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| Martensitic stainless steel for oil wells and method for manufacturing martensitic stainless steel pipe for oil wells |
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The present invention relates to a martensitic stainless steel for oil wells and a method for manufacturing a martensitic stainless steel pipe for oil wells; more specifically, a martensitic stainless steel for oil wells suitable for use in cold areas in a severe corrosive environment, containing corrosive materials such as hydrogen sulfide (H2S), carbon dioxide (CO2) and chloride ion (Cl-); and a method for manufacturing a martensitic stainless steel pipe using such a steel. Further specifically, the present invention relates to a martensitic stainless steel suitable for use in cold areas for production facilities of petroleum and natural gas, for carbon dioxide removal facilities, for geothermal power generation facilities, and for oil country tubular goods, such as seamless steel pipes, electric resistance welded steel pipes, and laser welded steel pipes used in oil wells and natural gas wells, and a method for manufacturing a martensitic stainless steel pipe using such a steel. In recent years, the environment of wells for collecting petroleum or natural gas has become increasingly more severe, and oil wells and gas wells containing corrosive gas, such as hydrogen sulfide and carbon dioxide, have been actively developed. Therefore, in oil country tubular goods which are used for extraction of petroleum or natural gas in a severe environment as mentioned above, the deterioration of the raw materials by corrosion is a major problem. However, the said 13Cr-type martensitic stainless steel as represented as SUS 420J1 is poor in corrosion resistance to hydrogen sulfide, and apt to cause sulfide stress cracking (hereinafter referred to as "SSC") in an environment which contains both carbon dioxide and hydrogen sulfide. Therefore, in an actual situation its use should be limited. On the other hand, oil wells and gas wells simultaneously containing chloride ion, wet carbon dioxide and trace hydrogen sulfide have been actively developed even in cold areas, and thus, a steel which has not only satisfactory SSC resistance in the coexistence of chloride ion, wet carbon dioxide and trace hydrogen sulfide but also excellent toughness in low temperature, has been increasingly demanded. The main objectives of the present invention are to provide a martensitic stainless steel for oil wells with high toughness and high SSC resistance, which is excellent in low temperature toughness as well as satisfactory SSC resistance in the coexistence of chloride ion, wet carbon dioxide and trace hydrogen sulfide, and is sufficiently usable even in an environment containing hydrogen sulfide, carbon dioxide and chloride ion in cold areas, and also to provide a method for manufacturing a martensitic stainless steel pipe for oil wells using the aforementioned steel. |