Classifications

• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/002—Ferrous alloys, e.g. steel alloys containing In, Mg, or other elements not provided for in one single group C22C38/001 - C22C38/60
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/19—Hardening; Quenching with or without subsequent tempering by interrupted quenching
  • C21D1/22—Martempering
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D1/00—General methods or devices for heat treatment, e.g. annealing, hardening, quenching or tempering
  • C21D1/18—Hardening; Quenching with or without subsequent tempering
  • C21D1/25—Hardening, combined with annealing between 300 degrees Celsius and 600 degrees Celsius, i.e. heat refining ("Vergüten")
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/08—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes
  • C21D9/14—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for tubular bodies or pipes wear-resistant or pressure-resistant pipes
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
  • C21D9/50—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for welded joints
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/001—Ferrous alloys, e.g. steel alloys containing N
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/02—Ferrous alloys, e.g. steel alloys containing silicon
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/04—Ferrous alloys, e.g. steel alloys containing manganese
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/06—Ferrous alloys, e.g. steel alloys containing aluminium
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C38/00—Ferrous alloys, e.g. steel alloys
  • C22C38/14—Ferrous alloys, e.g. steel alloys containing titanium or zirconium
• • C—CHEMISTRY; METALLURGY
  • C21—METALLURGY OF IRON
  • C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
  • C21D2211/00—Microstructure comprising significant phases
  • C21D2211/008—Martensite

