阅读说明：本技术 管用螺纹接头及管用螺纹接头的制造方法 (Threaded joint for pipe and method for manufacturing threaded joint for pipe ) 是由 后藤邦夫 于 2018-04-24 设计创作，主要内容包括：本发明提供一种具有高的过扭矩性能的管用螺纹接头及其制造方法。本实施方式的管用螺纹接头(1)具备公扣部(5)和母扣部(8)。公扣部(5)和母扣部(8)具备具有螺纹部(4)、(7)以及无螺纹金属接触部的接触表面(6)、(9)。管用螺纹接头(1)在公扣部(5)和母扣部(8)中的至少一者的接触表面(6)、(9)上具备固体润滑覆膜层(21),所述固体润滑覆膜层(21)含有树脂、固体润滑粉末以及Cr<Sub>2</Sub>O<Sub>3</Sub>。(The invention provides a threaded joint for pipes having high over-torque performance and a method of manufacturing the same. A threaded joint (1) for pipes according to the present embodiment is provided with a male buckle section (5) and a female buckle section (8). The male (5) and female (8) button portions have contact surfaces (6), (9) with threaded portions (4), (7) and unthreaded metal contact portions. A threaded joint (1) for pipes is provided with a solid lubricating coating layer (21) on the contact surfaces (6, 9) of at least one of a pin (5) and a box (8), the solid lubricating coating layer (21) containing a resin, a solid lubricating powder, and Cr 2 O 3 。)

1. A threaded joint for pipes, which is provided with a pin portion and a box portion,

the pin portion and the box portion having contact surfaces with a threaded portion and an unthreaded metal contact portion,

the threaded joint for pipes is provided with a solid lubricating coating layer on the contact surface of at least one of the pin portion and the box portion,

the solid lubricating coating layer contains:

resin, a,

Solid lubricating powder, and

Cr₂O₃。

2. a threaded joint for pipes as set forth in claim 1,

the solid lubricating coating layer contains 1.0 to 20.0 mass% of the Cr₂O₃。

3. A threaded joint for pipes as set forth in claim 2,

the solid lubricating coating layer contains:

1.0 to 20.0 mass% of the Cr₂O₃、

50.0 to 90.0 mass% of the resin, and

5.0 to 30.0 mass% of the solid lubricating powder.

4. A threaded joint for pipes as set forth in any of claims 1-3 wherein,

the resin is 1 or more than 2 selected from the group consisting of epoxy resin, phenolic resin, furan resin, polyamideimide resin, polyamide resin, polyimide resin, and polyether ether ketone resin.

5. A threaded joint for pipes as set forth in claim 4 wherein,

the resin is 1 or more than 2 selected from the group consisting of epoxy resin, phenolic resin, polyamide-imide resin and polyamide resin.

6. A threaded joint for pipes as set forth in any of claims 1-5 wherein,

the solid lubricant powder is 1 or more than 2 selected from the group consisting of graphite, zinc oxide, boron nitride, talc, molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, organic molybdenum, thiosulfate compound, polytetrafluoroethylene, and melamine cyanurate.

7. A threaded joint for pipes as set forth in claim 6 wherein,

the solid lubricant powder is 1 or more selected from the group consisting of graphite and polytetrafluoroethylene.

8. A method of manufacturing a threaded joint for pipes as set forth in any one of claims 1 to 7, wherein the method comprises:

coating the contact surface of at least one of the male and female snap parts with the resin, the solid lubricant powder, and the Cr₂O₃The step (2) of preparing the composition of (4); and the number of the first and second groups,

and a step of curing the composition applied to the contact surface to form the solid lubricating coating layer.

9. A method of manufacturing a threaded joint for pipes as set forth in claim 8,

the method further comprises, before the step of applying the composition, the steps of:

and a step of forming a Zn alloy plating layer on the contact surface of at least one of the male snap part and the female snap part by electroplating.

10. A method of manufacturing a threaded joint for pipes as set forth in claim 9,

the method further comprises, before the step of forming the Zn alloy plating layer, the steps of:

and forming a surface roughness on the contact surface of at least one of the male and female snap portions.

Technical Field

The present invention relates to a threaded joint for pipes and a method for manufacturing a threaded joint for pipes, and more particularly, to a threaded joint for oil well pipes and a method for manufacturing a threaded joint for oil well pipes.

Background

Oil well pipes are used for the production of oil and gas fields. An oil country tubular good is formed by connecting a plurality of steel pipes according to the depth of a well. The steel pipes are connected by tightly screwing pipe threaded joints formed at the ends of the steel pipes to each other. The oil country tubular goods are pulled up and loosened by inspection or the like, and are tightened again after inspection and reused.

A threaded joint for pipes is provided with a male buckle portion and a female buckle portion. The male portion includes a male thread portion and a non-threaded metal contact portion formed on an outer peripheral surface of a distal end portion of the steel pipe. The box portion includes a female screw portion and an unthreaded metal contact portion formed on an inner peripheral surface of a distal end portion of the steel pipe. The screw portions of the pin portion and the box portion and the unthreaded metal contact portion are repeatedly subjected to strong friction during tightening and loosening of the threads of the steel pipe. If these portions do not have sufficient durability against friction, galling (sintering that cannot be repaired) occurs when the screw is repeatedly tightened and loosened. Therefore, a threaded joint for pipes is required to have sufficient durability against friction, i.e., excellent seizure resistance.

Conventionally, in order to improve seizure resistance, heavy metal-containing compound grease called paint has been used. The seizure resistance of a threaded joint for pipes can be improved by applying the compound grease to the surface of the threaded joint for pipes. However, heavy metals such as Pb, Zn, and Cu contained in the compound grease may affect the environment. Therefore, it is desired to develop a threaded joint for pipes that does not use compound grease.

International publication No. WO2014/042144 (patent document 1) proposes a threaded joint for pipes that is excellent in seizure resistance even without compound grease.

