ASTM A182 F904L Weld Neck Flanges — Super Austenitic SS 904L (UNS N08904)
Tesco Steel & Engineering forges ASTM A182 F904L weld neck flanges in super austenitic stainless steel 904L — UNS N08904, Werkstoff Nr. 1.4539, the 20Cr-25Ni-4.5Mo alloy with deliberate copper — from 1/2″ NB to 56″ NB, in ASME B16.5 Class 150–2500 and European PN patterns. The copper makes it the industry's sulphuric acid grade; the quarter-nickel content buys near-immunity to chloride stress corrosion cracking; and a PREN in the mid-30s holds off pitting that ends 316L and 317L careers — all at prices still below the nickel alloys. Ultra-low 0.020% carbon keeps every weld sensitization-safe. Supplied pickled & passivated with IGC ASTM A262, PMI and EN 10204 3.1/3.2 on request. ISO 9001:2015, made in Mumbai, India — exported worldwide.
A182 F904L · UNS N08904 · 1.4539
20Cr-25Ni-4.5Mo-1.5Cu
Sulphuric Acid Duty
Chloride SCC Resistant
1/2″ – 56″ NB
Class 150 – 2500 · PN 2.5 – 400
ISO 9001:2015 · Exported Worldwide
ASTM A182 F904L Weld Neck Flange — Super Austenitic 904L (UNS N08904), Technical Specifications
What is an ASTM A182 F904L Weld Neck Flange?
ASTM A182 F904L is the forged-flange grade of super austenitic stainless steel 904L (UNS N08904 / 1.4539) — roughly 25% nickel, 4–5% molybdenum and 1–2% copper on a 20% chromium base, with carbon cut to an ultra-low 0.020%. The copper makes it the classic sulphuric acid material; the nickel buys near-immunity to chloride stress corrosion cracking. An F904L weld neck flange pairs that chemistry with a long tapered hub butt-welded to the pipe, bore matched to schedule, joint fully radiographable — the bridge between stainless and nickel-alloy pricing.
The grade's logic on the ladder: when 317L runs out against acids, and duplex 2205 is wrong for reducing chemistry, 904L takes the duty at a fraction of Hastelloy money. For the most severe hot-chloride pitting, the 6-Mo 254 SMO continues the family — all forged in-house.
Being fully austenitic and ultra-low carbon, 904L welds sensitization-safe and stays tough to cryogenic temperatures; its ceiling is ~400 °C, above which intermetallics start to erode the corrosion resistance the grade is bought for.
Also searched as: SS 904L weld neck flange, UNS N08904 flange, 1.4539 flange, 904L WNRF flange, SA182 F904L flange, super austenitic stainless flange — all refer to the product on this page; see also our
904L flanges overview.
Chemical Composition of ASTM A182 F904L
| C | Mn | Si | P | S | Cr | Mo | Ni | Cu |
|---|
| 0.020 max | 2.00 max | 1.00 max | 0.040 max | 0.030 max | 19.00-23.00 | 4.00-5.00 | 23.00-28.00 | 1.00-2.00 |
Values in weight %. The copper addition is the sulphuric-acid element; the 23–28% nickel is the SCC insurance; and the 0.020% carbon ceiling makes every weld sensitization-safe by chemistry.
Mechanical Properties of ASTM A182 F904L
| Tensile Strength, MPa | Yield Strength, Min, MPa | Elongation % min. | Hardness Rockwell HRB |
|---|
| 490 | 220 | 35 | 79-90 typical |
Minimums per our supply practice. Strength is deliberately modest — 904L is bought for its chemistry, not its muscle — and the flange pressure-temperature ratings already account for it. The solution-annealed condition is documented on every certificate.
Equivalent Grades of ASTM A182 F904L
| Standard | Werkstoff Nr. | UNS | JIS | BS | KS | AFNOR | EN |
|---|
| SS 904L | 1.4539 | N08904 | SUS 904L | 904S13 | STS 317J5 | Z2 NCDU 25-20 | X1NiCrMoCu25-20-5 |
System partners: ASTM B677 N08904 seamless pipe, B366 fittings and B625 plate. The corrosion family continues with 254 SMO and Hastelloy above, 317L and duplex 2205 below.
