Oil-well metal pipe

Abstract

Provided is an oil-well metal pipe that has an excellent anti-seize property, and is capable of keeping a threaded joint from loosening even when screwing and unscrewing are repeated. An oil-well metal pipe (1) according to the present disclosure comprises a pipe body (10) including a first end portion (10A) and a second end portion (10B). The pipe body (10) includes a pin (40) formed at the first end portion (10A), and a box (50) formed at the second end portion (10B). The pin (40) includes a pin contact surface (400) including a male thread portion (41). The box (50) includes a box contact surface (500) including a female thread portion (51). The oil-well metal pipe (1) further comprises a resin coating film (100) formed as an uppermost layer on at least one of the pin contact surface (400) and the box contact surface (500). The resin coating film (100) includes an epoxy resin, and an organic carboxylic acid.

Description

Metal pipe for oil well

[0001] The present disclosure relates to metal oil well pipes.

[0002] Metallic oil well pipes are used in oil wells and natural gas wells (hereinafter, oil wells and natural gas wells are collectively referred to as "oil wells"). Specifically, at oil well drilling sites, multiple metallic oil well pipes are connected to form a connected oil well pipe assembly, typically casing or tubing. A connected oil well pipe assembly is formed by screwing together threaded joints formed on metallic oil well pipes. Inspection of the connected oil well pipe assembly may be performed. When inspection is performed, 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 pipe is re-screwed together at its threaded joints, and the metallic oil well pipe is reused as part of a connected oil well pipe assembly.

[0003] A threaded joint formed in an oil well metal 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 oil well metal pipe. The box has a box contact surface including a female thread portion on the inner peripheral surface of the end of the oil well metal pipe. In this specification, the male thread portion and the female thread portion are also collectively referred to as "thread portion." In this specification, the pin contact surface and the box contact surface are also collectively referred to as "contact surface." 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 contact surfaces are repeatedly subjected to strong friction when threaded joints formed on metal oil well pipes are tightened and loosened. Therefore, the contact surfaces are prone to galling (irreparable seizure) when the threads are tightened and loosened repeatedly. Therefore, metal oil well pipes are 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 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 for the development of 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 No. 2002-348587 (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 solid lubricating coating composed of a lubricating powder and a binder formed on the contact surface of at least one of the pin and box members. The lubricating powder is composed of one or two types selected from molybdenum disulfide powder and tungsten disulfide powder, and graphite powder. The graphite powder accounts for 2 to 20 mass % of the lubricating powder. Patent Document 1 discloses that this oil well metal pipe can improve the seizure resistance of the oil well metal pipe.

[0008] The oil well metal pipe disclosed in Patent Document 2 is characterized by having a viscous liquid or semi-solid lubricating coating and a dry solid coating formed thereon on the contact surface of at least one of the pin and the box. Patent Document 2 discloses that this oil well metal pipe can suppress the occurrence of rust and improve seizure resistance and airtightness without using compound grease.

[0009] Patent Document 1: JP 2002-348587 A, International Publication No. 2006 / 104251

[0010] However, when a threaded joint loosens, its airtightness may decrease. Therefore, there is a demand for a threaded joint that not only has excellent galling resistance but also is resistant to loosening. Furthermore, as described above, threaded joints are repeatedly tightened and loosened for inspection. It is preferable that the resistance to loosening of a threaded joint be maintained even when tightening and loosening are repeated.

[0011] The techniques disclosed in Patent Documents 1 and 2 can improve the galling resistance of metal oil well pipes. However, Patent Documents 1 and 2 do not even consider achieving both galling resistance and resistance to loosening of threaded joints.

[0012] An object of the present disclosure is to provide a metal pipe for oil wells that has excellent seizure resistance and that can maintain the resistance to loosening of a threaded joint even when the threads are repeatedly tightened and loosened.

[0013] The metal oil well pipe according to the present disclosure comprises a pipe body having a first end and a second end, the pipe body including a pin formed at the first end and a box formed at the second end, the pin including a pin contact surface including a male thread portion, and the box including a box contact surface including a female thread portion, the metal oil well pipe further comprising a resin coating formed as an uppermost layer on at least one of the pin contact surface and the box contact surface, the resin coating including an epoxy resin and an organic carboxylic acid.

[0014] The metal oil well pipe according to the present disclosure has excellent seizure resistance, and furthermore, the threaded joint can maintain its resistance to loosening even when repeatedly tightened and loosened.

[0015] FIG. 1 is a diagram showing the results of a Bowden test of a resin coating containing an epoxy resin. FIG. 2 is a side view of a metallic oil well pipe according to this embodiment. FIG. 3 is a partial cross-sectional view showing a cross section (longitudinal cross section) parallel to the pipe axis direction of a coupling of the metallic oil well pipe shown in FIG. 2. FIG. 4 is a cross-sectional view parallel to the pipe axis direction of the metallic oil well pipe of a portion near a pin of the metallic oil well pipe shown in FIG. 3. FIG. 5 is a cross-sectional view parallel to the pipe axis direction of the metallic oil well pipe of a portion near a box of the metallic oil well pipe shown in FIG. 3. FIG. 6 is a partial cross-sectional view including a longitudinal section of a metallic oil well pipe according to this embodiment, which has another configuration different from that shown in FIG. 2. FIG. 7 is a partial cross-sectional view including a longitudinal section of an integral type metallic oil well pipe according to this embodiment. FIG. 8 is a cross-sectional view of the vicinity of the pin contact surface of the metallic oil well pipe according to this embodiment. FIG. 9 is a cross-sectional view of the vicinity of the box contact surface corresponding to FIG. 8. FIG. 10 is an enlarged view of the pin contact surface according to this embodiment, which is different from FIG. 8. FIG. 11 is a cross-sectional view of the vicinity of the box contact surface corresponding to FIG. 10. Fig. 12 is an enlarged view of the pin contact surface according to this embodiment, which differs from Fig. 8 and Fig. 10. Fig. 13 is a cross-sectional view of the vicinity of the box contact surface corresponding to Fig. 12.

[0016] 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.

[0017] The present inventors have conducted extensive research into means for achieving both excellent seizure resistance and loosening resistance in a metallic oil well pipe, and have made the following findings.

[0018] It is known that when metals contact each other, a friction coefficient exceeding 0.40, for example, seizure becomes significantly more likely. If the friction coefficient of the contact surface is low, seizure can be suppressed. For example, when a general-purpose API dope is used, the friction coefficient of the contact surface is approximately 0.05 to 0.20. In this case, seizure of the contact surface is suppressed. In previous studies, a method of lowering the friction coefficient of the contact surface has been proposed as a means of improving seizure resistance.

[0019] If the coefficient of friction of the contact surfaces is low, the pin contact surface and the box contact surface will slide more easily. In this case, the screw will rotate more easily in both the tightening and unscrewing directions. The inventors believed that simply lowering the coefficient of friction of the contact surfaces would improve seizure resistance, but make the screw more likely to loosen. The inventors believed that if the coefficient of friction of the contact surfaces could be maintained low enough to improve seizure resistance, yet high enough to make the screw less likely to loosen, it would be possible to achieve both excellent seizure resistance and resistance to loosening. Therefore, the inventors investigated means for maintaining the coefficient of friction of the contact surfaces within a range that improves the seizure resistance of a threaded joint and makes the threaded joint less likely to loosen.

[0020] Possible methods for adjusting the coefficient of friction of a contact surface include adjusting the coefficient of friction of the contact surface itself, and forming a coating on the contact surface and adjusting the coefficient of friction of the coating. The contact surface includes a threaded portion. The threaded portion has a complex shape in which threads and grooves are alternately arranged in the axial direction of the metal oil well pipe. Considering industrial production, it is considered difficult to adjust the coefficient of friction of the contact surface itself, including a threaded portion with a complex shape. Therefore, the inventors have investigated a means for forming a coating on the contact surface and adjusting the coefficient of friction of the coating.

[0021] Resin coatings are known as coatings formed on contact surfaces. The inventors believed that by incorporating an appropriate resin into the resin coating, the friction coefficient of the resin coating could be adjusted to a range that would enhance seizure resistance and make screws less likely to loosen.

[0022] The present inventors first investigated the resin to be contained in the resin coating. They believed that if the resin coating contained a resin with high adhesion to metal, peeling of the resin coating could be suppressed even when shear force was generated by screw tightening. If peeling of the resin coating was suppressed, it would be easier to adjust the friction coefficient of the contact surface even when screw tightening and loosening were repeated. Therefore, the present inventors investigated resins with high adhesion to metal. As a result, they obtained the following findings.

[0023] Epoxy resin is a thermosetting synthetic resin with reactive epoxy groups at the end of the molecular chain. A typical epoxy resin is bisphenol A epoxy resin. Bisphenol A epoxy resin has secondary hydroxyl groups in the repeating unit. Epoxy resin has higher adhesion to metals than other resins. The reason why epoxy resin has high adhesion to metals is not clear, but the following two reasons are thought to be the case: (1) Hydroxyl groups in the epoxy resin form hydrogen bonds with hydroxyl groups on the metal surface. (2) Regarding adhesion to iron and zinc, phenoxy groups are involved in the adhesive interface.

