METAL PIPE FOR OIL WELLS

Abstract

This invention provides a metal oil well pipe capable of achieving both high yield torque and excellent scaling resistance in a compatible manner. A metal oil well pipe of the present description includes a main pipe body. The main pipe body includes a bolt (40) formed in the first end portion (10A) and a box formed in the second end portion. A metallic coating layer is formed on a first contact surface, which is one of the contact surfaces of the bolt (40) and a box contact surface, and a solid lubricant layer is formed over the metallic coating layer. The arithmetic mean roughness Ra of a second contact surface, which is the other of the contact surface of the bolt (40) and the box contact surface, is from 0.5 to 10.0 µm, and a semi-solid or liquid antioxidant coating (80) is formed on the second contact surface.

Description

METAL PIPE FOR OIL WELLS FIELD OF INVENTION

[0001] This description refers to a metal pipe for oil wells. STATE OF THE ART

[0002] A metal oil well pipe is used for drilling into oil and natural gas reservoirs (hereafter, the oil and natural gas reservoirs will be collectively referred to as oil wells). A metal oil well pipe has a threaded connection. At the oil well drilling site, in accordance with the depth of the oil well, several metal oil well pipes are connected to form a connected oil well pipe body. The connected oil well pipe body is formed by clamping the metal oil well pipes together. The connected oil well pipe body is lifted and loosened for inspection and similar purposes, and after inspection, the connected oil well pipe body is clamped again and reused.

[0003] A metal oil well pipe includes a bolt and a box. The bolt has a bolt contact surface that includes an external threaded portion on an outer peripheral surface of an end portion of the metal oil well pipe. The box has a contact surface that includes an internal threaded portion on an inner peripheral surface of an end portion of the metal oil well pipe.

[0004] The bolt contact surface and the box contact surface repeatedly experience strong friction during the tightening and loosening of the metal oil well pipe. Unless there is sufficient durability with respect to friction on the bolt contact surface and the box contact surface, scaling (irreparable damage) will occur during repeated tightening and loosening. Therefore, a metal oil well pipe is required to have sufficient durability with respect to friction, i.e., excellent resistance to scaling.

[0005] Traditionally, heavy metal-containing compound greases, called doped greases or thread greases, have been used to improve scouring resistance. Applying a compound grease to the bolt contact surface and / or the box contact surface can improve the scouring resistance of a metal oil well pipe. However, the heavy metals contained in compound greases, such as Pb, Zn, and Cu, can affect the environment. For this reason, the development of a metal oil well pipe with excellent scouring resistance without the use of a compound grease is desired.

[0006] Therefore, techniques employing a solid lubricating coating instead of a compound grease have been proposed. For example, in a threaded pipe connection proposed in Publication of International Application No. W02009 / 072486 (Patent Document 1) describes the formation of a solid lubricating coating on a box contact surface and a solid anti-corrosive coating composed of a UV-curable resin on a bolt contact surface. Patent Document 1 further describes how the solid lubricating coating can suppress the occurrence of scoring even during repeated tightening and loosening operations.

[0007] In this respect, when a connected body of oil well tubing, in which a plurality of metal oil well tubing is fastened together, is pushed forward into an oil well, the connected body of oil well tubing is pushed forward while being rotated. The strata in which the oil is buried (oil-bearing strata) extend horizontally, not vertically. Therefore, oil drilling techniques such as directional drilling or horizontal drilling are being employed in an increasing number of cases in order to cover a wide interval of an oil-bearing stratum to increase the efficiency of oil production.In directional and horizontal drilling, a wellbore connected to a pipe is bent underground, with a portion of its lower end extending diagonally or horizontally. When an oil well is extended horizontally or at an angle, the greater the horizontal or inclined length, the greater the rotational torque required to advance the pipe. Under such high rotational torque, if the metal pipe undergoes plastic deformation, maintaining a high level of gas tightness may not always be possible.Therefore, a metal pipe for oil wells is needed that does not undergo plastic deformation even when a high rotational torque is applied; in other words, a metal pipe for oil wells that has a high creep torque.

[0008] In this regard, creep torque is defined as follows. Figure 1 is a graph illustrating the relationship between the number of turns of an oil well metal pipe and the torque when the oil well metal pipe is clamped. Referring to Figure 1, when oil well metal pipes are clamped, the torque initially increases moderately in proportion to the number of turns. As clamping continues, the springs of the oil well metal pipe come into contact with each other. The torque at this point is called the spring torque, Ts. Once the spring torque Ts is reached, as clamping continues, the torque increases rapidly in proportion to the number of turns. Clamping ends when the torque reaches a predetermined value (clamping torque To). At the clamping torque To, a bolt contact surface and a box contact surface interfere with each other with adequate interfacial pressure.In this case, the gas tightness of the connected body of oil well tubing formed by the clamping of a plurality of metal oil well tubing sections is high. However, if the torque applied to the metal oil well tubing is further increased, in some cases a portion of the bolt and the box will yield, and plastic deformation will occur. The torque at that point is called the yield torque Ty.

[0009] In this respect, in a case where a metal oil well pipe does not have a raised section, i.e., in the case of a metal oil well pipe having a so-called "wedge thread," the relationship between the number of turns of the metal oil well pipe and the torque is as shown in Figure 1, similar to the case of the metal oil well pipe having a raised section. In this respect, in the case of a wedge (triangular) thread, in the direction in which the bolt is tightened, the width of a thread crest of an external threaded portion gradually narrows along the thread helix, while the width of a thread groove of the external threaded portion gradually widens along the thread helix.Furthermore, in the direction in which the bolt is screwed in, the width of a thread groove of an internal threaded part gradually narrows along the thread helix, and the width of a thread crest of the internal threaded part gradually widens along the thread helix.

[0010] In the case of a metal oil well pipe having a wedge thread and no jump section, as clamping progresses, the loading flanks of the external threaded portion and the internal threaded portion come into contact, and the driving flanks of the external threaded portion and the internal threaded portion come into contact, resulting in locking (interference fit). The torque at the moment locking occurs is called locking torque. Locking torque is equivalent to jump torque in a metal oil well pipe having a jump section. Therefore, in the present description, unless specifically stated otherwise, no distinction is made between locking torque and jump torque, and the term jump torque is used to refer to both.In the case of a metal oil well pipe with a wedge thread, as with a metal oil well pipe with a jump section, once the jump torque Ts is reached, if clamping or tightening continues, the torque will increase rapidly in proportion to the number of turns. Furthermore, if tightening or clamping continues after that point, the yield torque Ty is produced.

[0011] As previously described, there is a recent need for a metal oil well pipe with high yield torque that is not susceptible to plastic deformation even under high rotational torque. International Application Publication No. 2013 / 176281 (Patent Document 2) proposes a pipe-like threaded connection that excels in high-torque clamping performance. In the pipe-like threaded connection described in Patent Document 2, a first solid lubricant coating is formed on a portion that includes a raised part of the contact surface of at least one bolt and housing. Furthermore, a second solid lubricant coating is formed on at least a portion of the contact surface. RQzznn / pznz / B / YiAi in which the first solid lubricant coating does not form. The Knoop hardness of the first solid lubricant coating is greater than the Knoop hardness of the second solid lubricant coating. During clamping, until the raised portion of the bolt and the raised portion of the housing make contact, the second solid lubricant coating, which has the lower Knoop hardness, acts, thus reducing the coefficient of friction during clamping. Therefore, the clamping torque remains low. After the raised portion of the bolt and the raised portion of the housing make contact, the first solid lubricant coating, which has the higher Knoop hardness, acts, thus increasing the coefficient of friction. In this way, the yield torque increases. LIST OF REFERENCES 10 PATENT DOCUMENTS

[0012] Patent Document 1: International Application Publication No. 2009 / 072486 Patent Document 2: International Application Publication No. 2013 / 176281 SUMMARY OF THE INVENTION15TECHNICAL PROBLEM

[0013] It is possible to increase the yield torque using the technique described in Patent Document 2. However, the yield torque can also be increased by other techniques. Furthermore, as described above, a metal pipe for oil wells is also required to have excoriation resistance. Therefore, it is desirable to be able to achieve both a high yield torque and excellent excoriation resistance in a compatible manner.

[0014] One objective of the present description is to provide a metal oil well pipe that is capable of achieving both high yield torque and excellent scouring resistance in a compatible manner. SOLUTION TO THE PROBLEM

[0015] A metal pipe for oil wells in accordance with the present description includes: a main tube body including a first end portion and a second end portion: where: The main tube body includes: a bolt formed in the first end portion and a box formed in the second end portion; The bolt includes: a bolt contact surface having at least one external threaded portion formed on an outer peripheral surface of the first end portion of the main tube body; RQzznn / pznz / B / γΐΛΐ the box includes: a box contact surface having at least one internally threaded portion formed on an internal peripheral surface of the second end portion of the main tube body; A metallic coating layer is formed on a first contact surface, the first contact surface being one of the bolt contact surface and the box contact surface; A layer of solid lubricant forms over the metallic coating layer; The arithmetic mean roughness Ra of a second contact surface is within a range of 0.5 to 10.0 pm, the second contact surface being the other bolt contact surface and the box contact surface; and on the second contact surface a semi-solid or liquid anti-rust coating is formed. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0016] A metal oil well pipe conforming to the present modality can achieve both high yield torque and excellent scouring resistance in a compatible manner. BRIEF DESCRIPTION OF THE FIGURES

[0017] Figure 1 is a graph illustrating the relationship between the number of turns of an oil well metal pipe and the torque when the oil well metal pipe is clamped. Figure 2 is a configuration diagram illustrating an example of a T&C type metal oil well pipe in accordance with the present modality. Figure 3 is a partial cross-sectional view illustrating a cross-section (longitudinal cross-section) parallel to a tube axis direction of a copy of a metal oil well pipe illustrated in Figure 2. Figure 4 is a cross-sectional view parallel to the axis direction of the metal oil well pipe illustrated in Figure 3, illustrating a portion in the vicinity of a bolt of the metal oil well pipe. Figure 5 is a cross-sectional view parallel to the axis direction of the metal oil well pipe illustrated in Figure 3, illustrating a portion in the vicinity of a box of the metal oil well pipe. Figure 6 is a configuration diagram illustrating another T&C type metal oil well tubing that is different from Figure 2. Figure 7 is a configuration diagram illustrating an integral-type metal pipe for oil wells in accordance with the present modality. RQzznn / pznz / B / YiAi Figure 8 is a cross-sectional view to describe the structure at a first contact surface in a case where the first contact surface is a box contact surface. Figure 9 is a cross-sectional view to describe the structure on a second contact surface in a case where the second contact surface is a bolt contact surface. Figure 10 is an enlarged view of a portion in the vicinity of the second contact surface (in Figure 9, the bolt contact surface) illustrated in Figure 9. Figure 11 is a cross-sectional view to describe the structure at a first contact surface in a case where the first contact surface is a bolt contact surface. Figure 12 is a cross-sectional view to describe the structure on a second contact surface in a case where the second contact surface is a box contact surface. Figure 13 is a view illustrating the structure of a second contact surface including a chemically treated coating in a case where the second contact surface is a bolt contact surface. Figure 14 is a torque table to describe a creep torque measurement test with respect to the Examples. DESCRIPTION OF THE MODALITIES

[0018] This modality will be described in detail below with reference to the accompanying drawings. The same reference symbols will be used throughout the drawings to refer to identical or similar parts, and their description will not be repeated.

[0019] The present inventors carried out several studies regarding a metal pipe for oil wells that can achieve both high yield torque and excellent resistance to scaling in a compatible manner. As a result, the present inventors obtained the following results.

[0020] To increase the resistance to scoring during the clamping of a metal oil well pipe, it is preferable to form a metallic coating layer on a contact surface (hereinafter referred to as the first contact surface) between a bolt contact surface (hereinafter referred to as the bolt contact surface) and a box contact surface (hereinafter referred to as the box contact surface'1), and also to form a layer of solid lubricant over the metallic coating layer. The resistance to scoring is increased by the lubricating action of the solid lubricant layer. The metallic coating layer also increases the resistance to scoring, and a metallic coating layer having high hardness and a high melting point further increases the resistance to scoring during clamping.Therefore, the present inventors thought that, taking into account the resistance to abrasion, it is preferable to form a metallic coating layer and a layer. RQzznn / pznz / B / YiAi of laminated solid lubricant on the first contact surface, which is one between the bolt contact surface and the box contact surface.

[0021] In a case where a metallic coating layer and a solid lubricant layer are laminated over the first contact surface, which is a contact surface between the bolt contact surface and the box contact surface, the present inventors also carried out studies regarding the structure of a second contact surface, which is the other contact surface between the bolt contact surface and the box contact surface, in order to increase the yield torque while maintaining the resistance to scoring.

