Metal pipe for oil well

Abstract

Provided is an oil well metal pipe having excellent high torque performance. This oil well metal pipe (1) is provided with a pipe body (10). The pipe main body (10) comprises a male buckle part (40) and a female buckle part (50). 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. When the resin coating (100) is measured by a 1H pulse NMR method and the obtained free induction decay signal is divided into three components, namely, a high-motility component, a medium-motility component, and a low-motility component, in this order from a component having a long spin-spin relaxation time (T2), the weighted average of the spin-spin relaxation time (T2) of the three components is 110.0 [mu] s or less.

Description

Technical Field

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

[0002] Oil well metal pipes are used in oil wells and natural gas wells (hereinafter, oil wells and natural gas wells are also collectively referred to as "oil wells"). Specifically, at the oil well mining site, multiple oil well metal pipes are connected to form an oil well pipe connection represented by casing and oil pipe. The oil well pipe connection is formed by threading the threaded joints together. There are cases where the oil well pipe connection is inspected. When the inspection is carried out, the oil well pipe connection is pulled up and the threads are loosened. The oil well metal pipe is removed from the oil well pipe connection by loosening the threads and inspected. After the inspection, the threaded joints of the oil well metal pipe are threaded together again and reused as part of the oil well pipe connection.

[0003] The metal pipe for oil wells comprises a pin buckle part and a box buckle part. The pin buckle part has a pin buckle part contact surface including an external threaded part on the outer peripheral surface of the end of the metal pipe for oil wells. The box buckle part has a box buckle part contact surface including an internal threaded part on the inner peripheral surface of the end of the metal pipe for oil wells. In the present specification, the external threaded part and the internal threaded part are also collectively referred to as "threaded part". In the present specification, the pin buckle part contact surface and the box buckle part contact surface are also collectively referred to as "contact surface". The pin buckle part contact surface also includes a metal contact part without a pin buckle part thread, and the metal contact part without a pin buckle part thread includes a pin buckle part sealing surface and a pin buckle part shoulder surface. Similarly, the box buckle part contact surface also includes a metal contact part without a box buckle part thread, and the metal contact part without a box buckle part thread includes a box buckle part sealing surface and a box buckle part shoulder surface.

[0004] The contact surface is repeatedly subjected to strong friction when the threads of the metal pipe for oil wells are tightened and loosened. Therefore, the contact surface is prone to galling and seizure (irreparable adhesion) when the threads are tightened and loosened repeatedly. Therefore, sufficient durability against friction, that is, excellent adhesion resistance, is required for the metal pipe for oil wells.

[0005] Conventionally, in order to improve the anti-seizing property of metal pipes for oil wells, compound greases mixed with heavy metal powders, called dopants, have been used. The anti-seizing property of metal pipes for oil wells can be improved by applying compound greases to the contact surface. However, there is a possibility that heavy metal powders such as Pb, Zn, and Cu contained in compound greases may affect the environment. Therefore, it is desirable to develop metal pipes for oil wells that have excellent anti-seizing property even without using compound greases.

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

[0007] The oil well metal pipe disclosed in Patent Document 1 has a solid lubricating film composed of lubricating powder and a binder formed on the contact surface of at least one of the pin buckle part and the box buckle part. 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. Patent Document 1 discloses that the oil well metal pipe can improve the anti-sticking property of the oil well metal pipe.

[0008] The oil well metal pipe disclosed in Patent Document 2 has a viscous liquid or semi-solid lubricating film and a dry solid film formed thereon on the contact surface of at least one of the pin and the box. Patent Document 2 discloses that the oil well metal pipe suppresses rust even without using a compound grease and improves anti-seizing and airtightness.

[0009] Prior art literature

[0010] Patent Literature

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

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

[0013] Problem that the invention aims to solve

[0014] However, it is desirable that the high torque performance of metal pipes for oil wells be high. High high torque performance means that the shoulder friction torque is large. The shoulder friction torque refers to the difference between the yield torque at which a part of the threaded joint (pin or box) of the metal pipe for oil wells yields and the shoulder torque at which the interference between the threaded joints (pin and box) increases sharply.

[0015] If the shoulder friction torque increases, the tightening torque can be easily adjusted. Even if the oil well metal pipe does not have a shoulder surface, if the torque increases steadily, the tightening torque can be easily adjusted.

[0016] The coating disclosed in Patent Documents 1 and 2 can improve the anti-seizure property of the metal pipe for oil wells. However, Patent Documents 1 and 2 do not study high torque performance.

[0017] An object of the present disclosure is to provide a metal pipe for oil wells having excellent high torque performance.

[0018] Solutions for solving problems

[0019] The oil well metal pipe disclosed herein includes a pipe body including a first end portion and a second end portion.

[0020] The pipe body comprises:

[0021] a male buckle portion formed at the first end portion; and

[0022] a female buckle portion formed at the second end portion,

[0023] The pin portion has a pin portion contact surface including an external thread portion,

[0024] The box portion has a box portion contact surface including an internal thread portion,

[0025] The oil well metal pipe further comprises a resin coating formed as the uppermost layer of at least one of the pin portion contact surface and the box portion contact surface,

[0026] The resin coating contains epoxy resin,

[0027] In 1 The resin coating is measured by the H pulse NMR method, and the obtained free induction decay signal is divided into three components, namely, a high mobility component, a medium mobility component, and a low mobility component, in order from the component with the longest spin-spin relaxation time (T2). The weighted average value of the spin-spin relaxation time (T2) of the three components is less than 110.0 μs.

[0028] Effects of the Invention

[0029] The oil well metal pipe disclosed herein has excellent high torque performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a diagram showing the relationship between the number of turns of the oil well metal pipe and the torque when the oil well metal pipe having a shoulder surface is tightened.

[0031] Figure 2 This is a diagram showing the relationship between the relaxation time T2 and the shoulder friction torque ΔT of a resin film containing epoxy resin.

[0032] Figure 3 It is a side view of the metal pipe for oil wells according to the present embodiment.

[0033] Figure 4 Yes means Figure 3 The illustrated partial cross-sectional view is a cross-sectional view of a pipe joint for an oil well metal pipe, taken along a section (longitudinal section) parallel to the pipe axis direction.

[0034] Figure 5 yes Figure 4A cross-sectional view of a portion near a pin portion of the oil well metal pipe shown in FIG. 1 , parallel to the pipe axis direction of the oil well metal pipe.

[0035] Figure 6 yes Figure 4 A cross-sectional view of a portion near a box portion of the oil well metal pipe shown in FIG. 1 , parallel to the pipe axis direction of the oil well metal pipe.

[0036] Figure 7 is with Figure 3 A partial cross-sectional view including a longitudinal section of an oil well metal pipe according to the present embodiment having another different structure.

[0037] Figure 8 It is a partial cross-sectional view including a longitudinal section of the integral oil well metal pipe according to the present embodiment.

[0038] Fig. 9 It is a cross-sectional view of the vicinity of the contact surface of the pin portion of the oil well metal pipe according to the present embodiment.

[0039] Fig.10 is with Fig. 9 A cross-sectional view of the corresponding female buckle portion near the contact surface.

