Broadly speaking, industrial coatings used in water-immersion conditions fail due to the following: Osmotic Blistering, Microbially Induced Corrosion (MIC), and Poor Surface Preparation and Application. In our previous blog post, we explored Osmotic Blistering as a common cause of coating failure in water-immersion conditions. This blog post explains how microbiologically influenced corrosion impacts the protective coating, how microbiological corrosion can be avoided, and what are the inspection techniques to identify the problem. Causes of Microbially Induced Corrosion (MIC) Known also as microbial corrosion or microbiologically influenced corrosion, MIC is corrosion caused or accelerated by microorganisms and can lead to the deterioration of both coatings and underlying substrates. Broadly, these bacteria can be aerobic bacteria (requires oxygen) or anaerobic (do not require oxygen) in nature, including sulfate-reducing bacteria (SRB), iron-oxidizing, and manganese-oxidizing bacteria. Often these organisms themselves do not consume metallic substances but instead can create aggressive environments where highly localized rapid corrosion processes can occur, leading to severe degradation in a short amount of time. The corrosion reactions commonly associated with microbiologically influenced corrosion on carbon steel are pitting corrosion and crevice corrosion, while stainless steels also suffer from stress corrosion cracking from microbial corrosion. Effects of Microbially Influenced Corrosion on Coatings The effects of microbial corrosion on polymeric coatings and composites can manifest in a range of ways. Standard, immersion-grade polymeric coatings often can not handle the localized pH reductions associated with biofilm formation. Waste products for microbes range depending on the organism but commonly include organic acids and alcohols, two very aggressive exposure conditions for most polymers. Coating failures due to waste excretion from microorganisms often look like isolated areas of chemical attack, generally located in corners, low-flow areas, and at coating pin-holes. Another way microbiologically influenced corrosion can create failures on stainless steel coatings is when anaerobic organisms are trapped behind the coating, in contact with metal. These organisms will degrade the metal, even without oxygen present, and cause localized delaminations from corrosion of the base metal. Substrates that have been exposed to microorganisms should receive a chemical treatment with bleach, peroxides, or other disinfectants to ensure the organisms do not get trapped behind the coating system. Deep pitting and degradation of a tubesheet where copper/nickel tubes meet a steel tubesheet. Degradation of the concrete in a raw sewage storage tank. MIC is very common in wastewater plants because of the high bacteria levels. Deep pitting on the cone section at the bottom of a tank that is commonly associated with MIC. Produced through-wall failures along the weld seam. Severe MIC pitting on a large water pump after grit blasting. Prevention and Remediation of Microbiologically Influenced Corrosion Unfortunately, the presence of microorganisms causing microbial corrosion cannot be eliminated from most industrial processes, rather the corresponding corrosion process has to be controlled. Three solutions for corrosion reduction in an industrial setting The first solution involves killing the iron-oxidizing bacteria causing the degradation and bacterial corrosion. For this solution, an assay to determine the exact nature of the microorganism must be carried out, then an appropriate, commercially available biocide is chosen. Continuous injection of this biocide should reduce the influence of microbiologically influenced corrosion; however, this requires a process modification including new tanks, injection ports, etc. The second solution is to eliminate any contact of the bacteria with the metallic substrate using an appropriate immersion-grade coating system. This is an excellent option if the degradation of the substrate is not severe, and the system can be taken offline and drained. It is critical to ensure any polymeric coating used in an active microbiologically influenced corrosion environment is not susceptible to degradation from the waste products created by these microorganisms and does not trap anaerobic bacteria behind the barrier materials. The third widely-used solution is to rebuild or reinforce the substrate with a non-metallic repair option that is not susceptible to microbial corrosion. Carbon-fiber-reinforced polymers A composite material, like carbon-fiber-reinforced polymers, can be used to rebuild the structural strength of severely corroded substrates or to repair through-wall failures. Pipes affected by microbiologically influenced corrosion can often be repaired externally by creating a structurally-independent pipe around your existing piping system, eliminating the need for internal access. Compliance with industry standards The creation of a comprehensive standard for Non-Metallic Repairs of Pressurized Systems, ASME PCC-2 (2015) Article 4.1, “Non-metallic Composite Repair Systems: High-Risk Applications”, has helped regulate the composite repair options and ensure the quality of systems engineered and tested to comply with this standard. How Advanced FRP Systems Can Help There are many reasons why coatings and the underlying substrate can fail in water-immersion conditions. Asset owners and maintenance staff should rely on a robust inspection program to proactively identify issues associated with microbiologically influenced corrosion and ensure the condition of their protective coatings. Long-term, maintenance-free repair options available If your facility is experiencing a high corrosion rate from microbially induced corrosion, there are a number of long-term, maintenance-free repairs or remediation options available. The best option will depend on the specifics of your process and the extent of the microbiologically influenced corrosion damage. Expert assistance with microbiologically influenced corrosion Advanced FRP Systems provides expert assistance in coatings assessments, thorough inspections, coating failure analyses, and detailed installation specifications. We work with many industries, including the nuclear power generation industry, water treatment industry, gas industry, and others. We do not believe in a “one-size-fits-all” approach to solving microbiologically influenced corrosion problems. Our team will work with your staff to identify the underlying causes and help formulate appropriate corrective actions to fit your process, timeframe, and budget. Reach out to corrosion engineers at Advanced FRP Systems and schedule a free consultation.