JP2001065753A - Threaded fittings for oil country tubular goods - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To suppress the occurrence of galling during repeated tightening and loosening without using compound grease, to achieve a low coefficient of friction during tightening, and to achieve high sealing performance with low tightening torque. To provide a threaded joint. SOLUTION: At least one of the pin and the box has a surface roughness Rmax of 5 on the surface of the screwless metal contact portion.
To 20 μm of a phosphate chemical conversion treatment film, and the average particle diameter is 0.005 to 3 μm on the surface of the phosphate chemical conversion treatment film.
m of solid fine particles dispersed and mixed at a ratio of 3 to 60% by weight to form a lubricating film of an inorganic polymer compound having a skeleton of Ti-O. Alternatively, a lubricating film of a resin in which solid fine particles having an average particle size of 0.005 to 0.4 μm are dispersed and mixed at a ratio of 5 to 70% by weight is formed on the surface of the phosphate chemical conversion treatment film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a threaded joint for an oil country tubular good having excellent seizure resistance, and more particularly, to repeated tightening and loosening in crude oil extraction in a poor environment such as a high depth, high temperature oil well or a steam injection oil well. The present invention relates to a threaded joint for oil country tubular goods which does not seize upon return, has excellent airtightness, and can be used repeatedly.

[0002]

2. Description of the Related Art A threaded joint is generally used in tubing and casing used for drilling an oil well. Normally, the depth of an oil well is 2,000 m to 3000 m, but in a deep oil well such as a recent marine oil field, it is 8,000 m to 10,000.
m. Threaded joints connecting these oil country tubular goods are subjected to combined pressure and heat such as axial tensile force and internal / external surface pressure caused by the weight of the oil country tubular goods and the joints themselves in the use environment. Is required to maintain airtightness without breakage. Furthermore, when lowering the tubing or casing, once tightened joints may be loosened and re-tightened. The API (American Petroleum Institute) tightens tubing joints ten times and casing joints three times (make up). Up),
It is required that airtightness be maintained without the occurrence of seizure called galling even when loosening back (breakout) is performed.

[0003] By the way, as a threaded joint, a threadless metal contact portion is usually formed at the tip of a male thread formed at the end of an oil country tubular good, and a threadless metal formed at the base of a female thread on the inner surface of the threaded joint member. A threaded joint is used in which a threaded metal contact portion and a threadless metal contact portion are subjected to surface treatment in a structure in which a metal seal portion is formed by fitting and tightening a metal contact portion and then abutting each other. Compound grease is applied during tightening to improve seizure resistance and airtightness.

[0004] However, since high surface pressure exceeding the yield point of the threaded joint material acts on the metal contact portion without thread, seizure is likely to occur, and various types of screws with improved seizure resistance have been used. Joints have been proposed.

For example, Japanese Unexamined Patent Publication (Kokai) No. 61-79797 discloses a threaded joint in which a screw portion is plated with Zn, Sn, or the like, and a metal seal portion (metal contact portion without a screw) is plated with gold, platinum, or the like. In Japanese Patent Publication No. Hei 3-78517, a particle size of 1
Japanese Patent Application Laid-Open No. H8-103724 discloses a pipe joint in which a coating of a synthetic resin in which molybdenum disulfide of 0 μm or less is dispersed and mixed at a ratio of 20 to 90% is provided on a manganese phosphate-based chemical conversion treatment coating layer. A surface treatment method of a steel pipe joint for forming a resin film containing molybdenum is disclosed in
Japanese Patent No. 1055582 discloses a pipe joint in which a nitriding layer is a first layer, an iron plating layer or an iron alloy plating layer is a second layer, and a third layer of a resin film containing molybdenum disulfide is formed thereon. A surface treatment method is disclosed.

[0006] However, the threaded joints disclosed in the above publications are all based on the premise that compound grease is used. This grease contains heavy metal powders such as zinc, lead and copper, and the applied grease may be washed out when joining screws, or the applied grease may overflow to the outer surface when tightened. If so, there is a concern that it may cause environmental pollution. In addition, the work of applying compound grease deteriorates the working environment and also reduces the working efficiency. Therefore, development of a threaded joint that does not use such compound grease is desired.

