UNS S31803 tube is the original registration of the 22Cr-5Ni-3Mo alloy, with a pitting resistance equivalent from 30.5. Exchanger work ordered against older project specifications continues to cite this designation.
View Duplex Steel UNS S31803 TubeDuplex Steel Tubes Manufacturer in India
MLTI Private Limited (Moonlight Tube Industries) manufactures, supplies and exports duplex steel tubes based in Gujarat, India. Established in 2008, our plant operates with an annual capacity of 8,000 MT and holds ISO 14001 and ISO 45001 certifications.
Duplex tube is produced from ferritic-austenitic stainless steel, a family holding ferrite and austenite in near-equal volume. ASTM A789 / ASME SA-789 governs seamless and welded duplex stainless steel tubing ordered to outside diameter and wall thickness; ASTM A1016 / ASME SA-1016 supplies the general requirements. Our range covers two registrations, UNS S31803 and UNS S32205, both certified as W.Nr. 1.4462. Chromium runs 21.0 to 23.0% and molybdenum 2.5 to 3.5% on S31803, tightened to 22.0 to 23.0% chromium and 3.0 to 3.5% molybdenum on S32205, with nitrogen at 0.08 to 0.20% and 0.14 to 0.20%, respectively, stabilising the austenite in both. Certified minimum yield is 450 MPa on S31803 tube and 485 MPa on S32205 tube, close to double the figure a standard austenitic tube certifies.
Seamless duplex steel tubes come from a pierced billet and carry no weld line, while welded duplex steel tubes start as a strip and are longitudinally fused, including ERW options that use high-frequency electric resistance to forge the seam closed under pressure without filler metal. Route does not change the certified minimum yield, which stays at 450 MPa on S31803 and 485 MPa on S32205, whether the tube is seamless or welded, so the choice turns on section shape, wall tolerance and cost. Condenser circuits, exchanger bundles and brine service account for most despatches. MLTI holds approvals like BIS, EIL and IBR, and is compliant with PED 2014/68/EU; every lot ships against an EN 10204 3.1 mill test certificate.
Duplex Steel Tubes Specifications
The specifications of duplex steel tubes, covering grades, standards and the dimensional envelope, are given in the table below.
| Parameter | Value |
|---|---|
| Grades | UNS S31803, UNS S32205 (2205) |
| Applicable Standard | ASTM A1016 / ASME SA-1016: General requirements for ferritic alloy steel, austenitic alloy steel and stainless steel tubes. ASTM A789: Seamless and welded ferritic/austenitic (duplex) stainless steel tubing for general service. |
| Supply Form | Seamless, welded (ERW) |
| Section | Round, square and rectangular on order |
| Outside Diameter | 10.30 mm to 273.10 mm (1/8" to 10" NB) |
| Wall Thickness | 1.02 mm to 12.70 mm |
| Length | Cut lengths to order, up to 24 ft |
| Delivery Condition | Solution annealed at 1020 to 1100°C, rapidly cooled |
| Hardness Limit | 290 HBW / 30 HRC / 290 HV maximum |
| Finish | Annealed and pickled; bright annealed; polished on request |
| End Type | Plain ends cut square; bevelled on request |
Duplex Steel Tube Grades
Our duplex tube material is produced in two registrations of one alloy family. Both are certified to the same European number, W.Nr. 1.4462.
The S32205 registration raises the chromium, molybdenum and nitrogen floors, certifying 485 MPa yield and a pitting resistance equivalent of at least 34. Enquiries for 2205 duplex stainless steel tubes in seawater duty are supplied to it.
View Duplex Steel UNS S32205 TubeDuplex Tube Forms and Types
Manufacturing route and section profile are settled separately for the order. Five configurations of duplex tubing cover the combinations we produce.
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Seamless Duplex Steel Tubes
Seamless duplex steel tubes are cold-finished from pierced hollows, so the wall carries no weld line. SA-789 subjects seamless tube to a flaring test requiring a minimum 10% expansion of the inside diameter, and instrumentation duty favours this route for bore uniformity.
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Welded (ERW) Duplex Steel Tubes
Welded and ERW duplex steel tubes both form solution-annealed strip without filler metal into tight-seamed profiles. Electric resistance heating fuses the edges before high-temperature solution annealing restores the 50/50 phase balance.
