EFFECT OF Ca2+ ON C02 CORROSION OF CARBON STEEL

In the sweet oil and gas fields, the formation water contained many cations such as Ca2+,
which lead to precipitation of scales and may influence the susceptibility to uniform and
localized corrosion during C02 corrosion. Previous research related to effect of Ca2
+
concentration in localized corrosion, less research focused on general COz corrosion of
carbon steel. The present study aimed at filling this gap by performing general COz
corrosion study in the solution of rich Ca2
+. Linear polarization resistance (LPR)
technique was used to investigate the effect of Ca2
+ concentration on general C02
corrosion of carbon steel X-52 under static condition. Ca2
+ was added to the solution of
NaCl as CaClz to simulate the formation water. Ca2
+ concentration in the simulated
solution was set up at 0, 7000, 10000 and 20000 ppm. The experiments were carried out
at constant cr concentration of 36397.54 ppm to eliminate the effect of cr on COz
corrosion of carbon steel. The temperature was set at 50°C and 80"C to simulate the real
field condition. The results show that at the same cr concentration, the corrosion rate
decreases with present of Ca2+ in the solution and increases with increasing Ca2+
concentration from 7000 ppm to 20000 ppm. CaC03 scale forms a protective layer on the
metal surface, hence reduce the corrosion rate. However, increase in Ca2+ will cause the
corrosion scales become looser, which will cause the protectiveness of scales decrease.
The corrosion rate increase with increasing temperature from 50°C to 80°C. This is due to
the acceleration of anodic and cathodic reactions when temperature increases.