[0024] The present inventors believed that if a resin coating contains an epoxy resin, peeling of the resin coating can be suppressed even when the screw is repeatedly tightened and unscrewed, and the friction coefficient can be easily adjusted. Therefore, the present inventors investigated means for adjusting the friction coefficient of a resin coating containing an epoxy resin. Specifically, they added various additives to a resin coating containing an epoxy resin and investigated the friction coefficient. As a result, they obtained the unprecedented finding that by adding an organic carboxylic acid to a resin coating containing an epoxy resin, it is possible to improve seizure resistance and adjust the friction coefficient to a range in which the screw is less likely to loosen.

[0025] Fig. 1 is a diagram showing the results of a Bowden test on a resin coating containing an epoxy resin. Fig. 1 was obtained from an example described later. In Fig. 1, the horizontal axis represents sliding distance (m). In Fig. 1, the vertical axis represents friction coefficient (μ). In Fig. 1, test number 1 is a chart showing the results of a Bowden test on a steel plate provided with a resin coating containing an epoxy resin but not an organic carboxylic acid. Test number 21 is a chart showing the results of a Bowden test on a steel plate provided with a resin coating containing an epoxy resin and an organic carboxylic acid.

[0026] As mentioned above, if the friction coefficient exceeds 0.40, the threaded joint is prone to seizure. On the other hand, if the friction coefficient is less than 0.25, the friction coefficient is too low. In this case, the threaded joint is prone to loosening. Therefore, a friction coefficient range of 0.25 to 0.40 can be said to be a range of friction coefficients that improves the seizure resistance of a threaded joint and makes the threaded joint less likely to loosen. In other words, if the sliding distance at a friction coefficient in the range of 0.25 to 0.40 in the Bowden test is long, it can be said that the threaded joint has excellent seizure resistance and can maintain its resistance to loosening even when repeatedly tightening and loosening the threads.

[0027] Referring to Figure 1, the chart for Test No. 21 had a longer sliding distance at friction coefficients in the range of 0.25 to 0.40 compared to the chart for Test No. 1. This means that the metal oil well pipe provided with the resin coating of Test No. 21 can achieve both excellent galling resistance and resistance to loosening. The resin coating of Test No. 21 contains an epoxy resin and an organic carboxylic acid. On the other hand, the resin coating of Test No. 1 contains an epoxy resin but does not contain an organic carboxylic acid. In other words, a resin coating containing an epoxy resin and an organic carboxylic acid can achieve both excellent galling resistance and resistance to loosening for the metal oil well pipe, and the resistance to loosening of the threaded joint can be maintained for a long time even when the threads are repeatedly tightened and loosened.

[0028] It is unclear why a resin coating containing an epoxy resin and an organic carboxylic acid can improve the seizure resistance of a threaded joint and maintain its resistance to loosening even after repeated tightening and loosening. However, the following possibility is considered: When an epoxy resin and an organic carboxylic acid coexist, the sliding heat generated during tightening or loosening causes the carboxyl group of the organic carboxylic acid to bond to the epoxy group in the epoxy resin through an addition reaction. The bond between an epoxy resin and an organic carboxylic acid functions as follows: The OH groups contained in the epoxy resin chain of the bond form hydrogen bonds with the OH groups on the metal surface of the thread, appropriately suppressing peeling of the resin coating from the thread surface and loosening of the thread. The hydrocarbon chain of the organic carboxylic acid at the end of the molecular chain of the bond has lubricity toward metal, thereby improving seizure resistance.

[0029] Although the above reasons are speculation, it has been proven by the examples described below that a resin coating containing an epoxy resin and an organic carboxylic acid can improve the seizure resistance of metal oil well pipes, and furthermore, can maintain the resistance to loosening of threaded joints even when the threads are repeatedly tightened and loosened.

[0030] The metallic oil well pipe according to the present embodiment, which has been completed based on the above findings, has the following features.

[0031] [1] A metal pipe for oil well use, comprising: a pipe body having a first end and a second end, the pipe body including: a pin formed at the first end; and a box formed at the second end, the pin including a pin contact surface including a male thread portion, and the box including a box contact surface including a female thread portion, the metal pipe for oil well use further comprising: a resin coating formed as an uppermost layer on at least one of the pin contact surface and the box contact surface, the resin coating including an epoxy resin and an organic carboxylic acid.

[0032] [2] The metal pipe for oil well use according to [1], wherein the organic carboxylic acid is an aliphatic carboxylic acid.

[0033] [3] The metal pipe for oil well use according to [1] or [2], wherein the organic carboxylic acid has 5 or more carbon atoms.

[0034] [4] The metallic pipe for oil well use according to any one of [1] to [3], wherein the organic carboxylic acid has 10 or less carbon atoms.

[0035] [5] The metallic pipe for oil well use according to any one of [1] to [4], wherein the organic carboxylic acid is a monocarboxylic acid.

[0036] [6] The metallic pipe for oil well use according to any one of [1] to [5], wherein the organic carboxylic acid has a branched chain hydrocarbon group.

[0037] [7] The metal pipe for oil well use according to any one of [1] to [6], wherein the organic carboxylic acid is 2,2-dimethylpropanoic acid, 3,5,5-trimethylhexanoic acid, 2-ethylhexanoic acid, 2-ethyl-2,3-dimethylhexanoic acid, 2-ethyl-2,4-dimethylhexanoic acid, 2-ethyl-2,5-dimethylhexanoic acid, 2-ethyl-3,4-dimethylhexanoic acid, 2-ethyl-3,5-dimethylhexanoic acid, 2-ethyl-4,5-dimethylhexanoic acid, 2-ethyl-3,3-dimethylhexanoic acid, 2-ethyl-4,4-dimethylhexanoic acid, 2-ethyl-5,5-dimethylhexanoic acid, 3-ethyl-2,3-dimethylhexanoic acid, Methylhexanoic acid, 3-ethyl-2,4-dimethylhexanoic acid, 3-ethyl-2,5-dimethylhexanoic acid, 3-ethyl-3,4-dimethylhexanoic acid, 3-ethyl-3,5-dimethylhexanoic acid, 3-ethyl-4,5-dimethylhexanoic acid, 3-ethyl-2,2-dimethylhexanoic acid, 3-ethyl-4,4-dimethylhexanoic acid, 3-ethyl-5,5-dimethylhexanoic acid, 4-ethyl-2,3-dimethylhexanoic acid, 4-ethyl-2,4-dimethylhexanoic acid, 4-ethyl-2,5-dimethylhexanoic acid, 4-ethyl 4-ethyl-3,4-dimethylhexanoic acid, 4-ethyl-3,5-dimethylhexanoic acid, 4-ethyl-4,5-dimethylhexanoic acid, 4-ethyl-2,2-dimethylhexanoic acid, 4-ethyl-3,3-dimethylhexanoic acid, 4-ethyl-5,5-dimethylhexanoic acid, 2-ethyl-2-methylheptanoic acid, 3-ethyl-3-methylheptanoic acid, 4-ethyl-4-methylheptanoic acid, 5-ethyl-5-methylheptanoic acid, 2,2-dimethyloctanoic acid, 3,3-dimethyloctanoic acid, 4,4-dimethyloctanoic acid, 5,5-dimethyl Dimethyloctanoic acid, 6,6-dimethyloctanoic acid, 7,7-dimethyloctanoic acid, 2,3-dimethyloctanoic acid, 2,4-dimethyloctanoic acid, 2,5-dimethyloctanoic acid, 2,6-dimethyloctanoic acid, 2,7-dimethyloctanoic acid, 3,4-dimethyloctanoic acid, 3,5-dimethyloctanoic acid, 3,6-dimethyloctanoic acid, 3,7-dimethyloctanoic acid, 4,5-dimethyloctanoic acid, 4,6-dimethyloctanoic acid, 4,7-dimethyloctanoic acid, 5,6-dimethyloctanoic acid, 5,7-dimethyloctanoic acid, 6,A metal pipe for oil wells, which is at least one selected from the group consisting of 7-dimethyloctanoic acid, octanoic acid, nonanoic acid, decanoic acid, 2,2,3,5-tetramethylhexanoic acid, and 2,4-dimethyl-2-isopropylpentanoic acid.

[0038] [8] The metal oil well pipe according to any one of [1] to [7], further comprising one or more layers selected from the group consisting of a metal plating layer and a chemical conversion treatment layer between the resin coating and at least one of the pin contact surface and the box contact surface.

[0039] The metallic oil well pipe according to this embodiment will be described in detail below.

[0040] [Configuration of Oil Well Metal Tubing] First, the configuration of the oil well metal tubing of this embodiment will be described. The oil well metal tubing has a well-known configuration. There are two types of oil well metal tubing: T&C type oil well metal tubing and integral type oil well metal tubing. Each type of oil well metal tubing will be described in detail below.

