Oil-well metal pipe and composition for forming lubricant coating layer of oil-well metal pipe

Abstract

           The present disclosure provides an oil-well metal pipe that has excellent galling resistance and has low shouldering torque and increased high torque performance.  An oil-well metal pipe (1) according to the present disclosure is provided with a pipe main body (10) that includes a pin (40) formed at a first end portion (10A) and having a pin contact surface (400) including an external thread part (41), and includes a box (50) formed at a second end portion (10B) and having a box contact surface (500) including an internal thread part (51).  A lubricant coating layer (100) that is formed as an uppermost layer on the pin contact surface (400) and / or the box contact surface (500) contains a metal particle: 12.0 to 35.0%, metal soap: 2.0 to 30.0%, wax: 2.0 to 30.0%, basic metal salt of an aromatic organic acid: 20.0 to 80.0%, rosin-based material: 2.0 to 30.0%, and lubricant powder: 0.1 to 10.0%, and a Vickers hardness of the metal particle is no more than a Vickers hardness of the pipe main body (10).           The present disclosure provides an oil-well metal pipe that has excellent galling resistance and has low shouldering torque and increased high torque performance.  An oil-well metal pipe (1) according to the present disclosure is provided with a pipe main body (10) that includes a pin (40) formed at a first end portion (10A) and having a pin contact surface (400) including an external thread part (41), and includes a box (50) formed at a second end portion (10B) and having a box contact surface (500) including an internal thread part (51).  A lubricant coating layer (100) that is formed as an uppermost layer on the pin contact surface (400) and / or the box contact surface (500) contains a metal particle: 12.0 to 35.0%, metal soap: 2.0 to 30.0%, wax: 2.0 to 30.0%, basic metal salt of an aromatic organic acid: 20.0 to 80.0%, rosin-based material: 2.0 to 30.0%, and lubricant powder: 0.1 to 10.0%, and a Vickers hardness of the metal particle is no more than a Vickers hardness of the pipe main body (10).

Description

DESCRIPTION TITLE OF INVENTION:OIL-WELL METAL PIPE AND COMPOSITION FOR FORMING LUBRICANT COATING LAYER OF OIL-WELL METAL PIPE TECHNICAL FIELD

[0001] The present disclosure relates to an oil-well metal pipe and a composition for forming a lubricant coating layer of the oil-well metal pipe. BACKGROUND ART

[0002] In oil wells and gas wells (hereafter, oil wells and gas wells are collectively referred to as simply "oil wells"), oil-well metal pipes are used. At a site of drilling an oil well, in accordance with the depth of the oil well, a plurality of oil-well metal pipes are connected together to form an oil country tubular goods connected body as typified by a casing pipe or a tubing pipe. For this reason, threaded connections (a pin and a box) are formed in the pipe main body of an oil-well metal pipe. As used in the present description, the term "pipe main body" means a pipe body (hollow pipe) having a pin and a box that are formed at the end portions by machining or the like. That is, an oil country tubular goods connected body is formed by fastening together and connecting a pin formed at an end portion of the pipe main body of an oil-well metal pipe and a box formed at an end portion of the pipe main body of another oil-well metal pipe.

[0003] Here, the pin has, on an outer peripheral surface on one end portion of the pipe main body, a pin contact surface including an external thread part. The box has, on an inner peripheral surface of an end portion at which the pin is not formed of the pipe main body of the oil-well metal pipe, a box contact surface including an internal thread part. The external thread part and the internal thread part are also herein collectively referred to as "thread parts". The pin contact surface and the box contact surface are also herein collectively referred to as "contact surfaces". Note that the pin contact surface may further include a pin unthreaded metal contact portion that includes a pin seal surface and a pin shoulder surface. Likewise, the box contact surface may further include a box unthreaded metal contact portion that includes a box seal surface and a box shoulder surface. Hereinafter, the pin unthreaded metal contact portion and the box unthreaded metal contact portion are also collectively referred to as "unthreaded metal contact portions". That is, the contact surfaces of the pipe main body may include only a thread part, or may include a thread part and an unthreaded metal contact portion.

[0004] In this connection, in some cases a formed oil country tubular goods connected body is subjected to an inspection. When an inspection is conducted, the oil country tubular goods connected body is drawn up, and pins and boxes are loosened. Then, oil-well metal pipes are detached from the oil country tubular goods connected body by the loosening and are inspected. After the inspection, the pins and boxes are fastened together again, and the oil-well metal pipes are reused as parts of an oil country tubular goods connected body. Thus, when oil-well metal pipes are used as an oil country tubular goods connected body, in some cases fastening and loosening of the pins and boxes are repeated.

[0005] On the other hand, when fastening or loosening pins and boxes, the contact surfaces (pin contact surface and box contact surface) repeatedly experience strong friction. Consequently, when fastening and loosening of a pin and a box are repeated, galling (unrepairable seizure) tends to occur on the contact surfaces. Therefore, oil-well metal pipes are required to have sufficient durability against friction, that is, to have excellent galling resistance.

[0006] In conventional practices, compound grease containing heavy metal powder, which is referred to as "dope", has been used to improve the galling resistance of oil-well metal pipes. By applying compound grease onto the contact surfaces, the galling resistance of an oil-well metal pipe can be improved. However, there is a concern that heavy metal powders such as Pb, Zn, and Cu contained in compound grease may adversely affect the environment. For this reason, the development of an oil-well metal pipe that has excellent galling resistance without using compound grease is desired.

[0007] Techniques for increasing the galling resistance of an oil-well metal pipe are proposed in, for example, Japanese Patent Application Publication No. 2002-348587 (Patent Literature 1), and International Application Publication No. WO2006 / 104251 (Patent Literature 2).

[0008] In the oil-well metal pipe disclosed in Patent Literature 1, a solid lubricant coating composed of a lubricant powder and a binder is formed on a contact surface of a pin and / or a box. The lubricant powder is composed of graphite powder and one or more types selected from a molybdenum disulfide powder and a tungsten disulfide powder. The graphite powder accounts for 2 to 20% by mass of the lubricant powder. Patent Literature 1 discloses that excellent galling resistance is obtained in this oil-well metal pipe.

[0009] In the oil-well metal pipe disclosed in Patent Literature 2, a viscous liquid or semisolid lubricant coating is formed on a contact surface of a pin and / or a box, and a dry solid coating is formed thereon. Patent Literature 2 discloses that in this oil-well metal pipe, excellent galling resistance is obtained without using compound grease. CITATION LISTPATENT LITERATURE

[0010] Patent Literature 1: Japanese Patent Application Publication No. 2002-348587Patent Literature 2: International Application Publication No. WO2006 / 104251 SUMMARY OF INVENTIONTECHNICAL PROBLEM

[0011] In this connection, when fastening together pins and boxes formed in pipe main bodies of oil-well metal pipes, torque varies with the number of turns of the fastening. This point will be described specifically using a drawing. FIG. 1 is a diagram illustrating the relation between the number of turns and the torque between the oil-well metal pipes. Changes in torque with respect to the number of turns illustrated in FIG. 1 are also called a torque chart. With reference to FIG. 1, fastening a pin and a box together includes a stage in which a slope of the torque chart is gentle (initial stage), a stage in which the slope of the torque chart becomes steep (steep slope stage), and a stage in which the slope of the torque chart becomes gentle again (overtorque stage). In the overtorque stage, plastic deformation occurs in part of the pin and the box, resulting in the shallow slope of the torque chart.

[0012] In addition, referring to FIG. 1, in the present description, torque when the slope of the torque chart changes into the steep slope is also called "shouldering torque Ts" (indicated as "Ts" in FIG. 1). In addition, a torque when the slope of the torque chart becomes gentle again is also called "yield torque Ty" (indicated as "Ty" in FIG. 1). Here, in the steep slope stage where the torque is higher than the shouldering torque Ts, the pin and the box are fastened together at a high torque, thus increasing gastightness performance. In contrast, in the overtorque stage where the torque is higher than the yield torque Ty, plastic deformation occurs the part of the pin and / or the box.

[0013] Thus, as illustrated in FIG. 1, a fastening torque To is set between the shouldering torque Ts and the yield torque Ty. From the above viewpoint, the greater the difference between the shouldering torque Ts and the yield torque Ty, the wider the range of torque that can be set as the fastening torque To, and this is preferable. Note that, in the present description, the difference between the shouldering torque Ts and the yield torque Ty is also called "torque-on-shoulder resistance ΔT'". In addition, in the present description, being high in torque-on-shoulder resistance ΔT' is also called "being high in high torque performance".

[0014] Here, to increase high torque performance of an oil-well metal pipe, decreasing a shouldering torque Ts of the oil-well metal pipe or increasing a yield torque Ty of the oil-well metal pipe is effective. However, it is known that the shouldering torque Ts and the yield torque Ty typically show similar behaviors. Therefore, when a friction coefficient of a surface of an oil-well metal pipe is increased to increase a yield torque Ty, a shouldering torque Ts increases with an increase in the yield torque Ty. This case brings about a need of setting a fastening torque To to be high.

[0015] Oil-well metal pipes are fastened together with, for example, a power tong. Therefore, if the set fastening torque To is too high, there is a possibility that the fastening torque To will exceed an available torque range of a tool typified by a power tong. That is, in increasing high torque performance of an oil-well metal pipe, it is not preferable that a shouldering torque Ts of the oil-well metal pipe is excessively increased.

[0016] That is, there has been a demand for oil-well metal pipes that have excellent galling resistance and have both low shouldering torque Ts and increased high torque performance. On the other hand, as described above, the techniques disclosed in Patent Literatures 1 and 2 can increase galling resistance of oil-well metal pipes. However, in the aforementioned Patent Literatures 1 and 2, there is no investigation about having both low shouldering torque Ts and increased high torque performance.

[0017] An objective of the present disclosure is to provide an oil-well metal pipe which has excellent galling resistance and has both low shouldering torque and increased high torque performance, and also to provide a composition for forming a lubricant coating layer on the oil-well metal pipe. SOLUTION TO PROBLEM

[0018] An oil-well metal pipe according to the present disclosure includes:a pipe main body including a first end portion and a second end portion,whereinthe pipe main body includes:a pin that is formed at the first end portion; anda box that is formed at the second end portion,the pin includes a pin contact surface including an external thread part,the box includes a box contact surface including an internal thread part,the oil-well metal pipe further comprises:a lubricant coating layer formed as an uppermost layer on the pin contact surface and / or the box contact surface,the lubricant coating layer contains, in mass%:when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder in the lubricant coating layer is taken as 100% by mass,the metal particle: 12.0 to 35.0%;the metal soap: 2.0 to 30.0%;the wax: 2.0 to 30.0%;the basic metal salt of an aromatic organic acid: 20.0 to 80.0%;the rosin-based material: 2.0 to 30.0%; andthe lubricant powder: 0.1 to 10.0%, anda Vickers hardness of the metal particle is not more than a Vickers hardness of the pipe main body.

