EN 10253-2 Type B buttweld pipe fittings in 2.4858 — Alloy 825 / Incoloy 825 (NiCr21Mo, N08825). A nickel-iron-chromium alloy with molybdenum, copper, and titanium additions. PRE ~32. The high nickel content (38–46%) provides SCC resistance in H₂S-containing environments per NACE MR0175, while Mo and Cu give resistance to sulphuric and phosphoric acids. Cost-positioned between 316L (too low PRE for sour gas) and Inconel 625 (PRE ~51, higher cost).
| Element | Min | Max | Role |
|---|---|---|---|
| Ni (Nickel) | 38.0% | 46.0% | SCC immunity in H₂S per NACE MR0175 |
| Cr (Chromium) | 19.5% | 23.5% | Passive film and pitting resistance |
| Mo (Molybdenum) | 2.5% | 3.5% | PRE contribution; acid resistance |
| Cu (Copper) | 1.5% | 3.0% | Reducing acid resistance (H₂SO₄, H₃PO₄) |
| Ti (Titanium) | 0.6% | 1.2% | Stabilisation — prevents sensitisation |
| Fe (Iron) | 22% min | — | Balance |
| Grade | PRE | Ni % | NACE MR0175 | Cu | Best Use |
|---|---|---|---|---|---|
| 316L (1.4404) | ~24 | 10–14% | Limited | None | Mild service |
| Alloy 825 (2.4858) | ~32 | 38–46% | Yes | 1.5–3% | Sour gas + mild acid — intermediate cost |
| Duplex 2205 (1.4462) | ≥35 | 4.5–6.5% | Yes (limited) | None | Chloride pitting; no acid need |
| Inconel 625 (2.4856) | ~51 | ≥58% | Yes | None | Aggressive seawater/mixed acid — higher cost |
| W.Nr. | 2.4858 |
| EN Name | NiCr21Mo |
| ASTM UNS | N08825 |
| Trade Name | Incoloy 825 / Alloy 825 |
Filler: ERNiCrMo-3 (Inconel 625 filler) commonly used. Dedicated Alloy 825 filler (ERNiFeCr-1) also available. No PWHT required.
