ASSESSINGTHEEFFECTIVENESSOFTHEALUMINIUMANODECATHODIC PROTECTION SYSTEM ON OIL STEEL PIPELINE ALONG THE MOSIMI- IBADAN SEGMENT IN NIGERIA.

Abstract

ABSTRACT

Pipeline networks are capital intensive yet efficient and safer method for transporting petroleum products, offering lower distribution costs compared to alternatives. However, the steel used in pipeline construction is highly susceptible to corrosion, which can compromise structural integrity, reduce service life, and increase maintenance costs. Therefore, the effectiveness of Aluminium sacrificial anode cathodic protection (CP) system on a multi products steel pipeline along the Mosimi-Ibadan segment is assessed in this study. Soil samples from three locations of Redeem, Ogere, and Olorunda were analysed for pH, electrical conductivity, temperature, and carbon dioxide (CO₂) concentration. The steel corrosion rates, and impedance were determined in soil solutions using Potentiodynamic Polarization and Electrochemical Impedance Spectroscopy (EIS) methods. The corrodedsteel samples from these test locations were characterizedusing X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), and Energy-DispersiveX-ray Spectroscopy (EDX) to determine crystalline structure, surface morphology, and elemental composition,respectively. The results from potentiodynamic polarization showed the steel sample atOgere hadthehighest corrosionrate(2.82 mm/yr),which correlated withthelowestpH(5.8) and highest conductivity (0.22 dS/m). This was followed by that from Olorunda, with a corrosion rate of 0.96 mm/yr, pH of 6.4, and conductivity of 0.20 dS/m while the sample at Redeem exhibited the lowest corrosion rate (0.68 mm/yr), with a pH of 7.3 and conductivity of0.14dS/m.Additionally,OgereshowedthehighestCorrosionProtectionEfficiency(CPE) of 67%, followed by Olorunda (19%) and Redeem (13%). The EIS results indicated higher impedance and better corrosion resistance at Redeem, followed by Olorunda, while Ogere exhibitedthelowestimpedance.TheXRDanalysisrevealedlowFe₂O₃contentatRedeem,

moderate levels at Olorunda, and high levels at Ogere. The phases revealed on samples from Ogere, showedlittle presence of SiO₂ (2.25%), compared to Redeem (0.34%) and Olorunda (0.33%).TheSEManalysisshowedasmoothsurfaceatsamplesfromRedeem,severepitting corrosion at Ogere, and interconnected corrosion features at Olorunda. Also, iron depletion supported the level of corrosion of the samples which stood at 60.02, 70.02, and 70.17% at Ogere, Olorunda and Redeem respectively, compared to a baseline of 96–98% as shown in EDX. These findings highlighted the influence of soil chemistry and sacrificial anode cathodic protection on pipeline corrosion. The study revealed that the Aluminium anode cathodic protection system employed on the pipeline was effective at the Ogere section.