Title of invention: Pipe threaded joint and method for manufacturing pipe threaded joint
Technical field
[0001]
　The present invention relates to a threaded joint for pipes and a method for manufacturing a threaded joint for pipes.
Background technology
[0002]
　Oil well pipes are used for mining oil and natural gas fields. The oil well pipe is formed by connecting a plurality of steel pipes according to the depth of the well. The steel pipes are connected by screwing together threaded joints for pipes formed at the ends of the steel pipes. The steel pipe is pulled up for inspection or the like, screwed back, inspected, screwed again, and used again.
[0003]
　The pipe threaded joint includes a pin and a box. The pin has a contact surface including an external thread portion on the outer peripheral surface of the end portion of the steel pipe. The box has a contact surface including an internal thread on the inner peripheral surface of the end of the steel pipe. The contact surface may further include unthreaded metal contacts. The contact surface including the threaded portion of the pin and the box and the unthreaded metal contact portion is repeatedly subjected to strong friction when the steel pipe is screwed and unscrewed. If these parts do not have sufficient durability against friction, galling (irreparable seizure) occurs when screwing and unscrewing are repeated. Therefore, the pipe threaded joint is required to have sufficient durability against friction, that is, excellent seizure resistance.
[0004]
　Conventionally, in order to improve the seizure resistance, a compound grease containing a heavy metal called a dope has been used. By applying compound grease to the surface of the threaded joint for pipes, the seizure resistance of the threaded joint for pipes can be improved. However, heavy metals such as Pb, Zn and Cu contained in the compound grease may affect the environment. Therefore, it is desired to develop a threaded joint for pipes that does not use compound grease.
[0005]
　International Publication No. 2016/170031 (Patent Document 1) and Japanese Patent Application Laid-Open No. 2008-69883 (Patent Document 2) propose a threaded joint for pipes having excellent seizure resistance even without compound grease. A lubricating coating is formed on the contact surfaces (screw portion and non-screw metal contact portion) of these threaded joints for pipes in order to improve seizure resistance.
[0006]
　A metal coating for rust prevention and seizure resistance is formed on a metal contact portion of a pin or a box of a threaded joint for pipes described in Patent Document 1. The main component of the metal film for rust prevention and seizure resistance is Zn. The metal coating is formed by electroplating. Paragraph [0173] of Patent Document 1 discloses that a smoothing effect can be obtained by this electroplating. This smoothing effect is also disclosed in Table 1 of Patent Document 1. In Table 1 of Patent Document 1, the arithmetic mean roughness Ra on the surface after electroplating is lower than the arithmetic mean roughness Ra on the surface before electroplating, regardless of whether or not sandblasting is performed on the contact surface.
[0007]
　The threaded joint for pipes described in patent document 2 consists of a pin and a box each provided with a contact surface having a threaded portion and an unthreaded metal contacting portion. The threaded joint for pipes described in Patent Document 2 is, on the contact surface of at least one of the pin and the box, softer than the first layer made of the first metal or alloy and the first metal or alloy in order from the bottom. It has a second layer of a second metal or alloy, and a top solid lubricant coating.
Prior art documents
Patent literature
[0008]
Patent Document 1: International Publication No. 2016/170031
Patent Document 2: Japanese Patent Laid-Open No. 2008-69883
Summary of the invention
Problems to be Solved by the Invention
[0009]
　By the way, in the threaded joint, in addition to the above-mentioned seizure resistance, it is required to suppress an increase in the shouldering torque when the screw is tightened a plurality of times. FIG. 1 is a diagram showing a relationship between a rotational speed and a torque of a threaded portion of a threaded joint for pipes when a threaded joint for pipes having a shoulder portion is screwed. Referring to FIG. 1, when the pin and the box are screwed, the shoulder portions of the pin and the box come into contact with each other when a certain number of rotations is reached. The torque generated at this time is called shouldering torque. When screwing the threaded portion of the threaded joint for pipes, after the shouldering torque is reached, further tightening is performed until the fastening is completed. This increases the airtightness of the threaded joint for pipes. When the screw is further tightened after the fastening is completed, the metal forming at least one of the pin and the box starts to undergo plastic deformation. The torque generated at this time is called yield torque.
[0010]
　The torque at the time of completion of fastening (hereinafter referred to as fastening torque) is set so that a sufficient sealing surface pressure can be obtained regardless of the magnitude of the screw interference amount. If the difference between the shouldering torque and the yield torque is sufficient, the range of the fastening torque becomes wider. As a result, the tightening torque can be easily adjusted. To widen the range of fastening torque, the shouldering torque may be lowered. Therefore, in addition to the above-mentioned seizure resistance, the threaded joint for pipes is required to be able to maintain a low shouldering torque even when the screw tightening and the screw returning are repeated.
[0011]
　The same is true for threaded joints for pipes that do not have unthreaded metal contacts (that is, do not have shoulders). If the difference between the torque at the initial stage of screw tightening and the torque at the final stage of screw tightening is sufficient, the range of tightening torque will be wide. As a result, the tightening torque can be easily adjusted. In order to widen the range of fastening torque, the torque at the initial stage of screw tightening may be lowered. The torque at the initial stage when screwing the pipe threaded joint having no threaded metal contact portion corresponds to the shouldering torque when screwing the pipe threaded joint having the shoulder portion.
[0012]
　However, Patent Document 1 and Patent Document 2 do not mention the above-mentioned shouldering torque.
[0013]
　On the other hand, as disclosed in Patent Document 1 and Patent Document 2, the seizure resistance of the threaded joint for pipes can be improved by forming a lubricating coating on the plating layer. Patent Documents 1 and 2 disclose that the surface roughness is formed by blasting or the like before forming the lubricating coating. As a result, the adhesion of the lubricating coating can be increased, and the seizure resistance of the threaded joint for pipes can be further improved.
[0014]
　However, the inventors of the present invention used the surface roughness obtained in the two steps of the blast treatment and the plating layer formation thereon or the plating layer formation and the blast treatment thereon to be one step of the plating layer formation. I thought it would be preferable if it could be obtained only by itself.
[0015]
　An object of the present invention is to have seizure resistance as excellent as that when blasting is performed without performing blasting, and low shouldering torque even when screw tightening and screw returning are repeated. It is intended to provide a pipe threaded joint having the above, and a method for manufacturing the pipe threaded joint capable of manufacturing the pipe threaded joint.
Means for solving the problem
[0016]
　The pipe threaded joint of the present embodiment includes a pin and a box. The pin and box each have a contact surface that includes threads. The pipe threaded joint includes a Zn—Ni alloy plating layer and a solid lubricating coating. The Zn-Ni alloy plating layer is formed on the contact surface of at least one of the pin and the box, and contains 10 to 16 mass% of Ni. The solid lubricating coating is formed on the Zn-Ni alloy plating layer. The contact surface on which the Zn—Ni alloy plating layer is formed is ground. The arithmetic average roughness of the surface of the Zn-Ni alloy plated layer measured by the laser microscope along the grinding direction of the contact surface is defined as Ra1. The arithmetic average roughness of the contact surface measured by the laser microscope along the grinding direction is defined as Ra2. The arithmetic average roughness Ra1 is 0.1 to 3.2 μm. The arithmetic average roughness Ra1 is larger than the arithmetic average roughness Ra2.
