The Influence Of Applied Potential On Corrosion Fatigue Life Of The Oil Well Tube Materials

As a key use component of the oil and gas industry,oil well pipes are closely related to the development and production of oil and natural gas.However,the working conditions of the oil well pipe are very bad.It is not only affected by the alternating load,but also affected by environmental factors.The combination of mechanical factors and environmental factors causes the oil well pipe material to be seriously damaged by corrosion fatigue.At the same time,due to the presence of corrosive media in environmental factors,the oil well pipe material is prone to very serious electrochemical corrosion.Therefore,it is of guiding significance to study the law of the potential variation of the oil well pipe material in the microscopic zone for the corrosion fatigue life of oil well pipe materials.In this paper,the influence of potential change on the corrosion fatigue crack growth life of P110 oil pipe steel is studied.Firstly,based on the existing fracture model of fatigue crack propagation of metallic materials,Comparing the difference between corrosion fatigue and pure mechanical fatigue crack propagation mechanisms,And consider the effects of potential changes.Finally,a corrosion fatigue crack propagation rate model under potential change is proposed.Then,under the loading frequency of 1Hz and 3Hz,the influence of the variation of loading frequency on the corrosion fatigue crack growth rate of P110 tubing steel was studied.Finally,when the loading frequency was 1Hz,the P110 sample was applied with a cathode polarization potential of-600 mV.At 3Hz,the P110 sample was applied with a cathodic polarization potential of-600 mV and an anodic polarization potential of 300 mV,respectively.Then use the data obtained to determine the corrosion fatigue crack propagation coefficient in the proposed model,and Compare the fitted expression with the corrosion fatigue crack propagation coefficient in the proposed model.After analysis,the following conclusions are obtained: The stress ratio is 0.1.In the 3.5wt% NaCl solution,the corrosion fatigue crack growth rate of the P110 specimen becomes larger,when the loading frequency is reduced from 3Hz to 1Hz.When the loading frequency is 1Hz,On the basis of the open circuit potential plus a cathodic polarization potential of-600 mV,The corrosion fatigue crack growth rate of P110 steel increases.When the load frequency is 3Hz,the corrosion fatigue crack growth rate of P110 steel increases faster after the cathode polarization potential is-600 mV on the basis of the open circuit potential.After the anodic polarization potential of 300 mV was applied,the corrosion fatigue crack growth rate of P110 steel was slowed down.In general,the addition of cathodic polarization potential shortens the life of P110 tubing steel,plus the anode polarization potential extends the lifetime.Finally,the expression of the corrosion fatigue crack propagation rate for a complete P110 steel at different applied frequencies was obtained,and the corrosion fatigue crack propagation coefficient obtained by the two methods is similar.