[0022] In this regard, after their manufacture, metal oil well pipes are stored outdoors in a local yard near the well drilling site until they are actually used for drilling. Therefore, a metal oil well pipe is also required to have some corrosion resistance, not just excoriation resistance. Thus, in a conventional metal oil well pipe, between the bolt contact surface and the box contact surface of the metal oil well pipe, a solid lubricating layer sometimes forms on the top layer of the first contact surface, and a solid anti-corrosion coating, composed of a UV-curable resin, forms on the top layer of the second contact surface. However, a solid anti-corrosion coating does not increase yield torque.

[0023] Therefore, the present inventors conceived the idea of ​​increasing the coefficient of friction and increasing the yield torque during clamping by giving the surface shape (texture) of the second contact surface a different shape than that of conventional metal oil well pipe, without employing a solid anti-corrosion coating. Furthermore, as a result of additional considerations, the present inventors conceived the idea that if the second contact surface is roughened to a certain degree, when the first and second contact surfaces come into strong contact during clamping, a high coefficient of friction will be achieved through the metallic coating layer under the solid lubricant layer of the first contact surface and the irregularity of the second contact surface, and as a result, the yield torque will be increased.

[0024] Furthermore, it is preferable that corrosion resistance be assured to some extent on the second contact surface. However, if a known conventional solid anti-corrosion coating is formed on the second contact surface, the surface of which has been roughened, the irregularity of the second contact surface will not be reflected on the surface of the solid anti-corrosion coating, and consequently, the surface of the solid anti-corrosion coating will not be rough to the extent of the irregularity of the second contact surface. RQzznn / pznz / Β / γΐΛΐ

[0025] Therefore, the present inventors conceived of forming a semi-solid or liquid anti-corrosive coating, rather than a solid coating, on the second contact surface, which is a rough surface. When a semi-solid or liquid anti-corrosive coating is formed on the rough second contact surface, the anti-corrosive property of the second contact surface is ensured by the anti-corrosive coating, and when the first contact surface and the second contact surface come into close contact during thread tightening, the anti-corrosive coating on the contact portion easily detaches from between the first and second contact surfaces.Thus, by means of the metallic coating layer under the solid lubricant layer of the first contact surface and the irregularity of the second contact surface, a high coefficient of friction is obtained and, as a result, the creep torque is increased.

[0026] A metal pipe for oil wells of the present modality, which has been completed based on the above results, has the following structure.

[0027] [1] A metal pipe for oil wells comprising: a main tube body including a first end portion and a second end portion, wherein: The main tube body includes: a bolt formed in the first end portion, and a box formed in the second end portion; The bolt includes: a bolt contact surface having at least one external threaded portion formed on an outer peripheral surface of the first end portion of the main tube body; The box includes: a box contact surface having at least one internal threaded portion formed on an internal peripheral surface of the second end portion of the main tube body; A metallic coating layer is formed on a first contact surface, the first contact surface being one of the contact surfaces of the bolt and the contact surface of the box; a layer of solid lubricant formed on the metallic coating layer; an arithmetic mean roughness Ra of a second contact surface is within a range of 0.5 to 10.0 pm, the second contact surface being the other bolt contact surface and the box contact surface; and a semi-solid or liquid anti-rust coating is formed on the second contact surface.

[0028] [2] The metal oil well pipe in accordance with [1], wherein: RQzznn / pznz / B / YiAi A chemical treatment coating is also formed on the second contact surface, and the antioxidant coating is formed on the chemical treatment coating.

[0029] [3] The metal pipe for oil wells in accordance with [1] or [2], wherein: The second contact surface is subjected to shot blasting treatment.

[0030] [4] The metal pipe for oil wells in accordance with [1] to [3], wherein: the metallic coating layer is composed of a Zn-Ni alloy.

[0031] The metal pipe for oil wells of the present modality will be described in detail below.

[0032] [Metal pipe structure for oil wells]. First, before describing the metal oil well pipe covered herein, the structures of the metal oil well pipes covered herein shall be described. The available types of metal oil well pipe are a T&C type metal oil well pipe and an integral type metal oil well pipe. Each type of metal oil well pipe shall then be described in detail.

[0033] [Case in which the metal pipe for oil wells 1 is of type T&C]. Figure 2 is a configuration diagram illustrating an example of a metal oil well pipe 1 conforming to this modality. Figure 2 is a configuration diagram illustrating the T&C (threaded and coupled) type metal oil well pipe 1. With reference to Figure 2, the metal oil well pipe 1 includes a main pipe body 10.

[0034] The main body of pipe 10 extends in the direction of the pipe axis. A cross-section perpendicular to the pipe axis direction of the main body of pipe 10 is circular. The main body of pipe 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is an end portion at the opposite end from the second end portion 10B. In the T&C type 1 oil well metal pipe illustrated in Figure 2, the main body of pipe 10 includes a bolt-on pipe body 1 and a copier 12. The copier 12 is attached to one end of the oil well metal pipe. The copier 12 is attached to one end of the bolt-on pipe body 11. More specifically, the copier 12 is threaded onto one end of the bolt-on pipe body 11.

[0035] Figure 3 is a partial cross-sectional view illustrating a cross-section (longitudinal cross-section) parallel to the tube axis direction of the copy 12 of the oil well metal pipe 1 illustrated in Figure 2. With reference to Figure 2 and Figure 3, the main body of pipe 10 includes a bolt 40 and a box 50. The bolt 40 is formed on the first end portion 10A of the main body of pipe 10. When making the fastening, the bolt 40 is inserted into the box of another oil well metal pipe (not illustrated), and is secured by screwing it into the box of the other oil well metal pipe.

[0036] Box 50 is formed on the second end portion 10B of the main body of pipe 10. When performing the clamping, the bolt of another metal oil well pipe 1 is inserted into box 50, and box 50 is secured by threading to the bolt of the other metal oil well pipe 1.

[0037] [Regarding the structure of bolt 40] Figure 4 is a cross-sectional view of a portion in the vicinity of bolt 40 of the oil well metal pipe 1 illustrated in Figure 3, which is a cross-sectional view parallel to the pipe axis direction of the oil well metal pipe 1. A dashed line portion in Figure 4 represents the box structure 50 of another oil well metal pipe in the case of clamping the oil well metal pipe 1 to another oil well metal pipe 1. With reference to Figure 4, bolt 40 includes a bolt contact surface 400 on the outer peripheral surface of the first end portion 10A of the main body of pipe 10. The bolt contact surface 400 comes into contact with the box contact surface 500 of the box 50 of the other oil well metal pipe 1 when clamping it to the other oil well metal pipe 1.

[0038] The contact surface of bolt 400 includes at least one external threaded portion 41 formed on the outer peripheral surface of the first end portion 10A. The contact surface of bolt 400 may further include a bolt sealing surface 42 and a bolt shoulder surface 43. In Figure 4, on the outer peripheral surface of the first end portion 10A, the bolt sealing surface 42 is disposed farther along the front end side of the first end portion 10A than the external threaded portion 41. In other words, the bolt sealing surface 42 is disposed between the external threaded portion 41 and the bolt shoulder surface 43. The bolt sealing surface 42 has a tapered shape.Specifically, the outside diameter of the bolt sealing surface 42 gradually decreases from the external threaded portion 41 towards the bolt shoulder surface 43 in the longitudinal direction (pipe axis direction) of the first end portion 10L.

[0039] When clamping with another metal oil well pipe 1, the sealing surface of bolt 42 comes into contact with a sealing surface of box 52 (described below) of the box 50 of the other metal oil well pipe 1. More specifically, during clamping, when bolt 40 is inserted into the box 50 of the other metal oil well pipe 1, the sealing surface of bolt 42 comes into contact with the sealing surface of box 52. Subsequently, when bolt 40 is further screwed into the box 50 of the other metal oil well pipe 1, the sealing surface of bolt 42 comes into close contact with the sealing surface of box 52. Thus, during clamping, the sealing surface of bolt 42 comes into close contact with the sealing surface of box 52, thereby forming a metal-to-metal seal.Therefore, gas tightness can be increased in metal oil well pipes 1 that are attached to each other.

[0040] In Figure 4, the bolt shoulder surface 43 is arranged on the front end face of the first end portion 10A. In other words, on the bolt 40 illustrated in Figure 4, the external threaded portion 41, the bolt sealing surface 42, and the bolt shoulder surface 43 are arranged sequentially in that order from the center of the main tube body 10 toward the front end of the first end portion 10A. During clamping to the other metal oil well pipe 1, the bolt 43 shoulder surface opposes and comes into contact with a box 53 shoulder surface (described below) of the box 50 of the other metal oil well pipe 1. More specifically, during clamping, the bolt 43 shoulder surface comes into contact with the box 53 shoulder surface as a result of the insertion of bolt 40 into the box 50 of the other metal oil well pipe 1.This method allows for high torque to be achieved during clamping. Furthermore, the positional relationship between bolt 40 and housing 50 can be stabilized in the clamped state.

[0041] Note that the contact surface of bolt 400 includes at least the external threaded portion 41. In other words, the contact surface of bolt 400 includes the external threaded portion 41, and need not include the sealing surface of bolt 42 and the shoulder surface of bolt 43. The contact surface of bolt 400 may include the external threaded portion 41 and the shoulder surface of bolt 43, and need not include the sealing surface of bolt 42. The contact surface of bolt 400 may include the external threaded portion 41 and the sealing surface of bolt 42, and need not include the shoulder surface of bolt 43. In the case of a metal oil well pipe having a wedge thread as described above, bolt 40 does not have the shoulder surface of bolt 43.Note that, in a case where bolt 40 does not have the shoulder surface of bolt 43, box 50 does not have the shoulder surface of box 53.

[0042] [Regarding box structure 50] Figure 5 is a cross-sectional view of a portion in the vicinity of box 50 of the oil well metal pipe 1 illustrated in Figure 3, which is a cross-sectional view parallel to the pipe axis direction of the oil well metal pipe 1. A dashed line portion in Figure 5 represents the bolt structure 40 of another oil well metal pipe 1 in the case of clamping the oil well metal pipe 1 to another oil well metal pipe 1. With reference to Figure 5, box 50 includes a box contact surface 500 on the inner peripheral surface of the second end portion 10B of the main body of pipe 10.When attaching to another metal oil well pipe 1, the contact surface of box 500 comes into contact with the contact surface of bolt 400 of bolt 40 of the other metal oil well pipe 1 when bolt 40 is screwed into box 50. RQzznn / pznz / Β / γΐΛΐ

[0043] The box contact surface 500 includes at least one internal threaded portion 51 formed on the inner peripheral surface of the second end portion 10B. When clamping, the internal threaded portion 51 engages with the external threaded portion 41 of the bolt 40 of the other metal oil well pipe.

[0044] The box contact surface 500 may further include the box sealing surface 52 and the box shoulder surface 53. In Figure 5, on the inner peripheral surface of the second end portion 10B, the box sealing surface 52 is disposed farther along the side of the main pipe body 10 than the internal threaded portion 51. In other words, the box sealing surface 52 is disposed between the internal threaded portion 51 and the box shoulder surface 53. The box sealing surface 52 has a tapered shape.Specifically, the inside diameter of the box sealing surface 52 gradually decreases from the internal threaded portion 51 towards the box shoulder surface 53 in the longitudinal direction (pipe axis direction) of the second end portion 10B.

[0045] When clamping to another metal oil well pipe 1, the sealing surface of box 52 comes into contact with the sealing surface of bolt 42 of bolt 40 of the other metal oil well pipe 1. More specifically, during clamping, when bolt 40 of the other metal oil well pipe 1 is screwed into box 50, the sealing surface of box 52 comes into contact with the sealing surface of bolt 42, and when bolt 40 is screwed in further, the sealing surface of box 52 comes into close contact with the sealing surface of bolt 42. Thus, during clamping, the sealing surface of box 52 comes into close contact with the sealing surface of bolt 42 to form a metal-to-metal seal. Therefore, the tightness of the metal oil well pipes 1 that are clamped together can be increased.

[0046] The box shoulder surface 53 is arranged closer to the center of the main tube body 10 in the axial direction of the tube than the box sealing surface 52. In other words, in the box 50, the box shoulder surface 53, the box sealing surface 52, and the internal threaded portion 51 are arranged sequentially in that order from the center of the main tube body 10 toward the front end of the second end portion 10B in the axial direction of the tube. When clamping to another metal oil well pipe 1, the box shoulder surface 53 opposes and makes contact with the bolt shoulder surface 43 of the bolt 40 of the other metal oil well pipe 1. More specifically, during clamping, the box shoulder surface 53 comes into contact with the bolt shoulder surface 43 as a result of the insertion of the bolt 40 of the other metal oil well pipe 1 into the box 50.In this way, a high torque can be achieved during clamping. Furthermore, the positional relationship between bolt 40 and housing 50 can be stabilized in the clamped state.

