Biological Corrosion Characteristics
Biological corrosion is the process of destruction of metals under the influence of living organisms (algae, bacteria, fungus). Therefore, microorganisms which live in the soil or in the air can significantly affect the corrosion processes.
Despite the fact that the biological corrosion can be considered a separate type of metal corrosion, it still conjugates with other kinds of the soil, sea and atmospheric corrosion. It is also true that the metal objects of the gas and oil industry are the most vulnerable to this type of corrosion. Speaking about the classification of the biological metal destruction, it is worth mentioning several subtypes that are listed
electromechanical process of destruction;
chemical corrosion attack;
direct destruction under the influence of microorganisms;
complex destruction (influence of all of the environmental factors).
Metal products are often used by the microorganisms as the feeding environment as well as the place for the allocation of their waste products (alkali, mineral and organic acids which enhance the corrosion environment aggressiveness). Some kinds of fungi, provoking the biological corrosion of the plane aluminum cans, could develop even in the aviation fuel. There is also thione mycobacteria which through the process of acid secretion significantly reduces soil acidity, thus, speeding up the process of metal corrosion.
There are two types of microorganisms:
aerobic – can harm metal products only in the presence of oxygen;
anaerobic – can harm metal products even in the absence of oxygen.
The bacteria that are the most dangerous to metal products are iron bacteria and sulfur bacteria which live in the soil.
Such microorganisms can adapt to various environmental conditions and are characterized by fast reproduction capabilities under the temperatures from 5 to 40 degrees Celsius.
Harm that can be caused to metal products by the biological corrosion can be more than 70 percent. Pipelines and gas pipelines, sea vessels and products made of metal such as steel, zinc and magnesium are also under the risk.
Copper, lead and nickel are more resistant to such kind of metal corrosion.