ASTM A182 F304 / F304L / F304H | UNS S30400 / S30403 / S30409 | EN 1.4301 / 1.4307 / 1.4948 | 18/8 Austenitic Stainless Steel
Stainless Steel 304 — universally known as "18/8 stainless" for its nominal composition of 18% chromium and 8% nickel — is the world's most widely produced and specified austenitic stainless steel grade. Classified as UNS S30400 and manufactured to ASTM A182 Grade F304 for forged flanges, Grade 304 owes its global dominance to a balanced combination of properties found in no other single grade: excellent corrosion resistance in a broad range of atmospheric, chemical, and food-contact environments; full austenitic microstructure providing outstanding toughness from cryogenic temperatures (–196°C) through to continuous service at 870°C; a naturally passive chromium-oxide surface film that is self-healing; non-magnetic response in the annealed condition; and excellent weldability using common TIG, MIG, and SMAW processes. The grade comes in three sub-variants — standard 304 (C max 0.08%), low-carbon 304L (C max 0.030%, UNS S30403, preferred for welded assemblies), and high-carbon 304H (C 0.04–0.10%, UNS S30409, for elevated-temperature creep service) — each fulfilling specific engineering roles that make the 304 family the most versatile stainless flange group in industrial piping.
Tesco Steel & Engineering manufactures 304 stainless steel flanges across the complete range of types — Weld Neck (WNRF/WNFF/WNRTJ), Slip-On (SORF/SOFF), Blind, Socket Weld, Threaded, Long Weld Neck, Lap Joint, Spectacle Blind, Plate, and Orifice flanges — in sizes NPS ½″ to 60″ and pressure classes ASME B16.5 Class 150 through 2500 and DIN/EN PN 10 through PN 400. Every flange is forged from ASTM A182 F304 / F304L / F304H material, solution-annealed after forging to restore the fully austenitic structure, and CNC-machined to ASME B16.5 and B16.47 dimensional tolerances. Supplied with EN 10204 3.1 mill test reports and dimensional inspection certificates as standard, our flanges are exported to EPC contractors, piping stockists, and end-users across 96 countries on six continents.
| Parameter | Details |
|---|---|
| Grade | SS 304 / SS 304L / SS 304H |
| UNS Number | S30400 (304) / S30403 (304L) / S30409 (304H) |
| Forged Flange Standard | ASTM A182 Grade F304 / F304L / F304H |
| Common Name | 18/8 Stainless Steel (18% Cr, 8% Ni nominal) |
| Flange Types | Weld Neck (WNRF/WNFF/WNRTJ), Slip-On (SORF/SOFF), Blind, Socket Weld, Threaded, Long Weld Neck, Lap Joint, Spectacle Blind, Plate, Orifice |
| Size Range | NPS ½″ to NPS 60″ (DN 15 to DN 1500) |
| Pressure Classes | ASME Class 150, 300, 600, 900, 1500, 2500 |
| DIN / EN Pressure Ratings | PN 10, PN 16, PN 25, PN 40, PN 64, PN 100, PN 160, PN 250, PN 320, PN 400 |
| Face Types | Raised Face (RF), Flat Face (FF), Ring Type Joint (RTJ) |
| Dimensional Standards | ASME B16.5 (NPS ½″–24″), ASME B16.47 Series A & B (NPS 26″–60″), DIN 2573–2638, EN 1092-1, JIS B2220 |
| Max Continuous Service Temp | 870°C (1600°F) — intermittent to 925°C. Use 304H above 550°C for creep resistance. |
| Cryogenic Service | Suitable to –196°C (LN₂) — austenitic structure has no ductile-to-brittle transition |