[0047] The box contact surface 500 includes at least the internal threaded portion 51. When clamping, the internal threaded portion 51 of the box contact surface 500 of box 50 makes contact with the external threaded portion 41 of the bolt contact surface 400 of bolt 40 such that the portion RQzznn / pznz / B / GALA internal threaded part 51 corresponds with the external threaded part 41. The box sealing surface 52 comes into contact with the bolt sealing surface 42 such that the box sealing surface 52 corresponds with the bolt sealing surface 42. The box shoulder surface 53 makes contact with the bolt shoulder surface 43 such that the box shoulder surface 53 corresponds with the bolt shoulder surface 43.

[0048] In an instance where the bolt contact surface 400 includes the external threaded portion 41 and does not include the bolt sealing surface 42 and the bolt shoulder surface 43, the box contact surface 500 includes the internal threaded portion 51 and does not include the box sealing surface 52 and the box shoulder surface 53. In an instance where the bolt contact surface 400 includes the external threaded portion 41 and the bolt shoulder surface 43 and does not include the bolt sealing surface 42, the box contact surface 500 includes the internal threaded portion 51 and the box shoulder surface 53 and does not include the box sealing surface 52.In a case where the contact surface of pemo 400 includes the external threaded part 41 and the sealing surface of pemo 42 and does not include the raised surface of pemo 43, the contact surface of box 500 includes the internal threaded part 51 and the sealing surface of box 52 and does not include the raised surface of box 53.

[0049] The contact surface of pemo 400 may include a plurality of the external thread portions 41, may include a plurality of the bolt sealing surfaces 42, and may include a plurality of the pemo 43 shoulder surfaces. For example, the pemo 43 shoulder surface, the pemo 42 sealing surface, the external thread portion 41, the pemo 42 sealing surface, the pemo 43 shoulder surface, the pemo 42 sealing surface, and the external thread portion 41 may be arranged in that order on the contact surface of pemo 400 of pemo 40 in the direction from the front end of the first end portion 10A toward the center of the main tube body 10.In that case, the internal threaded part 51, the box sealing surface 52, the box shoulder surface 53, the box sealing surface 52, the internal threaded part 51, the box sealing surface 52 and the box shoulder surface 53 are arranged in that order on the box contact surface 500 of the box 50 in the direction from the front end of the second end portion 10B towards the center of the main tube body 10.

[0050] Figure 4 and Figure 5 illustrate a so-called premium joint in which the bolt 40 includes the external threaded portion 41, the bolt sealing surface 42, and the bolt shoulder surface 43, and the box 50 includes the internal threaded portion 51, the box sealing surface 52, and the box shoulder surface 53. However, as described above, the bolt 40 may include the external threaded portion 41 and need not include the bolt sealing surface 42 and the bolt shoulder surface 43. In this case, the box 50 includes the internal threaded portion 51 and does not include the box sealing surface 52 and the box shoulder surface 53.Figure 6 is a view illustrating an example of the metal oil well pipe 1 in which the bolt 40 includes the external threaded portion 41 and does not include the bolt sealing surface 42 and the bolt shoulder surface 43, and the box 50 includes the internal threaded portion 51 and does not include the box sealing surface 52 and the box shoulder surface 53. [0051 ] [Case in which the metal pipe for oil wells 1 is of integral type]. The metal oil well pipe 1 illustrated in Figure 2, Figure 3, and Figure 6 is a metal oil well pipe 1 designated as type T&C, wherein the main pipe body 10 includes the bolt pipe body 11 and the copier 12. However, the metal oil well pipe 1 is of integral type. Nevertheless, the metal oil well pipe 1 in accordance with the present embodiment may be of integral type instead of type T&C.

[0052] Figure 7 is a configuration diagram of an integral-type oil well metal pipe 1, in accordance with the present modality. With reference to Figure 7, the integral-type oil well metal pipe 1 includes a main pipe body 10. The main pipe body 10 includes a first main pipe body. The main pipe body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is disposed on the opposite side from the second end portion 10B. As described above, in the T&C 1 type oil well metal pipe, the main pipe body 10 includes the bolt pipe body 11 and the copy 12. In other words, in the T&C 1 type oil well metal pipe, the main pipe body 10 consists of the fastening of two separate members (the bolt pipe body 11 and the copy 12).Conversely, in the integral type 1 oil well metal pipe, the main body of pipe 10 is integrally formed.

[0053] Bolt 40 is formed on the first end portion 10A of the main body of pipe 10. When performing the clamping, bolt 40 is inserted and screwed into the box 50 of another integral-type oil well metal pipe I, thereby clamping it to the box 50 of another integral-type oil well metal pipe 1. Box 50 is formed on the second end portion 10B of the main body of pipe 10. When performing the clamping, bolt 40 of another integral-type oil well metal pipe 1 is inserted and screwed into box 50, thereby clamping box 50 to bolt 40 of the other integral-type oil well metal pipe 1.

[0054] The structure of bolt 40 of integral type 1 oil well metal pipe is the same as the structure of bolt 40 of type T&C oil well metal pipe 1 illustrated in Figure 4. Likewise, the structure of box 50 of integral type 1 oil well metal pipe is the same as the structure of box 50 of type T&C oil well metal pipe 1 illustrated in Figure 5. Note that, in Figure 7, on bolt 40, the bolt shoulder surface, bolt sealing surface, external threaded portion, bolt sealing surface, bolt shoulder surface, bolt sealing surface, and external threaded portion are arranged in that order from the front end of the first end portion 10A toward the center of the main body of pipe 10 in the axial direction of the pipe.Therefore, in box 50, the internal threaded part, the box sealing surface, the box shoulder surface, the box sealing surface, the internal threaded part, the box sealing surface, and the box shoulder surface are arranged in this order from the front end of the second end portion 10B towards the center of the main tube body 10 in the axial direction of the tube. However, similar to Figure 4, it is sufficient that the contact surface of bolt 400 of bolt 40 of integral-type oil well metal pipe 1 includes at least the external threaded portion 41. Furthermore, similar to Figure 5, it is sufficient that the contact surface of box 500 of box 50 of integral-type oil well metal pipe 1 includes at least the internal threaded portion 51.

[0055] In summary, the oil well metal pipe 1 of the present embodiment may be of T&C type or integral type.

[0056] A metal pipe for oil wells 1 may be an Fe-based alloy steel pipe or an alloy pipe represented by a Ni-based alloy pipe. The steel pipe is, for example, a low-alloy pipe, a martensitic stainless steel pipe, and a duplex stainless steel pipe.

[0057] [With regard to the structure on the contact surface of bolt 400 or the contact surface of box 500] In the metal oil well pipe l of the present embodiment, a metallic coating layer 60 is formed on a first contact surface, which is one of the pin contact surface 400 and the box contact surface 500, and a solid lubricant layer 70 is also formed on the metallic coating layer 60. Furthermore, an arithmetic mean roughness Ra of a second contact surface, which is the other of the pin contact surface 400 and the box contact surface 500, is within a range of 0.5 to 10.0 pm, and a semi-solid or liquid anti-corrosive coating 80 is formed on the second contact surface.

[0058] The structure on the first contact surface and the structure on the second contact surface will now be described in a case where the first contact surface is the box contact surface 500 and the second contact surface is the bolt contact surface 400. However, the structure on the first contact surface and the structure on the second contact surface in a case where the first contact surface is the bolt contact surface 400 and the second contact surface is the box contact surface 500 are the same as in the case described below.

[0059] [Structure on the first contact surface] Figure 8 is a cross-sectional view illustrating the structure at the first contact surface in a case where the first contact surface is the box contact surface 500. Referring to Figure 8, the metallic coating layer 60 is formed on the first contact surface. Additionally, the solid lubricant layer 70 forms on top of the metallic coating layer 60. The metallic coating layer 60 and the solid lubricant layer 70 will be described below.

[0060] [With regard to the metallic coating layer 60] The type of metallic coating layer 60 is not particularly limited. For example, metallic coating layer 60 can be a zinc coating layer, a nickel coating layer, a copper coating layer, a zinc-ni alloy coating layer, a zinc-coated alloy coating layer, a nickel-metal alloy coating layer, a nickel-metal alloy coating layer, or a copper-stainless-zinc alloy coating layer. Metallic coating layer 60 can be formed by laminating multiple coating layers. For example, a nickel coating layer can be formed on the first contact surface, and a zinc-ni coating layer can then be laminated and formed on top of the nickel coating layer.

[0061] Where the metallic coating layer 60 is a Cu-Sn-Zn alloy metallic coating layer, the chemical composition of the Cu-Sn-Zn alloy coating consists of, for example, Cu: 40 to 70% by mass, Sn: 20 to 50% by mass, and Zn: 2 to 20% by mass, the remainder being impurities. Where the metallic coating layer 60 is a Cu metallic coating layer, the chemical composition of the Cu metallic coating layer consists of, for example, Cu and impurities.

[0062] Preferably, the metallic coating layer 60 is composed of a Zn alloy metallic coating made up of one or more types of elements selected from the group consisting of Ni, Fe, Mg, and Mn, and Zn. These Zn alloy metallic coatings have high hardness and a high melting point. Therefore, these Zn alloy metal coatings exhibit excellent resistance to scaling.Furthermore, because zinc is a more basic metal than the steel material that serves as the base metal of the main body of pipe 10, zinc exhibits sacrificial protection. Therefore, in a case where the metallic coating 60 is composed of a zinc alloy coating, the metallic coating 60 also exhibits excellent corrosion resistance, not just excoriation resistance.

[0063] Furthermore, preferably, the metallic coating layer 60 is a Zn-Ni alloy metallic coating layer. The Zn-Ni alloy metallic coating layer is composed of a Zn-Ni alloy. The Zn-Ni alloy includes zinc (Zn) and nickel (Ni). Occasionally, the Zn-Ni alloy may contain impurities. In this case, the term "impurities" with respect to the Zn-Ni alloy means substances other than Zn and Ni that become contained in the Zn-Ni alloy metallic coating layer during the production or similar processes of the oil well metal tubing, and whose content is within a range that does not influence the effects of the present modality. The Zn-Ni alloy not only has excellent corrosion resistance, but, as described above, it also has high hardness and a high melting point, and therefore has excellent resistance to scaling.

[0064] In the Zn-Ni alloy metallic coating layer, preferably when the total Zn and Ni are taken as 100% by mass, the proportion of Ni contained is within the range of 10 to 20% by mass. A preferred lower limit for the Ni content in the Zn-Ni alloy metallic coating layer is 11% by mass, and preferably 12% by mass. A preferred upper limit for the Ni content in the Zn-Ni alloy metallic coating layer is 18% by mass, more preferably 16% by mass, and even more preferably 15% by mass.

[0065] [Method for measuring the chemical composition of the metallic coating layer of Zn-Ni alloy], In a case where the metallic coating layer 60 is a Zn-Ni alloy coating, its chemical composition can be measured from a cross-section of the coating layer using an energy-dispersive X-ray spectrometer (EDX). For operational control during production, a simple, non-destructive measurement method is preferable. Therefore, the chemical composition of the Zn-Ni alloy coating can be measured, for example, from the coating surface using a fluorescence X-ray analyzer. In this case, a correction is made as needed using a standard sample whose chemical composition has been predetermined.

[0066] [Metallic coating layer thickness 60] The thickness of the metallic coating layer 60 is not particularly limited. For example, the thickness of the metallic coating layer 60 is within the range of 1 to 20 µm. If the thickness of the metallic coating layer 60 is 1 µm or more, sufficient resistance to scaling can be achieved. On the other hand, if the thickness of the metallic coating layer 60 exceeds 20 µm, the aforementioned effects will become saturated. The lower limit for the thickness of the metallic coating layer 60 is preferably 3 µm, and more preferably 5 µm. The upper limit for the thickness of the metallic coating layer 60 is preferably 18 µm, and more preferably 15 µm.

[0067] The thickness of the metallic coating layer 60 can be measured using the following method. A sample is taken that includes a cross-section of the metallic coating layer 60. The thickness of the metallic coating layer 60 is then measured at three arbitrary locations within the cross-section of the metallic coating layer 60. The arithmetic mean of the measured thicknesses is defined as the thickness (pm) of the metallic coating layer 60. Apart from the method mentioned above, the thickness of the metallic coating layer 60 can also be measured from the surface of the metallic coating layer using a fluorescent X-ray analyzer. RQzznn / pznz / B / YiAi is similar to the measurement of the chemical composition of the metallic coating layer described above. In this case, the correction is made as appropriate using a standard sample whose chemical composition has been determined beforehand.

[0068] [Solid lubricating layer 70] The solid lubricating layer 70 is further formed on top of the metallic coating layer 60. During clamping, the solid lubricating layer 70 increases the lubricity of the box 50 and bolt 40 of the metal oil well pipe 1. The solid lubricating layer 70 is a solid coating at normal temperature (20 °C ± 15 °C).

