Metal pipe for oil wells

Abstract

The present invention provides a metal pipe for oil wells that has excellent seizure resistance. A metal pipe (1) for oil wells according to the present disclosure comprises a pipe body (10). The pipe body (10) includes: a pin (40) that is formed in a first end part (10A) and that includes a pin contact surface (400) including a male screw part (41); and a box (50) that is formed in a second end part (10B) and that includes a box contact surface (500) including a female screw part (51). The metal pipe (1) for oil wells according to the present disclosure further comprises with a Zn-Ni alloy plating layer (100) formed on at least one of a pin contact surface (400) and a box contact surface (500). The Zn-Ni alloy plating layer (100) comprises 9.0‒20.0 mass% of Ni, the rest being Zn and impurities. The precipitation phase includes a gamma phase, and the crystallite diameter D (nm) and the Ni content [Ni] (mass%) of the gamma phase satisfy formula (1).　D ≤ 12.3 × [Ni] − 81.6 (1)

Description

Metal pipe for oil well

[0001] The present disclosure relates to a metal oil well pipe, and more particularly to a metal oil well pipe having a threaded joint formed therein.

[0002] Metallic oil well pipes are used for the extraction of oil fields and natural gas fields (hereinafter, oil fields and natural gas fields are collectively referred to as "oil wells"). Specifically, at oil well drilling sites, multiple metallic oil well pipes are connected to form a connected oil well pipe assembly, typically casing or tubing, depending on the depth of the oil well. A connected oil well pipe assembly is formed by screwing together threaded joints formed at the ends of metallic oil well pipes. Inspection of the connected oil well pipe assembly may be performed. When inspection is performed, the connected oil well pipe assembly is pulled up and the threaded joints are unscrewed. Then, the unscrewed and removed oil well pipe assembly is inspected. After inspection, the threaded joints of the metallic oil well pipe assembly are screwed again, and the metallic oil well pipe assembly is reused as part of the connected oil well pipe assembly.

[0003] The metal oil well pipe comprises a pipe body having a first end and a second end. The pipe body includes a pin formed at the first end and a box formed at the second end. The pin has a pin contact surface including a male thread portion on the outer peripheral surface of the first end of the pipe body. The box has a box contact surface including a female thread portion on the inner peripheral surface of the end (second end) of the pipe body opposite the pin. When a threaded joint formed at the end of the metal oil well pipe is screwed up, the pin contact surface comes into contact with the box contact surface.

[0004] The pin contact surface and the box contact surface are repeatedly subjected to strong friction when the metal oil well pipe is screwed in and unscrewed. If these parts do not have sufficient durability against friction, galling (irreparable seizure) will occur when the pipe is repeatedly screwed in and unscrewed. Therefore, metal oil well pipe is required to have sufficient durability against friction, i.e., excellent seizure resistance.

[0005] Conventionally, compound grease containing heavy metals, called dope, has been used to improve seizure resistance. The seizure resistance of oil well metal pipes can be improved by applying compound grease to the pin contact surface and / or the box contact surface. However, heavy metals such as Pb, Zn, and Cu contained in the compound grease may have an adverse effect on the environment. For this reason, there is a need to develop oil well metal pipes that have excellent seizure resistance without using compound grease.

[0006] In the oil well pipe disclosed in Patent Document 1 (WO 2016 / 170031), a Zn—Ni alloy plating layer is formed on the pin contact surface or box contact surface instead of compound grease. Zn in the Zn—Ni alloy plating layer formed on the contact surface of the oil well pipe enhances the corrosion resistance of the oil well pipe through sacrificial corrosion protection. Furthermore, Patent Document 1 discloses that the Zn—Ni alloy plating layer also has excellent wear resistance.

[0007] International Publication No. 2016 / 170031

[0008] In recent years, as the conditions in oil wells have become more severe, there has been a demand for metal oil well pipes having even better seizure resistance.

[0009] An object of the present disclosure is to provide a metal oil well pipe having excellent galling resistance.

[0010] The metal oil well pipe according to the present disclosure comprises a pipe body having a first end and a second end, the pipe body including a pin formed at the first end and a box formed at the second end, the pin including a pin contact surface including a male thread portion, and the box including a box contact surface including a female thread portion, the metal oil well pipe further comprising a Zn—Ni alloy plating layer formed on at least one of the pin contact surface and the box contact surface, the Zn—Ni alloy plating layer consisting of 9.0 to 20.0 mass % Ni, with the balance being Zn and impurities, the precipitate phase of the Zn—Ni alloy plating layer comprising a γ phase, and a crystallite diameter D of the γ phase and a Ni content [Ni] of the Zn—Ni alloy plating layer satisfying formula (1). D≦12.3×[Ni]−81.6 (1) Here, the crystallite diameter of the γ phase is substituted for D in formula (1) in the unit of nm, and the Ni content in the Zn—Ni alloy plating layer is substituted for [Ni] in formula (1) in the unit of mass %.

[0011] The metal oil well pipe according to the present disclosure has excellent galling resistance.

[0012] FIG. 1 is a diagram showing the relationship between the Ni content [Ni] (mass %) of a Zn—Ni alloy plating layer and the Vickers hardness HV (Hv) of the Zn—Ni alloy plating layer. FIG. 2 is a diagram showing the relationship between the Ni content [Ni] (mass %) of a Zn—Ni alloy plating layer, the crystallite diameter D (nm) of the γ phase, and the Vickers hardness HV (Hv) of the Zn—Ni alloy plating layer. FIG. 3 is a structural diagram showing an example of a metallic pipe for oil well use according to the present embodiment. FIG. 4 is a partial cross-sectional view showing a cross section (longitudinal cross section) along the pipe axis direction of a coupling of the metallic pipe for oil well use shown in FIG. 3. FIG. 5 is a cross-sectional view parallel to the pipe axis direction of the metallic pipe for oil well use, of a portion near a pin of the metallic pipe for oil well use shown in FIG. 4. FIG. 6 is a cross-sectional view parallel to the pipe axis direction of the metallic pipe for oil well use, of a portion near a box of the metallic pipe for oil well use shown in FIG. 4. FIG. 7 is a partial cross-sectional view showing a cross section (longitudinal cross section) along the pipe axis direction of a coupling of the metallic pipe for oil well use according to the present embodiment, which is different from FIG. 4. Fig. 8 is a diagram showing the configuration of an integral-type metal oil well pipe according to this embodiment. Fig. 9 is an enlarged view of the pin contact surface shown in Fig. 5. Fig. 10 is an enlarged view of the box contact surface shown in Fig. 6. Fig. 11 is an enlarged view of a pin contact surface having a different configuration from that shown in Fig. 9. Fig. 12 is an enlarged view of a box contact surface having a different configuration from that shown in Fig. 10. Fig. 13 is an enlarged view of a pin contact surface having a different configuration from that shown in Figs. 9 and 11. Fig. 14 is an enlarged view of a box contact surface having a different configuration from that shown in Figs. 10 and 12.

[0013] The present embodiment will be described in detail below with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and description thereof will not be repeated.

[0014] The present inventors have conducted detailed studies on means for improving the galling resistance of metal pipes for oil wells, and as a result, have made the following findings.

[0015] When connecting oil well pipes, the metals at the contact surfaces slide against each other under high pressure while in contact with each other. Heat may be generated due to the deformation resistance of the metals. On the other hand, if the temperature locally rises above the melting point of the metals, the molten metals will fuse together, causing seizure. Therefore, forming a plating layer with low deformation resistance, i.e., high hardness, is considered to be an effective way to improve the seizure resistance of oil well pipes. The Zn—Ni alloy that constitutes the Zn—Ni alloy plating layer has high hardness and a high melting point. Therefore, a technique for improving the seizure resistance of oil well pipes by forming a Zn—Ni alloy plating layer on at least one of the pin contact surface and the box contact surface of the oil well pipe has been proposed.

[0016] Incidentally, it is known that the precipitate phase of a Zn-Ni alloy changes depending on the Ni content. Specifically, the Zn-Ni alloy can have the eta phase (η phase), gamma phase (γ phase), and alpha phase (α phase) as precipitate phases. More specifically, the η phase of a Zn-Ni alloy is a Zn phase in which Ni is dissolved. The γ phase of a Zn-Ni alloy is an intermetallic compound (Ni ５ Zn ２１ ) phase. The α phase of a Zn—Ni alloy is a Ni phase in which Zn forms a solid solution. Among the η phase, γ phase, and α phase, which are precipitated phases of a Zn—Ni alloy, the γ phase has the highest hardness. Therefore, it is preferable that the precipitated phase of the Zn—Ni alloy plating layer contains the γ phase.

[0017] Here, in a Zn—Ni alloy consisting of Ni and the balance being Zn and impurities, if the Ni content is less than 9.0%, the precipitation phase may contain an excess of η phase, and the precipitation phase may not be mainly γ phase. Furthermore, in a Zn—Ni alloy, if the Ni content exceeds 20.0%, the precipitation phase may contain an excess of α phase, and the precipitation phase may not be mainly γ phase. On the other hand, if the Ni content of the Zn—Ni alloy is 9.0 to 20.0%, the precipitation phase will stably contain γ phase, and the precipitation phase will be mainly γ phase. Note that, in this specification, "the precipitation phase will be mainly γ phase" means that 50% or more by volume of the precipitation phase of the Zn—Ni alloy plating layer is γ phase. Therefore, the Zn—Ni alloy plating layer according to this embodiment has a chemical composition consisting of 9.0 to 20.0 mass% Ni, and the balance being Zn and impurities. As a result, the hardness of the Zn—Ni alloy plating layer may be increased, and the seizure resistance may be improved.

