Microbiologically Induced Corrosion (MIC) and It’s Mechanism

Microbiologically Induced Corrosion (MIC) is a type of corrosion caused by the presence and activity of microorganisms, such as bacteria, archaea, algae, and fungi, on metal surfaces. These microorganisms can accelerate the corrosion process by directly or indirectly altering the chemical environment at the metal surface.

Microbiologically Induced Corrosion (MIC).

Microbiologically induced corrosion (MIC) is the corrosion induced by the living  micro-
organism. These micro‐organisms include various kinds of bacteria and algae groomed 
in services where stagnant or low flowing water is present. 

There are various kinds of organisms which have ability to survive and grow in the harsh condition like high salinity, pH from 0 to 12, and absence of oxygen. Some of these  organisms have ability to survive in the temperature range of –17^o C to 113^oC. However  MIC is most active at the ambient temperature services. Bacteria are usually classified as aerobic or anaerobic due to their ability to grow with or without the presence of oxygen. 

Most common bacteria responsible for MIC are Anaerobic bacteria, which can survive  without oxygen. Out of this group most notorious for corrosion are Sulphate Reducing Bacteria (SRB), The SRBs reduce the sulphates present in the process streams, which react  with the adjacent metal and produces the ferrous sulfides. 

This process causes the localized cavitations in the process equipment where the  reducing reaction takes place. Since there is no flow (or very little flow) the bacteria are  not carried away so their colonies thrive in the cavities. Further reduction reaction makes  these cavities grow in depths and diameter along with time. The cavities formed are  usually cup shaped pits often filled with the blackish iron sulfide. 
 
Most vulnerable equipment for the MIC are Storage tanks, untreated or sea water cooled heat exchangers, fire water and deluge system, and equipment from which the  hydro‐test water  is not drained properly.  Periodic ultrasonic scanning  should be performed  on the bottom  of low laying areas  in the equipment and piping  having process conditions favorable for the MIC. 

Most of the time, due to unfavorable locations, the MIC is not detected unless the equipment is opened for inspection. Hence the lab samples should be tested for the presence of high counts of the SRBs in order to investigate for the potential of MIC. 
 
Further details on this damage mechanism can be seen from API‐RP‐571 Para 4.3.8. 

Mechanisms of MIC:

1. Direct Attack: Certain microorganisms produce corrosive byproducts, such as organic acids, hydrogen sulfide (H2S), or ammonia, which directly attack the metal surface, leading to localized corrosion.
2. Indirect Attack: Microorganisms can also influence the corrosion process indirectly by promoting the formation of biofilms or creating conditions that favor the growth of other corrosive agents, such as sulfate-reducing bacteria (SRB) that produce H2S.

Factors Influencing MIC:

• Microbial Activity: The type and metabolic activity of microorganisms present, as well as environmental factors like temperature, pH, and nutrient availability, influence the severity of MIC.
• Metal Properties: The composition, surface roughness, and presence of protective coatings on metal surfaces affect their susceptibility to MIC.
• Environmental Conditions: Conditions such as moisture, oxygen availability, and the presence of organic or inorganic compounds in the environment can influence microbial growth and corrosion rates.

Detection and Prevention:

• Monitoring: Regular inspection and monitoring of metal surfaces for signs of microbial growth, such as biofilm formation or localized corrosion, can help detect MIC early.
• Microbiological Testing: Techniques such as microbial culture, DNA analysis, and microscopy can be used to identify and characterize the microorganisms present.
• Control Measures: Prevention and control strategies include biocide treatment, use of corrosion inhibitors, optimization of environmental conditions, and proper design and maintenance practices to minimize microbial attachment and growth.

Importance in Industry:

• MIC poses significant challenges in various industries, including oil and gas, marine, water treatment, and infrastructure, where metal structures are exposed to diverse environments conducive to microbial growth.
• It can lead to costly repairs, equipment failure, and safety hazards if not properly managed, making it a focus area for corrosion control and asset integrity management programs.

Case Study:

In an offshore oil production platform, MIC was identified as a significant issue affecting the integrity of pipelines and storage tanks. Microorganisms present in the seawater produced corrosive byproducts, leading to localized corrosion and pitting in carbon steel components.

Impact: MIC resulted in premature failure of pipelines and storage tanks, leading to costly repairs, production downtime, and environmental risks due to oil spills. Implementing proactive monitoring and mitigation strategies, such as biocide treatment and corrosion-resistant coatings, helped mitigate the impact of MIC and improve asset integrity.

