Tesco Steel & Engineering manufactures ASTM A182 F304H long weld neck flanges — the 18-8 carbon dial turned up: UNS S30409, W.Nr. 1.4948 — with ASME B16.5 flange ends in Classes 150–2500 and the barrel made to order. The chemistry is one deliberate move: carbon held in a 0.04–0.10% band whose floor builds the carbides that pin grain boundaries against creep — the same logic as F11's creep carbon on the chrome-moly staircase and the Incoloy 800H band above — making this the austenitic bench's grade for refinery hot circuits, superheated steam and furnace-adjacent nozzles above ~525 °C metal temperature. The supply rule is absolute: ordered by name, never substituted by dual-certified 304/304L stock — the modern low-carbon heats that make dual marking possible sit below the H floor. Room-temperature certificate identical to 304's (515/205/30); the difference lives in the creep-range allowables. One forging, one closing weld — with carbon-floored 308H filler, never 308L. Dial and benches stay honest: 304 below 525 °C, 321H/347H when the duty cycle bites, 800H beyond the stainless ceiling. Facings: RF / FF / RTJ. Every lot with EN 10204 3.1/3.2 MTC, carbon band certified. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
ASTM A182 F304H · UNS S30409 · W.Nr. 1.4948C 0.04–0.10% — The Creep Carbon FloorCreep Duty Above ~525 °COrdered by Name — Never Substituted308H Filler — Never 308LB16.5 Flange Ends · Class 150–2500Barrel: Length & Bore to OrderEN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A182 F304H Long Weld Neck Flanges — Specifications at a Glance
What is an ASTM A182 F304H Long Weld Neck Flange?
The creep setting of the 18-8 dial, in the nozzle pattern. An ASTM A182 F304H flange (UNS S30409) whose neck continues as a long, heavy-walled straight barrel — the nozzle itself — bevelled for one closing butt weld at the header or shell. Carbon 0.04–0.10% — the floor is the purchase: deliberately retained carbon precipitates the carbides that carry creep duty above ~525 °C. Room-temperature certificate identical to 304 (515/205/30); the difference lives in the creep-range allowables. Never substituted by dual-certified stock; welded with 308H, never 308L. Supplied solution annealed with records, grain size where specified. Flange ends per ASME B16.5, Classes 150–2500; barrel length and bore stated by you. EN 10204 3.1 on every lot.
The rule of the dial: below ~500 °C carbon is a liability; above it, the strength mechanism — one dial, three benches: 304-family, chrome-moly's F11 floor, and the Incoloy band.
What the Carbon Floor Buys
Creep Allowables, Certified in the Chemistry
The 0.04% floor guarantees the carbide-forming carbon is in the metal — the H grade's higher creep-range allowable stresses exist because the certificate proves the mechanism, not assumes it.
Stainless Corrosion Resistance at Creep Temperatures
The same 18–20% chromium film as the everyday grade — oxidation and scaling resistance the chrome-moly staircase cannot offer, in the band where the two benches hand over.
Fewer Welds Where Every Joint Is an Audit Item
Hot nozzles are exactly where designers count welds — each joint at creep temperature is a long-term inspection point, and the one-forging LWN deletes one from every nozzle.
Segregated Supply You Can Audit
H stock lives apart from the general stainless shelf — carbon band on the certificate, PMI-backed traceability, grain size reported where specified: the paperwork proves the purchase.
Specification Notes — Getting F304H Long Weld Necks Right
Three honest notes.The substitution error is silent: dual-certified 304/304L stock passes every receiving inspection — identical room-temperature certificate — and only fails years later as accelerated creep; order F304H by name and demand the carbon band on the MTC. The filler carries the same rule:308H, never 308L — an L-grade weld in an H-grade system is the substitution error in miniature. And buy the floor only where it works: below ~525 °C metal temperature the straight grade serves — H there is creep capability paid for and never used; above the stainless ceiling the Incoloy 800H/HT bench continues the same logic.
How Our F304H LWN Flanges Are Manufactured
1
Forging — each piece individually forged from certified high-carbon heats kept segregated from general stainless stock, with the barrel integral — no welded build-ups.
2
Solution annealing — the cycle that puts the carbon into solution so service can precipitate it usefully; records retained against the heat number.
3
Verification — chemistry per heat with the 0.04–0.10% carbon band certified explicitly; mechanicals per heat; grain size measured and reported where the specification invokes it.
4
Machining — flange end to ASME B16.5; barrel turned to pattern (standard / HB / equal) and bored to the ordered schedule or drawing; RF serrations, flat face or RTJ groove per B16.20; weld end bevelled 37.5°.
