JP2002370067A - Screw joint for steel pipe excellent in seizure resistance and method for treating its surface - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw joint for a steel pipe capable of preventing seizure caused by repeating clamping and unclamping without applying compound grease even when it is used for crude oil drilling in hot environment. SOLUTION: At least one of the contact surfaces of a pin and a box in the screw joint for a steel pipe, which is composed of the pin and the box each having a contact surface comprising a screw part and a metallic contact part without a screw, is preheated to 50-200 deg.C, then is coated with a coating liquid where a solvent contains a resin and a lubricating powder. The coating film is dried by primary heating within a temperature range of 70 to 150 deg.C and secondary heating of 150 to 380 deg.C, which forms a solid lubricative coating film having a Rockwell M scale hardness of 70-140 and a bond strength of 500 N/m or more measured by the SAICAS method(surface and interfacial cutting analysis system).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel pipe thread joint, such as an oil country tubular good, which has a seizure resistance, an abrasion resistance, and an adhesion property so that compound grease containing heavy metal powder can be used without being applied. The present invention relates to a surface treatment method for forming a solid lubricating film having excellent properties.

[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 steel pipes, heat in the ground acts in addition to combined pressures such as an axial tensile force due to 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. In addition, when lowering the oil country tubular good, the joint once tightened may be loosened and then tightened again to fasten the joint. For this reason, the API (American Petroleum Institute) does not cause seizure called galling even if tightening (make-up) and loosening (breakout) are performed 10 times for tubing joints and 3 times for casing joints. It is required that airtightness be maintained.

[0004] In recent years, from the viewpoint of improving airtightness, special threaded joints that can perform metal sealing by metal-to-metal contact have been generally used. 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 threadless metal contact portions of the pin and the box come into contact with each other to form a metal seal portion by metal-metal contact, thereby improving airtightness.

[0005] In such a threaded joint, a highly lubricating grease called a compound grease has been used, particularly in order to prevent seizure of a metal contact portion. This grease, which is a liquid lubricant, 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.

Therefore, threaded joints for steel pipes that do not require the application of compound grease are disclosed in 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.

[0007] These publications disclose a manganese phosphate-based chemical conversion coating layer, a nitride layer and a manganese phosphate-based chemical conversion coating layer, 5 to 40 µm in order to enhance the adhesion between the solid lubricating coating and the substrate.
It is also disclosed to provide m irregularities. JP-A-8-10
Japanese Patent No. 3724 discloses that a heating and baking treatment for forming a solid lubricating coating is performed at a temperature in the range of 150 to 300 ° C. by heating for 20 to 30 minutes.

[0008]

The use of a threaded joint having a solid lubricating film formed by surface treatment to impart lubricity to the contact surface eliminates the need to apply compound grease, thereby reducing the above-mentioned environmental problems and work efficiency. Can be resolved.

However, the solid lubricating film formed by the above-described conventional surface treatment does not provide the high seizure prevention effect obtained when compound grease is applied, and the tightening and loosening are still repeated several times. In some cases, seizure flaws called galling may occur, and the effect of preventing seizure was insufficient.

Further, in recent years, 250-300
Threaded joints for heat-resistant steel pipes are required for use in high-temperature oil wells that are used in environments where the temperature is 0 ° C or steam-injected oil wells that inject high-temperature steam (350 ° C) that reaches the critical temperature in order to increase the efficiency of crude oil recovery. ing. Therefore, threaded joints for steel pipes include:
After performing a heat resistance test at a temperature of about 350 ° C. after the joint is fastened, performance that guarantees seizure resistance and airtightness has been required even when loosening and refastening are performed. The above-mentioned conventional solid lubricating coating has been particularly difficult to secure the performance required for such a heat-resistant joint.

[0011] The present invention forms a solid lubricating coating having excellent seizure resistance, which can effectively suppress the occurrence of seizure during repeated tightening and loosening even in a heat-resistant threaded joint for steel pipes. It is an object of the present invention to provide a surface treatment method for a threaded joint for steel pipes.

[0012]

SUMMARY OF THE INVENTION The inventor of the present invention has found that the conventional solid lubricating film formed on the contact surface of a threaded joint for steel pipe has insufficient seizure resistance due to insufficient hardness of the film. The deficiency was determined to be due to insufficient drying of the coating.

[0013] The solid lubricating coating of the threaded joint is generally formed by applying a coating liquid containing a resin and a lubricating powder (eg, molybdenum disulfide) in a volatile solvent to the contact surface of the threaded joint, and heating. It is formed by a surface treatment of drying (baking and baking) the coating film. 150 as in the prior art
Simply drying the coating by heating to ~ 300 ° C does not completely evaporate the solvent, even if the heating time is extended, and a small amount of solvent or moisture is trapped in the coating, causing internal defects. Therefore, it was found that sufficient hardening of the coating and abrasion resistance could not be obtained. With the solid lubricating film in such a state, as the threaded joint is repeatedly tightened and loosened, the solid lubricating film is worn out due to abrasion, eventually causing the film to break, leading to metal-to-metal contact and seizure. Will occur.

