Carbon dioxide (CO_2) corrosion product scales of three kinds of oil well steel were obtained from simulated tests in autoclaves at varying temperatures and pressures. The effect of temperature and CO_2 partial pressure on the thickness and grain size of the scales was studied with the help of scanning electron microscopy (SEM). The results show that the cross sections of the corrosion product scales of the three kinds of steel are all of a double-layer structure. The variation manner of the scale thickness of the three kinds of steel with the temperature are quite similar, and the maximum scale thickness appears at 120°C; however, the temperature for the minimum of the scale thickness is variable. The curves of the grain sizes with the temperature display a peak and a valley for the three kinds of steel. The variation of scale thickness with CO_2 partial pressure for the three kinds of steel is also quite similar, in which the maximum scale thickness appears at the CO_2 partial pressure qf 6.89 MPa and then decreases rapidly when the CO_2 partial pressure increases. The variation of grain size with CO_2 partial pressure shows two peaks and a valley for each kind of steel.
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