[0041] [When the oil well metal pipe is a T&C type] Fig. 2 is a side view of the oil well metal pipe 1 according to this embodiment. Fig. 2 is a side view of a so-called T&C (Threaded and Coupled) type oil well metal pipe 1. Referring to Fig. 2, the oil well metal pipe 1 includes a pipe main body 10.

[0042] 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. 2 , 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.

[0043] Figure 3 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 Figure 2. With reference to Figures 2 and 3, 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. When fastening, the pin 40 is inserted into a 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.

[0044] 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.

[0045] [Configuration of Pin] Fig. 4 is a cross-sectional view parallel to the pipe axis direction of the metal oil well pipe 1 of a portion near the pin 40 of the metal oil well pipe 1 shown in Fig. 3. The dashed line portion in Fig. 4 shows the configuration of the box 50 of another metal oil well pipe 1 when fastening to another metal oil well pipe 1. Referring to Fig. 4, 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.

[0046] 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. 4 , the pin shoulder surface 43 is located on the distal end 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 distal end 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.

[0047] 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 together can be improved.

[0048] In Fig. 4, 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. 4, 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 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 shoulder surface 43 contacts the box shoulder surface 53. This allows a high torque to be obtained during fastening. Furthermore, the positional relationship between the pin 40 and the box 50 in the fastened state can be stabilized.

[0049] 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.

[0050] [Configuration of the Box] Fig. 5 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. 3. The dashed line portion in Fig. 5 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. 5, 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.

[0051] 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 oil well metal pipe 1.

[0052] The box contact surface 500 may further include a box seal surface 52 and a box shoulder surface 53. In FIG. 5 , 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.

[0053] 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 to each other can be improved.

[0054] 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 during fastening. Furthermore, the positional relationship between the pin 40 and the box 50 in the fastened state can be stabilized.

[0055] 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.

[0056] 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.

[0057] The pin contact surface 400 may include a plurality of male thread portions 41, a plurality of pin seal surfaces 42, or a plurality of 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.

[0058] 4 and 5 show 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 and not include 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. 6 is a partial cross-sectional view including a longitudinal section of a metal oil well pipe of this embodiment, which has another configuration different from that shown in FIG. 2.

[0059] [When the oil well metal pipe is an integral type] The oil well metal pipe 1 shown in Figures 2, 3 and 6 is a so-called T&C type oil well metal pipe 1 in which the 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.

[0060] Fig. 7 is a partial cross-sectional view including a longitudinal section of an integral-type metal oil well pipe 1 according to this embodiment. Referring to Fig. 7, 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.

[0061] 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 and screwed into a box 50 of another integral type metal pipe for oil well use 1, and is fastened to the box 50 of another integral type metal pipe for oil well use 1. The box 50 is formed at a second end 10B of the pipe body 10. At the time of fastening, the pin 40 of another integral type metal 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 metal pipe for oil well use 1.

[0062] 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. 4. 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. 5. In Figs. 4 and 5, 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, it is sufficient that the pin contact surface 400 of the pin 40 of the integral type metal oil well pipe 1 includes 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.

[0063] In short, the metal oil well pipe 1 of this embodiment may be of the T&C type or the integral type.

[0064] [Resin Coating] The metal oil well pipe 1 according to this embodiment is provided with a resin coating 100 formed as an uppermost layer on at least one of the pin contact surface 400 and the box contact surface 500. Fig. 8 is a cross-sectional view of the vicinity of the pin contact surface 400 of the metal oil well pipe 1 according to this embodiment. Fig. 9 is a cross-sectional view of the vicinity of the box contact surface 500 corresponding to Fig. 8.

[0065] Referring to Fig. 8, the resin coating 100 may be formed as the uppermost layer of the pin contact surface 400. In this case, the resin coating 100 may or may not be formed on or above the corresponding box contact surface 500. Also, referring to Fig. 9, the resin coating 100 may be formed as the uppermost layer of the box contact surface 500. In this case, the resin coating 100 may or may not be formed on or above the corresponding pin contact surface 400. In short, in the metal oil well pipe 1 according to this embodiment, the resin coating 100 is formed as the uppermost layer of either the pin contact surface 400 or the box contact surface 500. It is sufficient that the resin coating 100 is formed as the uppermost layer of at least a portion of the pin contact surface 400 or the box contact surface 500 (for example, only the pin seal surface 42 or the box seal surface 52).

[0066] The resin coating 100 contains an epoxy resin. The amount of epoxy resin in the resin coating 100 is not particularly limited, but the amount is, for example, 15 to 80% by mass. If the amount of epoxy resin in the resin coating 100 is 15% by mass or more, the resin coating 100 can be more stably molded. On the other hand, if the amount of epoxy resin in the resin coating 100 is 80% by mass or less, the predetermined film thickness can be more stably ensured. Therefore, the amount of epoxy resin in the resin coating 100 that can be molded to a stable film thickness is preferably 15 to 80% by mass. The lower limit of the amount of epoxy resin in the resin coating 100 is more preferably 18% by mass, even more preferably 20% by mass, even more preferably 25% by mass, and even more preferably 30% by mass. The upper limit of the amount of epoxy resin in the resin coating 100 is more preferably 70% by mass, even more preferably 65% ​​by mass, and even more preferably 60% by mass.

[0067] [Method for Measuring Epoxy Resin Content] The epoxy resin content in the resin coating 100 is measured using reflux extraction (Soxhlet extraction) using a solvent. Specifically, reflux extraction is performed on the resin coating 100 using methyl ethyl ketone as the solvent. Specifically, the amount of resin coating 100 required for measurement is scraped off from the pin contact surface 400 or the box contact surface 500, and reflux extraction is performed. Reflux extraction is performed for four hours using 0.4 L of methyl ethyl ketone for five resin coatings 100 measuring 20 μm thick, 120 mm long, and 15 mm wide. If the thickness of the resin coating 100 is greater than 20 μm, the number of resin coatings 100 is adjusted to achieve the same volume as the resin coating 100. Similarly, if the thickness of the resin coating 100 is less than 20 μm, the number of resin coatings 100 is adjusted to achieve the same volume as the resin coating 100. The weight of the resin coating 100 after reflux extraction corresponds to the weight of the epoxy resin. Therefore, the content of the epoxy resin in the resin coating 100 is determined by dividing the weight of the resin coating 100 after reflux extraction by the weight of the resin coating 100 before reflux extraction.

[0068] [Organic Carboxylic Acid] The organic carboxylic acid is a carboxylic acid having a hydrocarbon group. When the resin coating 100 contains an epoxy resin and an organic carboxylic acid, the friction coefficient of the resin coating 100 can be maintained within a range that improves the seizure resistance of the threaded joint and makes it difficult for the thread to loosen even when repeatedly tightened and loosened.

[0069] The organic carboxylic acid may be an aliphatic carboxylic acid or an aromatic carboxylic acid, and preferably has a chain hydrocarbon group.

[0070] If the organic carboxylic acid has 5 or more carbon atoms, the organic carboxylic acid molecule is large. Therefore, after the resin coating 100 is cured, the organic carboxylic acid molecules slip through the three-dimensionally crosslinked epoxy resin network, protrude to the surface of the resin coating 100, and escape from the resin coating 100, a phenomenon known as "bleed-out," is suppressed. Therefore, if the organic carboxylic acid has 5 or more carbon atoms, the effect obtained by the coexistence of the epoxy resin and the organic carboxylic acid can be obtained more stably. Therefore, the organic carboxylic acid preferably has 5 or more carbon atoms.

[0071] On the other hand, if the carbon number of the organic carboxylic acid is 10 or less, the organic carboxylic acid becomes more soluble in water. In this case, the organic carboxylic acid is more easily dispersed in a composition for forming a resin coating containing an epoxy resin. Therefore, the organic carboxylic acid preferably has 10 or less carbon atoms. In other words, if the carbon number of the organic carboxylic acid is 5 to 10, the epoxy resin and the organic carboxylic acid can coexist more stably, which is even more preferable.

[0072] If the organic carboxylic acid is a monocarboxylic acid, compatibility with the epoxy resin is improved, and therefore the organic carboxylic acid is preferably a monocarboxylic acid.

[0073] The aliphatic carboxylic acid is, for example, a linear saturated monocarboxylic acid, such as one or more selected from the group consisting of methanoic acid (formic acid), ethanoic acid (acetic acid), propanoic acid (propionic acid), butanoic acid (butyric acid), pentanoic acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, tetradecanoic acid, pentadecanoic acid, hexadecanoic acid, heptadecanoic acid, octadecanoic acid, nonadecanoic acid, icosanoic acid, eicosanoic acid, heneicosanoic acid, heneicosanoic acid, docosanoic acid, tricosanoic acid, tetracosanoic acid, pentacosanoic acid, hexacosanoic acid, heptacosanoic acid, octacosanoic acid, nonacosanoic acid, and triacontanoic acid.

