Metal pipes for oil wells

Abstract

The present invention provides a metal pipe for oil wells, the metal pipe having a high shear strength. A metal pipe for oil wells according to the present disclosure is provided with a resin film (100) on or above at least one of a pin contact surface (400) and a box contact surface (500). The resin film (100) contains 50.0% to 99.5% by mass of a resin, 0% to 10.0% by mass of a wax, 0% to 30.0% by mass of a fluorine-based additive, 0% to 10.0% by mass of graphite, 0% to 30.0% by mass of a rust preventive pigment, 0% to 10.0% by mass of a coloring pigment and 0% to 10.0% by mass of a coupling agent, while additionally containing 1.5% to 50.0% by mass of a hydrated magnesium silicate powder and / or 0.5% to 30.0% by mass of TiO2, and satisfying formula (1).　(1): (W + F + G) / (M + T) ≤ 5.00

Description

[Technical Field]

[0001] The present disclosure relates to metal tubing, and more particularly to metal tubing for oil wells. [Background technology]

[0002] Metallic oil well pipes are used in oil wells and gas wells (hereinafter, oil wells and gas wells will be collectively referred to simply as "oil wells"). Metallic oil well pipes have threaded joints. Specifically, at oil well drilling sites, multiple metallic oil well pipes are connected according to the depth of the oil well to form a connected oil well pipe assembly, typically casing or tubing. A connected oil well pipe assembly is formed by screwing metallic oil well pipes together. Inspection of the connected oil well pipe assembly may also be carried out. When inspection is carried out, the connected oil well pipe assembly is pulled up and unscrewed. Then, the metallic oil well pipe is removed from the connected oil well pipe assembly by unscrewing, and inspected. After inspection, the metallic oil well pipes are screwed together again, and the metallic oil well pipe is reused as part of the connected oil well pipe assembly.

[0003] The metal oil well pipe includes a pin and a box. The pin has a pin contact surface including a male thread portion on the outer peripheral surface of the end of the metal oil well pipe. The box has a box contact surface including a female thread portion on the inner peripheral surface of the end of the metal oil well pipe. In this specification, the male thread portion and the female thread portion are collectively referred to as "thread portion." Note that the pin contact surface may further include a pin-unthreaded metal contact portion including a pin seal surface and a pin shoulder surface. Similarly, the box contact surface may further include a box-unthreaded metal contact portion including a box seal surface and a box shoulder surface.

[0004] The pin contact surface and the box contact surface of an oil well metal pipe are repeatedly subjected to strong friction when the pipe is screwed in and out. Therefore, the pin contact surface and the box contact surface are prone to galling (irreparable seizure) when the pipe is screwed in and out repeatedly. Therefore, oil well metal pipe is required to have sufficient durability against friction, i.e., excellent seizure resistance.

[0005] Conventionally, compound grease containing heavy metal powder, called dope, has been used to improve the seizure resistance of oil well metal pipes. The application of compound grease to the pin contact surface and / or box contact surface can improve the seizure resistance of oil well metal pipes. However, the heavy metal powders, such as Pb, Zn, and Cu, contained in the compound grease may have an adverse effect on the environment. Therefore, there is a need to develop oil well metal pipes that have excellent seizure resistance without the use of compound grease.

[0006] Techniques for improving the galling resistance of metal pipes for oil wells have been proposed, for example, in Japanese Patent Laid-Open Publication No. 2003-021278 (Patent Document 1) and International Publication No. 2006 / 104251 (Patent Document 2).

[0007] The oil well metal pipe disclosed in Patent Document 1 has a threaded joint and is composed of a pin and a box, each having a contact surface including a threaded portion and an unthreaded metal contact portion. Furthermore, a solid lubricant coating consisting of a solid lubricant and a binder is provided on the contact surface of at least one of the pin and the box. In a cross section in the thickness direction of the solid lubricant coating, secondary particles of the solid lubricant with an equivalent area diameter of 15 to 60 μm account for 5 to 90% of the area. Patent Document 1 discloses that this oil well metal pipe can reliably ensure seizure resistance and airtightness without the application of compound grease.

[0008] The oil well metal pipe disclosed in Patent Document 2 has a threaded joint and is composed of a pin and a box, each having a contact surface with a threaded portion and an unthreaded metal contact portion. Furthermore, the contact surface of at least one of the pin and box has a viscous liquid or semi-solid lubricating coating and a dry solid coating formed thereon. Patent Document 2 discloses that this oil well metal pipe inhibits rust formation and exhibits excellent seizure resistance and airtightness without the use of compound grease. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-021278 [Patent Document 2] International Publication No. 2006 / 104251 Summary of the Invention [Problem to be solved by the invention]

[0010] In oil and natural gas drilling, vertical wells, which are drilled vertically, and directional wells, which are drilled at an angle, are typically used. On the other hand, horizontal drilling is another method of drilling oil and natural gas. Horizontal drilling involves drilling a vertically drilled oil well, gradually bending it horizontally, and finally drilling it horizontally along the oil and natural gas reservoir. Compared to conventional vertical wells and directional wells, horizontal wells allow for greater contact with the oil and natural gas reservoir, thereby increasing the amount of oil and natural gas produced per well. In recent years, the use of horizontal drilling has been increasing in oil and natural gas drilling. Therefore, there is a demand for metal oil well tubular structures that can be used in oil well tubular structure assemblies designed for horizontal drilling.

[0011] In horizontal drilling, when the drilling direction changes from vertical to horizontal, the OCTG connected body bends. In the bent portion of horizontal drilling, the OCTG connected body is rotated circumferentially while drilling to reach the target oil and natural gas reservoir. Therefore, particularly in the bent portion of the OCTG connected body, torsion is applied to the OCTG connected body due to the bending and circumferential rotation of the OCTG connected body. When torsion is applied under a high load, the OCTG is likely to loosen. When the drilling direction is vertical, the OCTG is primarily subjected to torsion in the circumferential direction of the OCTG. However, in horizontal drilling, in addition to the torsion in the circumferential direction of the OCTG, torsion due to bending of the OCTG is also applied to the OCTG. Therefore, compared to vertical drilling, even more excessive torsion is applied to the OCTG in horizontal drilling. Therefore, the OCTG is even more likely to loosen.

[0012] If the oil well pipe can be fastened with a torque higher than conventionally, the oil well pipe will be less likely to loosen even at the bent portion of an oil well pipe connection body during horizontal drilling. Therefore, when used in horizontal drilling, there is a demand for an oil well pipe that can be fastened with a torque higher than conventionally.

