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Madani Sani, Fzlollah | 2013

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 44150 (07)
  4. University: Sharif University of Technology
  5. Department: Materials Science and Engineering
  6. Advisor(s): Afshar, Abdollah
  7. Abstract:
  8. Microbiologically influenced corrosion has substantial role in degradation of steel pipelines. It is believed that 20% of total corrosion damages are related to microbial corrosion. The most important micro-organisms which affect this type of corrosion are Sulfate Reducing Bacteria (SRB). Although many studies have been done on the effect of SRB on corrosion of buried steel pipelines, no decisive and identical thought has been made so far. In the present study, the role of SRB on corrosion of API 5L X65 steel in different conditions was investigated by performing weight loss, linear polarization, electrochemical impedance spectroscopy and X-ray diffraction tests. Experiments were accomplished in two types of soils-Aghajari and coral formations- from Kharg Island, in 15, 20 and 25 % wt. moisture contents and in sterile and SRB- active conditions. The results showed that the presence of SRB in both types of soil increased the corrosion rate of steel specimens in the beginning of experiments. However, over time the corrosion products of SRB corrosion have protective effects and thus the corrosion rate decreases compared to sterile condition. Moreover, in low moisture contents (15% wt.), in soils with SRB, corrosion rate is more than sterile mode and the presence of SRB enhances pitting corrosion. Whereas, by increasing moisture content, corrosion rate in SRB-active mode becomes less than sterile mode and uniform corrosion is dominant. In addition, in soils with SRB bacteria two layers of corrosion products form on surface of steel which the inner layer is a mixture of Fe3O4 and Iron sulfides like Fe1-xS, FeS, FeS2, and Fe3O4 and the outer layer is a mixture of Fe(OH)2 compounds. In sterile soils the outer layer is the same as SRB- active condition but the inner layer just consists of Fe3O4
  9. Keywords:
  10. Moisture ; Sulfate Reduction Bacterias ; Microbiologically Influenced Corrosion (MIC) ; API 5L X65 Steel Pipelines ; Coral Soils

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