[0019] A composition according to the present disclosure is a composition for forming the lubricant coating layer that is included in the aforementioned oil-well metal pipe, the composition containing, in mass%:when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder is taken as 100% by mass,the metal particle: 12.0 to 35.0%;the metal soap: 2.0 to 30.0%;the wax: 2.0 to 30.0%;the basic metal salt of an aromatic organic acid: 20.0 to 80.0%;the rosin-based material: 2.0 to 30.0%; andthe lubricant powder: 0.1 to 10.0%, whereina Vickers hardness of the metal particle is not more than a Vickers hardness of the pipe main body. ADVANTAGEOUS EFFECTS OF INVENTION

[0020] The oil-well metal pipe according to the present disclosure has excellent galling resistance and has both low shouldering torque and increased high torque performance. The composition according to the present disclosure can form a lubricant coating layer of the aforementioned oil-well metal pipe. BRIEF DESCRIPTION OF DRAWINGS

[0021] [FIG. 1] FIG. 1 is a diagram illustrating the relation between the number of turns and torque between oil-well metal pipes.[FIG. 2] FIG. 2 is a configuration diagram illustrating an example of an oil-well metal pipe 1 according to the present embodiment.[FIG. 3] FIG. 3 is a sectional view (longitudinal section) parallel to a pipe axis direction of a second end portion 10B of the oil-well metal pipe 1 illustrated in FIG. 2.[FIG. 4] FIG. 4 is a sectional view (longitudinal section) of one part of a pin 40, that is a sectional view parallel to the pipe axis direction.[FIG. 5] FIG. 5 is a sectional view (longitudinal section) of one part of a box 50, that is a sectional view parallel to the pipe axis direction.[FIG. 6] FIG. 6 is a sectional view (longitudinal section) parallel to the pipe axis direction of the second end portion 10B of the oil-well metal pipe 1, that is a longitudinal sectional view illustrating an example that is different from the example in FIG. 3.[FIG. 7] FIG. 7 is a sectional view (longitudinal section) parallel to the pipe axis direction of the second end portion 10B of the oil-well metal pipe 1, that is a longitudinal sectional view illustrating an example that is different from the examples in FIG. 3 and FIG. 6.[FIG. 8] FIG. 8 is a sectional view (longitudinal section) parallel to the pipe axis direction of one part in the vicinity of the pin 40.[FIG. 9] FIG. 9 is a sectional view (longitudinal section) parallel to the pipe axis direction of one part in the vicinity of the box 50.[FIG. 10] FIG. 10 is a sectional view (longitudinal section) parallel to the pipe axis direction of one part in the vicinity of the pin 40, that is a longitudinal sectional view illustrating an example that is different from the example in FIG. 8.[FIG. 11] FIG. 11 is a sectional view (longitudinal section) parallel to the pipe axis direction of one part in the vicinity of the box 50, that is a longitudinal sectional view illustrating an example that is different from the example in FIG. 9.[FIG. 12] FIG. 12 is a sectional view (longitudinal section) parallel to the pipe axis direction of one part in the vicinity of the pin 40, that is a longitudinal sectional view illustrating an example that is different from the examples in FIG. 8 and FIG. 10.[FIG. 13] FIG. 13 is a sectional view (longitudinal section) parallel to the pipe axis direction of one part in the vicinity of the box 50, that is a longitudinal sectional view illustrating an example that is different from the examples in FIG. 9 and FIG. 11. DESCRIPTION OF EMBODIMENTS

[0022] An oil-well metal pipe and a composition according to the present embodiment will be described in detail below with reference to the drawings. The same reference symbols will be used throughout the drawings to refer to the same or like parts, and description thereof will not be repeated.

[0023] The present inventors conducted various studies regarding the relation between an oil-well metal pipe and a composition for forming a lubricant coating layer of the oil-well metal pipe, and the galling resistance, the shouldering torque Ts, and high torque performance of the oil-well metal pipe. As a result, the present inventors obtained the following findings.

[0024] As described above, by simply increasing a friction coefficient of a lubricant coating layer to increase high torque performance of an oil-well metal pipe, a yield torque Ty increases, but a shouldering torque Ts also increases. Thus, the present inventors conducted studies with regard to increasing the high torque performance of an oil-well metal pipe by introducing a particle to the lubricant coating layer. As a result of conducting detailed studies by the present inventors, the present inventors found that if particles having a hardness at a certain level or higher are contained in the lubricant coating layer, high torque performance of the oil-well metal pipe is increased.

[0025] The present inventors thus evaluated the particles introduced to the lubricant coating layer, and the high torque performance, the shouldering torque Ts, and the galling resistance of the oil-well metal pipe. This point will be described specifically using a table that is an excerpt of part of Example.

[0026] [Table 1]TABLE 1Test No.Pipe main bodyParticleFastening testHardness (Hv)Hardness (Hv)Content (mass%)Ts (ft-lbs)ΔT' (ft-lbs)Galling resistance1254--36571419E220510.045561109E320518.033303034E760020.040191723NA1075018.044921500NA 

[0027] Table 1 is a table that is an excerpt of part of Example that is described later. Referring to Table 1, Test No. 1 is an example in which no particles were contained in the lubricant coating layer. On the other hand, Test Nos. 2, 3, 7, and 10 are examples in which particles were contained in the lubricant coating layer. In Table 1, "E (Excellent)" in the column "Galling resistance" means that the galling resistance was excellent. In Table 1, "NA (Not Acceptable)" in the column "Galling resistance" means that the galling resistance was not excellent.

[0028] Referring to Table 1, a comparison of Test Nos. 1 and 2, and Test Nos. 3, 7, and 10 shows that when more than 10.0% by mass of the particles are contained in the lubricant coating layer, the torque-on-shoulder resistance ΔT' is increased. Further, referring to Table 1, a comparison of Test No. 3, and Test Nos. 7 and 10 shows that when particles having a hardness higher than that of the pipe main body are contained in the lubricant coating layer, the torque-on-shoulder resistance ΔT' increases, but the shouldering torque Ts also increases. In addition, Test No. 3 also had excellent galling resistance.

[0029] That is, as a result of detailed studies conducted by the present inventors, it was revealed that when more than 10.0% by mass of a metal particle having a hardness being moderate and lower than that of a pipe main body is contained in a lubricant coating layer, an oil-well metal pipe having excellent galling resistance and having both low shouldering torque Ts and increased high torque performance is obtained.

[0030] The detailed reason that the oil-well metal pipe has the excellent galling resistance and has both the low shouldering torque Ts and the increased high torque performance when more than 10.0% by mass of the metal particle having a hardness lower than that of the pipe main body is contained in the lubricant coating layer is not clear. However, the present inventors presume as follows. With hard particles contained in the lubricant coating layer, when oil-well metal pipes are fastened together, there is a possibility that the hard particles are pressed against the pipe main bodies to produce resistance force. The present inventors thus presume that when more than 10.0% by mass of a metal particle having a hardness at a certain level is contained in the lubricant coating layer, the torque-on-shoulder resistance ΔT' increases. On the other hand, if the particles in the lubricant coating layer are too hard, the hard particles pressed against the pipe main bodies tend to scratch the pipe main bodies. When the pipe main bodies are scratched, base metals of the pipe main bodies tend to contact each other, and there is a possibility that galling tends to occur. Further, when the pipe main bodies are scratched, a friction coefficient increases, and there is a possibility that the shouldering torque Ts tends to increase.

[0031] That is, when more than 10.0% by mass of a metal particle being moderately hard and having a hardness lower than that of a pipe main body is contained in a lubricant coating layer, it is possible not only to stably increase the yield torque Ty while keeping the shouldering torque Ts low but also to make it difficult for galling due to the scratched pipe main bodies to occur. The present inventors presume that, as a result, there is a possibility of providing an oil-well metal pipe which has excellent galling resistance and has both low shouldering torque Ts and increased high torque performance. Note that there can be a possibility that the oil-well metal pipe which has excellent galling resistance and has both low shouldering torque Ts and increased high torque performance is provided by a mechanism other than the mechanism described above. However, Example that is described later prove that the oil-well metal pipe having the excellent galling resistance and having both the low shouldering torque Ts and the increased high torque performance is obtained when more than 10.0% by mass of the metal particle being moderately hard and having a hardness lower than that of the pipe main body is contained in the lubricant coating layer.

[0032] Therefore, the oil-well metal pipe according to the present embodiment includes a lubricant coating layer that is formed as an uppermost layer on a pin contact surface and / or a box contact surface, the lubricant coating layer containing, in mass%: when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder in the lubricant coating layer is taken as 100% by mass, the lubricant coating layer contains, the metal particle: 12.0 to 35.0%, the metal soap: 2.0 to 30.0%, the wax: 2.0 to 30.0%, the basic metal salt of an aromatic organic acid: 20.0 to 80.0%, the rosin-based material: 2.0 to 30.0%, and the lubricant powder: 0.1 to 10.0%, and further, a Vickers hardness of the metal particle is not more than a Vickers hardness of a pipe main body. As a result, the oil-well metal pipe according to the present embodiment has excellent galling resistance and has both low shouldering torque Ts and increased high torque performance.

[0033] The gist of the oil-well metal pipe and the composition according to the present embodiment that were completed based on the above findings is as follows.

[0034] [1]An oil-well metal pipe including:a pipe main body including a first end portion and a second end portion,whereinthe pipe main body includes:a pin that is formed at the first end portion; anda box that is formed at the second end portion,the pin includes:a pin contact surface including an external thread part,the box includes:a box contact surface including an internal thread part,the oil-well metal pipe further includes:a lubricant coating layer formed as an uppermost layer on the pin contact surface and / or the box contact surface,the lubricant coating layer contains, in mass%:when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder in the lubricant coating layer is taken as 100% by mass,the metal particle: 12.0 to 35.0%;the metal soap: 2.0 to 30.0%;the wax: 2.0 to 30.0%;the basic metal salt of an aromatic organic acid: 20.0 to 80.0%;the rosin-based material: 2.0 to 30.0%; andthe lubricant powder: 0.1 to 10.0%, anda Vickers hardness of the metal particle is not more than a Vickers hardness of the pipe main body.

[0035] [2]The oil-well metal pipe according to [1], wherein a chemical composition of the metal particle contains, in mass%, Fe: 50% or more.

[0036] [3]The oil-well metal pipe according to [1] or [2], wherein a particle size of the metal particle is within a range of 15 to 250 μm.

[0037] [4]The oil-well metal pipe according to any one of [1] to [3], wherein a thickness of the lubricant coating layer is within a range of 10 to 500 μm.

[0038] [5]The oil-well metal pipe according to any one of [1] to [4], whereinthe oil-well metal pipe further includes:one or more types selected from the group consisting of a metal plating layer and a chemical conversion treatment layer formed as an underlayer of the lubricant coating layer.

[0039] [6]The oil-well metal pipe according to any one of [1] to [5], whereinthe pin contact surface further includes:a pin seal surface and a pin shoulder surface, andthe box contact surface further includes:a box seal surface and a box shoulder surface.

[0040] [7]A composition for forming the lubricant coating layer that is included in the oil-well metal pipe according to any one of [1] to [6], the composition containing, in mass%:when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder is taken as 100% by mass,the metal particle: 12.0 to 35.0%;the metal soap: 2.0 to 30.0%;the wax: 2.0 to 30.0%;the basic metal salt of an aromatic organic acid: 20.0 to 80.0%;the rosin-based material: 2.0 to 30.0%; andthe lubricant powder: 0.1 to 10.0%, whereina Vickers hardness of the metal particle is not more than a Vickers hardness of the pipe main body.

[0041] [8]The composition according to [7], the composition further containing a volatile organic solvent.

[0042] Hereunder, the oil-well metal pipe according to the present embodiment is described in detail.

[0043] [Configuration of Oil-Well Metal Pipe]First, a configuration of the oil-well metal pipe according to the present embodiment will be described. The oil-well metal pipe has a well-known configuration. Oil-well metal pipes include oil-well metal pipes of a T & C type and oil-well metal pipes of an integral type. Each type of oil-well metal pipe will be described in detail below.

[0044] [Case where Oil-Well Metal Pipe 1 is T & C Type]FIG. 2 is a configuration diagram illustrating an example of an oil-well metal pipe 1 according to the present embodiment. FIG. 2 is a configuration diagram of the oil-well metal pipe 1, which is of what is called T&C type. Referring to FIG. 2, the oil-well metal pipe 1 includes a pipe main body 10.

[0045] The pipe main body 10 extends in a pipe axis direction. A cross section perpendicular to the pipe axis direction of the pipe main body 10 has a round shape. The pipe main body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is an end portion on the opposite side to the second end portion 10B. In the oil-well metal pipe 1 of the T & C type illustrated in FIG. 2, the pipe main body 10 includes a pin pipe body 11 and a coupling 12. The coupling 12 is attached to one end of the pin pipe body 11. More specifically, the coupling 12 is fastened to the one end of the pin pipe body 11 with a thread.

