SS 321 FlangesASTM A182 F321 · Manufacturer, stockist & exporter, India
Also sold as AISI 321 · UNS S32100 · W.Nr 1.4541 · Titanium-stabilised stainless
SS 321 flanges are forged to ASTM A182 F321 and machined to ASME B16.5 (½"–24", Class 150–2500) or ASME B16.47 for larger sizes. 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 Flanges?
SS 321 flanges is a titanium-stabilised austenitic stainless steel supplied as flanges to ASTM A182 F321 (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
- Material
- ASTM A182 F321
- Dimensions
- ASME B16.5 · B16.47 · EN 1092-1
- Classes
- 150 · 300 · 600 · 900 · 1500 · 2500
- Facing
- RF · FF · RTJ
- Best at
- High-temperature service between 425 and 815 °C
SS 321 Flanges Specification & Sizes
| Material standard | ASTM A182 F321 |
|---|---|
| Dimensional standards | ASME B16.5 (½"–24") · B16.47 Series A / B (26"–60") · B16.36 orifice · B16.48 line blanks · EN 1092-1 |
| Pressure classes | Class 150, 300, 400, 600, 900, 1500, 2500 · PN 6 – PN 100 |
| Facing | Raised face (RF) · flat face (FF) · ring type joint (RTJ) · tongue & groove |
| Bore | To match the pipe schedule — specify it on the order |
| Types | Weld neck flange · Slip-on flange · Blind flange · Socket weld flange · Threaded flange · Lap joint flange · Long weld neck flange · Orifice flange · Spectacle blind · Reducing flange · Ring type joint flange · Expander flange · Anchor flange · Swivel ring flange |
| Testing | PMI · dimensional · UT of forgings · IGC on request |
| Documents | EN 10204 3.1 · 3.2 with third-party inspection |
Standards on this page
SS 321 Flange Pressure–Temperature Rating
The class is not a pressure: the allowable pressure for 321 flanges comes from the ASME B16.5 table for its material group, and falls as temperature rises (how ratings work). ASTM A182 F321 is in material group 2.4.
Take the actual pressures from the B16.5 rating table for group 2.4; your piping class sheet governs.
Bolting & Gaskets for 321 Flanges
For SS 321 flanges the usual bolting is ASTM A193 B8T studs with A194 8T nuts — see SS 321 fasteners. Spiral-wound gaskets with a 304 or 316 winding suit most stainless raised-face joints. Facing and gasket options are compared in the flange guide.
SS 321 Flanges 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 Flanges 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 flange dimensions — ASME B16.5 Class 150 & 300
Outside dimensions depend only on size and class, not on the alloy, so 321 flanges bolt to any B16.5 flange of the same size and class. Values in mm; thickness excludes the 1.6 mm raised face.
| NPS | Cl 150 OD | Cl 150 thickness | Cl 150 bolt circle | Cl 150 bolts | Cl 300 OD | Cl 300 thickness | Cl 300 bolt circle | Cl 300 bolts |
|---|---|---|---|---|---|---|---|---|
| ½" | 90 | 9.6 | 60.3 | 4 × ½" | 95 | 12.7 | 66.7 | 4 × ½" |
| 1" | 110 | 12.7 | 79.4 | 4 × ½" | 125 | 15.9 | 88.9 | 4 × ⅝" |
| 1½" | 125 | 15.9 | 98.4 | 4 × ½" | 155 | 19.1 | 114.3 | 4 × ¾" |
| 2" | 150 | 17.5 | 120.7 | 4 × ⅝" | 165 | 20.7 | 127.0 | 8 × ⅝" |
| 3" | 190 | 22.3 | 152.4 | 4 × ⅝" | 210 | 27.0 | 168.3 | 8 × ¾" |
| 4" | 230 | 22.3 | 190.5 | 8 × ⅝" | 255 | 30.2 | 200.0 | 8 × ¾" |
| 6" | 280 | 23.9 | 241.3 | 8 × ¾" | 320 | 35.0 | 269.9 | 12 × ¾" |
| 8" | 345 | 27.0 | 298.5 | 8 × ¾" | 380 | 39.7 | 330.2 | 12 × ⅞" |
| 10" | 405 | 28.6 | 362.0 | 12 × ⅞" | 445 | 46.1 | 387.4 | 16 × 1" |
| 12" | 485 | 30.2 | 431.8 | 12 × ⅞" | 520 | 49.3 | 450.8 | 16 × 1⅛" |
Full chart: ASME B16.5 flange 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 Flanges 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 Flanges Price — What Decides It
Two quotes for "321 flanges" can differ by 20% and both be fair. We quote 321 flanges 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 flanges by type
SS 321 Flanges 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 Flanges vs 304, 347 and 310S
| Grade | Flanges standard | PREN (approx.) | Pick it when |
|---|---|---|---|
| SS 304 | ASTM A182 F304 | ≈ 18 | General corrosion resistance, food, water and architectural work |
| SS 347 | ASTM A182 F347 | ≈ 18 | Welded high-temperature piping in refineries and power plants |
| SS 321 | ASTM A182 F321 | ≈ 18 | High-temperature service between 425 and 815 °C |
| SS 310 / 310S | ASTM A182 F310 | ≈ 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 flanges 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 Flanges
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 Flanges: RFQ Checklist
Get an accurate quote the first time. Copy this list into your enquiry:
- Flange type and dimensional standard (B16.5 / B16.47 / EN 1092-1)
- Size, pressure class and facing
- Bore / schedule for weld neck and socket weld flanges
- Material standard and grade marking
- Certificate type and extra tests
- Delivery port, Incoterm and required date
SS 321 flanges for export
FOB / CIF · Nhava Sheva (JNPT), MumbaiSS 321 flanges — 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 flanges is ordered to ASTM A182 F321 whichever name is on the enquiry.
Which standard covers SS 321 flanges?
ASTM A182 F321 is the material specification for the forging; dimensions follow ASME B16.5 for ½"–24" and ASME B16.47 for 26" and above. European projects use EN 1092-1.
What pressure can a SS 321 Class 300 flange take?
It depends on temperature. ASTM A182 F321 is in ASME B16.5 material group 2.4; read the Class 300 column of that group's table at your design temperature.
Which bolts should I use with SS 321 flanges?
Usually ASTM A193 B8T studs with A194 8T nuts. In corrosive or sour service the bolting material is set by the project specification.
Can a SS 321 flange be welded to a different pipe material?
Yes — ER309L (or E309L electrode) is the usual filler when joining it to carbon steel. Weld neck bores must match the mating pipe schedule.
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