ASTM A182 F904L Weld Neck Flange Specifications
| ASTM A182 904L Weld Neck Flanges are available in the following specifications: |
|---|
| Size | 1/2"NB to 56"NB |
| Class | 150#, 300#, 400#, 600#, 900#, 1500#, 2500# |
| Sch (Schedule) | XS, XXS, STD & Schedule 20, 40, 80, 160 |
| Pressure Ratings | PN 2.5 - PN 400 |
| Standards | ASME B16.5, ASME B16.47, EN 1092-1 Type 11, DIN 2631–2635, BS 4504 |
| Condition | Solution Annealed |
| Other Services | Pickling & passivation on ASTM A182 904L Weld Neck Flanges
Sand Blasting on ASTM A182 904L Weld Neck Flanges
Shot Peening on ASTM A182 904L Weld Neck Flanges
IGC (ASTM A262) & PMI testing
Project-specific marking, wrapping & export packing |
Why 904L Bridges Stainless and Nickel Alloys
The Sulphuric Acid Grade
Copper stabilizes the passive film in reducing acids — 904L handles sulphuric across a famously wide concentration window that dissolves the 300 series.
Chloride SCC Practically Solved
SCC resistance climbs steeply with nickel; at 23–28% Ni, 904L sits far above the cracking threshold that limits every lean austenitic.
Mid-30s PREN
4–5% molybdenum on a 20% chromium base holds off the pitting and crevice attack of brines and chloride process streams.
Weld-Safe by Chemistry
0.020% carbon means no sensitization, no post-weld anneal — joints enter acid service exactly as welded, with matching ER385 filler.
The Economic Middle
Where 317L fails and Hastelloy is overkill, 904L takes the duty at stainless-family logistics and a fraction of nickel-alloy money.
Welding 904L — Austenitic Discipline
904L welds with matching ER385 filler — or nickel-base consumables where the specification calls for over-matching — using low heat input and cool interpass temperatures: the fully austenitic pool needs discipline against hot cracking and molybdenum segregation. No preheat, no PWHT; the ultra-low carbon keeps the heat-affected zone sensitization-safe as-welded, and a post-weld pickle restores the surface where the service warrants.
Grade-selection note: 904L is built for
wet, acidic, chloride-bearing chemistry below ~400 °C — not the creep range, and not the harshest hot seawater, where
254 SMO or
super duplex take over. Name the acid and concentration in your enquiry and we confirm the economic grade.
Where ASTM A182 F904L Weld Neck Flanges Are Used
Acid plants lead: sulphuric and phosphoric acid production and handling — the chemistry the grade was invented for — plus fertilizer complexes and pickling lines. Flue gas desulphurisation, pulp and paper bleach circuits, seawater and brine systems, pharmaceutical and fine-chemical reactors, and offshore duties where acids meet chlorides complete the range. Our weld neck production below:
F904L Weld Neck Flanges — Assorted Sizes, Machined & Ready
ASTM A182 F904L Weld Neck Flange Dimensions
F904L weld neck flanges share their dimensions with every other material in the same class — OD, thickness, hub, bore, bolt circle and bolting per the standard tables. Full ASME B16.5 charts:
European PN dimensions are published on the EN 1092-1 Type 11, DIN 2631–2635 and BS 4504 pages.
Price List & How to Order
904L pricing tracks its heavy nickel and molybdenum content plus the testing scope, so we quote live with a stated validity rather than publish a static list. To get a firm quotation, usually within 24 hours:
1
List your requirement — size (NB), class or PN, standard (ASME B16.5 / B16.47 / EN / DIN / BS), grade (F904L / N08904 / 1.4539), pipe schedule or bore, and quantity.
