WO2020149310A1

WO2020149310A1 - Threaded joint for pipes and method for manufacturing threaded joint for pipes

Info

Publication number: WO2020149310A1
Application number: PCT/JP2020/001097
Authority: WO
Inventors: 後藤　邦夫
Original assignee: 日本製鉄株式会社; バローレック・オイル・アンド・ガス・フランス
Priority date: 2019-01-16
Filing date: 2020-01-15
Publication date: 2020-07-23
Also published as: AR117811A1; JPWO2020149310A1

Abstract

The present invention provides a threaded joint for pipes that has excellent high torque performance and a method for manufacturing the same. This threaded joint for pipes includes a pin (3), a box (4), and a solid lubrication film (21). The pin (3) has a pin-side contacting surface (34) that includes a pin-side threaded portion (31). The box (4) has a box-side contacting surface (44) that includes a box-side threaded portion (41). The solid lubrication film (21) is disposed on the pin-side contacting surface (34) and/or the box-side contacting surface (44). The solid lubrication film (21) comprises a binder, a lubricant, and glass frit.

Description

Pipe threaded joint and method for manufacturing pipe threaded joint

The present disclosure relates to a threaded joint for pipes and a method for manufacturing a threaded joint for pipes.

　The oil well pipes such as tubing and casing used for oil well drilling for crude oil and gas oil are generally connected (fastened) using tubular threaded joints. The depth of the oil well was conventionally 2000 to 3000 m. However, in deep oil wells such as offshore oil fields in recent years, it reaches 8,000 to 10,000 meters. The length of each oil well pipe is typically a dozen meters. A plurality of casings enclose the circumference of the tubing in which a fluid such as crude oil flows. The number of connected oil country tubular goods may reach an enormous number such as over 1,000.

▽ Under the operating environment, a load such as an axial tensile force due to the mass of the oil well pipe and the joint itself, a combined pressure such as inner and outer surface pressure, and even underground heat act on the threaded joint for the oil well pipe. Therefore, the pipe threaded joint is required to maintain airtightness without being damaged even under such a severe environment.

A typical pipe threaded joint used for fastening oil country tubular goods has a pin-box structure composed of a member called a pin having a male screw and a member called a box having a female screw. The pin includes a pin side screw portion (male screw portion) formed on the outer peripheral surface of the end portion of the steel pipe. The pin may further include a pin side metal seal portion and a pin side shoulder portion. The box includes a box side screw portion (female screw portion) formed on the inner peripheral surface of the end portion of the steel pipe. The box may further include a box-side metal seal portion and a box-side shoulder portion. When the steel pipes are screwed together, the male screw portion and the female screw portion come into contact with each other. When the threaded joint for pipes includes the metal seal portion and the shoulder portion, the metal seal portions and the shoulder portions contact each other during screw tightening.

　During tubing or casing lowering work to an oil well, due to various reasons such as trouble, loosening the threaded joints for pipes that have been once tightened, pulling up these joints once from the oil well, and then re-fastening them may lower them. The pin, the screw part of the box, the metal seal part, and the shoulder part are 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 screw tightening and unscrewing are repeated. Therefore, the pipe threaded joint is required to have sufficient durability against friction, that is, excellent seizure resistance.

Conventionally, in order to improve seizure resistance and airtightness of threaded joints for pipes, a viscous liquid lubricant (grease lubricating oil) containing heavy metal powder called "compound grease" is used as a contact surface (that is, When a threaded portion or a threaded joint for pipes has a metal seal portion and a shoulder portion, it has been applied to the screw portion, the metal seal portion and the shoulder portion). An example of compound grease is described in API standard BUL 5A2.

However, heavy metals such as Pb contained in compound grease may affect the environment. Therefore, it is desired to develop a threaded joint for pipes that does not use compound grease.

International Publication No. 2014/042144 (Patent Document 1) and International Publication No. 2015/141159 (Patent Document 2) propose a threaded joint for pipes which is excellent in seizure resistance even without compound grease.

The composition for forming a solid lubricating coating described in Patent Document 1 is a powdery organic compound which is at least partially soluble in a dipolar aprotic solvent in a mixed solvent containing water and a dipolar aprotic solvent. It is a composition containing a resin. In the composition for forming a solid lubricating coating of Patent Document 1, the powdery organic resin exists in the mixed solvent in a dissolved state or a dispersed state. It is described in Patent Document 1 that this makes it possible to suppress the generation of rust and to have excellent seizure resistance without using compound grease.

The threaded joint for pipes described in Patent Document 2 has a solid lubricating coating on the contact surface. The solid lubricating coating contains a binder, a fluorine-based additive, a solid lubricant, and an anticorrosive additive. In Patent Document 2, the binder contains an ethylene vinyl acetate resin, a polyolefin resin, and a wax having a melting point of 110° C. or less, and the ratio of the mass of the ethylene vinyl acetate resin to the mass of the polyolefin resin is 1.0 to The ratio of the mass of the polyolefin resin and the ethylene vinyl acetate resin to the mass of the wax is 0.7 to 1.6. As a result, it is possible to obtain a threaded joint for pipes that suppresses rust generation, exhibits excellent seizure resistance and airtightness, and has a surface that is not sticky easily even in an extremely low temperature environment without using compound grease. 2 is described.

International Publication No. 2014/042144 International Publication No. 2015/141159

By the way, when tightening a threaded joint for pipes, 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 amount of screw interference.

▽In the final stage of screw tightening, the surface pressure between screws becomes high. Even if the surface pressure becomes high, if the high torque is maintained without seizure, the fastening torque can be easily adjusted. Therefore, the threaded joint for pipes is required to have high torque performance, which is the performance of maintaining high torque at high surface pressure.

In the case of a pipe threaded joint having a shoulder, high torque performance can be expressed as torque-on-shoulder resistance ΔT'.

If the pipe threaded joint has a shoulder, the shoulders of the pin and box will contact each other when tightening the screw. The torque generated at this time is called shouldering torque. When tightening the threaded joint for pipes, after reaching the shouldering torque, further tightening is performed until the tightening is completed. Thereby, the airtightness of the threaded joint for pipes is enhanced. If the screws are tightened excessively, 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. The torque on-shoulder resistance ΔT′ means a difference between the shouldering torque and the yield torque.

When the threaded joint for pipes has a shoulder portion, if the torque-on-shoulder resistance ΔT' is large, the tightening torque can be easily adjusted. Even if the pipe threaded joint does not have a shoulder portion, the fastening torque can be easily adjusted if a high torque is maintained at a high surface pressure.

According to the above technology, excellent seizure resistance can be obtained without compound grease. However, there are cases where sufficient high torque performance cannot be obtained.

An object of the present disclosure is to provide a pipe threaded joint having excellent seizure resistance and excellent high torque performance, and a manufacturing method thereof.

The threaded joint for pipes according to the present disclosure includes a pin, a box, and a solid lubricating coating. The pin has a pin side contact surface that includes a pin side thread. The box has a box-side contact surface that includes box-side threads. The solid lubricating coating is disposed on at least one of the pin side contact surface and the box side contact surface. The solid lubricating coating contains a binder, a lubricant and a glass frit.

The method for manufacturing a threaded joint for pipes according to the present disclosure includes a preparation step and a solid lubricant film forming step. In the preparation step, a pin, a box, and a composition for forming a solid lubricating coating are prepared. The pin has a pin side contact surface that includes a pin side thread. The box has a box-side contact surface that includes box-side threads. The composition for forming a solid lubricating coating contains a binder, a lubricant and a glass frit. In the solid lubricating coating forming step, the solid lubricating coating forming composition is applied to at least one of the pin-side contact surface and the box-side contact surface and then solidified to form a solid lubricating coating.

The pipe threaded joint according to the present disclosure has excellent seizure resistance and excellent high torque performance. The method for manufacturing a threaded joint for pipes according to the present disclosure can manufacture a threaded joint for pipes having excellent seizure resistance and excellent high torque performance.

FIG. 1 is a diagram showing a relationship between a rotational speed and a torque of a steel pipe when a pipe threaded joint having a shoulder portion is screwed. FIG. 2 is a graph showing the relationship between the glass frit content in the solid lubricating coating and the torque on-shoulder resistance ΔT'. FIG. 3 is a diagram showing the relationship between the glass frit content in the solid lubricating coating and seizure resistance. FIG. 4 is a diagram showing the configuration of the coupling type threaded joint for pipes according to the present embodiment. FIG. 5: is a figure which shows the structure of the integral type threaded joint for pipes by this embodiment. FIG. 6 is a sectional view of a threaded joint for pipes. FIG. 7 is a cross-sectional view of the pipe threaded joint according to the present embodiment. FIG. 8 is a sectional view of a threaded joint for pipes according to another embodiment, which is different from FIG. 7. FIG. 9 is a cross-sectional view of a threaded joint for pipes according to another embodiment, which is different from FIGS. 7 and 8. FIG. 10 is a diagram for explaining the torque on-shoulder resistance ΔT′ in the embodiment. FIG. 11 is a micrograph of a glass frit in the example. FIG. 12 is a micrograph of whiskers in the example.

Hereinafter, the present embodiment will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts will be denoted by the same reference characters and description thereof will not be repeated.

The present inventor has conducted various studies on the relationship between a threaded joint for pipes, seizure resistance, and high torque performance, using a pipe screw having a shoulder. As a result, the following findings were obtained.

