[0001]
　TECHNICAL FIELD The present disclosure relates to an electroplating apparatus, and more particularly, to an electroplating apparatus for a steel pipe having threads on an inner peripheral surface or an outer peripheral surface of a pipe end portion.
BACKGROUND ART
[0002]
　In oil wells and natural gas wells, oil country tubular goods are used for mining underground resources. The oil country tubular is constituted by steel pipes connected in order. A threaded joint is used to connect steel pipes. The type of the threaded joint is roughly divided into a coupling type and an integral type.
[0003]
　In the case of the coupling type, a tubular coupling is used for connecting steel pipes. Female threads are provided on the inner peripheral surfaces of both ends of the coupling. Male threads are provided on the outer peripheral surfaces of both ends of the steel pipe. The male thread of the steel pipe is screwed into each of the internal threads of the coupling, whereby the steel pipes are connected to each other.
[0004]
　In the case of the integral type, in each steel pipe, a male screw is provided on the outer peripheral surface of one end portion and a female screw is provided on the inner peripheral surface of the other end portion. The male thread of one steel pipe is screwed into the female screw of the other steel pipe, whereby the steel pipes are connected to each other.
[0005]
　Conventionally, a lubricant is used for connecting steel pipes to each other. The lubricant is applied to at least one of the male thread and the female thread in order to prevent seizure of the joint portion. A lubricant (hereinafter referred to as "API dope") defined by the API (American Petroleum Institute) standard contains heavy metals such as lead (Pb).
[0006]
　In areas where strict environmental regulations have been imposed, the use of API dope is restricted. A lubricant not containing heavy metals (hereinafter referred to as green dope) is used in the area. The lubricity of the green dope is lower than the lubricity of the API dope. Therefore, when using green dope, it is desirable to form an electroplated layer on male screw and / or female screw to compensate for lack of lubricity. Japanese Patent Laid-Open No. 60-9893 discloses a local automatic plating apparatus for forming an electroplated layer on an external thread.
[0007]
　At the time of electroplating treatment, bubbles of hydrogen and oxygen are generated at the same time as the electroplating layer. When such air bubbles stay on the surface of the screw, a region where the electroplated layer is not formed (hereinafter referred to as "non-plating region") is generated on the surface of the screw, and the seizure resistance of the joint part decreases.
[0008]
　On the other hand, in Japanese Patent No. 5699253, an electroplating apparatus for forming a uniform electroplating layer without a non-plating region has been proposed. The electroplating apparatus includes a plurality of nozzles for spraying a copper plating solution. Each nozzle extends radially around the tube axis of the steel tube, and its tip is disposed between the female screw and the insoluble electrode. The jetting direction of the nozzle intersects the extending direction and is configured to be oriented in the same direction as the jetting direction of the other nozzle around the tube axis. Therefore, a spiral jet of the plating solution is generated between the female screw and the insoluble electrode, and minute bubbles generated by the electroplating process are detached from the screw bottom. As a result, occurrence of non-plating regions is suppressed.
Disclosure of invention
[0009]
　According to the electroplating apparatus of Japanese Patent No. 5699253, a copper plating layer which is a single metal plating layer can be formed on the surface of a screw without generating a non-plating region. However, when attempting to form an alloy plating layer (for example, a zinc-nickel alloy plating layer) on the surface of the screw using this electroplating apparatus, unevenness in appearance and microscopic appearance which did not occur in the case of forming a copper plating layer Plating defects such as plating peeling may occur.
[0010]
　The present disclosure aims to provide an electroplating apparatus capable of suppressing the occurrence of the plating defects described above when forming an alloy plating layer on the surface of a thread of a steel pipe.
[0011]
　The electroplating apparatus according to the present disclosure is used for a steel pipe having threads on an inner peripheral surface or an outer peripheral surface of a pipe end portion. The electroplating apparatus includes a first seal member, a second seal member, an electrode, and a plurality of nozzles. The first seal member is disposed in the steel pipe. The second seal member is attached to a pipe end portion of the steel pipe and forms a housing space for containing the plating solution together with the steel pipe and the first seal member. The electrode is disposed in the receiving space and faces the screw. The plurality of nozzles are arranged in the housing space around the tube axis of the steel pipe, and jet the plating solution between the screw and the electrode. The spray direction of the plating solution by each of the nozzles is inclined at an angle larger than 20 degrees and less than 90 degrees toward the screw side with respect to a plane orthogonal to the tube axis.
