Alloy 20
Alloy 20 is a nickel-iron-chromium based austenitic alloy with excellent corrosion resistance in chemical environments containing sulfuric acid and many other aggressive media. This alloy is stabilized with niobium to resist intergranular corrosion.
While alloy 20 outperforms standard stainless steel, it can offer potential cost savings when carefully compared to higher nickel-based alloys
Description
Alloy 20 is a nickel-iron-chromium based, austenitic alloy with excellent corrosion resistance in chemical environments containing sulfuric acid and many other aggressive media. This alloy is stabilized with niobium to resist intergranular corrosion. Alloy 20 may provide potential cost savings when carefully compared to higher nickel-based alloys, while out performing standard stainless steels.
Industries and Applications
Alloy 20 is used in a variety of industries including chemical processing, petrochemical and refining, marine, pharmaceutical and food processing.
End uses include storage tanks, mixing tanks, agitators, pump and valve parts, food processing equipment, fixtures and fittings.
Application is limited to a maximum temperature of 1000°F per ASME.
It is also important to determine whether the required corrosion resistance can be achieved within a given environment.
Resistance to Corrosion
Alloy 20 is very resistant to sulfuric acid.
The alloy is also moderately resistant to phosphoric acid, nitric acid and aqueous salt solutions.
Alloy 20 is resistant to leaching and crack corrosion, making it an excellent option when chloride stress corrosion cracking is an issue.
Care must be taken in environments containing chloride ions, as corrosion rates can increase significantly.
Fabrication and Heat Treatment
Alloy 20 can be formed either by hot working or cold working by conventional methods.
Hot forging materials must be heated between 2100°F and 2250°F with careful temperature control to ensure that the material does not drop below 1800°F prior to forging. After hot working, the material is annealed by heating to 1725°F and 1850°F for a minimum of 30 minutes per inch of thickness, followed by immersion in water.
If stress relief is required, heat to a temperature below 1000°F and water quench after the desired time. Anneal Alloy 20 should be between 1725°F and 1850°F for 30 minutes at temperature per thickness.
Lower hardness can be achieved by heating to 2100°F, but its hardness can negatively affect the stabilization of the alloy.
Weld alloy 20 is typically done through SAW using matched filler metals, ER320LR for TIG and MIG and E320LR for SAW.
When welding to more than 316 dissimilar alloys such as C276 and Alloy 22, AWS ERNiCrMo-3 can be used for TIG and MIG, while ENiCrMo-3 can be used for SAW.
