Environmental and Microbial Influences on Corrosion of Selected Types of Petroleum Industry Steel

Abstract

This study explored the influence of brackish water sediment, mangrove swamp sediment, clayey/lateritic soil, and river water (freshwater) sediment on the corrosion rates of carbon, mild, and stainless steels and the species of sulphate reducing bacteria (SRB) and iron bacteria associated with the process. The material loss following burial of the steel samples for a 9-month period was assessed. Standard and specialised microbiological techniques were employed in the characterisation of the bacterial species. Qualitative assessment for corrosion was done via optical microscopy and macroscopy. Corrosion was highest on steel buried in brackish water sediment and lowest in that from river water sediment. Carbon steel was the most susceptible to corrosion while stainless steel was the most resistant. Sulphite, sulphide, nitrate and phosphate concentrations had a strong impact on corrosion rates. Thiobacillus, Leptothrix and Gallionella dominated amongst the iron bacteria while Desulfobacter and Desulfovibrio dominated amongst the SRB. There were significant differences in corrosion rates and bacterial abundance from one environment to the other. Iron bacteria showed greater abundance than SRB across the different environments and steel types. Iron bacteria counts, however, did not correlate positively with corrosion rates. The findings suggest that oil industry facilities in brackish water environments are more liable to corrosion than those located in fresh water ecosystems.