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MLTI Private Limited (Moonlight Tube Industries) is a manufacturer and exporter of duplex stainless steel heat exchanger tubes based in Gujarat, India, with experience in producing stainless steel tubular products since 2008. Our DSS heat exchanger tubes are supplied in UNS S31803 and UNS S32205 to ASTM A789 / ASME SA-789 for heat exchanger, condenser and general service applications. Both grades are ferritic-austenitic duplex stainless steels with higher strength and better resistance to chloride-induced corrosion than conventional austenitic grades such as 304L and 316L.
We supply Duplex Steel S31803 Heat Exchanger Tubes and Duplex Steel S32205 Heat Exchanger Tubes in seamless (solid billets are pierced to form a hollow shell, which is then sized or drawn to final dimensions, leaving no longitudinal weld) and welded construction, with outside diameters from 12.7 mm to 101.6 mm and wall thicknesses from 1.07 mm to 3.40 mm. Straight lengths and U-bent tubes are available against bundle drawings. All tubes are solution annealed and rapidly cooled. Tension and hardness testing is carried out as required by ASTM A789, together with the flaring test on seamless tubes and the flange and reverse flattening tests on welded tubes, and every tube is subjected to a hydrostatic or non-destructive electric test. MLTI holds ISO 14001 and 45001 certification with BIS, EIL, IBR and PED 2014/68/EU approvals.
The duplex steel heat exchanger tube specifications below cover the grades, applicable standards, manufacturing routes, dimensions, heat treatment, finishes, and inspection requirements.
| Parameter | Value |
|---|---|
| Grades | UNS S31803, UNS S32205 |
| Applicable standard | ASTM A789 / ASME SA-789: Standard Specification for Seamless and Welded Ferritic/Austenitic Stainless Steel Tubing for General Service ASTM A1016 / ASME SA-1016: Standard Specification for General Requirements for Ferritic Alloy Steel, Austenitic Alloy Steel, and Stainless Steel Tubes |
| Construction | Seamless; welded |
| Outside diameter | 12.7 mm to 101.6 mm (1/2" to 4") |
| Wall thickness | 1.07 mm to 3.40 mm (19 BWG to 10 BWG) |
| Configuration | Straight lengths; U-bent to drawing |
| Delivery condition | Solution annealed at 1020–1100°C, followed by rapid cooling |
| Finish | Mill finish; annealed and pickled; bright annealed; polished to order |
| Wall basis | Nominal wall to ASTM A789, with wall tolerance of ±10% for outside diameters of 12.7 mm and above |
We supply only two duplex grades for heat exchanger tube applications:
UNS S31803 is the established 2205 duplex grade used where chloride corrosion resistance and higher mechanical strength are required. Duplex Steel S31803 Heat Exchanger Tubes are available in seamless and welded construction for cooling, condenser and process-service duties.
UNS S32205 is the higher-alloy-controlled 2205 designation with tighter chromium, molybdenum and nitrogen requirements. Duplex Steel S32205 Heat Exchanger Tubes provide higher specified tensile and yield strength than S31803 and are selected for demanding chloride-bearing service.
Our duplex stainless steel heat exchanger tubes are supplied in seamless, welded and U-bent configurations. Seamless tubes have no longitudinal weld; welded tubes are formed and autogenously welded from strip, while U-tubes are bent to the specified radius and leg dimensions.
Duplex Steel Seamless Heat Exchanger Tubes are produced from solid material through piercing and subsequent sizing or drawing. The absence of a longitudinal weld makes this construction suitable where the design specification or material requisition calls for seamless tubing.
Duplex Steel Welded Heat Exchanger Tubes are formed from strip and longitudinally welded without filler metal. Subsequent solution annealing and rapid cooling restore the required duplex microstructure through the welded area and parent metal.
Duplex Steel U-Tubes are supplied by bending straight tubes to the radius, leg length and centre-to-centre dimensions shown on the exchanger drawing. U-bending can be specified for shell-and-tube bundles, where the return bend removes the need for a second tubesheet and halves the number of tube-to-tubesheet joints.
