Corrosion failure analysis of 20# steel in the process of natural gas purification

The present work investigated the corrosion on 20# steel in the process of natural gas purification of PG gas field. According to the analyzing the corrosion condition of the desulfurization device, the research found that the main corrosion was caused by H2S/CO2 and there was also the obvious corrosive pitting caused by chloride ion. The morphology and composition of the corrosion scale were characterized by scanning electron microscopy, X-ray power diffraction, and energy-dispersive spectroscopy. Results showed that corrosion scale consists of FeS, Fe2S, and FeCO3. The weight loss experiment was conducted to estimate the actual corrosion rate of 20# steel. Electrochemical methods such as polarization curve and electrochemical impedance spectroscopy were used to analyze the effects of chloride ion concentration and temperature on the corrosion. It can be found that the corrosion rate increased with the increasing of chloride ion concentration and temperature.