Alloy 22 / UNS N06022 / W.Nr. 2.4602
Alloy 22 is a fully austenitic, nickel-chromium-molybdenum-tungsten alloy with better overall corrosion resistance compared to other nickel-chromium-molybdenum alloys, including alloy C-276, alloy C4 and alloy 625. The high chromium content provides good resistance to oxidizing media while the molybdenum and tungsten content gives good resistance to reducing media. This combination of corrosion resistance makes alloy 22 particularly useful in applications where mixed acids are present.
Industries and Applications
Alloy 22 is utilized in many aggressive environments across a wide range of industries, including chemical processing, oil and gas, pharmaceutical, food processing, pulp and paper, waste water treatment, pollution control, and nuclear. End use applications for alloy 22 include waste incinerators, equipment for flue-gas desulfurization scrubbers, nuclear fuel reprocessing/spent fuel containers, pickling systems, heat exchanger components, equipment for chemical manufacturing, flow meters and many other highly corrosive applications. The maximum service temperature for alloy 22 is 1250 °F due to the potential formation of detrimental phases.
Resistance to Corrosion
Alloy 22 displays exceptional resistance to a broad range of corrosive environments. This alloy has excellent resistance to oxidizing aqueous media, including wet chlorine and mixtures containing nitric acid or oxidizing acids with chlorine ions. Resistance to reducing acids such as sulfuric and hydrochloric can also be expected. Other corrosive chemicals to which the alloy has resistance include oxidizing acid chlorides, wet chlorine, formic and acetic acids, ferric and cupric chlorides, sea water, brine and many mixed or contaminated chemical solutions, both organic and inorganic. Alloy 22 offers optimum resistance to environments where reducing and oxidizing conditions are encountered in process streams. This is beneficial in multi-purpose plants where “upset” conditions occur frequently.
Fabrication and Heat Treatment
Alloy 22 can be formed by standard processes used for nickel alloys. Although ductile enough to be formed by cold working, intermediate annealing may be necessary due to work hardening. Forging should be between be performed between 1750°F and 2050°F followed by rapid cooling. Annealing can be performed at a temperature range between 2020°F and 2150°F followed by a rapid quench. Cooling at an accelerated rate avoids the formation of detrimental phases which form between 400°F and 1800°F. Welding can be by gas tungsten-arc, gas metal-arc, and shielded metal-arc processes.
Common Trade Names
INCONEL® alloy 22, HASTELLOY® C-22® alloy
INCONEL® is a registered trademark of the Special Metals Corporation group of companies. HASTELLOY® is a registered trademark of Haynes International Inc.