The composition for forming a solid lubricating coating layer described in patent document 1 is a composition containing a powdery organic resin that is at least partially soluble in a dipolar aprotic solvent in a mixed solvent containing water and the dipolar aprotic solvent. In the composition for forming a solid lubricating coating layer of patent document 1, a powdery organic resin is present in a mixed solvent in a dissolved state or a dispersed state. Patent document 1 describes: this can suppress rust without using compound grease, and has excellent seizure resistance.

Disclosure of Invention

Problems to be solved by the invention

However, the threaded and unthreaded metal contact portions of the pin portion and the box portion include a metal seal portion and a shoulder portion. When screwing the threaded joint for pipes, the shoulder portions of the pin portion and the box portion contact each other. The torque generated at this time is referred to as shoulder torque. In screwing up a threaded joint for pipes, the screwing up is further performed until the fastening is completed after the shoulder torque is reached. This improves the airtightness of the threaded joint for pipes. When the screw is further tightened, plastic deformation of the metal constituting at least one of the pin portion and the box portion starts. The torque generated at this time is referred to as yield torque.

The torque at the time of completion of fastening (hereinafter referred to as fastening torque) is set so that a sufficient seal surface pressure can be obtained regardless of the magnitude of the thread interference amount. If the difference between the shoulder torque and the yield torque (hereinafter referred to as shoulder friction torque Δ T') is sufficient, the range of tightening torque becomes wide. As a result, the fastening torque can be easily adjusted. Therefore, a threaded joint for pipes is required to have high shoulder friction torque Δ T', i.e., an overtorque performance, in addition to the seizure resistance described above.

In patent document 1, the shoulder friction torque Δ T' is not considered, and thus the over-torque performance may be low.

The present invention aims to provide a threaded joint for pipes having high over-torque performance and a method for manufacturing the same.

Means for solving the problems

The threaded joint for pipes of the present embodiment is a threaded joint for pipes provided with a pin portion and a box portion. The pin portion and the box portion have contact surfaces with a threaded portion and an unthreaded metal contact portion. A threaded joint for pipes is provided with a solid lubricating coating layer on the contact surface of at least one of a pin portion and a box portion. The solid lubricating coating layer contains resin, solid lubricating powder and Cr₂O₃。

The method for manufacturing a threaded joint for pipes according to the present embodiment includes: and a step of forming the solid lubricating coating layer on the contact surface of at least one of the male and female snap parts.

ADVANTAGEOUS EFFECTS OF INVENTION

The threaded joint for pipes of the present embodiment has a solid lubricantAnd a slip film layer. The solid lubricating coating layer contains Cr₂O₃. Therefore, the threaded joint for pipes of the present embodiment has high over-torque performance.

Drawings

Fig. 1 is a diagram showing a relationship between the number of revolutions and the torque of a threaded joint for pipes.

FIG. 2 is a view showing Cr in a solid lubricating coating layer₂O₃Graph of content versus over-torque performance.

FIG. 3 is a view showing Cr in a solid lubricating coating layer₂O₃Graph of the relationship between the content and the sintering resistance.

Fig. 4 is a diagram showing a structure of a threaded joint for pipes according to the present embodiment.

Fig. 5 is a sectional view of a threaded joint for pipes.

Fig. 6 is a sectional view of a contact surface of a threaded joint for pipes according to the present embodiment.

Fig. 7 is a diagram for explaining the shoulder friction torque Δ T' in the embodiment.

Detailed Description

Hereinafter, the present embodiment will be described in detail with reference to the drawings. The same or corresponding portions in the drawings are denoted by the same reference numerals, and description thereof will not be repeated.

The present inventors have variously studied the relationship between the torque overload performance and the seizure resistance of a threaded joint for pipes. As a result, the following findings were obtained.

[ over-torque performance ]

When the steel pipes are threaded tightly with each other, the optimum torque for ending the threading is determined in advance. Fig. 1 is a diagram showing a relationship between the number of rotations of a steel pipe and torque at the time of tightening a thread in a threaded joint for pipes having a shoulder portion. Referring to fig. 1, when screwing a threaded joint for pipes, torque initially rises in proportion to the number of revolutions. The rate of increase in torque at this time is low. If the screwing is further performed, the shoulder portions come into contact with each other. The torque at this time is referred to as shoulder torque. When the thread tightening is further performed after the shoulder torque is reached, the torque rises again in proportion to the number of revolutions. The torque rise rate at this time is high. When the torque reaches a predetermined value (tightening torque), tightening of the thread is completed. If the torque at the time of tightening the threads reaches the tightening torque, the metal seal portions interfere with each other with an appropriate surface pressure. In this case, the gas tightness of the threaded joint for pipes is improved.

If the tightening is further performed after the tightening torque is reached, the torque becomes excessively high. If the torque becomes too high, plastic deformation occurs in a part of the male and female snap portions. The torque at this time is referred to as yield torque. If the shoulder friction torque Δ T', which is the difference between the shoulder torque and the yield torque, is large, the range of the tightening torque is sufficient. As a result, the fastening torque can be easily adjusted. Therefore, the shoulder friction torque Δ T' is preferably large. In the present specification, the high over-torque performance means that the shoulder friction torque Δ T' is high.

In order to increase the shoulder friction torque Δ T', it is effective to reduce the shoulder torque or increase the yield torque. It is considered that when the solid lubricating coating layer contains hard particles, the yield torque increases at high surface pressure. If the yield torque increases, the shoulder friction torque Δ T' increases.

However, the present inventors have conducted investigations and found that a high shoulder friction torque Δ T' cannot be obtained even when hard particles are simply contained in the solid lubricating coating layer. Such as CaF₂Although hard particles are used, CaF is used as shown in examples described later₂A high shoulder friction torque Δ T' cannot be obtained.

Accordingly, the present inventors have further made various studies and found that by containing Cr in the solid lubricating coating layer₂O₃The high shoulder friction torque Δ T' can be obtained.