[0012]
　According to the present disclosure, when forming an alloy plating layer such as a zinc-nickel alloy plating layer on the surface of a screw, it is possible to suppress occurrence of plating defects such as appearance unevenness and minute plating peeling.
Brief Description of the Drawings
[0013]
[FIG. 1] FIG. 1 is a schematic diagram for explaining a state during electroplating.
FIG. 2 is a longitudinal sectional view showing a schematic configuration of an electroplating apparatus according to the first embodiment.
FIG. 3 is a front view schematically showing a plating solution supply unit of the electroplating apparatus shown in FIG. 1.
4 is a schematic view of the nozzle of the plating solution supply unit shown in FIG. 3 as viewed from the extending direction of the main body.
FIG. 5 is a longitudinal sectional view showing a schematic configuration of an electroplating apparatus according to a second embodiment.
6 is a front view schematically showing a plating solution supply unit of the electroplating apparatus shown in FIG. 5. FIG.
7 is a schematic view of the nozzle of the plating solution supply unit shown in FIG. 6 as viewed from the extending direction of the main body.
FIG. 8 is a graph showing the relationship between the composition (Ni content) and the color tone (L value) of the Zn - Ni alloy plating layer.
FIG. 9 is a comparative photograph of a steel pipe according to an example and a steel pipe according to a comparative example.
MODE FOR CARRYING OUT THE INVENTION
[0014]
　In general, when electroplating is applied to the surface of a thread of a steel pipe, in order to suppress disturbance of the liquid flow, it is said that it is preferable not to directly apply the plating solution to the surface of the screw. For example, in the electroplating apparatus disclosed in Japanese Patent No. 5699253, the tilt toward the screw side in the plating solution injection direction is made small so that the plating solution injected from the nozzle hardly hits the screw.
[0015]
　However, in the case of forming an alloy plating layer (for example, a zinc-nickel alloy plating layer) on the surface of the screw, plating defects such as uneven appearance and minute plating peeling are likely to occur when the inclination of the plating solution injection direction is too small . The present inventors presumed the reason why the plating defect occurs when forming the alloy plating layer as follows.
[0016]
　FIG. 1 is a schematic view for explaining a state during electroplating. As shown in FIG. 1, the material M and the adjacent diffusion layer D are generated in the plating solution L during the electroplating process. The diffusion layer D is a layer in which a plating solution body and a concentration gradient are generated due to mass transfer by diffusion. The moving speed of the substance in the diffusion layer D is not affected by the agitation of the plating solution L. Agitation of the plating solution L affects the thickness of the diffusion layer D.
[0017]
　The thickness of the diffusion layer D decreases as the plating solution L is strongly stirred. When the agitation of the plating solution L is weak, the thickness of the diffusion layer increases as indicated by reference symbol T1. When the stirring of the plating solution L is strong, the thickness of the diffusion layer becomes small as indicated by reference symbol T 2.
[0018]
　The thickness of the diffusion layer D during the electroplating process is not microscopically uniform and has a fluctuation of about 10% of the average thickness in the stationary state. That is, as the thickness of the diffusion layer D increases, the fluctuation also increases. In the example shown in FIG. 1, the fluctuation of the thickness of the diffusion layer D is larger than the case where the average thickness in the stationary state is T 2 when the average thickness in the stationary state is T 1.
[0019]
　The thickness fluctuation of the diffusion layer D affects the deposition rate of metal on the surface of the material M. That is, in the diffusion layer D, in a portion where the distance from the interface with the plating solution main body to the surface of the material M is short, the metal ion I + quickly reaches the surface of the material M and the surface of the material M from the interface with the plating solution main body , The metal ion I + reaches the surface of the material M at a later time. For this reason, the deposition rate of metal varies.
[0020]
　Such variations in the deposition rate of the metal do not pose a problem when forming a single metal plating layer. However, in the case of forming the alloy plating layer, due to variations in the deposition rate of the metal, for example, the amount of precipitated metal locally on the surface of the material M is increased, and thus the alloy plating layer formed on the surface of the material M The composition becomes nonuniform. As a result, the adhesion of the alloy plating layer to the surface of the material M decreases, so that plating peeling may occur or nonuniformity (unevenness) in appearance color tone may occur.
