A preliminary study on Microbiologically influenced corrosion (MIC) of mild steel by Pseudomonas aeruginosa by using infinite focus microscope (IFM)

Abstract

This study investigates the corrosion behavior of mild steel immersed in artificial seawater based medium in the presence and absence of bacteria Pseudomonas aeruginosa. The bacterium was chosen because of its abundance in the seawater and most metals are inclined to be attacked by this bacterium. Pitting corrosion on the mild steel coupon as a result of the bacteria attack was investigated. A set of mild steel coupon sample was immersed in sterile artificial seawater while another set was immersed in bacteria inoculated artificial seawater for 12 days. The samples were viewed under Infinite Focus Microscope to obtain information on the biofilm surface and thickness, dimension of the pits and the surface roughness. It was found that biofilm with thickness of 37 μm was formed on the mild steel surface after 12 days of immersion in bacteria inoculated medium. This finding suggested that MIC had taken place. The existence of pitting corrosion on mild steel coupon immersed in bacteria inoculated medium was attributed to the concentration cells originating from the heterogeneous surface of biofilm, while the absence of pitting corrosion on mild steel coupon exposed to sterile medium further proved that heterogeneous biofilm is a crucial factor for the initiation of pitting corrosion. Surface roughness value increased from 156.03 nm for non-immersed coupons to 433.07 nm for coupons immersed in sterile artificial seawater and finally to 900.3nm for coupons immersed in bacteria inoculated artificial seawater. The increased value of roughness was attributed to the formation of uniform corrosion and pitting corrosion when immersed in sterile and bacteria inoculated medium.