The Role of Sulfur Oxidizing Bacteria on Corrosion of X65 Low Carbon Steels and its Mitigation Using Sodium Tungstate and Nickel Biocides

Abstract

Metals in service often give a superficial impression of permanence, but all except gold are chemically unstable in air and air-saturated water at ambient temperatures and most are also unstable in air-free water. Corrosion can be defined in general terms as the degradation of a material, usually a metal, or its properties because of a reaction with its environment. It results to damage cost between 1 – 5 % GNP as reported from different countries. Corrosion can be initiated by differences in chemical potential, stress or chemical reactivity between two points. It can also be influenced or initiated by microorganisms, a form of corrosion that is often ignored by many people. The latter is a form of corrosion called Microbial Induced Corrosion (MIC) or Biocorrosion and it accounts for 50% of the total corrosion damage cost. The focus of this work is to understand the role played by Sulphur Oxidizing Bacteria (SOB) on corrosion of X65 low carbon steels, its kinetics and the possible ways to mitigate this form of corrosion. The experiment for the isolation of SOB showed a maximum pH drop of 3 in the Thiosulphate broth, followed by 2.3 in the Starkey broth and 1.5 in the NCL broth. The results from the corrosion experiment show a higher weight loss for samples 3 and 4, which were exposed in the culture media with SOB, compared to samples 1 and 2 in the same media but without SOB. Corrosion by SOB was reduced by 96.73% using 80 mg/L of Sodium Tungstate and 100 mg/L of Nickel.