Study Of Pipeline Internal Corrosion Of Sulfate-reducing Bacteria In The Presence Of Carbon Dioxide

With the increase in the depth of exploitation in oil and gas field, the problem of pipeline corrosion could become more and more serious, the phenomenon has caused wide public concern in the world. This paper studies the influence of mesotherm SRB and thermophilic SRB on X60 steel corrosion in the presence of carbon dioxide, respectively.In this thesis, the growth curves and environmental adaptability of SRB isolated from submarine pipeline WC15-1 and BZ26-2 were studied. In order to distinguish and identify the species of SRB, the FT-IR technique was initially applied to the study. Corrosion behavior of sulfate-reducing bacteria under submarine pipeline environment in the presence of carbon dioxide was studied by using weight-loss method, electrochemical methods and modern technology of surface analysis.The results show that the optimum growth temperature of the bacteria isolated from submarine pipeline WC15-1 sewage is 30℃, while the optimum growth pH is 7.5, carbon dioxide-saturated medium had little influence on the growth of bacteria. For a specified period of time, the weight loss measurement indicates that the presence of SRB can decrease the CO₂ corrosion in CO₂ saturated sewage at 30℃, with the increase of temperature, the presence of SRB can increase the CO₂ corrosion. Meanwhile, it is found that SRB function as protection on the CO₂ corrosion of X60 steel within the CO₂ partial pressure less than 1.0MPa when SRB aggravate the CO₂ corrosion of X60 steel within the CO₂ partial pressure at 1.0MPa. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDAX) shows that SRB participate in the biomineralization of corrosion product scales. The growth and breeding of SRB directly affects the structure of surface corrosion production scales on X60 steel, and corrosion mainly occurred during the initial state and the death phase of SRB. Using atomic force microscope (AFM), the formation and subsequent detachment of the corrosion products film and biofilm were observed on the X60 steel surface, it can explain the influence of the structure of surface corrosion production scales on X60 steel corrosion.The results show that the optimum growth temperature of the bacteria isolated from submarine pipeline BZ26-2 sewage is 60℃, while the optimum growth pH is 7.5, carbon dioxide-saturated medium results in prolonged lag phase of SRB. For a specified period of time, in low temperature zone (30⁴5℃), SRB caused the CO₂ corrosion mainly in CO₂-saturated sewage, while in high temperature zone(60⁷5℃), SRB caused the CO₂ corrosion mainly in CO₂-saturated sludge,with the increase of CO₂ partial pressure at static state, corrosion rate of X60 steel in sludge and in sewage increased, and the corrosion rate in sludge was always higher than that in sewage, moreover, the corrosion rate increased quickly with the rising CO₂ partial pressure at dynamic state. Fluorescence microscope micrographs in CO₂-saturated sewage with thermophile SRB results shows that SRB tends to gather on the edge of electrode, thus displays for the corrosion of electrode edge after 3 days'culture, after 10 days of culture, heterogeneous corrosion products scales adhered to the surface of X60 steel led directly to the characteristics of the pit corrosion.