JP2008291322A - Steel pipe for oil well having excellent pipe expandability and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive steel pipe for oil well having excellent pipe expandability. <P>SOLUTION: The steel pipe is characterized in that: it has ≥350 MPa yield strength and ≥0.08 n-value; and n-value and uniform elongation u-El satisfy n>0.007×(25-u-El) (where (n) is n-value and u-El is uniform elongation (%)). Excellent pipe expandability can hereby be secured. This steel pipe can be obtained by applying, as heat treatment, quenching and tempering treatments, or normalizing and tempering treatments, or tempering treatment to a steel pipe which has a composition containing, by mass, ≤0.35% C, ≤1.5% Si, 0.10 to 3.50% Mn and proper amounts of P, S and Al or further containing one or more groups selected from among: a group of Cr and Cu; a group of Ni; a group of Mo, V, Nb, Ti, Zr, B and W; and a group of Ca. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to oil well steel pipes that are embedded in crude oil or natural gas oil wells or gas wells (hereinafter collectively referred to simply as oil wells), and more particularly to improvement of pipe expandability.

  In order to lay an oil well pipe from the ground surface to an underground oil field, first, excavation from the ground surface to a predetermined depth is carried out, and a steel pipe called a casing is buried therein to prevent the collapse of the wall. Thereafter, the basement is further excavated from the tip of the casing to form a deeper well, and a new casing is buried through the previously buried casing. By repeating this operation, an oil well pipe (tubing) that finally reaches the oil field is laid. When excavating deep wells, many types of casings with different diameters are required. The diameter of the oil well pipe (tubing) through which crude oil or gas passes is fixed, so when drilling a deep well, it is necessary to increase the drilling area in the radial direction, and the cost required for drilling will increase become. For this reason, it is strongly desired to reduce the drilling cost of oil wells.

  In response to such a request, for example, Patent Document 1 and Patent Document 2 describe a method of expanding a casing (steel pipe) in a well by means of expansion or the like. According to the techniques described in Patent Document 1 and Patent Document 2, the diameter of each casing having a multistage structure can be kept small by expanding the casing (steel pipe) in the radial direction in the well. It is said that it is possible to reduce the drilling cost of the oil well by keeping the upper casing size small.

Further, for example, Patent Document 3 includes, in mass%, C: 0.10 to 0.45%, Si: 0.1 to 1.5%, Mn: 0.10 to 3.0%, and P, S, Al, and N are adjusted to appropriate amounts, Alternatively, it has a composition containing an appropriate amount of one or more of Cr, Mo, V and / or an appropriate amount of Nb, Ti, and / or an appropriate amount of Ca. The strength (yield strength YS (MPa)) and crystal grain size (d (μm)) of the steel pipe before pipe expansion is expressed by the following formula: ln (d) ≦ −0.0067YS + 8.09
The oil well steel pipe for pipe expansion with excellent corrosion resistance after pipe expansion processing that satisfies the above relationship is described. However, in the technique described in Patent Document 3, the limit pipe expansion rate is 30% or less at the maximum, and from the demand for further cost reduction, an oil well steel pipe excellent in pipe expandability exceeding 30% is required. .

In response to such demands, Patent Document 4 includes, in mass%, C: 0.05 to 0.30%, Si: 0.2 to 2%, Mn: 0.7 to 4.0%, and appropriate amounts of P, S, N, and O. Or a composition containing one or more of Al, Cr, Ni, Cu, Nb, V, Ti, Mo, B, and Ca in an appropriate amount, and 5 vol% or more in the structure There is described a seamless steel pipe for oil wells having excellent residual expandability with a residual γ phase.
JP 7-507610 International Publication No. WO98 / 00626 Japanese Patent Laid-Open No. 2002-266055 Japanese Unexamined Patent Publication No. 2006-9078

However, in the technique described in Patent Document 4, it is said that a seamless steel pipe having a limit pipe expansion rate exceeding 30% is obtained, but it has high strength and requires high energy for the pipe expansion and is expensive. For this reason, there is a need for oil well steel pipes with excellent pipe expandability that can be expanded more inexpensively.
It is an object of the present invention to advantageously solve the problems of the prior art and to provide an oil well steel pipe that is less expensive than the prior art and has excellent pipe expandability.

