An investigation of corrosion in dehumidification bubble caps in a gas refinery

One of the severe challenges in the oil, gas and petrochemical industry is associated with reducing the costs of corrosion damages by removing oil fluid moisture and humidity in facilities. An essential component of moisture absorption towers in the dehumidification section is the bubble cap, which loses its efficiency in a short time due to continuous contact with steam. In the present work, the causes of the destruction of a piece of bubble cap were investigated thoroughly by employing visual and microstructural observation, chemical composition study using a quantometer, energy-dispersive X-ray spectroscopy and X-ray diffraction assessments and corrosion behavior study by polarization and electrochemical impedance spectrometry analysis. The mechanism and type of corrosion that occurred in the bubble cap and its capability against the corrosion were assessed. The results showed that the corrosion products after service were iron (II,III) oxide (Fe₃O₄), iron (III) oxide (Fe₂O₃), iron (III) hydroxide (Fe(OH)₃) and iron (II) carbonate (FeCO₃), which decreased the microhardness from 121.3 to 99.3 HV. The corrosion rate was found to be 0.03116 mm/year in saline solution. The poor performance of the material against corrosion was attributed to casting defects and ineffective microstructural phases, formed due to deficient alloying elements. According to the results, some recommendations and solutions, as effective preventive ways, are proposed to hinder corrosion and lead to higher durability and lower replacement costs.