Metal pipe for oil well

Abstract

Provided is a metal pipe for oil wells, which is provided with a Zn-Ni alloy plating layer having high hardness. This oil well metal pipe is provided with a pipe main body comprising a pin part and a box part, and is also provided with a Zn-Ni alloy plating layer formed on the pin part contact surface or the box part contact surface. The Ni content in the Zn-Ni alloy plating layer is 14.8-25.0% by mass, and the volume density of the Zn-Ni alloy plating layer is 7.00 g / cm3 or more.

Description

Technical Field

[0001] The present disclosure relates to a metal pipe, and more particularly to a metal pipe for oil wells. Background Art

[0002] In order to mine oil wells and gas wells (hereinafter, oil wells and gas wells are collectively referred to as "oil wells"), metal pipes for oil wells are used. Metal pipes for oil wells have threaded joints. Specifically, at the oil well mining site, a plurality of metal pipes for oil wells are connected according to the depth of the oil well to form an oil well pipe connection body represented by casing and oil pipe. The oil well pipe connection body is formed by screwing the metal pipes for oil wells together. In addition, there are cases where the oil well pipe connection body is inspected. In the case of an inspection, the oil well pipe connection body is pulled up and the threads are loosened. In addition, the oil well metal pipe is removed from the oil well pipe connection body by loosening the threads and inspected. After the inspection, the metal pipes for oil wells are screwed together again, and the metal pipes for oil wells are reused as part of the oil well pipe connection body.

[0003] An oil well metal pipe includes a pin and a box. The pin has a pin contact surface comprising an external thread on the outer circumferential surface of the end portion of the oil well metal pipe. The box has a box contact surface comprising an internal thread on the inner circumferential surface of the end portion of the oil well metal pipe opposite the pin. When the oil well metal pipes are screwed together, the pin contact surface and the box contact surface come into contact.

[0004] The pin and box contact surfaces are repeatedly subjected to strong friction during the tightening and loosening of oil well metal pipes. Consequently, these surfaces are susceptible to galling (irreparable wear) during repeated tightening and loosening. Consequently, oil well metal pipes are required to exhibit sufficient durability against friction, specifically, excellent wear resistance.

[0005] Conventionally, compound greases containing heavy metal powders, known as dopants, have been used to improve the wear resistance of oil-well metal pipes. Applying compound grease to the contact surfaces of the pin and / or box can improve the wear resistance of oil-well metal pipes. However, heavy metal powders such as lead, zinc, and copper contained in compound greases pose a potential environmental risk. Therefore, there is a desire to develop oil-well metal pipes that exhibit excellent wear resistance even without the use of compound greases.

[0006] In the oil well metal pipe disclosed in Patent Document 1 (International Publication No. 2016 / 170031), a Zn-Ni alloy plating is formed on the contact surface of the pin or box portion, instead of a composite grease. The Zn in the Zn-Ni alloy plating formed on the contact surface of the oil well metal pipe improves the corrosion resistance of the base material of the oil well metal pipe through sacrificial corrosion protection. Patent Document 1 also states that the Zn-Ni alloy exhibits excellent wear resistance.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: International Publication No. 2016 / 170031 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] As mentioned above, the Zn-Ni alloy coating improves the corrosion resistance of oil well metal pipes through the Zn. In addition, since the hardness of the Zn-Ni alloy coating itself is high, it is possible to obtain good wear resistance. Generally, the higher the hardness of the coating, the higher the wear resistance, and the higher the wear resistance. Therefore, in order to further improve the wear resistance of the oil well metal pipe during the tightening and loosening of the threads in the Zn-Ni alloy coating with excellent corrosion resistance, it is desirable to further improve the hardness. In particular, in large oil well metal pipes and oil well metal pipes formed from high alloys, wear sensitivity is high. Therefore, in order to obtain corrosion resistance and excellent wear resistance in these oil well metal pipes, it is desirable to further improve the hardness of the Zn-Ni alloy coating.

[0012] An object of the present disclosure is to provide an oil well metal pipe having a Zn—Ni alloy plating layer having relatively high hardness.

[0013] Solutions for solving problems

[0014] The oil well metal pipe disclosed herein includes a pipe body having a first end and a second end. The pipe body includes a pin portion formed at the first end and a box portion formed at the second end. The pin portion has a pin contact surface including an external thread portion, and the box portion has a box contact surface including an internal thread portion. The oil well metal pipe further includes a Zn-Ni alloy plating layer formed on the pin contact surface or the box contact surface and composed of a Zn-Ni alloy. The Ni content of the Zn-Ni alloy plating layer is 14.8 to 25.0% by mass, and the bulk density of the Zn-Ni alloy plating layer is 7.00 g / cm 3 above.

[0015] Effects of the Invention

[0016] The oil well metal pipe of the present embodiment includes a Zn—Ni alloy plating layer having relatively high hardness. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 This is a graph showing the relationship between the Ni content and Vickers hardness of conventional Zn—Ni alloy plating.

[0018] Figure 2 This is a graph showing the relationship between the Ni content and bulk density of conventional Zn—Ni alloy plating.

[0019] Figure 3 is Figure 2 A graph showing the relationship between the Ni content and the bulk density of the Zn—Ni alloy plating layer according to this embodiment is added to the graph of .

[0020] Figure 4 is Figure 1 A graph showing the relationship between the Ni content and the Vickers hardness of the Zn—Ni alloy plating layer according to the present embodiment is added to the graph of .

[0021] Figure 5 It is a side view of the oil well metal pipe according to this embodiment.

[0022] Figure 6 Yes Figure 5 The illustrated diagram is a partial cross-sectional view of a coupling for an oil well metal pipe, taken along the pipe axis (longitudinal section).

[0023] Figure 7 yes Figure 5 A cross-sectional view of a portion near a pin portion of the oil well metal pipe shown, parallel to the pipe axis direction of the oil well metal pipe.

[0024] Figure 8 yes Figure 5 A cross-sectional view of a portion near a box portion of the oil well metal pipe shown, parallel to the pipe axis direction of the oil well metal pipe.

[0025] Figure 9 Is to express Figure 6 A partial cross-sectional view of a longitudinal section of an oil well metal pipe according to the present embodiment having another different structure.

[0026] Figure 10 This is a partial cross-sectional view including a longitudinal section of the integral oil well metal pipe according to the present embodiment.

[0027] Figure 11 yes Figure 7 An enlarged view of the contact surface of the pin is shown.

[0028] Figure 12yes Figure 8 An enlarged view of the contact surface of the female buckle is shown.

[0029] Figure 13 is with Figure 11 Enlarged views of the contact surface of the pintle with different configurations.

[0030] Figure 14 is with Figure 12 Enlarged views of the contact surface of the box buckle with different structures. DETAILED DESCRIPTION

[0031] Hereinafter, the present embodiment will be described in detail with reference to the accompanying drawings. The same reference numerals are used for the same or corresponding parts in the figures, and their description will not be repeated. In addition, in the following description, "%" of the element content in the Zn-Ni plating layer refers to mass %.

[0032] The present inventors believed that if the Ni content in the Zn-Ni alloy plating layer is increased, the hardness of the Zn-Ni alloy plating layer will be further increased. Therefore, the present inventors first investigated the relationship between the Ni content of the Zn-Ni alloy plating layer formed on the contact surface (pin contact surface or box contact surface) of the oil well metal pipe using the conventional method and the hardness (Vickers hardness) of the Zn-Ni alloy plating layer, and found that Figure 1 .

