Corrosion Behaviour Of High Strength Sucker Pole In Sodium Bicarbonate Solutions Containing Chloride

The increasing of difficulty on oil extraction raises a higher claim on bearing ability of sucker rod,so high strength sucker rod becomes common.The application in field found that the service life of high strength sucker rod was generally lower than the predicted life,which will become the main limiting factor.The increasing of oil well produced water salinity and harsh working conditions leads to accelerate the corrosion or fatigue of high strength sucker rod,which causing enormous economic loss.Herein,factors which have influence on high strength sucker rod's performance of resistance to stress-corrosion are studied,which favors the oilfield company choosing proper high strength sucker rod,designing standard sucker rod,reducing accidents caused by the stress-corrosion or fatigue of high strength sucker rod and improving the work efficiency.Based on our previous work,chemical composition of liquid produced from Shengli oilfield were confirmed.In this paper,corrosion behavior and mechanism of high strength sucker rod in solution of Na HCO₃-Na Cl.The influence of p H,HCO₃-and Cl-were also studied and the results were as follows:?1?According to the research on the working conditions of high strength sucker rod,we founded that the service life of high strength sucker rod was mainly influenced by the no symmetric load forced on the the bolt and corrosion caused by different corrosive mediums.Which Belonging to typical stress corrosion fatigue damage.Based on the above reasons and combining the actual conditions of sucker rod fatigue damage,in this paper,the experiments were carried out under constant stress and high strength sucker rod's performance of resistance to stress-corrosion were measured by the material's loss of strength and ductility.?2?Main factors influenced the stress-corrosion or fatigue of high strength sucker rod were p H,HCO₃-and Cl-.which were confirmed by field research.And we determines the reasonable test scope of each influence factor and distribution..?3?4330,30 Cr Mo A and 20 Cr Mo A's performance of corrosion resistance were studied by orthogonal test method.It was found that the concentration of Cl-could significantly affect the loss of ductility for 20 Cr Mo A in alkaline environment.As for the concentration of HCO₃-,it couldn't do much impact on 4330,but it could cause complex impact on 30 Cr Mo A and 20 Cr Mo A.The HCO₃-could do harm to the loss of strength but better to inhibit the loss of ductility for 30 Cr Mo A and 20 Cr Mo A.Besides,changing of p H had remarkable influence on loss of strength rather than ductility for 4330.?4?In order to further study the effect of each influence factor on the test results,single factor experiment were designed to study the suitability of different materials.And we found that chromium alloy matched the high salinity liquid well,while 4330 showed opposite results.30 Cr Mo A showed stability of ductility in different corrosive mediums,which can be used under different operating condition.30 Cr Mo A was suggested to be chosen in high salinity liquid well,next was chromium alloy.Therefore,safety factor could be increased in the process of designing to improve its service life.