Therefore, the solid lubricating coating is completely dried,
As a result of exploring means for forming a harder and improved abrasion-resistant coating, drying was performed in at least two stages, first heating at a low temperature, and then performing secondary heating at a higher temperature. The present inventors have found out that a solid lubricating film having higher hardness and excellent wear resistance and seizure resistance is formed as compared with the case of heating at a constant temperature as in the prior art, and reached the present invention.

The present invention, in one aspect, is a surface treatment method for a threaded joint for steel pipes comprising a pin and a box each having a contact surface including a threaded portion and a threadless metal contact portion, wherein the resin is contained in a solvent. Applying a coating liquid containing at least one of a pin and a box to the contact surface of the pin and the box, and applying a primary heating in a temperature range of 70 ° C to 150 ° C and a range of more than 150 ° C to 380 ° C. And drying by multi-stage heating at least composed of
A surface treatment method for a threaded joint for steel pipes, comprising a step of forming a solid lubricating film on the surface.

One embodiment of the method of the present invention further comprises the step of heating the contact surface to be applied to a temperature of 50 to 200 ° C. before the applying step. According to the method of the present invention, the formed solid lubricating film has a hardness of 70 to 70 on a Rockwell M scale.
140, indicating that the adhesion strength obtained by the SAICAS method (surface-interface cutting method) can be 500 N / m or more.

According to the present invention, in a threaded joint for steel pipes comprising a pin and a box each having a contact surface including a threaded portion and a threadless metal contact portion, at least one contact surface of the pin and the box is provided with disulfide. A threaded joint for steel pipes, comprising a solid lubricating coating containing a solid lubricating powder of molybdenum and / or tungsten disulfide in a resin, and having a hardness of 70 to 140 on a Rockwell M scale. Also provided. This solid lubricating coating has an adhesion strength determined by the SAICAS method of 500 N /
m or more. In one embodiment, the solid lubricating coating has been dried by multi-stage heating at at least two different temperatures.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 2 is a schematic view schematically showing the configuration of a typical threaded joint for steel pipes. 1 is a pin, 2
Is a box, 3 is a screw part, 4 is a metal contact part without a screw, 5
Indicates a shoulder portion. Hereinafter, the screwless metal contact portion is simply referred to as a metal contact portion.

As shown in FIG. 2, a typical threaded joint comprises a pin 1 having a threaded portion 3 (ie, a male threaded portion) and an unthreaded metal contact portion 4 formed on the outer surface of a steel pipe end;
A box 2 having a threaded portion 3 (ie, a female threaded portion) and a threadless metal contact portion 4 formed on the inner surface of the threaded joint member. However, the pins and boxes are not limited to those shown. For example, one end of the steel pipe can be a pin and the other end can be a box without using a joint member, or the joint member can be a pin (male thread) and both ends of the steel pipe can be boxes.

A thread 3 and a (no thread) 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. Conventionally, compound grease containing heavy metal powder has been applied to the contact surface for this purpose. However, as described above, use of compound grease has many problems in terms of environment and work efficiency.

In order to solve this problem, Japanese Patent Laid-Open Publication No.
As disclosed in Japanese Patent Publication No. 24, a coating solution containing a resin and a lubricating powder in a solvent is applied to at least one contact surface of a pin and a box, and the coating film is heated to a temperature of 150 to 300 ° C. to make contact. A threaded joint with a solid lubricating film formed on the surface and no application of compound grease was developed. However, in the conventional threaded joint of this type, as described above, the wear resistance of the solid lubricating coating, particularly at high temperatures, is not sufficient, and the coating is worn out during repeated tightening and loosening. The anti-seizure effect (seizure resistance) was insufficient.

According to the invention, the coating is dried in at least two stages. That is, first, primary heating is performed in a low temperature range, and the solvent and moisture are reliably evaporated while the coating film has fluidity. Thereafter, by performing secondary heating in a temperature range higher than the primary heating to evaporate the solvent and moisture, a solid lubricating film having high hardness and high wear resistance can be formed.

Specifically, the drying of the coating film is performed by multi-stage heating comprising at least primary heating in a temperature range of 70 to 150 ° C. and secondary heating in a temperature range of more than 150 ° C. to 380 ° C. Performed by The heating time (temperature holding time) may be appropriately set according to the size and shape of the threaded joint, but is preferably 20 minutes or more in each step, and more preferably 30 to 60 minutes.

