MIC was first identified over 100 years ago and was described mechanistically as early as 1934. Since that time, MIC has received considerable attention in power generation, oil production, chemical processing, transportation, and the pulp and paper industries. During the 1980s and continuing into the 1990s, the electric power industry, particularly the nuclear industry, has devoted increased attention to MIC and other forms of degradation that affect the reliability, and operating and maintenance costs of the balance of plant systems. The tubercles create a hydraulic resistance to cooling water flow as well as sites for additional microbial activity.
Tubercles can grow together, eventually becoming a severe impediment to cooling water flow.
Pitting is also often observed beneath tubercles as mechanical and chemical conditions are established that encourage localized corrosion effects. A wide variety of bacteria, from the aerobic acid formers to the more well known anaerobic sulfate reducing bacteria, can contribute to tuberculation and pitting of carbon steels. Rusty streaks appear on piping or tanks, often running both up and down the surfaces. As shown in the scanning electron micrograph to the right, MIC of stainless steel weld metal often produces through-wall pits as essentially all of the austenite is removed from the duplex microstructure, leaving behind a skeleton of delta ferrite. MIC of stainless steels most often produces pitting at welds, generally in the weld metal itself.