OA22063A - Metal Pipe For Oil Well. - Google Patents

Abstract

Provided is an oil-well metal pipe including a ZnNi alloy plating layer that has excellent galling resistance. An oil-well metal pipe (1) according to the present disclosure includes a pipe main body (10) including a first end po11ion (10A) and a second end portion (10B). The pipe main body (10) includes a pin (40) fom1ed at the first end portion (10A), and a box (50) fonned at the second end portion (10B). The pin (40) includes a pin contact surface (400) including an extemal thread part (41). The box (50) includes a box contact surface (500) including an internai thread part (51). The oil-well metal pipe (1) further includes a Ni plating layer (100) fonned on at least one of the pin contact surface (400) and the box contact surface (500), and a Zn-Ni allo y plating layer (110) fonned on the Ni plating layer (100). The deposition amount of the Ni plating layer (100) is 6.00 g/m2 or more.

Description

DESCRIPTION

TITLE OF INVENTION

METAL PIPE FOR OIL WELL

TECHNICAL FIELD

The présent disclosure relates to a métal pipe, and more particularly to an oil-well métal pipe.

BACKGROUND ART

Oil-well métal pipes are used in oil wells and gas wells (hereinafter, oil wells and gas wells are collectively referred to simply as oil wells). An oil-well métal pipe has a threaded connection. Specifically, at an oil-well drilling site, a plurality of oil-well métal pipes are connected to form an oil country tubular goods connected body, which is typified by a casing pipe and a tubing pipe, depending on the depth ofthe oil well. The oil country tubular goods connected body is formed by fastening oil-well métal pipes to each other. Moreover, the oil country tubular goods connected body may be subjected to inspection. When inspection is performed, the oil country tubular goods connected body is lifted up and loosened. Then, the oil-well métal pipes are detached from the oil country tubular goods connected body by loosening and are inspected. After the inspection, the oil-well métal pipes are refastened to each other again so that the oil-well métal pipes are reused as a part ofthe oil country tubular goods connected body.

An oil-well métal pipe includes a pin and a box. The pin has a pin contact surface, which includes an extemal thread part, on an outer peripheral surface of an end portion of the oil-well métal pipe. The box has a box contact surface, which includes an internai thread part, on an inner peripheral surface of an end portion of the oil-well métal pipe. In the présent description, the extemal thread part and the internai thread part are also collectively referred to as thread parts. In addition, in the présent description, the pin contact surface and the box contact surface are also collectively referred to as contact surface. Note that the pin contact surface may further include a pin unthread métal contact portion, which includes a pin sealing surface and a pin shoulder surface. Likewise, the box contact surface may further include a box unthread métal contact portion, which includes a box sealing surface and a box shoulder surface.

The pin contact surface and the box contact surface (contact surface) of the oil-well métal pipe repeatedly expérience strong friction during fastening and loosening. For that reason, in

-2the pin contact surface and the box contact surface, galling (unrepairable galling) is liable to occur when the fastening and loosening are repeated. Therefore, the oil-well métal pipe is requircd to hâve sufficient durability against friction, that is, to hâve excellent galling résistance.

In an oil-well métal pipe disclosed in Patent Literaturc 1 (International Application Publication No. 2016/170031 ), a Zn-Ni alloy plating layer is fonned on a pin contact surface or a box contact surface in place of a compound grease. The Zn containcd in the Zn-Ni alloy plating layer formcd on a contact surface of the oil-well métal pipe cnhanccs the corrosion résistance of the oil-well métal pipe by sacrificial protection. In addition, it is described in Patent Literature 1 that the Zn-Ni alloy is also excellent in a wear résistance characteristic.

CITATION LIST

PATENT LITERATURE

Patent Literature 1 : International Application Publication No. 2016/170031

Patent Literature 2: Japanese Patent Application Publication No. 2014-91244

Patent Literature 3: Japanese Patent Application Publication No. 2017-179510

SUMMARY OF INVENTION

TECHN1CAL PROBLEM

In this connection, in recent years there is a demand for an oil-well métal pipe which has more excellent galling résistance. In particular, in a large-sizcd oil-well métal pipe, because the circumference of the pipe main body is longer, sliding over a longer distance is necessary from the start of fastening until the completion of fastening. Consequently, in a large-sized oil-well métal pipe, there is a tendency for galling to occur more easily than in a conventional oil-well métal pipe. Thus, there has been a need for an oil-well métal pipe which has more excellent galling résistance than the conventional oil-well métal pipes.

It is an objective of the présent disclosure to provide an oil-well métal pipe including a Zn-Ni alloy plating layer which has excellent galling résistance.

SOLUTION TO PROBLEM

An oil-well métal pipe according to the présent disclosure includes:

a pipe main body including a First end portion and a second end portion, the pipe main body including:

a pin fonned at the fîrst end portion, and a box fonned at the second end portion;

- 3 wherein:

the pin includes a pin contact surface including an extemal thread part; and the box includes a box contact surface including an internai thread part;

the oil-well métal pipe further including:

a Ni plating layer formed on at least one ofthe pin contact surface and the box contact surface, and a Zn-Ni alloy plating layer formed on the Ni plating layer;

wherein:

a déposition amount ofthe Ni plating layer is 6.00 g/m² or more.

ADVANTAGEOUS EFFECT OF INVENTION

The oil-well métal pipe including a Zn-Ni alloy plating layer according to the présent disclosure has excellent galling résistance.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] FIG. 1 is a graph illustrating the relation between a déposition amount (g/m²) of a Ni plating layer and a sliding distance (mm) that is an index of galling résistance, in examples to be described later.

[FIG. 2] FIG. 2 is a configuration diagram illustrating one example of an oil-well métal pipe according to the présent embodiment.

[FIG. 3] FIG. 3 is a partial cross-sectional view to illustrate a cross section (longitudinal cross section) parallel to the pipe axial direction, of a coupling of the oil-well métal pipe illustrated in FIG. 2.

[FIG. 4] FIG. 4 is a cross-sectional view, which is parallel to the pipe axis direction of the oilwell métal pipe, of a portion in the vicinity of a pin of the oil-well métal pipe illustrated in FIG. 3.

[FIG. 5] FIG. 5 is a cross-sectional view, which is parallel to the pipe axis direction of the oilwell métal pipe, of a portion in the vicinity of a box of the oil-well métal pipe illustrated in FIG. 3.

[FIG. 6] FIG. 6 is a view illustrating one example of an oil-well métal pipe in which the pin includes an external thread part but does not include a pin sealing surface and a pin shoulder surface, and the box includes an internai thread part but does not include a box sealing surface and a box shoulder surface.

[FIG. 7] FIG. 7 is a configuration diagram illustrating an intégral type oil-well métal pipe

-4 according to the présent embodiment.

[FIG. 8] FIG. 8 is a cross-sectional view of the vicinity of a pin contact surface in a case where a Ni plating layer is formed on the pin contact surface.

[FIG. 9] FIG. 9 is a cross-sectional view of the vicinity of a box contact surface in a case where a Ni plating layer is formed on the box contact surface.

[FIG. 10] FIG. 10 is a cross-sectional view of the vicinity of the pin contact surface of a configuration different from that of FIG. 8.

[FIG. 11] FIG. 11 is a cross-sectional view of the vicinity of the box contact surface of a configuration different from that of FIG. 9.

DESCRIPTION OF EMBODIMENTS

Hereinafter, referring to the drawings, the présent embodiment will be described in detail. The like or corresponding parts are given like symbols throughout the drawings, and the description thereof will not be repeated.

