Anti-Corrosion Methods and Materials

Purpose – The purpose of this paper is to present a study of corrosion properties of the highly corrosion-resistant stainless steel Prokron 11Nb, which is suitable for use in high-temperature and high-pressure systems.

Design/methodology/approach – Prokron 11Nb was immersed in 0.1?M H2SO4 that had been previously sparged with CO2 and was exposed to high pressures within the range of 1-300 bar at a constant temperature of 25°C. Treated surfaces were scanned with an electronic microscope (scanning electron microscope) equipped with energy spectrum distribution (energy dispersive spectroscopy) to analyze the morphologies and compositions of surface deposits. Corrosion properties were measured using the potentiodynamic method and electrochemical impedance spectroscopy.

Findings – The corrosion rate decreased with increasing CO2 pressure, which accelerated surface passivity, but only up to a pressure of 200 bar. Higher pressures (300 bar) increased the corrosion rate. The trends in corrosion rate with CO2 pressure agree with the stability of a protective layer where iron carbonate is present.

Originality/value – A high-pressure CO2 treatment at low temperature is found to be a useful method for improving the passivity of stainless steel. Iron carbonate, which is the result of CO2 corrosion, forms a stable protective layer on the steel surface and this lowers the corrosion rate.