Effects of silty sand on CO2 corrosion behavior of low-Cr tubing steel

An experimental study was carried out to assess the effects of silty sand on the CO2 corrosion behavior of 1 wt% Cr (1Cr) and 3 wt% Cr (3Cr) tubing steel under 0.5 MPa CO2 at 100°C and 1.5 m/s flow velocity. The 1Cr and 3Cr specimens both suffered general corrosion, but the surface was coarser in the pure CO2 corrosion environment. Under silty sand conditions, severe pitting corrosion occurred on the 1Cr specimens and some acicular pitting appeared on the 3Cr specimens. The average corrosion rates of 1Cr and 3Cr steels increased by factors of 3 and 1.6, respectively. The corrosion products were analyzed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and electrical impedance spectroscopy (EIS). The results show that silty sand acts as an inclusion in corrosion product films and reduces the homogeneity and density of the products, rather than abrading the corrosion film. Ion-diffusion channels may build up around the irregular silty sand; this would degrade the protective capabilities of the product films and aggravate corrosion.