Metal pipe for oil well

Abstract

Provided is a metal pipe for oil wells, which has excellent wear resistance and is capable of maintaining the resistance to loosening of a threaded joint even when screwing and unscrewing are performed repeatedly. This oil well metal pipe (1) is provided with a pipe body (10) comprising a first end (10A) and a second end (10B). The pipe main body (10) is provided with: a pin part (40) formed at the first end part (10A); and a female buckle part (50) formed on the second end part (10B). The pin portion (40) has a pin portion contact surface (400) including a male thread portion (41). The female portion (50) has a female portion contact surface (500) including an internally threaded portion (51). The oil well metal pipe (1) is further provided with a resin film (100) which is formed as the uppermost layer of the pin contact surface (400) and / or the box contact surface (500). The resin coating (100) contains an epoxy resin and an organic carboxylic acid.

Description

Technical Field

[0001] The present disclosure relates to metal pipes for oil wells. Background Art

[0002] Metal pipes for oil wells 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 an oil well production site, a plurality of metal pipes for oil wells are connected to form an oil well pipe connection body represented by a casing and an oil pipe. The oil well pipe connection body is formed by screwing together the threaded joints formed on the metal pipes for oil wells. There are cases where inspections are carried out on the oil well pipe connection body. In the case of carrying out an inspection, the oil well pipe connection body is lifted and unscrewed. And, the metal pipes for oil wells are detached from the oil well pipe connection body by unscrewing, and inspected. After the inspection, the threaded joints of the metal pipes for oil wells are screwed together again and reused as part of the oil well pipe connection body.

[0003] The threaded joint formed on the metal pipe for oil wells includes a male thread portion and a female thread portion. The male thread portion has a male thread portion contact surface including an external thread portion on the outer peripheral surface of the end of the metal pipe for oil wells. The female thread portion has a female thread portion contact surface including an internal thread portion on the inner peripheral surface of the end of the metal pipe for oil wells. In this specification, the external thread portion and the internal thread portion are also collectively referred to as "thread portions". In this specification, the male thread portion contact surface and the female thread portion contact surface are also collectively referred to as "contact surfaces". The male thread portion contact surface also includes a case where there is a non-male thread portion threaded metal contact portion including a male thread portion sealing surface and a male thread portion shoulder surface. Similarly, the female thread portion contact surface also includes a case where there is a non-female thread portion threaded metal contact portion including a female thread portion sealing surface and a female thread portion shoulder surface.

[0004] The contact surface is repeatedly subjected to strong friction during the screwing and unscrewing of the threaded joint formed on the metal pipe for oil wells. Therefore, when the screwing and unscrewing are repeatedly carried out, the contact surface is liable to develop galling (irreparable wear). Thus, sufficient durability against friction, i.e., excellent abrasion resistance, is required for the metal pipes for oil wells.

[0005] Conventionally, in order to improve the abrasion resistance of metal pipes for oil wells, a composite grease incorporating heavy metal powder, called a dopant, has been used. By applying the composite grease to the contact surface, the abrasion resistance of the metal pipes for oil wells can be improved. However, there is a possibility that heavy metal powders such as Pb, Zn, and Cu contained in the composite grease may have an impact on the environment. Therefore, it is desired to develop metal pipes for oil wells that have excellent abrasion resistance even without using the composite grease.

[0006] Techniques for improving the wear resistance of metal pipes for oil wells are proposed, for example, in Japanese Patent Application Laid-Open No. 2002-348587 (Patent Document 1) and International Publication No. 2006 / 104251 (Patent Document 2).

[0007] In the metal pipe for oil wells disclosed in Patent Document 1, a solid lubricating coating film composed of a lubricating powder and an adhesive is formed on the contact surface of at least one of the male thread portion and the female thread portion. The lubricating powder is composed of one or two selected from molybdenum disulfide powder and tungsten disulfide powder and graphite powder. The graphite powder accounts for 2 to 20% by mass of the lubricating powder. It is disclosed in Patent Document 1 that this metal pipe for oil wells can improve the wear resistance of the metal pipe for oil wells.

[0008] The metal pipe for oil wells disclosed in Patent Document 2 is characterized in that it has a viscous liquid or semi-solid lubricating coating film on the contact surface of at least one of the male thread portion and the female thread portion and a dry solid coating film formed thereon. It is disclosed in Patent Document 2 that this metal pipe for oil wells inhibits rusting and improves wear resistance and airtightness even without using a compound grease.

[0009] Prior Art Documents

[0010] Patent Documents

[0011] Patent Document 1: Japanese Patent Application Laid-Open No. 2002-348587

[0012] Patent Document 2: International Publication No. 2006 / 104251 Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] However, if the threaded joint becomes loose, the airtightness of the threaded joint may be reduced. Therefore, a threaded joint that not only has excellent wear resistance but is also not easily loosened is sought. In addition, as described above, for inspection, the threaded joint is repeatedly tightened and loosened. Preferably, even when the threaded joint is repeatedly tightened and loosened, the non-loosening property of the threaded joint can be maintained.

[0015] According to the techniques disclosed in Patent Document 1 and Patent Document 2, the wear resistance of the metal pipe for oil wells can be improved. However, in Patent Document 1 and Patent Document 2, no research has been conducted on achieving both wear resistance and non-loosening property of the threaded joint.

[0016] An object of the present disclosure is to provide a metal pipe for oil wells that has excellent wear resistance and can maintain the non-loosening property of the threaded joint even when the threaded joint is repeatedly tightened and loosened.

[0017] Solution for Solving Problems

[0018] The metal pipe for oil wells of the present disclosure includes a pipe body having a first end and a second end,

[0019] The pipe body includes:

[0020] A male thread portion formed at the first end; and

[0021] A female thread portion formed at the second end,

[0022] The male thread portion has a male thread portion contact surface including an external thread portion,

[0023] The female thread portion has a female thread portion contact surface including an internal thread portion,

[0024] The metal pipe for oil wells further includes a resin coating film formed as the outermost layer of at least one of the male thread portion contact surface and the female thread portion contact surface,

[0025] The resin coating film contains epoxy resin and organic carboxylic acid.

[0026] Effects of the Invention

[0027] The metal pipe for oil wells of the present disclosure has excellent wear resistance, and can maintain the non-loosening property of the threaded joint even when the thread tightening and thread loosening are repeated. Brief Description of the Drawings

[0028] Figure 1 It is a graph showing the results of the Bowden test of the resin coating film containing epoxy resin.

[0029] Figure 2 It is a side view of the metal pipe for oil wells of the present embodiment.

[0030] Figure 3 It shows Figure 2 A partial cross-sectional view (longitudinal cross-section) of the coupling of the metal pipe for oil wells shown, parallel to the pipe axis direction.

[0031] Figure 4 It is Figure 3 A cross-sectional view parallel to the pipe axis direction of a portion near the male thread portion in the metal pipe for oil wells shown.

[0032] Figure 5 It is Figure 3 A cross-sectional view parallel to the pipe axis direction of a portion near the female thread portion in the metal pipe for oil wells shown.

[0033] Figure 6 It is related to Figure 2Partial cross-sectional view of the longitudinal section of the metal pipe for oil wells according to this embodiment with different other structures.

[0034] Figure 7 Partial cross-sectional view of the longitudinal section of the integral type metal pipe for oil wells according to this embodiment.

[0035] Figure 8 Cross-sectional view near the contact surface of the male thread portion of the metal pipe for oil wells according to this embodiment.

[0036] Figure 9 It is Figure 8 Cross-sectional view near the contact surface of the corresponding female thread portion.

[0037] Figure 10 It is Figure 8 Enlarged view of the contact surface of the male thread portion of this embodiment, which is different from

[0038] Figure 11 It is Figure 10 Cross-sectional view near the contact surface of the corresponding female thread portion.

[0039] Figure 12 It is Figure 8 and Figure 10 Enlarged view of the contact surface of the male thread portion of this embodiment, which is different from

[0040] Figure 13 It is Figure 12 Cross-sectional view near the contact surface of the corresponding female thread portion. Detailed implementation mode

[0041] Hereinafter, this embodiment will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals and will not be described repeatedly.

[0042] The inventors of the present invention have studied a method for achieving both excellent wear resistance and non-loosening property of the metal pipe for oil wells. As a result, the following insights have been obtained.

[0043] It is known that in the contact between metals, when the friction coefficient is greater than 0.4, for example, it becomes very easy to wear. If the friction coefficient of the contact surface is low, wear can be suppressed. For example, when using general API doping, the friction coefficient of the contact surface becomes about 0.05 to 0.20. In this case, wear of the contact surface is suppressed. In previous studies, as a method for improving wear resistance, a method of reducing the friction coefficient of the contact surface has been proposed.