Definitions

• this invention relates to an oil well pipe for expandable tubular applications excellent in post-expansion toughness, namely to such an oil well pipe suitable for implementing expandable tubular technology for finishing an oil or gas well by expanding the oil well pipe in the oil well or gas well.
• the invention relates to a method of manufacturing the oil well pipe.
• the present invention provides an oil well pipe for expandable tubular applications excellent in post-expansion toughness, particularly to such an oil well pipe having a pre-expansion yield strength of 482 to 689 MPa (70 to 100 ksi) that is suitable for implementing expandable tubular technology for finishing an oil or gas well by expanding the oil well pipe in the oil well or gas well.
• This invention also provides a method of manufacturing the oil well pipe.
• the pre-expansion strength is the strength needed to prevent the steel pipe from breaking, bursting due to internal pressure, and crushing due to external pressure between insertion into an oil well and expansion therein. It is the strength standard generally applied in oil well design.
• the inventors carried out an in-depth study on how steel chemical composition and manufacturing method affect toughness after pipe expansion and learned that imparting a structure of tempered martensite low in added C content gives the best results.
• the present invention was achieved based on this knowledge and the gist thereof is as follows:
• tempered martensite which is of uniform structure, is excellent in pipe expandability and that the most effective way to improve post-expansion toughness is to impart a structure of tempered martensite low in added C content.
• Japanese Patent No. 3562461 teaches with regard to the invention set out therein that the strength of the steel pipe declines and that reduction of C content is required.
• an electric-resistance-welded steel pipe is especially preferable owing to its excellent thickness uniformity.
• the oil well pipe under the aforesaid manufacturing conditions is basically required to be made of a high-strength steel having a yield strength of 482 to 689 MPa and a thickness of 7 to 15 mm, and be excellent in expandability and post-expansion toughness.
• the chemical composition was defined to meet these requirements. Since the temperature in an oil well is 0 °C or greater, toughness at 0 °C was taken into account.
• C is a required element for enhancing hardenability and improving steel strength.
• the lower limit of C content necessary for achieving the desired strength is 0.03 mass%.
• post-expansion toughness decreases when the C content is excessive.
• the upper limit of C content is therefore defined as 0.14 mass%.
• Si is an element added to improve deoxidation and strength. However, it markedly degrades low-temperature toughness when added in a large amount.
• the upper limit of Si content is therefore made 0.8 mass%. Either Al or Si suffices for deoxidation of the steel, so that addition of Si is not absolutely necessary. Therefore, no lower limit is defined, but 0.1 mass% or greater is usually entrained as an impurity.
• Mn is an indispensable element for enhancing hardenability and ensuring high strength.
• the lower limit of Mn content is 0.3 mass%.
• an excessive Mn content makes the strength too high by causing formation of much martensite.
• the upper limit is therefore defined as 2.5 mass%.
• the invention steel further contains B and Ti as required elements.
• B is an element required for increasing low carbon steel hardenability and obtaining martensite structure by hardening.
• B content of less than 0.0005 mass% does not improve hardenability sufficiently and one of greater than 0.003 mass% lowers toughness owing to precipitation of B at the grain boundaries.
• B content is therefore defined as 0.0005 to 0.003 mass%.
• B to contribute to hardenability it is necessary to prevent formation of BN, which in turn makes it necessary to fix N as TiN.
• N content is low, Ti needs to be added to a content of at least 0.005 mass%, but addition in a large amount exceeding 0.03 mass% lowers toughness by causing precipitation of coarse TiN and TiC.
• the relationship Ti ⁇ 3.4 N should preferable be satisfied for fixing N as TiN.
• Al is an element usually included in steel as a deoxidizer and also has a structure refining effect. But an Al content exceeding 0.1 mass% impairs steel cleanliness by increasing Al nonmetallic inclusions. The upper limit is therefore defined as 0.1 mass%. However, addition of Al is not absolutely necessary because Ti or Si can be used as deoxidizer. Therefore, no lower limit is defined, but 0.001 mass% or greater is usually entrained as an impurity.
• N forms TiN, thereby improving low-temperature toughness by inhibiting austenite grain coarsening during slab reheating.
• the minimum amount required for this is 0.001 mass%.
• an excessive N content causes TiN grain coarsening, which gives rise to adverse effects such as surface flaws and toughness degradation.
• the upper limit of N content must therefore be held to 0.01 mass%.
• the present invention further limits the content of the impurity elements P and S to 0.03 mass% or less and 0.01 mass% or less, respectively.
• the chief purpose of this limitation is to further improve the low-temperature toughness of the base metal, particularly to enhance weld toughness.
• Reduction of P content mitigates center segregation in the continuously cast slab and also improves low-temperature toughness by preventing grain boundary fracture.
• Reduction of S content minimizes MnS inclusions elongated by hot rolling and thus works to improve ductility and toughness.
• Toughness is optimum when S content is lowered to 0.003 mass% or less.
• the contents of both P and S are preferably as low as possible but the extent to which they are lowered needs to be decided taking the balance between steel properties and cost into account.
• Nb, Ni, Mo, Cr, Cu and V The purpose of adding Nb, Ni, Mo, Cr, Cu and V will now be explained.
• the primary reason for adding these elements is to further improve the strength and toughness of the invention steel and increase the size of the steel product that can be manufactured, without loss of the superior properties of the steel.
• Nb when present together with B, enhances the hardenability improving effect of B. Nb also inhibits coarsening of crystal grains during hardening, thereby improving toughness. These effects are inadequate at an Nb content of less than 0.01 mass%. When B is added excessively to greater than 0.3 mass%, it conversely lowers toughness by causing heavy precipitation of NbC during tempering. Nb content is therefore defined as 0.01 to 0.3 mass%.
• Ni is added for the purpose of improving hardenability. Ni addition causes less degradation of low-temperature toughness than does Mn, Cr or Mo addition. The hardening improvement effect of Ni is insufficient at a content of less than 0.1 mass%. Excessive addition of Ni increases the likelihood of reverse transformation during tempering. The upper limit of Ni content is therefore defined as 1.0 mass%.
