Cathodic protection of cast iron pipes in water supply network

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.

As an important component of urban infrastructure, the research on corrosion and anti-corrosion technology of water supply network has been paid close attention. Metal pipe has the advantages of high strength and low price. There are a lot of cast iron pipe and steel pipe in water supply network system.

As far as our country is concerned, the proportion of cast iron pipe, ductile iron pipe, steel pipe and other metal pipes in the current water supply system is about 90%. In the foreign pipe network system, the proportion of cast iron pipe and steel pipe and other metal pipes is relatively high: about 53% in Poland, 56% in the United States, and more than 65% in Italy. Among them, steel pipe and cast iron pipe account for the highest proportion in large cities. In Warsaw and sbruck, for example, steel pipes and cast iron pipes account for 91% and 93% respectively.

The inner wall of water supply pipeline contacts with the transmission medium. After a long time of operation, the environmental medium transported continuously impacts and erodes the inner wall of the pipeline, and has complex physical, chemical and biological reactions with the inner wall of the pipeline, resulting in continuous corrosion of the pipe wall. The corrosion products produced in this process accumulate continuously on the inner surface of the pipeline and form nodules.

On the one hand, it hinders the water delivery of the pipeline, resulting in the decline of the water delivery capacity of the pipeline and the increase of the energy consumption required in the water delivery process; on the other hand, the continuous corrosion of the pipeline will cause the inner wall of the pipeline to become thinner, and the pipeline strength will become lower, and even lead to the pipeline perforation and cracking, resulting in the occurrence of pipe leakage and pipe burst, resulting in serious waste of water resources and huge economic losses 。

It is found that due to pipeline leakage, more than 32 billion m3 of drinking water is lost in the world every year, accounting for 35% of the total water supply. Taking the data of 2010 "statistical yearbook of urban construction" as an example, the total leakage water volume in China is 62.7552 × 108 m3, equivalent to the annual domestic water consumption of 1.40 × 108 people. Some developed countries, such as the United States, Japan and other countries, the leakage rate of the pipeline network is also very alarming, which is more than 15% and about 25% respectively.

The corrosion of water supply pipe not only causes a lot of waste of water resources and shortens the service life of pipes, but also worsens the quality of drinking water and seriously affects the safety of people's living water. After the corrosion products of cast iron pipe and other metal pipes are released to the water supply network, they can re precipitate to form nodules and adhere to the inner wall of the pipeline.

The surface structure of the nodule is loose, which can not only continue to release iron and its oxides to the water supply network, leading to the occurrence of "yellow water" and "red water" events, but also react with chlorination disinfection by-products, nitrate or natural organic matter in water, resulting in deterioration of water quality of pipe network and secondary pollution of drinking water quality. As a result, the iron content in the effluent of the user terminal is too high, bacteria and turbidity exceed the standard, which seriously affects people's water safety and threatens people's health. Therefore, in order to control the leakage of pipe network and ensure the safety of drinking water quality, it is urgent to study the anti-corrosion technology of water supply pipeline.

Shandong Linyi Bosi conductive materials Co., Ltd. is a high-tech enterprise specializing in the production of MMO flexible anode, conductive polymer flexible anode and titanium coated anode, mainly providing cathodic protection technology, engineering design, installation and technical services. Tel: 0539 3712117, 15588026668.