ASTM B366 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.
DN15–DN600 and larger. Outside diameters follow the EN 10220 / EN ISO 1127 pipe series; wall thickness is matched to your connecting pipe.
| Size | OD (mm) |
|---|---|
| DN 15 | 21.3 |
| DN 20 | 26.9 |
| DN 25 | 33.7 |
| DN 32 | 42.4 |
| DN 40 | 48.3 |
| DN 50 | 60.3 |
| DN 65 | 76.1 |
| DN 80 | 88.9 |
| DN 100 | 114.3 |
| DN 125 | 139.7 |
| DN 150 | 168.3 |
| DN 200 | 219.1 |
| DN 250 | 273.0 |
| DN 300 | 323.9 |
| DN 350 | 355.6 |
| DN 400 | 406.4 |
| DN 450 | 457.0 |
| DN 500 | 508.0 |
| DN 600 | 610.0 |
Monel 400 (2.4360, NiCu30Fe) is the only commercially practical metallic alloy with broad resistance to hydrofluoric acid (HF) at all concentrations. In HF service, Monel 400 forms a protective fluoride film (NiF₂ + CuF₂) that passivates the surface and prevents continued corrosion. Stainless steels (even duplex and super duplex) are attacked by HF even at low concentrations. Hastelloy C-276 has limited HF resistance at low concentrations but is not suitable for concentrated HF. Only Monel 400 can handle HF across the full concentration range — which is why it is specified universally for HF alkylation unit piping (API 751).
Yes — Monel 400 in HF service must be stress-relief heat treated at 870–900°C before installation. High residual stress (from forming, welding, or straightening) makes Monel 400 susceptible to stress corrosion cracking (SCC) in HF environments. As-welded Monel 400 piping is not acceptable for HF alkylation service. API 751 (Safe Operation of Hydrofluoric Acid Alkylation Units) requires stress-relief of all Monel 400 components in HF contact.
EN 2.4360, NiCu30Fe, UNS N04400: a nickel-copper alloy.
