Study on Formation Mechanism and Protection Characteristic of Corrosion Scale on X65 Pipeline Steel in CO2 Environment

摘要

Carbon dioxide (CO2) corrosion is one of the most serious corrosion problems in oil and gas industry for many years. The corrosion scale formed during CO2 corrosion process plays an important role in the corrosion mechanism of pipeline steels. In this study, the formation mechanism of corrosion scale on X65 pipeline steel, as well as its protective characteristic to steel, were investigated in NaCI solution at 80 °C and 1 MPa. Immersion experiments were conducted with different time: 0.5h, 2h, 8h, 12h, 24h, 50h, 96h, 168h. The weight loss tests showed that before the immersion of 50h, the weight loss increased dramatically with the increasing immersion time, while after 50 h, the weight loss slightly increased with the increase of immersion time. The surface morphology of corrosion scale and EIS results indicated that, FeCCb corrosion scale formed between 24 h and 50 h immersion, corresponding to the transition point of weight loss after which the increasing rate of weight loss was decreased significantly. The formation of FeCO3 corrosion scale decreased the corrosion rate of X65 steel significantly.