[0021]
　In order to make the composition of the alloy plating layer uniform, it is preferable to reduce the fluctuation of the thickness of the diffusion layer D. In order to reduce the fluctuation of the thickness of the diffusion layer D, it is necessary to reduce the thickness itself of the diffusion layer D.
[0022]
　Based on the above findings, the present inventors completed the electroplating apparatus according to the embodiment.
[0023]
　The electroplating apparatus according to the present disclosure is used for a steel pipe having threads on an inner peripheral surface or an outer peripheral surface of a pipe end portion. The electroplating apparatus includes a first seal member, a second seal member, an electrode, and a plurality of nozzles. The first seal member is disposed in the steel pipe. The second seal member is attached to a pipe end portion of the steel pipe, and forms a storage space for containing the plating solution together with the first seal member. The electrode is arranged in the receiving space and faces the screw. The plurality of nozzles are arranged in the housing space around the tube axis of the steel pipe, and jet the plating solution between the screw and the electrode. The spray direction of the plating solution by each of the nozzles is inclined at an angle larger than 20 degrees and less than 90 degrees toward the screw side with respect to a plane orthogonal to the tube axis.
[0024]
　The electroplating apparatus according to the embodiment is used for a steel pipe having threads on the inner peripheral surface or the outer peripheral surface of the pipe end portion. The electroplating apparatus includes a first seal member, a second seal member, an electrode, and a plurality of nozzles. The first seal member is disposed in the steel pipe. The second seal member is attached to a pipe end portion of the steel pipe, and forms a housing space together with the steel pipe and the first seal member for accommodating the plating solution. The electrode is disposed in the receiving space and faces the screw. The plurality of nozzles are accommodating spaces and are arranged around the tube axis of the steel pipe, and the plating solution is injected between the screw and the electrode. The spray direction of the plating solution by each of the nozzles is inclined at an angle larger than 20 degrees and less than 90 degrees toward the screw side with respect to a plane orthogonal to the tube axis.
[0025]
　In the electroplating apparatus, the spray direction of the nozzle is inclined toward the screw side at an angle larger than 20 degrees and less than 90 degrees. Therefore, during the electroplating process, the plating solution is sprayed towards the screw, causing strong stirring of the plating solution in the vicinity of the screw. For this reason, the thickness of the diffusion layer itself is reduced, and its fluctuation is also reduced. As a result, variation in the deposition rate of the metal is unlikely to occur, and the composition of the alloy plating layer formed on the surface of the screw becomes uniform. As a result, occurrence of plating defects such as uneven appearance and fine plating peeling can be suppressed.
[0026]
　In the above electroplating apparatus, the plurality of nozzles may be six or more nozzles.
[0027]
　Hereinafter, embodiments will be described in more detail with reference to the drawings. Identical and corresponding components in the figure are denoted by the same reference numerals, and the same description will not be repeated. For the sake of convenience of explanation, in each drawing, the configuration may be simplified or schematically shown, and a part of the configuration may be omitted.
[0028]
　First Embodiment
　Configuration of Electroplating Apparatus
　FIG. 2 is a longitudinal sectional view showing a schematic configuration of an electroplating apparatus 10 according to a first embodiment. The electroplating apparatus 10 is used for applying electroplating treatment to the steel pipe P 1. More specifically, the electroplating apparatus 10 forms an alloy plating layer on the surface of the external thread Tm formed on the outer peripheral surface of the pipe end of the steel pipe P1. The pipe end portion of such a steel pipe P1 is generally called a "pin".
[0029]
　As shown in FIG. 2, the electroplating apparatus 10 includes an electrode 1, a seal member 2, a container 3, and a plating solution supply unit 4.
[0030]
　The electrode 1 is a known insoluble anode used for electroplating treatment. As the electrode 1, for example, a titanium plate coated with iridium oxide, a stainless steel plate or the like formed into a desired shape can be used. The shape of the electrode 1 is not particularly limited, but is preferably cylindrical.
[0031]
　A current-carrying rod 9 is connected to the electrode 1. As the energizing rod 9, for example, a titanium rod, a stainless steel rod, or the like can be used. The number of the current-carrying rods 9 is not particularly limited, but is, for example, three.