Our duplex steel tube size charts outline nominal diameters, outside dimensions, and unit weights per meter across standard BWG wall thicknesses for seamless configurations.
| Nominal Size | OD (mm) | 10 BWG (3.40 mm) | 12 BWG (2.77 mm) | 14 BWG (2.11 mm) | 16 BWG (1.65 mm) | 18 BWG (1.25 mm) | 19 BWG (1.07 mm) |
|---|---|---|---|---|---|---|---|
| 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 |
Dimensions are in millimetres and tabulated weights are in kilograms per metre. Permissible variations in outside diameter, wall thickness and length are those given in ASTM A789 / ASME SA-789, unless the purchase order specifies tighter requirements.
Duplex heat exchangers use these tubes in refinery coolers, seawater systems, desalination equipment, power-plant cooling circuits, fertiliser units and pulp-and-paper heat recovery systems.
Duplex Steel Heat Exchanger Tubing is used for process coolers, condensers, and reboilers exposed to chloride-bearing cooling water. S31803 and S32205 provide higher strength and resistance to chloride stress corrosion cracking than standard austenitic grades.
Closed cooling systems, condenser services and flue-gas desulphurisation equipment can expose exchanger tubes to chloride-containing water and acidic process streams. Duplex grades are selected where both corrosion resistance and mechanical strength are required.
Seawater and concentrated brine impose demanding chloride exposure on duplex heat exchanger surfaces. Duplex Steel Heat Exchanger Tubes are used in seawater coolers, brine heaters and desalination equipment where 304L or 316L may have insufficient resistance.
Process coolers, condensers and solution circuits in fertiliser and chemical plants may combine chlorides, acidic media and elevated temperatures. Duplex 2205 Heat Exchanger Tubes are selected according to the process chemistry and required mechanical properties.
Bleach-plant and process-water systems can expose exchanger tubes to chlorides, acidic liquor and oxidising chemicals. Duplex tubing is used for heat recovery, cooling and evaporator services where austenitic stainless steel may require a higher corrosion allowance.
Our specialised shipping and packaging protocols ensure structural cargo protection, precise bundle identification, and flexible international transport options.
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 covers seamless and welded ferritic/austenitic stainless steel tubing, including UNS S31803 and UNS S32205, for general service. MLTI supplies tubing to this specification for heat exchanger and condenser duties. General requirements and test methods are those of ASTM A1016 / ASME SA-1016, except where ASTM A789 provides otherwise; dimensional tolerances are given in Table 5 of ASTM A789.
We supply UNS S31803 and UNS S32205 (Duplex 2205) heat exchanger tubes. UNS S32205 features narrower composition limits with higher minimum mechanical properties, while most available inventory is dual-certified S31803/S32205.
Yes. Both seamless and longitudinally welded duplex heat exchanger tubes are supplied. Selection depends on design pressure, operating temperature, dimensional tolerance requirements, and the shell-and-tube exchanger design code.
Yes. Duplex S31803 and S32205 U-tubes are supplied precision-bent to custom leg lengths, centerline dimensions, and bend radii per engineering drawings, complete with mandatory solution heat treatment in the bend area when required.
Standard sizes range from 12.7 mm to 101.6 mm OD (1/2" to 4"), with wall thicknesses from 1.07 mm to 3.40 mm (19 SWG to 10 SWG). Custom cut lengths are manufactured to drawing.
Both belong to the 2205 alloy family, but UNS S32205 has higher minimum limits for chromium (22.0%), molybdenum (3.0%), and nitrogen (0.14%), delivering superior pitting resistance and higher mechanical strength than base S31803.
Yes. Duplex 2205 offers excellent resistance to chloride pitting and stress corrosion cracking in brackish and seawater cooling circuits, provided operating temperatures remain moderate and flow velocities prevent stagnant fouling or crevice attack.
Consignments include an EN 10204 3.1 mill test certificate covering chemical composition and mechanical properties, together with the result of the hydrostatic or non-destructive electric test carried out on every tube. Supplementary reports such as eddy-current inspection, positive material identification, ferrite content determination and third-party EN 10204 3.2 certification are supplied on request.