FIG. 2 is a view showing Cr in a solid lubricating coating layer₂O₃Graph of content versus over-torque performance. FIG. 2 is obtained by the examples described later. The horizontal axis in FIG. 2 represents Cr in the solid lubricating coating layer₂O₃The content of (a). The vertical axis of fig. 2 represents the over-torque performance. The over-torque performance is obtained as follows: in test No. 1 in the examples described later, the shoulder friction torque when the solid lubricating coating layer was replaced with the API standard coatingThe value of Δ T' is determined as a relative value with reference to (100). The white circle marks (∘) in fig. 2 indicate the over-torque performance of the example formed with the solid lubricating coating layer. The white triangular mark (Δ) in fig. 2 indicates the over-torque performance when API (american petroleum institute) standard paint is used in place of the solid lubricating coating layer.

As can be seen from FIG. 2, if the solid lubricating coating layer contains Cr₂O₃The over-torque performance exceeds 100. That is, if Cr is contained₂O₃High over-torque performance can be obtained.

[ sintering resistance ]

The present inventors have further found that Cr in the solid lubricating coating layer is adjusted₂O₃When the content (b) is (d), the over-torque performance is improved and the seizure resistance is also improved.

FIG. 3 is a view showing Cr in a solid lubricating coating layer₂O₃Graph of the relationship between the content and the sintering resistance. FIG. 3 is obtained by the following examples. The horizontal axis in FIG. 3 represents Cr in the solid lubricating coating layer₂O₃The content of (a). The vertical axis of fig. 3 indicates the number of times (times) the fastening can be performed without sintering.

According to FIG. 3, if Cr₂O₃When the content is 1.0 to 20.0 mass%, the number of times of fastening without sintering exceeds 10 times. I.e., if Cr₂O₃When the content is 1.0 to 20.0 mass%, high sintering resistance can be obtained.

The threaded joint for pipes according to the present embodiment completed based on the above-described findings has the following features. A threaded joint for pipes is provided with a male buckle portion and a female buckle portion. The pin portion and the box portion have contact surfaces with a threaded portion and an unthreaded metal contact portion. A threaded joint for pipes is provided with a solid lubricating coating layer on the contact surface of at least one of a pin portion and a box portion. The solid lubricating coating layer contains resin, solid lubricating powder and Cr₂O₃。

The threaded joint for pipes of the present embodiment contains Cr in the solid lubricating coating layer₂O₃. Therefore, high over-torque performance is achieved.

In the aboveIn the solid lubricating coating layer, Cr₂O₃The content of (B) is preferably 1.0 to 20.0 mass%.

If Cr is contained in the solid lubricating coating layer₂O₃When the content of (b) is 1.0 to 20.0 mass%, the sintering resistance of the solid lubricating coating layer is improved.

The solid lubricating coating layer may contain 1.0 to 20.0 mass% of Cr₂O₃50.0 to 90.0 mass% of a resin, and 5.0 to 30.0 mass% of a solid lubricant powder.

Preferably, the resin is 1 or 2 or more selected from the group consisting of an epoxy resin, a phenol resin, a furan resin, a polyamideimide resin, a polyamide resin, a polyimide resin, and a polyether ether ketone resin.

In this case, the over-torque performance and the seizure resistance of the solid lubricating coating layer are further improved.

The resin may be 1 or 2 or more selected from the group consisting of epoxy resin, phenol resin, polyamideimide resin, and polyamide resin.

Preferably, the solid lubricant powder is 1 or 2 or more selected from the group consisting of graphite, zinc oxide, boron nitride, talc, molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, organic molybdenum, thiosulfate compound, polytetrafluoroethylene, and melamine cyanurate.

Preferably, the solid lubricant powder is 1 or more selected from the group consisting of graphite and polytetrafluoroethylene.

In this case, the over-torque performance and the seizure resistance of the solid lubricating coating layer are further improved.

The method of manufacturing a threaded joint for pipes according to the present embodiment includes a coating step and a curing step. In the coating step, a coating composition containing a resin, a solid lubricant powder and Cr is applied to the contact surface of at least one of the male and female portions₂O₃The composition of (1). In the curing step, the composition applied to the contact surface is cured to form a solid lubricating coating layer.

The above-described manufacturing method may further include a Zn alloy plating layer formation step before the coating step. In the Zn alloy plating layer forming step, a Zn alloy plating layer is formed by electroplating on the contact surface of at least one of the pin portion and the box portion.

The above-described manufacturing method may further include a surface roughness forming step before the Zn alloy plating layer forming step. In the surface roughness forming step, surface roughness is formed on a contact surface of at least one of the pin portion and the box portion.

The threaded joint for pipes and the method of manufacturing the threaded joint for pipes according to the present embodiment will be described in detail below.

[ threaded joints for pipes ]

A threaded joint for pipes is provided with a male buckle portion and a female buckle portion. Fig. 4 is a diagram showing a structure of a threaded joint for pipes according to the present embodiment. The threaded joint for pipes 1 includes a steel pipe 2 and a coupling 3. Male-threaded portions 5 having male-threaded portions 4 on the outer surfaces are formed at both ends of the steel pipe 2. Female thread portions 8 having female thread portions 7 on the inner surface are formed at both ends of the coupling 3. The male and female coupling parts 5 and 8 are tightly threaded, and the coupling 3 is mounted on the end of the steel pipe 2. Although not shown, in order to protect each screw portion, a protector (not shown) may be attached to the pin portion 5 of the steel pipe 2 and the box portion 8 of the coupling 3 to which the corresponding member is not attached.

A typical threaded joint for pipes 1 is a coupling type including a steel pipe 2 and a coupling 3, as shown in fig. 4. On the other hand, there is also a threaded joint for pipes in which one end of the steel pipe 2 is a pin part 5 and the other end is a box part 8 as a whole without using the coupling 3. The threaded joint for pipes 1 of the present embodiment can be applied to both the collar system and the integral system.

