Study On Corrosion Failure On Weld Seam Of Oil Pipe

In this thesis,the corrosion characteristics of carbon steel tubing in different environments were studied,and the effect of microstructure and corrosion products on the corrosion characteristics of carbon steel tubing was analyzed.In this thesis,the failure of carbon steel tube was analyzed,and the corrosion products of the welded joint were analyzed by XRD and optical microscope.The simulated working conditions of the base metal and welded joint of the failure of the steel tube were CO₂ immersion test.The results show that: CO₂ has an important influence on the corrosion process of the welding seam.The open circuit potential,polarization curves,electrochemical impedance spectroscopy,zero resistance current technology and metallographic microscope and X ray diffraction method,a comparative study of the electrochemical corrosion behavior of weld pipe,with or without CO₂ in the simulated oil field environment under different temperature of the galvanic corrosion and corrosion product components to tilt.Through the study found: organization of base metal weld than uniform microstructure at different temperature capacitive arc radius is larger than the base metal weld,weld corrosion resistance is greater than the parent material.The self corrosion potential of base metal is higher than that in the weld zone,and the welding seam is preferentially corroded.At the same time,the corrosion products are mainly FeO?OH?and Fe3O4,which have some protective effects on the weld area.After joining CO₂,weld and base metal potential negative shift of EIS capacitive arc small,poor corrosion resistance,galvanic current becomes larger,the corrosion tendency to strengthen.At the same time,the corrosion products are mainly FeCO3,corrosion product film is loose,can not form a protective effect on the weld area,thus accelerating the corrosion of the weld area.In this thesis,salt spray test and weight loss test and electrochemical test were used to study the corrosion behavior of tubing and weld in normal process.It was found in the study that the parent material in the 3.5% Nacl solution had the corrosion of the anode.Electrochemical impedance spectroscopy,polarization curve and galvanic current test results showed that compared with the weld and parent material corrosion potential is negative,the current density is large,as the anode occurs preferentially corrosion,and the weld zone is basically not corroded.All the experimental results show that the failure of the tube weld area in the oil and gas field,the welding seam as the anode corrosion,the addition of CO₂ will accelerate the corrosion.The normal welded steel tube weld area in salt spray environment is the parent material as the anode preferential corrosion,the corrosion rate of the welding seam is slower.