When screwing steel pipes together, the optimum torque to finish screwing is predetermined. FIG. 1 is a diagram showing a relationship between a rotational speed and a torque of a steel pipe when a pipe threaded joint having a shoulder portion is screwed. FIG. 1 is also called a torque chart. Referring to FIG. 1, when the pipe threaded joint is screwed, initially, the torque increases in proportion to the rotation speed. At this time, the rate of increase in torque is low. If the screws are further tightened, the shoulders will come into contact with each other. The torque at this time is called shouldering torque. If the screwing is further tightened after reaching the shouldering torque, the torque rises again in proportion to the rotation speed. The rate of increase in torque at this time is higher than that before reaching the shouldering torque. When the torque reaches a predetermined value (fastening torque), screw tightening is completed. If the torque for tightening the screws reaches the tightening torque, the metal seal portions interfere with each other with an appropriate surface pressure. In this case, the airtightness of the pipe threaded joint is increased.

If the screw is tightened further after reaching the tightening torque, the torque will be too high. If the torque becomes too high, some of the pin and box will plastically deform. The torque at this time is called yield torque. If the torque on-shoulder resistance ΔT′, which is the difference between the shouldering torque and the yield torque, is large, there is a margin in the fastening torque range. As a result, the tightening torque can be easily adjusted. Therefore, it is preferable that the torque on-shoulder resistance ΔT′ is large. In the present specification, excellent high torque performance means that the torque-on-shoulder resistance ΔT′ is large when the pipe threaded joint has a shoulder portion.

In order to obtain excellent high torque performance, it is effective to reduce the shouldering torque or increase the yield torque when the pipe threaded joint has a shoulder portion. The present inventor has focused on a method of increasing the yield torque. The present inventor considered that the inclusion of hard particles in the solid lubricating coating would increase the yield torque at high surface pressure, and as a result, enhance the high torque performance.

However, as a result of the investigation by the present inventors, excellent high torque performance could not be obtained even if the solid particles were simply contained in the solid lubricating coating. For example, polytetrafluoroethylene (PTFE) is a hard particle. However, as shown in the examples below, PTFE did not provide excellent high torque performance.

The inventor conducted various studies and found that excellent high torque performance can be obtained by including glass frit in the solid lubricating coating.

FIG. 2 is a diagram showing the relationship between the glass frit content in the solid lubricating coating and the torque on shoulder resistance ΔT′. FIG. 2 was obtained by the example described below. The torque-on-shoulder resistance ΔT′ was obtained by using the numerical value of the torque-on-shoulder resistance ΔT′ when API standard dope was used instead of the solid lubricating coating in Test No. 9 in Examples described later as a reference (100). Further, it is a relative value of the torque on-shoulder resistance ΔT′ in the present embodiment. The white circles (◯) in FIG. 2 indicate the torque-on-shoulder resistance ΔT′ of the example in which the solid lubricating coating is formed. The triangle mark (Δ) in FIG. 2 indicates the torque on-shoulder resistance ΔT′ when the API standard dope is used instead of the solid lubricating coating.

From Fig. 2, if the solid lubricating coating contains glass frit, the torque on shoulder resistance ΔT' exceeds 100. That is, if the solid lubricating coating contains glass frit, excellent high torque performance can be obtained.

If the solid lubricating coating contains glass frit, it is not clear why excellent high torque performance can be obtained. However, it is presumed that: At the final stage of screw tightening, the contact pressure between the contact surfaces becomes high (high contact pressure). The glass frit is present on the contact surface at the time of high surface pressure and in the powder generated by the wear of the solid lubricating coating and the threaded joint for pipes. Glass frits increase the coefficient of friction between contacting surfaces. As a result, high torque is maintained at high surface pressure, and excellent high torque performance is obtained. The glass frit exhibits excellent high torque performance by increasing the friction coefficient at high surface pressure. Therefore, even when the pipe threaded joint having no shoulder is used, the glass frit exhibits excellent high torque performance in the final stage of screw tightening.

The present inventor has further found that not only excellent high torque performance but also excellent seizure resistance can be obtained by adjusting the content of the glass frit in the solid lubricating coating.

FIG. 3 is a diagram showing the relationship between the glass frit content in the solid lubricating coating and seizure resistance. FIG. 3 was obtained by the example described below. In FIG. 3, the vertical axis represents the number of times (times) the fastening could be performed without burning.

From Fig. 3, if the glass frit content is 10.0 mass% or less, the number of times that it can be fastened without burning is 8 or more. That is, when the glass frit content is 10.0 mass% or less, excellent seizure resistance is obtained in addition to excellent high torque performance.

The threaded joint for pipes according to the present embodiment completed based on the above findings includes pins, a box, and a solid lubricating coating. The pin has a pin side contact surface that includes a pin side thread. The box has a box-side contact surface that includes box-side threads. The solid lubricating coating is disposed on at least one of the pin side contact surface and the box side contact surface. The solid lubricating coating contains a binder, a lubricant and a glass frit.

The solid lubricating coating of the threaded joint for pipes according to the present embodiment contains glass frit. As a result, the pipe threaded joint according to the present embodiment has excellent high torque performance.

Preferably, the above-mentioned solid lubricating coating contains 0.01 to 10.0% by mass of glass frit.

In this case, the pipe threaded joint has excellent seizure resistance in addition to excellent high torque performance.

The above glass frit is, in mass %, SiO ₂ : 40 to 70%, Al ₂ O ₃ : 1 to 20%, CaO: 0.1 to 25%, B ₂ O ₃ :0 to 40%, MgO: 0 to 3%, Na ₂ O: 0 to 15%, K ₂ O: 0 to 10%, and ZnO: 0 to 10% may be contained.

Preferably, the binder is one or more selected from the group consisting of epoxy resin, phenol resin, furan resin, polyamideimide resin, polyamide resin, polyimide resin, urethane resin and polyetheretherketone resin.

Preferably, the lubricant is one or more selected from the group consisting of molybdenum disulfide, graphite, polytetrafluoroethylene and fluorinated graphite.

Preferably, the pin further includes a pin side metal seal and a pin side shoulder portion, and the box further includes a box side metal seal portion and a box side shoulder portion.

The method for manufacturing a threaded joint for pipes according to the present embodiment includes a preparation step and a solid lubricant film forming step. In the preparation step, a pin, a box, and a composition for forming a solid lubricating coating are prepared. The pin has a pin side contact surface that includes a pin side thread. The box has a box-side contact surface that includes box-side threads. The composition for forming a solid lubricating coating contains a binder, a lubricant and a glass frit. In the solid lubricating coating forming step, the solid lubricating coating forming composition is applied to at least one of the pin-side contact surface and the box-side contact surface and then solidified to form a solid lubricating coating.

In the above-mentioned manufacturing method, a solid lubricating coating is manufactured using a composition for forming a solid lubricating coating containing glass frit. Therefore, a pipe threaded joint having excellent high torque performance can be obtained.

The above-described manufacturing method may further include a step of forming a Zn alloy plating layer by electroplating on at least one of the pin-side contact surface and the box-side contact surface before the step of forming the solid lubricating coating. ..

In this case, seizure resistance and corrosion resistance of the threaded joint for pipes are further enhanced.

The above-described manufacturing method may further include a step of roughening at least one of the pin side contact surface and the box side contact surface before the step of forming the Zn alloy plating layer by electroplating.

In this case, the adhesion of the solid lubricating coating is further increased.

Preferably, in the above manufacturing method, the pin further includes a pin side metal seal and a pin side shoulder portion, and the box further includes a box side metal seal portion and a box side shoulder portion.

Hereinafter, the pipe threaded joint according to the present embodiment and the method for manufacturing the same will be described in detail.

[Pipe threaded joint]
The pipe threaded joint includes a pin and a box. FIG. 4 is a diagram showing the configuration of the coupling type threaded joint for pipes according to the present embodiment. Referring to FIG. 4, in the case of a coupling type threaded joint for pipes, the threaded joint for pipes includes a steel pipe 1 and a coupling 2. At both ends of the steel pipe 1, pins 3 having male threads on the outer surface are formed. At both ends of the coupling 2, a box 4 having an internal thread portion on the inner surface is formed. The coupling 2 is attached to the end of the steel pipe 1 by screwing the pin 3 and the box 4 together. Although not shown, a protector may be attached to the pin 3 of the steel pipe 1 and the box 4 of the coupling 2 to which the mating members are not attached, in order to protect the respective screw portions.

On the other hand, without using the coupling 2, an integral type oil well pipe threaded joint in which one end of the steel pipe 1 is the pin 3 and the other end is the box 4 may be used. FIG. 5: is a figure which shows the structure of the integral type threaded joint for pipes by this embodiment. With reference to FIG. 5, in the case of an integral type threaded joint for pipes, the threaded joint for pipes includes a steel pipe 1. A pin 3 having a male screw portion on the outer surface is formed at one end of the steel pipe 1. At the other end of the steel pipe 1, a box 4 having an internal thread portion on its inner surface is formed. The steel pipes 1 can be connected to each other by screwing the pin 3 and the box 4 together. The pipe threaded joint of the present embodiment can be used for both coupling type and integral type pipe threaded joints.