[0046] FIG. 3 is a fragmentary sectional view illustrating a cross section of the coupling 12 of the oil-well metal pipe 1 illustrated in FIG. 2 parallel to the pipe axis direction (longitudinal section). Referring to FIG. 2 and FIG. 3, the pipe main body 10 includes a pin 40 and a box 50. The pin 40 is formed at the first end portion 10A of the pipe main body 10. At the time of fastening, the pin 40 is inserted into a box 50 of another oil-well metal pipe 1 (not illustrated) and fastened to the box 50 of the other oil-well metal pipe 1 with a thread.

[0047] The box 50 is formed at the second end portion 10B of the pipe main body 10. At the time of fastening, a pin 40 of another oil-well metal pipe 1 is inserted into the box 50, and the box 50 is fastened to the pin 40 of the other oil-well metal pipe 1 with a thread.

[0048] [Configuration of Pin 40]FIG. 4 is a sectional view of a part in the vicinity of the pin 40 of the oil-well metal pipe 1 illustrated in FIG. 3, that is a sectional view parallel to a pipe axis direction of the oil-well metal pipe 1. A dashed line portion in FIG. 4 represents a configuration of a box 50 of another oil-well metal pipe 1 in the case of fastening to the other oil-well metal pipe 1. Referring to FIG. 4, the pin 40 includes a pin contact surface 400 on an outer peripheral surface of the first end portion 10A of the pipe main body 10. When the oil-well metal pipe 1 is being fastened to the other oil-well metal pipe 1, the pin contact surface 400 is screwed into the box 50 of the other oil-well metal pipe 1 to come into contact with a box contact surface 500 (described later) of the box 50.

[0049] The pin contact surface 400 includes at least an external thread part 41 that is formed on the outer peripheral surface of the first end portion 10A. The pin contact surface 400 may further include a pin seal surface 42 and a pin shoulder surface 43. In FIG. 4, the pin shoulder surface 43 is disposed at the front-end face of the first end portion 10A, and the pin seal surface 42 is disposed on the outer peripheral surface of the first end portion 10A in such a manner that the pin seal surface 42 is closer to the front end of the first end portion 10A than the external thread part 41. That is, the pin seal surface 42 is disposed between the external thread part 41 and the pin shoulder surface 43. The pin seal surface 42 is provided in a tapered shape. Specifically, at the pin seal surface 42, the outer diameter of the first end portion 10A gradually decreases as the first end portion 10A extends from the external thread part 41 toward the pin shoulder surface 43 in a longitudinal direction (the pipe axis direction) of the first end portion 10A.

[0050] When the oil-well metal pipe 1 is being fastened to the other oil-well metal pipe 1, the pin seal surface 42 comes into contact with a box seal surface 52 (described later) of the box 50 of the other oil-well metal pipe 1. More specifically, during fastening, insertion of the pin 40 into the box 50 of the other oil-well metal pipe 1 causes the pin seal surface 42 to come into contact with the box seal surface 52. Then, further screwing of the pin 40 into the box 50 of the other oil-well metal pipe 1 brings the pin seal surface 42 into intimate contact with the box seal surface 52. By this means, when fastening is performed, the pin seal surface 42 comes into intimate contact with the box seal surface 52 to thereby form a seal based on metal-to-metal contact. Therefore, gastightness can be increased in the oil-well metal pipes 1 that are fastened to each other.

[0051] In FIG. 4, the pin shoulder surface 43 is disposed on the front-end face of the first end portion 10A. That is, in the pin 40 illustrated in FIG. 4, the external thread part 41, the pin seal surface 42, and the pin shoulder surface 43 are disposed in this order from the middle of the pipe main body 10 toward the first end portion 10A. When the oil-well metal pipe 1 is being fastened to the other oil-well metal pipe 1, the pin shoulder surface 43 faces and then comes into contact with a box shoulder surface 53 (described later) of the box 50 of the other oil-well metal pipe 1. More specifically, during fastening, the insertion of the pin 40 into the box 50 of the other oil-well metal pipe 1 causes the pin shoulder surface 43 to come into contact with the box shoulder surface 53. By this means, high torque can be obtained when fastening is performed. In addition, the positional relation between the pin 40 and the box 50 in the fastening state can be stabilized.

[0052] Note that the pin contact surface 400 of the pin 40 includes at least the external thread part 41. That is, the pin contact surface 400 may include the external thread part 41 and may not include the pin seal surface 42 and the pin shoulder surface 43. The pin contact surface 400 may include the external thread part 41 and the pin shoulder surface 43 and may not include the pin seal surface 42. The pin contact surface 400 may include the external thread part 41 and the pin seal surface 42 and may not include the pin shoulder surface 43.

[0053] [Configuration of Box 50]FIG. 5 is a sectional view of a part in the vicinity of the box 50 of the oil-well metal pipe 1 illustrated in FIG. 3, that is a sectional view parallel to a pipe axis direction of the oil-well metal pipe 1. In a case where the oil-well metal pipe 1 is fastened to another oil-well metal pipe 1, a region enclosed by broken lines in FIG. 5 represents a configuration of a pin 40 of the other oil-well metal pipe 1. Referring to FIG. 5, the box 50 includes the box contact surface 500 on an inner peripheral surface of the second end portion 10B of the pipe main body 10. When the oil-well metal pipe 1 is being fastened to the other oil-well metal pipe 1, the pin 40 of the other oil-well metal pipe 1 is screwed into the box contact surface 500, and then the box contact surface 500 comes into contact with the pin contact surface 400 of the pin 40.

[0054] The box contact surface 500 includes at least an internal thread part 51 that is formed on the inner peripheral surface of the second end portion 10B. During fastening, the internal thread part 51 meshes with an external thread part 41 of the pin 40 of the other oil-well metal pipe 1.

[0055] The box contact surface 500 may further include a box seal surface 52 and a box shoulder surface 53. In FIG. 5, the box seal surface 52 is disposed on the inner peripheral surface of the second end portion 10B in such a manner that the box seal surface 52 is closer to the pipe main body 10 than the internal thread part 51. That is, the box seal surface 52 is disposed between the internal thread part 51 and the box shoulder surface 53. The box seal surface 52 is provided in a tapered shape. Specifically, at the box seal surface 52, the inner diameter of the second end portion 10B gradually decreases as the second end portion 10B extends from the internal thread part 51 toward the box shoulder surface 53 in a longitudinal direction (the pipe axis direction) of the second end portion 10B.

[0056] When the oil-well metal pipe 1 is being fastened to the other oil-well metal pipe 1, the box seal surface 52 comes into contact with a pin seal surface 42 of the pin 40 of the other oil-well metal pipe 1. More specifically, during fastening, screwing of the pin 40 of the other oil-well metal pipe 1 into the box 50 causes the box seal surface 52 to come into contact with the pin seal surface 42, and further screwing of the pin 40 brings the box seal surface 52 into intimate contact with the pin seal surface 42. By this means, when fastening is performed, the box seal surface 52 comes into intimate contact with the pin seal surface 42 to thereby form a seal based on metal-to-metal contact. Therefore, gastightness can be increased in the oil-well metal pipes 1 that are fastened to each other.

[0057] The box shoulder surface 53 is disposed closer to the pipe main body 10 than the box seal surface 52. That is, in the box 50, the box shoulder surface 53, the box seal surface 52, and the internal thread part 51 are disposed in this order from the middle of the pipe main body 10 toward the front end of the second end portion 10B. When the oil-well metal pipe 1 is being fastened to the other oil-well metal pipe 1, the box shoulder surface 53 faces and then comes into contact with a pin shoulder surface 43 of the pin 40 of the other oil-well metal pipe 1. More specifically, during fastening, the insertion of the pin 40 of the other oil-well metal pipe 1 into the box 50 causes the box shoulder surface 53 to come into contact with the pin shoulder surface 43. By this means, high torque can be obtained when fastening is performed. In addition, the positional relation between the pin 40 and the box 50 in the fastening state can be stabilized.

[0058] The box contact surface 500 includes at least the internal thread part 51. When fastening is performed, the internal thread part 51 of the box contact surface 500 of the box 50 corresponds to the external thread part 41 of the pin contact surface 400 of the pin 40 and comes into contact with the external thread part 41. The box seal surface 52 corresponds to the pin seal surface 42 and comes into contact with the pin seal surface 42. The box shoulder surface 53 corresponds to the pin shoulder surface 43 and comes into contact with the pin shoulder surface 43.

[0059] In a case where the pin contact surface 400 includes the external thread part 41 and does not include the pin seal surface 42 and the pin shoulder surface 43, the box contact surface 500 includes the internal thread part 51 and does not include the box seal surface 52 and the box shoulder surface 53. In a case where the pin contact surface 400 includes the external thread part 41 and the pin shoulder surface 43 and does not include the pin seal surface 42, the box contact surface 500 includes the internal thread part 51 and the box shoulder surface 53 and does not include the box seal surface 52. In a case where the pin contact surface 400 includes the external thread part 41 and the pin seal surface 42 and does not include the pin shoulder surface 43, the box contact surface 500 includes the internal thread part 51 and the box seal surface 52 and does not include the box shoulder surface 53.

[0060] The pin contact surface 400 may include a plurality of external thread parts 41, may include a plurality of pin seal surfaces 42, and may include a plurality of pin shoulder surfaces 43. For example, on the pin contact surface 400 of the pin 40, the pin shoulder surface 43, the pin seal surface 42, the external thread part 41, the pin seal surface 42, the pin shoulder surface 43, the pin seal surface 42, and the external thread part 41 may be disposed in this order from the front end of the first end portion 10A toward the middle of the pipe main body 10. In this case, on the box contact surface 500 of the box 50, the internal thread part 51, the box seal surface 52, the box shoulder surface 53, the box seal surface 52, the internal thread part 51, the box seal surface 52, and the box shoulder surface 53 are disposed in this order from the front end of the second end portion 10B toward the middle of the pipe main body 10.

[0061] FIG. 4 and FIG. 5 each illustrate a so-called "premium joint" in which the pin 40 includes the external thread part 41, the pin seal surface 42, and the pin shoulder surface 43, and the box 50 includes the internal thread part 51, the box seal surface 52, and the box shoulder surface 53. However, as described above, a configuration may be adopted in which the pin 40 includes the external thread part 41 and does not include the pin seal surface 42 and the pin shoulder surface 43. In this case, the box 50 includes the internal thread part 51 and does not include the box seal surface 52 and the box shoulder surface 53. FIG. 6 is a diagram illustrating an example of the oil-well metal pipe 1 in which the pin 40 includes the external thread part 41 and does not include the pin seal surface 42 and the pin shoulder surface 43, and the box 50 includes the internal thread part 51 and does not include the box seal surface 52 and the box shoulder surface 53.

[0062] [Case where Oil-Well Metal Pipe 1 is Integral Type]The oil-well metal pipe 1 illustrated in FIG. 2, FIG. 3, and FIG. 6 is the oil-well metal pipe 1 of the so-called "T & C type" in which the pipe main body 10 includes the pin pipe body 11 and the coupling 12. However, the oil-well metal pipe 1 according to the present embodiment may be of the integral type rather than the T & C type.

[0063] FIG. 7 is a configuration diagram of an oil-well metal pipe 1 of the integral type according to the present embodiment. Referring to FIG. 7, the oil-well metal pipe 1 of the integral type includes a pipe main body 10. The pipe main body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is disposed on an opposite side to the second end portion 10B. As described above, in the oil-well metal pipe 1 of the T & C type, the pipe main body 10 includes the pin pipe body 11 and the coupling 12. That is, in the oil-well metal pipe 1 of the T & C type, the pipe main body 10 is formed by fastening two separate members (the pin pipe body 11 and the coupling 12). In contrast, in the oil-well metal pipe 1 of the integral type, the pipe main body 10 is formed as a single piece.

[0064] The pin 40 is formed at the first end portion 10A of the pipe main body 10. When performing fastening, the pin 40 is inserted and screwed into a box 50 of another oil-well metal pipe 1 of the integral type to be fastened to the box 50 of the other oil-well metal pipe 1 of the integral type. The box 50 is formed at the second end portion 10B of the pipe main body 10. When performing fastening, a pin 40 of another oil-well metal pipe 1 of the integral type is inserted and screwed into a box 50, and the box 50 is fastened to the pin 40 of the other oil-well metal pipe 1 of the integral type.