A Zn-Ni alloy plating layer has excellent wear résistance because of the high hardness thereof. Further, in a case where a plating layer has excellent wear résistance, there is a tendency for excellent galling résistance to be obtained. Therefore, a Zn-Ni alloy plating layer has been applied in oil-well métal pipes in which galling résistance is required. On the other hand, as mentioned above, in a large-sized oil-well métal pipe which has a large diameter, the sliding distance during fastening and loosening is longer than in the case of conventîonal oil-well métal pipes. Therefore, even amongst oil-well métal pipes which hâve a Zn-Ni alloy plating layer, in the case of large-sized oil-well métal pipes, excellent galling résistance is not obtained in some cases. Therefore, the présent inventors investigated various techniques for increasing the galling résistance of an oil-well métal pipe which has a Zn-Ni alloy plating layer. As a resuit, the présent inventors obtained the following findings.

Because a Zn-Ni alloy plating layer has high hardness, the ductility of a Zn-Ni alloy plating layer is low compared to other plating layers, such as a Cu plating layer. Further, because oil-well métal pipes are used in hostile environments, in an oil-well métal pipe a Zn-Ni alloy plating layer is formed to hâve a thicker thickness than in the case of a plated Steel plate or the like. Therefore, the internai stress of a Zn-Ni alloy plating layer formed in an oil-well métal pipe is liable to be high. The présent inventors considered that, as a resuit, in an oil-well métal pipe the adhesiveness between the Zn-Ni alloy plating layer and the contact surface is liable to decrease, and the galling résistance is liable to decrease. That is, if the adhesiveness between the Zn-Ni alloy plating layer and the contact surface can be increascd, there is a possibility that

- 5 the galling résistance of the oil-well métal pipe will be enhanced.

Up to now, a métal strike plating layer has been used for the purpose of increasing adhesiveness between a Steel material and a plating layer. Patent Literature 2 (Japanese Patent Application Publication No. 2014-91244) discloses technology pertaining to a resin-coated métal plate for a container in which a métal strike plating layer is formed. Specifically, in Patent Literature 2 it is stated that Until now, métal strike plating has been carried out for the primary objective of improving adhesiveness between a base métal and a plating layer (paragraph of Patent Literature 2), and that As the type of métal strike plating, nickel plating or copper plating is suitable because these are already established as practical techniques (paragraph of Patent Literature 2). On the other hand, in Patent Literature 2 it is stated that if the déposition amount is less than 0.1 g/m², it will be difficult to form a uniform plating layer, and good plating adhesiveness cannot be obtained, and that since a métal strike plating layer is formed with a plating bath in which the cathodic précipitation efficiency is low, if the film thickness becomes more than 3.0 g/m², angular electro-deposits on the métal strike plating surface will coarsen (both of these statements appear in paragraph [0026] of Patent Literature 2). Patent Literature 2 States to the effect that for this reason the plating déposition amount of a métal strike plating layer is set in the range of 0.1 to 3.0 g/m².

Similarly, a technique that forms a Ni plating layer between a Steel material and a plating layer has been used to increase the adhesiveness between the Steel material and the plating layer. Patent Literature 3 (Japanese Patent Application Publication No. 2017-179510) discloses a technique that forms a Ni plating layer to increase the adhesiveness of a Cu plating layer. Specifically, in Patent Literature 3 it is stated that From the viewpoint of improving the adhesiveness between a stainless Steel plate and a Cu plating layer, the déposition amount of a Ni plating layer is preferably 0.4 g/m² or more, and also that From the viewpoint of improving the adhesiveness between the stainless Steel plate and the Cu plating layer, preferably the déposition amount is 4 g/m² or less (both of these statements appear in paragraph [0017] of Patent Literature 3). That is, Patent Literature 3 States to the effect that by forming a Ni plating layer between a Steel material and a Cu plating layer, the adhesiveness of the Cu plating layer to the Steel material is increased, however if the Ni plating layer is too thick, the adhesiveness of the Cu plating layer to the Steel material will, on the contrary, be reduced.

Referring to these disclosures of the prior art, there is a possibility that if a thin Ni plating layer is formed between a contact surface of an oil-well métal pipe and a Zn-Ni alloy plating layer, the adhesiveness of the Zn-Ni alloy plating layer will increase and the galling résistance of the oil-well métal pipe will be enhanced. Therefore, the présent inventors produced varions oil22063

-6well métal pipes having a Ni plating layer formed on a contact surface, and a Zn-Ni alloy plating layer formed on the Ni plating layer, and evaluated the galling résistance of the oil-well métal pipes. As a resuit, contrary to what was cxpccted based on the prior art, it has been revealed that if the déposition amount of the Ni plating layer is increased to 6.00 g/m² or more, the galling résistance of the oil-well métal pipe markedly increases. This point is described in detail hcreunder using the drawings.

FIG. 1 is a graph illustrating the relation between a déposition amount (g/m²) of a Ni plating layer and a sliding distance (mm) that is an index of galling résistance, in examples to be described later. FIG. I was created using déposition amounts (g/m²) of Ni plating layers fbrmed on Steel plates simulating a contact surface, and sliding distances (mm) in a slidability évaluation test in examples to be described later.

Referring to FIG. 1, it is shown that when the déposition amount of the Ni plating layer was less than 6.00 g/m², the sliding distance was almost the same level as in a case where a Ni plating layer was not fonned. That is, even when a thin Ni plating layer disclosed in the prior art was formed, there was no substantial change in the galling résistance of an oil-well métal pipe in which a Zn-Ni alloy plating layer was formed. On the other hand, when the déposition amount of the Ni plating layer was 6.00 g/m² or more, the sliding distance was significantly longer compared to the cases where a thin Ni plating layer was formed. That is, it has been revealed that when the thin Ni plating layer which has been used from the viewpoint of adhesiveness up to now is purposely formed to hâve a thick thickness, the galling résistance of the oil-well métal pipe is markedly enhanced.

Note that, the reason why the galling résistance of an oil-well métal pipe in which a Zn-Ni alloy plating layer is formed is enhanced by increasing the déposition amount of a Ni plating layer formed on a contact surface to 6.00 g/m² or more has not been clarified in detail. However, the présent inventors infer as follows. As described above, when a Zn-Ni alloy plating layer fbrmed in an oil-well métal pipe is thickly formed, the internai stress thereof is liable to become high. That is, in the oil-well métal pipe, the influence of internai stress of the formed Zn-Ni alloy plating layer is easily actualized. On the other hand, by thickly fonning a Ni plating layer, a distance can be created between the contact surface and the Zn-Ni alloy plating layer, and there is a possibility that the internai stress of the Zn-Ni alloy plating layer can be dispersed. Therefore, there is a possibility that the effect of dispersing the internai stress of the Zn-Ni alloy plating layer produced by the thick Ni plating layer surpasses the effect of a decrease in adhesiveness caused by fonning the thick Ni plating layer, and as a resuit the galling résistance of the oil-well métal pipe increases.

The présent inventors surmisc that, due to the above mechanism, the galling résistance of an oil-well métal pipe in which a Zn-Ni alloy plating layer is formed is enhanced by increasing the déposition amount of a Ni plating layer formed on a contact surface to 6.00 g/m² or more. Note that there is also a possibility that the galling résistance of an oil-well métal pipe in which a Zn-Ni alloy plating layer is formed is enhanced by increasing the déposition amount of a Ni plating layer formed on a contact surface to 6.00 g/m² or more because of a mechanism that is different to the mechanism described above. However, it has been proved by examples described below that the galling résistance of an oil-well métal pipe in which a Zn-Ni alloy plating layer is formed is enhanced by increasing the déposition amount of a Ni plating layer formed on a contact surface to 6.00 g/m² or more.

The gist of the oil-well métal pipe of the présent embodiment that has been completed based on the findings described so far is as follows.

