Iron-chromium-nickel alloys stress-corrosion cracking

CAUSTIC CRACKING - A form of stress-corrosion cracking most frequently encountered in carbon steels or iron-chromium-nickel alloys that are exposed to concentrated hydroxide solutions at temperature of 200 to 250°C. 

An example of a nickel-based alloy that is resistant to stress-corrosion cracking is inconel. Inconel is composed of 72% nickel, 14-17% chromium, 6-10% iron, and small amounts of manganese, carbon, and copper. 

See ASTM G 35, Practice for Determining the Susceptibility of Stainless Steels and Related Nickel-Chromium-Iron Alloys to Stress Corrosion Cracking in Polythionic Acids. 

Though nickel alloys are more resistant to chloride and caustic SCC than stainless steels, they are equally susceptible to cracking in polythionic acid (PTA) when in the sensitized condition. See ASTM G 35, Practice for Determining the Susceptibility of Stainless Steels and Related Nickel-Chromium-Iron Alloys to Stress Corrosion Cracking in Polythioiuc Acids, for test details. 

ASTM Standard Recommended Practice G35, Determining the susceptibility of stainless steels and related nickel-chromium-iron alloys to stress corrosion cracking in polythionic acids. 

Description and corrosion resistance. Incoloy 825 is a nickel-iron-chromium alloy with additions of molybdenum and copper. It has excellent resistance to both reducing and oxidizing acids, stress-corrosion cracking, and localized attack such as pitting and crevice corrosion. The alloy is especially resistant to sulfuric and phosphoric acids. 

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