JP2002327874A - Screw joint for steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw joint for a steel pipe capable of maintaining seizure resistance, even if fastening/loosening is repeated in a state for generating misalignment, without using liquid lubricant containing heavy metal powder and having excellent seizure resistance and airtightness, in the screw joint for the steel pipe constituted of a pin and a box having each contact surface including a screw part and a metal contact part without a screw. SOLUTION: Solid lubricating film layers of each of two or more layers containing lubricating powder are formed on the contact surface of at least one of the pin and the box. The external layer is made of a film layer of a low coefficient of friction, that is, a film layer in which binding agent is inorganic high polymer or the binding agent is resin and has high contents of lubricating powder, for instance. In the internal layer, one layer or two layers of film layers made of resin and lubricating powder are arranged, and the rate of lubricating powder is reduced toward the internal layer side.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is excellent in seizure resistance and airtightness, which makes it unnecessary to apply compound grease containing heavy metal powder which has been conventionally used for preventing seizure when fastening a threaded joint for oil country tubular goods. To threaded joints for steel pipes.

[0002]

2. Description of the Related Art Oil country tubular goods, which are steel pipes used for oil well drilling, are fastened with threaded steel pipe joints. This threaded joint is composed of a pin with an external thread and a box with an internal thread. As shown schematically in FIG. 1, usually, a male screw 3A is formed on the outer surface of both ends of a steel pipe A to form a pin 1, and a female screw 3B is formed from both sides on the inner surface of a separate sleeve-type joint member B. Let it be 2. As shown in FIG. 1, the steel pipe A is
Usually, it is shipped with the joint member B fastened to one end thereof.

[0003] In a threaded joint for a steel pipe tube, heat in the ground acts in addition to a combined pressure such as an axial tensile force caused by the weight of the steel pipe and the joint and internal and external pressures in the ground. It is required to maintain hermeticity (sealability) without being damaged even in a mild environment. Also, at the time of oil well pipe descent work,
There is a case where the joint once tightened is loosened and then re-tightened to re-tighten. Therefore, the API (American Petroleum Institute) states that even if the tubing joint is tightened (make-up) and loosened (break-out) ten times for the tubing joint and three times for the casing joint, seizure called galling occurs. It is required that airtightness be maintained.

In recent years, from the viewpoint of airtightness, metal-
Special threaded joints capable of metal sealing by direct metal contact have come to be used in general. In this type of threaded joint, both the pin and the box have an unthreaded metal contact in addition to a thread consisting of a male thread or a female thread, both of which are contact surfaces. The screwless metal contact portions of the pin and the box come into contact with each other, and a metal seal portion is formed by metal-metal contact, thereby improving airtightness.

FIG. 2 schematically shows the structure of a threaded joint for steel pipe having such a threadless metal contact portion. Reference numeral 1 denotes a pin, 2 denotes a box, 3 denotes a screw portion, 4 denotes a screwless metal contact portion, and 5 denotes a shoulder portion. Hereinafter, the screwless metal contact portion is simply referred to as a metal contact portion. The thread 3 and the threadless metal contact 4 provided on each of the pin 1 and the box 2 are the contact surfaces of the threaded joint. Seizure resistance is required for this contact surface, especially for a metal contact portion where seizure is more likely to occur.

As shown in FIG. 2, a typical threaded joint of this type has a pin 3 having a thread 3 (ie, a male thread) and an unthreaded metal contact 4 formed on the outer surface of the end of the steel pipe. 1 and a box 2 having a threaded portion 3 (that is, a female threaded portion) and a threadless metal contact portion 4 formed on the inner surface of the threaded joint member.

[0007] In such a threaded joint, a highly lubricating liquid lubricant called compound grease has been used, particularly in order to prevent seizure of a metal contact portion. This grease is applied to the contact surface of at least one of the pin and the box before tightening. However, this grease contains a large amount of harmful heavy metals, and grease that has protruded to the surroundings due to tightening is washed with a cleaning solution.In this operation, the compound grease and its cleaning solution flow out to the ocean and soil, causing environmental damage. Contamination has become a problem.
Further, there is also a problem that grease application and cleaning, which are required every time the tightening is repeated, lowers work efficiency on site.

Accordingly, as threaded joints for steel pipes that do not require the application of compound grease, JP-A-8-103724, JP-A-8-233163, JP-A-8-233164, and JP-A-9-72467.
In each of the publications, a screw in which a solid lubricating coating composed of a resin and a solid lubricant molybdenum disulfide or tungsten disulfide is formed on a screw portion or a metal contact portion without a screw (that is, a contact surface) by surface treatment. A coupling is disclosed.

[0009]

However, in the conventional threaded joint for steel pipe having such a solid lubricating film formed thereon, when a misalignment (misalignment) which cannot be avoided in actual oil well pipe tightening work occurs. There is a problem that the solid lubricating film is apt to peel off, and seizure easily occurs, particularly in the initial stage of tightening and loosening.

FIG. 3 schematically shows the state of misalignment of the oil country tubular goods. The degree of misalignment depends on the size of the drilling rig and the size of the oil country tubular good, but the misalignment angle θ may be up to about 10 °. This misalignment is likely to occur early in the tightening, especially during the first tightening, whereby the pin-box contact surface is subjected to an unusually high shear stress. Cannot withstand this stress,
When the solid lubricating film formed on the contact surface peels off, the seizure resistance of the threaded joint is significantly reduced.

In the case where liquid compound grease is applied to the contact surface of the threaded joint to prevent seizure, since the grease has fluidity, even if the grease is partially removed due to misalignment, it is not Grease can wrap around from around. Therefore, even if misalignment occurs, the seizure resistance does not significantly decrease.
However, since the solid lubricating coating has no fluidity, once the coating is peeled off, a remarkable decrease in seizure resistance cannot be avoided. With conventional solid lubricating coatings, the coating is easy to peel off due to the impact due to misalignment.
Seizure sometimes occurred at the beginning of loosening.

The present invention provides anti-seizure even when repeatedly tightening and loosening a threaded joint that causes misalignment without using a liquid lubricant containing heavy metal powder such as compound grease, which is problematic in terms of environment and work. An object of the present invention is to provide a threaded joint for a steel pipe which does not show a remarkable decrease in the property and has excellent seizure resistance and airtightness.

[0013]

Means for Solving the Problems The present inventor investigated the cause of peculiar seizure in fastening of a threaded joint with misalignment using a conventional threaded joint formed with a solid lubricating film. As a result, (1) the friction of the coating at the time of the first tightening operation is extremely high, that is, the sliding property (conformability) of the coating at the start of contact is poor, and (2) the formed solid lubricating coating and the base material It was presumed that two factors, that is, insufficient adhesion, were involved. That is, the conventional solid lubricating coating has a high friction of the coating, especially at the start of contact, and has insufficient adhesion to the coating.
It is considered that when the compression force is increased, the film is easily peeled off.

The present inventor has noted that the above (1) is the property of the coating surface on the side opposite to the substrate, and the above (2) is the property of the coating on the interface side in contact with the substrate. did. The structure of the solid lubricating film is not made to be a uniform structure in the thickness direction as in the conventional case, but is provided with low friction on the surface side and high adhesion on the interface side with the base material. As described above, it has been found that the object of the present invention can be solved by adopting a structure having a tilt function in the thickness direction.

The present invention, in its broadest sense, is a threaded joint for a steel pipe comprising a pin and a box each having a contact surface including a threaded portion and a threadless metal contact portion,
A threaded joint for steel pipes, wherein two or more solid lubricating film layers each containing a lubricating powder are formed on a contact surface of at least one member of a pin and a box.

The present invention includes the following various embodiments. (1) A solid lubricating film layer containing no lubricating powder is formed as a lower layer of two or more solid lubricating film layers containing the lubricating powder.

(2) The two or more solid lubricating film layers are formed only on the contact surface between the pin and one member of the box, and the contact surface between the pin and the other member of the box contains a lubricating powder. , Or a single solid lubricating layer is formed.

