Research on corrosion control strategy of SCAL type indirect cooling circulating water system

In recent years, many thermal power units in China that equipped with SCAL type indirect cooling systems have commonly encountered corrosion and leakage problems with aluminum radiators. This study conducted field research and systematic analysis on more than ten units of the same type to reveal the corrosion mechanism of pure aluminum materials. Cl- ions destroy the passivation film protective layer on the surface of pure aluminum and undergo a secondary reaction with aluminum corrosion product Al(OH)3 to generate OH-, resulting in an abnormal increase in the pH of the indirect cooling circulating water. The alkaline environment accelerates the dissolution process of the passivation film, thereby further exacerbating the corrosion of the aluminum substrate. In addition, SO42- accelerate the corrosion of carbon steel and generate corrosion product of Fe3O4. After the passivation film on the surface of pure aluminum dissolves extensively in an alkaline environment,Fe3O4 will have a significant erosion corrosion effect on the exposed aluminum substrate under the high-speed fluid. Based on the above results, this article proposes three targeted corrosion control measures: 1) adding bypass purification devices to improve the quality of circulating water; 2) Installing protective sleeves at the aluminum radiator nozzle to reduce erosion and corrosion; 3) Scientifically adding corrosion inhibitors to enhance the anti-corrosion performance of the system.