[0074] When the organic carboxylic acid has a branched-chain hydrocarbon group, the branched-chain hydrocarbon group extends laterally from the long chain. The branched-chain hydrocarbon group in the organic carboxylic acid is likely to entangle with the hydrocarbon group in the epoxy resin. When the epoxy resin and the carboxylic acid having the branched-chain hydrocarbon group approach each other, they are likely to entangle with each other due to intermolecular forces, thereby improving compatibility. Therefore, the organic carboxylic acid preferably has a branched-chain hydrocarbon group. On the other hand, if the branched-chain hydrocarbon group in the organic carboxylic acid has a small carbon number and / or a small number of substitutions, the organic carboxylic acid is likely to move easily in the composition for forming the resin coating. If the organic carboxylic acid is likely to move easily in the composition, the reaction between the epoxy group at the terminal of the epoxy resin and the organic carboxylic acid is promoted. As a result, it is likely that the lubrication during screw tightening and unscrewing is further improved and stable. Therefore, the branched-chain hydrocarbon group is preferably one or more selected from the group consisting of a methyl group, an ethyl group, a propyl group, and an isopropyl group. Preferably, the number of substitutions of the branched chain hydrocarbon group in the organic carboxylic acid is 3 or less when the branched chain hydrocarbon group is only methyl or ethyl groups. Preferably, the number of substitutions of the branched chain hydrocarbon group in the organic carboxylic acid is 1 when the branched chain hydrocarbon group contains a propyl or isopropyl group.

[0075] The aliphatic carboxylic acid is, for example, a saturated monocarboxylic acid having a branched chain. Examples of saturated monocarboxylic acids having a branched chain include 2-methylpropanoic acid, 2,2-dimethylpropanoic acid, 2-methylbutanoic acid, 3-methylbutanoic acid, 2,2-dimethylbutanoic acid, 3,3-dimethylbutanoic acid, 2,3-dimethylbutanoic acid, 2,2,3-trimethylbutanoic acid, 2,3,3-trimethylbutanoic acid, 2-isopropylbutanoic acid, 2-methylpentanoic acid, 3-methylpentanoic acid, 4-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, and 2-propylpentanoic acid. Acid, 2-isopropylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 4,4-dimethylpentanoic acid, 2,3-dimethylpentanoic acid, 3,4-dimethylpentanoic acid, 2,4-dimethylpentanoic acid, 2,2-diethylpentanoic acid, 3,3-diethylpentanoic acid, 2,3-diethylpentanoic acid, 2-methyl-3-ethylpentanoic acid, 2-ethyl-2-methylpentanoic acid, 2-ethyl-3-methylpentanoic acid, 2-ethyl-4-methylpentanoic acid, 3-ethyl- 2-Methylpentanoic acid, 3-ethyl-3-methylpentanoic acid, 3-ethyl-4-methylpentanoic acid, 2,2,3-trimethylpentanoic acid, 2,2,4-trimethylpentanoic acid, 2,3,3-trimethylpentanoic acid, 3,3,4-trimethylpentanoic acid, 2,3,4-trimethylpentanoic acid, 2-ethyl-2,3-dimethylpentanoic acid, 2-ethyl-2,4-dimethylpentanoic acid, 2-ethyl-3,3-dimethylpentanoic acid, 2-ethyl-3,4-dimethylpentanoic acid, 2-ethyl- 4,4-dimethylpentanoic acid, 3-ethyl-2,2-dimethylpentanoic acid, 3-ethyl-2,3-dimethylpentanoic acid, 3-ethyl-2,4-dimethylpentanoic acid, 3-ethyl-3,4-dimethylpentanoic acid, 3-ethyl-4,4-dimethylpentanoic acid, 2,2-diethyl-3-methylpentanoic acid, 2,2-diethyl-4-methylpentanoic acid, 2,3-diethyl-2-methylpentanoic acid, 2,3-diethyl-3-methylpentanoic acid, 2,3-diethyl-4-methylpentanoic acid, 3,3-diethyl-4-methylpentanoic acid, 2-methylhexanoic acid, 3-methylhexanoic acid, 4-methylhexanoic acid, 5-methylhexanoic acid, 2-ethylhexanoic acid, 3-ethylhexanoic acid, 4-ethylhexanoic acid, 2-propylhexanoic acid, 3-propylhexanoic acid, 2-isopropylhexanoic acid, 3-isopropylhexanoic acid, 2,2-dimethylhexanoic acid, 3,3-dimethylhexanoic acid, 4,4-dimethylhexanoic acid, 5,5-dimethylhexanoic acid, 2,3-dimethylhexanoic acid, 2,4-dimethylhexanoic acid, 2,5-dimethylhexanoic acid, 3,4 -dimethylhexanoic acid, 3,5-dimethylhexanoic acid, 4,5-dimethylhexanoic acid, 2,2-diethylhexanoic acid, 3,3-diethylhexanoic acid, 4,4-diethylhexanoic acid, 2,3-diethylhexanoic acid, 2,4-diethylhexanoic acid, 3,4-diethylhexanoic acid, 2-ethyl-2-methylhexanoic acid, 2-ethyl-3-methylhexanoic acid, 2-ethyl-4-methylhexanoic acid, 2-ethyl-5-methylhexanoic acid, 3-ethyl-2-methylhexanoic acid, 3-ethyl-3-methylhexanoic acid, 3-ethyl-4-methylhexanoic acid, 3-ethyl-5 -methylhexanoic acid, 4-ethyl-2-methylhexanoic acid, 4-ethyl-3-methylhexanoic acid, 4-ethyl-4-methylhexanoic acid, 4-ethyl-5-methylhexanoic acid, 2,2,3-trimethylhexanoic acid, 2,2,4-trimethylhexanoic acid, 2,2,5-trimethylhexanoic acid, 2,3,3-trimethylhexanoic acid, 3,3,4-trimethylhexanoic acid, 3,3,5-trimethylhexanoic acid, 2,4,4-trimethylhexanoic acid, 3,4,4-trimethylhexanoic acid, 4,4,5-trimethylhexanoic acid, 2,5,5-trimethylhexanoic acid, 3 , 5,5-trimethylhexanoic acid, 4,5,5-trimethylhexanoic acid, 2,3,4-trimethylhexanoic acid, 3,4,5-trimethylhexanoic acid, 2,3,5-trimethylhexanoic acid, 2,4,5-trimethylhexanoic acid, 2-ethyl-2,3-dimethylhexanoic acid, 2-ethyl-2,4-dimethylhexanoic acid, 2-ethyl-2,5-dimethylhexanoic acid, 2-ethyl-3,4-dimethylhexanoic acid, 2-ethyl-3,5-dimethylhexanoic acid, 2-ethyl-4,5-dimethylhexanoic acid, 2-ethyl-3,3-dimethylhexanoic acid, 2-ethyl-4,4-dimethylhexanoic acid, 2-ethyl-5,5-dimethylhexanoic acid, 3-ethyl-2,3-dimethylhexanoic acid, 3-ethyl-2,4-dimethylhexanoic acid, 3-ethyl-2,5-dimethylhexanoic acid, 3-ethyl-3,4-dimethylhexanoic acid, 3-ethyl-3,5-dimethylhexanoic acid, 3-ethyl-4,5-dimethylhexanoic acid, 3-ethyl-2,2-dimethylhexanoic acid, 3-ethyl-4,4-dimethylhexanoic acid, 3-ethyl-5,5-dimethylhexanoic acid, 4-ethyl-2,3-dimethylhexanoic acid, 4-ethyl-2,4-dimethylhexanoic acid hexanoic acid, 4-ethyl-2,5-dimethylhexanoic acid, 4-ethyl-3,4-dimethylhexanoic acid, 4-ethyl-3,5-dimethylhexanoic acid, 4-ethyl-4,5-dimethylhexanoic acid, 4-ethyl-2,2-dimethylhexanoic acid, 4-ethyl-3,3-dimethylhexanoic acid, 4-ethyl-5,5-dimethylhexanoic acid, 2-methylheptanoic acid, 3-methylheptanoic acid, 4-methylheptanoic acid, 5-methylheptanoic acid, 6-methylheptanoic acid, 2-ethylheptanoic acid, 3-ethylheptanoic acid, 4-ethylheptanoic acid, 5-ethylheptanoic acid, 2,2-dimethylhexanoic acid Dimethylheptanoic acid, 3,3-dimethylheptanoic acid, 4,4-dimethylheptanoic acid, 5,5-dimethylheptanoic acid, 6,6-dimethylheptanoic acid, 2,3-dimethylheptanoic acid, 3,4-dimethylheptanoic acid, 4,5-dimethylheptanoic acid, 5,6-dimethylheptanoic acid, 2,4-dimethylheptanoic acid, 2,5-dimethylheptanoic acid, 2,6-dimethylheptanoic acid, 3,5-dimethylheptanoic acid, 3,6-dimethylheptanoic acid, 4,6-dimethylheptanoic acid, 2,2,3-trimethylheptanoic acid, 2,2,4-trimethylheptanoic acid, 2,2,5-trimethyl Heptanoic acid, 2,2,6-trimethylheptanoic acid, 2,3,3-trimethylheptanoic acid, 3,3,4-trimethylheptanoic acid, 3,3,5-trimethylheptanoic acid, 3,3,6-trimethylheptanoic acid, 2,4,4-trimethylheptanoic acid, 3,4,4-trimethylheptanoic acid, 4,4,5-trimethylheptanoic acid, 4,4,6-trimethylheptanoic acid, 2,5,5-trimethylheptanoic acid, 3,5,5-trimethylheptanoic acid, 4,5,5-trimethylheptanoic acid, 5,5,6-trimethylheptanoic acid, 2,6,6-trimethylheptanoic acid, 3,6,6-trimethylheptanoic acid, 4,6,6-trimethylheptanoic acid, 5,6,6-trimethylheptanoic acid, 2,3,4-trimethylheptanoic acid, 3,4,5-trimethylheptanoic acid, 4,5,6-trimethylheptanoic acid, 2,4,5-trimethylheptanoic acid, 2,5,6-trimethylheptanoic acid, 2,3,6-trimethylheptanoic acid, 2,3,5-trimethylheptanoic acid, 2,4,6-trimethylheptanoic acid, 3,4,6-trimethylheptanoic acid, 3,5,6-trimethylheptanoic acid, 2-ethyl-2-methylheptanoic acid, 2-ethyl-3-methylheptanoic acid acid, 2-ethyl-4-methylheptanoic acid, 2-ethyl-5-methylheptanoic acid, 2-ethyl-6-methylheptanoic acid, 3-ethyl-2-methylheptanoic acid, 3-ethyl-3-methylheptanoic acid, 3-ethyl-4-methylheptanoic acid, 3-ethyl-5-methylheptanoic acid, 3-ethyl-6-methylheptanoic acid, 4-ethyl-2-methylheptanoic acid, 4-ethyl-3-methylheptanoic acid, 4-ethyl-4-methylheptanoic acid, 4-ethyl-5-methylheptanoic acid, 4-ethyl-6-methylheptanoic acid, 5-ethyl-2-methylheptanoic acid, 5-ethyl-3 -methylheptanoic acid, 5-ethyl-4-methylheptanoic acid, 5-ethyl-5-methylheptanoic acid, 5-ethyl-6-methylheptanoic acid, 2-methyloctanoic acid, 3-methyloctanoic acid, 4-methyloctanoic acid, 5-methyloctanoic acid, 6-methyloctanoic acid, 7-methyloctanoic acid, 2,2-dimethyloctanoic acid, 3,3-dimethyloctanoic acid, 4,4-dimethyloctanoic acid, 5,5-dimethyloctanoic acid, 6,6-dimethyloctanoic acid, 7,7-dimethyloctanoic acid, 2,3-dimethyloctanoic acid, 2,4-dimethyloctanoic acid, 2,5-dimethyloctanoic acid Octanoic acid, 2,6-dimethyloctanoic acid, 2,7-dimethyloctanoic acid, 3,4-dimethyloctanoic acid, 3,5-dimethyloctanoic acid, 3,6-dimethyloctanoic acid, 3,7-dimethyloctanoic acid, 4,5-dimethyloctanoic acid, 4,6-dimethyloctanoic acid, 4,7-dimethyloctanoic acid, 5,6-dimethyloctanoic acid, 5,7-dimethyloctanoic acid, 6,7-dimethyloctanoic acid, 2-methylnonanoic acid, 3-methylnonanoic acid, 4-methylnonanoic acid, 5-methylnonanoic acid, 6-methylnonanoic acid, 7-methylnonanoic acid, 8-methylnonanoic acid, 2,2,3,One or more selected from the group consisting of 5-tetramethylhexanoic acid and 2,4-dimethyl-2-isopropylpentanoic acid.