[0018] On the other hand, even when a Zn—Ni alloy plating layer having a chemical composition consisting of 9.0 to 20.0 mass % Ni and the balance Zn and impurities and containing a γ phase as a precipitate phase is formed, the galling resistance of the metal oil well pipe may not be sufficiently improved. Therefore, the present inventors have focused on the crystal structure of the Zn—Ni alloy plating layer and investigated ways to increase the hardness of the Zn—Ni alloy plating layer and thereby improve the galling resistance of the metal oil well pipe.

[0019] FIG. 1 is a diagram showing the relationship between the Ni content (mass%) of a Zn—Ni alloy plating layer and the Vickers hardness HV (Hv) of the Zn—Ni alloy plating layer. FIG. 1 was created using the Ni content (mass%) and the Vickers hardness HV (Hv) determined by the method described below for the examples described below. Referring to FIG. 1 , it can be seen that the Vickers hardness increases as the Ni content increases. Specifically, the open circles (◯) in FIG. 1 indicate cases where the Vickers hardness HV (Hv) and the Ni content [Ni] (mass%) satisfy the following formula (2): HV≧40×[Ni]−145 (2) Here, the Vickers hardness of the Zn—Ni alloy plating layer in units of Hv is substituted for HV in formula (2), and the Ni content in the Zn—Ni alloy plating layer in units of mass% is substituted for [Ni] in formula (2).

[0020] On the other hand, the black circles (●) in Fig. 1, unlike the white circles (◯) in Fig. 1, do not satisfy the above-mentioned formula (2). In other words, even with a Zn—Ni alloy plating layer having the above-mentioned chemical composition, there are cases where the Vickers hardness cannot be sufficiently increased. Therefore, the present inventors have conducted a detailed study on factors other than the Ni content that affect the hardness of the Zn—Ni alloy plating layer. As a result, it has been revealed that the crystallite size of the γ phase, among the precipitated phases of the Zn—Ni alloy plating layer, affects the hardness of the Zn—Ni alloy plating layer.

[0021] The crystallite size refers to the size of minute crystals present as single crystals in a polycrystalline body. In other words, the smaller the crystallite size of the γ phase, the more minute the Zn—Ni alloy plating becomes as an aggregate of single crystals. The relationship between the Ni content of the Zn—Ni alloy plating layer, the crystallite size of the γ phase, and the Vickers hardness will be explained below using a table. Table 1 is a table that excerpts some of the examples described below.

[0022]

[0023] Referring to Table 1, in test numbers 3 to 8, as the Ni content [Ni] increases, the Vickers hardness HV also increases. On the other hand, it can be confirmed that test number 10, which has a large crystallite diameter D, has a lower Vickers hardness HV than test numbers 7 and 8, which have small crystallite diameters D, despite having a higher Ni content [Ni]. In other words, the present inventors have found that by reducing the crystallite diameter D rather than simply increasing the Ni content, the hardness of the Zn—Ni alloy plating layer can be increased, and the galling resistance of the oil well metal pipe can be improved. This point will be explained in more detail using the drawings.

[0024] Fig. 2 is a diagram showing the relationship between the Ni content [Ni] (mass%) of a Zn-Ni alloy plating layer, the crystallite diameter D (nm) of the γ phase, and the Vickers hardness HV (Hv) of the Zn-Ni alloy plating layer. Fig. 2 was created using the Ni content (mass%), the crystallite diameter D (nm) determined by a method described later, and the Vickers hardness HV (Hv) determined by a method described later for the examples described later. In Fig. 2, open circles (○) represent examples in which the Ni content and Vickers hardness satisfy formula (2). In Fig. 2, filled circles (●) represent examples in which the Ni content and Vickers hardness do not satisfy formula (2).

[0025] 2, it can be seen that the crystallite diameter D tends to increase as the Ni content [Ni] increases. Furthermore, with reference to FIG. 2, it can be seen that when the crystallite diameter D and the Ni content [Ni] satisfy the following formula (1), the Vickers hardness HV satisfies formula (2), and the hardness of the Zn—Ni alloy plating layer increases: D≦12.3×[Ni]−81.6 (1) Here, the crystallite diameter of the γ phase (unit: nm) is substituted for D in formula (1), and the Ni content in the Zn—Ni alloy plating layer (unit: mass%) is substituted for [Ni] in formula (1).

[0026] Therefore, the metal oil well pipe according to this embodiment includes a Zn—Ni alloy plating layer formed on at least one of the pin contact surface and the box contact surface, the Zn—Ni alloy plating layer consisting of 9.0 to 20.0 mass % Ni, with the remainder being Zn and impurities, the precipitate phase of the Zn—Ni alloy plating layer contains a γ phase, and the crystallite diameter D of the γ phase and the Ni content [Ni] in the Zn—Ni alloy plating layer satisfy formula (1). As a result, the Vickers hardness of the Zn—Ni alloy plating layer is increased, and the galling resistance of the metal oil well pipe can be improved.

[0027] The details of why the Vickers hardness of a Zn—Ni alloy plating layer increases when the crystallite diameter D of the γ phase and the Ni content [Ni] of the Zn—Ni alloy plating layer satisfy formula (1) are not clear. However, the present inventors speculate as follows. As described above, a crystallite refers to a minute crystal that exists as a single crystal. Therefore, by definition, no strain, such as lattice defects, exists inside a crystallite. In other words, the smaller the crystallite diameter D, the more strain, such as lattice defects, exists between the crystallites. The present inventors speculate that, as a result, the total amount of strain increases, which may increase the hardness of the Zn—Ni alloy plating layer.

[0028] It is possible that the hardness of the Zn—Ni alloy plating layer is increased and the seizure resistance of the OCTG is improved by a mechanism different from that speculated by the present inventors. However, it has been proven by the examples described below that the Vickers hardness of the Zn—Ni alloy plating layer is increased by the crystallite diameter D of the γ phase of the Zn—Ni alloy plating layer and the Ni content [Ni] satisfying the formula (1) rather than by simply increasing the Ni content [Ni].

[0029] The metallic oil well pipe according to the present embodiment, which has been completed based on the above findings, has the following features.

[0030] [1] A metal pipe for oil well use, comprising: a pipe body having a first end and a second end, the pipe body including: a pin formed at the first end; and a box formed at the second end, the pin including a pin contact surface including a male thread portion, and the box including a box contact surface including a female thread portion, the metal pipe for oil well use further comprising: a Zn—Ni alloy plating layer formed on at least one of the pin contact surface and the box contact surface, the Zn—Ni alloy plating layer consisting of 9.0 to 20.0 mass % Ni, with the balance being Zn and impurities, a precipitated phase of the Zn—Ni alloy plating layer including a γ phase, and a crystallite diameter D of the γ phase and a Ni content [Ni] of the Zn—Ni alloy plating layer satisfying formula (1). D≦12.3×[Ni]−81.6 (1) Here, the crystallite diameter of the γ phase is substituted for D in formula (1) in the unit of nm, and the Ni content in the Zn—Ni alloy plating layer is substituted for [Ni] in formula (1) in the unit of mass %.

[0031] [2] The metal oil well pipe according to [1], wherein a Vickers hardness HV of the Zn—Ni alloy plating layer and a Ni content [Ni] of the Zn—Ni alloy plating layer satisfy the following formula (2): HV≧40×[Ni]−145 (2) where HV in formula (2) is substituted with the Vickers hardness of the Zn—Ni alloy plating layer in units of Hv, and [Ni] in formula (2) is substituted with the Ni content in the Zn—Ni alloy plating layer in units of mass%.

[0032] [3] The metal oil well pipe according to [1] or [2], comprising, as an upper layer of the Zn—Ni alloy plating layer, one or more layers selected from the group consisting of a chemical conversion coating layer and a lubricating coating.

[0033] The metallic oil well pipe according to this embodiment will be described in detail below.

[0034] [Configuration of Oil Well Metal Tubing] First, the configuration of the oil well metal tubing according to this embodiment will be described. The oil well metal tubing has a well-known configuration. There are two types of oil well metal tubing: T&C type oil well metal tubing and integral type oil well metal tubing. Each type of oil well metal tubing will be described in detail below.

[0035] [When the oil well metal pipe is a T&C type] Fig. 3 is a structural diagram showing an example of the oil well metal pipe 1 according to this embodiment. Fig. 3 is a structural diagram of a so-called T&C type (Threaded and Coupled) oil well metal pipe 1. Referring to Fig. 3, the oil well metal pipe 1 includes a pipe main body 10.

[0036] The pipe body 10 extends in the pipe axis direction. A cross section of the pipe body 10 perpendicular to the pipe axis direction is circular. The pipe body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is the end portion opposite the second end portion 10B. In the T&C type metal oil well pipe 1 shown in FIG. 3 , the pipe body 10 includes a pin pipe body 11 and a coupling 12. The coupling 12 is attached to one end of the pin pipe body 11. More specifically, the coupling 12 is fastened to one end of the pin pipe body 11 by a screw.

