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Monel 400 is a nickel-copper alloy (about 67% Ni – 23% Cu) that is resistant to sea water and steam at high temperatures as well as to salt and caustic solutions.
Table of Contents
What is Monel 400?
Monel 400 is a solid solution alloy that can only be hardened by cold working. This nickel alloy exhibits characteristics like good corrosion resistance, good weldability and high strength. A low corrosion rate in rapidly flowing brackish or seawater combined with excellent resistance to stress-corrosion cracking in most freshwaters, and its resistance to a variety of corrosive conditions led to Monel 400’s wide use in marine applications and other non-oxidizing chloride solutions. This nickel alloy is particularly resistant to hydrochloric and hydrofluoric acids when they are de-aerated. As would be expected from its high copper content, Monel 400 is rapidly attacked by nitric acid and ammonia systems.
Monel 400 has great mechanical properties at subzero temperatures, can be used in temperatures up to 1000° F, and its melting point is 2370-2460° F. However, alloy 400 is low in strength in the annealed condition so, a variety of tempers may be used to increase the strength.
Monel 400 can easily be welded by gas-tungsten arc, gas metal arc or shielded metal arc processes using appropriate filler metals. There is no need for post weld heat treatment, however, thorough cleaning after welding is critical for optimum corrosion resistance, otherwise there is the risk of contamination and embrittlement. Finished fabrications can be produced to a wide range of mechanical properties when proper control of the amount of hot or cold working and the selection of appropriate thermal treatments is done.
Like most other nickel alloys, Monel 400 is typically tough to machine and will work harden. However, excellent results can be obtained if you make the correct choices for tooling and machining.
Chemical Composition of Monel 400
| Element | Content (%) |
|---|---|
| Nickel, Ni | Remainder |
| Copper, Cu | 28-34 |
| Iron, Fe | 2.5 max |
| Manganese, Mn | 2 max |
| Silicon, Si | 0.5 max |
| Carbon, C | 0.3 max |
| Sulphur, S | 0.024 |
Physical properties of Monel 400
| Properties | Metric | Imperial |
|---|---|---|
| Density | 8.8 gm/cm3 | 0.318 lb/in3 |
| Melting Point | 1300 – 1350 °C | 2370 – 2460 °F |
Mechanical properties of Monel 400
| Properties | Metric | Imperial |
|---|---|---|
| Tensile strength (annealed) | 517-620 MPa | 75-90 ksi |
| Yield strength | 172-345 MPa | 25-50 ksi |
| Modulus of elasticity | 179 GPa | 26000 ksi |
| Poisson’s ratio | 0.32 | 0.32 |
Applicable specifications of Monel 400
| Form | ASTM | ASME | Federal Specification |
|---|---|---|---|
| Bar | B164, B5641 | SB164, SB5641 | QQ-N-2812 |
| Plate & Sheet | B127 | SB127 | QQ-N-2813,4 |
| Seamless Pipe/Tube | B165 | SB165 | – |
| Welded Pipe | B725 | SB725 | – |
| Welded Tube | B730 | SB730 | – |
Applications of Monel 400
Because of its resistance to acids, alkalis, seawater, and more, Monel 400 often is used in applications where corrosion might be a concern.
Other applications sometimes include chemical plants, including environments using sulfuric acid and hydrofluoric acid.
Another area where Monel 400 is popular is the eyeglass industry. It is among the most popular materials in use for frames, specifically for components along the temples and over the bridge of the nose. According to Eyecare Business, the combination of strength and resistance to corrosion makes it useful for frames. A drawback, however, is that it is difficult to shape, limiting its usefulness for some frames.
- Marine engineering
- Chemical and hydrocarbon processing equipment
- Gasoline and freshwater tanks
- Crude petroleum stills
- De-aerating heaters
- Boiler feed water heaters and other heat exchangers
- Valves, pumps, shafts, fittings, and fasteners
- Industrial heat exchangers
- Chlorinated solvents
- Crude oil distillation towers
Corrosion resistance
The corrosion resistance of Monel is generally better than that of nickel and copper. It is more resistant to corrosion by reducing media than pure nickel, and is more resistant to corrosion by oxidative media than pure copper. It has very good corrosion resistance to sulfuric acid, phosphoric acid and carbon. In particular, it is resistant to corrosion by hydrochloric acid, and also has excellent corrosion resistance to hot concentrated alkali. Monel400 alloy has excellent corrosion resistance in fluorine gas, hydrochloric acid, sulfuric acid, hydrofluoric acid and their derivatives. At the same time, it is more corrosion resistant than copper-based alloys in seawater
Monel400 is a deformable nickel-copper-based nickel-based alloy with good seawater corrosion resistance and chemical corrosion resistance, as well as chloride stress corrosion cracking resistance. This alloy is one of the few alloys that can be used in fluoride. It has good resistance to oxide stress fission corrosion in hydrofluoric acid and fluorine gas media, such as seawater and saltwater environments.
Monel 400 also has very good corrosion resistance in moderately concentrated alkaline and salt solutions.
In cooler alkaline environments, the alloy is used in weak acids such as sulfur and hydrogen fluoride.
Acid medium: Monel400 is corrosion resistant in sulfuric acid with a concentration of less than 85%. Monel400 is one of the few important materials that can resist hydrofluoric acid.
Water corrosion: Monel400 alloy not only has excellent corrosion resistance in most water corrosion cases, but also pitting corrosion and stress corrosion are rarely found, and the corrosion rate is less than 0.025mm/a.
High temperature corrosion: The maximum temperature of Monel400 working continuously in air is generally around 600℃, and in high temperature steam, the corrosion rate is less than 0.026mm/a. Ammonia: Due to the high nickel content of Monel400 alloy, it is resistant to corrosion under anhydrous ammonia and ammoniated conditions below 585°C.
Supporting welding consumables
Monel Monel400 electrode (ENiCu-7), Monel400 welding wire (ERNiCu-7).
Edit this paragraph application areas: marine heat exchangers, seawater desalination equipment, salt production equipment, marine and chemical processing equipment, propeller shafts and pumps, gasoline and water tanks, etc.