[0076] If the organic carboxylic acid is a branched saturated monocarboxylic acid having 5 or more carbon atoms, it will have a small environmental impact and will not produce an unpleasant odor. Furthermore, as described above, if the organic carboxylic acid has 10 or less carbon atoms, the organic carboxylic acid will be more easily dispersed in a composition for forming a resin coating containing an epoxy resin. Therefore, the organic carboxylic acid according to this embodiment is more preferably a branched saturated monocarboxylic acid having 5 to 10 carbon atoms.

[0077] The aliphatic carboxylic acid is, for example, a linear saturated dicarboxylic acid, such as one or more selected from the group consisting of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, 1,7-heptanedicarboxylic acid, 1,8-octanedicarboxylic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,11-undecanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,13-tridecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,15-pentadecanedicarboxylic acid, 1,16-hexadecanedicarboxylic acid, 1,17-heptadecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, 1,19-nonadecanedicarboxylic acid, and 1,20-eicosanedicarboxylic acid.

[0078] The aliphatic carboxylic acid is, for example, an unsaturated carboxylic acid, such as acrylic acid, 2-butenoic acid, 3-butenoic acid, 2-pentenoic acid, 3-pentenoic acid, 4-pentenoic acid, 2-hexenoic acid, 3-hexenoic acid, 4-hexenoic acid, 5-hexenoic acid, 2-heptenoic acid, 3-heptenoic acid, 4-heptenoic acid, 5-heptenoic acid, 6-heptenoic acid, 2-octenoic acid, 3-octenoic acid, 4-octenoic acid, The octenoic acid is at least one selected from the group consisting of 5-octenoic acid, 6-octenoic acid, 7-octenoic acid, 2-nonenoic acid, 3-nonenoic acid, 4-nonenoic acid, 5-nonenoic acid, 6-nonenoic acid, 7-nonenoic acid, 8-nonenoic acid, 2-decenoic acid, 3-decenoic acid, 4-decenoic acid, 5-decenoic acid, 6-decenoic acid, 7-decenoic acid, 8-decenoic acid, and 9-decenoic acid.

[0079] The aromatic carboxylic acid is, for example, one or more selected from the group consisting of benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, and salicylic acid.

[0080] More preferably, the organic carboxylic acid is 2,2-dimethylpropanoic acid, 3,5,5-trimethylhexanoic acid, 2-ethylhexanoic acid, 2-ethyl-2,3-dimethylhexanoic acid, 2-ethyl-2,4-dimethylhexanoic acid, 2-ethyl-2,5-dimethylhexanoic acid, 2-ethyl-3,4-dimethylhexanoic acid, 2-ethyl-3,5-dimethylhexanoic acid, 2-ethyl-4,5-dimethylhexanoic acid, 2-ethyl-3,3-dimethylhexanoic acid, 2-ethyl-4,4-dimethylhexanoic acid, 2-ethyl-5,5-dimethylhexanoic acid, 3-ethyl- 2,3-dimethylhexanoic acid, 3-ethyl-2,4-dimethylhexanoic acid, 3-ethyl-2,5-dimethylhexanoic acid, 3-ethyl-3,4-dimethylhexanoic acid, 3-ethyl-3,5-dimethylhexanoic acid, 3-ethyl-4,5-dimethylhexanoic acid, 3-ethyl-2,2-dimethylhexanoic acid, 3-ethyl-4,4-dimethylhexanoic acid, 3-ethyl-5,5-dimethylhexanoic acid, 4-ethyl-2,3-dimethylhexanoic acid, 4-ethyl-2,4-dimethylhexanoic acid, 4-ethyl-2,5-dimethylhexanoic acid, 4-ethyl-3,4-dimethyl ethylhexanoic acid, 4-ethyl-3,5-dimethylhexanoic acid, 4-ethyl-4,5-dimethylhexanoic acid, 4-ethyl-2,2-dimethylhexanoic acid, 4-ethyl-3,3-dimethylhexanoic acid, 4-ethyl-5,5-dimethylhexanoic acid, 2-ethyl-2-methylheptanoic acid, 3-ethyl-3-methylheptanoic acid, 4-ethyl-4-methylheptanoic acid, 5-ethyl-5-methylheptanoic acid, 2,2-dimethyloctanoic acid, 3,3-dimethyloctanoic acid, 4,4-dimethyloctanoic acid, 5,5-dimethyloctanoic acid, 6,6-dimethyloctanoic acid, 7,7-dimethyloctanoic acid, 2,3-dimethyloctanoic acid, 2,4-dimethyloctanoic acid, 2,5-dimethyloctanoic acid, 2,6-dimethyloctanoic acid, 2,7-dimethyloctanoic acid, 3,4-dimethyloctanoic acid, 3,5-dimethyloctanoic acid, 3,6-dimethyloctanoic acid, 3,7-dimethyloctanoic acid, 4,5-dimethyloctanoic acid, 4,6-dimethyloctanoic acid, 4,7-dimethyloctanoic acid, 5,6-dimethyloctanoic acid, 5,7-dimethyloctanoic acid, 6,7-dimethyloctanoic acid, octanoic acid, nonanoic acid, decanoic acid, 2,2,3,One or more selected from the group consisting of 5-tetramethylhexanoic acid and 2,4-dimethyl-2-isopropylpentanoic acid.

[0081] The organic carboxylic acid may have other functional groups in addition to the carboxy group. The other functional groups may be, for example, one or more selected from the group consisting of a hydroxy group, an aldehyde group, an amino group, a carbonyl group, an ether bond, an ester bond, a nitro group, and a sulfo group. The organic carboxylic acid may be a compound comprising a chain hydrocarbon group and a carboxy group.

