Effect of Hydrazine on Corrosion Behavior of 20 Steel in Alkaline Aqueous Solution at Normal Temperature

To eliminate reliance on hydrazine for boiler layup protection and find its alternatives, the corrosion behavior of 20 steel in ammonia solution of different pH at room temperature was studied through electrochemical experiments. The results show that the corrosion rate of 20 steel in ammonia solution without hydrazine decreased with the increase of pH, and the surface of the steel gradually passivated. The 20 steel had the minimum corrosion rate and the maximum impedance modulus, when the pH of the solution was 10.5. In ammonia-hydrazine solutions at pH 9.5 and 10.0, the corrosion rate of 20 steel decreased with increasing hydrazine content, suggesting effective inhibition through hydrazine adsorption and oxygen displacement. Conversely, in solutions at pH 10.5 and 11.0, the corrosion rate increased with increasing hydrazine content, indicating corrosion acceleration where hydrazine likely suppressed passive film formation. Within the experimental range, the 20 steel got the lowest corrosion rate in both hydrazine-free ammonia solution at pH 10.5 and in ammonia solution containing 200 mg/L hydrazine at pH 9.5.