When the temperature of the primary heating is lower than 70 ° C., the effect of sufficiently evaporating the solvent and the water from the inside of the coating is small. On the other hand, when the temperature exceeds 150 ° C., the solvent and the water solidify while remaining inside the coating. A sufficient hardening and abrasion resistance of the coating cannot be obtained. If the secondary heating temperature is 150 ° C or less,
Solvent and water cannot be completely removed from the coating,
On the other hand, if the temperature exceeds 380 ° C., on the other hand, sufficient hardness cannot be obtained due to the heat resistance of the solid lubricating coating itself.

The temperature range of the primary heating is preferably from 80 to 140 ° C. from the viewpoint of the transpiration of the solvent and water. From the viewpoint of coating hardness, the temperature range of the secondary heating is preferably 180 to 350 ° C.

Heating for drying the coating film comprises at least primary heating and secondary heating. FIG. 3 shows an example of a temperature profile (heat pattern) of the two-stage heating composed of the primary heating and the secondary heating. Alternatively, secondary heating may be performed after primary heating.

Furthermore, by making the primary heating and / or the secondary heating itself a multi-stage heating, it is possible to carry out heating at three or more stages. However, from the viewpoint of economy, two-stage heating composed of primary heating and secondary heating is desirable.

As shown in the figure, both the primary heating and the secondary heating, particularly the primary heating, may be carried out while the temperature is slowly increased, instead of being maintained at a constant temperature. In this case, for primary heating, 70 ° C
If the time required to raise the temperature from to 150 ° C. is 20 minutes or more, it is determined that the primary heating is the primary heating according to the present invention. For example, when heating at a temperature of 150 to 300 ° C. as in the prior art, the time required for raising the temperature from 70 ° C. to 150 ° C. is generally within 5 minutes, and the difference from the present invention is clear.

The coating liquid used to form the solid lubricating film by the method according to the present invention is a dispersion liquid containing a resin serving as a binder and a lubricating powder in a solvent. The resin is preferably soluble in the solvent used, but may be dispersed.

The resin is not particularly limited as long as it functions as a binder. Those having heat resistance, moderate hardness and abrasion resistance are preferred. 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.

The lubricating powder used in the present invention is not particularly limited as long as it has lubricating properties. However, considering that a high load is applied, molybdenum disulfide, tungsten disulfide, graphite, boron nitride, PTFE (polyethylene) It is desirable to use one or more powders selected from tetrafluoroethylene). Of these, particularly preferred are
It is a powder of molybdenum disulfide and / or tungsten disulfide having a high antifriction effect, or a mixed powder obtained by mixing other lubricating powder with the powder.

The average particle size of the lubricating powder is not particularly limited, but is preferably in the range of 0.5 to 60 μm. 0.5 μ
If it is less than m, the powders are likely to agglomerate, difficult to uniformly disperse in the coating solution, and a solid lubricating film in which the lubricating powder is uniformly dispersed is not formed, and the seizure resistance may be insufficient. On the other hand, when the thickness exceeds 60 μm, the strength of the solid lubricating coating is reduced, so that occurrence of seizure may not be suppressed.

The mixing ratio of the resin and the lubricating powder is not particularly limited, but is usually 10 to 80% of the resin and 20 to 90% of the lubricating powder in mass% based on the total amount of the resin and the lubricating powder. Within range.

As the solvent used for forming the coating solution, various low-boiling solvents such as hydrocarbons (eg, toluene) and alcohols (eg, isopropyl alcohol) can be used alone or in combination. . The solvent used in the present invention preferably has a boiling point of 150 ° C. or lower.

The coating liquid for forming the solid lubricating film is:
Components other than the solvent, the resin, and the lubricating powder can be contained. For example, one or more of zinc powder, chromium pigment, silica, and alumina pigment can be added as a rust preventive or the like. Further, a colorant may be contained to color the formed solid lubricating film. Also,
One or two or more additives such as a dispersant, an antifoaming agent, and a thickener can be appropriately contained.

The above-mentioned coating solution is applied to at least one contact surface of the pin and the box (the threaded portion and the threadless metal contact portion). The application method may be a known appropriate method such as brushing, dipping, or air spraying.

The coating is desirably performed so that the thickness after drying (that is, the thickness of the formed solid lubricating film) is 5 μm or more and 50 μm or less. The lubricating powder contained in the solid lubricating coating spreads over the entire contact surface as abrasion powder under high sliding surface pressure and exhibits excellent seizure resistance. However, if the film thickness is less than 5 μm, the lubricating powder is lubricated. In some cases, the content of the lubricating powder is reduced, and the effect of improving the lubricity is reduced. On the other hand, if the film thickness is larger than 50 μm, the tightening amount becomes insufficient, the airtightness becomes insufficient, or if the surface pressure is increased to secure the airtightness, seizure is likely to occur, and the lubricating film is peeled off. May be easier.