[0044] If the coefficient of friction of the contact surface is low, the contact surfaces of the male fitting part and the female fitting part are liable to slide. In this case, the thread is liable to rotate in both the direction of thread tightening and the direction of thread loosening. The inventors considered that, even if the wear resistance is improved only by reducing the coefficient of friction of the contact surface, the thread is liable to become loose. The inventors considered that if the coefficient of friction of the contact surface can be maintained at a level low enough to improve the wear resistance and high enough to prevent the thread from becoming loose, excellent wear resistance and resistance to thread loosening can be achieved concurrently. Therefore, the inventors studied a method for maintaining the coefficient of friction of the contact surface within a range that improves the wear resistance of the threaded joint and prevents the threaded joint from becoming loose.

[0045] As a method for adjusting the coefficient of friction of the contact surface, a method of adjusting the coefficient of friction of the contact surface itself and a method of forming a coating film on the contact surface and adjusting the coefficient of friction of the coating film are conceivable. The contact surface includes a threaded portion. The threaded portion has a complex shape in which thread teeth and thread grooves are alternately arranged along the axial direction of the oil well metal pipe. Considering industrial production, it can be considered difficult to adjust the coefficient of friction of the contact surface itself including the threaded portion having a complex shape. Therefore, the inventors studied a method of forming a coating film on the contact surface and adjusting the coefficient of friction of the coating film.

[0046] As the coating film formed on the contact surface, a resin coating film is known. The inventors considered that if an appropriate resin is contained in the resin coating film, the coefficient of friction of the resin coating film can be adjusted to a range that improves the wear resistance and prevents the thread from becoming loose.

[0047] The inventors first studied the resin contained in the resin coating film. The inventors considered that if the resin coating film contains a resin having a high adhesiveness to metal, peeling of the resin coating film can be suppressed even if a shearing force is generated due to thread tightening. If peeling of the resin coating film can be suppressed, the coefficient of friction of the contact surface can be easily adjusted even if thread tightening and thread loosening are repeated. Therefore, the inventors studied a resin having a high adhesiveness to metal. As a result, the following insights were obtained.

[0048] Epoxy resin is a thermosetting synthetic resin having reactive epoxy groups at the ends of the molecular chains. A representative epoxy resin is bisphenol A type epoxy resin. Bisphenol A type epoxy resin has secondary hydroxyl groups in the repeating unit. Epoxy resin has a higher adhesiveness to metal compared with other resins. The reason why epoxy resin has a high adhesiveness to metal is not determined, but the following two reasons are conceivable. (1) Hydrogen bonding occurs between the hydroxyl groups in the epoxy resin and the hydroxyl groups on the metal surface. (2) For the adhesiveness to iron and zinc, the phenoxy group is related to the adhesive interface.

[0049] The inventors believe that: If the resin coating film contains epoxy resin, even if screwing and unscrewing of the thread are repeated, peeling of the resin coating film can be suppressed, and the friction coefficient can be easily adjusted. Therefore, the inventors have studied a method for adjusting the friction coefficient of a resin coating film containing epoxy resin. Specifically, various additives were added to the resin coating film containing epoxy resin, and the friction coefficient was investigated. As a result, by making the resin coating film containing epoxy resin contain an organic carboxylic acid, the abrasion resistance can be improved and it can be adjusted to a range where the thread is not easily loosened, and a different view from the past has been obtained.

[0050] Figure 1 It is a graph showing the results of the Bowden test of a resin coating film containing epoxy resin. Figure 1 It is obtained through the examples described later. In Figure 1 the horizontal axis represents the sliding distance (m). In Figure 1 the vertical axis represents the friction coefficient (μ). In Figure 1 Test No. 1 is a graph showing the results of the Bowden test of a steel plate having a resin coating film containing epoxy resin and not containing an organic carboxylic acid. Test No. 21 is a graph showing the results of the Bowden test of a steel plate having a resin coating film containing epoxy resin and an organic carboxylic acid.

[0051] As described above, if the friction coefficient is greater than 0.40, the threaded joint is likely to wear. 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 likely to loosen. Therefore, the range of the friction coefficient of 0.25 to 0.40 can be said to be the range of the friction coefficient that improves the abrasion resistance of the threaded joint and the threaded joint is not easily loosened. That is to say, it can be said that in the Bowden test, if the sliding distance at a friction coefficient in the range of 0.25 to 0.40 is long, it has excellent abrasion resistance, and even if screwing and unscrewing of the thread are repeated, the non-loosening property of the threaded joint can be maintained.

[0052] Referring to Figure 1 , in the graph of Test No. 21, compared with the graph of Test No. 1, the sliding distance at a friction coefficient in the range of 0.25 to 0.40 is long. This means that the oil well metal pipe having the resin coating film of Test No. 21 can achieve both excellent abrasion resistance and non-loosening property. The resin coating film of Test No. 21 contains epoxy resin and an organic carboxylic acid. On the other hand, the resin coating film of Test No. 1 contains epoxy resin but does not contain an organic carboxylic acid. That is to say, if it is a resin coating film containing epoxy resin and an organic carboxylic acid, it can achieve both excellent abrasion resistance and non-loosening property of the oil well metal pipe, and even if screwing and unscrewing of the thread are repeated, the non-loosening property of the threaded joint can be maintained for a long time.

[0053] A resin coating film containing an epoxy resin and an organic carboxylic acid can improve the wear resistance of a threaded joint, and can maintain the non-loosening property of the threaded joint even when the thread tightening and thread loosening are repeated, but the reason is not certain. However, the following possibilities can be considered. In the coexistence of an epoxy resin and an organic carboxylic acid, under the action of sliding heat during thread tightening or thread loosening, the carboxyl group of the organic carboxylic acid combines with the epoxy group in the epoxy resin through an addition reaction. The combination of the epoxy resin and the organic carboxylic acid plays the following roles. The OH groups contained in the epoxy resin chain of the combination are hydrogen-bonded to the OH groups on the threaded metal surface, moderately suppressing the peeling of the resin coating film from the threaded surface and the loosening of the thread. The hydrocarbon chain of the organic carboxylic acid at the molecular chain end of the combination has lubricating ability for the metal, thus improving the wear resistance.

[0054] Although the above reasons are speculative, the following examples prove that: for a resin coating film containing an epoxy resin and an organic carboxylic acid, it can improve the wear resistance of a metal pipe for oil wells, and can maintain the non-loosening property of the threaded joint even when the thread tightening and thread loosening are repeated.

[0055] The gist of the metal pipe for oil wells of the present embodiment completed based on the above insights is as follows.

[0056] [1] A metal pipe for oil wells, which includes a pipe body having a first end and a second end, the pipe body including: a male thread portion formed at the first end; and a female thread portion formed at the second end, the male thread portion having a male thread portion contact surface including an external thread portion, the female thread portion having a female thread portion contact surface including an internal thread portion, and the metal pipe for oil wells further includes a resin coating film formed as the outermost layer of at least one of the male thread portion contact surface and the female thread portion contact surface, the resin coating film containing an epoxy resin and an organic carboxylic acid.

[0057] [2] The metal pipe for oil wells according to [1], wherein the organic carboxylic acid is an aliphatic carboxylic acid.

[0058] [3] The metal pipe for oil wells according to [1] or [2], wherein the organic carboxylic acid has 5 or more carbon atoms.

[0059] [4] The metal pipe for oil wells according to any one of [1] to [3], wherein the organic carboxylic acid has 10 or less carbon atoms.

[0060] [5] The metal pipe for oil wells according to any one of [1] to [4], wherein the organic carboxylic acid is a monocarboxylic acid.

[0061] [6] The metal pipe for oil wells according to any one of [1] to [5], wherein the organic carboxylic acid has a branched chain hydrocarbon group.

[0062] [7] The metal pipe for oil wells according to any one of [1] to [6], wherein the organic carboxylic acid is selected from the group consisting of 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 2,4-dimethyl-2-isopropylpentanoic acid, and is one or more.

[0063] [8] The metal pipe for oil wells according to any one of [1] to [7], wherein at least one of the male thread contact surface and the female thread contact surface further has one or more selected from the group consisting of a metal coating layer and a chemical conversion treatment layer between the resin coating film.

[0064] Hereinafter, the metal pipe for oil wells of the present embodiment will be described in detail.

[0065] [Structure of Metal Pipe for Oil Well]

[0066] First, the structure of the metal pipe for oil well of the present embodiment will be described. The metal pipe for oil well has a well-known structure. There are T&C type metal pipes for oil well and integral type metal pipes for oil well. Hereinafter, each type of metal pipe for oil well will be discussed in detail.

