Analysis of the Electrochemical Behaviour and Corrosion Protection Performance of Polymer Coatings on Steel Pipelines Used in Nigerian Oil Fields

Pipeline corrosion remains one of the most economically damaging infrastructure challenges in the Nigerian oil and gas sector, with polymer coatings representing the primary corrosion protection strategy for buried and subsea pipelines in Niger Delta operations. This study analyses the electrochemical behaviour and corrosion protection performance of four commercial polymer coating systems, epoxy, polyurethane, fusion-bonded epoxy, and three-layer polyethylene, applied on carbon steel pipeline specimens tested under conditions simulating Niger Delta soil and water exposure. Accelerated corrosion testing was conducted in synthetic soil extract and seawater at 35 degrees Celsius. Electrochemical impedance spectroscopy monitored coating barrier resistance evolution over 2160 hours of immersion. Salt spray testing and cathodic disbondment testing assessed adhesion durability under electrochemical stress. Scratch and peel tests evaluated mechanical durability of coatings before and after thermal cycling representative of operational temperature fluctuations. Results demonstrate that three-layer polyethylene coating maintained electrochemical impedance above 10^9 ohm.cm2 throughout the 2160-hour test, far superior to fusion-bonded epoxy at 10^7 ohm.cm2 after 1000 hours. Cathodic disbondment radius at 28-day testing was 2.8 mm for three-layer polyethylene compared to 12.4 mm for standard epoxy coating. Polyurethane coatings showed superior flexibility during thermal cycling without cracking, contrasting with fusion-bonded epoxy that exhibited microcracking after 20 thermal cycles. The study recommends three-layer polyethylene as the performance benchmark for buried pipeline corrosion protection in Niger Delta conditions and provides quantitative coating selection criteria for pipeline integrity engineers. Keywords: polymer coating, pipeline corrosion, electrochemical impedance spectroscopy, Niger Delta, corrosion protection