Corrosion Behavior of Hydrophobic Coatings in Aqueous CO₂ Environments

Steel pipelines, the backbone of natural gas transportation, face a significant challenge: internal corrosion. Internal corrosion is caused by gas impurities such as CO₂, moisture, and H₂S, leading to material degradation. To combat this, the National Energy Technology Laboratory (NETL) developed a novel hydrophobic coating to reduce surface hydrophobicity and enhance the corrosion resistance of steel. NETL’s approach uses multi-layer hydrophobic coatings, a novel and promising coating that could potentially revolutionize the industry's approach to internal corrosion mitigation. This work aims to investigate the corrosion performance of the hydrophobic coating and determine the water uptake. Electrochemical corrosion experiments were carried out on bare X65 carbon steel without and with coating in 3.5 wt.% NaCl saturated with CO₂ at 20 °C to follow the water uptake as a function of exposure time. Linear polarization resistance (LPR) was used to determine the corrosion rate for carbon steel immersed in a NaCl electrolyte saturated with CO₂. Electrochemical impedance spectroscopy (EIS) of uncoated and coated bare carbon steel was investigated. The analyses of impedance models and water uptake behaviors of hydrophobic coatings were studied for 200 hours during the corrosion process. The water uptake was estimated using the Brasher and Kingsbury relation. The corrosion of the base metal without coating (3.8 mm/y) was compared to coated carbon steel (0.02 mm/y). The results showed that the superhydrophobic coating that was developed used innovative nano-based materials to act as protection layers on the surface of metallic parts against mechanical aggressors, corrosion, and fouling agents. These coatings have proven to be ideal candidates to protect steel pipelines.