[0033] Reference Figure 1 In conventional Zn-Ni alloy plating, the Vickers hardness increases with increasing Ni content until the Ni content reaches 14.8%. However, when the Ni content exceeds 14.8%, the Vickers hardness decreases with increasing Ni content.

[0034] Therefore, the present inventors investigated the reason why the hardness of the Zn-Ni alloy coating decreases when the Ni content is 14.8% or more. As a result, the following matters were clarified. When the Ni content in the Zn-Ni alloy coating is increased, many pores are formed in the Zn-Ni alloy coating. Therefore, the present inventors investigated the reason why the pores are formed relative to the Figure 1 The volume density of the Zn-Ni alloy coating was investigated as an indicator of the ratio of the coating to the Zn-Ni alloy. Figure 2 .

[0035] Reference Figure 2 The results of the investigation showed that in conventional Zn-Ni alloy coatings, the bulk density increased with increasing Ni content until the Ni content reached 14.8%. However, when the Ni content exceeded 14.8%, the bulk density decreased rapidly with increasing Ni content.

[0036] Based on the above research results, the present inventors believe that the Zn-Ni alloy coating, Ni content and bulk density have the following relationship. Increasing the Ni content in the Zn-Ni alloy coating helps to improve the hardness of the Zn-Ni alloy coating. However, if the Ni content becomes higher, the bulk density decreases rapidly. Figure 1 and Figure 2 In the case where the Ni content is 14.8% or more, the decrease in hardness associated with the decrease in bulk density is greater than the increase in hardness associated with the increase in Ni content. Therefore, when the Ni content is 14.8% or more, the Vickers hardness of the Zn-Ni alloy coating decreases as the Ni content increases ( Figure 1 ).

[0037] Based on the above insights, the present inventors believe that if the Ni content in the Zn-Ni alloy coating can be increased and the decrease in bulk density can be suppressed, the Vickers hardness of the Zn-Ni alloy coating can be further improved as the Ni content increases. Based on the above considerations, the following experiments were conducted and the following results were obtained: Figure 3 and Figure 4 .

[0038] Figure 3 is Figure 2 A graph showing the relationship between the Ni content and the bulk density of the Zn—Ni alloy plating layer according to this embodiment is added to the graph of . Figure 4 is Figure 1 A graph showing the relationship between the Ni content and the Vickers hardness of the Zn—Ni alloy plating layer according to the present embodiment is added to the graph of . Figure 3 and Figure 4 The "○" mark in the table corresponds to the present invention example in the embodiment described later. Figure 3 In the Zn-Ni alloy plating layer of this embodiment, even when the Ni content is set to 14.8% or more, the bulk density is 7.00 g / cm 3 In this case, if Figure 4 As shown in FIG. 2 , even when the Ni content is 14.8% or more, the Vickers hardness increases significantly as the Ni content increases.

[0039] As described above, the present inventors have found that in a Zn-Ni alloy plating layer, when the Ni content is 14.8% or more and the bulk density is 7.00 g / cm 3 Above, the hardness of the Zn-Ni alloy plating layer is significantly improved.

[0040] The oil well metal pipe of the present embodiment, which was completed based on the above findings, has the following configuration.

[0041] [1] A metal pipe for oil wells, comprising a pipe body including a first end and a second end, the pipe body comprising: a pin portion formed at the first end; and a box portion formed at the second end, the pin portion having a pin portion contact surface including an external thread portion, the box portion having a box portion contact surface including an internal thread portion, the metal pipe for oil wells further comprising a Zn-Ni alloy plating formed on the pin portion contact surface or the box portion contact surface and formed of a Zn-Ni alloy, the Ni content in the Zn-Ni alloy plating being 14.8 to 25.0% by mass, and the bulk density of the Zn-Ni alloy plating being 7.00 g / cm 3 above.

[0042] In the oil well metal pipe of this embodiment, the Ni content in the Zn-Ni alloy plating layer is 14.8 to 25.0% by mass, and the bulk density of the Zn-Ni alloy plating layer is 7.00 g / cm 3 The Zn-Ni alloy plating layer with such a structure has a significantly higher hardness. Therefore, it can suppress the occurrence of wear when tightening and loosening the thread. In addition, the Zn-Ni alloy plating layer contains Zn. Therefore, the corrosion resistance can be improved through sacrificial corrosion protection.

[0043] [2] The oil well metal pipe according to [1], wherein the Ni content in the Zn—Ni alloy plating layer is 17.0% or more in terms of mass %.

[0044] Hereinafter, the oil well metal pipe according to the present embodiment will be described in detail.

[0045] [Structure of Metal Pipes for Oil Wells]

[0046] First, the structure of the oil well metal pipe of this embodiment will be described. Oil well metal pipe has a well-known structure. There are two types of oil well metal pipe: T&C type and integral type. Each type of oil well metal pipe will be discussed in detail below.

[0047] [When the oil well metal pipe 1 is a T&C type]

[0048] Figure 5 It is a side view of the oil well metal pipe 1 according to the present embodiment. Figure 5 This is a side view of a so-called T&C type (Threaded and Coupled) oil well metal pipe 1. Figure 5 The oil well metal pipe 1 includes a pipe body 10 .

[0049] The pipe body 10 extends in the pipe axis direction. The cross section of the pipe body 10 perpendicular to the pipe axis direction is circular. The pipe body 10 includes a first end 10A and a second end 10B. The first end 10A is the end on the opposite side of the second end 10B. Figure 5 In the illustrated T&C type oil well metal pipe 1, 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 threads.

[0050] Figure 6 Yes Figure 5 The illustrated partial cross-sectional view of the coupling 12 of the oil well metal pipe 1 is a cross-sectional view parallel to the pipe axis direction (longitudinal cross-sectional view). Figure 5 and Figure 6 The pipe body 10 includes a pin 40 and a box 50. The pin 40 is formed at the first end 10A of the pipe body 10. During tightening, the pin 40 is inserted into the box 50 of another oil well metal pipe 1 (not shown) and screwed to the box 50 of the other oil well metal pipe 1.

[0051] The box portion 50 is formed at the second end portion 10B of the pipe body 10. During fastening, the pin portion 40 of another oil well metal pipe 1 is inserted into the box portion 50 and fastened to the pin portion 40 of the other oil well metal pipe 1 by screws.

[0052] [Regarding the structure of the male buckle portion 40]

[0053] Figure 7 yes Figure 5 The illustrated cross-sectional view is of a portion of the oil well metal pipe 1 near the pin portion 40 , parallel to the pipe axis direction of the oil well metal pipe 1 . Figure 7 The dotted line portion in FIG represents the structure of the box buckle portion 50 of the other oil well metal pipe 1 when fastened to the other oil well metal pipe 1. Figure 7 The pin 40 includes a pin contact surface 400 on the outer peripheral surface of the first end portion 10A of the pipe body 10. When the pin 40 is fastened to another oil well metal pipe 1, the pin 40 is screwed into the box 50 of the other oil well metal pipe 1, and the pin contact surface 400 contacts the box contact surface 500 (described later) of the box 50.

