A Systematic Study on the Effects of Surface Profile on Pull-Off Adhesion Strength of Organic Anticorrosion Coatings

Pull-off testing is widely used to quantify coating adhesion strength. This study investigates how substrate surface profile and abrasive morphology (spherical, sharp, and angular) influence the adhesion and performance of protective coatings. Steel plates were prepared with abrasives of varying sizes and shapes and then coated with a three-layer coating system. Pull-off adhesion testing was conducted on both freshly coated plates and after exposure to cyclic aging according to ISO 12944-9, Annex B. Surface characterization included electrochemical impedance spectroscopy and scanning electron microscopy (SEM) for abrasive morphology analysis and cross-sectional examination. Terahertz time-domain imaging (THz-TDI) was also used as a potential nondestructive technique to visualize the steel/coating interface after aging. The results revealed that abrasive types did not affect the initial pull-off adhesion strength of the coating. All panels show high adhesion strength between (17 MPa and 21 MPa), and the abrasive type had minimal effect on initial adhesion. However, only the glass bead–blasted panel showed a significant adhesion loss after aging (from 18.03 MPa to 5.74 MPa), linked to an average 10 μm interfacial gap observed via SEM and THz-TDI. In contrast, angular abrasives preserved high adhesion, indicating that surface morphology, rather than surface roughness height, is critical for long-term performance. These findings underscore the importance of abrasive selection in surface preparation to enhance coating longevity and reduce maintenance in offshore, pipeline, and marine environments.