[0040] Fig.11 is with Fig. 9 Differently, this is a cross-sectional view of the male buckle portion near the contact surface of the present embodiment.

[0041] Fig.12 is with Fig.11 A cross-sectional view of the corresponding female buckle portion near the contact surface. DETAILED DESCRIPTION

[0042] Hereinafter, the present embodiment will be described in detail with reference to the drawings. The same reference numerals are given to the same or corresponding parts in the drawings, and their description will not be repeated.

[0043] The present inventors have studied methods for improving the high torque performance of oil well metal pipes and have obtained the following findings.

[0044] When oil well metal pipes are fastened to each other, an optimum torque for completing the fastening is determined in advance. Figure 1 This is a graph showing the relationship between the number of turns and torque when tightening an oil well metal pipe having a shoulder surface. Figure 1If the metal pipe for oil wells is tightened by threads, the torque initially rises gently in proportion to the number of threads. If the threads are further tightened, the shoulder surfaces come into contact with each other. The torque at this time is called the shoulder torque Ts. If the threads are further tightened after reaching the shoulder torque Ts, the torque rises sharply in proportion to the number of threads. At the moment when the torque reaches a predetermined value (tightening torque To), the tightening is completed. At the tightening torque To, the contact surfaces interfere with each other with an appropriate surface pressure. In this case, the metal pipe for oil wells can obtain higher air tightness. If the threads are further excessively tightened after reaching the tightening torque To, the torque reaches the yield torque Ty, and a portion of the male and female buckles yield. In this specification, the difference between the shoulder torque Ts and the yield torque Ty is called the shoulder friction torque ΔT.

[0045] In addition, as another form of oil well metal pipe, there is an oil well metal pipe having a wedge thread instead of a shoulder surface. In the case of such an oil well metal pipe having a wedge thread, the relationship between the number of threads and the torque of the oil well metal pipe is similar to that of the oil well metal pipe having a shoulder surface. Figure 1 so.

[0046] Among them, the wedge-type thread refers to a thread having the following structure. In the external thread portion of the wedge-type thread, as the male buckle portion is screwed in, the width of the thread teeth gradually narrows along the helical line of the thread, and the width of the thread groove gradually widens along the helical line of the thread. Moreover, in the internal thread portion of the wedge-type thread, as the female buckle portion is screwed in, the width of the thread groove gradually narrows along the helical line of the thread, and the width of the thread teeth gradually widens along the helical line of the thread. In the case of a metal pipe for oil wells with a wedge-type thread, as the thread is tightened, the load-bearing tooth side surfaces of the external thread portion and the internal thread portion and the insertion tooth side surfaces contact each other and produce locking (interference fit). The torque when locking is produced is also called locking torque or locking tooth side surface torque.

[0047] In this specification, unless otherwise stated, no distinction is made between the locking torque and the shoulder torque, and the shoulder torque is referred to as Ts. In the case of a metal pipe for oil wells having a wedge-shaped thread, similar to the case of a metal pipe for oil wells having a shoulder surface, if the thread is further tightened after reaching the shoulder torque Ts, the torque rises sharply in proportion to the number of threads. In other words, after the shoulder torque Ts, the interference between the threaded joints (the pin and the box) increases sharply. And, if the thread is further tightened, the tightening torque To is reached. If the thread is further excessively tightened after reaching the tightening torque To, the yield torque Ty is reached, and a portion of the pin and the box yields.

[0048] Oil well metal pipes having a coating containing resin are known as disclosed in Patent Documents 1 and 2. Therefore, the present inventors have considered that a resin coating capable of improving the high torque performance of the oil well metal pipe may be formed on the oil well metal pipe.

[0049] The inventors of the present invention first studied the resin contained in the resin coating. The inventors of the present invention believed that if the resin coating contained a resin with high adhesion to metal, the peeling of the resin coating could be suppressed even if shear force was generated by screw tightening. Therefore, the inventors of the present invention studied the resin with high adhesion to metal. As a result, the following findings were obtained.

[0050] Epoxy resin is a thermosetting synthetic resin having a reactive epoxy group at the end. A representative epoxy resin is bisphenol A epoxy resin. Bisphenol A epoxy resin has a secondary alcohol hydroxyl group in the repeating unit. Epoxy resin has higher adhesion to metals than other resins. The reason why epoxy resin has higher adhesion to metals is not certain, but the following two reasons are considered. (1) The hydroxyl groups in the epoxy resin form hydrogen bonds with the hydroxyl groups on the metal surface. (2) For the adhesion between iron and zinc and epoxy resin, the phenoxy group is related to the bonding interface.

[0051] The inventors of the present invention believe that if the resin coating contains epoxy resin, the peeling of the resin coating can be suppressed even if shear force is generated by screw tightening. Therefore, the inventors of the present invention conducted research on improving the high torque performance of the resin coating containing epoxy resin. As a result, the following insights were obtained.

[0052] The inventors of the present invention investigated the relationship between the crosslinking density of a resin coating containing epoxy resin and the shoulder friction torque ΔT. Epoxy resin coatings with different crosslinking densities were formed on steel plates. The steel plates with epoxy resin coatings were subjected to a Bowden sliding test to measure the initial friction coefficient. The shoulder friction torque ΔT was calculated from the initial friction coefficient using FEM analysis. The results are shown in Figure 2 middle.

[0053] Figure 2 The horizontal axis is 1 The weighted average value (μs) of the spin-spin relaxation time T2 during epoxy resin coating was measured by H pulse NMR. Figure 2 The spin-spin relaxation time T2 is 1 When the free induction decay signal obtained by measuring the epoxy resin coating by the H pulse NMR method is divided into three components, namely, a high mobility component, a medium mobility component, and a low mobility component, in order from the component with the longest spin-spin relaxation time T2, the weighted average value of the spin-spin relaxation times T2 of the three components is obtained. Figure 2The vertical axis of is the shoulder friction torque ΔT (ft.lb). The spin-spin relaxation time T2 is an index showing the decay characteristics of the magnetization intensity.

[0054] The crosslinking density of the resin is related to 1 The relationship is proportional to the inverse of the spin-spin relaxation time T2 measured by the H pulse NMR method. In other words, the higher the crosslinking density of the resin, the shorter the spin-spin relaxation time T2. Figure 2 , if the weighted average value of the spin-spin relaxation time T2 is reduced, the shoulder friction torque ΔT will increase. In other words, if the crosslinking density of the epoxy resin coating is increased, the shoulder friction torque ΔT will increase. Specifically, if the weighted average value of the spin-spin relaxation time T2 is less than 110.0μs, the shoulder friction torque ΔT will increase. The high torque performance of the oil well metal pipe with a resin coating having a high shoulder friction torque ΔT is excellent.

[0055] Based on the above research, the inventors of the present invention believe that the high torque performance of the metal pipe for oil wells can be improved by increasing the crosslinking density of the resin coating containing epoxy resin. Specifically, if the weighted average value of the spin-spin relaxation time T2 of the resin coating containing epoxy resin is 110.0 μs or less, the high torque performance of the metal pipe for oil wells is improved.

