Investigations on corrosion behaviors of super-strength sucker rod FG20 steel in high SO 4 2? environment

摘要

In some sour reservoirs and tertiary oil recovery blocks, SO42?in the well fluid can cause the corrosion and corrosion fatigue of the sucker rods. In this paper, the corrosion behaviors of super-strength sucker rod FG20 (16Mn2SiCrMoVTiA) steel in the well fluid are investigated by electrochemical measurements, and electron probe micro-analyzer (EPMA) analysis. The results show that FG20 steel has a favorable corrosion resistance in neutral solution. When the hydrogen ions increase, the hydrolysis of SO42?greatly accelerates the corrosion of FG20 steel. The energy dispersive X-ray (EDX) results demonstrate that the corrosion process of FG20 steel in neutral well fluid is an oxygen concentration process, and the protective FeCO3and Fe2O3on the surface of the samples can prevent the further corrosion. With the increase of the acidity in the well fluid, the corrosion process converts into a sulphide concentration process, and the sloppy FeS and mackinawite film cannot provide effective protection for the specimens, resulting in the increase of corrosion rate.