Corrosion Behavior Of Q235B Carbon Steel In Sediment Water From Crude Oil

Corrosion is one of the main causes of the damage of most tanks.The corrosion of tank bottom plate is the most serious one.Generally,there is a large amount of sediment water and deposit in the bottom plate of the oil storage tank.The composition is very complicated,which contains a large amount of corrosive medium,and very easy to cause the corrosion of tank bottom plate.Therefore,this paper systematically studied the corrosion mechanism of the sediment water and deposit on the tank bottom plate,and studied the influence of different experimental conditions on the corrosion.First,the crevice corrosion of Q235 B carbon steel in 3.5%NaCl solution was investigated using wire beam electrode and EIS.The results showed that at the initial stage,the area at the crevice mouth was cathode region,the other areas inside the crevice were anode region,corrosion distribution was inhomogeneous.With increasing time,the cathode area expanded to crevice area and the anode area was becoming increasingly smaller,distribution of corrosion tended to homogenization.The corrosion rate decreased first,and then increased with the extension of time.Second,WBE,EIS,SEM/EDS,XRD,and mass loss techniques were used to study the corrosion of Q235 B carbon steel in sediment water from crude oil.and carry out the contrast experiment between oxygen-free conditions,aerobic conditions,aerobic + oily sludge conditions.The study found that under the condition of anaerobic corrosion products on the coupon surface of the structure is compact,and the structure of the aerobic conditions is relatively loose;after the removal of corrosion products to observe coupon surface morphology,Pitting corrosion was observed on the metal surface in anaerobic conditions;Aerobic conditions,observed comprehensive ulcer corrosion on metal surface;And under the condition of aerobic + oily sludge metal surface is characterized by local corrosion,other area almost no corrosion.Under the different three conditions,coupon corrosion weightlessness were gradually increased with the extension of corrosion time,the average corrosion rate of anaerobic and aerobic conditions are decrease first and then increase;under the aerobic + oily sludge conditions the average corrosion rate showed the trend of first increased and then decreased,the trend of average corrosion rate of weight loss measured under three different conditions were basically same with EIS test results.the corrosion rates measured under aerobic conditions are far greater than the anaerobic conditions,indicating that oxygen participation to accelerate the metal corrosion,and the presence of oily sludge has further accelerated the corrosion of the metal.In this subject research,the sediment water and oily sludge were used as the corrosion medium,which were more close to the real corrosion environment,the experimental results was more authentic,and provided a reliable theoretical basis for corrosion protection.