The pipelines have been investigated using various methods:
Visual evaluation of the pipelines
The detected bulges were visually inspected. All three pipelines were covered with these bulges. It was concluded that the bulges were so-called tubercles. The formation of tubercles is a typical indication of MIC corrosion.
Microbiological analyses of the samples
The samples were analysed for the presence of microorganisms that are known for promoting microbiologically influenced corrosion (MIC).
The test results showed that the samples contain high levels of MIC related bacteria and archaea. Subsequently, Microbial Analysis identified by means of the 16S amplicon sequencing, which kinds of bacteria and archaea were present. Striking is the high level of sulphur related bacteria. Furthermore, the results showed so-called methane producing archaea. Both groups of microorganisms are strongly related to MIC corrosion processes.
Chemical and mineralogical analyses of the formed corrosion
Determination of the composition of the corrosion product gives information about the probability that microorganisms are causing the problems. This research showed that the samples of the corrosion products from the pipelines contained high concentrations of iron, in the form of iron sulphites and iron carbonates. Particularly the presence of iron sulphites is an indication for MIC corrosion.
Environmental conditions
It has been assessed whether the water in the pipelines contains the necessary nutrients to make microbiological activity possible. Analysis of water samples showed that the presence of phosphor and sulphate, and the acidity of the water are favourable for microbial growth.
