0 mm | Heat exchanger / condenser tubes |
| 38.1 – 60.3 mm | 2.0 – 5.0 mm | Process lines, skid piping |
| 60.3 – 114.3 mm | 3.0 – 8.0 mm | Offshore manifolds, risers, structural piping |
| 114.3 – 168.3 mm | 4.0 – 10.0 mm | Main headers, high-pressure brine lines |
Lengths:
| Alloy / Grade | Typical PREN* | Chloride / Seawater Resistance | Typical Service |
|---|---|---|---|
| 316L (for comparison) | ~25 | Moderate | General marine/chemical |
| Duplex 2205 (S31803 / S32205) | 34–36 | Very High | Offshore, chemical, desalination |
| Lean Duplex S32304 | 26–28 | High (better than 316L) | Cost-effective chloride service |
| Super Duplex 2507 (S32750) | 40–45 | Extreme | Subsea, high-pressure seawater |
| Super Duplex S32760 (Zeron 100) | 40–47 | Extreme | Highly aggressive, sour, subsea |
*PREN ≈ %Cr + 3.3×%Mo + 16×%N
Higher PREN = higher pitting & crevice corrosion resistance.
Duplex & Super Duplex maintain high strength up to approx. 250–315°C (grade-dependent). At low temperatures (down to –46°C or lower), they show excellent impact toughness (after proper heat treatment).
Result for designers:
Welding Behaviour
Post-Weld Treatment
Fabrication
INOX supplies project-ready weld procedure-compliant tubes suitable for offshore & critical piping packages.
Mandatory Standard Tests
Advanced / Project-Specific Tests
INOX can supply with 3.1 / 3.2 EN 10204 + third-party inspection (BV / DNV / LR / TUV) as required.
| Requirement / Condition | Recommended Material | Reason |
|---|---|---|
| Better than 316L, but cost-effective | Lean Duplex S32304 | Higher strength & corrosion vs 316L |
| General offshore / high chloride | Duplex 2205 (S31803/S32205) | Balanced performance & cost |
| Very high chloride, high pressure, subsea | Super Duplex 2507 (S32750) | PREN > 40, high strength |
| Highly aggressive, sour + chloride + high pressure | S32760 (Zeron 100) | Top-tier corrosion resistance |
| Property | 316L | Duplex 2205 | Super Duplex 2507 |
|---|---|---|---|
| Yield Strength | ~220 MPa | ~450 MPa | ~550 MPa |
| PREN | ~25 | ~35 | >40 |
| SCC in Chlorides | Moderate risk | Very Low | Very Low |
| Weight for Same Pressure | Higher | Lower | Lower |
| Cost per Kg | Lower | Higher | Higher |
| Total Lifecycle Cost | Higher | Lower | Lowest in harsh service |
| Alloy | Product | Indicative Price (INR/Kg) | Indicative Price (USD/Kg) |
|---|---|---|---|
| Duplex 2205 | Welded Tubes | ₹ 550 – ₹ 800 | $7 – $11 |
| Lean Duplex S32304 | Welded Tubes | ₹ 480 – ₹ 720 | $6 – $9 |
| Super Duplex 2507 / S32760 | Welded Tubes | ₹ 850 – ₹ 1,300 | $10 – $16 |
Pricing varies with: OD, WT, origin (mill), testing scope & project documentation.
| Condition | Application |
|---|---|
| Pickled & Passivated | Standard for offshore, chemical & desalination |
| Bead-Rolled Weld | Better flow & corrosion resistance |
| Polished OD | Skids / visible manifolds |
| Shot Blasted | Heavy-duty structural use |
1. Controlled Metallurgy (Austenite–Ferrite Balance)
2. Weld Integrity for Critical Service
3. High PREN, High Confidence
4. EPC & Project-Ready Supply
Oil & Gas (Onshore / Offshore)
Desalination & Water Treatment
Chemical & Petrochemical
Marine & Offshore Engineering
Power & Energy
Standard / Project Packaging
Offshore / Export Packaging
Documentation
52-A, Mulji Thackersi Bldg, Islampura Street, Shop No. 10, Near Alankar Cinema, Mumbai – 400 004
steel@inoxsteelindia.in
+91 9930796690
Duplex offers ~2× strength and far superior chloride SCC resistance, reducing wall thickness and lifecycle cost.
For very high chloride, high-pressure, subsea, or desalination environments where PREN >40 is required.
Yes—when welded with controlled heat input and tested. INOX supplies project-approved welded tubes with NDT.
Yes—DNV, BV, LR, TUV inspections available.
INOX STEEL INDIA supplies ASTM A789 / A790 duplex and super duplex welded tubes in grades S31803, S32205, S32750 & S32760. High-strength, high-PREN tubing for offshore, desalination, chemical & power applications. EN 10204 certified, project & export ready.