The contact surface of the pin and / or the box to which the coating liquid is applied is used to further enhance the effect of the present invention.
It is desirable to roughen the surface so that the surface roughness Rmax is 5 to 40 μm, which is larger than the roughness after machine cutting (3 to 5 μm). If the Rmax of the coating surface is less than 5 μm, the adhesion of the solid lubricating film is reduced, while if it exceeds 40 μm, the friction increases, the wear of the solid lubricating film is accelerated, and the solid lubricating film may not withstand repeated tightening and loosening. is there. However, it is needless to say that the effects of the present invention can be obtained even outside the above range.

As a method of roughening, the steel surface itself is roughened, such as a method of projecting a sand or a grid, a method of immersing in a strong acid solution such as sulfuric acid, hydrochloric acid, nitric acid, or hydrofluoric acid to roughen the skin. In addition to the method, a method is also possible in which an undercoating layer having a rougher surface than the steel surface is formed to roughen the coated surface.

As an example of such a base treatment, a method of forming a chemical conversion coating film of phosphate, oxalate, borate, or the like (the roughness of the crystal surface increases as the generated crystal grows),
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, a projection plating method, a nitriding 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 projection plating is preferable. A manganese phosphate film is more preferable from the viewpoint of adhesion, and a film of zinc or a zinc-iron alloy is more preferable from the viewpoint of rust prevention. Since both phosphate-based chemical conversion coatings and zinc or zinc-iron alloy coatings formed by projection plating are porous coatings, if a solid lubricating coating is formed thereon, the adhesion of the solid lubricating coating will increase. Increase.

When the undercoat layer is formed, its thickness is not particularly limited, but is preferably 5 to 40 μm from the viewpoint of rust prevention and adhesion.
It is preferable that If it is less than 5 μm, sufficient rust prevention may not be ensured. On the other hand, if it exceeds 40 μm,
Adhesion with the solid lubricating coating may decrease.

Before the application of the coating liquid, the contact surface to be applied is applied in order to enhance the adhesion of the solid lubricating film to be formed.
It is desirable to heat (preheat) the (coated substrate) to a temperature of 50 to 200 ° C. When the heating temperature is lower than 50 ° C., the effect of improving the adhesion is hardly obtained. On the other hand, when the temperature exceeds 200 ° C., the viscosity of the applied coating solution (coating film) decreases, so that it becomes difficult to form a solid lubricating film having a required thickness, and the adhesiveness also decreases. The heating and holding time may be appropriately set according to the size of the threaded steel pipe joint, but it is preferable that the base material temperature be maintained in the above range during the coating operation. Even if the temperature of the substrate immediately before the application is within the above-mentioned temperature range, and thereafter the application is performed without maintaining the temperature, the effect of improving the adhesion is obtained.

The substrate can be heated by a known general method such as an atmosphere furnace or hot air. It is efficient and economical to heat the box by placing the box in an atmosphere furnace and bringing the surface to a predetermined temperature. The pin may be heated by placing only the thread at the end of the tube into an atmosphere furnace or heating the surface to a predetermined temperature with hot air.

After the application of the coating solution, the coating film is dried.
As described above, the heating is performed by multi-stage heating including at least primary heating and secondary heating. This heating can also be carried out by the same means as the above-mentioned preheating, but since it is necessary to control the temperature within a certain temperature range, heating in an atmosphere furnace is preferable to hot air. The atmosphere in the furnace is not particularly limited, but an air atmosphere is sufficient.

According to the present invention, a hardened solid lubricating coating can be formed by drying the coating by multi-stage heating as described above. The solid lubricating coating of the present invention has a Rockwell M scale hardness (hereinafter, simply referred to as Rockwell M hardness) of 70 to stipulated in JIS-K7202.
Preferably, it has a hardness in the range of 140. If the Rockwell M hardness of the coating is less than 70, the coating will wear quickly due to sliding friction during repeated tightening and loosening, and the seizure resistance may be insufficient. On the other hand, if the hardness exceeds 140, the wear is too small, and it may not be possible to supply sufficient lubricating powder to prevent seizure at the contact interface.
From the viewpoint of wear resistance, the Rockwell M hardness of the coating hardness is more preferably in the range of 90 to 140.

A solid lubricating film using molybdenum disulfide and / or tungsten disulfide as a lubricating powder can be formed by a conventional method using a single-stage heating method such as Rockwell M.
The hardness was about 50. According to the present invention, it is possible to provide a threaded joint for steel pipes having a solid lubricating coating containing molybdenum disulfide and / or tungsten disulfide as a lubricating powder and having a coating hardness of Rockwell M70 to 140. Become.

The solid lubricating coating in the threaded joint for steel pipes is as follows:
Due to shear stress under high load when tightening and loosening,
If the adhesiveness is low, the adhesive will be peeled off and the effect of preventing seizure cannot be sufficiently exhibited, so that it is required to have excellent adhesiveness.

