Grade 321 (UNS S32100) is a titanium-stabilised austenitic stainless steel developed specifically to solve the problem of sensitisation — the intergranular chromium carbide precipitation that occurs when standard grades like 304 are held or cooled through the temperature range of 425–870 °C. In Grade 321, a controlled addition of titanium (minimum 5 × carbon content) preferentially combines with carbon to form stable titanium carbide, leaving the chromium in solution and preserving full corrosion resistance in the heat-affected zone and in components operating continuously within the sensitisation temperature band. This makes 321 the correct material choice for heat exchangers, expansion joints, aircraft exhaust manifolds, furnace components, and refinery piping systems that operate at moderate-to-high temperatures where post-weld heat treatment is impractical or impossible.
Tesco Steel & Engineering manufactures 321 and 321H Stainless Steel Flanges across all standard types — Weld Neck (WNRF), Slip-On (SORF), Blind (BFF), Socket Weld (SWRF), Lap Joint (LJRF), Threaded (TRFF), Long Weld Neck (LWN), and Orifice — in sizes from ½" NB to 56" NB and pressure classes from 150# through 2500# (PN 6 to PN 400). All flanges are produced to ASTM A182 Grade F321 or F321H and machined to ASME B16.5, ASME B16.47, EN 1092-1, DIN, and JIS B2220 dimensional standards. Our ISO-certified facility supports EN 10204 3.1 / 3.2 material certification, PMI testing, and third-party inspection by any nominated agency. We hold ready stock of standard 321 flanges and export to customers across 96 countries on 6 continents.
| 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 | ½" NB to 56" NB (DN 15 to DN 1400) |
| ANSI Pressure Classes | 150#, 300#, 600#, 900#, 1500#, 2500# |
| DIN Pressure Ratings | PN 6, PN 10, PN 16, PN 25, PN 40, PN 64, PN 100, PN 160, PN 250, PN 320, PN 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 diameters, bolt circle, number of holes, flange thickness, and raised face height conform to ASME B16.5 (½" to 24" NB) and ASME B16.47 Series A & B (26" NB and above).
| View Full 321 Stainless Steel Flange Dimension Tables → |
The defining feature of Grade 321 is the addition of titanium at a minimum of 5 times the sum of carbon and nitrogen content. Titanium has a stronger affinity for carbon than chromium does, so it preferentially forms TiC precipitates at high temperatures rather than allowing carbon to combine with chromium as Cr₂₃C₆ carbides. This keeps chromium uniformly distributed in the matrix, preventing the chromium-depleted grain boundary zones that cause intergranular corrosion in unstabilised grades. Grade 321H increases the carbon minimum to 0.04% to ensure adequate carbide precipitation for enhanced creep rupture strength at elevated temperatures 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 / 321H SS Weld Neck Flange (WNRF) — The weld neck is the standard choice for high-temperature 321 piping that will be welded and placed into continuous service in the sensitisation temperature range. The long tapered hub transfers pipe-end stress away from the flange face, while the 321 base metal ensures the weld HAZ remains free of intergranular attack even during slow cool-down through 425–870 °C. Specified to ASME B16.5 Class 150 through 2500 in both F321 and F321H.
321 / 321H SS Slip-On Flange (SORF) — Used in moderate-pressure, elevated-temperature 321 systems where installation flexibility is needed. Common in heat exchanger inlet/outlet nozzles, secondary boiler piping, and petrochemical plant expansion connections operating in the sensitisation range. Two fillet welds in 321 ensure no sensitisation of the connection zone.
321 / 321H SS Blind Flange (BFF) — Blind flanges in Grade 321 seal high-temperature vessel and pipeline terminations where the piping system operates continuously between 425–870 °C. Used extensively on heat exchanger bonnets, autoclave nozzles, and furnace atmosphere piping where periodic inspection access is required.
321 / 321H SS Socket Weld Flange (SWRF) — Specified for small-bore instrument and sample connections (½" to 2" NB) in high-temperature process streams. The titanium stabilisation of Grade 321 ensures the single fillet weld remains corrosion-resistant even in lines carrying hot aggressive process fluids in the sensitisation temperature range.
