This publication provides a comprehensive guide to selecting nickel-containing alloys for use in caustic soda (sodium hydroxide) environments. It explains the chemical behavior of caustic soda, key corrosion mechanisms, and the performance of various materials—including carbon steel, stainless steels, nickel alloys, duplex alloys, and copper alloys—under different concentrations, temperatures, and contamination conditions. The document also outlines alloy selection for caustic soda production processes (diaphragm, membrane, and mercury cell) and for industries that use caustic soda, such as refining, pulp and paper, and chemical manufacturing. Practical recommendations, corrosion data, and case studies help engineers choose suitable materials to ensure safety, durability, and cost-effectiveness.