[0013] An object of the present disclosure is to provide a metal oil well pipe having high shear strength. [Means for solving the problem]

[0014] The metal pipe for oil well use according to the present disclosure comprises: a tube body including a first end and a second end; The tube body is a pin formed on the first end; a box formed at the second end; The pin is a pin contact surface including an external thread; The box a box contact surface including an internal thread; The oil well metal pipe further comprises: a resin coating on or above at least one of the pin contact surface and the box contact surface; The resin coating is Resin: 50.0~99.5% by mass, Wax: 0 to 10.0 mass% Fluorine-based additives: 0 to 30.0 mass% Graphite: 0~10.0% by mass, Anti-rust pigment: 0 to 30.0 mass%, Color pigment: 0 to 10.0% by mass, and Coupling agent: 0 to 10.0 mass% Hydrous magnesium silicate powder: 1.5 to 50.0 mass%; and TiO2: 0.5 to 30.0 mass% containing one or two types selected from the group consisting of, Satisfying equation (1), Metal pipes for oil wells. (W+F+G) / (M+T)≦5.00 (1) Here, in formula (1), W is substituted with the wax content in mass%, F is substituted with the fluorine-based additive content in mass%, G is substituted with the graphite content in mass%, M is substituted with the magnesium silicate hydrate powder content in mass%, and T is substituted with the TiO2 content in mass%, respectively. [Effects of the Invention]

[0015] The metal oil well pipe according to the present disclosure has high shear strength. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a graph showing the relationship between the friction coefficient of the resin coating and the yield torque. [Figure 2] FIG. 2 is a diagram showing the relationship between the shear strength of the resin coating and the yield torque. [Figure 3] FIG. 3 is a diagram showing the relationship between F1 (=(W+F+G) / (M+T)) and the shear strength of the resin coating. [Figure 4] FIG. 4 is a structural view showing an example of the metallic oil well pipe according to this embodiment. [Figure 5] 5 is a partial cross-sectional view showing a cross section (longitudinal cross section) parallel to the pipe axis direction of the coupling for the metal pipe for oil well use shown in FIG. [Figure 6] FIG. 6 is a cross-sectional view of a portion of the metallic oil well pipe shown in FIG. 5 near a pin, taken along a line parallel to the axial direction of the metallic oil well pipe. [Figure 7] FIG. 7 is a cross-sectional view of a portion of the metallic oil well pipe shown in FIG. 5 near the box, taken along a line parallel to the axial direction of the metallic oil well pipe. [Figure 8] FIG. 8 is a diagram showing an example of a metal oil well pipe in which the pin includes a male thread portion but does not include a pin seal surface or a pin shoulder surface, and the box includes a female thread portion but does not include a box seal surface or a box shoulder surface. [Figure 9] FIG. 9 is a diagram showing the configuration of an integral type metallic oil well pipe according to this embodiment. [Figure 10] FIG. 10 is an enlarged view of the pin contact surface shown in FIG. [Figure 11] FIG. 11 is an enlarged view of the box contact surface shown in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present embodiment will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and description thereof will not be repeated.

[0018] First, the present inventors have investigated a metal oil well pipe that can be applied to oil well tubular goods connectors used in horizontal drilling and that can be fastened with a torque higher than conventional ones. As a result, the following findings have been obtained.

[0019] As described above, an oil well pipe connection is formed by screwing together threaded joints of oil well pipes. When screwing together threaded joints, the torque increases according to the rotation speed. In particular, the torque increases rapidly in the final stage of screwing. On the other hand, if the torque during screwing becomes too high, the oil well pipe may yield. In this specification, the torque at which the oil well pipe yields when screwed together is also referred to as the "yield torque." The higher the yield torque, the higher the torque at which the oil well pipe can be fastened. In other words, the yield torque can be used as an indicator of whether the oil well pipe can be fastened with a high torque.

[0020] To date, methods have been proposed to increase the fastening torque of oil well metal pipes by increasing the friction coefficient of the resin coating formed on the oil well metal pipe. When screwing together oil well metal pipes, if resin coatings with high friction coefficients come into contact and slide against each other, it is expected that the screw tightening torque will increase. Therefore, increasing the friction coefficient of the resin coating may also increase the yield torque. Therefore, the present inventors adjusted the friction coefficient of the resin coating by incorporating solid powders, such as hydrated magnesium silicate powder and / or TiO2, into the resin coating, and investigated the relationship between the friction coefficient and yield torque.

[0021] FIG. 1 is a diagram showing the relationship between the friction coefficient of the resin coating and the yield torque. The horizontal axis of FIG. 1 shows the friction coefficient (μ) of the resin coating. The vertical axis of FIG. 1 shows the yield torque (ft.lbs) when a metal oil well pipe with a resin coating formed thereon is screwed. Referring to FIG. 1, the correlation coefficient R between the friction coefficient of the resin coating and the yield torque is 2 The coefficient of friction of the resin coating was 0.144. From these results, it was found that there was almost no positive correlation between the friction coefficient of the resin coating and the yield torque. In other words, contrary to the inventors' expectations, it was revealed that the correlation between the friction coefficient and the yield torque was weak. In short, the results of the inventors' investigation revealed that simply increasing the friction coefficient of the resin coating does not effectively increase the yield torque.

[0022] Therefore, the present inventors conducted further studies on metal oil well pipes that can be fastened with high torque. First, the present inventors focused on the behavior of the resin coating in the final stage of screw tightening. In the final stage of screw tightening, the resin coatings come into contact with each other at high surface pressure and slide against each other. The present inventors suspected that at this time, the resin coating would be subjected to a force (shear force) that would cause it to slide completely from the pin contact surface and the box contact surface. If the resin coating were subjected to a shear force that exceeded its shear strength, the resin coating would be destroyed. As a result, the metal oil well pipe may be more likely to yield.

[0023] That is, the inventors of the present invention considered that increasing the shear strength of the resin coating could increase the yield torque of the metal oil well pipe. Therefore, the inventors of the present invention conducted a detailed investigation into the relationship between the shear strength of the resin coating and the yield torque of the metal oil well pipe. Figure 2 is a graph showing the relationship between the shear strength of the resin coating and the yield torque. The horizontal axis of Figure 2 represents the shear strength (MPa) of the resin coating. The vertical axis of Figure 2 represents the yield torque (ft.lbs) when the metal oil well pipe with the resin coating formed thereon is screwed together.

[0024] Referring to Figure 2, the correlation coefficient R between the shear strength of the resin coating and the yield torque 2The shear strength of the resin coating was 0.874. This result indicates a strong positive correlation between the shear strength of the resin coating and the yield torque. In other words, the detailed study by the inventors has revealed that increasing the shear strength of the resin coating can effectively increase the yield torque of the oil well metal pipe.

[0025] Next, the present inventors investigated methods for increasing the shear strength of resin coatings. As a result, it became clear that the shear strength of resin coatings could be increased by adding hydrous magnesium silicate powder and / or TiO2, which are solid powders. Therefore, the present inventors conducted a detailed investigation into the shear strength of resin coatings containing hydrous magnesium silicate powder and / or TiO2.

[0026] First, the present inventors focused on the components in the resin coating and investigated means for increasing shear strength. As a result, they concluded that a resin coating containing 50.0 to 99.5 mass% resin, 0 to 10.0 mass% wax, 0 to 30.0 mass% fluorine-based additive, 0 to 10.0 mass% graphite, 0 to 30.0 mass% rust-preventive pigment, 0 to 10.0 mass% color pigment, and 0 to 10.0 mass% coupling agent, and containing one or two selected from the group consisting of 1.5 to 50.0 mass% hydrous magnesium silicate powder and 0.5 to 30.0 mass% TiO2, could potentially increase shear strength. Further detailed investigation by the present inventors revealed that, assuming the above components are contained, the shear strength of the resin coating can be increased if the following formula (1) is satisfied: (W+F+G) / (M+T)≦5.00 (1) Here, in formula (1), W is substituted with the wax content in mass%, F is substituted with the fluorine-based additive content in mass%, G is substituted with the graphite content in mass%, M is substituted with the magnesium silicate hydrate powder content in mass%, and T is substituted with the TiO2 content in mass%, respectively.

[0027] F1 is defined as (W+F+G) / (M+T). FIG. 3 is a diagram showing the relationship between F1 in the resin coating and the shear strength of the resin coating. FIG. 3 is an excerpt of some of the results of the Examples described below. The horizontal axis of FIG. 3 represents F1. The vertical axis of FIG. 3 represents the shear strength (MPa) of the resin coating. Referring to FIG. 3, if F1 is 5.00 or less, the shear strength of the resin coating will be 36.00 MPa or more. The details of the reason for this are not clear, but the inventors speculate as follows.

