In 1824, Sir Humpry Davy, in a series of papers presented to the Royal Society of London, first described the cathodic protection design. Davy found that he could preserve copper in sea water by the attachment of small quantities of iron or zinc; for Davy the copper became “cathodically protected”. The first noted application of cathodic protection was to the HMS Samarang.
In 1834, Michael Faraday, the one who assisted Davy on his experiments, discovered the quantitative connection between corrosion weight loss and electric current and thus laid foundation to the modern application of cathodic protection. After Faraday’s discovery, other series of experiments was conducted such as those of Thomas Edison in 1890.
Cathodic protection principle is in connecting outside anode to the metal for protection and electricity is passed in order that the surface of the metal is cathodic therefore preventing corrosion. A sound cathodic protection design involves half cell (a structure that contains a conductive electrode and a surrounding conductive electrolyte) with test point all over the protected area.
There are two ways in achieving cathodic protection. It is either by using galvanic anodes (also called sacrificial anodes) or by using “impressed current”. Cathodic protection using galvanic anode systems uses reactive metals as secondary anodes and they are directly connected electrically to the steel to be protected. Commonly used metals as sacrificial anodes are aluminum, magnesium and zinc. They are alloyed metals are used and they are used to improve lasting performance and dissolution characteristics. Cathodic protection using impressed-current systems uses inactive anodes and uses an external source of dc power to impress a current from an external anode onto the cathode surface.
“Cathodic protection design which involves a half cell with test point all over the protected area can be used to prevent corrosion”
