JP2002266582A - Steel pipe subjected to pipe-expanding work - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel pipe which is subjected to pipe-expanding work while being inserted into an oil well or a gas well, and is for use in the inserted state. SOLUTION: The steel pipe has a lubricating film arranged on an internal surface substantially over the entire length thereof. The lubricating film is formed of a resin film containing a solid lubricant. It is preferable that the mass ratio (mass of the solid lubricant/resin mass) between a resin in the resin film and the solid lubricant is set to a range from 0.01 to 0.50, and the coefficient of kinetic friction of the lubricating film is set within a range from 0.1 to 0.4 inclusive.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel pipe which is expanded in a state where it is inserted into an oil well or a gas well and is used as it is.

[0002]

2. Description of the Related Art FIG. 1 shows an oil well or a gas well (hereinafter referred to as an oil well).
FIG. 4 is a vertical sectional view schematically showing a conventional construction of a well. As shown in FIG.
Is buried in the soil of the well, the second pipe 2 is buried inside the well, the third pipe 3 and the fourth pipe are buried sequentially, and finally, the fifth pipe reaching the oil or gas well. The well 10 has been constructed by burying the pipe 5 of FIG. Therefore, in order to construct a deeper well, the amount of steel pipe to be used increases according to the depth and the excavation area also increases,
Significant construction costs were required.

Heretofore, steel pipes used for wells have been made thinner by increasing the strength of the material itself, and the construction cost has been reduced by reducing the amount of material used. There was a feeling that the reduction in construction costs had reached its limit. Therefore, in order to further reduce the construction cost, a new construction method has been developed that inserts another steel pipe into the already buried steel pipe and expands this steel pipe to reduce the amount of steel pipe used. It is being studied for practical use.

FIG. 2 shows a well 1 according to this new construction method.
It is explanatory drawing which shows the construction point of 0 typically. As shown in the figure, this construction method inserts a pipe 8 having an outer diameter smaller than the outer diameter of a pipe 7 previously buried in the soil into a well, and expands this pipe with a mandrel 9 or the like. The pipe expansion process is performed using a tool, whereby the pipe 8 is used in a state of being fitted to the pipe 7, and the operation is repeated an appropriate number of times according to the depth of the well. According to this construction method, it is possible to greatly increase the depth at which pipes having the same outer diameter are used, as compared with the related art.

FIG. 3 is an explanatory view showing an example of a well 10 constructed by this construction method. As shown in the figure,
According to this new construction method, the diameter of the outermost pipe 11 can be reduced as compared with the conventional construction method, and the total usage and excavation area of the pipes 11 to 14 per well can be reduced. .

[0006]

However, steel pipes buried underground are required to have collapse resistance, that is, crush resistance, because they are subjected to underground pressure. In general, it is known that collapse-resistant steel pipes that have undergone pipe expansion have a reduced resistance. Although it is not intended for steel pipes to be used in this new construction method, as a technique for improving the collapse resistance, for example, Japanese Patent Application Laid-Open No. 9-31639 discloses a technique for warm straightening a quenched and tempered steel pipe. At this time, the circumferential compressive residual stress generated on the inner surface of the steel pipe is offset by the circumferential tensile residual stress generated on the inner surface of the steel pipe by water cooling in the next step,
There is disclosed a technique for reducing circumferential residual stress of a product and improving collapse resistance.

[0007] Since the steel pipe used for the new construction method is used as it is after being expanded in the well, heat treatment cannot be performed after the expansion, and the quality after the expansion can hardly be confirmed. Even if the quality can be confirmed after the pipe expansion, it is actually impossible to pull up the already expanded steel pipe from underground. For this reason, the steel pipe used for this new construction method is required to have a small reduction in collapse resistance due to the pipe expansion process.

It is an object of the present invention to provide a steel pipe which is used after being expanded in a state where it is inserted into a well, wherein the collapse resistance due to the expansion is small.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies on a steel pipe with a small decrease in collapse resistance and obtained the following findings a to e. Hereinafter, a steel pipe is also simply called a pipe.