[0017]
　A method for manufacturing a threaded joint for pipes of the present disclosure is a method for manufacturing a threaded joint for pipes, which includes a pin and a box each having a contact surface including a threaded portion. The manufacturing method includes a Zn-Ni alloy plating layer forming step and a solid lubricating coating forming step. In the Zn-Ni alloy plating layer forming step, the Zn-Ni alloy plating layer is formed on the contact surface of at least one of the pin and the box by electroplating without performing blast treatment. The Zn-Ni alloy plating layer contains 10 to 16% by mass of Ni. The Zn-Ni alloy plated layer has a surface arithmetic mean roughness Ra1 of 0.1 to 3.2 μm measured by a laser microscope along the grinding direction of the contact surface. In the solid lubricating coating forming step, the solid lubricating coating is formed on the Zn—Ni alloy plating layer without performing blast treatment.
Effect of the invention
[0018]
　The threaded joint for pipes of the present disclosure has seizure resistance as excellent as that in the case where blasting is performed without performing blasting, and has a low shoulder even when screw tightening and screw returning are repeated. Has ring torque. Further, such a pipe threaded joint is obtained by the above-described manufacturing method.
Brief description of the drawings
[0019]
FIG. 1 is a diagram showing a relationship between a rotational speed of a threaded portion of a threaded joint for a pipe and torque when the threaded joint for a pipe having a shoulder portion is screwed.
FIG. 2 is a diagram showing the relationship between the number of fastenings (number of times) of a threaded joint for pipes and the shouldering torque (%).
FIG. 3 is a diagram showing a configuration of a threaded joint for pipes of the present embodiment.
FIG. 4 is a sectional view of the threaded joint for pipes according to the present embodiment.
FIG. 5 is a sectional view of a contact surface of the threaded joint for pipes according to the present embodiment.
MODE FOR CARRYING OUT THE INVENTION
[0020]
　Hereinafter, the present embodiment will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and the description thereof will not be repeated.
[0021]
　The present inventors conducted various studies on the relationship between the blast treatment and the seizure resistance of the threaded joint for pipes, and the shouldering torque of the threaded joint for pipes. As a result, the following findings were obtained.
[0022]
　The zinc (Zn) plating layer enhances rust prevention. However, the zinc plating layer has lower hardness and melting point than the copper (Cu) plating layer that has been conventionally used as the plating layer. Therefore, the present inventors have studied a zinc alloy plating layer having excellent rust prevention, high hardness and high melting point. As a result, they have found that if a Zn-Ni alloy plating layer containing Ni in an amount of 10 to 16 mass% is formed on the contact surface of a threaded joint for pipes, anti-seizure property is enhanced and seizure resistance is enhanced. A Zn—Ni alloy containing 10 to 16% by mass of Ni has a sufficiently high hardness as compared with Cu and has a melting point significantly higher than that of Zn. Therefore, the Zn-Ni alloy plating layer containing Ni in an amount of 10 to 16% by mass can improve seizure resistance.
[0023]
　Patent Document 1 discloses that a Zn-Ni alloy plating layer is formed and a lubricating coating is formed thereon. Patent Document 2 does not disclose Zn-Ni alloy plating, but discloses forming a plating layer and forming a solid lubricating coating thereon.
[0024]
　For example, paragraph [0160] of Patent Document 1 discloses that sandblasting is performed on the metal coating to increase the adhesion of the lubricating coating thereon. In addition, paragraph [0164] of Patent Document 1 discloses that a sandblast treatment is performed before forming a metal coating, and the metal coating is formed thereon. Further, paragraph [0026] of Patent Document 2 discloses that the adhesion of the solid lubricating coating is enhanced by imparting an appropriate surface roughness by shot blasting or sand blasting before forming the solid lubricating coating. ..
[0025]
　As disclosed in the above-mentioned prior documents, when a plating layer is formed on the surface of a threaded joint for pipes and a lubricating film is formed on the plating layer, blasting such as sandblasting may be performed. Thereby, the adhesiveness of the lubricating coating can be improved. As a result, seizure resistance of the threaded joint for pipes can be improved. In the present specification, the blast treatment means sand blast, shot blast and grit blast.
[0026]
　The blast treatment may be performed before the formation of the plating layer or may be performed after the formation of the plating layer. When the blast treatment is performed before forming the plating layer, the blast treatment is performed directly on the contact surface, that is, the surface of the base material. The surface roughness imparted to the contact surface is maintained up to the surface of the plating layer, although it is somewhat buried by the plating layer on the contact surface. The surface roughness of the plating layer surface enhances the adhesion of the lubricating coating thereon. In addition, it is disclosed in Table 1 of Patent Document 1 that the surface roughness is lowered in ordinary electroplating.
[0027]
　When the blast treatment is performed after the plating layer is formed, the blast treatment is performed on the surface of the plating layer.
[0028]
　On the other hand, the present inventors compared the surface roughness obtained in the two steps of the blast treatment and the formation of the plating layer thereon, or the formation of the plating layer and the blast treatment thereon to that of the formation of the plating layer. We thought that it would be preferable if it could be obtained only by steps.
[0029]
　More specifically, the present inventors considered that there is a possibility that seizure resistance of the threaded joint for pipes can be better maintained even if the blast treatment is omitted. Therefore, the present inventors have studied a method of enhancing seizure resistance of a threaded joint for pipes to the same extent as when the blast treatment is performed even if the blast treatment is omitted.
[0030]
[table 1]

[0031]
　Table 1 is a table showing a part of examples described below and reference examples. Referring to Table 1, in Reference Example, a box was prepared by a conventional method. That is, after sandblasting was performed on the contact surface, a bright Zn—Ni alloy plating layer was formed and a solid lubricating coating was formed thereon. In the reference example, the arithmetic mean roughness Ra2 of the contact surface Ra2=2.700 is lowered to the arithmetic mean roughness Ra1=2.680 of the Zn—Ni alloy plating layer due to the formation of the Zn—Ni alloy plating layer. Nevertheless, the seizure resistance of the threaded joint for pipes was high because the surface of the Zn—Ni alloy plated layer maintained a sufficiently large arithmetic average roughness of Ra1=2.680. Specifically, screw tightening and screw unscrewing were possible 10 times before seizure occurred.
[0032]
　In test number 2, no sandblasting was performed. Therefore, the arithmetic mean roughness Ra2 of the contact surface of Test No. 2 was as small as 0.061. This is because the contact surface is ground. In this specification, grinding refers to grinding for forming a threaded portion. The arithmetic average roughness Ra2 of the contact surface after grinding is small. In test number 2, the box was prepared by a method different from the conventional method. That is, without performing sandblasting on the contact surface, a matte Zn-Ni alloy plating layer was formed, and a solid lubricating coating was formed thereon. As a result, the arithmetic mean roughness Ra2 of the contact surface was increased to 0.061 due to the formation of the matte Zn-Ni alloy plating layer. The seizure resistance of the threaded joint for pipes of test number 2 was high. Specifically, screw tightening and screw unscrewing were possible 10 times before seizure occurred. This had seizure resistance equivalent to that of the reference example in which sandblasting was performed.
[0033]
　From the above examination, the present inventors have obtained the following findings. This is a completely different finding from the prior art that by forming a non-glossy Zn-Ni alloy plating layer, seizure resistance equivalent to that obtained by sandblasting can be obtained even if the sandblasting is omitted.
[0034]
　In general, plating is preferred for its decorative appearance to have a more beautiful appearance, and thus gloss plating with less surface irregularities is often used. In addition, some bright platings can achieve a more beautiful appearance by a leveling effect that reduces irregularities such as scratches on the substrate.
