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MLTI Private Limited (Moonlight Tube Industries) has been a reliable manufacturer and exporter of DSS tubular products from Gujarat since 2008. Duplex Steel S31803 tube is part of the corrosion resistance range we supply to Indian plants and export accounts. S31803 is a ferritic-austenitic duplex stainless steel tube grade designated UNS S31803 and Werkstoff 1.4462, with a microstructure holding roughly equal volumes of ferrite and austenite. ASTM A789 and ASME SA-789 cover seamless and welded tubing, requiring welded routes without filler metal. SA-789 sets the same chemical, mechanical and dimensional requirements for both routes; the seamless wall carries no weld seam or heat-affected zone, while the welded route is roll-formed from solution-annealed strip.
Chromium runs 21.0 to 23.0%, molybdenum 2.5 to 3.5%, and nitrogen 0.08 to 0.20%. Those three elements set the pitting index. Minimum tensile strength is 620 MPa (90 ksi) and minimum yield is 450 MPa (65 ksi) in the solution-annealed condition, with 25% minimum elongation. Ferrite in the structure also leaves the material magnetic. Round section runs 12.7 mm to 101.6 mm outside diameter in 1.02 mm to 3.40 mm wall (19 SWG to 10 SWG welded; 19 BWG to 10 BWG seamless), with square and rectangular sections made to ordered dimensions. Chloride-bearing and sour duty accounts for most enquiries: umbilical and instrumentation runs, desalination heat exchanger bundles and bleach plant cooling coils. Our company holds ISO 14001 and 45001 certifications alongside EIL, IBR, and PED approval, and each lot ships against an EN 10204 3.1 certificate.
We supply UNS S31803 tubing under ASTM A789 and ASME SA-789. The table below details dimensions, conditions, tolerances, and certification.
| Parameter | Value |
|---|---|
| Applicable standard | ASTM A789 / ASME SA-789: Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service |
| General requirements | ASTM A1016 / ASME SA-1016 |
| Manufacturing process | Seamless; welded (ERW) |
| Sections | Round, square and rectangular to order |
| Outside diameter, round | 12.7 mm to 101.6 mm (1/2" to 4") |
| Wall thickness, round | 1.02 mm to 3.40 mm (19 SWG to 10 SWG welded; 19 BWG to 10 BWG seamless) |
| Wall designation | Average wall or minimum wall, as stated on the order |
| Length | Cut to the ordered length |
| Delivery condition | Solution annealed 1020 to 1100°C (1870 to 2010°F), rapid cooling in air or water |
| Outside diameter tolerance | ±0.13 mm below 38.1 mm OD; ±0.25 mm from 38.1 mm up to but excluding 88.9 mm OD; ±0.38 mm from 88.9 mm up to but excluding 139.7 mm OD |
| Average wall tolerance | ±10%; ±12.5% where the ordered inside diameter is 60% or less of the outside diameter |
| Finish | Mill finish; annealed and pickled; bright annealed; polished to order |
| End type | Plain end, cut square |
The SA 789 UNS S31803 chemical composition is fixed, which sets chromium at 21.0 to 23.0% and nitrogen at 0.08 to 0.20%. Every element limit appears in the table below.
| Element | Composition, % by mass |
|---|---|
| Carbon (C) | 0.030 max |
| Manganese (Mn) | 2.00 max |
| Phosphorus (P) | 0.030 max |
| Sulphur (S) | 0.020 max |
| Silicon (Si) | 1.00 max |
| Chromium (Cr) | 21.0 to 23.0 |
| Nickel (Ni) | 4.5 to 6.5 |
| Molybdenum (Mo) | 2.5 to 3.5 |
| Nitrogen (N) | 0.08 to 0.20 |
| Iron (Fe) | Balance |
Corrosion behaviour is indexed by PREN, on the basis given in the footnotes to SA-789: %Cr plus 3.3 times %Mo plus 16 times %N. Applied to the limits above, S31803 spans roughly 30.5 to 37.8.
UNS S31803 mechanical properties are certified in the solution annealed condition and apply equally to seamless and welded tubing. Room-temperature minima and the hardness ceiling are listed in the table below.
| Property | Value |
|---|---|
| Tensile strength, min | 620 MPa (90 ksi) |
| Yield strength, 0.2% offset, min | 450 MPa (65 ksi) |
| Elongation in 50 mm (2 in.), min | 25% |
| Hardness, max | 290 HBW / 30 HRC / 290 HV |
Yield at this level is roughly two and a half times the 170 MPa a 316L tube certifies, so a thinner wall often carries the same pressure.
Recognised designations for S31803 are collected in the table below, including EN, Werkstoff Number, BS, and others.
| Country / Standard | Designation |
|---|---|
| USA (UNS) | S31803 |
| Europe (EN 10088 number) | 1.4462 |
| Europe (EN 10088 name) | X2CrNiMoN22-5-3 |
| Germany (Werkstoff) | W.Nr. 1.4462 |
| United Kingdom (BS) | 318S13 |
| Sweden (SS) | SS 2377 |
| Japan (JIS) | SUS 329J3L |
Two manufacturing processes and three section profiles make up our duplex stainless steel tubing range. SA-789 recognises seamless and welded construction; round, square and rectangular profiles cover the fabricated side.
Duplex S31803 seamless tube is pierced and cold-drawn from solid, so no weld seam or heat-affected zone exists in the finished wall. Seamless is specified where cyclic pressure or downhole duty makes weld integrity the governing risk.
