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Cathodic Protection

Offshore Marine

General Information on Corrosion & Cathodic Protection

Corrosion has been a problem since man began to use metals. Except for gold and a few other metals, metals do not occur as a basic element in nature. They are found primarily as oxides and sulfides in various forms. From this bonded form, the metals must be manufactured industrially under the addition of energy.

Most pure metals represent a higher energy state than they have in nature as ore. One can therefore also expect these metals to spontaneously try to return to the natural, more stable state. This is precisely what happens when corrosion occurs. In order to counter this natural process, there is an opportunity to electrochemically corrosion protect the object.

In comparison with other protection methods such as. painting, cathodic protection has many advantages. The main difference is that the protection can be applied at any time, even on old constructions that have already begun to corrode. Cathodic protection today is standard for ships, offshore facilities and gas pipelines, and constructions where no corrosion is allowed at all.

Corrosion Explained

We can tell you a few things, with over 30 years of experience we can tell you a lot.But we'll keep it simple.

Corrosion on steel in water or soil is always of electrochemical nature. This means that when the steel corrodes, an electric current flows while some chemical reactions occur.

It can also be said that the chemical reactions generate an electrical current, the corrosion current flowing out of the corrosive metal. In order for a metal to corrode, two chemical reactions, an oxidation, consisting of a metal dissolution, and a reduction of any other substance, usually oxygen or hydrogen ions, are required.

Oxidation is called anode reaction and the reduction, cathode response.

Corrosion Explained

We can tell you a few things, with over 30 years of experience we can tell you a lot.But we'll keep it simple.

Corrosion on steel in water or soil is always of electrochemical nature. This means that when the steel corrodes, an electric current flows while some chemical reactions occur.

It can also be said that the chemical reactions generate an electrical current, the corrosion current flowing out of the corrosive metal. In order for a metal to corrode, two chemical reactions, an oxidation, consisting of a metal dissolution, and a reduction of any other substance, usually oxygen or hydrogen ions, are required.

Oxidation is called anode reaction and the reduction, cathode response.

Protection Against Corrosion

If you send a current through the water, the earth or any other electrolyte to the protected object, you counteract the current exiting the object. If the current is large enough, the corrosion can be completely eliminated.

There are two different ways of obtaining cathodic protection, namely cathodic protection with sacrificial anodes, and partly cathodic protection with a pressurized current. With sacrificial anodes, two different metals are electrically connected in a common electrolyte. The barest becomes the anode and corrodes, while the noblest becomes cathodic and protected. Because the bare (anodes) corrodes and so are used, they are commonly called sacrificial anodes.

In case of a cathodic protection with pressurized current, the protection current is generated in an external source of power, the negative pole of which is connected to the object to be protected, and the plus to one or more anodes. Regardless of which of these two methods is used, the aim is the same, namely to provide the protection medium with such a low electrode potential that a resolution (oxidation, anode reaction) of its material cannot occur.

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