Corrosion Study of Nitrided X-52 Carbon Steel in C02 Environment

• Main Author: SUBRAMANIAM, SHALINI
• Format: Final Year Project
• Language: English
• Published: Universiti Teknologi PETRONAS 2011
• Subjects: TJ Mechanical engineering and machinery
• Online Access: http://utpedia.utp.edu.my/10289/1/2011%20Bachelor%20-%20Corrosion%20Study%20Of%20Nitrided%20X-52%20Carbon%20Steel%20In%20CO2%20Environment.pdf; http://utpedia.utp.edu.my/10289/

Carbon Dioxide (C02) corrosion is one the most studied fonn of corrosion in oil and gas industry. Carbon is preferred material of construction for offshore pipelines due to economy, availability and strength but this material are not corrosion resistant. As such the use of carbon steel is usually implemented with the corrosion control such as corrosion allowance, corrosion inhibitor and coating. Since corrosion involves interaction between metal surface and the environment, surface alteration by surface hardening method such as nitriding could protect the metal from corrosion. The objective of the project is to study the performance of different nitrided carbon steel based on 450°C, 480°C and 520°C in C02 environment. The corrosion rates of the nitrided samples were investigated at pH 3 and pH 4 by linear polarization resistance and electrochemical impedance spectroscopy. At ph 4, corrosion rate of sample nitrided at 450°C and 480°C decreases by 30%. However the corrosion rate increases by 50% for sample nitrided at 520°C. This may be due to the poor surface preparation of the sample and uneven nitride layer fails to protect the sample. At pH 3, the corrosion rates of nitrided samples at 480°C and 520°C were higher than untreated sample by 3% for sample nitrided at 480°C and by 70% for sample nitrided at 520°C. For the sample nitrided at 450°C, the corrosion rate was similar as the untreated sample. The slight decrease and increase in the corrosion rate at pH 3 indicate that the presence of nitriding layer was detrimental. This negative effect can be linked to porous nitriding layer that lead to galvanic coupling between the nitriding layer and bare metal. Further studies need to be conducted to confirm this possibility.