2
Name the service chemistry — acid and concentration, chlorides, temperature — plus any testing scope (IGC A262, 3.2 witness, PMI); it lets us confirm 904L is the economic grade before you commit.
ASTM A182 F904L Weld Neck Flanges — Frequently Asked Questions
What is an ASTM A182 F904L weld neck flange?
It is a weld neck flange forged from ASTM A182 grade F904L — super austenitic stainless steel 904L, UNS N08904 / 1.4539, carrying roughly 25% nickel, 4 to 5% molybdenum and a deliberate copper addition. The long tapered hub is butt-welded to the pipe with the bore matched to the pipe schedule, giving a radiographable, fatigue-resistant joint in the grade chemical plants specify for sulphuric acid and severe chloride service — the bridge between standard stainless and nickel alloys.
What makes 904L a 'super austenitic' stainless steel?
Alloying far beyond the 300 series: nickel climbs from 316L's ~11% to 23-28%, molybdenum from 2-3% to 4-5%, and copper joins at 1-2% — with carbon cut to an ultra-low 0.020%. The result is a fully austenitic structure with a pitting resistance number in the mid-30s, near-immunity to chloride stress corrosion cracking (courtesy of the high nickel) and acid resistance the 300 series cannot approach — at a price still well below nickel alloys.
Why is 904L the sulphuric acid grade?
The copper addition. In reducing acids like sulphuric, copper promotes a stable passive film that plain chromium-molybdenum stainless cannot hold, so 904L handles sulphuric acid across a famously wide concentration range at moderate temperatures — the duty it was invented for. Phosphoric acid plants, pickling lines and acid-handling systems specify it for the same reason; where 317L dissolves and Hastelloy is overkill, 904L is the engineered middle.
What is the difference between 904L and 316L?
A different league of alloying: double the nickel and molybdenum plus copper, for a PREN in the mid-30s against 316L's mid-20s. In practice that means 904L survives hot sulphuric and phosphoric acids, brines and chloride-bearing streams that pit and crack 316L — with genuine resistance to chloride SCC, which no lean austenitic can claim. 316L remains the economical choice until the chemistry defeats it; 904L is several rungs up the same ladder.
When should I choose 904L versus duplex 2205 or 254 SMO?
By failure mode and chemistry. Duplex 2205 wins on strength and price in chloride service without strong acids. 904L wins where reducing acids — sulphuric, phosphoric — drive the corrosion, thanks to its copper and high nickel. 254 SMO, the 6-Mo super austenitic, takes over in hot seawater and the most severe chloride pitting. We forge all three, so the enquiry can name the service and we confirm the economic grade.
What temperature range can F904L flanges be used in?
From cryogenic — the fully austenitic structure has no ductile-brittle transition — to roughly 400 °C for continuous pressure duty; above that, intermetallic precipitation begins to erode the corrosion resistance the grade is bought for. Its territory is wet, aggressive chemistry at low and moderate temperatures, not the creep range.
What are the equivalent designations for A182 F904L?
SS 904L in general usage; UNS N08904; Werkstoff Nr. 1.4539 (EN X1NiCrMoCu25-20-5); JIS SUS 904L; BS 904S13; KS STS 317J5; and AFNOR Z2 NCDU 25-20. System partners: ASTM B677 N08904 seamless pipe, B366 fittings and B625 plate. An enquiry in any of these designations is quoted as the same material.
What is the chemical composition of ASTM A182 F904L?
Per our supply practice: carbon 0.020% max — ultra-low, weld-safe by chemistry — manganese 2.00% max, silicon 1.00% max, phosphorus 0.040% max, sulphur 0.030% max, chromium 19.00 to 23.00%, molybdenum 4.00 to 5.00%, nickel 23.00 to 28.00% and copper 1.00 to 2.00%. The copper is the sulphuric-acid element; the quarter-nickel content is the SCC insurance.
What are the mechanical properties of A182 F904L flanges?