[0007]

As a threaded joint that does not use compound grease, Japanese Patent Application Laid-Open Nos. 8-233163, 8-233164, and 9-72 disclose a joint.
No. 467 discloses a threaded joint in which a resin film in which molybdenum disulfide is dispersed and mixed is formed. However, when the resin coating is reused in a high-temperature environment,
There is a problem that the resin coating layer is deteriorated. Further, compared with the case of using compound grease, there is a problem that the friction coefficient of the contact surface when tightening the threaded joint is high and a large tightening force is required. In oil well pipe line assembly, it is important to reduce the tightening force of threaded joints in order to improve workability, and to achieve this, threaded joints with low friction coefficient at the contact surface and excellent lubrication performance Is required.

An object of the present invention is to provide a threaded joint having excellent seizure resistance and lubricating performance. More specifically,
An object of the present invention is to provide a threaded joint that suppresses the occurrence of galling at the time of repeated tightening and loosening without using compound grease, has a low friction coefficient at the time of tightening, and obtains high sealing performance with a low tightening torque. .

[0009]

Means for Solving the Problems In order to solve the above problems, the present inventors have used a solid fine particle having a particle size of about several μm or less and a lubricating coating using a polymer compound as a binder for the solid fine particle. With the aim of formation, from a viewpoint of seizure resistance and lubricity, a basic study was conducted on a lubricant, a binder, and a base treatment when forming a lubricating film, and the following findings were obtained.

(A) The use of solid fine particles having a particle size in a specific range as the solid fine particles contained in the lubricating coating improves the seizure resistance and friction performance of the lubricating coating.
Specifically, when using a resin as the binder,
In the case of using solid fine particles having an average particle diameter of 0.4 μm or less and using an inorganic polymer compound having a skeleton of Ti—O described later as a binder, solid fine particles having an average particle diameter of 3.0 μm or less are used.

(B) When a resin is used as a binder, there is no problem in heat resistance even at a long time exceeding 24 hours under a use condition of 200 ° C. or less. However, in a high-temperature environment of about 400 ° C. or more, deterioration, decomposition, or carbonization of the resin proceeds for a long time exceeding 24 hours, and the function as a binder is lost. As a result, the lubricating performance of the lubricating film is significantly reduced. Therefore, a resin can be used as a binder for a lubricating film formed on a threaded joint having a small thermal load, for example, a casing threaded joint.

(C) Inorganic compounds such as oxides, carbides and nitrides such as Si, Ti and Al are thermally stable.
No function as a binder. Therefore, since a film cannot be formed, lubricity is low.

(D) Titanium alkoxide (Ti (OR)
₍₄ , R = alkyl group) has an alkyl group, and thus exhibits organic properties and functions as a binder. This substance is unstable in the air, absorbs moisture and causes co-hydrolysis, and the decomposed products are bonded to each other to form a thermally stable inorganic polymer compound with a skeleton of Ti-O having a network structure. Change. Formula (1) illustrates a molecular structural formula of a typical inorganic polymer compound.

[0014]

Embedded image

(E) The inorganic polymer compound is stable even in a high temperature environment of about 400 ° C. Therefore, by mixing and applying titanium alkoxide as a binder of solid fine particles, and by performing humidification treatment, containing solid fine particles,
Ti-O with excellent lubricity and heat resistance even under high temperature environment
And a lubricating coating of an inorganic polymer having a skeleton as a skeleton.

Based on the above basic study results, the appropriate conditions for forming the lubricating coating on the threaded joint were examined, and the following findings were obtained.

(F) Seizure is suppressed by forming a lubricating coating on at least one of the threadless metal contact portions of the pin or the box.

(G) In the case of a lubricating coating of a resin, the content of solid fine particles should be within the range of 5 to 70% by weight.
3 in the case of a lubricating coating of an inorganic polymer compound having a skeleton of
It is good to be in the range of ６０60% by weight.

(H) Since a high surface pressure acts on the contact surface of the threaded joint, it is necessary to firmly fix the lubricating film to the contact surface. However, if the contact surface is smooth, the lubricating film peels off. Cheap. Therefore, as a base treatment when forming a lubricating film, the surface roughness is previously 5 to 20 μm in Rmax by a chemical conversion treatment.
By forming a phosphate conversion coating of m and forming a lubricating coating thereon, the adhesion of the lubricating coating can be increased.

The present invention has been completed based on the above findings, and the gist thereof is as follows.