A. The pipe expansion reduces the wall thickness of the pipe and reduces the collapse resistance. The decrease in the pipe wall thickness becomes more remarkable as the frictional force between the pipe expanding tool and the inner surface of the pipe increases.
Therefore, a decrease in the wall thickness of the pipe is suppressed by reducing the coefficient of friction between the pipe expanding tool and the pipe inner surface.

B. By the pipe expansion, a tensile residual stress or a compressive residual stress is generated in the circumferential direction of the inner surface of the pipe. When the frictional force between the pipe expanding tool and the inner surface of the pipe is small, tensile residual stress is generated, and when the frictional force is large, compressive residual stress is generated. In particular, when compressive residual stress occurs, the collapse resistance is significantly reduced.

C. By using a steel pipe having a lubricating film formed on the inner surface in advance as a steel pipe for pipe expansion, a decrease in pipe wall thickness is suppressed, a residual stress is optimized, and a reduction in collapse resistance is suppressed.

D. As the lubricating film, for example, a resin film in which a solid lubricant such as graphite or molybdenum disulfide is dispersed in a resin can be used. The mass ratio of the resin in the resin film to the solid lubricant (the mass of the solid lubricant / the mass of the resin) is preferably 0.01 to 0.50.

E. When the dynamic friction coefficient of the lubricating coating exceeds 0.4, compressive residual stress is generated, and the collapse resistance may be significantly reduced. On the other hand, when the dynamic friction coefficient is less than 0.1, the tensile residual stress becomes large, and the collapse resistance may be greatly reduced.

F. If the coefficient of kinetic friction of the lubricating coating exceeds 0.4, the reduction in the wall thickness of the tube becomes large, and the collapse resistance may be significantly reduced. g. Therefore, the coefficient of kinetic friction of the lubricating coating is 0.1 or more and 0.1 or more.
It is better to be 4 or less.

The kinetic friction coefficient of the lubricating film is defined as a value measured by a Bowden test shown below.
FIG. 4 is a schematic diagram schematically showing a method for measuring the dynamic friction coefficient of a lubricating film using a Bowden-type test apparatus. In the figure, reference numeral 21 denotes a test piece, 22 denotes a hemispherical presser, and 23 denotes a spring. As shown in FIG. 4, the Bowden-type test apparatus includes a hemispherical pressing element 22 and a spring 23, and has a lubricating film formed on the surface thereof and slides in the left-right direction (the direction of the arrow) in the drawing.
Then, the hemispherical pressing element 22 is pressed with a predetermined pressing load P, the displacement of the spring 23 at that time is measured, and the frictional force F between the test piece and the hemispherical pressing element is determined from the displacement of the spring and the spring rigidity. As a result, the dynamic friction coefficient μ of the lubricating film is calculated by μ = F / P. However, the relative speed between the test piece and the hemispherical pressing element: 40 mm / sec, pressing load: 30 MPa, test temperature:
Room temperature, hemispherical presser is made of high carbon bearing steel (SUJ
In 2), the Rockwell hardness is 63 or more, and the surface roughness of the hemispherical presser is 0.1 μm or less in Rmax.

The present invention has been completed based on the above findings, and the gist thereof is as follows. (1) A steel pipe which is used by being expanded while being inserted into an oil well or a gas well, and which is provided with a lubricating coating over substantially the entire length of the inner surface of the steel pipe. Steel pipe for processing.

(2) The steel pipe for expanding work according to the above (1), wherein the lubricating film is a resin film containing a solid lubricant. (3) The pipe expansion according to the above (2), wherein the mass ratio of the resin in the resin film to the solid lubricant (mass of the solid lubricant / mass of the resin) is 0.01 to 0.50. Steel pipe for processing.

(4) The lubricating film has a coefficient of kinetic friction of 0.1 or more and 0.4 or less.
(3) The steel pipe for pipe expansion processing according to any of (3).

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of a steel pipe according to the present invention will be described in detail for each feature. (1) Lubricating coating: Since the steel pipe on which the lubricating coating is formed is transported to the well where the pipe expansion process is performed, it is required to ensure high adhesion that does not fall off during transport and high lubricity. Examples of such a lubricating film include a resin film in which a solid lubricant is dispersed in a resin, and a semi-solid lubricating film such as compound grease. Further, as the lubricating film, a solid film in which molybdenum disulfide, tungsten disulfide, or the like is laminated by ion plating may be used.
In particular, the resin film has high adhesion and high lubricity, and is easy to form and has high practicality. Therefore, a resin film is desirable as the lubricating film.

