MIC explained without the jargon
What is microbiologically influenced corrosion (MIC)?
MIC is corrosion that is caused or accelerated by microorganisms living on or near a material surface. It can create severe, highly localised damage even when the rest of an asset appears to be in good condition.
No laboratory data required for a first conversation. Tell us what you are seeing and where it occurs.
The basic idea
MIC is not a special type of rust. It is an influence on the corrosion process.
Microorganisms are present almost everywhere. Most are harmless, and some biofilms may even have a protective effect. A problem develops when the local microbial community and the surrounding conditions together speed up damaging electrochemical reactions.
The microorganisms do not have to “eat the steel”. They can remove or supply chemicals, produce acids or sulfides, move electrons, trap deposits and create different conditions underneath a biofilm. The result may be a small but aggressive corrosion cell on the surface.
MIC in three easy steps
How can microscopic organisms damage a large industrial asset?
The exact mechanism differs between systems, but the practical sequence is usually easy to understand.
Microorganisms settle on a surface
Where water and nutrients are available, microorganisms can attach to metal, coatings, concrete or deposits.
A biofilm changes the local environment
The thin microbial layer can create differences in oxygen, acidity, salts, sulfides and other chemicals over just a few millimetres.
Corrosion becomes concentrated
Local electrochemical reactions may accelerate, causing pitting, under-deposit corrosion, coating damage or unexpected material loss.
When to investigate
Common warning signs of MIC
None of these signs proves MIC on its own. They are reasons to collect better evidence before selecting a treatment.
Deep or irregular pitting
Localised pits appear while nearby surfaces show much less wall loss, or damage progresses faster than the general corrosion rate suggests.
Damage beneath deposits or slime
Corrosion is found below sludge, tubercles, black deposits, scale, sediment or a visible biofilm.
Problems in low-flow areas
Dead legs, tank bottoms, stagnant branches, intermittently operated lines and shielded areas provide time for biofilms and deposits to develop.
Recurring corrosion despite treatment
Damage continues after biocide, inhibitor, cleaning or coating measures, suggesting that the treatment is not reaching or controlling the actual process.
Typical environments
Where can microbiologically influenced corrosion occur?
MIC can develop wherever a susceptible material, moisture, microorganisms and suitable operating conditions come together.
Oil and gas systems
Production water, gathering lines, injection water, pipelines, separators, tanks, pig debris and water-wet sections.
Marine and offshore assets
Vessels, ballast systems, offshore structures, monopiles, closed compartments, seawater systems and splash-zone interfaces.
Cooling and process water
Cooling towers, heat exchangers, recirculating water systems, dead legs, filters and low-flow process equipment.
Tanks and storage
Tank bottoms, buried tanks, fuel-water interfaces, sediment layers and areas where water can collect unnoticed.
Water and wastewater
Pipelines, pumps, sewer systems, treatment equipment and concrete structures exposed to microbial sulfur cycling.
Other industrial systems
Pulp and paper, food processing, mining, geothermal installations, infrastructure and other water-contact assets.
From suspicion to evidence
How do you confirm whether MIC is contributing to corrosion?
A strong MIC assessment uses multiple lines of evidence. The goal is not simply to find microorganisms, but to determine whether the available evidence supports a biologically influenced corrosion process.
1. Microbiology
Which microbial groups and functional processes are present, where are they located, and how do they change over time or after treatment?
2. Material and corrosion products
What does the damage look like, what materials are affected, and what do deposits, scales and corrosion products reveal?
3. Chemical environment
Do pH, oxygen, sulfide, nutrients, salts and available electron donors or acceptors support the suspected process?
4. Operating conditions
Do flow, temperature, pressure, water behaviour, shutdowns, dead legs, cleaning and chemical treatment explain where and when the damage occurs?
A practical workflow
How MICBUSTERS helps you measure the biological part of the problem
MICBUSTERS uses targeted qPCR to detect and quantify genetic markers associated with MIC-relevant microorganisms and processes. The data become most useful when they are collected from the right location and interpreted alongside the other lines of evidence.
Sample where the process happens
Collect representative water, biofilm, deposit, corrosion product, swab or pig-debris samples. Good sampling is essential because MIC is often highly localised.
Measure relevant microbial targets
Use qPCR to rapidly quantify selected microbial groups or functional biomarkers rather than relying only on broad total counts.
Translate results into decisions
Compare sites, establish trends, investigate failures and verify whether cleaning, biocide or other mitigation changes the microbial signal.
Move from a delayed laboratory snapshot to faster field information
The MICBUSTERS workflow is designed for industrial samples and practical use at or near the sampling location. It helps teams preserve the sample, prepare DNA and perform targeted qPCR without a conventional molecular laboratory.
Control starts with diagnosis
How can MIC be controlled?
There is no universal “MIC chemical”. Effective control depends on the asset, material, water chemistry, biofilm location, operating conditions and the microbial processes involved.
- Remove or disrupt biofilm and deposits through suitable cleaning or pigging.
- Use biocides or other chemical treatments with an appropriate dose, contact time and verification plan.
- Reduce stagnant zones, water accumulation, oxygen ingress or nutrient availability where practical.
- Review coatings, materials, cathodic protection and design details that can create shielded areas.
- Trend microbiology and corrosion indicators to confirm that the control measure continues to work.
Frequently asked questions
Questions about microbiologically influenced corrosion
What does MIC stand for?
MIC stands for microbiologically influenced corrosion. The term describes corrosion in which microorganisms influence, accelerate or help sustain the deterioration process.
Does the presence of bacteria prove that corrosion is MIC?
No. Microorganisms are common in water and industrial systems. A MIC diagnosis should combine microbiological data with the corrosion morphology, material and corrosion products, local chemistry and operating history.
Can MIC occur without visible slime?
Yes. A biofilm can be thin, patchy or hidden beneath deposits and corrosion products. Visual inspection alone can therefore miss the biological part of the process.
Is MIC always caused by sulfate-reducing bacteria?
No. Sulfate-reducing microorganisms are important in many systems, but MIC can involve several microbial groups and interacting processes, including methanogenesis, acid production, sulfur oxidation, iron cycling and extracellular electron transfer.
What samples can be used for MIC testing?
Depending on the question, useful samples may include water, swabs, biofilms, deposits, corrosion products, pig debris, sludge or material removed from a pit. Samples collected close to the affected surface are often more informative than bulk water alone.
How quickly can qPCR provide MIC-related information?
With a prepared field workflow, targeted qPCR results can typically be generated in approximately two hours. Total project time depends on access, sampling, the number of targets and the required interpretation.
Take the next step
Unsure whether MIC could be involved?
Share the asset type, medium, material and what you are observing. A MICBUSTERS specialist can help you identify the most useful first samples and avoid an unnecessarily broad investigation.
Request a first MIC risk check
For the best first response, include the asset, material, fluid and observed damage or operational problem.
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