[0054] The pin contact surface 400 includes at least an external thread portion 41 formed on the outer peripheral surface of the first end portion 10A. Alternatively, the pin contact surface 400 may further include a pin sealing surface 42 and a pin shoulder surface 43. Figure 7In the embodiment, the pin shoulder surface 43 is arranged at the top end surface of the first end portion 10A, and the pin sealing surface 42 is arranged on the outer peripheral surface of the first end portion 10A, closer to the top end side of the first end portion 10A than the external thread portion 41. In other words, the pin sealing surface 42 is arranged between the external thread portion 41 and the pin shoulder surface 43. The pin sealing surface 42 is configured to be tapered. Specifically, in the pin sealing surface 42, the outer diameter of the pin 40 gradually decreases as it moves from the external thread portion 41 toward the pin shoulder surface 43 in the longitudinal direction (tube axis direction) of the first end portion 10A.

[0055] When tightening with other metal pipes 1 for oil wells, the pin buckle sealing surface 42 contacts the female buckle sealing surface 52 (described later) of the female buckle 50 of the other metal pipes 1 for oil wells. More specifically, when tightening, the pin buckle 40 is inserted into the female buckle 50 of the other metal pipes 1 for oil wells, so that the pin buckle sealing surface 42 contacts the female buckle sealing surface 52. Then, by further screwing the pin buckle 40 into the female buckle 50 of the other metal pipes 1 for oil wells, the pin buckle sealing surface 42 and the female buckle sealing surface 52 are in close contact. Thus, when tightening, the pin buckle sealing surface 42 and the female buckle sealing surface 52 are in close contact to form a seal based on metal-metal contact. Therefore, in the metal pipes 1 for oil wells that are tightened to each other, the airtightness can be improved.

[0056] exist Figure 7 In the embodiment, the male buckle shoulder surface 43 is arranged on the top surface of the first end portion 10A. Figure 7 In the illustrated pin 40, an external threaded portion 41, a pin sealing surface 42, and a pin shoulder surface 43 are arranged in order from the center of the pipe body 10 toward the first end portion 10A. When tightening to another oil well metal pipe 1, the pin shoulder surface 43 faces and contacts the female shoulder surface 53 (described later) of the female portion 50 of the other oil well metal pipe 1. More specifically, during tightening, the pin 40 is inserted into the female portion 50 of the other oil well metal pipe 1, so that the pin shoulder surface 43 contacts the female shoulder surface 53. This allows for a higher torque to be obtained during tightening. In addition, the positional relationship between the pin 40 and the female portion 50 in the tightened state can be stabilized.

[0057] Furthermore, the pin contact surface 400 of the pin 40 includes at least the external threaded portion 41. In other words, the pin contact surface 400 may include the external threaded portion 41, but not the pin sealing surface 42 or the pin shoulder surface 43. Alternatively, the pin contact surface 400 may include the external threaded portion 41 and the pin shoulder surface 43, but not the pin sealing surface 42. Alternatively, the pin contact surface 400 may include the external threaded portion 41 and the pin sealing surface 42, but not the pin shoulder surface 43.

[0058] [Regarding the Structure of the Female Buckle 50]

[0059] Figure 8 yes Figure 5 The cross-sectional view of the oil well metal pipe 1 is parallel to the pipe axis direction of the oil well metal pipe 1 and is of a portion near the box portion 50 . Figure 8 The dotted line portion in FIG represents the structure of the male buckle portion 40 of the other oil well metal pipe 1 when fastened to the other oil well metal pipe 1. Figure 8 The box portion 50 includes a box contact surface 500 on the inner circumferential surface of the second end portion 10B of the pipe body 10. The box contact surface 500 is screwed into the pin 40 of another oil well metal pipe 1 when fastened to the box 50 and contacts the pin contact surface 400 of the pin 40.

[0060] The box contact surface 500 includes at least an internal thread portion 51 formed on the inner peripheral surface of the second end portion 10B. During fastening, the internal thread portion 51 meshes with the external thread portion 41 of the pin portion 40 of another oil well metal pipe.

[0061] Alternatively, the female buckle contact surface 500 further includes a female buckle sealing surface 52 and a female buckle shoulder surface 53. Figure 8 In the embodiment, the box portion sealing surface 52 is located on the inner circumferential surface of the second end portion 10B, closer to the pipe body 10 than the internal thread portion 51. Specifically, the box portion sealing surface 52 is located between the internal thread portion 51 and the box portion shoulder surface 53. The box portion sealing surface 52 is tapered. Specifically, along the box portion sealing surface 52, the inner diameter of the box portion 50 gradually decreases from the internal thread portion 51 toward the box portion shoulder surface 53 in the longitudinal direction (pipe axis) of the second end portion 10B.

[0062] When tightening to another oil well metal pipe 1, the box buckle sealing surface 52 contacts the pin buckle sealing surface 42 of the pin buckle 40 of the other oil well metal pipe 1. More specifically, during tightening, the pin buckle 40 of the other oil well metal pipe 1 is screwed into the box buckle 50, causing the box buckle sealing surface 52 to contact the pin buckle sealing surface 42. Further screwing causes the box buckle sealing surface 52 to tightly fit the pin buckle sealing surface 42. Thus, during tightening, the box buckle sealing surface 52 and the pin buckle sealing surface 42 tightly fit together, forming a seal based on metal-to-metal contact. Therefore, in the mutually tightened oil well metal pipes 1, the airtightness can be improved.

[0063] The box shoulder surface 53 is positioned closer to the pipe body 10 than the box sealing surface 52. Specifically, in the box 50, the box shoulder surface 53, the box sealing surface 52, and the internal thread portion 51 are arranged in order from the center of the pipe body 10 toward the tip of the second end portion 10B. During tightening with 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, during tightening, the pin 40 of the other oil well metal pipe 1 is inserted into the box 50, causing the box shoulder surface 53 to contact the pin shoulder surface 43. This allows for a higher torque to be achieved during tightening. Furthermore, the positional relationship between the pin 40 and the box 50 in the tightened state can be stabilized.

[0064] The box contact surface 500 includes at least an internal threaded portion 51. During tightening, the internal threaded portion 51 of the box contact surface 500 of the box 50 corresponds to and contacts the external threaded portion 41 of the pin contact surface 400 of the pin 40. The box sealing surface 52 corresponds to and contacts the pin sealing surface 42. The box shoulder surface 53 corresponds to and contacts the pin shoulder surface 43.

[0065] Where the pin contact surface 400 includes the external threaded portion 41 but does not include the pin sealing surface 42 and the pin shoulder surface 43, the box contact surface 500 includes the internal threaded portion 51 but does not include the box sealing surface 52 and the box shoulder surface 53. Where the pin contact surface 400 includes the external threaded portion 41 and the pin shoulder surface 43 but does not include the pin sealing surface 42, the box contact surface 500 includes the internal threaded portion 51 and the box shoulder surface 53 but does not include the box sealing surface 52. Where the pin contact surface 400 includes the external threaded portion 41 and the pin sealing surface 42 but does not include the pin shoulder surface 43, the box contact surface 500 includes the internal threaded portion 51 and the box sealing surface 52 but does not include the box shoulder surface 53.

[0066] The pin contact surface 400 may include multiple external threaded portions 41, multiple pin sealing surfaces 42, or multiple pin shoulder surfaces 43. For example, the pin contact surface 400 of the pin 40 may be arranged, in order from the tip of the first end portion 10A toward the center of the pipe body 10, with the pin shoulder surface 43, the pin sealing surface 42, the external threaded portion 41, the pin sealing surface 42, the pin shoulder surface 43, the pin sealing surface 42, and the external threaded portion 41. In this case, the box contact surface 500 of the box 50 may be arranged, in order from the tip of the second end portion 10B toward the center of the pipe body 10, with the internal threaded portion 51, the box sealing surface 52, the box shoulder surface 53, the box sealing surface 52, the internal threaded portion 51, the box sealing surface 52, and the box shoulder surface 53.