321 / 321H SS Lap Joint Flange (LJRF) — Used with a 321 stub end in high-temperature systems requiring frequent disassembly — such as heat exchanger manifolds and reactor inlet piping that must be opened for inspection, tube bundle cleaning, or catalyst replacement at regular intervals. The stub end absorbs the weld heat; the backing ring rotates freely for bolt alignment.
321 / 321H SS Threaded Flange (TRFF) — Used for instrument taps, pressure gauge connections, and utility branches in moderate-temperature 321 piping. Suitable for service up to approximately 260 °C in threaded configurations; above that temperature, weld neck or socket weld flanges are preferred to eliminate thread relaxation risk.
321 / 321H SS Long Weld Neck Flange (LWN) — Extended nozzle flanges in 321H are specified on high-temperature pressure vessels, columns, and reactors operating in the creep temperature range (above 550 °C). The 321H grade's higher carbon content provides improved creep rupture strength at these temperatures compared to standard 321.
321 / 321H SS Orifice Flange — Paired orifice flanges in Grade 321 are used for flow metering in high-temperature process lines. The titanium stabilisation ensures the pressure tap bores and orifice seat remain free of intergranular corrosion over the service life of the metering installation.
Engineers evaluating 321 frequently compare it against 304, 316, and 347. The table below covers the properties most relevant to high-temperature and sensitisation-sensitive applications.
| Property | 321 (S32100) | 321H (S32109) | 304 (S30400) | 316L (S31603) | 347 (S34700) |
|---|---|---|---|---|---|
| Stabiliser | Ti (titanium) | Ti (titanium) | None | None | Nb+Ta (niobium) |
| 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, heat exchangers | High-temp creep, boilers | General service | Marine, chemical | Nuclear, high-temp corrosion |
Note: 321 and 347 offer similar sensitisation immunity. 347 (niobium-stabilised) is preferred in nuclear applications due to lower neutron activation of niobium vs. titanium. 321H is the better choice when long-term creep strength above 550 °C is the primary design constraint.
Tesco Steel & Engineering manufactures and supplies 321 / 321H flanges with Mill Test Certificates to EN 10204 Type 3.1 as standard, or Type 3.2 on request.
| Standard | Scope |
|---|---|
| ASTM A182 / ASME SA182 | Material standard for forged alloy and stainless steel flanges — Grade F321 and F321H |
| ASME B16.5 | Pipe flanges and flanged fittings — ½" 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 Standards stainless flanges and piping |
| GOST 12820 / 12821 | Russian standard flanges |
| MSS SP-44 | Steel pipeline flanges — large diameter |
| ASME Section VIII / B31.3 | F321H commonly specified for elevated-temperature pressure vessel and process piping |
Grade 321 is straightforward to weld by all standard arc processes. The titanium stabilisation means the base metal itself is immune to sensitisation, but the choice of filler metal and heat input still requires attention.
Filler Metal: The preferred filler for 321 is ER347 (AWS A5.9) wire or E347-15/16 electrodes — not ER321. Titanium does not transfer reliably across the arc in GTAW/SMAW processes due to its oxidation characteristics; niobium in ER347 provides equivalent weld metal stabilisation. For GTAW root passes on thin-wall 321 piping, ER321 can be used with high-purity argon back-purging if ER347 is not available. Never use 304 or 316 fillers on 321 base metal in elevated-temperature service — unstabilised weld metal would be susceptible to sensitisation.
Heat Input: Keep heat input moderate and interpass temperature below 175 °C. Excessive heat input increases the size of the heat-affected zone and risks titanium nitride and carbide coarsening, which can slightly reduce toughness without affecting sensitisation resistance.
Preheat: No preheat is required for standard 321 welding. A light warm-up to 30–60 °C in cold conditions to eliminate moisture is acceptable.
Post-Weld Heat Treatment (PWHT): PWHT is not required for Grade 321 in sensitisation-sensitive service — this is the entire purpose of the titanium stabilisation. If solution annealing is specified for other reasons (e.g., stress relief in pressure vessel manufacture), anneal at 1010–1120 °C and water quench. For 321H, a stabilising anneal at 900–925 °C for 2–4 hours following solution annealing is sometimes specified to ensure full titanium carbide precipitation and optimise creep properties for long-term service above 550 °C.
