Influence of alternating, direct and superimposed alternating and direct current on the corrosion of mild steel in marine environments

The corrosion of mild steel in marine environments was studied with respect to induced alternating current (AC), direct current (DC) and the superimposed AC+DC sources. Corrosion rate determination at the different applied AC, DC and AC+DC current densities was carried out by conventional weight loss method for the exposure period of 24 h. The quantitative estimation of leaching of iron into solution was done by using inductively coupled plasma spectrometry (ICP). Mild steel specimens were subjected to surface examinations after treatment with various AC, DC and AC+DC current densities. Surface analysis was done by optical microscopy. The salient features of this investigation are AC source accelerate the corrosion of mild steel in the presence of marine environments, but the extent of corrosion was increased when it was superimposed with DC. Especially, upto the corrosion current density, the AC field is not a great threat for mild steel and uniform corrosion was observed, But after the corrosion current density, AC accelerate the pitting corrosion of mild steel in marine media. Surface micrographs showed severe pitting at the higher AC sources. The concentration of iron was increased above the corrosion current density. The electrochemical measurements coupled with surface examination and solution analysis proved to be a very effective tool by means of characterizing the AC corrosion effect of mild steel in marine environments.