  In order to achieve the above-mentioned object, the present inventors diligently studied the influence of various factors on tube expandability. As a result, in order to ensure excellent tube expandability, it has been found that it is important to have a yield strength within a desired range and an n value equal to or greater than a predetermined value as a material factor. Also, in order to ensure the desired strength, C, Si, Mn, Al, or even Cr, Cu, and / or Ni, and / or Mo, V, Nb, Ti, Zr, B, W, and It has been found that an oil well steel pipe having a desired strength and excellent pipe expandability can be obtained by adjusting the Ca content within an appropriate range and devising heat treatment.

The present invention has been completed based on the above findings and further studies. That is, the gist of the present invention is as follows.
(1) An oil well steel pipe that is expanded in a state of being inserted into an oil well, having a yield strength of 350 MPa or more, an n value of 0.08 or more, and an n value and uniform elongation u-El ( 1) Formula
n> 0.007 × (25−u-El) (1)
(Where n: n value, u-El: uniform elongation (%))
Satisfying the requirements and excellent pipe expandability.
(2) In (1), the oil well steel pipe is, by mass%, C: 0.35% or less, Si: 1.5% or less, Mn: 0.10 to 3.50%, P: 0.07% or less, S: 0.01% or less, Al : A steel pipe for oil wells containing 0.05% or less and having a composition comprising the balance Fe and inevitable impurities.
(3) In (2), in addition to the above composition, in addition to mass%, the following group A to group D: group A: Cr: 2.0% or less, Cu: 3.5% or less ,
Group B: Ni: 2.0% or less,
Group C: Mo: 2.0% or less, V: 0.20% or less, Nb: 0.20% or less, Ti: 0.30% or less, Zr: 0.20% or less, B: 0.01% or less, W: 1.0% or less One or more,
Group D: Ca: 0.0005 to 0.01%
An oil well steel pipe characterized by having a composition containing one group or two or more groups selected from among them.
(4) By mass%, C: 0.35% or less, Si: 1.5% or less, Mn: 0.10 to 3.50%, P: 0.07% or less, S: 0.01% or less, Al: 0.05% or less, the balance Fe and A method of manufacturing a steel pipe for oil wells, comprising subjecting a steel pipe having a composition composed of inevitable impurities to quenching and tempering, or normalizing and tempering, or tempering as heat treatment.
(5) In addition to the above-mentioned composition in (4), in addition to mass%, the following group A to group D group A: Cr: 2.0% or less, Cu: 3.5% or less selected from the following:
Group B: Ni: 2.0% or less,
Group C: Mo: 2.0% or less, V: 0.20% or less, Nb: 0.20% or less, Ti: 0.30% or less, Zr: 0.20% or less, B: 0.01% or less, W: 1.0% or less One or more,
Group D: Ca: 0.0005 to 0.01%
The manufacturing method of the steel pipe for oil wells characterized by setting it as the composition containing 1 group or 2 groups or more selected from these.

  According to the present invention, it is possible to easily manufacture an inexpensive oil well steel pipe having excellent pipe expandability that can withstand severe pipe expansion processing, and has a remarkable industrial effect.

  The oil well steel pipe of the present invention is a steel pipe having a yield strength of 350 MPa or more. The pipe expansion performed in a state where the oil well steel pipe is inserted into the oil well is usually performed through the pipe for expansion into the steel pipe. If the yield strength of the oil well steel pipe is less than 350 MPa, there may be a problem such as buckling when the pipe for pipe expansion is passed, and proper pipe expansion may not be performed. For this reason, in order to ensure sufficient pipe expandability, in the present invention, the yield strength of the oil well steel pipe is limited to 350 MPa or more, preferably 550 MPa or less. More preferably, it is 350 to 480 MPa.

  The oil well steel pipe of the present invention is a steel pipe having an n value of 0.08 or more. According to the study by the present inventors, the n value is an important material factor affecting the pipe expandability of the steel pipe. In order to ensure excellent pipe expandability, the n value is limited to 0.08 or more in the present invention. If the n value is less than 0.08, the desired tube expandability cannot be ensured. In addition, Preferably it is 0.10 or more. The “n value” here is a value measured in accordance with the provisions of JIS Z 2253 using a tensile test piece having the tube axis direction as the tensile direction.

In addition, if the uniform elongation u-El of the oil well steel pipe is sufficiently large, it is possible to expand the tube with a high expansion ratio even if the n value is low. However, if the uniform elongation u-El is small, sufficient expansion is possible. Cannot be secured. According to the study by the present inventors, in order to stably ensure excellent tube expandability, the n value in the above-described range and a predetermined value related to the uniform elongation u-El, that is, the following (1) formula
n> 0.007 × (25−u-El) (1)
(Where n: n value, u-El: uniform elongation (%))
It has been found that it is necessary to have an n value that satisfies the above. If the n value cannot satisfy the formula (1), the desired excellent tube expandability cannot be ensured. The uniform elongation u-El uses a value measured in accordance with the provisions of JIS Z 2241 using a tensile test piece with the tube axis direction as the tensile direction.