[0037] Figure 4 is a partial cross-sectional view showing a cross section (longitudinal cross section) parallel to the pipe axis direction of the coupling 12 of the metal oil well pipe 1 shown in Figure 3. With reference to Figures 3 and 4, the pipe body 10 includes a pin 40 and a box 50. The pin 40 is formed at a first end 10A of the pipe body 10. When fastening, the pin 40 is inserted into the box 50 of another metal oil well pipe (not shown) and fastened to the box 50 of the other metal oil well pipe 1 by a screw.

[0038] The box 50 is formed at the second end 10B of the pipe body 10. At the time of fastening, the pin 40 of another metal pipe for oil well use 1 is inserted into the box 50, and the box 50 is fastened to the pin 40 of the other metal pipe for oil well use 1 by a screw.

[0039] [Configuration of Pin] Fig. 5 is a cross-sectional view parallel to the pipe axis direction of the metal oil well pipe 1 of a portion near the pin 40 of the metal oil well pipe 1 shown in Fig. 4. The dashed line portion in Fig. 5 shows the configuration of a box 50 of another metal oil well pipe 1 when fastening to another metal oil well pipe 1. Referring to Fig. 5, the pin 40 has a pin contact surface 400 on the outer circumferential surface of the first end 10A of the pipe body 10. The pin contact surface 400 comes into contact with the box 50 of the other metal oil well pipe 1 when fastening to another metal oil well pipe 1.

[0040] The pin contact surface 400 includes at least a male thread portion 41 formed on the outer circumferential surface of the first end portion 10A. The pin contact surface 400 may further include a pin seal surface 42 and a pin shoulder surface 43. In FIG. 5 , the pin seal surface 42 is located on the outer circumferential surface of the first end portion 10A closer to the tip of the first end portion 10A than the male thread portion 41. In other words, the pin seal surface 42 is located between the male thread portion 41 and the pin shoulder surface 43. The pin seal surface 42 is tapered. Specifically, the outer diameter of the pin seal surface 42 gradually decreases from the male thread portion 41 toward the pin shoulder surface 43 in the longitudinal direction (pipe axis direction) of the first end portion 10A.

[0041] When fastening another oil well metal pipe 1, the pin seal surface 42 comes into contact with a box seal surface 52 (described later) of the box 50 of the other oil well metal pipe 1. More specifically, when fastening, the pin 40 is inserted into the box 50 of the other oil well metal pipe 1, so that the pin seal surface 42 comes into contact with the box seal surface 52. Then, when the pin 40 is further screwed into the box 50 of the other oil well metal pipe 1, the pin seal surface 42 comes into close contact with the box seal surface 52. As a result, when fastening, the pin seal surface 42 comes into close contact with the box seal surface 52, forming a seal based on metal-metal contact. Therefore, the airtightness of the oil well metal pipes 1 fastened together can be improved.

[0042] In Fig. 5, the pin shoulder surface 43 is disposed on the tip surface of the first end portion 10A. That is, in the pin 40 shown in Fig. 5, the male thread portion 41, the pin seal surface 42, and the pin shoulder surface 43 are disposed in this order from the center of the pipe body 10 toward the first end portion 10A. When fastening with another oil well metal pipe 1, the pin shoulder surface 43 faces and contacts a box shoulder surface 53 (described later) of the box 50 of the other oil well metal pipe 1. More specifically, when fastening, the pin 40 is inserted into the box 50 of the other oil well metal pipe 1, so that the pin shoulder surface 43 contacts the box shoulder surface 53. This allows a high torque to be obtained during fastening. Furthermore, the positional relationship between the pin 40 and the box 50 in the fastened state can be stabilized.

[0043] The pin contact surface 400 of the pin 40 includes at least the male thread portion 41. In other words, the pin contact surface 400 may include the male thread portion 41, but not the pin seal surface 42 or the pin shoulder surface 43. The pin contact surface 400 may include the male thread portion 41 and the pin shoulder surface 43, but not the pin seal surface 42. The pin contact surface 400 may include the male thread portion 41 and the pin seal surface 42, but not the pin shoulder surface 43.

[0044] [Configuration of the Box] Fig. 6 is a cross-sectional view parallel to the pipe axis direction of the metal oil well pipe 1 of a portion near the box 50 of the metal oil well pipe 1 shown in Fig. 4. The dashed line portion in Fig. 6 shows the configuration of the pin 40 of another metal oil well pipe 1 when fastening to another metal oil well pipe 1. Referring to Fig. 6, the box 50 has a box contact surface 500 on the inner circumferential surface of the second end 10B of the pipe body 10. When fastening to another metal oil well pipe 1, the pin 40 of the other metal oil well pipe 1 is screwed into the box contact surface 500, and the box contact surface 500 comes into contact with the pin contact surface 400 of the pin 40.

[0045] The box contact surface 500 includes at least a female thread portion 51 formed on the inner circumferential surface of the second end portion 10B. During fastening, the female thread portion 51 meshes with the male thread portion 41 of the pin 40 of another oil well metal pipe 1.

[0046] The box contact surface 500 may further include a box seal surface 52 and a box shoulder surface 53. In FIG. 6 , the box seal surface 52 is located on the inner circumferential surface of the second end portion 10B closer to the pipe body 10 than the female thread portion 51. In other words, the box seal surface 52 is located between the female thread portion 51 and the box shoulder surface 53. The box seal surface 52 is tapered. Specifically, the inner diameter of the box seal surface 52 gradually decreases from the female thread portion 51 toward the box shoulder surface 53 in the longitudinal direction (pipe axial direction) of the second end portion 10B.

[0047] When fastening another metal oil well pipe 1, the box seal surface 52 comes into contact with the pin seal surface 42 of the pin 40 of the other metal oil well pipe 1. More specifically, when fastening, the pin 40 of the other metal oil well pipe 1 is screwed into the box 50, so that the box seal surface 52 comes into contact with the pin seal surface 42, and when further screwed, the box seal surface 52 comes into close contact with the pin seal surface 42. As a result, when fastening, the box seal surface 52 comes into close contact with the pin seal surface 42, forming a seal based on metal-metal contact. Therefore, the airtightness of the metal oil well pipes 1 fastened to each other can be improved.

[0048] The box shoulder surface 53 is located closer to the pipe body 10 than the box seal surface 52. That is, in the box 50, the box shoulder surface 53, the box seal surface 52, and the female thread portion 51 are located in this order from the center of the pipe body 10 toward the tip of the second end 10B. When fastening another oil well metal pipe 1, the box shoulder surface 53 faces and contacts the pin shoulder surface 43 of the pin 40 of the other oil well metal pipe 1. More specifically, when fastening, the pin 40 of the other oil well metal pipe 1 is inserted into the box 50, so that the box shoulder surface 53 contacts the pin shoulder surface 43. This allows a high torque to be obtained during fastening. Furthermore, the positional relationship between the pin 40 and the box 50 in the fastened state can be stabilized.

[0049] The box contact surface 500 includes at least an internal thread portion 51. During fastening, the internal thread portion 51 of the box contact surface 500 of the box 50 corresponds to and contacts the external thread portion 41 of the pin contact surface 400 of the pin 40. The box seal surface 52 corresponds to and contacts the pin seal surface 42. The box shoulder surface 53 corresponds to and contacts the pin shoulder surface 43.

[0050] When the pin contact surface 400 includes the male thread portion 41 but does not include the pin seal surface 42 or the pin shoulder surface 43, the box contact surface 500 includes the female thread portion 51 but does not include the box seal surface 52 or the box shoulder surface 53. When the pin contact surface 400 includes the male thread portion 41 and the pin shoulder surface 43 but does not include the pin seal surface 42, the box contact surface 500 includes the female thread portion 51 and the box shoulder surface 53 but does not include the box seal surface 52. When the pin contact surface 400 includes the male thread portion 41 and the pin seal surface 42 but does not include the pin shoulder surface 43, the box contact surface 500 includes the female thread portion 51 and the box seal surface 52 but does not include the box shoulder surface 53.

[0051] The pin contact surface 400 may include a plurality of male thread portions 41, a plurality of pin seal surfaces 42, and a plurality of pin shoulder surfaces 43. For example, on the pin contact surface 400 of the pin 40, the pin shoulder surface 43, the pin seal surface 42, the male thread portion 41, the pin seal surface 42, the pin shoulder surface 43, the pin seal surface 42, and the male thread portion 41 may be arranged in this order from the tip of the first end 10A toward the center of the pipe body 10. In this case, on the box contact surface 500 of the box 50, the female thread portion 51, the box seal surface 52, the box shoulder surface 53, the box seal surface 52, the female thread portion 51, the box seal surface 52, and the box shoulder surface 53 are arranged in this order from the tip of the second end 10B toward the center of the pipe body 10.

[0052] 5 and 6 illustrate a so-called premium joint in which the pin 40 includes a male thread portion 41, a pin seal surface 42, and a pin shoulder surface 43, and the box 50 includes a female thread portion 51, a box seal surface 52, and a box shoulder surface 53. However, as described above, the pin 40 may include the male thread portion 41 but not the pin seal surface 42 or the pin shoulder surface 43. In this case, the box 50 includes the female thread portion 51 but not the box seal surface 52 or the box shoulder surface 53. FIG. 7 is a diagram showing an example of the metal oil well pipe 1 in which the pin 40 includes the male thread portion 41 but not the pin seal surface or the pin shoulder surface, and the box 50 includes the female thread portion 51 but not the box seal surface or the box shoulder surface. The metal oil well pipe 1 according to this embodiment may have the configuration shown in FIG. 7.