[0028] In the resin coating having the above-described composition, the hydrous magnesium silicate is a particle with high intracrystalline shear strength. Furthermore, in the resin coating having the above-described composition, TiO2 is a hard particle. If the resin coating contains a large amount of these components, when the resin coating is subjected to shear force, the particles themselves will resist the shear, suppressing shear failure of the resin coating. In other words, it is believed that the shear strength of the resin coating increases as the content of the hydrous magnesium silicate powder and TiO2 increases. On the other hand, the wax, fluorine-based additives, and graphite decrease the hardness of the resin coating. Therefore, it is believed that the shear strength of the resin coating decreases as the content of the wax, fluorine-based additives, and graphite increases. Therefore, the inventors speculate that the shear strength can be increased by decreasing the ratio of the total content of the wax, fluorine-based additives, and graphite to the total content of the hydrous magnesium silicate powder and TiO2.

[0029] From the above, it has become clear that, contrary to conventional knowledge, simply increasing the friction coefficient of the resin coating does not effectively increase yield torque, and that it can only be effectively increased by increasing the shear strength of the resin coating. Furthermore, it has become clear that the shear strength of the resin coating can only be increased by adjusting the contents of each component in the resin coating so as to satisfy formula (1). By increasing the shear strength of the resin coating and thereby increasing the yield torque, a metal oil well pipe that can also be used in horizontal drilling can be obtained. The metal oil well pipe of the present disclosure has been completed based on the above knowledge and has the following configuration.

[0030] [1] A metal pipe for oil wells, a tube body including a first end and a second end; The tube body is a pin formed on the first end; a box formed at the second end; The pin is a pin contact surface including an external thread; The box a box contact surface including an internal thread; The oil well metal pipe further comprises: a resin coating on or above at least one of the pin contact surface and the box contact surface; The resin coating is Resin: 50.0~99.5% by mass, Wax: 0 to 10.0 mass% Fluorine-based additives: 0 to 30.0 mass% Graphite: 0~10.0% by mass, Anti-rust pigment: 0 to 30.0 mass%, Color pigment: 0 to 10.0% by mass, and Coupling agent: 0 to 10.0 mass% Hydrous magnesium silicate powder: 1.5 to 50.0 mass%; and TiO2: 0.5 to 30.0 mass% containing one or two types selected from the group consisting of, Satisfying equation (1), Metal pipes for oil wells. (W+F+G) / (M+T)≦5.00 (1) Here, in formula (1), W is substituted with the wax content in mass%, F is substituted with the fluorine-based additive content in mass%, G is substituted with the graphite content in mass%, M is substituted with the magnesium silicate hydrate powder content in mass%, and T is substituted with the TiO2 content in mass%, respectively.

[0031] [2] The metal pipe for oil well use according to [1], The resin is One or two resins selected from the group consisting of epoxy resins and urethane resins; Metal pipes for oil wells.

[0032] [3] The metal pipe for oil well use according to [1] or [2], the pin contact surface further includes a pin seal surface and a pin shoulder surface; The box contact surface further includes a box seal surface and a box shoulder surface. Metal pipes for oil wells.

[0033] The metallic oil well pipe according to this embodiment will be described in detail below.

[0034] [Configuration of metal pipe for oil wells] First, the configuration of the oil well metallic pipe of this embodiment will be described. The oil well metallic pipe has a well-known configuration. There are two types of oil well metallic pipe: T&C type oil well metallic pipe and integral type oil well metallic pipe. Each type of oil well metallic pipe will be described in detail below.

[0035] [When oil well metal pipe 1 is T&C type] Fig. 4 is a structural view showing an example of a metal oil well pipe 1 according to this embodiment. Fig. 4 is a structural view of a so-called T&C (Threaded and Coupled) metal oil well pipe 1. Referring to Fig. 4, the metal oil well pipe 1 includes a pipe main body 10.

[0036] The pipe body 10 extends in the pipe axis direction. A cross section of the pipe body 10 perpendicular to the pipe axis direction is circular. The pipe body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is the end portion opposite the second end portion 10B. In the T&C type metal pipe for oil well use 1 shown in FIG. 4, the pipe body 10 includes a pin pipe body 11 and a coupling 12. The coupling 12 is attached to one end of the pin pipe body 11. More specifically, the coupling 12 is fastened to one end of the pin pipe body 11 by a screw.

[0037] Fig. 5 is a partial cross-sectional view showing a cross section (longitudinal cross section) parallel to the pipe axis direction of the coupling 12 of the metal oil well pipe 1 shown in Fig. 4. With reference to Figs. 4 and 5, the pipe body 10 includes a pin 40 and a box 50. The pin 40 is formed at a first end 10A of the pipe body 10. At the time of fastening, the pin 40 is inserted into the box 50 of another metal oil well pipe 1 (not shown) and fastened to the box 50 of the other metal oil well pipe 1 by a screw.

[0038] The box 50 is formed at the second end 10B of the pipe body 10. At the time of fastening, the pin 40 of another metal pipe for oil well use 1 is inserted into the box 50, and the box 50 is fastened to the pin 40 of the other metal pipe for oil well use 1 by a screw.

[0039] [About the configuration of pin 40] Fig. 6 is a cross-sectional view parallel to the pipe axis direction of the metal oil well pipe 1 of a portion near a pin 40 of the metal oil well pipe 1 shown in Fig. 5. The dashed line portion in Fig. 6 shows the configuration of a box 50 of another metal oil well pipe 1 when fastening to another metal oil well pipe 1. Referring to Fig. 6, the pin 40 has a pin contact surface 400 on the outer circumferential surface of the first end 10A of the pipe body 10. When fastening to another metal oil well pipe 1, the pin contact surface 400 is screwed into the box 50 of the other metal oil well pipe 1 and comes into contact with a box contact surface 500 (described later) of the box 50.

[0040] The pin contact surface 400 includes at least a male thread portion 41 formed on the outer circumferential surface of the first end portion 10A. The pin contact surface 400 may further include a pin seal surface 42 and a pin shoulder surface 43. In FIG. 6, the pin shoulder surface 43 is located on the tip surface of the first end portion 10A, and the pin seal surface 42 is located on the outer circumferential surface of the first end portion 10A closer to the tip of the first end portion 10A than the male thread portion 41. In other words, the pin seal surface 42 is located between the male thread portion 41 and the pin shoulder surface 43. The pin seal surface 42 is tapered. Specifically, the outer diameter of the pin seal surface 42 gradually decreases from the male thread portion 41 to the pin shoulder surface 43 in the longitudinal direction (pipe axis direction) of the first end portion 10A.

[0041] When fastening another oil well metal pipe 1, the pin seal surface 42 comes into contact with a box seal surface 52 (described later) of the box 50 of the other oil well metal pipe 1. More specifically, when fastening, the pin 40 is inserted into the box 50 of the other oil well metal pipe 1, so that the pin seal surface 42 comes into contact with the box seal surface 52. Then, when the pin 40 is further screwed into the box 50 of the other oil well metal pipe 1, the pin seal surface 42 comes into close contact with the box seal surface 52. As a result, when fastening, the pin seal surface 42 comes into close contact with the box seal surface 52, forming a seal based on metal-metal contact. Therefore, the airtightness of the oil well metal pipes 1 fastened to each other can be improved.

