Microbiological corrosion: a threat to sheet piling in saltwater and freshwater

Microbiological corrosion (MIC) can cause significant damage to sheet piling in both saltwater and freshwater environments. It is essential to identify the specific corrosion processes through visual, microbiological, chemical and mineralogical analyses. These insights will enable us to implement appropriate measures to prevent further damage. To illustrate the impact of MIC corrosion, we present two case studies, one in salt water and one in fresh water.

2. Corrosion damage in sheet piling of a freshwater lock

During an underwater inspection of a dam wall in a lock in a freshwater environment, significant corrosion damage was discovered. This damage was suspected to be caused by microbiologically influenced corrosion (MIC). We were asked to carry out a comprehensive survey to investigate what was going on.

Research approach
Our investigation brought together several lines of evidence: visual inspection, microbiological analysis of corrosion products and chemical analysis of the water.

Findings:

• Visual inspection: the photograph of the corrosion damage showed orange colour, often indicative of oxygen related corrosion, but does not rule out MIC.
• Microbiological analysis: the samples contain high levels of MIC related bacteria and archaea, particularly sulphur and sulphate related bacteria.
• Chemical analysis: the water contains an adequate quantity of organic and inorganic carbon, sulphur, and nitrogen to sustain the growth of MIC microorganisms.
• Mineralogical analysis: the corrosion product was found to contain high concentrations of iron and silicon, as well as lepidocrocite and goethite, which are indirect indicators of MIC.

 

Conclusion and Advice

 

The results of the analyses indicated the presence of MIC corrosion and other corrosion processes in the sheet piling. In order to prevent further damage, it was recommended that measures such as complete replacement of the sheet piling, application of cathodic protection and coating be considered. If the current system is maintained, it was suggested that mitigation measures be employed to prevent the formation of biofilms and inhibit MIC processes.

1. High-speed corrosion in sheet piling caused by bacteria

A significant issue was identified in a saltwater environment: lightning-fast corrosion on sheet piling. In just one decade, the 8 mm thick sheet piling had completely disappeared in some places, leading to subsidence. This rapid corrosion suggested that microbiologically influenced corrosion (MIC) was likely.

Research approach
To uncover the causes of the rapid corrosion, a team of experts was called in. A diving team filmed the suspected locations of the sheet piles and took samples of the corroded parts. These samples were then subjected to thorough analysis in our lab.

Results
Visual Inspection: clear presence of pitting corrosion, typical of MIC.

• Microbiological Analysis: in de samples sulphur-related bacteria, sulphate-reducing and sulphate-oxidising bacteria, and iron-reducing bacteria were found.
• Chemical Analysis: the composition of the salt harbour water promotes microbial growth with sufficient nutrients such as organic and inorganic carbon, and sulphur.
• Mineralogical Analysis: the results of the mineralogical and chemical examination of the corrosion products support the diagnosis of MIC. The results do not rule out the possibility of other corrosion processes.

Conclusion and Advice
The study results confirmed that the rapid corrosion of the sheet piling was due to MIC, with a high corrosion rate indicating Accelerated Low Water Corrosion (ALWC). This is more often seen in places where the water level is highly fluctuating. Given the adverse environmental conditions, such as the presence of several species of MIC bacteria and sufficient nutrients, we created an appropriate mitigation plan for this site to limit further damage. This included special coating and cathodic protection.

If you want to know more about corrosion damage in sheet piling or want to prevent damage, contact our experts.