[0032]
　The electrode 1 is arranged inside the container 3 on the outer peripheral side of the steel pipe P 1. When the electrode 1 has a cylindrical shape, the electrode 1 is arranged coaxially with the steel pipe P 1. The electrode 1 faces the male screw Tm of the steel pipe P 1. By supplying a plating solution between the electrode 1 and the male screw Tm and applying a potential difference between the electrode 1 and the steel pipe P1, a plating layer is formed on the surface of the external thread Tm.
[0033]
　The seal member 2 is disposed at the end of the steel pipe P 1 and seals the steel pipe P 1. In the present embodiment, the seal member 2 is attached to the pipe end in the steel pipe P 1. The seal member 2 closely adheres to the inner circumferential surface of the steel pipe P 1 over the entire circumference to close the inside of the steel pipe P 1. Although not particularly limited, as the seal member 2, for example, a hexaplug for piping work can be used.
[0034]
　The container 3 has an opening 33 for receiving a pipe end portion of the steel pipe P 1, and is for accommodating the plating solution and functions as a sealing member. More specifically, the container 3 is attached to the pipe end portion of the steel pipe P1. The container 3 is attached to the pipe end portion of the steel pipe P1 so as to cover the pipe end portion of the steel pipe P1 from the outer peripheral side.
[0035]
　The container 3 is formed in a substantially cylindrical shape in which one end in the axial direction is sealed. On the end face of the container 3, the electrode 1 is supported via a current-carrying rod 9. The energizing rod 9 is fixed to the end face of the container 3. Therefore, the peripheral wall of the container 3 is disposed on the outer peripheral side of the electrode 1.
[0036]
　The other end in the axial direction of the container 3 is brought into close contact with the outer peripheral surface of the steel pipe P 1. The other end portion in the axial direction of the seal member 3 comes into contact with the outer peripheral surface of the steel pipe P1 on the pipe center side rather than the male screw Tm. As a result, the container 3 forms the accommodation space 8 together with the steel pipe P 1 and the seal member 2. In the housing space 8, the electrode 1 and the male screw Tm are accommodated. The accommodating space 8 is filled with the plating solution in the electroplating process.
[0037]
　The container 3 further has openings 31, 32. The opening 31 is mainly used for discharging the plating solution during plating and after plating. It is preferable that the opening 31 is disposed below the steel pipe P1 in a state where the container 3 is mounted on the steel pipe P1.
[0038]
　The opening 32 is used to promote discharge of the plating solution after plating. By quickly discharging the used plating solution from the accommodating space 8, discoloration of the alloy plating layer formed on the male thread Tm due to corrosion can be prevented. The opening 32 is also used as an outlet of gas (air) when filling plating solution into the accommodation space 8. It is preferable that the opening 32 be disposed above the steel pipe P1 in a state where the seal member 3 is attached to the steel pipe P1.
[0039]
　The opening 32 may be configured to be opened and closed by an electromagnetic valve or the like. In this case, by opening the opening 32 as required, discharge of the plating solution from the housing space 8 can be promoted. Alternatively, by supplying compressed air from the opening 32 into the housing space 8, the discharge of the plating solution can be promoted.
[0040]
　A hose extending upward may be connected to the opening 32. In this case, it is possible to balance the pressure of the plating solution to be supplied into the housing space 8 and its own weight, and it is possible to prevent the plating solution from blowing out to the outside of the container 3.
[0041]
　The plating solution supply unit 4 supplies the plating solution into the accommodation space 8. The plating solution supply unit 4 has a support member 41 and a plurality of nozzles 42.
[0042]
　The support member 41 is disposed on the side opposite to the opening 33 of the container 3 and supports the plurality of nozzles 42. The support member 41 extends from the outside of the housing space 8 to the inside of the housing space 8 through the end face of the container 3. The support member 41 is connected to the seal member 2 by a fastening member. That is, the seal member 2 is fixed to the support member 41. The support member 41 has a flow path 43 extending along the tube axis X 1 and a plating liquid flow path 44 for supplying the plating solution to the nozzle 42. The plating liquid flow path 44 also extends along the tube axis X 1 and is formed around the flow path 43. The seal member 2 includes a circular plate 21 and a packing 22. The disk 21 has a flow path 23 extending to the outer periphery and communicating with the flow path 43. The packing 22 is mounted on the outer periphery of the circular plate 21 and makes contact with the inner peripheral surface of the steel pipe P1. When high pressure air is supplied to the flow passage 23 through the flow passage 43, the packing 22 is strongly pressed against the inner circumferential surface of the steel pipe P 1.