[0053] [When the oil well metal pipe is an integral type] The oil well metal pipe 1 shown in Figures 3, 4 and 7 is a so-called T&C type oil well metal pipe 1 in which the pipe body 10 includes a pin pipe body 11 and a coupling 12. However, the oil well metal pipe 1 according to this embodiment may be an integral type instead of a T&C type.

[0054] Fig. 8 is a structural diagram of an integral-type metal oil well pipe 1 according to this embodiment. Referring to Fig. 8, the integral-type metal oil well pipe 1 includes a pipe body 10. The pipe body 10 includes a first end 10A and a second end 10B. The first end 10A is located on the opposite side to the second end 10B. As described above, in the T&C type metal oil well pipe 1, the pipe body 10 includes a pin pipe body 11 and a coupling 12. That is, in the T&C type metal oil well pipe 1, the pipe body 10 is formed by fastening two separate members (the pin pipe body 11 and the coupling 12). In contrast, in the integral-type metal oil well pipe 1, the pipe body 10 is integrally formed.

[0055] 8 , the pin 40 is formed at the first end 10A of the pipe body 10. At the time of fastening, the pin 40 is inserted into and screwed into a box 50 of another integral type metallic pipe for oil well use 1, and is fastened to the box 50 of the other integral type metallic pipe for oil well use 1. The box 50 is formed at the second end 10B of the pipe body 10. At the time of fastening, the pin 40 of another integral type metallic pipe for oil well use 1 is inserted into and screwed into the box 50, and is fastened to the pin 40 of the other integral type metallic pipe for oil well use 1.

[0056] The configuration of the pin 40 of the integral type oil well metal pipe 1 is the same as the configuration of the pin 40 of the T&C type oil well metal pipe 1 shown in Fig. 5 . Similarly, the configuration of the box 50 of the integral type oil well metal pipe 1 is the same as the configuration of the box 50 of the T&C type oil well metal pipe 1 shown in Fig. 6 . In Fig. 8 , in the pin 40, the pin shoulder surface, pin seal surface, and male thread portion 41 are arranged in this order from the tip of the first end 10A toward the center of the pipe body 10. Therefore, in the box 50, the female thread portion 51, box seal surface, and box shoulder surface are arranged in this order from the tip of the second end 10B toward the center of the pipe body 10. However, as in Fig. 5 , it is sufficient that the pin contact surface 400 of the pin 40 of the integral type oil well metal pipe 1 includes at least the male thread portion 41. As in Fig. 6 , it is sufficient that the box contact surface 500 of the box 50 of the integral type oil well metal pipe 1 includes at least the female thread portion 51.

[0057] In short, the metal oil well pipe 1 according to this embodiment may be of either a T&C type or an integral type.

[0058] [Chemical Composition of Pipe Body] In the oil well metal pipe 1 according to this embodiment, the chemical composition of the pipe body 10 is not particularly limited. The pipe body 10 may have a chemical composition corresponding to carbon steel, a chemical composition corresponding to stainless steel, or a chemical composition corresponding to a Ni-based alloy. When the pipe body 10 has a chemical composition corresponding to stainless steel, the stainless steel may be, for example, martensitic stainless steel, ferritic stainless steel, ferritic-martensite duplex stainless steel, ferritic-austenite duplex stainless steel, or austenitic stainless steel. The pipe body 10 may further have a plating layer formed on its surface. For example, the pipe body 10 may be composed of a base material having a chemical composition corresponding to carbon steel and a plating layer formed on the surface of the base material. In this case, the plating layer may be, for example, a Ni plating layer, a Cu plating layer, or a Cr plating layer.

[0059] [Zn—Ni alloy plating layer] In the oil well metal pipe 1 according to this embodiment, a Zn—Ni alloy plating layer is formed on at least one of the pin contact surface 400 and the box contact surface 500. That is, the Zn—Ni alloy plating layer may be formed on the pin contact surface 400, but not on the box contact surface 500. Alternatively, the Zn—Ni alloy plating layer may be formed on the box contact surface 500, but not on the pin contact surface 400. Alternatively, the Zn—Ni alloy plating layer may be formed on both the pin contact surface 400 and the box contact surface 500.

[0060] In the following explanation, the structure on the pin contact surface 400 when a Zn—Ni alloy plating layer is formed on the pin contact surface 400, and the structure on the box contact surface 500 when a Zn—Ni alloy plating layer is formed on the box contact surface 500 will be explained.

[0061] [Configuration on Pin Contact Surface When Zn—Ni Alloy Plating Layer is Formed on Pin Contact Surface] Fig. 9 is a cross-sectional view of the vicinity of the pin contact surface 400 when the Zn—Ni alloy plating layer 100 is formed on the pin contact surface 400. Referring to Fig. 9, in this case, the metal oil well pipe 1 further includes the Zn—Ni alloy plating layer 100 formed on the pin contact surface 400 of the pin 40.

[0062] The Zn—Ni alloy plating layer 100 may be formed on a portion of the pin contact surface 400, or may be formed on the entire pin contact surface 400. The pin seal surface 42 experiences particularly high surface pressure in the final stage of screw tightening. Therefore, when the Zn—Ni alloy plating layer 100 is formed on a portion of the pin contact surface 400, it is preferable that the Zn—Ni alloy plating layer 100 be formed on at least the pin seal surface 42. As described above, the Zn—Ni alloy plating layer 100 may be formed on the entire pin contact surface 400.

[0063] [Configuration of the Box Contact Surface When a Zn—Ni Alloy Plating Layer is Formed on the Box Contact Surface] FIG. 10 is a cross-sectional view of the vicinity of the box contact surface 500 when a Zn—Ni alloy plating layer 100 is formed on the box contact surface 500. Referring to FIG. 10 , in this case, the Zn—Ni alloy plating layer 100 is formed on the box contact surface 500. The Zn—Ni alloy plating layer 100 may be formed on a portion of the box contact surface 500 or may be formed on the entire box contact surface 500. The box seal surface 52 experiences particularly high surface pressure during the final stage of screw tightening. Therefore, when the Zn—Ni alloy plating layer 100 is formed only partially on the box contact surface 500, it is preferable that the Zn—Ni alloy plating layer 100 be formed on at least the box seal surface 52.

[0064] [Composition of Zn—Ni Alloy Plating Layer] As described above, the Zn—Ni alloy plating layer 100 is formed on at least one of the contact surfaces of the pin contact surface 400 and the box contact surface 500. Here, the Zn—Ni alloy plating layer 100 is made of a Zn—Ni alloy. Specifically, the Zn—Ni alloy plating layer 100 according to this embodiment has a chemical composition consisting of 9.0 to 20.0 mass% Ni, with the remainder consisting of Zn and impurities. That is, in this embodiment, the Ni content [Ni] in the Zn—Ni alloy plating layer 100 is 9.0 to 20.0 mass%.

[0065] The higher the Ni content [Ni] in the Zn—Ni alloy plating layer 100, the higher the hardness of the Zn—Ni alloy plating layer 100 and the higher the seizure resistance of the metal oil well pipe 1. On the other hand, if the Ni content [Ni] is too high, the desired precipitate phase described below cannot be obtained. Therefore, in this embodiment, the Ni content [Ni] in the Zn—Ni alloy plating layer 100 is set to 9.0 to 20.0% by mass.

[0066] The lower limit of the Ni content [Ni] in the Zn—Ni alloy plating layer 100 is preferably 10.0%, more preferably 11.0%, and even more preferably 12.0%, by mass. The upper limit of the Ni content [Ni] in the Zn—Ni alloy plating layer 100 is preferably 19.0%, more preferably 18.0%, and even more preferably 17.0%, by mass. Here, the impurities in the Zn—Ni alloy plating layer refer to substances other than Zn and Ni that are contained in the Zn—Ni alloy plating layer 100 during the manufacturing process of the metal oil well pipe 1, etc., and that are contained in an amount that does not affect the effects of this embodiment.

[0067] In this embodiment, the chemical composition of the Zn—Ni alloy plating layer 100 can be measured by the following method. A sample containing the Zn—Ni alloy plating layer 100 (including the contact surface on which the Zn—Ni alloy plating layer 100 is formed) is collected from the metal oil well pipe 1. The Zn—Ni alloy plating layer 100 of the collected sample is dissolved in 10% hydrochloric acid to obtain a solution. The obtained solution is subjected to elemental analysis by inductively coupled plasma atomic emission spectrometry (ICP-AES) to determine the Ni content (mass%) and Zn content (mass%) in the Zn—Ni alloy plating layer 100.

[0068] [Thickness of Zn—Ni Alloy Plating Layer] In this embodiment, the thickness of the Zn—Ni alloy plating layer 100 is not particularly limited. The thickness of the Zn—Ni alloy plating layer 100 is, for example, 1 to 20 μm. If the thickness of the Zn—Ni alloy plating layer 100 is 1 μm or more, the seizure resistance can be further improved. Even if the thickness of the Zn—Ni alloy plating layer 100 exceeds 20 μm, the above effect saturates. The lower limit of the thickness of the Zn—Ni alloy plating layer 100 is preferably 3 μm, more preferably 5 μm. The upper limit of the thickness of the Zn—Ni alloy plating layer 100 is preferably 18 μm, more preferably 15 μm.

