The article about steel corrosion in Lerwick Harbour (NCE 19 October) yet again illustrates the lack of knowledge and activity surrounding this subject.
Cathodic protection using either impressed currents or sacrificial anodes is the only sensible way of controlling this corrosion problem. All marine structures use cathodic protection but at the moment most are using the anodic corrosion sites to protect the rest of the steel. Repairing holes in sheet piling or spalling areas of concrete merely moves the corrosion to an adjacent site.
Many engineers treat cathodic protection as a black art and this ignorance is leaving us with embarrassingly large holes in our sheet piles and reinforced structures.
Ideally, cathodic protection should be installed on every marine structure during initial construction. The additional cost is minimal and could easily be offset by reducing sheet pile thicknesses (designed to corrode) or concrete cover/ quality (designed to protect).
John Drewitt, Concrete Repairs, Cathite House, 23a Willow Lane, Micham, Surrey, CR4 4TU