The activity of microbes can cause excessive pitting corrosion in ships bilges, stern tubes, tanks (bilge, ballast, fuel, oil and cargo) and associated pipework.
When microbes are involved with corrosion this is referred to as Microbiologically influenced Corrosion (MIC). Most metals, including steel, aluminium, copper and their alloys can be affected by MIC.
The principal corrosion mechanism in marine systems usually involves bacteria known as Sulphate Reducing Bacteria (SRB). SRB reduce sulphate and generate corrosive hydrogen sulphide. The mechanism by which SRB causes corrosion is complex but it involves the deposition of an iron sulphide film, which becomes cathodic to the steel underneath, and direct influences on electron flow, resulting in pit formation.
Systems prone to seawater ingress or seawater compensated fuel tanks are prone to MIC caused by SRB due to the abundance of sulphate in seawater. MIC caused by SRB is typified by deep pitting. Pits may be steep sided or saucer shaped depressions; occasionally they are observed to have terraced edges with a flat bottom which has further smaller pits within. MIC involving SRB usually occurs at considerably faster rates than normal for steel exposed to seawater, typically 1 to 3 mm per annum loss of thickness.
Other mechanisms of MIC include the iron oxidising bacteria and the production of acids by microbes, for example corrosion of stainless steel heat exchanger plates due to fungal colonization.
- Conduct assessments of material susceptibility and analysis of samples of corrosion deposits from your vessel or facility in our laboratory to assess the extent of microbiological contamination and the risk of MIC. Learn more about our lab analysis service here.
- Provide on-board microbial Test Kits. ECHA’s Sig Sulphide test kit can be used on-site or in the laboratory by non-microbiologists for the detection of SRB. Learn more about the test here.
- Conduct surveys of tanks and systems on board your vessel or platform if you have a concern about MIC. Learn more about our Site Surveys here.
- Investigate corrosion incidents or provide advice on remediation, control, monitoring strategies and best practice. Learn more about our Consultancy Services here.
- Offer comprehensive, tailored training courses on microbiological contamination of marine fuels including management of issues such as MIC. Learn more about our Training Courses here.