The pin portion and the box portion have contact surfaces with a threaded portion and an unthreaded metal contact portion. Fig. 5 is a sectional view of the threaded joint for pipes 1. The male buckle portion 5 includes a male thread portion 4 and an unthreaded metal contact portion. The unthreaded metal contact portion of the pin portion 5 is formed at the tip of the pin portion 5 and includes a metal seal portion 10 and a shoulder portion 11. The female snap portion 8 includes a female screw portion 7 and an unthreaded metal contact portion. The unthreaded metal contact portion of the box portion 8 is formed at the tip of the box portion 8 and includes a metal seal portion 13 and a shoulder portion 12. The portions that the pin portion 5 and the box portion 8 contact when they are screwed are referred to as contact surfaces 6, 9. Specifically, when the pin portion 5 and the box portion 8 are screwed, the shoulder portions (shoulder portions 11 and 12), the metal seal portions (metal seal portions 10 and 13), and the screw portions (male screw portion 4 and female screw portion 7) contact each other. That is, in fig. 5, the contact surface 6 on the male buckle portion 5 side includes the shoulder portion 11, the metal seal portion 10, and the threaded portion 4. The contact surface 9 on the female snap portion 8 side includes a shoulder portion 12, a metal seal portion 13, and a threaded portion 7. In fig. 5, the male snap portion 5 has respective configurations in the order of the shoulder portion 11, the metal seal portion 10, and the male screw portion 4 from the tip of the steel pipe 2. The box portion 8 has respective configurations in the order of the internal thread portion 7, the metal seal portion 13, and the shoulder portion 12 from the tip of the steel pipe 2 or the coupling 3. However, the arrangement of the shoulder portions 11, 12, the metal seal portions 10, 13, and the screw portions 4, 7 is not limited to fig. 5. The arrangement of the structures is appropriately adjusted.

[ solid lubricating coating layer 21]

The threaded joint for pipes 1 is provided with a solid lubricating coating layer on the contact surfaces 6, 9 of at least one of the pin portion 5 and the box portion 8. Fig. 6 is a sectional view of the contact surfaces 6, 9 of the threaded joint for pipes 1 of the present embodiment. As described in the manufacturing method described later, the composition for forming the solid lubricating coating layer 21 is applied to the contact surfaces 6, 9 of at least one of the pin portion 5 and the box portion 8 and cured, thereby forming the solid lubricating coating layer 21.

The solid lubricating coating layer 21 contains resin, solid lubricating powder, and Cr₂O₃. Therefore, the composition for forming the solid lubricating coating layer 21 also contains a resin, a solid lubricating powder, and Cr₂O₃. The composition may be a solvent-free composition (i.e., containing only the above components) or a solvent-based composition obtained by dissolving the above components in a solvent. In the case of solvent-based compositions, the mass% of the components refers to: the total mass of all components other than the solvent contained in the composition is defined as 100% by mass. That is, the content of each component in the composition is the same as the content of each component in the solid lubricating coating layer 21. In addition, the method can be used for producing a composite materialThe components other than the solvent in the composition are the same as those in the solid lubricating coating layer 21. Hereinafter, the composition for forming the solid lubricating coating layer 21 is also simply referred to as "composition".

The components are described in detail below.

[ resin ]

The resin has the function of acting as a binder. The resin may be a known resin.

The resin is, for example, 1 or 2 selected from the group consisting of a thermosetting resin and a thermoplastic resin. The thermosetting resin is, for example, 1 or 2 or more selected from the group consisting of epoxy resin, phenol resin, furan resin, and polyimide resin. The thermoplastic resin is, for example, 1 or 2 or more selected from the group consisting of a polyamideimide resin, a polyamide resin, and a polyether ether ketone resin.

Preferably, the resin is 1 or 2 or more selected from the group consisting of epoxy resin, phenol resin, furan resin, polyamideimide resin, polyamide resin, polyimide resin, and polyether ether ketone resin. These resins have appropriate hardness. Therefore, the wear resistance, the seizure resistance, and the over-torque performance of the solid lubricating coating layer 21 are further improved.

More preferably, the resin is 1 or 2 or more selected from the group consisting of epoxy resin, phenol resin, furan resin, polyamideimide resin and polyamide resin.

Particularly preferably, the resin is 1 or 2 or more selected from the group consisting of epoxy resin, polyamideimide resin and polyamide resin.

Epoxy resins are thermosetting resins. When the epoxy resin is subjected to a thermosetting treatment, the epoxy groups remaining in the polymer crosslink and network. Thereby, the epoxy resin is cured.

The polyamideimide resin is a thermoplastic resin.

The polyamide resin is a thermoplastic resin. The polyamide resin is a polymer in which a plurality of monomers are bonded through amide bonds.

The content of the resin in the solid lubricating coating layer 21 is preferably 50.0 to 90.0 mass%. When the content of the binder is 60.0 mass% or more, the adhesion of the solid lubricating coating layer 21 is further improved. Therefore, the lower limit of the content of the resin in the solid lubricating coating layer 21 is more preferably 60.0 mass%, even more preferably 64.0 mass%, even more preferably 70.0 mass%. The upper limit of the content of the resin in the solid lubricating coating layer 21 is more preferably 85.0 mass%, even more preferably 80.0 mass%, even more preferably 75.0 mass%.

[ solid lubricating powder ]

In order to further improve the lubricity of the solid lubricating coating layer 21, the solid lubricating coating layer 21 contains solid lubricating powder. The solid lubricating powder is a solid powder having lubricity. The solid lubricant powder may be any known one.

The lubricants are roughly classified into, for example, the following 5 types. The solid lubricating powder contains at least 1 selected from the group consisting of the following (1) to (4).

