Corrosion of vertical steel strips exposed in the marine tidal zone and implications for ALWC

In the Accelerated Low Water Corrosion (ALWC) of sheet and other steel piling exposed in the tidal zone, various researchers have implicated microbial activity as contributing to the problem. However, a definitive understanding of the mechanisms involved and the environmental conditions of importance remains to be given. The present paper is a contribution to this aim. It presents results for exposures up to 2 years of the corrosion of vertical mild steel strips exposed at various tidal exposure locations on the Australian Eastern seaboard. At some locations there is clear evidence of ALWC already within a short period of time and certainly after 2 years. At other locations this does not occur and the corrosion profiles agree closely with the classical results reported by Larrabee, LaQue in which the most severe corrosion occurs at around the high water mark. An interpretation is given for the Australian results as a function of data for water quality measured at the various test sites. This is then interpreted through an extension of the model for longer-term corrosion proposed previously by the authors, modified for the effect of differential aeration along the vertical strips. That model includes the effect of bacterial activity and the factors, such as the availability of necessary nutrients, that influence such activity. Importantly, the mere presence of SRB at the corroding surface is not sufficient to claim them as ‘the' causative agent as has at times been proposed.