Saltwater champion. Fluorine resistant. Oil & gas standard.
Monel (nickel-copper alloy family) offers superior corrosion resistance in saltwater, better than stainless steel. Handles fluorine and HF acid where almost nothing else can. Standard for marine hardware, chemical processing, oil and gas downhole, pump shafts in aggressive service.
At a glance
- Density
- 8.8 g/cc
- Tensile strength
- 480 MPa
- Yield strength
- 170 MPa
- Elongation
- 35%
- Hardness
- 110-150 HB
- CTE
- 13.9 ppm/°C
- Corrosion (saltwater)
- Excellent
- Non-magnetic
- Mostly (Ms point -100 °C)
Key data
- Density
- 8.8 g/cc
- Tensile strength
- 480 MPa
- Yield strength
- 170 MPa
- Elongation
- 35%
- Hardness
- 110-150 HB
- CTE
- 13.9 ppm/°C
- Corrosion (saltwater)
- Excellent
- Non-magnetic
- Mostly (Ms point -100 °C)
Monel family.
Monel 400
Nickel-copper 67/33. Workhorse grade. General marine, chemical, oil and gas. Moderate strength.
Monel K-500
K-500 age-hardened to 3× the strength of M400. Used for pump shafts, valve stems, high-strength marine fasteners.
Monel 404
Special grade with minimized magnetic properties. Used for military sonar, sensor housings.
Monel R-405
Sulfur addition for improved machinability. Used for production screw-machine parts, precision fittings.
Monel 502
Weldable precipitation-hardenable grade. Used where both strength and weldability are needed.
NiCu 30
European designation for Monel 400 equivalent. Interchangeable for most applications.
Monel 400 is the general-purpose grade. K-500 is the precipitation-hardenable variant offering higher strength. Special grades address specific applications.
Why Monel wins.
Saltwater corrosion
Better than 316L stainless. Standard for sea-water immersion hardware, high-velocity seawater service.
Fluorine resistant
Monel handles fluorine gas and HF acid — almost nothing else does. Standard for uranium enrichment, specialty chemistry.
Sour service (NACE)
NACE MR0175-qualified for H2S environments. Standard for oil and gas downhole tools, production equipment.
Non-hardenable by heat
Monel 400 doesn't harden with heat treatment — parts maintain consistent properties regardless of service.
Monel's specific corrosion resistance pattern — especially to chlorides, fluorine, and HF — creates applications no other alloy handles.
Monel applications.
Marine propeller shafts
K-500 propeller shafts for large ships — high strength + saltwater resistance
Submarine hardware
Non-magnetic Monel 404 for submarine sonar and sensor equipment
Chemical pump shafts
K-500 pump shafts handling chlorides, brine, aggressive chemicals
HF acid handling
Fluorine and HF-contact hardware — valve bodies, piping, tanks
Oil & gas downhole
Sour-service downhole valves, safety equipment (NACE qualified)
Cryogenic service
Cryogenic valve and piping — Monel retains toughness at low temperature
Desalination
Heat exchanger tubes, valve components for desalination plants
Marine fasteners
K-500 marine bolts, high-strength hardware in saltwater service
Uranium enrichment
UF6 gas handling equipment for uranium enrichment facilities
Monel finishing.
As-machined
Silver metallic, similar to stainless. Ra 1.6 µm typical.
Polished
Ra 0.2 µm achievable. Marine decorative applications.
Welded
Excellent weldability. TIG or MIG with matching Monel filler.
Heat-treated (K-500)
K-500 age hardened at 595 °C to reach full properties. Dimensions stable.
Passivation
Generally not required — Monel is inherently corrosion resistant. Clean/degrease sufficient.
Cannot anodize
Not applicable — Monel is not aluminum.
Plated
Can accept plating but rarely needed due to inherent corrosion resistance.
Laser marked
Standard for identification and serial numbers.
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Saltwater champion — questions
Monel vs 316L stainless for marine?
In stagnant or low-velocity seawater, 316L is adequate and much cheaper. In high-velocity seawater, crevice-corrosion environments, or elevated temperature: Monel wins. Pitting/crevice corrosion: 316L can initiate pits in seawater; Monel doesn't. Stress corrosion cracking: 316L susceptible in chloride + stress; Monel more resistant. For critical marine service (propeller shafts, pump shafts in seawater), Monel K-500 is the standard despite being 3-5× cost of 316L.
Machining Monel — considerations?
Monel is tough and work-hardens — similar to stainless or harder. Slow cutting speeds (40-80 m/min), heavy feed to stay ahead of work hardening, flood coolant, sharp tools. R-405 (free-machining grade) is significantly easier. For production parts, specify R-405 if composition allows; otherwise plan for slower machining. Tool wear higher than steel or stainless.
Fluorine and HF resistance explanation?
Monel's nickel-copper composition forms a protective fluoride layer when exposed to fluorine gas or HF acid. This layer is stable and prevents further attack. Almost no other metal does this — iron alloys corrode rapidly, aluminum corrodes, titanium reacts. Monel is the material of choice for uranium enrichment (UF6 gas handling), HF acid production, fluorine chemistry equipment. Very specialty but critical applications.
Cost of Monel parts?
Monel 400 raw: $30-50/kg vs $3-5/kg for 316L stainless. K-500: $40-70/kg. Finished parts: 3-5× cost of equivalent stainless. For marine and chemical applications where corrosion matters, Monel premium is usually justified by 2-3× longer service life and avoiding catastrophic failures. For general applications where stainless works, Monel is unjustified premium.
NACE compliance for oil & gas?
NACE MR0175 governs materials for H2S (sour) service in oil and gas. Monel 400 and K-500 are NACE-qualified for specific hardness and heat-treatment conditions. For oil and gas applications requiring sour-service qualification, Monel K-500 heat-treated to specific hardness (typically 35 HRC max) meets NACE requirements. Documentation and material traceability included for oil and gas customer audits.
Lead times?
Monel 400: 3-4 weeks material lead time. K-500: 4-6 weeks (less common, specialty). R-405: 4-5 weeks. K-500 with heat treatment: add 2-3 weeks for heat treatment scheduling. Typical Monel project: 6-10 weeks from PO to shipping. Plan ahead.
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