To develop an economical new alloyed steel, the effects of alloying elements such as Cr and Cu, and microstructure were investigated in CO2 environments with and without a little amount of H2S. In laboratory tests, the Cr steels with martensitic microstructure showed good corrosion resistance. But the double corrosion prevention effect of Cr addition to steels and ferritic-pearlitic microstructure, which are
recognized as corrosion improvement factors, was not observed in those corrosion tests. The Cu and Mo additions to Cr steels were not effective in CO2 environments with H2S. Field tests were also carried out in some production wells of Statoil. In particularly, long term field test result of 5 months showed superior resistance to general and localized corrosion in 5Cr alloyed steel, and the life extension above 5 times to Steel J55 with ferritic-pearlitic microstructure was confirmed in that steel. The
developed-5Cr alloyed steel has been successfully used in Siri Field that is Oil & Gas Field located in the Danish Sector of the North Sea.
Keywords: CO2 corrosion, Cr bearing steel, Oil country tubular goods(OCTG), Ferritic-pearlitic steel, Martensitic steel