Tesco Steel & Engineering manufactures SS 321 & 321H flanges — titanium-stabilised austenitic stainless (ASTM A182 F321 / F321H, UNS S32100 / S32109, EN 1.4541 / 1.4878). A controlled titanium addition (min 5× carbon) locks up carbon as stable titanium carbide, so the grade is immune to weld sensitisation through the critical 425–870 °C range — the right choice for heat exchangers, expansion joints, exhaust manifolds and refinery/boiler piping where post-weld annealing is impractical. Oxidation-resistant to 900 °C; 321H adds creep strength above 550 °C. Available in weld neck, slip-on, blind, socket-weld, threaded, lap-joint, orifice and long weld neck types to ASME B16.5 / B16.47. Class 150 to 2500, NPS 1/2″ to 56″. ISO 9001:2015 certified. Made in India.
SS 321 / 321H (ASTM A182 F321) Flanges
SS 321H Weld Neck & Blind Flanges
Tesco Steel & Engineering manufactures SS 321 / 321H flanges per ASTM A182 F321 / F321H and ASME B16.5, in all flange types from weld neck to blind, Class 150 to 2500 — supplied with EN 10204 3.1 / 3.2 certification, PMI and third-party inspection on request. Explore the wider stainless steel flange range, SS 347 flanges, SS 310S flanges, and the flange dimension charts.
| 321 / 321H SS Flange Specifications at a Glance | |
|---|---|
| Material Standard | ASTM A182 Grade F321 / F321H |
| UNS Numbers | S32100 (321) · S32109 (321H) |
| Stabilising Element | Titanium (Ti): min 5 × (C+N), max 0.70% |
| Size Range | 1/2″ NB to 56″ NB (DN 15 to DN 1400) |
| ANSI Pressure Classes | 150#, 300#, 600#, 900#, 1500#, 2500# |
| DIN Pressure Ratings | PN 6, 10, 16, 25, 40, 64, 100, 160, 250, 320, 400 |
| Bore Schedule | STD, XS, XXS, SCH 10, 20, 40, 60, 80, 120, 160 |
| Flange Types | Weld Neck (WNRF), Slip-On (SORF), Blind (BFF), Socket Weld (SWRF), Lap Joint (LJRF), Threaded (TRFF), Long Weld Neck (LWN), Orifice |
| Flange Faces | Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ) |
| Max Continuous Service Temp (321) | 900 °C (oxidising atmosphere) |
| Max Continuous Service Temp (321H) | 900 °C with superior creep resistance above 550 °C |
| Sensitisation-Free Range | 425 °C – 870 °C (key advantage over 304/316) |
All 321 and 321H flanges are machined to published dimensional tolerances — bore, bolt circle, number of holes, flange thickness and raised-face height conform to ASME B16.5 (1/2″–24″ NB) and ASME B16.47 Series A & B (26″ NB and above).
| Reference | Dimension Chart |
|---|---|
| 321 Stainless Steel Flange Dimensions (ASME B16.5 / B16.47) | View Flange Dimensions → |
| Flange Weight Chart | View Flange Weights → |
| RTJ Gasket Size Chart | View RTJ Size Chart → |
The defining feature of Grade 321 is titanium at a minimum of 5× the sum of carbon and nitrogen. Titanium has a stronger affinity for carbon than chromium, so it preferentially forms TiC precipitates rather than letting carbon combine with chromium as Cr₂₃C₆. This keeps chromium uniformly distributed, preventing the chromium-depleted grain-boundary zones that cause intergranular corrosion in unstabilised grades. 321H raises carbon to 0.04% min for enhanced creep rupture strength above 550 °C.