[0069] In this embodiment, the thickness of the Zn—Ni alloy plating layer 100 can be measured by the following method. The thickness of the Zn—Ni alloy plating layer 100 is measured at any four locations on the pin contact surface 400 or the box contact surface 500 on which the Zn—Ni alloy plating layer 100 is formed, using an eddy current phase-type film thickness meter PHASCOPE PMP10 manufactured by Helmut Fischer GmbH. The measurement is performed by a method conforming to ISO (International Organization for Standardization) 21968 (2005). The measurement locations are four locations (four locations at 0°, 90°, 180°, and 270°) in the circumferential direction of the metal oil well pipe 1. The arithmetic mean value of the measurement results is defined as the thickness of the Zn—Ni alloy plating layer 100.

[0070] [Precipitation Phase of Zn—Ni Alloy Plated Layer] In this embodiment, the precipitate phase of the Zn—Ni alloy plated layer 100 includes a γ phase. Here, the precipitate phase of the Zn—Ni alloy layer 100 formed by electroplating may include an η phase, a γ phase, and an α phase. Here, the η phase in the Zn—Ni alloy is a phase having a hexagonal crystal structure with a chemical formula of Zn and lattice constants a = 0.267 nm and c = 0.495 nm. The γ phase in the Zn—Ni alloy is a phase having a chemical formula of Ni ５ Zn ２１ The α phase in a Zn—Ni alloy is a phase with a face-centered cubic crystal structure, the chemical formula of which is Ni, and the lattice constant of which is a = 0.352 nm.

[0071] As described above, the chemical composition of the Zn—Ni alloy plating layer 100 according to this embodiment is 9.0 to 20.0 mass % Ni, with the remainder being Zn and impurities. Therefore, the precipitate phase of the Zn—Ni alloy plating layer 100 according to this embodiment stably contains the γ phase. Note that even in the Zn—Ni alloy plating layer 100 having the above-described chemical composition, the precipitate phase may contain not only the γ phase but also the η phase and the α phase. Therefore, the precipitate phase of the Zn—Ni alloy plating layer 100 according to this embodiment contains at least the γ phase.

[0072] Preferably, the precipitate phase of the Zn—Ni alloy plating layer 100 according to this embodiment is mainly composed of the γ phase. In this specification, "mainly composed of the γ phase" means that the precipitate phase of the Zn—Ni alloy plating layer 100 has a volume fraction of 50% or more of the γ phase. A higher volume fraction of the γ phase is preferable. Therefore, the volume fraction of the γ phase may be 60% or more, 70% or more, 80% or more, or even 90% or more. Most preferably, the precipitate phase of the Zn—Ni alloy plating layer 100 according to this embodiment is composed of the γ phase and the remainder is impurities. In other words, it is most preferable that the precipitate phase of the Zn—Ni alloy plating layer 100 according to this embodiment has a negligible amount of phases other than the γ phase.

[0073] In this embodiment, the precipitated phase of the Zn—Ni alloy plating layer 100 can be identified by the following method. X-ray diffraction measurement is performed on the surface of the Zn—Ni alloy plating layer 100 under the following measurement conditions. The phase can be identified by comparing the obtained measured profile with the value recorded on the ASTM card. Apparatus: Rigaku Corporation RINT-2500 X-ray tube: Co-Kα ray Scan range: 2θ = 10 to 110° Scan step: 0.02°

[0074] [Gamma Phase Crystallite Diameter of Zn—Ni Alloy Plating Layer] In the present embodiment, the gamma phase crystallite diameter D (nm) and the Ni content [Ni] (mass %) of the Zn—Ni alloy plating layer 100 satisfy the following formula (1): D≦12.3×[Ni]−81.6 (1) Here, the gamma phase crystallite diameter in the Zn—Ni alloy plating layer 100 is substituted for D in formula (1) and the Ni content in the Zn—Ni alloy plating layer 100 is substituted for [Ni] in formula (1) in unit of mass %.

[0075] Here, the term "crystallite" refers to a minute crystal present as a single crystal in a polycrystalline body. Furthermore, a crystal grain is usually defined as a grain boundary having a misorientation of 15 degrees or more. Therefore, one crystal grain thus defined contains multiple crystallites. In other words, in this embodiment, the crystallite diameter D of the γ phase is defined as the grain size of a crystallite, which is a structure finer than the crystal grains of the γ phase.

[0076] Up until now, no attention has been paid to the crystallite diameter of the Zn—Ni alloy plating layer 100. However, as a result of detailed studies by the present inventors, it has become clear that in the Zn—Ni alloy plating layer 100 having the above-mentioned chemical composition, the crystallite diameter D (nm) of the γ phase increases as the Ni content [Ni] (mass%) increases. Furthermore, in the Zn—Ni alloy plating layer 100 having the above-mentioned chemical composition, if the crystallite diameter D (nm) of the γ phase and the Ni content [Ni] (mass%) of the Zn—Ni alloy plating layer 100 satisfy the above-mentioned formula (1), the hardness of the Zn—Ni alloy plating layer 100 increases, as proven by the examples described below.

[0077] The upper limit of the γ-phase crystallite diameter D is preferably 12.3 × [Ni] − 85.0 nm, more preferably 12.3 × [Ni] − 88.0 nm, and even more preferably 12.3 × [Ni] − 90.0 nm. In this embodiment, the smaller the γ-phase crystallite diameter D of the Zn—Ni alloy plating layer 100, the better. The lower limit of the γ-phase crystallite diameter D may be, for example, more than 0 nm, 10 nm, or 20 nm.

[0078] In this embodiment, the crystallite size of the γ phase of the Zn—Ni alloy plating layer 100 can be measured by the following method. X-ray diffraction measurement is performed on the surface of the Zn—Ni alloy plating layer 100 under the same measurement conditions as those used for identifying the precipitated phase of the Zn—Ni alloy plating layer 100. The measurement locations are four locations (four locations at 0°, 90°, 180°, and 270°) in the circumferential direction of the metal oil well pipe 1.

[0079] The crystallite size is calculated based on the diffraction peak at 2θ = 49.0 to 52.0° in the measured profile obtained by X-ray diffraction measurement and the Scherrer formula (formula (I)) described below. The arithmetic mean value of the crystallite sizes (nm) determined at four locations is defined as the crystallite size D (nm) of the γ phase of the Zn—Ni alloy plating layer 100. Note that in the Zn—Ni alloy plating layer 100 having the above-described chemical composition, the diffraction peak at 2θ = 49.0 to 52.0° is the diffraction peak of the (411) plane of the γ phase. Crystallite size (nm) = (0.9 × λ) / (B × cos θ) (I) Here, λ in formula (I) is substituted with the wavelength of the incident X-rays in nm, B in formula (I) is substituted with the full width at half maximum of the diffraction peak in radians, and θ in formula (I) is substituted with the Bragg angle of the diffraction peak in radians.

[0080] [Vickers Hardness of Zn—Ni Alloy Plating Layer] The Zn—Ni alloy plating layer 100 according to this embodiment has a chemical composition consisting of 9.0 to 20.0 mass % Ni, with the remainder being Zn and impurities, the precipitate phase of the Zn—Ni alloy plating layer 100 contains a γ phase, and the crystallite diameter D (nm) of the γ phase and the Ni content [Ni] (mass %) of the Zn—Ni alloy plating layer 100 satisfy formula (1). As a result, the Zn—Ni alloy plating layer 100 according to this embodiment has a Vickers hardness HV (Hv) and the Ni content [Ni] (mass %) of the Zn—Ni alloy plating layer 100 satisfy the following formula (2). HV≧40×[Ni]−145 (2) Here, HV in formula (2) is substituted with the Vickers hardness of the Zn—Ni alloy plating layer 100 in the unit of Hv, and [Ni] in formula (2) is substituted with the Ni content in the Zn—Ni alloy plating layer 100 in the unit of mass %.

[0081] As described above, in the Zn—Ni alloy plating layer 100 having the above-described chemical composition, the Vickers hardness HV increases as the Ni content [Ni] increases. On the other hand, the Zn—Ni alloy plating layer 100 according to this embodiment does not simply increase the Ni content [Ni], but reduces the crystallite diameter D according to the Ni content [Ni]. As a result, the Vickers hardness HV of the Zn—Ni alloy plating layer 100 can be further increased compared to simply increasing the Ni content [Ni]. As a result, the seizure resistance of the metal oil well pipe 1 can be improved.

[0082] The lower limit of the Vickers hardness HV of the Zn—Ni alloy plating layer 100 is preferably 40×[Ni]−140 Hv, and more preferably 40×[Ni]−135 Hv. In this embodiment, the larger the Vickers hardness HV of the Zn—Ni alloy plating layer 100, the more preferable. The upper limit of the Vickers hardness HV of the Zn—Ni alloy plating layer 100 may be, for example, 40×[Ni]+150 Hv.

[0083] In this embodiment, the Vickers hardness HV of the Zn—Ni alloy plating layer 100 can be measured by the following method. The metal oil well pipe 1 on which the Zn—Ni alloy plating layer 100 is formed is cut in a direction perpendicular to the pipe axis direction. A Vickers hardness test is performed on any five points on the Zn—Ni alloy plating layer 100 of the obtained cut surface using a method in accordance with JIS Z 2244 (2009). The test temperature is room temperature (25°C), and the test force (F) is 0.01 N. A Fischer Scope HM2000 microhardness tester manufactured by Fischer Instruments Inc. is used for the measurement. The arithmetic mean value of three points, excluding the maximum and minimum values, out of the five measurement results obtained is defined as the Vickers hardness HV (Hv) of the Zn—Ni alloy plating layer 100. In other words, the Vickers hardness HV in this embodiment means Hv 0.001.