[0043]
　The support member 41 has a supply port 41 a. The supply port 41 a is disposed outside the housing space 8. The supply port 41 a is connected to a storage tank (not shown) that stores the plating solution via piping (not shown). The plating solution sent from the storage tank flows into the plating solution flow path 44 in the support member 41 from the supply port 41 a. The plating solution is supplied to the nozzle 42 through the plating liquid flow path 44.
[0044]
　Examples of the plating solution used for forming the alloy plating layer include zinc-nickel (Zn - Ni) plating solution, zinc - iron (Zn - Fe) plating solution, zinc - cobalt (Zn - Co) plating solution, Tin (Cu - Sn) plating solution and the like. Examples of the plating solution include a copper-tin-zinc (Cu-Sn-Zn) plating solution, a copper-tin-bismuth (Cu - Sn - Bi) plating solution and the like.
[0045]
　A plurality of nozzles 42 are connected to the end portion of the support member 41 arranged in the housing space 8. The plurality of nozzles 42 are arranged around the tube axis X 1 of the steel pipe P 1 in the housing space 8. The plurality of nozzles 42 are radially arranged at regular intervals when viewed from the tube axis direction.
[0046]
　Each nozzle 42 is disposed on one end side of the external thread Tm in the housing space 8. In the present embodiment, each nozzle 42 is disposed between the pipe end of the steel pipe P 1 and the end surface of the seal member 3. Each nozzle 42 ejects the plating solution supplied from the support member 41 between the external thread Tm and the electrode 1.
[0047]
　FIG. 3 is a schematic view of the plating solution supply unit 4 as viewed from the axial direction of the support member 41. As shown in FIG. 3, in the present embodiment, the plating solution supply unit 4 includes eight nozzles 42. The number of the nozzles 42 is not limited to this, but is preferably six or more.
[0048]
　Each nozzle 42 includes a main body portion 42 a and a distal end portion 42 b. The main body portion 42 a extends substantially in parallel with the plane orthogonal to the tube axis X 1 of the steel pipe P 1. The main body portion 42 a extends from the tube axis X 1 side of the steel pipe P 1 toward the radial direction outer side.
[0049]
　The distal end portion 42 b is provided continuously with the main body portion 42 a. The plating solution passes through the inside of the main body portion 42 a and is injected from the injection port of the front end portion 42 b. The injection port of the tip portion 42 b is positioned between the electrode 1 and the male screw Tm when the electroplating apparatus 10 is viewed from the tube axis direction of the steel pipe P 1 (FIG. 2).
[0050]
　Each nozzle 42 ejects a plating solution in one direction around the tube axis X 1 from the injection port of the tip end portion 42 b. In other words, the injection direction S 1 of each nozzle 42 is set to the right or left side around the tube axis X 1. Therefore, the plating solution injected from each nozzle 42 forms a helical flow around the tube axis X 1. It is preferable that the direction of the helical flow formed by each nozzle 42 coincides with the thread cutting direction of the male thread Tm (FIG. 2).
[0051]
　FIG. 4 is a schematic view of the nozzle 42 as seen from the extending direction R 1 of the main body 42 a. The tip portion 42 b is inclined toward the male screw Tm with respect to a plane orthogonal to the tube axis X 1 of the steel pipe P 1. A direction along a plane orthogonal to the tube axis X 1, that is, a direction orthogonal to the extension direction R 1 and the tube axis X 1 is defined as a reference direction V 1.
[0052]
　As shown in FIG. 4, when viewing the nozzle 42 from the extending direction R 1 of its main body 42 a, the distal end 42 b is inclined from the reference direction V 1 toward the male screw Tm by an inclination angle α 1. In other words, the spray direction S1 of the plating solution in the nozzle 42 is inclined from the reference direction V1 toward the male screw Tm by an inclination angle α1.
[0053]
　The inclination angle α 1 is set to be greater than 20 degrees and less than 90 degrees. More preferably, the tilt angle α 1 is greater than 30 ° and less than or equal to 60 °.