(3) The two or more solid lubricating film layers are formed on the contact surface between the pin and one member of the box,
The contact surface of the pin and the other member of the box has a surface roughness R
max is 10 μm or less.

(4) The two or more solid lubricating film layers and / or one solid lubricating film layer are formed on a base surface having a surface roughness Rmax of 5 to 40 μm. (5) The two or more solid lubricating film layers are each composed of two solid lubricating film layers of an inner layer and an outer layer made of a resin and a lubricating powder, and the mass of the lubricating powder / resin in the two layers. The ratio (M) satisfies the following relationship: 1.0 ≦ M of outer layer ≦ 9.0 0.5 ≦ M of inner layer ≦ 4.5 M of inner layer <M of outer layer.

M: Mass ratio of lubricating powder / resin in coating layer (6) The two or more solid lubricating coating layers are composed of an inner layer composed of resin and lubricating powder, and an inorganic polymer and lubricating powder. It is composed of two outer layers.

(7) Each of the two or more solid lubricating film layers is composed of three solid lubricating film layers of an inner layer, an intermediate layer, and an outer layer, all of which are made of resin and lubricating powder. 1.0 ≦ M of the outer layer ≦ 9.0 0.5 ≦ M of the intermediate layer ≦ 4.5 M of the inner layer <M of the intermediate layer <M of the outer layer, wherein the mass ratio (M) of the conductive powder / resin satisfies the following relationship.

M: Mass ratio of lubricating powder / resin in the coating layer (8) The two or more solid lubricating coating layers are each composed of an inner layer and an intermediate layer composed of a resin and a lubricating powder, an inorganic polymer and It is composed of three outer layers made of lubricating powder.

(9) The lubricating powder comprises one or more materials selected from molybdenum disulfide, tungsten disulfide, graphite, boron nitride, and polytetrafluoroethylene (PTFE).

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A threaded joint for steel pipes to which the present invention is applied is composed of a pin 1 and a box 2, as shown in FIG. And a contact surface including the contact portion 4. FIG. 1 shows an example in which the pipe end of the steel pipe is a pin and the joint member is a box. However, the joint member is not used, and one end of the steel pipe is a pin and the other end is a box. It is also possible to use a box at both ends of the steel pipe.

The contact surface between the pin and the box, especially the metal contact portion where seizure is more likely to occur, requires seizure resistance. Conventionally, compound grease containing heavy metal powder has been applied to the contact surface for this purpose. As described above, application of compound grease is effective for misalignment, but has many problems in terms of environment and work efficiency.

It has been proposed to form a solid lubricating coating composed of resin and lubricating powder on the contact surface of the threaded joint in order to eliminate the need for applying compound grease. In the fastening of a threaded joint with alignment, at the initial stage of tightening, the coating cannot easily withstand friction and tends to peel off, and the seizure resistance tends to decrease early.

The solid lubricating film provided on the contact surface of the threaded joint receives a high sliding surface pressure when tightening or loosening the threaded joint, and generates wear powder including lubricating powder. The wear powder containing the lubricating powder spreads over the entire contact surface of the threaded joint,
It is presumed that it contributes to the prevention of metal-to-metal contact and the reduction of friction at the contact interface, and exhibits an anti-seizure effect.

The conventional solid lubricating coating is designed to harden the coating by heat treatment so as to enhance wear resistance and prevent seizure due to wear of the coating when tightening and loosening are repeated. This hardening of the coating is effective in preventing seizure when fastening a threaded joint with no or little misalignment. However, when fastening threaded joints with misalignment that requires frictional relaxation immediately at the start of contact, the supply of lubricating powder to the contact surface in the initial stage of contact is insufficient, increasing the coefficient of friction and further increasing the adhesion of the coating. In addition to the low level, the solid lubricating coating is peeled off, resulting in seizure.

In the threaded joint according to the present invention, a solid lubricating film having a laminated structure composed of two or more solid lubricating film layers having different functions is formed on at least one contact surface of the pin and the box.

Each solid lubricating film layer may be a film layer composed of a lubricating powder and a binder resin or an inorganic polymer, or a film layer composed of a resin alone. However, in the present invention, there are two or more solid lubricating coating layers containing a lubricating powder. The outer solid lubricating film layer that forms the surface of the solid lubricating film must contain lubricating powder in order to ensure good lubricity. This is because a lubricating powder is still necessary for securing the same. Thereby, even if the outer layer is consumed due to misalignment, seizure resistance can be secured by the inner layer when the tightening and loosening are repeated thereafter. Therefore, when a coating layer made of resin alone is provided, the solid lubricating coating layer has a multilayer structure of three or more layers.

Each solid lubricating film layer constituting the solid lubricating film having a laminated structure has different functions by changing the constitution such as the kind of lubricating powder and binder used and / or the amount of lubricating powder blended. Can be provided. For example, as the blending amount of the lubricating powder increases, the coefficient of friction of the coating layer decreases, and performance suitable for the surface side is exhibited. Tends to be unsuitable. Regarding the type of binder, if the conditions (type and blending amount) of the lubricating powder are the same and the binder is an inorganic polymer, the coating layer is relatively soft (low hardness), A larger amount of lubricating powder can be supplied to the contact surface than in the case of resin, which is very effective in reducing the friction coefficient.

As described above, in the solid lubricating film formed on the contact surface of the threaded joint, in order to prevent the peeling of the film, which is likely to occur in the initial stage of the tightening accompanied by misalignment, the adhesion on the interface side with the base material is required. Advantageously, the coefficient of friction is high on the opposite surface side. Therefore, the configuration of each coating layer constituting the solid lubricating coating can be selected so as to exhibit desirable characteristics in the thickness direction.

For example, a solid lubricating film layer made of a resin alone containing no lubricating powder can be used as the lowermost layer of the solid lubricating film because it has good adhesion to the substrate. In this case, in the present invention, two or more solid lubricating film layers containing a lubricating powder are further formed thereon. A solid lubricating film layer containing no lubricating powder is a resin capable of forming a film having excellent adhesion to a substrate, for example, a resin used as a primer in the coating of steel materials (e.g.,
Epoxy resin, acrylic resin, urethane resin, etc.) are suitable.

When the solid lubricating film layer containing the lubricating powder is 2
If it is a layer, the inner layer in contact with the substrate is a coating layer that has high adhesion and can maintain seizure resistance, and the outer layer is a coating layer that has excellent slipperiness at the initial stage of tightening and loosening, that is, the coefficient of friction is higher than that of the inner layer It is advantageous to have a coating layer with a low.

The misalignment of the threaded joint is determined by tightening
It is easy to occur in the initial stage of loosening, especially in the first time, and hardly occurs in the second and subsequent times. Further, even if misalignment occurs after the second time, seizure due to the misalignment is unlikely to occur because the conformability between the contact surfaces (the first slip property) has already been secured. Therefore, if the outer layer provided as a countermeasure against misalignment is effective for reducing friction,
It may be a solid lubricating film layer that is consumed at the second time,
The earlier the outer layer is consumed, the more the effect of improving the seizure resistance by the inner layer is not hindered.

In the case of a two-layer solid lubricating coating, when the binder is a resin, particularly the same resin, in both layers, the content of the lubricating powder is increased in the outer layer than in the inner layer, so that the multi-layer is preferable for achieving the object of the present invention. It becomes a film structure. That is, the outer layer containing a large amount of the lubricating powder has a high effect of alleviating the high friction phenomenon that occurs when the pin and the box are first tightened, and improving the initial slipperiness (conformability). In addition, even when fastening is performed with misalignment (center misalignment), slippage of the contact surface can be promoted, and seizure can be suppressed.

In this case, it is preferable that the mass ratio (M) of the lubricating powder / resin in the two layers satisfies the following relationship. 1.0 ≦ M of the outer layer ≦ 9.0 0.5 ≦ M of the inner layer ≦ 4.5 M of the inner layer <MM of the outer layer M: mass ratio of lubricating powder / resin in the coating layer.