[0056] The reason why the high torque performance of the metal pipe for oil wells can be improved by increasing the crosslinking density of the resin coating containing epoxy resin is not clear. However, in the examples described below, it is shown that the high torque performance of the metal pipe for oil wells can be improved if the weighted average value of the spin-spin relaxation time T2 of the resin coating containing epoxy resin is 110.0 μs or less.

[0057] The gist of the metal pipe for oil wells of the present embodiment completed based on the above findings is as follows.

[0058] [1] A metal pipe for oil wells, comprising a pipe body including a first end portion and a second end portion,

[0059] The pipe body comprises:

[0060] a male buckle portion formed at the first end portion; and

[0061] a female buckle portion formed at the second end portion,

[0062] The pin portion has a pin portion contact surface including an external thread portion,

[0063] The box portion has a box portion contact surface including an internal thread portion,

[0064] The oil well metal pipe further comprises a resin coating formed as the uppermost layer of at least one of the pin portion contact surface and the box portion contact surface,

[0065] The resin coating contains epoxy resin,

[0066] In 1 The resin coating is measured by the H pulse NMR method, and the obtained free induction decay signal is divided into three components, namely, a high mobility component, a medium mobility component, and a low mobility component, in order from the component with the longest spin-spin relaxation time (T2). The weighted average value of the spin-spin relaxation time (T2) of the three components is less than 110.0 μs.

[0067] [2] The metal pipe for oil wells according to [1], wherein

[0068] In the above 1 When the resin film is measured by H pulse NMR, the ratio of the intermediate motility component to the sum of the high motility component, the intermediate motility component, and the low motility component is higher than the ratio of the low motility component to the sum.

[0069] [3] The metal pipe for oil wells according to [1] or [2], wherein

[0070] One or more selected from the group consisting of a phosphate coating, a plating layer, a chromate coating, and a zirconium coating is further provided between at least one of the pin portion contact surface and the box portion contact surface and the resin coating.

[0071] Hereinafter, the oil well metal pipe according to the present embodiment will be described in detail.

[0072] [Structure of metal pipe for oil wells]

[0073] First, the structure of the oil well metal pipe of this embodiment is described. The oil well metal pipe has a well-known structure. There are T&C type oil well metal pipes and integral type oil well metal pipes. The following describes each type of oil well metal pipe in detail.

[0074] [When the metal pipe for oil well 1 is of T&C type]

[0075] Figure 3 It is a side view showing the oil well metal pipe 1 according to the present embodiment. Figure 3 This is a side view of a so-called T&C (Threaded and Coupled) type oil well metal pipe 1. Figure 3 The oil well metal pipe 1 includes a pipe body 10 .

[0076] 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 10A and a second end 10B. The first end 10A is an end on the opposite side of the second end 10B. Figure 3 In the illustrated T&C type oil well metal pipe 1, the pipe body 10 includes a pin pipe body 11 and a pipe joint 12. The pipe joint 12 is attached to one end of the pin pipe body 11. More specifically, the pipe joint 12 is fastened to one end of the pin pipe body 11 by screws.

[0077] Figure 4 Yes means Figure 3 The cross-sectional view of the pipe joint 12 of the oil well metal pipe 1 shown is a partial cross-sectional view of a section (longitudinal section) parallel to the pipe axis direction. Figure 3 and Figure 4 The pipe body 10 includes a pin part 40 and a box part 50. The pin part 40 is formed at the first end 10A of the pipe body 10. When fastening, the pin part 40 is inserted into the box part 50 of another oil well metal pipe 1 (not shown) and fastened to the box part 50 of the other oil well metal pipe 1 by using threads.

[0078] The box portion 50 is formed at the second end portion 10B of the pipe body 10. When fastening, the pin portion 40 of another oil well metal pipe 1 is inserted into the box portion 50 and fastened to the pin portion 40 of another oil well metal pipe 1 by screws.

[0079] [Structure of the male buckle portion 40]

[0080] Figure 5 yes Figure 4 The cross-sectional view of the vicinity of the pin portion 40 of the oil well metal pipe 1 is parallel to the pipe axis direction of the oil well metal pipe 1 . Figure 5 The dotted line portion in shows the structure of the box buckle portion 50 of the other oil well metal pipe 1 when fastened to the other oil well metal pipe 1. Figure 5 The pin part 40 includes a pin contact surface 400 on the outer peripheral surface of the first end portion 10A of the pipe body 10. When fastened to another oil well metal pipe 1, the pin part 40 is screwed into the box part 50 of the other oil well metal pipe 1, and the pin contact surface 400 contacts the box contact surface 500 (described later) of the box part 50.

[0081] The pin contact surface 400 includes at least an external thread portion 41 formed on the outer peripheral surface of the first end portion 10A. Alternatively, the pin contact surface 400 may further include a pin sealing surface 42 and a pin shoulder surface 43. Figure 5In the embodiment, the shoulder surface 43 of the male buckle part is arranged at the top end surface of the first end portion 10A, and the sealing surface 42 of the male buckle part is arranged at a position on the outer peripheral surface of the first end portion 10A that is closer to the top end side of the first end portion 10A than the external thread portion 41. In other words, the sealing surface 42 of the male buckle part is arranged between the external thread portion 41 and the shoulder surface 43 of the male buckle part. The sealing surface 42 of the male buckle part is set to be conical. Specifically, in the sealing surface 42 of the male buckle part, in the longitudinal direction (tube axis direction) of the first end portion 10A, the outer diameter gradually decreases as it moves from the external thread portion 41 toward the shoulder surface 43 of the male buckle part.

[0082] When tightened with other metal pipes 1 for oil wells, the male buckle sealing surface 42 contacts the female buckle sealing surface 52 (described later) of the female buckle 50 of the other metal pipes 1 for oil wells. More specifically, when tightening, the male buckle 40 is inserted into the female buckle 50 of the other metal pipes 1 for oil wells, so that the male buckle sealing surface 42 contacts the female buckle sealing surface 52. Then, by further screwing the male buckle 40 into the female buckle 50 of the other metal pipes 1 for oil wells, the male buckle sealing surface 42 and the female buckle sealing surface 52 fit tightly together. Thus, when tightening, the male buckle sealing surface 42 and the female buckle sealing surface 52 fit tightly together to form a seal based on metal-metal contact. Therefore, in the mutually tightened metal pipes 1 for oil wells, the air tightness can be improved.

[0083] exist Figure 5 In the embodiment, the male buckle shoulder surface 43 is arranged on the top end surface of the first end portion 10A. Figure 5 In the pin buckle part 40 shown, an external threaded part 41, a pin buckle sealing surface 42, and a pin buckle shoulder surface 43 are sequentially arranged from the center of the pipe body 10 toward the first end 10A. When tightened with other metal pipes 1 for oil wells, the pin buckle shoulder surface 43 is opposite to and in contact with the female buckle shoulder surface 53 (described later) of the female buckle part 50 of the other metal pipes 1 for oil wells. More specifically, when tightening, the pin buckle part 40 is inserted into the female buckle part 50 of the other metal pipes 1 for oil wells, so that the pin buckle shoulder surface 43 is in contact with the female buckle shoulder surface 53. As a result, a higher torque can be obtained during tightening. In addition, the positional relationship between the pin buckle part 40 and the female buckle part 50 in the tightened state can be stabilized.