(1) In a threaded joint composed of a pin and a box each having a threaded portion and a threadless metal contact portion, at least one of the pin and the box has a surface roughness Rmax on the surface of the threadless metal contact portion. 5 to 2
A phosphoric acid conversion treatment film of 0 μm is formed, and solid fine particles having an average particle size of 0.005 to 3 μm are dispersed and mixed on the surface of the phosphate conversion treatment film at a ratio of 3 to 60% by weight.
A threaded joint for oil country tubular goods, wherein a lubricating film of an inorganic polymer compound having O as a skeleton is formed.

(2) In a threaded joint composed of a pin and a box each having a threaded portion and a threadless metal contact portion, at least one of the pin and the box has a surface roughness Rmax on the surface of the threadless metal contact portion. 5 to 2
A phosphate conversion coating of 0 μm, and the average particle size is 0.005 to 0.4 μm on the surface of the phosphate conversion coating.
A threaded joint for oil country tubular goods characterized by forming a lubricating coating of a resin in which the solid fine particles are dispersed and mixed at a ratio of 5 to 70% by weight.

[0023]

FIG. 1 is a schematic view schematically showing a configuration of a threaded joint for an oil country tubular good according to the present invention. Reference numeral 1 is a box, 2 is a pin, 3 is a screw portion, 4 is a metal contact portion without a screw,
5 indicates a shoulder portion.

FIG. 2 is an enlarged cross-sectional view of a threadless metal contact portion of a pin showing an example of a state of forming a lubricating film according to the present invention. Reference numeral 6 denotes a lubricating coating, 7 denotes a resin or an inorganic polymer compound, 8 denotes solid fine particles, 9 denotes a phosphate chemical conversion coating, and FIG.
The same elements as those described above are denoted by the same reference numerals.

As shown in FIG. 1, a threaded joint for an oil country tubular good (hereinafter also referred to as a threaded joint) of the present invention is a box 1 comprising a threaded portion 3 formed on the inner surface of a threaded joint member and a threadless metal contact portion 4. And a pin 2 comprising a screw portion 3 and a screwless metal contact portion 4 formed on the outer surface of the end of the oil country tubular good. Further, in the threaded joint of the present invention, as shown in FIG. 2, a phosphate chemical conversion coating layer 9 was formed on the surface of the threadless metal contact portion 4 of the pin, and solid fine particles 8 were further dispersed and mixed thereon. A lubricating coating of an inorganic polymer compound having a skeleton of resin or Ti-O is formed. Although FIG. 2 illustrates the case where the phosphate chemical conversion coating layer is formed on the threadless metal contact portion of the pin, it may be formed on at least one of the threadless metal contact portion of the pin and the box.

The non-threaded metal contact portion (hereinafter, also simply referred to as a metal contact portion) has a higher contact surface pressure than the thread portion and is in a severely lubricated state, and the threaded joint fastens the pin and the box by screwing each other. Therefore, by forming a lubricating coating on at least one of the metal contact portions of the pin and the box, seizure resistance can be improved. In addition,
In threaded joints with high material strength and high contact surface pressure acting on the threaded parts and threaded joints made of alloys with a large amount of alloying elements such as Cr and Ni, seizure is likely to occur. It is desirable to form a lubricating film also on the threaded portion.

As the resin, a material having a function as a binder for solid fine particles and having heat resistance, moderate hardness and wear resistance is used. Examples of such a material include a thermosetting resin such as an epoxy resin, a polyimide resin, a polyamideimide resin, a polyether sulfone, and a polyether ether ketone, a phenol resin, a polyethylene resin, and a silicone resin. Preferably, it is a thermosetting resin.

As the inorganic high molecular compound, a material having a function as a binder for solid fine particles and having heat resistance, moderate hardness and wear resistance is used. Such materials include:
It has a molecular structure exemplified in the formula (1), and the alkyl group in the formula (1) is methyl, ethyl, isopropyl, propyl,
Ti-O having an alkyl group such as isobutyl and butyl
And a high molecular compound having a skeleton. Preferably, it is a polymer compound having a skeleton of Ti-O in which the alkyl group is methyl.