If the M of the outer layer is less than 1.0, the slipperiness of the surface of the solid lubricating coating is insufficient, and seizure may not be prevented at the time of initial tightening and loosening with misalignment. On the other hand, when M of the outer layer exceeds 9.0, the film strength and the adhesion to the inner layer are reduced, and sufficient seizure resistance may not be obtained upon repeated tightening and loosening.

When the M of the inner layer is less than 0.5, the seizure resistance of the film is insufficient, and seizure may not be prevented during repeated tightening and loosening after the outer layer is consumed. On the other hand, if the M of the inner layer exceeds 4.5, the adhesion to the substrate may be reduced and sufficient seizure resistance may not be obtained, depending on the underlying treatment.

By making the value of M larger in the outer layer than in the inner layer and making the outer layer contain a larger amount of lubricating powder, a large amount of lubricating powder is supplied due to abrasion of the outer layer during misalignment, and the film has low friction. At the same time, sufficient adhesion is secured in the inner layer on the interface side, and peeling during misalignment is prevented. Further, even if the outer layer is consumed, the inner layer maintains high seizure resistance.

When an inorganic polymer is used as the binder, the film in which the lubricating powder is bonded with the inorganic polymer has lower abrasion resistance than the film in which the resin is bonded. Slipperiness (conformability) is improved and high friction reduction effect is exhibited. Therefore, it is preferable to use a solid lubricating film layer composed of an inorganic polymer and a lubricating powder for the outer layer, and to combine an inner layer with a solid lubricating film layer composed of a resin having excellent seizure resistance and a lubricating powder.

In the case of this combination, the amount of the lubricating powder in the inner layer and the outer layer is not particularly limited, and the ratio of the lubricating powder is
The inner layer may be more than the outer layer. It is preferable that the value of M of the solid lubricating film layer composed of the resin and the lubricating powder of the inner layer be within the preferable range defined above for the inner layer. The ratio of the lubricating powder in the outer layer composed of the inorganic polymer and the lubricating powder is represented by the mass ratio of lubricating powder / inorganic polymer,
It is preferred to be in the range of about 0.5 to 5.0.

The solid lubricating film composed of the inorganic polymer and the lubricating powder in the outer layer may be consumed relatively early, for example, by the first tightening, particularly when it is subjected to misalignment.
Even if the outer layer remains after the second time, there is no problem in seizure resistance thereafter. Further, even if the outer layer is consumed, there is a solid abrasion-resistant solid lubricating film layer composed of the inner layer resin and the lubricating powder, which is gradually worn to maintain the seizure resistance.

It is also possible for both the outer layer and the inner layer to be made of an inorganic polymer. In that case, it is preferable that the ratio of the lubricating powder be larger in the outer layer than in the inner layer, as in the case where the binder is a resin. Further, in order to harden the inner coating layer, the inner layer may be heated to a high temperature after application to partially crystallize the inorganic polymer in the inner layer.

When the solid lubricating film has a three-layer structure, as described above, the lowermost layer may be a solid lubricating film layer made of a resin alone containing no lubricating powder. In that case, the above-mentioned inner layer and outer layer containing a lubricating powder are formed thereon to form a three-layer structure.

In another solid lubricating coating having a three-layer structure, all three solid lubricating coating layers contain a lubricating powder. In that case, if the binder is resin in all three layers, the inner layer, the intermediate layer,
It is preferable that the value of M (mass ratio of lubricating powder / resin) of the three layers consisting of the outer layer satisfy the following.

1.0 ≦ M of the outer layer ≦ 9.0 0.5 ≦ M of the intermediate layer ≦ 4.5 M of the inner layer <M of the intermediate layer <M of the outer layer.

When M of the outer layer is less than 1.0, the initial slip property
(Fitness) may be insufficient, and seizure may not be prevented during initial tightening and loosening with misalignment.
If it exceeds 9.0, the film strength and adhesion to the intermediate layer decrease,
During repeated tightening and loosening, sufficient seizure resistance may not be obtained. If the M of the intermediate layer is less than 0.5, seizure resistance is insufficient, and seizure cannot be prevented during repeated tightening and loosening after the outer layer has been consumed.
If it exceeds, the film strength enough to withstand repeated tightening and loosening may not be obtained.

The value of M of the inner layer in the case of three layers is not specified above, but is preferably 1.5 or less. If the M of the inner layer is larger than this, the adhesion to the base material may be reduced and sufficient seizure resistance may not be obtained depending on the underlying treatment.

The value of M is determined by increasing the gradient distribution in the order of inner layer <intermediate layer <outer layer, thereby reducing the friction of the outer layer, preventing seizure during repeated tightening and loosening of the intermediate layer, and improving the inner layer base. Adhesion with the material can be efficiently achieved.

When an inorganic polymer is used as the binder, the solid lubricating film layer composed of the inorganic polymer and the lubricating powder is used for the outer layer, and the intermediate layer and the inner layer are both made of resin for the reasons described above. And a lubricating powder. In that case, the M of the middle layer and the inner layer
Is preferably larger than that of the inner layer for the same reason as described above. Further, it is also preferable that the value of M of the intermediate layer and the inner layer be in the same range as described above. Thereby, when repeatedly tightening and loosening after the outer layer exhibiting a high friction reducing effect has been consumed, the intermediate layer exhibits high seizure resistance while gradually abrading. The inner layer has the effect of increasing the adhesion between the intermediate layer and the substrate.

The solid lubricating film in the threaded joint according to the present invention may have a multilayer structure of four or more layers. For example, it is also possible to form a solid lubricating film layer of a resin alone containing no lubricating powder under the three-layered solid lubricating film containing a lubricating powder described above. However, considering costs, two or three layers are usually sufficient.

The solid lubricating film layer containing the lubricating powder, which is formed on the contact surface of the threaded joint according to the present invention, is formed by uniformly dispersing the lubricating powder in a binder solution (which may be a dispersion). The coating liquid (powder dispersion liquid) prepared by adjusting the viscosity accordingly can be applied to the contact surface of at least one member of the pin and the box of the threaded joint, and dried to form a coating film. The method for applying the coating liquid may be a known appropriate method such as brushing, dipping, or air spraying.

As the lubricating powder, molybdenum disulfide,
It is preferable to use one or more powders selected from tungsten disulfide, graphite, boron nitride, and PTFE (polytetrafluoroethylene).

The average particle size of the lubricating powder is not particularly limited, but is generally preferably in the range of 0.5 to 60 μm. 0.5 μm
If it is less than 1, the powders tend to agglomerate with each other, making it difficult to uniformly disperse the powder in each coating layer, and the performance may be locally insufficient. On the other hand, if it exceeds 60 μm, not only the strength of the film is reduced, but also the adhesion to the base is reduced, so that the occurrence of seizure may not be suppressed in some cases.

As the binder, either an organic resin or an inorganic polymer (sometimes called an inorganic resin) can be used. As the organic resin, those having heat resistance, appropriate hardness and wear resistance are preferable. Examples of such resins include epoxy resins, polyimide resins, polycarbodiimide resins, polyethersulfone, polyetheretherketone resins, phenol resins, furan resins, urea (urea) resins, thermosetting resins such as acrylic resins, and the like. Examples thereof include thermoplastic resins such as polyamide imide resin, polyethylene resin, silicone resin, and polystyrene resin.

As the solvent for the organic resin, various low-boiling solvents such as hydrocarbons (eg, toluene) and alcohols (eg, isopropyl alcohol) can be used alone or in combination.

A predetermined amount of lubricating powder and PT
FE powder is added and uniformly dispersed to prepare a coating solution.
From the viewpoint of the adhesion and abrasion resistance of the coating, it is preferable that the coating liquid is applied to the contact surface of the threaded joint and then heated to harden the coating. The heating temperature is preferably 120 ° C. or more, more preferably 150 to 380 ° C.
It may be set depending on the size of the threaded joint for steel pipes, but is preferably 30 minutes or more, more preferably 30 to 60 minutes.

