SS 904L FlangesASTM A182 F904L · Manufacturer, stockist & exporter, India
Also sold as Alloy 904L · UNS N08904 · W.Nr 1.4539 · 2RK65
SS 904L flanges are forged to ASTM A182 F904L and machined to ASME B16.5 (½"–24", Class 150–2500) or ASME B16.47 for larger sizes. It is a super-austenitic stainless steel with high nickel, molybdenum and copper, chosen for dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water. Kanak Steel & Engineering Co. supplies it with EN 10204 3.1 mill certificates from Mumbai to buyers across India, the Gulf, South-East Asia, South America, Europe, the UK and the USA.
- Stock & mill supply
- EN 10204 3.1 / 3.2
- PMI on request
- Export packing
Reviewed by the Kanak Steel & Engineering Co. technical team · Updated October 2026
What is SS 904L Flanges?
SS 904L flanges is a super-austenitic stainless steel with high nickel, molybdenum and copper supplied as flanges to ASTM A182 F904L (UNS N08904). Buyers specify it for dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water. It is also sold as Alloy 904L, UNS N08904, W.Nr 1.4539.
- What it is
- Super-austenitic stainless steel with high nickel, molybdenum and copper
- Material
- ASTM A182 F904L
- Dimensions
- ASME B16.5 · B16.47 · EN 1092-1
- Classes
- 150 · 300 · 600 · 900 · 1500 · 2500
- Facing
- RF · FF · RTJ
- Best at
- Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water
SS 904L Flanges Specification & Sizes
| Material standard | ASTM A182 F904L |
|---|---|
| Dimensional standards | ASME B16.5 (½"–24") · B16.47 Series A / B (26"–60") · B16.36 orifice · B16.48 line blanks · EN 1092-1 |
| Pressure classes | Class 150, 300, 400, 600, 900, 1500, 2500 · PN 6 – PN 100 |
| Facing | Raised face (RF) · flat face (FF) · ring type joint (RTJ) · tongue & groove |
| Bore | To match the pipe schedule — specify it on the order |
| Types | Weld neck flange · Slip-on flange · Blind flange · Socket weld flange · Threaded flange · Lap joint flange · Long weld neck flange · Orifice flange · Spectacle blind · Reducing flange · Ring type joint flange · Expander flange · Anchor flange · Swivel ring flange |
| Testing | PMI · dimensional · UT of forgings · IGC on request |
| Documents | EN 10204 3.1 · 3.2 with third-party inspection |
SS 904L Flange Pressure–Temperature Rating
The class is not a pressure: the allowable pressure for 904L flanges comes from the ASME B16.5 table for its material group, and falls as temperature rises (how ratings work). Check the material group for ASTM A182 F904L in B16.5 Table 1A before choosing the class.
Take the actual pressures from the B16.5 rating table for your material’s group. A class is not a project pressure rating — your piping class sheet and design conditions govern.
Bolting & Gaskets for 904L Flanges
For SS 904L flanges the usual bolting is as the project specifies — see SS 904L fasteners. Spiral-wound gaskets with a 304 or 316 winding suit most stainless raised-face joints. Facing and gasket options are compared in the flange guide.
SS 904L Flanges Chemical Composition
Under technical review for TDS.
| Element | Current requirement |
|---|---|
| Nickel | As specified |
| Chromium | As specified |
| Molybdenum | As specified |
| Copper | As specified |
| Carbon | As specified |
| Manganese | As specified |
| Silicon | As specified |
| Nitrogen | As specified |
| Phosphorus | As specified |
| Sulphur | As specified |
| Iron | As specified |
Numerical specification requirements are published only after the applicable current standard edition has been verified. Governing specification to be verified: ASTM A240 for UNS N08904.
SS 904L Flanges Mechanical Properties
Under technical review for TDS.
| Property | Current requirement |
|---|---|
| Tensile strength | As specified |
| Yield strength 0.2% | As specified |
| Elongation | As specified |
| Hardness | As specified |
Numerical specification requirements are published only after the applicable current standard edition has been verified. Governing specification and condition to be verified: ASTM A240 for UNS N08904 — Annealed plate & sheet.
