The purpose of this paper is to investigate the influence of Cl‐ions on the pitting corrosion of water‐wall tube of a boiler and the principle behind it.
The specimens were immersed for seven hours at 300°C in deaerated water subjected to simulation‐modified equilibrium phosphate treatment, containing Cl‐ions at various concentrations. The effects of Cl‐ions on pitting corrosion were assessed by the rate mass loss, transmission reflection metallurgical microscopy, SEM, EDS, and XRD.
The results indicated that Cl‐ions cause the breakdown of passive films. The corrosion mechanism of Cl‐is proposed to involve an intermediate dissolution stage. The Cl‐ions act as a catalyst of corrosion, by inducing the hydrolysis of Fe2+. The critical susceptive Cl‐concentrations are 0.2 and 0.6 mg·L‐1 for the passivated specimens and for the unpassivated specimens, respectively.
The paper provides information regarding the relationship between Cl‐concentrations and pitting corrosion, useful for understanding the mechanism of Cl‐induced pitting corrosion, and the research results can provide theoretical guidelines for preventing water‐wall of power plants from corroding.