FIG. 6 is a sectional view of a pipe threaded joint. In FIG. 6, the pin 3 includes a pin side screw portion 31, a pin side metal seal portion 32, and a pin side shoulder portion 33. In FIG. 6, the box 4 includes a box-side screw portion 41, a box-side metal seal portion 42, and a box-side shoulder portion 43. The portions that come into contact when the pin 3 and the box 4 are screwed are referred to as contact surfaces 34 and 44. Specifically, when the pin 3 and the box 4 are screwed together, the screw parts (pin side screw part 31 and box side screw part 41), metal seal parts (pin side metal seal part 32 and box side metal seal part). 42) and the shoulder portions (the pin side shoulder portion 33 and the box side shoulder portion 43) contact each other. In FIG. 6, the pin-side contact surface 34 includes a pin-side screw portion 31, a pin-side metal seal portion 32, and a pin-side shoulder portion 33. In FIG. 6, the box-side contact surface 44 includes a box-side screw portion 41, a box-side metal seal portion 42, and a box-side shoulder portion 43.

In FIG. 6, in the pin 3, the pin side shoulder portion 33, the pin side metal seal portion 32, and the pin side screw portion 31 are arranged in this order from the end of the steel pipe 1. Further, in the box 4, the box-side screw portion 41, the box-side metal seal portion 42, and the box-side shoulder portion 43 are arranged in this order from the end of the steel pipe 1 or the coupling 2. However, the arrangement of the pin-side screw portion 31 and the box-side screw portion 41, the pin-side metal seal portion 32 and the box-side metal seal portion 42, and the pin-side shoulder portion 33 and the box-side shoulder portion 43 is limited to the arrangement of FIG. 6. Instead, it can be changed as appropriate. For example, as shown in FIG. 5, in the pin 3, from the end of the steel pipe 1, the pin side screw part 31, the pin side metal seal part 32, the pin side shoulder part 33, the pin side metal seal part 32 and the pin side screw part. They may be arranged in the order of 31. In the box 4, the box-side screw portion 41, the box-side metal seal portion 42, the box-side shoulder portion 43, the box-side metal seal portion 42, and the box-side screw portion 41 are arranged in this order from the end of the steel pipe 1 or the coupling 2. May be.

5 and 6, a so-called premium joint including a metal seal portion (pin side metal seal portion 32 and box side metal seal portion 42) and a shoulder portion (pin side shoulder portion 33 and box side shoulder portion 43) is shown. .. However, the metal seal portion (pin side metal seal portion 32 and box side metal seal portion 42) and shoulder portion (pin side shoulder portion 33 and box side shoulder portion 43) may be omitted. The solid lubricating coating of the present embodiment can be suitably applied to a pipe threaded joint having no metal seal portion and shoulder portion. Without the metal seal and shoulder, the pin-side contact surface 34 includes the pin-side threaded portion 31. Without the metal seal and shoulder, the box-side contact surface 44 includes the box-side threaded portion 41.

[Solid lubrication film]
The pipe threaded joint comprises a solid lubricating coating on at least one of the pin side contact surface 34 and the box side contact surface 44. FIG. 7 is a cross-sectional view of the pipe threaded joint according to the present embodiment. The solid lubricating coating 21 is formed by applying a composition for forming a solid lubricating coating to at least one of the pin-side contact surface 34 and the box-side contact surface 44 and then solidifying the composition, as in the production method described later.

The solid lubricating coating 21 contains a binder, a lubricant and a glass frit. Therefore, the composition for forming the solid lubricating coating 21 also contains the binder, the lubricant and the glass frit. The composition may be a solvent-free composition or a solvent-type composition dissolved in a solvent. In the case of a solvent type composition, the mass% of each component means the mass% when the total mass of all components other than the solvent contained in the composition is 100%. That is, the content of each component in the composition and the content of each component in the solid lubricating coating 21 are the same. Hereinafter, the composition for forming the solid lubricating coating 21 is also simply referred to as “composition”.

Details of each component are given below.

[Binder]
The binder enhances the adhesion of the lubricant and the glass frit on the contact surface of the threaded joint for pipes. The binder is one or two selected from the group consisting of organic resins and inorganic polymers.

Known organic resins can be selected. The organic resin is, for example, one or two selected from the group consisting of thermosetting resins and thermoplastic resins. The thermosetting resin is, for example, epoxy resin, phenol resin, furan resin, polyimide resin, melamine resin, urea resin, silicone resin, polyurethane resin (thermosetting), unsaturated polyester resin, casein resin, alkyd resin, diallyl phthalate resin. And one or more selected from the group consisting of polyamino bismaleimide resin. The thermoplastic resin is, for example, polyamideimide resin, polyamide resin, polyetheretherketone resin, polyvinyl chloride resin, polyvinyl acetate resin, polyethylene resin, polypropylene resin, polystyrene resin, polymethyl methacrylate resin, polyphenylene oxide resin, polyurethane resin. (Thermoplastic), ionomer resin, acrylonitrile/butadiene/styrene resin, acrylonitrile/styrene resin, polyvinyl alcohol resin, polyvinyl butyral resin, polyvinylidene chloride resin, polyethylene terephthalate resin, polyacetal resin, polycarbonate resin, polyphenylene ether resin, polybutylene terephthalate One or more selected from the group consisting of resin, polyvinylidene fluoride resin, polysulfone resin, polyethersulfone resin, polyphenylene sulfide resin, polyarylate resin and polyetherimide resin.

The inorganic polymer is polymetalloxane. Polymetalloxane is a polymer compound having a main chain skeleton that is an MO bond that is a bond between a metal (M) and oxygen (O). M (metal) in the MO bond of polymetalloxane is Si, Al, Ti, V, Cr, Mn, Fe, Ba, Co, Ni, Cu, Zn, Ga, Ge, Zr, Ce, Nb, Mo. , Ru, Rh, Pd, Ag, In, Sn, Sb, Hf, Ta, W, Re, Os, Ir, Pt, Au, and Bi. The polymetalloxane includes, for example, polytitanoxane (Ti-O), polysiloxane (Si-O), polyaluminoxane (Al-O), polyzirconoxane (Zr-O), and polytantaloxane (Ta-O). It is one kind or two or more kinds selected from the group. Preferably, the polymetalloxane is one or two selected from the group consisting of polytitanoxane (Ti-O) and polysiloxane (Si-O).

Preferably, the binder is one or more selected from the group consisting of epoxy resin, phenol resin, furan resin, polyamideimide resin, polyamide resin, polyimide resin, urethane resin and polyetheretherketone resin. These organic resins have appropriate hardness. Therefore, the wear resistance, seizure resistance, and high torque performance of the solid lubricating coating 21 are further enhanced.

More preferably, the binder is one or more selected from the group consisting of epoxy resin, phenol resin, furan resin, polyamide-imide resin and polyamide resin.

Particularly preferably, the binder is one or more selected from the group consisting of epoxy resin, polyamide-imide resin and polyamide resin.

The content of the binder in the solid lubricating coating 21 is preferably 50 to 90% by mass. When the content of the binder is 60% by mass or more, the adhesion of the solid lubricating coating 21 to the

contact surface

34 or 44 of the pipe threaded joint is further enhanced. Therefore, the lower limit of the content of the binder in the solid lubricating coating 21 is more preferably 60% by mass.

[lubricant]
The solid lubricating coating 21 contains a lubricant in order to further enhance the lubricity of the solid lubricating coating 21. Lubricant is a general term for substances having lubricity. A known lubricant can be used.

Lubricants are roughly classified into the following five types. That is, the lubricant contains one kind or two or more kinds selected from the group consisting of the following (1) to (5).
(1) A material exhibiting lubricity by having a specific crystal structure that is slippery, for example, a hexagonal layered crystal structure (for example, graphite, earth graphite, zinc oxide, boron nitride and talc),
(2) Those that exhibit a lubricity by having a reactive element in addition to the crystal structure (for example, molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide and organic molybdenum),
(3) Those exhibiting lubricity due to chemical reactivity (for example, thiosulfate compounds),
(4) Those exhibiting lubricity by plastic or viscoplastic behavior under frictional stress (for example, polytetrafluoroethylene (PTFE), copper (Cu), melamine cyanurate (MCA)), and (5) liquid or grease And has lubricity by being present at the boundary of the contact surfaces and preventing direct contact between the surfaces (for example, perfluoropolyether (PFPE)).

Preferably, the lubricant contains one or more selected from the group consisting of (1) to (5) above. That is, preferably, the lubricant is graphite, earth graphite, zinc oxide, boron nitride, talc, molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, organic molybdenum, thiosulfate compound, poly One or more selected from the group consisting of tetrafluoroethylene (PTFE), copper (Cu), melamine cyanurate (MCA), and perfluoropolyether (PFPE). More preferably, the lubricant is a solid lubricating powder. Here, the "solid lubricating powder" means a solid powder exhibiting lubricity. That is, the lubricant preferably contains one kind or two or more kinds selected from the group consisting of the above (1) to (4). When the lubricant is a solid lubricating powder, the lubricant is preferably one or more selected from the group consisting of molybdenum disulfide, graphite, polytetrafluoroethylene (PTFE) and graphite fluoride. The lubricant is preferably graphite from the viewpoints of adhesion and rustproofness of the solid lubricating coating 21, and earth graphite is preferred from the viewpoint of film-forming property. The lubricant is preferably polytetrafluoroethylene (PTFE) from the viewpoint of lubricity.