[0065] A configuration of the pin 40 of the oil-well metal pipe 1 of the integral type is the same as the configuration of the pin 40 of the oil-well metal pipe 1 of the T & C type illustrated in FIG. 4. Likewise, a configuration of the box 50 of the oil-well metal pipe 1 of the integral type is the same as the configuration of the box 50 of the oil-well metal pipe 1 of the T & C type illustrated in FIG. 5. Note that, in FIG. 4 and FIG. 5, in the pin 40, the pin shoulder surface 43, the pin seal surface 42, and the external thread part 41 are disposed in this order from the front end of the first end portion 10A toward the middle of the pipe main body 10. Therefore, in the box 50, the internal thread part 51, the box seal surface 52, and the box shoulder surface 53 are disposed in this order from the front end of the second end portion 10B toward the middle of the pipe main body 10. However, as with the pin contact surface 400 of the pin 40 of the oil-well metal pipe 1 of the T & C type, the pin contact surface 400 of the pin 40 of the oil-well metal pipe 1 of the integral type needs only to include at least the external thread part 41. Further, as with the box contact surface 500 of the box 50 of the oil-well metal pipe 1 of the T & C type, the box contact surface 500 of the box 50 of the oil-well metal pipe 1 of the integral type needs only to include at least the internal thread part 51.

[0066] The oil-well metal pipe 1 according to the present embodiment may be of the T & C type or may be of the integral type.

[0067] [Chemical Composition of Pipe Main Body]The chemical composition of the pipe main body 10 of the oil-well metal pipe 1 according to the present embodiment is not limited to a specific chemical composition. That is, in the present embodiment, a steel type of the pipe main body 10 of the oil-well metal pipe 1 is not limited to a specific steel type. The pipe main body 10 may be formed of, for example, carbon steel, stainless steel, an alloy, or the like. That is, the pipe main body 10 may be a steel pipe made of an Fe-based alloy or may be an alloy pipe typified by a Ni-based alloy pipe. Here, the steel pipe is, for example, a low alloy steel pipe, a martensitic stainless steel pipe, a ferritic stainless steel pipe, an austenitic stainless steel pipe, a duplex stainless steel pipe, or the like. Examples of the alloy pipe include a Ni-based alloy pipe and a NiCrFe alloy pipe.

[0068] Among alloys, so-called "high alloys" such as Ni-based alloys and duplex stainless steels that contain alloying elements such as Cr, Ni, and Mo have high corrosion resistance. Therefore, if these high alloys are used as the pipe main body 10, excellent corrosion resistance will be obtained in a corrosive environment that contains hydrogen sulfide or carbon dioxide or the like.

[0069] [Lubricant Coating Layer 100]The oil-well metal pipe 1 according to the present embodiment includes a lubricant coating layer formed as an uppermost layer on the pin contact surface 400 and / or the box contact surface 500. In other words, in the present embodiment, the lubricant coating layer may be formed on the contact surface 400 and / or 500 directly, or may be formed on a certain layer that is formed on the contact surface 400 and / or 500. That is, another layer may be formed between the lubricant coating layer and the contact surface 400 and / or 500, or no other layer may be formed between the lubricant coating layer and the contact surface 400 and / or 500.

[0070] Specifically, FIG. 8, FIG. 10, and FIG. 12 are sectional views (longitudinal sections) of one part in the vicinity of the pin 40, that are sectional views parallel to the pipe axis direction. In addition, FIG. 9, FIG. 11, and FIG. 13 are sectional views (longitudinal sections) of one part in the vicinity of the box 50, that are sectional views parallel to the pipe axis direction. Referring to FIG. 8, the lubricant coating layer 100 may be formed directly on the pin contact surface 400. Referring to FIG. 9, the lubricant coating layer 100 may be formed directly on the box contact surface 500. Referring to FIG. 10 and FIG. 12, one or more other layers may be formed between the lubricant coating layer 100 and the pin contact surface 400. In addition, referring to FIG. 11 and FIG. 13, one or more other layers may be formed between the lubricant coating layer 100 and the box contact surface 500.

[0071] Although the thickness of the lubricant coating layer 100 is not limited to a specific thickness, the thickness is, for example, within the range of 10 to 500 μm. When the thickness of the lubricant coating layer 100 is 10 μm or more, the aforementioned effects are stably obtained. On the other hand, when the thickness of the lubricant coating layer 100 is 500 μm or less, the adhesiveness of the lubricant coating layer 100 increases. Therefore, with consideration given to productivity, the thickness of the lubricant coating layer according to the present embodiment is within the range of 10 to 500 μm.

[0072] In the present embodiment, the thickness of the lubricant coating layer 100 can be measured by the following method. A wet gauge is brought into contact with the pin contact surface 400 or the box contact surface 500 on which the lubricant coating layer 100 is formed. The wet gauge includes a plurality of end faces that each correspond to a thickness. The wet gauge is brought into contact with the lubricant coating layer 100, and which of the end faces of the wet gauge the lubricant coating layer 100 adheres to is checked. In this way, the thickness of the lubricant coating layer 100 is determined. Spots for the measurement are 12 spots on the oil-well metal pipe 1 in a tube circumferential direction (the 12 spots including 0, 30, 60, 90, 120, 150, 180, 210, 240, 270, 300, and 330 degrees). An arithmetic mean value of the measurement results at the 12 spots is defined as the thickness of the lubricant coating layer 100.

[0073] When a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder in the lubricant coating layer 100 is taken as 100% by mass, the lubricant coating layer 100 contains, in mass%, the metal particle: 12.0 to 35.0%, the metal soap: 2.0 to 30.0%, the wax: 2.0 to 30.0%, the basic metal salt of an aromatic organic acid: 20.0 to 80.0%, the rosin-based material: 2.0 to 30.0%, and the lubricant powder: 0.1 to 10.0%. In addition, the lubricant coating layer 100 may contain other components in addition to the metal particle, the metal soap, the wax, the basic metal salt of an aromatic organic acid, the rosin-based material, and the lubricant powder. Note that, the content (mass%) of components other than the metal particle, the metal soap, the wax, the basic metal salt of an aromatic organic acid, the rosin-based material, and the lubricant powder is 0 to 10.0%. In other words, when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder in the lubricant coating layer 100 is taken as 100% by mass, the lubricant coating layer 100 according to the present embodiment may contain, in mass%, the metal particle: 12.0 to 35.0%, the metal soap: 2.0 to 30.0%, the wax: 2.0 to 30.0%, the basic metal salt of an aromatic organic acid: 20.0 to 80.0%, the rosin-based material: 2.0 to 30.0%, the lubricant powder: 0.1 to 10.0%, and the other components: 0 to 10.0%. Each component is described hereunder. Note that, unless otherwise stated, the symbol "%" in relation to each component means the content (mass%) of each component when a total of the contents of the metal particle, the metal soap, the wax, the basic metal salt of an aromatic organic acid, the rosin-based material, and the lubricant powder in the lubricant coating layer 100 is taken as 100% by mass.

[0074] [Metal Particle]In the present embodiment, the metal particle means a particle that is mainly composed of a metal. That is, in the present embodiment, the metal particle may contain impurities in addition to metal. The metal may be a single metal, made of one type of metal, or may be an alloy including two or more types of metal. Preferably, the chemical composition of the metal particle contains, in mass%, Fe: 50% or more. That is, the metal particle is preferably pure iron or Fe-based alloy. More specifically, the metal of the metal particle is preferably one or more types selected from the group consisting of pure iron, carbon steel, and alloy steel that are defined in JIS G 0203:2009. More preferably, the metal of the metal particle is a stainless steel defined in JIS G 0203:2009.

[0075] In the present embodiment, the Vickers hardness of the metal particle is not more than the Vickers hardness of the pipe main body. As described above, although the chemical composition of the pipe main body according to the present embodiment is not limited to a specific chemical composition, the pipe main body is made of, for example, a carbon steel, a stainless steel, an alloy, or the like. That is, in the present embodiment, the metal particle can be selected in accordance with the chemical composition of the pipe main body. In addition, although the Vickers hardness of the metal particle is not limited to a specific Vickers hardness, the Vickers hardness is, for example, within the range of 130 to 250 Hv. When the Vickers hardness of the metal particle is within the range of 130 to 250 Hv, the Vickers hardness can be stably kept low compared with that of the pipe main body that is widely used as oil-well metal pipes, and this is preferable.

[0076] In addition, as described above, the metal of the metal particle is preferably a stainless steel. In addition, when the metal particle is made of an austenitic stainless steel, the Vickers hardness can be stably decreased, and this is preferable. Examples of the austenitic stainless steel include SUS301, SUS301L, SUS301J1, SUS302, SUS302B, SUSXM15J1, SUS303, SUS303Cu, SUS304, SUS304L, SUS304LN, SUS304N1, SUS304N2, SUS304Cu, SUSXM7, SUS304J1, SUS304J2, SUS305, SUS305J1, SUS309S, SUS310S, SUS315J1, SUS315J2, SUS316, SUS316L, SUS316N, SUS316LN, SUS316J1, SUS316J1L, SUS317, SUS317J1, SUS317L, SUS312L, SUS836L, SUS890L, SUS321, and SUS347. More preferably, the metal of the metal particle is SUS316L.

[0077] In the present embodiment, the Vickers hardness of the metal particle can be measured by the following method. Specifically, from the lubricant coating layer 100 of the oil-well metal pipe 1 according to the present embodiment, metallic particles are extracted. The metal particle can be separated from other components by a person skilled in the art. The extracted metal particle is embedded and fixed in resin, and a sample whose surface was polished is prepared. A loading-unloading test is then performed in which a triangular pyramid-shaped indenter made of diamond is pressed into the prepared sample surface while controlling the test force and load speed. The Vickers hardness (Hv) can be determined using a test force-indentation depth curve obtained from the loading-unloading test. For example, Dynamic Ultra Micro Hardness Tester (DUH-211S) manufactured by Shimadzu Corporation can be used as the Vickers testing machine used in the loading-unloading test.

[0078] In the present embodiment, a preferable particle size of the metal particle is within the range of 15 to 250 μm. When the particle size of the metal particle is 15 μm or more, the effect of increasing the yield torque Ty while keeping the shouldering torque Ts low can be further increased with an increase in the content of the metal particle. That is, when the particle size of the metal particle is 15 μm or more, the high torque performance is more likely to be increased while the shouldering torque Ts is kept low. On the other hand, the metal particle whose particle size is 15 μm or more tends to scratch the pipe main body 10 when oil-well metal pipes 1 are being fastened together. Therefore, when oil-well metal pipes 1 formed with lubricant coating layers 100 containing metal particle whose particle size is 15 μm or more are fastened together, there is a tendency for the galling resistance to be decreased.

[0079] Thus, the metal particle according to the present embodiment are made to have a Vickers hardness that is not more than that of the pipe main body 10. Therefore, the metal particle according to the present embodiment is not liable to decrease the galling resistance even when the particle size of the metal particle is 15 μm or more. On the other hand, if the particle size of the metal particle is too high, the adhesiveness of the lubricant coating layer 100 may decrease. Therefore, in the present embodiment, a preferable particle size of the metal particle is within the range of 15 to 250 μm.

[0080] In the present embodiment, the particle size of the metal particle can be measured by the following method. The metal particle that is extracted by the same method as in the measurement of the Vickers hardness is subjected to particle size distribution measurement performed by a laser diffraction and scattering method. The particle size distribution measurement can be performed by a well-known method. An arithmetic mean value of an effective particle size distribution obtained using, for example, SALD series manufactured by Shimadzu Corporation as a particle counter is adopted as the particle size of the metal particle in the present embodiment.

