Effect of calcium ions on CO2 corrosion of 3Cr low-alloy steel

The effect of calcium ions on the corrosion behavior of 3Cr low-alloy steel in CO2-containing sodium chloride solution was investigated by immersion test and electrochemical measurements. It is found that with the addition of Ca2+ to CO2-containing solution, the crazing level of the corrosion scale on the specimen is much slighter than that of the specimen immersed in solution without Ca2+. The pitting on the surface of the specimens immersed in the solution with Ca2+ is relatively small and distributes uniformly all over the surface. The significant change in the anodic polarization curve is attributed to the deposition of the CaCO3. CaCO3 deposits on the specimen surface and gives a protection to the metal substrate. And with the anodic proceeding, the concentration of H+ in the solution increases. The CaCO3 deposition dissolves in the low pH solution and the protection effect disappears.