[0035]
　On the contrary, the present inventors have found that a non-glossy Zn-Ni alloy plating layer is effective when the seizure resistance of the threaded joint for pipes is taken into consideration. By forming the non-glossy Zn-Ni alloy plating layer, the arithmetic surface roughness Ra1 of the Zn-Ni alloy plating layer can be increased and the seizure resistance of the threaded joint for pipes can be increased. The arithmetic mean roughness Ra1 of the non-glossy Zn-Ni alloy plating layer tends to be smaller than the arithmetic mean roughness Ra1 formed by the surface roughness forming step such as sandblasting. However, according to the study by the present inventors, the seizure resistance of the threaded joint for pipes can be sufficiently enhanced even with the arithmetic average roughness Ra1 of the non-glossy Zn—Ni alloy plating layer.
[0036]
　Furthermore, the present inventors considered that if the adhesion between the solid lubricating coating and the plating layer is high, the peeling of the solid lubricating coating is suppressed. If the peeling of the solid lubricating film is suppressed, high lubricity is maintained even when screw tightening and screw returning are repeated. Therefore, the shouldering torque of the threaded joint for pipes can be kept low even when the screw tightening and the screw returning are repeated.
[0037]
　FIG. 2 is a diagram showing the relationship between the number of fastenings (number of times) of the threaded joint for pipes and the shouldering torque (%). FIG. 2 was obtained by the example described below. The mark “◯” in FIG. 2 shows the result of test number 2 which is an example of the present invention. In Test No. 2, the arithmetic average roughness Ra1 of the Zn—Ni alloy plated layer was 0.276 μm. The mark “Δ” in FIG. 2 shows the result of test number 1 which is a comparative example. In Test No. 1, the arithmetic average roughness Ra1 of the Zn—Ni alloy plated layer was 0.056 μm. With reference to FIG. 2, when the arithmetic average roughness Ra1 of the Zn—Ni alloy plated layer is large to some extent as in the example of the present invention, the shouldering torque can be kept low even when the screw tightening and the screw returning are repeated. .. On the other hand, when the arithmetic mean roughness Ra1 of the Zn—Ni alloy plating layer is small as in the comparative example, the shouldering torque increases when the screw tightening and unscrewing are repeated, and unrepairable seizure occurs at the fifth tightening. appear. In other words, the threaded joint for pipes, in which the arithmetic mean roughness Ra1 of the Zn-Ni alloy plated layer under the solid lubricating coating is relatively large, lowers the shouldering torque of the threaded joint for pipes even after repeated screw tightening and unscrewing. Can be maintained.
[0038]
　As a result of further studies, the present inventors have found that when the arithmetic average roughness Ra1 on the surface of the Zn—Ni alloy plating layer is 0.1 μm or more, the Zn—Ni alloy plating layer enhances seizure resistance. It has been found that even when the screw tightening and the screw returning are repeated, peeling of the solid lubricating coating is suppressed, and the tightening torque can be easily adjusted. As a result, excellent fastening performance can be obtained. On the other hand, it was also found that if the arithmetic average roughness Ra1 exceeds 3.2 μm, the airtightness of the screwless metal contact portion (seal portion) is deteriorated. Therefore, the arithmetic average roughness Ra1 is 0.1 to 3.2 μm.
[0039]
　The pipe threaded joint of the present disclosure completed based on the above findings includes a pin and a box. The pin and box each have a contact surface that includes threads. The pipe threaded joint includes a Zn—Ni alloy plating layer and a solid lubricating coating. The Zn-Ni alloy plating layer is formed on the contact surface of at least one of the pin and the box, and contains 10 to 16% by mass of Ni. The solid lubricating coating is formed on the Zn-Ni alloy plating layer. The contact surface on which the Zn—Ni alloy plating layer is formed is ground. The arithmetic average roughness of the surface of the Zn-Ni alloy plated layer measured by the laser microscope along the grinding direction of the contact surface is defined as Ra1. The arithmetic average roughness of the contact surface measured by the laser microscope along the grinding direction is defined as Ra2. The arithmetic average roughness Ra1 is 0.1 to 3.2 μm. The arithmetic average roughness Ra1 is larger than the arithmetic average roughness Ra2.
[0040]
　The threaded joint for pipes of the present disclosure has a non-luster Zn-Ni alloy plating layer. This increases the arithmetic average roughness Ra1 of the Zn-Ni alloy plating layer. That is, the arithmetic average roughness Ra1 of the Zn—Ni alloy plating layer is higher than the arithmetic average roughness Ra2 of the contact surface. Therefore, the adhesion of the solid lubricating coating thereon is increased. As a result, even if the blast treatment is omitted, seizure resistance equivalent to that when the blast treatment is performed can be obtained. The pipe threaded joint of the present disclosure also has low shouldering torque during repeated screw tightening and unscrewing. Grinding in this specification refers to grinding for forming a threaded portion. In the present specification, the blast treatment means sand blast, shot blast and grit blast.
[0041]
　The arithmetic average roughness Ra1 on the surface of the Zn—Ni alloy plating layer may be 0.1 to 0.4 μm.
[0042]
　The contact surface may further include a threadless metal contact.
[0043]
　The screwless metal contact portion includes a metal seal portion and a shoulder portion.
[0044]
　A method for manufacturing a threaded joint for pipes of the present disclosure is a method for manufacturing a threaded joint for pipes, which includes a pin and a box each having a contact surface including a threaded portion. The manufacturing method includes a Zn-Ni alloy plating layer forming step and a solid lubricating coating forming step. In the Zn-Ni alloy plating layer forming step, the Zn-Ni alloy plating layer is formed on the contact surface of at least one of the pin and the box by electroplating without performing blast treatment. The Zn-Ni alloy plating layer contains 10 to 16% by mass of Ni. The Zn-Ni alloy plated layer has a surface arithmetic mean roughness Ra1 of 0.1 to 3.2 μm measured by a laser microscope along the grinding direction of the contact surface. In the solid lubricating coating forming step, the solid lubricating coating is formed on the Zn—Ni alloy plating layer without performing blast treatment.
[0045]
　The method for producing a threaded joint for pipes of the present disclosure forms a non-luster Zn-Ni alloy plating layer without performing blasting. Further, a solid lubricating coating is formed on the non-lustrous Zn-Ni alloy plating layer without performing blast treatment. As a result, a pipe threaded joint having seizure resistance equivalent to that when blasting is performed, and further having low shouldering torque even when screw tightening and screw returning are repeated is obtained. In the present specification, the blast treatment means sand blasting, shot blasting, and grit blasting. Further, the grinding direction of the contact surface means the direction of grinding for forming the screw portion on the contact surface.
[0046]
　Hereinafter, a threaded joint for pipes and a method for manufacturing the threaded joint for pipes according to the present disclosure will be described in detail.
[0047]
　[Pipe Threaded Joint 50] The
　pipe threaded joint 50 includes a pin 13 and a box 14. FIG. 3 is a diagram showing a configuration of the pipe threaded joint 50 according to the present embodiment. With reference to FIG. 3, the pipe threaded joint 50 includes a steel pipe 11 and a coupling 12. Pins 13 having male threads on the outer surface are formed at both ends of the steel pipe 11. At both ends of the coupling 12, boxes 14 having internal threaded portions are formed. The coupling 12 is attached to the end of the steel pipe 11 by screwing the pin 13 and the box 14 together. On the other hand, there is also an integral type oil well pipe threaded joint in which one end of the steel pipe 11 is a pin 13 and the other end is a box 14 without using the coupling 12. The threaded joint for pipes of the present embodiment can be used for both threaded couplings for pipes of the coupling type and the integral type.