The solid fine particles enhance the lubricity of the lubricating film,
Acts to improve seizure resistance. As solid particles forming such an action, carbonates, silicates, oxides, carbides, carbides, nitrides, sulfides, fluorides, graphite, molybdenum disulfide, calcium stearate, cluster diamonds, fullerene C _60, etc. Examples can be given. Examples of the carbonate include carbonates of alkali metals and alkaline earth metals such as Na ₂ CO ₃ , CaCO ₃ and MgCO ₃ .
The _{silicate, M x O y SiO 2 (} M: alkali metals, alkaline earth metals) and the like. As the oxide, Al
₂ O ₃ , TiO ₂ , CaO, ZnO, ZrO ₂ , SiO ₂ , Fe ₂ O ₃ , Fe
₃ O ₄ , Y ₂ O _{3 and the} like. As carbides, SiC, Ti
C, etc., as nitrides, TiN, BN, AlN, Si ₃ N ₄ etc., as sulfides, as PbS, etc., as fluorides, as Ca
F ₂ , BaF _{2 and the} like. These may be used alone or as a mixture of two or more. Preferably, cluster diamond, Al ₂ O ₃ , CaCO ₃ , SiC
, Graphite and molybdenum disulfide.

The average particle size of the solid fine particles contained in the lubricating coating of the inorganic high molecular compound is 0.005 μm or more and 3.0 μm.
The following is assumed. If the average particle size is less than 0.005 μm, the particles are likely to agglomerate during mixing, making uniform dispersion difficult,
Partial seizure is likely to occur. On the other hand, if the average particle size exceeds 3 μm, the friction coefficient of the contact portion between the pin and the box increases, and the seizure resistance decreases. Preferably it is 0.005 μm or more and 1.0 μm or less, more preferably 0.005 μm or more and 0.5 μm or less.

The average particle size of the solid fine particles to be contained in the resin lubricating film is not less than 0.005 μm and not more than 0.4 μm. If the average particle size is less than 0.005 μm, the particles are likely to agglomerate during mixing, making uniform dispersion difficult, and causing partial seizure. In addition, the average particle size is 0.4
If it exceeds μm, the coefficient of friction at the contact portion between the pin and the box increases, and the seizure resistance decreases.

The content of the solid fine particles in the lubricating coating of the inorganic polymer compound is set to 3% by weight or more and 60% by weight or less. If the content is less than 3% by weight, the amount of the solid fine particles is insufficient, so that the improvement in seizure resistance is insufficient. On the other hand, if the content exceeds 60% by weight, the function of the inorganic polymer compound as a binder is reduced, so that the solid fine particles cannot be held as a film, and the film is remarkably peeled during repeated use, and seizure occurs. Preferably, the content is 5% by weight or more,
0% by weight or less, more preferably 10% by weight or more,
30% by weight or less.

The content of the solid fine particles in the lubricating coating of the resin is 5% by weight or more and 70% by weight or less. The above content is 5
If the amount is less than% by weight, the amount of solid fine particles is insufficient, so that the improvement in seizure resistance is insufficient. On the other hand, if the content exceeds 70% by weight, the function of the resin as a binder is reduced and the solid fine particles cannot be retained as a film, and the film is remarkably peeled during repeated use, resulting in seizure. Preferably, the content is 10% by weight or more and 60% by weight or less,
More preferably, the content is 15% by weight or more and 40% by weight or less.

The thickness of the lubricating film is 5 μm or more and 30 μm
It is desirable to do the following. The solid fine particles contained in the lubricating coating are subjected to a high surface pressure, spread over the entire contact surface including the opposing surface, and exhibit excellent seizure resistance. However, if the thickness of the lubricating coating is less than 5 μm, the solid fine particles are solid. The diffusion amount of fine particles is small, and the effect of improving lubricity is small. On the other hand, when the film thickness is 30
If the thickness exceeds μm, the above effect is saturated, but there is a problem that the tightening amount is insufficient and the airtightness is reduced, and there is a problem that the surface pressure is increased to maintain the airtightness and seizure easily occurs. In particular, the lubricating coating made of an inorganic polymer compound is relatively hard and hardly deformed. More preferably, the film thickness is 5 μm or more,
5 μm or less.