[0084] [Other Optional Configurations of the Oil Well Metal Tubular Article 1 of the Present Embodiment] The oil well metal tubular article 1 of the present embodiment may further include one or more layers selected from the group consisting of a chemical conversion layer and a lubricating coating as an upper layer of the Zn—Ni alloy plating layer 100. The chemical conversion layer and the lubricating coating will be described below.

[0085] [Chemical Conversion Treatment Layer] The metal oil well pipe 1 of this embodiment may further include a chemical conversion treatment layer as an upper layer of the Zn—Ni alloy plating layer 100. Referring to Fig. 11 , in the case where the Zn—Ni alloy plating layer 100 is formed on the pin contact surface 400, the chemical conversion treatment layer 110 may be formed on the Zn—Ni alloy plating layer 100.

[0086] The chemical conversion treatment layer 110 is not particularly limited, and a well-known chemical conversion treatment layer can be used. The chemical conversion treatment layer 110 may be, for example, an oxalate chemical conversion treatment layer, a phosphate chemical conversion treatment layer, a borate chemical conversion treatment layer, or a chromate coating. When the chemical conversion treatment layer 110 is a chromate coating, it is preferable that the chromate coating does not contain hexavalent chromium.

[0087] The oil well metal pipe 1 may be stored outdoors for a long period of time before it is actually used in an oil well field. When the oil well metal pipe 1 is exposed to the atmosphere outdoors for a long period of time, the chemical conversion treatment layer 110 can improve the corrosion resistance of the contact surfaces 400, 500 and suppress the formation of rust (white rust) on the contact surfaces 400, 500. The film thickness of the chemical conversion treatment layer 110 is not particularly limited. The film thickness of the chemical conversion treatment layer 110 is, for example, 10 to 200 nm.

[0088] [Lubricating Coating] The oil well metal pipe 1 of this embodiment may further include a lubricating coating as an upper layer of the Zn—Ni alloy plating layer 100. With reference to Fig. 12 , in the case where the Zn—Ni alloy plating layer 100 is formed on the box contact surface 500, the lubricating coating 120 may be formed on the Zn—Ni alloy plating layer 100.

[0089] 13, when the Zn—Ni alloy plating layer 100 is formed on the pin contact surface 400, the lubricating coating 120 may be formed on the chemical conversion treatment layer 110 formed on the Zn—Ni alloy plating layer 100. Also, with reference to Fig. 14, when the Zn—Ni alloy plating layer 100 is formed on the box contact surface 500, the lubricating coating 120 may be formed on the Zn—Ni alloy plating layer 100. That is, with reference to Figs. 12 to 14, the lubricating coating 120 may be formed directly on the Zn—Ni alloy plating layer 100, or may be formed on the chemical conversion treatment layer 110 formed on the Zn—Ni alloy plating layer 100.

[0090] The arrangement of the chemical conversion layer 110 and the lubricating coating 120 is not limited to the arrangements shown in Figures 11 to 14. In other words, the chemical conversion layer 110 may be formed on the pin contact surface 400 on which the Zn—Ni alloy plating layer 100 is not formed, on the box contact surface 500 on which the Zn—Ni alloy plating layer 100 is not formed, on the Zn—Ni alloy plating layer 100 formed on the pin contact surface 400, or on the Zn—Ni alloy plating layer 100 formed on the box contact surface 500. The lubricating coating 120 may be formed on the pin contact surface 400 on which the Zn—Ni alloy plating layer 100 is not formed, or on the box contact surface 500 on which the Zn—Ni alloy plating layer 100 is not formed, or on the Zn—Ni alloy plating layer 100 formed on the pin contact surface 400, or on the Zn—Ni alloy plating layer 100 formed on the box contact surface 500, or on the chemical conversion coating layer 110 formed on the pin contact surface 400, or on the chemical conversion coating layer 110 formed on the box contact surface 500, or on the chemical conversion coating layer 110 formed on the Zn—Ni alloy plating layer 100 formed on the pin contact surface 400, or on the chemical conversion coating layer 110 formed on the Zn—Ni alloy plating layer 100 formed on the box contact surface 500.

[0091] The lubricating coating may be solid, semi-solid, or liquid. Commercially available lubricants can be used for the lubricating coating. The lubricating coating contains, for example, lubricating particles and a binder. The lubricating coating may contain a solvent and other components as needed. There are no particular limitations on the lubricating particles as long as they are particles with lubricity. Examples of lubricating particles include graphite and MoS. ２ (Molybdenum disulfide), WS ２ (tungsten disulfide), BN (boron nitride), PTFE (polytetrafluoroethylene), CFx (graphite fluoride) and CaCO ３ (calcium carbonate).

[0092] The binder is, for example, one or two types selected from the group consisting of organic binders and inorganic binders. The organic binder is, for example, one or two types selected from the group consisting of thermosetting resins and thermoplastic resins. The thermosetting resin is, for example, one or more types selected from the group consisting of polyethylene resins, polyimide resins, and polyamideimide resins. The inorganic binder is, for example, one or two types selected from the group consisting of compounds containing alkoxysilanes and siloxane bonds. An example of a commercially available lubricant is SEAL-GUARD ECF (trade name) manufactured by JET-LUBE Co., Ltd. Another example of a lubricating coating is a lubricating coating containing rosin, metal soap, wax, and lubricating powder.

[0093] [Method for manufacturing the metal oil well pipe 1] A method for manufacturing the metal oil well pipe 1 of this embodiment will be described below. Note that the method for manufacturing the metal oil well pipe 1 of this embodiment is not limited to the following method as long as it has the above-mentioned configuration. However, the manufacturing method described below is a suitable example for manufacturing the metal oil well pipe 1 of this embodiment.

[0094] The method for manufacturing the metal oil well pipe 1 includes a preparation step (S1) of preparing a mother pipe on which the pin 40 or the box 50 is formed, and a Zn—Ni alloy plating layer formation step (S2). Each step of the method for manufacturing the metal oil well pipe 1 of this embodiment will be described in detail below.

[0095] [Preparation Step (S1)] In the preparation step (S1), a mother pipe on which pins 40 or boxes 50 are formed is prepared. In this specification, the term "mother pipe on which pins or boxes are formed" means any of the pipe main body 10 and pin pipe body 11 of the T&C type metal pipe for oil well use 1, and the pipe main body 10 of the integral type metal pipe for oil well use 1.

[0096] The mother pipe on which the pin 40 or the box 50 is formed is manufactured, for example, by the following method. A raw material is manufactured using molten steel. Specifically, a cast piece (slab, bloom, or billet) is manufactured using the molten steel by continuous casting. An ingot may be manufactured using the molten steel by ingot casting. If necessary, the slab, bloom, or ingot may be bloomed to manufacture a billet. A raw material (slab, bloom, or billet) is manufactured through the above steps. A mother pipe is manufactured by hot working the prepared raw material. The hot working method may be piercing-rolling using the Mannesmann method or hot extrusion. The mother pipe after hot working is subjected to well-known quenching and well-known tempering to adjust the strength of the mother pipe. A mother pipe is manufactured through the above steps. Note that when the oil well metallic tubular product 1 is a T&C type, a mother pipe for a coupling 12 is also prepared. The manufacturing method of the mother pipe for the coupling 12 is the same as the manufacturing method of the mother pipe described above.

[0097] When the oil well metal pipe 1 is of the T&C type, threading is performed on the outer surfaces of both end portions of a mother pipe for the pin pipe body 11 to form pins 40 including pin contact surfaces 400. By the above-mentioned steps, a mother pipe (pin pipe body 11) on which pins 40 are formed is prepared when the oil well metal pipe 1 is of the T&C type. Note that when the oil well metal pipe 1 is of the T&C type, a coupling 12 may also be prepared. Specifically, threading is performed on the inner surfaces of both end portions of a mother pipe for the coupling 12 to form a box 50 including a box contact surface 500. The coupling 12 is manufactured by the above-mentioned steps.

[0098] When the oil well metal pipe 1 is of an integral type, threading is performed on the outer surface of the first end 10A of the mother pipe to form pins 40 including pin contact surfaces 400. Furthermore, threading is performed on the inner surface of the second end 10B of the mother pipe to form boxes 50 including box contact surfaces 500. Through the above steps, a mother pipe (pipe body 10) on which pins 40 and boxes 50 are formed is prepared when the oil well metal pipe 1 is of an integral type.

[0099] [Other Optional Steps] The preparation step (S1) of this embodiment may further include at least one step of a grinding step and a Ni strike plating step.

[0100] When a grinding process is performed in the preparation process (S1) according to this embodiment, the grinding process may include, for example, sandblasting and mechanical grinding. Sandblasting is a process in which a blasting material (abrasive) and compressed air are mixed and projected onto the contact surface. The blasting material may be, for example, spherical shot or angular grit. Sandblasting can increase the surface roughness of the contact surface. Sandblasting can be performed by a known method. For example, air is compressed using a compressor, and the compressed air is mixed with the blasting material. Examples of the blasting material include stainless steel, aluminum, ceramic, and alumina. The projection speed and other conditions of the sandblasting process are not particularly limited and can be appropriately adjusted according to known conditions.