Detection Methods:

1. Microbial Culture: This traditional method involves collecting samples from the affected surfaces or environments and culturing them in suitable growth media. Microbial colonies are then identified and characterized based on their morphological, biochemical, and physiological properties.
2. DNA Analysis: Molecular techniques, such as polymerase chain reaction (PCR) and next-generation sequencing (NGS), can be used to analyze microbial DNA extracted from environmental samples. These methods provide rapid and accurate identification of microbial species present, allowing for targeted control measures.
3. Microscopy: Microscopic examination of samples using techniques like scanning electron microscopy (SEM) or fluorescence microscopy can reveal the presence and morphology of microorganisms, as well as the formation of biofilms on metal surfaces.

Control Measures:

1. Biocide Treatment: Chemical biocides, such as chlorine, ozone, or quaternary ammonium compounds, can be applied to water systems or affected surfaces to inhibit microbial growth and activity. Biocide dosing systems and monitoring protocols are used to ensure effective control while minimizing environmental impact.
2. Corrosion Inhibitors: Corrosion inhibitors are chemicals that can be added to water systems or applied to metal surfaces to inhibit corrosion caused by microbial activity. These inhibitors form a protective film on metal surfaces, reducing the rate of corrosion and extending equipment lifespan.
3. pH Adjustment: Manipulating the pH of water systems can affect microbial growth and activity. Maintaining alkaline conditions (pH > 9) using additives like lime or sodium hydroxide can suppress microbial proliferation and mitigate MIC in certain environments.
4. Biofilm Disruption: Mechanical methods, such as high-pressure water jetting or brushing, can be used to physically remove biofilms from metal surfaces. Chemical agents, such as enzymes or surfactants, can also be employed to disrupt biofilm formation and enhance biocide efficacy.
5. Cathodic Protection: Cathodic protection systems, such as sacrificial anode or impressed current systems, can be installed to protect metal structures from corrosion, including MIC. By imposing a negative potential on the metal surface, cathodic protection prevents the initiation and propagation of corrosion.
6. Non-Metallic Materials: Substituting metal components with non-metallic materials, such as fiberglass-reinforced polymers (FRP) or high-density polyethylene (HDPE), can eliminate the risk of MIC altogether. Non-metallic materials are inherently resistant to microbial degradation and offer long-term corrosion protection.

Recent Advancements and Ongoing Research.

Discussing recent advancements and ongoing research in the field of Microbiologically Induced Corrosion (MIC) can provide readers with insights into emerging trends, innovative technologies, and potential solutions for addressing MIC-related challenges. Here are some recent developments worth mentioning:

1. Advanced Microbial Analysis Techniques:

Recent advancements in microbial analysis techniques, such as metagenomics, metatranscriptomics, and metaproteomics, have enabled researchers to study microbial communities in greater detail. These high-throughput sequencing and omics-based approaches allow for comprehensive profiling of microbial populations and their metabolic activities in corrosion environments.

2. Biofilm Engineering and Control:

Research efforts are focused on understanding the formation, structure, and dynamics of biofilms on metal surfaces. Novel biofilm engineering strategies, including biofilm dispersal agents, quorum sensing inhibitors, and biofilm-resistant coatings, are being explored to prevent or mitigate biofilm formation and reduce MIC susceptibility.

3. Microbial Corrosion Mechanisms:

Advances in molecular microbiology and corrosion science have led to a deeper understanding of microbial corrosion mechanisms. Studies elucidating the metabolic pathways, enzymatic activities, and molecular interactions involved in MIC provide valuable insights into the underlying processes and potential targets for intervention.

4. Antimicrobial Materials and Surfaces:

Researchers are developing antimicrobial materials and surface treatments to inhibit microbial colonization and activity on metal surfaces. Nanotechnology-based approaches, such as antimicrobial nanoparticles and surface coatings containing antimicrobial agents, show promise for preventing MIC and extending the lifespan of metal components in corrosive environments.

5. Integrated Corrosion Management Strategies:

There is growing recognition of the need for integrated corrosion management strategies that combine microbiological control measures with traditional corrosion mitigation techniques. Holistic approaches, incorporating monitoring, modeling, predictive analytics, and decision support systems, are being developed to optimize corrosion prevention and maintenance practices.

In summary, Microbiologically Induced Corrosion (MIC) is a complex form of corrosion influenced by the presence and activity of microorganisms, which can significantly impact the integrity and lifespan of metal structures. Understanding its mechanisms, factors influencing its occurrence, and implementing effective detection and prevention strategies are essential for mitigating its adverse effects in industrial applications.