They are primarily used for their corrosion properties, but are also used for their heat resistance, low expansion characteristics and electrical resistance.
The most important group of general-purpose nickel alloys are the Inconel ®types which are based on the heat resistant alloy 600 made of nickel, chrome and iron. These alloys are used in applications from cryogenic processes at -196ºC to elevated temperatures of up to 1 000ºC. They are also used in power generation for steam turbine power plants, aircraft gas turbines, nuclear power plants, furnaces as well as in the chemical and petrochemical industries.
Monel 400 is an alloy made from nickel and copper, used in marine and offshore environments for the fabrication of heat exchangers, evaporators, piping and vessels as well as in the chemical, petrochemical, and power generation industries.
These alloys are known by many other proprietary alloy names in the industries in which they are used, such as Inconel ®, Monel and Incoloy®from Special Metals, Nicrofer®and Nicorros ®from Krupp VDM, Pyromet®from Carpenter Alloys and Hastelloy ®from Haynes International Inc. Generally, these alloys are readily joined by most welding processes.
Nickel alloys can be joined by all the common types of welding process such as Manual Metal Arc (MMA), Metal Inert Gas (MIG), Tungsten Inert Gas (TIG) and Submerged Arc Welding (SAW), but not by the forge welding or oxy-acetylene processes. For the majority of applications on wrought nickel alloys, no preheat or post weld heat treatment will be required. In certain special cases, a post weld heat treatment may be required for stress relief of a fabricated structure or to avoid age hardening and stress corrosion cracking problems in acid or caustic environments. Nickel and nickel alloys can however be susceptible to embrittlement by low melting point elements such as sulphur, lead and phosphorous. These elements can occur in grease, paint, oil crayons, inks, cutting fluids, shop dirt or processing chemicals. It is therefore important that components to be welded are completely free of these contaminants before welding begins.