[1]

An oil-well métal pipe including:

a pipe main body including a first end portion and a second end portion, the pipe main body including:

a pin formed at the first end portion; and a box formed at the second end portion, wherein:

the pin includes a pin contact surface including an extemal thread part; and the box includes a box contact surface including an internai thread part;

the oil-well métal pipe further including:

a Ni plating layer formed on at least one of the pin contact surface and the box contact surface, and a Zn-Ni alloy plating layer formed on the Ni plating layer;

wherein:

a déposition amount ofthe Ni plating layer is 6.00 g/m² or more.

[2]

The oil-well métal pipe according to [1], further including:

a lubricant coating layer on or above the Zn-Ni alloy plating layer.

Hereinafter, the oil-well métal pipe according to the présent embodiment will be described in detail.

[Structure of oil-well métal pipe]

- 8 First, the structure of an oil-wcll métal pipe of the présent embodiment will be described. The oil-well métal pipe has a well-known structure. The available types of oil-well métal pipe are a T&C type oil-well métal pipe and an intégral type oil-wcll métal pipe. Hereinaftcr, each type of oil-well métal pipe will be described in detail.

[When oil-well métal pipe 1 is T&C type]

FIG. 2 is a configuration diagram illustrating one example of an oil-wcll métal pipe 1 according to the présent embodiment. FIG. 2 is a configuration diagram of an oil-well métal pipe 1 of a so-called T&C (Threaded and Coupled) type. Referring to FIG. 2, the oil-well métal pipe 1 includes a pipe main body 10.

The pipe main body 10 extends in the pipe axis direction. A cross section perpendicular to the pipe axis direction of the pipe main body 10 is of a circular shape. The pipe main body 10 includes a first end portion Ι0Α and a second end portion 10B. The first end portion Ι0Α is an end portion on the opposite side to the second end portion 10B. In the T&C type oil-well métal pipe 1 shown in FIG. 2, the pipe main body 10 includes a pin tube body 11 and a coupling 12. The coupling 12 is attached to onc end of the pin tube body 11. More specifically, the coupling 12 is fastened by threading to the one end of the pin tube body 11.

FIG. 3 is a partial cross-sectional view to illustrate a cross section (longitudinal cross section) parallel to the pipe axis direction of the coupling 12 of the oil-well métal pipe 1 illustrated in FIG. 2. Referring to FIGS. 2 and 3, the pipe main body 10 includes a pin 40 and a box 50. The pin 40 is formed at the first end portion 10A of the pipe main body 10. At the time of fastening, the pin 40 is inserted into the box 50 of another oil-well métal pipe 1 (not shown) to be fastened by threading to the box 50 of the other oil-well métal pipe 1.

The box 50 is formed at the second end portion 10B of the pipe main body 10. At the time of fastening, a pin 40 of another oil-well métal pipe I is inserted into the box 50, and thus the box 50 is fastened by threading to the pin 40 of the other oil-well métal pipe 1.

[Structure of pin 40]

FIG. 4 is a cross-sectional view, which is parallel to a pipe axis direction of the oil-well métal pipe 1, of a portion in the vicinity of a pin 40 of the oil-well métal pipe 1 illustrated in FIG. 3. A dashed line portion in FIG. 4 represents the structure of the box 50 of another oil-wcll métal pipe 1 in the case of fastening to the other oil-well métal pipe 1. Referring to FIG. 4, the pin 40 includes a pin contact surface 400 on an outer peripheral surface of the first end portion 10A of the pipe main body 10. At the time of fastening to another oil-well métal pipe 1, the pin

- 9 contact surface 400 is screwed into the box 50 of the other oil-well métal pipe 1 to corne into contact with the box contact surface 500 (to be described later) of the box 50.

The pin contact surface 400 at least includes an extemal thread part 41 formed on the outer peripheral surface of the first end portion 10A. The pin contact surface 400 may further include a pin sealing surface 42 and a pin shoulder surface 43. In FIG. 4, the pin shoulder surface 43 is disposed at the front end face of the first end portion 10A, and the pin sealing surface 42 is disposed on the front end side of the first end portion 10A with respect to the extemal thread part 41 in the outer peripheral surface of the first end portion 10A. That is, the pin sealing surface 42 is disposed between the extemal thread part 41 and the pin shoulder surface 43. The pin sealing surface 42 is provided in a tapered shape. Specifically, in the pin sealing surface 42, the extemal diameter thereof gradually decreases from the extemal thread part 41 toward the pin shoulder surface 43 in the longitudinal direction (pipe axis direction) of the first end portion 10A.

At the time of fastening to another oil-well métal pipe 1, the pin sealing surface 42 cornes into contact with the box sealing surface 52 (to be described later) of the box 50 of the other oilwell métal pipe 1. More specifically, at the time of fastening, as a resuit of the pin 40 being inserted into the box 50 of another oil-well métal pipe 1, the pin sealing surface 42 cornes into contact with the box sealing surface 52. Then, as a resuit of the pin 40 being further screwed into the box 50 of another oil-well métal pipe 1, the pin sealing surface 42 cornes into close contact with the box sealing surface 52. As a resuit, at the time of fastening, the pin sealing surface 42 cornes into close contact with the box sealing surface 52, thus forming a seal bascd on metal-metal contact. For that reason, it is possible to improve gastîghtness in mutually fastened oil-well métal pipes 1.

In FIG. 4, the pin shoulder surface 43 is disposed at a front end face of the first end portion 10A, That is, in the pin 40 illustrated in FIG. 4, an extemal thread part 41, a pin sealing surface 42, and a pin shoulder surface 43 are disposed in that order from the center of the pipe main body 10 toward the first end portion 10A. At the time of fastening to another oil-well métal pipe 1, the pin shoulder surface 43 opposes and contacts the box shoulder surface 53 (to be described later) of the box 50 of another oil-well métal pipe 1. More specifically, at the time of fastening, as a resuit of the pin 40 being inserted into the box 50 of another oil-well métal pipe 1, the pin shoulder surface 43 cornes into contact with the box shoulder surface 53. As a resuit of this, at the time of fastening, it is possible to achieve a high torque. Moreover, it is possible to stabilize the positional relation between the pin 40 and the box 50 in a fastened State.

Note that the pin contact surface 400 of the pin 40 includes at least the extemal thread part 41. That is, the pin contact surface 400 includes the extemal thread part 41, and needs not include the pin sealing surface 42 and the pin shoulder surface 43. The pin contact surface 400 includes the extemal thread part 41 and the pin shoulder surface 43, and needs not include the pin sealing surface 42. The pin contact surface 400 includes the extemal thread part 41 and the pin sealing surface 42, and needs not include the pin shoulder surface 43.

[Structure ofbox 50]

FIG. 5 is a cross-sectional view, which is parallel to the pipe axis direction of the oil-well métal pipe 1, of a portion in the vicinity of a box 50 of the oil-well métal pipe 1 illustrated in FIG. 3. A dashed line portion in FIG. 5 represents the structure ofthe pin 40 of another oil-well métal pipe 1 in the case of fastening to the other oil-well métal pipe I. Referring to FIG. 5, the box 50 includes a box contact surface 500 on an inner peripheral surface ofthe second end portion 10B ofthe pipe main body 10. At the time of fastening to another oil-well métal pipe 1, the pin 40 of the other oil-well métal pipe 1 is screwed into the box contact surface 500, and the box contact surface 500 cornes into contact with the pin contact surface 400 ofthe pin 40.

The box contact surface 500 includes at least an internai thread part 51 formed in the inner peripheral surface of the second end portion 10B. At the time of fastening, the internai thread part 51 engages with the extemal thread part 41 ofthe pin 40 ofthe other oil-well métal pipe 1.