As a base treatment for forming a lubricating film,
A phosphate film is formed in advance by a chemical conversion treatment. The phosphate conversion coating is a reaction layer formed by a chemical reaction on the surface of the joint material, and the surface has a structure in which fine crystal grains are established. Therefore, the adhesiveness with the material below the layer is extremely high, and the so-called anchor effect of capturing the lubricating film formed on the layer is enhanced, the adhesiveness of the lubricating film is improved, and the lubricating film is separated. Is blocked.

Examples of the phosphate chemical conversion coating include chemical conversion coatings such as manganese phosphate, zinc phosphate, calcium phosphate and calcium zinc phosphate. The geometries of these crystals are different, with manganese phosphate crystals being the most delicate and carpet-like. Therefore,
From the viewpoint of improving the anchor effect, it is desirable to use a manganese phosphate coating.

It is desirable that the surface roughness of the phosphate chemical conversion treatment film be 5 μm or more and 20 μm or less in Rmax. When the surface roughness is less than Rmax 5 μm, the anchor effect is small, and the lubricating film is easily peeled off. On the other hand, when Rmax exceeds 20 μm, the lubricating film formed on the convex portion of the roughness at the time of tightening / unfastening is broken, and seizure tends to occur. More preferable surface roughness is 5 μm or more and 10 μm or less. The surface roughness of the opposing surface on which the phosphate chemical conversion coating is not formed is preferably less than the surface roughness of the phosphate chemical conversion coating. The surface roughness of the base when forming the phosphate chemical conversion coating is not particularly limited, but is preferably 3 μm or more and 15 μm or less.

The threaded joint of the present invention can remarkably improve the galling resistance without using any lubricant such as compound grease applied before make-up.

In the threaded joint of the present invention, a rust-preventive additive or a corrosion inhibitor is added to the lubricating coating to prevent rust while maintaining seizure resistance. Known rust preventive additives and corrosion inhibitors can be used.

Next, the method of forming a lubricating film according to the present invention will be described with reference to an example of forming a lubricating film of an inorganic polymer compound.

In forming the lubricating coating according to the present invention,
First, the surface of the metal contact portion of at least one of the pin and the box is subjected to a chemical conversion treatment to form a phosphate chemical conversion coating, and then a titanium alkoxide (Ti (OR) ₄ ,
R: an alkyl group) and solid fine particles are mixed with a dispersion medium, and these are coated on a phosphate chemical conversion treatment film, and further subjected to humidification treatment to co-hydrolyze to form Ti-O as a skeleton to form a solid. A lubricating film of an inorganic polymer compound containing fine particles is formed. In the case of forming a lubricating coating of a resin, for example, a dispersing medium is added to and mixed with the thermosetting resin and the solid fine particles, and the lubricating coating is formed by applying these on a phosphate chemical conversion coating. be able to. The humidification process is not required when forming a resin lubricating film.

The formation of the above-mentioned phosphate chemical conversion coating film can be carried out by a known method. The surface roughness of the chemical conversion coating film can be adjusted by adjusting the immersion time in the chemical conversion treatment solution and the temperature of the chemical conversion treatment solution. Can be adjusted. That is, by shortening the immersion time and lowering the processing solution temperature,
Reduce surface roughness, conversely, increase immersion time, and
The surface roughness can be increased by increasing the temperature of the processing solution.

As the titanium alkoxide, a titanium alkoxide having an alkyl group such as methyl, ethyl, isopropyl, propyl, isobutyl and butyl can be used.

As a dispersant for titanium alkoxide, low boiling liquids such as xylene, methylene chloride, butyl alcohol and methyl ethyl ketone can be used alone or as a mixture of two or more.

As the resin dispersant, xylene,
Low boiling liquids such as toluene and isopropyl alcohol can be used alone or in combination of two or more.

The humidification treatment can be performed by leaving the humidification treatment in the atmosphere for a predetermined time, but it is preferable to perform the humidification treatment in an atmosphere having a humidity of 70% or more. Further, it is desirable to perform a heat treatment after the humidification treatment. The co-hydrolysis is promoted by the heat treatment, and the discharge of the alkyl substance, which is a hydrolyzate, from the inside of the film can be promoted, whereby the adhesion of the film becomes strong and the seizure resistance is improved. The heating is preferably performed after the dispersion medium has evaporated. The heating temperature is preferably 100 to 200 ° C., which is close to the boiling point of the alkyl substance.
Hot air is more effective.

