There are two methods of cathodic protection, one is sacrificial anode method, the other is impressed current method. When the metal on the cathode polarization by cathodic current on the surface of the cathode, most preferential flow to the cathode area, reducing the original potential, cathodic polarization, follow the increase of current, the negative polarization also increase of steel on the surface of the cathode area, when the polarization potential difference to the cathode and anode area is zero, the corrosion current disappear, and thus possessed the erosion process, achieve the goal of the protection. The erosion in the seawater input pump belongs to the electrochemical erosion under the action of seawater.

3. Sacrificial anode protection;

2. Impressed current protection (using the technology of Qingdao Marine Erosion Research Institute, General Iron and Steel Research Institute);

1. Choose materials resistant to sea water erosion;

To sum up, the following measures are mainly adopted for the anti-corrosion of cyclic pump:

According to the first and second phase of zhanjiang power plant cycle pump site use, in order to solve the main shaft erosion and guide vane body erosion and cavitation problems, the cycle pump above two parts of the material are made of seawater erosion and cavitation resistance function of better stainless steel.

1) Erosion pool is formed in Yin and anode region simultaneously;

The occurrence of water pump erosion must have the following two prerequisites:

Metal erosion refers to the destruction or deterioration of metal materials caused by chemical or physical dissolution of environmental media. Because sea water is a conductive dielectric, has a strong corrosive effect on metal, in the natural state, within a few years will make the pump erosion perforation and scrapped. In order to prolong the service life of the pump, the cathodic protection measures are generally taken for the inner wall of the pump. Sacrificial anode is a method in which a metal with a negative potential is connected with a metal structure with a positive potential in a certain medium, and the metal structure is protected by the current generated by the continuous dissolution of the metal with a negative potential. Dc power is generally used potentiostat, its role is to convert alternating current into direct current, to provide energy for the whole system, is the heart of the system.

One, electrochemical corrosion prevention:

. Impressed current cathodic protection law is to connect the negative electrode of the impressed DC power supply to the protected metal structure, and the positive electrode to the auxiliary anode installed outside the metal structure and insulated with it. When the circuit is closed, the current from the auxiliary anode through seawater to the metal structure

Cathodic protection is a method to eliminate electrochemical erosion by providing cathodic protection current to the protected metal structure to make it cathodic polarized. The erosion of metal in seawater is caused by an electrochemical reaction. If the electrochemical reaction can be prevented, the electrochemical erosion of metal can be inhibited.

After mechanical derusting and surface blasting, the inner and outer surfaces of the circulating pump are coated with double component modified epoxy resin coating. In order to ensure that the shaft and impeller get good protection, special shaft grounding device, each shaft grounding device is composed of a copper slip ring and two brushes, the brush and the pump shell electric connection, so that the potential of the shaft and impeller is consistent with the pump body, to avoid erosion.

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2) Sea water as conductive medium.

4. The inner and outer surfaces of the parts are coated with BWH9300 series heavy anti-corrosion coating which is resistant to sea water erosion.

A closed loop is formed so that the metal structure can be cathodic polarized to avoid erosion. According to the working environment of the pump, Ag/AgCl and Zn reference electrodes can be used, whose role is to monitor the potential of the pump, while providing control signals to the automatic DC power supply, so that the pump is always in the range of protection potential.

Two, physical anti-corrosion

The applied current cathodic protection system for the inner wall of water pump consists of four parts: auxiliary pole, reference electrode, DC power supply and shaft grounding device. The dissolved metal is called the sacrificial anode. There are three kinds of sacrificial anodes commonly used: zinc alloy, aluminum alloy and magnesium alloy.

In the seawater, the metal in the anode region transmits a current to the cathode region through seawater. At this time, the metal in the anode region loses electrons and becomes ions which enter the seawater to be eroded, while the metal in the cathode region gains electrons and is protected. The external electrode connected with the positive pole of the DC power supply is called the auxiliary anode, whose role is to make the current from the anode through the medium to the protected structure, the general selection of platinum coated niobium as the anode material. Metal erosion is a chemical or electrochemical heterogeneous reaction occurring on the surface or at the interface, the structure of which is to convert the metal into an oxidized (ionic) state.