What Does Biologically Induced Corrosion Mean?
The term "biological" is mostly used in the context of living things, and this type of metal corrosion is due to interaction of bacteria with metals and metal alloys. The term "induce" means that the microorganisms are not primarily the causatives agents of corrosion. Their presence on the metal surface leads to corrosion. It is through this interaction that the microorganisms increase the corrosion rates. These microorganisms release waste products from their metabolic processes. As the waste product is being broken down, it releases a substance that causes corrosion in the form of pitting on the metal surface.
Corrosionpedia Explains Biologically Induced Corrosion
Biologically induced corrosion is mainly caused by microorganisms that form colonies called biofilms. The biofilms attach themselves to the metal surface through weak intermolecular forces, known as Van der Waal forces. The microfilms are sessile, meaning they are anchored to the metal surface by a matrix they secrete. The matrix provides good adhesion for bacteria and provides a communication link to attract other bacteria so that they may colonize the whole surface.
The strength of any colony will attract any passing bacteria. Once the microfilm is established, it may contain millions of cells overlapped in many layers. As a result, the surface will be completely encased by the layer of microfilms. Efforts to spray them with antibiotics and other chemical poisons are fruitless since the layer is impervious.
The colony continues to grow, and once it has matured, part may detach itself and move to another surface where it establishes another colony. These bacteria can establish themselves on any type of material, making it impossible to eliminate them completely. When the cells in the colonies metabolize, gases and waste products are released. Depending on the acidity of the waste products, this can cause pitting on the surface of the metal. This type of corrosion is mostly evident in pipes.