SS 321 Pipe FittingsASTM A403 WP321 · Manufacturer, stockist & exporter, India
Also sold as AISI 321 · UNS S32100 · W.Nr 1.4541 · Titanium-stabilised stainless
SS 321 pipe fittings are made to ASTM A403 WP321 for buttweld fittings and ASTM A182 F321 for forged socket-weld and threaded fittings, with dimensions to ASME B16.9 and B16.11. It is a titanium-stabilised austenitic stainless steel, chosen for high-temperature service between 425 and 815 °C. Kanak Steel & Engineering Co. supplies it with EN 10204 3.1 mill certificates from Mumbai to buyers across India, the Gulf, South-East Asia, South America, Europe, the UK and the USA.
- Stock & mill supply
- EN 10204 3.1 / 3.2
- PMI on every heat
- Export packing
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is SS 321 Pipe Fittings?
SS 321 pipe fittings is a titanium-stabilised austenitic stainless steel supplied as pipe fittings to ASTM A403 WP321 (UNS S32100). Buyers specify it for high-temperature service between 425 and 815 °C. It is also sold as AISI 321, UNS S32100, W.Nr 1.4541.
- What it is
- Titanium-stabilised austenitic stainless steel
- Buttweld
- ASTM A403 WP321
- Forged
- ASTM A182 F321
- Dimensions
- ASME B16.9 · B16.11 · MSS SP-43
- Sizes
- Buttweld ½" – 48" · forged ⅛" – 4"
- Best at
- High-temperature service between 425 and 815 °C
SS 321 Pipe Fittings Specification & Sizes
| Buttweld fittings | ASTM A403 WP321 — dimensions to ASME B16.9, MSS SP-43 |
|---|---|
| Forged fittings | ASTM A182 F321 — dimensions to ASME B16.11 |
| MSS SP-43 light-wall fittings | ASTM A403 CR321 — the A403 CR grade for MSS SP-43 dimensions (no class suffix) |
| Short-radius elbows | ASME B16.9 (formerly B16.28) |
| Buttweld sizes | NPS ½" to 48", schedule to match the pipe |
| Forged classes | Socket weld 3000 / 6000 / 9000 · threaded 2000 / 3000 / 6000 |
| Types | Elbow · Tee · Reducer · Cap · Stub end · Cross · Bend · Lateral · Coupling · Union · Nipple · Plug |
| Testing | PMI · dimensional · radiography of welded fittings · IGC on request |
| Documents | EN 10204 3.1 · 3.2 with third-party inspection |
Standards on this page
Choosing SS 321 Fittings: Elbow Radius, Schedule & Class
ASTM A403 fittings come in classes: S seamless, W welded (welds made by the fitting maker radiographed), WX all welds radiographed, WU all welds ultrasonically tested. Write the class after the grade, e.g. WP321-S.
Radius (LR, SR, 3D), the schedule-to-class map and the 1.5 mm socket-weld gap are explained in the fittings guide. For 321, buttweld fittings are ASTM A403 WP321 and forged fittings ASTM A182 F321.
SS 321 Pipe Fittings Chemical Composition
| Element | Weight % |
|---|---|
| Chromium | 17.0 – 19.0 |
| Nickel | 9.0 – 12.0 |
| Titanium | 5 × (C + N) min, 0.70 max |
| Carbon | 0.08 max |
| Manganese | 2.00 max |
| Silicon | 0.75 max |
| Nitrogen | 0.10 max |
| Phosphorus | 0.045 max |
| Sulphur | 0.030 max |
| Iron | Balance |
SS 321 Pipe Fittings Mechanical Properties
| Annealed plate & sheet | Value |
|---|---|
| Tensile strength | 515 MPa · 75 ksi |
| Yield strength 0.2% | 205 MPa · 30 ksi |
| Elongation | 40% |
| Hardness | 217 HB max |
Density & Physical Properties
| Property | Value |
|---|---|
| Density | 7.92 g/cm³ |
| Melting range | 1400 – 1425 °C |
| Magnetic | Non-magnetic annealed |
| PREN (approx.) | ≈ 18 |
SS 321 Equivalent Grades
Values follow ASTM A240 for UNS S32100. Always check against the edition named on your purchase order.
SS 321 buttweld fitting dimensions — ASME B16.9
Centre-to-end and end-to-end dimensions are the same for every alloy; the wall thickness follows the pipe schedule. Values in mm.
| NPS | OD | 90° LR elbow A | 45° elbow B | Tee C | Reducer H | Cap E |
|---|---|---|---|---|---|---|
| ½" | 21.3 | 38 | 16 | 25 | — | 25 |
| 1" | 33.4 | 38 | 22 | 38 | 51 | 38 |
| 1½" | 48.3 | 57 | 29 | 57 | 64 | 38 |
| 2" | 60.3 | 76 | 35 | 64 | 76 | 38 |
| 3" | 88.9 | 114 | 51 | 86 | 89 | 51 |
| 4" | 114.3 | 152 | 64 | 105 | 102 | 64 |
| 6" | 168.3 | 229 | 95 | 143 | 140 | 89 |
| 8" | 219.1 | 305 | 127 | 178 | 152 | 102 |
| 10" | 273.1 | 381 | 159 | 216 | 178 | 127 |
| 12" | 323.9 | 457 | 190 | 254 | 203 | 152 |
Full chart to 24": ASME B16.9 fitting dimensions.
