A New Corrosion Mechanism for X100 Pipeline Steel Under Oil-Covered Chloride Droplets

A 1.7 mM NaCl droplet on X100 pipeline steel covered by paraffin oil is used to simulate the corrosive environment encountered in heavy oil or bitumen pipelines. The development of corrosion under the droplet was monitored and explored in two stages. In the initial stage (1 h), the distribution of corrosion pits was heterogeneous with one area under the droplet presenting a higher pit density. As the corrosion proceeded (24 h), the localized corrosion in the area under the droplet with the higher pit density switched to general corrosion, while the other region of the droplet continued to pit. The mechanisms driving this new distinctive corrosion form developed beneath an underoil droplet are explained.