Effect of Immersion Depth on Marine Corrosion of Mild Steel

Marine corrosion data for mild steel coupons exposed at various immersion depths at various geographical locations are reviewed. Analysis of the data confirms that oxygen concentration and water temperature are important parameters influencing corrosion weight loss as a function of time and that there is no obvious effect of depth per se. However, it does not follow that these parameters govern corrosion behavior at all time, since it is known that longer-term corrosion behavior is governed by anaerobic conditions. The recently proposed multi-phase corrosion-time model for marine immersion corrosion is then adapted to allow for variation in dissolved oxygen concentration. It is shown that the model is consistent with the data. The data is applied to obtain a preliminary calibration of the model. It is argued that for very long-term corrosion the influence of anaerobic conditions is likely to be important, although relevant data are very scarce.