There are various methods for evaluating the adhesion of the coating. A simple and well-known method is the so-called grid test. However, since the solid lubricating coating of the threaded joint requires much higher adhesion than can be measured by a grid test, this test method cannot be adopted.

The present inventors have reported that the adhesion (peeling resistance) of a solid lubricating coating applied to a threaded joint is described in "Coating Technology", April 1995.
SAlCAS method detailed on pages 123 to 135 [Surface and Interfacial Cutting Analysis Syst
em], which can be quantitatively determined by the adhesive strength measured.
It has been found that peeling of the solid lubricating coating during tightening and loosening can be prevented.

In the SAICAS method, a sharp cutting edge is pressed against the surface of the coating under a load while moving the substrate to which the coating is attached in the horizontal direction, and the coating is cut obliquely from the surface to the interface with the substrate. After reaching the interface, the load is adjusted to move the cutting blade horizontally. The adhesive strength of the coating can be determined as the peeling force (N / m) per peeling width (width of the cutting blade) during the movement of the interface. A measuring device for the SAICAS method is commercially available from Daipla Wintes under the trade name SAICAS.

In a preferred embodiment of the present invention, the solid lubricating coating formed on the contact surface of the threaded joint as the base material is a SAIC
It has an adhesion strength of 500 N / m or more as measured by the AS method.
If the adhesion strength to the substrate is less than 500 N / m, a sufficient anti-seizure effect may not be exhibited.

The solid lubricating film dried by multi-stage heating according to the present invention tends to have improved adhesive strength as compared with the conventional drying method. The formation and / or preheating can further improve the formed bond strength.

Since the object of the present invention can be sufficiently achieved only by forming the solid lubricating film on one of the contact surfaces of the pin and the box, it is advantageous to form the solid lubricating film on only one of them. . In this case, the box is easier to form the coating film, especially to heat. The contact surface of the other member (preferably a pin) which does not form a solid lubricating film 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. The solid lubricating coating may be formed only on a portion of the contact surface, preferably only on the metal contact.

However, if the box is attached only to the pin at one end of the steel pipe during assembly, the pin at the other end remains exposed. Therefore, in order to impart rust prevention or rust prevention and lubricity to such exposed pins, a coating can be formed by applying an appropriate surface treatment and / or protected by a protector. You can also. Of course, even when the other contact surface is not exposed, a coating may be formed on this surface.

The threaded joint for steel pipe surface-treated in accordance with the present invention is tightened without applying compound grease. If desired, oil may be applied to the solid lubricating coating or the threaded portion of the mating member and the threadless metal contact portion. Is also good. 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. Various additives commonly used in lubricating oils such as rust preventive additives and extreme pressure additives can be added to this oil. When these additives are liquid, they can be used alone as an oil and applied.

As a rust preventive additive, a basic metal sulfonate, a basic metal phenate, a 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. In addition, antioxidants, pour point depressants, viscosity index improvers, and the like can be added to the oil.

[0058]

EXAMPLE A steel pipe (outer diameter: 7 inches <178) made of carbon steel A, Cr-Mo steel B, 13% Cr steel C or high alloy steel D shown in Table 1
mm>, wall thickness: 0.408 inch <10.4 mm>) Any one of the surface treatments Nos. 1 to 5 shown in Table 2 on the contact surface of the pin and box of the threaded joint ). In this example, the base treatment was performed on both contact surfaces of the pin and the box, and the solid lubricating coating was formed on only one contact surface of the pin or the box.

The coating liquid used for forming the solid lubricating film is a dispersion liquid in which a lubricating powder is dispersed in a resin solution obtained by dissolving a resin in a solvent. The solvent used in a polyamideimide resin is ethanol / toluene (50/50). ), N-methyl-2-pyrrolidone / xylene (65/35) for phenolic resins and tetrahydrofuran / cyclohexane (50/50) for epoxy resins. Preheating of the base material before coating and drying after coating were all performed in an atmosphere using an atmosphere furnace. Number of surface treatment adopted, substrate preheating temperature (substrate temperature before application)
Table 3 shows the heating conditions (temperature of primary heating and secondary heating × time) for drying the coating film after coating.

Separately, a steel plate (10 mm × 50 m
m, thickness 2 mm) and the same combination as shown in Table 2 was used for undercoating and formation of a solid lubricating film. That is, the base treatment is performed on the member on which the solid lubricating film is formed (that is, N
It was the same as that performed on the contact surface of the box (o. 1-4) and the pin (No. 5). The adhesive strength and hardness of the formed solid lubricating coating were measured. The adhesive strength was measured using SAICAS BN-1 manufactured by Daipla Wintes.
The coating hardness was measured on a Rockwell M scale according to JIS-K7202. Table 3 shows the results of these measurements.
Are shown together.