The content of the lubricant in the solid lubricating coating 21 is preferably 5 to 30% by mass. When the content of the lubricant is 5% by mass or more, the seizure resistance is further enhanced. For this reason, the number of times the screw can be tightened and unscrewed without causing seizure increases. A more preferable lower limit of the content of the lubricant is 10% by mass. On the other hand, when the content of the lubricant is 30% by mass or less, the strength of the solid lubricating coating 21 is further increased. Therefore, the wear of the solid lubricating coating 21 is suppressed.

[Glass frit]
In the present specification, the glass frit refers to glass particles. The shape of the glass frit is not fibrous but granular, lumpy and spherical. The glass frit is generally used mainly in various fields of electronics, such as sealing (sealing, adhesion) of a display panel and various electronic components, coating (protective film), and insulating film. However, the present inventor has found that the high torque performance of the threaded joint for pipes is enhanced by including the glass frit in the solid lubricating coating 21.

As the glass frit, a commercially available glass frit can be used. The glass frit is, for example, one or two kinds such as (trade name) ASF-1560 and (trade name) ASF-1561 manufactured by Asahi Glass Co., Ltd., and (trade name) VY0144 and (trade name) EY0077 manufactured by Nippon Frit Co., Ltd. The above can be mixed and used.

Preferably, the major axis of the glass frit is 1 to 40 μm. The major axis refers to the maximum Feret diameter of each particle (Feret diameter: spacing between parallel lines when a particle image is sandwiched between two parallel lines), which is defined in JIS Z8827-1 (2008). When the major axis of the glass frit is 1 μm or more, excellent high torque performance of the threaded joint for pipes can be obtained more stably. When the major axis of the glass frit is 40 μm or less, the moldability of the solid lubricating coating 21 is improved.

　The major axis of the glass frit is calculated by the following method. First, a part of the solid lubricating coating 21 is sampled. The solid lubricating coating 21 is burned at 600° C., and the burning residue is collected. The glass frit is recovered from the residue by the difference in specific gravity. The obtained glass frit is analyzed according to the dynamic image analysis method specified in JIS Z8827-1 (2008) and JIS Z8827-1-2 (2010). From the analysis result, the arithmetic average of the maximum Feret diameters of the respective particles of the glass frit within the same visual field is calculated, and the major axis (μm) is calculated.

Preferably, the glass frit has an aspect ratio of 10 or less. Here, the aspect ratio of the glass frit is a value defined by JIS Z8827-1 (2008), which is obtained by dividing the maximum Feret diameter of each particle by the minimum Feret diameter of each particle. When the glass frit has an aspect ratio of 10 or less, excellent high torque performance can be stably obtained. The aspect ratio of the glass frit is more preferably less than 10, still more preferably 5 or less, and most preferably 3 or less.

　The aspect ratio of the glass frit is calculated by the following method. First, a part of the solid lubricating coating 21 is sampled. The solid lubricating coating 21 is burned at 600° C., and the burning residue is collected. The glass frit is recovered from the residue by the difference in specific gravity. The obtained glass frit is analyzed according to the dynamic image analysis method specified in JIS Z8827-1 (2008) and JIS Z8827-1-2 (2010). From the analysis result, the arithmetic mean of the maximum Feret diameters of the respective particles of the glass frit within the same visual field is calculated. From the analysis result, the arithmetic average of the minimum Feret diameters of the respective particles of the glass frit within the same visual field is calculated. The arithmetic mean of the largest Feret diameter is divided by the arithmetic mean of the smallest Feret diameter. This is the aspect ratio of the glass frit.

High torque performance is enhanced if the solid lubricating coating 21 contains even a small amount of glass frit. Therefore, the lower limit of the content of the glass frit in the solid lubricating coating 21 is, for example, 0.001% by mass. However, when the solid lubricating coating 21 contains 0.01% by mass or more of glass frit, excellent high torque performance can be obtained more stably. Therefore, the content of the glass frit is preferably 0.01% by mass or more. The lower limit of the content of the glass frit is more preferably 0.5% by mass, further preferably 1.0% by mass.

The upper limit of the glass frit content is not particularly limited. The content of the glass frit may be appropriately adjusted within the range that the solid lubricating coating 21 can contain the binder, the lubricant and the glass frit. The upper limit of the content of the glass frit is, for example, 45.0% by mass. On the other hand, when the upper limit of the content of the glass frit is 10.0 mass% or less, in addition to high torque performance, seizure resistance of the threaded joint for pipes is enhanced. Therefore, the content of the glass frit is preferably 10.0 mass% or less. The upper limit of the content of the glass frit is more preferably 8.0% by mass, further preferably 5.0% by mass.

The chemical composition of the glass frit can be adjusted appropriately. The glass frit is, for example, in mass %, SiO ₂ : 40 to 70%, Al ₂ O ₃ : 1 to 20%, CaO: 0.1 to 25%, B ₂ O ₃ : 0 to 40%, MgO: 0 to 3%, Na ₂ O: 0 to 15%, K ₂ O: 0 to 10%, and ZnO: 0 to 10% may be contained.

[Other ingredients]
The solid lubricating coating 21 may also contain other known rust preventive additives, preservatives and the like.

[Rust preventive additive]
The solid lubricating coating 21 needs to have rust-preventive properties for a long period of time before being actually used. Therefore, the solid lubricating coating 21 may contain a rust preventive additive. The anticorrosive additive is a general term for additives having corrosion resistance. The rust preventive additive is, for example, one or more selected from the group consisting of aluminum tripolyphosphate, aluminum phosphite and calcium ion exchange silica. Preferably, the antirust additive contains one or two selected from the group consisting of calcium ion exchange silica and aluminum phosphite. As the rust preventive additive, a commercially available reaction water repellent agent or the like can also be used.

[Preservative]
The solid lubricating coating 21 may further contain a preservative. The antiseptic is a general term for additives having corrosion resistance.

It is preferable that the total content of other components (corrosion preventive additives, preservatives, etc.) in the solid lubricating coating 21 is 10% by mass or less. When the total content of other components is 10% by mass or less, the lubricity of the solid lubricating coating 21 is stably enhanced.

A solid lubricant film-forming composition (hereinafter also simply referred to as a composition) can be produced by mixing the above-mentioned binder, lubricant, glass frit, and other components and solvent if necessary. For a pipe according to the present embodiment, which has the solid lubricating coating 21 by applying the solid lubricating coating forming composition to at least one of the pin-side contact surface 34 and the box-side contact surface 44 of the threaded joint for pipe and solidifying the composition. Can manufacture threaded joints.

[Thickness of solid lubricant film]
The thickness of the solid lubricating coating 21 is not particularly limited. The thickness of the solid lubricating coating 21 is, for example, 10 to 50 μm. When the thickness of the solid lubricating coating 21 is 10 μm or more, excellent high torque performance can be obtained more stably. When the thickness of the solid lubricating coating 21 is 50 μm or less, the adhesion of the solid lubricating coating 21 is stable. Further, when the thickness of the solid lubricating coating 21 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.

[Measurement method of thickness of solid lubricating film]
The thickness of the solid lubricating coating 21 is measured by the following method. The thickness of the solid lubricating coating 21 is measured at four points on the

contact surface

34 or 44 on which the solid lubricating coating 21 is formed, using an eddy current phase type film thickness meter PHASCOPE PMP910 manufactured by Helmut Fischer GmbH. The measurement is performed by a method according to ISO (International Organization for Standardization) 21968 (2005). The measurement points are four points (four points of 0°, 90°, 180°, 270°) in the pipe circumferential direction of the pipe threaded joint. The arithmetic average of the measurement results is the thickness of the solid lubricating coating 21.

[Arrangement of solid lubricating coating]
The solid lubricating coating 21 may be disposed on at least one of the pin side contact surface 34 and the box side contact surface 44. In FIG. 7, the solid lubricant coating 21 is disposed on both the pin side contact surface 34 and the box side contact surface 44. However, the arrangement of the solid lubricating coating 21 is not limited to that shown in FIG. 7. As shown in FIG. 8, the solid lubricating coating 21 may be disposed only on the pin side contact surface 34. Further, as shown in FIG. 9, the solid lubricating coating 21 may be arranged only on the box-side contact surface 44.

Further, the solid lubricating coating 21 may be disposed on the entire surface of at least one of the pin-side contact surface 34 and the box-side contact surface 44, or may be disposed only on a part thereof. When the pipe threaded joint has a metal seal portion (pin side metal seal portion 32 and box side metal seal portion 42) and a shoulder portion (pin side shoulder portion 33 and box side shoulder portion 43), the

metal seal portions

32 and 42. The

shoulder portions

33 and 43 have particularly high surface pressure at the final stage of screw tightening. Therefore, the solid lubricating coating 21 is provided with a pin side contact surface 34 having a metal seal portion (pin side metal seal portion 32 and box side metal seal portion 42) and a shoulder portion (pin side shoulder portion 33 and box side shoulder portion 43). When partially arranged on at least one of the box side contact surfaces 44, it is arranged at at least one of the pin side metal seal portion 32, the box side metal seal portion 42, the pin side shoulder portion 33 and the box side shoulder portion 43. May be. On the other hand, if the solid lubricating coating 21 is arranged on at least one of the pin side contact surface 34 and the box side contact surface 44, the production efficiency of the threaded joint for pipes is increased.

