Research On Electrochemical Corrosion Mechanism Of Water Supply Pipes

Long-term contact with the carried water and the surrounding soil makes water supply pipe prone to electrochemical corrosion,which will lead to pipeline leakage or burst.At the same time,corrosion scales of pipe inner wall not only reduces the water supply capacity of the pipe network but also causes the'red water'phenomenon through the iron release,which threatens the safe operation of the water distribution system.Based on the electrochemistry of corrosion and through the dynamic integration of weight-loss method,electrochemical measurement and microscopic analysis technology,this paper establishes the flow corrosion simulating and monitoring system?FCSMS?and the soil accelerated corrosion device?SACD?,systematically studies the behavior and mechanism of the internal and soil corrosion of three common metallic pipe materials,namely ductile iron?DI?,gray cast iron?GI?and carbon steel?CS?,the composition and corrosive action of corrosion products as well as influencing factors of corrosion.?1?By conducting internal corrosion experimental with the FCSMS,the in situ monitoring of the growth of corrosion scale layer can be achieved,after which the physical model of corrosion scale layer was established through electrochemical impedance spectroscopy?EIS?and the growth mechanism of corrosion scale and the corrosion control effect were revealed.Upon formation of a stable corrosion scale layer,the corrosion rate control step changed from charge transfer to oxygen diffusion,microscopic analysis of which showed that?-FeOOH and CaCO₃ were the characteristic crystal structures of the stable corrosion scale layer.?2?Through linear polarization resistance?LPR?method,EIS and polarization curve test,it was determined how the six influencing factors?including temperature,flow rate etc.?affect the corrosion rate,corrosion scale structure and the anodic and cathodic reaction process.Then the effect mechanism of each influencing factor in internal corrosion process was expounded,and the ranking of such influencing factors based on their importance was determined through the correlation analysis:temperature>p H>dissolved oxygen>total hardness>flow velocity>total residual chlorine.?3?Utilizing the field coupon test developed from the Wathte-Treseder method,this paper explained the localised corrosion behavior of three materials in the typical coastal saline soil.It was found that the corrosion rate fluctuated significantly with the seasons.The effect mechanism of iron oxychlorides on soil corrosion acceleration was revealed in a high chloride ion environment.?4?Through the soil corrosion simulated accelerated test,in combination with EIS and polarization curve analysis,it was revealed that in the coastal salt soil the initial corrosion stage was subject to both the cathodic diffusion and anodic activation,while the stable corrosion stage was mainly controlled by the cathodic diffusion effect.The orthogonal experiment was conducted to research the effects of temperature,salinity and humidity on the soil corrosion.?5?By contrast analysis of the mechanism and characteristics of internal and soil corrosion of water supply pipe,the power function model of corrosion depth changing with time and corrosion rate prediction model were established.Through which the safety hazards caused by internal and soil corrosion on water supply pipe were discussed and the corresponding anti-corrosion measures were put forward.