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

Abstract

The effect of surface roughness and humidity on the corrosion behavior of X70 pipeline steel in supercritical CO2 environments with SO2, H2O, and O2 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 0.03mm/y to 1.78mm/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 0.8mm/y. Corrosion rate increases as humidity increases. The safe limit of humidity is estimated to be 2450ppm under 10MPa and 50°C. The O2 environment enhanced the corrosion behavior, and high O2 concentration induced localized corrosion, such as pitting and mesa attack.