5
Testing & marking — PMI-checked on every piece; marked with grade — the H stated — size, schedule and heat number, so the shelf can never confuse it with everyday stock.
6
Certification & packing — EN 10204 3.1 MTC carrying the carbon band, anneal records and grain size where specified (3.2 witnessed on request); H-grade WPS guidance naming 308H fillers; faces and bevels protected, packed sea-worthy.
Where F304H LWN Flanges Are Used
Where stainless meets sustained heat: refinery hot circuits — catalytic reformer and FCC-adjacent piping, hot separators, furnace transfer lines — superheated steam systems in the stainless band, hot-gas ducting connections, and the furnace-adjacent thermowell standpipes and instrument nozzles that hold metal temperatures above 525 °C for decades. Production and supply below:
Stainless Long Weld Necks — Machined at Our WorksLong Weld Neck — Heavy Barrel, Bevelled Weld EndDN600 RF Long Weld Neck — Large Diameter, B16.5 Drilling
F304H LWN Flange Dimensions
Flange-end dimensions are class-governed per ASME B16.5 (ratings per the austenitic material group, elevated-temperature tables governing); barrel length and bore per order. Full class-by-class charts:
Seven elements — the metal temperature confirms the H purchase:
1
Size & standard — e.g. 6″ NB ASME B16.5.
2
Pressure class & facing — 150#–2500#; RF, FF or RTJ with ring number.
3
Barrel length — overall, face to weld end: 150 / 230 / 300 mm stock or any stated length.
4
Barrel bore & pattern — pipe schedule to match or finished bore in mm; standard, heavy barrel or equal barrel; weld-end prep if non-standard.
5
Grade line & service — ASTM A182 F304H by name (UNS S30409); design metal temperature stated — it confirms the H purchase against 304 below and the Incoloy bench above; any grain-size requirement named.
6
Certification — EN 10204 3.1 with the carbon band, anneal records and grain size where specified (our standard) / 3.2 witnessed.
Example: “LWN Flange RF, 6″ NB, ASME B16.5 Class 600, barrel 230 mm, Sch 40S bore, heavy barrel, ASTM A182 F304H, reformer hot-separator nozzles — 565 °C metal temperature, grain size reported, EN 10204 3.1 — 6 pcs.” Quotations normally within 24 hours with price, unit weight and delivery.
An ASTM A182 F304H long weld neck flange is a forged high-carbon austenitic stainless steel flange — UNS S30409, W.Nr. 1.4948 — whose neck continues as a long, heavy-walled straight barrel that is itself the nozzle, bevelled at its far end for one closing butt weld made out at the header, vessel or exchanger shell. F304H is the 18-8 carbon dial turned up: carbon is held in a deliberate 0.04-0.10% band whose floor builds the chromium carbides that pin grain boundaries against creep, making this the austenitic bench's answer to sustained service above roughly 525°C metal temperature — refinery hot circuits, superheated steam, furnace-adjacent plant. Flange ends follow ASME B16.5 in Classes 150 to 2500; the barrel is machined to the ordered length and bore. Supplied solution annealed with records, the carbon band certified, grain size reported where specified.
How does a long weld neck differ from a standard weld neck flange?
Geometry and mission. A standard weld neck's hub tapers quickly down to the pipe's outside diameter and wall, ending in a weld bevel a few centimetres from the flange face — it is built to butt-weld to pipe and continue as a piping run. A long weld neck keeps a full-section straight barrel for its entire length: no taper to pipe dimensions, wall far heavier than the matching schedule, length made to order. The mission follows the shape — the LWN is not a fitting on a pipe run but a nozzle in its own right, projecting through insulation, vessel walls or exchanger channels, with the butt weld relocated to the shell side where the fabricator wants it. In one certified forging it replaces the weld neck flange, the pipe nipple and one whole circumferential weld.
Why does 304H have a carbon floor?
Because at creep temperatures, carbon changes sides. Below roughly 500°C carbon is the austenitic family's liability — the sensitisation risk that 304L exists to remove. Above it, deliberately retained carbon becomes the strength mechanism: fine chromium carbides precipitate on grain boundaries and dislocations, pinning the structure against the slow plastic flow that is creep, and the difference shows directly in the design codes — the H grade holds usefully higher allowable stresses through the creep range, and some code paths simply require the H chemistry there. The 0.04% floor is the guarantee that the mechanism exists; the 0.10% ceiling keeps weldability and toughness in hand. This is the same carbon logic the site follows everywhere heat is the enemy: F11's creep carbon floor on the chrome-moly staircase, and Incoloy 800H's carbon band at still higher temperatures — one dial, three benches.
