Effect of Anaerobic Bacterium Clostridium sp. on the Corrosion Behavior of the API X42MicroalloyedPipeline Steel in Saline Simulated Soil Solution

In this study, the effect of bacterium clostridium sp. as ananaerobic sulfate-reducing bacteria on the corrosion behavior ofAPI X42 micro-alloyed pipeline steel was evaluated in a saline simulated soil solution at different immersion times (varying from 3 days to 40 days) under biotic condition. In this process, a soil sample containing sludge was used as a source of production sulfate-reducing bacteria and a saline soil sample was used as the basis of the saline simulated soil solution. The corrosion behavior and microstructure of the corrosion products were evaluated as a function of immersion time. Microstructural examinations show the accumulation of bacteria on the steel surface after 7 days. By further immersed times to the middle times (21-24 days), a biofilm comprised of the dense extracellular polymeric substances was formed. After that, biofilm exfoliation was observed showing physical biofilm breakdown. This microstructural variation is associated with aremarkable variation in corrosion resistance. At first, the corrosion resistance decreases sharply from 1019Ω.cm2at 3 days to 274Ω.cm2at 7 days due to the metabolic bacterial activity. As a result of this high corrosion rate, a densely packed biofilm was formed at the middle times in such a way that corrosion resistance rises sharply to 7330Ω.cm2at 21 days. However, the dense protective biofilm formed at the surface was unstable and biofilm was degraded rapidly; consequently, the corrosion resistance decreases to 480 Ω.cm2at 40 days.