[0081] The content of the metal particle for effectively obtaining the aforementioned effect is within the range of 12.0 to 35.0%. If the content of the metal particle is too low, the aforementioned effect is not obtained sufficiently. On the other hand, if the content of the metal particle is too high, the adhesiveness of the lubricant coating layer 100 may decrease. Therefore, the content of the metal particle in the lubricant coating layer 100 according to the present embodiment is within the range of 12.0 to 35.0%. A preferable lower limit of the content of the metal particle in the lubricant coating layer 100 is 13.0%, further preferably is 14.0%, further preferably is 15.0%, and further preferably is 16.0%. A preferable upper limit of the content of the metal particle in the lubricant coating layer 100 is 34.0%, further preferably is 32.0%, further preferably is 30.0%, and further preferably is 29.0%.

[0082] [Metal Soap]A metal soap is a salt of an aliphatic acid with a metal. Here, the term "aliphatic acid" means an aliphatic organic acid. That is, by definition, aromatic organic acids are not included in the aliphatic acids.

[0083] In the present embodiment, the aliphatic acid of the metal soap may be a mixture of aliphatic acids, or may be a single compound. The mixture of aliphatic acids is, for example, beef tallow, lard, wool fat, palm oil, rapeseed oil, coconut oil, or the like. Examples of the aliphatic acid that is a single compound include lauric acid, tridecylic acid, myristic acid, palmitic acid, lanopalmitic acid, stearic acid, isostearic acid, 12-hydroxystearic acid, oleic acid, elaidic acid, arachic acid, behenic acid, erucic acid, lignoceric acid, lanoceric acid, ricinoleic acid, montanic acid, linoleic acid, linolenic acid, ricinoleic acid, octylic acid, and sebacic acid. One or more kinds selected from the group consisting of the aforementioned examples of an aliphatic acid can be used as the aliphatic acid according to the present embodiment. Preferably the carbon number of the aliphatic acid according to the present embodiment is 12 to 30. Aliphatic acids having a carbon number of 12 to 30 are, for example, lauric acid, tridecylic acid, myristic acid, palmitic acid, lanopalmitic acid, stearic acid, isostearic acid, 12-hydroxystearic acid, oleic acid, elaidic acid, arachic acid, behenic acid, erucic acid, lignoceric acid, lanoceric acid, ricinoleic acid, montanic acid, linoleic acid, linolenic acid, and ricinoleic acid.

[0084] In the present embodiment, the metal of the metal soap is not particularly limited as long as the metal can form a salt with an aliphatic acid. The metal of the metal soap is, for example, calcium, sodium, magnesium, zinc, or barium. In the present embodiment, the metal soap may be a neutral salt or may be a basic salt. That is, the metal soap according to the present embodiment is not particularly limited as long as the metal soap is a salt of the aforementioned aliphatic acid and the aforementioned metal.

[0085] In the present embodiment, the content of the metal soap in the lubricant coating layer 100 is 2.0 to 30.0%. If the content of the metal soap is 2.0% or more, the galling resistance and anti-rust properties of the oil-well metal pipe 1 can be stably increased. If the content of the metal soap is 30.0% or less, the adhesiveness and strength of the lubricant coating layer 100 can be stably increased. Therefore, the content of the metal soap in the lubricant coating layer 100 according to the present embodiment is within the range of 2.0 to 30.0%. A preferable lower limit of the content of the metal soap in the lubricant coating layer 100 is 5.0%, further preferably is 7.0%, and further preferably is 10.0%. A preferable upper limit of the content of the metal soap in the lubricant coating layer 100 is 28.0%, further preferably is 25.0%, and further preferably is 20.0%.

[0086] [Wax]The term "wax" is a generic name for an organic substance which is solid at normal temperature and becomes liquid when heated. In the present embodiment, the wax is one or more types selected from the group consisting of animal wax, vegetable wax, mineral wax, and synthetic wax. Examples of the animal wax include beeswax and spermaceti wax. Examples of the vegetable wax include Japan wax, carnauba wax, candelilla wax, and rice bran wax. Examples of the mineral wax include paraffin wax, microcrystalline wax, petrolatum, montan wax, ozokerite, and ceresin. Examples of the synthetic wax include oxidized wax, polyethylene wax, Fischer-Tropsch wax, amide wax, and hydrogenated castor oil (castor wax). As one example, the molecular weight of the wax is 1000 or less. Preferably, the wax is paraffin wax having a molecular weight of 150 to 500.

[0087] That is, the wax is, for example, one or more types selected from the group consisting of beeswax, spermaceti wax, Japan wax, carnauba wax, candelilla wax, rice bran wax, paraffin wax, microcrystalline wax, petrolatum, montan wax, ozokerite, ceresin, oxidized wax, polyethylene wax, Fischer-Tropsch wax, amide wax, and hydrogenated castor oil (castor wax). Preferably, the wax is one or more types of wax selected from the group consisting of paraffin wax, microcrystalline wax, and oxidized wax.

[0088] In the present embodiment, the content of the wax in the lubricant coating layer 100 is 2.0 to 30.0%. If the content of the wax is 2.0% or more, friction of the lubricant coating layer 100 can be reduced and the galling resistance of the oil-well metal pipe 1 can be stably increased. If the content of the wax is 30.0% or less, the adhesiveness and strength of the lubricant coating layer 100 can be stably increased. Therefore, the content of the wax in the lubricant coating layer 100 according to the present embodiment is within the range of 2.0 to 30.0%. A preferable lower limit of the content of the wax in the lubricant coating layer 100 is 5.0%, further preferably is 7.0%, and further preferably is 10.0%. A preferable upper limit of the content of the wax in the lubricant coating layer 100 is 28.0%, further preferably is 25.0%, and further preferably is 20.0%.

[0089] [Basic Metal Salt of Aromatic Organic Acid]The basic metal salt of an aromatic organic acid is a basic salt of an aromatic organic acid with a metal. The basic metal salt of an aromatic organic acid, for example, is a substance which is present in a grease form or semisolid form at normal temperature.

[0090] In the present embodiment, the aromatic organic acid is, for example, a sulfonate, a phenate, or a salicylate. The metal of the basic metal salt of an aromatic organic acid in the present embodiment is an alkali metal (lithium, sodium, potassium, rubidium, cesium, or francium) or an alkaline earth metal (beryllium, magnesium, calcium, barium, or radium). Preferably, the metal of the basic metal salt of an aromatic organic acid is one or more types selected from the group consisting of sodium, potassium, calcium, barium, and magnesium. Further preferably, the metal of the basic metal salt of an aromatic organic acid is one or more types selected from the group consisting of calcium, barium, and magnesium.

[0091] That is, the basic metal salt of an aromatic organic acid is, for example, one or more types selected from the group consisting of basic sodium sulfonate, basic potassium sulfonate, basic magnesium sulfonate, basic calcium sulfonate, basic barium sulfonate, basic sodium phenate, basic potassium phenate, basic magnesium phenate, basic calcium phenate, basic barium phenate, basic sodium salicylate, basic potassium salicylate, basic magnesium salicylate, basic calcium salicylate, and basic barium salicylate.

[0092] The higher a base number of the basic metal salt of an aromatic organic acid is, the larger an amount of fine particle metal salt functioning as a solid lubricant is. Therefore, the galling resistance of the oil-well metal pipe 1 is further enhanced by using a basic metal salt of an aromatic organic acid with a high base number. Further, if the base number is made a certain level or higher, an effect that neutralizes an acid component is obtained. Therefore, by using a basic metal salt of an aromatic organic acid with a high base number, the antirust capability of the oil-well metal pipe 1 also increases. Therefore, the basic metal salt of an aromatic organic acid preferably has a base number (JIS K2501) (when two or more types of basic metal salt of an aromatic organic acid are used, a weighted average of their base numbers with their amounts taken into account) of 50 to 500 mg KOH / g.

[0093] When the base number of the basic metal salt of an aromatic organic acid is 50 mg KOH / g or more, the aforementioned effects are sufficiently obtained. When the base number is 500 mg KOH / g or less, hydrophilicity can be decreased, and sufficient anti-rust properties are obtained. A more preferable lower limit of the base number of the basic metal salt of an aromatic organic acid is 100 mg KOH / g, further preferably is 200 mg KOH / g, and further preferably is 250 mg KOH / g. A more preferable upper limit of the base number of the basic metal salt of an aromatic organic acid is 450 mg KOH / g.

[0094] As described above, the basic metal salt of an aromatic organic acid is a substance which is present in a grease form or semisolid form, and can also function as a base of the lubricant coating layer 100. Therefore, the content of the basic metal salt of an aromatic organic acid in the lubricant coating layer 100 can be made as high as 80.0%. That is, in the lubricant coating layer 100 according to the present embodiment, the content of the basic metal salt of an aromatic organic acid is 20.0 to 80.0%.

[0095] In the present embodiment, a preferable lower limit of the content of the basic metal salt of an aromatic organic acid in the lubricant coating layer 100 is 30.0%, further preferably is 35.0%, and further preferably is 40.0%. A preferable upper limit of the content of the basic metal salt of an aromatic organic acid in the lubricant coating layer 100 is 75.0%, further preferably is 71.0%, and further preferably is 70.0%.

[0096] [Rosin-Based Material]The rosin-based material is a compound selected from rosin or a derivative of rosin. In the present description, the rosin means a natural resin that is secreted by a Pinus tree. The rosin is composed mainly of a resin acid (rosin acid) with the chemical formula C20H30O2 and colophony acid with the chemical formula CnHn+10O4. Examples of the derivative of rosin being the rosin-based material include rosin ester, hydrogenated rosin, polymerized rosin, and disproportionated rosin. That is, in the present embodiment, the rosin-based material is, for example, one or more types selected from the group consisting of rosin being a natural resin, rosin ester, hydrogenated rosin, polymerized rosin, and disproportionated rosin.

[0097] In the present embodiment, the content of the rosin-based material in the lubricant coating layer 100 is 2.0 to 30.0%. If the content of the rosin-based material is 2.0% or more, friction of the lubricant coating layer 100 can be reduced and the galling resistance of the oil-well metal pipe 1 can be stably increased. If the content of the rosin-based material is 30.0% or less, the adhesiveness and strength of the lubricant coating layer 100 can be stably increased. Therefore, the content of the rosin-based material in the lubricant coating layer 100 according to the present embodiment is within the range of 2.0 to 30.0%. A preferable lower limit of the content of the rosin-based material in the lubricant coating layer 100 is 5.0%, further preferably is 7.0%, and further preferably is 10.0%. A preferable upper limit of the content of the rosin-based material in the lubricant coating layer 100 is 28.0%, further preferably is 25.0%, and further preferably is 20.0%.

[0098] [Lubricant Powder]The term "lubricant powder" is a generic name for solid powders that have lubricity. In the present embodiment, a well-known solid powder that has lubricity can be used as the lubricant powder.

[0099] Specifically, as one example, lubricant powders are broadly categorized into the following four types:(1) Lubricant powders that exhibit lubricity by having a specific crystalline structure that is slippery, for example, a lamellar hexagonal crystal structure (e.g., graphite, earthy graphite, zinc oxide, boron nitride, and talc);(2) Lubricant powders that exhibit lubricity by having, in addition to the crystalline structure, a reactive element (e.g., molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, and organomolybdenum);(3) Lubricant powders that exhibit lubricity due to chemical reactivity (e.g., thiosulfate compounds); and(4) Lubricant powders that exhibit lubricity due to a plastic or viscoplastic behavior under frictional stresses (e.g., polytetrafluoroethylene (PTFE), polyamide, copper (Cu), and melamine cyanurate (MCA)).

[0100] Preferably, the lubricant powder contains one or more types selected from the group consisting of the above (1) to (4). That is, preferably the lubricant powder is one or more types selected from the group consisting of graphite, earthy graphite, zinc oxide, boron nitride, talc, molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, organomolybdenum, thiosulfate compounds, polytetrafluoroethylene (PTFE), polyamide, copper (Cu), and melamine cyanurate (MCA). More preferably the lubricant powder is one or more types selected from the group consisting of molybdenum disulfide, graphite, polytetrafluoroethylene (PTFE), and graphite fluoride. Further preferably the lubricant powder is one or more types selected from the group consisting of graphite and polytetrafluoroethylene (PTFE).