[0042] In Fig. 6, the pin shoulder surface 43 is disposed on the tip surface of the first end portion 10A. That is, in the pin 40 shown in Fig. 6, the male thread portion 41, the pin seal surface 42, and the pin shoulder surface 43 are disposed in this order from the center of the pipe body 10 toward the first end portion 10A. When fastening with another oil well metal pipe 1, the pin shoulder surface 43 faces and contacts a box shoulder surface 53 (described later) of a box 50 of the other oil well metal pipe 1. More specifically, when fastening, the pin 40 is inserted into the box 50 of the other oil well metal pipe 1, so that the pin shoulder surface 43 contacts the box shoulder surface 53. This allows a high torque to be obtained when fastening. Furthermore, the positional relationship between the pin 40 and the box 50 in the fastened state can be stabilized.

[0043] The pin contact surface 400 of the pin 40 includes at least the male thread portion 41. In other words, the pin contact surface 400 may include the male thread portion 41, but not the pin seal surface 42 or the pin shoulder surface 43. The pin contact surface 400 may include the male thread portion 41 and the pin shoulder surface 43, but not the pin seal surface 42. The pin contact surface 400 may include the male thread portion 41 and the pin seal surface 42, but not the pin shoulder surface 43.

[0044] [About the composition of Box 50] 7 is a cross-sectional view parallel to the pipe axis direction of the metal oil well pipe 1 of a portion near the box 50 of the metal oil well pipe 1 shown in FIG. 5. The dashed line portion in FIG. 7 shows the configuration of the pin 40 of another metal oil well pipe 1 when fastening to another metal oil well pipe 1. Referring to FIG. 7, the box 50 has a box contact surface 500 on the inner circumferential surface of the second end 10B of the pipe body 10. When fastening to another metal oil well pipe 1, the pin 40 of the other metal oil well pipe 1 is screwed into the box contact surface 500, and the box contact surface 500 comes into contact with the pin contact surface 400 of the pin 40.

[0045] The box contact surface 500 includes at least a female thread portion 51 formed on the inner circumferential surface of the second end portion 10B. During fastening, the female thread portion 51 meshes with the male thread portion 41 of the pin 40 of another metal oil well pipe 1.

[0046] The box contact surface 500 may further include a box seal surface 52 and a box shoulder surface 53. In FIG. 7, the box seal surface 52 is located on the inner circumferential surface of the second end portion 10B, closer to the pipe body 10 than the female thread portion 51. In other words, the box seal surface 52 is located between the female thread portion 51 and the box shoulder surface 53. The box seal surface 52 is tapered. Specifically, the inner diameter of the box seal surface 52 gradually decreases from the female thread portion 51 toward the box shoulder surface 53 in the longitudinal direction (pipe axial direction) of the second end portion 10B.

[0047] When fastening another metal oil well pipe 1, the box seal surface 52 comes into contact with the pin seal surface 42 of the pin 40 of the other metal oil well pipe 1. More specifically, when fastening, the pin 40 of the other metal oil well pipe 1 is screwed into the box 50, so that the box seal surface 52 comes into contact with the pin seal surface 42, and when further screwed, the box seal surface 52 comes into close contact with the pin seal surface 42. As a result, when fastening, the box seal surface 52 comes into close contact with the pin seal surface 42, forming a seal based on metal-metal contact. Therefore, the airtightness of the metal oil well pipes 1 fastened together can be improved.

[0048] The box shoulder surface 53 is located closer to the pipe body 10 than the box seal surface 52. That is, in the box 50, the box shoulder surface 53, the box seal surface 52, and the female thread portion 51 are located in this order from the center of the pipe body 10 toward the tip of the second end 10B. When fastening another oil well metal pipe 1, the box shoulder surface 53 faces and contacts the pin shoulder surface 43 of the pin 40 of the other oil well metal pipe 1. More specifically, when fastening, the pin 40 of the other oil well metal pipe 1 is inserted into the box 50, so that the box shoulder surface 53 contacts the pin shoulder surface 43. This allows a high torque to be obtained when fastening. Furthermore, the positional relationship between the pin 40 and the box 50 in the fastened state can be stabilized.

[0049] The box contact surface 500 includes at least an internal thread portion 51. During fastening, the internal thread portion 51 of the box contact surface 500 of the box 50 corresponds to and contacts the external thread portion 41 of the pin contact surface 400 of the pin 40. The box seal surface 52 corresponds to and contacts the pin seal surface 42. The box shoulder surface 53 corresponds to and contacts the pin shoulder surface 43.

[0050] When the pin contact surface 400 includes the male thread portion 41 but does not include the pin seal surface 42 or the pin shoulder surface 43, the box contact surface 500 includes the female thread portion 51 but does not include the box seal surface 52 or the box shoulder surface 53. When the pin contact surface 400 includes the male thread portion 41 and the pin shoulder surface 43 but does not include the pin seal surface 42, the box contact surface 500 includes the female thread portion 51 and the box shoulder surface 53 but does not include the box seal surface 52. When the pin contact surface 400 includes the male thread portion 41 and the pin seal surface 42 but does not include the pin shoulder surface 43, the box contact surface 500 includes the female thread portion 51 and the box seal surface 52 but does not include the box shoulder surface 53.

[0051] The pin contact surface 400 may include multiple male thread portions 41, multiple pin seal surfaces 42, or multiple pin shoulder surfaces 43. For example, on the pin contact surface 400 of the pin 40, the pin shoulder surface 43, the pin seal surface 42, the male thread portion 41, the pin seal surface 42, the pin shoulder surface 43, the pin seal surface 42, and the male thread portion 41 may be arranged in this order from the tip of the first end 10A toward the center of the pipe body 10. In this case, on the box contact surface 500 of the box 50, the female thread portion 51, the box seal surface 52, the box shoulder surface 53, the box seal surface 52, the female thread portion 51, the box seal surface 52, and the box shoulder surface 53 are arranged in this order from the tip of the second end 10B toward the center of the pipe body 10.

[0052] 6 and 7 illustrate a so-called premium joint in which the pin 40 includes a male thread portion 41, a pin seal surface 42, and a pin shoulder surface 43, and the box 50 includes a female thread portion 51, a box seal surface 52, and a box shoulder surface 53. However, as described above, the pin 40 may include the male thread portion 41 but not the pin seal surface 42 or the pin shoulder surface 43. In this case, the box 50 includes the female thread portion 51 but not the box seal surface 52 or the box shoulder surface 53. FIG. 8 illustrates an example of a metal oil well pipe 1 in which the pin 40 includes the male thread portion 41 but not the pin seal surface 42 or the pin shoulder surface 43, and the box 50 includes the female thread portion 51 but not the box seal surface 52 or the box shoulder surface 53.

[0053] [When the oil well metal pipe 1 is an integral type] The oil well metal pipe 1 shown in Figures 4, 5 and 8 is a so-called T&C type oil well metal pipe 1 in which a pipe body 10 includes a pin pipe body 11 and a coupling 12. However, the oil well metal pipe 1 of this embodiment may be an integral type instead of a T&C type.

[0054] FIG. 9 is a structural diagram of an integral-type metal oil well pipe 1 according to this embodiment. Referring to FIG. 9, the integral-type metal oil well pipe 1 includes a pipe body 10. The pipe body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is located on the opposite side to the second end portion 10B. As described above, in the T&C type metal oil well pipe 1, the pipe body 10 includes a pin pipe body 11 and a coupling 12. That is, in the T&C type metal oil well pipe 1, the pipe body 10 is formed by fastening two separate members (the pin pipe body 11 and the coupling 12). In contrast, in the integral-type metal oil well pipe 1, the pipe body 10 is integrally formed.