The solid lubricating coating 21 may be a single layer or multiple layers. The multi-layer means a state in which the solid lubricating coating 21 is laminated in two or more layers from the

contact surface

34 or 44 side. By repeating the application and solidification of the composition, two or more solid lubricating coatings 21 can be formed. The solid lubricating coating 21 may be directly arranged on at least one of the pin-side contact surface 34 and the box-side contact surface 44, or may be arranged after being subjected to a base treatment described later.

[Base material for threaded joints for pipes]
The composition of the base material of the threaded joint for pipes is not particularly limited. The base material is, for example, carbon steel, stainless steel, alloy steel or the like. Among alloy steels, duplex stainless steels containing alloy elements such as Cr, Ni and Mo and high alloy steels such as Ni alloys have high corrosion resistance. Therefore, when these high alloy steels are used as the base material, excellent corrosion resistance can be obtained in a corrosive environment containing hydrogen sulfide, carbon dioxide and the like.

[Production method]
Hereinafter, the method for manufacturing the pipe threaded joint according to the present embodiment will be described. The method for manufacturing a threaded joint for pipes according to the present embodiment includes a preparing step and a solid lubricating coating forming step.

[Preparation process]
In the preparation step, the pin 3, the box 4 and the composition for forming a solid lubricating coating are prepared. The pin 3 has a pin-side contact surface 34 including a pin-side threaded portion 31, as described above. The pin 3 may have the pin-side contact surface 34 including the pin-side screw portion 31, the pin-side metal seal portion 32, and the pin-side shoulder portion 33, as described above. The box 4 has a box-side contact surface 44 including a box-side threaded portion 41, as described above. The box 4 may have a box-side contact surface 44 including a box-side threaded portion 41, a box-side metal seal portion 42, and a box-side shoulder portion 43, as described above. Well-known pretreatment may be performed on at least one of the pin-side contact surface 34 and the box-side contact surface 44. The pretreatment is, for example, degreasing. The degreasing removes oil and oily dirt adhering to at least one of the pin-side contact surface 34 and the box-side contact surface 44. Degreasing is, for example, solvent degreasing, alkaline degreasing, and electrolytic degreasing. As a pretreatment, pickling may be further performed. By pickling, the rust on at least one of the pin-side contact surface 34 and the box-side contact surface 44 and the oxide film formed during processing can be removed.

The composition for forming the solid lubricating coating has the same composition as the solid lubricating coating 21 except for the solvent as described above. That is, the composition for forming a solid lubricating film (composition) contains a binder, a lubricant and a glass frit. A solventless composition can be produced, for example, by heating a binder to a molten state, adding a lubricant and a glass frit, and kneading the mixture. The composition may be a powder mixture obtained by mixing all components in powder form.

The solvent type composition can be produced, for example, by dissolving or dispersing a binder, a lubricant and a glass frit in a solvent and mixing them. The solvent is, for example, one or two selected from the group consisting of water and an organic solvent. The ratio of the solvent is not particularly limited. The proportion of the solvent may be adjusted to an appropriate viscosity according to the coating method. The ratio of the solvent is, for example, 30 to 50% by mass based on 100% by mass of all components other than the solvent.

[Solid lubrication film formation process]
The solid lubricant film forming step includes a coating step and a solidifying step. In the coating step, the solid lubricating coating forming composition is coated on at least one of the pin-side contact surface 34 and the box-side contact surface 44. In the solidifying step, the solid lubricating coating forming composition applied on at least one of the pin-side contact surface 34 and the box-side contact surface 44 is solidified to form the solid lubricating coating 21.

[Coating process]
In the coating step, the composition is coated on at least one of the pin side contact surface 34 and the box side contact surface 44 by a known method.

In the case of a solventless composition, the composition can be applied using the hot melt method. In the hot melt method, the composition is heated to melt the resin and bring it into a low-viscosity fluid state. It is carried out by spraying the composition in a fluid state from a spray gun having a temperature maintaining function. The composition is heated and melted in a tank equipped with a suitable stirring device, and is supplied to a spray head (maintained at a predetermined temperature) of a spray gun through a metering pump by a compressor to be sprayed. The holding temperature in the tank and in the spraying head is adjusted according to the melting point of the resin in the composition. The coating method may be brush coating, dipping or the like instead of spray coating. The heating temperature of the composition is preferably 10 to 50° C. higher than the melting point of the resin. At the time of applying the composition, at least one of the pin-side contact surface 34 and the box-side contact surface 44 to which the composition is applied is preferably heated to a temperature higher than the melting point of the base. As a result, good coverage can be obtained.

In the case of a solvent type composition, the composition in a solution state is applied to at least one of the pin side contact surface 34 and the box side contact surface 44 by spray coating or the like. In this case, the viscosity of the composition is adjusted so that the composition can be spray-applied at room temperature and atmospheric pressure.

[Solidification process]
In the solidifying step, the solid lubricant film 21 is formed by solidifying the composition applied to at least one of the pin side contact surface 34 and the box side contact surface 44.

In the case of a solvent-free composition, by cooling the composition applied to at least one of the pin-side contact surface 34 and the box-side contact surface 44, the composition in a molten state solidifies to solid lubricant coating 21. Is formed. A known cooling method can be used. The cooling method is, for example, air cooling or air cooling.

In the case of a solvent type composition, by drying the composition applied to at least one of the pin side contact surface 34 and the box side contact surface 44, the composition is solidified to form the solid lubricating coating 21. .. The drying method can be carried out by a known method. The drying method is, for example, natural drying, low temperature blast drying and vacuum drying.

ㆍThe solidification process may be performed by rapid cooling such as a nitrogen gas and carbon dioxide cooling system. When performing rapid cooling, it is indirectly cooled from the opposite surface of the contact surface 34 or 44 (the outer surface of the steel pipe 1 or the coupling 2 in the case of the box 4, the inner surface of the steel pipe 1 in the case of the pin 3). As a result, deterioration of the solid lubricating coating 21 due to rapid cooling can be suppressed.

[surface treatment]
The method for manufacturing the threaded joint for pipes according to the present embodiment may include a base treatment step before the solid lubricant film forming step. The base treatment step is, for example, one or more selected from the group consisting of a surface roughness forming step, a Zn alloy plating layer forming step, and a trivalent chromate processing step.

[Surface roughness forming step]
In the surface roughness forming step, at least one of the pin side contact surface 34 and the box side contact surface 44 is roughened. This imparts surface roughness to at least one of the pin-side contact surface 34 and the box-side contact surface 44. As for the surface roughness, it is preferable that the arithmetic mean roughness Ra is 1.0 to 8.0 μm and the maximum height roughness Rz is 10.0 to 40.0 μm. When the arithmetic average roughness Ra is 1.0 μm or more and the maximum height roughness Rz is 10.0 μm or more, the adhesion effect of the solid lubricating coating 21 is further enhanced by the anchor effect. When the arithmetic average roughness Ra is 8.0 μm or less and the maximum height roughness Rz is 40.0 μm or less, friction is suppressed, and damage and peeling of the solid lubricating coating 21 are suppressed.

The arithmetic mean roughness Ra and the maximum height roughness Rz referred to in this specification are measured based on JIS B 0601 (2001). Measurement is performed using a scanning probe microscope SPI3800N manufactured by SII Nano Technology. The measurement condition is a region of 2 μm×2 μm of the sample as a unit of the number of acquired data, and the number of acquired data is 1024×1024. The standard length is 2.5 mm.

As for the surface roughness of the contact surfaces 34 and 44 of the threaded joint for pipes, the maximum height roughness Rz is generally about 3.0 to 5.0 μm. If the surface roughness of the contact surfaces 34 and 44 is appropriately large, the adhesiveness of the coating film (the solid lubricating coating 21 or the Zn alloy plating layer) formed thereon is enhanced. As a result, seizure resistance and corrosion resistance of the threaded joint for pipes are further enhanced. Therefore, it is preferable that the

contact surface

34 or 44 before being coated with the composition for forming the solid lubricating coating 21 is subjected to a base treatment. The formation of the surface roughness is, for example, one or more selected from the group consisting of sandblasting treatment, pickling treatment and chemical conversion treatment.

[Sandblast processing]
The sandblast treatment is a treatment in which a blast material (abrasive) and compressed air are mixed and projected onto at least one of the pin-side contact surface 34 and the box-side contact surface 44. The blast material is, for example, a spherical shot material and a square grid material. The sandblast treatment can increase the surface roughness of at least one of the pin-side contact surface 34 and the box-side contact surface 44. The sandblast treatment can be performed by a known method. For example, the air is compressed by a compressor, and the compressed air and the blast material are mixed. The material of the blast material is, for example, stainless steel, aluminum, ceramic, alumina or the like. The conditions such as the projection speed of the sandblast process can be set as appropriate.

[Pickling treatment]
The pickling treatment is a treatment for roughening the

contact surface

34 or 44 by immersing at least one of the pin-side contact surface 34 and the box-side contact surface 44 in a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid or hydrofluoric acid. This can increase the surface roughness of the

contact surface

34 or 44.

