ASTM A182 F904L Long Weld Neck Flanges — Copper-Bearing Super Austenitic LWN Manufacturer
Tesco Steel & Engineering manufactures ASTM A182 F904L long weld neck flanges — the acid specialist: UNS N08904, W.Nr. 1.4539 / X1NiCrMoCu25-20-5 — with ASME B16.5 flange ends in Classes 150–2500 and the barrel made to order. This page brings the acid ladder to the LWN family: where the chloride ladder fights brine, 904L fights the reducing acids that strip passivity and dissolve naked stainless — its 1.00–2.00% copper ennobles the alloy in sulphuric's mid-concentration gauntlet, the chemistry phosphoric-acid fertiliser plants standardised on. Its second credential is the third route to SCC safety: 23–28% nickel — not the lean austenitics' temperature wall, not duplex's ferrite, but massive nickel that takes the cracking mechanism's grip away — with PREN ~35 as the chloride side-benefit. The identity is the border itself: an N-number alloy, melted and priced with the nickel bench, fabricated like a stainless — no PWHT, no phase balance, ordinary austenitic welding. The ladder stays honest: 317L below by economics, Alloy 20 above for dedicated sulphuric duty, the nickel bench beyond, duplex across when the enemy is brine. One forging, one closing weld with matching 904L filler. Facings: RF / FF / RTJ; small bore on the F904L socketweld. Every lot with EN 10204 3.1/3.2 MTC. ISO 9001:2015, made in Mumbai, India — exported to 50+ countries.
ASTM A182 F904L · UNS N08904 · W.Nr. 1.4539The Acid Specialist — Copper-BearingSulphuric & Phosphoric — The Fertiliser StandardSCC Near-Immune — The Nickel RoutePREN ~35 — The Chloride Side-BenefitN-Number Alloy · Stainless FabricationB16.5 Flange Ends · Class 150–2500EN 10204 3.1 / 3.2 · ISO 9001:2015
ASTM A182 F904L Long Weld Neck Flanges — Specifications at a Glance
What is an ASTM A182 F904L Long Weld Neck Flange?
The acid specialist, in the nozzle pattern. An ASTM A182 F904L flange (UNS N08904) whose neck continues as a long, heavy-walled straight barrel — the nozzle itself — bevelled for one closing butt weld at the acid-plant column, absorber or shell. Copper 1.00–2.00% for the reducing acids; nickel 23–28% making chloride SCC near-immune; Mo 4–5% lifting PREN to ~35.Half a nickel alloy by its N-number and melt — fabricated like a stainless: no PWHT, ordinary austenitic welding. 490/215/35 solution annealed; C ≤0.020. The acid ladder: 316L → 904L → Alloy 20 → C-276. 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 acid ladder: state the acid, its concentration, its temperature and its impurities — sulphuric's aggressiveness swings enormously with all four — and the rung follows; 904L's breadth makes it the default when the duty is real but not extreme.
What the Copper-Nickel Recipe Buys
Survival in the Reducing Acids
Copper ennobles the alloy where passivity is stripped — sulphuric's broad middle concentrations, hot impure phosphoric — dropping corrosion rates by orders of magnitude against ordinary stainless.
SCC Near-Immunity by the Third Route
23–28% nickel takes the cracking mechanism's grip away — warm chloride duty above the ~60 °C wall, without duplex's ferrite, welding discipline or temperature window.
The N-number alloy that welds like a stainless — no PWHT, no phase balance, cryogenic capability kept: the grade's commercial genius and the reason projects reach for it.
PREN ~35 as the Side-Benefit
The heavy molybdenum earns duplex-altitude pitting resistance on the way to the acid franchise — FGD and offshore duty ride the same certificate.
Specification Notes — Getting F904L Long Weld Necks Right
Three honest notes.Read past the PREN: 904L and duplex share ~35 and almost nothing else — brine and strength say duplex; acid and austenitic fabrication say 904L. Name the acid fully: concentration, temperature and impurities decide whether the rung is 317L, this page, Alloy 20 or the nickel bench. And respect the alloy market: N08904 melts and prices with nickel — lead times follow the alloy world, quoted honestly up front.
