904L Buttweld Pipe Fittings
ASTM A403 WP904L / EN 1.4539 (X1NiCrMoCu25-20-5) — high-alloy austenitic stainless with 25Ni-20Cr-4.5Mo-Cu for exceptional sulphuric acid, phosphoric acid and mixed-acid resistance across all concentrations. Pulp & paper, phosphoric acid, fertiliser, sour gas. ASME B16.9 and EN 10253-2 Type B. EN 10204 3.1/3.2. PED 2014/68/EU.
½″–48″
Size Range
PRE ~33
Pitting Index
490 MPa
Min UTS (ASTM)
H2SO4 0–98%
All Conc.
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904L Grade Equivalents
| ASTM | EN W.Nr. | EN Name | UNS | ASME P-No. |
|---|---|---|---|---|
| A403 WP904L | 1.4539 | X1NiCrMoCu25-20-5 | N08904 | 45 |
| A182 F904L (flanges) | 1.4539 | X1NiCrMoCu25-20-5 | N08904 | 45 |
| A312 TP904L (pipe) | 1.4539 | X1NiCrMoCu25-20-5 | N08904 | 45 |
P-No. 45 — requires separate WPS qualification from P-No. 8 austenitic grades. A WPS qualified for 316L (P-No. 8) cannot be reused for 904L.
Chemical Composition — 904L / EN 1.4539
| Standard | C | Cr | Ni | Mo | Cu | Mn |
|---|---|---|---|---|---|---|
| ASTM A403 WP904L | ≤0.020 | 19.0–23.0 | 23.0–28.0 | 4.0–5.0 | 1.0–2.0 | ≤2.0 |
| EN 1.4539 (X1NiCrMoCu25-20-5) | ≤0.020 | 19.0–21.0 | 24.0–26.0 | 4.0–5.0 | 1.2–2.0 | ≤2.0 |
Ultra-low carbon (≤0.020%) and copper (Cu) addition are the defining features. Cu enhances sulphuric acid resistance particularly at intermediate concentrations (30–70% H2SO4).
Mechanical Properties — 904L / EN 1.4539
| Standard | Min. UTS (MPa) | Min. YS (MPa) | Elongation (%) | Max Hardness | HT Condition |
|---|---|---|---|---|---|
| ASTM A403 WP904L | 490 | 220 | ≥35% | 190 HBW | Solution annealed |
| EN 1.4539 | 490–690 | ≥220 | ≥35% | 220 HBW | Solution annealed |
Heat Treatment & Welding Requirements
✓ No PWHT Required — Solution Annealed 1050–1150°C, Water Quench
904L is supplied in the solution-annealed condition. Post-weld heat treatment is not required for corrosion resistance, as the ultra-low carbon content (≤0.020%) prevents sensitization. Avoid prolonged heating in the 425–850°C sensitization range.
Welding Filler — GTAW
ER385 (AWS A5.9). Match filler composition carefully — high Ni filler prevents hot cracking. Confirm Ni and Mo content on filler certificate.
Welding Filler — SMAW
E385-16 (AWS A5.4). Matching composition essential — do not substitute 316L or 317L filler.
Inter-pass Temperature
Maximum 150°C. Keep inter-pass temperature low to minimise heat input and preserve corrosion resistance.
Sensitization Risk
904L is NOT susceptible to sensitization due to ultra-low carbon (≤0.020%). No PWHT or stabilisation treatment needed after welding.
P-No. Qualification
P-No. 45 requires a WPS specifically qualified for 904L — cannot reuse P-No. 8 (316L) procedures. Verify WPS scope before fabrication.
Preheat
No preheat required at ambient temperature. For heavy wall or cold conditions, a low preheat of 20°C minimum is recommended to prevent condensation.
904L vs 316L vs Duplex 2205 — Comparison
| Grade | PRE | Ni% | H2SO4 Resistance | Chloride SCC | Cost vs 316L |
|---|---|---|---|---|---|
| 316L (EN 1.4404) | ~24 | 12% | Moderate | Susceptible | Baseline |
| 904L (EN 1.4539) | ~33 | 25% | Excellent | Better | +50–60% |
| Duplex 2205 (EN 1.4462) | ≥35 | 5% | Limited | Good | +30–40% |
904L is optimised for acidic service; duplex 2205 for chloride service. They are not direct substitutes. For seawater or high-chloride environments, specify duplex 2205 or super duplex 2507 — not 904L.
904L Pipe Fitting Types Available
90° Elbow (LR & SR)
Long Radius & Short Radius
ASME B16.9 / EN 10253-2
45° Elbow
Long Radius
ASME B16.9 / EN 10253-2
180° Return Bend
LR & SR configurations
ASME B16.9
Equal Tee
Straight tee, equal branch
ASME B16.9 / EN 10253-2
Reducing Tee
Reduced branch outlet
ASME B16.9 / EN 10253-2
Concentric Reducer
Inline bore reduction
ASME B16.9 / EN 10253-2
Eccentric Reducer
Flat bottom / top configurations
ASME B16.9 / EN 10253-2
End Cap
Pipe end closure
ASME B16.9 / EN 10253-2
Stub End (Lap Joint)
For use with lap joint flanges
ASME B16.9 / MSS SP-43
Principal Applications
Sulphuric Acid Handling
H2SO4 piping systems across all concentrations (0–98%). The Cu addition provides exceptional resistance at intermediate concentrations (30–70%).
Phosphoric Acid Production
Fertilizer and phosphoric acid plants where resistance to H3PO4 and mixed acid environments is required.
Pulp & Paper — Bleaching Circuits
Digesters and bleaching plant piping where oxidising acids and chlorine compounds are present.
Fertiliser Plants
Nitric acid and mixed acid service in NPK fertiliser production, where 316L is inadequate.
Sour Gas Service
H2S-containing environments in offshore and onshore gas processing. Better SCC resistance than standard 316L.
Chemical Storage Tanks
Tank nozzles, manifolds and connecting pipework for aggressive inorganic acid storage applications.
Frequently Asked Questions
What is 904L stainless steel used for?
904L (EN 1.4539, X1NiCrMoCu25-20-5) is a high-alloy austenitic stainless with 25% Ni, 20% Cr, 4.5% Mo and copper additions. Its primary advantage is exceptional resistance to sulphuric acid across all concentrations (0–98%) at moderate temperatures, and resistance to phosphoric acid, acetic acid and mixed acids. Principal industries: pulp & paper (bleaching circuits), phosphoric acid production, sulphuric acid handling, fertilizer plants, and sour gas service. PRE ~33 — better than 316L (~24) but below duplex grades. Not typically used for seawater (specify duplex 2205 or 2507 instead).
What is the difference between 904L and 316L?
904L has roughly 2× the nickel (25% vs 12%), similar chromium, higher molybdenum (4.5% vs 2.2%), and copper additions. This gives 904L a PRE of ~33 vs ~24 for 316L and dramatically better resistance to sulphuric and phosphoric acids, chloride pitting, and SCC. However, 904L costs significantly more (~50–60% premium over 316L). For general chemical, pharma and food service, 316L is adequate and preferred. Specify 904L only where the specific acid chemistry demands it.
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