Abstract. Corrosion damages of metal structures of wastewater treatment facilities affect the work process parameters and operation safety. The analysis of the factors causing corrosion of metal elements and the assessment of corrosion resistance of the steel grades St08ps, St3sp and St5sp during the treatment stages, including the chlorine treatment, were conducted based on the data obtained from the Rostov-on-Don aeration plant. The article search techniques to determine the corrosiveness of water towards the metal structures. It is established that in this case it is advantageous to use redox indicator systems (rH2), which is calculated on the basis of field measurements of redox potential (ORP) of water. Based on the conducted studies, the correlation dependence for determining the corrosion rate of the steel grades St08ps and St5sp was suggested and statistically assessed for the aeration plant structures.