When manufacturing chemical apparatus, particularly for use in sulphuric and hydrochloric acid, steels maintaining corrosion resistance higher than austenitic steels such as iron-nickel, nickel-molybdenum, chrome-nickel and chrome-nickel-molybdenum based alloys shall be used.
Nickel will alloy readily with many other metals, including chromium, iron, molybdenum and copper. This allows for a wide variety of alloys that demonstrate outstanding resistance to corrosion and high-temperature scaling, exceptional high-temperature strength and other unique properties, such as shape memory and low coefficient of expansion.
Pure nickel UNS N02200 is used in the chemical industry for its corrosion resistance - particularly to alkalis. It is also used for its properties in shielding against electromagnetic interference and in transducers.
These are used as soft magnetic materials, as glass-to-metal seals and as materials with defined thermal expansion properties. Invar® (UNS K93600), with 36% nickel and the remainder iron, is unique in having an almost zero coefficient of thermal expansion around room temperature. This makes it valuable where high dimensional stability is required, such as in precision measuring instruments and thermostat rods. It is also used at cryogenic temperatures because of its very low thermal expansion rates.Alloys containing 72-83% nickel have the best soft magnetic properties and are used in transformers, inductors, magnetic amplifiers, magnetic shields and memory storage devices.
These are highly resistant to corrosion by alkaline solutions, non-oxidizing salts and seawater. The best-known is Alloy 400.
These are highly resistant to reducing acids in the absence of oxidizing ions, such as ferric and cupric or dissolved oxygen. The best-known is Alloy B-2.
These are characterised by their high resistance to corrosion at both normal and high temperatures (resistance to scaling), good high-temperature strength and high electrical resistance. There are three main groups of alloys:
There are basically two groups of alloys:
These are highly corrosion-resistant, of which Alloy C-276 (N10276) is the best-known. They offer exceptional resistance to reducing acids such as hydrochloric and sulphuric. There are a number of variants based on this composition, which have modified the Cr and Mo levels and, in some cases, added Cu or W in order to extend the corrosion resistance to conditions that are more oxidising or more reducing. These include Alloy C-22 (N06022), Alloy 59 (N08059), Alloy C-2000 (UNS N06200), and Alloy 686 (N06686).
The addition of cobalt and molybdenum imparts solid-solution strengthening and high levels of creep-rupture strength to alloy 617 (UNS N06617). The addition of cobalt to HR-160 (N12160) provides outstanding resistance to various forms of high-temperature corrosion attacks, such as sulphidation and chloride attack in both reducing and oxidizing atmospheres.
55% nickel-titanium alloy (UNS N01555) (also known as Nitinol) has shape-memory properties. When formed at one temperature and then deformed at a lower one, it regains its original form when reheated. The transition temperatures can be adjusted through careful control of the composition. Medical devices and specialised connectors are two of specific the applications. The same alloy can also undergo considerable elastic deformation and still return to its original shape (super-elastic property). This property has been exploited for applications as diverse as spectacle frames and shock absorbers that provide earthquake resistance in historic stone buildings.