PROBLEM TO BE SOLVED: To provide a method for suppressing corrosion of a carbon steel pipe capable of further reducing the corrosion of the carbon steel pipe. SOLUTION: In a BWR plant, oxygen is supplied to a purification system pipe 18 which is connected to RPV3 and is composed of a Cr-containing carbon steel pipe containing Cr in a proportion of more than 0.052 wt% and less than 0.4 wt%. Oxygen is injected from the injection device 30 to generate furnace water at 150 ° C. having a dissolved oxygen concentration of 30 μg / L. The furnace water is brought into contact with the inner surface of the purification system pipe 18, and the inner surface thereof is subjected to an oxidation treatment to form an oxide film containing Cr on the inner surface thereof. Therefore, after the oxide film is formed, hydrogen is injected into the furnace water in the RPV3 through the water supply pipe 11 connected to the RPV3, and the dissolved oxygen concentration of the furnace water in contact with the inner surface of the purification system pipe 18 is reduced to 2 μg / L. However, the corrosion of the purification system pipe 18 is remarkably suppressed. [Selection diagram] Fig. 1
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