[0084] In addition, the pin part contact surface 400 of the pin part 40 includes at least the external threaded portion 41. In other words, the pin part contact surface 400 may include the external threaded portion 41, but not include the pin part sealing surface 42 and the pin part shoulder surface 43. The pin part contact surface 400 may include the external threaded portion 41 and the pin part shoulder surface 43, but not include the pin part sealing surface 42. The pin part contact surface 400 may include the external threaded portion 41 and the pin part sealing surface 42, but not include the pin part shoulder surface 43.

[0085] [Structure of the female buckle portion 50]

[0086] Figure 6 yes Figure 4 The cross-sectional view of the portion near the box portion 50 of the oil well metal pipe 1 is parallel to the pipe axis direction of the oil well metal pipe 1 . Figure 6 The dotted line portion in shows the structure of the male buckle portion 40 of another oil well metal pipe 1 when fastened to another oil well metal pipe 1. Figure 6 The box portion 50 includes a box portion contact surface 500 on the inner peripheral surface of the second end portion 10B of the pipe body 10. The box portion contact surface 500 is screwed into the male portion 40 of the other oil well metal pipe 1 when fastened to the other oil well metal pipe 1, and contacts the male portion contact surface 400 of the male portion 40.

[0087] The box portion contact surface 500 includes at least an internal thread portion 51 formed on the inner peripheral surface of the second end portion 10B. During fastening, the internal thread portion 51 meshes with the external thread portion 41 of the pin portion 40 of the other oil well metal pipe 1.

[0088] Alternatively, the female buckle portion contact surface 500 further includes a female buckle portion sealing surface 52 and a female buckle portion shoulder surface 53. Figure 6 In the embodiment, the box buckle portion sealing surface 52 is arranged at a position on the inner peripheral surface of the second end portion 10B that is closer to the pipe body 10 than the internal thread portion 51. That is, the box buckle portion sealing surface 52 is arranged between the internal thread portion 51 and the box buckle portion shoulder surface 53. The box buckle portion sealing surface 52 is set to be tapered. Specifically, in the box buckle portion sealing surface 52, the inner diameter gradually decreases as it moves from the internal thread portion 51 toward the box buckle portion shoulder surface 53 in the longitudinal direction (pipe axis direction) of the second end portion 10B.

[0089] When tightened with other metal pipes 1 for oil wells, the sealing surface 52 of the female buckle part contacts the sealing surface 42 of the male buckle part 40 of the other metal pipes 1 for oil wells. More specifically, when tightening, the male buckle part 40 of the other metal pipes 1 for oil wells is screwed into the female buckle part 50, so that the sealing surface 52 of the female buckle part contacts the sealing surface 42 of the male buckle part, and by further screwing in, the sealing surface 52 of the female buckle part and the sealing surface 42 of the male buckle part fit tightly. Thus, when tightening, the sealing surface 52 of the female buckle part and the sealing surface 42 of the male buckle part fit tightly to form a seal based on metal-metal contact. Therefore, in the mutually tightened metal pipes 1 for oil wells, the airtightness can be improved.

[0090] exist Figure 6In the embodiment, the shoulder surface 53 of the box buckle part is arranged at a position closer to the pipe body 10 side than the sealing surface 52 of the box buckle part. That is, in the box buckle part 50, the shoulder surface 53 of the box buckle part, the sealing surface 52 of the box buckle part, and the internal thread part 51 are arranged in sequence from the center of the pipe body 10 toward the top of the second end 10B. When fastened with other metal pipes 1 for oil wells, the shoulder surface 53 of the box buckle part is opposite to and in contact with the shoulder surface 43 of the male buckle part 40 of the other metal pipes 1 for oil wells. More specifically, when fastening, by inserting the male buckle part 40 of the other metal pipes 1 for oil wells into the box buckle part 50, the shoulder surface 53 of the box buckle part is in contact with the shoulder surface 43 of the male buckle part. Thus, a higher torque can be obtained during fastening. In addition, the positional relationship between the male buckle part 40 and the box buckle part 50 in the fastened state can be stabilized.

[0091] The box contact surface 500 includes at least an internal thread portion 51. When tightened, the internal thread portion 51 of the box contact surface 500 of the box 50 corresponds to and contacts the external thread portion 41 of the pin contact surface 400 of the pin 40. The box sealing surface 52 corresponds to and contacts the pin sealing surface 42. The box shoulder surface 53 corresponds to and contacts the pin shoulder surface 43.

[0092] In the case where the pin part contact surface 400 includes the external threaded portion 41 and does not include the pin part sealing surface 42 and the pin part shoulder surface 43, the box part contact surface 500 includes the internal threaded portion 51 and does not include the box part sealing surface 52 and the box part shoulder surface 53. In the case where the pin part contact surface 400 includes the external threaded portion 41 and the pin part shoulder surface 43 and does not include the pin part sealing surface 42, the box part contact surface 500 includes the internal threaded portion 51 and the box part shoulder surface 53 and does not include the box part sealing surface 52. In the case where the pin part contact surface 400 includes the external threaded portion 41 and the pin part sealing surface 42 and does not include the pin part shoulder surface 43, the box part contact surface 500 includes the internal threaded portion 51 and the box part sealing surface 52 and does not include the box part shoulder surface 53.

[0093] The pin contact surface 400 may include a plurality of external threaded portions 41, a plurality of pin sealing surfaces 42, or a plurality of pin shoulder surfaces 43. For example, the pin shoulder surface 43, the pin sealing surface 42, the external threaded portion 41, the pin sealing surface 42, the pin shoulder surface 43, the pin sealing surface 42, and the external threaded portion 41 may be sequentially arranged on the pin contact surface 400 of the pin 40 from the top of the first end 10A toward the center of the pipe body 10. In this case, the internal threaded portion 51, the box sealing surface 52, the box shoulder surface 53, the box sealing surface 52, the internal threaded portion 51, the box sealing surface 52, and the box shoulder surface 53 may be sequentially arranged on the box contact surface 500 of the box 50 from the top of the second end 10B toward the center of the pipe body 10.

[0094] exist Figure 5 and Figure 6 In the figure, the pin part 40 includes an external threaded portion 41, a pin part sealing surface 42, and a pin part shoulder surface 43, and the box part 50 includes an internal threaded portion 51, a box part sealing surface 52, and a box part shoulder surface 53, which is a so-called advanced joint. However, as described above, the pin part 40 may include an external threaded portion 41, but not include a pin part sealing surface 42 and a pin part shoulder surface 43. In this case, the box part 50 includes an internal threaded portion 51, but not include a box part sealing surface 52 and a box part shoulder surface 53. Figure 7 is with Figure 3 A partial cross-sectional view including a longitudinal section of an oil well metal pipe according to the present embodiment having another different structure.