[0069] The terms solid, semisolid, and liquid used in this description are defined as follows, respectively. The term solid means a state in which the shape is fixed at normal temperature, and even when an external force is applied, the shape remains unchanged or at least some part of it breaks. The term semisolid refers to a state in which, although a certain shape is maintained at normal temperature, in the event of an external force being applied, at least some part of it that receives the external force readily changes shape without breaking. In this description, a fatty state and a semi-dry state are included within the scope of the definition of semisolid. The term liquid refers to the state of a liquid. Note that a state in which the volatile components of a liquid evaporate and the non-volatile components with viscosity remain also corresponds to a semisolid or liquid.

[0070] Solid lubricant layer 70 contains, for example, a solid lubricant powder and a binder that serves as a matrix. In other words, solid lubricant layer 70 is a layer made of a heterogeneous system coating in which the solid lubricant powder is bonded with a binder.

[0071] [Solid lubricating powder] A solid lubricating powder is a powder that exhibits lubricating action. A known material conventionally used as a solid lubricant may be used as a solid lubricating powder. A material that does not adversely affect the environment is preferable as a solid lubricating powder.

[0072] The preferred solid lubricating powder contains one or more types selected from a group consisting of molybdenum sulfide (MoS2), tungsten disulfide (WS2), graphite or boron nitride (BN), carbon black, polytetrafluoroethylene (PTFE) powder, and graphitic fluoride (CFx). Molybdenum sulfide (MoS2) and tungsten disulfide (WS2) are inorganic powders having a graphitic crystalline structure. The average particle diameter of the solid lubricating powder is not particularly limited. The average particle diameter of the solid lubricating powder is, for example, within the range of 0.5 to 15 µm.

[0073] In the solid lubricant layer 70, the preferred mass ratio of the total amount of solid lubricant powder to the total amount of binder is within the range of 0.3 to RQzznn / pznz / Β / γΐΛΐ 0.9. If the mass ratio between the total amount of solid lubricating powder and the total amount of binder is 0.3 or more, the abrasion resistance of the solid lubricating layer 70 increases even further. If the mass ratio of the total amount of solid lubricating powder to the total amount of binder is 0.9 or less, the adhesiveness of the solid lubricating layer 70 increases even further, and the resistance of the solid lubricating layer 70 increases even further.

[0074] Solid lubricating layer 70 may also contain a powder other than a solid lubricating powder. For example, solid lubricating layer 70 contains solid lubricating powder and silica. The other powder is, for example, an inorganic powder that does not have a graphitic crystalline structure. When solid lubricating layer 70 contains solid lubricating powder and the other powder, the preferred mass ratio of the total amount of solid lubricating powder and the other powder to the total amount of binder is 0.9 or less.

[0075] [Binder] The binder in the 70 solid lubricant layer consists of an organic resin and / or an inorganic macromolecular compound.

[0076] An organic resin binder is preferably an organic resin that has heat resistance, moderate hardness, and moderate abrasiveness. An organic resin binder consists, for example, of one or more types selected from the group consisting of a thermosetting resin and a thermoplastic resin. The organic resin consists of one or more types selected from the group consisting of epoxy resin, polyimide resin, polyamide-imide resin, polycarbodiimide resin, polyethersulfone, polyether ether ketone, phenol resin and furan resin, polyvinyl resin, acrylic resin and polyurethane resin, polyethylene resin, silicone resin, and fluororesin.

[0077] From the standpoint of improving the adhesion of the solid lubricant layer 70, the solid lubricant layer 70 can be formed by performing a heat curing process on a liquid composition that is the raw material for the solid lubricant layer 70 and contains a solid lubricant powder and a binder (hereinafter referred to as an organic liquid composition). The heat curing treatment temperature is preferably 80 °C or higher, and more preferably within the range of 150 to 380 °C. The treatment time is preferably 5 minutes or more, and more preferably from 20 to 60 minutes. The heat curing process may include a pre-drying process and a baking process. In the pre-drying process, the temperature is maintained at 80–100 °C for 2 to 15 minutes. The baking process is performed after the pre-drying process. In the baking process, the temperature is maintained at 150 to 380 °C for 10 to 50 minutes.

[0078] An inorganic macromolecular compound used as a binder is, for example, a compound with a structure in which the metal-oxygen bonds are three-dimensionally crosslinked, such as Ti-O, Si-O, Zr-O, Mn-O, Ce-O, or Ba-O. Such inorganic macromolecular compounds can be formed RQzznn / pznz / B / YiAi by hydrolysis and condensation of a hydrolyzable metal compound, such as a metal alkoxide or chloride. The inorganic transmolecular compound can be formed using a hydrolyzable metal compound containing a functional group such as an amine or an epoxy group. A hydrolyzable metal compound containing a functional group such as an amine or an epoxy group is, for example, a silane coupling agent or a titanate coupling agent.

[0079] When an inorganic macromolecular compound is contained as a binder, the solid lubricating layer 70 is formed, for example, by the following method. A liquid composition containing a solvent of a hydrolyzable metallic compound or a partial hydrolysate thereof and a solid lubricating powder (hereinafter referred to as the inorganic liquid composition) is applied to the metallic coating layer 60. The applied liquid composition is subjected to a humidification and / or heating treatment. Through the above processes, the solid lubricating layer 70 containing an inorganic macromolecular compound as a binder is formed.

[0080] As described above, a humidification treatment can be performed to promote the hydrolysis of a hydrolyzable metal compound. In the humidification treatment, the applied liquid composition is left in atmospheric air, preferably in a humidified atmosphere with a relative humidity of 70% or higher, for a predetermined period of time. Preferably, heating is performed after the humidification treatment. The condensation of the hydrolysate produced by the hydrolysis of the metal compound and the discharge of a byproduct (water) from the condensation of a byproduct (alcohol in the case that the metal compound is a metal alkoxide) of the hydrolysis are promoted by heating. As a result, the 70% solid lubricant layer can form in a short period.Furthermore, heating after the humidification treatment strengthens the adhesiveness of the solid lubricant layer 70. Heating after the humidification treatment is preferably performed after the remaining solvent in the coating film has evaporated. The heating temperature for this process is preferably set to between 50 and 200°C, which is close to the boiling point of the alcohol produced as a byproduct. Heating in a hot air oven is also effective.

[0081] The thickness of the 70 solid lubricant layer is 3 to 50 µm. A preferred thickness for the 70 solid lubricant layer is 10 to 40 µm. When the thickness of the 70 solid lubricant layer is 10 µm or more, high lubricity with greater consistency can be achieved. On the other hand, when the thickness of the 70 solid lubricant layer is 40 µm or less, the adhesion of the 70 solid lubricant layer is more consistent. Furthermore, when the thickness of the 70 solid lubricant layer is 40 µm or less, the thread clearance of the sliding surfaces increases. In this case, the interfacial pressure during sliding decreases. Therefore, excessively high clamping torque can be prevented. RQzznn / pznz / B / YiAi Therefore, a preferred thickness of the 70 solid lubricant layer is within the range of 10 to 40 µm. A more preferred lower limit for the thickness of the 70 solid lubricant layer is 15 µm, and even more preferably 20 µm. A more preferred upper limit for the thickness of the 70 solid lubricant layer is 35 µm, and even more preferably 30 µm.

[0082] The thickness of the solid lubricant 70 layer is measured using the following method. A sample is taken that includes the first contact surface on which the solid lubricant 70 layer forms. A surface between the sample surfaces corresponds to a cross-section cut perpendicular to the axial (longitudinal) direction of the metal oil well pipe. This cross-section is hereby referred to as the observation surface. On the observation surface, a region that includes the solid lubricant 70 layer is subjected to microscopic observation. The magnification ratio for microscopic observation is set to 500x. The thickness of the solid lubricant 70 layer is determined in 10 arbitrary fields of view. In each field of view, the thickness of the solid lubricant 70 layer is measured at three arbitrary locations.The arithmetic mean of the thicknesses of the solid lubricant layer 70 in the 10 visual fields (total 10x3 = 30 thickness values) is defined as the thickness (pm) of the solid lubricant layer 70.

[0083] [Structure on the second contact surface] Figure 9 is a cross-sectional view illustrating the structure of the second contact surface, specifically the contact surface of bolt 400. Referring to Figure 9, the arithmetic mean roughness (Ra) of the second contact surface is within the range of 0.5 to 10.0 µm. Additionally, a liquid or semi-solid anti-corrosion coating (80) forms on the second contact surface (in Figure 9, the contact surface of bolt 400). The arithmetic mean roughness (Ra) and the anti-corrosion coating (80) of the second contact surface will be described below.

[0084] [Arithmetic mean roughness Ra of the second contact surface]. The arithmetic mean roughness Ra of the second contact surface (in Figure 9, the contact surface of bolt 400) is measured using a method for measuring arithmetic mean roughness defined in JIS B 0601 (2013). Specifically, 10 arbitrary positions along the extension direction of the thread crest (thread cutting direction) of the threaded portion on the second contact surface are adopted as measurement locations. At each measurement point, the arithmetic mean roughness Ra is measured along an evaluation length extending in the direction of the pipe axis. The evaluation length is set at a multiple of five times the sample length (cutting wavelength). The arithmetic mean roughness Ra measurement is performed using a stylus-type roughness gauge, and the measurement speed is set to 0.5 mm / s.Among the 10 arithmetic mean roughness (Ra) values ​​that are determined, the arithmetic mean of the arithmetic mean roughness (Ra) values ​​at six locations, excluding the highest arithmetic mean roughness (Ra), the second highest arithmetic mean roughness (Ra), the lowest arithmetic mean roughness (Ra), and the second lowest arithmetic mean roughness (Ra), is defined as the arithmetic mean roughness (Ra). For example, a surface roughness gauge with the trade name SURFTEST SJ-301, manufactured by Mitutoyo Corporation, is used as a contact-type roughness gauge.

[0085] The arithmetic mean roughness of the second contact surface after threading is less than 0.1 pm. In a case where the arithmetic mean roughness Ra of the second contact surface is within the range of 0.5 to 10.0 pm, the roughness of the second contact surface is adjusted by subjecting the second contact surface to some type of surface treatment. The surface treatment is, for example, shot blasting.

[0086] Preferably, the second contact surface is subjected to shot blasting. The term shot blasting refers to a treatment in which a shot blasting apparatus is used to cause a blasting material (an abrasive) to impact the second contact surface. Shot blasting includes, for example, sandblasting, shot blasting, or shear blasting. In shot blasting, a blasting material (abrasive) is mixed with compressed air, and the mixture is propelled onto the second contact surface. The roughness of the second contact surface can be appropriately set by adjusting the blasting material used in the shot blasting treatment, as well as the propulsion speed and other factors.

[0087] [Anti-rust coating 80] Antioxidant coating 80 forms on the second contact surface. Antioxidant coating 80 is semi-solid or liquid at normal temperature (20 °C ± 15 °C).

[0088] Figure 10 is an enlarged view of a portion near the second contact surface illustrated in Figure 9 (in Figure 9, the contact surface of bolt 400). With reference to Figure 10, a minute unevenness of such extent that the arithmetic mean roughness Ra falls within the range of 0.5 to 10 pm is formed on the second contact surface (in this case, the contact surface of bolt 400). Through this irregularity, the coefficient of friction between the contact surface of bolt 400 and the contact surface of box 500 is increased during clamping, and the yield torque is increased.

[0089] [Types of antioxidant coating 80] Anti-rust coating 80 can be one of the following two types. (A) A liquid antioxidant coating (B) A semi-solid antioxidant coating RQzznn / pznz / B / YiAi A liquid antioxidant coating and a semi-solid antioxidant coating are described below.

[0090] [(A) With regard to a liquid antioxidant coating] A liquid rust-preventative coating is a rust-preventative coating that is in a liquid state. The term "liquid" refers to the state of a liquid. Note that a state in which the volatile components of a liquid evaporate and the non-volatile components that have viscosity remain also corresponds to a semi-solid or a liquid. A liquid rust-preventative coating can be formed, for example, by applying a commercially available rust-preventative lubricant, also called a light oil, such as WD-40 (trade name). The chemical composition of the liquid rust-preventative coating contains, for example, a mineral volatile in an amount of 50 to 75% by mass, and a petroleum-based oil in an amount of 25% by mass or less.

[0091] [Mineral volatile] Mineral volatile is a solvent equivalent to No. 4 industrial gasoline as defined in JIS K 2201 (1991). A preferred lower limit for mineral volatile content is, by mass %, 52%, more preferably 54%, more preferably 56%, and more preferably 58%. A preferred upper limit for mineral volatile content is, by mass %, 70%, more preferably 68%, more preferably 66%, more preferably 64%, and more preferably 62%.

[0092] [Petroleum-based oil] Petroleum-based oil is an oil obtained by refining crude oil. Petroleum-based oil is composed, for example, of one or more types selected from the group consisting of a paraffinic oil, a nagnenic oil, and an aromatic oil. A preferred lower limit for the content of petroleum-based oil is, in % by mass, 2%, more preferably 4%, more preferably 6%, and more preferably 8%. A preferred upper limit for the content of petroleum-based oil is 22%, more preferably 20%, more preferably 18%, and more preferably 16%.