How Our F904L LWN Flanges Are Manufactured
1
Forging — each piece individually forged from certified copper-bearing heats kept segregated from the stainless shelf, with the barrel integral — no welded build-ups.
2
Solution annealing — the full-solution cycle and quench that sets the clean fully-austenitic structure; records retained against the heat number.
3
Verification — chemistry per heat with the ≤0.020% carbon and the copper addition certified; mechanicals per heat; impacts at MDT where cryogenic duty requires them.
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 reads the copper and nickel lines on every piece — F904L can mix with neither the stainless shelf nor the nickel bench; marked with grade, size, schedule and heat number.
6
Certification & packing — EN 10204 3.1 MTC with solution-anneal records (3.2 witnessed on request); WPS guidance naming matching 904L consumables; faces and bevels protected, packed sea-worthy.
Where F904L LWN Flanges Are Used
Where the acids are real: sulphuric acid plants — absorption towers, dilution and storage circuits, loading systems — phosphoric acid and fertiliser process from reactor to filter, FGD absorbers where acid condensates join the chlorides, pulp bleach and fine-chemical duty beyond 317L's rung, and offshore systems that want SCC immunity with austenitic fabrication. Large diameters, modest pressures, chemistry as the load — and every nozzle one forging with one closing weld. 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
F904L LWN Flange Dimensions
Flange-end dimensions are class-governed per ASME B16.5 (ratings per the alloy's material group); barrel length and bore per order. Full class-by-class charts:
Seven elements — the acid's four numbers confirm the rung:
1
Size & standard — e.g. 8″ 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 F904L (UNS N08904); the acid stated fully — type, concentration, temperature, impurities — or the chloride duty and stress state; they confirm the rung against 317L below, Alloy 20 above and duplex across.
6
Certification — EN 10204 3.1 with solution-anneal records (our standard) / 3.2 witnessed.
Example: “LWN Flange RF, 8″ NB, ASME B16.5 Class 150, barrel 300 mm, Sch 10S bore, standard pattern, ASTM A182 F904L, phosphoric acid reactor nozzles — 54% P2O5 process acid, 80 °C, chlorides and fluorides present, EN 10204 3.1 — 6 pcs.” Quotations normally within 24 hours with price, unit weight and delivery.
An ASTM A182 F904L long weld neck flange is a forged copper-bearing super austenitic stainless steel flange — UNS N08904, W.Nr. 1.4539, the X1NiCrMoCu25-20-5 of European practice — 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 acid-plant column, absorber or vessel shell. F904L is the corrosion bench's acid specialist: 1.00-2.00% copper buys survival in the reducing acids that dissolve ordinary stainless, 23-28% nickel makes chloride stress corrosion cracking near-immune, and molybdenum at 4-5% lifts PREN to around 35 as the chloride side-benefit — half a nickel alloy by melt and price, fabricated like a stainless. 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.
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.
What does the copper do — the reducing-acid mechanism?
It changes which war the alloy can fight. Ordinary stainless survives by its passive film, and oxidising environments help that film maintain itself — but reducing acids, sulphuric's broad middle concentrations above all, actively strip passivity and then dissolve the naked metal. Copper's contribution is electrochemical: dissolving and re-depositing at the metal surface, it ennobles the alloy in reducing media, dropping the corrosion rate by orders of magnitude and letting the chromium-molybdenum film re-establish where plain grades never repassivate. That is why 904L was designed around sulphuric acid service — usable across wide concentration and temperature ranges where 316L's rate is measured in millimetres per year — and why phosphoric acid plant, with its hot impure process acid, made the grade a fertiliser-industry standard. The nickel supports the copper's work; the copper is the signature.
Why is 904L near-immune to chloride SCC — the third route?
