Cobra Consultancy calls in Microbial Analysis to investigate corrosion problems in wine tanks and heat exchangers

Leakage in wine tanks

At a French winery, stainless steel 304 tanks have been installed in which the wine is stored. The wine is kept at the correct temperature using cooling fins, ensuring that the yeasts develop the desired aromas and flavours in the wine.

Shortly after the tanks were made operational, leaks were discovered in 27 of the 54 tanks. The corrosion rate and observed characteristics, such as discolouration and dark corrosion near the weld, strongly indicated MIC. To investigate this, we took a surface sample from the inside of the wine tanks and performed a qPCR analysis. This revealed a high concentration of microorganisms, including sulphur-oxidising bacteria.

MIC caused by stagnant water

A high concentration of microorganisms on the inner surface of wine tanks indicates the presence of a biofilm. Additionally, sulphur-oxidising bacteria are known to cause MIC. The analysis results indicate that MIC was involved in the damage.

To prevent further damage to the wine tanks, an investigation was conducted to determine the cause of the MIC. Enquiries revealed that the manufacturer had not completely dried the tanks after performing a pressure test. Consequently, a layer of water remained at the bottom of the tanks for several months while they were stored outside in the French sun. These conditions are ideal for bacterial growth, including MIC bacteria.

Heat exchangers in swimming pools

Another example of a project in which Microbial Analysis was called in to investigate the presence of MIC bacteria had a similar start. Stagnant water led to leaks in several 316 stainless steel heat exchangers in swimming pools. This resulted in over 20 leaks.

During the period 2020–22, swimming pools in the Netherlands were closed due to the Covid-19 pandemic. As a result, the water systems were shut down, but not completely dried out, leaving stagnant water in which bacteria could grow. Microbiological analyses therefore revealed high concentrations of microorganisms, including MIC-related bacteria.

These two cases clearly demonstrate that MIC can occur in both 304 and 316 stainless steel when conditions are favourable for bacterial growth. Two important recommendations can be drawn from this: avoid stagnant water where possible and have the water checked for the presence of MIC microorganisms before use.

Neem contact op met Reinoud Homan.

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