Study On Cathodic Protection Of Cast Iron In Drinking Water Distribution Systems

The research of anti-corrosion technology in drinking water distribution systems has attracted people's attention.The corrosion occurred on metal pipeline not only causes a serious waste of water resources and enormous economic losses,but also lead to the secondary pollution of drinking water quality,which will pose a serious threat to people's health.The cathodic protection technology is one of the widely used methods to suppress the corrosion process of metals.However,studies about cathodic protection in drinking water were less,especially the research with cast iron as the object in this environment.Therefore,the research on the cathodic protection of metal pipe in drinking water distribution systems is of great significance to effectively con-trol the occurrence of corrosion,prolong the service life of pipe,prevent secondary pollution of drinking water quality and guarantee the safety of drinking water.Methods such as electrochemical test and surface analysis technology were used to study the influences of different potentials on the cathodic protection of cast iron specimens in drinking water.And then,the effects of drinking water quality factors on cathodic protection were studied.The results indicated:?1?Polarization voltage is an important factor affecting the cathodic protection effect,which can significantly affect the formation and coverage of surface sediments on cast iron.Application of cathodic polarization voltage can effectively inhibit the occurrence of corrosion,but only when the polarization voltage was large enough can it effectively prevent metal corrosion.When the applied polarization voltage is higher than 1.95V,it was able to supply sufficient current to the cast iron specimen with an area of 1cm² so that its potential can be shifted to the cathodic protection potential range and the corrosion is completely inhibited.The larger the applied initial polariza-tion voltage was,the more negative the metal potential was;?2?Under the condition of natural corrosion,the surface of cast iron specimens produced reddish-brown rust,and the microscopic appearance was more regular prism while a thin layer of gray-white sedimentary appeared on the surface of the cast iron when the cathodic protection was applied.Its microcosmic morphology is cauliflow-er-shaped,and according to the results of XRD,the layer of gray-white sedimentary was mainly aragonite structure of CaCO₃.?3?With the increase of the polarization voltage,the polarization resistance of cast iron specimens increased,the protection effect on the base metal improved,and the corrosion rate of the metal decreased accordingly.?4?The water quality of drinking water has a significant impact on the cathodic protection effect.When the pH value is alkaline,it was more conducive for the for-mation of cathodic protection products.When the amount of anions such as SO₄^2- and Cl^- in water was too high or too low,they were adverse for the formation and coverage of the cathodic protection product film on the metal surface,which affect ed the ca-thodic protection effect of cast iron.Appropriate concentration of SO₄^2- and Cl^- in drinking water will better control corrosion,and improve the effect of cathodic protec-tion.