Sheet-pile corrosion rates within an existing outfall channel in Dublin Port

A new cooling water intake channel structure is being constructed as part of the Dublin Waste to Energy (DWtE) facility in Ringsend. This has required the extraction of old sheet-piles that had been in place for over 50 years.... [ view full abstract ]

A new cooling water intake channel structure is being constructed as part of the Dublin Waste to Energy (DWtE) facility in Ringsend. This has required the extraction of old sheet-piles that had been in place for over 50 years. These sheet-piles formed part of an existing power station cooling water outfall channel. Extraction of the sheet-piles has allowed the loss in steel thickness to be measured over their full length and for average corrosion rates to be established. The age and type of the existing sheet-piles were determined by carrying out a detailed desk study. The average corrosion rates were found to give a good match with the general corrosion rates in the relevant Irish Standard (IS EN 1993-5:2007). The authors are not aware of any published data on corrosion rates for Irish coastal waters, so this case study provides useful data for the particular conditions present which include elevated water temperature and chlorine levels in the cooling water discharge. The effect of different flow conditions on corrosion rates could also be observed, with some sheet-piles being in the direct line of high velocity turbulent flow and other sheet-piles in more benign conditions. The Irish Standards and the relevant British Standard for Maritime Works, BS 6349-1-4:2013, differ in relation to their requirements for concentrated corrosion, sometimes referred to as Accelerated Low Water Corrosion (ALWC). In the absence of site-specific information, the rates of concentrated corrosion given in BS 6349-1-4:2013 are very onerous when compared to the general corrosion rates, and therefore the economic benefits of taking site measurements can be considerable.