The inorganic polymer used as a binder in the present invention includes Ti-O, Si-O, Zr-O, Mn-O, Ce-O, B
It is a film-forming material such as aO having a structure in which metal-oxygen bonds are three-dimensionally crosslinked, and is formed by a film forming method called a sol-gel method. Such an inorganic polymer can be formed by hydrolysis and condensation of a metal alkoxide. As the metal alkoxide, a compound in which the alkoxy group is a lower alkoxy group such as methoxy, ethoxy, isopropoxy, propoxy, isobutoxy, butoxy and tert-butoxy can be used. Preferred metal alkoxides are titanium or silicon alkoxides, with titanium alkoxides being particularly preferred. Among them, titanium isopropoxide is preferable because of its excellent film-forming properties. In addition to metal alkoxides, metal chlorides such as titanium tetrachloride and metal carboxylates can also be used.

The metal alkoxide forming the inorganic polymer may be a compound in which part of an alkoxy group is substituted with an alkyl group which may have a functional group, such as a silane coupling agent. .

When the binder is an inorganic polymer, examples of the solvent include polar solvents such as alcohols (eg, ethyl alcohol, isopropyl alcohol, butyl alcohol) and ketones, and various organic solvents such as hydrocarbons and halogenated hydrocarbons. Can be used. In order to promote film formation, the metal alkoxide in the solution may be partially hydrolyzed before coating. In order to promote hydrolysis after coating, a small amount of water and / or an acid for a hydrolysis catalyst may be added to the metal alkoxide solution.

A coating liquid is formed by uniformly dispersing a lubricating powder and a PTFE powder in a solution of such a metal alkoxide or another inorganic polymer-forming material, and applied to the contact surface of a pin and / or a box. Dry the coating. Humidification treatment may be performed after application in order to promote film formation by hydrolysis after application. This can be carried out by leaving it in the air for a predetermined time, but it is more preferable to be in the air having a humidity of 70% or more. Preferably, heating is performed after the humidification treatment. The heating promotes hydrolysis and condensation of the hydrolyzate, and discharge of alcohol which is a by-product of the hydrolysis. The film can be formed in a short time, the adhesion of the formed film becomes strong, and the seizure resistance is improved. This heating is preferably performed after the solvent has evaporated. The heating temperature is preferably 100 to 200 ° C., which is close to the boiling point of the by-produced alcohol, and it is more effective to apply hot air.

Each solid lubricating film layer has a thickness of 5 μm or more,
It is desirable that the thickness be not more than μm. The lubricating powder contained in each solid lubricating film layer spreads over the entire contact surface as abrasion powder under high sliding surface pressure, and exhibits excellent seizure resistance. However, if the film layer thickness is less than 5 μm, lubrication will occur. Content of the conductive powder is small, and the seizure resistance may be insufficient. On the other hand, when the thickness of each coating layer is more than 50 μm, the tightening amount is insufficient, the airtightness is reduced, or when the surface pressure is increased to secure the airtightness, seizure is likely to occur, The solid lubricating coating may be easily peeled off.

A coating layer exhibiting seizure resistance mainly at the time of repeated tightening and loosening, that is, an inner layer in the case of a two-layer coating,
Alternatively, the thickness of the solid lubricating coating layer serving as an intermediate layer in the case of a three-layer coating is preferably in the range of 10 to 40 μm. On the other hand, the thickness of the solid lubricating film layer, which is the outer layer of two or three layers, is set to 5 to 10 μm from the viewpoint of securing the slipperiness at the time of the initial tightening / loosening and promptly consuming the film.
m is more preferable.

Various additives such as a rust preventive may be added to each solid lubricating film layer as long as the seizure resistance is not impaired. For example, one or more powders of zinc powder, chromium pigment, silica, and alumina can be added. A colorant may be contained in the outer layer to color the formed solid lubricating film. The coating liquid may appropriately contain one or more additives such as a dispersant, an antifoaming agent, and a thickener.

In order to ensure the adhesion of the solid lubricating film, the contact surface of at least one member of the pin and the box forming the multilayer solid lubricating film according to the present invention has a surface roughness Rmax before forming the film. Steel surface roughness after cutting
It is desirable that the surface is previously roughened so as to have a range of 5 to 40 μm which is larger than (3 to 5 μm). When the surface roughness (Rmax) of the contact surface on which the solid lubricating film is formed is smaller than 5 μm, the adhesion of the solid lubricating film tends to decrease. On the other hand, when the surface roughness exceeds 40 μm, the friction increases, the wear of the solid lubricating film is accelerated, and it may not be able to withstand repeated tightening and loosening.

The surface of the steel itself is roughened by, for example, a method of projecting a sand or a grid or a method of roughening the skin by dipping in a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid, or hydrofluoric acid. In addition to the method, a method is also possible in which a base treatment layer that is rougher than the steel surface is formed and the coated surface is roughened.

Examples of such an undercoating process include a method of forming a chemical conversion coating film of phosphate, oxalate, borate or the like (the roughness of the crystal surface increases with the growth of the generated crystal),
A method of electroplating a metal such as copper plating or iron plating (the surface is slightly roughened because the projections are preferentially plated, and the iron core is coated with zinc or a zinc-iron alloy, etc.) The particles are projected using centrifugal force or air pressure to form a coating of zinc or a zinc-iron alloy, an impact plating method, a nitrocarburizing method for forming a nitride layer (for example, tuftride), and solid fine particles dispersed in a metal. And a composite metal coating method for forming a porous film.

From the viewpoint of the adhesion of the solid lubricating coating, a porous coating, particularly a phosphate conversion treatment (manganese phosphate, zinc phosphate, iron manganese phosphate, zinc calcium phosphate)
Also, a coating of zinc or a zinc-iron alloy by impact plating is preferable. From the viewpoint of adhesion, a manganese phosphate coating is more preferable, and from the viewpoint of rust prevention, a coating of zinc or a zinc-iron alloy is more preferable.

The phosphate conversion coating and the zinc or zinc-iron alloy coating formed by impact plating are:
Since both are porous films, forming a solid lubricating film thereon increases the adhesion of the solid lubricating film. As a result, even if tightening and loosening are repeated, the solid lubricating coating does not peel off, metal-to-metal contact is effectively prevented, and seizure resistance, airtightness, and rust resistance are further improved.

Even if the undercoat layer is porous, by forming a solid lubricating coating thereon on the basis of which the pores of the underlying porous coating are closed, the rust prevention and the airtightness are reduced. Does not occur. In addition, when the porous coating layer is a zinc or zinc-iron alloy coating formed by impact plating, zinc is a metal lower than iron, so it is preferentially ionized over iron to prevent corrosion of iron. It exhibits anticorrosion ability and can achieve even better rust prevention.

The porous zinc or zinc-iron alloy layer can be formed by a dry impact plating method. As the impact plating method, there are a mechanical plating method in which particles collide with an object to be plated in a rotary barrel, and a projection plating method in which particles collide with the object using a blast device.

In the case of a threaded joint, only the contact surface needs to be plated, so that projection plating, which allows local plating, is suitable. Projection (blasting) devices used for projection plating include a high-pressure fluid projection device that sprays particles using a high-pressure fluid such as compressed air, and a mechanical projection device that uses a rotating wing such as an impeller. May be used.

The particles used for impact plating such as projection plating are metal particles having zinc or a zinc-iron alloy on at least the surface. Particles composed entirely of zinc or a zinc-iron alloy may be used, but preferred are the projection materials disclosed in JP-B-59-9312. This projection material
Iron or iron alloy as the core, the surface of which
It consists of particles coated with a zinc or zinc-iron alloy layer via an iron alloy layer.

Such particles can be obtained, for example, by coating a core iron or iron alloy powder with zinc or a zinc alloy (eg, Zn—Fe—Al) by electroless and / or electrolytic plating.
It can be manufactured by a method of forming an iron-zinc alloy layer at a plating interface by heat treatment, or a mechanical alloying method. As a commercially available product of such particles, there is Z Iron manufactured by Dowa Iron Powder Co., Ltd., which can also be used. The content of zinc or zinc alloy in the particles is 20 ~
It is preferably in the range of 60% by weight, and the particle size of the particles is 0.1%.
A range of 2 to 1.5 μm is preferred.

