Determination of Corrosion Rate in Galvanized Pipes in Centralized Hot Water Supply Systems

To counteract possible corrosion, steel pipes are coated with a protective layer of zinc with a thickness of 20 to 85 microns, depending on the requirements of regulatory documentation. It is proven that hot-deposited zinc can effectively protect steel surfaces for 20 to 120 years. However, in centralized hot water supply (CHWS) systems, the period of protective action can decrease to two to three years, with further damage to the zinc layer and the appearance of fistulas. In order to counteract adverse factors, it is necessary to take into account the operating mode and design features of the system, the properties of the coating, and the environment in which the pipes operate. In this article, the main attention is paid to the study of the behavior of zinc coating. The protective properties and corrosion rate of zinc coating in tap water were evaluated. It was established that the protective effect of zinc is effectively manifested in the ratio of the protected area to the unprotected, as SZn/SFe ≥ 9:1. The influence of iron-containing sediment, when it accumulates in the pipes of a CHWS system, on the corrosion rate of the zinc coating was studied. It was also noted that the corrosion rates of the new zinc coating and uncoated steel pipe measured in short-term tests differed slightly.