On the corrosion mechanism of CO 2 transport pipeline steel caused by condensate: Synergistic effects of NO 2 and SO 2

Abstract

To study the effects of condensed acid liquid, hereafter referred to as condensate, on the CO 2 transport pipeline steels, gas mixtures containing a varying concentration of H 2 O, O 2 , NO 2 , and SO 2 , were proposed and resulted in the condensate containing H2SO4 and HNO3 with the pH ranging from 0.5 to 2.5. By exposing the pipeline steel to the synthetic condensate with different concentration of acidic components, the corrosion kinetic is significantly changed. Reaction kinetic was studied using electrochemical methods coupled with water analysis and compared with surface analysis (scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray diffractometry (XRD)) of corroded coupons. The results showed that, although the condensation of NO 2 in the form of HNO3 causes faster general corrosion rate, it is the condensation of SO 2 in the form of H2SO4 or the combination of SO 2 and NO 2 that may cause much more severe problems in the form of localized and pitting corrosions. The resulting corrosion forms were depended on the chemical nature of acids and their concentration at the same investigated pH. The effects of changing CO 2 flow rate and renewing condensate on pitting corrosion were further studied.