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Abstract
The novel Cr-containing low alloy steels have exhibited good corrosion resistance in CO2 environment, mainly owing to the formation of Cr-enriched corrosion film. In order to evaluate whether it is applicable to the CO2 and H2S coexistence conditions, the corrosion behavior of low-chromium steels in CO2-H2S environment with high pressure and high temperature was investigated using weight loss measurement and surface characterization. The results showed that P110 steel suffered localized corrosion and both 3Cr-P110 and 5Cr-P110 steels exhibited general corrosion. However, the corrosion rate of 5Cr-P110 was the highest among them. The corrosion process of the steels was simultaneously governed by CO2 and H2S. The outer scales on the three steels mainly consisted of FeS1−x crystals, whereas the inner scales on Cr-containing steels comprised of amorphous FeS1−x, Cr(OH)3 and FeCO3, in contrast with the amorphous FeS1−x and FeCO3 mixture film of P110 steel. The more chromium the steel contains, the more chromium compounds the corrosion products contain. The addition of chromium in steels increases the uniformity of the Cr-enriched corrosion scales, eliminates the localized corrosion, but cannot decrease the general corrosion rates. The formation of FeS1−x may interfere with Cr-enriched corrosion scales and lowering the corrosion performance of 3Cr-P110 and 5Cr-P110 steels.
Highlights
The CO2 /H2 S corrosion problems of oil country tubular goods (OCTG) become increasingly prominent with the exploitation of oil and gas field under high temperature and high CO2 and/or H2 S pressure [1,2,3,4,5,6]
9, 200(1.12 mm/y), taking into account the experimental error. This suggests that 4 of corrosion resistance of P110 tube steel cannot be significantly improved by increasing Cr content in a condition
1s 284.8 the results suggested that the inner scale of
Summary
The CO2 /H2 S corrosion problems of oil country tubular goods (OCTG) become increasingly prominent with the exploitation of oil and gas field under high temperature and high CO2 and/or H2 S pressure [1,2,3,4,5,6]. Corrosion resistant alloys (CRAs), such as stainless steels and high-nickel alloys, have been developed to mitigate the CO2 /H2 S corrosion long time ago, but the high cost constrains their application in oil and gas field containing CO2 and/or H2 S. The novel Cr-containing low alloy steels have been developed to balance the cost advantage and corrosion resistance between carbon steel and CRAs [5,6,7,8,9,10,11,12,13]. Many studies indicate that the low Cr alloy steels with 3–5 wt % Cr can remarkably reduce the CO2 corrosion rate, and avoid localized corrosion in CO2 environment, mainly due to the formation of the amorphous Cr(OH) in the scales on low Cr alloy steel [8,9,10,11,12,13]. Sun et al [12] reported that, with an addition of 3% chromium in X65 steel, the corrosion rate dropped significantly from 11.59 to 1.57 mm/y and the localized corrosion was Materials 2016, 9, 200; doi:10.3390/ma9030200 www.mdpi.com/journal/materials
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