There are many ways to classify corrosion. However, in general, corrosion is divided into 3 major groups namely Wet corrosion, Dry corrosion, and biological corrosion. Wet corrosion, as the name implies, occurs only in the presence of an aqueous solution or an electrolyte. Dry corrosion or dry corrosion occurs when there is no fluid present or temperature above the dew point of the environment. Biological corrosion or biological corrosion is a specific type of wet corrosion that occurs in the presence of living organisms. sometimes wet corrosion is named as aqueous corrosion.
Wet corrosion is an electrochemical process, and electrochemical reactions are used to explain it. Wet corrosion, as the name implies, occurs only in the presence of an aqueous solution (including condensation of moisture) or electrolyte and is the most common type of corrosion.
Wet corrosion can be further categorized by the appearance of rusty metals :
a. Uniform Corrosion
b. Galvanic Corrosion
c. Crevice Corrosion
e. Intergranular Corrosion
f. Selective Dealloying
g. Erosion corrosion
h. Stress Corrosion Cracking (SCC)
Metals corrode through simultaneous oxidation and reduction reactions. The oxidation reaction generates electrons and places the ions in the solution. This reaction occurs at the corrosion anode and is therefore also called an anodic reaction. The reduction reaction consumes the electrons generated by the oxidation reaction. Reduction reactions are also called cathodic reactions; they occur in the cathode, which does not corrode.
Fe –> Fe2+ + 2e–
Cathodic reaction in the deaerated environment
2H+ + 2e– –> H2
Cathodic reaction in the aerated environment
4H+ + O2 + 4e– –> 2H2O
2Fe + 2H2O + O2 —> 2 Fe(OH)2
This wet corrosion is a serious problem in oil and gas industry. the corrosion impact such as thinning, cracking & pitting formation, appearance modification, a decrease of structural strength and embrittlement.
How to control this wet corrosion in oil and gas industry?
there are many ways to control this corrosion. we can use material like stainless steel which have corrosion resistant or we can apply a coating to prevent corrosion in the equipment. But the most frequent way is adding a corrosion inhibitor inside the equipment. After we conduct corrosion control, then we conduct corrosion monitoring to make sure the effectiveness of our recommendation.