Investigation of Corrosion Behaviour of Heat Treated Standard Steels in Nigerian Rich Tar Sand.
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Date
2023
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Department of Materials Engineering, Faculty of Technology, Obafemi Awolowo University.
Abstract
This study determined the corrosion rates of as-received and heat-treated standard duplex stainless (UNS S32205) steel in tar sand processing environment, characterized microstructurally the corrosion coupons, and correlated the corrosion rates of the stainless steel with their respective microstructures. These were with a view to assessing the suitability of heat-treated standard duplex stainless steels as candidate materials for the hot water tar-sands pilot plant. The Nigerian-rich tar sand sourced from Ilubinrin town, near Agbabu in Ondo State was chiselled into bits of 6mm and 25 g of it was processed using 0.5 M sodium hydroxide (NaOH), which acted as the surfactant in the bitumen recovery. The as-received stainless samples were subjected to annealing, normalizing, and quenching (water and oil) heat treatments. A processing temperature of 90oC and processing time of 4 hours was employed. After immersion, the corrosion coupons were cleaned with non-bleaching scurry powder and wiped with acetone to remove grease. The corrosion rates were determined by gravimetric technique and the microstructural analyses of the degraded corrosion coupons were carried out using scanning electron microscope while the correlation of the respective microstructures of the corrosion coupons with their uniform corrosion rates was carried out using localized corrosion rates derived from surface profilometry of the coupons. The study showed that water-quenched samples exhibited improved general corrosion resistance with longer precipitation times, while oil-quenched sample with precipitation time of 2 hours showed the lowest general corrosion rate, followed by water-quenched sample with a precipitation time of 4 hours. Microstructural analysis provided insights into the degree of pitting, with the annealed sample showing the highest and the water-quenched sample with a precipitation time of 4 hours displaying the lowest degree of pitting. These variations were attributed to passivity and an imbalance between ferrite and austenite phases due to secondary precipitates. The correlation between uniform corrosion rates and microstructures revealed that the sample with a precipitation time of 4 hours, followed by water quenching, demonstrated the best corrosion resistance. These differences in localized corrosion rates were attributed to chromium and molybdenum depletion in the grain boundaries. This study concluded that the heat-treated standard stainless steels were suitable for the construction of hot water tar sand pilot plant.
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xvi, 114p
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Citation
Ogundare, O.J. (2023). Investigation of corrosion behaviour of heat treated standard steels in nigerian rich tar sand.Department of Materials Engineering, Faculty of Technology, Obafemi Awolowo University.