Monel 400
Monel 400 is a binary nickel-copper alloy (approximately 67% Ni, 31.5% Cu) strengthened by solid solution. It offers broad corrosion resistance in marine, reducing acid, and alkali environments. The alloy performs reliably from cryogenic temperatures up to about 480°C under most service conditions.
1. Chemical Composition
The table below lists the controlled elemental ranges for Monel 400. The high nickel-copper ratio defines its corrosion behaviour and sets it apart from other nickel-base alloys.
| GRADE | UNS Designation |
Standard (Pipe) |
Chemical Requirement (Max) | |||||||||||||
| C | Mn | P | S | Si | Ni | Cr | Mo | Cu | Fe | Ti | Al | Co | ||||
| Monel 400 | N04400 | B165 | ≤ 0.30 | ≤ 2.00 | ≤ 0.024 | ≤ 0.50 | ≤ 63.0 | 28.0-34.0 | ≤ 2.5 | |||||||
2. Equivalent Grade
The table below maps Monel 400 to its international equivalents across major standards systems. These designations are useful for cross-border procurement and material qualification documentation.
| GRADE | UNS | GB | JIS | ISO | DIN/EN | GOST | |
| ISC | NEW | ||||||
| Monel 400 | N04400 | H04400 | NS6400 | - | - | 2.4360 | - |
3. Key Technical Advantages
- Seawater and Marine Corrosion Resistance: Monel 400 resists pitting and crevice corrosion in seawater and brackish water. It does not suffer the chloride-induced SCC that limits austenitic stainless steels in marine service.
- Hydrofluoric Acid Compatibility: Monel 400 is one of the few engineering alloys that withstands hydrofluoric acid (HF) across a wide concentration range at sub-boiling temperatures. It is the standard alloy choice for HF alkylation unit piping and equipment.
- Reducing Acid Resistance: In non-oxidising conditions, Monel 400 has good resistance to hydrochloric and dilute sulfuric acids. Corrosion rates stay low when dissolved oxygen and other oxidising agents are absent from the acid stream.
- Technical Note: Monel 400 is susceptible to stress corrosion cracking (SCC) in moist aerated hydrofluoric acid vapours and in mercury-containing environments. It also corrodes faster in oxidising acids (nitric, chromic). Aeration of HF acid, even at low concentrations, significantly increases corrosion rates and the risk of SCC.
4. Common Manufacturing Standards
- ASTM B165: Standard specification for nickel-copper alloy (UNS N04400) seamless pipe and tube. This is the primary product standard for Monel 400 tubular forms.
- ASTM B163: Standard specification for seamless nickel and nickel alloy condenser and heat exchanger tubes, applicable to Monel 400 in heat transfer service configurations.
- ISO 9723: European standard for nickel alloy bars; DIN 2.4360 is the EN equivalent for Monel 400 material in bar form.
- DIN EN 10216-5 / DIN 17752: German/European standards covering nickel-copper alloy tube products in 2.4360 designation.
- JIS H4552: Japanese Industrial Standard for nickel and nickel alloy tubes, covering NW4400 (Monel 400) tubular products.
- GOST 492: Russian standard covering nickel-copper alloy grades including МНЖМц 28-2.5-1.5.
Manufacturing Standards Comparison Table:
| Standard | GB | EN/DIN | JIS | GOST |
| ASTM B165 (Pipe/Tube) | GB/T 5235 | DIN 2.4360 / EN ISO | JIS H4552 (NW4400) | GOST 492 |
| ASTM B163 (HX Tube) | GB/T 5235 | DIN 2.4360 | JIS H4552 | GOST 492 |
5. Primary Applications
- HF Alkylation Units: Piping, heat exchanger tubes, and vessel components in petroleum refinery hydrofluoric acid alkylation process units. Monel 400 is the standard material of construction for these systems.
- Marine Hardware and Seawater Piping: Pump shafts, propeller shafts, valve bodies, and seawater intake piping in naval vessels and offshore platforms that need biofouling resistance and marine corrosion protection.
- Chemical Processing: Transfer lines and storage piping for hydrochloric acid at low concentrations, sulfuric acid in reducing conditions, and fluorine compound streams.
- Brine and Saltwater Evaporators: Evaporator tubes and heat exchanger components in salt production and food-grade brine concentration plants where both scaling and corrosion must be managed.
- Crude Oil Distillation: Overhead condenser tubes and transfer lines use Monel 400. These systems are exposed to naphthenic acid, hydrogen sulfide, and chloride compounds, and they require a corrosion-resistant, hydrogen-resistant alloy.