As the solid lubricant, it is desirable to use graphite, molybdenum disulfide or tungsten disulfide alone or as a mixture of two or more thereof. In addition,
As solid lubricants, metal soaps such as phosphate ester-based, sulfate ester-based, or fatty acid ester-based Ca
A salt or a Zn salt may be used.

As the resin, a material having a function as a binder of a solid lubricant and an appropriate hardness is used. Such materials include epoxy resins, polyamide-imide resins,
Examples thereof include a polyimide resin.

If the thickness of the lubricating film is too small, the effect of improving the lubricity is small, and if the thickness is too large, it is easy to peel off. Therefore, it is desirable that the thickness of the lubricating coating be 1 μm or more and 50 μm or less. More preferably, the lower limit of the thickness of the lubricating coating is 10 μm.

The steel pipe of the present embodiment is provided with such a lubricating coating over substantially the entire length of the inner surface. Provision substantially over the entire length of the inner surface means that a lubricating coating is formed at least on the entire length of the inner surface on which the pipe expanding process is performed.

(2) Mass ratio of resin to solid lubricant in the resin film: The solid lubricant has the effect of improving the lubricity of the resin film. However, when the proportion of the solid lubricant in the resin film increases, the adhesiveness of the resin film decreases. When the proportion of the solid lubricant in the resin film decreases, the lubricity of the resin film decreases. Therefore, the mass ratio of the resin in the resin film to the solid lubricant (mass of solid lubricant / mass of resin) is:
It is desirable to be 0.01 or more and 0.50 or less. More preferably, it is 0.01 or more and 0.15 or less.

(3) Coefficient of kinetic friction of the lubricating coating: When the kinetic friction coefficient between the inner surface of the pipe and the lubricating coating is increased, the tensile force in the pipe axis direction at the time of expanding the pipe is increased, which causes a reduction in collapse resistance. The decrease in pipe wall thickness increases. If the coefficient of kinetic friction is excessive, the residual stress is compressed, and the collapse resistance may be significantly reduced. On the other hand, when the coefficient of kinetic friction between the inner surface of the pipe and the lubricating coating is too small, the tensile residual stress increases, and the degradation of the collapse resistance may increase. Therefore, the coefficient of kinetic friction of the lubricating coating is preferably 0.1 or more and 0.4 or less as specified in the Bowden test described above. More preferably, 0.1 or more,
0.3 or less, more preferably 0.2 or more and 0.3 or less.

Next, a method of forming a lubricating film according to the present invention will be described by taking a resin film as an example. For example, after descaling the inner surface of a steel pipe manufactured by rolling, immersing the descaled steel pipe in a liquid obtained by adding a dispersant such as toluene or isopropyl alcohol to the solid lubricant and the resin described above, Then, a resin coating can be formed on the inner surface of the steel pipe by performing a heat treatment at 100 to 200 ° C.

In the case of a high Cr steel tube having a Cr content exceeding 10% by mass, in order to improve the adhesion of the coating, after descaling, the inner surface of the tube is subjected to a base treatment such as nitriding treatment or iron alloy plating. It is preferable to form a resin film thereon.

When a semi-solid lubricating film such as compound grease is formed, the lubricating film can be formed by directly applying grease to the inner surface of the descaled steel pipe. As described above, since the steel pipe of the present embodiment is used after being expanded while being inserted into the well, the method of manufacturing the raw steel pipe itself is not particularly limited. For example, a welded steel pipe in which butted portions of steel plates are welded, a seamless steel pipe manufactured seamlessly from a billet, or the like can be applied.

Similarly, the material of the steel pipe is not particularly limited. For example, carbon steel, low alloy steel, high alloy steel, or the like can be used. However, when a resin film is formed on a high Cr steel pipe, it is desirable to use a steel pipe whose inner surface is subjected to a base treatment.

