Effect of temperatures and pH values on the hydrochloric dew point corrosion behavior of 20^# steel

Hydrogen dew point corrosion often occurs in the overhead condensing and cooling system of an atmospheric distillation unit at the initial process of petroleum refining because of the formation of a highly suitable corrosive environment. The consequent thinning and leakage of equipment cause serious environmental pollution and endanger personal safety. Hydrochloric dew point corrosion is affected by various factors, among which temperature and pH values are the most critical. In this study, the hydrochloric dew point corrosion behavior of the 20^# steel of an atmospheric tower overhead system as well as its corrosion rate, corrosion morphology, and corrosion products at different temperatures and pH values were analyzed by some analytical methods, such as weight loss method, scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and X-ray diffraction (XRD). The results indicate that the hydrochloric dew point corrosion rate of the 20^# steel first increases and then decreases with temperature increase, and reaches its peak at 90℃. The hydrochloric acid dew point corrosion rate of the 20^# steel is negatively correlated with the pH values of HCl solution, and the dew point corrosion rate decreases rapidly with an increase of the pH value of HCl solution. Generally, uniform corrosion occurs on the steel surface accompanied with local corrosion pits. When the temperature is higher than 90℃, the number of corrosion pits increases with temperature. The corrosion pits become shallower and decreases with an increase of pH value. In addition, the chloride ions in the solution deepen the pits and accelerate the corrosion. The XRD analysis shows that the main compositions of the corrosion products are α-FeOOH, Fe₃O₄, and γ-FeOOH.