Because nickel content is the austenitic family's own escape from the cracking mechanism. The site's ladder pages tell two routes already: stay below the ~60°C wall (the lean austenitics' compromise) or remove the mechanism with a ferrite half (the duplex route). The third route is massive nickel: chloride SCC susceptibility in austenitics peaks near the 8-12% nickel of the everyday grades and falls steeply as nickel climbs — by 904L's 23-28%, the cracking mechanism has essentially lost its grip, which corrosion engineering shorthand calls near-immunity. The practical consequence: 904L serves warm chloride-bearing duty above the wall that retires 316L and 317L, without duplex's welding discipline, temperature ceiling or ferrite-related limits — one reason offshore and FGD practice reaches for it where cracking is the fear and fabrication is austenitic-shaped.
What is the half-nickel-alloy identity — the N-number story?
904L sits on the border between two worlds, and its designation says so: N08904 is a nickel-alloy UNS number, not a stainless S-number — at 23-28% nickel the alloy is melted, sourced and priced closer to the nickel bench than to commodity stainless. Yet its fabrication behaviour stays graciously stainless: fully austenitic, no preheat, no PWHT, ordinary welding technique with matching consumables, machining and forming that any stainless shop handles. That combination is the grade's commercial genius — nickel-bench corrosion performance at stainless-shop fabrication cost — and its supply-chain caveat: 904L stocks thinner and prices with nickel, so lead times and market swings follow the alloy world. Our certificates, PMI segregation and marking treat it accordingly: this is an alloy that must never mix with the stainless shelf, and never needs the nickel bench's exotic procedures.
What is the chemical composition of ASTM A182 F904L?
Carbon ≤0.020% — tighter than the ordinary L grades' 0.030 — manganese ≤2.00%, silicon ≤1.00%, phosphorus ≤0.045%, sulphur ≤0.035%, chromium 19.0-23.0%, nickel 23.0-28.0%, molybdenum 4.00-5.00%, copper 1.00-2.00%. Every column works: the ultra-low carbon keeps the fully austenitic structure weld-safe without stabilisers, the chromium and heavy molybdenum build the film and the PREN, the massive nickel holds the structure and defeats the cracking mechanism, and the deliberate copper — the column no other grade on the stainless bench carries — buys the reducing-acid franchise. Chemistry is verified per heat, PMI-confirmed with the copper and nickel lines read, and travels on the EN 10204 3.1 MTC.
What are the mechanical properties of F904L long weld neck flanges?
Solution annealed: tensile strength 490 MPa (71 ksi) minimum, yield strength 215 MPa (31 ksi) minimum, elongation 35% minimum — the grade's own certificate, modest on paper and entirely sufficient in practice: B16.5 flange geometry is class-governed, the alloy's rating group sets the pressure-temperature envelope, and the generous 35% elongation reflects a fully austenitic structure that forges and machines beautifully. The austenitic gifts apply — no ductile-brittle transition, toughness to cryogenic temperatures with impacts documented where required — and hardness sits low with nothing to manage. As across the corrosion bench, the numbers are the entry ticket: what 904L sells is the copper's acid franchise and the nickel's cracking immunity, neither of which appears on a tensile certificate.
What is the acid ladder — and where does 904L sit?
The site's third great ladder, climbed by reducing-acid severity rather than chlorides or heat. 316L holds the bottom rung — dilute, cool, incidental acid exposure. 904L takes the working rung: designed for sulphuric service across wide concentration ranges, proven in hot impure phosphoric acid, the fertiliser and acid-plant standard. Above it, Alloy 20 — with more copper and niobium stabilisation — narrows the focus to sulphuric acid specifically, its dedicated specialist. And beyond the iron-based alloys entirely, the nickel bench's C-276 and its siblings handle the acids that dissolve everything below. The rule of the ladder: state the acid, its concentration, its temperature and its impurities — sulphuric's aggressiveness swings enormously with all four — and the rung follows; 904L's breadth makes it the default answer when the acid duty is real but not extreme.