[0067] [When the Metal Pipe for Oil Well is of T&C Type]

[0068] Figure 2 is a side view showing the metal pipe 1 for oil well of the present embodiment. Figure 2 is a side view of the so-called T&C (Threaded and Coupled) type metal pipe 1 for oil well. Refer to Figure 2 , the metal pipe 1 for oil well includes a pipe body 10.

[0069] The pipe body 10 extends in the pipe axis direction. The 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 on the opposite side of the second end portion 10B. In Figure 2 the T&C type metal pipe 1 for oil well shown, the pipe body 10 includes a male-threaded portion pipe body 11 and a coupling 12. The coupling 12 is installed at one end of the male-threaded portion pipe body 11. More specifically, the coupling 12 is fastened to one end of the male-threaded portion pipe body 11 by threads.

[0070] Figure 3 is showing Figure 2 a partial cross-sectional view (longitudinal cross-section) parallel to the pipe axis direction of the coupling 12 of the metal pipe 1 for oil well shown. Refer to Figure 2 and Figure 3 , the pipe body 10 includes a male-threaded portion 40 and a female-threaded portion 50. The male-threaded portion 40 is formed at the first end portion 10A of the pipe body 10. At the time of fastening, the male-threaded portion 40 is inserted into the female-threaded portion 50 of another metal pipe 1 for oil well (not shown) and fastened to the female-threaded portion 50 of the other metal pipe 1 by threads.

[0071] The female-threaded portion 50 is formed at the second end portion 10B of the pipe body 10. At the time of fastening, the male-threaded portion 40 of another metal pipe 1 is inserted into the female-threaded portion 50 and fastened to the male-threaded portion 40 of the other metal pipe 1 by threads.

[0072] [Structure of Male-Threaded Portion]

[0073] Figure 4 is Figure 3 a cross-sectional view parallel to the pipe axis direction of a portion near the male-threaded portion 40 in the metal pipe 1 for oil well shown. Figure 4The dashed line portion in [Figure] shows the structure of the female thread portion 50 of the other metal pipe 1 for oil wells in the case of being fastened to the other metal pipe 1 for oil wells. Refer to Figure 4 , the male thread portion 40 includes a male thread portion contact surface 400 on the outer peripheral surface of the first end portion 10A of the pipe body 10. When fastening to the other metal pipe 1 for oil wells, the male thread portion 40 is screwed into the female thread portion 50 of the other metal pipe 1 for oil wells, and the male thread portion contact surface 400 contacts the female thread portion contact surface 500 (described later) of the female thread portion 50.

[0074] The male thread portion contact surface 400 at least includes an external thread portion 41 formed on the outer peripheral surface of the first end portion 10A. Optionally, the male thread portion contact surface 400 may further include a male thread portion sealing surface 42 and a male thread portion shoulder surface 43. In Figure 4 , the male thread portion shoulder surface 43 is disposed on the top surface of the first end portion 10A, and the male thread portion sealing surface 42 is disposed at a position on the outer peripheral surface of the first end portion 10A that is closer to the top side of the first end portion 10A than the external thread portion 41. That is, the male thread portion sealing surface 42 is disposed between the external thread portion 41 and the male thread portion shoulder surface 43. The male thread portion sealing surface 42 is conical. Specifically, in the male thread portion sealing surface 42, in the length direction (pipe axis direction) of the first end portion 10A, the outer diameter gradually decreases as it goes from the external thread portion 41 toward the male thread portion shoulder surface 43.

[0075] When fastening to the other metal pipe 1 for oil wells, the male thread portion sealing surface 42 contacts the female thread portion sealing surface 52 (described later) of the female thread portion 50 of the other metal pipe 1 for oil wells. More specifically, during fastening, the male thread portion 40 is inserted into the female thread portion 50 of the other metal pipe 1 for oil wells, so that the male thread portion sealing surface 42 contacts the female thread portion sealing surface 52. Then, by further screwing the male thread portion 40 into the female thread portion 50 of the other metal pipe 1 for oil wells, the male thread portion sealing surface 42 and the female thread portion sealing surface 52 are brought into close contact. Thus, during fastening, the male thread portion sealing surface 42 and the female thread portion sealing surface 52 are brought into close contact to form a seal based on metal-metal contact. Therefore, in the mutually fastened metal pipes 1 for oil wells, the airtightness can be improved.

[0076] In Figure 4 , the male thread portion shoulder surface 43 is disposed on the top surface of the first end portion 10A. That is, in Figure 4In the male coupling portion 40 shown, an external thread portion 41, a male coupling portion sealing surface 42, and a male coupling portion shoulder surface 43 are arranged in sequence from the center of the pipe body 10 toward the first end portion 10A. When fastening with another metal pipe 1 for oil wells, the male coupling portion shoulder surface 43 faces and contacts the female coupling portion shoulder surface 53 (described later) of the female coupling portion 50 of the other metal pipe 1 for oil wells. More specifically, when fastening, the male coupling portion 40 is inserted into the female coupling portion 50 of the other metal pipe 1 for oil wells, so that the male coupling portion shoulder surface 43 contacts the female coupling portion shoulder surface 53. Thereby, a higher torque can be obtained during fastening. In addition, the positional relationship in the fastened state between the male coupling portion 40 and the female coupling portion 50 can be made stable.

[0077] In addition, the male coupling portion contact surface 400 of the male coupling portion 40 includes at least the external thread portion 41. That is to say, it may be that the male coupling portion contact surface 400 includes the external thread portion 41 and does not include the male coupling portion sealing surface 42 and the male coupling portion shoulder surface 43. It may be that the male coupling portion contact surface 400 includes the external thread portion 41 and the male coupling portion shoulder surface 43 and does not include the male coupling portion sealing surface 42. It may be that the male coupling portion contact surface 400 includes the external thread portion 41 and the male coupling portion sealing surface 42 and does not include the male coupling portion shoulder surface 43.

[0078] [Structure of female coupling portion]

[0079] Figure 5 is Figure 3 A cross-sectional view parallel to the pipe axis direction of a portion near the female coupling portion 50 in the metal pipe 1 for oil wells shown. Figure 5 The dotted line portion in shows the structure of the male coupling portion 40 of the other metal pipe 1 for oil wells in the case of fastening with the other metal pipe 1 for oil wells. Refer to Figure 5 , the female coupling portion 50 includes a female coupling portion contact surface 500 on the inner peripheral surface of the second end portion 10B of the pipe body 10. The female coupling portion contact surface 500 is for the male coupling portion 40 of the other metal pipe 1 for oil wells to be screwed in when fastening with the other metal pipe 1 for oil wells, and contacts the male coupling portion contact surface 400 of the male coupling portion 40.

[0080] The female coupling portion contact surface 500 includes at least an internal thread portion 51 formed on the inner peripheral surface of the second end portion 10B. When fastening, the internal thread portion 51 meshes with the external thread portion 41 of the male coupling portion 40 of the other metal pipe 1 for oil wells.

[0081] It may be that the female coupling portion contact surface 500 further includes a female coupling portion sealing surface 52 and a female coupling portion shoulder surface 53. In Figure 5In [the figure], the female coupling portion sealing surface 52 is disposed at a position on the inner circumferential surface of the second end portion 10B closer to the pipe body 10 than the internal thread portion 51. That is to say, the female coupling portion sealing surface 52 is disposed between the internal thread portion 51 and the female coupling portion shoulder surface 53. The female coupling portion sealing surface 52 is formed in a conical shape. Specifically, in the female coupling portion sealing surface 52, in the longitudinal direction (pipe axis direction) of the second end portion 10B, the inner diameter gradually decreases as it goes from the internal thread portion 51 toward the female coupling portion shoulder surface 53.

[0082] When fastening to another metal pipe 1 for oil wells, the female coupling portion sealing surface 52 contacts the male coupling portion sealing surface 42 of the male coupling portion 40 of the other metal pipe 1 for oil wells. More specifically, during fastening, by screwing the male coupling portion 40 of the other metal pipe 1 into the female coupling portion 50, the female coupling portion sealing surface 52 contacts the male coupling portion sealing surface 42, and by further screwing in, the female coupling portion sealing surface 52 is closely fitted with the male coupling portion sealing surface 42. Thereby, during fastening, the female coupling portion sealing surface 52 is closely fitted with the male coupling portion sealing surface 42 to form a seal based on metal-metal contact. Therefore, in the metal pipes 1 for oil wells that are fastened to each other, the airtightness can be improved.

