Failure Investigation on water pipeline: corrosion by ferrobacteria
When one thinks of corrosion in a water pipe, it is natural to imagine aggressive agents, inadequate materials, or extreme operating conditions. It is almost never imagined that the origin of the damage could be a microscopic living organism, capable by itself of compromising the functionality of an entire system.
Yet that is exactly what emerged from the analysis of this failure investigation: a serious leak in a water pipe, caused not by a material defect, but by a silent and often underestimated phenomenon: microbiological corrosion by ferrobacteria.
The object
A comparative Failure Investigation was performed on a water pipeline in TEC Eurolab’s Materials Analysis Center. Two sections of pipeline were analyzed:
- One with extensive and deep corrosion (KO sample),
- The other with limited corrosion (sample OK).
TEC Eurolab’s approach
Within the Materials Analysis Center of TEC Eurolab metallographic and chemical-physical analyses were performed for material characterization.
The results show that both specimens are made of the same extra mild steel for structural uses, supplied in the raw state from rolling, with a homogeneous ferritic-pearlitic microstructure, free of discontinuities or metallurgical anomalies.
The material is found to be compliant, intact and suitable. The problem, therefore, lies elsewhere.
Visual analysis, micrographs, and fractographic analysis showed:
- Generalized and intense corrosion,
- Soft and muddy corrosion products, with coloration varying between brown, yellow, and rust,
- Morphologies typical of an accelerated and continuous process,
- Absence of localized patterns consistent with galvanic corrosion or traditional pitting.
Laboratory analysis excludes electrochemical corrosion phenomena. Instead, the phenomenon is attributable to microbiologically induced corrosion (MIC).
What is Microorganism Influenced Corrosion (MIC)?
MIC is an electrochemical phenomenon in which the presence of microorganisms: triggers, facilitates, and accelerates corrosion reactions.
It is typical of wet or watery environments: pipelines, wells, reservoirs, underground and marine systems.
Many microorganisms can generate MIC (bacteria, fungi, diatom algae), but in industrial pipelines the most common players are iron-oxidizing bacteria, better known as ferrobacteria.
Ferrobacteria: the “natural chemists” that live in water
Ferrobacteria are aerobic microorganisms that derive their energy from the oxidation of dissolved iron in water. Their metabolism is as simple as it is devastating:
Fe²⁺ → Fe³⁺ + ferritic hydroxides
The water in the pipeline naturally contains oxygen: this results in minimal oxidation of metallic iron, producing Fe²⁺ ions.
These ions become the biological fuel of ferrobacteria.
Once active, the bacteria enzymatically oxidize Fe²⁺ to Fe³⁺ and produce abundant amounts of ferric hydroxide, a gelatinous deposit that accumulates on the inner wall forming a thick, adherent biofilm.
This biofilm:
- Traps oxygen and corrosive ions,
- generates differentiated microenvironments (micro-anoxia and differential aeration),
- Locally lowers the pH,
- creates potential differences between neighboring areas (galvanic cells),
- Accelerates the solubilization of metallic iron.
The result? An extremely corrosive environment, 10-100 times more aggressive than normal aqueous corrosion.
The vicious cycle of microbiological corrosion
This corrosion dynamic is self-powered:
- The tube corrodes → releases Fe²⁺.
- Ferrobacteria consume Fe²⁺ → proliferate.
- The bacterial colony produces biofilm.
- Biofilm increases corrosion.
- The corrosion releases additional Fe²⁺.
- Bacteria are still growing.
The process accelerates until it leads, even in a short time, to widespread and devastating corrosion, with loss of thickness and structural failure.
How to recognize the presence of ferrobacteria
From a practical point of view, the signature of ferrobacteria is characteristic:
- Cloudy water with brown or rusty hues,
- Gelatinous, brown-orange sediment,
- Unpleasant smell similar to stagnant or ferrous water,
- Internal deposits resembling mucilage.
Their origin is natural: they proliferate in iron-rich soils and are transported by the water table within: wells, pumps, lift units, filters, and delivery pipes.
In the presence of dissolved iron and oxygen, they rapidly colonize entire sections of pipe.
Are ferrobacteria dangerous to human health?
Ferrobacteria are not pathogenic to humans or animals: they do not cause disease and pose no direct health risk.
The problem they generate is technical in nature: in fact, they act exclusively on the systems, as they produce biofilms, alter the color and odor of water, promote corrosion, and can harbor other secondary microorganisms, thus compromising the functionality of the infrastructure.
How can ferrobacterial corrosion be avoided? The remedies
The management of ferrobacteria requires a combined approach: prevention, remediation and appropriate design.
- Water treatment (primary prevention)
- Chlorination or hyperchlorination: reduces microbial load and degrades biofilm.
- Chlorine dioxide: more effective than chlorine in penetrating biofilms.
- Filtration and aeration: reduction of dissolved iron (Fe²⁺) → less nutrients for bacteria.
- Remediation of contaminated pipes
- Mechanical fluxing (pigging): physical removal of ferric mucilage.
- Controlled acid washes: removal of ferric base deposits.
- Design precautions
- Reduction of stagnant areas,
- Increased flow velocities,
- Use of stronger materials (stainless steel, polymers),
- Application of interior protective coatings.
Conclusions
The culprit for the damage to the water pipe turned out to be groundwater, which was naturally contaminated by a population of iron-oxidizing ferrobacteria. In fact, the material was suitable for the context of use and was properly used.
These microorganisms have transformed a perfectly compliant pipeline into an ideal environment for accelerated microbiologically induced corrosion to the point of complete leakage and water leakage.
This case demonstrates how even a suitable material and a properly made implant can become vulnerable when an often underestimated factor comes into play: biology.
A microscopic bacterium, under favorable conditions, can seriously compromise the water system of an entire building.