Electrochemical Behaviour of Duplex Stainless Steel in Simulated Oilfield Brine from the Offshore Niger Delta

This study investigates the electrochemical corrosion behaviour of Grade 2205 duplex stainless steel (DSS) in synthetic brine solutions formulated to replicate the ionic composition and CO2 and H2S partial pressures of produced water from deepwater Niger Delta oilfields. Duplex stainless steel is increasingly specified for offshore process equipment and umbilical tubing in Nigeria's deepwater sector, yet its electrochemical behaviour in the specific produced water chemistry of the pre-salt Niger Delta formations is not fully characterised. Synthetic brine solutions are prepared at two salinity levels with varied CO2 and H2S partial pressures, and electrochemical measurements including open circuit potential evolution, potentiodynamic polarisation, cyclic polarisation, and electrochemical impedance spectroscopy are conducted at 25 and 80 degrees Celsius in a glass cell system. Critical pitting temperature is determined as a function of chloride concentration. Corrosion product films are characterised by XPS and Raman spectroscopy. Results indicate that DSS maintains passive behaviour in CO2-saturated brine up to 80 degrees Celsius, but the introduction of H2S partial pressure above 0.05 bar causes passive film destabilisation and shifts the critical pitting temperature downward by approximately 15 degrees Celsius. The study provides quantitative pitting susceptibility data directly applicable to material qualification decisions for Niger Delta deepwater facilities. Keywords: duplex stainless steel, electrochemical corrosion, oilfield brine, Niger Delta, pitting.