Cathodic protection

Here is some information for reference: Sacrificial anode cathodic protection for the inner walls of steel circulating water pipes. In thermal power plants where seawater is used for cooling, circulating water is transported through steel pipes. It is an essential device in the cooling water system. Most circulating water pipes are made of carbon steel, and due to the combined effect of electrochemical corrosion factors and fluid dynamics factors, their corrosion damage is much more severe than under normal conditions. The corrosion rate of steel in seawater is generally 0.06–0.17 mm/year. And when the flow rate increases to 1 m/s, its corrosion rate triples ； Increases to 4 times at 2 m/s ； At 4.57m(15in)/s, it increases to 5.7 times. It can be seen that the flow velocity of seawater is the most prominent physical factor among various factors affecting the corrosion of the pipe interior wall. 1. Protection potential: The protection potential range for the inner wall of seawater pipelines should generally be between -0.80 and -1.00 V (with respect to the silver/silver chloride electrode/seawater, the same applies hereafter). In special cases, when the position where the anode is placed is restricted, the protection potential range can be -0.75 to -1.00 V. 2. Protection current density: For cathodic protection of the inner walls of seawater pipelines, the required protection current density varies significantly depending on the flow rate of seawater. Generally, the lower the flow rate, the smaller the protective current required ； The higher the flow rate, the greater the protective current required. The table below shows the cathodic protection current density of steel at different seawater flow rates. Table 1 Cathodic protection current density of steel at different seawater flow rates Environmental conditions Surface condition Protection current density/(mA/m2) Still seawater None 120–150 Several layers of vinyl resin paint (good condition) 15–20 Several layers of anti-rust paint (good condition) 25–30 Two layers of anti-rust paint 40–50 Flow rate/(m/s) 2 None 2500 44000 87000 1211000

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