Alloy 20 was designed specifically to withstand sulfuric acid. Its nickel, chromium, molybdenum and copper levels all provide excellent general corrosion resistance. Restricted carbon plus columbium stabilization permits welded fabrications to be used in corrosive environments, normally without post-weld heat treatment. At 33% nickel, Alloy 20 has practical immunity to chloride stress corrosion cracking. This alloy is often chosen to solve SCC problems, which may occur with 316L stainless.
Alloy 20 is an austenitic, nickel-iron-chromium based super alloy with additions of Copper and Molybdenum which provide resistance to hostile environments, pitting, and crevice corrosion. It is also stabilized with Columbium to minimize carbide precipitation during welding. Alloy 20 appears to fall between both the stainless and nickel categories as it contains characteristics of both. It was designed for maximum resistance to acid attack and demonstrates superior resistance to stress-corrosion cracking in boiling 20% to 40% sulfuric acid, and also has excellent general corrosion resistance to sulfuric acid and to chloride stress corrosion cracking. Alloy 20 has good mechanical properties at both ambient and elevated temperatures, up to approximately
930°F (500°C) and is readily fabricated by usual industrial processes.