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Cathodic Protection Survey of Underwater Hull

Published: 23 March 2017
steel yacht
Cathodics protection and corrorion survey

Cathodic protection is a technique used to control the corrosion of a metal surface that it is in electrical contact with. It comes in two forms Impressed Current Cathodic Protection (ICCP) and Sacrificial. ICCP uses an external power source to supply an electrical current, whereas a sacrificial system uses galvanic anodes to sacrifice themselves in order to protect the yacht or structure.

We can verify that the CP system is providing enough current by measuring the potential of the yacht or structure against a standard reference electrode (in sea water this is usually a silver / silver chloride reference cell). Current flow on to a metal surface depresses the potential in a negative direction and if enough current is received, corrosion is essentially prevented at potentials more negative than -800 mV (For a correctly designed CP system the potential will be in the range -900 to -1050 mV).

nC² recently undertook a cathodic protection and corrosion survey of a steel yacht moored in a Guernsey marina. During recent refits it was noted that blistering was occurring on the coating of the underwater hull. nC² was invited to attend the yacht to assess the cathodic protection levels and to determine whether the cathodic protection system or the electrical systems on board were the cause of the blistering. Potential results obtained suggest that the vessel was well protected and was not being affected by any of the electrical systems. This implied that the electrical or cathodic protection systems were not the cause of the blistering.

nC² engineers are able to carry out cathodic protection surveys on ships, yachts and marine structures. Please contact us for more information.

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