Study On Corrosion Mechanism And Prediction Model Of SPHC In Tianjin Atmospheric Environment

Metal faces serious atmospheric corrosion problems during its service.Whether it is a stationary building structure or a frequently moving vehicle,it will suffer a certain degree of atmospheric corrosion damage.At present,most researches on atmospheric corrosion focus on the structure of materials in static service,and there is a lack of research on the atmospheric corrosion laws of metal materials in the constantly changing state of the service environment.Therefore,this paper starts from the dynamic and static atmospheric exposure experiments to explores the difference of atmospheric corrosion laws under static and dynamic service conditions through three aspects:the comparison of atmospheric exposure experiment results,prediction model construction,and indoor acceleration experiments on key environmental factors of dynamic and static conditions.First,the atmospheric corrosion laws of SPHC under two service conditions are studied by carrying out static atmospheric exposure experiments and dynamic atmospheric exposure experiments on vehicles:（1）The corrosion kinetics under static service conditions were studied,and the results showed that the corrosion rate first increased,then decreased,and finally stabilized.After 24 months of exposure,the static atmospheric corrosion rates reached 13.64μm/year;（2）The morphology and rust composition changes of SPHC under two service conditions are studied.The results show that the corrosion products under two service conditions are mainlyγ-Fe OOH andα-Fe OOH.During the dynamic atmospheric corrosion process,the SPHC surface rust layer contains a large amount of Si O₂ and the rust layer falls off during the service process.（3）The corrosion resistance changes of SPHC under two service conditions were explored.During 24 months of exposure,the SPHC’s self-corrosion current density under static and dynamic service conditions was replaced from 5.47×10^-5 A/cm² to 0.35×10^-5 A/cm² and 0.55×10^-5 A/cm²,respectively.The results showed that the corrosion resistance of SPHC under both service conditions showed an increasing trend and the rust layer had a stronger protective effect on the substrate under dynamic service conditions.Secondly,based on the dynamic and static atmospheric exposure experiment and the neural network method coupled with genetic algorithm,the atmospheric corrosion prediction models under two service conditions were constructed respectively:（1）A method for establishing a static atmospheric corrosion model by screening the exposure experimental data of international projects under a small sample was proposed.Its validity was proved and a static atmospheric corrosion map of Tianjin was drawn.（2）For dynamic service conditions,a model building method that comprehensively considers static atmospheric environmental factors and vehicle driving characteristics factors is proposed.Through this method,a dynamic atmospheric corrosion prediction model is established based on the experimental data of dynamic atmospheric exposure of vehicles and its accuracy is proved.Finally,the influence of rainfall and vehicle speed on static and dynamic atmospheric corrosion are studied by building simulated rainfall and simulated vehicle speed indoor acceleration experimental platforms.The results show that:（1）Rainfall has an accelerating effect on static atmospheric corrosion.When rainfall reaches a certain threshold,the magnitude of the accelerating effect is negatively correlated with rainfall.（2）The vehicle speed accelerates the corrosion in the initial stage of dynamic atmospheric corrosion,which mainly accelerates the corrosion by affecting the movement of corrosive media on the surface of the sample.