Density & Physical Properties
| Property | Value |
|---|---|
| Density | 7.95 g/cm³ |
| Melting range | 1300 – 1390 °C |
| Magnetic | Non-magnetic (annealed) |
| PREN (approx.) | ≈ 35 |
SS 904L Equivalent Grades
SS 904L flange dimensions — ASME B16.5 Class 150 & 300
Outside dimensions depend only on size and class, not on the alloy, so 904L flanges bolt to any B16.5 flange of the same size and class. Values in mm; thickness excludes the 1.6 mm raised face.
| NPS | Cl 150 OD | Cl 150 thickness | Cl 150 bolt circle | Cl 150 bolts | Cl 300 OD | Cl 300 thickness | Cl 300 bolt circle | Cl 300 bolts |
|---|---|---|---|---|---|---|---|---|
| ½" | 90 | 9.6 | 60.3 | 4 × ½" | 95 | 12.7 | 66.7 | 4 × ½" |
| 1" | 110 | 12.7 | 79.4 | 4 × ½" | 125 | 15.9 | 88.9 | 4 × ⅝" |
| 1½" | 125 | 15.9 | 98.4 | 4 × ½" | 155 | 19.1 | 114.3 | 4 × ¾" |
| 2" | 150 | 17.5 | 120.7 | 4 × ⅝" | 165 | 20.7 | 127.0 | 8 × ⅝" |
| 3" | 190 | 22.3 | 152.4 | 4 × ⅝" | 210 | 27.0 | 168.3 | 8 × ¾" |
| 4" | 230 | 22.3 | 190.5 | 8 × ⅝" | 255 | 30.2 | 200.0 | 8 × ¾" |
| 6" | 280 | 23.9 | 241.3 | 8 × ¾" | 320 | 35.0 | 269.9 | 12 × ¾" |
| 8" | 345 | 27.0 | 298.5 | 8 × ¾" | 380 | 39.7 | 330.2 | 12 × ⅞" |
| 10" | 405 | 28.6 | 362.0 | 12 × ⅞" | 445 | 46.1 | 387.4 | 16 × 1" |
| 12" | 485 | 30.2 | 431.8 | 12 × ⅞" | 520 | 49.3 | 450.8 | 16 × 1⅛" |
Full chart: ASME B16.5 flange dimensions.
Six-digit Harmonized System heading (iron and steel, chapter 72–73). Your country adds its own digits — confirm with your customs broker. All HS codes.
How to Verify SS 904L Flanges with PMI
Positive material identification with a handheld XRF gun confirms the alloy on the piece itself, in seconds, before it is cut or welded. SS 904L is most often mixed up with Inconel 825 — the table shows which elements tell them apart.
Handheld XRF does not measure carbon or nitrogen; those come from the mill certificate or optical emission (OES) testing. PMI can be arranged on request — state it on your enquiry.
Under technical review for TDS.
| Element | SS 904L | Inconel 825 |
|---|---|---|
| Nickel | As specified | As specified |
| Chromium | As specified | As specified |
| Molybdenum | As specified | As specified |
| Copper | As specified | As specified |
| Titanium | — | As specified |
| Iron | As specified | As specified |
| Manganese | As specified | As specified |
SS 904L Flanges Price — What Decides It
Two quotes for "904L flanges" can differ by 20% and both be fair. We quote 904L flanges per kg for full sizes and per piece for cut sizes. These six things move the price per kg, so you can compare offers like for like.
SS 904L flanges by type
SS 904L Flanges Applications
SS 904L is specified when the cheaper grade will not survive the service but a higher alloy would be more than the job needs. These are the jobs our buyers use it for.