[0083] The female coupling portion shoulder surface 53 is disposed at a position closer to the pipe body 10 than the female coupling portion sealing surface 52. That is to say, in the female coupling portion 50, the female coupling portion shoulder surface 53, the female coupling portion sealing surface 52, and the internal thread portion 51 are sequentially disposed from the center of the pipe body 10 toward the tip of the second end portion 10B. When fastening to another metal pipe 1 for oil wells, the female coupling portion shoulder surface 53 faces and contacts the male coupling portion shoulder surface 43 of the male coupling portion 40 of the other metal pipe 1. More specifically, during fastening, by inserting the male coupling portion 40 of the other metal pipe 1 into the female coupling portion 50, the female coupling portion shoulder surface 53 contacts the male coupling portion shoulder surface 43. Thereby, a higher torque can be obtained during fastening. In addition, the positional relationship in the fastened state between the male coupling portion 40 and the female coupling portion 50 can be stabilized.

[0084] The female coupling portion contact surface 500 includes at least the internal thread portion 51. During fastening, the internal thread portion 51 of the female coupling portion contact surface 500 of the female coupling portion 50 corresponds to and contacts the external thread portion 41 of the male coupling portion contact surface 400 of the male coupling portion 40. The female coupling portion sealing surface 52 corresponds to and contacts the male coupling portion sealing surface 42. The female coupling portion shoulder surface 53 corresponds to and contacts the male coupling portion shoulder surface 43.

[0085] When the male connection contact surface 400 includes the external thread portion 41 and does not include the male connection sealing surface 42 and the male connection shoulder surface 43, the female connection contact surface 500 includes the internal thread portion 51 and does not include the female connection sealing surface 52 and the female connection shoulder surface 53. When the male connection contact surface 400 includes the external thread portion 41 and the male connection shoulder surface 43 and does not include the male connection sealing surface 42, the female connection contact surface 500 includes the internal thread portion 51 and the female connection shoulder surface 53 and does not include the female connection sealing surface 52. When the male connection contact surface 400 includes the external thread portion 41 and the male connection sealing surface 42 and does not include the male connection shoulder surface 43, the female connection contact surface 500 includes the internal thread portion 51 and the female connection sealing surface 52 and does not include the female connection shoulder surface 53.

[0086] The male connection contact surface 400 may include a plurality of external thread portions 41, may include a plurality of male connection sealing surfaces 42, and may include a plurality of male connection shoulder surfaces 43. For example, it may also be that at the male connection contact surface 400 of the male connection 40, the male connection shoulder surface 43, the male connection sealing surface 42, the external thread portion 41, the male connection sealing surface 42, the male connection shoulder surface 43, the male connection sealing surface 42, and the external thread portion 41 are sequentially arranged from the top end of the first end portion 10A toward the center of the pipe body 10. In this case, at the female connection contact surface 500 of the female connection 50, the internal thread portion 51, the female connection sealing surface 52, the female connection shoulder surface 53, the female connection sealing surface 52, the internal thread portion 51, the female connection sealing surface 52, and the female connection shoulder surface 53 are sequentially arranged from the top end of the second end portion 10B toward the center of the pipe body 10.

[0087] In Figure 4 and Figure 5 shown is a so-called high-class joint in which the male connection 40 includes the external thread portion 41, the male connection sealing surface 42, and the male connection shoulder surface 43 and the female connection 50 includes the internal thread portion 51, the female connection sealing surface 52, and the female connection shoulder surface 53. However, it may also be that, as described above, the male connection 40 includes the external thread portion 41 and does not include the male connection sealing surface 42 and the male connection shoulder surface 43. In this case, the female connection 50 includes the internal thread portion 51 and does not include the female connection sealing surface 52 and the female connection shoulder surface 53. Figure 6 is a partial cross-sectional view including a longitudinal section of an oil well metal pipe of the present embodiment having a structure different from Figure 2 .

[0088] [When the oil well metal pipe is of an integral type]

[0089] Figure 2 , Figure 3 and Figure 6The metal pipe 1 for oil wells shown is a so-called T&C type metal pipe 1 for oil wells in which the pipe body 10 includes a male-threaded pipe body 11 and a coupling 12. However, the metal pipe 1 for oil wells in the present embodiment may not be of the T&C type but an integral type.

[0090] Figure 7 It is a partial cross-sectional view including a longitudinal section of the integral type metal pipe 1 for oil wells in the present embodiment. Refer to Figure 7 , the integral type metal pipe 1 for oil wells has 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 disposed on the side opposite to the second end portion 10B. As described above, in the T&C type metal pipe 1 for oil wells, the pipe body 10 includes a male-threaded pipe body 11 and a coupling 12. That is, in the T&C type metal pipe 1 for oil wells, the pipe body 10 is formed by fastening two separate members (the male-threaded pipe body 11 and the coupling 12). In contrast, in the integral type metal pipe 1 for oil wells, the pipe body 10 is integrally formed.

[0091] A male-threaded portion 40 is formed at the first end portion 10A of the pipe body 10. At the time of fastening, the male-threaded portion 40 is inserted into the female-threaded portion 50 of another integral type metal pipe 1 for oil wells and screwed in to be fastened to the female-threaded portion 50 of another integral type metal pipe 1 for oil wells. The female-threaded portion 50 is formed at the second end portion 10B of the pipe body 10. At the time of fastening, the male-threaded portion 40 of another integral type metal pipe 1 for oil wells is inserted into the female-threaded portion 50 and screwed in, and the female-threaded portion 50 is fastened to the male-threaded portion 40 of another integral type metal pipe 1 for oil wells.

[0092] The structure of the male-threaded portion 40 of the integral type metal pipe 1 for oil wells is the same as that of the male-threaded portion 40 of the T&C type metal pipe 1 for oil wells shown in Figure 4 . Similarly, the structure of the female-threaded portion 50 of the integral type metal pipe 1 for oil wells is the same as that of the female-threaded portion 50 of the T&C type metal pipe 1 for oil wells shown in Figure 5 . In addition, in Figure 4 and Figure 5In the male coupling portion 40, a male coupling shoulder surface 43, a male coupling sealing surface 42, and an external thread portion 41 are arranged in sequence from the tip of the first end portion 10A toward the center of the pipe body 10. Therefore, in the female coupling portion 50, an internal thread portion 51, a female coupling sealing surface 52, and a female coupling shoulder surface 53 are arranged in sequence from the tip of the second end portion 10B toward the center of the pipe body 10. However, similar to the male coupling contact surface 400 of the male coupling portion 40 of the T&C type oil well metal pipe 1, the male coupling contact surface 400 of the male coupling portion 40 of the integral type oil well metal pipe 1 only needs to include at least the external thread portion 41. In addition, similar to the female coupling contact surface 500 of the female coupling portion 50 of the T&C type oil well metal pipe 1, the female coupling contact surface 500 of the female coupling portion 50 of the integral type oil well metal pipe 1 only needs to include at least the internal thread portion 51.

[0093] In short, the oil well metal pipe 1 of the present embodiment can be of the T&C type or the integral type.

[0094] [Resin coating film]

[0095] The oil well metal pipe 1 of the present embodiment includes a resin coating film 100 formed as the outermost layer of at least one of the male coupling contact surface 400 and the female coupling contact surface 500. Figure 8 It is a cross-sectional view near the male coupling contact surface 400 of the oil well metal pipe 1 of the present embodiment. Figure 9 It is corresponding to Figure 8 a cross-sectional view near the female coupling contact surface 500.

[0096] Referring to Figure 8 , the resin coating film 100 can also be formed as the outermost layer of the male coupling contact surface 400. In this case, above or over the corresponding female coupling contact surface 500, a resin coating film 100 may or may not be formed. In addition, referring to Figure 9 , the resin coating film 100 can also be formed as the outermost layer of the female coupling contact surface 500. In this case, above or over the corresponding male coupling contact surface 400, a resin coating film 100 may or may not be formed. In short, the oil well metal pipe 1 of the present embodiment is formed with a resin coating film 100 as the outermost layer of either the male coupling contact surface 400 or the female coupling contact surface 500. The resin coating film 100 only needs to be formed as the outermost layer of at least a part (for example, only the male coupling sealing surface 42 or the female coupling sealing surface 52) of the male coupling contact surface 400 and the female coupling contact surface 500.

[0097] The resin-coated film 100 contains an epoxy resin. The content of the epoxy resin in the resin-coated film 100 is not particularly limited, but for example, the content of the epoxy resin in the resin-coated film 100 is 15 to 80% by mass. If the content of the epoxy resin in the resin-coated film 100 is 15% by mass or more, the resin-coated film 100 can be formed more stably. On the other hand, if the content of the epoxy resin in the resin-coated film 100 is 80% by mass or less, a predetermined film thickness can be ensured more stably. Therefore, for the resin-coated film 100 to be formed with a stable film thickness, the preferred content of the epoxy resin in the resin-coated film 100 is 15 to 80% by mass. The further preferred lower limit of the content of the epoxy resin in the resin-coated film 100 is 18% by mass, more preferably 20% by mass, more preferably 25% by mass, and more preferably 30% by mass. The further preferred upper limit of the content of the epoxy resin in the resin-coated film 100 is 70% by mass, more preferably 65% by mass, and more preferably 60% by mass.