[0093] [Antioxidant Additive] Anti-corrosion coating 80 may also include an antioxidant additive in addition to a volatile mineral and a petroleum-based oil. The term "anti-corrosion additive" is a generic term for additives that provide corrosion resistance. The antioxidant additive contains, for example, one or more types selected from the group consisting of aluminum tripolyphosphate, aluminum phosphite, and ion-exchanged calcium silicate. Preferably, the antioxidant additive contains at least one type of additive selected from the group consisting of calcium ion-exchanged silica and aluminum phosphite. The antioxidant additive may also contain other known (commercially available) reactive water-repellent agents.

[0094] The antioxidant additive content in Antioxidant Coating 80 is preferably, by mass percent, 10% or less. A preferred upper limit for the antioxidant additive in Antioxidant Coating 80 is 9%, more preferably 8%, and even more preferably 5%. A preferred lower limit for the antioxidant additive in Antioxidant Coating 80 is 2%, and more preferably 3%. Note that Antioxidant Coating 80 need not contain the antioxidant additive. In other words, the chemical composition of Antioxidant Coating 80 may contain a volatile mineral and a petroleum-based oil, with the remainder being impurities.

[0095] Note that the 80 anti-corrosion coating is substantially free of heavy metal dust. In other words, in the 80 anti-corrosion coating, a heavy metal is an impurity. A heavy metal dust is, for example, powder or particles of Pb, Cu, Zn, or similar metals. The 80 anti-corrosion coating also does not contain a chlorine compound. Therefore, the metal oil well pipe of the present embodiment may also be used in an offshore oil well for which the use of grease containing a heavy metal or a chlorine compound or similar substance is prohibited.

[0096] [(B) With regard to the semi-solid antioxidant coating] A semi-solid anti-corrosion coating is an anti-corrosion coating in a state such that, although the coating maintains a certain shape at normal temperatures, when an external force is applied, at least the portion receiving the external force readily changes shape without breaking (without cracking). The semi-solid anti-corrosion coating may be in a greasy or semi-dry state.

[0097] The chemical composition of the semi-solid antioxidant coating contains, for example, in % by mass, refined mineral oil: 20 to 30%, petroleum-based wax: 8 to 13%, graphite: 3 to 5%, and rosin: 5 to 10%, the remainder being calcium sulfonate and impurities.

[0098] A refined mineral oil is a hydrocarbon compound obtained by refining petroleum oil, natural gas, or similar substances. A petroleum-based wax is a wax obtained from petroleum oil. The term wax designates an organic matter that is solid at normal temperatures and becomes liquid when heat is applied. Rosin is a resin obtained by steam distilling rosin to remove turpentine oil.

[0099] Note that the semi-solid antioxidant coating can be either a known yellow doped fat or a known green doped fat.

[0100] The antioxidant coating 80 is in a semi-solid or liquid state. Therefore, compared to the formation of a solid coating, special equipment is not normally required when forming the antioxidant coating 80 on the second contact surface. RQzznn / pznz / B / YiAi Depending on the properties of the 80 antioxidant coating and the specifications, heating drying can be performed.

[0101] The anti-corrosion coating 80 that forms on the second contact surface is in a semi-solid or liquid state. When the metal oil well pipe is secured, the semi-solid or liquid anti-corrosion coating 80 changes shape or flows with the clamping. As a result, the surface roughness of the anti-corrosion coating 80 formed on the second contact surface is substantially equal to the surface roughness of the second contact surface.

[0102] Note that a metallic coating layer does not form on the second contact surface. If a metallic coating layer forms on the second contact surface, which is a rough surface, and the anti-corrosion coating 80 forms on top of this metallic coating layer, the irregularity of the second contact surface will not be reflected on the surface of the metallic coating layer. In other words, the surface roughness of the metallic coating layer will be lower than the surface roughness of the second contact surface. Therefore, it will not be possible to adequately increase the creep torque during clamping. Furthermore, if a metallic coating layer forms on the second contact surface and the surface of the metallic coating layer is ground, and then the anti-corrosion coating 80 forms, the production cost will increase.Therefore, in the metal pipe for oil wells of the present modality, a metallic coating layer is not formed on the second contact surface.

[0103] [Case in which the pemo contact surface is the first contact surface, and the box contact surface is the second contact surface]. In the preceding description, the structures of the first and second contact surfaces were described taking the box 500 contact surface as the first contact surface and the pemo 400 contact surface as the second contact surface. However, as previously described, the pemo 400 contact surface can be the first contact surface and the box 500 contact surface can be the second contact surface. In this case, as illustrated in Figure 11, the metallic coating layer 60 forms on the bolt 400 contact surface (the first contact surface), and the solid lubricant layer 70 forms on the metallic coating layer 60.Furthermore, as illustrated in Figure 12, the surface roughness of the contact surface of box 500 (the second contact surface) is adjusted, and the arithmetic mean roughness Ra of the contact surface of box 500 is from 0.5 to 10.0 µm. In addition, the anti-corrosion coating 80 is formed on the contact surface of box 500.

[0104] As described above, in the metal oil well pipe 1 of the present embodiment, the metallic coating layer 60 is formed on the first contact surface, which RQzznn / pznz / B / YiAi is a contact surface between bolt 400 and box 500, and a solid lubricant layer 70 is formed on top of a metallic coating layer 60. Furthermore, the surface of the second contact surface, which opposes the first contact surface during clamping, is roughened, with an arithmetic mean roughness (Ra) of 0.5 to 10.0 µm. Additionally, a semi-solid or liquid anti-corrosion coating is formed on the roughened second contact surface. The resistance to scoring during clamping can be improved by the metallic coating layer 60 and the solid lubricant layer 70 on the first contact surface.Furthermore, in a case where the semi-solid or liquid antioxidant coating 80 forms on the second contact surface, which is a rough surface, a high coefficient of friction is achieved through the metallic coating layer 60 beneath the solid lubricant layer 70 of the first contact surface and the irregularity of the second contact surface. As a result, the creep torque increases.

[0105] [With regard to the chemical treatment coating 90 formed on the second contact surface] In the Melal oil well pipe 1 of the present embodiment, a chemically treated coating may be further formed on the second contact surface, and the anti-corrosion coating 80 may be formed on the chemically treated coating. Figure 13 is a view illustrating the structure of the second contact surface, which includes a chemically treated coating 90, in a case where the second contact surface is the contact surface of bolt 400. With reference to Figure 13, the chemically treated coating 90 is formed on the second contact surface, the roughness of which was adjusted so that the arithmetic mean roughness Ra was within the range of 0.5 to 10.0 pm, and the anti-corrosion coating 80 is formed on the chemically treated coating 90.At this time, the chemical treatment coating 90 is formed in contact with the second contact surface and the antioxidant coating 80 is formed in contact with the chemical treatment coating 90.

[0106] Chemical treatment coating 90 is composed, for example, of one or more coating types selected from the group consisting of a phosphate chemical treatment coating, an oxalate chemical treatment coating, and a borate chemical treatment coating. Preferably, chemical treatment coating 90 is a phosphate chemical treatment coating.

[0107] The chemical treatment coating 90 is porous. Therefore, when the anti-corrosion coating 80 is applied over the chemical treatment coating 90, the adhesion (holding power) of the second contact surface of the anti-corrosion coating 80 increases due to the so-called anchoring effect. In this case, the corrosion resistance of the second contact surface increases. The thickness of the chemical treatment coating 90 is not particularly limited. RQzznn / pznz / B / GALA The preferred thickness of the chemical treatment coating 90 is 5 to 40 µm. If the thickness of the chemical treatment coating 90 is 5 µm or more, the corrosion resistance increases even further. If the thickness of the chemical treatment coating is 40 µm or less, the adhesion of the anti-corrosion coating 80 increases with added consistency.

[0108] Note that Figure 13 illustrates a case where the second contact surface is the contact surface of bolt 400. However, even when the second contact surface is the contact surface of box 500, the chemical treatment coating 90 can be similarly formed on the second contact surface and the anti-rust coating 80 can be formed on the chemical treatment coating 90.

[0109] Note that the anti-corrosion coating 80 may be formed in direct contact with the second contact surface, and the chemical treatment coating 90 may not be formed on the second contact surface. Preferably, in a case where the Cr content is 1.00% or less by mass in the chemical composition of the oil well metal pipe 1, the chemical treatment coating 90 is formed on the second contact surface, and the anti-corrosion coating 80 is formed on the chemical treatment coating 90. In a case where the Cr content is 1.00% or less by mass in the chemical composition of the oil well metal pipe 1, the corrosion resistance of the base metal of the oil well metal pipe 1 itself is not as high. In a case where the Cr content is 1.00% by mass.00% or less in the chemical composition of the metal pipe for oil wells 1, if the chemical treatment coating 90 is formed on the second contact surface and, in addition, the anti-rust coating 80 is formed on the chemical treatment coating 90, the corrosion resistance of the second contact surface can be increased.

[0110] [Production Process]. An example of a method for producing the metal oil well pipe of the present type, having the structure described above, will now be described. Note that the production method described below is an example of such a method. Consequently, the production method is not particularly limited, provided it can produce the metal oil well pipe of the present type. The production method described below is a favorable example of such a method.

[0111] The method for producing the metal oil well pipe of the present embodiment includes a process for preparing a hollow casing with a threaded connection (process for preparing a hollow casing with a threaded connection), a process for forming the metallic coating layer 60 on the first contact surface (process for forming the metallic coating layer), a process for forming the solid lubricant layer 70 on the metallic coating layer 60 (process RQzznn / pznz / B / YiAi (solid lubricant layer formation), a process of adjusting the surface roughness of the second contact surface (second contact surface roughness adjustment process), and a process of forming an antioxidant coating on the second contact surface whose roughness has been adjusted (antioxidant coating formation process). Each of these processes is described in detail below.

[0112] [Process of preparing the hollow housing with a threaded connection]. In the process of preparing a hollow casing with a threaded connection, a hollow casing with a threaded connection is prepared. Here, the term hollow casing with a threaded connection refers to the main body of pipe 10. In a case where the metal oil well pipe is of the T&C type, the main body of pipe 10 includes the pipe body 11 and the copier 12. In a case where the metal oil well pipe is of the integral type, the main body of pipe 10 is integrally formed.

[0113] As the main body of tube 10, a product supplied by a third party may be used, or the main body of tube 10 may be prepared by producing the main body of tube 10. In the case of producing the main body of tube 10, the main body of tube 10 is produced, for example, by the following method.

[0114] A starting material is produced using molten steel. Specifically, a casting (a plate, billet, or bar) is produced by a continuous casting process using the molten steel. An ingot may also be produced by an ingot-making process using the molten steel. If necessary, the plate, billet, or ingot may be subjected to a melting process to produce a casting (bar). The starting material (plate, billet, or bar) is produced by the process described above. The prepared starting material is hot-worked to produce a hollow shell. The hot-working method may be a punch rolling process performed according to the Mannesmann process or a hot extrusion process. After hot-working, the hollow shell is subjected to a known quenching and tempering process to adjust its strength. The hollow shell is produced by the process described above.Note that, in the case of the metal oil well pipe being of the T&C type, a hollow cover for the copy 12 is also prepared. The method for producing the hollow cover for the copy 12 is the same as the method for producing the hollow cover described above.

[0115] In a case where the metal oil well tubing is of the T&C type, threading is performed with respect to the outer surface of both end portions of the hollow casing for the pipe body 11, to form the contact surface 400. In addition, threading is performed with respect to the inner surface of both end portions of the hollow casing for the copier 12, to form the contact surface 500. The threading of one end of the hollow casing for the pipe body RQzznn / pznz / B / YiAi bolt tube 11 is inserted and screwed into the box at one end of the hollow housing for the copier 12. The main tube body including the bolt tube body 11 and the copier 12 (hollow housing with a threaded connection) is produced by the above process.

[0116] In the case of the metal oil well pipe being of the integral type, the threading is performed 5 with respect to the outer surface of the first end portion 10A of the hollow casing corresponding to the main pipe body 10 to form the bolt contact surface 400. In addition, the threading is performed with respect to the outer surface of the second end portion 10B of the hollow casing corresponding to the main pipe body 10 to form the box contact surface 500. The main pipe body 10 which includes a bolt and a box (hollow casing with a threaded connection) is 10 produced by the above process.

[0117] [Metallic coating layer formation process]. The metallic coating layer 60 is formed on the first contact surface, which is one of the two contact surfaces of the prepared tube body, specifically the bolt contact surface 400 and the box contact surface 500. The formation of the metallic coating layer 60 can be achieved using a known method. This method can be either metal electrodeposition or electrodeless electroplating.

