Corrosion of alloy steels containing 2% chromium in CO2 environments

Scanning electron microscopy (SEM), X-ray Diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were employed to analyze the corrosion scale formed on API X65, 1Cr, 2Cr and 3Cr steels in CO2 containing environment. The evolution of scale on 2Cr steel was characterized with electrochemical impedance spectroscopy (EIS) and in situ pH monitoring. The results show that Cr content can alter the crystalline state of corrosion scale via changing pH value. Localized corrosion occurs on 2Cr steel when FeCO3 crystal stripes form on the amorphous scale. The critical Cr content for general corrosion is 3 wt.%.

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► We study the corrosion performance of 2% Cr steel and compare it with other steels.
► The amorphous inner scale of 2% Cr steel mainly consists of FeCO3 and Cr(OH)3.
► Localized corrosion occurs if crystalline FeCO3 strips form on the corrosion scale.
► Cr content changes the crystalline state of corrosion scale by changing pH.
► The critical Cr content for general corrosion is 3%.