| China’s oil production has entered its middle stage,pumping well under corrosive environment is more and more bad,the corrosion has become one of the main factors of sucker rod failure.The friction between the oil pumping rod and tubing,forming different surface morphology of the accelerated corrosion of pump rod,reduce the service life.The corrosion process and corrosion mechanism through the research of the sucker rod,oil is preferred good corrosion resistance of sucker rod and a sucker rod breakaway prevention reference.Sample selection is A,B,C,D,E 5 kinds of Cr-Mo sucker rod steel,metallographic analysis and hardness test of 5 kinds of Cr-Mo steel specimens.The results showed that 5kinds of Cr-Mo steel microstructure is tempered sorbite;hardness from the center to the edge presents a gradually increasing trend.Four point bending tests were carried out in a high temperature and high pressure reactor to simulate the corrosion of Cr-Mo steel in the well.By Scanning Electron Microscope（SEM）observation and analysis,the different types of Cr-Mo steel corrosion product film grain size is different,the smallest is A steel,the biggest is C steel;Corrosion product film are classified into two layers,inner denser than the surface;The grain size and thickness of corrosion product film were obtained,and the density of A steel corrosion product film was the best.By using Energy Dispersive Spectrometer（EDS）,the main elements of the corrosion product film are Fe,C and O.The corrosion products were analyzed by XRD and the corrosion product film was mainly composed of FeCO 3.The corrosion rate of 5 kinds of Cr-Mo steel was decreased rapidly after the formation of corrosion product film,which showed that the formation of corrosion product film played a protective role to the substrate,by electrochemical analysis.The corrosion product film and electrochemical characteristics analysis of 5 kinds of Cr-Mo steel showed that the comprehensive performance of A steel was optimized.Different surface morphology of A steel under high temperature and high pressure showed that the surface roughness is small,the formation of corrosion product film grain size is fine,the thicker the corrosion product film better protection by scanning electron microscopy and electrochemical analysis.Using ABAQUS finite element analysis software to simulate the expansion of corrosion pits on the surface of sucker rod under the force of sucker rod.The stress cloud and the output of the axial force can be seen that the different shapes of semi elliptical crack stress concentration point distribution is different.By the change o f crack opening distance,it is known that the crack length increases with the increase of crack length,and increases with the increase of crack length.When the crack depth is constant,the crack opening distance decreases with the increase of the ratio of crack depth and length.The ratio of crack depth to length is larger,and the critical crack size is smaller. |