Why can't dual-certified 304/304L stock substitute for 304H?
Because the modern convenience that makes dual certification possible is exactly what disqualifies it here. Dual-certified heats sit below 0.030% carbon to satisfy the L grade — comfortably beneath 304H's 0.04% floor — so the carbide-forming carbon the creep allowables depend on simply is not in the metal. The substitution error runs quietly: the room-temperature certificate looks identical (515/205/30 for both), the flange passes every receiving inspection, and the shortfall only expresses itself as accelerated creep years into hot service. The rule is therefore absolute: 304H is ordered by name, supplied against its own UNS number S30409, and never substituted from the general stainless shelf. Our marking, MTCs and PMI-backed traceability keep the H stock segregated for exactly this reason.
What is the chemical composition of ASTM A182 F304H?
Carbon 0.04-0.10% — the defining band, floor and ceiling both mandatory — manganese ≤2.00%, silicon ≤1.00%, phosphorus ≤0.045%, sulphur ≤0.030%, chromium 18.0-20.0%, nickel 8.0-11.0%. Beside plain 304 the frame is identical — same chromium for the film, same nickel for the austenite, still no molybdenum — and the entire difference is one column: where 304 caps carbon at 0.08% and modern heats drift far lower, 304H floors it at 0.04% and rides to 0.10%. That one column moves the grade from the everyday bench to the creep bench. Chemistry is verified per heat with the carbon band certified explicitly, PMI-confirmed, and travels on the EN 10204 3.1 MTC.
What are the mechanical properties of F304H long weld neck flanges?
Solution annealed: tensile strength 515 MPa (75 ksi) minimum, yield strength 205 MPa (30 ksi) minimum, elongation 30% minimum — numbers deliberately identical to plain 304, and deliberately not the point. What the room-temperature certificate cannot show is where the grade earns its keep: through the creep range the H grade's allowable stresses hold usefully above the straight grade's, which is the entire commercial reason it exists. As across the site's hot benches, the two-ceilings honesty applies to the joint: at 304H's working temperatures the gasket system and bolting are engineering questions of their own, and the flange metal is rarely what retires first. Hardness sits comfortably low; grain size — coarser structures creep slower — is reported on the certificate where the project specifies it.
Where do F304H LWN flanges serve?
Wherever austenitic corrosion resistance and creep strength are needed in the same forging: refinery hot circuits — catalytic reformer and FCC-adjacent piping, hot separator and furnace transfer lines — superheated steam systems in the band the chrome-moly staircase hands over to stainless, hot-gas ducting connections, and the furnace-adjacent instrument nozzles and thermowell standpipes that live at metal temperatures ordinary 304 should not hold for decades. The LWN construction suits the habitat: hot nozzles are exactly where designers want fewer welds — every joint at creep temperature is a long-term audit item — and the one-forging pattern deletes one from each nozzle while the heavy barrel does the reinforcement work at the vessel opening.
Doesn't high carbon invite sensitisation?
Yes — and the grade accepts that trade with open eyes. Held or welded in the sensitising band, 304H will precipitate grain-boundary carbides more readily than low-carbon stock; that is the same precipitation the creep strength depends on. The engineering answer is context: at the grade's design temperatures the whole component lives above the classic aqueous-corrosion regime, so weld-zone sensitisation rarely meets the wet, aggressive chemistry it needs to matter — the carbides that would be a corrosion liability at 60°C are the strengthening mechanism at 600°C. Where a service genuinely combines creep duty with aggressive condensing chemistry or frequent shutdowns into wet conditions, the stabilised H grades — 321H and 347H, titanium- and niobium-locked — are the honest alternative, and both benches are available from our works. State the full duty cycle and the bench places the grade.
How is the closing weld on an F304H LWN made?
With austenitic ease and one non-negotiable: the filler carries the carbon. Procedures are the friendly stainless kind — no preheat beyond dryness, no PWHT, ordinary technique and interpass control — but consumables must be the carbon-floored 308H class, not standard 308L: an L-grade weld in an H-grade system is the substitution error in miniature, a low-carbon zone whose creep allowables fall short of the metal around it, planted exactly where service stresses concentrate. Beyond that, qualification on coded hot work follows the project's elevated-temperature rules, and the closing weld at the header or shell inherits the system's own qualified H-grade procedure. WPS guidance travels with every supply, filler class stated.
