North Australia has several offshore natural gas fields with high temperature and high pressure (HT/HP) environments containing CO2 and small amounts of H2S. The corrosion performance of 17Cr martensitic stainless steel (17Cr SS) was evaluated in downhole conditions and compared to Super 13Cr martensitic stainless steel (S13Cr SS) and 22Cr duplex stainless steel (22Cr DSS). Sulfide stress cracking (SSC) / stress corrosion cracking (SCC) and localized corrosion tests were carried out in Fit-For-Purpose environments.
17Cr SS showed good resistance similar to 22Cr DSS for weight loss corrosion and pitting corrosion. The weight loss corrosion rate did not depend on chloride ion concentration. No evidence of SCC nor pitting/crevice were observed on the surface of 17Cr SS and 22Cr DSS after testing till 5 kPa of PH2S, while crevice corrosion was observed on S13Cr SS. However, the service limit temperature of 17Cr SS was lower than that of 22Cr-DSS according to the test results of polarization curve measurements and slow strain rate tests (SSRT). Based on these results 17Cr SS was qualified in such Fit-For-Purpose environments and definitely fills the gap between S13Cr SS and 22Cr DSS. This new material may also be an alternative to 22Cr DSS in line with a cost reduction philosophy for OCTG in some HP/HT gas wells.