[0095] [When the metal pipe for oil well 1 is of integral type]

[0096] Figure 3 , Figure 4 as well as Figure 7 The oil well metal pipe 1 shown is a so-called T&C type oil well metal pipe 1 in which the pipe body 10 includes a pin pipe body 11 and a pipe joint 12. However, the oil well metal pipe 1 of this embodiment may not be a T&C type but an integral type.

[0097] Figure 8 1 is a partial cross-sectional view including a longitudinal section of the integral oil well metal pipe 1 according to the present embodiment. Figure 8The integral type metal pipe for oil wells 1 includes a pipe body 10. The pipe body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is arranged on the side opposite to the second end portion 10B. As described above, in the T&C type metal pipe for oil wells 1, the pipe body 10 includes a male buckle portion pipe body 11 and a pipe joint 12. That is, in the T&C type metal pipe for oil wells 1, the pipe body 10 is formed by fastening two separate components (male buckle portion pipe body 11 and pipe joint 12). In contrast, in the integral type metal pipe for oil wells 1, the pipe body 10 is formed integrally.

[0098] The pin 40 is formed at the first end 10A of the pipe body 10. When fastening, the pin 40 is inserted into the box 50 of the other integral metal pipe for oil wells 1 and screwed in, and fastened to the box 50 of the other integral metal pipe for oil wells 1. The box 50 is formed at the second end 10B of the pipe body 10. When fastening, the pin 40 of the other integral metal pipe for oil wells 1 is inserted into the box 50 and screwed in, and the box 50 is fastened to the pin 40 of the other integral metal pipe for oil wells 1.

[0099] The structure of the male buckle part 40 of the integral oil well metal pipe 1 is Figure 5 The structure of the male buckle part 40 of the T&C type oil well metal pipe 1 shown in FIG. Figure 6 The structure of the female buckle portion 50 of the T&C type oil well metal pipe 1 shown is the same. Figure 5 and Figure 6 In the embodiment, in the pin part 40, the pin part shoulder surface 43, the pin part sealing surface 42, and the external threaded portion 41 are arranged in order from the top end of the first end 10A toward the center of the pipe body 10. Therefore, in the box part 50, the internal threaded portion 51, the box part sealing surface 52, and the box part shoulder surface 53 are arranged in order from the top end of the second end 10B toward the center of the pipe body 10. However, like the pin part contact surface 400 of the pin part 40 of the T&C type oil well metal pipe 1, the pin part contact surface 400 of the pin part 40 of the integral type oil well metal pipe 1 only needs to include at least the external threaded portion 41. Also, like the box part contact surface 500 of the box part 50 of the T&C type oil well metal pipe 1, the box part contact surface 500 of the box part 50 of the integral type oil well metal pipe 1 only needs to include at least the internal threaded portion 51.

[0100] In short, the oil well metal pipe 1 of the present embodiment may be of a T&C type or of an integral type.

[0101] [Resin coating]

[0102] The oil well metal pipe 1 of the present embodiment includes a resin coating 100 formed as the uppermost layer of at least one of the pin portion contact surface 400 and the box portion contact surface 500 . Fig. 9 It is a cross-sectional view of the vicinity of the pin portion contact surface 400 of the oil well metal pipe 1 according to the present embodiment. Fig.10 is with Fig. 9 A cross-sectional view of the vicinity of the corresponding female buckle portion contact surface 500 .

[0103] Reference Fig. 9 , the resin coating 100 may also be formed as the uppermost layer of the male buckle portion contact surface 400. In this case, the resin coating 100 may or may not be formed as the uppermost layer of the corresponding female buckle portion contact surface 500. Fig.10 , the resin coating 100 may also be formed as the uppermost layer of the box contact surface 500. In this case, the resin coating 100 may or may not be formed as the uppermost layer of the corresponding pin contact surface 400. In short, the oil well metal pipe 1 of the present embodiment has the resin coating 100 formed as the uppermost layer of at least one of the pin contact surface 400 and the box contact surface 500.

[0104] The resin coating 100 contains an epoxy resin. If the content of the epoxy resin in the resin coating 100 is 15% by mass or more, the resin coating 100 can be formed more stably. On the other hand, if the content of the epoxy resin in the resin coating 100 is 80% by mass or less, a predetermined film thickness can be ensured more stably. Therefore, the content of the epoxy resin in the resin coating 100 is, for example, 15 to 80% by mass. The lower limit of the content of the epoxy resin in the resin coating 100 is preferably 18% by mass, more preferably 20% by mass, further preferably 25% by mass, and further preferably 30% by mass. The upper limit of the content of the epoxy resin in the resin coating 100 is preferably 70% by mass, more preferably 65% ​​by mass, and further preferably 60% by mass.

[0105] [Method for measuring epoxy resin content]

[0106] The content of epoxy resin in the resin coating 100 was measured using reflux extraction (Soxhlet extraction), and the reflux extraction (Soxhlet extraction) used a solvent. Specifically, methyl ethyl ketone was used as a solvent to reflux extract the resin coating 100. Specifically, the resin coating 100 of the required amount for measurement was cut from the male buckle contact surface 400 or the female buckle contact surface 500, and reflux extraction was performed. 5 sheets of resin coating 100 with a thickness of 20μm, a length of 120mm, and a width of 15mm were reflux extracted for 4 hours using 0.4L of methyl ethyl ketone. In the case where the thickness of the resin coating 100 is thicker than 20μm, the number of sheets of the resin coating 100 is adjusted to become the same volume as the volume of the above-mentioned resin coating 100. In addition, in the case where the thickness of the resin coating 100 is thinner than 20μm, the number of sheets of the resin coating 100 is also adjusted to become the same volume as the volume of the above-mentioned resin coating 100. The weight of the resin film 100 after reflux extraction corresponds to the weight of the epoxy resin. Therefore, the content of the epoxy resin in the resin film 100 is determined by dividing the weight of the resin film 100 after reflux extraction by the weight of the resin film 100 before reflux extraction.

[0107] [Relaxation time of pulsed NMR]

[0108] In 1 When the resin coating 100 is measured by H pulse nuclear magnetic resonance method (NMR method), the obtained free induction decay signal is divided into three components, namely, high mobility component, medium mobility component, and low mobility component, starting from the component with the longest spin-spin relaxation time T2, and the weighted average value of the spin-spin relaxation time T2 of the three components is less than 110.0μs. As mentioned above, the shorter the relaxation time obtained by the pulse NMR method, the higher the cross-linking density. If the cross-linking density of the resin coating 100 is increased, the shoulder friction torque ΔT is increased. In this case, the high torque performance of the metal pipe 1 for oil wells is improved.

[0109] The lower limit of the weighted average value of the spin-spin relaxation time T2 of the resin coating 100 is not particularly limited, and is, for example, 0.5 μs. The lower limit of the weighted average value of the spin-spin relaxation time T2 of the resin coating 100 is preferably 3.0 μs, more preferably 5.0 μs, further preferably 10.0 μs, further preferably 15.0 μs, further preferably 20.0 μs, further preferably 25.0 μs. The upper limit of the weighted average value of the spin-spin relaxation time T2 of the three components is preferably 100.0 μs, more preferably 90.0 μs, further preferably 80.0 μs, further preferably 70.0 μs, further preferably 60.0 μs, further preferably 50.0 μs, further preferably 45.0 μs.