Six-digit Harmonized System heading (iron and steel, chapter 72–73). Your country adds its own digits — confirm with your customs broker. All HS codes.
How to Verify SS 321 Pipe Fittings with PMI
Positive material identification with a handheld XRF gun confirms the alloy on the piece itself, in seconds, before it is cut or welded. SS 321 is most often mixed up with SS 347 — the table shows which elements tell them apart.
Handheld XRF does not measure carbon or nitrogen; those come from the mill certificate or optical emission (OES) testing. We PMI-test nickel alloys as standard and any grade on request.
| Element | SS 321 | SS 347 |
|---|---|---|
| Nickel | 9.0 – 12.0 | 9.0 – 13.0 |
| Chromium | 17.0 – 19.0 | 17.0 – 19.0 |
| Titanium | 5 × (C + N) min, 0.70 max | residual |
| Niobium | residual | 10 × C min, 1.00 max |
| Iron | Balance | Balance |
| Manganese | 2.00 max | 2.00 max |
SS 321 Pipe Fittings Price — What Decides It
Two quotes for "321 pipe fittings" can differ by 20% and both be fair. We quote 321 pipe fittings per kg for full sizes and per piece for cut sizes. These six things move the price per kg, so you can compare offers like for like.
SS 321 pipe fittings by type
SS 321 Pipe Fittings Applications
SS 321 is specified when the cheaper grade will not survive the service but a higher alloy would be more than the job needs. These are the jobs our buyers use it for.
SS 321 Pipe Fittings vs 304, 347 and 310S
| Grade | Pipe Fittings standard | PREN (approx.) | Pick it when |
|---|---|---|---|
| SS 304 | ASTM A403 WP304 | ≈ 18 | General corrosion resistance, food, water and architectural work |
| SS 347 | ASTM A403 WP347 | ≈ 18 | Welded high-temperature piping in refineries and power plants |
| SS 321 | ASTM A403 WP321 | ≈ 18 | High-temperature service between 425 and 815 °C |
| SS 310 / 310S | ASTM A403 WP310S | ≈ 25 | Furnaces, burners and heat treatment at high temperature |
PREN = Cr + 3.3 Mo + 16 N, from mid-range chemistry. A screening guide, not a substitute for corrosion data on your medium.
SS 321 Corrosion Resistance — Element by Element
Each alloying addition has a job. Knowing which one protects against your medium is the quickest way to judge whether 321 fits.
About 18% chromium forms the passive film that makes the steel stainless.
Nickel keeps the structure austenitic — tough at low temperature and easy to form and weld.
Titanium ties up carbon, so 321 keeps its corrosion resistance after long service in the sensitising range.
321H with higher carbon is used above about 540 °C for better creep strength.
How your 321 pipe fittings order runs
- 01Enquiry review — we confirm size, standard edition and documents against your MR or drawing.
- 02Heat selection & PMI — the mill certificate is checked and material is PMI-tested before processing.
- 03Processing — cutting, machining or bevelling to your specification, with heat numbers marked.
- 04Inspection — your third-party inspector witnesses, or we share photos and test reports.
- 05Packing & dispatch — seaworthy packing from Nhava Sheva (JNPT), Mumbai, FOB or CIF, documents sent before the vessel sails.
Standards on this page
Welding & Fabricating SS 321 Pipe Fittings
SS 321 welds by all common arc processes. A few points our buyers ask about:
| Matching filler | ER347 (AWS A5.9) |
|---|---|
| Over-alloyed filler | ER321 is rare; ER347 is the usual filler |
| Preheat | Not required; keep interpass temperature low |
| Cutting | Thermal or abrasive cutting; grind off heat-tinted edges before welding |
Follow your approved WPS; this is general guidance. See also 321 fittings and 321 flanges for the matching pipe-system parts.
How to Order SS 321 Pipe Fittings: RFQ Checklist
Get an accurate quote the first time. Copy this list into your enquiry:
- Fitting type, size and schedule / class
- Buttweld, socket weld or threaded
- Seamless or welded (buttweld fittings)
- Material standard and grade marking
- Certificate type and extra tests
- Delivery port, Incoterm and required date
SS 321 pipe fittings for export
FOB / CIF · Nhava Sheva (JNPT), MumbaiSS 321 pipe fittings — questions buyers ask
Is SS 321 the same as AISI 321?
Yes. AISI 321, UNS S32100, W.Nr 1.4541 all refer to the same material, and pipe fittings is ordered to ASTM A403 WP321 whichever name is on the enquiry.
Which standard covers SS 321 buttweld fittings?
ASTM A403 WP321 is the material specification; dimensions follow ASME B16.9 (light-wall MSS SP-43 fittings are ordered as CR321). Forged socket-weld and threaded fittings are made from ASTM A182 F321 material to ASME B16.11.
What is the difference between SS 321 WP-S and WP-W fittings?
S is seamless; W is welded from plate or welded pipe with the maker's welds radiographed. WX means all welds radiographed and WU all welds ultrasonically tested. Seamless costs more and is preferred for critical service.
Can SS 321 fittings be welded to carbon steel?
Yes — ER309L (or E309L electrode) is the usual filler when joining it to carbon steel.
SS 321 or SS 310 / 310S — which should I choose?
SS 321 is chosen for high-temperature service between 425 and 815 °C. SS 310 / 310S is the step up when you need more pitting resistance or strength. See the comparison table on this page, or ask us with your process conditions.
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026