Using the threaded joint surface-treated as described above, tightening and loosening operations were carried out up to 20 times in the manner shown in Table 4, and the state of seizure during that time was investigated. That is, as shown in Table 4, 1st to 4th, 6 to 14th, 16 to
Twisting was performed at room temperature for tightening and loosening, and fifth and fifteenth tightening was performed at room temperature, followed by heat treatment at 350 ° C. for 24 hours, followed by cooling and loosening at room temperature. The tightening / loosening state corresponds to the use state of the heat-resistant joint. Tightening speed is 10 rpm, tightening torque is 10
It was 340 ft · lbs. Table 5 shows the state of seizure occurrence.

Example 1 A carbon steel threaded joint of symbol A shown in Table 1 was subjected to the following surface treatment. The contact surface of the box is sprayed with No. 60 sand, after a base treatment to make the surface roughness 31 μm, the box is pre-ripened to 60 ° C., and a polyamideimide resin containing molybdenum disulfide as a lubricating powder on it A solid lubricating film having a thickness of 30 μm was formed. The solid lubricating coating is a coating containing a mass ratio of molybdenum disulfide 4 as a lubricating powder to the polyamideimide resin 1. Drying after coating was carried out by primary heating at 100 ° C. for 30 minutes, and after cooling to room temperature, secondary heating at 260 ° C. for 30 minutes.

The contact surface of the pin was only machine-finished (surface roughness 3 μm). As shown in Table 5,
In the loosening test, seizure did not occur and the airtightness was maintained in 20 times of tightening and loosening, and it was extremely good.

Example 2 Example 1 was repeated except that the preheating temperature of the box before coating was changed from 60 ° C. to 100 ° C.
Further, the heating conditions after the application were changed so that the primary heating at 100 ° C. for 30 minutes was followed by the secondary heating at 260 ° C. for 30 minutes without cooling.

As shown in Table 5, in the tightening / loosening test, no seizure occurred, the airtightness was maintained, and the results were extremely good after 20 times of tightening / loosening. As shown in Table 3, as compared with Example 1, in this example having a higher preheating temperature, the hardness of the coating was slightly reduced, and the adhesion strength of the coating was improved.

Example 3 A threaded joint made of Cr-Mo steel indicated by symbol B shown in Table 1 was subjected to the following surface treatment. The contact surface of the box was ground-treated by forming a 15-μm-thick manganese phosphate chemical conversion coating (surface roughness 20 μm) on the surface after mechanical grinding finish (surface roughness 4 μm). After that, the box was preheated to 130 ° C., and a solid lubricating film having a thickness of 28 μm, made of an epoxy resin containing molybdenum disulfide and graphite as lubricating powder was formed thereon. The solid lubricating film is a film containing the lubricating powder molybdenum disulfide and graphite (mass ratio = 9: 1) in a total amount of 4.0 with respect to the epoxy resin 1. Drying after coating was performed by primary heating at 100 ° C. for 30 minutes and secondary heating at 230 ° C. for 30 minutes after cooling to room temperature.

The contact surface of the pin was only machine-finished (surface roughness 3 μm). As shown in Table 5, in the tightening / loosening test, no seizure occurred and the airtightness was maintained, and the results were extremely good after 20 times of tightening / loosening.

Example 4 Example 3 was repeated, except that the primary heating temperature after coating was changed from 100 ° C. in Example 3 to 70 ° C.

As shown in Table 5, in the tightening / loosening test, no seizure occurred up to the 16th test. After 17 times, slight seizure occurred, but it was possible to tighten and loosen up to 20 times with care. There was no problem with airtightness. Primary heating temperature
It can be seen that Example 3, which is as high as 100 ° C., has a more complete drying of the film, and is a solid lubricating film having higher hardness and higher adhesive strength than Example 4.

(Example 5) A threaded joint made of 13% Cr steel of symbol C shown in Table 1 was subjected to the following surface treatment. The contact surface of the box is finished by mechanical grinding (surface roughness 4μm) and then electroplated to a 10μm thick copper plating (surface roughness 11μm)
To form a base. After that, the box is preheated to 180 ° C. and then made of phenolic resin containing tungsten disulfide as lubricating powder on it.
A solid lubricating coating layer having a thickness of 32 μm was formed. The solid lubricating coating is a coating containing 4.0 mass ratio of tungsten disulfide as a lubricating powder to phenolic resin 1. Drying after coating was performed by primary heating at 80 ° C. for 20 minutes and secondary heating at 170 ° C. for 60 minutes after cooling to room temperature.

The contact surface of the pin was only machine-finished (surface roughness 3 μm). As shown in Table 5,
In the loosening test, there is no seizure until the 14th test. Slight seizures occurred from the 15th time onward, but they could be tightened and loosened up to 20 times with care. There was no problem with airtightness. In the present example, the reason why the slight seizure occurred after the fifteenth time is because the material of the threaded joint is easily seized. If the material of the threaded joint is A or B, it is estimated that seizure does not occur.

