The corrosion behavior of five sets of stainless steel in the simulating oilfield downhole and wellhead corrosive environment containing oil, H2S, CO2, and Cl2 was investigated using weight loss measurement, scanning electron microscope, and energy dispersive spectroscopy, The stainless steel includes martensitic stainless steel 13Cr (UNS S41000), supermartensitic stainless steel S13Cr (UNS S41426), duplex stainless steel 22Cr (UNS S32205), super duplex stainless steel 25Cr (UNS S32750), and Ni-based alloy 2550 (UNS N06975). In addition, the tests of pitting corrosion resistance of stainless steels in the ferric chloride solution, electrochemical measurements, and scanning Kelvin probe force microscopy were also employed to investigate their corrosion resistance. The results show that local corrosion occurred on 13Cr was because of the heterogeneous adsorption of crude oil. The pitting corrosion that occurred on 22Cr was due to the two-phase austenite-ferrite microstructure and the combined effect of the passivation film. The adsorption of crude oil contributed to the corrosion of 22Cr as well. The poor protective effect for the substrate of passivation film in the aqueous environment containing crude oil, H2S, CO2, and Cl- led to uniform corrosion on S13Cr, 25Cr, and 2550. The influence mechanism on corrosion behavior of these five materials by crude oil was explained. In addition, some findings in this study, such as the influence on corrosion behavior by water cut and the corrosion resistance property of 22Cr were quite different from the previous understanding.
M. B. Kermani pointed out that 25% of equipment failures in the oil and gas industry are caused by corrosion, and more than half of corrosion events are related to produced fluids containing CO2 and H2S.1 In recent years, the exploitation of sour oil and gas fields (containing H2S or H2S/CO2 mixture) has become more and more common, and prominent problems such as tubing ruptures caused by pitting and uniform corrosion have appeared.2,3,4,5,6,7,8,9 In oil fields containing CO2 and H2S, local corrosion is a key factor restricting the selection of tubing and casing materials. In an oilfield containing CO2 and H2S in the Middle East, the authors corroded coupons on site, and carried out indoor simulation experiments for the problems found in the field test. The authors systematically studied 13Cr, S13Cr, 22Cr, 25Cr and 2550 in the presence of H2S, CO2 and high mineralization.