Further, according to the present invention, when forming a phosphate conversion coating, a blasting process is performed as a base treatment on a screwless metal contact portion on which a phosphate conversion coating is to be formed, and the screwless metal contact portion is formed. The surface roughness of Rmax is 3 to
It is desirable that the thickness be 15 μm. By performing the blasting process, an active new surface appears on the surface, the adhesion of the phosphate chemical conversion treatment film is strengthened, and the peeling resistance of the phosphate chemical conversion treatment film is improved. The blasting process may be performed by a known sand blasting method, shot blasting method, grid blasting method, or the like, and can be performed by a method of spraying a hard material such as sand, shot, grid or cut wire at high speed.

[0048]

(Embodiment 1) A block 10 having the configuration shown in FIG.
Using a friction tester having a ring and a ring 11, a test was conducted in which various lubricating films were formed on the block, and the ring and box simulated the sliding between the pin and the box at the screwless metal contact portion when tightening the screw joint. The test was performed under the conditions shown in Table 1 to evaluate the friction characteristics and the seizure resistance when the block and the ring slide. Both the ring and the block are made of carbon steel, and their chemical compositions are shown in Table 2. The sliding distance per rotation of the ring was equivalent to a pipe having an outer diameter of 127 mm, and a high surface pressure equivalent to that of a real joint was applied to the contact surface between the block and the ring.

[0049]

[Table 1]

[0050]

[Table 2]

The ring had a surface roughness Rmax of 3 μm as it was machine-finished. The block was made to have a surface roughness of 3 μm in Rmax by mechanical grinding, and then a manganese phosphate coating having a surface roughness of 15 μm was formed on the surface by a chemical conversion treatment, and further contained 30% by weight of solid fine particles thereon. A 10 μm thick resin or inorganic polymer compound lubricating film was formed.

The solid fine particles have an average particle diameter of 5 nm.
Cluster diamond, 33 nm Al ₂ O ₃ , 0.
Each powder of 12 μm CaCO ₃ , 0.4 μm SiC, 3 μm graphite, and 5 μm sodium stearate was used alone.

In forming the lubricating coating of the resin, the polyamideimide resin and the solid fine particles were mixed, and a mixture of xylene, toluene and isopropyl alcohol was applied as a dispersion medium. Next, after drying, a heat treatment was performed at 180 ° C. for 30 minutes.

In forming a lubricating film of an inorganic polymer compound, a titanium alkoxide having a methyl alkyl group and the solid fine particles were mixed, and a mixture of xylene, methylene chloride and butyl alcohol was applied as a dispersion medium. Then, it was left in the air for 4 hours.

As a comparative example, a test was conducted under the condition that a compound grease (equivalent to API-Bul5A2) was applied to a block on which a manganese phosphate film having a thickness of 15 μm was formed, and a compound grease was formed only by forming the manganese phosphate film. A test was also performed under the conditions in which No. was applied. Table 3 shows the coefficient of friction measured by the friction tester.

[0056]

[Table 3]

As shown in Table 3, Test No. 1 was conducted with the particle diameter of the solid fine particles being the constitutional range of the present invention. Examples of the present invention Nos. 1 to 5 and 7 to 10 use the test Nos.
The coefficient of friction is the same or smaller than that of Comparative Example 13;
It was found that it had excellent lubricity equal to or better than that of compound grease application. Test No. In Comparative Examples 6, 11, and 12, the particle diameters were out of the range of the composition of the present invention, and the friction coefficients of Test Nos. Thirteen comparative examples were higher and defective. In Comparative Example 14, the coefficient of friction was extremely high, and image sticking occurred when the number of ring rotations was four. Except for Comparative Example 14, the occurrence of image sticking was not observed up to a ring rotation speed of 40 times.

(Example 2) In the same manner as in Example 1, the friction characteristics of the block and the ring and the seizure resistance were examined using a friction tester.

The ring had a surface roughness Rmax of 3 μm while being finished by mechanical grinding. The block is made by mechanical grinding to have a surface roughness of 3 μm in Rmax, and then a manganese phosphate film having a surface roughness of 3 to 40 μm is formed on the surface by a chemical conversion treatment, and a particle diameter of 0.4 μm is further formed thereon. A lubricating film of an inorganic polymer compound having a thickness of 10 μm and containing 30% by weight of SiC powder was formed.