[0118] For example, in the case of forming the metallic coating layer 60, which is composed of a Zn-Ni alloy, by a metal electrodeposition method, the metallic coating bath 20 contains zinc ions and nickel ions. The composition of the metallic coating bath preferably contains zinc ions from 1 to 100 g / L and nickel ions from 1 to 50 g / L. The conditions for the metal electrodeposition method are, for example, pH of the deposition bath: 1 to 10, temperature of the deposition bath: 25 to 80 °C, current density: 1 to 100 A / dm², and treatment time: 0.1 to 30 minutes. For example, in the case of forming the metallic coating layer 60 which is composed of a Cu-Sn-Zn alloy 25 by a metallic electrodeposition method, the coating bath contains copper ions at 50 g / L, tin ions 1 to 50 g / L, and zinc ions: 1 to 50 g / L.The conditions for metal electrodeposition can be the same as those mentioned above for forming the metallic coating layer 60, which is composed of a Zn-Ni alloy. In a case where the metallic coating layer 60 is a metallic coating layer composed of Cu or a Cu alloy, the metallic coating layer 60 can be produced by a known method.

[0119] [Solid Lubricant Layer Formation Process] In the solid lubricant layer formation process, the solid lubricant layer 70 is formed on top of the metallic coating layer 60. The solid lubricant layer formation process includes an application process and a curing process. RQzznn / pznz / B / YiAi

[0120] [Application Process] In the application process, a composition for forming the solid lubricant layer 70 on the metallic coating layer 60 is applied onto the metallic coating layer 60 by a known method.

[0121] For example, in a case where the composition is an organic liquid composition as described above, the organic liquid composition is applied to the first contact surface by spray coating. In this case, the viscosity of the organic liquid composition is adjusted so that it can be applied by spraying at normal temperature and pressure. Another application method, such as brushing or dipping, may be used instead of spray application. The same applies in the case where the composition is an inorganic liquid compound.

[0122] [Curing Process] In the case where the composition is an organic liquid composition, the applied organic liquid composition is cured to form the solid lubricating layer 70 during a curing process. The solid lubricating layer 70 is formed by drying and / or thermally curing the resin solution applied over the metallic coating layer 60. The drying and / or thermal curing can be carried out using a known method depending on the type of binder. Favorable and similar conditions for carrying out this process are those described above. In the case where the composition is an inorganic liquid composition, as described above, the applied inorganic liquid composition is subjected to a humidification and / or heating treatment during the curing process.

[0123] The solid lubricant layer 70 is formed over the metallic coating layer 60 by carrying out the application process and the curing process described above.

[0124] [Second process of adjusting the roughness of the contact surface] In the process of adjusting the roughness of the second contact surface, the surface roughness of the second contact surface, which is between the contact surface of bolt 400 and the contact surface of box 500 of the main body of tube 10, is adjusted to make the arithmetic mean roughness Ra of the second contact surface within the range of 0.5 to 10.0 pm.

[0125] The adjustment of surface roughness is carried out, for example, by means of a shot blasting treatment.

[0126] [Shot blasting treatment] Shot blasting is a treatment in which a shot blasting machine is used to force a blasting material (an abrasive) against a secondary contact surface, roughening it. Shot blasting is, for example, a type of sandblasting. Sandblasting involves mixing a blasting material (abrasive) with compressed air, and the mixture is propelled onto the secondary contact surface. Examples of abrasive materials include spherical shot and angular shot. Sandblasting can be carried out using a standard method. For example, air is compressed by a compressor, and the abrasive material is mixed with the compressed air. The abrasive material can be composed of, for example, stainless steel, aluminum, ceramic material, or alumina.The sandblasting treatment conditions, such as the propulsion speed, can be adjusted accordingly. By properly selecting the abrasive material used for the blasting treatment and appropriately adjusting the propulsion speed and similar factors, the arithmetic mean roughness Ra of the second contact surface can be adjusted within the range of 0.5 to 10.0 µm.

[0127] [Antioxidant coating formation process] In the process of forming the anti-corrosion coating, an anti-corrosion lubricant is applied to form a semi-solid or liquid anti-corrosion coating on the second contact surface of the main body of pipe 10 after the roughness of the second contact surface has been adjusted. The anti-corrosion coating is not solid but rather in a semi-solid or liquid state. Therefore, if a semi-solid or liquid anti-corrosion lubricant is applied to the second contact surface, a semi-solid or liquid anti-corrosion coating can easily form. The method for applying the semi-solid or liquid anti-corrosion lubricant is not particularly limited, provided that an anti-corrosion coating can form on the second contact surface. For example, the anti-corrosion lubricant can be applied by spraying. The anti-corrosion lubricant can also be applied by brushing.Another known method can also be used to apply the antioxidant lubricating agent to the second contact surface to form the antioxidant coating.

[0128] [Optional Process] [Chemical treatment coating formation process] If the chemical treatment coating 90 is to be applied to the second contact surface, this application can take place after the surface roughness adjustment process and before the application of the anti-corrosion coating. In other words, the chemical treatment coating application is optional and not mandatory.

[0129] In the case of performing the chemical treatment coating formation process, a known chemical treatment is carried out in the chemical treatment coating formation process to form the chemical treatment coating 90 on the second contact surface after adjusting the roughness of the second contact surface. The chemical treatment can be carried out by a known method. A common chemical treatment solution can be used as the treatment solution. For example, in a case where the chemical treatment coating 90 is a phosphate chemical treatment coating, an example of the solution that can be mentioned is a zinc phosphate chemical treatment solution containing 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.A manganese phosphate chemical treatment solution can also be used. The solution temperature ranges from room temperature to 100°C, for example. The treatment time can be adjusted according to the desired coating thickness and, for instance, is in the range of 5 to 20 minutes. To facilitate coating formation, surface modification can be performed prior to chemical treatment. Surface modification refers to a treatment that includes immersion in an aqueous surface modification solution containing colloidal titanium. After chemical treatment, rinsing with water or warm water before drying is preferable.

[0130] The metal pipe for oil wells of the present modality can be produced by the above production process. EXAMPLES

[0131] Some examples are described below. However, the metal oil well tubing of the present type is not limited by the Examples. The % symbol used in the Examples means % by mass, unless specifically stated otherwise.

[0132] [Example 1] Metal oil well pipes with various structures were prepared. The test described below was performed using these prepared metal oil well pipes, and the yield torque (ft-lb) was measured. First, the metal oil well pipes shown in Table 1 were prepared.

[0133] Table 1 RQzznn / pznz / Β / γΐΛΐ Test No. Outside Diameter (inches) Wall Thickness (mm) Steel Type Second Contact Surface First Contact Surface Yield Torque Ratio 100% Metallic Coating Layer Solid Lubricant Layer Grit Treatment Ra (pm) Zinc Phosphate Anti-corrosion Coating Type 11 7 10.36 L80 - <0.5 Yes Liquid Anti-corrosion Coating Zn-Ni Yes 12 7 10.36 L80 - <0.5 - Semi-solid Anti-corrosion Coating Zn-Ni Yes 102% 13 7 10.36 L80 Yes 2.5 Yes Liquid Anti-corrosion Coating Zn-Ni Yes 122% 14 7 10.36 L80 Yes 2.4 - Semi-solid Anti-corrosion Coating Zn-Ni Yes 122% 15 7 10.36 L80 Yes 2.5 Yes Yellow Doped Grease Zn-Ni Yes 134% 16 7 10.36 L80 Yes 2.7 Yellow doped fat Zn-Ni Yes 168% RQzznn / pznz / Β / γΐΛΐ

[0134] The outside diameter of the metal oil well pipes in tests 11 through 16 was 7 inches (177.80 mm), and the wall thickness was 10.36 mm. The chemical composition of each metal oil well pipe corresponded to L80 as defined in AP1-5CT.

[0135] In tests II through 16, the first contact surface was taken as the box contact surface and the second contact surface as the bolt contact surface. A Zn-Ni alloy metallic coating layer was formed on the first contact surface of each test number. Specifically, the first contact surface was immersed in a coating solution and subjected to metal electroplating, resulting in the formation of a Zn-Ni alloy metallic coating layer. DAIN Zinalloy N2-PL (trade name) manufactured by Daiwa Fine Chemicals Co., Ltd. was used as the Zn-Ni alloy metallic coating solution.In each of the test numbers, the chemical composition of the Zn-Ni alloy metallic coating layer formed by the above process was a chemical composition containing Ni in an amount between 10 and 16% by mass, the remainder being Zn. Note that the thickness of the Zn-Ni alloy metallic coating layer in each test number was within the range of 5 to 15 µm.

[0136] In addition, a solid lubricant layer was formed over the Zn-Ni alloy metallic coating layer. Specifically, an organic liquid composition was applied over the Zn-Ni alloy metallic coating layer. The organic liquid composition contained epoxy resin, pure water, ethyl glycol mono-n-butyl ether, isopropyl alcohol, 1-butanol, and PTFE particles. After applying the organic liquid composition to the Zn-Ni alloy metallic coating layer by spraying, a known curing treatment was performed to form a solid lubricant layer. Specifically, the curing treatment consisted of preliminary drying (at 85 °C for 10 minutes) and baking (at 210 °C for 20 minutes). The average coating thickness of the resulting solid lubricant layer was within the range of 20 to 30 µm in each test number.

[0137] The second contact surface of tests 13 to 16 was sandblasted. The arithmetic mean roughness Ra of the second contact surface after sandblasting was measured in accordance with the arithmetic mean roughness measurement method defined in JIS B 0601 (2013). Specifically, 10 arbitrary locations on the second contact surface were adopted as measurement locations. At each measurement point, the arithmetic mean roughness Ra was measured along an evaluation length extending in the direction of the pipe axis. The evaluation length was set to a multiple of five times the sampling length (shear wavelength). The arithmetic mean roughness Ra measurement was performed using a Stylus-type roughness gauge, and the measurement speed was set to 0.5 mm / s.Among the 10 arithmetic mean roughness (Ra) values ​​determined, the arithmetic mean of the Ra values ​​at six locations, excluding the highest, second highest, lowest, and second lowest arithmetic mean roughness (Ra), is defined as the arithmetic mean roughness (Ra). A surface roughness tester, the SURFTEST SJ-301, manufactured by Mitutoyo Corporation, was used as the contact roughness tester. The obtained arithmetic mean roughness (Ra) (pm) is shown in Table 1. Note that the second contact surface of tests II and 12 was not subjected to sandblasting (indicated by the symbol in the Blast Treatment column of Table 1).The arithmetic mean roughness Ra of the second contact surface of the metal pipe for oil wells in tests 11 and 12, where no sandblasting treatment was performed, was approximately 0.2 pm, respectively, and was therefore less than 0.5 pm. The arithmetic mean roughness Ra of the second contact surface of the metal pipe for oil wells in tests 13 through 16 was 2.7, and therefore each of these values ​​was within the range of 0.5 to 10.0 pm.

[0138] In addition, with regard to tests number 11, 13 and 15, the second contact surface (bolt contact surface) was immersed in a zinc phosphate chemical treatment solution RQzznn / pznz / B / YiAi (PALBOND 181X (trade name) manufactured by Nihon Parkerizing Co., Ltd.) was heated to 75–85°C for 10 minutes, forming a zinc phosphate chemical treatment layer. The thickness of the zinc phosphate chemical treatment layer was 12 µm. Note that a zinc phosphate chemical treatment layer did not form on the second contact surface of tests 12, 14, and 16 (indicated by the symbol in the Zinc Phosphate column of Table 1).

[0139] In tests 11 and 13, an antioxidant coating formed on the zinc phosphate chemical treatment layer. Specifically, a liquid antioxidant coating formed on the zinc phosphate chemical treatment layer in tests 11 and 13. Additionally, a semi-solid (greasy) antioxidant coating formed on the second contact surface in tests 12 and 14. On the second contact surface in tests 15 and 16, a semi-solid antioxidant coating composed of yellow doped grease formed. In each test, a liquid antioxidant lubricating agent or a semi-solid antioxidant lubricating agent was sprayed onto the surface of the zinc phosphate chemical treatment layer or the second contact surface from a distance of 300 mm to form a liquid antioxidant coating or a semi-solid antioxidant coating.Alternatively, a liquid or semi-solid anti-corrosive lubricating agent was applied to the surface of the zinc phosphate chemical treatment layer or the second contact surface by brushing to form a liquid or semi-solid anti-corrosive coating. During spray coating, the metal oil well pipe was rotated around its central axis, and a liquid or semi-solid anti-corrosive coating was formed over the entire surface of the zinc phosphate chemical treatment layer or the entire second contact surface.

[0140] Note that the liquid antioxidant lubricating agent contained a volatile mineral in an amount of 50 to 75% by mass and a petroleum-based oil in an amount of 25% by mass or less. The semi-solid antioxidant lubricating agent contained, in % by mass, refined mineral oil: 20 to 30%, petroleum-based wax: 8 to 13%, graphite: 3 to 5%, and rosin: 5 to 10%, the remainder being calcium sulfonate. As described above, in tests number 15 and 16, yellow doped grease (BoL4010NM (trade name) manufactured by Bestolife Corporation) was used as the semi-solid antioxidant lubricating agent.

[0141] The metal oil well tubes for tests number 11 to 16 were produced by the production process described above.