[0101] In the present embodiment, the content of the lubricant powder in the lubricant coating layer 100 is 0.1 to 10.0%. If the content of the lubricant powder is 0.1% or more, friction of the lubricant coating layer 100 can be reduced and the galling resistance of the oil-well metal pipe 1 can be stably increased. If the content of the lubricant powder is 10.0% or less, the adhesiveness and strength of the lubricant coating layer 100 can be stably increased. Therefore, in the lubricant coating layer 100 according to the present embodiment, the content of the lubricant powder is 0.1 to 10.0%. A preferable lower limit of the content of the lubricant powder in the lubricant coating layer 100 is 0.5%, further preferably is 1.0%, and further preferably is 2.0%. A preferable upper limit of the content of the lubricant powder in the lubricant coating layer 100 is 8.0%, further preferably is 7.0%, and further preferably is 6.0%.

[0102] [Other Components]The lubricant coating layer 100 may contain other components in addition to the metal particle, the metal soap, the wax, the basic metal salt of an aromatic organic acid, the rosin-based material, and the lubricant powder. Such other components are, for example, a well-known antirust addition agent, antiseptic, coloring pigment, and impurity.

[0103] If an antirust addition agent is contained in the lubricant coating layer 100, the anti-rust properties of the oil-well metal pipe 1 will be enhanced. If the anti-rust properties of the oil-well metal pipe 1 are enhanced, rusting of the oil-well metal pipe 1 caused by long-term storage can be suppressed. Examples of the antirust addition agent include aluminum tripolyphosphate, aluminum phosphite, and calcium ion-exchanged silica. A commercially available reactive water repellent agent can also be used as the antirust addition agent.

[0104] If an antiseptic is contained in the lubricant coating layer 100, the corrosion resistance of the oil-well metal pipe 1 will be enhanced. If the corrosion resistance of the oil-well metal pipe 1 is enhanced, corrosion of the oil-well metal pipe 1 caused by long-term storage can be suppressed. Further, as an impurity, in some cases a very small amount of a volatile organic solvent contained in a composition that is described later may be contained in the lubricant coating layer 100. In the lubricant coating layer 100 according to the present embodiment, the total content of other components is 0 to 10.0%.

[0105] [Composition for Forming Lubricant Coating Layer 100]In the present embodiment, a composition for forming the lubricant coating layer 100 contains: when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder in the lubricant coating layer 100 is taken as 100% by mass, the composition contains, the metal particle: 12.0 to 35.0%, the metal soap: 2.0 to 30.0%, the wax: 2.0 to 30.0%, the basic metal salt of an aromatic organic acid: 20.0 to 80.0%, the rosin-based material: 2.0 to 30.0%, and the lubricant powder: 0.1 to 10.0%. In short, the contents of the metallic particles, the metal soap, the wax, the basic metal salt of an aromatic organic acid, the rosin-based material, and the lubricant powder in the composition are the same as in the lubricant coating layer 100.

[0106] The composition according to the present embodiment may further contain a volatile organic solvent. In a case of performing the application at normal temperature, the composition is prepared by adding a volatile organic solvent to the mixture of the components of the lubricant coating layer 100. Unlike the other substances contained in the composition, the volatile organic solvent mostly evaporates during the process of forming the lubricant coating layer 100. However, in some cases the volatile organic solvent remains as an impurity in the lubricant coating layer 100 according to the present embodiment. Note that, in the present description the term "volatile" means that the substance exhibits a tendency to evaporate at a temperature in the range of room temperature to 150°C.

[0107] In the present embodiment, the type of the volatile organic solvent is not particularly limited. For example, the volatile organic solvent is a petroleum solvent. The petroleum solvent is, for example, one or more types selected from the group consisting of a solvent corresponding to industrial gasoline defined by JIS K2201:2006, mineral sprit, aromatic petroleum naphtha, xylene, and Cellosolve. A volatile organic solvent having a flash point of 30°C or more, an initial boiling point of 150°C or more, and an end point of 210°C or less is preferable. In this case, handling of the volatile organic solvent is relatively easy, and furthermore the volatile organic solvent evaporates rapidly, and thus the drying time is short.

[0108] In the present embodiment, the content of the volatile organic solvent may be appropriately adjusted so that the composition can be adjusted to an appropriate viscosity according to the method used to apply the composition. The content of the volatile organic solvent is, for example, 20 to 50 g when taking the total amount of non-volatile components as 100 g.

[0109] [Other Layers]In the oil-well metal pipe 1 according to the present embodiment, a layer or layers other than the lubricant coating layer 100 may be formed on the contact surface 400 and / or 500. The other layers are, for example, a metal plating layer and a chemical conversion treatment layer.

[0110] [Metal Plating Layer 110]The oil-well metal pipe 1 according to the present embodiment may, in addition, include a metal plating layer between the lubricant coating layer 100 and the pin contact surface 400 and / or the box contact surface 500. Specifically, referring to FIG. 10, a metal plating layer 110 may be formed as an underlayer of the lubricant coating layer 100 on the pin contact surface 400. Similarly, referring to FIG. 11, the metal plating layer 110 may be formed as an underlayer of the lubricant coating layer 100 on the box contact surface 500. Thus, in the case of forming both the lubricant coating layer 100 and the metal plating layer 110, the metal plating layer 110 is to be formed between the contact surface 400 and / or 500, and the lubricant coating layer 100.

[0111] In the present embodiment, the type of the metal plating layer 110 is not particularly limited. Further, the metal plating layer 110 may be constituted by a single plating layer, or may be constituted by a multi-layer plating layer (double plating layer or triple plating layer). In a case where the metal plating layer 110 is a single plating layer, the metal plating layer 110 is, for example, a single plating layer composed of Cu, Sn, or Ni metal, or a single plating layer composed of a Zn-Ni alloy, a Cu-Sn alloy, or a Cu-Sn-Zn alloy. In a case where the metal plating layer 110 is a multi-layer plating layer, the metal plating layer 110 is, for example, a double plating layer composed of a Cu layer and a Sn layer, a triple plating layer composed of a Ni layer, a Cu layer, and a Sn layer, or a multi-layer plating layer formed by combining the aforementioned single plating layers.

[0112] Preferably, the hardness of the metal plating layer is a micro-Vickers hardness of 200 or more. If the hardness of the metal plating layer is 200 or more, there is a further stable increase in the corrosion resistance of the oil-well metal pipe 1. In the present embodiment, the hardness of the metal plating layer is measured as follows. Five arbitrary regions are specified on the metal plating layer 110 formed on the contact surface 400 or 500 of the oil-well metal pipe 1. The Vickers hardness (HV) in each of the specified regions is measured in accordance with JIS Z 2244 (2009). The test conditions are, for example, a test temperature of normal temperature (25°C) and a test force of 2.94 N (300 gf). The arithmetic mean value of the obtained values is defined as the hardness of the metal plating layer 110.

[0113] In the present embodiment, the thickness of the metal plating layer 110 is not particularly limited. However, when forming a multi-layer plating layer as the metal plating layer 110, the thickness of the plating layer that is the undermost layer is preferably made less than 1 μm. Further, the thickness of the metal plating layer 110 (the total thickness in the case of a multi-layer plating layer) is preferably made 5 to 15 μm.

[0114] The thickness of the metal plating layer 110 according to the present embodiment is measured as follows. A probe of an eddy current phase-type film thickness measuring instrument conforming to ISO (International Organization for Standardization) 21968 (2005) is brought into contact with the contact surface 400 or 500 on which the metal plating layer 110 is formed. A phase difference between a high-frequency magnetic field on the input side of the probe and an eddy current on the metal plating layer that is excited by the high-frequency magnetic field is measured. The phase difference is converted into the thickness of the metal plating layer 110.

[0115] [Chemical Conversion Treatment Layer 120]The oil-well metal pipe 1 according to the present embodiment may also include a chemical conversion treatment layer that is provided between the pin contact surface 400 and / or the box contact surface 500, and the lubricant coating layer 100, and has a surface that contacts the lubricant coating layer 100. Specifically, referring to FIG. 12, a chemical conversion treatment layer 120 may be formed as an underlayer of the lubricant coating layer 100, on the metal plating layer 110 that is formed on the pin contact surface 400. Further, referring to FIG. 13, the chemical conversion treatment layer 120 may be formed as an underlayer of the lubricant coating layer 100, on the metal plating layer 110 that is formed on the box contact surface 500. Similarly, although not illustrated in the drawing, on the pin contact surface 400, the chemical conversion treatment layer 120 may be formed as an underlayer of the lubricant coating layer 100. Likewise, although not illustrated in the drawing, on the box contact surface 500, the chemical conversion treatment layer 120 may be formed as an underlayer of the lubricant coating layer 100.

[0116] In the present embodiment, the type of the chemical conversion treatment layer 120 is not particularly limited. The chemical conversion treatment layer 120 is, for example, a phosphate chemical conversion treatment layer, an oxalate chemical conversion treatment layer, and a borate chemical conversion treatment layer. Here, the chemical conversion treatment layer 120 is porous. Therefore, if the lubricant coating layer 100 is formed on the chemical conversion treatment layer 120, the adhesiveness of the lubricant coating layer 100 is further increased by the so-called "anchoring effect". Further, in the present embodiment, the thickness of the chemical conversion treatment layer 120 is not particularly limited. A preferable thickness of the chemical conversion treatment layer 120 according to the present embodiment is 5 to 40 μm.

[0117] [Blast-Treated Surface or Pickled Surface]In the oil-well metal pipe 1 according to the present embodiment, the contact surface 400 and / or 500 may be subjected to a blasting treatment or pickling. In other words, in the oil-well metal pipe 1, a surface which the lubricant coating layer 100 is formed as an uppermost layer may be a blast-treated surface or a pickled surface. That is, in the pipe main body 10 of the oil-well metal pipe 1, the contact surface 400 and / or 500 may be subjected to a blasting treatment or pickling, and the lubricant coating layer 100 may be formed thereon. Further, in a case where the oil-well metal pipe 1 includes the metal plating layer 110, the contact surface 400 and / or 500 of the oil-well metal pipe 1 may be subjected to a blasting treatment or pickling, the metal plating layer 110 may be provided thereon, and the lubricant coating layer 100 may be provided on the metal plating layer 110. In addition, in a case where the oil-well metal pipe 1 includes the metal plating layer 110, the oil-well metal pipe 1 may include the metal plating layer 110 that was subjected to a blasting treatment or pickling, and may include the lubricant coating layer 100 thereon.

[0118] The surface roughness of a blast-treated surface or a pickled surface increases. Specifically, preferably an arithmetic average roughness Ra with respect to the surface roughness of a surface which the lubricant coating layer 100 contacts is within the range of 1 to 8 μm (sampling length of 2.5 mm). When the arithmetic average roughness Ra of the surface which the lubricant coating layer 100 contacts is 1 μm or more, the adhesiveness of the lubricant coating layer 100 is further increased. When the arithmetic average roughness Ra of the surface which the lubricant coating layer 100 contacts is 8 μm or less, it is difficult for delamination of the lubricant coating layer 100 to occur.

[0119] In the present embodiment, the arithmetic average roughness Ra is measured based on JIS B 0601 (2001). For example, the arithmetic average roughness Ra can be measured using a scanning probe microscope SPI 3800N, manufactured by SII NanoTechnology Inc. As measurement conditions, for example, a 2 μm × 2 μm region is set on a sample as a unit of the number of acquired data points, and the number of acquired data points is 1024 × 1024. The sampling length is set to 2.5 mm. The greater the arithmetic average roughness Ra is, the more the contact area with the lubricant coating layer 100 increases. Therefore, the adhesiveness with respect to the lubricant coating layer 100 increases by the anchoring effect. When the adhesiveness of the lubricant coating layer 100 increases, the galling resistance of the oil-well metal pipe 1 is further enhanced.

