Corrosion of steel piling in seawater harbours

Unexpectedly high levels of corrosion of sheet and other steel piling were observed in UK harbours during the 1980s, and a phenomenon termed ‘accelerated low water corrosion’ (ALWC) caused considerable concern about the structural safety of harbour quays and facilities. This paper shows that the severity of corrosion of steel piling both in the tidal zone and in the immersion zone is correlated with the concentration of dissolved inorganic nitrogen (DIN) in the local seawater. In the lower tidal zone this is consistent with the thinning of piles associated with ALWC. Previously it has been shown that in the horizontal direction the ALWC phenomenon is associated with material variability. Models are developed to allow the prediction of expected average corrosion loss both in the immersion zone and for the lower tidal zone (the ALWC effect) as a function of DIN, water temperature and exposure period. Data are presented to show the relatively low beneficial effect of changes in steel composition. It is concluded that for long-term protection against corrosion reliance must be placed on protective and preventive measures.