How are the barrel length and bore of a LWN specified?
Two numbers that belong on every enquiry. Length: measured overall from the flange face to the weld end — 150 mm (6"), 230 mm (9") and 300 mm (12") are the common stock lengths, and any length machines to order; state it explicitly, because 'long' is not a dimension. Bore: the barrel is drilled and bored to order — most commonly to match the inside diameter of the connecting pipe schedule, sometimes cylindrical special bores for level bridles, instrument standpipes or restriction work; state the schedule or the finished bore in millimetres. Add the weld-end preparation (standard 37.5° bevel unless told otherwise) and the nozzle is fully defined.
What does the H-grade paperwork add to the certificate?
Three lines the everyday grades never carry. The carbon band: the certified analysis must show carbon inside 0.04-0.10% — the floor is the purchase. The solution-anneal record: H grades are annealed to put the carbon into solution so service can precipitate it usefully; our MTCs carry the cycle against the heat number. Grain size: creep resistance favours coarser grains, and where a specification invokes a grain-size requirement the measured ASTM number is reported on the certificate. Add the ordinary framework — mechanicals per heat, PMI confirmation, EN 10204 3.1 as standard or 3.2 witnessed — and the H-grade certificate does what the grade itself does: prove that the high-temperature mechanism is really in the metal, not assumed.
When does F304H hand off — down the dial or up the benches?
Down the dial by temperature: below roughly 525°C metal temperature the straight grade's allowables serve and dual-certified 304/304L stock is the economical buy — H there is creep capability paid for and never used. Sideways by duty cycle: where creep service meets aggressive wet chemistry or frequent excursions through the sensitising band, the stabilised pair 321H and 347H lock their carbon to titanium and niobium instead. Up by temperature: when the stainless creep bench itself runs out — scaling and allowables both fading — the site's Incoloy 800H/800HT pages carry the same carbon-band logic into nickel-iron-chromium territory, and beyond them the nickel superalloys. Heat without corrosion belongs to the chrome-moly staircase and F91. State metal temperature, medium and duty cycle; the benches sort themselves.
What sizes and pressure classes do F304H LWN flanges come in?
Flange ends follow ASME B16.5 from ½" to 24" NB in Classes 150, 300, 400, 600, 900, 1500 and 2500 — with the full class-by-class LWN dimension charts on this site — and larger diameters forge to order against B16.47 or drawing dimensions, with EN 1092-1 drilling machined on the same barrels. The F304H order book follows the hot end of its habitat: refinery hot circuits and superheated steam concentrate in Classes 300-1500, where the austenitic material group's elevated-temperature ratings do the governing and heavy-barrel patterns serve the high-temperature nozzle loads. State size, class, barrel length and bore together — the four numbers define the forging — and our quotation returns price, unit weight and delivery per class.
What details are needed to get an accurate F304H LWN flange quotation?
Seven elements plus commercial terms: (1) size and dimensional standard — e.g. 6" NB ASME B16.5; (2) pressure class — 150 to 2500; (3) facing — RF (the default), FF or RTJ with ring number; (4) barrel length overall, face to weld end — 150/230/300 mm stock or any stated length; (5) barrel bore — pipe schedule to be matched or finished bore in millimetres, with pattern (standard, heavy barrel, equal barrel) and weld-end prep if non-standard; (6) the grade line — ASTM A182 F304H by name, UNS S30409 — with the design metal temperature stated so the H purchase is confirmed against plain 304 below and the stabilised or Incoloy benches beyond, and any grain-size requirement named; (7) certification — EN 10204 3.1 with the carbon band, solution-anneal records and grain size where specified (our standard) or 3.2 witnessed. Add quantity and destination; quotations normally within 24 hours.
Who manufactures ASTM A182 F304H long weld neck flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, producing ASTM A182 F304H long weld neck flanges with B16.5 flange ends from ½" to 24" NB (larger to order) in Classes 150-2500, in standard, heavy-barrel and equal-barrel patterns — each forged individually from certified high-carbon heats kept segregated from general stainless stock, solution annealed with records retained, machined with the barrel bored to the ordered schedule or drawing, bevelled for the closing weld, PMI-checked, and marked with grade, size, schedule and heat number. Supplied with EN 10204 3.1/3.2 certification carrying the carbon band and grain size where specified, and H-grade WPS guidance naming 308H fillers — alongside the 304/304L rungs of the dial, the 321H/347H stabilised bench, the Incoloy 800H/800HT pages above, and the complete long weld neck range. Exported to more than 50 countries.
