Influence of Formic Acid and Water on General Corrosion of Carbon Steel in Methanol

Abstract

The utilization of methanol as an alternative marine fuel is increasing due to its potential to achieve carbon neutrality; however, there are concerns regarding the corrosion of steel structures, such as fuel tanks, induced by formic acid and water present in methanol. To elucidate the influence of impurities on the corrosion behavior of carbon steel in methanol, corrosion loss was quantified through corrosion tests, and the corrosion mechanisms were investigated using electrochemical measurements. Test specimens obtained from TS490 MPa shipbuilding steel plates were immersed for up to 56 days in methanol solutions containing various impurities. General corrosion loss was quantified based on the weight loss of the specimens after immersion, and the results revealed that corrosion increased with higher concentrations of formic acid and water. Furthermore, potentiodynamic polarization tests conducted in methanol solutions containing electrolytes revealed that an increase in formic acid concentration accelerated both proton reduction and anodic reactions, thereby promoting general corrosion. Additionally, whereas water addition induced passivation of carbon steel, excessive water led to active dissolution, accelerating general corrosion. It was found that the formation and stability of the passive film are strongly influenced by the composition ratio of formic acid and water.