[0098] [Method for measuring the content of epoxy resin]

[0099] The content of the epoxy resin in the resin-coated film 100 is measured by reflux extraction (Soxhlet extraction) using a solvent. Specifically, methyl ethyl ketone is used as the solvent for reflux extraction of the resin-coated film 100. Specifically, an amount of the resin-coated film 100 required for measurement is scraped from the male contact surface 400 or the female contact surface 500 and subjected to reflux extraction. Five resin-coated films 100 with a thickness of 20 μm, a longitudinal length of 120 mm, and a transverse length of 15 mm are reflux-extracted with 0.4 L of methyl ethyl ketone for 4 hours. When the thickness of the resin-coated film 100 is thicker than 20 μm, the number of resin-coated films 100 is adjusted to have the same volume as the above resin-coated film 100. Also, when the thickness of the resin-coated film 100 is thinner than 20 μm, the number of resin-coated films 100 is similarly adjusted to have the same volume as the above resin-coated film 100. The weight of the resin-coated film 100 after reflux extraction corresponds to the weight of the epoxy resin. Therefore, the content of the epoxy resin in the resin-coated film 100 is obtained by dividing the weight of the resin-coated film 100 after reflux extraction by the weight of the resin-coated film 100 before reflux extraction.

[0100] [Organic carboxylic acid]

[0101] The organic carboxylic acid is a carboxylic acid having a hydrocarbon group. If the resin-coated film 100 contains an epoxy resin and an organic carboxylic acid, the coefficient of friction of the resin-coated film 100 can be maintained within a range that improves the wear resistance of the threaded joint and is not easily loosened even when threading tightening and threading loosening are repeated.

[0102] The organic carboxylic acid can be an aliphatic carboxylic acid or an aromatic carboxylic acid. The organic carboxylic acid preferably has a chain hydrocarbon group.

[0103] If the carbon number of the organic carboxylic acid is 5 or more, the organic carboxylic acid molecule is relatively large. Therefore, so-called "bleeding" can be suppressed as follows: after the resin coating film 100 is cured, the organic carboxylic acid molecules pass through the three-dimensionally crosslinked epoxy resin network and float to the surface of the resin coating film 100 and expose outside the resin coating film 100. Therefore, if the carbon number of the organic carboxylic acid is 5 or more, the effect obtained by the coexistence of the epoxy resin and the organic carboxylic acid can be obtained more stably. Thus, the carbon number of the organic carboxylic acid is preferably 5 or more.

[0104] On the other hand, if the carbon number of the organic carboxylic acid is 10 or less, the organic carboxylic acid is easily soluble in water. In this case, the organic carboxylic acid is easily dispersed in the composition for forming the resin coating film containing the epoxy resin. Thus, the carbon number of the organic carboxylic acid is preferably 10 or less. That is to say, 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, and thus it is further preferred.

[0105] If the organic carboxylic acid is a monocarboxylic acid, the compatibility with the epoxy resin is improved. Thus, the organic carboxylic acid is preferably a monocarboxylic acid.

[0106] The aliphatic carboxylic acid is, for example, a straight-chain saturated monocarboxylic acid. The straight-chain saturated monocarboxylic acid is, for example, 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), valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, margaric acid, stearic acid, nonadecanoic acid, arachidic 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.

[0107] In the case where the organic carboxylic acid has a branched chain hydrocarbon group, the branched chain hydrocarbon group extends laterally to 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. It is considered that if the epoxy resin approaches the carboxylic acid having a branched chain hydrocarbon group, they are likely to entangle with each other under the action of intermolecular forces, and the compatibility is improved. Therefore, it is preferred that the organic carboxylic acid has a branched chain hydrocarbon group. On the other hand, if the number of carbon atoms and / or the number of substituents of the branched chain hydrocarbon group in the organic carboxylic acid is small, the organic carboxylic acid is likely to move in the composition for forming the resin coating film. If the organic carboxylic acid is likely to move in the composition, the reaction between the epoxy group at the end of the epoxy resin and the organic carboxylic acid is promoted. As a result, it is considered that the lubricity during screwing and unscrewing of the screw is further stably improved. Therefore, preferably, the branched chain hydrocarbon group is at least one selected from the group consisting of methyl, ethyl, propyl, and isopropyl. In addition, for the number of substituents of the branched chain hydrocarbon group in the organic carboxylic acid, when the branched chain hydrocarbon group is only methyl or ethyl, the number of substituents is preferably 3 or less. For the number of substituents of the branched chain hydrocarbon group in the organic carboxylic acid, when the branched chain hydrocarbon group contains propyl or isopropyl, the number of substituents is preferably 1.

[0108] Aliphatic carboxylic acids are, for example, saturated monocarboxylic acids with branched chains. Saturated monocarboxylic acids with branched chains are, for example, selected from 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, 2-propylpentanoic 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, 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-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-trimethylheptanoic acid, 2,One or more selected from the group consisting of 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, 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-methylcaprylic acid, 3-methylcaprylic acid, 4-methylcaprylic acid, 5-methylcaprylic acid, 6-methylcaprylic acid, 7-methylcaprylic acid, 2,2-dimethylcaprylic acid, 3,3-dimethylcaprylic acid, 4,4-dimethylcaprylic acid, 5,5-dimethylcaprylic acid, 6,6-dimethylcaprylic acid, 7,7-dimethylcaprylic acid, 2,3-dimethylcaprylic acid, 2,4-dimethylcaprylic acid, 2,5-dimethylcaprylic acid, 2,6-dimethylcaprylic acid, 2,7-dimethylcaprylic acid, 3,4-dimethylcaprylic acid, 3,5-dimethylcaprylic acid, 3,6-dimethylcaprylic acid, 3,7-dimethylcaprylic acid, 4,5-dimethylcaprylic acid, 4,6-dimethylcaprylic acid, 4,7-dimethylcaprylic acid, 5,6-dimethylcaprylic acid, 5,7-dimethylcaprylic acid, 6,7-dimethylcaprylic acid, 2-methylnonanoic acid, 3-methylnonanoic acid, 4-methylnonanoic acid, 5-methylnonanoic acid, 6-methylnonanoic acid, 7-methylnonanoic acid, 8-methylnonanoic acid, 2,2,3,5-tetramethylhexanoic acid, and 2,4-dimethyl-2-isopropylvaleric acid.,

[0109] When the organic carboxylic acid is a branched-chain saturated monocarboxylic acid with 5 or more carbon atoms, the environmental burden is small and no unpleasant odor is generated. In addition, as described above, when the carbon number of the organic carboxylic acid is 10 or less, the organic carboxylic acid is easily dispersed in the composition for forming the resin coating film containing the epoxy resin. Therefore, the organic carboxylic acid of the present embodiment is further preferably a branched-chain saturated monocarboxylic acid with 5 to 10 carbon atoms.

[0110] The aliphatic carboxylic acid is, for example, a straight-chain saturated dicarboxylic acid. The straight-chain saturated dicarboxylic acid is, for example, 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.

[0111] The aliphatic carboxylic acid is, for example, an unsaturated carboxylic acid. The unsaturated carboxylic acid is, for example, one or more selected from the group consisting of 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, 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.

[0112] 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.

[0113] More preferably, the organic carboxylic acid is one or more selected from the group consisting of 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 2,4-dimethyl-2-isopropylvaleric acid.

[0114] In addition to having a carboxyl group, the organic carboxylic acid may also have other functional groups. The other functional groups are, for example, one or more selected from the group consisting of a hydroxyl 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 composed of a chain hydrocarbon group and a carboxyl group.

[0115] If the content of the organic carboxylic acid in the resin coating film 100 is 0.2 mass% or more, the effect of the organic carboxylic acid can be obtained more stably. On the other hand, if the content of the organic carboxylic acid in the resin coating film 100 is 20 mass% or less, the resin coating film 100 can be formed more stably. Therefore, the content of the organic carboxylic acid in the resin coating film 100 is, for example, 0.2 to 20 mass%. The lower limit of the content of the organic carboxylic acid in the resin coating film 100 is preferably 0.5 mass%, more preferably 1.0 mass%, and further preferably 2.0 mass%. The upper limit of the content of the organic carboxylic acid in the resin coating film 100 is preferably 15 mass%, more preferably 10 mass%, further preferably 8.0 mass%, further preferably 5.0 mass%, and further preferably 4.0 mass%.

