Corrosion of mild steel and protection against it in environments of a liquid mineral fertilizer-ammonium sulphate

In the present article the corrosion-electrochemical behavior of St3 mild steel in liquid mineral fertilizer (LMF), namely in ammonium sulfate, at different concentrations (5, 10, 25, 40%) and temperatures (20 and 50 degrees C) as well as its contact duration with metal was studied. Assessment of corrosiveness of LMF included the study of steel corrosion in three areas: in the liquid volume, in saturated vapor above the solution and along the waterline. The results of electrochemical and corrosion tests showed that the maximum corrosion rate of steel at 20 degrees C was observed in a 10% (NH4)2SO4 solution, and the minimum was in a 40% solution. All investigated (NH4)2SO4 solutions at 20 degrees C are characterized by a decrease in the corrosion rate of steel over time. Increasing the temperature of LMF to 50 degrees C leads to an acceleration of corrosion of mild steel, especially along the waterline and in the vapor-gas phase. At the same time, the dependence of corrosiveness of LMF on its concentration does not change. In general, the highest corrosion rate of St3 steel is observed when it is partially immersed in (NH4)2SO4 solution regardless of its concentration and temperature due to the intensification of metal dissolution in the waterline region. The maximum corrosion rate of steel was 0.7 mm/year in 10% (NH4)2SO4 solution at its partial immersion and 50 degrees C. The protective effect of mixed corrosion inhibitor based on amino alcohols and organic acids (GSMCh) in relation to mild steel in the most corrosive 10% (NH4)2SO4 solution both in the liquid bulk and in the vapor phase was shown.