[0067] exist Figure 7 and Figure 8 In the figure, a so-called advanced joint is shown in which the pin portion 40 includes an external thread portion 41, a pin sealing surface 42, and a pin shoulder surface 43, and the box portion 50 includes an internal thread portion 51, a box sealing surface 52, and a box shoulder surface 53. However, as described above, the pin portion 40 may include an external thread portion 41 but not include the pin sealing surface 42 and the pin shoulder surface 43. In this case, the box portion 50 includes an internal thread portion 51 but not include the box sealing surface 52 and the box shoulder surface 53. Figure 9 Is to express Figure 6 A partial cross-sectional view of a longitudinal section of a metal pipe for oil wells of this embodiment having a different structure. Figure 9 In the oil well metal pipe 1, the pin part 40 includes an external thread part 41, but does not include a pin part sealing surface 42 and a pin part shoulder surface 43. In addition, the box part 50 includes an internal thread part 51, but does not include a box part sealing surface 52 and a box part shoulder surface 53. The oil well metal pipe 1 of this embodiment may also have Figure 9 The structure shown.

[0068] [When the oil well metal pipe 1 is a one-piece type]

[0069] Figure 5 、 Figure 6 as well as Figure 9 The illustrated oil well metal pipe 1 is a so-called T&C type oil well metal pipe 1 in which the pipe body 10 includes a pin 11 and a coupling 12. However, the oil well metal pipe 1 of this embodiment may be an integral type rather than a T&C type.

[0070] Figure 10 This is a partial cross-sectional view including a longitudinal section of the integral oil well metal pipe 1 of this embodiment. Figure 10The integral oil well metal 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 side opposite to the second end 10B. As described above, in the T&C type oil well metal pipe 1, the pipe body 10 includes a pin 11 and a coupling 12. In other words, in the T&C type oil well metal pipe 1, the pipe body 10 is constructed by fastening two separate components (the pin 11 and the coupling 12). In contrast, in the integral oil well metal pipe 1, the pipe body 10 is formed integrally.

[0071] The pin 40 is formed at the first end 10A of the pipe body 10. During fastening, the pin 40 is inserted into and screwed into the box 50 of another integral oil-well metal pipe 1, thereby fastening the pin 40 to the box 50 of the other integral oil-well metal pipe 1. The box 50 is formed at the second end 10B of the pipe body 10. During fastening, the pin 40 of another integral oil-well metal pipe 1 is inserted into and screwed into the box 50, thereby fastening the pin 40 to the other integral oil-well metal pipe 1.

[0072] The structure of the male buckle portion 40 of the integral oil well metal pipe 1 is similar to Figure 7 The structure of the male buckle 40 of the T&C type oil well metal pipe 1 is the same as that of the female buckle 50 of the integral type oil well metal pipe 1. Figure 8 The structure of the box buckle portion 50 of the T&C type oil well metal pipe 1 shown is the same. Figure 7 and Figure 8 In the pin portion 40, the pin shoulder surface 43, the pin sealing surface 42, and the external threaded portion 41 are arranged in this order from the tip of the first end portion 10A toward the center of the pipe body 10. Accordingly, in the box portion 50, the internal threaded portion 51, the box sealing surface 52, and the box shoulder surface 53 are arranged in this order from the tip of the second end portion 10B toward the center of the pipe body 10. However, similar to the pin contact surface 400 of the pin portion 40 of the T&C type oil well metal pipe 1, the pin contact surface 400 of the pin portion 40 of the integral oil well metal pipe 1 only needs to include at least the external threaded portion 41. Furthermore, similar to the box contact surface 500 of the box portion 50 of the T&C type oil well metal pipe 1, the box contact surface 500 of the box portion 50 of the integral oil well metal pipe 1 only needs to include at least the internal threaded portion 51.

[0073] In short, the oil well metal pipe 1 of the present embodiment may be of the T&C type or of the integral type.

[0074] [About Zn-Ni alloy plating]

[0075] In the oil well metal pipe 1 of 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. In other words, 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. Furthermore, the Zn-Ni alloy plating layer may be formed on both the pin contact surface 400 and the box contact surface 500.

[0076] In the following description, the structure on the pin buckle contact surface 400 when a Zn-Ni alloy plating layer is formed on the pin buckle contact surface 400 and the structure on the box buckle contact surface 500 when a Zn-Ni alloy plating layer is formed on the box buckle contact surface 500 are described.

[0077] [Structure on Pin Contact Surface 400 When Zn—Ni Alloy Plating Layer 100 is Formed on Pin Contact Surface 400]

[0078] Figure 11 1 is a cross-sectional view of the pin contact surface 400 and its vicinity when the Zn-Ni alloy plating layer 100 is formed on the pin contact surface 400. Figure 11 The oil well metal pipe 1 further includes a Zn—Ni alloy plating layer 100 formed on the pin contact surface 400 of the pin 40 .

[0079] The Zn-Ni alloy plating layer 100 can be formed partially on the pin contact surface 400 or entirely on the pin contact surface 400. The surface pressure of the pin sealing surface is particularly high during the final stages of thread tightening. Therefore, when the Zn-Ni alloy plating layer 100 is formed partially on the pin contact surface 400, it is preferably formed at least on the pin sealing surface. Alternatively, the Zn-Ni alloy plating layer 100 can be formed entirely on the pin contact surface 400 as described above.

[0080] [Structure on the Box Part Contact Surface 500 When the Zn—Ni Alloy Plating Layer 100 is Formed on the Box Part Contact Surface 500]

[0081] Figure 12 1 is a cross-sectional view of the box buckle contact surface 500 and its vicinity when the Zn-Ni alloy plating layer 100 is formed on the box buckle contact surface 500. Figure 12A Zn-Ni alloy plating layer 100 is formed on the box contact surface 500. The Zn-Ni alloy plating layer 100 can be formed on a portion of the box contact surface 500 or on the entire box contact surface 500. The surface pressure of the box sealing surface is particularly high during the final stages of thread tightening. Therefore, when the Zn-Ni alloy plating layer 100 is formed partially on the box contact surface 500, it is preferably formed at least on the box sealing surface.

[0082] [About Zn-Ni alloy plating 100]

[0083] As described above, the Zn-Ni alloy plating layer 100 is formed on the contact surface of at least one of the pin buckle contact surface 400 and the box buckle contact surface 500. The Zn-Ni alloy plating layer 100 may also be formed in contact with the contact surface (the pin buckle contact surface 400 and / or the box buckle contact surface 500). That is, the Zn-Ni alloy plating layer 100 may also be formed directly on the contact surface (the pin buckle contact surface 400 and / or the box buckle contact surface 500). Furthermore, another plating layer may be formed between the Zn-Ni alloy plating layer 100 and the contact surface (the pin buckle contact surface 400 and / or the box buckle contact surface 500). For example, the other plating layer may be a Ni plating layer.

[0084] The Zn-Ni alloy coating 100 is formed of a Zn-Ni alloy. The Zn-Ni alloy contains zinc (Zn) and nickel (Ni). Preferably, the Zn-Ni alloy is composed of Zn and Ni, with the remainder being impurities. The impurities in the Zn-Ni alloy refer to substances other than Zn and Ni, and are substances contained in the Zn-Ni alloy coating 100 during the manufacturing process of oil well metal pipes, etc., and are contained in a range of amounts that do not affect the effects of the present embodiment.