[0082] When the content of organic carboxylic acid in the resin coating 100 is 0.2% by mass or more, the effect of the organic carboxylic acid can be obtained more stably. On the other hand, when the content of organic carboxylic acid in the resin coating 100 is 20% by mass or less, the resin coating 100 can be formed more stably. Therefore, the content of organic carboxylic acid in the resin coating 100 is, for example, 0.2 to 20% by mass. The lower limit of the content of organic carboxylic acid in the resin coating 100 is preferably 0.5% by mass, more preferably 1.0% by mass, and even more preferably 2.0% by mass. The upper limit of the content of organic carboxylic acid in the resin coating 100 is preferably 15% by mass, more preferably 10% by mass, even more preferably 8.0% by mass, even more preferably 5.0% by mass, and even more preferably 4.0% by mass.

[0083] [Method for Measuring Organic Carboxylic Acid Content] The content of organic carboxylic acid in the resin coating 100 is measured using liquid chromatography / mass spectrometry (LC / MS) after reflux extraction (Soxhlet extraction) of the resin coating 100. Specifically, the amount of resin coating 100 required for measurement is scraped off from the pin contact surface 400 or the box contact surface 500, and reflux extraction is performed. Reflux extraction is performed for four hours using 0.4 L of ethanol for five resin coatings 100 measuring 20 μm thick, 120 mm long, and 15 mm wide. If the resin coating 100 is thicker than 20 μm, the number of resin coatings 100 is adjusted to achieve the same volume as the resin coating 100. Similarly, if the resin coating 100 is thinner than 20 μm, the number of resin coatings 100 is adjusted to achieve the same volume as the resin coating 100. The ethanol after reflux extraction is quantitatively analyzed using LC / MS to determine the content of organic carboxylic acid in the resin coating 100. If the organic carboxylic acid is not dissolved in ethanol and cannot be extracted, the content of the organic carboxylic acid in the resin film 100 is determined by similar reflux extraction using methyl ethyl ketone as the solvent.

[0084] [Lubricating Material] The resin coating 100 may contain a lubricating material. The lubricating material may be any material that enhances the lubricity of the resin coating 100, and is not particularly limited. The lubricating material may be, for example, graphite, zinc oxide, boron nitride, talc, molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, organic molybdenum, thiosulfate, polytetrafluoroethylene (PTFE), melamine cyanurate (MCA), or perfluoropolyether (PFPE). A combination of multiple types of the above-mentioned lubricating materials may also be contained. The content of the lubricating material in the resin coating 100 is, for example, 0.1 to 25% by mass.

[0085] [Other Materials] The resin coating 100 may contain other materials. The other materials may be, for example, pigments, anti-rust additives, or preservatives. The content of the other materials in the resin coating 100 is, for example, 0.1 to 25 mass %.

[0086] [Thickness of Resin Coating] There are no particular limitations on the thickness of the resin coating 100. The thickness of the resin coating 100 is, for example, 1 to 100 μm.

[0087] [Arrangement of Resin Coating] In this embodiment, the resin coating 100 is formed as the uppermost layer of at least one of the pin contact surface 400 and the box contact surface 500. That is, in this embodiment, the resin coating 100 may be formed as the outermost layer of the pin contact surface 400 or as the uppermost layer of the box contact surface 500. Furthermore, in this embodiment, when the resin coating 100 is formed as the uppermost layer of the pin contact surface 400, a lubricating coating other than the resin coating 100 of this embodiment may be formed as the uppermost layer of the box contact surface 500. Furthermore, in this embodiment, when the resin coating 100 is formed as the uppermost layer of the box contact surface 500, a lubricating coating other than the resin coating 100 of this embodiment may be formed as the uppermost layer of the pin contact surface 400. Furthermore, in this embodiment, the resin coating 100 may be formed as the uppermost layer of both the pin contact surface 400 and the box contact surface 500.

[0088] When a lubricating coating other than the resin coating 100 is formed, the lubricating coating other than the resin coating 100 is not particularly limited and may be a well-known lubricating coating. The lubricating coating may be, for example, a resin coating using a thermosetting resin such as an epoxy resin as a binder, a resin coating using a thermoplastic resin such as a polyamide resin as a binder, or a lubricating coating based on mineral oil that is grease-like or semi-solid at room temperature. In other words, any well-known lubricating coating may be used as long as it is applicable to the metal oil well pipe 1.

[0089] Furthermore, the resin coating 100 may be formed as a top layer on the entirety of at least one of the pin contact surface 400 and the box contact surface 500, or may be formed as a top layer on only a portion of one of the surfaces. When the pipe body 10 has a pin seal surface 42, a box seal surface 52, a pin shoulder surface 43, and a box shoulder surface 53, the surface pressure on the seal surfaces 42, 52 and the shoulder surfaces 43, 53 becomes particularly high in the final stage of tightening. Therefore, when the resin coating 100 is formed as a top layer on only a portion of at least one of the contact surfaces 400, 500, which have the seal surfaces 42, 52 and the shoulder surfaces 43, 53, the resin coating 100 may be formed as a top layer on at least one of the seal surfaces 42, 52 and the shoulder surfaces 43, 53. On the other hand, forming the resin coating 100 as a top layer on the entirety of at least one of the contact surfaces 400, 500 improves the production efficiency of the metal oil well pipe 1.

[0090] [Other Layers] The metal oil well pipe 1 according to this embodiment may have layers other than the resin coating 100 formed on the contact surfaces 400, 500. The other layers are, for example, metal plating layers and chemical conversion treatment layers.

[0091] [Metal Plating Layer 110] The metal oil well pipe 1 according to this embodiment may further include a metal plating layer between the resin coating 100 and at least one of the pin contact surface 400 and the box contact surface 500. Specifically, with reference to Fig. 10 , the metal plating layer 110 may be formed on the pin contact surface 400 as an underlying layer of the resin coating 100. Similarly, with reference to Fig. 11 , the metal plating layer 110 may be formed on the box contact surface 500 as an underlying layer of the resin coating 100. In this way, when both the resin coating 100 and the metal plating layer 110 are formed, the metal plating layer 110 is formed between the resin coating 100 and at least one of the contact surfaces 400, 500.

[0092] In the present embodiment, the type of the metal plating layer 110 is not particularly limited. The metal plating layer 110 may be a single-layer plating layer or a multi-layer plating layer (a two-layer plating layer or a three-layer plating layer). When the metal plating layer 110 is a single-layer plating layer, the metal plating layer 110 may be, for example, a single-layer plating layer of Cu, Sn, or Ni metal, or a single-layer plating layer of a Zn—Ni alloy, a Cu—Sn alloy, or a Cu—Sn—Zn alloy. When the metal plating layer 110 is a multi-layer plating layer, the metal plating layer 110 may be, for example, a two-layer plating layer of a Cu layer and a Sn layer, a three-layer plating layer of a Ni layer, a Cu layer, and a Sn layer, or a multi-layer plating layer combining the above single-layer plating layers.

[0093] [Chemical Conversion Layer 120] The oil well metal pipe 1 according to this embodiment may further include a chemical conversion layer disposed between the resin coating 100 and at least one of the pin contact surface 400 and the box contact surface 500. The chemical conversion layer 120 has a surface in contact with the resin coating 100. Specifically, with reference to FIG. 12 , the chemical conversion layer 120 may be formed on the metal plating layer 110 formed on the pin contact surface 400, as an underlying layer of the resin coating 100. With reference to FIG. 13 , the chemical conversion layer 120 may be formed on the metal plating layer 110 formed on the box contact surface 500, as an underlying layer of the resin coating 100. Similarly, although not shown, the chemical conversion layer 120 may be formed on the pin contact surface 400, as an underlying layer of the resin coating 100. Similarly, although not shown, the chemical conversion layer 120 may be formed on the box contact surface 500, as an underlying layer of the resin coating 100.

[0094] In this embodiment, the type of chemical conversion treatment layer 120 is not particularly limited. The chemical conversion treatment layer 120 may be, for example, a phosphate chemical conversion treatment layer, an oxalate chemical conversion treatment layer, a borate chemical conversion treatment layer, a chromate chemical conversion treatment layer, or a zirconium chemical conversion treatment layer. Here, the chemical conversion treatment layer 120 is porous. Therefore, if a resin coating 100 is formed on the chemical conversion treatment layer 120, the adhesion of the resin coating 100 is further enhanced due to the so-called anchor effect. Furthermore, in this embodiment, the thickness of the chemical conversion treatment layer 120 is not particularly limited. A preferred thickness of the chemical conversion treatment layer 120 in this embodiment is 5 to 40 μm.

