Comparison and Study of Coating Properties of Three-layer Polyethylene, Polyurethane and Fusion Bonded Epoxy for Pipelines

To reduce corrosion, choosing proper coating for the outer surface of oil and gas transportation pipelines is considered the most important part in developing a protection system. The issue of cathodic disbondment is one of the problems of pipeline coatings which is caused by impressed cathodic current and generation of alkali environment at the coating-metal interface and result in coating disbondment. In this research, three coating types including, 3-layer polyethylene, polyurethane, and dual fusion bond epoxy powder are investigated and their physical, chemical, and mechanical properties are studied. The results of cathodic disbondment with simulating long-term working conditions provide an appropriate view on coatings behavior at long-term service exposure. Coating advantage in different properties such as surface adhesion to sublayer and impact resistance are investigated using mechanical tests results. Hardness test results showed that sample hardness with dual fusion bond epoxy powder coating compared to samples with polyurethane and 3-layer polyethylene coatings is 14% and 40% higher, respectively. Impact and holiday test on three coating also showed an acceptable level of resistance to external factors. Performing cathodic disbondment test at ambient and high temperature showed that increasing temperature has a direct influence on increasing coatings disbondment radius. 4.49 mm lowest disbondment radius was observed on 3-layer polyethylene coating due to its intrinsic nature and high thickness.