If you’re looking for a more cost effective alternative to commercially pure nickel, but still need high corrosion resistance and good strength, it may be worth a look at the MONEL line of Nickel-Copper alloys.
The MONEL range of alloys are Nickel-Copper alloys, some with significant additions of other alloying metals to create high-quality, versatile materials that serve a wide-range of purposes.
One of the main benefits of a Nickel-Copper alloy is that it provides similar properties to commercially pure nickel but at a lower cost, which is useful for projects with a tighter budget. Corrotherm has two different MONEL products, which are suitable for various uses.
MONEL alloy 400
MONEL alloy 400 was derived directly from the refined Nickel and Copper ore bodies of Canada, and has a copper content of 28-34% alongside a high quantity of nickel (a minimum of 63%). It is an alloy with a long history – it was discovered by Robert Crooks Stanley who worked for the International Nickle Company ( INCO) in 1901 and named in honour of the Company president, Ambrose Monell. It was introduced to the market in 1905 – and it has been utilised in petroleum distillation tower internals, fasteners and fittings, pumps and valve internals for over 100 years.
Its properties mean that it is often employed in other industry areas too. It is a solid-solution alloy that can be hardened by cold working. Its composition means that it has high strength and toughness, even over a wide temperature range. It has excellent mechanical properties at sub-zero temperatures, with only a slight reduction in ductility and impact resistance. It does not even undergo a ductile-to-brittle transition when cooled to the temperature of liquid hydrogen. It also performs well in high-temperature conditions, which makes it useful for use in extreme environments such as for boiler feedwater heaters and other heat exchangers, and deaerating heaters.
The material displays excellent resistance to many corrosive environments and it is often used in marine and chemical processing plants. It is considered more resistant to attack by oxidising media, for example, than alloys with a higher copper inclusion. It also shows low corrosion rates in flowing seawater, though stagnant conditions may induce stress and pitting corrosion. However, the alloy is resistant to stress corrosion cracking and pitting in most fresh and industrial waters.
The alloy gives exceptional resistance to hydrofluoric acid in all concentrations up to boiling point and is considered the most resistant of all commonly used engineering alloys. It’s also resistant to sulfuric and hydrochloric acids under reducing conditions.
MONEL alloy K-500
MONEL alloy K-500 is a variation on the basic MONEL alloy 400. It is a precipitation-strengthened version that has controlled quantities of both titanium (0.35-0.85%) and aluminium (2.3-3.15%) added during melting. It retains the excellent corrosion resistance present in MONEL alloy 400, but with added strength and hardness thanks to the inclusion of the other metals and an age hardening process.
MONEL alloy K-500 is used in oil extraction and marine and chemical processing for fasteners and valve internals. The alloy can be hot or cold worked and heat treated to give the additional toughness that is required by these particular industry uses.
Other uses for the material include sea water pumps, shafts and valve shafts, and valve plate spring seals. It’s also widely used as doctor blades for the separation of paper strip from rollers in the continuous production of paper products.
Because of its excellent corrosion resistance, particularly to anhydrous hydrofluoric acid, it is well suited to valves, stems and internals in these environments. It can also be constructed in combination with MONEL alloy 400 for seawater service screens, housings, filters, piping and fittings.