Corrosive behavior of austenitic stainless steel 321 in environments containing ammonium chloride

Abstract The main objective of this study is to determine the corrosive behavior of class 321 austenitic stainless steel by carrying out laboratory corrosion tests using the potentiodynamic polarization technique, using a standard solution of sodium chloride (NaCl) and an ammonium chloride solution (NH4Cl), both solutions at a concentration of 3.5% wt./v. Ammonium chloride salt is formed in the reaction sections of gasoline and diesel hydrotreating units by the reaction between ammonia and hydrochloric acid present in the cargo to be processed. It is a highly aggressive form of corrosion on various types of metallic materials, commonly used in the construction of equipment and pipelines in the oil and gas industry. Its damage can cause unscheduled downtime, loss of equipment containment, and loss of production, as well as potentially causing damage to people, installations, and the environment. The ASTM 321 steel showed higher corrosion resistance in ammonium chloride solutions than the ASTM 304 and 316L steels. During the general maintenance shutdown of a gasoline hydrotreating unit at a Brazilian oil refinery in 2024, the industrial application of this material will be demonstrated in a heat exchanger tube bundle for the effluent from the reaction section, made of 321 austenitic stainless steel.