Biocorrosion caused by native microbial communities in seawater could destroy the passive layer locally on stainless steel, causing pitting corrosion. Several previous studies have investigated the biocorrosion behaviour on the material, especially the influence of sulfate-reducing bacteria (SRB), by using electrochemical and surface characterization methods with a biological quantitative polymerase chain reaction. However, there is not yet a technique that could visualize the microbial distribution on the metal surface by their communities. This thesis aimed to adapt and modify a protocol of applied DNA hybridization chain reaction-fluorescence in situ hybridization (HCR-FISH) to visualize targeted microbial cells on the austenitic stainless-steel surface, providing a unique distribution map of bacteria, archaea, and SRB on the metallic surface. The modified HCR-FISH method was first tested for pure microbial cultures in the laboratory and environmental samples. The method was then applied in a lab-scale biocorrosion study of stainless steel EN 1.4404 with surface finish 2R and 2B in a circuit system of natural brackish seawater. As a result, the method was suitable to directly apply on stainless-steel surfaces to visualize the biofilm distribution which was supportive for a biocorrosion study. Besides, SRB was found to be associated with biocorrosion in stainless steel, and the microbial adhesion was affected by the steel surface roughness. Here, a smoother metallic surface might encourage biofilm adhesion rather than a rougher surface, resulting in a more defective passivation layer in stainless steel.

2024