Role of anaerobic and aerobic bacteria in localised corrosion: field and laboratory morphological study

Bacterial evidence was found in the biofilm deposited on the surface of an API X52 steel coupon following exposure to flowing seawater within a pipeline for 60 days. Extensive corrosion pitting was observed on the steel surface after removing the biofilm. Several types of anaerobic and aerobic bacteria were isolated from the biofilm. The anaerobic bacteria were cultured and grown in API RP 38 culture medium and the aerobic bacteria were grown in a general heterotrophic culture medium. The morphological and chemical characteristics of the bacteria were determined. Subsequently, separate specimens of API X52 pipeline steel were inoculated with each bacterial strain in under laboratory conditions. The specimen exposed to the anaerobic bacteria showed several micropits of different sizes on its surface while that exposed to the aerobic bacteria showed freedom from surface pits.