| Testing | Hydrostatic, PMI, IGC test (ASTM A262), UT, MT, PT, radiography per project spec |
| Documentation | EN 10204 3.1 Mill TC, Hydrostatic test certificate, Dimensional inspection report |
| Element | SS 304 (UNS S30400) | SS 304L (UNS S30403) | SS 304H (UNS S30409) |
|---|---|---|---|
| Chromium (Cr) | 18.00–20.00% | 18.00–20.00% | 18.00–20.00% |
| Nickel (Ni) | 8.00–10.50% | 8.00–12.00% | 8.00–10.50% |
| Carbon (C) | 0.080% max | 0.030% max — low C prevents sensitisation | 0.04–0.10% — higher C for creep strength |
| Manganese (Mn) | 2.00% max | 2.00% max | 2.00% max |
| Silicon (Si) | 0.75% max | 0.75% max | 0.75% max |
| Phosphorus (P) | 0.045% max | 0.045% max | 0.045% max |
| Sulfur (S) | 0.030% max | 0.030% max | 0.030% max |
| Nitrogen (N) | 0.10% max | 0.10% max | — |
| Iron (Fe) | Balance | Balance | Balance |
| Property | SS 304 (F304) | SS 304L (F304L) | SS 304H (F304H) |
|---|---|---|---|
| Tensile Strength (min) | 515 MPa (75 ksi) | 485 MPa (70 ksi) | 515 MPa (75 ksi) |
| 0.2% Yield Strength (min) | 205 MPa (30 ksi) | 170 MPa (25 ksi) | 205 MPa (30 ksi) |
| Elongation (min) | 40% | 40% | 40% |
| Hardness (max) | 92 HRB / 201 HB | 92 HRB / 201 HB | 92 HRB / 201 HB |
| Density | 8.00 g/cm³ | 8.00 g/cm³ | 8.00 g/cm³ |
| Magnetic Response | Non-magnetic (annealed); may become slightly magnetic after cold work | Non-magnetic (annealed) | Non-magnetic (annealed) |
| Key Characteristic | General-purpose — balanced corrosion resistance & weldability | Lower strength; preferred for welded assemblies (no sensitisation) | Higher C for creep strength above 550°C; grain size ≥ ASTM 7 |
| Standard | 304 | 304L | 304H |
|---|---|---|---|
| UNS (USA) | S30400 | S30403 | S30409 |
| ASTM / ASME (Flanges) | A182 F304 | A182 F304L | A182 F304H |
| EN / W. Nr. (Europe) | 1.4301 / X5CrNi18-10 | 1.4307 / X2CrNi18-9 | 1.4948 / X6CrNi18-10 |
| JIS (Japan) | SUS304 | SUS304L | SUS304J1 |
| IS (India) | IS 6911 Gr. 04Cr18Ni10 | IS 6911 Gr. 02Cr18Ni11 | IS 6911 Gr. 07Cr18Ni10 |
| GOST (Russia) | 08Х18Н10 | 03Х18Н11 | 08Х18Н10 |
| BS (UK — old) | 304S31 | 304S11 | 304S51 |
| GB (China) | 0Cr18Ni9 | 00Cr19Ni10 | 0Cr19Ni9 |
| Flange Type | Standard | Key Features & 304-Specific Use |
|---|---|---|
| Weld Neck (WNRF / WNFF / WNRTJ) | ASME B16.5 / B16.47 | Long tapered hub butt-welded to pipe. Highest integrity joint — ideal for Class 600–2500 and cyclic service. Use F304L filler on 304 pipe to prevent sensitisation in the HAZ. Most common 304 flange type in chemical, cryogenic, and pharmaceutical plants. |
| Slip-On (SORF / SOFF) | ASME B16.5 | Slips over the pipe and receives two fillet welds. Lower cost and easier to align than weld neck. Suitable for Class 150–600, low-pressure water, dairy, food, and HVAC systems. Specify 304L to prevent HAZ sensitisation at the double fillet welds. |
| Blind Flange | ASME B16.5 / B16.47 | Solid disc used to blank off or isolate a pipe end or vessel nozzle. SS 304 blind flanges are the most common grade in chemical plant, water treatment, and food processing where system access or pressure testing is required. Available in all classes up to 2500#. |