[0120] [Production Method]A method for producing the oil-well metal pipe 1 according to the present embodiment will be described below.

[0121] The method for producing the oil-well metal pipe 1 according to the present embodiment includes a preparation step and a lubricant coating layer formation step.

[0122] [Preparation Step]In the preparation step, the oil-well metal pipe 1 provided with the pipe main body 10 that includes the pin 40 having the pin contact surface 400 including the external thread part 41, and includes the box 50 having the box contact surface 500 including the internal thread part 51 is prepared. As described above, the oil-well metal pipe 1 according to the present embodiment has a well-known configuration. That is, in the preparation step, it is only required to prepare the oil-well metal pipe 1 having a well-known configuration.

[0123] [Lubricant Coating Layer 100 Formation Step]In the lubricant coating layer formation step, firstly, a composition containing the aforementioned components is prepared. The composition for forming the lubricant coating layer 100 contains a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder. The composition is liquified by solvent addition and / or heating, and then applied onto the pin contact surface 400 and / or the box contact surface 500. The applied composition is dried as necessary, to thereby form the lubricant coating layer 100.

[0124] Specifically, first, a composition containing the aforementioned components is prepared. The composition of a solventless type can be produced, for example, by heating a mixture of the constituent components of the aforementioned composition to a molten state, and kneading them. The composition may be made of a powder mixture prepared by mixing all the components in powder form. The composition of a solvent type can be produced, for example, by dissolving or dispersing the metal particle, the metal soap, the wax, the basic metal salt of an aromatic organic acid, the rosin-based material, and the lubricant powder in a volatile organic solvent and mixing them.

[0125] The prepared composition is applied on the contact surface 400 and / or 500. Specifically, for the composition of a solventless type, a hot melt process may be employed to apply the composition. In the hot melt process, the composition is heated to melt to a fluid state with low viscosity. In addition, the composition in a fluid state is sprayed from a spray gun having functions for temperature holding. In this case, the composition is heated and melted within a tank including a suitable stirring mechanism, is supplied via a metering pump to the spray head (held at a predetermined temperature) of the spray gun by a compressor, and is sprayed. The heating temperature is, for example, in a range of 90 to 130°C. The holding temperatures for the tank interior and the spray head are adjusted in accordance with the melting point of the composition. Another application method, such as brushing or dipping, may be employed in place of spray coating. The temperature to which the composition is heated is preferably higher than the melting point of the composition by 10 to 50°C. Prior to application of the composition, a surface to which the composition is to be applied (contact surface 400 and / or 500, surface of metal plating layer 110, or surface of chemical conversion treatment layer 120) is preferably heated to a temperature higher than the melting point of the base.

[0126] In the case of the composition of a solvent type, the composition in solution form to which a solvent was added is applied on the contact surface 400 and / or 500 by spray coating or by another method. In this case, the viscosity of the composition is to be adjusted so that it can be applied by spraying in an environment at normal temperature and normal pressure.

[0127] In the case of the composition of a solventless type, the lubricant coating layer 100 is formed by cooling the composition applied to the pin contact surface 400 and / or the box contact surface 500 to allow the composition in a molten state to dry. The cooling of the composition can be carried out by a well-known method. Examples of the cooling method include allowing to cool in the atmosphere and air cooling. In the case of the composition of a solvent type, the lubricant coating layer 100 is formed by drying the composition that was applied on the contact surface 400 and / or 500. The drying of the composition can be carried out by a well-known method. Examples of the drying method include natural drying, low-temperature air drying, and vacuum drying.

[0128] Note that, the aforementioned cooling may be carried out by rapid cooling using a nitrogen gas cooling system, a carbon dioxide cooling system, or the like. In the case where rapid cooling is performed, the cooling is carried out in an indirect manner at the opposite surface to the contact surface. Specifically, in the case of forming the lubricant coating layer 100 as an uppermost layer on the pin contact surface 400, the cooling is carried out from the inner surface side of the pipe main body 10. Similarly, in the case of forming the lubricant coating layer 100 as an uppermost layer on the box contact surface 500, the cooling is carried out in an indirect manner from the outer surface side of the pipe main body 10.

[0129] Note that, the lubricant coating layer 100 may be formed of a single layer or may be formed of multiple layers. The term "multiple layers" means two or more layers of the lubricant coating layer 100 deposited in sequence in the radial direction of the pipe main body 10 from the side of the contact surface 400 and / or 500. The two or more layers of the lubricant coating layer 100 can be formed by repeating the application and drying of the composition. The lubricant coating layer 100 may be formed on the contact surface 400 and / or 500 directly, or may be formed thereon after surface preparation treatment described below is performed.

[0130] Through the above steps, the oil-well metal pipe 1 according to the present embodiment is produced.

[0131] [Other Steps]The method for producing the oil-well metal pipe 1 according to the present embodiment may also include other steps. The other steps are, for example, a metal plating step, a chemical conversion treatment step, a blasting treatment step, and a pickling treatment step. Each step is described below.

[0132] [Metal Plating Step]The method for producing the oil-well metal pipe 1 according to the present embodiment may further include a metal plating step before the lubricant coating layer formation step. The metal plating layer 110 can be formed, for example, by an electroplating treatment or an impact plating treatment.

[0133] [Electroplating Treatment]In the present embodiment, the electroplating treatment is a treatment that forms the metal plating layer 110 by electroplating. As described above, the metal plating layer 110 is, for example, a single plating layer composed of Cu, Sn, or Ni metal, or a single plating layer composed of a Zn-Ni alloy, a Cu-Sn alloy, or a Cu-Sn-Zn alloy, or a double plating layer composed of a Cu layer and a Sn layer, a triple plating layer composed of a Ni layer, a Cu layer, and a Sn layer, or a multi-layer plating layer formed by combining the aforementioned single plating layers.

[0134] The electroplating treatment can be carried out by a well-known method. For example, a plating bath containing ions of the metallic elements to be contained in the alloy plating is prepared. Next, the contact surface 400 and / or 500 is immersed in the plating bath. Further, by current conduction through the contact surface 400 and / or 500, the metal plating layer 110 is formed on the contact surface 400 and / or 500. Conditions such as the temperature of the plating bath and the duration of the plating treatment can be set as appropriate.

[0135] More specifically, for example, in the case of forming a Cu-Sn-Zn alloy plating layer, the plating bath contains copper ions, tin ions, and zinc ions. In this case, the composition of the plating bath is preferably Cu: 1 to 50 g / L, Sn: 1 to 50 g / L, and Zn: 1 to 50 g / L. The electroplating conditions are, for example, a plating bath pH of 1 to 10, a plating bath temperature of 60°C, a current density of 1 to 100 A / dm2, and a treatment time of 0.1 to 30 minutes.

[0136] Similarly, for example, in the case of forming a Zn-Ni alloy plating layer, the plating bath contains zinc ions and nickel ions. In this case, the composition of the plating bath is preferably Zn: 1 to 100 g / L and Ni: 1 to 50 g / L. The electroplating conditions are, for example, a plating bath pH of 1 to 10, a plating bath temperature of 60°C, a current density of 1 to 100 A / dm2, and a treatment time of 0.1 to 30 minutes.

[0137] [Impact Plating Treatment]The impact plating treatment is a treatment that can be performed by mechanical plating in which particles and an object to be plated are caused to collide with each other in a rotating barrel, or by projection plating in which particles are caused to collide with an object to be plated using a blasting device.

[0138] [Chemical Conversion Treatment Step]The method for producing the oil-well metal pipe 1 according to the present embodiment may also include a chemical conversion treatment step before the lubricant coating layer formation step. In the chemical conversion treatment step, a chemical conversion treatment is performed to form, as an underlayer of the lubricant coating layer 100, the chemical conversion treatment layer 120 having a surface that contacts the lubricant coating layer 100.

[0139] In the present embodiment, the chemical conversion treatment can be carried out by a well-known method. A common chemical conversion treatment solution can be used as the treatment solution. For example, a solution for zinc phosphate chemical conversion treatment solution containing 1 to 150 g / L of phosphate ions, 3 to 70 g / L of zinc ions, 1 to 100 g / L of nitrate ions, and 0 to 30 g / L of nickel ions can be used. Alternatively, a manganese phosphate chemical conversion treatment solution can also be used. It is also possible to use a chemical conversion treatment solution according to the chemical conversion treatment layer 120 desired to form. The temperature of the treatment solution is, for example, in the range of normal temperature to 100°C. The treatment time of the chemical conversion treatment can be appropriately set depending on the desired thickness, and, for example is 15 minutes. In the case of forming a phosphate chemical conversion treatment layer, to facilitate the formation of the chemical conversion treatment layer, surface modification may be performed prior to the phosphate chemical conversion treatment. The term "surface modification" means a treatment in which immersion in a surface modification aqueous solution containing colloidal titanium is performed. After the phosphate chemical conversion treatment, it is preferable to perform rinsing with water or warm water, followed by drying.

[0140] [Blasting Treatment Step]In the present embodiment, the blasting treatment is, for example, a treatment in which particles are caused to collide with an object using a blasting device. The blasting treatment is, for example, a sand blasting treatment. The sand blasting treatment is a treatment in which a blast material (abrasive) and compressed air are mixed together and propelled at an object. Examples of the blast material include spherical shot material and angular grit material. By performing the sand blasting treatment, the surface roughness of the contact surface 400 and / or 500 or the surface of the metal plating layer 110 can be increased.

[0141] In the present embodiment, the sand blasting treatment can be carried out by a well-known method. In the sand blasting treatment, for example, air is compressed by a compressor, and a blast material is mixed with the compressed air. The blast material may be made of, for example, stainless steel, aluminum, ceramic, alumina, or the like. Further, the sand blasting treatment conditions such as the propelling speed can be set as appropriate.

[0142] [Pickling Treatment Step]In the present embodiment, the term "pickling treatment step" means a treatment in which a surface is immersed in a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid, or hydrofluoric acid to roughen the surface. That is, by immersing the contact surface 400 and / or 500 or the surface of the metal plating layer 110 in a strong acid solution, the surface roughness of these surfaces can be increased. EXAMPLE

[0143] Hereunder, the oil-well metal pipe and the composition according to the present embodiment are described more specifically using Example. However, the oil-well metal pipe and the composition according to the present embodiment are not limited to the following Example. Hereunder, in Example, the pin contact surface is referred to as a "pin surface", and the box contact surface is referred to as a "box surface". Further, unless otherwise specified, percent (%) in Example means mass%.

[0144] In the present Examples, VAM21 (registered trademark) manufactured by NIPPON STEEL CORPORATION was used as a pipe main body. VAM21 (registered trademark) is a pipe main body having an outer diameter of 177.80 mm (7 inches) and a wall thickness of 11.506 mm (0.453 inches). The steel type was a carbon steel. The carbon steel had a composition consisting of: C: 0.250%, Si: 0.29%, Mn: 0.85%, P: 0.008%, S: 0.0040%, Cu: 0.02%, Cr: 1.14%, Ni: 0.03%, Mo: 0.33%, and the balance being Fe and impurities. Further, the pipe main body used in the present Examples has a Vickers hardness of 254 Hv.

[0145] As pipe main bodies, sample materials 1 for a repeated fastening test and sample materials 2 for measuring the yield torque Ty were prepared. On the pin surfaces of the sample materials 1 of Test Nos. 1 to 9, zinc phosphate chemical conversion treatment layers were formed after the pin surfaces were subjected to finish grinding. The pin surface of the sample material 1 of Test No. 10 was subjected to finish grinding. On the box surfaces of the sample materials 1 of Test Nos. 1 to 10, manganese phosphate chemical conversion treatment layers were formed after the box surfaces were subjected to finish grinding. The pin surfaces of the sample materials 2 of Test Nos. 1 to 10 were subjected to finish grinding. On the box surfaces of the sample materials 2 of Test Nos. 1 to 10, manganese phosphate chemical conversion treatment layers were formed after the box surfaces were subjected to finish grinding.