321H Considerations: When welding 321H for high-temperature creep service, ensure both base metal and filler metal meet the 321H carbon minimum of 0.04%. Verify heat-specific carbon content on the MTC before welding. Weld procedures for 321H at elevated temperature service should be qualified to ASME Section IX with appropriate creep rupture supplementary essential variables.
Grade 321 flanges are specified wherever piping operates continuously or intermittently in the 425–870 °C sensitisation range and welded construction makes post-weld solution annealing impractical.
| 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 unit nozzles, reformer piping flanges |
| Power Generation | Superheater and reheater piping flanges, steam turbine inlet connections, header nozzles (321H) |
| Aerospace & Defence | Jet engine exhaust manifold flanges, auxiliary power unit connections, high-temp test rig piping |
| Chemical Processing | Sulphuric acid production (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 (321 is used where 347 is not required for neutron considerations) |
| Pulp & Paper | Digester nozzle flanges, black liquor evaporator connections, high-temperature bleach plant piping |
Specify Grade 321 (F321) when: The piping system operates between 425–870 °C and the primary concern is preventing intergranular corrosion in welded connections. 321 is the standard choice for heat exchangers, expansion joints, and process piping in refineries and chemical plants where fabricated assemblies cannot be solution-annealed after welding.
Specify Grade 321H (F321H) when: The system operates above 550 °C for extended periods and long-term creep rupture strength is a design requirement. 321H's higher controlled carbon content (0.04–0.10%) ensures adequate carbide precipitation for creep resistance. It is the grade of choice for superheater headers, reformer tubes, and high-temperature pressure vessels designed to ASME Section VIII Division 1 or 2 with elevated temperature allowable stress requirements. Confirm with your pressure design code — ASME B31.3 Table A-1 and ASME Section II Part D list separate allowable stresses for 321 and 321H at each temperature.
Consider 347 over 321 when: The application is in a nuclear environment where neutron activation of titanium (from 321) must be avoided. Niobium (in 347) has much lower neutron activation products, making 347 the preferred stabilised grade for nuclear service.
Consider 310S over 321H when: Operating temperatures exceed 900 °C. Grade 321H loses its sensitisation advantage above its maximum service temperature, and Grade 310S (24–26% Cr, 19–22% Ni) is required for continuous service up to 1100 °C.
What is a 321 stainless steel flange?
A 321 stainless steel flange is a pipe fitting manufactured from Grade 321 (UNS S32100), a titanium-stabilised austenitic stainless steel. The titanium addition (minimum 5 × carbon content) prevents sensitisation — intergranular chromium carbide precipitation — when the material is exposed to or held at temperatures between 425–870 °C. Flanges are forged to ASTM A182 F321 and machined to ASME B16.5 or B16.47 dimensional standards. They are used in heat exchangers, exhaust piping, boiler connections, and process piping that operates continuously in the sensitisation temperature range.
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 content. Grade 321 allows up to 0.08% carbon with no defined minimum. Grade 321H requires carbon between 0.04% and 0.10% — the controlled minimum ensures adequate carbide precipitation for superior creep rupture strength above 550 °C. For flanges in heat exchangers and general high-temperature piping below 550 °C, standard 321 is sufficient. For power generation superheaters, reformers, and long-term elevated-temperature pressure vessel nozzles, 321H is specified.
What is sensitisation in stainless steel, and why does 321 prevent it?
Sensitisation is the precipitation of chromium carbide (Cr₂₃C₆) at grain boundaries when standard austenitic stainless steel (e.g., 304, 316) is heated or slowly cooled through 425–870 °C. The chromium migrates to the grain boundaries to form carbides, leaving a chromium-depleted zone adjacent to each boundary that is vulnerable to intergranular corrosion. In Grade 321, titanium has a stronger affinity for carbon than chromium does. Titanium preferentially combines with carbon to form titanium carbide (TiC), which is stable in the sensitisation temperature range. Chromium therefore remains uniformly distributed in the matrix, and no grain-boundary depletion occurs. This is the sole reason for using 321 over 304 — it provides sensitisation immunity without the need for post-weld solution annealing.