The box contact surface 500 may further include a box sealing surface 52 and a box shoulder surface 53. In FIG. 5, the box sealing surface 52 is disposed on the pipe main body 10 side with respect to the internai thread part 51, in the inner peripheral surface of the second end portion 10B. That is, the box sealing surface 52 is disposed between the internai thread part 51 and the box shoulder surface 53. The box sealing surface 52 is provided in a tapered shape. Specifically, the internai dîameter of the box sealing surface 52 gradually decreases from the internai thread part 51 toward the box shoulder surface 53 in the longitudinal direction (pipe axis direction) ofthe second end portion 10B.

At the time of fastening to another oil-well métal pipe 1, the box sealing surface 52 cornes into contact with the pin sealing surface 42 ofthe pin 40 of the other oil-well métal pipe 1. More specifically, at the time of fastening, as the resuit of the pin 40 of the other oil-well métal pipe 1 being screwed into the box 50, the box sealing surface 52 cornes into contact with the pin sealing surface 42, and as a resuit of the pin 40 being screwed in further, the box sealing surface 52 cornes into close contact with the pin sealing surface 42. As the resuit of this, at the time of fastening, the box sealing surface 52 cornes into close contact with the pin sealing surface 42,

-11thereby forming a seal based on metal-metal contact. Therefore, it is possible to improve the gastightness in the mutually fastencd oil-well métal pipes 1.

The box shoulder surface 53 is disposed on the pipe main body 10 side with respect to the box sealing surface 52. That is, in the box 50, the box shoulder surface 53, the box scaling surface 52 and the internai thread part 51 are disposed in that order from the center of the pipe main body 10 toward the front end of the second end portion 10B. At the time of fastening to another oil-well métal pipe 1, the box shoulder surface 53 opposes and contacts the pin shoulder surface 43 of the pin 40 of the other oil-well meta! pipe 1. More specifically, at the time of fastening, as a resuit of the pin 40 of the other oil-well métal pipe 1 being inserted into the box 50, the box shoulder surface 53 cornes into contact with the pin shoulder surface 43. As the resuit of this, at the time of fastening, it is possible to achieve a high torque. Further, it is possible to stabilize the positional relation between the pin 40 and the box 50 in a fastened State.

The box contact surface 500 includes at least the internai thread part 51. At the time of fastening, the internai thread part 51 of the box contact surface 500 of the box 50 corresponds to the extemal thread part 41 of the pin contact surface 400 of the pin 40, and cornes into contact with the extemal thread part 41. The box sealing surface 52 corresponds to the pin sealing surface 42, and cornes into contact with the pin sealing surface 42. The box shoulder surface 53 corresponds to the pin shoulder surface 43, and cornes into contact with the pin shoulder surface 43.

When the pin contact surface 400 includes the extemal thread part 41 and does not include the pin sealing surface 42 and the pin shoulder surface 43, the box contact surface 500 includes the internai thread part 51, and does not include the box sealing surface 52 and the box shoulder surface 53. When the pin contact surface 400 includes the extemal thread part 41 and the pin shoulder surface 43 and does not include the pin sealing surface 42, the box contact surface 500 includes the internai thread part 51 and the box shoulder surface 53, and does not include the box sealing surface 52. When the pin contact surface 400 includes the extemal thread part 41 and the pin sealing surface 42 and does not include the pin shoulder surface 43, the box contact surface 500 includes the internai thread part 51 and the box sealing surface 52, and does not include the box shoulder surface 53.

The pin contact surface 400 may include a plurality of the extemal thread parts 41, may include a plurality of the pin sealing surfaces 42, and may include a plurality of the pin shoulder surfaces 43. For example, on the pin contact surface 400 of the pin 40, the pin shoulder surface 43, the pin sealing surface 42, the external thread part 41, the pin sealing surface 42, the pin shoulder surface 43, the pin sealing surface 42 and the extemal thread part 41 may be disposed in

- 12 that order from the front end ofthe first end portion I OA toward the center ofthe pipe main body 10. In this case, on the box contact surface 500 ofthe box 50, the internai thread part 51, the box sealing surface 52, the box shoulder surface 53, the box sealing surface 52, the internai thread part 51, the box sealing surface 52 and the box shoulder surface 53 are disposed in that order trom the front end ofthe second end portion 10B toward the ccnter ofthe pipe main body 10.

FIGS. 4 and 5 illustrate a so-called premium joint in which a pin 40 includes an extemal thread part 41, a pin sealing surface 42, and a pin shoulder surface 43, and a box 50 includes an internai thread part 51, a box sealing surface 52, and a box shoulder surface 53. However, as described above, the pin 40 includes the extemal thread part 41 and needs not include the pin sealing surface 42 and the pin shoulder surface 43. In this case, the box 50 includes the internai thread part 51 and does not include the box sealing surface 52 and the box shoulder surface 53. FIG. 6 is a view illustrating one examplc of the oil-well métal pipe 1 in which the pin 40 includes the external thread part 41 and does not include the pin sealing surface 42 and the pin shoulder surface 43, and the box 50 includes the internai thread part 51 and does not include the box sealing surface 52 and the box shoulder surface 53.

[When oil-well métal pipe 1 is intégral type]

The oil-well métal pipe 1 illustrated in FIG. 2, FIG. 3 and FIG. 6 is a so-called T&C type oil-well métal pipe 1, in which the pipe main body 10 includes the pin tube body 11 and the coupling 12. However, the oil-well métal pipe 1 according to the présent embodiment may be of an intégral type instead of a T&C type.

FIG. 7 is a configuration diagram illustrating an intégral type oil-well métal pipe 1 according to the présent embodiment. Referring to FIG. 7, the intégral type oil-well métal pipe 1 includes a pipe main body 10. The pipe main body 10 includes a first end portion 10A and a second end portion 10B. The first end portion 10A is disposed on the opposite side to the second end portion 10B. As described above, in the T&C type oil-well métal pipe 1, the pipe main body 10 includes the pin tube body 11 and the coupling 12. That is, in the T&C type oilwell métal pipe 1, the pipe main body 10 is constituted by fastening two separate members (the pin tube body 11 and the coupling 12). In contrast, in the intégral type oil-well métal pipe 1, the pipe main body 10 is formed in an intégral manner.

The pin 40 is formed at the first end portion 10A of the pipe main body 10. At the time of fastening, the pin 40 is inserted in and screwed into the box 50 of another intégral type oilwell métal pipe 1, and thereby fastened to the box 50 of the other intégral type oil-well métal

- 13 pipe 1. The box 50 is fonned at the second end portion 10B of the pipe main body 10. At the time of fastening, the pin 40 of another intégral type oil-well métal pipe 1 is inserted in and screwed into the box 50, and thereby fastened to the pin 40 of the other intégral type oil-well métal pipe 1.

The structure of the pin 40 of the intégral type oil-well métal pipe 1 is the same as the structure of the pin 40 of the T&C type oil-well métal pipe 1 illustrated in FIG. 4. Similarly, the structure of the box 50 of the intégral type oil-well métal pipe 1 is the same as the structure of the box 50 of the T&C type oil-well métal pipe 1 illustrated in FIG. 5. Note that, in FIG. 4 and FIG. 5, the pin shoulder surface 43, the pin sealing surface 42 and the extemal thread part 41 are disposed in that order in the pin 40 from the front end of the first end portion 10A toward the center of the pipe main body 10. Therefore, the internai thread part 51, the box sealing surface 52 and the box shoulder surface 53 are disposed in that order in the box 50 from the front end of the second end portion 10B toward the center of the pipe main body 10. However, similarly to the pin contact surface 400 of the pin 40 of the T&C type oil-well métal pipe 1, it suffices that the pin contact surface 400 of the pin 40 of the intégral type oil-well métal pipe 1 includes at least the extemal thread part 41. Further, similarly to the box contact surface 500 of the box 50 of the T&C type oil-well métal pipe 1, it suffices that the box contact surface 500 of the box 50 of the intégral type oil-well métal pipe 1 includes at least the internai thread part 51.