[0055] The pin 40 is formed at a first end 10A of the pipe body 10. When fastening, the pin 40 is inserted into and screwed into a box 50 of another integral type metallic pipe for oil well use 1, and is fastened to the box 50 of another integral type metallic pipe for oil well use 1. The box 50 is formed at a second end 10B of the pipe body 10. When fastening, the pin 40 of another integral type metallic pipe for oil well use 1 is inserted into and screwed into the box 50, and is fastened to the pin 40 of another integral type metallic pipe for oil well use 1.

[0056] The configuration of the pin 40 of the integral type metal oil well pipe 1 is the same as the configuration of the pin 40 of the T&C type metal oil well pipe 1 shown in Fig. 6. Similarly, the configuration of the box 50 of the integral type metal oil well pipe 1 is the same as the configuration of the box 50 of the T&C type metal oil well pipe 1 shown in Fig. 7. In Figs. 6 and 7, in the pin 40, the pin shoulder surface 43, the pin seal surface 42, and the male thread portion 41 are arranged in this order from the tip of the first end 10A toward the center of the pipe body 10. Therefore, in the box 50, the female thread portion 51, the box seal surface 52, and the box shoulder surface 53 are arranged in this order from the tip of the second end 10B toward the center of the pipe body 10. However, like the pin contact surface 400 of the pin 40 of the T&C type metal oil well pipe 1, the pin contact surface 400 of the pin 40 of the integral type metal oil well pipe 1 only needs to include at least the male thread portion 41. Furthermore, like the box contact surface 500 of the box 50 of the T&C type metal pipe for oil well use 1, the box contact surface 500 of the box 50 of the integral type metal pipe for oil well use 1 may include at least the female thread portion 51.

[0057] In short, the metal oil well pipe 1 of this embodiment may be of the T&C type or the integral type.

[0058] [Resin coating] The oil well metal pipe 1 of this embodiment has a resin coating 100 on or above at least one of the pin contact surface 400 and the box contact surface 500. FIG. 10 is an enlarged view of the pin contact surface 400 shown in FIG. 6. FIG. 11 is an enlarged view of the box contact surface 500 shown in FIG. 7. As shown in FIGS. 10 and 11, the oil well metal pipe 1 of this embodiment may have the resin coating 100 on both the pin contact surface 400 and the box contact surface 500. However, the oil well metal pipe 1 of this embodiment may have the resin coating 100 on only one of the pin contact surface 400 or the box contact surface 500. For example, as shown in FIG. 10, when the resin coating 100 is provided on the pin contact surface 400, the resin coating 100 does not have to be provided on the box contact surface 500. Furthermore, as shown in FIG. 11, when the resin coating 100 is provided on the box contact surface 500, the resin coating 100 does not have to be provided on the pin contact surface 400. In other words, the metal oil well pipe 1 according to this embodiment has the resin coating 100 on the pin contact surface 400 and / or the box contact surface 500 .

[0059] [Resin coating components] The resin coating 100 contains the following components:

[0060] Resin: 50.0~99.5% by mass The resin contained in the resin coating 100 according to this embodiment is not particularly limited. However, it is believed that the resin coating 100 is subjected to shear force when the oil well metal pipe 1 is fastened. Therefore, to stably increase the yield torque of the oil well metal pipe 1 on which the resin coating 100 is formed, it is preferable to use a resin with appropriate hardness. From the above perspectives, the resin in the resin coating 100 according to this embodiment is one or more resins selected from the group consisting of epoxy resins, phenolic resins, acrylic resins, urethane resins, polyester resins, polyamideimide resins, polyamide resins, polyimide resins, and polyetheretherketone resins. Preferably, the resin in this embodiment is one or more resins selected from the group consisting of epoxy resins, urethane resins, polyimide resins, and phenolic resins, more preferably one or two resins selected from the group consisting of epoxy resins and urethane resins, and even more preferably either an epoxy resin or a urethane resin. The resin coating 100 may contain multiple types of resins. When multiple types of resins are contained, the resin content refers to the total content of the multiple types of resins.

[0061] The resin is the base material of the resin coating 100. Here, the base material refers to the component contained in the resin coating 100 in the largest amount. If the resin content is too low, it becomes difficult to disperse compositions such as the hydrous magnesium silicate powder described below in the resin. As a result, the shear strength of the resin coating decreases. On the other hand, if the resin content is too high, other components including the hydrous magnesium silicate powder and / or TiO2 cannot be contained sufficiently. As a result, the shear strength of the resin coating 100 decreases. Therefore, the resin content is 50.0 to 99.5 mass%. The lower limit of the resin content is preferably 55.0 mass%, more preferably 60.0 mass%, and even more preferably 65.0 mass%. The upper limit of the resin content is preferably 97.0 mass%, more preferably 95.0 mass%, and even more preferably 90.0 mass%.

[0062] The resin coating 100 according to this embodiment contains one or two components selected from the group consisting of hydrous magnesium silicate powder and TiO. Specifically, it contains one or two components selected from the group consisting of 1.5 to 50.0 mass% hydrous magnesium silicate powder and 0.5 to 30.0 mass% TiO. Both of these components increase the shear strength of the resin coating 100.

[0063] Hydrous magnesium silicate powder: 1.5 to 50.0 mass% In this embodiment, the hydrous magnesium silicate powder is an optional component and may not be included. That is, the content of the hydrous magnesium silicate powder may be 0% by mass. When included, the hydrous magnesium silicate powder increases the shear strength of the resin coating 100. The hydrous magnesium silicate powder is a solid powder with a layered structure. The hydrous magnesium silicate powder further has a high interlayer bonding strength and high shear strength. In other words, the hydrous magnesium silicate powder is a particle with high intracrystalline shear strength. Therefore, when the resin coating 100 is subjected to a shear force, the hydrous magnesium silicate powder resists the shear and suppresses shear failure of the resin coating 100. In this way, the hydrous magnesium silicate powder is thought to increase the shear strength of the resin coating 100. On the other hand, if the content of the hydrous magnesium silicate powder is too high, the resin content will be relatively reduced, which will actually reduce the shear strength of the resin coating 100. Therefore, when contained, the content of the hydrous magnesium silicate powder is 1.5 to 50.0 mass%. The lower limit of the content of the hydrous magnesium silicate powder is preferably 2.0 mass%, more preferably 4.0 mass%, even more preferably 7.0 mass%, and even more preferably 10.0 mass%. The upper limit of the content of the hydrous magnesium silicate powder is preferably 45.0 mass%, more preferably 43.0 mass%, and even more preferably 40.0 mass%.

[0064] TiO2:0.5~30.0% by mass In this embodiment, TiO2 is an optional component and does not necessarily need to be included. That is, the TiO2 content may be 0% by mass. When included, TiO2 increases the shear strength of the resin coating 100. TiO2 is a hard powder particle. Therefore, when the resin coating 100 is subjected to a shear force, TiO2 resists the shear and suppresses shear fracture of the resin coating 100. In this way, TiO2 is thought to increase the shear strength of the resin coating 100. On the other hand, if the TiO2 content is too high, abrasive wear may be promoted, which may reduce the seizure resistance of the metal oil well pipe 1. Therefore, when included, the TiO2 content is 0.5 to 30.0% by mass. The preferred lower limit of the TiO2 content is 0.7% by mass, more preferably 1.0% by mass, even more preferably 2.0% by mass, even more preferably 2.5% by mass, and even more preferably 5.0% by mass. The upper limit of the TiO2 content is preferably 25.0 mass %, more preferably 20.0 mass %, and even more preferably 15.0 mass %.