[0116] [Method for measuring the content of organic carboxylic acid]

[0117] Regarding the content of the organic carboxylic acid in the resin coating film 100, after subjecting the resin coating film 100 to reflux extraction (Soxhlet extraction), liquid chromatography / mass spectrometry (LC / MS) is used to measure the content of the organic carboxylic acid in the resin coating film 100. Specifically, an amount of the resin coating film 100 required for measurement is scraped from the male contact surface 400 or the female contact surface 500, and reflux extraction is performed. Five resin coating films 100 with a thickness of 20 μm, a longitudinal length of 120 mm, and a transverse length of 15 mm are subjected to reflux extraction for 4 hours using 0.4 L of ethanol. When the thickness of the resin coating film 100 is thicker than 20 μm, the number of resin coating films 100 is adjusted to have the same volume as the above resin coating film 100. In addition, when the thickness of the resin coating film 100 is thinner than 20 μm, the number of resin coating films 100 is similarly adjusted to have the same volume as the above resin coating film 100. LC / MS is used to quantitatively analyze the ethanol after reflux extraction, and the content of the organic carboxylic acid in the resin coating film 100 is determined. When the organic carboxylic acid is insoluble in ethanol and cannot be extracted, methyl ethyl ketone is used as a solvent for reflux extraction in the same manner, and thereby the content of the organic carboxylic acid in the resin coating film 100 is determined.

[0118] [Lubricating material]

[0119] The resin coating film 100 may also contain a lubricating material. Any material that can improve the lubricity of the resin coating film 100 is sufficient, and there is no particular limitation. The lubricating material can be, for example, graphite, zinc oxide, boron nitride, talc, molybdenum disulfide, tungsten disulfide, fluorinated graphite, tin sulfide, bismuth sulfide, organic molybdenum, thiosulfate, polytetrafluoroethylene (PTFE), melamine cyanurate (MCA), perfluoropolyether (PFPE). In addition, it can also be contained in a manner of combining multiple of the above lubricating materials. The content of the lubricating material in the resin coating film 100 is, for example, 0.1 to 25% by mass.

[0120] [Other materials]

[0121] The resin coating film 100 may also contain other materials. The other materials can be, for example, pigments, rust preventive additives, or preservatives. The content of the other materials in the resin coating film 100 is, for example, 0.1 to 25% by mass.

[0122] [Thickness of the resin coating film]

[0123] The thickness of the resin coating film 100 is not particularly limited. The thickness of the resin coating film 100 is, for example, 1 to 100 μm.

[0124] [Configuration of the resin coating film]

[0125] In the present embodiment, the resin coating film 100 is formed as the outermost layer of at least one of the male fastener contact surface 400 and the female fastener contact surface 500. That is, in the present embodiment, the resin coating film 100 can be formed as the outermost layer of the male fastener contact surface 400, or can be formed as the outermost layer of the female fastener contact surface 500. In addition, in the present embodiment, when the resin coating film 100 is formed as the outermost layer of the male fastener contact surface 400, a lubricating coating film other than the resin coating film 100 of the present embodiment can be formed as the outermost layer of the female fastener contact surface 500. And, in the present embodiment, when the resin coating film 100 is formed as the outermost layer of the female fastener contact surface 500, a lubricating coating film other than the resin coating film 100 of the present embodiment can be formed as the outermost layer of the male fastener contact surface 400. And, in the present embodiment, the resin coating film 100 can be formed as the outermost layer of both the male fastener contact surface 400 and the female fastener contact surface 500.

[0126] When forming a lubricating coating other than the resin coating 100, the lubricating coating other than the resin coating 100 is not particularly limited and is a well-known lubricating coating. The lubricating coating can be, for example, a resin coating using a thermosetting resin represented by epoxy resin as an adhesive, a resin coating using a thermoplastic resin represented by polyamide resin as an adhesive, or a lubricating coating using mineral oil as a base material and being in a grease-like or semi-solid state at normal temperature. That is, if it is a lubricating coating that can be applied to the metal pipe 1 for oil wells, a well-known lubricating coating can be used.

[0127] In addition, the resin coating 100 can be formed as the outermost layer of the entire surface of at least one of the male thread contact surface 400 and the female thread contact surface 500, or can be formed as the outermost layer of a part of at least one of the male thread contact surface 400 and the female thread contact surface 500. When the pipe body 10 has a male thread sealing surface 42, a female thread sealing surface 52, a male thread shoulder surface 43, and a female thread shoulder surface 53, the surface pressure of the sealing surfaces 42, 52 and the shoulder surfaces 43, 53 will particularly increase in the final stage of thread tightening. Therefore, when the resin coating 100 is formed as the outermost layer of a part of at least one of the contact surfaces 400, 500 having the sealing surfaces 42, 52 and the shoulder surfaces 43, 53, the resin coating 100 can be formed as the outermost layer of at least one of the sealing surfaces 42, 52 and the shoulder surfaces 43, 53. On the other hand, if the resin coating 100 is formed as the outermost layer of the entire surface of at least one of the contact surfaces 400, 500, the production efficiency of the metal pipe 1 for oil wells is higher.

[0128] [Other layers]

[0129] The metal pipe 1 for oil wells of the present embodiment can also have a layer other than the resin coating 100 formed on the contact surfaces 400, 500. The other layers are, for example, a metal plating layer and a chemical conversion treatment layer.

[0130] [Metal plating layer 110]

[0131] It can also be that the metal pipe 1 for oil wells of the present embodiment further has a metal plating layer between at least one of the male thread contact surface 400 and the female thread contact surface 500 and the resin coating 100. Specifically, referring to Figure 10 , the metal plating layer 110 can also be formed as the lower layer of the resin coating 100 on the male thread contact surface 400. Similarly, referring to Figure 11 , the metal plating layer 110 can also be formed as the lower layer of the resin coating 100 on the female thread contact surface 500. Thus, when both the resin coating 100 and the metal plating layer 110 are formed, the metal plating layer 110 is formed between at least one of the contact surfaces 400, 500 and the resin coating 100.

[0132] In this embodiment, the type of the metal coating 110 is not particularly limited. In addition, the metal coating 110 may be composed of a single-layer coating or may be composed of a multi-layer coating (a double-layer coating, a triple-layer coating). When the metal coating 110 is a single-layer coating, the metal coating 110 is, for example, a single-layer coating based on Cu, Sn or Ni metal, a single-layer coating of Zn-Ni alloy, Cu-Sn alloy or Cu-Sn-Zn alloy. When the metal coating 110 is a multi-layer coating, the metal coating 110 is, for example, a double-layer coating of Cu layer and Sn layer, a triple-layer coating based on Ni layer, Cu layer and Sn layer, or a multi-layer coating formed by combining the above single-layer coatings.

[0133] [Chemical conversion treatment layer 120]

[0134] Alternatively, the metal pipe 1 for oil wells of this embodiment further includes a chemical conversion treatment layer, which is disposed between at least one of the male thread portion contact surface 400 and the female thread portion contact surface 500 and the resin coating film 100 and has a surface in contact with the resin coating film 100. Specifically, referring to Figure 12 , the chemical conversion treatment layer 120 can be formed as a lower layer of the resin coating film 100 on the metal coating 110 formed on the male thread portion contact surface 400. In addition, referring to Figure 13 , the chemical conversion treatment layer 120 can be formed as a lower layer of the resin coating film 100 on the metal coating 110 formed on the female thread portion contact surface 500. Similarly, the chemical conversion treatment layer 120 can be formed as a lower layer of the resin coating film 100 on the male thread portion contact surface 400, and this case is not shown. Similarly, the chemical conversion treatment layer 120 can be formed as a lower layer of the resin coating film 100 on the female thread portion contact surface 500, and this case is not shown.

[0135] In this embodiment, the type of the chemical conversion treatment layer 120 is not particularly limited. The chemical conversion treatment layer 120 can be, for example, a phosphate chemical conversion treatment layer, a 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 the resin coating film 100 is formed on the chemical conversion treatment layer 120, the adhesion of the resin coating film 100 can be further improved by the so-called anchoring effect. In addition, in this embodiment, the thickness of the chemical conversion treatment layer 120 is not particularly limited. The preferred thickness of the chemical conversion treatment layer 120 in this embodiment is 5 to 40 μm.