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Round Duplex Steel Tubes
The round section holds the largest share of production, and SA-789 sets the outside diameter and wall tolerances for tubes up to 203.2 mm outside diameter. Round tube is supplied to outside diameter and wall thickness rather than to schedule, across the sizes and gauges listed in the size tables below.
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Duplex Square Tube
Duplex square tube is a welded box profile made to the side dimension and wall thickness on order. A high-strength duplex square tube frames platforms and supports in coastal and process installations.
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Duplex Rectangular Tube
A rectangular duplex section suits a member loaded about one principal axis, where the deeper face adds stiffness without extra mass. Flat dimensions, wall and finish are finalised at the order stage.
Duplex Steel Tube Size
This reference guide details standard outside diameters and linear weights per meter across common SWG and BWG wall thicknesses for ERW and Seamless duplex stainless steel tubes.
Duplex Steel ERW tube size:
| Size | OD (mm) | 10 SWG - 3.25 mm Weight/MTR | 12 SWG - 2.64 mm Weight/MTR | 14 SWG - 2.03 mm Weight/MTR | 16 SWG - 1.63 mm Weight/MTR | 18 SWG - 1.22 mm Weight/MTR | 19 SWG - 1.02 mm Weight/MTR |
|---|---|---|---|---|---|---|---|
| 1/2" | 12.7 | 0.75 | 0.65 | 0.55 | 0.45 | 0.34 | 0.29 |
| 5/8" | 15.875 | 1.01 | 0.86 | 0.72 | 0.58 | 0.44 | 0.37 |
| 3/4" | 19.05 | 1.26 | 1.06 | 0.88 | 0.71 | 0.53 | 0.45 |
| 1" | 25.4 | 1.76 | 1.47 | 1.21 | 0.97 | 0.72 | 0.61 |
| 1 1/4" | 31.75 | 2.27 | 1.88 | 1.54 | 1.23 | 0.91 | 0.76 |
| 1 1/2" | 38.1 | 2.77 | 2.29 | 1.88 | 1.49 | 1.10 | 0.92 |
| 2" | 50.8 | 3.78 | 3.11 | 2.54 | 2.01 | 1.48 | 1.24 |
| 2 1/2" | 63.5 | 4.79 | 3.93 | 3.20 | 2.53 | 1.85 | 1.55 |
| 3" | 76.2 | 5.79 | 4.75 | 3.86 | 3.05 | 2.23 | 1.87 |
| 3 1/2" | 88.9 | 6.80 | 5.57 | 4.52 | 3.57 | 2.61 | 2.18 |
| 4" | 101.6 | 7.81 | 6.39 | 5.18 | 4.09 | 2.99 | 2.50 |
Seamless Duplex Stainless Steel Tube Size:
| Size | OD (mm) | 10 BWG - 3.40 mm Weight/MTR | 12 BWG - 2.77 mm Weight/MTR | 14 BWG - 2.11 mm Weight/MTR | 16 BWG - 1.65 mm Weight/MTR | 18 BWG - 1.25 mm Weight/MTR | 19 BWG - 1.07 mm Weight/MTR |
|---|---|---|---|---|---|---|---|
| 1/2" | 12.7 | 0.78 | 0.68 | 0.55 | 0.45 | 0.35 | 0.31 |
| 5/8" | 15.875 | 1.05 | 0.89 | 0.72 | 0.58 | 0.45 | 0.39 |
| 3/4" | 19.05 | 1.31 | 1.11 | 0.88 | 0.71 | 0.55 | 0.47 |
| 1" | 25.4 | 1.85 | 1.55 | 1.21 | 0.97 | 0.74 | 0.64 |
| 1 1/4" | 31.75 | 2.38 | 1.98 | 1.54 | 1.23 | 0.94 | 0.81 |
| 1 1/2" | 38.1 | 2.91 | 2.41 | 1.87 | 1.48 | 1.13 | 0.97 |
| 2" | 50.8 | 3.98 | 3.28 | 2.53 | 2.00 | 1.52 | 1.31 |
| 2 1/2" | 63.5 | 5.04 | 4.15 | 3.19 | 2.52 | 1.91 | 1.64 |
| 3" | 76.2 | 6.11 | 5.01 | 3.85 | 3.04 | 2.30 | 1.98 |
| 3 1/2" | 88.9 | 7.18 | 5.88 | 4.51 | 3.55 | 2.69 | 2.31 |
| 4" | 101.6 | 8.24 | 6.75 | 5.17 | 4.07 | 3.08 | 2.65 |
Duplex Steel Tube Industrial Application
Our duplex steel tubes excel in high-chloride environments, offering superior strength, corrosion resistance, and reduced wall thickness across major chemical, offshore, and industrial applications.