In forming a lubricating film of an inorganic polymer compound, a titanium alkoxide having an alkyl group of methyl and the above-mentioned SiC powder were mixed, and a mixture of xylene, methylene chloride and butyl alcohol was applied as a dispersion medium. Then, it was left in the air for 4 hours.

Table 4 shows the friction coefficient measured by the above friction tester and the number of ring rotations until the occurrence of image sticking.

[0062]

[Table 4]

As shown in Table 4, Test No. In the inventive examples of Nos. 2 to 5, the friction coefficients were the same as those of Test Nos. No burn-in was observed up to a ring rotation speed of 20 times smaller than that of Comparative Example 1. Test No. In Comparative Example 1, the coefficient of friction was large, and seizure occurred after 5 rotations of the ring. Test No. 6
In Comparative Example No., image sticking occurred at the 20th rotation of the ring.

(Example 3) A threaded part of one or both of a pin and a box of a carbon steel screw joint (outer diameter: 7 inches, wall thickness: 0.408 inches) having the chemical composition shown in Table 1 The surface of the metal contact portion without thread was subjected to a surface treatment for forming various phosphate conversion coatings and a lubricating coating of an inorganic polymer compound as shown in Table 5. Hereinafter, the surfaces of the pin and the screw portion and the metal contact portion of the box are referred to as a pin surface and a box surface, respectively.

[0065]

[Table 5]

As shown in Table 5, either one or both of the pin surface and the box surface having a surface roughness of about 3 to 5 μm by a mechanical grinding finish, as shown in Table 5,
A zinc phosphate or manganese phosphate coating having a surface roughness of 5 to 10 μm is formed as a first layer by a chemical conversion treatment, and a titanium alkoxide having an alkyl group of methyl and graphite powder having an average particle size of 3 μm are formed on the upper surface of the coating. Alternatively, 0.12 μm CaCO ₃ powder or 5 nm cluster diamond powder is mixed in a dry state after forming a lubricating film so that the content of solid fine particles is 2 to 65% by weight, and xylene, methylene chloride, and butyl alcohol are mixed. After applying the mixture as a dispersion medium, the mixture was allowed to stand in the air for 4 hours to form a lubricating film as a second layer. Lubricating film thickness is 5-1
The thickness was 5 μm.

Next, using the threaded joint having been subjected to the surface treatment, the tightening and retightening operations were repeated up to 20 times in the manner shown in Table 6 to investigate the occurrence of seizure. That is, as shown in Table 6, the first to tenth, 12
Tighten at room temperature for 15th and 17-20th
On the other hand, the eleventh and sixteenth heat treatments were performed at 400 ° C. for 24 hours after tightening at room temperature.
Thereafter, it was cooled and retightened at room temperature. Table 7 shows the conditions of the tightening speed and the tightening torque.

[0068]

[Table 6]

[0069]

[Table 7]

Table 8 shows the state of occurrence of image sticking: No image sticking: 、, and image sticking: X.

[0071]

[Table 8]

As shown in Table 8, Test No. In Examples 1 to 8 of the present invention, seizure was not observed in 20 times of tightening and retightening shown in Table 6 and was extremely good. Also, the tightening amount and the tightening torque at the time of tightening were appropriate and good. Test No. In Comparative Examples 9 and 10, the graphite content was out of the range of the constituent conditions of the present invention,
Seizure occurred at the 16th and 20th tightening respectively.

(Example 4) A carbon steel threaded joint (outer diameter: 7 inches, wall thickness: 0.408 inches) having the chemical composition shown in Table 1 was applied to one or both of the pin surface and the box surface. Various surface treatments for forming a phosphate conversion coating and a resin lubricating coating shown in FIG. 9 were performed.

[0074]

[Table 9]

As shown in Table 9, any one or both of the surface of the pin and the surface of the box were machine-finished to a surface roughness of about 3 to 5 μm.
A coating of zinc phosphate or manganese phosphate having a surface roughness of 5 to 10 μm is formed as a first layer by a chemical conversion treatment, and a polyamideimide resin and an average particle size of 0.4 are formed on the upper surface of the coating.
The solid fine particles of SiC powder of 0.1 μm or CaCO ₃ powder of 0.12 μm or cluster diamond powder of 5 nm are mixed so that the content of the solid fine particles becomes 4 to 75% by weight in a dry state after the formation of a lubricating film, and xylene is mixed. Then, a mixed solution of toluene and isopropyl alcohol was applied as a dispersion medium, dried, and then subjected to heat treatment at 180 ° C. for 30 minutes to form a lubricating coating of resin as a second layer. The thickness of the lubricating coating was 5 to 15 μm.

