AbstractMicrobially influenced corrosion (MIC) of marine steel piling is a globally phenomenon that carries with it a financial and safety burden for the operators of harbours and ports. It has been observed to drastically reduce the service life of marine infrastructure and in extreme cases has resulted in collapse of quaysides. Despite this, it is not extensively researched, and those studies that have been conducted concentrate on the specialised form of marine MIC known as ‘accelerated low water corrosion’ (ALWC).
This study aimed to take a broader approach than other studies by identify the microbial and mineralogical composition of corrosion taken from several locations on a section of marine steel piling, rather than solely within the ‘ALWC’ region, and to contextualise these with data obtained from the surrounding environment. The sampling site was situated within an active port facility on the south coast of England. Corrosion, marine sediment, and seawater samples were all extracted from a tidal location within the port. X-ray powder diffraction, Fourier-transform infrared and inductively coupled plasma optical emission spectrometry were employed alongside GeoChip functional gene array, denaturing gradient gel electrophoresis, and high-resolution melt analysis to analyse the environmental samples, and seawater conditions monitored via a site-installed sonde.
The data obtained allowed construction of a model to explain the presence of microbes within marine corrosion formations. Diversity and cluster analysis of environmental samples revealed a strong link between key microbial groups in marine sediment and corrosion, with seawater providing a lesser influence. Turbidity measurements provided evidence for periodic exposure of corrosion formations to significant levels of resuspended marine sediment. Analysis of fifteen functional genes identified 116 microbial genera of prokaryote linked to MIC. Comprising eight microbial groups, these indicated the microbial diversity within MIC formations and demonstrated the microbial continuity that exists between MIC in different environments.
Mineralogical, chemical and gene analysis of a vertical section of carbon steel piling discerned regions in which MIC was active and regions of normal water corrosion. MIC was found to be characterised by the presence of reduced sulfur species as well as the mineral maghemite, whereas normal water corrosion was characterised by the minerals akaganeite and hematite, and chloride green rust. As well as a clearly defined mineralogy, the microbial communities in the corrosion formed clusters of similar genetic composition in line with the mineral groups. It was confirmed that the region of piling affected by MIC was not limited to the low water region but extended throughout the intertidal zone, from the sediment bed up to mean tide level.
|Date of Award
|Martin Smith (Supervisor), Heidi Burgess (Supervisor) & Jon Caplin (Supervisor)