When particles around the iron-based core coated with zinc or a zinc alloy are projected onto a substrate, only the zinc or zinc alloy, which is a coating layer of the particles, adheres to the substrate, and the zinc or zinc alloy coating is applied to the substrate. Formed on top. This projection plating can form a plating film with good adhesion on the steel surface regardless of the material of the steel. Therefore, on the contact surfaces of threaded joints of various materials, from carbon steel to high alloy steel,
A porous zinc or zinc alloy layer having excellent adhesion can be formed.

In the case of forming the above-mentioned various undercoating layers, the thickness thereof is not particularly limited, but is preferably 5 to 40 μm from the viewpoint of rust prevention and adhesion. If it is less than 5 μm, sufficient rust prevention may not be ensured. Meanwhile, 40
If it exceeds μm, the adhesion to the solid lubricating coating may decrease.

The method for forming a multilayer solid lubricating coating according to the present invention is not particularly limited. Two or more solid lubricating film layers may be formed in order using coating liquids having different compositions, each containing a binder and a lubricating powder, prepared for each layer.
As the innermost layer, a solid lubricating film made of a resin alone may be formed from a resin liquid containing no lubricating powder. The contact surface of the threaded joint on which the coating is formed is preferably subjected to one or more types of undercoat treatment as described above to ensure adhesion.

When the binder in all the layers is a resin, the threaded joint of the substrate is preferably preheated to a temperature of 200 ° C. or less before coating. Thereafter, a coating liquid for forming each solid lubricating film layer is sequentially applied. Before the previous coating film is completely dried, it is desirable to apply the next coating solution so that the layers are welded to each other. Optionally, the substrate may be reheated before the next application. After the final application, it is desirable to perform a heat treatment to harden the entire coating.

When the binder of the outer layer is an inorganic polymer, after forming the inner layer or the inner layer and the intermediate layer in which the binder is a resin as described above, before or after the heat treatment for hardening. The outer layer can be formed by applying a coating solution containing an inorganic polymer as a binder, humidifying treatment, and heating treatment. The last heat treatment may also serve as a heat treatment for hardening the inner layer and the intermediate layer.

When two or more solid lubricating coating layers are formed of a resin as a binder, if the resin type of the binder is the same for each layer, high adhesion at the interface between the coating layers can be reliably obtained. . However, if the resin type is appropriately selected, it is possible to obtain high adhesion at the interface of the coating layer using a different resin type as a binder.

Even if the multi-layer solid lubricating film according to the present invention is formed only on the contact surface between the pin and one of the members of the box, the object of the present invention can be sufficiently achieved. preferable. In that case, it is easier to form the solid lubricating coating on the contact surface of the box (ie, the short joint member).

The contact surface of the other member on which the solid lubricating film is not formed (the pin if a solid lubricating film is formed on the box) may be left uncoated. In particular, as shown in FIG.
If the pin and the box are temporarily tightened at the time of assembly, even if the contact surface of the other member, for example, the pin is bare (as it is cut), it will adhere to the coating formed on the contact surface of the box at the time of assembly. Rust on the surface can also be prevented.

However, at the time of assembly, the box is attached only to the pin at one end of the steel pipe, and the pin at the other end is exposed. Therefore, a coating can be formed by applying an appropriate surface treatment to the exposed pins, in particular, in order to impart rust resistance, or rust resistance and lubricity. Of course, even if the other contact surface is not exposed,
It is also possible to form an appropriate coating on this surface. The exposed contact surface may be oiled in place of the surface treatment to impart rust resistance.

When a solid lubricating film is formed only on the contact surface of one member of the pin and the box, it is desirable that the contact surface of the other member has a surface roughness Rmax of 10 μm or less. If the surface roughness of the other member exceeds 10 μm, the coefficient of friction with the solid lubricating coating increases, and the wear of the solid lubricating coating increases at an accelerating rate with the increase in roughness, and the solid is repeatedly tightened and loosened. In some cases, the lubricating coating is worn out early and seizure resistance, rust prevention, and airtightness cannot be maintained. When the solid lubricating film according to the present invention is formed on the contact surfaces of both the pin and the box, it is preferable that the surface roughness of the solid lubricating film of both members (the roughness after forming the film) is 10 μm or less.

On the contact surface of the other member, a single-layered solid lubricating film of the prior art, that is, a single-layered solid lubricating film containing or not containing a lubricating powder may be formed. In this case, before forming this solid lubricating coating, one or more selected from the above-mentioned various types of undercoating treatments are performed, and if the roughness of the undercoating surface is 5 to 40 μm in Rmax, the Adhesion and rust prevention are improved. The surface roughness after the formation of the solid lubricating film is preferably not more than 10 μm in Rmax, as described immediately above.

The threaded joint for steel pipes according to the present invention can be tightened without applying compound grease, but if desired, oil may be applied to the solid lubricating film or the contact surface of the mating member. In that case, the oil to be applied is not particularly limited, and any of mineral oil, synthetic ester oil, animal and vegetable oil, and the like can be used. The oil, antirust additives, such as extreme pressure additives, may be added to conventional various additives in lubricating oils. When these additives are liquid, they can be used alone as an oil and applied.

As the rust preventive additives, basic metal sulfonates, basic metal phenates, basic metal carboxylate and the like are used. Extreme pressure additives include sulfur,
Known compounds such as phosphorus-based, chlorine-based, and organic metal salts can be used. Other, antioxidants, pour point depressants, it can be added to the oil well as viscosity index improvers.

[0089]

The present invention will be described in more detail with reference to the following examples. Hereinafter, both surfaces of the screw portion and the metal contact portion of the pin are referred to as a pin surface, and both surfaces of the screw portion and the metal contact portion of the box are referred to as a box surface.

Table 1 shows carbon steel A, Cr-Mo steel B, and 13% Cr
Steel C or high alloy steel D (D is the most easily seized,
The surface treatments shown in Tables 2 and 3 were applied to the pin surface and box surface of a threaded joint (outer diameter: 7 inches, wall thickness: 0.408 inches) consisting of C, B, and A, respectively, in which seizure is less likely to occur. Treatment and formation of a solid lubricating film). The details of the processing are also described in each embodiment and comparative example.

Tables 2 and 3 show the content and surface roughness of the undercoating treatment, the composition of each solid lubricating film layer (hereinafter simply referred to as a film layer) of the solid lubricating film, ie, the type of the binder and the powder in the film. , The lubricating powder / binder mass ratio (M) and the thickness of the coating layer (t). Note that the multilayer solid lubricating film layers are referred to as a first layer, a second layer, and a third layer from the side closer to the base material.

The average particle size of the powders used was as follows: Molybdenum disulfide powder (MoS ₂ ): 15 μm Tungsten disulfide powder (WS ₂ ): 4 μm Graphite powder: 1 μm Boron nitride powder (BN): 2 μm PTFE powder: 0.8 μm.

Using the threaded joint that has been subjected to the surface treatment as described above, a misalignment (θ = 6 °) is provided each time, and tightening and loosening are performed up to 10 times at room temperature to check the occurrence of seizure. investigated. At this time, the tightening speed was 10 rpm, and the tightening torque was 10340 ft · lbs. Table 4 shows the state of seizure occurrence.

[0094]

[Table 1]

[0095]

[Table 2]

[0096]

[Table 3]

[0097]

[Table 4]

[0098]

Example 1 A carbon steel threaded joint having a composition A shown in Table 1 was subjected to the following surface treatment. The surface of the box is sprayed with # 80 sand and the surface roughness is adjusted to 15 μm. After preheating the box to 130 ° C in an atmosphere furnace, the polyamideimide containing molybdenum disulfide as a lubricating powder is placed on the box. A 30 μm-thick first (inner) film layer made of resin was formed. Further, when the first layer is in a semi-molten state before being completely dried and formed into a film, the second layer having a thickness of 10 μm and made of a polyamideimide resin containing molybdenum disulfide as a lubricating powder on the first layer ( Outer layer) was formed.
The first layer is a coating layer having a mass ratio of lubricating powder 4 to resin 1 and the second layer is a coating layer having a lubricating powder to resin 1 having a mass ratio of 5.7. After the formation of the first and second layers, a heat treatment was performed at 260 ° C. for 30 minutes to harden the film.