(1) Lubricants that exhibit lubricity by having a specific crystal structure that slides easily, such as a hexagonal layered crystal structure (e.g., graphite, zinc oxide, boron nitride, and talc);

(2) lubricants that exhibit lubricity by having a reactive element in addition to by a crystal structure (e.g., molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, and organic molybdenum);

(3) lubricants that exhibit lubricity through chemical reactivity (e.g., thiosulfate compounds);

(4) lubricants that exhibit lubricity by plastic or viscoplastic behavior under frictional stress (e.g., Polytetrafluoroethylene (PTFE) and Melamine Cyanurate (MCA)); and the number of the first and second groups,

(5) a lubricant (e.g., perfluoropolyether (PFPE)) which is liquid or greasy and exhibits lubricity by being present at the boundary between contact surfaces to prevent direct contact between the surfaces.

Any of the solid lubricating powders (1) to (4) above can be used. The solid lubricating powder may be used alone in any of the above-mentioned items (1) to (4). For example, (1) the solid lubricating powder may be used alone. The solid lubricating powder may be used in combination of a plurality of the above-mentioned components (1) to (4). For example, the compound (4) may be used in combination with the compound (1). That is, the solid lubricating powder is preferably 1 or 2 or more selected from the group consisting of graphite, zinc oxide, boron nitride, talc, molybdenum disulfide, tungsten disulfide, graphite fluoride, tin sulfide, bismuth sulfide, organic molybdenum, thiosulfate compound, Polytetrafluoroethylene (PTFE), and Melamine Cyanurate (MCA).

Preferably, the solid lubricating powder contains 1 or more selected from the group consisting of (1) and (4) above. As the solid lubricating powder (1), graphite is preferable from the viewpoint of the adhesion and rust prevention of the solid lubricating coating layer 21, and earthy graphite is preferable from the viewpoint of film forming properties. As the lubricant additive (4), Polytetrafluoroethylene (PTFE) is preferable.

It is further preferred that the solid lubricant powder is Polytetrafluoroethylene (PTFE).

The content of the solid lubricant powder in the solid lubricant coating layer 21 is preferably 5.0 to 30.0 mass%. If the content of the solid lubricating powder is 5.0 mass% or more, the seizure resistance is further improved. Therefore, the number of times the screwing and unscrewing can be performed without the occurrence of sintering increases. The lower limit of the content of the solid lubricant powder is more preferably 10.0 mass%, and still more preferably 15.0 mass%. On the other hand, if the content of the solid lubricating powder is 30.0 mass% or less, the strength of the solid lubricating coating layer 21 is further improved. Therefore, the loss of the solid lubricating coating layer 21 is suppressed. The upper limit of the content of the solid lubricant powder is more preferably 28.0 mass%, still more preferably 25.0 mass%, and still more preferably 20.0 mass%.

[Cr₂O₃]

Cr₂O₃Also known as chromium (III) oxide. Cr (chromium) component₂O₃Is an inorganic compound. Cr (chromium) component₂O₃Has an equation of 151.99. Cr (chromium) component₂O₃Is obtained by pyrolysis of ammonium dichromate (ammonium dichromate). Cr (chromium) component₂O₃The crystals were purified by sublimation to form dark green metallic luster crystals. Cr (chromium) component₂O₃Is extremely stable and harder than quartz. Cr (chromium) component₂O₃Has no toxicity and danger.

As described above, if the solid lubricating coating layer 21 contains Cr₂O₃The over-torque performance is improved. And if Cr₂O₃When the content is 1.0 to 20.0 mass%, the sintering resistance is improved.

Cr in solid lubricating coating layer 21₂O₃The content is preferably 1.0 to 20.0 mass%. If Cr₂O₃When the content is 1.0 mass% or more, sufficient over-torque performance can be obtained, and the seizure resistance is also improved. If Cr₂O₃When the content is 20.0 mass% or less, the strength of the solid lubricating coating layer 21 is reduced, the increase in friction is suppressed, and the seizure resistance is improved. Cr (chromium) component₂O₃The lower limit of the content is preferably 1.0% by mass, more preferably 5.0% by mass, still more preferably 7.0% by mass, and still more preferably 10.0% by mass. Cr (chromium) component₂O₃The upper limit of the content is preferably 20.0% by mass, more preferably 18.0% by mass, still more preferably 16.0% by mass, and yet more preferably 15.0% by mass.

Cr₂O₃For example dark green particles. Cr (chromium) component₂O₃Preferably, the particle diameter of (2) is 45 μm or less. From the viewpoint of uniform dispersibility, it is more preferably 10 μm or less. The particle size is an arithmetic average of effective particle size distribution obtained by particle size distribution measurement by a laser diffraction/scattering method (SALD series manufactured by Shimadzu corporation). Cr (chromium) component₂O₃The lower limit of the preferred particle diameter of (2) is, for example, 1 μm.

Cr₂O₃For example, chromium (III) oxide available from Wako pure chemical industries, Ltd.

[ other ingredients ]

The solid lubricating coating layer 21 may contain other known rust-proofing additives, corrosion inhibitors, and the like.

[ Rust-preventive additive ]

The solid lubricating coating layer 21 needs to have rust-proofing properties for a long period of time until it is actually used. Therefore, the solid lubricating coating layer 21 may contain a rust-preventing additive. The rust-preventive additive is a generic name of additives having corrosion resistance. The rust-preventive additive contains, for example, at least 1 selected from the group consisting of aluminum tripolyphosphate, aluminum phosphite, and calcium ion-exchanged silica. Preferably, the rust inhibitive additive contains at least 1 selected from the group consisting of calcium ion exchanged silica and aluminum phosphite. Other commercially available reactive hydrophobizing agents and the like can also be used as the rust-preventing additive.

The content of the rust-preventive additive in the solid lubricating coating layer 21 is preferably 2 to 10 mass%. If the content of the rust-preventing additive is 2 mass% or more, the rust-preventing property of the solid lubricating coating layer 21 is further stably improved. On the other hand, if the content of the rust-preventing additive is 10 mass% or less, the lubricity of the solid lubricating coating layer 21 is stably improved. If the content of the rust-preventing additive exceeds 10 mass%, the rust-preventing effect is saturated.