[0065] Wax: 0 to 10.0% by mass The type of wax contained in the resin coating 100 according to this embodiment is not particularly limited. The wax may be, for example, one or more selected from the group consisting of animal wax, vegetable wax, mineral wax, and synthetic wax. More specifically, the wax may be one or more selected from the group consisting of beeswax, spermaceti (all animal-derived), Japan wax, carnauba wax, candelilla wax, rice wax (all vegetable-derived), paraffin wax, microcrystalline wax, petrolatum, montan wax, ozokerite, ceresin (all mineral-derived), oxidized wax, polyethylene wax, polypropylene wax, Fischer-Tropsch wax, amide wax, and hydrogenated castor oil (castor wax) (all synthetic wax). More preferably, the wax is one or two selected from the group consisting of polyethylene wax and polypropylene wax. The resin coating 100 may contain multiple types of wax. When multiple types of wax are contained, the wax content refers to the total content of the multiple types of wax.

[0066] In this embodiment, wax is an optional component and may not be included. That is, the wax content may be 0% by mass. When included, wax increases the lubricity of the resin coating 100. Even if even a small amount of wax is included, the above effect can be obtained to some extent. On the other hand, if the wax content is too high, the hardness of the resin coating 100 decreases. As a result, the shear strength of the resin coating 100 decreases. Therefore, the wax content is 0 to 10.0% by mass. The preferred lower limit of the wax content is 0.1% by mass, more preferably 0.5% by mass, even more preferably 1.0% by mass, and even more preferably 2.0% by mass. The preferred upper limit of the wax content is 9.0% by mass, more preferably 8.0% by mass, and even more preferably 7.5% by mass.

[0067] Fluorine-based additives: 0 to 30.0 mass% In this specification, additives containing fluorine are also collectively referred to as fluorine-based additives. The fluorine-based additive is, for example, one or two selected from the group consisting of perfluoropolyether (PFPE) and polytetrafluoroethylene (PTFE). The resin coating 100 may contain multiple types of fluorine-based additives. When multiple types of fluorine-based additives are contained, the content of the fluorine-based additives means the total content of the multiple types of fluorine-based additives.

[0068] In this embodiment, the fluorine-based additive is an optional component and may not be included. That is, the content of the fluorine-based additive may be 0% by mass. When included, the fluorine-based additive enhances the lubricity of the resin coating 100. Even if even a small amount of the fluorine-based additive is included, the above effect can be obtained to a certain extent. On the other hand, if the content of the fluorine-based additive is too high, the hardness of the resin coating 100 decreases. As a result, the shear strength of the resin coating 100 may decrease. Therefore, the content of the fluorine-based additive is 0 to 30.0% by mass. The preferred lower limit of the content of the fluorine-based additive is 1.0% by mass, more preferably 3.0% by mass, even more preferably 4.5% by mass, and even more preferably 7.5% by mass. The preferred upper limit of the content of the fluorine-based additive is 25.0% by mass, more preferably 20.0% by mass, even more preferably 15.0% by mass, and even more preferably 12.5% ​​by mass.

[0069] Graphite: 0~10.0% by mass In this embodiment, graphite is an optional component and does not necessarily need to be included. That is, the graphite content may be 0% by mass. When included, graphite enhances the lubricity of the resin coating 100. Even if even a small amount of graphite is included, the above effect can be obtained to some extent. On the other hand, if the graphite content is too high, the hardness of the resin coating 100 decreases. As a result, the shear strength of the resin coating 100 may decrease. Therefore, the graphite content is 0 to 10.0% by mass. The preferred lower limit of the graphite content is 1.0% by mass, more preferably 2.0% by mass, and even more preferably 3.0% by mass. The preferred upper limit of the graphite content is 9.0% by mass, more preferably 8.0% by mass, and even more preferably 7.0% by mass.

[0070] Anti-rust pigment: 0 to 30.0 mass% In this embodiment, the anti-rust pigment is not particularly limited as long as it is a well-known pigment that enhances the anti-rust properties of the resin coating 100. The anti-rust pigment is, for example, one or more selected from the group consisting of zinc phosphate, aluminum tripolyphosphate, aluminum phosphite, metal carboxylic acid soap, and sulfonate. The resin coating 100 may contain multiple types of anti-rust pigments. When multiple types of anti-rust pigments are contained, the content of the anti-rust pigments refers to the total content of the multiple types of anti-rust pigments.

[0071] In this embodiment, the anti-rust pigment is an optional component and does not necessarily need to be included. That is, the content of the anti-rust pigment may be 0% by mass. When included, the anti-rust pigment enhances the anti-rust properties of the resin coating 100. Even if even a small amount of the anti-rust pigment is included, the above effect can be obtained to a certain extent. On the other hand, if the content of the anti-rust pigment is too high, the resin coating 100 will not be formed properly. Therefore, the content of the anti-rust pigment is 0 to 30.0% by mass. The preferred lower limit of the content of the anti-rust pigment is 1.0% by mass, more preferably 2.0% by mass, even more preferably 3.0% by mass, and even more preferably 4.0% by mass. The preferred upper limit of the content of the anti-rust pigment is 25.0% by mass, even more preferably 20.0% by mass, and even more preferably 10.0% by mass.

[0072] Colored pigment: 0~10.0% by mass In this embodiment, the color pigment is not particularly limited as long as it is a well-known pigment that can color the resin coating 100. For example, the color pigment is one or more selected from the group consisting of copper phthalocyanine, zinc oxide, yellow iron oxide, iron oxide, and chromium hydroxide. The resin coating 100 may contain multiple types of color pigments. When multiple types of color pigments are contained, the content of the color pigments means the total content of the multiple types of color pigments.

[0073] In this embodiment, the color pigment is an optional component and may not be included. That is, the content of the color pigment may be 0% by mass. When included, the color pigment colors the resin coating 100. As a result, damage to the resin coating 100 becomes easier to visually recognize. Even if even a small amount of color pigment is included, the above effect can be achieved to some extent. On the other hand, if the content of the color pigment is too high, the resin coating 100 will not be formed properly. Therefore, the content of the color pigment is 0 to 10.0% by mass. The preferred lower limit of the color pigment content is 0.1% by mass, more preferably 0.2% by mass, and even more preferably 0.5% by mass. When included, the preferred upper limit of the color pigment content is 8.0% by mass, more preferably 5.0% by mass, and even more preferably 3.0% by mass.

[0074] Coupling agent: 0 to 10.0% by mass In this embodiment, the coupling agent is not particularly limited, but may be, for example, one or two types selected from the group consisting of silane coupling agents and titanium coupling agents. The resin coating 100 may contain multiple types of coupling agents. When multiple types of coupling agents are contained, the content of the coupling agents refers to the total content of the multiple types of coupling agents.

[0075] In this embodiment, the coupling agent is an optional component and may not be included. That is, the content of the coupling agent may be 0% by mass. When included, the coupling agent enhances the adhesion of the resin coating 100. Therefore, peeling of the resin coating 100 is suppressed when the metal oil well pipe 1 is repeatedly screwed and unscrewed. Even if even a small amount of coupling agent is included, the above effect can be obtained to some extent. On the other hand, if the content of the coupling agent exceeds 10.0% by mass, the resin coating 100 will not be formed properly. Therefore, the content of the coupling agent is 0 to 10.0% by mass. The lower limit of the content of the coupling agent is preferably 0.1% by mass, more preferably 0.2% by mass, and even more preferably 0.5% by mass. The upper limit of the content of the coupling agent is preferably 8.0% by mass, more preferably 6.0% by mass, and even more preferably 4.0% by mass.

