THE WAVE NATURE OF TUBERCLE CORROSION IN STEEL AND CAST IRON PIPES OF WATER SUPPLY SYSTEMS

Subject: the article is devoted to the study of corrosion processes in the water supply pipeline network. Initial growth and spatial orientation of corrosive tubercle deposits in non-coated steel pipes were studied. Experimental data are presented and an analysis of conditions and mechanism of formation of corrosive tubercles in water pipes is carried out. An assumption is made about the effect of flow velocity on the formation, growth and spatial distribution of tubercle deposits on the inner surface of the pipe. Research objectives: study of the mechanism of metal pipes corrosion in the water supply systems; development and experimental verification of the hypothesis of formation of tubercle corrosion deposits in pipelines. Materials and methods: the literature data on morphology and composition of tubercle corrosion deposits is analyzed. An experimental study of the initial stage of steel pipe corrosion under static and dynamic conditions has been carried out. Shape and composition of corrosion deposits on the metal surface were analyzed with the help of scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). The rate of corrosion in a steel non-coated pipe in cold tap water was measured. Results: the study of corrosion sediment shows that its formation and properties are significantly influenced by water flow rate. In the static regime, a uniform distribution of the anode and cathode areas, covered with loose sediment, is observed over the entire area of the sample. In the dynamic mode, the sediment is partially or completely removed from sample surface and the corrosion rate increases. The corrosion process proceeds with oxygen and hydrogen depolarization and contribution of hydrogen depolarization is significant. Over the anodic sections, a dense layer forms with magnetite formation during the cathodic reduction of iron hydroxides. The corrosion rate gradually decreases with time. The presence of sediment on the metal surface slows down the corrosion rate. Conclusions: the conducted studies showed that in the presence of water movement, larger anode and cathode areas are formed on non-galvanized steel pipe samples. These areas, in the course of further corrosion, are transformed into tubercles. Formation of two structural elements of future tubercle deposits was experimentally verified. Water flow velocity, along with the electrochemical processes, is a factor that directly influences the tubercle spatial arrangement and growth on the inner surface of the pipe.