Effects of the concentration of calcium ions on the corrosion behavior of X80 steel

The effects of Ca²⁺ concentration on the corrosion behavior of X80 steel in Hami soil simulated solutions were investigated by using weight loss measurements, electrochemical testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD). When the steel is immersed in the simulated solutions with different Ca²⁺ concentrations for 60 d, uniform corrosion occurs on the steel surface and the corrosion products mainly consist of β-FeOOH. The corrosion rate of the steel in the simulated solution gradually increases with the decrement of Ca²⁺ concentration. When the steel is immersed in the simulated solution with the Ca²⁺ concentration of 63.5 mmol·L^-1 for 180 d, calcium salts continuously deposit on the steel surface to form a crystalline salt layer with the increasing of time. The calcium salt layer effectively hinders the migration process of dissolution oxygen, then promotes the formation of an oxygen concentration cell under its coverage region, and finally leads to the generation of pitting corrosion on the steel surface. At the same time, the compactness of the calcium salt layer that deposited on the inner corrosion product is gradually improved during this process, which can inhibit the corrosion effects of Cl^- and dissolved oxygen on the steel to a certain extent, and also makes the uniform corrosion of the steel gradually slow down.