What is the difference between 321 and 347 stainless steel flanges?
Both grades use a stabilising element to prevent sensitisation — 321 uses titanium (Ti), while 347 uses niobium (Nb) plus tantalum (Ta). Their corrosion resistance and high-temperature properties are broadly similar. The key differences are: (1) 347 is preferred in nuclear applications because niobium has lower neutron activation than titanium; (2) 321 titanium may form a thin surface layer after high-temperature service but this is cosmetic, not structural; (3) 347 has slightly better resistance to polythionic acid stress corrosion cracking (SCC) — a failure mode in sulphur-rich refinery environments during shutdowns. For most non-nuclear applications, 321 and 347 are interchangeable, with selection driven by availability and project specification.
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. Grade 321H extends creep rupture life at temperatures above 550 °C due to its controlled carbon content. For service above 900 °C, Grade 310S (UNS S31008) should be specified instead. When determining the allowable pressure at elevated temperature for 321 flanges, consult ASME B16.5 Table 2-1.1, which lists specific pressure-temperature ratings for F321 in each pressure class.
Can 321 stainless steel flanges be used without post-weld heat treatment?
Yes — this is the primary reason for specifying 321 over 304. Because the titanium stabilisation prevents sensitisation in the weld heat-affected zone, Grade 321 flanges and piping assemblies do not require post-weld solution annealing to restore corrosion resistance. This is a significant cost and schedule advantage in large fabricated assemblies — heat exchangers, pressure vessels, and long pipe runs — that would be impractical to solution-anneal after welding.
What filler metal should be used to weld 321 flanges?
ER347 (AWS A5.9) wire and E347-15/16 (AWS A5.4) electrodes are the standard consumables for welding Grade 321 flanges. Niobium in ER347 provides weld metal stabilisation equivalent to the titanium in the 321 base metal. ER321 filler is available but titanium's tendency to oxidise during arc welding makes it less reliable as a stabiliser in the deposited weld metal. Never use unstabilised 304 or 308 fillers for 321 in elevated-temperature service, as the weld metal would be susceptible to sensitisation and intergranular corrosion.
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 records. On request: EN 10204 Type 3.2 (third-party witnessed), PMI (Positive Material Identification) reports, hydrostatic test certificates, ultrasonic (UT) or radiographic (RT) test reports, ASME Section II Part D compliance for F321H elevated-temperature allowables, and NACE MR0175 declarations. Third-party inspection by Lloyd's, Bureau Veritas, TÜV, SGS, or any nominated agency can be arranged.
What is the price of 321 stainless steel flanges in India?
The price of 321 stainless steel flanges depends on size (NB), pressure class, schedule, flange type, grade (321 or 321H), quantity, and current nickel and titanium raw material prices. Grade 321 typically carries a modest premium over 304 and 316L due to the titanium addition and more controlled manufacturing process. 321H commands a further premium for the tighter carbon specification and additional qualification testing. Tesco Steel & Engineering offers competitive ex-works pricing from Mumbai with full export documentation. Request a current price list and stock availability here.
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. The company supplies to EPC contractors, refineries, power plant builders, and process plant operators across 96 countries worldwide.
Tesco Steel & Engineering maintains ready stock of 321 Stainless Steel Flanges in the most commonly specified sizes, pressure classes, and types. Custom sizes, 321H grade, dual-certified material, and special schedule flanges are produced to order with full material traceability from melt to finished product.
To receive a current price list, ready stock confirmation, and lead time, submit an enquiry with the following: grade (321 or 321H), flange type, size (NB), pressure class or PN rating, quantity, delivery port, and any inspection or documentation requirements. Our technical sales team responds within 24 hours.
Global Export: Tesco Steel & Engineering exports 321 & 321H Stainless Steel Flanges to customers across the UAE, Saudi Arabia, USA, UK, Germany, Australia, Canada, Singapore, Malaysia, Oman, Qatar, Kuwait, Bahrain, South Africa, Nigeria, Kenya, Indonesia, Thailand, Vietnam, Brazil, and 76 other countries worldwide.