Cathode Protection Of The Static Pressure Vessel's Inside Wall

Metal corrosion produces an important influence with the safe production. It can make huge losing of the notional economy. A three-phase separator of a natural gas company in Daqing oil field included examine and repair, because the intrinsic coat brushed off, infected the normal product. Therefore, the paper researched the reason of the pressure vessel's inside wall corrosion, and studied the cathode protection of it.1.The static corrosion experiment measure the corrosion rate of 16MnR (using diesel oil, glycol and water confect the electrolyte to imitate actual oil field liquid), and we get the average corrosion rate in the water A1 is 0.004580(mg·cm-2·h-1), the rate in the boundary of water and oil A2 is 0.002283(mg·cm-2·h-1), the rate in the boundary of oil and gas A3 is 0.000599(mg·cm-2·h-1);2.Reviewed the configuration, design parameter, and working environment of the three-phase separator, we analyzed the component of the liquid and corrosion product. Scanned the coupons by electron microscope, realized the corrosion figure, and compared them with the three-phase separator in the factory, and then we analyzed the mechanism of corrosion.(1)The coupons complete immerged in the water arise mostly pitting corrosion. It was mostly occurred by SRB corrosion, Cl? corrosion, CO2 corrosion and oxygen corrosion.①SRB corrosion:SRB can participate in the cathode depolarization, constantly consume the dissociate electron, accelerate the anodic depolarization, then constantly make the metal ion release. Advance the metal's electrochemistry corrosion, and the reaction equation as following: SO2? + 10H++ 8e→H2S↑+ 4H2O xFe + yH2S→FexSy + yH2↑②Cl- corrosion:HCl except can make corrosion, it can also accelerate for each other with H2S. Composing the circle corrosion the reaction equation as following: Fe+2HC1→FeCl2+2[H](penetrate) FeCl2+H2S→FeS↓+HCl Fe+H2S→FeS↓+2[H] (penetrate) FeS+2HC1→FeCl2+H2S③CO2 corrosion:CO2 can form H2CO3 in the dankest environment, make the metal corrosion, the reaction equation as following: CO2+H2O→H2CO3 Fe+H2CO3 FeCO3+H2↑④oxygen corrosion:Water have minim oxygen, it can make the depolarization with water at the cathode, make for corrosion. O2+2H2O+4e→4OH- Fe→Fe2++2e- Fe2++2OH-→Fe(OH)2...