The key points from this module are as follows:
Corrosion is the deterioration of materials in presence of a chemical environment leading to a loss in their function.
The thermodynamics of corrosion involves the following:
Corrosion of metals and alloys involves oxidation from their metallic states.
Metallic corrosion must at least have two partial reactions.
There are several forms of corrosion but the most common are as follows:
The difference between chemical and electrochemical reactions to corrosion is that the chemical reaction is a functional temperature, pressure, and activity of the species while the rate of the electrochemical reaction is a functional temperature, pressure, activity, and potential.
There are two types of anodes, namely;
Sacrificial Anode: They are created from a metal alloy with a more negative electrochemical potential than the other metal it will be used to protect.
Impressed Current Anode: It uses electrical support in the form of a controlled amount of direct current connection between the anode and the structure.
How to interpret pipe-to-soil potential in relation to corrosion potential of a pipeline:
If it is cathodically protected, the potential has to be low (more negative).
If not, it should be more (relatively positive).
Aqueous corrosion is electrochemical in nature.
Corrosion rate can be suppressed by polarizing towards negative potential. Polarization can be done through impressed current or sacrificial anode.
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