Cathodic protection of cast iron pipes in water supply network(1)

The anti-corrosion technology research of water supply network has been the focus of people's attention. The corrosion of water supply network not only causes serious waste of water resources and economic losses, but also causes secondary pollution of drinking water quality, which seriously threatens people's health. Cathodic protection technology is one of the widely used methods to inhibit metal corrosion process.

At present, most of the researches on cathodic protection are focused on the metal structures in marine environment, and the application of cathodic protection in drinking water environment is relatively few. Therefore, the research on cathodic protection of metal pipes in drinking water is of great significance to effectively control the corrosion process of pipe network, prolong the service life of pipe network, prevent the secondary pollution of drinking water quality, and ensure the safety of water use.

Polarization voltage is an important factor affecting the effect of cathodic protection, which can significantly affect the formation and covering effect of metal surface deposits. The application of cathodic polarization voltage can effectively inhibit the occurrence of corrosion, but only when sufficient polarization voltage is applied to the corrosion system, can the corrosion of metal be effectively prevented.

In this corrosion system, when the applied polarization voltage is greater than 1.95V, enough current can be supplied to the cast iron specimen with an area of 1cm2 to make its potential move to the cathodic protection potential range, and the corrosion can be completely inhibited;

Under the natural corrosion condition, the surface of cast iron specimen forms reddish brown rust, and the micro morphology is regular prism. Under the condition of cathodic protection, a thin gray white deposition layer was formed on the surface of cast iron specimen, and the microstructure was cauliflower like, mainly aragonite structure of calcium carbonate;

With the increase of the applied polarization voltage, the polarization resistance of the products on the surface of the cast iron specimen increases gradually, and the protection effect on the base metal is enhanced, and the corrosion rate of the metal decreases accordingly;

The drinking water quality has a significant impact on the cathodic protection effect, and the pH value is more alkaline, which is more conducive to the formation of cathodic protection product film. When the content of SO42 - and Cl - in water is too high or too low, it is not conducive to the formation and coverage of cathodic protection product film on metal surface, which will affect the cathodic protection effect of cast iron. The concentration of SO42 - and Cl - should be controlled in a proper range to better control the corrosion of pipe network and improve the effect of cathodic protection.

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