Next, the reason for limiting the composition of the steel pipe for oil well of the present invention will be described. Unless otherwise specified, mass% is simply expressed as%.
C: 0.35% or less C is an important element related to the strength of steel pipes. To ensure the desired strength, it is desirable to contain 0.04% or more. Sometimes the risk of burning cracks increases. For this reason, C was limited to 0.35% or less.

Si: 1.5% or less
Si is an element useful as a deoxidizer in a normal steelmaking process. In order to acquire such an effect, it is desirable to contain 0.05% or more, but inclusion exceeding 1.5% reduces hot workability and furthermore toughness. For this reason, Si was limited to 1.5% or less. In addition, Preferably it is 0.7% or less.

Mn: 0.10 to 3.50%
Mn is an element that has the effect of increasing the steel pipe strength by solid solution and contributes effectively to the improvement of the n value. In order to ensure a desired strength as an oil well steel pipe, it is necessary to contain 0.10% or more. On the other hand, a large content exceeding 3.50% adversely affects the toughness and increases the risk of causing fire cracks during steel pipe production. For this reason, Mn was limited to the range of 0.10 to 3.50%. In addition, Preferably it is 0.3 to 3.5%.

P: 0.07% or less P is an element that reduces hot workability and deteriorates resistance to sulfide stress corrosion cracking. In the present invention, its content is preferably as small as possible. Reduction leads to an increase in manufacturing costs. Therefore, in the present invention, P is limited to 0.07% or less, which is a range that can be implemented industrially at a relatively low cost and does not reduce hot workability and sulfide stress corrosion cracking resistance. In addition, Preferably it is 0.03% or less.

S: 0.01% or less S is an element that remarkably deteriorates the hot workability in the pipe-making process. In the present invention, the content is preferably as low as possible, but extreme reduction increases the manufacturing cost. Invite. Therefore, in the present invention, S is limited to 0.01% or less, which is a range in which pipe production in a normal process is possible. In addition, Preferably it is 0.005% or less.

Al: 0.05% or less
Al is an element that acts as a strong deoxidizer and also has an effect of combining with N to refine crystal grains. In order to ensure such an effect stably, it is desirable to contain 0.005% or more, but inclusion exceeding 0.05% adversely affects toughness. For this reason, Al was limited to 0.05% or less. In addition, Preferably it is 0.007 to 0.03%.

Although the above-described components are basic components, in the present invention, in addition to the basic composition described above, one or more groups selected from Group A to Group D can be further contained.
Group A: Cr: 2.0% or less, Cu: One or two selected from 3.5% or less Group A: Cr and Cu are elements that improve corrosion resistance, and are selected as necessary Can be contained.

Cr is an element that improves resistance to CO ₂ corrosion resistance and corrosion resistance, such as resistance to CO ₂ stress corrosion cracking resistance. Such an effect becomes remarkable when the content is 0.2% or more. On the other hand, if the content exceeds 2.0%, the toughness decreases. For this reason, it is preferable to limit Cr to 2.0% or less. More preferably, it is 0.3 to 1.5%.
Cu is an element having an action of strengthening the protective film and suppressing the penetration of hydrogen into the steel and improving the resistance to sulfide stress corrosion cracking. Such an effect becomes remarkable when the content is 0.2% or more. However, when the content exceeds 3.5%, CuS precipitates at the grain boundary at a high temperature, thereby reducing the hot workability. For this reason, it is preferable to limit Cu to 3.5% or less. In addition, More preferably, it is 0.2 to 2.0%.

Group B: Ni: 2.0% or less,
Group B: Ni is an element that contributes effectively to improving toughness. Moreover, when it contains Cu, it contributes effectively in preventing the crack at the time of rolling. In order to acquire such an effect, it is desirable to contain 0.1% or more, but even if it contains exceeding 2.0%, the effect is saturated and an effect commensurate with the content cannot be expected. For this reason, it is preferable to limit Ni to 2.0% or less. More preferably, it is 0.1 to 1.0%.