• Mo improves the hardenability of the steel and is added to achieve high strength. Moreover, when present together with Nb, Mo inhibits recrystallization of austenite during controlled rolling and thus also has an effect of refining the austenite structure before hardening. These effects are inadequate at an Mo content of less than 0.05 mass%. Excessive Mo addition causes formation of much martensite, making the steel strength too high. The upper limit of Mo content is therefore defined as 0.6 mass%.
• Cr increases the strength of the base metal and welds. This effect is inadequate at a Cr content of less than 0.1 mass%, so this value is defined as the lower limit. When the Cr content is excessive, coarse carbide forms at the grain boundaries to lower toughness. The upper limit of Cr content is therefore defined as 1.0 mass%.
• Cu is added for the purpose of improving hardenability. This effect is insufficient at a Cu content of less than 0.1 mass%. Excessive addition of Cu to greater than 1.0 mass% makes flaws more likely to occur during hot rolling. Cu content is therefore defined as 0.1 to 1.0 mass%.
• V has substantially the same effect as Nb. But the effect of V is weaker than that of Nb and cannot be sufficiently obtained when the amount added is less than 0.01 mass%. Since excessive addition of V degrades low-temperature toughness, the upper limit of V content is defined as 0.3 mass%.
• Ca and REM control the form of sulfides (MnS and the like), thereby improving low-temperature toughness. This effect is insufficient at a Ca content of less than 0.001 mass% and an REM content of less than 0.002 mass%.
• Addition of Ca to greater than 0.01 mass% or REM to greater than 0.02 mass% causes formation of a large amount of CaO-CaS or REM-CaS, giving rise to large clusters and large inclusions that impair steel cleanliness.
• the upper limits of Ca and REM addition are therefore defined as 0.01 mass% and 0.02 mass%, respectively.
• the preferred upper limit of Ca addition is 0.006 mass%.
• A 2.7 C + 0.4 Si + Mn + 0.45 Ni + 0.45 Cu + 0.8 Cr + 2 Mo.
• A 2.7 C + 0.4 Si + Mn + 0.45 Ni + 0.45 Cu + 0.8 Cr + Mo -1, so that the value of A cannot be made 1.8 or greater owing to the large amount of alloy that must be added.
• the symbols C, Si, Mn, Ni, Cu, Cr and Mo are the contents (mass%) of the respective elements.
• the contents of the optionally contained elements Ni, Cu, Cr and Mo are at the impurity level, specifically when the content of each of Ni, Cr and Cu is less than 0.05 mass% and the content of Mo is less than 0.02 mass%, the value of A is calculated using zero (mass%) as the content of each of these elements.
• the present invention restricts the structure of the steel pipe to low-carbon tempered martensite.
• the tempered martensite structure is a required condition of an oil well pipe for expandable tubular applications.
• it is necessary to give the steel pipe a structure that is predominantly martensite or bainite.
• strain concentrates at the soft ferrite portions during pipe expansion with the result that the pipe expansion ratio is small and cracking occurs.
• a bainite structure a mixed structure occurs that makes uniformity hard to achieve. Also in this case, strain concentrates at the relatively soft portions, so that the pipe expansion ratio is low and cracking occurs.
• martensite formation requires heating to within the austenite single phase range and quenching (hardening). If the heating temperature is made the Ac 3 point, it is in the austenite range but for fully realizing the hardening improvement effect of B, heating to the Ac 3 point + 30 °C or higher is required. Quenching (hardening) as termed here presumes cooling at around 20 °C/sec or greater at all locations in the thickness direction. The hardened steel pipe is tempered for strength adjustment. A stable structure is not obtained at a hardening temperature below 350 °C, while austenite forms when the temperature exceeds 720 °C. The tempering temperature is therefore defined as 350 to 720 °C..
• Tempered martensite which is a structure exhibiting uniform expandability, is excellent for avoiding cracking at a high pipe expansion ratio. However, if small thickness regions are present, the pipe expansion ratio may be lowered as a result of cracking caused by strain concentrating at these regions.
• the effect of the small thickness regions on expandability is very small if the thickness of the thinnest region is not less than 95%, preferably not less than 97%, the average thickness.
• ERW electric-resistance-welded
• the steel pipe manufactured in this manner is run down an oil well and thereafter expanded 10 to 30% for use. This is done, for example, by passing a cone-shaped plug of an outer diameter larger than the inner diameter of the steel pipe through the pipe interior from bottom to top.
• the pipe expansion ratio is calculated by dividing the difference in inner diameter between before and after expansion by the inner diameter before expansion and converting the result to a percentage.
• a cone-shaped plug having a maximum diameter 20% larger than the inner diameter of the pipe was inserted into the pipe bore to expand the pipe at a pipe expansion ratio of 20%, thereby obtaining steel pipe of 201.96 mm inner diameter.
• the plug surface was coated with a spray-type lubricant containing molybdenum disulfide so as to prevent seizing between the plug and steel pipe inner wall during insertion. After the expansion, the steel pipe surface was carefully examined for cracking.
• the steel pipes manufactured in the foregoing manner were subjected to Charpy testing for assessing toughness.
• the Charpy test was conducted in accordance with JIS Z 2242 at 0 °C using a V-notch specimen.
• the steel pipes were further subjected to flare testing to evaluate expansion performance.
• the flare test was conducted by driving a punch of 60 degree apex angle into the pipe bore until cracking occurred and stopping the insertion at this point.
• the pipe expansion ratio was calculated by determining the difference in inner diameter of the pipe between that at the time cracking occurred and that before testing, dividing the difference by the inner diameter of the pipe before testing, and converting the result to a percentage.
• the comparative examples that experienced cracking when expanded at a pipe expansion ratio of 20% were also poor in flare pipe expansion ratio.
• the seamless steel pipe No. 7 was somewhat low in pipe expansion ratio in the flare test because it had a low minimum thickness ratio.
• the present invention enables provision of an oil well pipe for expandable tubular applications excellent in post-expansion toughness in an oil well.

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• Crystallography & Structural Chemistry (AREA)
• Heat Treatment Of Articles (AREA)
• Heat Treatment Of Steel (AREA)

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• 2006
  • 2006-06-09 JP JP2007520213A patent/JP4943325B2/ja not_active Expired - Fee Related
  • 2006-06-09 CN CN201110110567.0A patent/CN102206789B/zh not_active Expired - Fee Related
  • 2006-06-09 WO PCT/JP2006/312080 patent/WO2006132441A1/ja active Application Filing
  • 2006-06-09 US US11/921,349 patent/US20090044882A1/en not_active Abandoned
  • 2006-06-09 EP EP06747307.4A patent/EP1892309B1/de not_active Ceased

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