Carbon steel

Oxygen corrosion is a major threat to seawater injection systems that are part of offshore drilling operations. Seawater is typically deoxygenated to an industry standard of <20 parts per billion dissolved oxygen (DO) by injection through a deaeration column followed with oxygen scavenging chemicals. Commercial simulation software like OLI Studio: Corrosion Analyzer predicts high corrosion rates when injection seawater contains high DO levels, justifying deoxygenation. However, a notable lack of experimental data exists concerning the effect of varying levels of dissolved oxygen on corrosion rate. The goal of this project is to measure the effect of three dissolved oxygen levels (0, 65, and 650 ppb) on the corrosion rate of 1018 and 410 steels in comparison to predictions made by OLI Studio: Corrosion Analyzer. Corrosion immersion testing was performed on quadruplicate specimens for 24 hours according to ASTM standards. Corrosion rates based on gravimetric mass loss measurements after removal of corrosion products were then computed and compared to simulation results. While OLI underpredicted corrosion rates experienced during laboratory testing, increasing dissolved oxygen in seawater generally resulted in a nonlinear increase in corrosion rate. Microscopy of the specimens confirmed that significant localized corrosion occurs near crevices, and uniform corrosion in the form of rusting occurs on the surfaces of the coupons at higher dissolved oxygen concentrations. Calculated corrosion rates were also lower than the maximum design corrosion rate for seawater injection systems.