[0048]
　The pin 13 and the box 14 have contact surfaces with threads. FIG. 4 is a sectional view of the pipe threaded joint 50 according to the present embodiment. With reference to FIG. 4, the pin 13 includes a male screw portion 15 and a non-screw metal contact portion. The threadless metal contact portion is formed at the tip of the pin 13 and includes a metal seal portion 16 and a shoulder portion 17. The box 14 includes an internal thread portion 20 and a non-threaded metal contact portion. The unthreaded metal contact portion is formed on the box 14 and includes a metal seal portion 19 and a shoulder portion 18. The portion that comes into contact when the pin 13 and the box 14 are screwed together is called a contact surface. Specifically, when the pin 13 and the box 14 are screwed together, the shoulder portions (shoulder portions 17 and 18), the metal seal portions (metal seal portions 16 and 19), and the screw portions (male screw portions 15 and 18) The female thread portions 20) come into contact with each other. That is, the contact surface includes a shoulder portion, a metal seal portion, and a screw portion.
[0049]
　Although not shown, the threaded metal contact portion of the pipe threaded joint 50 may be omitted. In that case, the contact surface comprises a thread. Specifically, the pin 13 includes a male screw portion 15. The box 14 includes an internal thread portion 20.
[0050]
　FIG. 5 is a cross-sectional view of the contact surface of the threaded joint for pipes 50 according to the present embodiment. Referring to FIG. 5, the pipe threaded joint 50 includes a Zn—Ni alloy plating layer 21 and a solid lubricating coating 23 on the contact surface of at least one of the pin 13 and the box 14 in order from the contact surface side. The arithmetic average roughness of the surface of the Zn—Ni alloy plating layer 21 measured by the laser microscope along the grinding direction of the contact surface is defined as Ra1. The arithmetic average roughness of the contact surface measured by a laser microscope along the grinding direction of the contact surface is defined as Ra2. The arithmetic average roughness Ra1 is 0.1 to 3.2 μm in the arithmetic average roughness measured by a laser microscope in the grinding direction. The arithmetic average roughness Ra1 is larger than the arithmetic average roughness Ra2.
[0051]
　[Arithmetic Average Roughness Ra2 on
　Contact Surface ] The arithmetic average roughness Ra2 on the contact surface measured along the grinding direction by the laser microscope is the same as the grinding direction by the laser microscope on the surface of the Zn-Ni alloy plating layer 21 described later. Is lower than the arithmetic mean roughness Ra1 measured along.
[0052]
　The contact surface is the grinding surface. Grinding surface means the contact surface as ground to form the threads. That is, the ground surface of the contact surface means the contact surface after the grinding for forming the threaded portion and without the coating film formed thereon.
[0053]
　The ground surface of the contact surface is formed by cutting the material of the pipe threaded joint 50 with a screw grinder or the like to form valleys and peaks. Therefore, the grinding surface has grinding marks extending in the grinding direction.
[0054]
　The roughness of the ground surface differs greatly between the tube axis direction and the grinding direction. The roughness in the tube axis direction is a large value because it is measured across the grinding marks. On the other hand, the roughness in the grinding direction is very small.
[0055]
　The arithmetic average roughness referred to in this specification is measured as the arithmetic average roughness Ra based on JIS B0601 (2001). Usually, a contact type roughness meter is used to measure the surface roughness of the pipe threaded joint 50. The contact type roughness meter is, for example, a surf coder SEF-30D manufactured by Kosaka Laboratory Ltd. When measured using a contact type roughness meter, the measured arithmetic mean roughness value may be larger than the actual value. This is because the measurement direction is adjusted visually by only measuring in one direction. In this case, the roughness due to the grinding mark may be measured as the arithmetic average roughness due to the error of the installation angle.
[0056]
　Therefore, the arithmetic average roughness in the present invention is measured using a laser microscope without using a contact type roughness meter. A laser microscope VK-X110 manufactured by Keyence Corporation is used as the laser microscope. Data of 1.25 mm square at 0.85 μm pitch is collected by mapping. The standard value of JIS B0601 (1994) is used for the cutoff value λ c and the measurement length for calculating the roughness curve . The arithmetic mean roughness Ra2 on the contact surface is measured along the grinding direction of the contact surface. “Along the grinding direction” means along a direction parallel to a grinding mark for forming a threaded portion. The direction parallel to the grinding mark includes an error of ±0.5 degrees when the direction parallel to the grinding mark is 0 degree. If it exceeds ±0.5 degrees, the error of the arithmetic mean roughness Ra becomes large. In the present embodiment, the surface roughness is measured more accurately without measuring the roughness due to grinding marks as the surface roughness. The measurement direction of the surface roughness is determined based on the observation result of mapping with a laser microscope.
[0057]
　In this embodiment, a Zn—Ni alloy plating layer is formed on the contact surface. Therefore, the arithmetic average roughness Ra2 on the contact surface can also be measured as the contact surface roughness after the Zn—Ni alloy plating layer on the contact surface is peeled off. The Zn-Ni alloy plating layer on the contact surface is peeled off using hydrochloric acid containing a commercially available corrosion inhibitor (inhibitor) in an appropriate amount. A commercially available corrosion inhibitor is, for example, product name Ibit 710 manufactured by Asahi Chemical Industry Co., Ltd.
[0058]
　[Zn-Ni alloy plating layer 21] The
　Zn-Ni alloy plating layer 21 is formed on the contact surface of at least one of the pin 13 and the box 14. The Zn—Ni alloy plating layer 21 may be formed on the contact surfaces of both the pin 13 and the box 14. The Zn—Ni alloy plating layer 21 may be formed only on the contact surface of the pin 13 or may be formed only on the contact surface of the box 14.
[0059]
　The Zn-Ni alloy plating layer 21 is an electroplating layer made of a Zn-Ni alloy. The hardness and melting point of the Zn—Ni alloy plating layer 21 are high. If the hardness of the Zn-Ni alloy plating layer 21 is high, the plating layer on the contact surface is less likely to be damaged during screw tightening and unscrewing. Further, if the melting point of the Zn—Ni alloy plating layer 21 is high, the plating layer is unlikely to melt even when the temperature is locally increased during screw tightening and unscrewing. Therefore, seizure resistance of the pipe threaded joint 50 is enhanced. Furthermore, since Zn contained in the Zn—Ni alloy plating layer 21 is a base metal, the rust preventive property of the threaded joint for pipes 50 is enhanced.
[0060]
　The Zn-Ni alloy forming the Zn-Ni alloy plating layer 21 has a Ni content of 10 to 16 mass %. In this composition range, the structure is almost a γ phase single phase. The Zn-Ni alloy plating layer 21 as described above has anti-rust property, high hardness and high melting point.
[0061]
　The preferable thickness of the Zn—Ni alloy plating layer 21 is 1 to 20 μm. If the thickness of the Zn—Ni alloy plating layer 21 is 1 μm or more, the seizure resistance and rust resistance of the threaded joint 50 for a pipe can be more stably enhanced. When the thickness of the Zn—Ni alloy plating layer 21 is 20 μm or less, the adhesion of the Zn—Ni alloy plating layer 21 is further stabilized. Therefore, the preferable thickness of the Zn—Ni alloy plating layer 21 is 1 to 20 μm. However, other thicknesses may be used. The lower limit of the thickness of the Zn—Ni alloy plating layer 21 is more preferably 3 μm, further preferably 5 μm. The upper limit of the thickness of the Zn—Ni alloy plating layer 21 is more preferably 18 μm, further preferably 15 μm.
