Mitigation of stress corrosion cracking of carbon steel exposed to CO-CO2-H2O environments through inhibitor addition

Abstract

PURPOSE – This investigation aims to find the degree of passivation required to completely inhibit the stress corrosion cracking of carbon steel exposed to CO-CO2-H2O environments. DESIGN / METHODOLOGY / APPROACH – A516 pressure vessel steel was exposed to distilled water with 25 per cent CO and 75 per cent CO2 at an overall pressure of 800 kPa with the introduction of potassium bichromate as an additional inhibitor. Slow strain-rate tests were performed to evaluate the steel for sensitivity to cracking. Electrochemical characteristics were investigated in parallel in order to determine the extent of passivation required with the addition of the inhibitor. FINDINGS – Slow strain-rate tests showed that between 100 and 1,000 ppm potassium bichromate was required to completely mitigate cracking with a significant reduction in passivation current densities. RESEARCH LIMITATIONS / IMPLICATIONS – The chosen inhibitor is not ideal for practical applications as an inhibitor, but gave an indication of the passivation required. PRACTICAL IMPLICATIONS – The results showed that the added inhibitor might even cause increased sensitivity to cracking in this environment, with significant passivation required for resistance to cracking. ORIGINALITY / VALUE – The degree of passivation required for complete resistance of carbon steel in 25 per cent CO-75 per cent CO2-H2O.