[0085] The Zn-Ni alloy plating layer 100 contains Zn. Compared to Fe, Zn is a base metal. Therefore, the Zn-Ni alloy plating layer 100 corrodes preferentially over the steel material (sacrificial corrosion protection). This improves the corrosion resistance of the oil well metal pipe 1.

[0086] [Regarding the Ni Content and Volume Density of the Zn-Ni Alloy Plating Layer 100]

[0087] The Ni content of the Zn-Ni alloy plating layer 100 of the present embodiment is 14.8 to 25.0% by mass. Preferably, the chemical composition of the Zn-Ni alloy plating layer 100 contains 14.8 to 25.0% Ni by mass, with the remainder being Zn and impurities. Furthermore, the bulk density of the Zn-Ni alloy plating layer 100 of the present embodiment is 7.00 g / cm 3In the conventional Zn-Ni alloy coating, when the Ni content is increased to 14.8% or more, as shown in FIG. Figure 1 However, in the Zn-Ni alloy plating layer 100 of the present embodiment, the Ni content is as high as 14.8% or more, and the bulk density is 7.00 g / cm 3 As a result, Figure 4 As shown, the hardness of the Zn—Ni alloy plating layer 100 is significantly higher than that of the conventional Zn—Ni alloy plating layer.

[0088] If the Ni content in the Zn-Ni alloy plating layer 100 is too low, the hardness of the Zn-Ni alloy plating layer 100 will not become sufficiently high. On the other hand, if the Ni content in the Zn-Ni alloy plating layer 100 is too high, a large amount of hydrogen will be generated during the formation of the Zn-Ni alloy plating layer 100. In this case, there are many voids (pores) in the formed Zn-Ni alloy plating layer 100, and the volume density is excessively reduced. As a result, the hardness of the Zn-Ni alloy plating layer 100 cannot be fully obtained. Therefore, the Ni content in the Zn-Ni alloy plating layer 100 is 14.8% to 25.0%. The preferred lower limit of the Ni content in the Zn-Ni alloy plating layer 100 is 15.2%, more preferably 15.5%, more preferably 15.7%, more preferably 16.0%, more preferably 16.2%, more preferably 16.5%, more preferably 17.0%, and more preferably 17.5%. The upper limit of the Ni content is preferably 24.5%, more preferably 24.0%, and even more preferably 23.5%.

[0089] If the bulk density of the Zn-Ni alloy plating layer 100 is too low, many pores will exist in the Zn-Ni alloy plating layer 100. In this case, the hardness of the Zn-Ni alloy plating layer 100 cannot be fully obtained. 3 As mentioned above, sufficient hardness can be obtained in the Zn-Ni alloy plating layer 100 under the premise that the Ni content is 14.8 to 25.0%. Therefore, the bulk density of the Zn-Ni alloy plating layer 100 is 7.00 g / cm 3 The preferred lower limit of the bulk density in the Zn-Ni alloy plating layer 100 is 7.30 g / cm 3 , more preferably 7.50g / cm 3 , more preferably 7.60g / cm 3 , more preferably 7.70 g / cm 3 , more preferably 7.80%, more preferably 7.90 g / cm 3The upper limit of the bulk density is not particularly limited. However, when the Ni content of the Zn-Ni alloy plating layer 100 is 14.8 to 25.0%, the upper limit of the bulk density is, for example, 10.00 g / cm 3 .

[0090] [Method for measuring the chemical composition of the Zn-Ni alloy plating layer 100]

[0091] The chemical composition of the Zn-Ni alloy coating 100 is determined by the following method. A sample including the Zn-Ni alloy coating 100 (including the contact surface formed with the Zn-Ni alloy coating 100) is collected from the oil well metal pipe 1. The Zn-Ni alloy coating 100 of the collected sample is dissolved in 10% hydrochloric acid to obtain a solution. The solution is subjected to ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) to obtain the chemical composition of the Zn-Ni alloy coating 100. The Ni content (mass %) and Zn content (mass %) in the Zn-Ni alloy coating 100 are determined by the above method.

[0092] [Method for measuring the volume density of the Zn-Ni alloy plating layer 100]

[0093] The volume density of the Zn-Ni alloy coating 100 is determined by the following method. The Zn-Ni alloy coating 100 of the above sample is dissolved in a predetermined volume of 10% concentration hydrochloric acid to obtain a solution. The solution is subjected to elemental analysis of the chemical composition based on ICP-AES to determine the total mass (g) of Ni and Zn in the solution. The total mass of Ni and Zn in the solution is divided by the surface area of ​​the sample (the surface area of ​​the surface on which the Zn-Ni alloy coating 100 is formed) to determine the adhesion amount (g / cm2) per unit area of ​​the Zn-Ni alloy coating 100. 2 ).

[0094] In addition, the thickness of the Zn-Ni alloy coating 100 is determined by the following method. Before measuring the chemical composition of the Zn-Ni alloy coating 100 of the above-mentioned sample, a sample with a cross section in the depth direction of the Zn-Ni alloy coating 100 as the observation surface is collected from the sample. The observation surface of the sample is observed using a scanning electron microscope with a reflected electron image (BSE) of 3000 times. In the observation of the reflected electron image (BSE) of the scanning electron microscope (SEM), the base material (steel pipe) and the Zn-Ni alloy coating 100 can be easily distinguished by contrast. On the observation surface, the thickness of the Zn-Ni alloy coating 100 is measured at any 5 locations. The arithmetic mean of the measured thicknesses is defined as the thickness (μm) of the Zn-Ni alloy. Based on the adhesion amount per unit area (g / cm 2 ) and the thickness (μm) of the Zn-Ni alloy plating layer 100, and calculate the volume density (g / cm 3 ).

[0095] [Thickness of Zn-Ni Alloy Plating Layer 100]

[0096] 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 wear resistance can be further improved. Even if the thickness of the Zn-Ni alloy plating layer 100 exceeds 20 μm, the above effect is saturated. 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.

[0097] As described above, in the oil well metal pipe 1 of this embodiment, the Ni content in the Zn-Ni alloy plating layer 100 is 14.8 to 25.0%, and the bulk density of the Zn-Ni alloy plating layer 100 is 7.00 g / cm 3 Therefore, if Figure 4 As shown, in this embodiment, the Vickers hardness of the Zn-Ni alloy coating 100 can be increased. The hardness of the coating is positively correlated with the wear resistance during thread tightening and loosening. That is, the higher the hardness of the coating, the higher the wear resistance during thread tightening and loosening. Therefore, the oil well metal pipe 1 of this embodiment has excellent wear resistance. Furthermore, the Zn-Ni alloy coating 100 suppresses corrosion of the steel material through sacrificial corrosion protection. Therefore, the oil well metal pipe 1 of this embodiment also has excellent corrosion resistance.

[0098] [Regarding Other Arbitrary Structures of the Oil Well Metal Pipe 1 of the Present Embodiment]

[0099] [About chromate coating]

[0100] The oil well metal pipe 1 of this embodiment may further include a chromate film 110 on the Zn-Ni alloy plating layer 100. Figure 13 In the case where the Zn-Ni alloy plating layer 100 is formed on the male buckle contact surface 400, the chromate film 110 may also be formed on the Zn-Ni alloy plating layer 100. Figure 14 In the case where the Zn—Ni alloy plating layer 100 is formed on the female buckle contact surface 500 , the chromate film 110 may also be formed on the Zn—Ni alloy plating layer 100 .