[0110] [Ratio of middle motility component]

[0111] Preferably, in 1 When the resin coating 100 is measured by the H pulse NMR method, the ratio of the medium mobility component to the sum of the high mobility component, the medium mobility component, and the low mobility component is higher than the ratio of the low mobility component to the sum of the high mobility component, the medium mobility component, and the low mobility component. The distance between the crosslinking points of the molecular chain of the medium mobility component is larger than the distance between the crosslinking points of the molecular chain of the low mobility component. In other words, the crosslinking density of the medium mobility component is smaller than the crosslinking density of the low mobility component. Therefore, the medium mobility component is less constrained by crosslinking than the low mobility component. Compared with the low mobility component, the molecular chain of the medium mobility component is easily deformed and elongated under the strong shear stress when the thread is tightened and loosened. If the ratio of the medium mobility component is higher than the ratio of the low mobility component, the resin coating 100 is easily sheared and deformed, and therefore, it is easy to suppress the peeling of the resin coating 100.

[0112] [Measurement method of relaxation time by pulsed NMR]

[0113] The weighted average value of the spin-spin relaxation time T2 of the resin coating 100 is obtained by the following method. A nuclear magnetic resonance measuring device (NMR device) is used to obtain the decay curve (free induction decay signal) of the magnetization intensity of the resin coating 100 by the pulse NMR method. Specifically, an NMR device with an observation frequency of 20 MHz is used. The measurement is performed by the following measurement method: Solid echo method, observation nucleus: 1H. Measurement object: spin-spin relaxation time T2 (μs), pulse amplitude: 2.50~3.50μs, pulse interval: 5.00~15.00μs, repetition time: 4 seconds, cumulative number of times: 32 times, measurement temperature: 35°C. The least squares method is used to make the obtained decay curve consistent with the fitting curve. The Lorentz function is used in the straight line part, and the Gaussian function is used in the curve part. From the fitting curve, subtract the components with the longest spin-spin relaxation time T2 in sequence. As a result, the waveform is separated into three components: a high-motility component with relatively high motility, a medium-motility component with relatively medium motility, and a low-motility component with relatively low motility. The spin-spin relaxation time T2 of the high-motility component, the spin-spin relaxation time T2 of the medium-motility component, and the spin-spin relaxation time T2 of the low-motility component are calculated. The ratio of the high motility component to the sum of the high motility component, the medium motility component, and the low motility component, the ratio of the medium motility component to the sum of the high motility component, the medium motility component, and the low motility component, and the ratio of the low motility component to the sum of the high motility component, the medium motility component, and the low motility component are calculated. The spin-spin relaxation time T2 of each component is multiplied by the ratio of each component. The spin-spin relaxation time T2 multiplied by the ratio of each component is summed up to calculate the weighted average of the spin-spin relaxation time T2.

[0114] [Lubricating materials]

[0115] The resin coating 100 may also contain a lubricating material. The lubricating material is sufficient as long as it is a material that improves the lubricity of the resin coating 100, and is not particularly limited. The lubricating material is, for example, one or more selected from the group consisting of graphite, zinc oxide, boron nitride, talc, molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, organic molybdenum, thiosulfate, polytetrafluoroethylene (PTFE), melamine cyanurate (MCA), and perfluoropolyether (PFPE). The total content of the lubricating material in the resin coating 100 is, for example, 0.1 to 25% by mass.

[0116] [Other materials]

[0117] The resin coating 100 may contain other materials. For example, the other materials are one or more selected from the group consisting of pigments, rust-proof additives, and antiseptics. The content of the other materials in the resin coating 100 is, for example, 0.1 to 25% by mass.

[0118] [Thickness of resin coating]

[0119] The thickness of the resin coating 100 is not particularly limited. The thickness of the resin coating 100 is, for example, 1 to 100 μm.

[0120] [Other layers]

[0121] The oil well metal pipe 1 of the present embodiment may include another layer 80 between at least one of the pin portion contact surface 400 and the box portion contact surface 500 and the resin coating 100 as the uppermost layer. Fig.11 , another layer 80 may be provided under the resin coating 100 as the uppermost layer, that is, between the male buckle contact surface 400 and the resin coating 100. Fig.12 Another layer 80 may be provided under the resin coating 100 , that is, between the female buckle portion contact surface 500 and the resin coating 100 as the uppermost layer.

[0122] The other layer 80 is, for example, one or more selected from the group consisting of a phosphate coating, a plating layer, a chromate coating, and a zirconium coating. The phosphate coating is, for example, selected from the group consisting of a zinc phosphate coating, a manganese phosphate coating, a calcium phosphate coating, and an iron phosphate coating. A plurality of other layers 80 may also be stacked in the radial direction of the oil well pipe. For example, a plating layer may be arranged on the male buckle contact surface 400, a chromate coating may be arranged on the plating layer, and a resin coating 100 as the uppermost layer may be arranged on the chromate coating.

[0123] [Chemical Composition of the Tube Main Body 10]

[0124] The chemical composition of the pipe body 10 of the metal pipe for oil wells 1 of the present embodiment is not particularly limited. The pipe body 10 may be formed of, for example, carbon steel, stainless steel, and alloy steel. The metal pipe for oil wells 1 may also be a steel pipe including an Fe-based alloy, or an alloy pipe represented by a Ni-based alloy pipe. Among them, the steel pipe is, for example, a low-alloy steel pipe, a martensitic stainless steel pipe, a duplex stainless steel pipe, and the like. Among alloy steels, high-alloy steels such as duplex stainless steel containing Ni alloys and alloy elements such as Cr, Ni, and Mo have higher 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, and the like.

[0125] [Manufacturing method]

[0126] Hereinafter, a method for manufacturing the oil well metal pipe 1 according to the present embodiment will be described.

[0127] The method for producing the oil well metal pipe 1 according to the present embodiment includes a preparation step, a composition coating step, and a composition curing step.

[0128] [Preparation process]

[0129] In the preparation process, the oil well metal pipe 1 having the pipe body 10 including the pin part 40 and the box part 50 is prepared. The pin part 40 has the pin part contact surface 400 including the external thread part 41, and the box part 50 has the box part contact surface 500 including the internal thread part 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, the oil well metal pipe 1 having a well-known structure may be prepared.