[Chemical conversion treatment]
The chemical conversion treatment is a treatment for forming a porous chemical conversion film having a large surface roughness. The chemical conversion treatment is, for example, a phosphate chemical conversion treatment, an oxalate chemical conversion treatment, and a borate chemical conversion treatment. From the viewpoint of the adhesion of the solid lubricating coating 21, the phosphate chemical conversion treatment is preferable. The phosphate chemical conversion treatment is, for example, a phosphate chemical conversion treatment using manganese phosphate, zinc phosphate, iron manganese phosphate or zinc calcium phosphate.

The phosphate chemical conversion treatment can be carried out by a well-known method. As the treatment liquid, a general acidic phosphate chemical conversion treatment liquid for galvanized materials can be used. For example, there may be mentioned a zinc phosphate chemical conversion treatment containing 1 to 150 g/L of phosphate ions, 3 to 70 g/L of zinc ions, 1 to 100 g/L of nitrate ions, and 0 to 30 g/L of nickel ions. A manganese phosphate-based chemical conversion treatment liquid commonly used for pipe threaded joints can also be used. The liquid temperature is, for example, room temperature to 100°C. The treatment time can be appropriately set according to the desired film thickness, and is, for example, 15 minutes. In order to promote the formation of the chemical conversion film, the surface may be adjusted before the phosphate chemical conversion treatment. Surface conditioning is a treatment of immersing in a surface conditioning aqueous solution containing colloidal titanium. After the phosphate conversion treatment, it is preferable to wash with water or hot water and then dry.

The chemical conversion coating is porous. Therefore, if the solid lubricating coating 21 is formed on the chemical conversion coating, the adhesion of the solid lubricating coating 21 is further enhanced by the so-called "anchor effect". The preferred thickness of the phosphate coating is 5-40 μm. If the thickness of the phosphate coating is 5 μm or more, sufficient corrosion resistance can be secured. When the thickness of the phosphate coating is 40 μm or less, the adhesiveness of the solid lubricating coating 21 is stably enhanced.

The thickness of the phosphate coating is calculated by the following method. The threaded pipe joint with the phosphate coating is cut in the thickness direction of the phosphate coating (perpendicular to the axial direction of the thread joint for the pipe). The cross section of the phosphate coating is observed with an optical microscope at a magnification of 500 times to measure the thickness of the phosphate coating. When the thickness of the phosphate coating measured by the above measuring method is 10 μm or less, the cutting is performed again by cutting again. In this case, the threaded joint for pipes is cut in a direction inclined by 60° from the direction perpendicular to the axial direction of the threaded joint for pipes. The cross section of the obtained phosphate coating is observed with an optical microscope at a magnification of 500 times to measure the thickness of the phosphate coating. When the thickness of the phosphate coating is measured again, the thickness measured again is the thickness of the phosphate coating.

[Zn alloy plating layer forming step]
In the Zn alloy plating layer forming step, a Zn alloy plating layer is formed by electroplating on at least one of the pin side contact surface 34 and the box side contact surface 44.

Alternatively, in the Zn alloy plating layer forming step, a Zn alloy plating layer is formed by electroplating on the surface roughness formed on at least one of the pin side contact surface 34 and the box side contact surface 44.

Conducting the Zn alloy plating layer formation process improves seizure resistance and corrosion resistance of the threaded joint for pipes. The Zn alloy plating layer forming step includes, for example, a single layer plating process using Cu, Sn or Ni metal, a single layer plating process using a Cu—Sn alloy, a two layer plating process including a Cu layer and a Sn layer, and a Ni layer and Cu. It is a three-layer plating process using a layer and a Sn layer. For the steel pipe 1 made of steel having a Cr content of 5% or more, Cu-Sn alloy plating treatment, Cu plating-Sn plating two-layer plating treatment, and Ni plating-Cu plating-Sn plating three-layer plating Treatment is preferred. More preferable are Cu plating-Sn plating two-layer plating treatment, Ni strike plating-Cu plating-Sn plating three-layer plating treatment, Zn-Co alloy plating treatment, Cu-Sn-Zn alloy plating treatment, and Zn-Ni alloy plating treatment.

The electroplating process can be performed by a known method. For example, a bath containing ions of a metal element contained in alloy plating is prepared. Next, at least one of the pin side contact surface 34 and the box side contact surface 44 is immersed in a bath. By energizing the

contact surface

34 or 44 immersed in the bath, an alloy plating film is formed on at least one of the pin side contact surface 34 and the box side contact surface 44. Conditions such as bath temperature and plating time can be appropriately set.

More specifically, for example, when forming a Cu—Sn—Zn alloy plating layer, the plating bath contains copper ions, tin ions and zinc ions. The composition of the plating bath is preferably Cu: 1 to 50 g/L, Sn: 1 to 50 g/L and Zn: 1 to 50 g/L. The electroplating conditions are, for example, a plating bath pH: 1 to 10, a plating bath temperature: 60° C., a current density: 1 to 100 A/dm ^2, and a treatment time: 0.1 to 30 minutes.

When forming a Zn—Ni alloy plating layer, the plating bath contains zinc ions and nickel ions. The composition of the plating bath is preferably Zn: 1 to 100 g/L and Ni: 1 to 50 g/L. The electroplating conditions are, for example, a plating bath pH: 1 to 10, a plating bath temperature: 60° C., a current density: 1 to 100 A/dm ^2, and a treatment time: 0.1 to 30 minutes.

The hardness of the Zn alloy plating layer is preferably 300 or more in micro Vickers. When the hardness of the Zn alloy plating layer is 300 or more, the corrosion resistance of the threaded joint for pipes is more stably enhanced.

The hardness of the Zn alloy plating layer is measured as follows. In the Zn alloy plating layer of the obtained threaded joint for pipes, five arbitrary regions are selected. In each selected area, the Vickers hardness (HV) is measured according to JIS Z2244 (2009). The test conditions are, for example, a test temperature of room temperature (25° C.) and a test force of 2.94 N (300 gf). The average of the obtained values (5 in total) is defined as the hardness of the Zn alloy plating layer.

In the case of multi-layer plating, it is preferable that the thickness of the lowermost plating layer be less than 1 μm. The thickness of the plating layer (total thickness in the case of multi-layer plating) is preferably 5 to 15 μm.

Measure the thickness of the Zn alloy plating layer as follows. A probe of an overcurrent phase type film thickness meter conforming to ISO (International Organization for Standardization) 21968 (2005) is brought into contact with the

contact surface

34 or 44 on which the Zn alloy plating layer is formed. The phase difference between the high frequency magnetic field on the input side of the probe and the overcurrent excited by it on the Zn—Ni alloy plating is measured. This phase difference is converted into the thickness of the Zn alloy plating layer.

[Trivalent chromate treatment]
When the above-mentioned Zn alloy plating treatment is carried out, trivalent chromate treatment may be carried out after the Zn alloy plating treatment. The trivalent chromate treatment is a treatment for forming a chromate film of trivalent chromium. The coating film formed by the trivalent chromate treatment suppresses white rust on the surface of the Zn alloy plating layer. This improves the product appearance. (The white rust of the Zn alloy plating layer is not the rust of the pipe thread joint base material. Therefore, it does not affect the seizure resistance and corrosion resistance of the thread joint for pipe.) The solid lubricating film 21 on the trivalent chromate film By forming, the adhesiveness of the solid lubricating coating 21 is further enhanced.

The trivalent chromate treatment can be performed by a known method. For example, at least one of the pin-side contact surface 34 and the box-side contact surface 44 is dipped in the chromate treatment liquid or the chromate treatment liquid is sprayed on at least one of the pin-side contact surface 34 and the box-side contact surface 44. Then, the contact surface is washed with water. Alternatively, the

contact surface

34 or 44 is dipped in a chromate treatment liquid, and after being energized, washed with water. Alternatively, the chromate treatment liquid is applied to the

contact surface

34 or 44 and dried by heating. The treatment conditions of trivalent chromate can be set appropriately. The thickness of the trivalent chromate coating can be measured by the same method as the solid lubricating coating 21.

The above-mentioned base treatments may be carried out for only one type, but a plurality of base treatments may be combined. When one kind of undercoating is carried out, it is preferable to carry out at least one kind of undercoating selected from the group consisting of sandblasting, pickling, phosphate chemical conversion and Zn alloy plating. Two or more types of base treatment may be implemented. In that case, for example, the phosphate chemical conversion treatment is carried out after the sandblast treatment. Alternatively, a Zn alloy plating treatment is performed after the sandblast treatment. Alternatively, the zinc alloy plating treatment is performed after the sandblast treatment, and the trivalent chromate treatment is further performed. After performing these base treatments, the solid lubricating coating 21 is formed. Thereby, the adhesion and corrosion resistance of the solid lubricating coating 21 can be further improved.

As for the base treatment, the same base treatment may be performed on the pin 3 and the box 4, or different base treatment may be performed on the pin 3 and the box 4.

The present disclosure is not limited to the embodiments. In the examples, the contact surface of the pin is called the pin surface and the contact surface of the box is called the box surface. In addition,% in the examples is% by mass unless otherwise specified.

As the fastening performance, seizure resistance (repeated fastening test) and high torque performance were evaluated using a real pipe (length of about 12 m). The repeated fastening test was performed with a fastening torque of 28450 Nm. Fastening was carried out until irreversible seizure of the threaded portion or seizure of the metal seal portion occurred. The number of times that screw tightening and screw returning could be repeated without seizure was judged to be acceptable when the number of times was 5 or more.