904L or duplex — same PREN, different enemies?
The two grades share a number — PREN around 35 — and almost nothing else, which makes the comparison a perfect lesson in reading past PREN. Duplex F51 is a strength-and-brine grade: 450 MPa yield, chloride SCC removed by ferrite, the splash-zone and produced-water workhorse — but its ferrite half brings the -50 to 300°C service window, phase-balance welding, and no acid franchise at all. 904L is an acid-and-fabrication grade: reducing acids answered by copper, SCC answered by nickel, ordinary austenitic welding and cryogenic capability — at half duplex's yield and a higher price. The decision rule: if the duty is brine, seawater-adjacent or strength-driven, duplex; if it is acid, acid-contaminated chlorides, or chloride duty on a project that wants austenitic fabrication, 904L. Same altitude on the pitting ladder, different mountains entirely.
How is the closing weld on an F904L LWN made?
Like a stainless, with a super austenitic's care points. No preheat beyond dryness, no PWHT; matching 904L-type consumables carry the copper and the full analysis into the joint — leaner stainless fillers would plant an acid-vulnerable band exactly where the process wets the weld. Two disciplines earn attention: fully austenitic weld metal runs the family's known hot-cracking sensitivity, so procedures favour low heat input, controlled bead shapes and clean consumables; and interpass temperatures are kept modest to preserve corrosion performance in the as-welded zone. The ultra-low carbon means nothing sensitises, heat tint is removed by pickling or passivation where acid service will interrogate the surface, and the closing weld at the column or shell inherits the plant's own qualified 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.
When does F904L hand off — along the acid ladder or across the benches?
Down by economics: where acid exposure is dilute, cool or incidental, 316L and 317L serve the wet-chemistry world at stainless prices — 904L there is franchise paid for and never used. Up the acid ladder: dedicated sulphuric duty at the aggressive end names Alloy 20, and the acids beyond iron's reach belong to the nickel bench — C-276 and its siblings, with their own pages on this site. Across by enemy: brine and seawater questions go to the duplex family and the super duplex twins — the same-PREN-different-mountain comparison the earlier FAQ resolves — and 254 SMO carries the pure-pitting austenitic route. State the acid, concentration, temperature and impurities on the enquiry; the acid ladder places the rung in one line, and descending honestly is quoted as readily as climbing.
What sizes and pressure classes do F904L 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 order book mirrors the habitat: acid-plant columns, FGD absorbers and fertiliser process concentrate in Classes 150 and 300 — large diameters, modest pressures, chemistry as the load — with offshore and pressure-bearing process work climbing higher. 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, with the nickel-alloy supply-chain honesty stated up front.
What details are needed to get an accurate F904L LWN flange quotation?
Seven elements plus commercial terms: (1) size and dimensional standard — e.g. 8" 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 F904L, UNS N08904 — with the service stated (acid, concentration, temperature, impurities; or chloride duty and stress state) so the rung is confirmed against 317L below, Alloy 20 above and duplex across; (7) certification — EN 10204 3.1 with solution-anneal records (our standard) or 3.2 witnessed. Add quantity and destination; quotations normally within 24 hours, with the alloy-market lead time quoted honestly.
Who manufactures ASTM A182 F904L long weld neck flanges in India?
Tesco Steel & Engineering is an ISO 9001:2015 certified flange manufacturer based in Mumbai, India, producing ASTM A182 F904L 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 copper-bearing heats kept segregated from the stainless shelf, solution annealed with records retained, machined with the barrel bored to the ordered schedule or drawing, bevelled for the closing weld, PMI-checked with the copper and nickel lines read on every piece, and marked with grade, size, schedule and heat number. Supplied with EN 10204 3.1/3.2 certification and WPS guidance naming matching 904L consumables — alongside the 317L rung below, the Alloy 20 specialist above, the nickel bench beyond, and the complete long weld neck range. Exported to more than 50 countries.
