Common types of corrosion found in the metal industry are:
Uniform corrosion: This is the most common form of corrosion and leads to general loss of material over the surface of the structure. As a result, the corroded structure could eventually lose its overall strength and failure tends to occur at the weakest cross-section.
Pitting corrosion: Unlike uniform corrosion, pitting corrosion is a localised attack occurring on random spots where the protective oxide layer breaks down. Each pit can be shallow, deep or undercut. This type of corrosion is especially common where halide ions are present in the media such as pipes used in seawater applications. The depth, size and growth rate of the pits are impossible to predict and thus failures due to pitting corrosion can occur unexpectedly or much faster than those caused by uniform corrosion.
Galvanic corrosion: This corrosion process is caused by contact between dissimilar metals. The corrosion rate depends on the position of the metals on the galvanic series and various other factors.
Crevice corrosion: When two pieces of similar or dissimilar metals are positioned next to each other by means such as fastening, pressing, screwing or stacking, there exists a small gap between them. This confined region or gap is subjected to a higher concentration of corrosive environment due to higher electro-chemical activity and hence, higher risks of uniform and pitting corrosion.
Intergranular corrosion: This type of corrosion occurs along the grain boundary of the material due to the loss of chemical stability in the alloy metallurgy.
Dealloying: This type of corrosion is caused by the attack of certain alloying elements in the metal causing them to dissolve. This leads to metallurgical instability and loss of integrity of the structure.
Environmentally induced cracking: This type of corrosion is caused by specific environment and leads to micro cracks which could grow into larger cracks causing catastrophic failure in the structure. Hydrogen-induced cracking (HIC), stress-corrosion cracking (SCC) and corrosion fatigue are common examples of environmentally induced cracking.