Cathodic protection: introduction and recent developments

Abstract

Corrosion of metals and alloys, on which the modern world depends completely, fromelectronic components to printed circuit boards, from nuts and bolts to bridges, fromautomobiles to railway parts to boiler tubes and nuclear reactors, is a practical problem oftremendous technological significance. Corrosion leads to colossal financial losses, whichare estimated to be 3-4% of GNP of a nation, not to speak of the loss of human lives,reputation, environment, aesthetics as well as shut-down and production losses. Of thevarious preventive measures like alloying, corrosion inhibitors, protective coatings, paints,design etc. to combat corrosion, only cathodic protection can guarantee 100% protection, ifproperly designed, executed and supplemented by protective coatings.The ABC ofcorrosion, principle of cathodic protection, with special reference to the development ofaluminium based sacrificial anodes like SUPERAL (medium output) and HOPAL (highoutput) as also insoluble anode like Sintered Magnetite Anode (SMA) in the NationalMetallurgical Laboratory in India, have been included in the paper. While the technology forthe sacrificial Al-based anodes has been transferred to two parties in India, SMA developedby NML is found to be the best because of its unique properties and low cost, compared to theconventionally used insoluble anodes. A cathodic protection system has also been designedand developed by NML with SMA, which is auto-controlled and very economical.AML hasalso successfully designed and executed the cathodic protection of the old water main lines(made from bare steel) in Calcutta, using Al-based sacrificial anodes.Merits and demerits ofgalvanic system compared to impressed current system and major research institutesengaged in corrosion area are listed Pertinent references have been cited for access to theoriginal and detailed literature.