[0101] The metal pipe 1 for oil wells may be stored outdoors for a long period of time until it is actually used at an oil production site. When the metal pipe 1 for oil wells is exposed to the atmosphere outdoors for a long period of time, the chromate film 110 can improve the corrosion resistance of the pin contact surface 400 and can suppress rust (white rust) on the pin contact surface 400. The chromate film 110 is a coating of chromate containing trivalent chromium. Preferably, the chromate film 110 does not contain hexavalent chromium. The film thickness of the chromate film 110 is not particularly limited. The film thickness of the chromate film 110 is, for example, 10 to 200 nm. The preferred lower limit of the film thickness of the chromate film 110 is 20 nm, and more preferably 30 nm. The preferred upper limit of the film thickness of the chromate film 110 is 100 nm, and more preferably 90 nm.

[0102] [Lubricating coating]

[0103] Oil well metal pipe 1 may also include a lubricating coating on Zn-Ni alloy plating 100, chromate film 110, or on contact surfaces (pin contact surface 400 or box contact surface 500) not formed with Zn-Ni alloy plating 100. The lubricating coating further enhances the lubricity of oil well metal pipe 1.

[0104] The lubricating coating can be solid, semi-solid, or liquid. A commercially available lubricant can be used as the lubricating coating. The lubricating coating may contain, for example, lubricating particles and a binder. The lubricating coating may also contain solvents and other components as needed.

[0105] The lubricating particles are not particularly limited as long as they have lubricity. Examples of the lubricating particles include one or more selected from the group consisting of graphite, MoS2 (molybdenum disulfide), WS2 (tungsten disulfide), BN (boron nitride), PTFE (polytetrafluoroethylene), CFx (graphite fluoride), and CaCO3 (calcium carbonate).

[0106] The binder may be, for example, one or two selected from the group consisting of organic binders and inorganic binders. The organic binder may be, for example, one or two selected from the group consisting of thermosetting resins and thermoplastic resins. The thermosetting resin may be, for example, one or more selected from the group consisting of polyethylene resins, polyimide resins, and polyamide-imide resins. The inorganic binder may be, for example, one or two selected from the group consisting of alkoxysilanes and compounds containing siloxane bonds.

[0107] An example of a commercially available lubricant is SEAL-GUARD ECF (trade name) manufactured by JET-LUBE Co., Ltd. Other lubricating coatings include, for example, lubricating coatings containing rosin, metallic soap, wax, and lubricating powder.

[0108] [Regarding the Pipe Body 10 of the Oil Well Metal Pipe 1]

[0109] The chemical composition of the pipe body 10 of the oil well metal pipe 1 of this embodiment is not particularly limited. The pipe body 10 may be formed of, for example, carbon steel, stainless steel, or an alloy. Specifically, the oil well metal pipe 1 may be a steel pipe formed of an Fe-based alloy or an alloy pipe such as a Ni-based alloy pipe. Examples of the steel pipe include low alloy steel pipes, martensitic stainless steel pipes, and duplex stainless steel pipes.

[0110] [Method for Manufacturing Oil Well Metal Pipe 1]

[0111] The following describes a method for manufacturing the oil well metal pipe 1 of this embodiment. Furthermore, as long as the oil well metal pipe 1 of this embodiment has the above-described structure, the manufacturing method is not limited to the following method. However, the manufacturing method described below is a preferred example for manufacturing the oil well metal pipe 1 of this embodiment.

[0112] The method for manufacturing an oil well metal pipe 1 includes a preparation step (S1) of preparing a tube blank having a pin 40 or a box 50 formed thereon, and a Zn-Ni alloy plating step (S2). In this embodiment, in the Zn-Ni alloy plating step (S2), electroplating is performed using a chloride bath containing nickel ions and zinc ions at a specific concentration. This allows the pin contact surface 400 and / or the box contact surface 500 of the oil well metal pipe 1 to be formed with a Ni content of 14.8 to 25.0% by mass and a bulk density of 7.00 g / cm 3 The above Zn-Ni alloy plating layer 100. Hereinafter, each step of the method for manufacturing the oil well metal pipe according to the present embodiment will be described in detail.

[0113] [Preparation process (S1)]

[0114] First, a base pipe having a pin 40 or a box 50 formed thereon is prepared. In this specification, the "base pipe having a pin or a box formed thereon" refers to any of the pipe body 10 and the pin body 11 of a T&C type oil well metal pipe 1, and the pipe body 10 of a one-piece type oil well metal pipe 1.

[0115] The tube blank having the pin 40 or the box 50 formed therein is manufactured, for example, by the following method. Molten steel is used to manufacture a billet. Specifically, the molten steel is used to manufacture a cast billet (bloom or billet) by continuous casting. Alternatively, the molten steel can be used to manufacture an ingot by ingot casting. Alternatively, the bloom or ingot can be opened to manufacture steel sheets (billets) as needed. The billet (bloom or billet) is manufactured using the above steps. The prepared billet is hot-worked to manufacture a tube blank. The hot-working method can be either piercing and rolling based on the Mannesmann method or hot extrusion. The hot-worked tube blank is subjected to well-known quenching and well-known tempering to adjust the strength of the tube blank. The tube blank is manufactured using the above steps. Furthermore, when the oil well metal pipe is a T&C type, a tube blank for the coupling 12 is also prepared. The method for manufacturing the tube blank for the coupling 12 is the same as the method for manufacturing the tube blank described above.

[0116] When the oil well metal pipe 1 is a T&C type, the outer surfaces of both ends of the base pipe for the pin body 11 are threaded to form a pin 40 including a pin contact surface 400. The above steps prepare the base pipe (pin body 11) with the pin 40 formed thereon, in the case of a T&C type oil well metal pipe 1. Furthermore, when the oil well metal pipe is a T&C type, a coupling 12 may also be prepared in advance. Specifically, the inner surfaces of both ends of the base pipe for the coupling 12 are threaded to form a box 50 including a box contact surface 500. The above steps manufacture the coupling 12.

[0117] When the oil well metal pipe 1 is a one-piece type, the outer surface of the first end portion 10A of the mother pipe is threaded to form a pin portion 40 including a pin contact surface 400. Furthermore, the inner surface of the second end portion 10B of the mother pipe is threaded to form a box portion 50 including a box contact surface 500. Through the above steps, the mother pipe (pipe body 10) having the pin portion 40 and the box portion 50 formed thereon is prepared when the oil well metal pipe 1 is a one-piece type.

[0118] The preparation step ( S1 ) of the present embodiment may further include at least one of a grinding step and a Ni flash plating step.

[0119] When the grinding process is performed, sandblasting and mechanical grinding finishing are performed in the grinding process. The surface roughness of the contact surface can be increased by sandblasting. The sandblasting can be performed by a known method.

[0120] When a Ni flash plating process is performed, a Ni flash layer is formed on the surface of the tube. The Ni flash layer is a very thin base plating layer that improves the adhesion of the Zn-Ni alloy plating layer 100 described later. The plating bath used in the Ni flash plating process is not particularly limited, and well-known solutions can be used. Furthermore, the conditions for forming the Ni flash layer are not particularly limited and can be adjusted appropriately.