Minimum tensile strength 490 MPa (71 ksi), minimum yield strength 220 MPa (31 ksi) and minimum elongation 35%, with hardness typically running 79 to 90 HRB. Strength is deliberately modest — 904L is bought for its chemistry, not its muscle — and the flange pressure-temperature ratings already account for it. The solution-annealed condition is documented on every certificate.
Which pipe grades do F904L weld neck flanges mate with?
ASTM B677 UNS N08904 seamless and welded pipe is the standard partner, with B366 butt-weld fittings and B625 plate completing the system. The weld neck bore is machined to the pipe schedule you state, so the bore runs flush through the joint and the bevel arrives ready for a matched-chemistry butt weld.
How are 904L flanges welded to pipe?
With matching ER385 (904L) filler — or nickel-base consumables where the specification calls for over-matching — using low heat input and cool interpass temperatures: the fully austenitic weld pool needs discipline against hot cracking and molybdenum segregation. No preheat, no PWHT. The ultra-low carbon keeps the heat-affected zone sensitization-safe as-welded.
Is 904L resistant to chloride stress corrosion cracking?
Effectively yes — resistance to chloride SCC rises steeply with nickel content, and at 23 to 28% nickel 904L sits far above the threshold where the lean austenitics crack. Combined with a mid-30s PREN against pitting, that lets 904L serve warm brines, coastal and process chloride duty that ends 316L and 317L careers — one of the two properties, alongside acid resistance, that justify its price.
What testing and certification do you supply with F904L flanges?
Every lot ships with EN 10204 3.1 mill test certificates covering chemical analysis — including copper, molybdenum and the ultra-low carbon — mechanical properties and the solution-anneal record, with 3.2 certification witnessed by Lloyd's, DNV, BV or TÜV on request. We also offer intergranular corrosion testing to ASTM A262, PMI verification and hydrostatic testing to project specifications, with full heat-number traceability.
Where are ASTM A182 F904L weld neck flanges used?
Sulphuric and phosphoric acid plants above all — the grade's home chemistry — plus fertilizer complexes, flue gas desulphurisation, pulp and paper bleach circuits, seawater and brine systems, pickling lines, pharmaceutical and fine-chemical reactors, and offshore process duties where acids meet chlorides. Wherever the ladder runs out of stainless before the budget reaches Hastelloy, 904L is the answer in between.
What sizes and standards do you manufacture F904L weld neck flanges in?
From 1/2 inch NB to 56 inch NB: ASME B16.5 Class 150 to 2500 up to 24 inch, ASME B16.47 above, and European PN 2.5 to PN 400 patterns to EN 1092-1 Type 11, DIN and BS 4504. Raised face is standard, flat face and ring joint on request, and every bore is machined to the mating pipe schedule from Sch 10 through XXS.
Do you keep A182 F904L weld neck flanges in stock? What is the lead time?
904L moves in project quantities, so common acid-plant sizes in Class 150 and 300 rotate through production with popular items often available, while larger diameters, higher classes and witness-tested lots are forged to order — typically 3 to 5 weeks. Prices track the heavy nickel and molybdenum content, so quotations carry a validity period — send the size list and we confirm the stock position the same day.
What information should I include in an F904L flange enquiry?
Six things: size (NB), pressure class or PN rating, dimensional standard (ASME B16.5, B16.47 or EN/DIN/BS), grade (F904L / N08904 / 1.4539), pipe schedule or bore, and quantity. Add any testing scope — IGC ASTM A262, 3.2 witness, PMI — and, usefully, the service chemistry: naming the acid and concentration lets us confirm 904L is the economic grade before you commit. Quotations usually return within 24 hours.
Do you export ASTM A182 F904L flanges outside India?
Yes. Tesco Steel & Engineering is an ISO 9001:2015 certified manufacturer based in Mumbai, and F904L flanges ship to acid plant, fertilizer and chemical projects across the Middle East, Europe, Africa, Southeast Asia and the Americas. Flanges travel pickled, face-protected and seaworthy-packed, with full heat-number and test traceability.
