Dual-layer smart coating system with a hybrid corrosion inhibitor for improved durability of carbon steel pipeline

This study aims to develop a hybrid dual-layer smart coating system incorporating multiple corrosion inhibitors to enhance the durability and corrosion resistance of carbon steel substrates. The proposed system consists of a hydrophobic zinc oxide–stearic acid (ZnO-STA) top layer and a self-healing epoxy bottom layer containing benzotriazole-loaded halloysite nanotubes (BTA-HNT) and boiled linseed oil microcapsules (BLO-MC). Five coating systems were fabricated, including pure epoxy, conventional dual-layer coating, and hybrid dual-layer coatings with ZnO-to-epoxy ratios of 2:1, 4:1, and 6:1. Structural and chemical characteristics were verified using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy. At the same time, corrosion performance was evaluated using Electrochemical Impedance Spectroscopy and scratch tests over 2 weeks of immersion in 3.5 wt.% NaCl solution. The results indicate that the hybrid coating with a ZnO: epoxy ratio of 4:1 exhibited the best corrosion resistance, maintaining impedance values between 4.45 Ω and 4.16 Ω at low frequency and showing the lowest corrosion area of 4.4% after 2 weeks of exposure. However, the hybrid coatings demonstrated reduced adhesion strength, approximately 77.30% lower than the conventional dual-layer coating. Overall, the integration of ZnO-STA, BTA-HNT, and BLO-MC in a hybrid dual-layer system enhances corrosion protection through synergistic hydrophobic barrier and self-healing mechanisms. However, further optimisation is required to improve coating adhesion for long-term application.