| Socket Weld (SWRF) | ASME B16.5 | Pipe inserted into socket bore and secured with a single fillet weld. Used for small-bore piping (NPS ½″–2″) in Class 3000–9000 high-pressure service. Common in pharmaceutical, instrumentation, and chemical injection lines where 304 is the standard process material. |
| Threaded (Screwed) | ASME B16.5 | NPT or BSP internally threaded — no welding required. Used in NPS ½″–4″, Class 150–300 for low-pressure steam, water, and gas utility lines where disassembly without cutting is preferred. Widely used in brewery, food, and utility instrument connections. |
| Long Weld Neck (LWN) | ASME B16.5 / B16.11 | Extended hub serves as an integral nozzle. Used on pressure vessel and heat exchanger nozzles where the flange hub length replaces a short pipe nipple. Common in 304 for pharmaceutical vessel nozzles and chemical reactor outlets. |
| Lap Joint (LJ) | ASME B16.5 | Used with a stub end — the flange rotates freely around the stub, simplifying alignment during assembly. Ideal where regular dismantling is required or where bolt-hole alignment is critical. 304 lap joint flanges with 304L stub ends are common in dairy and food-grade piping where frequent cleaning access is required. |
| Spectacle Blind | ASME B16.48 | Figure-8 plate with one solid disc (blind) and one open ring (spacer). Rotated between open and closed position for system isolation during maintenance. 304 spectacle blinds are standard in chemical plants for isolating piping sections during shutdown. |
For full dimensional data by flange type and class, visit: Flange Dimensions
| Property | SS 304 (S30400) | SS 304L (S30403) | SS 304H (S30409) | SS 316L (S31603) |
|---|---|---|---|---|
| Carbon Content | ≤ 0.08% | ≤ 0.030% | 0.04–0.10% | ≤ 0.030% |
| Molybdenum (Mo) | None | None | None | 2.00–3.00% |
| Tensile Strength (min) | 515 MPa | 485 MPa | 515 MPa | 485 MPa |
| Yield Strength (min) | 205 MPa | 170 MPa | 205 MPa | 170 MPa |
| PREN (Pitting Resistance) | ~18–20 | ~18–20 | ~18–20 | ~24–26 |
| Sensitisation Risk (Welding) | Moderate — carbide precipitation 425–870°C | Very low — low C prevents Cr₂₃C₆ | Higher — but intended for high-temp service not welds | Very low — low C like 304L |
| Chloride / Seawater Resistance | Limited — pitting above ~200 ppm Cl⁻ | Limited — same as 304 | Limited — same as 304 | Good — Mo significantly improves Cl⁻ resistance |
| High-Temp Creep (above 550°C) | Moderate | Lower (low C) | Best — high C + grain size requirement | Moderate |
| Cryogenic Service (down to –196°C) | Excellent | Excellent | Excellent | Excellent |
| Relative Cost | Base (lowest) | Slightly higher than 304 | Similar to 304 | ~20–30% higher than 304 (Mo content) |
| Best Suited For | General-purpose: food, pharma, water, chemical (non-chloride) | Welded assemblies: vessels, heat exchangers, piping systems | High-temp: boilers, pressure vessels, power plant piping | Marine, offshore, high-chloride, pharmaceutical critical |
Key decision rule: If your system involves welding and operates in the 425–870°C range (or if post-weld heat treatment is not performed), always specify 304L instead of 304. If your environment contains chlorides above ~200 ppm or seawater, step up to 316L. If service temperature exceeds 550°C continuously, specify 304H.