[0121] Furthermore, when the Ni flash plating process is performed, a Ni flash layer is formed between the pipe body 10 and the Zn-Ni alloy plating layer 100. However, the thickness of the formed Ni flash layer is negligibly thin compared to the thickness of the Zn-Ni alloy plating layer 100. That is, in the oil well metal pipe 1 of this embodiment, the Zn-Ni alloy plating layer 100 may include a Ni flash layer.

[0122] [Zn-Ni alloy plating layer forming step (S2)]

[0123] In the Zn—Ni alloy plating forming step ( S2 ), a Zn—Ni alloy plating layer 100 is formed by electroplating on the pin contact surface 400 of the tube blank having the pin 40 formed thereon or on the box contact surface 500 of the tube blank having the box 50 formed thereon.

[0124] In the Zn-Ni alloy plating layer forming step (S2), it is preferable to use a plating bath containing chloride ions (hereinafter referred to as a chloride bath) rather than a plating bath containing sulfuric acid (hereinafter referred to as a sulfuric acid bath). As shown in the examples described below, the Zn-Ni alloy plating layer 100 of this embodiment can be formed by electroplating using a chloride bath within a range that satisfies the conditions described below.

[0125] The plating bath is further adjusted to have a Ni ion ratio in the range of 50 to 70%. Here, the Ni ion ratio is defined by the following formula.

[0126] Ni ion ratio = Ni concentration in plating bath / (Ni concentration in plating bath + Zn concentration in plating bath) × 100

[0127] By using a plating bath containing chloride ions and having a Ni ion ratio adjusted to 50-70%, and adjusting the electroplating conditions within the range described below, it is possible to form a coating having a Ni content of 14.8-25.0% and a bulk density of 7.00 g / cm 3The above Zn-Ni alloy plating layer 100. In addition, the type and / or amount of the supporting electrolyte and / or various additives (brightening agent, etc.) also affect the obtained plating layer, and therefore should be appropriately selected.

[0128] The Ni ion ratio in the above-mentioned plating bath is lower than that of conventional Zn-Ni alloy plating baths. For example, the Ni ion ratio of DAIN ZIN ALLOY N-PL, a well-known Zn-Ni alloy plating bath manufactured by Yamato Chemical Industry Co., Ltd., is 75-90%. The Ni ion ratio of the above-mentioned plating bath is even lower. In this embodiment, as described above, the Zn-Ni alloy plating layer 100 having the above-mentioned structure is formed by using a plating bath having a low Ni ion ratio and being a chloride bath. Furthermore, the chloride ion concentration of the plating bath is set to 215-230 g / L.

[0129] The Zn-Ni alloy plating layer 100 is formed by electroplating using the above-mentioned plating bath. Assuming the use of the above-mentioned plating bath, the electroplating conditions can be appropriately adjusted under known conditions. For example, the electroplating conditions include a plating bath pH greater than 4.5 and less than 6.0, a plating bath temperature of 10 to 60°C, and a current density of 1 to 15 A / dm 2 , and treatment time: 0.1 to 30 minutes. When the pH of the plating bath deviates from the above range, sufficient bulk density and sufficient Ni content cannot be obtained. In addition, if the current density is too high, sufficient bulk density cannot be obtained in the Zn-Ni alloy plating layer, and sufficient Ni content cannot be obtained. Within the range that satisfies the above conditions, the plating bath and electroplating conditions are adjusted to appropriately obtain the adhesion amount and composition of the Zn-Ni alloy plating layer 100. When forming the Zn-Ni alloy plating layer 100 on the male buckle contact surface 400, the male buckle contact surface 400 is immersed in the above plating bath and electroplating is performed. On the other hand, when forming the Zn-Ni alloy plating layer 100 on the female buckle contact surface 500, the female buckle contact surface 500 is immersed in the above plating bath and electroplating is performed.

[0130] Through the above-described manufacturing steps, the oil well metal pipe 1 of the present embodiment having the above-described structure is manufactured.

[0131] [Other optional steps]

[0132] The method for manufacturing oil well metal pipes of this embodiment may further include at least one of the following steps: a chromate treatment step, a base treatment step, and a film formation step. These steps are optional and may not be performed.

[0133] [Chromate treatment process]

[0134] The chromate treatment process is implemented as needed. That is, the chromate treatment process is an arbitrary process. When the chromate film 110 is formed on the Zn-Ni alloy plating 100, the Zn-Ni alloy plating 100 after the Zn-Ni alloy plating forming process (S2) is pickled and then a well-known chromate treatment process is implemented. In the chromate treatment process, a chromate treatment solution is first prepared. The chromate treatment solution contains, for example, trivalent chromium ions. Trivalent chromium ions can be contained, for example, by dissolving chromium (III) chloride and chromium (III) sulfate. Preferably, the chromate treatment solution does not contain hexavalent chromium. The chromate treatment solution can use a commercially available chromate treatment solution. An example of a commercially available chromate treatment solution is DAIN CHROMATE TR-02 (trade name) manufactured by Yamato Chemical Industry Co., Ltd. The contact surface (pin contact surface 400 and / or box contact surface 500 ) on which the Zn—Ni alloy plating layer 100 is formed is immersed in a chromate treatment solution to perform chromate treatment, thereby forming a chromate film 110 on the Zn—Ni alloy plating layer 100 .

[0135] [Substrate treatment process]

[0136] The manufacturing method of the present embodiment can be provided with a substrate treatment process before the Zn-Ni alloy coating forming process (S2) as needed. That is, the substrate treatment process is an arbitrary process. The substrate treatment process is, for example, pickling and alkali degreasing. In the substrate treatment process, the oil content attached to the contact surface is cleaned. The substrate treatment process can further be implemented by grinding processes such as sandblasting and / or mechanical grinding finishing. These substrate treatments can be implemented by only one or by combining multiple substrate treatments.

[0137] [Film forming process]

[0138] The manufacturing method of this embodiment can include a film-forming step as needed. In other words, the film-forming step is an optional step. During the film-forming step, a lubricating coating is formed on the Zn-Ni alloy plating layer 100 and / or on the contact surface (pin buckle contact surface 400 or box buckle contact surface 500) where the Zn-Ni alloy plating layer 100 is not formed.

[0139] In the film-forming step, a composition or lubricant containing the components of the lubricating film is applied. This forms the lubricating film. The application method is not particularly limited. Examples include spraying, brushing, and dipping. When spraying, the composition or lubricant may be heated to increase its fluidity before spraying. The composition or lubricant is then dried to form the lubricating film.

[0140] Example

[0141] The effects of the oil well metal pipe according to this embodiment will be further specifically described below using examples. The conditions in the following examples are examples of conditions employed to confirm the feasibility and effects of the oil well metal pipe according to this embodiment. Therefore, the oil well metal pipe according to this embodiment is not limited to these conditions.

[0142] In this example, a commercially available cold-rolled steel sheet was used to simulate oil well metal pipe. The cold-rolled steel sheet measures 150 mm long by 100 mm wide (the area where the Zn-Ni alloy coating is formed is 100 mm long by 100 mm wide). The steel is ultra-low carbon steel. The chemical composition of the cold-rolled steel sheet is C: 0.19%, Si: 0.25%, Mn: 0.8%, P: 0.02%, S: 0.01%, Cu: 0.04%, Ni: 0.1%, Cr: 13%, Mo: 0.04%, and the balance is Fe and impurities.

