Impact of surface roughness and humidity on X70 steel corrosion in supercritical CO2 mixture with SO2, H2O, and O2

The effect of surface roughness and humidity on the corrosion behavior of X70 pipeline steel in super-critical CO2 environments with SO2, H2O, and O-2 was investigated. Scanning electron microscopy, 3D surface profilometry, energy-dispersive X-ray spectroscopy, X-ray diffraction, and 3D measuring laser microscopy were used to analyze the corrosion behavior. Weight loss analysis showed that the time-averaged corrosion rate varied from 0.03 mm/y to 1.78 mm/y depending on the initial humidity and surface roughness. Initial surface roughness exerts no influence on corrosion rates under relative humidity of <55% and >88%. However, at relative humidity between 60% and 75%, a rougher surface leads to high corrosion rate of 0.8 mm/y. Corrosion rate increases as humidity increases. The safe limit of humidity is estimated to be 2450 ppm under 10 MPa and 50 degrees C. The O-2 environment enhanced the corrosion behavior, and high O-2 concentration induced localized corrosion, such as pitting-and mesa attack. (C) 2015 Elsevier B.V. All rights reserved.