Assessment of protective coatings adhesion on steel linear structures under laser nanostructuring

Introduction. Due to the extensive use of steel linear structures, the standards for the surface quality of pipelines used for oil fluid production have been increased. In this case, studies of the interfacial boundary during the application and bonding of protective coatings are the interesting subjects to do. Recent research describes the potential of laser nanostructuring for steel surface pretreatment prior to polymer layer application. The introduction of laser technology into industry requires not only research on surface properties, but also an evaluation of operational characteristics. Usually, the semi-quantative criteria of mechanical strength of polymer bonding to metallic substrate is the adhesive strength. Methods and Materials. In this study, steel plates were used as a substrate for laser surface treatment with two pulsed ytterbium-doped fiber lasers. The polymer layer was based on epoxy-phenolic resin liquid paint. The liquid paint composition was applied via airless spraying. The curing process was carried out in a drying oven at 150 °C. Results and Discussion. In the process of the study, the surface of the metal plates was treated with laser irradiation to form nanostructures on the metallic surface. Following this treatment, increase in submicroscale surface roughness was up to 230–470% compared to the initial condition. Pull-of adhesion tests of polymer coating vary from 2.2 to 20.6 MPa. This depends on the type of laser irradiation and the type of equipment used. Conclusion. The test results demonstrated that the nanostructured surface facilitates the formation of an array of nano-scale asperities. This array enhances the adhesive bonding with the epoxyphenolic polymer layer and, consequently, improves the adhesive strength. A comparative analysis of the test results obtained using two different types of laser equipment confirmed the effectiveness of a laser system to perform combined polishing and nanostructuring of the metallic surface.