| Element | 321 (S32100) | 321H (S32109) |
|---|---|---|
| Carbon (C) | 0.08% max | 0.04 – 0.10% |
| Chromium (Cr) | 17.00 – 19.00% | 17.00 – 19.00% |
| Nickel (Ni) | 9.00 – 12.00% | 9.00 – 12.00% |
| Titanium (Ti) — stabiliser | 5×(C+N) min, 0.70% max | 5×(C+N) min, 0.70% max |
| Manganese (Mn) | 2.00% max | 2.00% max |
| Silicon (Si) | 1.00% max | 1.00% max |
| Phosphorus (P) | 0.045% max | 0.045% max |
| Sulfur (S) | 0.030% max | 0.030% max |
| Nitrogen (N) | 0.10% max | 0.10% max |
| Mechanical Property | 321 (F321) | 321H (F321H) |
|---|---|---|
| Tensile Strength (min) | 515 MPa (75 ksi) | 515 MPa (75 ksi) |
| Yield Strength 0.2% offset (min) | 205 MPa (30 ksi) | 205 MPa (30 ksi) |
| Elongation in 2″ (min) | 35% | 35% |
| Hardness (max) | 217 HBW / 95 HRB | 217 HBW / 95 HRB |
| Density | 7.90 g/cm³ | 7.90 g/cm³ |
| International Equivalent Grades | |
|---|---|
| UNS (USA) | S32100 (321) / S32109 (321H) |
| EN / DIN (Europe) | 1.4541 / X6CrNiTi18-10 (321) · 1.4878 / X12CrNiTi18-9 (321H) |
| JIS (Japan) | SUS 321 / SUS 321H |
| BS (UK) | 321S31 (321) / 321S51 (321H) |
| GOST (Russia) | 08Kh18N10T |
| IS (India) | FG 321 (IS 6911) |
321 Weld Neck Flange (WNRF)
321 Slip-On Flange (SORF)
321H Blind Flange (BFF)
| Flange Type | Description & 321-Specific Use |
|---|---|
| Weld Neck (WNRF) | Standard for high-temperature 321 piping welded into continuous sensitisation-range service; tapered hub transfers stress while the HAZ stays free of intergranular attack. Class 150–2500, F321 & F321H. |
| Slip-On (SORF) | Moderate-pressure elevated-temperature systems — heat-exchanger nozzles, secondary boiler piping, petrochemical expansion connections. Two fillet welds, no sensitisation. |
| Blind (BFF) | Seals high-temperature vessel and pipeline terminations operating continuously between 425–870 °C — exchanger bonnets, autoclave nozzles, furnace atmosphere piping. |
| Socket Weld (SWRF) | Small-bore (1/2″–2″) instrument and sample connections in hot process streams; titanium stabilisation keeps the single fillet weld corrosion-resistant. |
| Lap Joint (LJRF) | Used with a 321 stub end where high-temperature systems need frequent dismantling — exchanger manifolds, reactor inlet piping for tube/catalyst access. |
| Threaded (TRFF) | Instrument taps, gauge connections and utility branches in moderate-temperature 321 piping (to ~260 °C); above that use weld neck / socket weld. |
| Long Weld Neck (LWN) | Extended nozzle flanges in 321H for high-temperature vessels, columns and reactors in the creep range (>550 °C). |
| Orifice | Paired flanges for flow metering in hot process lines; titanium stabilisation keeps tap bores and seat free of intergranular corrosion. |
| Property | 321 (S32100) | 321H (S32109) | 304 (S30400) | 316L (S31603) | 347 (S34700) |
|---|---|---|---|---|---|
| Stabiliser | Ti | Ti | None | None | Nb+Ta |
| Sensitisation Immunity | Yes | Yes | No | Partial (low C) | Yes |
| Max Continuous Temp | 900 °C | 900 °C | 870 °C | 870 °C | 900 °C |
| Creep Resistance >550 °C | Moderate | Superior | Moderate | Moderate | Good |
| Chloride Resistance | Moderate | Moderate | Moderate | Good (Mo) | Moderate |
| Weld HAZ Corrosion Resistance | Excellent | Excellent | Poor if sensitised | Good (low C) | Excellent |
| Tensile Strength (min) | 515 MPa | 515 MPa | 515 MPa | 485 MPa | 515 MPa |
| ASTM Flange Grade | A182 F321 | A182 F321H | A182 F304 | A182 F316L | A182 F347 |
| Best For | Sensitisation range, exchangers | High-temp creep, boilers | General service | Marine, chemical | Nuclear, high-temp corrosion |
321 and 347 offer similar sensitisation immunity. 347 (niobium-stabilised) is preferred in nuclear service due to lower neutron activation; 321H is the better choice when long-term creep strength above 550 °C is the primary constraint.