[0136] [Surface to be spray-treated or surface to be pickled]

[0137] The contact surfaces 400 and 500 of the metal pipe 1 for oil wells of the present embodiment can be subjected to shot peening or pickling. That is, the surfaces of the metal pipe 1 for oil wells on which the resin coating film 100 is to be formed as the outermost layer can be surfaces subjected to shot peening or pickling. That is, it can be that the contact surfaces 400 and 500 in the pipe body 10 of the metal pipe 1 for oil wells are subjected to shot peening or pickling treatment, and the resin coating film 100 is formed thereon. In addition, when the metal pipe 1 for oil wells has a metal coating 110, it can be that the contact surfaces 400 and 500 of the metal pipe 1 for oil wells are subjected to shot peening or pickling treatment, a metal coating 110 is provided thereon, and a resin coating film 100 is provided on the metal coating 110. In addition, when the metal pipe 1 for oil wells has a metal coating 110, it can also be that the metal pipe 1 for oil wells has a metal coating 110 subjected to shot peening or pickling, and a resin coating film 100 is provided thereon.

[0138] [Chemical composition of pipe body]

[0139] The chemical composition of the pipe body 10 of the metal pipe 1 for oil wells of the present embodiment is not particularly limited. That is, in the present embodiment, the steel type of the pipe body 10 of the metal pipe 1 for oil wells is not particularly limited. The pipe body 10 can be formed of, for example, carbon steel, stainless steel, and alloy steel. That is, the pipe body 10 can also be a steel pipe including an Fe-based alloy, or an alloy pipe represented by a Ni-based alloy pipe. Here, the steel pipe is, for example, a low alloy steel pipe, a martensitic stainless steel pipe, a ferritic stainless steel pipe, an austenitic stainless steel pipe, and a duplex stainless steel pipe. The alloy pipe is, for example, a Ni-based alloy pipe and a NiCrFe alloy pipe.

[0140] Among alloy steels, high alloy steels such as duplex stainless steel containing Ni alloy and alloy elements such as Cr, Ni, and Mo have high corrosion resistance. Therefore, if these high alloy steels are used as the pipe body 10, excellent corrosion resistance can be obtained in a corrosive environment containing hydrogen sulfide, carbon dioxide, etc.

[0141] [Manufacturing method]

[0142] Hereinafter, the manufacturing method of the metal pipe 1 for oil wells of the present embodiment will be described.

[0143] The manufacturing method of the metal pipe 1 for oil wells of the present embodiment includes a preparation process, a composition coating process, and a composition curing process.

[0144] [Preparation process]

[0145] In the preparation process, an oil well metal pipe 1 having a pipe body 10 is prepared. The pipe body 10 includes a male thread portion 40 and a female thread portion 50. The male thread portion 40 has a male thread portion contact surface 400 including an external thread portion 41, and the female thread portion 50 has a female thread portion contact surface 500 including an internal thread portion 51. As described above, the oil well metal pipe 1 of the present embodiment has a well-known structure. That is, in the preparation process, it is only necessary to prepare an oil well metal pipe 1 having a well-known structure.

[0146] [Composition coating process]

[0147] In the composition coating process, a composition containing unreacted epoxy resin, a curing agent for epoxy resin, and an organic carboxylic acid is coated on at least one of the male thread portion contact surface 400 and the female thread portion contact surface 500, or on a metal plating layer 110 formed by a process described later, or on a chemical conversion treatment layer 120 formed by a process described later. The composition is a composition for forming the above resin coating film 100. The composition contains unreacted epoxy resin, a curing agent for epoxy resin, and an organic carboxylic acid. In addition, in the present specification, "unreacted epoxy resin" refers to a monomer, oligomer, prepolymer, or a mixture thereof having a plurality of unreacted epoxy groups in each molecule. The composition may further contain a solvent in addition to containing unreacted epoxy resin, a curing agent for epoxy resin, and an organic carboxylic acid. In addition, the composition of the composition for forming the resin coating film 100 other than the solvent is the same as the composition of the above resin coating film 100. In addition, the curing agent for epoxy resin is not particularly limited, and a well-known curing agent can be used according to the type of epoxy resin.

[0148] The composition is manufactured by dissolving or dispersing unreacted epoxy resin, a curing agent for epoxy resin, 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 an organic solvent. The solvent may also 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 according to the coating method. For example, when the total amount of all components other than the solvent is set to 100% by mass, the proportion of the solvent is 40 to 100% by mass.

[0149] The method of coating the composition on at least one of the male thread portion contact surface 400 and the female thread portion contact surface 500 is not particularly limited, and any well-known method can be used. For example, the composition in a solution state can be coated on at least one of the male thread portion contact surface 400 and the female thread portion contact surface 500 by spraying. In this case, the viscosity is adjusted so that the composition can be sprayed in an environment of normal temperature and normal pressure. The method of coating the composition on at least one of the male thread portion contact surface 400 and the female thread portion contact surface 500 may also be brushing, dipping, or the like instead of spraying.

[0150] [Composition curing process]

[0151] In the composition curing process, the coated composition is cured to form the resin coating film 100. The conditions for the curing treatment are well-known conditions. The time until complete curing varies depending on the composition of the composition, particularly the type of curing agent and the thickness of the coating film. For example, when using a curing agent of the normal temperature and short-time curing type and the content of unreacted epoxy resin in the composition is about 30% by mass, the time until complete curing is 3 to 16 hours at 5 to 30°C or 5 to 180 minutes at 30 to 70°C. And, for example, when using a curing agent of the high-temperature curing type, in order to suppress the heat generation caused by the curing reaction, the time until complete curing is 0.5 to 2 hours of heating at 50 to 100°C and then 1 to 4 hours at 150 to 240°C.

[0152] Here, when the organic carboxylic acid contained in the composition is a dicarboxylic acid, the heat treatment temperature in the curing process is preferably lower. If the organic carboxylic acid is a dicarboxylic acid and the heat treatment temperature is too high, the curing due to crosslinking proceeds excessively, and the formed resin coating film 100 becomes too hard. Therefore, when the organic carboxylic acid is a dicarboxylic acid, the heat treatment temperature is preferably 100°C or lower, for example.

[0153] By the above manufacturing method, the metal pipe 1 for oil wells of the present embodiment can be manufactured.

[0154] [Other processes]

[0155] The metal pipe 1 for oil wells of the present embodiment may also include other processes in the manufacturing process. The other processes are, for example, one or more selected from the group consisting of a spraying treatment process, a pickling treatment process, a metal plating process, and a chemical conversion treatment process.

[0156] [Spraying treatment process]

[0157] Alternatively, the manufacturing method of the metal pipe 1 for oil wells of the present embodiment may further include a spraying treatment process before the composition coating process. In the present embodiment, the spraying treatment is, for example, a treatment in which particles are collided using a spraying device. The spraying treatment is, for example, a sandblasting treatment. The sandblasting treatment is a treatment in which a sandblasting material (abrasive) is mixed with compressed air and projected. The sandblasting material is, for example, a spherical pellet material and an angular sand grain material. By the sandblasting treatment, the surface roughness of the contact surfaces 400, 500, and the surface of the metal plating 110 can be increased.

[0158] In the present embodiment, the sandblasting treatment can be carried out by a well-known method. In the sandblasting treatment, for example, air is compressed by a compressor, and the compressed air is mixed with the sandblasting material. The material of the sandblasting material is, for example, stainless steel, aluminum, ceramic, alumina, etc. In addition, conditions such as the projection speed of the sandblasting treatment can be appropriately set.

[0159] [Pickling treatment process]

[0160] Alternatively, the method for manufacturing the metal pipe 1 for oil wells according to the present embodiment may further include a pickling treatment process before the composition coating process. In the present embodiment, the pickling treatment process refers to a treatment in which the surface is roughened by immersion in a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid, or hydrofluoric acid. That is, by immersing the contact surfaces 400, 500, and the surface of the metal plating layer 110 in the strong acid solution, the surface roughness of these surfaces can be increased.

[0161] [Metal plating process]

[0162] Alternatively, the method for manufacturing the metal pipe 1 for oil wells according to the present embodiment may further include a metal plating process before the composition coating process. The metal plating layer 110 can be formed, for example, by electroplating treatment or strike plating treatment.

[0163] [Electroplating treatment]

[0164] In the present embodiment, the electroplating treatment is a treatment for forming the metal plating layer 110 by electroplating. As described above, the metal plating layer 110 is, for example, a single-layer plating layer based on Cu, Sn, or Ni metal, a single-layer plating layer of Zn-Ni alloy, Cu-Sn alloy, or Cu-Sn-Zn alloy, a double-layer plating layer of Cu layer and Sn layer, a three-layer plating layer based on Ni layer, Cu layer, and Sn layer, and a multi-layer plating layer formed by combining the above single-layer plating layers.