Example 6 A high alloy threaded joint with a component code D shown in Table 1 was subjected to the following surface treatment. The contact surface of the box was machine-finished (surface roughness 4 μm), and then ground-treated by forming a 7 μm thick zinc-iron alloy layer (surface roughness 18 μm) by dry impact plating. Thereafter, the box was heated to 100 ° C., and a 20 μm thick solid lubricating coating layer made of a polyamideimide resin containing molybdenum disulfide as a lubricating powder was formed thereon. The solid lubricating coating is a coating containing a mass ratio of molybdenum disulfide 4 as a lubricating powder to the polyamideimide resin 1. The coating was dried by primary heating at 80 ° C. for 30 minutes, and after cooling to room temperature, secondary heating at 170 ° C. for 40 minutes.

The contact surface of the pin was only machine-finished (surface roughness 4 μm). As shown in Table 5,
In the loosening test, there is no seizure until the 14th test. After 15 times, slight seizure occurred, but it could be tightened and loosened up to 20 times by care. There was no problem with airtightness. Also in this example, the seizure is a high alloy steel that is susceptible to seizure, so slight seizure occurred after the 15th time, but if the material is A or B, seizure does not occur up to 20 times. There will be.

(Example 7) The threaded joint made of carbon steel indicated by the symbol A shown in Table 1 was subjected to the following surface treatment. The contact surface of the box is finished by mechanical grinding (surface roughness 4 μm), and then its surface is coated with a 10 μm-thick manganese phosphate conversion coating (surface roughness).
10 μm) only.

The contact surface of the pin was subjected to a mechanical grinding finish (surface roughness 4 μm), and then subjected to a base treatment for forming a zinc phosphate chemical conversion coating (surface roughness 20 μm) with a thickness of 15 μm on the surface. After that, put only the pin part in the atmosphere furnace,
Preheated to a thickness consisting of a polyamideimide resin containing molybdenum disulfide as a lubricating powder on it
A solid lubricating film of 28 μm was formed. The solid lubricating coating is a coating containing a mass ratio of molybdenum disulfide 4 as a lubricating powder to the polyamideimide resin 1. The coating film was dried by first heating at 140 ° C. for 20 minutes by placing only the pin portion in an atmosphere furnace, and by once cooling to room temperature and then secondary heating at 280 ° C. for 30 minutes.

As shown in Table 5, in the tightening / loosening test, no seizure occurred, the airtightness was maintained, and the results were extremely good after 20 times of tightening / loosening. (Comparative Example 1) The following surface treatment was applied to a threaded joint made of carbon steel indicated by symbol A shown in Table 1.

The contact surface of the box was mechanically ground (surface roughness 4 μm), and then subjected to a base treatment for forming a 15 μm-thick manganese phosphate chemical conversion coating (surface roughness 20 μm). Thereafter, the box was preheated to 175 ° C., and a 28 μm thick solid lubricating film made of an epoxy resin containing molybdenum disulfide and graphite as a lubricating powder was formed thereon. The solid lubricating film is a film containing the total amount of lubricating powder molybdenum disulfide and graphite with respect to the epoxy resin 1 at a mass ratio of 4. Drying of the coating film was carried out by heating at 150 ° C. in 1/50 step.

The contact surface of the pin was only machine-finished (surface roughness 3 μm). As shown in Table 5,
In the loosening test, mild seizure occurred at the first time, and after cleaning, the second tightening / loosening was performed. However, the seizure was so severe that it could not be loosened, so the test was terminated.

This example corresponds to the case where only the primary heating in the present invention is performed. However, although the solvent and moisture evaporate from the solid lubricating coating to some extent, there is no secondary heating. And a coating with low hardness was obtained. Further, even if preheating was performed, the adhesion strength was insufficient. It is considered that seizure occurred early because the hardness and adhesion strength of the solid lubricating film were insufficient.

Comparative Example 2 Example 1 was repeated, except that the preheating temperature was increased to 180 ° C., and heating after coating was performed by one-step heating at 240 ° C. for 50 minutes.

As shown in Table 5, in the tightening / loosening test, no seizure occurred up to the fourth time. However, a slight seizure occurred at the fifth time, and it was possible to tighten and loosen up to six times with care. However, the severe seizure occurred at the sixth time, so the test was terminated.

This example is a conventional heating method, and corresponds to a case where only secondary heating in the present invention is performed. Because there is no primary heating at low temperature, the undried coating film begins to solidify rapidly, and the solvent and moisture are trapped inside the coating, resulting in large variations in the hardness of the formed solid lubricating coating and the adhesion strength to the substrate. Occurred. As a result, it is considered that seizure easily occurred.

(Comparative Example 3) Comparative Example 1 was repeated, but the preheating temperature was lowered to 130 ° C, and the heating after coating was performed by primary heating at 50 ° C for 30 minutes, cooling to room temperature, and then heating at 230 ° C. This was performed by secondary heating for 30 minutes.