| Industry | Specific Application |
|---|---|
| Heat Exchangers & Boilers | Shell-side nozzle flanges, tube-sheet connections, expansion-joint end flanges, steam-drum nozzles |
| Oil Refining & Petrochemical | Crude heater piping, atmospheric & vacuum distillation nozzles, reformer piping flanges |
| Power Generation | Superheater & reheater piping flanges, turbine inlet connections, header nozzles (321H) |
| Aerospace & Defence | Jet-engine exhaust manifold flanges, APU connections, high-temp test-rig piping |
| Chemical Processing | Sulphuric acid converter piping, nitric acid absorber connections, high-temp reactor nozzles |
| Pharmaceutical | Autoclave and steriliser nozzle flanges, high-temperature CIP circuit connections |
| Food & Beverage | High-temperature sterilisation retort flanges, UHT processing line connections |
| Nuclear | Intermediate heat-exchanger nozzle flanges (where 347 not required for neutron considerations) |
| Pulp & Paper | Digester nozzle flanges, black-liquor evaporator connections, high-temperature bleach piping |
| Standard | Scope |
|---|---|
| ASTM A182 / ASME SA182 | Forged stainless flanges — Grade F321 and F321H |
| ASME B16.5 | Pipe flanges & flanged fittings — 1/2″ to 24″ NB, Class 150 to 2500 |
| ASME B16.47 | Large-diameter flanges — 26″ to 60″ NB (Series A: MSS SP-44, Series B: API 605) |
| ASME B16.36 | Orifice flanges — Class 300 to 2500 |
| EN 1092-1 | European flanges — PN 6 to PN 400, material 1.4541 (321) / 1.4878 (321H) |
| DIN 2631 – 2638 | German DIN flanges — PN 6 to PN 160 |
| JIS B2220 | Japanese flanges — 5K to 63K, material SUS 321 / SUS 321H |
| BS 3605 / BS 4504 | British Standard stainless flanges and piping |
| GOST 12820 / 12821 | Russian standard flanges |
| ASME Section VIII / B31.3 | F321H commonly specified for elevated-temperature pressure vessels & process piping |
Immune to intergranular corrosion through 425–870 °C — welded assemblies need no post-weld solution anneal.
Controlled 0.04% C minimum gives superior creep rupture strength above 550 °C for boilers and reformers.
WNRF, SORF, blind, socket-weld, threaded, lap-joint, LWN and orifice — in RF, FF and RTJ faces.
EN 10204 3.1 / 3.2 MTC, PMI, ASME Section II Part D allowables for F321H, and TPI on request.
321 flange prices depend on size, pressure class, schedule, flange type, grade (321 or 321H), quantity and current nickel/titanium rates. Grade 321 carries a modest premium over 304/316L for the titanium addition; 321H commands a further premium for the tighter carbon spec and qualification testing. Tesco Steel & Engineering offers competitive ex-works pricing from Mumbai with full export documentation and material traceability from melt to finished product. Click Ask for Quote or message us on WhatsApp at +91 92233 66922 with grade, flange type, size (NB), pressure class, quantity and documentation requirements.
Q1. What is a 321 stainless steel flange?
A 321 stainless steel flange is a pipe flange made from Grade 321 (UNS S32100), a titanium-stabilised austenitic stainless steel. The titanium addition (minimum 5× carbon) prevents sensitisation — intergranular chromium carbide precipitation — when the material is exposed to or held at 425–870 °C. Flanges are forged to ASTM A182 F321 and machined to ASME B16.5 or B16.47, used in heat exchangers, exhaust piping, boiler connections and process piping operating continuously in the sensitisation range.
Q2. What is the difference between 321 and 321H stainless steel flanges?
