JPH06346988A - Oil well pipe joint and surface treatment method thereof - Google Patents

Abstract

PURPOSE:To provide an oil well pipe wherein a surface treated surface having an excellent film strength and adhesion and improved galling resistance is formed at a steel pipe joint part made of high Cr-contained steel having specified percent Cr content. CONSTITUTION:When surface treatment to provide seizure resistance for the slide part of the coupling of an oil well pipe formed of high Cr content alloy having 10% or more Cr content is effected, nitriding treatment as base material treatment is applied to form a nitride layer. Thereafter, ordinary chemical conversion treatment or metal plating is applied. The film, brought into a passive state, of a coupling part is fused and removed by means of molten salt, and a nitride layer consisting mainly of iron nitride layer is formed on a surface layer with the progress of Cr removal reaction. An iron nitride layer formed on the surface thereof has excellent drape with formation treatment and lead or copper plating treatment, and forms a film having an excellent strength and adhesion, and improves galling resistance of a coupling part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coupling joint for connecting oil country tubular goods used for crude oil or natural gas mining.

[0002]

2. Description of the Related Art The joint portion used to connect oil country tubular goods is
Rotating and tightening the joint part consisting of the screw part formed at the tip of the oil country tubular good and the taper part formed at the base of the oil well pipe, the screw part that engages with this screw part, and the joint member that forms the tapered part at the tip. , A high surface pressure is generated on the contact surfaces of both tapered portions to form a metal-metal seal to maintain perfect sealing performance.

However, since this joint is repeatedly slid at a high surface pressure at the time of make-up and break-out, seizure and rusting occur between the joint and the pipe material.
This hinders the sealing property. For this reason, for example, as described in Japanese Patent Publication No. 12995/1989, generally, a chemical conversion film is formed on the screw portion and the metal-metal seal portion by various chemical conversion treatments, or Cu, Z.
Soft metals such as n and Pb, or Fe, Ni, Co,
Plating such as Pt is applied to prevent baking and rusting. That is, the galling between the joint portion of the oil country tubular good and the joint member is prevented.

On the other hand, in recent years, high pressure steel oil well pipes made of high alloy steel in which 10% or more of high Cr content steel and further Ni, Mo, etc. are added to increase pressure resistance have come to be used. .

In performing the chemical conversion treatment or alloy plating on the joint portion of the oil well pipe having such a high Cr content,
There is a passivation film containing Cr oxide on the surface of the joint part, which hinders the chemical conversion treatment or plating process to form a uniform film, which causes insufficient galling resistance. There is.

Therefore, when applying a surface treatment layer to the oil well pipe joint portion made of such a high Cr content alloy steel, the passivation film made of oxide on the surface of the Cr steel is removed by strong pickling, and activation is performed by a strike plating method or the like. Treated,
Furthermore, in order to improve the adhesion between the plating layer and Cr steel, a Ni plating layer is provided, and Cu plating or Z
A method of performing n plating or the like is usually adopted.

That is, in order to provide a surface treatment layer having excellent galling resistance of a seal portion due to contact between metals in an oil well pipe joint portion of a high Cr content steel alloy, it is extremely necessary to provide a high Cr content steel joint portion. Since it is necessary to form a surface-treated film having excellent adhesion, the complicated treatment process is required as described above, which is extremely disadvantageous in terms of productivity and cost. Further, in the conventional treatment method, since hydrogen is exposed to a hydrogen gas generating atmosphere in the activation treatment process by strong pickling and strike plating for removing oxides containing Cr, hydrogen intrusion into the high Cr alloy steel does not occur. It is unavoidable, and as a result, there is a problem that embrittlement of the steel pipe joint may occur.

Further, by the chemical conversion treatment with manganese phosphate, which has been conventionally performed to prevent the joint portion of a steel pipe from being baked and rusting, a film having good adhesion to a steel sheet containing a high Cr content of 10% or more. It is known that it is extremely difficult to uniformly generate.