| Standard | Scope |
|---|---|
| ASTM A182 / ASME SA-182 | Forged or rolled alloy and stainless steel pipe flanges — Grade F304, F304L, F304H |
| ASME B16.5 | Pipe flanges and flanged fittings NPS ½ through 24, Class 150–2500 |
| ASME B16.47 | Large diameter steel flanges NPS 26–60 (Series A and Series B) |
| ASME B16.48 | Line blinds (spectacle blinds, spacers, and blanks) |
| ASME B16.20 | Metallic gaskets for pipe flanges — ring-joint, spiral-wound, jacketed |
| ASME B16.21 | Nonmetallic flat gaskets for pipe flanges |
| EN 1092-1 | Flanges and their joints — circular flanges for pipes (European standard) |
| DIN 2573 / 2576 / 2631–2638 | German DIN standard flanges — PN 6 through PN 400 |
| JIS B2220 | Japanese steel pipe flanges — 5K through 30K |
| ASTM A262 | Detecting susceptibility to intergranular attack (sensitisation) in austenitic stainless — Practices A–F; specify Practice E (Strauss test) for 304L weld qualification |
| ASME B31.3 | Process piping design code — governs 304 flange selection in chemical plants and refineries |
| ASME Section VIII / PED 2014/68/EU | Pressure vessel design codes for 304 flanged nozzle design |
| ISO 9001:2015 | Quality management system — Tesco's manufacturing QMS certification |
The most important welding consideration for SS 304 flanges is sensitisation. When standard 304 (C max 0.08%) is heated to the sensitisation range of 425–870°C — which occurs automatically in the heat-affected zone (HAZ) during welding — chromium combines with carbon to form chromium carbides (Cr₂₃C₆) at grain boundaries. This depletes the surrounding matrix of chromium below the 12% threshold needed for passivity, creating a network of corrosion-susceptible zones susceptible to intergranular attack (IGA) in corrosive environments.
Solution: Specify ASTM A182 F304L (C max 0.030%) for all flanges that will be welded without subsequent solution annealing. The very low carbon content of 304L does not allow sufficient chromium carbide formation to cause sensitisation, even after welding. The trade-off is marginally lower yield strength (170 MPa vs 205 MPa for 304), which is acceptable in most piping applications. Many projects specify "304/304L dual certified" material — bar stock that simultaneously meets both 304 and 304L composition and mechanical requirements, providing 304L corrosion protection with 304 mechanical strength credit.
| Base Metal | Recommended Filler (GTAW/GMAW) | Recommended Electrode (SMAW) | Notes |
|---|---|---|---|
| 304 to 304 | ER308 / ER308L | E308-16 / E308L-16 | ER308L preferred to minimise sensitisation risk in HAZ |
| 304L to 304L | ER308L | E308L-16 | Low-carbon filler mandatory to maintain 304L properties |
| 304H to 304H | ER308H | E308H-16 | High-carbon filler for creep-strength matching above 550°C |
| 304 / 304L to Carbon Steel | ER309L | E309L-16 | Dissimilar metal weld — 309L provides buffer layer |
Post-weld heat treatment (PWHT) of 304 is generally not recommended — solution annealing at 1040–1150°C followed by rapid quench is the correct remedy if sensitisation has occurred, not stress-relief annealing which holds the part in the sensitisation range.
| Industry | Typical Application | Sub-Grade Recommended |
|---|---|---|
| Food & Beverage Processing | Dairy process piping, brewing tanks, fruit juice lines, CIP return headers | F304L (welded) or F304 (machined/threaded) |
| Pharmaceutical & Biotech | WFI (Water for Injection) distribution, API process piping, fermentation vessel nozzles | F304L electropolished — for hygienic Ra ≤ 0.5 μm finish. Note: critical pharma often upgrades to 316L. |
| Water Treatment & Distribution | Potable water pipelines, desalination pre-treatment, municipal water plant flanged joints | F304 / F304L — non-chloride fresh water. Use 316L for seawater or brackish water. |
| Chemical Processing | Acetic acid, phosphoric acid, dilute nitric acid, caustic soda handling; reactor nozzles | F304 (acid concentrations and temperatures must be verified — not suitable for HCl or reducing acids) |
| Cryogenic & LNG | Liquid nitrogen, liquid oxygen, and LNG transfer lines to –196°C; cold box flanged joints | F304 / F304L — austenitic structure has no ductile-to-brittle transition; retains impact toughness to cryogenic temperatures |
| Power Generation | Feedwater heater nozzles, steam extraction piping, condenser water boxes | F304H for service above 550°C — higher creep rupture strength; standard F304 for below 550°C |
| Oil & Gas — Onshore | Sweet (non-sour) gas processing, gas metering, above-ground utility piping, instrument air systems | F304L for welded systems — avoid 304 in chloride-containing environments (use 316L instead) |
| Pulp & Paper | White liquor and bleach plant piping (low chloride bleaching), mechanical pulping water lines | F304 / F304L — Note: chlorinated bleaching stages require 316L or duplex |
| HVAC & Architecture | Chilled water and hot water distribution flanges, building mechanical systems, ornamental piping | F304 — cost-effective for indoor non-corrosive service |
| Semiconductor & Electronics | Ultra-pure water (UPW) distribution, process chemical handling in clean rooms | F304L electropolished — UPW systems; confirm material suitability for specific process chemicals |
SS 304 (UNS S30400) is the most widely produced austenitic stainless steel in the world, containing 18% chromium and 8% nickel (hence "18/8 stainless"). The chromium forms a thin, self-healing passive oxide film on the surface that provides corrosion resistance across a wide range of environments. The nickel stabilises the austenitic crystal structure, making 304 non-magnetic in the annealed condition and giving it excellent toughness from cryogenic temperatures (–196°C) to elevated service temperatures (870°C continuous). It is governed by ASTM A182 Grade F304 for forged flanges.