[0165] The electroplating treatment can be carried out by a well-known method. For example, a plating bath containing ions of the metal elements included in the alloy plating layer is prepared. Next, at least one of the contact surfaces 400, 500 is immersed in the plating bath. And, at least one of the contact surfaces 400, 500 is energized to form the metal plating layer 110 on at least one of the contact surfaces 400, 500. Conditions such as the temperature of the plating bath and the plating time can be appropriately set.

[0166] More specifically, for example, in the case of forming a Cu-Sn-Zn alloy plating layer, the plating bath contains copper ions, tin ions, and zinc ions. In this case, the composition of the plating bath is preferably Cu: 1 to 50 g / L, Sn: 1 to 50 g / L, and Zn: 1 to 50 g / L. The conditions for electroplating are, for example, plating bath pH: 1 to 10, plating bath temperature: 60 °C, current density: 1 to 100 A / dm 2 and treatment time: 0.1 to 30 minutes.

[0167] Similarly, for example, in the case of forming a Zn-Ni alloy plating layer, the plating bath contains zinc ions and nickel ions. In this case, the composition of the plating bath is preferably Zn: 1 to 100 g / L and Ni: 1 to 50 g / L. The conditions for electroplating are, for example, plating bath pH: 1 to 10, plating bath temperature: 60 °C, current density: 1 to 100 A / dm 2 and treatment time: 0.1 to 30 minutes.

[0168] [Impact plating treatment]

[0169] The impact plating treatment is a treatment that can be carried out by mechanical plating in which particles and the object to be plated collide in a rotating drum, or projection plating in which particles are made to collide with the object to be plated using a spraying device.

[0170] [Chemical conversion treatment process]

[0171] The manufacturing method of the metal pipe 1 for oil wells of the present embodiment may also include a chemical conversion treatment process before the composition coating process. In the chemical conversion treatment process, a chemical conversion treatment layer 120 is formed by carrying out a chemical conversion treatment.

[0172] In the present embodiment, the chemical conversion treatment can be carried out by a well-known method. For the treatment liquid, a usual chemical conversion treatment liquid can be used. For example, a zinc phosphate-based chemical conversion treatment liquid 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 can also be used. Alternatively, a chromate treatment liquid can also be used. In addition to this, a chemical conversion treatment liquid can be used according to the chemical conversion treatment layer 120 to be formed. The liquid temperature of the treatment liquid is, for example, room temperature to 100 °C. The treatment time of the chemical conversion treatment can be appropriately set according to the desired film thickness, for example, 15 minutes. In the case of forming a phosphate chemical conversion treatment layer, in order to promote the formation of the chemical conversion treatment layer, surface adjustment may be carried out before the phosphate chemical conversion treatment. The surface adjustment is a treatment of immersing in an aqueous surface adjustment solution containing colloidal titanium. After the phosphate chemical conversion treatment, it is preferably washed with water or hot water first and then dried.

[0173] The metal pipe 1 for oil wells of the present embodiment is manufactured using the above processes. However, the above manufacturing method is an example of the manufacturing method of the metal pipe 1 for oil wells of the present embodiment and is not limited to this manufacturing method. The metal pipe 1 for oil wells of the present embodiment can also be manufactured using other methods.

[0174] Examples

[0175] Hereinafter, the effects of the metal pipe for oil wells of the present embodiment will be further specifically described using examples. The conditions in the following examples are an example of the conditions adopted to confirm the feasibility and effects of the metal pipe for oil wells of the present embodiment. Therefore, the metal pipe for oil wells of the present embodiment is not limited to this example of conditions.

[0176] A commercially available cold-rolled steel sheet was used assuming the pipe body of the metal pipe for oil wells. The size of the cold-rolled steel sheet was 150 mm in length and 70 mm in width. The steel type was SPCC steel described in JIS G 3141 (2021).

[0177] [Composition Coating Step]

[0178] The composition was coated on the surface of the cold-rolled steel sheet. The composition contained unreacted epoxy resin, a room-temperature curing type curing agent, and the organic carboxylic acids shown in Table 1. In Table 1, the compound names of the organic carboxylic acids contained are shown in the "Compound Name" column. In the test No. 1 where "-" is recorded in the "Compound Name" column, the composition does not contain organic carboxylic acids. In addition, in Table 1, in the column of "Content (mass%)", the content of the organic carboxylic acid is expressed in mass%. The compositions of test Nos. 1 to 29 contained water as a solvent in addition to unreacted epoxy resin, a room-temperature curing type curing agent, and organic carboxylic acids.

[0179] [Table 1]

[0180] Table 1

[0181]

[0182] [Composition Curing Step]

[0183] The compositions of each test number were cured. Specifically, the cold-rolled steel sheet coated with the composition was placed in a heating furnace and heated at 50 °C for 3 to 10 minutes, and then left to stand at room temperature for 24 hours. Thereby, a resin coating film was formed.

[0184] [Bowden Sliding Test]

[0185] The Bowden sliding test was performed on the cold-rolled steel sheets of each test number having the resin coating film formed thereon under the following conditions. The number of sliding times within the range where the coefficient of friction (μ) was 0.25 or more and less than 0.40 without wear was counted. In addition, for the number of sliding times, one reciprocating slide was counted as one sliding time. The sliding distance (m) was obtained by multiplying the obtained number of sliding times by twice the sliding width. The results are shown in Table 1. In addition, the change in the coefficient of friction during the tests of test No. 1 and test No. 21 is shown in Figure 1 .

[0186] Steel ball: 3 / 16” SUJ2

[0187] Load: 3 kgf

[0188] Sliding width: 10 mm or 14 mm

[0189] Sliding speed: 4 mm / s

[0190] Lubricating oil: None (no oil coating)

[0191] Test temperature: Normal temperature (25 °C)

[0192] [Evaluation results]

[0193] Refer to Table 1 and Figure 1 , the resin coatings of Test Nos. 2 to 29 contain epoxy resin and organic carboxylic acid. As a result, the sliding distance with a coefficient of friction of 0.25 or more and less than 0.40 is 2.00 m or more. It can be known that the resin coatings of Test Nos. 2 to 29 improve the abrasion resistance of the metal pipe for oil wells, and moreover, the non-loosening property of the threaded joint can be maintained even when the thread tightening and thread loosening are repeated.

[0194] On the other hand, the resin coating of Test No. 1 contains epoxy resin but does not contain organic carboxylic acid. As a result, the sliding distance with a coefficient of friction of 0.25 or more and less than 0.40 is less than 2.00 m. It can be known that the resin coating of Test No. 1 cannot maintain the non-loosening property of the threaded joint when the thread tightening and thread loosening are repeated.

[0195] The above has described the embodiments of the present disclosure. However, the above embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above embodiments, and the above embodiments can be appropriately changed without departing from the gist thereof for implementation.

[0196] Explanation of reference numerals

[0197] 1, Metal pipe for oil wells; 10, Pipe body; 10A, First end; 10B, Second end; 11, Male thread part pipe body; 12, Coupling; 40, Male thread part; 41, External thread part; 42, Male thread part sealing surface; 43, Male thread part shoulder surface; 50, Female thread part; 51, Internal thread part; 52, Female thread part sealing surface; 53, Female thread part shoulder surface; 100, Resin coating; 110, Metal plating; 120, Chemical conversion treatment layer; 400, Male thread part contact surface; 500, Female thread part contact surface.

Claims

1. A metal pipe for oil wells, comprising a pipe body including a first end portion and a second end portion, The pipe body includes: A male thread portion formed at the first end portion; and A female thread portion formed at the second end portion, The male thread portion has a male thread portion contact surface including an external thread portion, The female thread portion has a female thread portion contact surface including an internal thread portion, The metal pipe for oil wells further includes a resin coating film formed as the outermost layer of at least one of the male thread portion contact surface and the female thread portion contact surface, The resin coating film contains an epoxy resin and an organic carboxylic acid.

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

3. The metal pipe for oil wells according to claim 1 or claim 2, wherein The organic carboxylic acid has 5 or more carbon atoms.

4. The metal pipe for oil wells according to any one of claims 1 to 3, wherein The organic carboxylic acid has 10 or less carbon atoms.

5. The metal pipe for oil wells according to any one of claims 1 to 4, wherein The organic carboxylic acid is a monocarboxylic acid.

6. The metal pipe for oil wells according to any one of claims 1 to 5, wherein The organic carboxylic acid has a branched chain hydrocarbon group.

7. The metal pipe for oil wells according to any one of claims 1 to 6, wherein The organic carboxylic acid is at least one selected from the group consisting of 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 2,4-dimethyl-2-isopropylvaleric acid.

8. The metal pipe for oil wells according to any one of claims 1 to 7, wherein at least one of the male thread portion contact surface and the female thread portion contact surface further has at least one selected from the group consisting of a metal coating layer and a chemical conversion treatment layer between the resin coating film.

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