Abstract
A study of the hydrodynamic corrosion behaviour of carbon steel and cast irons in concentrated sulphuric acid has been made using the rotating cylinder electrode, (RCE), to simulate the corrosion phenomena that occurs under flowing conditions.
The carbon steel-sulphuric acid system has been investigated by the present authors at sulphuric acid concentrations of 68%, 93% and 98%. In these systems the liquid concentration boundary layer has been identified as the sole resistance to mass transfer, and expressions have been deduced for the corrosion rate in terms of the physical and hydrodynamic parameters at the three concentrations.
In contrast to the carbon steel, the corrosion behaviour of cast irons, in 93% and 98% sulphuric acid, was found to be greatly influenced by the presence of surface films. A model, in which the overall measured mass transfer factor is the sum of the mass transfer factor in the liquid boundary layer and the mass transfer factor in the film, is proposed and values for the film mass transfer coefficients have been determined. Significant differences in behaviour were observed between the various cast irons at the two temperatures studied. It is suggested therefore that in cases where significant film growth is occurring, corrosion can be predicted provided that the mass transfer characteristics of the film are known. When mass transfer in the film dominates, the effect of the flow geometry may be expected to become less prominent. Conversely, when the film does not significantly impede mass transfer, then the previously derived mass transfer correlations for the geometry of interest may still be useful for corrosion prediction.
