Pipelines during and after hydrotesting are vulnerable to microbiologically influenced corrosion (MIC), which can result in severe pinhole leaks. Instead of the current MIC studies in the field practice, this study investigated the MIC phenomenon in hydrotesting under laboratory conditions, and a variety of issues that arose during this process are discussed.
The MIC process during hydrotesting was found to be dependent on water sources due to different concentrations of nutrients and native organisms. In order to accelerate the MIC process, a simulated worst-case scenario with a lab strain SRB (sulfate-reducing bacteria) and key nutrients added proved to be a useful approach. Furthermore, the technique of polymerase chain reaction (PCR) was adopted to MIC research for detecting very low concentrations of targeted planktonic microbes.
A novel MIC mitigation method, using biocides THPS (TetrakisHydroxymethyl-Phosphonium Sulfate) and glutaraldehyde, in combination with EDTA (Ethylene-DiamineTetraAcetic acid) was found to be more effective for controlling the growth of planktonic SRB. A mechanistic THPS degradation model, with great consistency to experimental results, was developed to predict residual THPS concentration to assure that it does not fall below the desired minimum required for MIC control.
Based on the mechanism of biocatalytic cathodic sulfate reduction (BCSR), a first generation MIC mechanistic model was developed to predict the MIC pitting rate under certain conditions; thus providing a basis for a more comprehensive mechanistic MIC modeling. Futhermore, a new biomarker EPS (extracellular polymeric substances), a potential replacement of existing biofilm probes, was proposed to serve for locating biofilms.