MIC is not “a single type of corrosion”. It’s a situation where microorganisms (usually living in biofilms) change local conditions at the metal surface—oxygen, pH, redox, metabolites, deposits—so corrosion becomes more likely, more localized, or harder to predict.

That’s why many failures labelled “MIC” are only confirmed when multiple observations point in the same direction.

What biofilms do to metal surfaces

• Create micro-environments: under-deposit zones with oxygen depletion and steep gradients.
• Shift electrochemistry: different anodic/cathodic areas can form centimeters apart.
• Produce reactive metabolites: organic acids, sulfides, ammonia, oxidants, and more.
• Trap solids: deposits can keep nutrients in and inhibitors out.

Common “MIC suspicion” signals (not proof on their own)

• Localized pitting under deposits or tubercles.
• Black iron sulfide and sour odours in anaerobic systems.
• Corrosion where chemistry looks “too mild” to explain the damage alone.
• Recurring issues after cleaning if biofilm regrowth is fast.

Important: morphology and “bugs present” are rarely enough. You need a structured investigation.

A pragmatic diagnosis mindset: multiple lines of evidence

1. Corrosion evidence: pit morphology, rate estimates (coupons/ER/LPR), deposit mapping.
2. Microbiological evidence: sessile + planktonic sampling, qPCR targets, activity proxies (ATP).
3. Process evidence: flow/stagnation, oxygen ingress, temperature, nutrients, biocide performance.

When all three lines align, you can move from “possible MIC” to a defensible root-cause statement—and design mitigation that can be monitored.

How MICBUSTERS helps

We focus on measuring the microbiological processes that drive or accelerate corrosion and translating results into actionable monitoring plans—so you can validate whether your mitigation actually works over time.

Next step: see our overview on MIC: 3 easy steps to protect your assets or read how to detect MIC (sampling & standards).

FAQ

Is MIC always caused by sulfate-reducing bacteria (SRB)?

No. SRB are common in anaerobic systems, but many microbial groups can influence corrosion depending on conditions and materials.

Can I confirm MIC with a single water sample?

Usually not. MIC is often driven by sessile biofilms on surfaces; a one-off planktonic sample can miss the key organisms and activity.

Does biocide automatically solve MIC?

Not always. If biofilms persist, dosing and contact time may be insufficient, and deposits can shield microbes. Measurement and trending are essential.