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SS 321 Seamless Tube
The 321 seamless tube is pierced from a solid billet and drawn to size, so no weld line runs along it. ASTM A213 / ASME SA-213 cover it, and superheater elements come under this category.
Stainless Steel 321 Tube Manufacturer in India
MLTI (Moonlight Tube Industries) has been a manufacturer, supplier, and exporter of stainless steel 321 tube in Gujarat since 2008. Grade 321, UNS S32100, is the titanium-stabilised member of the 18/8 austenitic family. We produce it as ASTM A213 / ASME SA-213 seamless tube and ASTM A249 / ASME SA-249 welded tube. Both specifications were drafted for boiler, superheater and heat-exchanger duty, which is the primary use of 321 stainless steel tubes.
Titanium at five times the combined carbon and nitrogen content ties up carbon as titanium carbide, so grain boundaries keep their chromium through welding and through service between 425 and 815 °C. Chromium sits at 17.0 to 19.0% and nickel at 9.0 to 12.0%. Minimum tensile strength is 515 MPa (75 ksi) and the yield floor sits at 205 MPa (30 ksi), with 35% minimum elongation. Round AISI 321 tube spans 12.7 mm to 101.6 mm outside diameter, on 19 to 10 SWG walls in ERW and 19 to 10 BWG walls in seamless, in lengths up to 24 metres. Square and rectangular sections carry the same grade. Square and rectangular sections carry the same grade and are supplied in ERW form. Seamless and SS 321 welded tubes serve refineries, power stations, sugar plants, and chemical works, delivering durable performance for demanding industrial applications. Refineries, power stations, sugar plants and chemical works absorb most of this output. Each length is proved by 100% hydrostatic test, under ISO 14001 and 45001, BIS / ISI Mark, IBR, PED 2014/68/EU and EIL approval.
Stainless Steel 321 Tube Specifications
We supply 321 SS tubing in seamless and welded form. Applicable standards, the dimensional envelope, supply condition, and finish are listed in the specification table below.
| Parameter | Value |
|---|---|
| Applicable Standards | ASTM A213 / ASME SA-213 (seamless ferritic and austenitic alloy-steel boiler, superheater and heat-exchanger tube); ASTM A269 (seamless and welded austenitic stainless steel tubing for general service); ASTM A554 (welded mechanical and ornamental tubing) |
| Manufacturing Form | Seamless and Welded (ERW) |
| Profile | Round, Square, Rectangular |
| Outside Diameter | 12.7 mm (1/2") to 101.6 mm (4") round |
| Wall Thickness | 1.02 mm (19 SWG) to 3.25 mm (10 SWG) round ERW; 1.07 mm (19 BWG) to 3.40 mm (10 BWG) round seamless; 1.0 mm to 6.0 mm box section |
| Length | Up to 24 metres round; up to 12 metres box section; cut to nominated length |
| Condition | Annealed |
| Surface Finish | Mill finish after passivation; brushed, polished OD, or polished OD and ID to order |
SS 321 Tube Chemical Composition
Type 321 stainless steel tubing is a chromium-nickel austenitic alloy carrying a deliberate titanium addition. Element limits for TP321 under ASME SA-213, including the titanium ratio that defines the grade, appear in the composition table underneath.
| Element | Composition (%) |
|---|---|
| Carbon (C) | 0.08 max |
| Manganese (Mn) | 2.00 max |
| Phosphorus (P) | 0.045 max |
| Sulphur (S) | 0.030 max |
| Silicon (Si) | 1.00 max |
| Chromium (Cr) | 17.0 – 19.0 |
| Nickel (Ni) | 9.0 – 12.0 |
| Titanium (Ti) | 5 x (C+N) min, 0.70 max |
| Iron (Fe) | Balance |
SA-213 sets no nitrogen limit for TP321. Where welded tube is ordered to ASME SA-249, nitrogen is capped at 0.10 % maximum.
Why Titanium Stabilisation Prevents Weld Decay in 321 Tube
Unstabilised austenitic grades shed corrosion resistance when chromium carbide forms at the grain boundaries, and that carbide precipitation range runs from roughly 425 to 815 °C. A weld heat-affected zone passes straight through the band. Titanium holds a stronger affinity for carbon, so in 321 Ti material, the carbon reports to titanium carbide and chromium stays in solution. Welded joints normally retain their intergranular corrosion resistance without further treatment, although ASME SA-213 permit a stabilisation heat treatment where an intergranular corrosion test to Practice A262, Practice E is specified.
321 Stainless Steel Tube Mechanical Properties
Acceptance values for TP321 round tube in the annealed condition come from ASTM A213 / ASME SA-213, and are matched by ASME SA-249 for welded round tube. Square and rectangular sections to ASTM A554 are governed by that specification's own requirements. Four limits cover the release of round material, and the table below states tensile strength, yield strength, elongation and hardness.
| Property | Value |
|---|---|
| Tensile strength (min) | 515MPa (75ksi) |
| Yield strength (min, 0.2% offset) | 205MPa (30ksi) |
| Elongation in 50 mm (min) | 35% |
| Hardness (max) | 90 HRB / 192 HBW |
A 515 MPa floor with 35% elongation leaves enough ductility for a U-bending exchanger tube. The mean coefficient of expansion is 19.8 x 10⁻⁶ cm/cm/°C between 200 and 870 °C, which sets the movement a tube-to-tubesheet joint absorbs. Titanium carbides are abrasive, so 321 stainless tube machinability trails Type 304.