Group C: Mo: 2.0% or less, V: 0.20% or less, Nb: 0.20% or less, Ti: 0.30% or less, Zr: 0.20% or less, B: 0.01% or less, W: 1.0% or less 1 type or 2 types or more Group C: Mo, V, Nb, Ti, Zr, B, and W are all elements that have an effect of increasing the strength of steel pipes. It can be contained above.
Mo is an element that contributes to an increase in steel pipe strength through improvement in hardenability, but is also an element that improves resistance to sulfide stress corrosion cracking in an environment where hydrogen sulfide is present. In order to acquire such an effect, it is desirable to contain 0.1% or more, but even if it contains exceeding 2.0%, an effect is saturated and the effect corresponding to content cannot be expected. For this reason, it is preferable to limit Mo to 2.0% or less. More preferably, it is 0.2 to 1.5%.

V is an element that contributes to an increase in steel pipe strength through an improvement in hardenability, but is also an element that improves the resistance to sulfide stress corrosion cracking. In order to acquire such an effect, it is desirable to contain 0.02% or more, but inclusion exceeding 0.20% reduces toughness. For this reason, it is preferable to limit V to 0.20% or less. In addition, More preferably, it is 0.02 to 0.15%.
Nb is an element that contributes effectively to increasing the strength and toughness of steel. Such an effect becomes remarkable when the content is 0.01% or more, but when the content exceeds 0.20%, the toughness is lowered. For this reason, Nb is preferably 0.20% or less. In addition, More preferably, it is 0.02 to 0.12%.

Ti is an element that has an effect of increasing the steel pipe strength and improving the stress corrosion cracking resistance. Such an effect becomes remarkable when Ti is contained by 0.01% or more. On the other hand, a content exceeding 0.30% deteriorates toughness. For this reason, it is preferable to limit Ti to 0.30% or less. In addition, More preferably, it is 0.02 to 0.18%.
Zr is also an element having an action of increasing the steel pipe strength and improving the stress corrosion cracking resistance. Such an effect becomes remarkable when the content of Zr is 0.01% or more. On the other hand, the content exceeding 0.20% deteriorates toughness. For this reason, it is preferable to limit Zr to 0.20% or less. In addition, More preferably, it is 0.02 to 0.15%.

B is also an element having an action of increasing the steel pipe strength and improving the stress corrosion cracking resistance. Such an effect becomes remarkable when the content is 0.0003% or more. On the other hand, the content exceeding 0.01% deteriorates toughness. For this reason, it is preferable to limit B to 0.01% or less. In addition, More preferably, it is 0.0005 to 0.005%.
W is also an element having an action of increasing the steel pipe strength and improving the stress corrosion cracking resistance. Such an effect becomes remarkable when the content is 0.2% or more. On the other hand, the content exceeding W: 1.0% deteriorates toughness. For this reason, it is preferable to limit W to 1.0% or less.

Group D: Ca: 0.0005 to 0.01%
Group D: Ca is an element having an effect of reducing the trapping ability of hydrogen by reducing the lattice strain of the matrix around the inclusions by fixing S as CaS and making the S-based inclusions spherical. In order to obtain such an effect, the content of 0.0005% or more is necessary. However, if the content exceeds 0.01%, CaO increases, and the resistance to CO ₂ corrosion resistance and pitting corrosion resistance decreases. For this reason, it is preferable to limit Ca to 0.0005 to 0.01% of range. In addition, More preferably, it is 0.001 to 0.005%.

The balance other than the above components is Fe and inevitable impurities. As an inevitable impurity, O: 0.01% or less is acceptable.
Next, a preferred method for producing the steel pipe for oil well of the present invention will be described by taking a seamless steel pipe as an example. In the present invention, it is needless to say that the steel pipe is not limited to a seamless steel pipe, and may be a welded steel pipe (electrically welded steel pipe).

  Molten steel having the above composition is melted by a normal melting method such as a converter, electric furnace, vacuum melting furnace, etc., and a steel pipe such as a billet by a normal method such as a continuous casting method or an ingot-bundling rolling method. It is preferable to use a raw material. Subsequently, these steel pipe materials are heated and hot-worked and formed using a normal Mannesmann-plug mill method or Mannesmann-Mandrel mill manufacturing process to obtain seamless steel tubes having desired dimensions. After the pipe making, the steel pipe is preferably cooled to a temperature of about room temperature at a cooling rate of about air cooling, as in the normal process.