In short, the oil-well métal pipe 1 of the présent embodiment may be of a T&C type or may be of an intégral type.

[Chemical composition of pipe main body]

The Chemical composition of the pipe main body 10 of the oil-well métal pipe 1 according to the présent embodiment is not particularly limited. That is, in the présent embodiment, the type of Steel of the pipe main body 10 of the oil-well métal pipe 1 is not particularly limited. The pipe main body 10 may be fonned of, for example, carbon Steel, stainless Steel, an alloy, or the like. That is, the oil-well métal pipe 1 may be a pipe made of a Fe-based alloy or an alloy pipe represented by a Ni-based alloy pipe. Here, examples of the pipe include a low-alloy pipe, a martensitic stainless Steel pipe, a ferritic stainless Steel pipe, an austenitic stainless Steel pipe and a duplex stainless Steel pipe. Examples of the alloy pipe include a Ni-based alloy pipe and a NiCrFe alloy pipe. Meanwhile, among alloy steels, Nibased alloys and high alloy steels such as duplex stainless steels that contain alloying éléments such as Cr, Ni and Mo hâve high corrosion résistance. Therefore using these high alloy steels as the pipe main body 10 will enable to obtain excellent corrosion résistance in a corrosive

- 14 environment that contains hydrogen sulfide or carbon dioxide or the like.

[Ni plating layer]

In the oil-well métal pipe 1 accordmg to the présent embodiment, a Ni plating layer is formed on at least one contact surface among the pin contact surface 400 and the box contact surface 500. That is, the Ni plating layer may be formed on the pin contact surface 400, and need not be formed on the box contact surface 500. Alternativeiy, the Ni plating layer may be formed on the box contact surface 500, and need not be formed on the pin contact surface 400. Further, the Ni plating layer may be formed on the pin contact surface 400 and on the box contact surface 500.

[Zn-Ni alloy plating layer]

In the oil-well métal pipe I according to the présent embodiment, a Zn-Ni alloy plating layer is formed on a Ni plating layer. That is, in a case where a Ni plating layer is formed on the pin contact surface 400, a Zn-Ni alloy plating layer is formed on the Ni plating layer that is formed on the pin contact surface 400. In this case, on the box contact surface 500, a Ni plating layer may be formed, a Zn-Ni alloy plating layer may be formed, or no plating layer need be formed. Further, in a case where a Ni plating layer is formed on the box contact surface 500, a Zn-Ni alloy plating layer is formed on the Ni plating layer that is formed on the box contact surface 500. In this case, on the pin contact surface 400, a Ni plating layer may be formed, a Zn-Ni alloy plating layer may be formed, or no plating layer need be formed. That is, in the présent embodiment, it suffices that a Ni plating layer is formed on at least either one of the pin contact surface 400 and the box contact surface 500, and a Zn-Ni alloy plating layer is formed on the Ni plating layer.

In the following description, the structure on the pin contact surface 400 in a case where the Ni plating layer is formed on the pin contact surface 400, and the structure on the box contact surface 500 in a case where the Ni plating layer is formed on the box contact surface 500 are described.

[Structure on pin contact surface in case where Ni plating layer is formed on pin contact surface]

FIG. 8 is a cross-sectional view ofthe vicinity of the pin contact surface 400 in a case where a Ni plating layer 100 is formed on the pin. contact surface 400. Referring to FIG. 8, the oil-well métal pipe 1 in this case further includes the Ni plating layer 100 formed on the pin contact surface 400 of the pin 40, and a Zn-Ni alloy plating layer 110 formed on the Ni plating

- 15 layer 100.

The Ni plating layer 100 and the Zn-Ni alloy plating layer 110 may be formed on one part of the pin contact surface 400 or may be formed on the entire pin contact surface 400. Note that in the final stage of fastening, the interfacial pressure increases, in particular, at the pin sealing surface 42. Therefore, in a case where the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 are partially formed on the pin contact surface 400, the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 are preferably formed on at least the pin sealing surface 42.

[Structure on box contact surface in case where Ni plating layer is formed on box contact surface]

FIG. 9 is a cross-sectional view of the vicinity of the box contact surface 500 in a case where a Ni plating layer 100 is formed on the box contact surface 500. Referring to FIG. 9, the oil-well métal pipe 1 in this case further includes a Ni plating layer 100 formed on the box contact surface 500 of the box 50, and a Zn-Ni alloy plating layer 110 formed on the Ni plating layer 100.

The Ni plating layer 100 and the Zn-Ni alloy plating layer 110 may be formed on one part of the box contact surface 500 or may be formed on the entire box contact surface 500. Note that in the final stage of fastening, the interfacial pressure increases, in particular, at the box sealing surface 52. Therefore, in a case where the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 are partially formed on the box contact surface 500, the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 are preferably formed on at least the box sealing surface 52.

[Déposition amounts of Ni plating layer and Zn-Ni alloy plating layer]

In the présent embodiment, the déposition amount of the Ni plating layer 100 is 6.00 g/m² or more. In a case where the déposition amount of the Ni plating layer 100 is 6.00 g/m² or more, the galling résistance of the oil-well métal pipe 1 markedly increases compared to a case where the déposition amount of the Ni plating layer 100 is less than 6.00 g/m². Therefore, in the oil-well métal pipe 1 according to the présent embodiment, the déposition amount of the Ni plating layer 100 formed on at least one of the pin contact surface 400 and the box contact surface 500 is set to 6.00 g/m² or more. As a resuit, the internai stress of the Zn-Ni alloy plating layer 110 formed on the Ni plating layer 100 is alleviated and the galling résistance of the oil-well métal pipe 1 increases.

In the présent embodiment, a préférable lower limit of the déposition amount of the Ni

- 16plating layer 100 Is 6.50 g/m², more preferably is 7.00 g/m³, further preferably is 8.00 g/m², further preferably is 9.00 g/m², further preferably is 9.30 g/m², and further preferably is 10.00 g/nr. Although an upper limit ofthe déposition amount ofthe Ni plating layer 100 is not particularly limited, for example the upper limit is 60.00 g/m².

In the présent embodiment, the déposition amount ofthe Zn-Ni alloy plating layer 110 is not particularly limited. However, in order to obtain excellent galling résistance, there is a tendency for the Zn-Ni alloy plating layer 110 formed on the oil-well métal pipe 1 to be formed comparatively thickly. Specifically, the déposition amount of the Zn-Ni alloy plating layer 110 according to the présent embodiment is for example, 20 to 160 g/m³. Whilst the Zn-Ni alloy plating layer 110 that is formed to a thickness of such a degree exhibits excellent wear résistance, on the other hand the internai stress thereof is liable to become high. Therefore, it is considered that by forming the Ni plating layer 100 having a déposition amount of 6.00 g/m² or more as an underlayer, the internai stress ofthe Zn-Ni alloy plating layer 110 is alleviated, and as a resuit the galling résistance of the oil-well métal pipe 1 increases.

The déposition amount of the Ni plating layer 100 and Zn-Ni alloy plating layer can be determincd using a film dissolution process. Specifically, a sample including the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 (including a contact surface on which the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 hâve been formed) is taken from the oilwell métal pipe 1. The areas ofthe Ni plating layer 100 and the Zn-Ni alloy plating layer 110 formed on the obtained sample are measured in advance. A dilute hydrochloric acid solution is used to dissolve the Zn-Ni alloy plating layer 110 of the obtained sample, to thereby obtain a liquid solution of the Zn-Ni alloy plating layer 110. Thereafter, a dilute nitric acid solution is used to dissolve the Ni plating layer 100 of the obtained sample from which the Zn-Ni alloy plating layer 110 had been removed by dissolving, to thereby obtain a liquid solution of the Ni plating layer 100.

