Study On Corrosion Model And Evaluation Method Of Marine Steel In Sea Water

There are significant amounts of marine resources including oil,gas and minerals in the deep ocean.Efficient exploration in the deep ocean poses a great challenge for the facilities due to the high corrosive nature of the environment.Presently,the researches on this field are mainly focused on atmospheric environments and solution systems with ordinary pressure.The corrosion behavior and protection method of metals used in the high water pressure environments of the deep ocean are not very clear.It becomes an issue urgently needed to discuss in a greater depth.Due to the shortage of oil and gas resources in the land and the need of energy security,humans began to focused on deep sea marine development,but the deep sea environment is a very severe corrosive environment,efficient resources exploration in the deep ocean poses a great challenge for the metal facilities.Presently,the researches on this field are mainly focused on shallow environments and solution systems with ordinary pressure,the corrosion behavior and protection method of metals used in the high water pressure environments of the deep ocean are not very clear.Pressure as the most important and significant in deep-sea characteristic factors has played a significant effect on the metal corrosion,it becomes an issue urgently needed to discuss in a greater depth.Low alloy steel because of its excellent mechanical and corrosion resistant properties have been deployed in service in marine applications as a major marine production structural material for many years.Accordingly,it is of great significance to understand the corrosion behavior systemically and develop the corresponding effective protection methods for long-term stably and safely running of the facilities served in deep ocean pressure environment.Studied the corrosion resistant performance and mechanism on typical marine steel 907 A and 921 A and 980 in laboratory simulate deep-sea pressure environment contrast of Q235 carbon steel,through electrochemical methods such as polarization curves,electrochemical impedance spectroscopy measurement(EIS)etc,in conjunction with static weight loss test,slow strain stress corrosion tests and some analysis technology like X-ray diffraction(XRD),scanning electron microscopy(SEM),Raman spectroscopy and three-dimensional image analysis technology etc.From the view of mathematics,obtained the mathematical relation is suitable for the corrosion rate changing with time and stress of selected materials in the lab simulation deep ocean pressure environment.The main conclusions are:Slow tensile test results show that the fracture morphology are mainly toughening nest group,ductile fracture are mainly fracture form despatch,grain refinement,tensile strength and tress corrosion cracking sensitivity increased with increasing of steel strength level.With the increase of pressure,the stress corrosion cracking sensitivity of 980 steel is reduced,may be due to the high pressure increased anode surface resistance and reduced the liquid phase mass transfer process makes the anodic dissolution rate,thus inhibited the crack nucleation and propagation.Static weight-loss results show that,low alloy has good corrosion resistance compared with Q235 carbon steel,907 A steel more vulnerable to the effects of pressure and corrosion was accelerated,consequently corrosion resistance of 921 A is relatively good,overall the water pressure accelerated the low alloy steel anodic dissolution process.With simulated pressure increases,the corrosion form change from uniform corrosion in low pressure to local corrosion in high pressure,and accelerate the initiation and growth of local corrosion process.From the point of corrosion situation,the corrosion of carbon steel is more serious,that marine corrosion resistance of low alloy steel is relatively good.The content of ?-FeOOH is higher and the content of ?-FeOOH and Fe3O4 will be more low in corrosion product film weakened the rust layer of protection,so as to promote the marine corrosion of steel.Early with prolongation of immersion time drops rapidly then swings slow,and the change trend of steady,namely corrosion under the conditions of different pressure dynamics has similar characteristics.Marine steel electrochemical performance study shows that hydrostatic pressure decreases impedance arc radius and the impedance value gradually decreases,water pressure promote corrosion.As pressure increased,marine steel corrosion potential happens obvious negative shift,cathodic current density is higher than that of neritic environment in the process,may be due to pressure accelerated the activation of anodic dissolution process and the inhibition of cathodic process.From the perspective of mathematical curve fitting,finding out the regularities of corrosion rate with the change of pressure and corrosion cycle in laboratory simulation conditions,and further got the function relation D-Ax~n regression to fit weightlessness results in laboratory simulation,and predict corrosion results of laboratory simulation environment and actual area,error rate are controlled within 20%,the prediction error within the scope is feasible,can reflect the corrosion law,Found that the method of power function regression can be used to predict the marine corrosion behavior of steel.