Monel 400 is a popular nickel-copper alloy that is characterized by its high resistance to seawater and steam at high temperatures. This alloy is also resistant to salt and caustic solutions. Featuring about 67% Ni – 23% Cu in its composition, this is a solid solution alloy that can only be hardened with the help of a cold working process. This nickel alloy boasts having advantageous features like high strength, impressive weldability, and commendable corrosion resistance. Alloy 400 is extensively used in marine applications and a host of other non-oxidizing chloride solutions due to its low corrosion rate in rapidly flowing seawater or brackish water, as well as high resistance to stress-corrosion cracking in the majority of freshwaters. This material is known to be particularly resistant to hydrofluoric and hydrochloric when they are de-aerated. This alloy, however, tends to be rapidly attacked by ammonia systems and nitric acid due to its high copper content.
MONEL® ALLOY 400 UNS N04400 Chemical Composition, %
| CHEMICAL ANALYSIS | |
| C | Carbon 0.30 max |
| Mn | Manganese 2.00 max |
| Si | Silicon 0.50 max |
| S | Sulfur 0.024 |
| Fe | Iron 2.50 max |
| Ni (plus Co) | Nickel + Cobalt 63.0 min |
| Cu | Copper 28.0 – 34.0 |
ASTM Specifications of MONEL® ALLOY 400
| Pipe Smls | Pipe Welded | Tube Smls | Tube Welded | Sheet/Plate | Bar | Forging | Fitting | Wire |
| B165 | B725 | B163 | B127 | B164 | B564 | B366 |
The key characteristics of Monel 400
- Commendable resistant to steam and seawater at high temperatures
- High resistance to rapidly flowing seawater or brackish water
- Incredible resistance to stress corrosion cracking in the majority of freshwaters
- This alloy is specifically resistant hydrofluoric and hydrochloric acids when they are de-aerated
- While Alloy 400 is usually not the choice for hydrochloric and sulfuric acids, it is able to provide some resistance to them at modest concentrations and temperatures
- Provides impressive resistance to both neutral and alkaline salt
- Enjoys good resistance to stress corrosion cracking that is chloride-induced
- Have impressive mechanical properties from the range of sub-zero temperatures up to 1020° F
- High resistance to alkalis
MONEL 400 Mechanical Properties
Typical room temperature Tensile Properties of Annealed Material
| Product Form | Condition | Tensile (ksi) | .2% Yield (ksi) | Elongation (%) | Hardness (HRB) |
| Rod & Bar | Annealed | 75-90 | 25-50 | 60-35 | 60-80 |
| Rod & Bar | Cold-Drawn Stress Relieved | 84-120 | 55-100 | 40-22 | 85-20 HRC |
| Plate | Annealed | 70-85 | 28-50 | 50-35 | 60-76 |
| Sheet | Annealed | 70-85 | 30-45 | 45-35 | 65-80 |
| Tube & Pipe Seamless | Annealed | 70-85 | 25-45 | 50-35 | 75 max * |
*The ranges shown are composites for various product sizes and therefore are not suitable for specification purposes. Hardness values are suitable for specification purposes provided tensile properties are not also specified.
Corrosion Resistance
Alloy 400 is known to exhibit resistance to corrosion in a number of reducing media. It additionally tends to also be superiorly resistant to attack by oxidizing media in comparison to typical higher copper alloys. The high versatility of Monel Alloy 400 makes it well suited for use in a number of environments, and especially in distinct marine applications. However, even though the products made with this material do exhibit quite low corrosion rates in flowing seawater, it ideally experiences crevice and pitting corrosion in stagnant conditions. Alloy 400 additionally is resistant to the stress corrosion cracking and pitting in the majority of industrial and freshwaters. This nickel alloy is especially known to provide incredible resistance to hydrofluoric acid in a wide range of concentrations up the boiling point, and is one of the most resistant of all of the prominent engineering alloys. Under reducing conditions, Alloy 400 even is resistant to multiple forms of hydrochloric and sulfuric acids.
Heat treatment and fabrication
Typical operations of machining, shaping, joining and forming can be used when fabricating Monel 400. The temperature range of 1200°F and 2150°F must usually be used when performing hot working operations. When it comes to heavy reductions, the temperature range of 1700°F and 2150°F would be more preferable. Annealed material must be used for the purpose of cold working. Depending on the mechanical properties needed, the heat treatments available to Alloy 400 are annealing, stress-relieving and stress equalizing.
The major applications of Monel Alloy 400
- Packed columns
- Pressure vessels and reactors
- Brine heaters
- Heat exchangers
- Salt production equipment
- Pump and valve components
- Pipe work and pipe spools
This alloy is among the favorites of nickel pipes and pipe fittings owing to the major advantageous features and characteristics it enjoys. It tends to commonly be used marine fixtures and fasteners as well.
Monel 400 Equivalent
| STANDARD | UNS | WERKSTOFF NR. | AFNOR | EN | JIS | BS | GOST |
| Monel 400 | N04400 | 2.4360 | NU-30M | NiCu30Fe | NW 4400 | NA 13 | МНЖМц 28-2,5-1,5 |
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