API 571 Certification (Corrosion & Materials) Practice Test

Which materials are most susceptible to microbiologically influenced corrosion (MIC)?

1. Only nickel-based alloys

2. High-strength steels

3. Carbon steels and aluminum alloys

4. All ferrous and non-ferrous alloys

The correct answer is: Carbon steels and aluminum alloys

Microbiologically influenced corrosion (MIC) is a phenomenon where microorganisms, such as bacteria, fungi, and algae, contribute to the corrosion of materials. Carbon steels and aluminum alloys are particularly susceptible to MIC due to their composition and galvanic characteristics when in contact with the right environmental conditions, such as moisture, nutrients, and a conducive pH level. Carbon steels, being relatively reactive materials, can easily interact with microbial activity, especially in environments where anaerobic bacteria thrive, leading to localized corrosion such as pitting or sulfidic corrosion. Aluminum alloys, while generally more resistant to corrosion due to the protective oxide layer they form, can also be affected under certain conditions, particularly when the oxide layer is compromised or in a conducive environment for microbial activity. The other options do not accurately capture the full range of materials that are most susceptible to MIC. While nickel-based alloys and high-strength steels can experience corrosion, they tend to have better resistance against MIC due to their inherent properties and corrosion-resistant features. The option stating "all ferrous and non-ferrous alloys" is overly broad as not all materials in these categories are uniformly susceptible to MIC; many are engineered to resist microbial-induced corrosion effectively.