[0130] [Composition coating step]

[0131] In the composition coating step, a composition containing an epoxy resin is coated as the uppermost layer of at least one of the male buckle contact surface 400 and the female buckle contact surface 500. The composition is a composition for forming the above-mentioned resin coating 100. The method of setting the weighted average value of the spin-spin relaxation time T2 of the resin coating 100 to 110.0 μs or less is not particularly limited. For example, the composition for forming the resin coating 100 contains an epoxy resin, an acrylate curing agent containing an unsaturated bond, and an N-containing catalyst. The acrylate curing agent containing an unsaturated bond is, for example, selected from the group consisting of 2-ethylhexyl 3-(4-methoxyphenyl)acrylate, ethyl 3-(4-methoxyphenyl)acrylate, isoamyl 4-methoxycinnamate, and isopropyl cinnamate. The N-containing catalyst is, for example, selected from the group consisting of 2-methylpyrazine, 2,5-dimethylpyrazine, 3,5-dimethylpyridine, and 3-quinuclidine. As another method, the composition for forming the resin coating 100 contains an epoxy resin, an acrylate curing agent containing an unsaturated bond, and a nitrile curing agent. The acrylate curing agent containing an unsaturated bond is selected from the group consisting of, for example, 3-(4-methoxyphenyl) 2-ethylhexyl acrylate, 3-(4-methoxyphenyl) ethyl acrylate, 4-methoxycinnamic acid isoamyl ester, and cinnamic acid isopropyl ester. The nitrile curing agent is selected from the group consisting of, for example, 4-methyl-2-oxopentanonitrile, ethyl cyanoacetate, dimethylmalononitrile, 2-methyl-2-phenylpropionitrile, and 4,4-dimethyl-3-oxopentanonitrile. For example, if the composition for forming the resin coating 100 has the above-mentioned composition, the weighted average value of the spin-spin relaxation time T2 of the resin coating 100 can be adjusted to less than 110.0 μs. The composition for forming the resin coating 100 may also contain a solvent as needed. The solvent is, for example, one or more selected from the group consisting of water, alcohol, and an organic solvent. The solvent may contain a trace amount of a surfactant. The proportion of the solvent is not particularly limited. For example, when the sum of all components excluding the solvent is 100% by mass, the proportion of the solvent is 40 to 100% by mass.

[0132] Hereinafter, the composition for forming the resin coating 100 will also be referred to as the composition. The method for applying the composition to at least one of the male buckle contact surface 400 and the female buckle contact surface 500 is not particularly limited, and any well-known method may be used. For example, the composition in a solution state can be applied to at least one of the male buckle contact surface 400 and the female buckle contact surface 500 by spraying. In this case, the viscosity is adjusted so that the composition can be sprayed under normal temperature and pressure. The method for applying the composition to at least one of the male buckle contact surface 400 and the female buckle contact surface 500 may also be brushing and dipping instead of spraying.

[0133] [Composition curing step]

[0134] In the composition curing step, the applied composition is cured to form the resin coating 100. For example, the composition is cured at 5 to 30°C for 3 to 16 hours, or at 30 to 70°C for 5 to 180 minutes.

[0135] The oil well metal pipe 1 of the present embodiment can be manufactured by the above-described manufacturing method.

[0136] [Other processes]

[0137] The oil well metal pipe 1 of this embodiment may include other steps in the manufacturing process. For example, the other steps are one or more selected from the group consisting of a phosphate film forming step, a plating step, a chromate film forming step, a zirconium film forming step, and a sandblasting process.

[0138] [Phosphate film forming step]

[0139] In the phosphate film forming process, at least one of the male buckle contact surface 400 and the female buckle contact surface 500 of the metal pipe for oil well 1 is subjected to phosphate chemical conversion treatment to form a phosphate film. As a treatment liquid for phosphate chemical conversion treatment, a well-known phosphate chemical conversion treatment liquid can be used. As a treatment liquid, for example, a zinc phosphate chemical conversion treatment liquid containing 1 to 150 g / L of phosphate ions, 0.5 to 30 g / L of zinc ions, 1 to 100 g / L of nitrate ions, 0 to 10 g / L of nickel ions, and 0 to 10 g / L of manganese ions can be used. As a phosphate chemical conversion treatment liquid, a manganese phosphate chemical conversion treatment liquid commonly used for the metal pipe for oil well 1 can also be used. The liquid temperature of the phosphate chemical conversion treatment liquid is, for example, room temperature to 95°C. The treatment time of the phosphate chemical conversion treatment can be appropriately set according to the desired film thickness, for example, 0.5 to 15 minutes.

[0140] [Plating process]

[0141] In the plating step, at least one of the pin contact surface 400 and the box contact surface 500 of the oil well metal pipe 1 is plated to form a plated layer. The plating process can be performed by a well-known method. The plating process is, for example, electroplating.

[0142] When forming a Zn-Ni alloy plating layer as a plating layer, the plating bath contains zinc ions and nickel ions. The composition of the plating bath is, for example, Zn: 1 to 100 g / L and Ni: 1 to 50 g / L. The conditions for electroplating can be appropriately set. For example, the pH of the plating bath can be set to 1 to 10, the temperature of the plating bath can be set to 30 to 80° C., and the current density can be set to 1 to 100 A / dm 2 The plating treatment is performed with the treatment time set to 0.1 to 30 minutes.

[0143] [Chromate coating forming step]

[0144] In the chromate coating forming step, at least one of the pin contact surface 400 and the box contact surface 500 of the oil well metal pipe 1 is subjected to chromate treatment to form a chromate coating. As a treatment liquid for the chromate treatment, a well-known chromate treatment liquid can be used. The liquid temperature of the chromate treatment liquid is, for example, room temperature to 95° C. The treatment time of the chromate treatment can be appropriately set according to the desired film thickness, for example, 0.5 to 15 minutes.

[0145] [Zirconium coating forming step]

[0146] In the zirconium coating forming process, the oil well metal pipe 1 is subjected to a zirconium chemical conversion treatment to form a zirconium oxide coating. The zirconium chemical conversion treatment can be carried out by a well-known method. The zirconium chemical conversion treatment can be carried out, for example, by immersing at least one of the pin buckle contact surface 400 and the box buckle contact surface 500 in a treatment liquid. The zirconium chemical conversion treatment can also be carried out by sprinkling water on at least one of the pin buckle contact surface 400 and the box buckle contact surface 500. In addition, a commercially available treatment liquid can be used as the zirconium chemical conversion treatment liquid. In addition, the treatment conditions in the zirconium coating forming process can be appropriately set. For example, the concentration of the treatment liquid can be set to 3 to 20 g / L, the temperature of the treatment liquid can be set to 20 to 45°C, and the treatment time can be set to 30 to 240 seconds to carry out the zirconium chemical conversion treatment.

[0147] The oil well metal pipe 1 of this embodiment is manufactured by the above steps. However, the above manufacturing method is an example of a manufacturing method of the oil well metal pipe 1 of this embodiment, and the present invention is not limited to this manufacturing method. The oil well metal pipe 1 of this embodiment can also be manufactured by other methods.

[0148] Example

[0149] The effects of the metal pipe for oil wells of the present embodiment will be further specifically described below using examples. The conditions in the following examples are one example of conditions used 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 one example of conditions.

[0150] A commercially available cold-rolled steel sheet was used assuming the pipe body of a 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).

