Monel
Monel is a nickel-copper alloy (Monel 400 and precipitation-hardened K-500) with excellent resistance to seawater, brine, hydrofluoric acid and alkalis. It is used for marine fasteners, pump shafts, valves and chemical equipment.
What it is
Monel 400 (about 65% nickel, 30% copper) resists corrosion in flowing seawater and many acids and alkalis, with good strength and toughness. K-500 adds aluminium and titanium so it can be age hardened for about three times the yield strength.
Monel is used where stainless steels suffer pitting or stress corrosion in chloride environments.
Typical applications
- Marine fasteners and fittings
- Pump shafts and propeller shafts
- Valves and pump parts for seawater
- Hydrofluoric acid equipment
- Oil and gas components
Materials & grades
- Monel 400 (UNS N04400)
- Monel K-500 (N05500)
- Monel R-405 (free machining)
Points to consider
- Can pit in stagnant seawater; performs best in flowing conditions.
- R-405 is a free-machining grade for turned parts.
- Specify ageing condition for K-500.
- Costlier than stainless; use where its corrosion resistance is needed.
Frequently asked questions
What is Monel used for?
Seawater and marine parts, pump shafts, valves and equipment handling hydrofluoric acid or alkalis.
What is the difference between Monel 400 and K-500?
K-500 can be age hardened for much higher strength, while keeping similar corrosion resistance.
Is Monel better than stainless steel in seawater?
In flowing seawater it generally outperforms common stainless grades, resisting pitting and stress corrosion.