A baffled customer turned to the Steinbeis Transfer Center for Chemical Engineering: One of his sprinkler systems was showing signs of leakage despite carefully selected base materials. What was the culprit? Defective materials? Or was it corrosion, even though no contact elements or low-alloy steels were used? The Steinbeis team, based in Reutlingen, was able to help. It determined corrosion, induced by microbiological factors.
After examining the micrographs under both a scanning electron microscope and a fluorescence microscope, microfissures could be excluded as the source of the problem. The culprit was definitely corrosion, but the cause of the corrosion was mystifying.
To prove that the corrosion is being induced by microbiological factors requires a special analysis method, since these initially look the same as any other type of corrosion source. Thanks to the MSB-FISH method (Metal Surface Biofilm – Fluorescence in situ Hybridization), a unique technique developed by The Steinbeis Transfer Center for Chemical Engineering, there is an accurate and quick way to analyze such situations. The method helps identify microorganisms directly on metal surfaces (without intermediate cultivation) by using probes marked with nucleic acid. The major advantage of this method lies in the precise chronological representation of microbiological colonization.
Using the MSB-FISH method, the Steinbeis team was able to detect microbiologically induced corrosion. An image of the chronological colonization sequence explained the state of the individual section of pipe. They were also able to give a prognosis regarding further corrosion development. As a result, the customer was able to take preventative measures and protect the sprinkler system over the long term.
The cause of corrosion in Microbiologically Induced Corrosion (MIC) is typically a biofilm. This is a term used to describe biocorrosion or biofouling. Biofilms are the oldest known sign of life. In fact it would be impossible to imagine our modern environment without them. Every classic type of corrosion can be triggered or made worse by microorganisms that embed themselves in biofilms. The rate of deterioration can increase up to 30-fold. MIC is triggered by the metabolic byproducts of microorganisms which form substances such as hydrogen sulfide and nitric acid. Sulfate-reducing bacteria and acidic bacteria play a primary role in biocorrosion. Sulfate-reducing substances contribute to local acid concentrations that can damage even high-alloy materials. Practically no surface is safe from colonies of microorganisms: nearly all metals, organic materials, glass, ceramics and plastics can be affected. Other than titanium, molybdenum and nickel-cadmium, no metal is resistant to corrosion caused by the effects of microorganisms. Simple conditions suffice: moisture, nutrients, microorganisms, and a surface. And this can cause far-reaching technical and hygiene-related problems. Biofilms can result in complete and irreversible blockages in the membranes of ultra-filtration and reverse osmosis systems. Corrosion related to MIC is often found in systems using cutting fluid, machining systems and parts cleaning equipment. Even coolant recirculation systems and sprinkler systems are often affected, without the root cause being identified.
Dr. Ulrich Schekulin
Steinbeis Transfer Center Chemical Engineering (Reutlingen)
su0348@stw.de