This course outlines the performance of stainless steel in municipal wastewater treatment environments, highlighting why grades such as 304L and 316L have become standard materials for aeration systems, sludge handling, digester gas lines, and structural components. It summarizes corrosion-test data from real operating conditions, compares stainless steel with carbon steel, and explains how design, fabrication practices, flow conditions, and chemical additives influence long-term durability. Practical considerations—including welding quality, pickling, mitigation of crevice corrosion, and the impact of chlorides, chlorine, and ferric compounds—are also addressed to support reliable material selection and plant performance.