SS 904L Flanges vs 316L, 2205 and 825
| Grade | Flanges standard | PREN (approx.) | Pick it when |
|---|---|---|---|
| SS 316 / 316L | ASTM A182 F316L | ≈ 24 | Chloride-bearing process fluids, marine air and pharmaceutical service |
| Inconel 825 | ASTM B564 | ≈ 31 | Sulphuric and phosphoric acid service, chloride stress-corrosion cracking and sour gas |
| Duplex 2205 | ASTM A182 F51 / F60 | ≈ 35 | Strength with chloride resistance at a stainless-steel budget |
| SS 904L | ASTM A182 F904L | ≈ 35 | Dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water |
PREN = Cr + 3.3 Mo + 16 N, from mid-range chemistry. A screening guide, not a substitute for corrosion data on your medium.
SS 904L Corrosion Resistance — Element by Element
Each alloying addition has a job. Knowing which one protects against your medium is the quickest way to judge whether 904L fits.
Elevated nickel gives far better resistance to chloride cracking than 316L.
Molybdenum lifts pitting resistance well above ordinary austenitic grades (screening PREN on the grade page).
Copper is what makes 904L the stainless steel of choice for dilute sulphuric acid.
Very low carbon limits carbide precipitation, so welds keep their corrosion resistance.
How your 904L flanges order runs
- 01Enquiry review — we confirm size, standard edition and documents against your MR or drawing.
- 02Heat selection & PMI — the mill certificate is checked against your order; PMI before processing is available on request.
- 03Processing — cutting, machining or bevelling to your specification, with heat numbers marked.
- 04Inspection — your third-party inspector witnesses, or we share photos and test reports.
- 05Packing & dispatch — seaworthy packing from Nhava Sheva (JNPT), Mumbai, FOB or CIF, documents sent before the vessel sails.
Standards on this page
Welding & Fabricating SS 904L Flanges
SS 904L welds by all common arc processes. A few points our buyers ask about:
| Matching filler | ER385 (AWS A5.9) |
|---|---|
| Over-alloyed filler | ERNiCrMo-3 for severe chloride service |
| Preheat | Not required; keep interpass temperature low |
| Cutting | Thermal or abrasive cutting; grind off heat-tinted edges before welding |
Follow your approved WPS; this is general guidance. See also 904L fittings and 904L flanges for the matching pipe-system parts.
How to Order SS 904L Flanges: RFQ Checklist
Get an accurate quote the first time. Copy this list into your enquiry:
- Flange type and dimensional standard (B16.5 / B16.47 / EN 1092-1)
- Size, pressure class and facing
- Bore / schedule for weld neck and socket weld flanges
- Material standard and grade marking
- Certificate type and extra tests
- Delivery port, Incoterm and required date
SS 904L flanges for export
FOB / CIF · Nhava Sheva (JNPT), MumbaiSS 904L flanges — questions buyers ask
Is SS 904L the same as Alloy 904L?
Alloy 904L, UNS N08904, W.Nr 1.4539 are names used for SS 904L (W.Nr / EN numbers and older UNS variants are the closest designations; their limits can differ slightly, so specify the UNS number and ASTM grade on the order), and flanges is ordered to ASTM A182 F904L whichever name is on the enquiry.
Which standard covers SS 904L flanges?
ASTM A182 F904L is the material specification for the forging; dimensions follow ASME B16.5 for ½"–24" and ASME B16.47 for 26" and above. European projects use EN 1092-1.
What pressure can a SS 904L Class 300 flange take?
It depends on temperature and the material group of ASTM A182 F904L in ASME B16.5; read the Class 300 column of that group's rating table at your design temperature.
Which bolts should I use with SS 904L flanges?
Usually as the project specifies. In corrosive or sour service the bolting material is set by the project specification.
Can a SS 904L flange be welded to a different pipe material?
Yes — ER309L (or E309L electrode) is the usual filler when joining it to carbon steel. Weld neck bores must match the mating pipe schedule.
SS 904L or Inconel 825 — which should I choose?
SS 904L is chosen for dilute sulphuric acid, phosphoric acid and chloride-bearing cooling water. Inconel 825 is the step up when you need more pitting resistance or strength. See the comparison table on this page, or ask us with your process conditions.
Sources: the ASTM / ASME specifications named on this page and producer datasheets · Last updated October 2026