[0095] [Blast-treated surface or pickled surface] In the metal oil well pipe 1 according to this embodiment, the contact surfaces 400, 500 may be blast-treated or pickled. That is, in the metal oil well pipe 1, the surface on which the resin coating 100 is formed as the uppermost layer may be blast-treated or pickled. That is, the contact surfaces 400, 500 of the pipe body 10 of the metal oil well pipe 1 may be blast-treated or pickled, and the resin coating 100 may be formed thereon. Furthermore, in the case where the metal oil well pipe 1 has the metal plating layer 110, the metal oil well pipe 1 may have the contact surfaces 400, 500 blast-treated or pickled, and the metal plating layer 110 may be formed thereon, and the resin coating 100 may be formed on the metal plating layer 110. Furthermore, when the metal pipe for oil well use 1 has the metal plating layer 110, the metal pipe for oil well use 1 may further have a metal plating layer 110 that has been subjected to blasting or pickling, and a resin coating 100 thereon.

[0096] [Chemical Composition of Pipe 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 steel, etc. That is, the pipe body 10 may be a steel pipe made of an Fe-based alloy, or an alloy pipe represented by a Ni-based alloy pipe. Here, examples of steel pipes include low-alloy steel pipes, martensitic stainless steel pipes, ferritic stainless steel pipes, austenitic stainless steel pipes, and duplex stainless steel pipes. Examples of alloy pipes include Ni-based alloy pipes and NiCrFe alloy pipes.

[0097] Among alloy steels, high alloy steels such as Ni alloys and duplex stainless steels containing alloying elements such as Cr, Ni, and Mo have high corrosion resistance. Therefore, if these high alloy steels are used for the pipe body 10, excellent corrosion resistance can be obtained in a corrosive environment containing hydrogen sulfide, carbon dioxide, etc.

[0098] [Manufacturing Method] Hereinafter, a manufacturing method of the metal oil well pipe 1 according to this embodiment will be described.

[0099] The method for manufacturing the metal oil well pipe 1 according to this embodiment includes a preparation step, a composition application step, and a composition hardening step.

[0100] [Preparation Step] 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.

[0101] [Composition Application Process] In the composition application process, a composition containing unreacted epoxy resin, an epoxy resin curing agent, and an organic carboxylic acid is applied to at least one of the pin contact surface 400 and the box contact surface 500, the metal plating layer 110 formed by a process described below, or the chemical conversion coating layer 120 formed by a process described below. The composition is a composition for forming the resin coating 100 described above. The composition contains unreacted epoxy resin, an epoxy resin curing agent, and an organic carboxylic acid. Note that, in this specification, "unreacted epoxy resin" refers to a monomer, oligomer, prepolymer, or mixture thereof having multiple unreacted epoxy groups in each molecule. In addition to the unreacted epoxy resin, epoxy resin curing agent, and organic carboxylic acid, the composition may also contain a solvent. Note that the composition for forming the resin coating 100, excluding the solvent, has the same composition as the resin coating 100 described above. The epoxy resin curing agent is not particularly limited, and well-known curing agents can be used depending on the type of epoxy resin.

[0102] The composition is produced by dissolving or dispersing unreacted epoxy resin, an epoxy resin curing agent, and an organic carboxylic acid 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 100% by mass, where the total of all components other than the solvent is 100% by mass.

[0103] The method for applying the composition to at least one of the pin contact surface 400 and the box contact surface 500 is not particularly limited, and may be a well-known method. For example, the composition in a solution state may be applied to at least one of the pin contact surface 400 and 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 normal pressure. The method for applying the composition to at least one of the pin contact surface 400 and the box contact surface 500 may be brush application, dipping, or the like instead of spray application.

[0104] [Composition Curing Step] In the composition curing step, the applied composition is cured to form the resin coating 100. The conditions for the curing process are well known. The time required for complete curing varies depending on the composition, particularly the type of curing agent and the coating thickness. For example, when a room temperature, short-time curing type curing agent is used and the content of unreacted epoxy resin in the composition is approximately 30% by mass, the time required for complete curing is 3 to 16 hours at 5 to 30°C, or 5 to 180 minutes at 30 to 70°C. For example, when a high-temperature curing type curing agent is used, the time required for complete curing is 0.5 to 2 hours at 50 to 100°C to suppress heat generation due to the curing reaction, followed by 1 to 4 hours at 150 to 240°C.

[0105] Here, when the organic carboxylic acid contained in the composition is a dicarboxylic acid, a low heat treatment temperature in the curing step is preferable. If the organic carboxylic acid is a dicarboxylic acid and the heat treatment temperature is too high, curing by crosslinking will proceed too much, and the formed resin coating 100 will become too hard. Therefore, when the organic carboxylic acid is a dicarboxylic acid, the heat treatment temperature is preferably 100°C or less, for example.

[0106] By the above-described manufacturing method, the metal oil well pipe 1 according to this embodiment can be manufactured.

[0107] [Other Steps] The manufacturing process of the metal oil well pipe 1 according to this embodiment may include other steps, such as one or more steps selected from the group consisting of a blasting step, a pickling step, a metal plating step, and a chemical conversion treatment step.

[0108] [Blasting Process] The method for manufacturing the metal oil well pipe 1 according to this embodiment may further include a blasting process prior to the composition application process. In this embodiment, the blasting process is, for example, a process in which particles are collided using a blasting device. The blasting process is, for example, sandblasting. The sandblasting process is a process in which a blasting material (abrasive) is mixed with compressed air and projected. The blasting material is, for example, spherical shot material and angular grit material. The sandblasting process can increase the surface roughness of the contact surfaces 400, 500 and the surface of the metal plating layer 110.

[0109] In this embodiment, the sandblasting process can be performed by a well-known method. For example, in the sandblasting process, air is compressed with a compressor and the compressed air is mixed with a blasting material. The blasting material may be made of stainless steel, aluminum, ceramic, alumina, or the like. In addition, the conditions of the sandblasting process, such as the projection speed, can be set appropriately.

[0110] [Pickling Treatment Step] The method for manufacturing the metal oil well pipe 1 according to this embodiment may further include a pickling treatment step before the composition application step. In this embodiment, the pickling treatment step refers to a treatment of roughening the surface by immersion in a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid, or hydrofluoric acid. In other words, immersing the contact surfaces 400, 500 and the surface of the metal plating layer 110 in a strong acid solution can increase the surface roughness of these surfaces.

[0111] [Metal Plating Step] The method for producing the metal oil well pipe 1 according to this embodiment may further include a metal plating step prior to the composition application step. The metal plating layer 110 can be formed by, for example, electroplating or impact plating.

[0112] [Electroplating Process] In the present embodiment, the electroplating process is a process of forming the metal plating layer 110 by electroplating. As described above, the metal plating layer 110 is, for example, a single-layer plating layer of Cu, Sn, or Ni metal, a single-layer plating layer of a Zn—Ni alloy, a Cu—Sn alloy, or a Cu—Sn—Zn alloy, a two-layer plating layer of a Cu layer and an Sn layer, a three-layer plating layer of a Ni layer, a Cu layer, and an Sn layer, or a multi-layer plating layer that combines the above single-layer plating layers.

[0113] The electroplating process can be performed by a known method. For example, a plating bath containing ions of the metal elements contained in the alloy plating is prepared. Next, at least one of the contact surfaces 400, 500 is immersed in the plating bath. Further, a current is passed through at least one of the contact surfaces 400, 500 to form the metal plating layer 110 on at least one of the contact surfaces 400, 500. The conditions, such as the temperature of the plating bath and the plating time, can be set as appropriate.

[0114] More specifically, for example, when a Cu—Sn—Zn alloy plating layer is formed, the plating bath contains copper ions, tin ions, and zinc ions. In this case, the plating bath preferably has a composition of Cu: 1 to 50 g / L, Sn: 1 to 50 g / L, and Zn: 1 to 50 g / L. The electroplating conditions are, for example, plating bath pH: 1 to 10, plating bath temperature: 60° C., and current density: 1 to 100 A / dm ２ The treatment time is 0.1 to 30 minutes.

[0115] Similarly, for example, when forming a Zn—Ni alloy plating layer, the plating bath contains zinc ions and nickel ions. In this case, the plating bath preferably has a composition of Zn: 1 to 100 g / L and Ni: 1 to 50 g / L. The electroplating conditions are, for example, plating bath pH: 1 to 10, plating bath temperature: 60° C., current density: 1 to 100 A / dm ２ The treatment time is 0.1 to 30 minutes.

[0116] [Impact Plating] Impact plating is a treatment that can be carried out by mechanical plating, in which particles collide with the object to be plated in a rotating barrel, or projection plating, in which particles are collided with the object to be plated using a blasting device.

[0117] [Chemical Conversion Treatment Step] The method for manufacturing the metal oil well pipe 1 according to this embodiment may include a chemical conversion treatment step prior to the composition application step. In the chemical conversion treatment step, a chemical conversion treatment is performed to form the chemical conversion treatment layer 120.