[0142] [Creep Torque Measurement Test] The creep torque was measured using the following method with one (2) pair of metal oil well pipes (metal oil well pipes with a wedge thread and no raised surface) from each test number. Specifically, the clamping torque value was gradually increased at a tightening speed of 0.5 rpm, and the test ended when RQzznn / pznz / B / YiAi The material yielded. The torque was measured at the moment of clamping, and a torque graph illustrated in Figure 14 was prepared. The reference characters Ts in Figure 14 denote the boost torque. A line segment L is a straight line that has the same slope as the slope of a linear region of the torque graph after the boost torque, and for which the number of turns is 0.2% higher compared to the linear region. In this example, a torque value at which the linear segment L and the torque graph intersect was defined as the yield torque Ty. A ratio (%) of the yield torque Ty of each test number to the yield torque Ty of test number 11, in which the second contact surface was not sandblasted, was defined as the yield torque ratio. The yield torque ratio is shown in Table 1.

[0143] [Evaluation Results] Referring to Table 1, in tests 13 through 16, a Zn-Ni metallic coating and a solid lubricant layer were laminated onto the first contact surface. The second contact surface was sandblasted to a surface roughness between 0.5 and 10.0 µm, and a semi-solid or liquid anti-corrosion coating was formed on it. Therefore, the yield torque ratio was high compared to tests 11 and 12, where the second contact surface was not sandblasted. In other words, excellent high-torque performance was achieved.

[0144] [Example 2] The metal pipes for oil wells shown in Table 2 were prepared.

[0145] Table 2 Test No. Outside Diameter (inches) Wall Thickness (mm) Steel Type Second Contact Surface First Contact Surface Yield Torque Ratio Metallic Coating Layer Solid Lubricant Layer Shot Peening Treatment Ra (µm) Zinc Phosphate Anti-corrosion Coating Type 21 22 7 10.36 L8013CR - <0.5 - Liquid Anti-corrosion Coating Zn-Ni Yes 100% 7 10.36 L80-13CR - <0.5 - Semi-solid Anti-corrosion Coating Zn-Ni Yes 94% 23 7 10.36 L80-13CR Yes 2.4 - Liquid Anti-corrosion Coating Zn-Ni Yes 146% 24 7 10.36 L80-13CR Yes 2.7 - Semi-solid Anti-corrosion Coating Zn-Ni Yes 131%

[0146] The outside diameter of the metal oil well pipes in tests 21 through 24 was 7 inches (177.80 mm), and the wall thickness was 10.36 mm. The chemical composition of each metal oil well pipe corresponded to L80-13CR as defined in AP1-5CT.

[0147] In tests 21 through 24, the first contact surface was taken as the box contact surface and the second contact surface as the bolt contact surface. A Zn-Ni alloy metallic coating layer was formed on the first contact surface of each test number by the same method as in Example 1. In each test number, the chemical composition of the Zn-Ni alloy metallic coating layer contained Ni in an amount between 10 and 16% by mass, the remainder being Zn. The thickness of the Zn-Ni alloy metallic coating layer in each test number was within the range of 5 to 15 pm.

[0148] In addition, a layer of solid lubricant of the same type as in Example 1 was formed over the Zn-Ni alloy metallic coating layer. In each test number, the average coating thickness of the resulting solid lubricant layer was within the range of 20 to 30 pm.

[0149] On the other hand, the second contact surface of tests 23 and 24 was sandblasted using the same method as in Example 1. The arithmetic mean roughness Ra of the second contact surface after sandblasting was measured using the same method as in Example 1. The resulting arithmetic mean roughness Ra (pm) is shown in Table 2. Note that the second contact surface of tests 21 and 22 was not sandblasted (indicated by the symbol in the Shot Blasting Treatment column of Table 2). The arithmetic mean roughness Ra of the second contact surface of the metal oil well pipe of tests 21 and 22, which were not sandblasted, was approximately 0.2 pm, respectively, and was therefore less than 0.5 pm.

[0150] An antioxidant coating was formed on the second contact surface of each test number. Specifically, a liquid antioxidant coating was formed on the second contact surface of tests 21 and 23. In addition, a semi-solid antioxidant coating was formed on the second contact surface of tests 22 and 24. The formation methods were the same as in Example L. The metal oil well tubes of tests 21 through 24 were manufactured using the production process described above.

[0151] [Creep torque measurement test] The yield torque ratio of the metal pipe for oil wells for each test number was determined by the same method as in Example 1.

[0152] [Evaluation Results] Referring to Table 2, in tests 23 and 24, a Zn-Ni alloy metallic coating and a solid lubricant layer were laminated onto the first contact surface. The second contact surface was sandblasted to a surface roughness between 0.5 and 10.0 µm, and a liquid or semi-solid anti-corrosion coating was formed on it. Therefore, the yield torque ratio was high compared to tests 21 and 22, where the second contact surface was not sandblasted. In other words, excellent high-torque performance was achieved.

[0153] [Example 3] The metal pipes for oil wells shown in Table 3 were prepared.

[0154] Table 3 RQzznn / pznz / B / YiAi No. dc Test Outside Diameter (inches) Wall Thickness (mm) Steel Type Second Contact Surface First Contact Surface Yield Torque Ratio Metallic Coating Layer Type Solid Lubricant Layer Granitic Treatment Ra (pm) Zinc Phosphate Anti-corrosive Coating 31 9-5 / 8 13.84 Pilo - <0.5 - Liquid Anti-corrosive Coating Zn-Ni Si 100% 32 9-5 / 8 13.84 P110 Yes 2.4 - Liquid Anti-corrosive Coating Zn-Ni Yes 121%

[0155] The outside diameter of the metal oil well pipes from tests number 31 and 32 was 244.475 tnm (9-5 / 8 inches) and the wall thickness was 13.84 mm. The chemical composition of each of the metal oil well pipes corresponded to P110 as defined in AP1-5CT.

[0156] In tests number 31 and 32, the first contact surface was taken as the box contact surface and the second contact surface as the bolt contact surface. A Zn-Ni alloy metallic coating layer was formed on the first contact surface of each test number by the same method as in Example 1. In each of the test numbers, the chemical composition of the Zn-Ni alloy metallic coating layer contained Ni in an amount between 10 and 16% by mass, the remainder being Zn. The thickness of the Zn-Ni alloy metallic coating layer of each test number was within the range of 5 to 15 pm.

[0157] In addition, a solid lubricant layer of the same type as in Example 1 was formed over the Zn-Ni alloy metallic coating layer. In each test number, the average thickness of the resulting solid lubricant coating was within the range of 20 to 30 pm.

[0158] On the other hand, the second contact surface of test number 32 was sandblasted using the same method as in Example 1. The arithmetic mean roughness Ra of the second contact surface after sandblasting was measured using the same method as in Example 1. The resulting arithmetic mean roughness Ra (pin) is shown in Table 3. Note that the second contact surface of test number 31 was not sandblasted (indicated by the symbol in the Shot Blasting Treatment column of Table 3). The arithmetic mean roughness Ra of the second contact surface of the metal oil well pipe of test number 31, which was not sandblasted, was approximately 0.2 pm, and therefore less than 0.5 pm.

[0159] An antioxidant coating was formed on the second contact surface of each test number. Specifically, a semi-solid antioxidant coating was formed on the second contact surface of tests number 31 and 32. The formation method was the same as in Example 1. The metal oil well pipes of tests number 31 and 32 were manufactured using the production process described above.

[0160] [Test of creep torque measurement and evaluation results]. The yield torque ratio of the metal pipe for oil wells in each test number was determined by the same method as in Example 1. With reference to Table 3, in test number 32, a layer of Zn-Ni alloy metallic coating and a layer of solid lubricant were rolled onto the first contact surface. The second contact surface was sandblasted, and the surface roughness was within the range of 0.5 to 10.0 µm. A liquid anti-corrosion coating was also formed on the second contact surface. Therefore, the yield torque ratio was high compared to test number 31, in which the second contact surface was not sandblasted. In other words, excellent high-torque performance was achieved. RQzznn / pznz / B / YiAi

[0161] [Example 4] The metal pipes for oil wells shown in Table 4 were prepared.

[0162] Table 4 Test No. Outside Diameter (inches) Wall Thickness (mm) Steel Type Second Contact Surface First Contact Surface Yield Torque Ratio Coating Layer Solid Lubricant Layer Shot Blasting Treatment Ra (pm) Zinc Phosphate Anti-corrosion Coating Type 41 7 11.51 SM13CRS- 110 - <0.5 - Semi-solid Zn-Ni Si 100% antioxidant coating 42 7 11.51 SM13CRS- 110 - <0.5 - Liquid Zn-Ni Si 99% antioxidant coating 43 •Jfl» 11.51 SM13CRS- 110 Si 2.5 - Semi-solid Zn-Ni Si 118% antioxidant coating

[0163] The outside diameter of the metal oil well pipes in tests 41 through 43 was 7 inches (177.80 mm), and the wall thickness was 11.51 mm. A material with the trade name SM13CRS-110, produced by Nippon Steel Corporation, was used for the metal oil well pipe.

[0164] In tests number 41 to 43, the first contact surface was taken as the box contact surface and the second contact surface as the bolt contact surface. A Zn-Ni alloy metallic coating layer was formed on the first contact surface of each test number by the same method as in Example 1. In each of the test numbers, the chemical composition of the Zn-Ni alloy metallic coating layer contained Ni in an amount between 10 and 16% by mass, the remainder being Zn. The thickness of the Zn-Ni alloy metallic coating layer of each test number was between 5 and 15 pm.

[0165] In addition, a layer of solid lubricant of the same type as in Example 1 was formed over the Zn-Ni alloy metallic coating layer. In each test number, the average coating thickness of the resulting solid lubricant layer was within the range of 20 to 30 pm.

[0166] Furthermore, the second contact surface of test number 43 was sandblasted using the same method as in Example 1. The arithmetic mean roughness Ra of the second contact surface after sandblasting was measured using the same method as in Example 1. The resulting arithmetic mean roughness Ra (pm) is shown in Table 4. Note that the second contact surface of tests 41 and 42 was not sandblasted (indicated by the symbol in the Shot Blasting Treatment column of Table 4). The arithmetic mean roughness Ra of the second contact surface of the metal oil well pipe of tests 41 and 42, which were not sandblasted, was approximately 0.2 pm, respectively, and therefore less than 0.5 pm.

[0167] In each test number, an antioxidant coating was formed on the second contact surface. Specifically, a semi-solid antioxidant coating was formed on the second contact surface of tests 41 and 43. In addition, a liquid antioxidant coating was formed on the second contact surface of test 42. The formation methods were the same as in Example 1. The metal oil well pipes of tests 41 to 43 were produced by the production process described above.

[0168] [Test of measurement of creep torque and evaluation results] The yield torque ratio of the metal oil well tubing for each test number was determined using the same method as in Example 1. Referring to Table 4, in test number 43, a layer of Zn-Ni alloy metallic coating and a layer of solid lubricant were rolled onto the first contact surface. The second contact surface was sandblasted, and the surface roughness was within the range of 0.5 to 10.0 µm. A semi-solid anti-corrosion coating was formed on the second contact surface. Therefore, the yield torque ratio was high compared to tests number 41 and 42, where the second contact surface was not sandblasted. In other words, excellent high-torque performance was achieved.

[0169] Example 5 The metal pipes for oil wells shown in Table 5 were prepared.

[0170] Table 5 RQzznn / pznz / B / YiAi Test No. Outside Diameter (inches) Wall Thickness (mm) Type of Steel Second Contact Surface First Contact Surface Yield Torque Ratio Coating Layer Solid Lubricant Layer Grinding Treatment Ra (mm) Zinc Phosphate Antioxidant Coating Type 51 4-1 / 2 6.88 L80-13CR - <0.5 - Liquid Antioxidant Coating Zn-Ni Si 100% 52 4-1 / 2” 6.88 L80-13CR - <0.5 - Semi-Solid Antioxidant Coating Zn-Ni Si 95% 53 4-1 / 2 6.88 L8013CR Yes 2.7 - Liquid Antioxidant Coating Zn-Ni Si 149% 54 4-1 / 2” 6.88 L80-13CR Yes 2.5 - Semi-Solid Antioxidant Coating Zn-Ni Si 136%

[0171] The outside diameter of the metal oil well pipes in tests 51 through 54 was 114.3 mm (4.5 in.) and the wall thickness was 6.88 mm. The chemical composition of each of the metal oil well pipes corresponded to L80-13CR as defined in API-5CT.

[0172] In tests 51 through 54, the first contact surface was taken as the box contact surface and the second contact surface as the bolt contact surface. A Zn-Ni alloy metallic coating layer was formed on the first contact surface of each test number by the same method as in Example 1. In each test number, the chemical composition of the Zn-Ni alloy metallic coating layer contained Ni in an amount between 10 and 16% by mass, the remainder being Zn. The thickness of the Zn-Ni alloy metallic coating layer in each test number was within the range of 5 to 15 pm.

