This paper sets out to study the corrosion of No. 20 carbon steel without film and with films of different qualities in high‐temperature boiler water with different Cl− concentrations.
The static simulated experiment in high‐pressure autoclave and the surface analysis methods of EPMA and XRD were carried out to study the corrosion effect.
Under the following conditions: T=360±3°C, pH = 9.40±0.10, cO2<0.020 mg/l, the density of pitting corrosion on specimens without a protective film increased with the increase of CCl− content, while CCl− was > 0.2 mg/l. The film on specimens with integral films would not dissolve observably even until the CCl− concentration was as high as 0.8 mg/l. Films with corrosion pits would begin dissolving when the Cl− concentration reached 0.4 mg/l. The main constituents of the oxidative films in the gas and liquid phases both were Fe3O4.
In order to prevent carbon steel from corroding in boiler water containing Cl− under conditions of low‐phosphate and low‐sodium hydroxide treatment, the concentration of Cl− should be strictly controlled.
It was found that the presence of excessive Cl− in boiler water accelerated the corrosion of No. 20 carbon steel and the maximum permissible concentration of Cl− under the conditions (temperature and pressure) of sub‐critical drum boilers was 0.2 mg/l. The research results can provide theoretical guidelines for preventing the facilities of power plants from corroding.