Each of the obtained liquid solutions is subjected to elemental analysis by Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES). The déposition amount (g/m²) of the Ni plating layer 100 can be determined using the Ni content obtained as a resuit of the elemental analysis performed with respect to the Ni plating layer 100 and the area of the Ni plating layer 100 that had been formed on the sample. The déposition amount (g/m²) of the ZnNi alloy plating layer 110 can be determined using the Ni content and Zn content obtained as a resuit ofthe elemental analysis performed with respect to the Zn-Ni alloy plating layer 110 and the area of the Zn-Ni alloy plating layer 110 that had been formed on the sample.

- 17 [Chemical compositions of Ni plating layer and Zn-Ni alloy plating layer] The Ni plating layer 100 has a Chemical composition consisting of Ni and impurities.

The Zn-Ni alloy plating layer I 10 is constituted by a Zn-Ni alloy and has a Chemical composition consisting of Ni: 5 to 25%, and the balance: Zn and impurities. Here, the impurities in the Chemical composition of the Ni plating layer mean substances other than Ni that are contained in the Ni plating layer 100 due to the production process and the like of the oil-well métal pipe I, and whose contents are within a range that does not influence the effects of the oil-well métal pipe 1 according to the présent embodiment. In addition, the impurities in the chemical composition of the Zn-Ni alloy plating layer 110 mean substances other than Zn and Ni that are contained in the Zn-Ni alloy plating layer 110 due to the production process and the like of the oil-well métal pipe 1, and whose contents are within a range that does not influence the effects of the oil-well métal pipe 1 according to the présent embodiment.

Here, the Zn-Ni alloy plating layer 110 contains Zn. Zn is a base métal in comparison to Fe. Therefore, the Zn-Ni alloy plating layer 110 is corroded with priority relative to the Steel material (sacrificial protection). By this means, the corrosion résistance property of the oil-well métal pipe 1 is improved. Note that, when determining the déposition amounts by the aforementioned film dissolution process, the Chemical compositions of the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 can be identified at the same time.

[Other optional structures of oil-well métal pipe 1 of présent embodiment] [Chemical conversion treatment layer]

The oil-well métal pipe 1 of the présent embodiment may further include a Chemical conversion treatment layer on the Zn-Ni alloy plating layer 110. For example, in a case where the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 are formed on the pin contact surface 400, a Chemical conversion treatment layer may be formed on the Zn-Ni alloy plating layer 110. Further, in a case where the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 are formed on the box contact surface 500, a Chemical conversion treatment layer may be formed on the Zn-Ni alloy plating layer 110.

The Chemical conversion treatment layer is not particularly limited, and may be a wellknown chemical conversion treatment layer. The Chemical conversion treatment layer for example, may be an oxalate chemical conversion treatment layer, may be a phosphate chemical conversion treatment layer, may be a borate chemical conversion treatment layer, or may be a chromate coating. In a case where the chemical conversion treatment layer is a chromate coating, preferably the chromate coating does not contain hexavalent chromium.

- 18 In some cases the oil-well métal pipe 1 will be stored outdoors for a long period of time until actually being used at an oil drilling site. In a case where the oil-well métal pipe 1 is exposcd to the atmosphère for a long period of time outdoors, the Chemical conversion treatment layer cnhances the corrosion résistance ofthe pin contact surface 400, and can suppress the occurrence of rust (white rust) on the pin contact surface 400. The thickness ofthe Chemical conversion treatment layer is not particularly limited. The thickness of the Chemical conversion treatment layer is, for example, within the range of 10 to 200 nm.

[Lubricant coating layer]

The oil-well métal pipe 1 may further include a lubricant coating layer on the Zn-Ni alloy plating layer 110, on the Chemical conversion treatment layer, or on a contact surface on which the Zn-Ni alloy plating layer 110 is not formed (on the pin contact surface 400 or on the box contact surface 500). The lubricant coating layer further enhances the lubricity ofthe oil-well métal pipe 1. Referring to FIG. 10, in a case where the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 are fonned on the pin contact surface 400, a lubricant coating layer 120 may be formed on the Zn-Ni alloy plating layer 110. Further, referring to FIG. 11, in a case where the Ni plating layer 100 and the Zn-Ni alloy plating layer 110 are formed on the box contact surface 500, a lubricant coating layer 120 may be fonned on the Zn-NÎ alloy plating layer 110.

The lubricant coating layer 120 may be solid, or may be in a semi-solid State or a liquid State. The lubricant coating layer 120 can be fonned using a commercially available lubricant. The lubricant coating layer 120 contains, for example, lubricating particles and a binder. As necessary, the lubricant coating layer 120 may also contain a solvent and other components.

The lubricating particles are not particularly limited as long as they are particles having lubricity. The lubricating particles are, for example, one or more types selected from the group consisting of particles of graphite, M0S2 (molybdenum disulfide), WS2 (tungsten disulfïde), BN (boron nitride), PTFE (polytetrafluoroethylene), CFx (graphite fluoride), and CaCOi (calcium carbonate).

The binder, for example, is one or two types selected from the group consisting of an organic binder and an inorganic binder. The organic binder is, for example, one or two types selected from the group consisting of a thennosetting resin and a thermoplastic resin. The thermosetting resin, for example, is one or more types selected from the group consisting of polyethylene resin, polyimide resin and polyamide-imide resin. The inorganic binder, for example, is one or two types selected from the group consisting of compounds containing alkoxysilane and siloxane bonds.

- 19 The commercially available lubricant is, for example, Seal-Guard ECF (trade name) manutactured by Jet-Lube LLC. Other examples ofthe lubricant coating layer 120 include a lubricant coating layer 120 containing rosin, metallic soap, wax and a lubricant powder.

[Method for producing oil-well métal pipe 1]

A method for producing the oil-well métal pipe 1 according to the présent embodiment is described hereunder. Note that as long as the oil-well métal pipe 1 ofthe présent embodiment has the structure described above, a method for producing the oil-well métal pipe 1 is not limited to the following production method. However, the production method described hereunder is one favorable example for producing the oil-well métal pipe 1 according to the présent embodiment.

The method for producing the oil-well métal pipe 1 includes a préparation process (S 1 ) of preparing a hollow shell in which the pin 40 or the box 50 is formed, a Ni plating layer formation process (S2), and a Zn-Ni alloy plating layer formation process (S3). Hereunder, each process of the method for producing the oil-well métal pipe 1 of the présent embodiment is described in detail.

[Préparation process (SI)]

In the préparation process (S 1 ), a hollow shell in which the pin 40 or the box 50 is formed is prepared. In the présent description, the phrase hollow shell in which the pin or the box is formed means either of the pipe main body 10 and the pin tube body 11 in a T&C type oil-well métal pipe 1 and the pipe main body 10 in the integra! type oil-well métal pipe 1.

The hollow shell in which the pin 40 or the box 50 is formed is produced, for example, by the following method. A starting material is produced using molten steel. Specifically, a cast piece (a slab, bloom or billet) is produced by a continuous casting process using the molten steel. An ingot may also be produced by an ingot-making process using the molten steel. As necessary, the slab, bloom or ingot may be subjected to blooming to produce a billet. The starting material (a slab, bloom or billet) is produced by the above described process. The prepared starting material is subjected to hot working to produce a hollow shell. The hot working method may be piercing-rolling by means of the Mannesmann process, or may be a hotextrusion process. The hollow shell after hot working is subjected to well-known quenching and well-known tempering to adjust the strength of the hollow shell. A hollow shell is produced by the above process. Note that in a case where the oil-well métal pipe 1 is the T&C type, a hollow shell for the coupling 12 is also prepared. The method for producing the hollow

-20shcll for the coupling 12 is the same as the method for producing the hollow shell described above.

