Study On Corrosion Behavior Of Bottom Plate Of Large Crude Oil Storage Tank

As China’s strategic crude oil reserves rise,the larger size and more intensive crude oil storage tanks were built,and the operational safety of crude oil storage tanks has been the hotpoint.The corrosion of crude oil storage tank floor is one of the main causes of failure of crude oil storage tanks,and the development of large-scale crude oil storage tanks has exacerbated the risk and consequences of tank floor failure.In this paper,the corrosion behavior of 12MnNiVR steel,used in larger-size storage was investigated in deposited water solution.The effect of dissolved oxygen,Cl^-,HCO₃^-and SO₄^2-ion and the synergistic effect these ions was analyzed using weight-loss experiment and electrochemistry experiment at room temperature and pressure.The corrosion morphology are observed by SEM and the component of corrosion scales are analyzed by EDS and XPS.The main conclusions obtained are as follows:（1）The ppm-level dissolved oxygen can lead to the significat increase on the mass-loss rate of samples.Compared with the Q235B steel and Q345R steel used in traditional storage,the mass-loss rate of 12MnNiVR steel is higer.The addition of alloy elements improves the mechanical properties,but reduces the corrosion resistance of 12MnNiVR.（2）In the tested Cl^-concentration range（5 g/L～saturation）,12MnNiVR has a high weight loss rate when the Cl^-concentration is lower.As the Cl^-concentration increases,the weight-loss rate of the material decreases linearly.Compared with Q235B and Q345R steel,the average weight-loss rate of 12MnNiVR is relatively lower.（3）The results show that the presence of lower concentration of HCO₃^-promotes the corrosion of the bottom plate of the storage tank in deposited water contained 25 g/L Cl^-ion,while higher concentration of HCO₃^-inhibits the corrosion induced by Cl^-ion.This synergistic effect has the obvious influence on the corrosion rate of 12MnNiVR;the presence of SO₄^2-ion significantly reduces the average weight-loss rate of crude oil storage tank bottom plate material in Cl^-containing solution.（4）Pitting immersion test showed that the increasing rate of 12MnNiVR in the deposited water solution decreased with immersion time.The rang of depth of pits are 5～10μm,and the pitting coefficients ranged from 2 to 2.5.The pitting level of 12MnNiVR is A4B1C1.