In the examples, screw joints VAM21 (registered trademark) for oil country tubular goods made by Nippon Steel Co., Ltd. (outer diameter: 244.48 mm (9 inches 5 minutes), wall thickness: 11.99 mm (0.472 inches)), steel grade Is carbon steel (C: 0.25%, Si: 0.22%, Mn: 0.7%, P: 0.02%, S: 0.01%, Cu: 0.04%, Ni: 0. 05%, Cr: 0.95%, Mo: 0.15%, balance: iron and impurities).

The surface treatment (appropriate) shown in Table 1 and the solid lubricating coating or the other lubricating coating formed by the composition for forming a solid lubricating coating according to the present embodiment are formed on the pin surface and the box surface of each test number, and each test is performed. Numbered pins and boxes were prepared.

Blasting was performed on the pin surface and the box surface of each test number with the test numbers as shown in Table 1. The blasting was performed by sandblasting (abrasive grain Mesh100) to form a surface roughness. The arithmetic mean roughness Ra and the maximum height roughness Rz of each test number were as shown in Table 1. The arithmetic average roughness Ra and the maximum height roughness Rz were measured based on JIS-B0601 (2001). A scanning probe microscope SPI3800N manufactured by SII Nano Technology was used to measure the arithmetic average roughness Ra and the maximum height roughness Rz. The measurement conditions were a region of 2 μm×2 μm of the sample as a unit of the number of acquired data, and the number of acquired data was 1024×1024.

After that, a Zn-Ni alloy plating layer, a Cu-Sn-Zn alloy plating layer, and a solid lubricating coating shown in Table 1 were formed to prepare pins and boxes for each test number. In Table 1, only the main components are described in the column of "solid lubricating coating". The detailed composition of the solid lubricating coating was as follows. In Table 1, "thickness" in the column of "solid lubricating coating" describes the thickness of the obtained solid lubricating coating. The method for measuring the thickness of the solid lubricating coating was as described above.

The glass frit shown in Table 1 used the glass frit shown in Table 2. FIG. 11 shows a micrograph of glass frit A.

The method of forming each Zn-Ni alloy plating layer, Cu-Sn-Zn alloy plating layer, and solid lubricating coating was as follows. The thicknesses of the alloy plating layer and other coating layers were as shown in Table 1. The method for measuring the thickness of each layer was as described above.

[Test number 1]
In test number 1, mechanical grinding finish was performed on the pin and box surfaces. The composition for forming a solid lubricating coating was applied thereon. The composition for forming a solid lubricating coating contained an epoxy resin (the balance), PTFE particles (20%), glass frit A (0.8%), and a solvent (water, alcohol, surfactant). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After heating and drying, solidification treatment was performed at 210° C. for 20 minutes to form a solid lubricating coating.

[Test number 2]
In Test No. 2, mechanical grinding finish was performed on the pin and box surfaces. The composition for forming a solid lubricating coating was applied thereon. The composition for forming a solid lubricating coating contained an epoxy resin (the balance), PTFE particles (10%), glass frit B (2.0%), and a solvent (water, alcohol, surfactant). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After heating and drying, solidification treatment was performed at 210° C. for 20 minutes to form a solid lubricating coating.

[Test number 3]
In Test No. 3, surface roughness was formed on the pin surface by blasting. Zn—Ni alloy plating was performed by electroplating on the pin surface having surface roughness to form a Zn—Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, a trivalent chromate treatment was performed on the obtained Zn—Ni alloy plated layer to form a film. As the trivalent chromate treatment liquid, Dyne Chromate TR-02 manufactured by Daiwa Kasei Co., Ltd. was used. The trivalent chromate treatment conditions were: bath pH: 4.0, bath temperature: 25° C., and treatment time: 50 seconds.

Mechanical finishing was performed on the box surface. The composition for forming a solid lubricating coating was applied thereon. The composition for forming a solid lubricating coating contained an epoxy resin (the balance), molybdenum disulfide particles (10%), glass frit C (4.0%), and a solvent (water, alcohol, surfactant). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After heating and drying, solidification treatment was performed at 210° C. for 20 minutes to form a solid lubricating coating.

[Test number 4]
In Test No. 4, surface roughness was formed on the pin surface by blasting. Zn—Ni alloy plating was performed by electroplating on the pin surface having surface roughness to form a Zn—Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, a trivalent chromate treatment was performed on the obtained Zn—Ni alloy plated layer to form a film. As the trivalent chromate treatment liquid, Dyne Chromate TR-02 manufactured by Daiwa Kasei Co., Ltd. was used. The trivalent chromate treatment conditions were: bath pH: 4.0, bath temperature: 25° C., and treatment time: 50 seconds.

Surface roughness was formed on the box surface by blasting. Zn-Ni alloy plating was performed by electroplating on the surface of the box having surface roughness to form a Zn-Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, the composition for forming a solid lubricating coating was applied on the obtained Zn-Ni alloy plated layer. The composition for forming a solid lubricating coating contained a polyamideimide resin (the balance), fluorinated graphite particles (10%), glass frit D (8.0%), and a solvent (water, alcohol, surfactant). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After drying by heating, solidification treatment was performed at 230° C. for 20 minutes to form a solid lubricating coating.

[Test number 5]
In test number 5, the pin surface was subjected to mechanical grinding finish. Zn-Ni alloy plating was performed thereon by electroplating to form a Zn-Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, a trivalent chromate treatment was performed on the obtained Zn—Ni alloy plated layer to form a film. As the trivalent chromate treatment liquid, Dyne Chromate TR-02 manufactured by Daiwa Kasei Co., Ltd. was used. The trivalent chromate treatment conditions were: bath pH: 4.0, bath temperature: 25° C., and treatment time: 50 seconds.

Surface roughness was formed on the box surface by blasting. Zn-Ni alloy plating was performed by electroplating on the surface of the box having surface roughness to form a Zn-Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, the composition for forming a solid lubricating coating was applied on the obtained Zn-Ni alloy plated layer. The composition for forming a solid lubricating coating contained a phenol resin (the balance), PTFE particles (15%), glass frit A (10.0%), and a solvent (water, alcohol, surfactant). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After drying by heating, solidification treatment was performed at 230° C. for 20 minutes to form a solid lubricating coating.

[Test number 6]
In test number 6, the pin surface was mechanically ground. Zn-Ni alloy plating was performed thereon by electroplating to form a Zn-Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, a trivalent chromate treatment was performed on the obtained Zn—Ni alloy plated layer to form a film. As the trivalent chromate treatment liquid, Dyne Chromate TR-02 manufactured by Daiwa Kasei Co., Ltd. was used. The trivalent chromate treatment conditions were: bath pH: 4.0, bath temperature: 25° C., and treatment time: 50 seconds.

Surface roughness was formed on the box surface by blasting. Cu-Sn-Zn alloy plating was carried out by electroplating on the surface of the box having a surface roughness to form a Cu-Sn-Zn alloy plating layer. As the Cu-Sn-Zn alloy plating bath, a plating bath manufactured by Nippon Kagaku Sangyo Co., Ltd. was used. The Cu-Sn-Zn alloy plating layer was formed by electroplating. The electroplating conditions were: plating bath pH: 14, plating bath temperature: 45° C., current density: 2 A/dm ^2, and treatment time: 40 minutes. The composition of the Cu—Sn—Zn alloy plated layer was Cu: 60%, Sn: 30%, Zn: 10%. Further, the composition for forming a solid lubricating coating was applied on the obtained Cu—Sn—Zn alloy plated layer. The composition for forming a solid lubricating coating contained a polyamide resin (the balance), graphite particles (5%), glass frit A (8.0%), and a solvent (water, alcohol, surfactant). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After drying by heating, solidification treatment was performed at 230° C. for 20 minutes to form a solid lubricating coating.

[Test number 7]
In test number 7, the pin surface was mechanically ground. Zn-Ni alloy plating was performed thereon by electroplating to form a Zn-Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, a trivalent chromate treatment was performed on the obtained Zn—Ni alloy plated layer to form a film. As the trivalent chromate treatment liquid, Dyne Chromate TR-02 manufactured by Daiwa Kasei Co., Ltd. was used. The trivalent chromate treatment conditions were: bath pH: 4.0, bath temperature: 25° C., and treatment time: 50 seconds.

Surface roughness was formed on the box surface by blasting. Zn-Ni alloy plating was performed by electroplating on the surface of the box having surface roughness to form a Zn-Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, the composition for forming a solid lubricating coating was applied on the obtained Zn-Ni alloy plated layer. The composition for forming a solid lubricating coating contained an epoxy resin (the balance), PTFE particles (10%), glass frit A (15.0%), and a solvent (water, alcohol, surfactant). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After heating and drying, solidification treatment was performed at 210° C. for 20 minutes to form a solid lubricating coating.

[Test number 8]
In test number 8, the pin surface was mechanically ground. Zn-Ni alloy plating was performed thereon by electroplating to form a Zn-Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, a trivalent chromate treatment was performed on the obtained Zn—Ni alloy plated layer to form a film. As the trivalent chromate treatment liquid, Dyne Chromate TR-02 manufactured by Daiwa Kasei Co., Ltd. was used. The trivalent chromate treatment conditions were: bath pH: 4.0, bath temperature: 25° C., and treatment time: 50 seconds.