[0151] [Composition coating step]

[0152] A composition was applied to the surface of a cold-rolled steel sheet. The composition of test number 1 contained an epoxy resin, 2-ethylhexyl 3-(4-methoxyphenyl)acrylate, 2-methylpyrazine, and water as a solvent. The composition of test number 2 contained an epoxy resin, 2-ethylhexyl 3-(4-methoxyphenyl)acrylate, 4-methyl-2-oxopentanonitrile, and water as a solvent. The composition of test number 3 contained an epoxy resin, 2-ethylhexyl 3-(4-methoxyphenyl)acrylate, 3,5-dimethylpyridine, and water as a solvent. The composition of test number 4 contained an epoxy resin. However, the composition of test number 4 did not contain any of an acrylate curing agent containing an unsaturated bond, an N-containing catalyst, and a nitrile curing agent. The composition of test number 5 contained an epoxy resin and 2-ethylhexyl 3-(4-methoxyphenyl)acrylate. However, the composition of test number 5 did not contain any of an N-containing catalyst and a nitrile curing agent.

[0153] [Composition curing step]

[0154] The composition of each test number was cured. Specifically, the cold-rolled steel sheet coated with the composition was heated in a heating furnace at 50 to 70° C. for 5 minutes. Thus, a resin coating was formed.

[0155] [Test for measuring relaxation time using pulsed NMR]

[0156] The weighted average of the spin-spin relaxation time T2 of the resin coating of each test number was obtained by the following method. An NMR device (Minispec mq20 (20 MHz) manufactured by Bruker Japan Co., Ltd.) was used to obtain the decay curve (free induction decay signal) of the magnetization intensity of the resin coating by pulse NMR method. Specifically, the observation frequency was 20 MHz, the measurement method was Solid echo method, and the observation core was: 1H. Measurement object: spin-spin relaxation time T2 (μs), pulse amplitude: 3.06μs, pulse interval: 10.00μs, repetition time: 4 seconds, cumulative number of times: 32 times, measurement temperature: 35°C. The least squares method was used to make the obtained decay curve consistent with the fitting curve. The Lorentz function was used for the straight line part, and the Gaussian function was used for the curve part. From the fitting curve, the components with the longest spin-spin relaxation time T2 were subtracted in sequence. As a result, the waveform was separated into three components: a high-motility component with relatively high motility, a medium-motility component with relatively medium motility, and a low-motility component with relatively low motility. The spin-spin relaxation time T2 of the high-motility component, the spin-spin relaxation time T2 of the medium-motility component, and the spin-spin relaxation time T2 of the low-motility component were calculated. The ratio of the high mobility component to the sum of the high mobility component, the medium mobility component, and the low mobility component, the ratio of the medium mobility component to the sum of the high mobility component, the medium mobility component, and the low mobility component, and the ratio of the low mobility component to the sum of the high mobility component, the medium mobility component, and the low mobility component are obtained. The spin-spin relaxation time T2 of each component is multiplied by the ratio of each component. The spin-spin relaxation time T2 multiplied by the ratio of each component is summed up to obtain the weighted average of the spin-spin relaxation time T2. The results are shown in Table 1.

[0157] [Table 1]

[0158] Table 1

[0159]

[0160] [Shoulder friction torque measurement test]

[0161] The cold-rolled steel sheets of each test number with a resin coating formed thereon were subjected to a Bowden sliding test under the following conditions. The friction coefficient was measured using a Bowden sliding tester manufactured by Kobelco Seiki Co., Ltd. under the following conditions: steel ball: 3 / 16" SUJ2, load: 3kgf, sliding width: 10mm, sliding speed: 4mm / s, lubricant: none (no oiling), and test temperature: room temperature (25°C). One reciprocating sliding is defined as 1 time, and the arithmetic mean of the friction coefficients from the 1st to the 5th time from the start of sliding is defined as the initial friction coefficient. Using the initial friction coefficient, the shoulder torque and yield torque are determined using FEM analysis. In the FEM analysis, it is assumed that Figure 3 , Figure 5 as well as Figure 6The structure shown is a metal pipe for oil wells with an outer diameter of 9"-5 / 8 and a yield strength of 552 to 655 MPa. The contact surface of the pin part includes an external thread part, a pin part sealing surface, and a pin part shoulder surface, and the contact surface of the box part includes an internal thread part, a box part sealing surface, and a box part shoulder surface. In the FEM analysis, it is assumed that a resin film is formed only on the contact surface of the pin part. The shoulder friction torque ΔT is obtained by subtracting the shoulder torque from the yield torque obtained in the FEM analysis. The results are shown in Table 1.

[0162] [Evaluation results]

[0163] Referring to Table 1, the resin coatings of Test No. 1 to Test No. 3 contain epoxy resin. 1 The weighted average of the spin-spin relaxation times T2 of the high mobility component, the medium mobility component, and the low mobility component obtained by H pulse NMR was 110.0 μs or less. As a result, the shoulder friction torque ΔT of the resin coatings of test numbers 1 to 3 was higher than that of the resin coatings of test numbers 4 and 5. The resin coatings of test numbers 1 to 3 can improve the high torque performance of the metal pipe for oil wells.

[0164] On the other hand, the results of test numbers 4 and 5 are 1 The weighted average of the spin-spin relaxation times T2 of the high mobility component, the medium mobility component, and the low mobility component obtained by H pulse NMR exceeded 110.0 μs. As a result, the shoulder friction torque ΔT of the resin coatings of Test Nos. 4 and 5 was lower than that of the resin coatings of Test Nos. 1 to 3. The resin coatings of Test Nos. 4 and 5 could not improve the high torque performance of the metal pipe for oil wells.

[0165] The embodiments of the present disclosure have been described above. 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 modified and implemented within the scope of the present disclosure.

[0166] Description of Reference Numerals

[0167] 1. Metal pipe for oil well; 10. Pipe body; 10A. First end; 10B. Second end; 11. Pin pipe body; 12. Pipe joint; 40. Pin; 41. External thread; 42. Pin sealing surface; 43. Pin shoulder surface; 50. Box; 51. Internal thread; 52. Box sealing surface; 53. Box shoulder surface; 100. Resin coating; 400. Pin contact surface; 500. Box contact surface.

Claims

1. A metal pipe for oil wells, comprising a pipe body including a first end portion and a second end portion, The pipe body comprises: a male buckle portion formed at the first end portion; and a female buckle portion formed at the second end portion, The pin portion has a pin portion contact surface including an external thread portion, The box portion has a box portion contact surface including an internal thread portion, The oil well metal pipe further comprises a resin coating formed as the uppermost layer of at least one of the pin portion contact surface and the box portion contact surface, The resin coating contains epoxy resin, In 1 The resin coating is measured by the H pulse NMR method, and the obtained free induction decay signal is divided into three components, namely, a high mobility component, a medium mobility component, and a low mobility component, in order from the component with the longest spin-spin relaxation time (T2). The weighted average value of the spin-spin relaxation time (T2) of the three components is less than 110.0 μs.

2. The metal pipe for oil wells according to claim 1, wherein: In the above 1 When the resin film is measured by H pulse NMR, the ratio of the intermediate motility component to the sum of the high motility component, the intermediate motility component, and the low motility component is higher than the ratio of the low motility component to the sum.

3. The metal pipe for oil wells according to claim 1 or 2, wherein: One or more selected from the group consisting of a phosphate coating, a plating layer, a chromate coating, and a zirconium coating is further provided between at least one of the pin portion contact surface and the box portion contact surface and the resin coating.

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