Both grades have the same chromium (17–19%), nickel (9–12%) and titanium stabilisation. The difference is carbon: 321 allows up to 0.08% with no minimum, while 321H requires 0.04–0.10%. The controlled minimum in 321H ensures adequate carbide precipitation for superior creep rupture strength above 550 °C. Below 550 °C standard 321 is sufficient; for superheaters, reformers and long-term elevated-temperature vessel nozzles, 321H is specified.
Q3. What is sensitisation, and why does 321 prevent it?
Sensitisation is the precipitation of chromium carbide (Cr₂₃C₆) at grain boundaries when standard austenitic stainless (304, 316) is heated or slowly cooled through 425–870 °C, leaving chromium-depleted zones vulnerable to intergranular corrosion. In Grade 321, titanium has a stronger affinity for carbon than chromium and preferentially forms stable titanium carbide (TiC), so chromium stays uniformly distributed and no depletion occurs — giving sensitisation immunity without post-weld solution annealing.
Q4. What is the difference between 321 and 347 stainless steel flanges?
Both use a stabilising element — 321 uses titanium, 347 uses niobium (plus tantalum). Corrosion and high-temperature properties are broadly similar. Key differences: 347 is preferred in nuclear service (niobium has lower neutron activation than titanium) and has slightly better resistance to polythionic acid SCC in sulphur-rich refinery shutdowns. For most non-nuclear applications 321 and 347 are interchangeable, chosen by availability and project spec.
Q5. What is the maximum temperature for 321 stainless steel flanges?
Grade 321 can be used in continuous service up to 900 °C in oxidising atmospheres; 321H extends creep rupture life above 550 °C. For service above 900 °C, specify Grade 310S. For allowable pressure at elevated temperature, consult ASME B16.5 Table 2-1.1 for the F321 pressure-temperature ratings in each class.
Q6. Can 321 flanges be used without post-weld heat treatment?
Yes — this is the primary reason for specifying 321 over 304. Titanium stabilisation prevents sensitisation in the weld HAZ, so 321 flanges and assemblies do not require post-weld solution annealing to restore corrosion resistance. This is a major cost and schedule advantage in large fabricated assemblies — exchangers, vessels and long pipe runs — that would be impractical to anneal after welding.
Q7. What filler metal should be used to weld 321 flanges?
ER347 (AWS A5.9) wire and E347-15/16 (AWS A5.4) electrodes are standard for welding Grade 321. Niobium in ER347 provides weld-metal stabilisation equivalent to the titanium in the base metal. ER321 is available but titanium oxidises during arc welding, making it less reliable. Never use unstabilised 304 or 308 fillers on 321 in elevated-temperature service.
Q8. What is the equivalent grade of SS 321 in EN/DIN and JIS standards?
SS 321 (UNS S32100) equals EN/DIN 1.4541 (X6CrNiTi18-10) and JIS SUS321; SS 321H (UNS S32109) equals EN/DIN 1.4878 (X12CrNiTi18-9) and JIS SUS321H. The Russian equivalent is GOST 08Kh18N10T and the Indian equivalent is FG 321 (IS 6911).
Q9. What certifications are available with 321 flanges from Tesco Steel?
Standard supply includes EN 10204 Type 3.1 mill test certificates confirming chemistry, mechanical properties, heat number and heat treatment. On request: Type 3.2 (third-party witnessed), PMI reports, hydrostatic test certificates, UT/RT reports, ASME Section II Part D compliance for F321H elevated-temperature allowables, and NACE MR0175 declarations. TPI by Lloyd's, Bureau Veritas, TÜV or SGS can be arranged.
Q10. Who manufactures 321 stainless steel flanges in India?
Tesco Steel & Engineering, based in Mumbai, India, is an ISO-certified manufacturer and exporter of 321 and 321H stainless steel flanges to ASTM A182, ASME B16.5, B16.47, EN 1092-1, DIN, JIS B2220 and GOST standards, supplying EPC contractors, refineries, power-plant builders and process-plant operators across 96 countries.