Cathodic Protection to Swanson Dock West in Melbourne
EurroCorr, Nice, France, 2009
Ian Godson & Associates Pty Ltd, Australia
The Swanson Dock is Melbourne’s main container port with two wharves, Swanson Dock East and West, both approximately 1 kilometre long. Both wharves were scheduled for repair and strengthening coinciding with major port deepening project to accommodate larger vessels. Swanson Dock West was constructed in stages from 1974 to 1988, with the various ages of the berths differing in construction type and condition. Cathodic Protection (CP) based repair was selected by the Port of Melbourne and the resulting CP systems to protect the elements of this structure are the subject of this paper.
The stages of the development of the CP systems are outlined from the commencement of design and trials in 2007, installation through 2008 to commissioning in early 2009. There are 3 major CP systems in the Swanson Dock West project including:
Tidally effected beams in berths 3 & 4, utilizing internal anodes in zones to protect the tidal and atmospheric beam sections
Fender Beam Sections in berths 1 & 2, using Titanium ribbon based CP system
Water anode system of 3500 Amp to protect the tidal concrete beams and the submerged steel sheet piling and piles
The paper follows the design of the concrete CP systems for both the tidal beams and fender beams and illustrates how the trials illustrated required modifications to the design prior to large scale installation.
The water anode CP incorporates a major departure from traditional design, with the resultant system far more efficient and economical over the 30 year design life. The transformer rectifiers are rack based switch mode units placed in air conditioned control rooms at either end of the wharf (1 km apart). The T/R’s output high DC voltage, low current ( maximum 300V, 4 amp) through 2.5mm2 distribution cables (up to 600m in length) to a series of “multiplier” units adjacent to the water anodes. The multiplier converts the low current, high voltage to the required high current, low voltage ( Max 9V, 45 Amp) for the titanium cylindrical anodes. The conversion at the multiplier takes place at a set conversion ratio (approximately 25:1) allowing full control of the current from the T/R control rooms at the end of the wharves. The systems efficiency stems from the reduced losses in the distribution cabling and the high efficiency T/R and multiplier units.
The design, trials, installation and commissioning of all the CP systems are illustrated during the phases of this large project.