The only compositional difference is carbon content: 304 has a maximum carbon of 0.08%, while 304L has a maximum of 0.030%. This seemingly small difference has a large practical consequence: when 304 is welded, the heat-affected zone (HAZ) reaches the sensitisation temperature range (425–870°C) and chromium carbides (Cr₂₃C₆) precipitate at grain boundaries, depleting adjacent areas of chromium and creating susceptibility to intergranular corrosion. 304L's ultra-low carbon prevents this carbide formation, making it the preferred grade for all welded piping assemblies. The mechanical property trade-off is a slightly lower yield strength (170 MPa vs 205 MPa minimum for standard 304).
SS 316 (UNS S31600) adds 2–3% molybdenum (Mo) to the 304 composition, which significantly increases resistance to pitting and crevice corrosion in chloride-containing environments. The Pitting Resistance Equivalent Number (PREN) for 304 is approximately 18–20, while 316 is approximately 24–26 — meaning 316 resists pitting initiation at roughly 30–40% higher chloride concentrations. Specify 316L (not 304) wherever the process contains seawater, brackish water, coastal chloride-laden atmospheres, or halide-containing chemicals. 316 costs approximately 20–30% more than 304 due to the molybdenum addition.
Specify ASTM A182 F304H (UNS S30409) when the design temperature continuously exceeds 550°C. The higher carbon content (0.04–0.10%) in 304H significantly improves creep rupture strength — the resistance to slow deformation under sustained stress at high temperatures — compared to standard 304. ASTM A182 also requires F304H to have a grain size of ASTM No. 7 or coarser, which further enhances creep resistance. Typical 304H applications include boiler superheater headers, steam cracker transfer line flanges, and high-temperature furnace piping. Do not use 304H where welded joints will be in corrosive service — the high carbon content makes it very susceptible to sensitisation.
In the fully annealed (as-manufactured) condition, 304 flanges are non-magnetic — the austenitic FCC crystal structure is paramagnetic. However, cold working (machining, forming, drilling bolt holes) can partially transform the austenite to martensite, which is ferromagnetic. This means machined 304 flanges may show weak magnetic attraction, particularly at corners and machined surfaces. This is not a defect and does not affect corrosion resistance or mechanical properties. If complete non-magnetic response is critical (e.g., MRI environments), specify a fully annealed condition with magnetic permeability testing, or consider 316L which is more stable against strain-induced martensite transformation.
Yes. SS 304 and 304L flanges are excellently suited to cryogenic service down to –196°C (liquid nitrogen temperature). The austenitic crystal structure of 304 has no ductile-to-brittle transition temperature — unlike ferritic and martensitic steels and carbon steels, 304 retains its toughness and impact resistance at all sub-zero temperatures. This makes 304 and 304L the standard flange material for liquid nitrogen (LN₂), liquid oxygen (LOX), and LNG (–162°C) transfer systems. No special cryogenic impact testing (CVN) is required for 304 under most codes, as its austenitic nature inherently satisfies low-temperature toughness requirements.
