A synergistic experimental and computational study on CO2 corrosion of X65 carbon steel under dispersed droplets within oil/water mixtures

摘要

In the oil and gas industry, the presence of oil/water mixtures is common during transportation pipelines, but which suffers complex corrosion for different water cuts[1-2]. At low water cuts, the average corrosion rate o f steel,wetted by the bulk oil solution and dispersed water -in-oil droplets, is low. Contrarily, at high water cuts, the steel is seriously corroded, due to that it is wetted by the bulk water solution and dispersed oil -in-water droplets. Though, the previ ous research have built a tight relationship between average corrosion rate and wetting phenomenon of steel [3-6], the localized corrosion behaviour, which is mainly attributed to the dispersed oil -in-water or water -in-oil droplets, has not attracted much attention. Consequently, the CO2 corrosion behaviour of X65 carbon steel under water -in-oil droplet and oil -in-water droplet was systematically investigated by a combination of scanning electron microscopy, Raman spectroscopy, NPFLex3D and COMSOL simulatio n in present research. Under the water -in-oil droplet, crystalline FeCO 3 was found, caused by the high concentration of Fe 2+ and CO 32-, according to COMOSL simulation results. Notably, around the oil/water interface, a ridge consisting of compact FeCO 3 was observed, because the precipitation of FeCO3 is accelerated by the short diffusion path of CO2 near the edge of the droplet. Under the oil-in-water droplet, corrosion islands caused by the invasion of water can be found, indicating that small water droplet s emphasised the development of localized corrosion underneath the oil droplet. The novel research findings contribute to further understanding of localized corrosion mechanism of pipeline exposed to oil/water mixture.