Industry Knowledge

Several commonly used ways of Cathodic protection method for tank bottom
Jul 11, 2017

       cathodic protection technology

        Cathodic protection is used to prevent the metal dielectric (in seawater, fresh water and soil medium) electrochemical corrosion protection , the basic principle of this technique is applied to DC current to the metal surface to be protected, the cathodic polarization potential, when the metal to a potential value, the anodic dissolution process corrosion will be effectively suppressed. Cathodic protection is divided into two kinds of sacrificial anode and impressed current method according to the different ways of providing cathode current. Mainly used for tank bottom corrosion protection. The optional cathodic protection methods for the bottom of tank are as follows:

        

       1 sacrificial anode system

       The sacrificial anode system is used to protect the tank, and the installation is simple and will not cause corrosion interference. However, the tank is not adequately protected unless the tank and pipe and other systems are well insulated. The driving voltage of the sacrificial anode system is generally less than 0.7V. During operation, the current output of the cathodic protection system is limited and the service life is shortened.

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       2 deep well anode system

       The deep well anode system is mainly used in the storage tank, especially for the narrow space area. The disadvantage is that the cathodic protection current is uneven, and some areas are not protected. Prone to corrosion interference. The anode is under very bad working conditions and is prone to premature damage.

        

       3 flexible anode system

       Flexible anode is a long line, flexible, cable type auxiliary anode, which is made of conductive adhesive wrapped outside the cable and covered with a layer of carbon powder to fill the filler. The system can be laid under the bottom of the tank, the current distribution is uniform, and it is difficult to produce corrosion interference. It can be used for old storage tanks and new storage tanks. But it has the following disadvantages:

        The transportation and installation cost of the system is higher than that of the network anode system, and the anode weight of each plate is very heavy, which increases the difficulty and cost of handling;

        The packing band is easy to break. Cause filling leakage, need to be filled later;

As a result of conductive rubber under the action of electric current, it is easy to age and crack over time, which leads to the rapid corrosion of copper core cable, resulting in premature failure of the system, and the system can not bend too much;

The site requires a lot of cable connection, the quality is difficult to guarantee.

Flexible Anode1.jpg

        

        4 mesh anode system

        The mesh anode is an applied current auxiliary anode consisting of a mixed metal oxide strip and a cross weld of a titanium metal connecting plate. The anode network is embedded in the tank foundation to provide a protective current for the tank bottom plate. Compared with other cathodic protection methods, the invention has the following advantages:

The current distribution is very uniform, the output can be adjusted, and the tank can be fully protected;

       Stray currents produced are very few and do not cause corrosion interference to the structure;

The installation is simple, and the quality is guaranteed. No insulation is needed between the tank and the pipe;

          Not easy to be damaged by Japanese construction, long service life.

         

         All of the above cathodic protection methods have advantages and disadvantages, and the investment of magnesium sacrificial anode is about 1.5~2 times of network anode, and the investment of flexible anode is about 1~1.5 times of net anode. Therefore, the use of network anode cathodic protection is not only the most reliable way, but also the most economical measures.

   

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