The pin surface is machine-finished (surface roughness 3
μm) only. As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, seizure did not occur, airtightness was maintained, and the results were extremely good.

[0100]

Example 2 A threaded joint made of carbon steel having a composition A shown in Table 1 was subjected to the following surface treatment. After the box surface is finished by mechanical grinding (surface roughness 4 μm), a 15 μm-thick manganese phosphate conversion coating (surface roughness 20 μm) is formed on the surface, and the box is preheated to 130 ° C. in an atmosphere furnace. A first layer (inner layer) having a thickness of 28 μm and made of a polyamideimide resin containing molybdenum disulfide as a lubricating powder was formed thereon. Further, when the first layer is in a semi-molten state before being completely dried and formed into a film, the second layer having a thickness of 10 μm and comprising a polyamideimide resin containing tungsten disulfide as a lubricating powder is formed on the first layer ( Outer layer) was formed. The first layer is a film layer having a mass ratio of lubricating powder 2.3 to resin 1 and the second layer is a film layer having a lubricating powder ratio of 4.0 to resin 1. After the formation of the first and second layers, a heat treatment was performed at 260 ° C. for 30 minutes to harden the film.

The pin surface is finished by mechanical grinding (surface roughness 3μ).
m) only. As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, seizure did not occur, airtightness was maintained, and the results were extremely good.

[0102]

Example 3 The following surface treatment was applied to a threaded joint made of a Cr-Mo steel having a composition B shown in Table 1. After the box surface is finished by mechanical grinding (surface roughness 4 μm), a 15 μm-thick manganese phosphate conversion coating (surface roughness 20 μm) is formed on the surface, and the box is preheated to 130 ° C. in an atmosphere furnace. Then, a 35 μm-thick first layer (inner layer) of a polyamideimide resin containing boron nitride as a lubricating powder is formed thereon, and a heat treatment is performed at 230 ° C. for 30 minutes. 1
The layer was hardened. Further, on the first layer, a 10 μm-thick second layer (outer layer) made of an inorganic polymer having a skeleton of Ti—O containing molybdenum disulfide as a lubricating powder was formed. At the time of forming the second layer, it was left in the air for 3 hours and then blown with hot air at 150 ° C. for 10 minutes. The first layer is a coating layer having a mass ratio of the lubricating powder 1 to the resin 1,
The layer was a coating layer having a mass ratio of lubricating powder 1.5 to inorganic polymer 1.

The pin surface is finished by mechanical grinding (surface roughness 3 μm).
After m), a 20-μm-thick zinc phosphate chemical conversion coating (surface roughness 15 μm) was formed on the surface. As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, seizure did not occur, airtightness was maintained, and the results were extremely good.

[0104]

Example 4 A threaded joint made of 13% Cr steel having a composition C shown in Table 1 was subjected to the following surface treatment. The box surface is finished by mechanical grinding (surface roughness 4 μm), and then a 7 μm thick zinc-iron alloy layer (surface roughness 18 μm) is formed by dry impact plating, and the box is preheated to 60 ° C. in an atmosphere furnace. Then, a 28 μm thick first layer (inner layer) of an epoxy resin was formed thereon. Furthermore, when the first layer is in a semi-molten state before being completely dried and formed into a film, the second layer having a thickness of 25 μm and made of an epoxy resin containing molybdenum disulfide as a lubricating powder is formed on the first layer. An intermediate layer) was formed. After the formation of the first and second layers, a heat treatment was performed at 260 ° C. for 30 minutes to harden the film. Next, on the second layer, a lubricating powder composed of an inorganic polymer having a skeleton of Ti—O containing molybdenum disulfide and graphite, having a thickness of 10 μm.
A third (outer layer) coating layer having a thickness of μm was formed to form a three-layer solid lubricating coating. At the time of forming the third layer, hot air of 150 ° C. was blown for 10 minutes after standing in the air for 3 hours.

The first layer is a resin only and does not contain lubricating powder, the second layer is a coating layer having a mass ratio of lubricating powder 4 to resin 1, and the third layer is a layer to inorganic polymer 1 The lubricating powder is a coating layer having a total weight ratio of 1.

The pin surface is mechanically ground (surface roughness 4 μm).
m) only. As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, seizure did not occur, airtightness was maintained, and the results were extremely good.

[0107]

Example 5 A threaded joint made of a high alloy steel having a component composition D shown in Table 1 was subjected to the following surface treatment. The surface of the box is finished by mechanical grinding (surface roughness: 4 μm), then a 6 μm thick zinc-iron alloy layer (surface roughness: 15 μm) is formed by dry impact plating, and the box is preheated to 130 ° C. in an atmosphere furnace. From
A 10 μm-thick first layer (inner layer) of a polyamideimide resin containing molybdenum disulfide as a lubricating powder was formed thereon. Next, when the first layer is in a semi-molten state before being completely dried and formed into a film, the second layer having a thickness of 28 μm and comprising a polyamideimide resin containing molybdenum disulfide as a lubricating powder is formed on the first layer. The coating layer of the layer (intermediate layer) was formed. Further, when the second layer is in a semi-molten state before being completely dried and formed into a film, the third layer having a thickness of 10 μm and comprising a phenol resin containing molybdenum disulfide and PTFE as lubricating powder is formed on the second layer. The coating layer of the layer (outer layer) was formed.

The first layer is a coating layer having a mass ratio of the lubricating powder 1 to the resin 1, and the second layer is a lubricating powder to the resin 1.
The third layer is a coating layer having a total of 9 weight ratio of lubricating powder to resin 1. After the formation of the first, second and third layers, the film is hardened to form a film.
Heat treatment was performed at 30 ° C. for 30 minutes.

The pin surface is machine-finished (surface roughness 3
μm), a 7 μm-thick zinc-iron alloy layer (18 μm in surface roughness) is formed by dry impact plating, and an inorganic material containing Ti—O containing molybdenum disulfide and graphite as a lubricating powder is formed thereon. A 10 μm thick film layer made of a polymer was formed. After forming the film, the film was left in the air for 3 hours and then blown with hot air at 150 ° C. for 10 minutes. This coating layer is made of inorganic polymer 1
On the other hand, the lubricating powder is a coating layer having a total mass ratio of 2.3.

As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, seizure did not occur, airtightness was maintained, and the results were extremely good.

[0111]

Example 6 A threaded joint made of 13% Cr steel having a composition C shown in Table 1 was subjected to the following surface treatment. The pin surface is machined by grinding (surface roughness 3 μm) and then dry-impact plated to a thickness of 7 mm.
μm of a zinc-iron alloy layer (surface roughness 18 μm), on which Ti containing molybdenum disulfide as a lubricating powder is formed.
A first layer (inner layer) having a thickness of 15 μm, made of an inorganic polymer having —O 2 as a skeleton, was formed. Further, the first layer contains molybdenum disulfide and graphite as lubricating powder.
A second layer (outer layer) of an inorganic polymer having a skeleton of Ti-O and a thickness of 5 μm was formed.

The first layer is composed of inorganic polymer 1 and lubricating powder 1.
The second layer is a coating layer having a total weight ratio of 4.0 of lubricating powder to inorganic polymer 1. Second
After the application of the layer, the coating having a two-layer structure was allowed to stand in the air for 3 hours, and hot air at 150 ° C. was blown for 10 minutes.

The box surface was machine-finished (surface roughness 4 μm), and then a copper plating layer (surface roughness 10 μm) having a thickness of 5 μm was formed by electroplating. As shown in Table 4,
In the tightening / loosening test, seizure does not occur until the seventh time in ten times of tightening / loosening with misalignment. After 8 times, slight seizure occurred, but it could be tightened and loosened up to 10 times by care. In this example, since the binder of the inner layer of the multilayer solid lubricating coating is a relatively soft inorganic polymer, the abrasion resistance of the coating is lower than that of the resin. Conceivable. Hermeticity was fine.