[0054]
　[Effect] In
　the electroplating apparatus 10 according to the first embodiment, the spray direction S1 of the plating solution by each nozzle 42 is inclined from the reference direction V1 to the male screw Tm side at an angle larger than 20 degrees and less than 90 degrees. As a result, during the electroplating process, the plating solution is sprayed toward the male thread Tm, so strong stirring of the plating solution occurs near the male thread Tm. Therefore, the diffusion layer generated adjacent to the external thread Tm becomes thinner, and the fluctuation of the thickness of the diffusion layer becomes smaller. Therefore, the variation in the deposition rate of the metal is alleviated, and the composition of the alloy plating layer formed on the surface of the male screw Tm can be prevented from becoming non-uniform. As a result, occurrence of plating defects such as uneven appearance and fine plating peeling can be suppressed.
[0055]
　Second Embodiment
　Configuration of Electroplating Apparatus
　FIG. 5 is a longitudinal sectional view showing a schematic configuration of an electroplating apparatus 20 according to a second embodiment. The electroplating apparatus 20 forms an alloy plating layer on the surface of the female screw Tf formed on the inner peripheral surface of the pipe end of the steel pipe P2. The pipe end portion of such a steel pipe P2 is generally called a "box".
[0056]
　As shown in FIG. 5, the electroplating apparatus 20 includes an electrode 1, seal members 2 and 3, and a plating solution supply unit 4, similarly to the electroplating apparatus 10 (FIG. 2) according to the first embodiment. However, in the electroplating apparatus 20, the arrangement of each part is different from that of the electroplating apparatus 10 according to the first embodiment.
[0057]
　The electrode 1 is arranged on the inner peripheral side of the steel pipe P 2. The electrode 1 faces the internal thread Tf of the steel pipe P 2. By supplying a plating solution between the electrode 1 and the female thread Tf and applying a potential difference between the electrode 1 and the steel pipe P2, a plating layer is formed on the surface of the female screw Tf.
[0058]
　The seal member 2 is disposed within the steel pipe P 2 and inside the tube end portion, and seals the steel pipe P 2. As in the first embodiment, the seal member 2 closely contacts the inner circumferential surface of the steel pipe P 2 over the entire circumference to close the interior of the steel pipe P 2. The seal member 2 of the present embodiment is arranged on the tube center side of the female screw Tf in the steel pipe P 2.
[0059]
　As in the first embodiment, the seal member 3 is attached to the pipe end portion of the steel pipe P 2. However, in the present embodiment, since the internal thread Tf, which is an object of the electroplating process, is formed on the inner peripheral surface of the steel pipe P 2, the position at which the seal member 3 contacts the outer peripheral surface of the steel pipe P 2 is not particularly limited. The seal member 3 can come into contact with the outer peripheral surface of the steel pipe P2 further on the tube end side. Here, the seal member 3 is disposed at the end of the steel pipe P 2, and forms a housing space 8 for accommodating the plating solution together with the steel pipe P 2 and the seal member 2. The electrode 1 is disposed in the housing space 8.
[0060]
　The plating solution supply unit 4 includes a plurality of nozzles 42 A. Each of the nozzles 42 A is disposed on one end side of the female screw Tf in the housing space 8. Each nozzle 42 A is disposed between the female screw Tf and the seal member 2. That is, each nozzle 42A is disposed closer to the tube center side than the female thread Tf in the steel pipe P2.
[0061]
　FIG. 6 is a schematic view of the plating solution supply unit 4 as seen from the axial direction of the support member 41. As shown in FIG. 6, also in the present embodiment, eight nozzles 42 A are radially arranged at equal intervals. Each nozzle 42 A includes a main body portion 42 Aa and a distal end portion 42 Ab.
[0062]
　The main body 42 Aa extends substantially in parallel with the plane orthogonal to the tube axis X 2 of the steel pipe P 2. The injection port of the tip portion 42 Ab is positioned between the electrode 1 and the female screw Tf when the electroplating apparatus 20 is viewed from the tube axis direction of the steel pipe P 2 (FIG. 5).
[0063]
　Like the nozzle 42 of the first embodiment, each nozzle 42 A injects a plating solution in one direction around the tube axis X 2 from the jet port of the tip portion 42 Ab. A spiral flow around the tube axis X 2 is formed by the plating solution injected from each nozzle 42 A. It is preferable that the direction of the helical flow coincides with the thread cutting direction of the female screw Tf (FIG. 5).