[0062]
　[Arithmetic Average Roughness Ra1 on Surface of
　Zn-Ni Alloy Plating Layer 21 ] The arithmetic average roughness Ra1 on the surface of the Zn-Ni alloy plating layer 21 measured along the grinding direction by a laser microscope is the surface of the pin 13 and It is higher than the arithmetic mean roughness Ra2 of the contact surface of the surface of the box 14 measured by a laser microscope along the grinding direction. The arithmetic average roughness Ra1 is 0.1 to 3.2 μm in the arithmetic average roughness measured by the laser microscope along the grinding direction.
[0063]
　If the Zn-Ni alloy plating layer 21 has an arithmetic mean roughness Ra1 of 0.1 to 3.2 μm, the adhesion of the solid lubricating coating 23 is enhanced by the anchor effect. The higher the adhesion of the solid lubricating coating 23, the higher the seizure resistance of the threaded joint 50 for pipes. If the adhesion of the solid lubricating coating 23 is increased, the shouldering torque during screw tightening can be kept low.
[0064]
　If the arithmetic average roughness Ra1 is less than 0.1 μm, the above effect cannot be obtained. On the other hand, when the arithmetic average roughness Ra1 exceeds 3.2 μm, the airtightness of the screwless metal contact portion (sealing portion) is deteriorated. Therefore, the arithmetic average roughness Ra1 is 0.1 to 3.2 μm. The arithmetic average roughness Ra1 may be 0.1 to 0.4 μm.
[0065]
　The arithmetic average roughness Ra1 on the surface of the Zn—Ni alloy plating layer 21 can be measured in the same manner as the arithmetic average roughness Ra2 on the contact surface.
[0066]
　In this embodiment, by forming the non-glossy Zn—Ni alloy plating layer 21, the arithmetic mean roughness Ra1 of the surface of the Zn—Ni alloy plating layer 21 is made higher than the arithmetic mean roughness Ra2 of the contact surface. it can. In this case, even if the blast treatment is omitted, the seizure resistance as excellent as that when the blast treatment is performed can be obtained.
[0067]
　[Solid Lubrication Coating 23] The
　solid lubrication coating 23 is formed on the Zn—Ni alloy plating layer 21 having an arithmetic average roughness Ra1 of 0.1 to 3.2 μm. Since the Zn—Ni alloy plating layer 21 has the arithmetic mean roughness Ra1 of 0.1 to 3.2 μm, the adhesion between the Zn—Ni alloy plating layer 21 and the solid lubricating coating 23 is high.
[0068]
　The solid lubricating coating 23 enhances the lubricity of the threaded joint 50 for a pipe. A well-known solid lubricant film 23 can be used. The solid lubricating coating 23 contains, for example, lubricating particles and a binder. The solid lubricating coating 23 may contain a solvent and other components as needed.
[0069]
　Lubricating particles reduce the friction coefficient of the surface of the solid lubricating coating 23. Lubricating particles are not particularly limited as long as they are particles having lubricity. Examples of the lubricating particles include graphite, MoS 2 (molybdenum disulfide), WS 2 (tungsten disulfide), BN (boron nitride), PTFE (polytetrafluoroethylene), CF x (graphite fluoride) and CaCO 3 (carbonic acid ). And one or more selected from the group consisting of calcium). Preferably, it is one or more selected from the group consisting of graphite, fluorinated graphite, MoS 2 and PTFE. The content of the lubricating particles is, for example, 1 to 40% by mass based on 100% by mass of all components other than the solvent.
[0070]
　The binder binds the lubricious particles into the solid lubricating coating 23. The binder is one or two selected from the group consisting of organic resins and inorganic resins. When an organic resin is used, it is one or two selected from the group consisting of thermosetting resins and thermoplastic resins. The thermosetting resin is selected from the group consisting of epoxy resin, polyimide resin, polyurethane resin, polycarbodiimide resin, polyether sulfone, polyether ether ketone resin, phenol resin, furan resin, urea resin and acrylic resin, for example. There are two or more species. The thermoplastic resin is, for example, one or more selected from the group consisting of polyamideimide resin, polyethylene resin, polypropylene resin, polystyrene resin and ethylene vinyl acetate resin.
[0071]
　When an inorganic resin is used as the binder, polymetalloxane can be used. The polymetalloxane refers to a polymer compound in which a repeating metal-oxygen bond has a main chain skeleton. Preferably, polytitanoxane (Ti-O) and polysiloxane (Si-O) are used. These inorganic resins are obtained by hydrolyzing and condensing a metal alkoxide. The alkoxy group of the metal alkoxide is, for example, a lower alkoxy group such as methoxy group, ethoxy group, propoxy group, isopropoxy group, isobutoxy group, butoxy group and tert-butoxy group.
[0072]
　That is, the binder is epoxy resin, polyimide resin, polyurethane resin, polycarbodiimide resin, polyether sulfone, polyether ether ketone resin, phenol resin, furan resin, urea resin, acrylic resin, polyamideimide resin, polyethylene resin, polypropylene. One or more selected from the group consisting of resin, polystyrene resin, ethylene vinyl acetate resin, and polymetalloxane. The content of the binder is, for example, 60 to 99% by mass based on 100% by mass of all components other than the solvent.
[0073]
　The solid lubricating coating 23 may contain other components as needed. The other component is, for example, one or more selected from the group consisting of a rust inhibitor, a corrosion inhibitor, a surfactant, a wax, a friction modifier, a pigment and a solvent. The respective contents of the lubricating particles, the binder, and the other components are set appropriately. The content of the other components is, for example, 10% by mass or less in total, with 100% by mass of all the components other than the solvent.
[0074]
　The solid lubricating coating 23 is formed by applying the composition described above on the contact surface of at least one of the pin 13 and the box 14 and solidifying the composition.
[0075]
　In the pipe threaded joint 50 that fastens the pin 13 and the box 14 at the time of shipment, the solid lubricating coating 23 may be formed only on one contact surface of the pin 13 and the box 14, and then fastened. In this case, the work of applying the composition is easier for the coupling 12 having a short dimension than for the steel pipe 11 having a long dimension. Therefore, it is preferable to form the solid lubricating coating 23 on the contact surface of the box 14 of the coupling 12. At the pipe end of the pipe threaded joint 50 where the pin 13 and the box 14 are not fastened at the time of shipment, a solid lubricating film 23 is formed on the contact surfaces of both the pin 13 and the box 14 to prevent lubrication and prevent it simultaneously. You may give rust property. Further, the solid lubricating coating 23 may be formed only on one contact surface of the pin 13 and the box 14, and the solid anticorrosive coating described later may be formed on the other contact surface. In any case, seizure resistance, airtightness, and rust prevention can be imparted to the pipe threaded joint 50.
[0076]
　The solid lubricating coating 23 preferably covers all contact surfaces of at least one of the pin 13 and the box 14. The solid lubricating coating 23 may cover only a part of the contact surface (for example, only the metal seal portions 16 and 19).