Chemical and Petrochemical Processing
Evaporator coils, overhead condensers and effluent coolers see halides and organic acids together. Plants order ASTM A789 duplex pipe here because molybdenum and nitrogen preserve the passive film while the higher yield trims the wall.
Marine and Desalination
Multi-stage flash trains circulate warm brine at roughly one and a half times the seawater chloride, while reverse osmosis plants reject a near-ambient concentrate at close to twice it. Duplex tubes resist the crevice attack that develops at rolled tube-sheet joints and tolerate periodic intake chlorination.
Offshore Oil and Gas
Hydraulic control lines, umbilical elements and produced-water coolers on topside modules carry a direct weight penalty. The strength-to-wall ratio of duplex tubing reduces that mass, and the alloy withstands chloride stress corrosion that shortens 316 service.
Power Generation
Flue-gas desulphurisation loops concentrate chloride in the recirculating slurry through every campaign. Absorber cooling circuits and condensate coolers at coastal stations specify duplex tubes, selected on pitting resistance equivalent.
Pulp and Paper
Bleach plant liquors combine chlorine dioxide, low pH and heat. Washer heat-recovery coils and liquor heaters run duplex tube because the alloy holds wall thickness through campaigns that perforate austenitic bundles.
Shipping and Packaging of DSS Tubes
As a leading duplex steel tube supplier, we ensure maximum product protection during transit using secure end caps, battens, polythene wrapping, robust timber casing, and complete mill documentation for global exports.
- Tubes are bundled by size and gauge, strapped, and capped at both ends.
- Light-gauge bundles are separated with battens to prevent surface damage in transit and sea consignments are wrapped in polythene and packed in fumigated timber cases.
- Every bundle is tagged with grade, size, wall, heat number and specification.
- Export orders move on FOB or CFR terms to Brazil, Turkey, Vietnam and Europe.
Why Choose MLTI Private Limited?
Buyers return to Moonlight Tubes for certified material, approved grades and stock that ships on schedule. Every order is backed by documented quality, a wide size range and delivery commitments we hold to.
Quality Certification
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IBR & EIL Approved
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Why
Choose Us
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Wide Range of Grades & Sizes
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Timely Global Delivery
FAQs about Duplex SS Tubes
Duplex Tubing is a Stainless Steel Tube whose microstructure contains austenite and ferrite in near-equal proportions. The balance roughly doubles yield strength and raises resistance to chloride pitting and stress corrosion cracking. Duplex Tubing is also ferromagnetic.
ASTM A790 / ASME SA-790 applies to Duplex Pipe in schedule sizes, covering seamless and welded ferritic/austenitic Stainless Steel Pipe. General requirements come from ASTM A999 / ASME SA-999. Duplex Tube ordered by outside diameter and wall thickness falls under ASTM A789 / ASME SA-789 instead.
Another name for Duplex Steel Tubes is 2205 Tubing, from the nominal 22% chromium and 5% nickel content. Ordering documents also cite UNS S31803, UNS S32205, W.Nr. 1.4462, EN X2CrNiMoN22-5-3 and JIS SUS 329J3L.
Super Duplex Tubes carry a pitting resistance equivalent of 40 or more, against 30.5 and 34 minima for standard duplex grades. Registrations such as UNS S32750 and UNS S32760 form the Super Duplex class; we don't manufacture tubing in Super Duplex grades.
Yes. Duplex Steel Tubes outperform 316 Stainless Steel Tubes in chloride service on two counts: yield strengths of 450 MPa or 485 MPa against 205 MPa and markedly higher resistance to chloride stress corrosion cracking. For potable water and clean steam, 316 Tube remains adequate at a lower cost.
Yes. Duplex Steel Tubes can be welded where heat input and interpass temperature are controlled so the joint keeps its phase balance. Rapid cooling leaves excess ferrite; prolonged holding precipitates intermetallic phases. Matching 2209 Filler suits joints that are not autogenous.