[0146] Note that, in the present Example, the zinc phosphate chemical conversion treatment layers were formed by the following method. Specifically, by immersing the sample materials in a chemical conversion treatment solution for zinc phosphate at 75 to 85°C for 10 minutes, zinc phosphate chemical conversion treatment layers having a thickness of 12 μm (a surface roughness of 8 μm) were formed. In the present Example, the manganese phosphate chemical conversion treatment layers were formed by the following method. Specifically, by immersing the sample materials in a manganese phosphate chemical conversion treatment solution at 80 to 95°C for 10 minutes, manganese phosphate chemical conversion treatment layers having a thickness of 15 μm (a surface roughness of 12 μm) were formed.

[0147] Lubricant coating layers having the compositions described in Table 2 were formed on the pin surface and the box surface of the respective test numbers prepared as described above. Note that, the numbers in the column "Composition of lubricant coating layer" in Table 2 except for the column "Type" and the column "Size" of the column "Particle" show the content of each component in mass% when taking the total of the contents of the particles, the metal soap, the wax, the basic metal salt of an aromatic organic acid, the rosin-based material, and the lubricant powder as 100% by mass. Further, the respective compositions for forming the lubricant coating layers of the test numbers were the same as the respective compositions of the lubricant coating layers described in Table 2.

[0148] [Table 2]TABLE 2Test No.Composition of lubricant coating layerParticleMetal soap (mass%)Wax (mass%)Basic metal salt of aromatic organic acid (mass%)Rosin-based material (mass%)Lubricant powder (mass%)TypeSize (μm)Content (mass%)1---20.1 10.5 56.6 10.3 2.5 2S316L2310.018.19.550.99.32.33S316L2318.016.58.646.48.42.14S316L2327.014.77.741.37.51.85S316L21018.016.58.646.48.42.16SiO21010.018.19.550.99.32.37SiO21020.016.18.445.38.22.08SiO21030.014.17.439.67.21.89SPM302310.018.19.550.99.32.310SPM302318.016.58.646.48.42.111Compound grease defined in API standard BUL 5A2 

[0149] In the present Example, "S316L" described in the column "Type" of the column "Particle" means a metal particle of the steel grade SUS316L manufactured by Sanyo Special Steel Co., Ltd. with the product name: PSS316L and the chemical composition: Fe-13Ni-17Cr-2Mo. S316L had a Vickers hardness of 205 Hv. Further, "SiO2" described in the column "Type" of the column "Particle" means quartz particles manufactured by AGC Inc. with the product name: SUNSPHERE and the chemical composition: SiO2. SiO2 had a Vickers hardness of 600 Hv. In addition, "SPM30" described in the column "Type" of the column "Particle" means a metal particle manufactured by Sanyo Special Steel Co., Ltd. with the product name: SPM30 and the chemical composition: Fe-1.3C-4Cr-5Mo-3V-6W-8Co. SPM30 had a Vickers hardness of 755 Hv.

[0150] Note that, in the present Example, zinc stearate was used as the metal soap. Paraffin wax was used as the wax. Basic Ca sulfonate was used as the basic metal salt of an aromatic organic acid. Rosin was used as the rosin-based material. Graphite was used as the lubricant powder.

[0151] The pin surface and the box surface of each test number were prepared by the above method. A fastening test was performed using the obtained pin surface and box surface.

[0152] [Fastening Test]As the fastening test, a repeated fastening test in which the sample materials 1 were used and a fastening test in which the sample materials 2 were used and that was performed until plastic deformation occurred were performed. Specifically, in the repeated fastening test in which the sample materials 1 were used, fastening and loosening were repeated at room temperature (20°C), while the torque was measured. The fastening torque during the fastening was set to 24350 N⋅m. Each time one cycle of fastening and loosening was completed, the pin surface and the box surface were visually observed. The occurrence of galling on thread parts and seal surfaces was examined by visual inspection. With respect to the seal surfaces, the test was ended upon the occurrence of galling. When the galling on a thread part was minor and was repairable by repairing by filing or the like, the galling flaws were repaired and the test was continued. When unrepairable galling occurred on a thread part, the test was ended at that time point.

[0153] In the present Example, the maximum number of times fastening was performed without either unrepairable galling occurring at a thread part or galling occurring at a seal surface was taken as a possible number of fastenings (times). Note that, in Test No. 11, the compound grease was re-applied each time that fastening and loosening were performed once, and the sample material was subjected to the test. Further, at each time of the fastening, a torque chart as illustrated in FIG. 1 was prepared, and the shouldering torque Ts of each test number was determined. The maximum value of the resultant shouldering torques Ts obtained by the respective fastenings was taken as a shouldering torque Ts(ft-lbs).

[0154] Further, in the fastening test in which the sample materials 2 were used, fastening was performed at room temperature (20°C) until the sample materials 2 underwent plastic deformation, while the torque was measured. A torque chart as illustrated in FIG. 1 was prepared, and the yield torque Ty of each test number was determined. Specifically, the torque when changes in torque with the progress of the rotation lost linearity and started to leave a linear region after the shouldering torque Ts was reached was taken as a yield torque Ty(ft-lbs).

[0155] The obtained shouldering torque Ts(ft-lbs) of each test number is shown in the column "Ts(ft-lbs)" in Table 3. The obtained yield torque Ty(ft-lbs) of each test number is shown in the column "Ty(ft-lbs)" in Table 3. From the obtained yield torque Ty and shouldering torque Ts of each test number, the torque-on-shoulder resistance ΔT' (= Ty - Ts) was determined. The obtained torque-on-shoulder resistance ΔT'(ft-lbs) of each test number is shown in the column "ΔT'(ft-lbs)" in Table 3. The obtained possible number of fastenings (times) of each test number is shown in Table 3.

[0156] [Table 3]TABLE 3Test No.Fastening testTs (ft-lbs)Ty (ft-lbs)ΔT' (ft-lbs)Possible number of fastenings (times)1365750761419≥102455656651109≥103333063643034≥104389463572463≥105338261742792≥106412257281606474019574217234836136483287019435053691019910449259921500311422760541827≥10 

[0157] Referring to Table 2 and Table 3, the lubricant coating layers of the sample materials of Test Nos. 3 to 5 contained 12.0 to 35.0% of a metal particle having a Vickers hardness not more than that of the pipe main bodies. As a result, the shouldering torques Ts of these sample materials were as low as that of Test No. 1, in which the metal particle was not contained. Further, the torque-on-shoulder resistances ΔT' of these sample materials were more than 1800 ft-lbs, and thus these sample materials had increased high torque performance. Further, in these sample materials, galling did not occur even when fastening and loosening were repeated 10 times, and thus these sample materials had excellent galling resistance.

[0158] On the other hand, in Test No. 1, the lubricant coating layer of the sample material contained no metal particle. As a result, the torque-on-shoulder resistance ΔT' of this sample material was less than 1800 ft-lbs, and thus the sample material did not have increased high torque performance.

[0159] In Test No. 2, the content of the metal particle in the lubricant coating layer of the sample material was too low. As a result, the shouldering torque Ts of this sample material was significantly higher than that of Test No. 1, in which the metal particle was not contained. Further, the torque-on-shoulder resistance ΔT' of this sample material was less than 1800 ft-lbs, and thus the sample material did not have increased high torque performance.

[0160] In Test Nos. 6 and 7, the lubricant coating layers of the sample materials contained particles having a Vickers hardness higher than that of the pipe main body. As a result, the shouldering torques Ts of these sample materials were significantly higher than that of Test No. 1, in which the metal particle was not contained. Further, the torque-on-shoulder resistances ΔT' of these sample materials were less than 1800 ft-lbs, and thus the sample materials did not have increased high torque performance. Further, in these sample materials, galling occurred before fastening and loosening were repeated 10 times, and thus these sample materials did not exhibit excellent galling resistance.

[0161] In Test No. 8, the lubricant coating layer of the sample material contained particles having a Vickers hardness higher than that of the pipe main body. As a result, in this sample material, galling occurred before fastening and loosening were repeated 10 times, and thus this sample material did not exhibit excellent galling resistance.

[0162] In Test Nos. 9 and 10, the lubricant coating layers of the sample materials contained particles having a Vickers hardness higher than that of the pipe main body. As a result, the shouldering torques Ts of these sample materials were significantly higher than that of Test No. 1, in which the metal particle was not contained. Further, the torque-on-shoulder resistances ΔT' of these sample materials were less than 1800 ft-lbs, and thus the sample materials did not have increased high torque performance. Further, in these sample materials, galling occurred before fastening and loosening were repeated 10 times, and thus these sample materials did not exhibit excellent galling resistance.

[0163] In the sample material of Test No. 11, a lubricant coating layer was not formed, and compound grease was used. As a result, the shouldering torque Ts of this sample material was significantly higher than that of Test No. 1, in which the metal particle was not contained.

[0164] An embodiment of the present disclosure has been described above. However, the foregoing embodiment is merely an example for implementing the present disclosure. Accordingly, the present disclosure is not limited to the above embodiment, and the above embodiment can be appropriately modified and implemented within a range which does not deviate from the gist of the present disclosure. REFERENCE SIGNS LIST

[0165] 1: Oil-well metal pipe10: Pipe main body10A: First end portion10B: Second end portion11: Pin pipe body12: Coupling40: Pin41: External thread part42: Pin seal surface43: Pin shoulder surface50: Box51: Internal thread part52: Box seal surface53: Box shoulder surface100: Lubricant coating layer110: Metal plating layer120: Chemical conversion treatment layer400: Pin contact surface500: Box contact surface 

Claims

1. An oil-well metal pipe comprising: a pipe main body including a first end portion and a second end portion, wherein the pipe main body includes: a pin that is formed at the first end portion; and a box that is formed at the second end portion, the pin includes: a pin contact surface including an external thread part, the box includes: a box contact surface including an internal thread part, the oil-well metal pipe further comprises: a lubricant coating layer formed as an uppermost layer on the pin contact surface and / or the box contact surface, the lubricant coating layer contains, in mass%: when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder in the lubricant coating layer is taken as 100% by mass, the metal particle: 12.0 to 35.0%; the metal soap: 2.0 to 30.0%; the wax: 2.0 to 30.0%; the basic metal salt of an aromatic organic acid: 20.0 to 80.0%; the rosin-based material: 2.0 to 30.0%; and the lubricant powder: 0.1 to 10.0%, and a Vickers hardness of the metal particle is not more than a Vickers hardness of the pipe main body.

2. The oil-well metal pipe according to claim 1, wherein a chemical composition of the metal particle contains, in mass%, Fe: 50% or more.

3. The oil-well metal pipe according to claim 1, wherein a particle size of the metal particle is within a range of 15 to 250 μm.

4. The oil-well metal pipe according to any one of claim 1, wherein a thickness of the lubricant coating layer is within a range of 10 to 500 μm.

5. The oil-well metal pipe according to any one of claim 1, wherein the oil-well metal pipe further comprises: one or more types selected from the group consisting of a metal plating layer and a chemical conversion treatment layer formed as an underlayer of the lubricant coating layer.

6. The oil-well metal pipe according to any one of claim 1, wherein the pin contact surface further includes: a pin seal surface and a pin shoulder surface, and the box contact surface further includes: a box seal surface and a box shoulder surface.

7. A composition for forming the lubricant coating layer that is included in the oil-well metal pipe according to any one of claim 1, the composition containing, in mass%: when a total of contents of a metal particle, a metal soap, a wax, a basic metal salt of an aromatic organic acid, a rosin-based material, and a lubricant powder is taken as 100% by mass, the metal particle: 12.0 to 35.0%; the metal soap: 2.0 to 30.0%; the wax: 2.0 to 30.0%; the basic metal salt of an aromatic organic acid: 20.0 to 80.0%; the rosin-based material: 2.0 to 30.0%; and the lubricant powder: 0.1 to 10.0%, wherein a Vickers hardness of the metal particle is not more than a Vickers hardness of the pipe main body.

8. The composition according to claim 7, the composition further containing a volatile organic solvent. 

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