The surface roughness was formed on the box surface by blasting. Zn-Ni alloy plating was performed by electroplating on the surface of the box having surface roughness to form a Zn-Ni alloy plating layer. The electroplating conditions were the same as for the pin surface. The composition for forming a solid lubricating coating was applied onto the Zn-Ni alloy plating layer. The composition for forming a solid lubricating coating contained an epoxy resin (the balance), PTFE particles (10%), and a solvent (water, alcohol, surfactant). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After heating and drying, solidification treatment was performed at 210° C. for 20 minutes to form a solid lubricating coating.

[Test number 9]
In Test No. 9, mechanical grinding finish was performed on the pin and box surfaces. Then, the API standard dope was applied with a brush. The API standard dope is a compound grease for oil well pipe threads manufactured according to API Bul 5A2. The composition of the API standard dope is based on grease, and in mass%, graphite powder: 18±1.0%, lead powder: 30.5±0.6%, and copper flakes: 3.3±0.3% It is regulated to contain. In this component range, it is understood that the compound grease for oil country tubular goods screws has equivalent performance.

[Test number 10]
In Test No. 10, the pin surface was mechanically ground and finished. Zn-Ni alloy plating was performed thereon by electroplating to form a Zn-Ni alloy plating layer. The Zn-Ni alloy plating bath used was Dainjin Alloy N-PL manufactured by Daiwa Kasei Co., Ltd. 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 Zn—Ni alloy plating layer was Zn:85% and Ni:15%. Further, a trivalent chromate treatment was performed on the obtained Zn—Ni alloy plated layer to form a film. As the trivalent chromate treatment liquid, Dyne Chromate TR-02 manufactured by Daiwa Kasei Co., Ltd. was used. The trivalent chromate treatment conditions were: bath pH: 4.0, bath temperature: 25° C., and treatment time: 50 seconds.

The surface roughness was formed on the box surface by blasting. Zn-Ni alloy plating was performed by electroplating on the surface of the box having surface roughness to form a Zn-Ni alloy plating layer. The electroplating conditions were the same as for the pin surface. The composition for forming a solid lubricating coating was applied onto the Zn-Ni alloy plating layer. The composition for forming a solid lubricating coating is phenol resin (the balance), PTFE particles (15%), solvent (water, alcohol, surfactant), whisker (trade name) whisker manufactured by Maruo Calcium Co., Ltd. simulating glass fiber. It contained A (10%). The composition for forming a solid lubricating coating was applied by spraying, and then dried by heating at 90° C. for 5 minutes. After heating and drying, solidification treatment was performed at 210° C. for 20 minutes to form a solid lubricating coating.

[High torque performance evaluation test]
The torque-on-shoulder resistance ΔT′ was measured using the pins and boxes of test numbers 1 to 10. Specifically, the screw was tightened at a tightening speed of 10 rpm and a tightening torque of 42.8 kN·m. The torque was measured when tightening the screw, and a torque chart as shown in FIG. 10 was created. Ts in FIG. 10 represents shouldering torque. MTV in FIG. 10 represents a torque value at which the line segment L and the torque chart intersect. The line segment L is a straight line having the same slope as that of the linear region in the torque chart after shouldering and having the rotational speed increased by 0.2% as compared with the linear region. Normally, Ty (yield torque) is used when measuring the torque on-shoulder resistance ΔT′. However, in this embodiment, the yield torque (the boundary between the linear range and the non-linear range in the torque chart after shouldering) was unclear. Therefore, the line segment L is used to define MTV. The difference between MTV and Ts was set as the torque on-shoulder resistance ΔT′ in this embodiment. The torque-on-shoulder resistance ΔT′ was obtained by using the numerical value of the torque-on-shoulder resistance ΔT′ when the API standard dope was used instead of the solid lubricating coating in Test No. 9 as a reference (100). It is a relative value of the shoulder resistance ΔT′. The results are shown in Table 3.

[Seizure resistance evaluation test]
Using the pins and boxes of Test No. 1 to Test No. 10, they were tightened by hand tight (manually fastened state) until the screws were 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 and the surface of the box were visually observed each time the screw was tightened and the screw was unscrewed 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 the screw was tightened and unscrewed without causing irreversible seizure was measured. The results are shown in the column of "Seizure resistance (number of times of fastening without seizure (times))" in Table 3.

In Test No. 9, a new API standard dope was reapplied every time screw tightening and screw unscrewing were performed. This is because the API standard dope is usually repainted and used again each time screwing and unscrewing are performed. In addition, the API standard dope is supposed only for such usage. On the other hand, in Test Nos. 1 to 8 and Test No. 10, the test was continued until the test was completed without re-forming the solid lubricating coating.

[Evaluation results]
With reference to Table 1 and Table 3, the threaded joints for pipes of Test Nos. 1 to 7 had a solid lubricating coating on the contact surface of at least one of the pin and the box. The solid lubricating coating contained a binder, a lubricant, and a glass frit. Therefore, the threaded joints for pipes of Test Nos. 1 to 7 had torque-on-shoulder resistance ΔT' of over 100, and showed excellent high torque performance.

Further, in the threaded joints for pipes of Test Nos. 1 to 6, the glass frit content of the solid lubricating coating was 0.01 to 10.0% by mass. Therefore, the seizure resistance was excellent as compared with Test No. 7 in which the glass frit content was 15.0% by mass.

On the other hand, the pipe threaded joint of Test No. 8 had a solid lubricating coating on the box surface, but the solid lubricating coating did not contain glass frit. Therefore, excellent high torque performance could not be obtained.

Test number 9 is a comparative example using a conventional compound grease.

Test No. 10 was tested by simulating the case where glass fibers were contained in the solid lubricating coating instead of the glass frit. However, with glass fiber, excellent high torque performance could not be obtained. FIG. 12 shows a micrograph of the whiskers.

The embodiments of the present disclosure have been described above. However, the embodiments described above are merely examples for implementing the present disclosure. Therefore, the present disclosure is not limited to the above-described embodiments, and can be implemented by appropriately modifying the above-described embodiments without departing from the spirit thereof.

1 Steel Pipe 2 Coupling 3 Pin 4 Box 21 Solid Lubrication Film 31 Pin Side Screw Part 32 Pin Side Metal Seal Part 33 Pin Side Shoulder Part 34 Pin Side Contact Surface 41 Box Side Screw Part 42 Box Side Metal Seal Part 43 Box Side Shoulder Part 44 Box side contact surface

Claims

A threaded joint for pipes,
A pin having a pin-side contact surface including a pin-side threaded portion,
A box having a box-side contact surface including a box-side threaded portion,
A threaded joint for pipes, comprising a solid lubricating coating containing a binder, a lubricant and a glass frit on at least one of the pin side contact surface and the box side contact surface.
The pipe threaded joint according to claim 1,
The solid lubricating coating is
A threaded joint for pipes, which contains 0.01 to 10.0% by mass of the glass frit.
The pipe threaded joint according to claim 1 or 2, wherein
The glass frit is in mass %,
SiO 2 : 40-70%,
Al 2 O 3 : 1-20%,
CaO: 0.1-25%,
B 2 O 3 : 0-40%,
MgO: 0-3%,
Na 2 O: 0-15%,
A threaded joint for pipes containing K 2 O: 0-10% and ZnO: 0-10%.
The threaded joint for pipes according to any one of claims 1 to 3,
The binder is one or more kinds selected from the group consisting of epoxy resin, phenol resin, furan resin, polyamideimide resin, polyamide resin, polyimide resin, urethane resin and polyetheretherketone resin, a threaded joint for pipes ..
The threaded joint for pipes according to any one of claims 1 to 4,
A threaded joint for pipes, wherein the lubricant is one or more selected from the group consisting of molybdenum disulfide, graphite, polytetrafluoroethylene and fluorinated graphite.
The threaded joint for pipes according to any one of claims 1 to 5,
The pin further includes a pin side metal seal portion and a pin side shoulder portion,
The box further includes a pipe threaded joint including a box-side metal seal portion and a box-side shoulder portion.
A method for manufacturing a pipe threaded joint, comprising:
Preparing a pin having a pin side contact surface including a pin side thread portion, a box having a box side contact surface including a box side screw portion, and a composition for forming a solid lubricating coating containing a binder, a lubricant and a glass frit The process of
A method for producing a threaded joint for pipes, comprising the steps of applying the composition for forming a solid lubricating coating and then solidifying the composition to form a solid lubricating coating on at least one of the pin-side contact surface or the box-side contact surface. ..
The method for manufacturing a threaded joint for pipes according to claim 7, further comprising:
Before the step of forming the solid lubricating coating,
A method for manufacturing a threaded joint for pipes, comprising the step of forming a Zn alloy plating layer by electroplating on at least one of the pin-side contact surface and the box-side contact surface.
The method for producing a threaded joint for pipes according to claim 8, further comprising:
Before the step of forming the Zn alloy plating layer by the electroplating,
A method for manufacturing a threaded joint for pipe, comprising a step of roughening at least one of the pin-side contact surface and the box-side contact surface.
A method for manufacturing the threaded joint for pipes according to any one of claims 7 to 9,
The pin further includes a pin side metal seal portion and a pin side shoulder portion,
The said box is a manufacturing method of the threaded joint for pipes which further includes a box side metal seal part and a box side shoulder part.