A study of the influence of chloride ion concentration on the corrosion behavior of carbon steel in phosphate high-temperature boiler water chemistries

摘要

Purpose - 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. Design/methodology/approach - 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. Findings - Under the following conditions: T=360±3° C, pH = 9.40±0.10, cO2 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. Practical implications - 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. Originality/value - 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.