ASTM A182 is the ASTM International standard "Standard Specification for Forged or Rolled Alloy and Stainless Steel Pipe Flanges, Forged Fittings, and Valves and Parts for High-Temperature Service." The "F304" suffix denotes the specific material grade — Grade F304 — which is forged or rolled stainless steel with a composition equivalent to UNS S30400 (SS 304). A flange marked ASTM A182 F304 confirms it was manufactured from qualified material, heat-treated (solution annealed) to restore the austenitic microstructure, and tested to minimum mechanical properties per the standard. F304L and F304H are the low-carbon and high-carbon variants respectively, all under ASTM A182.
No — 304 stainless steel flanges are not recommended for seawater service. Seawater typically contains 15,000–35,000 ppm chlorides, far above the ~200 ppm threshold at which 304 becomes susceptible to pitting and crevice corrosion. In seawater, 304 flanges will develop pitting corrosion within weeks to months, even in ambient-temperature service. The correct stainless steel grades for seawater flanges are SS 316L (for moderate exposure), Duplex 2205 (UNS S32205, PREN ~35, for offshore service), or Super Duplex 2507 (PREN ~42, for warm seawater or higher-flow systems). Monel 400 and Titanium Grade 2 are also used for aggressive seawater applications.
A dual-certified 304/304L flange is manufactured from bar stock or forged material that simultaneously satisfies both the composition requirements of 304L (C ≤ 0.030%) and the mechanical property requirements of standard 304 (yield strength ≥ 205 MPa, tensile strength ≥ 515 MPa). Because the carbon is low enough to be 304L but the other composition and heat treatment parameters are optimised to achieve 304 mechanical strength, the material can be certified and marked as both "F304" and "F304L" on the same test report. This is particularly valuable in piping systems where some flanges will be welded (needing 304L designation for corrosion resistance) while the engineer wants full 304 strength credit in pressure design calculations.
IGC stands for Intergranular Corrosion test — a test to verify that a stainless steel component has not been sensitised and is resistant to intergranular attack. For 304 and 304L flanges, the relevant standard is ASTM A262. The most common practices are Practice B (ferric sulphate–sulfuric acid test) and Practice E (copper–copper sulfate–sulfuric acid, also called the "Strauss test"). Practice E is the most commonly specified IGC test for welded 304L piping in chemical and pharmaceutical industries. A passing result confirms that grain boundaries have not been depleted of chromium and the material will resist intergranular corrosion in service. IGC testing should be specified when 304 (not 304L) has been used for welded assemblies in corrosive service.
The price of 304 stainless steel flanges is influenced by: (1) Nickel and chromium market prices — as 304 contains ~8–10.5% Ni and ~18–20% Cr, global nickel price movements directly affect flange cost; (2) Flange size and pressure class — larger bore and higher class flanges require more material and more machining; (3) Sub-grade — 304L and 304H are typically priced similarly to standard 304, though heat and lot availability can vary; (4) Quantity — large orders attract better pricing; (5) Certification requirements — EN 10204 3.1 with full testing (PMI, hydrostatic, IGC) adds cost versus basic 2.2 certification; (6) Lead time — expedited orders from non-standard stock carry a premium. Request a quote from Tesco for current pricing based on your exact specification.
Tesco Steel & Engineering maintains ready stock of standard 304 and 304L stainless steel flanges in the most common sizes (NPS ½″–24″, Class 150, 300, and 600) for fast delivery. Larger sizes, higher pressure classes, 304H, and special face types or surface finishes are manufactured to order with typical lead times of 2–4 weeks.
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Global Export: Tesco Steel & Engineering exports 304 Stainless Steel Flanges to 96 countries including the USA, UK, Germany, France, Netherlands, Italy, Norway, Spain, Saudi Arabia, UAE, Qatar, Kuwait, Oman, Bahrain, Iraq, Singapore, Malaysia, Thailand, Indonesia, Vietnam, South Korea, Japan, Australia, Canada, Brazil, Mexico, South Africa, Nigeria, Kenya, Egypt, Turkey, Kazakhstan, Russia, and across the EU, Middle East, Southeast Asia, Africa, and the Americas. All shipments are supported by EN 10204 3.1 mill test reports, hydrostatic test certificates, dimensional inspection reports, and country-of-origin declarations.
