Modeling Study Of Electrochemical Corrosion Behavior Of Three Typical Materials In Deep-sea Environment

China has put forward the three-part strategy of "deep-sea entry","deep-sea exploration" and "deep-sea development",which makes deep-sea research and development a hot topic.An important challenge of the stratege is the corrosion problem of deep-sea equipment materials.Because deep-sea environment is drywet alternation,stress alternation,and temperature alternation,which is a severe corrosion condition for materials.In addition,due that the deep-sea equipment generally consists of dissimilar metals,it also bears the risk of galvanic corrosion.Therefore,it is necessary to study galvanic corrosion of equipment materials in deep sea environment.In the dissertation three typical deep-sea equipment materials,980 low alloy steel(980),of B10 copper alloy(B10)and 2205 dual-phase stainless steel(2205),were choosed to study the effect of deep-sea environmental factors(temperature,oxygen content and hydrostatic pressure)on their corrosion behavior.Then,prediction model of polarization curves for these materials in the deep-sea environment were established by artificial neural network.Last,complex galvanic corrosion in in deep-sea environment was studied by numerical simulation and experiment.The polarization behavior of 980 low alloy steels in different environments was obtained by the full-factor design of experiment method,and the relationship between the self-corrosion potential and current density and deep-sea environmental factors was established by polynomial fitting.The analysis results showed that the main influence factors of self-corrosion potential were temperature,followed by dissolved oxygen content.Relatively,the hydrostatic pressure had little influence,and the interaction effect was almost negligible.As temperature rised,and dissolved oxygen content decreased,self-corrosion potential decreased.The main influence factors of self-corrosion current density were temperature,followed by dissolved oxygen content and hydrostatic pressure,and self-corrosion current idensity was largely affected by the interaction between temperature and dissolved oxygen content.With the increase of dissolved oxygen content,hydrostatic pressure and temperature,self-corrosion current idensity increased.On the basis of polarization curve data in different environments,through artificial neural network method,polarization curve prediction models of 980 low alloy steel,B10 copper alloy and 2205 dual-phase stainless steel in the deep-sea environment were established,and prediction results were of good agreement with experimental results.A method forjudging the metal polarization state of the intermediate potential of complex galvanic couple was proposed.Corrosion rates of the complex galvanic couple 980/B10/2205 were calculated by the numerical simulation method,and it was in consistent with experimental results,which proved the reliability of the numerical simulation method of complex galvanic corrosion.Corrosion rates of the complex galvanic couple 980/B 10/2205 under different environments were obtained by numerical simulation method,and the relationship between complex galvanic corrosion rate and the deep-sea environmental factors was established by polynomial fitting method.The results suggested that the rank order from large to small of the influence factors on the average couple current density were dissolved oxygen content(34.00%),temperature(33.42%)and the interaction between temperature and oxygen content(32.58%),and the hydrostatic pressure had no influence.As temperature increased and dissolved oxygen content increased,the average galvanic current density increased.Effects of water depth,area ratio of cathode/anode and the configuration order on the corrosion rate of complex galvanic couple in the South China Sea were studied by numerical simulation.Both numerical simulation and experimental results demonstrated that corrosion rate of complex galvanic couple gradually decreased with the increase of seawater depth.The average current density of complex galvanic couple increased rapidly with the increase of the area ratio of cathode/anode.When the depth of seawater and the area ratio of cathode/anode remained unchanged,the higher the area proportion of metal of high self-corrosion potential in the complex galvanic couple was,the higher the average current density was.When area ratio of cathode/anode remained a certain constant,although the average galvanic current density under different configuration orders had not much difference,the trend of relative vaule was the same.The average galvanic current idensity with 980 low alloy steel in the middle was the largest,and it was in the middle with higher self-corrosion potential cathode metal in the middle,and it was smallest with lower self-corrosion potential cathode metal in the middle.