[ Corrosion inhibitor ]

The solid lubricating coating layer 21 may further contain an anticorrosive agent. The anticorrosive agent is also a general term for an additive having corrosion resistance.

[ thickness of solid lubricating coating layer ]

The thickness of the solid lubricating coating layer 21 is preferably 10 to 40 μm. If the thickness of the solid lubricating coating layer 21 is 10 μm or more, high lubricity can be stably obtained. On the other hand, if the thickness of the solid lubricating coating layer 21 is 40 μm or less, the adhesion of the solid lubricating coating layer 21 is stable. Further, when the thickness of the solid lubricating coating layer 21 is 40 μm or less, the thread tolerance (pitch) of the sliding surface becomes wider, and the surface pressure during sliding becomes lower. It is therefore possible to suppress the fastening torque from becoming excessively high. Therefore, the thickness of the solid lubricating coating layer 21 is preferably 10 to 40 μm.

The thickness of the solid lubricating coating layer 21 is measured by the following method. The thickness of the solid lubricating coating layer 21 was measured using a vortex phase type film thickness meter PHASCOPEPMP910 manufactured by Helmut Fischer GmbH at 4 positions on the contact surfaces 6, 9 on which the solid lubricating coating layer 21 was formed. The determination is carried out by a method according to ISO (International Organization for standardization)21968 (2005). The measurement position was 4 positions (4 positions of 0 °, 90 °, 180 °, and 270 °) in the pipe circumferential direction of the threaded joint for pipes 1. The arithmetic mean of the measurement results was taken as the thickness of the solid lubricating coating layer 21.

The solid lubricating coating layer 21 may be a single layer or a plurality of layers. The multilayer refers to a state in which 2 or more layers of solid lubricating coating layers 21 are stacked from the contact surface side. By repeating the application and curing of the composition, 2 or more layers of the solid lubricating coating layer 21 can be formed. The solid lubricating coating layer 21 may be formed directly on the contact surface, or may be formed after the subbing treatment described later.

[ base material of threaded joint for pipe ]

The composition of the base material of the threaded joint for pipes 1 is not particularly limited. The base material is, for example, carbon steel, stainless steel, alloy steel, or the like. Among the alloy steels, duplex stainless steels containing alloying 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 ]

A method of manufacturing the threaded joint for pipes 1 according to the present embodiment will be described below.

The method of manufacturing the threaded joint for pipes 1 of the present embodiment includes a solid lubricating coating layer forming step. In the solid lubricating coating layer forming step, the solid lubricating coating layer 21 is formed on the contact surface of at least one of the pin portion 5 and the box portion 8.

[ Process for Forming solid lubricating coating layer ]

The solid lubricating coating layer includes a coating step and a curing step. In the coating step, a solid lubricating coating layer-forming composition (also simply referred to as a composition) is coated on the contact surface of at least one of the pin portion 5 and the box portion 8. In the curing step, the composition applied to the contact surface is cured to form the solid lubricating coating layer 21.

First, a composition for forming a solid lubricating coating layer is produced. The composition for forming a solid lubricating coating layer contains a resin and a solid lubricating powderPowder and Cr₂O₃. The solvent-free composition can be prepared by, for example, heating a resin to a molten state and adding a solid lubricant powder and Cr₂O₃And kneading the mixture to produce the rubber composition. A powder mixture in which all the components are mixed in powder form may be used as the composition.

The solvent-based composition can be prepared by, for example, mixing a resin, a solid lubricant powder and Cr₂O₃Dissolved or dispersed in a solvent and mixed. Examples of the solvent include water, various alcohols, and organic solvents. The proportion of the solvent is not particularly limited. The ratio of the solvent may be adjusted to an appropriate viscosity according to the coating method. The proportion of the solvent is, for example, 30 to 50% by mass when the total amount of all components except the solvent is 100% by mass.

[ coating Process ]

In the coating step, the composition is coated on the contact surfaces 6, 9 by a known method.

In the case of solvent-free compositions, the compositions can be applied by the hot-melt method. In the hot melt method, the composition is heated to melt the resin, and a low-viscosity fluid state is formed. The composition in a fluid state is sprayed from a spray gun having a heat retention function. The composition is heated and melted in a tank equipped with an appropriate stirring device, supplied to a spray head of a spray gun (kept at a predetermined temperature) via a metering pump by a compressor, and sprayed. The holding temperature in the tank and the spray head is adjusted according to the melting point of the resin in the composition. The coating method may use brush coating, dipping, and the like instead of spraying. The heating temperature of the composition is preferably 10 to 50 ℃ higher than the melting point of the resin. In coating the composition, it is preferable that the contact surfaces 6, 9 of at least one of the pin part 5 and the box part 8 of the composition to be coated are heated in advance to a temperature higher than the melting point of the resin. This makes it possible to obtain a good coating property.

In the case of a solvent-based composition, the composition in a solution state is applied to the contact surface by spraying or the like. In this case, the viscosity is adjusted to enable the composition to be sprayed under normal temperature and pressure environments.

[ curing step ]

In the curing step, the composition applied to the contact surface is cured to form the solid lubricating coating layer 21.

In the case of a solvent-free composition, the composition applied to the contact surfaces 6, 9 is cooled, whereby the composition in a molten state is solidified to form the solid lubricating coating layer 21. The cooling method may be performed by a known method. The cooling method is, for example, atmospheric cooling and air cooling.

In the case of a solvent-based composition, the solid lubricating coating layer 21 is formed by drying the composition applied to the contact surfaces 6 and 9, thereby curing the composition. The drying method can be carried out by a known method. Drying methods are, for example, natural drying, low-temperature air-blow drying and vacuum drying.