[0143] [Zn-Ni alloy plating layer forming process]

[0144] On the cold-rolled steel sheet of each test number, a Zn-Ni alloy coating was formed by electroplating. The details of the manufacturing conditions of the Zn-Ni alloy coating of each test number are as follows. In test numbers 1 to 7 in Table 1, a sulfuric acid bath was used as the plating bath. Specifically, the plating bath of test numbers 1 to 7 contained 0.5 mol / L of sodium sulfate. In addition, ammonium chloride was used as the supporting electrolyte of the plating bath, and no brightener and / or pH buffer (such as boric acid) was added. In addition, in each test number 1 to 7, the Ni ion ratio in the plating bath was changed.

[0145] [Table 1]

[0146] Table 1

[0147]

[0148] In Test Nos. 8 to 24 in Table 1, a chloride bath was used as the plating bath. Specifically, the plating baths of Test Nos. 8 to 24 contained a chloride ion concentration of 215 to 230 g / L. In each of Test Nos. 8 to 24, the Ni ion ratio in the plating bath was varied. Furthermore, in Test Nos. 18 to 24, the Ni ion ratio in the plating bath was varied within a range of 50 to 70%. In Test Nos. 8 to 17, the Ni ion ratio in the plating bath was varied within a range lower than that of Test Nos. 18 to 24 (i.e., the Ni ion ratio was less than 50%).

[0149] In addition, the pH of the sulfuric acid bath was adjusted to 2.0, and the pH of the chloride bath was adjusted to 5.5. The electroplating conditions other than the plating bath were as follows: plating temperature: 10-60°C, current density: 1-15A / dm 2 , and processing time: appropriately adjusted within the range of 0.1 to 30 minutes.

[0150] By the above-described manufacturing method, a steel plate having a Zn—Ni alloy plating layer formed thereon, simulating an oil well metal pipe, was manufactured.

[0151] [Evaluation test]

[0152] [Test for measuring the Ni content in Zn-Ni alloy plating]

[0153] The Ni content in the Zn-Ni alloy coating of each test number was determined by the following method. Samples containing the Zn-Ni alloy coating (including the surface on which the Zn-Ni alloy coating 100 is formed) were collected from the steel plates of each test number. The Zn-Ni alloy coating of the collected sample was dissolved in 10% hydrochloric acid to obtain a solution. ICP-AES was performed on the solution to perform elemental analysis of the chemical composition to determine the Ni content (mass %) in the Zn-Ni alloy coating. The determined Ni content is shown in the "Ni content (mass %)" column of Table 1.

[0154] [Method for measuring the bulk density of Zn-Ni alloy plating]

[0155] The volume density of the Zn-Ni alloy coating of each test number was determined by the following method. The Zn-Ni alloy coating of the above sample was dissolved in a predetermined volume of 10% hydrochloric acid to obtain a solution. The solution was subjected to elemental analysis of the chemical composition based on ICP-AES to determine the total mass (g) of Ni and Zn in the solution. The total mass of Ni and Zn in the solution was divided by the surface area of ​​the sample to determine the adhesion amount (g / cm2) per unit area of ​​the Zn-Ni alloy coating. 2 ). Furthermore, the thickness of the Zn-Ni alloy coating was determined by the following method. Before measuring the chemical composition of the Zn-Ni alloy coating of the above-mentioned sample, a sample with a cross section in the depth direction of the Zn-Ni alloy coating as the observation surface was collected from the sample. The observation surface of the sample was observed using a scanning electron microscope with a 3000-fold reflected electron image (BSE). On the observation surface, the thickness of the Zn-Ni alloy coating was measured at any 5 locations. The arithmetic mean of the measured thicknesses was defined as the thickness of the Zn-Ni alloy (μm). Based on the adhesion amount per unit area of ​​the Zn-Ni alloy coating (g / cm 2 ) and the thickness of the Zn-Ni alloy coating (μm), calculate the volume density of the Zn-Ni alloy coating (g / cm 3 The obtained bulk density is shown in the "bulk density (g / cm 3 )" column.

[0156] [Vickers hardness test of Zn-Ni alloy coating]

[0157] The Vickers hardness (HV) of the Zn-Ni alloy coating of each test number was determined by the following method. A sample having a cross section in the thickness direction of the Zn-Ni alloy coating was collected. Five arbitrary points (measurement points) of the cross section of the Zn-Ni alloy coating were selected. The Vickers hardness of the selected measurement points was measured in accordance with JIS Z2244 (2009). In the measurement, a micro hardness tester Fischer scope HM2000 manufactured by Fisher Instruments Co., Ltd. was used. The test temperature was set to room temperature (25°C) and the test force (F) was set to 0.01N. The arithmetic mean of the three points after excluding the maximum and minimum values ​​of the five measurement results was defined as the Vickers hardness (Hv) of the Zn-Ni alloy coating. The obtained Vickers hardness is shown in "Vickers hardness (Hv)" in Table 1.

[0158] [Test results]

[0159] Referring to Table 1, in test numbers 18 to 24, the Ni content of the Zn-Ni alloy plating layer was 14.8% or more in mass %, and the bulk density of the Zn-Ni alloy plating layer was 7.00 g / cm 3 Therefore, the Vickers hardness of the Zn-Ni alloy plating layer in these test numbers exceeded 435 Hv, and excellent hardness was obtained. Therefore, in these test numbers, it can be expected that the wear resistance during thread tightening and loosening is excellent.

[0160] On the other hand, in Test Nos. 1 to 7, a sulfuric acid bath was used as the plating bath. Therefore, in the Zn-Ni alloy plating layers of Test Nos. 1 to 7, the Ni content was less than 14.8%, or the bulk density was less than 7.00 g / cm 3 As a result, the Vickers hardness of the Zn-Ni alloy plating layers of these test numbers was 435 Hv or less.

[0161] Furthermore, in Tests 8 to 17, although a chloride bath was used as the plating bath, the Ni ion ratio was less than 50%. Therefore, the Ni content of the Zn-Ni alloy plating layers in these Tests was less than 14.8%, and the Vickers hardness was less than 435 Hv.

[0162] The above describes the embodiments of the present invention. However, the above embodiments are merely examples for implementing the present invention. Therefore, the present invention is not limited to the above embodiments and can be implemented by appropriately modifying the above embodiments without departing from the scope of the present invention.

[0163] Description of Reference Numerals

[0164] 1. Oil well metal pipe; 10. Pipe body; 10A, first end; 10B, second end; 40, pin; 41, external thread; 50, box; 51, internal thread; 100, Zn-Ni alloy plating; 400, pin contact surface; 500, box contact surface.

Claims

1. A metal pipe for oil wells, comprising a pipe body including a first end portion and a second end portion, The pipe body has: a male buckle portion formed at the first end portion; and a female buckle portion formed at the second end portion, The pin portion has a pin portion contact surface including an external threaded portion, The box portion has a box portion contact surface including an internal thread portion, The oil well metal pipe further includes a Zn-Ni alloy plating layer formed on the contact surface of the pin portion or the contact surface of the box portion and made of a Zn-Ni alloy. The Ni content in the Zn-Ni alloy plating layer is 14.8-25.0% by mass. The volume density of the Zn-Ni alloy coating is 7.00 g / cm 3 above.

2. The metal pipe for oil wells according to claim 1, wherein: In the Zn—Ni alloy plating layer, the Ni content is 17.0% or more in terms of mass %.

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