[0076] Other ingredients: 0 to 10.0% by mass In this embodiment, the other components are optionally contained and may not be contained. That is, the content of the other components may be 0% by mass. The other components are, for example, one or two selected from the group consisting of preservatives and antioxidants. When other components are contained, the total content of the other components is 10.0% by mass or less. That is, the total content of the other components is 0 to 10.0% by mass.

[0077] The resin coating 100 may be a resin coating 100 consisting of one or two components selected from the group consisting of 50.0 to 99.5 mass% resin, 0 to 10.0 mass% wax, 0 to 30.0 mass% fluorine-based additive, 0 to 10.0 mass% graphite, 0 to 30.0 mass% anti-rust pigment, 0 to 10.0 mass% coloring pigment, 0 to 10.0 mass% coupling agent, 0 to 10.0 mass% other components, and 1.5 to 50.0 mass% hydrated magnesium silicate powder and 0.5 to 30.0 mass% TiO2.

[0078] [Formula (1)] The resin coating 100 satisfies formula (1) on the premise that it contains the above-mentioned components. (W+F+G) / (M+T)≦5.00 (1) Here, in formula (1), W is substituted with the wax content in mass%, F is substituted with the fluorine-based additive content in mass%, G is substituted with the graphite content in mass%, M is substituted with the magnesium silicate hydrate powder content in mass%, and T is substituted with the TiO2 content in mass%, respectively.

[0079] F1 (=(W+F+G) / (M+T)) is an index of the shear strength of the resin coating 100. As mentioned above, the shear strength of the resin coating 100 increases as the content of the hydrous magnesium silicate powder and TiO2 increases. On the other hand, the shear strength of the resin coating 100 decreases as the content of the wax, fluorine-based additives, and graphite increases. Therefore, the shear strength of the resin coating 100 can be increased by reducing the ratio of the total content of the wax, fluorine-based additives, and graphite to the total content of the hydrous magnesium silicate powder and TiO2. Note that the examples described below demonstrate that the shear strength of the resin coating 100 can be increased to 36.00 MPa or more by setting F1 to 5.00 or less in a resin coating 100 having the above-mentioned components.

[0080] Therefore, in this embodiment, assuming that the resin coating 100 has the above-mentioned components, F1 is set to 5.00 or less. The upper limit of F1 is preferably 4.90, more preferably 4.80, and even more preferably 4.70. The lower limit of F1 is not particularly limited and may be 0.00.

[0081] The resin coating 100 has increased shear strength by containing the above-mentioned components and satisfying formula (1), and as a result, the metal oil well pipe 1 provided with the resin coating 100 has increased yield torque.

[0082] Shear strength The shear strength of the resin coating 100 is not particularly limited, but a higher shear strength is preferable. If the shear strength of the resin coating 100 is 36.00 MPa or more, the yield torque of the metal oil well pipe 1 provided with the resin coating 100 can be significantly increased. Therefore, the shear strength of the resin coating 100 is preferably 36.00 MPa or more. A more preferred lower limit of the shear strength of the resin coating 100 is 36.50 MPa, even more preferably 36.70 MPa, and even more preferably 37.00 MPa. The upper limit of the shear strength of the resin coating 100 is not particularly limited, but is, for example, 70.00 MPa.

[0083] [Method for measuring shear strength] The shear strength of the resin coating 100 can be measured by the following method. The shear strength of a test piece coated with the resin coating 100 is measured using a surface / interface property analyzer (manufactured by Daipla Wintes Co., Ltd., trademark: SAICAS). Specifically, the resin coating 100 is formed on a cold-rolled steel sheet (chemical composition: C≦0.15%, Mn≦0.60%, P≦0.100%, S≦0.050%, and the balance: Fe and impurities). The target film thickness is 20 μm. A sharp cutting blade is used to cut the surface of the resin coating 100 at a 10° angle at a constant speed (horizontal speed: 2 μm / s, vertical speed: 0.2 μm / s) to peel the resin coating 100 from the cold-rolled steel sheet. All tests are performed at room temperature. The shear strength (MPa) of the resin coating 100 can be calculated from the horizontal force, vertical force, and vertical displacement applied to the cutting blade.

[0084] [Resin coating thickness] In this embodiment, the thickness of the resin coating 100 is not particularly limited. The thickness of the resin coating 100 is, for example, 1 to 100 μm. In this case, the yield torque of the metal oil well pipe 1 can be more stably increased. The lower limit of the thickness of the resin coating 100 is preferably 2 μm, more preferably 5 μm, and even more preferably 10 μm. The upper limit of the thickness of the resin coating 100 is preferably 50 μm, more preferably 40 μm, and even more preferably 30 μm.

[0085] [Method for measuring the thickness of resin coating] The thickness of the resin coating 100 can be measured by the following method. A probe of an electromagnetic induction type film thickness measuring instrument is brought into contact with the pin contact surface 400 or box contact surface 500 on which the resin coating 100 is formed. The probe has an electromagnet, and when a magnetic body is brought close, electromagnetic induction occurs, and the voltage changes depending on the distance between the probe and the magnetic body. The thickness of the resin coating 100 is determined from the change in voltage. The measurement points are 12 points around the circumferential direction of the metal oil well pipe 1 (12 points at 0°, 30°, 60°, 90°, 120°, 150°, 180°, 210°, 240°, 270°, 300°, and 330°). The arithmetic mean of the measurement results at the 12 points is taken as the thickness of the resin coating 100.

[0086] [Chemical composition of the tube body] The chemical composition of the pipe body 10 of the oil well metal pipe 1 according to this embodiment is not particularly limited. That is, in this embodiment, the steel type of the pipe body 10 of the oil well metal pipe 1 is not particularly limited. The pipe body 10 may be formed of, for example, carbon steel, stainless steel, alloy, or the like. That is, the oil well metal pipe 1 may be a steel pipe made of an Fe-based alloy, or an alloy pipe typified by a Ni-based alloy pipe. Here, the steel pipe may be, for example, a low-alloy steel pipe, a martensitic stainless steel pipe, a duplex stainless steel pipe, or the like. On the other hand, among alloy steels, high-alloy steels such as Ni-based alloys and duplex stainless steels containing alloy elements such as Cr, Ni, and Mo have high corrosion resistance. Therefore, when these high-alloy steels are used as the pipe body 10, excellent corrosion resistance can be obtained in corrosive environments containing hydrogen sulfide, carbon dioxide, and the like.

[0087] [Manufacturing method] A method for manufacturing the metal oil well pipe 1 according to this embodiment will be described below.

[0088] The method for manufacturing the metal oil well pipe 1 according to this embodiment includes a preparation step, a coating step, and a hardening step. The hardening step is carried out after the coating step.

[0089] [Preparation process] In the preparation step, a metal oil well pipe 1 is prepared, which includes a pipe body 10 including a pin 40 having a pin contact surface 400 including a male thread portion 41, and a box 50 having a box contact surface 500 including a female thread portion 51. As described above, the metal oil well pipe 1 according to this embodiment has a well-known configuration. That is, in the preparation step, it is sufficient to prepare a metal oil well pipe 1 having a well-known configuration.

[0090] [Coating process] In the coating step, a composition is applied to at least one of the pin contact surface 400 and the box contact surface 500 of the prepared oil well metal tubular article 1. The composition is a composition for forming the resin coating 100 described above. The composition contains 50.0 to 99.5 mass% of resin, 0 to 10.0 mass% of wax, 0 to 30.0 mass% of fluorine-based additive, 0 to 10.0 mass% of graphite, 0 to 30.0 mass% of rust-preventive pigment, 0 to 10.0 mass% of color pigment, and 0 to 10.0 mass% of coupling agent, and contains one or two selected from the group consisting of 1.5 to 50.0 mass% of hydrous magnesium silicate powder and 0.5 to 30.0 mass% of TiO2, and satisfies formula (1). The composition further contains a solvent. The composition for forming the resin coating 100, excluding the solvent, is the same as the composition of the resin coating 100 described above.

