How do biofilms contribute to microbiologically induced corrosion?

Biofilms are deposits of biological origin that form on surfaces such as the inside walls of pipes, process vessels, storage tanks, condensers and pumps. (Corrosion in process vessels is discussed in Introduction to Managing Internal Corrosion in Process Vessels.) These deposits, commonly referred to as slime, consist of both microbes and their extracellular products. In addition, inorganics such as calcium (Ca) and magnesium (Mg) salts, as well as other organic materials, may be found in these deposits.

Biofilms form because microbes readily attach to surfaces. Microbes realize certain advantages when growing in an attached or “sessile” mode as opposed to growing “planktonically” – that is, free-floating in the bulk water. If conditions are favorable, sessile microorganisms form biofilms.

Biofilms provide a low to no oxygen environment and create conditions that harbor problematic bacteria and microorganisms, including sulfate-reducing bacteria (SRB) that promote microbiologically induced corrosion (MIC).