As shown in Table 5, in the tightening / loosening test, no seizure occurred up to the sixth time. A slight seizure occurred on the seventh occasion, and tightening and loosening were continued by care. However, a severe seizure occurred on the ninth occasion, and the test was terminated. Since the temperature of the primary heating was too low, the evaporation of the solvent and moisture from the solidifying solid lubricating coating was insufficient, and the hardness and adhesion strength of the coating were reduced, as in the case of the conventional method of Comparative Example 2. It is presumed that partial variation occurred and seizure occurred.

(Comparative Example 4) Example 1 was repeated, but the pretreated box was not preheated, and the post-coating heating was performed at 100 ° C for 20 minutes by primary heating and after cooling to room temperature.
This was performed by secondary heating at 410 ° C. for 30 minutes.

As shown in Table 5, in the tightening / loosening test, slight seizure occurred at the first time and tightening / loosening was performed up to the second maintenance. However, severe seizing occurred such that it could not be loosened. The test was completed. This is because the temperature of the secondary heating was too high, the evaporation of the solvent and water from the solid lubricating film was insufficient, and the solid lubricating film itself was softened. It is considered that they peeled off at once when tightening.

[0087]

[Table 1]

[0088]

[Table 2]

[0089]

[Table 3]

[0090]

[Table 4]

[0091]

[Table 5]

[0092]

According to the present invention, a solid lubricating coating having excellent seizure resistance, abrasion resistance and adhesion to the surface of a threaded joint for steel pipes without using a liquid lubricant containing heavy metal powder such as compound grease. Can be formed, and the occurrence of seizure during repeated tightening and loosening can be significantly suppressed. In particular, threaded joints used in crude oil extraction in high-temperature environments such as high-depth, high-temperature oil wells, or steam-injected oil wells have significantly higher high-temperature wear resistance than threaded joints with conventional solid lubricating coatings. Since a solid lubricating film can be formed, remarkable seizure resistance is exhibited.

[Brief description of the drawings]

FIG. 1 is a schematic view schematically showing an assembling configuration of a steel pipe and a screw 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 pipes of the present invention.

FIG. 3 is a schematic diagram showing an example of a heat pattern (temperature profile) of primary heating and secondary heating in the surface treatment method for a threaded joint for steel pipes of the present invention.

[Explanation of symbols]

A: steel pipe, B: screw joint member, 1: pin, 2: box, 3: screw part, 4: screwless metal contact part, 5: shoulder part,

 ────────────────────────────────────────────────── ─── Continued on the front page F term (reference) 3H013 GA08 4D075 BB23X BB24Y BB24Z BB38Z BB91Z BB93X BB93Y BB93Z CA02 CA09 CA13 CA18 DA15 DA19 DA23 DA33 DB02 DC05 EA37 EB13 EB14 EB18 EB22 EB33 EB33 EB33 EB33 EB33 EB33

Claims (7)

[Claims] 1. A surface treatment method for a threaded joint for steel pipes comprising a pin and a box each having a contact surface including a threaded portion and a threadless metal contact portion, comprising: Applying the coating solution containing the coating solution to at least one of the contact surfaces of the pin and the box; and performing primary heating in a temperature range of 70 ° C. to 150 ° C.
A surface of a threaded joint for steel pipes, comprising a step of drying by multi-stage heating comprising at least secondary heating in a range of more than 0 ° C to 380 ° C to form a solid lubricating film on the surface. Processing method. 2. Prior to the application step, the contact surface to be applied is
The surface treatment method for a threaded joint for steel pipes according to claim 1, further comprising a step of heating to a temperature of 50 to 200 ° C. 3. The surface treatment method for a threaded joint for a steel pipe according to claim 1, wherein the hardness of the formed solid lubricating coating is 70 to 140 on a Rockwell M scale. 4. The threaded joint for a steel pipe according to claim 1, wherein an adhesion strength of the formed solid lubricating coating obtained by a SAICAS method (surface-interface cutting method) is 500 N / m or more. Surface treatment method. 5. A threaded joint for steel pipe comprising a pin and a box each having a contact surface including a threaded portion and a threadless metal contact portion, wherein at least one contact surface of the pin and the box is provided with molybdenum disulfide and / or molybdenum disulfide. A threaded joint for steel pipes comprising a solid lubricating coating containing a solid lubricating powder of tungsten disulfide in a resin, wherein the hardness of the coating is 70 to 140 on a Rockwell M scale. 6. The threaded joint for a steel pipe according to claim 5, wherein the adhesion strength of the solid lubricating film determined by the SAICAS method is 500 N / m or more. 7. The threaded joint for a steel pipe according to claim 5, wherein the solid lubricating coating is dried by multi-stage heating at at least two different temperatures.