Electrochemical techniques for determining corrosion rate of rusted steel in seawater

Corrosion rates of mild steel for long-term immersion were estimated by electrochemical and weight-loss methods. The results showed that application of electrochemical methods yielded erroneous values. The main reason was that, β-FeOOH, produced after long-term immersion with high electrochemical activity in the inner rust layer, exerted significant influence. In electrochemical tests, even small polarization can make β-FeOOH participate in cathodic reaction, which leads to overestimating corrosion rate. In order to confirm it, electrochemical behaviour was studied in aerated and deaerated conditions to investigate the effect of rust layers on reduction reaction. After calibration, the electrochemical measurement result was coincided with the weight loss.

Research highlights
► Electrochemical estimate coincided with mass loss during the initial immersion.
► Electrochemistry did not coincide with mass loss after long-term immersion.
► Reduction of rust layers increase the electrochemical results.
► Electrochemistry coincided with mass loss after calibration.