[0077]
　The solid lubricating coating 23 may be a single layer or multiple layers. The multi-layer means a state in which two or more layers of the solid lubricating coating 23 are laminated from the contact surface side. By repeating application and solidification of the composition, two or more solid lubricating coatings 23 can be formed. The solid lubricating coating 23 may be formed directly on the contact surface, or may be formed after the below-described base treatment.
[0078]
　The preferable thickness of the solid lubricating coating 23 is 5 to 50 μm. When the thickness of the solid lubricating coating 23 is 5 μm or more, high lubricity can be stably obtained. On the other hand, when the thickness of the solid lubricating coating 23 is 50 μm or less, the adhesion of the solid lubricating coating 23 is stable. Further, when the thickness of the solid lubricating coating 23 is 50 μm or less, the screw tolerance (clearance) of the sliding surface is widened, so that the surface pressure during sliding becomes low. Therefore, it is possible to prevent the fastening torque from becoming excessively high. Therefore, the preferable thickness of the solid lubricating coating 23 is 5 to 50 μm. The lower limit of the thickness of the solid lubricating coating 23 is more preferably 8 μm, further preferably 10 μm. The upper limit of the thickness of the solid lubricating coating 23 is more preferably 40 μm, further preferably 30 μm.
[0079]
　[Solid Corrosion Coating] The
　threaded joint 50 for pipes described above may include the solid lubricating coating 23 on one contact surface of the pin 13 and the box 14 and the solid corrosion coating on the other contact surface of the pin 13 and box 14. Good. The pipe threaded joint 50 may be stored for a long time before being actually used. In this case, if the solid anticorrosive coating is formed, the anticorrosion property of the pin 13 or the box 14 is enhanced.
[0080]
　The solid anticorrosive coating is, for example, a chromate coating made of chromate. The chromate film is formed by a known trivalent chromate treatment.
[0081]
　Solid anticorrosion coatings are not limited to chromate coatings. Other solid anticorrosion coatings contain, for example, UV curable resins. In this case, the solid anticorrosive coating has such strength that it is not destroyed by the force applied when the protector is attached. Furthermore, during transportation and storage, the solid anticorrosive coating does not dissolve even when exposed to condensed water due to the dew point. Further, the solid anticorrosive coating does not easily soften even at a high temperature exceeding 40°C. The ultraviolet curable resin is a known resin composition. The ultraviolet curable resin is not particularly limited as long as it contains a monomer, an oligomer and a photopolymerization initiator, and causes a photopolymerization reaction by being irradiated with ultraviolet rays to form a cured film.
[0082]
　A plating layer may be formed on the other contact surface of the pipe threaded joint 50, and the above-mentioned solid anticorrosion coating may be formed on the plating layer, or the solid anticorrosion coating may be directly formed on the other contact surface. Good.
[0083]
　[Base Material of Threaded Joint for Pipe 50]
　The composition of the base material of the threaded joint for pipe 50 is not particularly limited. The base material of the pipe threaded joint 50 is, for example, carbon steel, stainless steel, alloy steel, or the like. Among alloy steels, duplex alloy stainless steels containing alloy elements such as Cr, Ni and Mo and high alloy steels such as Ni alloys have high rust preventive properties. Therefore, if these high alloy steels are used as the base material of the threaded joint for pipes 50, excellent rustproofness can be obtained in a corrosive environment containing hydrogen sulfide, carbon dioxide and the like.
[0084]
　[Manufacturing Method] The manufacturing method
　of the pipe threaded joint 50 according to the present embodiment will be described below.
[0085]
　The method for manufacturing the pipe threaded joint 50 according to the present embodiment includes a Zn—Ni alloy plating layer forming step and a solid lubricating coating forming step.
[0086]
　In this embodiment, a non-lustrous Zn-Ni alloy plating layer is formed. Thereby, the arithmetic average roughness Ra1 of the surface of the Zn—Ni alloy plating layer 21 can be made higher than the arithmetic average roughness Ra2 of the contact surface without performing the back strike treatment. That is, in the method for manufacturing the threaded joint for pipes according to the present embodiment, sand blasting, shot blasting and grit blasting are omitted.
[0087]
　[Zn-Ni alloy plating layer forming step] In the
　Zn-Ni alloy plating layer forming step, the Zn-Ni alloy plating treatment is performed without performing the blasting treatment, and the contact surface of at least one of the pin 13 and the box 14 is performed. A non-lustrous Zn-Ni alloy plating layer 21 is formed thereon. The Zn—Ni alloy plating layer 21 may be formed on the contact surfaces of both the pin 13 and the box 14. The Zn-Ni alloy plating treatment is performed by electroplating treatment. The electroplating process for forming the non-lustrous Zn-Ni alloy plating layer 21 is performed by a known method. For example, it is performed by immersing the contact surface of at least one of the pin 13 and the box 14 in a plating bath containing zinc ions and nickel ions and applying current. A commercially available non-glossy plating bath can be used. The Zn-Ni alloy plating layer contains 10 to 16% by mass of Ni.
[0088]
　In the present embodiment, by performing a non-glossy Zn—Ni alloy plating treatment, the arithmetic average roughness Ra1 of the surface of the Zn—Ni alloy plating layer 21 can be set to 0.1 to 3.2 μm. Therefore, the adhesion effect of the solid lubricating coating 23 is enhanced by the anchor effect. The higher the adhesion of the solid lubricating coating 23, the higher the seizure resistance of the threaded joint 50 for pipes. If the adhesion of the solid lubricating coating 23 is increased, the shouldering torque during screw tightening can be kept low.
[0089]
　In the Zn—Ni alloy plating layer forming step, the plating bath for forming the non-bright Zn—Ni alloy plating layer 21 contains, for example, 12 to 60% by mass of nickel ions as a content ratio of zinc ions and nickel ions. To do. More specifically, the composition of the plating bath for forming the non-bright Zn—Ni alloy plating layer 21 is, for example, zinc: 20 g/L, nickel chloride: 21 g/L, ammonium chloride: 240 g/L and an additive. : 100 ml/L. In this case, the nickel ion content is 12.0 mass %. The additive is, for example, a product name Dainzin Alloy AD2 manufactured by Daiwa Chemical Research Institute Co., Ltd. By using the plating bath having the above composition, it is possible to form the non-gloss Zn—Ni alloy plating layer 21 having the arithmetic average roughness Ra1 of 0.1 to 3.2 μm. If the plating bath having the above composition is used, the arithmetic mean roughness Ra1 of the surface of the Zn—Ni alloy plating layer 21 can be made higher than the arithmetic mean roughness Ra2 of the contact surface. The composition of the plating bath for forming the non-glossy Zn-Ni alloy plating layer 21 is not limited to the above-mentioned composition, and can be appropriately set within a range in which the non-glossy Zn-Ni alloy plating layer 21 is obtained.
[0090]
　The processing conditions for electroplating can be set as appropriate. The electroplating treatment conditions are, for example, plating bath pH: 1 to 10, plating bath temperature: 10 to 60° C., current density: 1 to 100 A/dm 2 , and treatment time: 0.1 to 30 minutes. As described above, the preferable thickness of the Zn—Ni alloy plating layer 21 is 1 to 20 μm.
[0091]
　[Solid lubricating film forming step] After the
　Zn-Ni alloy plating layer forming step, a solid lubricating film forming step is performed. In the solid lubricating coating forming step, first, a composition for solid lubricating coating (hereinafter, also referred to as a composition) is prepared. The composition is formed by mixing the lubricious particles and binder described above. The composition may further contain the above-mentioned solvent and other components.
