Generation of free fatty acid during lockdown and its effect on the corrosion in rolling emulsion tank

•Long idle condition led to corrosion inside emulsion tank walls.•Cause often highlighted to bacterial attack.•Study finds acidic by-products generated in-situ responsible for corrosion.•Connection between the loss of protective nature and increase in acidity established. Corrosion in roll coolant tank is a rare phenomenon in the steel industry. The ability of the cold rolling emulsion to prevent corrosion on the cold rolled steel, the mild steel coolant tank, the mill housing and pipelines stems from the presence of oil soluble corrosion inhibitors, anti-oxidants or anti-wear additives present in rolling oil formulation. During normal operational conditions, the mill coolant (mixture of oil and water) along with the generated iron fines is continuously recirculated through the rolling mill application system. The concentration of the coolant is maintained by periodic addition of oil and demineralized water in the system. During Covid-19 unprecedented lockdown, voluminous corrosion was observed in the inner walls of coolant tanks, pipelines and other accessories, which remained in contact with the emulsion. Though normal rolling operations were halted, the bath temperature and recirculation of the mill coolant were maintained to sustain the emulsion health against bacterial attack. It has been earlier observed that during indefinite mill shutdowns, if emulsion is left without heating, circulation and stirring the health of emulsion deteriorates leaving a characteristic rancid odor which resembles bacterial attack. This study primarily highlights the role of acidic by-products formed due to depletion of anti-oxidants leading to rapid deterioration of emulsion triggering corrosion within the roll coolant tank. Techniques, like FTIR, SEM-EDS and Raman Spectroscopy were employed to understand the morphology and nature of the corrosion. Corrosion rust formed after simulation under accelerated laboratory conditions was finally subjected to Raman Spectroscopy, and Protective Ability Index (PAI) was applied to verify the variation in rust protection ability of the fresh and lockdown period rolling oil. It clearly shows the connection between the loss of protective nature of the rust and increase in acidity due to lockdown leading to accelerated corrosion of the tank system.