The solidification step may be performed by rapid cooling using a nitrogen or carbon dioxide gas cooling system. In the rapid cooling, the steel pipe is indirectly cooled from the opposite surfaces of the contact surfaces 6 and 9 (the outer surface of the steel pipe 2 or the coupling 3 in the case of the female portion 8, and the inner surface of the steel pipe 2 in the case of the male portion 5). This can suppress deterioration of the solid lubricating coating layer 21 due to rapid cooling.

The solid lubricating coating layer 21 preferably covers the entirety of the contact surfaces 6, 9 of at least one of the male snap portion 5 and the female snap portion 8. The solid lubricating coating layer 21 may cover only a part of the contact surfaces 6, 9 (for example, only the metal seal portions 10 and 13).

The method of manufacturing the threaded joint for pipes 1 according to the present embodiment may further include a Zn alloy plating layer forming step before the solid lubricating coating layer forming step. The Zn alloy plating layer formation step is performed before the solid lubricating coating layer formation step, that is, before the coating step. In the Zn alloy plating layer forming step, a Zn alloy plating layer is formed by electroplating on the contact surface of at least one of the pin part 5 and the box part 8.

[ Zn alloy plating layer formation step ]

In the Zn alloy plating layer forming step, a Zn alloy plating layer is formed by electroplating on the contact surface of at least one of the pin part 5 and the box part 8.

Alternatively, in the Zn alloy plating layer forming step, the Zn alloy plating layer is formed by electroplating on the contact surface of at least one of the pin part 5 and the box part 8 or on the surface roughness formed on the contact surface.

When the Zn alloy plating layer forming step is performed, the seizure resistance and corrosion resistance of the threaded joint for pipes 1 are improved. The Zn alloy plating layer forming step is, for example, a single layer plating treatment based on Zn metal, a 2-layer plating treatment based on a Zn layer and a Ni layer, and a 3-layer plating treatment based on a Zn layer, a Cu layer, and a Sn layer. For the steel pipe 2 formed of steel having a Cr content of 5% or more, a Zn-Co alloy plating treatment, a Cu-Sn-Zn alloy plating treatment, and a Zn-Ni alloy plating treatment are preferable.

The plating treatment can be performed by a known method. For example, a plating bath containing ions of the metal element contained in the Zn alloy plating layer is prepared. Then, at least one of the contact surfaces 6, 9 of the male and female snap portions 5, 8 is immersed in the plating bath. The contact surfaces 6, 9 are energized, so that a Zn alloy plating layer is formed on the contact surfaces. Conditions such as the temperature of the plating bath and the plating time can be appropriately set.

More specifically, for example, in the case of 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: 1-50 g/L, Sn: 1-50 g/L, and Zn: 1 to 50 g/L. The conditions of the plating are, for example, plating bath pH: 1-10, plating bath temperature: 60 ℃, current density: 1 to 100A/dm²And processing time: 0.1-30 minutes.

In the case of 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: 1-100 g/L and Ni: 1 to 50 g/L. The conditions of the plating are, for example, plating bath pH: 1-10, plating bath temperature: 60 ℃, current density: 1 to 100A/dm²And processing time: 0.1-30 minutes.

The hardness of the Zn alloy plating layer is preferably 300 or more in terms of micro vickers hardness. If the hardness of the Zn alloy plating layer is 300 or more, the corrosion resistance of the threaded joint for pipes 1 is further stably improved.

The hardness of the Zn alloy plating layer can be measured as follows. In the Zn alloy plating layer of the obtained threaded joint for pipes 1, any 5 regions were selected. In each selected region, vickers Hardness (HV) was measured according to JIS Z2244 (2009). For the test conditions, the test temperature was set to normal temperature (25 ℃) and the test force was set to 2.94N (300 gf). The average of the obtained values (5 in total) was defined as the hardness of the Zn alloy plating layer.

In the case of the multilayer plating treatment, the plating layer of the lowermost layer is preferably set to a film thickness of less than 1 μm. The thickness of the plating layer (total thickness in the case of multilayer plating) is preferably 5 to 15 μm.

The thickness of the Zn alloy plating layer was measured as follows. On the contact surface on which the Zn alloy plating layer was formed, a probe of a vortex phase type film thickness measuring instrument according to iso (international Organization for standardization)21968(2005) was brought into contact with the contact surface. The phase difference between the high-frequency magnetic field on the probe input side and the eddy current on the Zn-Ni alloy plating layer excited thereby was measured. The phase difference is converted into the thickness of the Zn alloy plating layer.

The method of manufacturing the threaded joint for pipes 1 according to the present embodiment may further include, before the Zn alloy plating layer forming step: a surface roughness is formed on the contact surface of at least one of the pin part 5 and the box part 8.

[ procedure for Forming surface roughness ]

In the surface roughness forming step, surface roughness is formed on the contact surface of at least one of the pin portion 5 and the box portion 8. The surface roughness preferably has an arithmetic mean deviation Ra of the profile of 1 to 8 μm and a maximum height Rz of the profile of 10 to 40 μm. When the arithmetic mean deviation Ra of the profile is 1 μm or more and the maximum height Rz of the profile is 10 μm or more, the adhesion of the solid lubricating coating layer 21 is further improved. When the arithmetic mean deviation Ra of the profile is 8 μm or less and the maximum height Rz of the profile is 40 μm or less, the friction is suppressed, and the damage and the peeling of the solid lubricating coating layer 21 are suppressed.

The maximum height Rz of the profile and the arithmetic mean deviation Ra of the profile mentioned in the present specification are measured based on JIS B0601 (2013). The measurement was performed using a scanning probe microscope SPI3800N manufactured by SII Nano Technology. For the measurement conditions, the number of data acquisitions was 1024 × 1024 in a2 μm × 2 μm region of the sample as a unit of the number of data acquisitions. The reference length was set to 2.5 mm. The larger the maximum height Rz of the profile is, the larger the contact area with the solid lubricating coating layer 21 is. Therefore, the adhesion to the solid lubricating coating layer 21 is improved due to the anchor effect. If the adhesiveness of the solid lubricating coating layer 21 is improved, the seizure resistance of the threaded joint for pipes 1 is further improved.