In a case where the oil-well métal pipe 1 is the T&C type, threading is performed with respect to the outer surface of both end portions of the hollow shell for the pin tube body 11, to form the pin 40 that includes the pin contact surface 400. By means of the above process, a hollow shell (the pin tube body 11 ) in which the pin 40 is formed is prepared for a case where the oil-well métal pipe 1 is the T&C type. Note that in a case where the oil-well métal pipe 1 is the T&C type, the coupling 12 may also be prepared. Specifically, threading is performed with respect to the inner surface of both end portions of the hollow shell for the coupling 12, to form the box 50 that includes the box contact surface 500. The coupling 12 is produced by the above process.

In a case where the oil-well métal pipe 1 is the intégral type, threading is performed on the outer surface of the first end portion 10A of the hollow shell to form the pin 40 that includes the pin contact surface 400. In addition, threading is performed with respect to the inner surface of the second end portion 10B of the hollow shell to form the box 50 that includes the box contact surface 500. By means of the above process, in a case where the oil-well métal pipe 1 is the intégral type, a hollow shell (pipe main body 10) in which the pin 40 and the box 50 are formed is prepared.

[Other optional process]

The préparation process (S 1 ) of the présent embodiment may further include a grinding process.

In the case of performing a grinding process in the préparation process (S 1 ) according to the présent embodiment, for example, sandblasting treatment, and finishing by machine grinding are performed in the grinding process. The sandblasting treatment is a treatment in which a blast material (abrasive) is mixed with compresscd air and the mixture is propelled onto the contact surface. Examples of the blast material include spherical shot material and angular grit material. The surface roughness of the contact surface can be increased by the sandblasting treatment. The sandblasting treatment can be carried out by a well-known method. For example, air is compressed by a compressor, and the blast material is mixed with the compressed air. The blast material may be composed of, for example, stainless Steel, aluminum, ceramic material, or alumina. The sandblasting treatment conditions such as the propelling speed are not particularly limited, and can be appropriately adjusted according to well-known conditions.

-21 [Ni plating layer formation process (S2)]

In the Ni plating layer formation process (S2), the Ni plating layer 100 is fonned by electroplating on the pin contact surface 400 of the hollow shell in which the pin 40 is fonned and/or on the box contact surface 500 of the hollow shell in which the box 50 is fonned, after the préparation process (SI).

In the Ni plating layer fonnation process (S2), the Ni plating layer 100 is fonned by electroplating using a plating bath containing nickel ions. The counter unions to the nickel ions are not particularly limited. For example, as counter anions to the nickel ions, chloride ions may be used, sulfate ions may be used, or sulfamatc ions may be used. That is, in the Ni plating layer fonnation process (S2) according to the présent embodiment, a chloride bath, a sulfate bath, or a sulfamic acid bath may be used as the plating bath.

Hereunder, specifically, a case of using a chloride bath as one example of the plating bath will be described. When using a chloride bath, for example, a chloride bath that contains nickel chloride: 240 g/L and hydrochloric acid: 125 mL/L can be used. Note that, as described above, in the Ni plating layer fonnation process (S2) according to the présent embodiment, the plating bath is not limited to a chloride bath, and another bath can also be used.

The conditions of the electroplating in the Ni plating layer fonnation process (S2) are not particularly limited, and well-known conditions can be appropriately adjusted. Specifically, as the electroplating conditions, conditions of a plating bath pH of 1 to 10, a plating bath température of 10 to 60°C, a current density of 1 to 100 A/dm², and a treatment time of 6.0 to 1800.0 secs can be adopted. Note that, as described above, the déposition amount of the Ni plating layer 100 according to the présent embodiment is 6.00 g/m² or more. When perfonning electroplating, the déposition amount ofthe Ni plating layer 100 can be adjusted by adjusting the current density and treatment time of the electroplating. That is, it suffîces to appropriately adjust the current density and treatment time of the electroplating in accordance with the type of plating bath that is used and conditions of the electroplating such as the température of the plating bath so as to adjust the déposition amount ofthe Ni plating layer 100 to 6.00 g/m² or more.

[Zn-Ni alloy plating layer formation process (S3)]

In the Zn-Ni alloy plating layer formation process (S3), after the Ni plating layer formation process (S2), the Zn-Ni alloy plating layer 110 is formed by electroplating on the Ni plating layer 100. Note that, as described above, the Zn-Ni alloy plating layer 110 may be formed on the pin contact surface 400 or on the box contact surface 500 on which the Ni plating

- 22 layer 100 is not formed.

In the Zn-Ni alloy plating layer formation process (S3), the Zn-Ni alloy plating layer 110 is formed by electroplating using a well-known plating bath containing zinc ions and nickel ions. For examplc, a plating bath containing zinc ions: I to 100 g/L and nickel ions: 1 to 100 g/L can be used. Further, the counter anions to the zinc ions and nickel ions are not particularly limited. For example, as counter anions, chloride ions may be used or sulfate ions may be used. That is, in the Zn-Ni alloy plating layer formation process (S3) according to the présent embodiment, a chloride bath or a sulfate bath may be used as the plating bath.

The conditions of the electroplating in the Zn-Ni alloy plating layer formation process (S3) are not particularly limited, and well-known conditions can be appropriately adjusted. The electroplating conditions are, for example, a plating bath pH of 1 to 10, a plating bath température of 10 to 60°C, a current density of 1 to 100 A/dm², and a treatment time of 0.1 to 30 minutes. In the case of fonning the Zn-Ni alloy plating layer 110 on the Ni plating layer 100 formed on the pin contact surface 400, the pin contact surface 400 is immersed in the aforementioned plating bath and electroplating is performed. Similarly, in the case of fonning the Zn-Ni alloy plating layer 110 on the Ni plating layer 100 fonned on the box contact surface 500, the box contact surface 500 is immersed in the aforementioned plating bath and electroplating is perfonned.

The oil-well métal pipe 1 of the présent embodiment having the structure described above is produced by the production processes described above. Note that the aforementioned production processes are one example of production processes for producing the oil-well métal pipe 1 according to the présent embodiment, and a method for producing the oil-well métal pipe 1 according to the présent embodiment is not limited to the production method described above.

[Other optional processes]

In the method for producing the oil-well métal pipe 1 according to the présent embodiment, at least one process among the following Chemical conversion treatment process and film formation process may also be performed. These processes are optional processes. Accordingly, these processes need not be performed.

[Chemical conversion treatment process]

In the production method of the présent embodiment, as necessary, a Chemical conversion treatment process may be performed. That is, the Chemical conversion treatment process is an optional process. In the case of performing a Chemical conversion treatment process, a

- 23 Chemical conversion treatment layer is formed on the Zn-Ni alloy plating layer 110. In the Chemical conversion treatment process, it suffices to perform a well-known Chemical conversion treatment. The Chemical conversion treatment, for example, may be an oxalate Chemical conversion treatment, may be a phosphate Chemical conversion treatment, or may be a borate Chemical conversion treatment. For example, in the case of performing a phosphate Chemical conversion treatment, a chcmical conversion treatment that uses zinc phosphate may be performed, a chcmical conversion treatment that uses manganèse phosphate may be performed, or a Chemical conversion treatment that uses calcium zinc phosphate may be performed.

Specifically, in the case of performing a zinc phosphate Chemical conversion treatment, as a treatment solution, for example, a Chemical conversion treatment solution containing 1 to 150 g/L of phosphate ions, 3 to 70 g/L of zinc ions, 1 to 100 g/L of nitrate ions, and 0 to 30 g/L of nickel ions can be used. In this case, the température of the Chemical conversion treatment solution is for example, 20 to 100°C. The chcmical conversion treatment layer can be formed by appropriately setting well-known conditions and performing a Chemical conversion treatment in this way.