Next, using the threaded joint having been subjected to the surface treatment, tightening and retightening operations were repeated up to 20 times in the manner shown in Table 10 to examine the occurrence of seizure.

[0077]

[Table 10]

That is, as shown in Table 10, 1 to 10
The first, the 12th to the 15th and the 17th to the 20th are tightened and retightened at room temperature, while the 11th and the 16th are
The first time, after tightening at room temperature, a heat treatment was performed at 200 ° C. for 24 hours, then cooled and tightened at room temperature.
The conditions of the tightening speed and the tightening torque are the same as in Table 7.

Table 11 shows the state of occurrence of image sticking: No image sticking: 、, and image sticking: X.

[0080]

[Table 11]

As shown in Table 11, Test No. In Examples 1 to 8 of the present invention, seizure was not observed in 20 times of tightening and retightening shown in Table 10 and was extremely good. Also, the tightening amount and the tightening torque at the time of tightening were appropriate and good. Test No. In Comparative Examples 9 and 10, the content of SiC was out of the range of the constitutional conditions of the present invention, and seizure occurred during the eleventh and fourteenth tightening, respectively.

[0082]

According to the present invention, a threaded joint formed with a lubricating film of an inorganic polymer compound containing solid fine particles of the present invention has a small friction coefficient, so that the tightening torque can be reduced.
Seizure resistance during repeated tightening and retightening including a heating step at 00 ° C. is significantly improved. In addition, the threaded joint formed with a lubricating coating of a resin containing solid fine particles of the present invention has a small coefficient of friction, so that the tightening torque can be reduced. Significantly improves seizure resistance. Therefore, the threaded joint formed with the lubricating coating of the inorganic polymer compound is suitable for mining of crude oil under a high temperature environment, and the threaded joint formed with a lubricating coating of a resin is suitable for mining of crude oil under an environment of about 200 ° C.

[Brief description of the drawings]

FIG. 1 is a schematic view schematically showing a configuration of a threaded joint for oil country tubular goods of the present invention.

FIG. 2 is an enlarged sectional view showing an example of a state of forming a lubricating film according to the present invention.

FIG. 3 is a schematic diagram schematically showing a configuration of a friction tester.

[Explanation of symbols]

1: box, 2: pin, 3: screw part, 4: screwless metal contact part, 5: shoulder part, 6: lubricating coating, 7: resin or inorganic polymer compound, 8: solid fine particles, 9: phosphate conversion Treated coating, 10: block, 11: ring.

Continued on the front page (72) Inventor Kunio Goto 4-53-3 Kitahama, Chuo-ku, Osaka-shi F-term in Sumitomo Metal Industries Co., Ltd. 3H013 JA02 4K026 AA21 AA25 BA03 BA05 BA08 BA12 BB04 BB10 EA02 EB05 EB08 4K044 AA02 AB03 BA12 BA17 BA21 BB03 BC01 BC11 CA07 CA16 CA53 CA64

Claims (2)

[Claims] 1. A screw joint comprising a pin and a box each having a threaded portion and a threadless metal contact portion, wherein at least one of the pin and the box has a surface roughness Rmax on the surface of the threadless metal contact portion. 5-20μ
m, and a phosphate chemical conversion coating film having a mean particle size of 0.005 to 3 μm dispersed and mixed at a ratio of 3 to 60% by weight on the surface of the phosphate chemical conversion coating film. A threaded joint for oil country tubular goods characterized by forming a lubricating film of an inorganic polymer compound. 2. A threaded joint comprising a pin and a box each having a threaded portion and a threadless metal contact portion, wherein at least one of the pin and the box has a surface roughness Rmax on the surface of the threadless metal contact portion. 5-20μ
m of a phosphate conversion-treated film, and solid fine particles having an average particle size of 0.005 to 0.4 μm dispersed and mixed at a ratio of 5 to 70% by weight on the surface of the phosphate conversion-treated film. A threaded joint for oil country tubular goods characterized by forming a coating.