The surface roughness of the contact surfaces 6, 9 of the threaded joint for pipes 1 is generally about 3 to 5 μm in the maximum height Rz of the profile. When the surface roughness of the contact surfaces 6 and 9 is appropriately large, the adhesion of the coating (the solid lubricating coating layer 21 or the Zn alloy plating layer) formed thereon is improved. As a result, the seizure resistance and corrosion resistance of the threaded joint for pipes 1 are further improved. Therefore, it is preferable to perform a surface roughness forming step on the contact surfaces 6 and 9 before applying the composition for forming the solid lubricating coating layer 21. The surface roughness forming step is, for example, 1 or more selected from the group consisting of blast treatment, pickling treatment, and chemical conversion treatment.

[ Sand blast treatment ]

The blasting treatment is a treatment of mixing a blasting material (abrasive) with compressed air and projecting it to the contact surfaces 6, 9. The blasting material is, for example, a spherical blasting material and an angular abrasive material. By the sand blasting, the surface roughness of the contact surfaces 6, 9 can be increased. The blasting treatment may be performed by a known method. For example, air is compressed by a compressor, and the compressed air is mixed with the blasting material. The material of the blasting material is, for example, stainless steel, aluminum, ceramic, alumina, or the like. Conditions such as the projection speed of the blast treatment can be appropriately set.

[ acid pickling treatment ]

The pickling process is a process of roughening the contact surfaces 6 and 9 by immersing them in a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid, or hydrofluoric acid. Thereby, the surface roughness of the contact surfaces 6, 9 can be increased.

[ chemical conversion treatment ]

The chemical conversion treatment is a treatment for forming a porous chemical conversion coating 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 adhesiveness of the solid lubricating coating layer 21, 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 known method. As the treatment liquid, an acidic phosphate chemical conversion treatment liquid for a general zinc-plated material can be used. For example, there is mentioned a zinc phosphate-based chemical conversion treatment containing 1 to 150g/L of phosphate ions, 3 to 70g/L of zinc ions, 1 to 100g/L of nitrate ions, and 0 to 30g/L of nickel ions. A manganese phosphate-based chemical conversion treatment liquid commonly used for the threaded joint 1 for pipes may be used. The liquid temperature is, for example, from room temperature to 100 ℃. The processing time may be set as appropriate according to the desired film thickness, and may be, for example, 15 minutes. In order to promote the formation of the chemical conversion coating, surface conditioning may be performed before the phosphate chemical conversion treatment. The surface conditioning is a treatment of immersing the titanium colloid-containing aqueous solution for surface conditioning. It is preferable to perform water washing or hot water washing after the phosphate chemical conversion treatment, and then to perform drying.

The chemical conversion coating is porous. Therefore, when the solid lubricating coating layer 21 is formed on the chemical conversion coating, the adhesion of the solid lubricating coating layer 21 is further improved by the so-called "anchor effect". The preferable thickness of the phosphate coating is 5 to 40 μm. When the thickness of the phosphate coating is 5 μm or more, sufficient corrosion resistance can be ensured. When the thickness of the phosphate coating is 40 μm or less, the adhesion of the solid lubricating coating layer 21 is stably improved.

In the surface roughness forming step, only 1 treatment may be performed, or a plurality of treatments may be combined. In the case of performing 1 treatment, it is preferable to perform a treatment selected from the group consisting of sand blast treatment, acid pickling treatment, and phosphate chemical conversion treatment. In the surface roughness forming step, 2 or more kinds of treatment may be performed. In this case, for example, the phosphate chemical conversion treatment may be performed after the blasting treatment. After the surface roughness forming step is performed, the solid lubricating coating layer 21 is formed. This can further improve the adhesion of the solid lubricating coating layer 21.

[ 3-valent chromate treatment ]

In the case of performing the Zn alloy plating treatment, the 3-valent chromate treatment may be performed after the Zn alloy plating layer formation step and before the solid lubricating coating layer formation step. The 3-valent chromate treatment is a treatment for forming a chromate film of 3-valent chromium. The coating film formed by the 3-valent chromate treatment suppresses white rust on the surface of the Zn alloy plating layer. Thereby, the product appearance is improved (the white rust of the Zn alloy plating layer is not rust of the base material of the threaded joint for pipe 1. therefore, the seizure resistance and the corrosion resistance of the threaded joint for pipe 1 are not affected). When the solid lubricating coating layer 21 is formed on the coating film based on the 3-valent chromate, the adhesion of the solid lubricating coating layer 21 is further improved.

The 3-valent chromate treatment can be carried out by a known method. For example, the contact surface 6, 9 of at least one of the male snap portion 5 and the female snap portion 8 is immersed in a chromate treatment liquid, or the chromate treatment liquid is sprayed to the contact surface 6, 9. The contact surfaces 6, 9 are then water-washed. Alternatively, the contact surfaces 6 and 9 are immersed in a chromate treatment solution, energized, and then washed with water. Alternatively, the chromate treatment liquid is applied to the contact surfaces 6 and 9 and heated to dry. The treatment conditions for the 3-valent chromate may be appropriately set.

The thickness of the 3-valent chromate coating can be measured by the same method as that for the solid lubricating coating layer 21.

In the method of manufacturing the threaded joint for pipes 1 according to the present embodiment, the step of forming the solid lubricating coating layer may be performed on the contact surfaces 6 and 9 of at least one of the pin portion 5 and the box portion 8. That is, the Zn alloy plating layer forming step, the surface roughness forming step, and the 3-valent chromate treatment may be performed in the same manner in the pin part 5 and the box part 8, or may be performed in different manners in the pin part 5 and the box part 8.