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I have been trying to understand how does the DC current contirbute to the Cathodic Protection,but it doesn't seem very clear to me. I know that its a way to protect pipelines from corroding and that there are anodes and cathodes. By some means when a DC source is there connected and Dc current flows the corrosion is prevented.

I don't quite understand because many of the explanaitions involve complicated answers and deep anaylsis.

user3052793
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  • One of the metals is more electro-negative than the other. There is a nett imbalance of EMF if they share the same electrolyte. The more 'reactive' metal will corrode while the other will try to have free ions plated onto it, if these are gas or reactive species then they will not plate but will bubble up or go back into solution. – KalleMP Sep 07 '15 at 11:48
  • I would say that the important thing is the DC voltage, not the DC current. The voltage prevents corrosion, the current is an inevitable side effect of applying a voltage. – Steve Byrnes Sep 17 '15 at 18:54

2 Answers2

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simply by making your metal acting like a cathode in a battery reaction. Corrosion is the result of presence of oxidizing agent (O2, Fe2...etc).
Use these oxidizing agent in Redox reaction, in presence of current what we call impressed current method, will help to neutralize the oxidizing agent and protect your metal from corrosion.

R Djorane
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First let's examine what corrosion is. "In the most common use of the word, this means electrochemical oxidation of metal in reaction with an oxidant such as oxygen. Rusting, the formation of iron oxides, is a well-known example of electrochemical corrosion." from wiki

Keeping it simple, when you put a DC charge across the cathode and anode you are polarizing the cathode thereby making it a more negative. Since there are more electrons at the cathode it will push the electrochemical process so that it protects the cathode from corroding and induces the anode to corrode in its place. The net electochemical pressure maintained by the DC current will push the oxidation reaction to take place at the sacrificial anode. The positive ions for ex. H+ will move to the cathode and the negative ions will move towards the anode. If all is working as planned the 2H+ + 2 electrons will bubble off at the cathode as H2 gas protecting the cathode and the Oxygen neg ion will Oxidize the Anode (the more reactive metal). The DC current insures this is the preferred Oxidation reaction. Keeping in mind both of the metals of the cathode or anode could have been oxidized overtime as is the case in a pipeline. The net is the DC current is a balancer or (EM)force to insure the intended metal is sacrificed.

StarDrop9
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