Corrosion of X70 steel under multi-phase flow

In this study, actual loops and independently-developed testing devices are used to simulate CO₂ corrosion of X70 steel for fluctuating pipelines with multi-phase flows. Electron microscopes and corrosion coupons are used to analyze surface topographic features and corrosion rates of such coupons to highlight impacts of multi-phase flow regime on CO₂ corrosion rate. The results show that, as gas/liquid ratio increased from low to high, flow pattern changed from full-pipe flow to slug flow, and eventually to dispersion flow. During the transition, uniform corrosion rate of the coupon increased slowly at first and reached the maximum during occurrence of slug flow. With flow pattern changing from slug flow to dispersion flow, corrosion rate on surfaces of the coupon decreased gradually. In the entire process, local corrosion on such coupons intensified continuously. In the state of dispersion flow, local corrosion reached the maximum degree due to existence of cavitation corrosion.