[0092]
　The composition obtained is applied onto the Zn—Ni alloy plating layer 21. The coating method is not particularly limited. For example, a composition using a solvent is sprayed onto the Zn—Ni alloy plating layer 21 using a spray gun. In this case, the composition is uniformly applied on the Zn—Ni alloy plating layer 21. The pin 13 or the box 14 coated with the composition is dried or heated and dried. The heat drying can be carried out using, for example, a commercially available hot air drying device. As a result, the composition is solidified and the solid lubricating coating 23 is formed on the Zn—Ni alloy plating layer 21. The heating and drying conditions can be appropriately set in consideration of the boiling point and melting point of each component contained in the composition.
[0093]
　When the solid lubricating coating 23 is formed using a composition that does not use a solvent, for example, a hot melt method can be used. In the hot melt method, the composition is heated to a fluid state. The composition in a fluidized state is sprayed using, for example, a spray gun having a temperature holding function. Thereby, the composition is uniformly applied onto the Zn—Ni alloy plating layer 21. The heating temperature of the composition can be appropriately set in consideration of the melting points and softening temperatures of the binder and other components described above. The pin 13 or box 14 coated with the composition is cooled by air cooling or the like. As a result, the composition is solidified and the solid lubricating coating 23 is formed on the Zn—Ni alloy plating layer 21.
[0094]
　[Formation of Solid Anticorrosion Coating (Trivalent Chromate Treatment)]
　As described above, the Zn-Ni alloy plating layer forming step and the solid lubricating coating forming step are carried out on one contact surface of the pin 13 and the box 14. The Zn—Ni alloy plating layer 21 and the solid lubricating coating 23 may be formed.
[0095]
　On the other hand, the Zn-Ni alloy plating layer 21 and the solid lubricating coating 23 may be formed on the other contact surface of the pin 13 and the box 14, or the Zn-Ni alloy plating layer 21 and/or the solid anticorrosive coating. May be formed. Hereinafter, the case of forming the solid anticorrosion coating including the Zn—Ni alloy plating layer 21 and the chromate coating on the other contact surface will be described.
[0096]
　In this case, the Zn—Ni alloy plating layer forming step described above is performed to form the Zn—Ni alloy plating layer 21. After the Zn-Ni alloy plating layer forming step, trivalent chromate treatment is performed to form a solid anticorrosion coating. The trivalent chromate treatment is a treatment for forming a chromate coating film of a chromate of trivalent chromium. The chromate film formed by the trivalent chromate treatment suppresses white rust on the surface of the Zn alloy plating layer. Thereby, the trivalent chromate treatment for improving the appearance of the product can be performed by a known method. For example, the contact surface of at least one of the pin 13 and the box 14 is dipped in the chromate treatment liquid, or the chromate treatment liquid is sprayed on the contact surface. Then, the contact surface is washed with water. The contact surface may be soaked in a chromate-treated solution, electrified and then washed with water. A chromate treatment liquid may be applied to the contact surface and dried by heating. The treatment conditions of trivalent chromate can be set appropriately.
[0097]
　[Pretreatment Step] The
　above-mentioned manufacturing step may optionally include a pretreatment step before the Zn—Ni alloy plating layer forming step. The pretreatment process is, for example, pickling and alkaline degreasing. In the pretreatment step, oil and the like adhering to the contact surface is washed. The pretreatment step may further include a grinding process such as mechanical grinding finishing. Here, the grinding processing such as mechanical grinding finishing means reducing the surface roughness by cutting.
[0098]
　The threaded joint 50 for a pipe of the present embodiment is manufactured by the above manufacturing process.
Example
[0099]
　Examples will be described below. However, the present invention is not limited to the examples. In the embodiment, the contact surface of the pin 13 is called a pin surface and the contact surface of the box 14 is called a box surface. In addition,% in the examples means mass% unless otherwise specified.
[0100]
　In this embodiment, VAM21 (registered trademark) product name SM13CRS-110 manufactured by Nippon Steel & Sumitomo Metal Corporation was used. VAM21 (registered trademark) product name SM13CRS-110 is a threaded joint for pipes having an outer diameter of 177.80 mm (7 inches) and a wall thickness of 11.506 mm (0.453 inches). The steel type was 13Cr steel. The composition of 13Cr steel is as follows: C: 0.03% or less, Si: 0.5% or less, Mn: 0.5% or less, Ni: 5.0 to 6.5%, Cr: 11.5-13.5. %, Mo: 1.5 to 3.0%, balance: Fe and impurities.
[0101]
　Mechanical grinding finish was performed on the pin surface and the box surface of each test number. The arithmetic average roughness Ra2 of the contact surface of each test number was as shown in Table 1. The arithmetic average roughness Ra2 was measured based on JIS B0601 (2001). A laser microscope VK-X110 manufactured by Keyence Corporation was used to measure the arithmetic average roughness Ra. Data of 1.25 mm square at 0.85 μm pitch was collected by mapping. The standard values ​​of JIS B0601 (1994) were used for the cutoff value λ c and the measurement length for calculating the roughness curve . The measuring direction of the arithmetic mean roughness was the grinding direction.
[0102]
　The Ni content of the Zn—Ni alloy plating layer 21 was 10 to 16 mass %.
[0103]
[Table 2]

[0104]
　The method of forming each plating layer or coating was as follows.
[0105]
　[Test No. 1] In
　Test No. 1, bright Zn—Ni electroplating was applied to the surfaces of the pins 13 and the box 14 to form a bright Zn—Ni alloy plating layer 21 having a thickness of 10 μm. The electroplating conditions were: plating bath pH: 6.5, plating bath temperature: 25° C., current density: 2 A/dm 2 , and treatment time: 18 minutes. The composition of the plating solution was Zn: 5 g/L, Ni: 24 g/L, ammonium chloride: 206 g/L, boric acid: 120 g/L, and additive: 20 mL/L. The additive was Dainjin Alloy AD1 manufactured by Daiwa Chemical Industry Co., Ltd. The composition of the bright Zn—Ni alloy plating layer 21 was Zn: 87% and Ni: 13%. The arithmetic mean roughness Ra after the bright Zn—Ni alloy plating treatment was measured by the same measuring method as the arithmetic mean roughness Ra2 of the contact surface. λ c was 0.25 mm, and the measurement length was 0.67 mm. A solid lubricating coating 23 was formed on the surface of the box 14. As the solid lubricating coating 23, a commercially available thermosetting epoxy resin coating was used. The thickness of the solid lubricating coating 23 was 25 μm.
[0106]
　[Test No. 2] In
　Test No. 2, the surface of the pin 13 and the box 14 was subjected to non-glossy Zn—Ni electroplating to form a 10 μm-thick non-glossy Zn—Ni alloy plating layer 21. The electroplating conditions were: plating bath pH: 5.5, plating bath temperature: 35° C., current density: 6 A/dm 2 , and treatment time: 400 seconds. The composition of the plating solution was Zn: 25 g/L, Ni: 28 g/L, ammonium chloride: 240 g/L, and additive: 100 mL/L. The additive was a product name: Dainjin Alloy AD2 manufactured by Daiwa Chemical Industry Co., Ltd. The composition of the non-bright Zn—Ni alloy plating layer 21 was Zn: 87% and Ni: 13%. The arithmetic mean roughness Ra after the non-bright Zn-Ni alloy plating treatment was measured by the same measuring method as the arithmetic mean roughness Ra2 of the contact surface. λ c was 0.8 mm and the measurement length was 1.25 mm. A solid lubricating coating 23 was formed on the surface of the box 14. As the solid lubricating coating 23, a commercially available thermosetting epoxy resin coating was used. The thickness of the solid lubricating coating 23 was 25 μm.
