Field Investigation into AC Corrosion at Coating Defects Simulated on 3LPE and HBPU Coating Systems in Low Resistance Sabkha Soils

Abstract This technical paper investigates the impact of high voltage alternating current (HVAC) interference due to overhead transmission lines (OHTL) on pipeline integrity, focusing on corrosion rates and coating effectiveness. Over several months, a pipeline section was evaluated using two coating systems: three-layer polyethylene (3LPE) and High Build Polyurethane (HBPU). Corrosion rates at simulated coating defects varied significantly, influenced by the presence of goethite and magnetite. Goethite, with its high resistivity, correlated with reduced corrosion rates, suggesting it may offer protective properties, while magnetite's lower resistivity was linked to more severe corrosion. HVAC-induced corrosion rates ranged from 1.06 mm/yr to 4.11 mm/yr, depending on the defect location and coating type. The study suggests that linear extrapolation of corrosion rates does not accurately predict long-term outcomes, as fieldwork suggests HVAC corrosion rates may decrease to negligible levels over time. This insight has led to ongoing long-term field investigations. Standards such as ISO18086, NACE SP0169, ISO22426, and NACE SP21424 are relevant to this investigation and the results discussed. The findings underscore the importance of continuous monitoring and tailored mitigation strategies to address the specific electrochemical conditions observed in the field.