Understanding Corrosion in Water Pipelines: A Guide for Pipeline Designers


Alloy C22

Last updated: December 12, 2018

What Does Alloy C22 Mean?

The alloy C22 is a nickel-chromium-molybdenum-tungsten alloy with outstanding resistance to pitting, stress-corrosion cracking and crevice corrosion. It has a superior resistance to a wide range of chemicals, seawater, brine solutions, oxidizing and reducing media. In addition, it has good weldability and resistance to intergranular attack, making it ideal for chemical processing equipment, paper processing, marine, power and waste disposal industries.

The alloy C22 is also known as Inconel Alloy 22, AL 22, Hastelloy C22 or Nicrofer 5621.


Corrosionpedia Explains Alloy C22

The alloy C22 percentage composition is Carbon .005, Cobalt – 1.5, Chromium 22, Iron – 3, Manganese – 3, Molybdenum – 13, Nickel – 56, Silicon – 05, Vanadium 0.25 and Tungsten 3%. The Nickel-Chromium-Molybdenum-Tungsten alloy has a better overall corrosion resistance compared to most Ni-Cr-Mo alloys. The iron, chromium, molybdenum and tungsten content enhance the material's resistance to uniform and localized corrosion in a wide range of environments including flowing and stagnant sea water. The alloying elements contribute to the resistance to wide variety of industrial chemicals, oxidizing and reducing media. The high chromium concentration contributes to the resistance to oxidizing media, while the tungsten and molybdenum increases the resistance to the reducing media.

Alloy C22 characteristics:

  • Resistant to stress-corrosion cracking, pitting, crevice corrosion
  • Outstanding resistance to oxidizing and reducing media
  • High resistance to chemical process environments, ferric acids, seawater, acetic anhydride, brine solutions, etc.
  • Grain-boundary precipitates not formed in the weld heat-affected zone
  • Excellent weldability

The moderate-to-difficult to machine alloy work hardens rapidly, generates a lot of heat and may weld to the cutting tool surface, while its high shear strength may cause it to resist metal removal. It is, however, to be adequately machined using the conventional methods. The alloy has good ductility and therefore easily cold worked. However, since it is stiffer than the austenitic stainless steels, more energy is required for the cold forming.

Available forms are sheet, plate, bar, pipe, tubing, strip, wire, billet and covered electrodes, seamless pipe, welded pipe, seamless tube, welded tube, forgings, fittings and flanges.

The alloy’s resistance to corrosion in strongly acidic, and oxidizing environments makes it suitable for a wide variety of process equipment. Some of the areas where it is used include:

  • Chemical process industries
  • Galvanizing line equipment
  • Chlorination systems
  • Acid production
  • Complex acid and chemical environments
  • Overalloy filler wire and in weld overlay consumables

The alloy should, however, not be used in service temperatures exceeding 1250° F, otherwise detrimental phases may form at the higher temperatures.


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