As described above, the steel pipe of the present embodiment is used after being expanded in a state where it is inserted into a well, and the method of expanding the pipe itself is not particularly limited. Absent. For example, examples of the pipe expanding method include a method of pulling up a tapered mandrel inserted into the inside of the pipe by hydraulic pressure, a method of attaching a cored bar to the tapered mandrel, and mechanically pulling out the mandrel. If the taper angle of the tapered mandrel is too small, the frictional force between the mandrel and the inner surface of the steel pipe increases, and there is a problem that the deformed state of the pipe tends to be unstable. The surface pressure at the contact portion becomes extremely large, and problems such as image sticking are likely to occur. Therefore, the taper angle is desirably 5 to 45 degrees. More preferably, it is 10 to 30 degrees.

[0032]

EXAMPLE After hot rolling by the Mannesmann-Mandrel pipe manufacturing method, reheating to the austenite region and soaking, water quenching and tempering treatment were performed to obtain an outer diameter of 139.7 mm and a wall thickness of 10.5 mm. Made of low alloy (C: 0.24 mass%, Mn:
1.3 mass%, Cr: 0.2 mass%, V: 0.01 mass%). The strength grade of this tube is API-L80 grade equivalent (tensile strength: 570
MPa).

After descaling the inner surface of the tube with a shot, a mixed solution of toluene and isopropyl alcohol was added as a dispersion medium to a mixed powder of molybdenum disulfide and graphite and an epoxy resin, and mixed. A method of forming a resin film over the entire length of the inner surface by immersing and then performing a heat treatment at 150 ° C., whereby six types of pipes having lubricating films having different mass ratios of the mixed powder as a solid lubricant and the resin. (P1 to P6) were manufactured. In the above liquid, the mass%
Thus, the total of the mixed powder and the epoxy resin was 35%, and the mixed liquid of the dispersion medium was 65%.

A sample was cut out from the tube provided with the lubricating film, and the dynamic friction coefficient of the lubricating film was measured using the sample. The measurement of the dynamic friction coefficient was performed using the Bowden-type test apparatus shown in FIG. 4 under the test methods and test conditions described above.
In addition, a sample was cut out from the tube (P7) in a state where it was descaled, and the dynamic friction coefficient of this tube was also investigated. Table 1
Fig. 2 shows the measurement results of the mass ratio of the solid lubricant to the resin and the dynamic friction coefficient.

[0035]

[Table 1]

As shown in Table 1, the kinetic friction coefficient decreased as the mass ratio increased, and the kinetic friction coefficient became 0.3 or less when the mass ratio was 0.01 (1%) or more. Next, a pipe expansion test was performed on the pipe having the lubricating film formed on the inner surface and the pipe in a state where the scale was descaled.

FIG. 5 is a schematic diagram showing the procedure of a pipe expansion test. In the figure, reference numeral 25 indicates a pipe, and reference numeral 26 indicates a plug which is a pipe expanding tool. As shown in FIG. 5, one end of the pipe 25 is fixed, and the plug 26 having a taper angle α of 10 degrees or 20 degrees inserted into the pipe 25 is pulled out. Amount (d1-d0) / tube inner diameter d0
× 100%) performs 20% or 30% pipe expansion,
A finished tube was obtained. Here, d1 is a finished pipe (tube after expanded processing).
The inside diameter, d0, is the inside diameter of the pipe before the pipe expanding process.

The thickness of the finished pipe obtained by the expanding process is measured, and the reduction rate of the wall thickness (amount of reduction in wall thickness / wall thickness of base tube × 100%)
Was calculated, and the residual stress on the inner surface of the finished tube and the crushing pressure (collapse strength) were measured. Note that the rate of decrease in wall thickness is also referred to as the rate of decrease in wall thickness.

The residual stress on the inner surface of the tube was measured by a strain gauge method. That is, after a strain gauge was attached in the circumferential direction of the inner surface of the pipe after the pipe expansion process, the pipe was cut into small pieces. At this time, the strain generated in the small pieces was measured, and the residual stress was determined from this strain.

