Research On Corrosion Characteristics And Influencing Factors Of Metal Pipes In Water Supply

In recent years,with people’s increasing pursuit of a better life and increasing requirements for water quality,water quality safety issues caused by the deterioration of water quality caused by the corrosion of the pipes of the water supply system have become a topic of close concern.In order to solve the corrosion problem of water supply pipe network,copper pipes and stainless steel pipes have been gradually used in water supply systems in recent years.However,there are not many studies on the corrosion of copper pipes and stainless steel pipes under water supply conditions and their effects on water quality.Therefore,it has theoretical significance and application value to investigate the corrosion status of different metal pipes under water supply conditions and the influence of the corrosion process on water quality changes.This article takes three common metal pipes(spheroidal graphite cast iron,copper,stainless steel 304)in the water supply system as the object.By making metal material test pieces,electrochemical testing,conventional water quality testing,SEM and metallographic microscopic observations are used to corrode pipe materials.Study the situation.The main research contents and results are as follows:First,using tap water as the experimental medium,using the static immersion method,the corrosion characteristics of three metal pipes and their influence on the changing laws of water quality were studied.The p H value,temperature,TDS,turbidity,total iron concentration,total number of bacterial colonies and other water quality indicators of the solution in the ductile iron group,copper group,and stainless steel group during the entire reaction period were tested.The results show that:during the corrosion period,the water quality indicators such as p H value,turbidity,TDS,and total iron concentration of the three pipe materials all increased to varying degrees.Among them,ductile iron will greatly increase the turbidity and total iron concentration of the tap water,and copper has an effect The impact is second,and stainless steel has the least impact.After 60 days of immersion in the experiment,the detection of free microorganisms in the water found that:the microorganisms in the water in each static device are stable,and the three metal pipes will increase the biomass in the tap water after corrosion.After the static device groups are stabilized,the number of bacteria in the water will be ranked as ductile iron.>Stainless steel 304>Copper.Therefore,the copper pipe has an inhibitory effect on the growth of microbial biomass in the water.Then,three metal pipe test pieces of ductile iron,copper and stainless steel 304 were used for dynamic simulation corrosion experiment.The detection of the biomass in the water in and out of the dynamic device found that the total number of bacteria in the water(162cfu/ml)<the total number of bacteria in the water(1500cfu/ml).Scanning electron microscopy(SEM)analysis shows that the surface of the ductile iron and copper test pieces is rough,while the surface of the stainless steel 304 test piece is smooth,that is,the corrosion degree of stainless steel in tap water is relatively low.The electrochemical test results show that the relationship between the corrosion current and polarization resistance of the three pipes is ductile iron<copper<stainless steel,indicating that the electrochemical corrosion strength of the three pipes is stainless steel,copper,and ductile iron in descending order.Finally,three electrochemical testing methods including polarization curve,AC impedance and cyclic voltammetry curve were used to observe the surface morphology of metal with metallographic microscopy to study the pitting behavior of stainless steel and copper at different Cl~-concentrations and temperatures in tap water.The analysis results show that with the increase of temperature and chloride ion concentration,the corrosion potential of stainless steel and copper will shift negatively,the pitting potential Eb will decrease,the number of pitting corrosion will increase,and the size of pitting pits will become larger.Increase the pitting sensitivity of passive metals(copper and stainless steel).The increase of Cl~-concentration and temperature will increase the number of active sites on the metal surface and increase the content of adsorbed Cl~-,which will accelerate the dissolution of the metal anode and cause pitting corrosion.The analysis of the corrosion characteristics of copper and stainless steel 304found that after immersing 304 stainless steel for 20 days under the same conditions,the self-corrosion potential and pitting potential(Ep)are high,the current density is low,the corrosion rate is low,and the corrosion resistance is good.