The formation of protective iron carbonate film on the surface of carbon steel depends on conditions such as temperature, partial pressure, pH and Fe2+ concentration which are interrelated to each other. In the absence of film forming conditions such as high temperature and pH greater than 6, increasing the partial pressure of CO2 increases the H2CO3 concentration following Henry’s law, which increases the corrosion rate by direct reduction of carbonic acid. An increase in partial pressure of CO2 increases the corrosion rate of carbon steel by increasing the concentration of H2CO3 in solution, while at favourable film forming conditions such as high pH; it gives an opposite effect of increasing the rate of iron carbonate precipitation and helps in reducing the corrosion rate.
At atmospheric pressure, an increase in temperature gives rise to the contrasting effect of increasing the kinetics of precipitation and reducing the supersaturation. Lin et al., found that the thickness of iron carbonate scale formed with increasing partial pressure reaches maximum at 6.89 MPa. Above 6.89 MPa the thickness of the scale decreases possibly due to the maximum corrosion rate reached at a particular environmental condition or due to the inhibiting property of the CO2 corrosion process. Laboratory experiments are usually carried out at low partial pressures of CO2, which are unusual in gas fields; only a few high pressure experimental results are available in open literature. Wu et al., conducted experiments at supercritical partial pressures (> 7.382 MPa) and found that a protective film is formed at supercritical partial pressure and provides an inhibiting function on the CO2 corrosion process.
See Also:
Effect of hydrodynamics on Carbon Dioxide CO2 corrosion on carbon steel pipe lines
Effect of CO2 partial pressure on CO2 corrosion on carbon steel pipe lines
Effect of Fe2+ concentration on Carbon Dioxide CO2 corrosion on carbon steel pipe lines
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