Stainless Steel 321 Tube Equivalent Grades
Eight systems name this titanium-stabilised alloy under codes of their own, and the equivalent-grade table below matches each against Type 321.
| Country / Standard | Designation |
|---|---|
| USA (UNS) | UNS S32100 |
| Europe (EN / W.Nr) | EN 1.4541 / X6CrNiTi18-10 |
| UK (BS) | 321S31 / EN58B |
| France (AFNOR) | Z6CNT18-10 |
| Japan (JIS) | SUS 321; SUS321TB to JIS G 3463 for boiler and heat-exchanger tube |
| China (GB/T) | 06Cr18Ni11Ti / 0Cr18Ni10Ti |
| Russia (GOST) | 12Kh18N10T / 08Kh18N10T |
| India (IS) | X04Cr18Ni10Ti |
A 1.4541 tube drawing and a SUS321TB drawing have identical material under two naming systems.
Stainless Steel 321 Tube Forms and Types
Five variants of SS 321 tube leave our works. Two of them are manufacturing routes: seamless and ERW welded. The other three are section profiles: round tube, square tube and rectangular box section.
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SS 321 Welded and ERW Tube
An SS 321 welded tube starts as an annealed strip, roll-formed and high-frequency welded, then solution annealed. ERW is our core process.
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SS 321 Round Tube
The round profile is the standard for pressure and thermal duty, covering all eleven stock diameters from 12.7 mm to 101.6 mm. Exchanger bundles and superheater coils take round SS321 tubes.
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SS 321 Square Tube
Our SS 321 square tube runs from 12 x 12 mm to 100 x 100 mm on 1.0 mm to 6.0 mm walls, to ASTM A554, in lengths reaching 12 metres. It is used in frames and guarding.
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SS 321 Rectangular Tube
Rectangular box section spans 13 x 25 mm to 100 x 50 mm, sharing the square range's walls and 12-metre limit. Structural work near furnaces and flue equipment is the usual destination.
Stainless Steel 321 Tube Sizes
Below is the size chart for Stainless Steel 321 seamless tube, showing the available outside diameters and corresponding weights per metre for each wall thickness.
Seamless 321 Tube Size Chart
| 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 | 0.92 | 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 |
ERW SS 321 Tube Size Chart
| 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 |
Stainless Steel 321 Tube Industrial Applications
Six sectors account for most of the 321 stainless steel tubes we dispatch, and each buys the grade for a different reason.
Power Generation
Boiler, superheater, reheater and economiser elements are the classic Alloy 321 duty. ASME SA-213 was drafted for exactly this equipment, and our IBR approval covers boiler-related supply in India.
Petroleum Refining
Petroleum refining industries run 321 tube through exchanger bundles, crude unit overhead condensers and catalytic reformer service lines. Repairs happen on-site, so weld-decay resistance decides the grade.
Chemical and Petrochemical Processing
Jacketed reactor coils and vent condensers carrying hot organic acids take grade 321. Where warm chlorides dominate rather than heat, a molybdenum-bearing product such as SS 316 Tube is the right choice.
Aerospace
Aerospace fabricators cut aircraft-grade stainless steel tube for engine bleed-air ducting, firewall penetrations and exhaust collectors. Cycling through the sensitisation band is routine there. A stabilised grade is mandatory.
Automotive and Motorsport
Header builders bend 321 stainless steel exhaust tubing into turbo manifolds, downpipes and racing collectors. Gas at 900 °C followed by a cold soak destroys unstabilised welds inside a season, which is why fabricators pay the premium.
Cryogenic and Industrial Gas
Air separation plants and LNG terminals take 321 SS tubing for transfer lines and vaporiser coils. Impact toughness holds at liquid nitrogen temperature. Austenite has no transition point.
Stainless Steel 321 Tube Shipping and Packaging
Here is an overview of how Stainless Steel 321 tubes are shipped and packed.
- SS 321 tube ships in bundles, with the packing method fixed according to the order.
- Heat number stencilling and custom marking are available on request.
- Export consignments clear from the port under FOB or CFR terms for Brazil, Vietnam and Turkey.
- Mill test certificates and hydrostatic reports travel with the material.
Stainless Steel 321 Tube Price
Welded stainless steel 321 tube trades at roughly ₹300–₹500/kg in India and US$3.00–4.50/kg, with seamless material at a premium over that. Six variables move the SS 321 price per kg: diameter, wall gauge, cut length, quantity, finish and form.
Why Choose Moonlight Tube Industries for Stainless Steel 321 Tube?
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
Frequently Asked Questions About Stainless Steel 321 Tube
Boiler, superheater and heat-exchanger duty takes most of it, ahead of refinery condensers and motorsport headers.
Specify 321 whenever the weldment runs above 425 °C or can't be annealed afterwards.
Grade 316 tube is used where chlorides attack, and grade 321 is specified where heat and welding are the main concerns.
Round 321 SS tubing covers 12.7 mm to 101.6 mm outside diameter, on 1.02 mm to 3.25 mm walls in ERW and 1.07 mm to 3.40 mm walls in seamless.
Seamless tube is pierced from billet under ASTM A213 and carries no weld line. Welded tube is rolled from strip under ASTM A249.
In most fabrication welding no post-weld anneal is required, because titanium stabilisation restricts chromium carbide precipitation in the heat-affected zone. Where an intergranular corrosion test is specified, ASME SA-213 and SA-249 permit a stabilisation heat treatment.
Indicative pricing starts roughly at ₹300–₹500/kg in India and US$3.00–4.50/kg for welded material, with diameter, wall, quantity and form shifting it.
Our SS321 tube answers to ASTM A213 / ASME SA-213 and ASTM A249 / ASME SA-249, plus ASTM A269 and A554.
Brazil, Vietnam and Turkey are regular destinations where we export SS 321 tubes on FOB or CFR terms.