[0064]
　FIG. 7 is a schematic view of the nozzle 42A viewed from the extending direction R2 of the main body 42Aa. The tip portion 42 Ab is inclined toward the female screw Tf with respect to a plane orthogonal to the tube axis X 2 of the steel pipe P 2. A direction along a plane orthogonal to the tube axis X 2, that is, a direction orthogonal to the extension direction R 2 and the tube axis X 2 is defined as a reference direction V 2.
[0065]
　As shown in FIG. 7, when the nozzle 42A is viewed from the extension direction R2 of the main body portion 42Aa, the front end portion 42Ab is inclined from the reference direction V2 by the inclination angle α2 toward the female screw Tf. In other words, the spray direction S2 of the plating solution by the nozzle 42A is inclined from the reference direction V2 by the inclination angle α2 toward the female thread Tf. The inclination angle α 2 is greater than 20 degrees and less than 90 degrees, preferably greater than 30 degrees but less than 60 degrees.
[0066]
　Here, the spraying direction S2 of the plating solution of the nozzle 42A is inclined to the side opposite to the spraying direction S1 of the plating solution of the nozzle 42 in the first embodiment. This is because the nozzle 42 A of the second embodiment is disposed at a position opposite to the nozzle 42 of the first embodiment in the tube axis direction.
[0067]
　Whether the spraying direction of the plating solution is inclined can be determined according to the relative positional relationship between the screw and the nozzle. In other words, the injection direction of each nozzle may be inclined to the screw side with respect to a plane orthogonal to the tube axis of the steel pipe so that the plating solution is sprayed to the screw side.
[0068]
　[Effect] Also in
　the electroplating apparatus 20 according to the second embodiment, the spraying direction S 2 of the plating solution of each nozzle 42 A is inclined from the reference direction V 2 to the female thread Tf side by an angle greater than 20 degrees and less than 90 degrees . For this reason, during electroplating treatment, strong stirring of the plating solution occurs near the female thread Tf. Therefore, the diffusion layer becomes thin, and the fluctuation of the thickness of the diffusion layer also decreases accordingly. This makes it possible to suppress the nonuniform composition of the alloy plating layer formed on the surface of the female screw Tf. As a result, occurrence of plating defects such as uneven appearance and fine plating peeling can be suppressed.
[0069]
　 Although
　the embodiments have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit thereof.
[0070]
　In each of the above embodiments, the main body of the nozzle extends in parallel with the plane orthogonal to the tube axis of the steel pipe, and the tip of the nozzle is inclined with respect to the plane, but the present invention is not particularly limited thereto. For example, the plating solution may be injected at a predetermined angle by inclining the entire nozzle with respect to a plane orthogonal to the tube axis of the steel pipe.
[0071]
　In each of the above embodiments, the seal member in the steel pipe is fixed to the support member of the plating solution supply unit by the fastening member. However, the seal member and the plating solution supply section need not be fixed to each other.
Example
[0072]
　Hereinafter, the effects of the present disclosure will be described more concretely by examples. However, the present disclosure is not limited to the following examples.
[0073]
　A bath was made of a degreasing solution (sodium hydroxide = 50 g / L), a Ni strike bath (nickel chloride = 250 g / L, hydrochloric acid = 80 g / L) and a Zn - Ni plating bath (Dainiin Kinzoku made Dynein alloy) Zn-Ni alloy plating (Ni content (aimed): 12 to 16%) was applied to the surface of the external thread (Tm) of the steel pipe (P1) by using the electroplating apparatus (10) shown in FIG. The steps and conditions of the electroplating treatment are shown in Table 1.
[0074]
[table 1]

　6. The 　electroplating apparatus according to claim 5, further comprising: a support member disposed on the second seal member and supporting the plurality of nozzles,
wherein the support member supplies the plating solution to the nozzle , And
　the first seal member is fixed to the support member.
[7]
　The electroplating apparatus according to claim 6,
　wherein the support member has a first flow path extending along the tube axis,
　the first seal member
　extends to the outer periphery and is connected to the first flow path A disc having a second flow path communicating with
　said packing, and a packing mounted on the outer circumference of said disc and contacting the inner circumferential surface of said steel pipe
.
[Claim 8]
　The electroplating apparatus according to any one of claims 1 to 7,
　wherein the number of the nozzles is six or more.