EN 10253-2 Type B buttweld pipe fittings in 2.4360 — Monel 400 nickel-copper alloy (NiCu30Fe, N04400). The only commercially practical metallic alloy with resistance to hydrofluoric acid (HF) at all concentrations. Also excellent in salt water, reducing acids, and marine environments. Mandatory stress-relief heat treatment (870–900°C) before HF service — as-welded Monel 400 is susceptible to SCC in HF.
Monel 400 in HF service MUST be stress-relief heat treated at 870–900°C before installation. Residual stress from forming or welding makes as-processed Monel 400 susceptible to stress corrosion cracking (SCC) in HF. API 751 (HF Alkylation Units) mandates stress-relief for all Monel 400 components in HF contact. Arshya supplies HF-service Monel 400 fittings with stress-relief documented on the EN 10204 3.1 certificate.
| Element | Min | Max | Role |
|---|---|---|---|
| Ni (Nickel) | 63.0% | — | Primary corrosion resistance |
| Cu (Copper) | 28.0% | 34.0% | Reducing acid resistance; HF film formation (CuF₂) |
| Fe (Iron) | — | 2.5% | Structure |
| Mn | — | 2.0% | — |
| C | — | 0.30% | — |
| W.Nr. | 2.4360 |
| EN Name | NiCu30Fe |
| ASTM UNS | N04400 |
| Trade Name | Monel 400 |
Filler: ERNiCu-7 (AWS A5.14). No PWHT for general service. Stress-relief 870–900°C mandatory for HF service.