[0173] In addition, a solid lubricant layer of the same type as in Example 1 was formed over the Zn-Ni alloy metallic coating layer. In each test number, the average thickness of the resulting solid lubricant coating was within the range of 20 to 30 pm.

[0174] On the other hand, the second contact surface of tests 53 and 54 was sandblasted using the same method as in Example 1. The arithmetic mean roughness Ra of the second contact surface after sandblasting was measured using the same method as in Example 1. The resulting arithmetic mean roughness Ra (pm) is shown in Table 5. Note that the second contact surface of tests 51 and 52 was not sandblasted (indicated by the symbol in the “Blasting Treatment” column of Table 5). The arithmetic mean roughness Ra of the second contact surface of the metal oil well pipe in tests 51 and 52, which were not sandblasted, was approximately 0.2 pm, respectively, and therefore less than 0.5 pm.

[0175] An antioxidant coating was formed on the second contact surface of each test number. Specifically, a liquid antioxidant coating was formed on the second contact surface of tests 51 and 53. In addition, a semi-solid antioxidant coating was formed on the second contact surface of tests 52 and 54. The formation methods were the same as in Example 1. The metal oil well pipes of tests 51 through 54 were manufactured using the production process described above.

[0176] [Test of creep torque measurement and evaluation results]. The yield torque ratio of the metal oil well tubing for each test number was determined using the same method as in Example 1. With reference to Table 5, in tests 53 and 54, a Zn-Ni alloy metallic coating and a solid lubricant layer were rolled onto the first contact surface. The second contact surface was sandblasted, and its surface roughness was within the range of 0.5 to 10.0 µm. A semi-solid or liquid anti-corrosion coating was formed on the second contact surface. Therefore, the yield torque ratio was high compared to tests 51 and 52, where the second contact surface was not sandblasted. In other words, excellent high-torque performance was achieved.

[0177] [Example 6] The metal pipes for oil wells shown in Table 6 were prepared. RQzznn / pznz / B / YiAi

[0178] Table 6 Test No. Outside Diameter (inches) Wall Thickness (mm) Steel Type Second Contact Surface First Contact Surface Yield Torque Ratio Metallic Coating Solid Lubricant Layer Shot Blasting Treatment Ra (pm) Zinc Phosphate Anti-corrosion Coating Type 61 4-1 / 2 6.88 SM13CRS-110 - <0.5 Liquid Anti-corrosion Coating Zn-Ni Yes 100% 62 4-1 / 2” 6.88 SM13CRS-110 - <0.5 - Semi-solid Anti-corrosion Coating Zn-Ni Yes 108% 63 4-1 / 2 6.88 SM13CRS-110 Yes 2.4 Liquid Anti-corrosion Coating Zn-Ni Yes 154% 64 4-1 / 2 6.88 SM13CRS-110 Yes 2.6 - Semi-solid Anti-corrosion Coating Zn-Ni Si 138%

[0179] The outside diameter of the metal oil well pipes in tests 61 through 64 was 114.3 mm (4.5 in.) and the wall thickness was 6.88 mm. The metal oil well pipe was made of a material with the trade name SM13CRS-110 produced by Nippon Steel Corporation.

[0180] In tests number 61 to 64, the first contact surface was taken as the box contact surface and the second contact surface as the bolt contact surface. A Zn-Ni alloy metallic coating layer was formed on the first contact surface of each test number by the same method as in Example 1. In each of the test numbers, the chemical composition of the Zn-Ni alloy metallic coating layer contained Ni in an amount between 10 and 16% by mass, the remainder being Zn. The thickness of the Zn-Ni alloy metallic coating layer of each test number was within the range of 5 to 15 mm.

[0181] In addition, a solid lubricant layer of the same type as in Example 1 was formed over the Zn-Ni alloy metallic coating layer. In each test number, the average coating thickness of the resulting solid lubricant layer was within the range of 20 to 30 pm.

[0182] On the other hand, the second contact surface of tests 63 and 64 was sandblasted using the same method as in Example 1. The arithmetic mean roughness Ra of the second contact surface after sandblasting was measured using the same method as in Example 1. The resulting arithmetic mean roughness Ra (pm) is shown in Table 6. Note that the second contact surface of tests 61 and 62 was not sandblasted (indicated by the symbol in the Shot Blasting Treatment column of Table 6). The arithmetic mean roughness Ra of the second contact surface of the metal oil well pipe in tests 61 and 62, which were not sandblasted, was approximately 0.2 pm, respectively, and was therefore less than 0–5 pm.

[0183] An antioxidant coating was formed on the second contact surface of each test number. Specifically, a liquid antioxidant coating was formed on the second contact surface of tests 61 and 63. In addition, a semi-solid antioxidant coating was formed on the second contact surface of tests 62 and 64. The formation methods were the same as in Example 1. The metal oil well pipes of tests 61 through 64 were manufactured using the production process described above.

[0184] [Test of creep torque measurement and evaluation results]. The yield torque ratio of the metal oil well tubing for each test number was determined using the same method as in Example 1. Referring to Table 6, in tests 63 and 64, a Zn-Ni alloy metallic coating and a solid lubricant layer were rolled onto the first contact surface. The second contact surface was sandblasted, and its surface roughness was within the range of 0.5 to 10.0 µm. A semi-solid or liquid anti-corrosion coating was formed on the second contact surface. Therefore, the yield torque ratio was high compared to tests 61 and 62, where the second contact surface was not sandblasted. In other words, excellent high-torque performance was achieved.

[0185] [Example?] Metal oil well pipes with various structures were prepared. A repeated clamping test, described below, was performed using the prepared metal oil well pipes, and their resistance to scouring was evaluated. First, the metal oil well pipes shown in Table 7 were prepared.

[0186] Table 7 Test No. Outside Diameter (inches) Wall Thickness (mm) Steel Type Second Contact Surface First Contact Surface Clamping Times Shot Peening Treatment Zinc Phosphate Anti-rust Coating Metallic Coating Layer Solid Lubricant 7) 7” 11.51 SM13CRS- 110 - Liquid Zn-Ni Si antioxidant coating 10 72 7 11.51 SM13CRS- 110 - Solid Zn-Ni Si antioxidant coating 10 _ 73 7« 11.51 SM13CRS- 110 Yes Liquid Zn-Ni Si antioxidant coating 7 74 7 11.51 SM13CRS- 110 Yes - Solid Zn-Ni Si antioxidant coating 6 75 7 11.51 SM13CRS- 110 Yes - Liquid Zn-Ni Si antioxidant coating 10 76 7 11.51 SM13CRS- 110 Yes - Solid Zn-Ni Si antioxidant coating 10 77 T 11.51 SM13CRS110 Yes Liquid Zn-Ni antioxidant coating Yes 10 78 7 11.51 SM13CRS110 Yes - Semisolid Zn-Ni antioxidant coating Yes 10 79 7 12.65 SM13CRS-110 • J Liquid Zn-Ni antioxidant coating Yes 10 80 7 12.65 SM13CRS-110 - Setnisolid Zn-Ni antioxidant coating Yes 10 81 7 12.65 SM13CRS-110 Yes - Liquid Zn-Ni antioxidant coating Yes 10 82 7 12.65 SM13CRS-110 Yes - Setnisolid Zn-Ni antioxidant coating Yes 10 83 7 H.51 SM13CRS110 Yes - Yellow doped Zn-Ni fat Yes 10 RQzznn / pznz / Β / γΐΛΐ

[0187] The outside diameter of the metal oil well pipes in tests 71 through 83 was 177.80 mm (7 in.), and the wall thickness was either 11.51 mm or 12.65 mm. For the metal oil well pipes in tests 71 through 83, a material with the trade name SM13CRS-110, produced by Nippon Steel Corporation, was used for these test numbers.

[0188] In tests number 71 to 83, the first contact surface was taken as the box contact surface and the second contact surface as the bolt contact surface. A Zn-Ni alloy metallic coating layer was formed on the first contact surface of each test number by the same method as in Example 1. In each of the test numbers, the chemical composition of the Zn-Ni alloy metallic coating layer contained Ni in an amount between 10 and 16% by mass, the remainder being Zn. The thickness of the Zn-Ni alloy metallic coating layer of each test number was within the range of 5 to 15 µm.

[0189] In addition, a solid lubricant layer of the same type as in Example 1 was formed on the Zn-Ni alloy metallic coating layer. In each test number, the average thickness of the resulting solid lubricant coating was within the range of 20 to 30 µm.

[0190] Furthermore, the second contact surface of tests 73 to 78, 81, and 82 was sandblasted using the same method as in Example 1. The arithmetic mean roughness Ra of the second contact surface after sandblasting was measured using the same method as in Example 1. The arithmetic mean roughness Ra obtained (pm) for each test number 10 was approximately 2.5 pm, falling within the range of 0.5 to 10.0 pm. Note that the second contact surface of tests 71, 72, 79, and 80 was not sandblasted (indicated by the symbol in the Shot Blasting Treatment column of Table 7). The arithmetic mean of the Ra roughness of the second contact surface in the test numbers in which no sandblasting treatment was performed was approximately 0.2pm, so it was lower than 0.5pm.

[0191] An anti-corrosive coating was formed on the second contact surface of each test number. Specifically, a liquid anti-corrosive coating was formed on the second contact surface of tests 71, 73, 75, 77, 79, and 81. In addition, a semi-solid anti-corrosive coating was formed on the second contact surface of tests 72, 74, 76, 78, 80, and 82. The formation methods were the same as in Example 1. Note that, in test 83, a yellow doped grease was applied, and a semi-solid anti-corrosive coating was formed. The metal oil well pipes of Test Numbers 71 through 83 were produced using the above production process.

[0192] [Excoriation resistance assessment test] The evaluation of excorry resistance was performed using a repeated clamping test. In Test Numbers 71 to 83 of Table 7, clamping and loosening were repeated at room temperature (20 °C) using one pair (two) of the oil well metal tubing from each test number, and excorry resistance was evaluated. The clamping torque was set at 24,350 Nm. Each time a clamping and loosening cycle was completed, the bolt contact surface and the box contact surface were visually inspected. The excorry status on the threaded portions, the bolt sealing surface, and the box sealing surface was visually examined. With respect to the bolt sealing surface and the box sealing surface, the test was terminated when excorry was confirmed.When the scoring on a threaded part was minor and could be repaired by filing or similar means, the scoring defects were corrected and the test continued. The maximum number of times the clamping could be repeated was set at 10. The index adopted for evaluating the scoring resistance was [missing value]. RQzznn / pznz / B / GALA greater number of clampings (maximum of 10 times) without irreparable scoring on a threaded portion or scoring on a bolt sealing surface and a box sealing surface. The results are shown in the Clamping Times column of Table 7. The API standard defines the clamping times for a 7-inch casing pipe as 3 times or more. Therefore, excellent resistance to fretting corrosion is determined to be exhibited where the clamping times are 3 times or more.

[0193] [Evaluation Results] With reference to Table 7, in each of the tests numbered 71 to 83, the number of clamping times was 3 times or more, and therefore the metal oil well pipes of these test numbers were excellent in resistance to scouring.

[0194] One embodiment of the present invention has been described above. However, the above embodiment is merely an example for implementing the present invention. Accordingly, the present invention is not limited to the above embodiment, and the above embodiment may be modified and implemented appropriately within a range that does not depart from the essence of the present invention.

[0195] LIST OF REFERENCE SIGNS Metal pipe for oil wells Main tube body 10A First end portion 10B Second end portion Bolt tube body Copy Pin Box Metallic coating layer Solid lubricant layer Anti-rust coating Chemical treatment coating 400 Pemo contact surface 500 Box contact surface

Claims

1. A metal pipe for oil wells, comprising: a main pipe body including a first end portion and a second end portion, wherein: the main pipe body includes: a bolt formed in the first end portion, and a box formed in the second end portion; the bolt includes: a bolt contact surface having at least one external threaded portion formed on an outer peripheral surface of the first end portion of the main pipe body; the box includes: a box contact surface having at least one internal threaded portion formed on an inner peripheral surface of the second end portion of the main pipe body; a metallic coating layer formed on a first contact surface, the first contact surface being one of the bolt contact surface and the box contact surface;A layer of solid lubricant forms over the metallic coating layer; an arithmetic mean roughness Ra of a second contact surface is within a range of 0.5 to 10.0 pm, the second contact surface being the other bolt contact surface and the box contact surface; and on the second contact surface a semi-solid or liquid anti-rust coating is formed.

2. The metal pipe for oil wells according to claim 1, wherein: a chemical treatment coating is additionally formed on the second contact surface, and the anti-rust coating is formed on the chemical treatment coating.

3. The metal pipe for oil wells according to claim 1 or claim 2, wherein: the second contact surface is subjected to shot blasting.

4. The metal pipe for oil wells according to claim 1, wherein: the metallic coating layer is composed of a Zn-Ni alloy.

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