FIG. 6 is a schematic diagram showing a method for measuring the crushing pressure. In the figure, reference numeral 31 denotes a container, 32 denotes a pipe, and 33 denotes water. As shown in FIG. 6, a pipe 32 is installed in a container 31, and a hydrostatic pressure (indicated by an arrow in the drawing) is applied from outside the pipe,
The hydrostatic pressure when the tube began to collapse was measured and was taken as the collapse pressure.

Table 2 shows the test conditions A (taper angle α: 10
Degree, magnification: 20%), test condition B (taper angle α: 20)
Degree, magnification: 20%) and test condition C (taper angle α:
The ratio of the wall thinning rate, the residual stress, and the crushing pressure (20 °, expansion ratio: 30%) (crushing pressure of the pipe after expansion / crushing pressure of the pipe before expansion) is shown.

[0042]

[Table 2]

FIG. 7 is a graph showing the relationship between the dynamic friction coefficient and the wall thinning rate in this example. FIG. 8 is a graph showing the relationship between the dynamic friction coefficient and the residual stress in this example. FIG.
Is a graph showing the relationship between the coefficient of dynamic friction and the ratio of the crushing pressure in this example.

As shown in Table 2 and FIG. 7, when a tube having a lubricating film having a dynamic friction coefficient of 0.3 or less was used, the wall thinning rate was significantly suppressed as compared with a tube having no lubricating film. Further, as shown in Table 2 and FIG. 8, it was found that when a tube having a lubricating coating having a dynamic friction coefficient of 0.3 or less was used, the circumferential residual stress on the inner surface of the tube was a tensile stress.

As shown in Table 2 and FIG. 9, in the pipe having the lubricating coating having a dynamic friction coefficient of 0.3 or less, the reduction in the crush pressure was significantly suppressed as compared with the pipe having no lubricating coating. In particular, a tube having a lubricating film having a dynamic friction coefficient of 0.2 to 0.3 was good.

[0046]

According to the present invention, it is possible to provide a pipe having a small decrease in collapse resistance due to pipe expansion, and more specifically, a pipe which is subjected to pipe expansion while inserted into a well and used as it is. Can be provided. Therefore, according to the present invention, the total amount of steel pipe used per well and the excavated area can be reduced.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view schematically showing conventional construction of a well.

FIG. 2 is an explanatory view schematically showing a construction procedure of a well by a new construction method.

FIG. 3 is an explanatory view showing an example of a well constructed by a new construction method.

FIG. 4 is a schematic diagram schematically showing a method for measuring a dynamic friction coefficient of a lubricating coating using a Bowden-type test apparatus.

FIG. 5 is a schematic diagram showing a procedure of a pipe expansion test.

FIG. 6 is a schematic view showing a method of measuring a crush pressure.

FIG. 7 is a graph showing a relationship between a dynamic friction coefficient and a wall thickness reduction rate in the present example.

FIG. 8 is a graph showing a relationship between a coefficient of dynamic friction and a residual stress in this example.

FIG. 9 is a graph showing the relationship between the coefficient of dynamic friction and the ratio of crushing stress in this example.

[Explanation of symbols]

1 to 5, 7, 8, 11 to 14, 25, 32: tube, 10:
Well, 9: mandrel, 21: test piece, 22: hemispherical presser, 23: spring, 26: plug, 31: container, 33:
water.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C10M 105/74 C10M 105/74 145/20 145/20 149/18 149/18 169/04 169/04 / / C10N 10:04 C10N 10:04 10:12 10:12 40:00 40:00 Z 50:02 50:02 50:08 50:08

Claims (4)

[Claims] 1. A steel pipe which is used by being expanded in an oil well or a gas well and is provided with a lubricating coating over substantially the entire length of an inner surface of the steel pipe. Steel pipe for pipe expansion. 2. The steel pipe for expanding work according to claim 1, wherein the lubricating coating is a resin coating containing a solid lubricant. 3. The mass ratio of the resin in the resin film to the solid lubricant (mass of solid lubricant / mass of resin) is 0.01 to 0.5.
The steel pipe for pipe expansion according to claim 2, wherein the value is 0. 4. The dynamic friction coefficient of the lubricating coating is 0.1 or more,
The steel pipe for pipe expansion according to any one of claims 1 to 3, wherein the diameter is 0.4 or less.