[0101] In the Ni strike plating step, a Ni strike plating layer is formed on the surface of the mother pipe. The Ni strike plating layer is a very thin undercoat plating layer that enhances the adhesion of the Zn—Ni alloy plating layer 100. The plating bath used in the Ni strike plating step is not particularly limited, and any known bath can be used. The conditions for forming the Ni strike plating layer are also not particularly limited, and can be adjusted as appropriate.

[0102] When the Ni strike plating process is performed, a Ni strike plating layer is formed on the contact surfaces 400, 500 of the pipe body 10. In other words, when the Ni strike plating layer is formed, the Ni strike plating layer is included in the pipe body 10.

[0103] [Zn—Ni alloy plating layer forming step (S2)] In the Zn—Ni alloy plating layer forming step (S2), a Zn—Ni alloy plating layer 100 is formed by electroplating on the pin contact surface 400 of the mother pipe on which the pin 40 is formed after the preparation step (S1) and / or on the box contact surface 500 of the mother pipe on which the box 50 is formed.

[0104] In the Zn—Ni alloy plating layer forming step (S2), a plating bath containing zinc ions and nickel ions is used to form the Zn—Ni alloy plating layer 100. Counter anions for the zinc ions and nickel ions are not particularly limited. For example, chloride ions or sulfate ions may be used as counter anions. That is, in the Zn—Ni alloy plating layer forming step (S2) according to this embodiment, a chloride bath or a sulfate bath may be used as the plating bath.

[0105] Preferred plating conditions are explained below. The plating solution contains zinc ions and nickel ions, and the total amount of metal ions, TM, is preferably 0.500 to 1.500 mol / L. Furthermore, the plating solution preferably has a nickel ion ratio (nickel ion content (g / L) / total zinc ion and nickel ion content (g / L)) of 30.0 to 55.0% among the metal ions. The plating solution preferably has a temperature, T, of 40°C or higher and a pH of 1 to 7. The plating solution flow rate, FR, is 0.2 to 1.5 m / s, and the plating solution current density, ASD, is 2 to 15 A / dm ２ More preferably, the plating solution temperature T (°C), the total amount of metal ions in the plating solution TM (mol / L), the flow rate FR (m / s), and the current density ASD (A / dm ２ ) is preferably 165 or more. ２ ) satisfy the above-mentioned ranges and FnA is 165 or more, the crystallite diameter D of the γ phase and the Ni content [Ni] of the Zn—Ni alloy plating layer 100 can stably satisfy the formula (1).

[0106] In the Zn—Ni alloy plating layer 100 having the above-described chemical composition, the γ-phase crystallite diameter D is affected by various factors. Specifically, the plating solution temperature T affects the reactivity of the electroplating reaction. Increasing the plating solution temperature T increases the reactivity of the electroplating reaction and reduces the crystallite size. Furthermore, the total amount of metal ions in the plating solution TM and the flow rate FR of the plating solution affect the amount of metal ions supplied. Furthermore, the current density ASD of the plating solution affects the force that precipitates the supplied metal ions as metal. Therefore, in the Zn—Ni alloy plating layer formation step (S2) according to this embodiment, the γ-phase crystallite size is reduced by adjusting the balance between the plating solution temperature T, the total amount of metal ions in the plating solution TM, the flow rate FR of the plating solution, and the current density ASD of the plating solution. As a result, the γ-phase crystallite diameter D and the Ni content [Ni] of the Zn—Ni alloy plating layer 100 stably satisfy formula (1).

[0107] When the Zn—Ni alloy plating layer 100 is formed on the pin contact surface 400, the pin contact surface 400 is immersed in the above-mentioned plating bath to perform electroplating. On the other hand, when the Zn—Ni alloy plating layer 100 is formed on the box contact surface 500, the box contact surface 500 is immersed in the above-mentioned plating bath to perform electroplating.

[0108] The above-described manufacturing process produces the metal oil well pipe 1 of the present embodiment having the above-described configuration. Note that the above-described manufacturing process is an example of a manufacturing process for the metal oil well pipe 1 of the present embodiment, and the manufacturing method for the metal oil well pipe 1 of the present embodiment is not limited to the above-described manufacturing process.

[0109] [Other Optional Steps] The method for manufacturing the metal oil well pipe 1 according to the present embodiment may further include at least one of the following chemical conversion treatment step and film formation step. These steps are optional steps. Therefore, these steps do not necessarily have to be performed.

[0110] [Chemical Conversion Treatment Step] In the manufacturing method of this embodiment, a chemical conversion treatment step may be carried out as necessary. In other words, the chemical conversion treatment step is an optional step. When the chemical conversion treatment step is carried out, a chemical conversion treatment layer 110 is formed on the Zn—Ni alloy plating layer 100. In the chemical conversion treatment step, a well-known chemical conversion treatment may be carried out. The chemical conversion treatment may be, for example, an oxalate chemical conversion treatment, a phosphate chemical conversion treatment, or a borate chemical conversion treatment. For example, when a phosphate chemical conversion treatment is carried out, a chemical conversion treatment using zinc phosphate may be carried out, a chemical conversion treatment using manganese phosphate may be carried out, or a chemical conversion treatment using zinc calcium phosphate may be carried out.

[0111] Specifically, when performing zinc phosphate conversion treatment, a chemical conversion treatment solution containing, for example, 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 as the treatment solution. In this case, the temperature of the chemical conversion treatment solution is, for example, 20 to 100°C. In this way, the chemical conversion treatment layer 110 can be formed by performing the chemical conversion treatment under appropriately set known conditions.

[0112] [Film Forming Step] The manufacturing method of this embodiment may include a film forming step as needed. That is, the film forming step is an optional step. In the film forming step, a lubricating coating is formed on the Zn—Ni alloy plating layer 100, and / or on the chemical conversion treatment layer 110, and / or on the contact surface (the pin contact surface 400 or the box contact surface 500) on which the Zn—Ni alloy plating layer 100 is not formed.

[0113] In the film-forming step, a composition or lubricant containing the components of the lubricating coating described above is applied. This allows the formation of a lubricating coating. The application method is not particularly limited. Examples of application methods include spray application, brush application, and immersion. When spray application is used, the composition or lubricant may be heated to increase fluidity before spraying. The composition or lubricant is dried to form a lubricating coating.

[0114] The metal oil well pipe 1 of this embodiment will be described in more detail below with reference to examples. The conditions in the following examples are one example of conditions adopted to confirm the feasibility and effects of the metal oil well pipe 1 of this embodiment. Therefore, the metal oil well pipe 1 of this embodiment is not limited to this one example of conditions.

[0115] [Plating Layer Formation Process] A Zn—Ni alloy plating layer was formed on a commercially available cold-rolled steel sheet under various conditions. A commercially available chloride bath for Zn—Ni alloy electroplating (Daiwa Kasei Co., Ltd., product name: Dyndine Alloy N2-PL) was used as the plating solution. Specifically, electroplating was performed under various plating conditions, with the metal components in the plating solution being as follows: total amount of metal ions: 0.500 to 0.900 mol / L, Ni ratio in the plating solution (nickel ion content (g / L) / total content of zinc ions and nickel ions (g / L)): 30.0 to 55.0%, and plating solution temperature: 35 to 50°C. Supporting salts and other additives were used within the standard conditions of the plating solution used. During electroplating, the plating solution was circulated by a pump. The circulation rate (flow rate of the plating solution) was varied in the linear velocity of the plating solution from 0.2 to 1.2 m / s. The current density was 4 to 8 A / dm ２ The thickness of the Zn—Ni alloy plating layer was 7 to 9 μm for all test numbers.

[0116] More specifically, the plating solution temperature T of Test No. 1 was 35°C, the plating solutions of Test Nos. 2 to 12 were 40°C, and the plating solution temperature T of Test Nos. 13 to 23 was 50°C. The total amount of metal ions in the plating solution of Test No. 1 was 0.600 mol / L, and the total amount of metal ions in the plating solutions of Test Nos. 2 to 23 was 0.891 mol / L. The Ni ratio in the plating solution of Test No. 1 was 49.4%, and the Ni ratio in the plating solutions of Test Nos. 2 to 23 was 35.7%.

[0117] The flow velocity FR of the plating solution in Test Nos. 2, 6, 10, 13, and 17 was 0.2 m / s, the flow velocity FR of the plating solution in Test Nos. 1, 3, 7, 14, 18, and 21 was 0.5 m / s, the flow velocity FR of the plating solution in Test Nos. 4, 8, 11, 15, 19, and 22 was 0.8 m / s, and the flow velocity FR of the plating solution in Test Nos. 5, 9, 12, 16, 20, and 23 was 2.2 m / s. The current density ASD in Test Nos. 2 to 5 and 13 to 16 was 4 A / dm ２ The current density ASD for test numbers 1, 6 to 9, and 17 to 20 was 6 A / dm ２ The current density ASD for test numbers 10 to 12 and 21 to 23 was 8 A / dm ２ was

[0118] The FnA calculated under the above conditions was 162 for test number 1, 276 for test number 2, 306 for test number 3, 336 for test number 4, 376 for test number 5, 184 for test number 6, 204 for test number 7, 224 for test number 8, 251 for test number 9, 138 for test number 10, 168 for test number 11, 188 for test number 12, 301 for test number 13, 331 for test number 14, 361 for test number 15, 401 for test number 16, 201 for test number 17, 221 for test number 18, 241 for test number 19, 267 for test number 20, 165 for test number 21, 180 for test number 22, and 200 for test number 23.

