Development of sour-resistant 13%Cr oil-country tubular goods with improved CO₂-corrosion resistance

A material design concept for 13%Cr oil-country tubular goods (OCTG) was established and its properties were made clear, which has a sharply improved CO₂-corrosion resistance and a sour resistance compared with those of 13%Cr OCTG of API specifications being generally used. It has been made possible to improve the CO₂-corrosion resistance without generating any ferrite phase by adding copper and nickel in combination. The mechanism of improving in the CO₂-corrosion resistance by adding copper and nickel in combination is presumed to be because that the corrosion film is made amorphous and that a copper layer is formed under the corrosion film. Further, the sour resistance is improved by adding molybdenum, especially adding more than 1.5% of molybdenum in weight. The low carbon-13%Cr-Cu-Ni-Mo steel developed on the basis of these basic studies is a high strength steel with good low temperature toughness being superior in the CO₂-corrosion resistance and the sour resistance, which can be applied to many cases of such severe environments as the duplex stainless steel is to be applied.