[0107]
　Reference Example In the
　reference example, the surface of the box 14 was sandblasted. The arithmetic average roughness Ra2 of the surface of the box 14 after the sandblast treatment was measured by the above method. The standard values ​​of JIS B0601 (1994) were used for the cutoff value λ c and the measurement length for calculating the roughness curve . The measuring direction of the arithmetic mean roughness was the grinding direction. Further, the pin 13 and the box 14 were subjected to bright Zn—Ni electroplating to form a bright Zn—Ni alloy plating layer 21 having a thickness of 10 μm. The electroplating conditions were: plating bath pH: 6.5, plating bath temperature: 25° C., current density: 2 A/dm 2 , and treatment time: 18 minutes. The composition of the plating solution was Zn: 5 g/L, Ni: 24 g/L, ammonium chloride: 206 g/L, boric acid: 120 g/L, and additive: 20 mL/L. The additive was Dainjin Alloy AD1 manufactured by Daiwa Chemical Industry Co., Ltd. The composition of the bright Zn—Ni alloy plating layer 21 was Zn: 87% and Ni: 13%. The arithmetic mean roughness Ra after the Zn—Ni alloy plating treatment was measured by the same measuring method as the arithmetic mean roughness Ra2 of the contact surface. The standard values ​​of JIS B0601 (1994) were used for the cutoff value λ c and the measurement length for calculating the roughness curve . The measuring direction of the arithmetic mean roughness was the grinding direction. On the surface of the box 14, a solid lubricating coating 23 was formed on it. As the solid lubricating coating 23, a commercially available thermosetting epoxy resin coating was used. The thickness of the solid lubricating coating 23 was 25 μm.
[0108]
　The seizure resistance and the shouldering torque were evaluated. In the reference example, only seizure resistance was evaluated, and shouldering torque was not evaluated.
[0109]
　[
　Seizure resistance evaluation test] The seizure resistance evaluation test was carried out in accordance with ISO13679 (2011). Specifically, the pin 13 and the box 14 of the test number 1 and the test number 2 were used and tightened by hand tight (a state of being fastened manually) until the screws are engaged at the initial stage of fastening. After fastening with Handtight, screw tightening and unscrewing were repeated with power tongs to evaluate seizure resistance. The surface of the pin 13 and the surface of the box 14 were visually observed each time the screw tightening and the screw returning were performed once. The occurrence of seizure was confirmed by visual observation. If the seizure was slight and recoverable, the seizure defect was repaired and the test was continued. The number of times of screw tightening and unscrewing at the time when irreversible seizure occurred was measured. The results are shown in the "Seizure resistance" column of Table 2.
[0110]
　[Shouldering torque measurement test]
　Screws are tightened using the pin 13 and the box 14 of test number 1 and test number 2, and the number of fastenings (one screw fastening and one screw return is one fastening number) and torque. Was measured. The shouldering torque was obtained by plotting the measured number of turns and the torque. The screwing torque and the screw return (fastening) were repeated, and the shouldering torque was calculated each time. From the obtained shouldering torque, the ratio (ShT%) of the shouldering torque to the target fastening torque was calculated. The target fastening torque was set to a constant value. The results are shown in Table 3. In Test No. 1, irreversible seizure occurred during the fifth screw tightening and screw unscrewing, so the subsequent tests were not performed.
[0111]
[Table 3]

[0112]
　[Evaluation Result] In
　Test No. 2, the non-glossy Zn—Ni alloy plating layer 21 was formed. Therefore, the arithmetic average roughness Ra1 of the surface of the Zn—Ni alloy plating layer 21 was 0.1 to 3.2 μm without performing a surface roughness forming step such as sandblasting. As a result, the seizure resistance was as high as 10 times. This was seizure resistance comparable to the seizure resistance of the sandblasted reference example. In Test No. 2, the non-glossy Zn-Ni alloy plating layer 21 was formed without performing sandblasting. Therefore, the arithmetic average roughness Ra1 of the surface of the Zn-Ni alloy plating layer 21 is the arithmetic average of the contact surface. The roughness was higher than Ra2. The test number 2 was able to maintain the shouldering torque lower than that of the test number 1 even after repeating the screw tightening and the screw returning.
[0113]
　In Test No. 1, since the bright Zn—Ni alloy plating layer 21 was formed, the arithmetic average roughness Ra1 of the surface of the Zn—Ni alloy plating layer 21 was less than 0.1 μm. Therefore, seizure resistance was low. In the test number 1, the shouldering torque increased as the screw tightening and the screw returning were repeated.
[0114]
　The embodiments of the present invention have been described above. However, the embodiments described above are merely examples for carrying out the present invention. Therefore, the present invention is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit thereof.
Explanation of symbols
[0115]
　11 Steel Pipe
　12 Coupling
　13 Pin
　14 Box
　15 Male
　Threaded Part 16, 19 Metal Sealing Part
　17, 18 Shoulder Part
　20 Female 　Threaded Part
　21 Zn-Ni Alloy Plating Layer
　23 Solid Lubrication Film
50 Pipe Threaded Joint
The scope of the claims
[Claim 1]
　A threaded joint for pipe,
　comprising a pin and a box each having a contact surface including a threaded portion, the threaded joint being formed on the contact surface of at least one of the pin and the box and containing 10 to 16% by mass of Ni. A Zn-Ni alloy plating layer and a
　solid lubricating coating formed on the
　Zn-Ni alloy plating layer, and the contact surface on which the Zn-Ni alloy plating layer is formed is ground.
　The arithmetic average roughness of the surface of the Zn—Ni alloy plating layer measured along the grinding direction of the contact surface by a laser microscope is defined as Ra1, and the
　contact surface along the grinding direction of the contact surface by the laser microscope is defined. A 　threaded joint for pipes , wherein the
　arithmetic mean roughness Ra1 is 0.1 to 3.2 μm, and the
arithmetic mean roughness Ra1 is larger than the arithmetic mean roughness Ra2, when the arithmetic mean roughness Ra measured is defined as Ra2.
[Claim 2]
　The pipe threaded joint according to claim 1,
　wherein the arithmetic average roughness Ra1 is 0.1 to 0.4 μm.
[Claim 3]
　The pipe threaded joint according to claim 1 or 2,
　wherein the contact surface further comprises a threadless metal contact.
[Claim 4]
　A method for manufacturing a threaded joint for pipes, each comprising a pin and a box having a contact surface including a threaded portion,
　wherein at least one of the contact surface of the pin and the box is subjected to electroplating without performing a blast treatment. Zn-Ni alloy containing 10 to 16% by mass of Ni and having an arithmetic average surface roughness Ra1 of 0.1 to 3.2 μm measured by a laser microscope along the grinding direction of the contact surface. A
　method for manufacturing a threaded joint for pipes , comprising: a step of forming a plating layer; and a step of forming a solid lubricating coating on the Zn—Ni alloy plating layer without performing blast treatment.
[Claim 5]
　The method for manufacturing the threaded joint for pipes according to claim 4,
　wherein the contact surface further includes a non-threaded metal contact portion.