API 571 Certification (Corrosion & Materials) Practice Test

Microbial-induced corrosion (MIC) is a type of corrosion that is caused by the metabolic activity of microorganisms, such as bacteria and fungi, on metal surfaces. One well-documented source of MIC is sulfate-reducing bacteria (SRB). These bacteria thrive in anaerobic (low oxygen) environments, such as those found in pipelines and tanks that contain organic materials or stagnant water.

SRBs play a significant role in the corrosion process by reducing sulfate ions to sulfide, which can lead to the formation of pits and localized corrosion on metal surfaces. The presence of these bacteria accelerates the degradation of metals, particularly in environments like oilfields, wetlands, and waste-water treatment plants, where conditions are favorable for their growth.

The other options, while they may contribute to corrosion in general, are not direct biological factors that lead to MIC. Sulfuric acid is a strong acid that causes corrosion through chemical means rather than biological ones, chloride ions are typically associated with stress corrosion cracking but do not specifically induce corrosion through microbial activity, and oxidizing agents can promote corrosion through chemical reactions but do not represent microbial processes. Hence, sulfate-reducing bacteria stand out as a typical source of MIC due to their specific role in the biological degradation of metals