[Film formation process]

In the production method of the présent embodiment, as necessary, a film formation process may be performed. That is, the film formation process is an optional process. In the film formation process, a lubricant coating layer 120 is formed on the Zn-Ni alloy plating layer 110 and/or on a contact surface (pin contact surface 400 or box contact surface 500) on which the Zn-Ni alloy plating layer 110 is not formed.

In the film formation process, a lubricant or a composition containing the components of the aforementioned lubricant coating is applied. In this way, the lubricant coating layer 120 can be formed. The application method is not particularly limited. Examples of the application method include spray coating, brushing, and immersion. When adopting spray coating as the application method, the composition or lubricant may be heated and then sprayed in a State in which the flowability has been increased. The composition or lubricant is then dried to form the lubricant coating layer 120.

The oil-well métal pipe 1 of the présent embodiment is described more specifically hereunder by way of examples. The conditions adopted in the following examples are one example of conditions which are employed for confirming the workability and advantageous effects of the oil-well métal pipe 1 of the présent embodiment. Accordingly, the oil-well métal pipe 1 of the présent embodiment is not limited to this one example of the conditions.

- 24 EXAMPLES

In the présent examples, a Ni plating layer and a Zn-Ni alloy plating layer were formed on steel plates simulating a contact surface, and the galling résistance of the respective Steel plates was evaluated. Specifically, the steel plates were cold rolled steel plates, and the Chemical composition was: C < 0,15%, Mn < 0.60%, P < 0.100%, S < 0.050%, and the balance: Fe and impurities.

As a preconditioning treatment, the Steel plate of each test number was subjected to electrolytic degreasing and immersion pickling, After the preconditioning treatment, a Ni plating layer was formed on the steel plate of each test number using a plating bath described in Table 1, and under conditions of a current densîty (A/dm²) and a treatment finie (secs) that are described in Table 1. Note that the Symbol in the Plating Bath column, Current Densîty column, and Treatment Time column in Table 1 means that a Ni plating layer was not formed.

[Table 1 ]

TABLE 1

Test Number	Plating Bath	C urrent Densîty (A/dm2)	Treatment Time (secs)	Ni Plating Layer Déposition Amount (g/m2)	Sliding Distance (mm)
1	-	-	-	0	6,384
2	A	5	30.0	0.17	6,710
3	A	6	180.0	3.85	6,937
4	A	5	180.0	4.24	7,741
5	A	10	180.0	6.87	10,355
6	A	15	180.0	9.39	13,371
7	B	4	75.0	8.68	9,877
8	B	4	230.0	14.53	14,376
9	B	4	380.0	42.37	13,220

Specifically, plating baths A and B were as described hereunder.

[Plating bath A]

A chloride bath was used as plating bath A. Plating bath A contained nickel chloride in an amount of 240 g/L, and contained hydrochloric acid in an amount of 125 mL/L. Note that the electroplating conditions in the case of using plating bath A were a plating bath pH of 1.5 or less, and a plating bath température of 25°C.

-25 [Plating bath B]

A sulfate bath was used as plating bath B. Plating bath B contained nickel sulfate in an amount of 240 to 300 g/L, nickel chloride in an amount of 40 to 70 g/L, and boric acid in an amount of 30 to 45 g/L. Note that the electroplating conditions in the case of using plating bath B were a plating bath pH of 3 to 4, and a plating bath température of 40 to 50°C.

Each Steel plate after formation of the Ni plating layer was subjected to a Zn-Ni alloy plating layer formation process. A weil-known plating bath that is commercially available was used as the plating bath for the Zn-Ni alloy plating layer formation process. The aforementioned préférable conditions were adoptcd as the other conditions of the Zn-Ni alloy plating layer formation process. A steel plate of each test number was produced by the production process described above.

The produced steel plate of each test number was subjected to measurement of the plating déposition amounts, and a galling résistance test.

[Plating déposition amount measurement]

The déposition amount of the Ni plating layer and the déposition amount of the Zn-Ni alloy plating layer of the steel plate of each test number were measured by the aforementioned film dissolution process. Specifically, a sample including the Ni plating layer and the Zn-Ni alloy plating layer was taken from the steel plate of each test number, and the Zn-Ni alloy plating layer and the Ni plating layer were dissolved using a dilute hydrochloric acid solution and a dilute nitric acid solution, respectively. Each of the obtained liquid solutions was subjected to elemental analysis by ICP-AES. The déposition amount (g/m²) of the Ni plating layer was determined using the obtained Ni content, and the area of the Ni plating layer that had been formed on the sample. The determined déposition amount of the Ni plating layer is shown in Table 1. Similarly, the déposition amount (g/m²) of the Zn-Ni alloy plating layer was determined using the obtained Ni content and Zn content, and the area of the Zn-Ni alloy plating layer that had been formed on the sample. In the présent examples, the déposition amount of the Zn-Ni alloy plating layer was 80 g/m² for each test number.

[Galling résistance test]

A lubricant coating layer was formed on the Zn-Ni alloy plating layer of the steel plate of each test number, and thereafter the steel plate of each test number was subjected to a galling résistance test. Specifically, a commercially available solid lubricant coating layer was formed on the Zn-Ni alloy plating layer of the steel plate of each test number. The thickness of the

- 26 formed solid lubricant coating layer was 30 μιη for each test number. The Steel plate of each test number was affixed onto a rotary disk, and the rotary disk was rotated under a sliding condition of a sliding speed of 31.4 mm/s w'hile a stcel bail remained pressed against the rotary disk with a force of 60 N (Hertz contact pressure: 1.25 GPa). The rotary disk was rotated with a reciprocating oscillation of 90 degrees. Note that, the sliding was performed without lubrication at room température. The coefficient of friction μ ofthe steel bail during sliding was measured, and the sliding distance (mm) until the coefficient of friction μ became more than 0.3 was determined. The determined sliding distances are shown in Table 1.

[Evaluation results]

Referring to Table 1, in the Steel plates of Test Numbers 5 to 9 the déposition amount of the Ni plating layer was 6.00 g/m² or more. As a resuit, the sliding distance in the galling résistance test was 9000 mm or more. That is, the Steel plates of Test Numbers 5 to 9 had excellent galling résistance.

On the other hand, in the steel plates of Test Numbers 1 to 4 the déposition amount of the Ni plating layer was less than 6.00 g/m². As a resuit, the sliding distance in the galling résistance test was less than 9000 mm. That is, the Steel plates of Test Numbers 1 to 4 did not hâve excellent galling résistance.

So far, the embodiments ofthe présent disclosure hâve been described. Howcver, the embodiments described above are merely examples for carrying out the présent disclosure. Therefore, the présent disclosure is not limited to the embodiments described above, and the embodiments described above can be appropriately modified and practiced within a range not departing from the spirit of the présent disclosure.

REFERENCE SIGNS LIST

Oil-well métal pipe

Pipe main body

10A First end portion

10B Second end portion

Pin

Extemal thread part

Box

Internai thread part

100 Ni plating layer

-27 110 Zn-Ni alloy plating layer

120 Lubricant coating layer 400 Pin contact surface 500 Box contact surface

Claims (2)

1. CLA1MS

   1. An oil-well métal pipe comprising:

   a pipe main body including a fîrst end portion and a second end portion, the pipe main body including:

   a pin fonned at the fîrst end portion; and a box fonned at the second end portion, wherein:

   the pin includes a pin contact surface including an extemal thread part; and the box includes a box contact surface including an internai thread part;

   the oil-well métal pipe further comprising:

   a Ni plating layer fonned on at least one of the pin contact surface and the box contact surface, and a Zn-Ni alloy plating layer fonned on the Ni plating layer;

   wherein:

   a déposition amount of the Ni plating layer is 6.00 g/m² or more.
2. 2,

   The oil-well métal pipe according to claim 1, further comprising: a lubricant coating layer on or above the Zn-Ni alloy plating layer.