[0091] The composition can be produced, for example, by dissolving or dispersing a resin, hydrous magnesium silicate powder and / or TiO2, and, if necessary, other components in a solvent and mixing them. The solvent is, for example, one or more selected from the group consisting of water, alcohol, and organic solvents. The solvent may contain a trace amount of a surfactant. The proportion of the solvent is not particularly limited. The proportion of the solvent may be adjusted so that the composition has an appropriate viscosity depending on the application method. The proportion of the solvent is, for example, 40 to 60% by mass, where the total of all components other than the solvent is 100% by mass.

[0092] The method for applying the composition to the pin contact surface 400 and / or the box contact surface 500 is not particularly limited, and may be a well-known method. For example, the composition in a solution state is applied to the pin contact surface 400 and / or the box contact surface 500 by spraying. In this case, the viscosity of the composition is adjusted so that it can be spray-applied under an environment of normal temperature and pressure. The method for applying the composition to the pin contact surface 400 and / or the box contact surface 500 may be brushing, dipping, or the like, instead of spraying.

[0093] [Curing process] In the curing step, the applied composition is cured to form the resin coating 100. By heating the composition applied to at least one of the pin contact surface 400 and the box contact surface 500, the composition is thermally cured to form the solid resin coating 100. The heating method is not particularly limited and may be a well-known method. For example, the heating method is a method in which the metal oil well pipe 1 to which the composition has been applied is placed in a well-known heating furnace and heated. The heating temperature is, for example, 200 to 250°C, and the heating time is, for example, 5 to 30 minutes.

[0094] The metal oil well pipe 1 according to this embodiment is manufactured through the above steps. Note that the method for manufacturing the metal oil well pipe 1 according to this embodiment may include other steps.

[0095] [Surface preparation process] The method for manufacturing the metal oil well pipe 1 according to this embodiment may further include a surface treatment step before the coating step. The surface treatment step may include, for example, one or more treatments selected from the group consisting of pickling treatment, blasting treatment, and alkaline degreasing treatment.

[0096] When performing pickling, the pin contact surface 400 and / or the box contact surface 500 are immersed in a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, or a mixed acid thereof to increase the surface roughness of the pin contact surface 400 and / or the box contact surface 500. When performing blasting, for example, sandblasting is performed in which a blasting material (abrasive) is mixed with compressed air and projected onto the pin contact surface 400 and / or the box contact surface 500. In this case, the surface roughness of the pin contact surface 400 and / or the box contact surface 500 is increased.

[0097] In the surface preparation step, the same treatment may be performed on the pin contact surface 400 and the box contact surface 500, or different treatments may be performed on the pin contact surface 400 and the box contact surface 500. In addition, the surface preparation step may be performed only on the pin contact surface 400, or only on the box contact surface 500.

[0098] The metal oil well pipe 1 according to this embodiment is manufactured by the above steps. However, the above-described manufacturing method is only one example of the manufacturing method of the metal oil well pipe 1 according to this embodiment, and the manufacturing method is not limited to this. The metal oil well pipe 1 according to this embodiment may be manufactured by other methods. [Example]

[0099] The effects of the metallic oil well pipe of this embodiment will be described in more detail below with reference to examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the metallic oil well pipe of this embodiment. Therefore, the metallic oil well pipe of this embodiment is not limited to this one example of conditions.

[0100] In the examples, compositions for forming resin films were prepared, and the shear strength of the resin films was evaluated. Specifically, the following procedures were carried out.

[0101] [Shear strength evaluation test] Compositions having the compositions shown in Table 1 were prepared. Table 1 shows the components (mass%) of the compositions for each test number, and F1 calculated from each component and formula (1). The compositions contained a solvent in addition to the components listed in Table 1. The solvent used was a mixed solution of water, alcohol, and a surfactant. The prepared compositions were applied to cold-rolled steel sheets (chemical composition: C≦0.15%, Mn≦0.60%, P≦0.100%, S≦0.050%, balance: Fe and impurities). The target film thickness was 20 μm. The cold-rolled steel sheets to which the compositions had been applied were heated in a heating furnace at 200 to 250°C for 5 to 30 minutes to form resin coatings.

[0102] [Table 1]

[0103] The shear strength of the cold-rolled steel sheet having each test number on which a resin coating was formed was measured using the method described above. The shear strength (MPa) obtained for each test number is shown in Table 1.

[0104] [Evaluation results] Referring to Table 1, the resin coatings of test numbers 1 to 22 had appropriate contents of each component and further satisfied formula (1). As a result, these resin coatings had high shear strength of 36.00 MPa or more.

[0105] On the other hand, the resin coatings of test numbers 23 and 24 did not contain either hydrous magnesium silicate powder or TiO2. As a result, the shear strength of these resin coatings was less than 36.00 MPa, and they did not have high shear strength.

[0106] Although the resin coatings of test numbers 25 to 28 had appropriate contents of each component, they did not satisfy formula (1). As a result, the shear strength of these resin coatings was less than 36.00 MPa, and they did not have high shear strength.

[0107] The resin contents of the resin coatings of test numbers 29 and 30 were too low, and as a result, the shear strength of these resin coatings was less than 36.00 MPa, and they did not have high shear strength.

[0108] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure. [Explanation of symbols]

[0109] 1 Metal pipe for oil well 10 Tube body 10A 1st end 10B 2nd end 11-pin body 12 Coupling 40-pin 41 Male thread 42 Pin seal surface 43 Pin shoulder surface 50 boxes 51 Female thread 52 Box seal surface 53 Box shoulder surface 100 Resin coating 400 pin contact surface 500 Box Contact Surface

Claims

1. A metal pipe for oil wells, a tube body including a first end and a second end; The tube body is a pin formed on the first end; a box formed at the second end; The pin is a pin contact surface including an external thread; The box a box contact surface including an internal thread; The oil well metal pipe further comprises: a resin coating on or above at least one of the pin contact surface and the box contact surface; The resin coating is Resin: 50.0 to 99.5% by mass, Wax: 0 to 10.0% by mass, Fluorine-based additives: 0 to 30.0 mass% Graphite: 0 to 10.0% by mass, Anti-rust pigment: 0 to 30.0 mass% Color pigment: 0 to 10.0% by mass, and Coupling agent: 0 to 10.0 mass % Hydrous magnesium silicate powder: 1.5 to 50.0 mass%, and TiO ２ : Contains one or two selected from the group consisting of 0.5 to 30.0 mass% Satisfying formula (1), Metal pipes for oil wells. (W+F+G) / (M+T)≦5.00 (1) In the formula (1), W represents the wax content in mass %, F represents the fluorine-based additive content in mass %, G represents the graphite content in mass %, M represents the magnesium silicate hydrate powder content in mass %, and T represents TiO ２ The contents of these are substituted in mass%.

2. The metal pipe for oil well use according to claim 1, The resin is One or two resins selected from the group consisting of epoxy resins and urethane resins; Metal pipes for oil wells.

3. The metal pipe for oil well use according to claim 1 or 2, the pin contact surface further includes a pin seal surface and a pin shoulder surface; The box contact surface further includes a box seal surface and a box shoulder surface. Metal pipes for oil wells.

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