In the present invention, it is preferable to further heat-treat the steel pipe as it is. The heat treatment is preferably quenching / tempering treatment, tempering / tempering treatment, or tempering treatment.
In place of the tempering treatment, a two-phase region treatment in which the temperature is heated to a two-phase region and cooled may be used. The tempering process and the two-phase region process may be repeated at least twice.
Furthermore, based on an Example, this invention is demonstrated still in detail.

Molten steel with the composition shown in Table 1 is melted in a vacuum melting furnace, fully degassed, made into a 100-kilo steel ingot, piped by hot working with a model seamless rolling mill for research, and seamless steel pipe (Outer diameter 3.3 in.φ (83.8 mmφ) × wall thickness 0.25 in. (6.35 mm)). In addition, it was made into air cooling to room temperature after pipe making.
Next, a specimen material (length: 300 mm) was cut out from each steel pipe and subjected to the heat treatment shown in Table 2. Some steel pipes were kept hot rolled.

In addition, from the test piece material that has been subjected to the above heat treatment, a tensile test piece (arc-shaped test piece: GL: 25.4 mm) with the tube axis direction as the tensile direction is cut out in accordance with the API regulations, and the API specifications are followed. In accordance with the tensile test, tensile properties (yield strength YS, tensile strength TS, uniform elongation u-El) were determined. At the same time, the n value was determined in accordance with JIS Z 2253.
In addition, a pipe expansion test piece (steel pipe: length 300 mm) was collected from the test piece material subjected to the above heat treatment. Plugs with various outer diameters larger than the inner diameter of the expanded test specimen (steel pipe) are sequentially pushed into these expanded test specimens (steel pipe) by pressing, and the plug diameter at the time when the crack occurs is obtained. Calculated.

Limit expansion ratio = [{(Outer diameter of plug when crack occurs) − (Inner diameter of test piece material)} / (Inner diameter of test piece material)] × 100 (%)
In addition, the outer diameter of the used plug was considered so that the expansion ratio might be 5%.
The obtained results are shown in Table 2.

Each of the examples of the present invention is a steel pipe having a yield strength of 350 MPa or more and an excellent pipe expandability of 25% or more. On the other hand, in a comparative example that is out of the scope of the present invention, the yield strength is less than 350 MPa, or the limit tube expansion rate is low and the tube expandability is lowered.

Claims (5)

An oil well steel pipe that is expanded while inserted into an oil well. It has a yield strength of 350 MPa or more, an n value of 0.08 or more, and the n value and uniform elongation u-El are expressed by the following formula (1) Satisfying the requirements and excellent pipe expandability.
Record
n> 0.007 × (25−u-El) (1)
Where n: n value,
u-El: Uniform elongation (%) The oil well steel pipe is in mass%,
C: 0.35% or less, Si: 1.5% or less,
Mn: 0.10 to 3.50%, P: 0.07% or less,
2. The oil well steel pipe according to claim 1, comprising S: 0.01% or less, Al: 0.05% or less, and having a composition comprising the balance Fe and inevitable impurities. In addition to the said composition, it is set as the composition containing 1 group or 2 groups or more selected from the following A group-D group by the mass%, The steel pipe for oil wells of Claim 2 characterized by the above-mentioned.
Group A: Cr: 2.0% or less, Cu: One or two selected from 3.5% or less,
Group B: Ni: 2.0% or less,
Group C: Mo: 2.0% or less, V: 0.20% or less, Nb: 0.20% or less, Ti: 0.30% or less, Zr: 0.20% or less, B: 0.01% or less, W: 1.0% or less One or more,
Group D: Ca: 0.0005 to 0.01% % By mass
C: 0.35% or less, Si: 1.5% or less,
Mn: 0.10 to 3.50%, P: 0.07% or less,
Steel pipes containing S: 0.01% or less, Al: 0.05% or less and having the composition of the balance Fe and unavoidable impurities are subjected to quenching treatment and tempering treatment, normalizing treatment and tempering treatment, or A method for producing a steel pipe for oil wells, characterized by performing a return treatment. In addition to the said composition, it is set as the composition containing 1 group or 2 or more groups chosen from the following A group-D group by the mass%, The steel pipe for oil wells of Claim 4 characterized by the above-mentioned. Production method.
Group A: Cr: 2.0% or less, Cu: One or two selected from 3.5% or less,
Group B: Ni: 2.0% or less,
Group C: Mo: 2.0% or less, V: 0.20% or less, Nb: 0.20% or less, Ti: 0.30% or less, Zr: 0.20% or less, B: 0.01% or less, W: 1.0% or less One or more,
Group D: Ca: 0.0005 to 0.01%