[0118] In this embodiment, the chemical conversion treatment can be performed using a known method. A typical chemical conversion treatment solution can be used. For example, a zinc phosphate-based chemical conversion treatment solution containing 1 to 150 g / L of phosphate ions, 3 to 70 g / L of zinc ions, 1 to 100 g / L of nitrate ions, and 0 to 30 g / L of nickel ions can be used. Alternatively, a manganese phosphate-based chemical conversion treatment solution can be used. Alternatively, a chromate treatment solution can be used. Other chemical conversion treatment solutions can be used depending on the desired chemical conversion treatment layer 120. The temperature of the treatment solution is, for example, room temperature to 100°C. The treatment time for the chemical conversion treatment can be appropriately set depending on the desired film thickness, for example, 15 minutes. When forming a phosphate conversion treatment layer, surface conditioning may be performed before the phosphate conversion treatment to promote the formation of the chemical conversion treatment layer. Surface conditioning refers to a treatment in which the substrate is immersed in a surface conditioning aqueous solution containing colloidal titanium. After the phosphate conversion treatment, it is preferable to rinse with water or hot water and then dry.

[0119] The oil well metal pipe 1 according to this embodiment is manufactured by the above-described steps. However, the above-described manufacturing method is only one example of the manufacturing method of the oil well metal pipe 1 according to this embodiment, and the manufacturing method is not limited to this. The oil well metal pipe 1 according to this embodiment may be manufactured by other methods.

[0120] 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.

[0121] A commercially available cold-rolled steel sheet was used for the main body of an oil well metal pipe. The cold-rolled steel sheet had a length of 150 mm and a width of 70 mm. The steel type was SPCC steel as specified in JIS G 3141 (2021).

[0122] [Composition Application Step] A composition was applied to the surface of a cold-rolled steel sheet. The composition contained unreacted epoxy resin, a room-temperature curing type curing agent, and an organic carboxylic acid shown in Table 1. In Table 1, the "Compound Name" column shows the compound name of the organic carboxylic acid contained. Test No. 1, for which "-" is written in the "Compound Name" column, did not contain an organic carboxylic acid in the composition. In addition, in Table 1, the "Content (mass %)" column shows the content of the organic carboxylic acid in mass %. The compositions of Test Nos. 1 to 29 contained water as a solvent in addition to the unreacted epoxy resin, the room-temperature curing type curing agent, and the organic carboxylic acid.

[0123]

[0124] [Composition curing step] The composition of each test number was thermally cured. Specifically, the cold-rolled steel sheet coated with the composition was placed in a heating furnace, heated at 50°C for 3 to 10 minutes, and then left to stand at room temperature for 24 hours. This formed a resin coating.

[0125] [Bowden sliding test] A Bowden sliding test was performed on the cold-rolled steel sheets of each test number on which a resin coating had been formed, under the following conditions. The number of sliding movements where no seizure occurred and the friction coefficient (μ) was in the range of 0.25 or more and less than 0.40 was counted. Note that one reciprocal sliding movement was counted as one sliding movement. The sliding distance (m) was calculated by multiplying the obtained number of sliding movements by twice the sliding width. The results are shown in Table 1. The changes in the friction coefficient during the test for test numbers 1 and 21 are also shown in Figure 1. Steel ball: 3 / 16" SUJ2 Load: 3 kgf Sliding width: 10 mm or 14 mm Sliding speed: 4 mm / s Lubricating oil: none (unoiled) Test temperature: room temperature (25°C)

[0126] [Evaluation Results] Referring to Table 1 and Figure 1, the resin coatings of test numbers 2 to 29 contained an epoxy resin and an organic carboxylic acid. As a result, the sliding distance at which the friction coefficient was 0.25 or more and less than 0.40 was 2.00 m or more. It was found that the resin coatings of test numbers 2 to 29 improved the seizure resistance of the metal oil well pipes, and furthermore, were able to maintain the resistance to loosening of the threaded joints even when the threads were repeatedly tightened and loosened.

[0127] On the other hand, the resin coating of Test No. 1 contained an epoxy resin but no organic carboxylic acid. As a result, the sliding distance at a friction coefficient of 0.25 or more and less than 0.40 was less than 2.00 m. It was found that the resin coating of Test No. 1 was unable to maintain the resistance to loosening of the threaded joint when the screw was repeatedly tightened and loosened.

[0128] 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.

[0129] REFERENCE SIGNS LIST 1 Metal pipe for oil well 10 Pipe body 10A First end 10B Second end 11 Pin pipe body 12 Coupling 40 Pin 41 Male threaded portion 42 Pin seal surface 43 Pin shoulder surface 50 Box 51 Female threaded portion 52 Box seal surface 53 Box shoulder surface 100 Resin coating 110 Metal plating layer 120 Chemical conversion coating layer 400 Pin contact surface 500 Box contact surface

Claims

1. A metal pipe for oil wells, comprising a pipe body including a first end portion and a second end portion, wherein the pipe body includes a pin formed at the first end portion, and a box formed at the second end portion, wherein the pin includes a pin contact surface including a male threaded portion, and the box includes a box contact surface including a female threaded portion, wherein the metal pipe for oil wells further comprises a resin coating formed as at least the outermost layer of at least one of the pin contact surface and the box contact surface, wherein the resin coating includes an epoxy resin, and an organic carboxylic acid, a metal pipe for oil wells.

2. The metal pipe for oil wells according to Claim 1, wherein the organic carboxylic acid is an aliphatic carboxylic acid, a metal pipe for oil wells.

3. The metal pipe for oil wells according to Claim 1, wherein the organic carboxylic acid has 5 or more carbon atoms, a metal pipe for oil wells.

4. The metal pipe for oil wells according to Claim 1, wherein the organic carboxylic acid has 10 or less carbon atoms, a metal pipe for oil wells.

5. The metal pipe for oil wells according to Claim 1, wherein the organic carboxylic acid is a monocarboxylic acid, a metal pipe for oil wells.

6. The metal pipe for oil wells according to Claim 1, wherein the organic carboxylic acid has a branched chain hydrocarbon group, a metal pipe for oil wells.

7. The metal pipe for oil wells according to Claim 1, wherein the organic carboxylic acid 2,2-Dimethylpropanoic acid, 3,5,5-Trimethylhexanoic acid, 2-Ethylhexanoic acid, 2-Ethyl-2,3-dimethylhexanoic acid, 2-Ethyl-2,4-dimethylhexanoic acid, 2-Ethyl-2,5-dimethylhexanoic acid, 2-Ethyl-3,4-dimethylhexanoic acid, 2-Ethyl-3,5-dimethylhexanoic acid, 2-Ethyl-4,5-dimethylhexanoic acid, 2-Ethyl-3,3-dimethylhexanoic acid, 2-Ethyl-4,4-dimethylhexanoic acid, 2-Ethyl-5,5-dimethylhexanoic acid, 3-Ethyl-2,3-dimethylhexanoic acid, 3-Ethyl-2,4-dimethylhexanoic acid, 3-Ethyl-2,5-dimethylhexanoic acid, 3-Ethyl-3,4-dimethylhexanoic acid, 3-Ethyl-3,5-dimethylhexanoic acid, 3-Ethyl-4,5-dimethylhexanoic acid, 3-Ethyl-2,2-dimethylhexanoic acid, 3-Ethyl-4,4-dimethylhexanoic acid, 3-Ethyl-5,5-dimethylhexanoic acid, 4-Ethyl-2,3-dimethylhexanoic acid, 4-Ethyl-2,4-dimethylhexanoic acid, 4-Ethyl-2,5-dimethylhexanoic acid, 4-Ethyl-3,4-dimethylhexanoic acid, 4-Ethyl-3,5-dimethylhexanoic acid, 4-Ethyl-4,5-dimethylhexanoic acid, 4-Ethyl-2,2-dimethylhexanoic acid, 4-Ethyl-3,3-dimethylhexanoic acid, 4-Ethyl-5,5-dimethylhexanoic acid, 2-Ethyl-2-methylheptanoic acid, 3-Ethyl-3-methylheptanoic acid, 4-Ethyl-4-methylheptanoic acid, 5-Ethyl-5-methylheptanoic acid, 2,2-Dimethyloctanoic acid, 3,3-Dimethyloctanoic acid, 4,4-Dimethyloctanoic acid, 5,5-Dimethyloctanoic acid, 6,6-Dimethyloctanoic acid, 7,7-Dimethyloctanoic acid, 2,3-Dimethyloctanoic acid, 2,4-Dimethyloctanoic acid, 2,5-Dimethyloctanoic acid, 2,6-Dimethyloctanoic acid, 2,7-Dimethyloctanoic acid, 3,4-Dimethyloctanoic acid, 3,5-Dimethyloctanoic acid, 3,6-Dimethyloctanoic acid, 3,7-Dimethyloctanoic acid, 4,5-Dimethyloctanoic acid, 4,6-Dimethyloctanoic acid, 4,7-Dimethyloctanoic acid, 5,6-Dimethyloctanoic acid, 5,7-Dimethyloctanoic acid, 6,7-Dimethyloctanoic acid, Octanoic acid, Nonanoic acid, Decanoic acid, 2,2,3,5-Tetramethylhexanoic acid, and 2,One or more selected from the group consisting of 4-dimethyl-2-isopropylpentanoic acid a metal pipe for oil wells.

8. The metal pipe for oil wells according to any one of Claims 1 to 7, further comprising at least one selected from the group consisting of a metal plating layer and a chemical conversion treatment layer between at least one of the pin contact surface and the box contact surface and the resin coating, a metal pipe for oil wells.