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

Abstract

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, c_O2<0.020 mg/l, the density of pitting corrosion on specimens without a protective film increased with the increase of C_Cl⁻ content, while C_Cl⁻ was > 0.2 mg/l. The film on specimens with integral films would not dissolve observably even until the C_Cl⁻ 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.

Citation

Shun'an, C., Qing, Z. and Zhixin, Z. (2008), "A study of the influence of chloride ion concentration on the corrosion behavior of carbon steel in phosphate high‐temperature boiler water chemistries", Anti-Corrosion Methods and Materials, Vol. 55 No. 1, pp. 15-19. https://doi.org/10.1108/00035590810842780