[0114]

Example 7 A high-alloy steel threaded joint having a composition D shown in Table 1 was subjected to the following surface treatment. The surface of the box is finished by mechanical grinding (surface roughness 4 μm) and then electroplated to a thickness of 6
A 15 μm-thick manganese phosphate chemical conversion coating (surface roughness 15 μm) was formed on the surface of an iron plating of μm. Thereafter, the box was preheated to 80 ° C. in an atmosphere furnace, and a 10 μm-thick first layer (inner layer) made of an epoxy resin containing molybdenum disulfide as a lubricating powder was formed on the surface of the box. . Further, a second layer having a thickness of 15 μm and comprising a polyamideimide resin containing molybdenum disulfide and graphite as a lubricating powder on the first layer in a semi-molten state before the first layer is completely dried and formed into a film. (Intermediate layer) was formed. After the formation of the first and second layers, a heat treatment was performed at 260 ° C. for 30 minutes to harden the film. next,
Molybdenum disulfide and PTFE as lubricating powder on the second layer
Was formed as a third layer (outer layer) having a thickness of 5 μm and made of an inorganic polymer having Ti—O 2 as a skeleton. After forming the third layer, it was left in the air for 3 hours and then blown with hot air at 150 ° C. for 10 minutes.

The first layer of the solid lubricating coating having a three-layer structure formed on the box surface is a coating layer having a mass ratio of lubricating powder to resin 1 of 0.5, and the second layer is a total of lubricating powder to resin 1. The third layer is a coating layer having a total mass ratio of lubricating powder to inorganic polymer 1 of 1.

The pin surface is machine-finished (surface roughness 3
μm), a 7 μm thick zinc-iron alloy layer (surface roughness 18 μm) is formed by dry impact plating, the pins are preheated to 60 ° C. in an atmosphere furnace, and then disulfide as lubricating powder is formed thereon. Molybdenum-containing epoxy resin, thickness 15
A first layer (inner layer) having a thickness of μm was formed. Heat treatment was performed at 260 ° C for 30 minutes to harden the film. Next, on the first layer, a 5 μm thick second layer (outer layer) made of an inorganic polymer having a skeleton of Ti—O containing molybdenum disulfide and PTFE as a lubricating powder was formed. . After forming the second layer for 3 hours in the air, hot air at 150 ° C. was blown for 10 minutes.

The first layer of the solid lubricating film having a two-layer structure formed on the pin surface is a film layer having a mass ratio of lubricating powder to resin of 0.5, and the second layer is lubricating powder to inorganic polymer. Are film layers having a mass ratio of 1 in total.

As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, seizure did not occur, airtightness was maintained, and the results were extremely good.

[0119]

Example 8 A threaded joint made of carbon steel having a composition A shown in Table 1 was subjected to the following surface treatment. After the box surface is finished by mechanical grinding (surface roughness 4 μm), a 15 μm-thick manganese phosphate conversion coating (surface roughness 16 μm) is formed on the surface, and the box is preheated to 130 ° C. in an atmosphere furnace. Then, a first layer (inner layer) having a thickness of 23 μm made of a polyamideimide resin containing boron nitride as a lubricating powder was formed thereon. Further, when the first layer is in a semi-molten state before being completely dried and formed into a film, a second layer having a thickness of 6 μm and comprising a polyamideimide resin containing molybdenum disulfide as a lubricating powder on the first layer ( Outer layer) was formed.

The first layer is a coating layer having a mass ratio of the lubricating powder 5 to the resin 1. The second layer is a coating layer having a mass ratio of lubricating powder to resin 8.0 of 8.0. After forming the first layer and the second layer, a heat treatment was performed at 260 ° C. for 30 minutes to harden the film.

The pin surface was machine-finished (surface roughness 3μ).
m) only. As shown in Table 4, in the tightening / loosening test, seizure did not occur until the eighth time in ten times of tightening / loosening with misalignment. Slight seizures occurred after 9 times, but could be tightened and loosened up to 10 times with care. In this example, the first of the multilayer solid lubricating coatings is
The lubricating powder / resin mass ratio of the coating layer of the layer (inner layer) is 4.5
It is considered that the strength of this coating layer was reduced, the wear was accelerated, and the seizure resistance was slightly lowered. Hermeticity was fine.

[0122]

Example 9 A carbon steel threaded joint having the composition A shown in Table 1 was subjected to the following surface treatment. After the box surface is finished by mechanical grinding (surface roughness 4 μm), a 15 μm-thick manganese phosphate conversion coating (surface roughness 20 μm) is formed on the surface, and the box is preheated to 130 ° C. in an atmosphere furnace. A first layer (inner layer) having a thickness of 27 μm and made of a polyamideimide resin containing molybdenum disulfide as a lubricating powder was formed thereon. Further, a heat treatment was performed at 230 ° C. for 30 minutes. Next, a 10 [mu] m-thick second layer (outer layer) made of an inorganic polymer having a skeleton of Ti-O containing molybdenum disulfide and graphite as a lubricating powder was formed on the first layer. . At the time of forming the second layer, hot air of 150 ° C. was blown for 10 minutes after standing in the air for 3 hours.

The first layer is a coating layer having a mass ratio of lubricating powder to resin 4.0 of 4.0, and the second layer is a coating layer having a total mass ratio of lubricating powder to inorganic polymer 1 of 1.5. The pin surface was sprayed with # 80 sand to make the surface roughness 15 μm.

As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, no seizure occurred up to the ninth time. Although slight seizure occurred on the 10th time, it could be tightened and loosened up to 10 times. In this example, it is considered that since the surface roughness on the pin side exceeded 10 μm, the coating layer on the box side was quickly consumed and the seizure resistance was insufficient. Hermeticity was fine.

[0125]

Example 10 A threaded joint made of carbon steel having a composition A shown in Table 1 was subjected to the following surface treatment. After finishing the box surface by mechanical grinding (surface roughness 4μm), place the box in an atmosphere furnace
After preheating to 130 ° C., a 28 μm-thick first layer (inner layer) made of a polyamideimide resin containing molybdenum disulfide as a lubricating powder was formed thereon.
This coating layer was subjected to a heat treatment at 230 ° C. for 30 minutes for hardening. Next, on the first layer, an 11 μm-thick second layer (outer layer) made of an inorganic polymer having a skeleton of Ti—O containing molybdenum disulfide and graphite as a lubricating powder was formed. . 150 hours after standing in the air for 3 hours when forming the second layer
The hot air of ° C. was blown for 10 minutes.

The first layer is a coating layer having a lubricating powder weight ratio of 4.0 to resin 1 and the second layer is a coating layer having a total lubricating powder weight ratio of 1.5 to inorganic polymer 1. . The pin surface was only machine-finished (surface roughness 4 μm).

As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, no seizure occurred up to the seventh time. After 8 times, slight seizure occurred, but it could be tightened and loosened up to 10 times by care. In this example, since the surface roughness of the base material on the box side was as small as 4 μm, the adhesion between the coating layer, particularly the first layer and the base material was insufficient, and the insufficient seizure resistance accompanying partial peeling of the coating layer was observed. Probably caused. Hermeticity was a problem.

[0128]

Comparative Example 1 A carbon steel threaded joint having a composition A shown in Table 1 was subjected to the following surface treatment. The surface of the box is finished by mechanical grinding (surface roughness: 4 μm), then a manganese phosphate conversion coating (surface roughness: 20 μm) is formed to a thickness of 15 μm, on which polyamideimide containing molybdenum disulfide as a lubricating powder A film layer of resin having a thickness of 28 μm was formed. This coating layer has a mass ratio of the lubricating powder 1 to the resin 1. This coating layer was subjected to a heat treatment at 230 ° C. for 30 minutes for hardening.

