EN 10253-2 Type B buttweld pipe fittings in 1.4539 — 904L high-alloy austenitic stainless steel (X1NiCrMoCu25-20-5, N08904). 4.5% Mo and 1.5% Cu give PRE ~35 — bridging the gap between 316L (PRE ~24) and duplex (PRE ≥35). The copper addition provides specific resistance to reducing acids, particularly sulphuric acid. PRE equivalent to Duplex 2205 but fully austenitic, no sigma phase risk.
| Element | Min | Max | Function |
|---|---|---|---|
| C (Carbon) | — | 0.020% | Ultra-low C — avoids sensitisation |
| Cr (Chromium) | 19.0% | 21.0% | Passive film |
| Ni (Nickel) | 24.0% | 26.0% | High Ni — SCC immunity, austenite stability |
| Mo (Molybdenum) | 4.0% | 5.0% | PRE contributor: 3.3×4.5% ~15 pts |
| Cu (Copper) | 1.2% | 2.0% | Reducing acid resistance (H₂SO₄, H₃PO₄) |
| Grade | PRE | Structure | Cu | When to Choose |
|---|---|---|---|---|
| 1.4404 (316L) | ~24 | Austenitic | None | Mild service — lower cost |
| 1.4539 (904L) | ~35 | Austenitic | 1.5% | H₂SO₄, H₃PO₄, seawater — need Cu + PRE ~35 |
| 1.4462 (Duplex) | ≥35 | Duplex | None | PRE ≥35, no temperature ceiling concern, no acid need |
| 1.4547 (254 SMO) | ≥43 | Austenitic | 0.5–1% | Higher PRE needed; 6Mo + Cu |
| W.Nr. | 1.4539 |
| EN Name | X1NiCrMoCu25-20-5 |
| ASTM UNS | N08904 |
| Common Name | 904L |
Filler: ERNiCrMo-3 (Inconel 625 filler) is widely used for 904L — matches or exceeds corrosion resistance. Dedicated 904L filler (ER320LR) also available. No PWHT required.
