Study On Oxidation Behavior Of 316L Stainless Steel In High Temperature Environment And Fluid Corrosion Of Oxide Film

High temperature corrosion and flow accelerated corrosion occur in many areas such as petrochemical engineering,energy,metallurgy,aerospace and so on.The multi-phase flow erosion-corrosion in complex environments such as high temperature high pressure,often cause metal materials to undergo irreversible physical and chemical reactions and degrade,causing significant safety hazards and economic losses to industrial production.In this paper,316L stainless steel was selected as the research object,and experiments were performed using a high-temperature autoclave and a liquid-solid two-phase jet equipment.The corrosion mechanism of high temperature,oxide film properties and flow accelerated corrosion mechanism of 316L stainless steel were studied by means of electrochemical test,element determination and surface morphology.The paper firstly studied the high temperature high pressure corrosion behavior of316L stainless steel in pure water,Na Cl solution and Na HCO₃ solution.Electrochemical research results showed that in the temperature range of 150℃-250℃,316L stainless steel had the worst corrosion resistance at 200℃,and the best corrosion resistance at150℃,which might be due to the oxide film formed in the metal surface at 150℃was the densest.Compared with the pure water environment at the same temperature,316L stainless steel had stronger corrosion resistance when the HCO₃^-concentration was low（0.05%,0.1%,0.3%）,showing the protection of bicarbonate ions on 316L stainless steel effect.However,when the HCO₃^-concentration increased to 4.2%,the corrosion resistance of 316L stainless steel in HCO₃^-solution was weaker than that of pure water,which was related to the simultaneous occurrence of oxygen absorption corrosion and hydrogen evolution corrosion on the metal surface.The paper then compared the corrosion of 316L stainless steel in solutions containing Cl^-and HCO₃^-.The results showed that when Cl^-and HCO₃^-were existing at the same time,there would be competitive position behavior on the surface of the material.When the bicarbonate ion concentration was less than the chloride ion concentration,the bicarbonate ion would be preferentially adsorbed on the sample surface,inhibiting the chloride pitting effect.When the bicarbonate ion concentration was greater than the chloride ion concentration,the bicarbonate ion and the chloride ion would have a synergistic effect to promote the corrosion of the material.The paper also studied the accelerated corrosion mechanism of the oxide film formed at high temperature under the 3.5%Na Cl solution.The results showed that there was a phenomenon of critical fluid velocity.,which made the corrosion resistance of 316L stainless steel after impact increasing first and then decreasing.The sample had the strongest corrosion resistance when the fluid velocity was 4m/s.The analysis results of the oxide film on the sample surface showed that when the velocity exceeded the critical value,the oxide film would be destroyed by high-speed erosion,which was the main reason for the reduction of corrosion resistance at high flow rate.When the velocity was lower than the critical fluid velocity.,the destruction of the oxide film on the surface of the sample caused by the erosion was very limited.And the increase in fluid velocity.was conducive to the mass transfer process and could promote the rapid repair of the oxide film through the passivation effect,which was the main reason for the increased corrosion resistance of samples at low fluid velocity.Compared with static corrosion,the corrosion of the sample was increased under dynamic fluid erosion,indicating that the fluid flow would accelerate the corrosion of the sample under the same conditions.