Duplex S31803 welded tube is roll-formed from strip and fused autogenously, with no filler metal permitted under SA-789. Electric Resistance Welding (ERW) uses high-frequency electrical currents to forge a high-integrity seam, ensuring tight dimensional tolerances and uniform wall thickness. The seam is then solution annealed and quenched with the parent metal, restoring phase balance across the weld.
The round section is the highest-volume profile and the only one SA-789 tolerances address directly. Heat exchanger and condenser bundles, umbilical lines, instrumentation runs and hydraulic circuits all draw on round DSS S31803 tube.
Square duplex tube is a welded box section, produced according to the side dimension and wall thickness stated on the order. Frames, walkways and equipment supports in chloride-laden process areas take this profile.
A Rectangular section follows the same welded route as a square and suits a member carrying a bending load about one principal axis. Wall and both flat dimensions are agreed upon at the order stage.
Duplex Steel S31803 tube size selection covers eleven nominal diameters from 12.7 mm to 101.6 mm, with wall thickness set by BWG gauge on the seamless range and SWG gauge on the welded range.
| 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 |
| 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 |
Diameters and gauges outside that band are produced to order.
Five sectors account for most of the S31803 duplex tubes we release, and each is set out below with the equipment involved.
Wet sour gas and produced water carry chloride, carbon dioxide and hydrogen sulphide together. S31803 tubing serves umbilicals, chemical injection lines and separator internals, since the duplex structure resists chloride cracking where 316L fails.
Reactor cooling coils, dosing lines and column overhead circuits handle organic acids mixed with halides. ASTM A789 UNS S31803 tube is specified here for its molybdenum and nitrogen content, and the higher yield allows thinner walls.
Multi-stage flash plants recirculate hot brine well above seawater salinity, and reverse osmosis trains reject a cold concentrate at roughly twice the feed chloride level. Brine heaters, heat rejection sections and feed loops use this grade where crevice attack at tube-sheet joints ends austenitic tube life.
Chlorine dioxide bleaching combines low pH, chloride and heat in one stream. Bleach tower cooling coils, washer liquor circuits and digester heating loops take duplex tubing, which resists pitting that would perforate a 316L wall.
Wet limestone flue-gas desulphurisation concentrates chloride in the recirculating slurry across each campaign. Absorber spray nozzle lances and quench cooling coils are built in S31803 duplex tubes, and coastal plants specify the grade for condenser service.
Heat input governs weld quality here far more than it does in austenitic material. Cooling too fast leaves excess ferrite in the heat-affected zone; cooling too slowly precipitates intermetallics that strip corrosion resistance. A solution anneal at 1020 to 1100°C with rapid cooling resets the balance. Five of our twelve gauges (three in the welded range and two in the seamless range) sit under the 0.065 in. (1.65 mm) wall at which SA-789 clause 9.4.2 permits to carry out Vickers hardness testing; where hardness is called for below that wall, we test to Vickers, and Rockwell applies across the balance of the range.
Temperature sets the boundary on where the grade belongs. ASME caps 22Cr duplex at 316°C (600°F), because sustained exposure above that band precipitates alpha-prime in the ferrite and, higher still, sigma phase. S31803 duplex tube isn't the right specification beyond 316°C; an austenitic tube is.
Duplex tubes are securely packaged in seaworthy timber cases, traceably marked, and prepared for global export under agreed trade terms.
Duplex Steel S31803 tube price ranges from ₹650–₹1,200 per kg in India and US$7.5–13.8 per kg. The price varies with ferrochrome, nickel and molybdenum input costs, so we quote the day's rate rather than a list that's stale within the week. Seven variables set the figure: diameter, wall gauge, section profile, quantity, manufacturing route, finish and certification level.
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.
ASTM A789 / ASME SA-789 applies to Duplex Steel S31803 tube, covering seamless and welded ferritic-austenitic stainless steel tubing for general service.
They are separate UNS numbers carrying separate limits. S31803 permits chromium from 21.0%, molybdenum from 2.5% and nitrogen from 0.08%, while S32205 tightens those floors to 22.0%, 3.0% and 0.14% and raises minimum tensile from 620 MPa to 655 MPa. The tighter ranges sit inside the wider ones, so a heat meeting the newer number can be dual certified to both. The reverse doesn't hold, so state the exact UNS number on the purchase order.
Chromium is 21.0 to 23.0%, nickel 4.5 to 6.5%, molybdenum 2.5 to 3.5% and nitrogen 0.08 to 0.20%, with iron as the balance.
UNS S31803 is 1.4462 and X2CrNiMoN22-5-3 in Europe, 318S13 in the United Kingdom, SS 2377 in Sweden and SUS 329J3L in Japan.
The S31803 vs 316L choice turns on chloride level, and S31803 wins on two counts. Its PREN band of roughly 30.5 to 37.8 sits well above the mid-twenties that a 316L heat delivers, raising the critical pitting temperature. Chloride stress corrosion cracking is also resisted where austenitic tubes fail, since cracks stall at the phase boundaries. On low-chloride duty, 316L remains adequate and more affordable.
Round tubing runs 12.7 mm to 101.6 mm outside diameter across eleven nominal sizes, in wall from 1.02 mm to 3.40 mm (19 SWG to 10 SWG welded, 19 BWG to 10 BWG seamless). Diameter tolerance is ±0.13 mm below 38.1 mm OD.
ASME limits 22Cr duplex to 316°C (600°F) in pressure-retaining service. Prolonged exposure above that band embrittles the ferrite phase, first through alpha-prime formation and then through sigma precipitation.
Every consignment carries an EN 10204 3.1 mill test certificate stating heat number, chemical analysis, tensile results and hardness. Third-party inspection is arranged on request.