[0119] By the above method, a Zn—Ni alloy plating layer was formed on the cold-rolled steel sheet of each test number. A chemical composition measurement test, a precipitated phase identification test, a γ-phase crystallite size measurement test, and a Vickers hardness test were performed on the formed Zn—Ni alloy plating layer. For test numbers 1, 3, and 18, a seizure resistance evaluation test was also performed using the oil well pipes on which the corresponding Zn—Ni alloy plating layer was formed.

[0120] [Chemical Composition Measurement Test] A chemical composition measurement test was carried out on the Zn—Ni alloy plating layer of each test number. The cold-rolled steel sheet on which the Zn—Ni alloy plating layer was formed was immersed in 10% hydrochloric acid at 25°C for 1 to 3 minutes to dissolve the Zn—Ni alloy plating layer. The obtained solution was analyzed using a high-frequency inductively coupled plasma (ICP) emission spectrometer, ICPS-7510, manufactured by Shimadzu Corporation. The Ni content (mass%) in the Zn—Ni alloy plating layer of each test number is shown in Table 2 as "[Ni] (mass%)".

[0121] Furthermore, the right-hand side F1 of formula (1) (= 12.3 × [Ni] − 81.6) and the right-hand side F2 of formula (2) (= 40 × [Ni] − 145) were calculated from the Ni content [Ni] in the obtained Zn—Ni alloy plating layer. The obtained F1 and F2 are shown in Table 2. Note that, in order to make the analytical values ​​obtained by the ICP optical emission spectrometer compatible with those obtained by the X-ray fluorescence spectrometer, a calibration curve for the X-ray fluorescence spectrometer was prepared using a standard Zn—Ni alloy-plated steel sheet whose Ni content was determined by the above-mentioned method using the ICP optical emission spectrometer. By performing X-ray fluorescence analysis of the Ni content of the target material using this calibration curve, an analysis equivalent to that using the ICP optical emission spectrometer can be performed.

[0122]

[0123] [Precipitate Phase Identification Test] A precipitate phase identification test was carried out on the Zn—Ni alloy plating layer of each test number. X-ray diffraction measurement was carried out on the surface of the Zn—Ni alloy plating layer under the following measurement conditions. The phase was identified by comparing the obtained measured profile with the value recorded on the ASTM card. In all test numbers, the Zn—Ni alloy in the Zn—Ni alloy plating layer had a precipitate phase mainly composed of γ phase. - Apparatus: Rigaku Corporation RINT-2500 - X-ray tube: Co-Kα ray - Scan range: 2θ = 10 to 110° - Scan step: 0.02°

[0124] [γ-Phase Crystallite Diameter Measurement Test] A γ-phase crystallite diameter measurement test was conducted on the Zn—Ni alloy plating layer of each test number. X-ray diffraction measurement was conducted on four arbitrary locations on the surface of the Zn—Ni alloy plating layer. The conditions for the X-ray diffraction measurement were the same as those for the above-mentioned precipitate phase identification test. In the obtained measured profile, the crystallite diameter was calculated based on the above-mentioned Scherrer equation for the diffraction peak at 2θ = 49.0 to 52.0°. The arithmetic mean value of the measurement results at the four locations was taken as the γ-phase crystallite diameter D (nm) of the γ-phase of the Zn—Ni alloy plating layer. The γ-phase crystallite diameter D (nm) of the Zn—Ni alloy plating layer of each test number is shown in Table 2 as "D (nm)."

[0125] [Vickers Hardness Test] A Vickers hardness test was performed on the Zn—Ni alloy plating layer of each test number except for test numbers 2, 11, and 12. The cold-rolled steel sheet of each test number was cut perpendicular to the surface on which the Zn—Ni alloy plating layer was formed. Vickers hardness tests were performed on any five points on the cross section of the Zn—Ni alloy plating layer using a method in accordance with JIS Z2244 (2009). For the measurements, a Fischer Scope HM2000 microhardness tester manufactured by Fischer Instruments Inc. was used. The test temperature was room temperature (25°C), and the test force (F) was 0.01 N. The arithmetic mean value of three points, excluding the maximum and minimum values, out of the five measurement results obtained was taken as the Vickers hardness HV (Hv) of the Zn—Ni alloy plating layer. The Vickers hardness HV (Hv) obtained for each test number is shown in the "HV (Hv)" column of Table 2.

[0126] [Seizure Resistance Evaluation Test] A seizure resistance evaluation test was conducted using metal oil well pipes on which the corresponding Zn—Ni alloy plating layers were formed for test numbers 1, 3, and 18. Specifically, pins and boxes were used, each having an outer diameter of 177.8 mm, a wall thickness of 11.51 mm, and a steel type SM13CRS-110, and on which threaded joints (pin and box) VAM21 (registered trademark) were formed. Zn—Ni alloy plating layers corresponding to test numbers 1, 3, and 18 were formed on the pins and boxes.

[0127] The seizure resistance evaluation was performed using a repeated tightening and loosening test in accordance with ISO 13679 (2011). The pin and box were repeatedly tightened and loosened at room temperature (approximately 25°C) with a tightening torque of 25,460 N m. The pin contact surface and box contact surface were visually inspected after each tightening and loosening. If seizure was observed on the pin seal surface and / or box seal surface, the test was terminated. If seizure was observed on the male thread portion and / or female thread portion and the seizure was minor and could be repaired by maintenance such as filing, the seizure defects were repaired and the test was continued. The maximum number of tightening and loosening cycles was 10.

[0128] Under the above conditions, a repeated make-up and dismantling test was conducted, and this was the maximum number of make-ups possible without any irreversible seizure of the male thread portion and / or female thread portion, or seizure of the pin seal surface and / or box seal surface. As a result of the seizure resistance evaluation test, Test No. 1 was able to make up four times without seizure. Test Nos. 3 and 18 were able to make up ten times without seizure.

[0129] [Evaluation Results] Referring to Table 2, in test numbers 2 to 9 and 11 to 23, the crystallite diameter D of the γ phase was F1 or less. That is, the crystallite diameter D (nm) of the γ phase and the Ni content [Ni] (mass%) of the Zn—Ni alloy plating layer satisfied formula (1). As a result, in test numbers 3 to 9 and 13 to 23 in which Vickers hardness HV was measured, the Vickers hardness HV was F2 or more. That is, the Vickers hardness HV (Hv) of the Zn—Ni alloy plating layer and the Ni content [Ni] (mass%) of the Zn—Ni alloy plating layer satisfied formula (2).

[0130] On the other hand, in test numbers 1 and 10, the crystallite diameter D of the γ phase exceeded F1. That is, the crystallite diameter D (nm) of the γ phase and the Ni content [Ni] (mass%) of the Zn—Ni alloy plating layer did not satisfy formula (1). As a result, the Vickers hardness HV was less than F2. That is, the Vickers hardness HV (Hv) of the Zn—Ni alloy plating layer and the Ni content [Ni] (mass%) of the Zn—Ni alloy plating layer did not satisfy formula (2).

[0131] The embodiments of the present disclosure have been described above. However, the above-described embodiments are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments within the scope of the present disclosure.

[0132] REFERENCE SIGNS LIST 1 Metal pipe for oil well 10 Pipe body 10A First end 10B Second end 40 Pin 41 Male threaded portion 50 Box 51 Female threaded portion 100 Zn-Ni alloy plating layer 110 Chemical conversion coating layer 120 Lubricating coating 400 Pin contact surface 500 Box contact surface

Claims

1. A metal pipe for oil well use, comprising: a pipe body having a first end and a second end, the pipe body including: a pin formed at the first end; and a box formed at the second end, the pin including a pin contact surface including a male thread portion, and the box including a box contact surface including a female thread portion, the metal pipe for oil well use further comprising: a Zn-Ni alloy plating layer formed on at least one of the pin contact surface and the box contact surface, the Zn-Ni alloy plating layer consisting of 9.0 to 20.0 mass% Ni, with the remainder being Zn and impurities, the precipitated phase of the Zn-Ni alloy plating layer including a gamma phase, and the crystallite diameter D of the gamma phase and the Ni content [Ni] of the Zn-Ni alloy plating layer satisfy formula (1). D≦12.3×[Ni]−81.6 (1) Here, the crystallite diameter of the γ phase is substituted for D in formula (1) in the unit of nm, and the Ni content in the Zn—Ni alloy plating layer is substituted for [Ni] in formula (1) in the unit of mass %.

2. The metal oil well pipe according to claim 1, wherein the Vickers hardness HV of the Zn-Ni alloy plating layer and the Ni content [Ni] of the Zn-Ni alloy plating layer satisfy the following formula (2): HV≧40×[Ni]−145 (2) where the Vickers hardness of the Zn-Ni alloy plating layer in units of Hv is substituted for HV in formula (2), and the Ni content in the Zn-Ni alloy plating layer in units of mass% is substituted for [Ni] in formula (2).

3. A metal pipe for oil well use according to claim 1 or 2, comprising, as an upper layer on the Zn-Ni alloy plating layer, one or more layers selected from the group consisting of a chemical conversion coating layer and a lubricating coating.

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