The Influence of Sulfate-Reducing Bacteria Metabolic Reactions on the Corrosion Behavior of API-5L X65 Carbon Steel Pipeline

摘要

Microbiologically influenced corrosion (MIC) by Sulfate Reducing Bacteria (SRB), Desulfovibrio africanus sp, on API-5L grade X65 carbon steel was investigated. The corrosion behavior was characterized by Electrochemical Impedance Spectroscopy (EIS), linear polarization resistance (Rp) and open circuit potential (OCP). EIS spectra displayed one time constants for the sterilized growth media. The time constant was related to a mixture layer of corrosion products with chlorides and organic compounds that precipitated out from the growth media. Conversely, one time constant with a finite Warburg element were observed in the SRB cultured media. The SRB Bio-catalytic activities promote the corrosion rate via formation of biofilm, production of hydrogen sulfide and biotic reduction of phosphates and subsequent formation of iron phosphide. Deeper pits were found along the grain boundaries (GB) and boundary triple points. The extensive attack on the grain boundaries has been related to the fact that bacterial initial attachment occurs on or near the grain boundaries. Corrosion products, biofilm and pitting morphology were characterized by X-ray diffraction and Environmental Scanning Electron Microscopy (ESEM).