Corrosion resistance of hot-dip galvanized steel in simulated soil solution: A factorial design and pit chemistry study

The soil corrosion of widely applied galvanized steel structures, such as power transmission towers, must be considered to prevent harm to their structural integrity and to mitigate the high costs associated with early failure. A full two-level factorial design was used to evaluate the relative significance of various influencing factors on the underground corrosion of hot-dip galvanized steel. Experiments were performed in simulated soil solutions. The effects of temperature and the concentrations of chloride, sulfate, bicarbonate and citric acid were evaluated using statistical analysis of the results. Using analysis of variance, temperature, citric acid and chloride were found to be individually significant. Also, temperature/citric acid and temperature/chloride significantly interacted to increase the corrosion rate. The lead-in pencil electrode technique was used to further evaluate the impact of the above mentioned factors on the dissolution behavior of the Zn coating. The results revealed that chloride and citric acid affect salt film formation at the pit bottom, while temperature alters the dissolution kinetics by changing the diffusion coefficient of the dissolving Zn(II) species. Moreover, the effect of bulk solution dissolved oxygen concentration on the corrosion rate of the galvanized steel was modeled. It was found that oxygen concentration does not have a dominant effect on the overall corrosion behavior of galvanized steel. Rather, the effect of temperature is dominant.