Comparative characteristics of water corrosion activity

It is proposed to determine the relative corrosivity of an aqueous medium as the metal corrosion rate at the initial stage of its contact with the medium in the absence of flow and at a constant temperature 25 °C. The measurements have been carried out using the electrochemical method of polarization resistance Rp, corrosion meter-indicators and a developed two-electrode electrochemical chamber with a cleaning device. The peculiarity of the methodology is that instantaneous values of polarization resistance have been measured on a freshly cleaned metal surface and the values of the corrosion rate have been obtained using a conversion factor of 104 Ohm·mm/year. Quantitative characteristics of water corrosivity of various origins with respect to steel 20, as well as solutions of salts with activating and passivating properties are obtained. Well- and artesian water, tap water (Dnieper and Desnian water abstraction), mineral bottled still water, model sea water and wastewater from the Bortnichy aeration station have been investigated. Water corrosivity ranges from 0.281 mm/year (Truskavets water) to 0.141 mm/year (Morshin water). The corrosivity of slightly mineralized aerated water corresponds to 0.145 mm/year. The corrosivity of wastewater in the process of biochemical treatment is the greatest – up to 0.4 mm/year. With sedimentation of the wastewater, the corrosivity has decreased by 2 times. It has been established that the mineralization of water significantly affects its corrosivity and stability. Depending on the content of anions in the water and their competing adsorption, which leads to the desorption of water dipoles on the metal surface and the removal of the oxygen barrier, the oxygen reduction rate can increase, and, accordingly, the metal corrosion rate increases. The dependence of the corrosivity of weakly mineralized water on the concentration of dissolved oxygen is linear and extrapolated to zero