Abstract
Biodeterioration/biocorrosion of concrete pipeline coating material by sulphate reducing bacteria (SRB) and Iron oxidizing bacteria was tested in the laboratory. The sulphate reducing bacteria and the Iron oxidizing bacteria were isolated from water samples collected from a swamp at a depth of 30 cm. The water samples had a viable, culturable, heterotrophic bacterial count of 1.2 x 10 3 cfu/ml for the sulfate reducing bacteria (SRB) and 4.0 x 10 3 cfu/ml for the Iron oxidizing bacteria. A loop-full of discrete colonies of the isolates of the two groups were used to initiate the biodeterioration tests. The pH of the set ups with the SRB showed a change in acidity from 8.24 in the fresh medium to 6.79 after 7 days and moved down to 5.23 in 28 days of incubation. In contrast, the pH of the set ups with Iron oxidizing bacteria showed an increase in alkalinity. The pH of the fresh Winogradsky medium changed from 6.60 to 7.80 in 7 days of incubation and to 9.02 after 28 days. The dissolved Iron II ion in the two set ups showed a gradual decrease in concentration as the time of incubation increased. The conductivity in the SRB set up increased from 0.41 s/m to 1.56 s/m in 28 days of incubation. On the other hand, the Iron oxidizing bacteria set up showed a decrease in conductivity from 1.12 s/m to 0.35 s/m in 28 days of incubation. The surfaces of the coupons of the concrete coating material used in the biodeterioration testing were slimy on touch indicating possible biofilm formation. There were changes in the physical appearance of the materials such as colour and texture. Corrosion rates were 0.6382 mpy and 0.3469 mpy for SRB and Iron bacteria respectively. Concrete coating of pipelines is a good strategy for swamp operations. The low rate of biodeterioration/biocorrosion of the concrete coating as indicated in this study is a useful piece of information for oilfield applications.
Highlights
Biodeterioration of materials can take the form of biocorrosion or biofouling
Biological activities that stimulate the anodic reaction by acidic metabolites or the cathodic reactions by microbial production of cathodic reactants such as hydrogen sulphide (H2S), the breakdown of protective films or the increase in conductivity of the liquid environment enhance corrosion [2]
It has been estimated that 40% of all internal pipeline corrosion in the gas industry can be attributed to microbial corrosion [4]
Summary
Corrosion of metals is believed to be an electrochemical process, which results in oxidation of a metal to its oxide and hydroxide thereby distorting the structural integrity of the metal. The electrochemical nature of corrosion remains valid, microorganisms influence metal corrosion by modifying the metal solution interface through biofilm formation [1], there is microbially influenced/ induced corrosion (MIC). Corrosion is a leading cause of pipeline failure and is a main component of the operating and maintenance cost of gas industry pipelines [3]. As reported by Koch et al [3], the annual cost of all forms of corrosion in 2001 in oil and gas industries was 13.4 billion dollars. Microbial induced corrosion (MIC) accounted for about 2 billion dollars [3]. It has been estimated that 40% of all internal pipeline corrosion in the gas industry can be attributed to microbial corrosion [4]
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