The pin surface is machine-finished (surface roughness 3
μm) only. As shown in Table 4, in the tightening / loosening test, in the tightening / loosening with 10 misalignments, any severe seizure occurred which could not be loosened after the first tightening, and the test was terminated.

As in the prior art, when the solid lubricating film containing the lubricating powder is a single film layer, if the mass ratio of the lubricating powder to the resin is too small, the initial phase may be reduced as in the case of tightening with misalignment. It was confirmed that in a situation where the contact of the steel was severe and a high slip property was required, the slip property for mitigating the slip was insufficient, and severe seizure occurred rapidly.

[0131]

Comparative Example 2 A threaded joint made of carbon steel having a composition A shown in Table 1 was subjected to the following surface treatment. The surface of the box is machine-grinded (surface roughness 4μm), then a 15μm thick manganese phosphate chemical conversion coating (surface roughness 20μm) is formed, on which a molybdenum disulfide and polyamideimide resin containing PTFE A film layer having a thickness of 28 μm was formed. This coating layer has a mass ratio of the total of the lubricating powders to the resin 1 of 9. Heat treatment was performed at 260 ° C for 30 minutes to harden the film.

The pin surface is machine-finished (surface roughness 3
μm) only. As shown in Table 4, in the tightening / loosening test, seizure did not occur until the second time in ten times of tightening / loosening with misalignment. However, care was continued for the third time because slight seizure occurred, but the test was terminated because severe seizure occurred for the fourth time.

As in the prior art, when the solid lubricating film containing the lubricating powder is a single layer, if the mass ratio of the lubricating powder to the resin is increased to, for example, 9 or more, tightening with misalignment is performed. In situations where the initial contact is severe and high slipperiness is required as in the above, it can be relaxed at first, but due to the decrease in adhesion and the speed of film wear, repeated tightening and loosening are necessary. It is intolerable and seizure occurs.

[0134]

Comparative Example 3 A threaded joint made of carbon steel having composition A shown in Table 1 was subjected to the following surface treatment. The box surface is mechanically finished (surface roughness 4 μm), then a manganese phosphate chemical conversion coating (surface roughness 18 μm) is formed with a thickness of 16 μm, and Ti-O containing molybdenum disulfide and graphite is formed thereon. An 18 μm-thick film layer composed of an inorganic polymer serving as a skeleton was formed.
After forming the film, leave it in the air for 3 hours,
Sprayed for 10 minutes. This coating layer is made of inorganic polymer 1
The total mass of the lubricating powder is 1.5 by mass.

The pin surface is machine-finished (surface roughness 3
After that, a zinc phosphate chemical conversion treatment film (surface roughness 22 μm) having a thickness of 20 μm was formed. As shown in Table 4,
In the loosening test, tighten and tighten with 10 misalignments.
During the loosening, no seizure occurred up to the first time.
However, care was continued for the second time because slight seizure occurred, but the test was terminated because severe seizure occurred for the third time.

A solid lubricating film composed of a single layer of a solid lubricating film layer in which a lubricating powder is dispersed in an inorganic polymer binder has a severe initial contact like tightening with misalignment and high slip. Although the ability to relieve such a property is high even in a situation where the property is required, sufficient seizure resistance in repeated tightening and loosening cannot be obtained due to low abrasion resistance as a film.

[0137]

The threaded joint for steel pipes according to the present invention does not use a liquid lubricant containing heavy metal powder such as compound grease, and is used to repeatedly tighten steel pipes with a threaded joint with misalignment in an actual well. -Seizure generation during loosening can be significantly suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic view schematically showing an assembling configuration of a steel pipe and a threaded joint member at the time of shipping the steel pipe.

FIG. 2 is a schematic view schematically showing a tightening portion of the threaded joint for steel pipe of the present invention.

FIG. 3 is a schematic view schematically showing a state when a steel pipe is fastened by a threaded joint with misalignment.

[Explanation of symbols]

 A: Steel pipe, B: Screw joint member 1: Pin, 2: Box 3: Screw part, 4: Metal contact part without screw 5: Shoulder part, θ: Misalignment angle (°)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C10M 103/06 C10M 103/06 C 107/28 107/28 107/32 107/32 107/38 107/38 107/44 107/44 143/02 143/02 143/10 143/10 145/14 145/14 145/20 145/20 145/24 145/24 149/18 149/18 151/04 151/04 155 / 02 155/02 F16L 15/00 F16L 15/00 // C10N 10:12 C10N 10:12 20:06 20:06 Z 30:06 30:06 40:00 40:00 G F-term (reference) 3H013 JA04 4D075 AE03 BB04X BB74X BB87X BB91X CA09 CA13 CA33 DA15 DA19 DA20 DA33 DA34 DB02 DC05 EA10 EA12 EA37 EB01 EB13 EB14 EB18 EB22 EB32 EB33 EB37 EB38 EB39 EB43 EB44 EB56 EC01 EC07 EC54 4H104 AA04A AA19A AA26A CA02C CA07 CB08A CB08C CB12A CB12C CB14C CD02A CE13A CE13C CE14C CG03C CJ03C EA08 FA06 LA03 PA38 QA15

Claims (10)

[Claims] 1. A threaded joint for a steel pipe comprising a pin and a box each having a contact surface including a threaded portion and a threadless metal contact portion, wherein a contact surface of at least one of the pin and the box has a contact surface. A threaded joint for steel pipes, wherein two or more solid lubricating film layers containing a lubricating powder are formed. 2. The threaded joint according to claim 1, wherein a solid lubricating film layer containing no lubricating powder is formed as a lower layer of the two or more solid lubricating film layers containing the lubricating powder. 3. The solid lubricating film layer of at least two layers is formed only on the contact surface between the pin and one member of the box, and the contact surface between the pin and the other member of the box contains a lubricating powder; The threaded joint for steel pipes according to claim 1 or 2, wherein a single solid lubricating film layer that does not contain is formed. 4. The solid lubricating film layer of at least two layers is formed on the contact surface of the pin and one member of the box, and the contact surface of the pin and the other member of the box has a surface roughness Rma.
The threaded joint for steel pipes according to any one of claims 1 to 3, wherein x is 10 µm or less. 5. The solid lubricating film layer of at least two layers and / or
Or one solid lubricating film layer is formed on a base surface having a surface roughness of Rmax 5 to 40 [mu] m.
The threaded joint for steel pipe according to any one of the above. 6. The two or more solid lubricating film layers are each composed of an inner layer and an outer layer of a solid lubricating film layer composed of a resin and a lubricating powder. The mass ratio (M) of the above satisfies the following relationship:
The threaded joint for steel pipe according to any one of claims 1 to 5. 1.0 ≦ M of outer layer ≦ 9.0 0.5 ≦ M of inner layer ≦ 4.5 M of inner layer <MM of outer layer M: Mass ratio of lubricating powder / resin in coating layer 7. The solid lubricating film layer of at least two layers includes an inner layer composed of a resin and a lubricating powder and an outer layer composed of an inorganic polymer and a lubricating powder.
The threaded joint for steel pipe according to any one of claims 1 to 5. 8. The two or more solid lubricating film layers are each composed of an inner layer, an intermediate layer, and an outer layer composed of a resin and a lubricating powder, and three lubricating layers. The mass ratio of powder / resin (M) satisfies the following relationship:
The threaded joint for steel pipes according to claim 1. 1.0 ≦ M of the outer layer ≦ 9.0 0.5 ≦ M of the intermediate layer ≦ 4.5 M of the inner layer <M of the intermediate layer <M of the outer layer M: Mass ratio of lubricating powder / resin in the coating layer 9. The two or more solid lubricating film layers are each composed of three layers: an inner layer and an intermediate layer composed of a resin and a lubricating powder, and an outer layer composed of an inorganic polymer and a lubricating powder. Item 6. A threaded joint for a steel pipe according to any one of Items 1 to 5. 10. The lubricating powder according to claim 1, wherein the lubricating powder comprises one or more materials selected from molybdenum disulfide, tungsten disulfide, graphite, boron nitride, and polytetrafluoroethylene. The threaded joint for steel pipes described in the above.