For oil wells and gas wells (in this description, oil wells and gas wells are generally called “oil wells”), oil country tubular goods are used. Since the oil wells have corrosive environments, the oil country tubular goods are required to be corrosion resistant. On the other hand, an austenitic alloy represented by an austenitic stainless steel has an excellent corrosion resistance. Therefore, the austenitic alloy pipe is used as the oil country tubular goods.
The oil country tubular goods includes two types: casing and tubing. The casing is inserted into the well. Between the casing and a well wall, cement is filled in, and thereby the casing is fixed in the well. The tubing is inserted into the casing to allow a produced fluid such as oil or gas to flow therein.
The oil country tubular goods is also required to have a high strength in addition to the excellent corrosion resistance. The strength grade of oil country tubular goods is generally defined in terms of tensile yield strength in the pipe axial direction. The user of oil country tubular goods deduces the environments (stratum pressure, temperature and pressure of produced fluid) of the well to be drilled from exploratory drilling and geological survey, and selects an oil country tubular goods of a durable strength grade.
“Temperature and texture effects on properties for CRA's, Corrosion 92 The NACE Annual Conference and Corrosion Show Paper No. 58” describes that for the cold-worked corrosion-resistant alloy pipe, the compressive yield strength in the pipe axial direction is lower than the tensile yield strength in the pipe axial direction. As described above, the strength grade of oil country tubular goods is generally defined in terms of tensile yield strength. Therefore, the difference between the compressive yield strength and the tensile yield strength is preferably smaller.
JP10-80715A and JP11-57842A propose producing methods for enhancing the compressive yield strength in the pipe axial direction.
JP10-80715A describes as described below. In the method for producing a steel tube disclosed in this Patent Document, the ratio Q of wall thickness working ratio to outside diameter working ratio (Q=RT/RD: RT is reduction of area of wall thickness, RD is reduction of area of outside diameter) at the cold working time is regulated to 1.5 or less. Thereby, a steel tube excellent in compressive strength in the tube axial direction can be obtained. Specifically, the compressive strength in the tube axial direction of steel tube is 80% or more of the tensile strength (0.2% yield stress).
JP11-57842A describes as described below. In the method for manufacturing a steel pipe disclosed in this Patent Document, a cold-worked steel pipe is subjected to heat treatment at a temperature of 200 to 400° C. The compressive strength in the pipe axial direction is enhanced by heat treatment because the dislocation introduced into the steel by cold working is relocated by heat treatment. Specifically, with the manufacturing method of this Patent Document, the compressive strength in the pipe axial direction of steel pipe becomes 80% or more of the tensile strength (0.2% yield stress).
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