Cathodic and Anodic Protection

THOMAS THANGADURAI K

PAVOORCHATRAM-627808

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Definition “The reduction or prevention of corrosion by making metallic

structure as cathode in the electrolytic cell is called cathodic protection”

Since there will not be any anodic area on the metal, corrosion does not occur.

There are two methods of applying cathodic protection to metallic structure.(i) Sacrificial anodic protection (galvanic protection) (ii) Impressed current cathodic protection

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Sacrificial anodic protection method In this method, Metallic structure is connected to more anodic

metal. Hence the corrosion is concentrated at the active metal only. And the active metal gets corroded slowly. The parent structure (cathodic part) is thus protected. The more active metal so employed is called sacrificial anode. Sacrificial anodes are commonly as Mg, Zn, Al and their alloys.

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Protection of underground pipeline witha magnesium anode

Applications of sacrificial method• Protection of buried pipelines.• Underground cables.• Marine structures.• Ship hulls.• Water tanks.• Pipes.

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Cathodic protection of a domestic hot water tank using a sacrificial anode.

Impressed current cathodic protection method The sufficient D.C current is given to underground tank. The negative terminal is connected to tank. And the positive terminal is connected to inert anode. When the power supply is ON, it converts corroding metal from

anode to cathode. Hence the corrosion can be prevented.

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Cathodic protection of an underground tank using impressed currents

Applications of impressed current method• it is useful for large structures• Applied to open water box coolers• Water tanks• Buried water and oil pipelines• Condensers• Transmission line towers.

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Stray currents resulting from cathodic protection

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Anodic protection (AP) is a technique to control the corrosion of a metal surface by making it the anode of an electrochemical cell and controlling the electrode potential in a zone where the metal is passive.

The application of anodic current to the structure decrease the rate of hydrogen evolution. To anodically protect the structure, potentiostat is required. Potentiostat is an electronic device that maintains a metal at a

constant potential. The use of potentiostat is to shift corrosion potential into passive

potential so that the corrosion of the metal is stopped. The potential range depends upon the relationship between the

metal and the environment.

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Applications of anodic protection Applicable in extremely corrosive environments. Low current requirement. Acid coolers in dilute sulphuric acid plants. Storage tanks for sulphuric tanks Chromium in contact with hydrofluoric acid.

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THANK YOU

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