Crude Oil Tank Inner Bottom Floor Corrosion Mechanism Analysis And Anti-corrosion Technology Research Of The Coating

In recent years, crude oil storage tank corrosion crisis has become one of the most acute problems of the petrochemical industry, tank inner bottom floor corrosion accounted for the largest proportion of the entire tank corrosion. Crude oil itself is not strong corrosive. The main reason is sedimentary water gathered on the tank inner bottom floor which formed by water and aggressive media from crude oil for a long time. The complex composition of sedimentary water is very corrosive. In this thesis, the mechanisms of corrosion for such storage tank are studied and discussed extansively, as follows:In this experiment, we did analysis of corrosion behavior of Q235steel in different sedimentary water with different levels of dissolved oxygen, various concentrations of NaCl solution and Na2SO4solution. The results suggested that high level of oxygen could promote the corrosion of carbon steel slightly in sedimentary water, sedimentary water of higher ion concentration, and lower pH values than other one could accelerate corrosion, the presence of Cl-and SO42-did not stimulate the corrosion rate of carbon steel obviously, but the rate could be much higher than in sedimentary water.Polarization curve method was used to explore the electrochemical behavior of the corrosion, the effects of main ingredient of the sedimentary water, temperature and pH value on the corrosion of carbon steel were proposed. The result showed that elevated temperature could promote the corrosion of carbon steel, the rate of corrosion was lowest when pH value was7～8, the presence of Cl-could greatly contribute to the corrosion of carbon steel, HCO3-could accelerate corrosion of carbon steel, and SO42-could slow down the rate of corrosion in their each mixed solution with Cl-.Insulating epoxy-modified silicone coating was used for this research. Impedance spectroscopy of different thickness and different layers coating systems at different immersion time were fitted with four kinds of equivalent model by using EIS technology and got data through calculation. These data could be converted into the diffusion coefficients of water for coating systems anti-corrosion behavior research combined with corrosion current density observed from experiment. This research suggested that two layers and threes layers coating anti-corrosion ability is much better than one layer coating. The water transport behavior was slightly influenced by the coating thickness.