Monel 400 (UNS N04400): Seawater-Resistant Nickel-Copper Alloy
ASTM B127 · Published: 2026-06-03 · Updated: July 2026
Monel 400 (67% Ni, 30% Cu) is a nickel-copper alloy with exceptional resistance to seawater, hydrofluoric acid, and caustic alkalis. It is the standard material for marine pump shafts, propeller shafts, seawater valve trim, and HF acid alkylation...
Monel 400 (67% Ni, 30% Cu) is a nickel-copper alloy with exceptional resistance to seawater, hydrofluoric acid, and caustic alkalis. It is the standard material for marine pump shafts, propeller shafts, seawater valve trim, and HF acid alkylation units in petroleum refineries. Unlike stainless steels, Monel 400 is immune to chloride stress corrosion cracking.
Quick Facts
| Category | Nickel Alloy |
| Standard | ASTM B127 |
| Density | 8.80 g/cm³ |
| Yield Strength | 195 MPa |
| Tensile Strength | 517 MPa |
Global Equivalents & Cross-Reference
| Alternative Standard / Grade | Action |
|---|---|
| EN 2.4360 | Compare |
| NiCu30Fe | Compare |
| JIS NW4400 | Compare |
| GB NCu30 | Compare |
Related Materials
🧮 Material Weight Calculator
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Frequently Asked Questions
Why is Monel 400 preferred over 316 stainless for marine shafts?
Monel 400 is immune to pitting and crevice corrosion in stagnant seawater — 316 is not. Additionally, Monel's galling resistance prevents seizing of close-fitting shaft components, which is critical for marine propeller shafts that may sit idle for months.
References & International Standards
- ASTM International. Standard Specifications for Steel & Metal Alloys. astm.org
- International Organization for Standardization (ISO). Metallic Materials — Cross-Reference Database. iso.org
- American Iron and Steel Institute (AISI). Steel Grade Designations & Equivalents. steel.org
- European Committee for Standardization (CEN). EN Steel Standards & Numbering System. cencenelec.eu