[0009]

The problem to be solved by the present invention is to solve the above-mentioned conventional high Cr content steel containing 10% or more, and further to this, a high Cr content steel pipe pipe joint portion containing Ni, Mo or the like. In order to solve the problems caused by the above-mentioned conventional means, a high Cr content steel pipe joint portion having a surface-treated coating having excellent coating adhesion, coating strength and galling resistance, and a surface treatment method thereof are provided. It is a thing.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a coating layer for preventing seizure and rusting on a sliding portion of a joint of an oil country tubular good made of an alloy steel having a high Cr content with a Cr content of 10% or more. When performing the surface treatment for imparting, a nitriding treatment is performed as a base treatment to form a nitride layer, and then a chemical conversion treatment or metal plating is performed.

The processing of the present invention is performed by a joint portion used for connecting oil country tubular goods, that is, a joint portion formed of a threaded portion formed at the tip of the oil country tubular goods and a taper portion formed at the base thereof, and the threaded portion and the screw portion. It may be applied to both the threaded portion to be fitted and the joint member having a tapered portion at the tip thereof, or may be applied to either one of them, particularly to the joint member.

Therefore, the nitriding treatment, which is the essence of the present invention,
After removing oils and fats attached during the manufacturing process of the joint portion, it is performed using a molten salt bath containing a nitrogen compound.

That is, the nitriding layer for achieving the object of the present invention can be formed by the nitriding treatment by the heat treatment under the condition that the bath temperature of the molten salt bath is 400 to 700 ° C.
In this treatment, if the temperature of the molten salt bath is less than 400 ° C, it is difficult to form a uniform nitride layer on the surface of the high Cr content alloy steel, and if the treatment temperature exceeds 700 ° C,
Evaporation of the molten salt bath is remarkable, and it is industrially difficult to perform stable nitriding treatment. Therefore, the nitriding treatment in the present invention is performed by heat treatment in a molten salt bath having a molten salt bath temperature of 400 to 700 ° C, preferably 450 to 600 ° C.

Therefore, the thickness of the nitride layer needs to be 1 μm to 30 μm in order to achieve the above-mentioned object of the present invention. The thickness of the nitride layer is 1μ
When the amount is less than the above, the nitride layer has many defects and does not have a function as a base layer for stably obtaining a surface-treated layer having good adhesion. Further, if the thickness exceeds 30 μ, the function and effect of the underlayer are saturated and it is economically disadvantageous. Rather, this nitrided layer has a high hardness, and therefore, if the thickness thereof is excessively increased, the material of the high Cr content alloy steel deteriorates, which is not preferable. Therefore, the thickness of the nitride layer in the present invention is limited to 1 to 30 μm, preferably 5 to 20 μm.

The bath composition of the molten salt and the treatment time for obtaining the nitrided layer are not particularly limited. For example, as the treatment bath composition, (A) NaCN 25% KCN 10% NaCNO 25% A molten salt bath containing a nitrogen compound such as KCNO 10% Na ₂ CO ₃ 20% K ₂ CO ₃ 10% (B) NaCNO 10% KCNO 45% Na ₂ CO ₃ 10% K ₂ CO ₃ 35% is used. At the same time, the processing is carried out for the processing time selected in accordance with the applied condition or size of the joint portion, the processing temperature and the like.

In the present invention, prior to the nitriding treatment in the molten salt bath, the surface of the high Cr content alloy steel is cleaned beforehand by mechanical means such as grit blasting and glass bead shot. It is possible to shorten the formation time of the nitride layer.

Next, as the surface treatment after forming the underlayer made of the nitrided layer, chemical conversion treatment with manganese phosphate, which has been conventionally performed for improving the galling resistance of the steel pipe joint portion, Cu, Zn, Corresponding to the intended function of the metal plating of Sn, Ni, etc., they are arbitrarily applied. That is, the method for applying each of these surface treatment layers to the underlying layer made of a nitride layer is not specified at all, and a known metal-plating method such as a manganese phosphate treatment method and an electroplating method is applied.

The thickness of this surface treatment layer is as follows.
Generally, a thickness of 5 μ to 25 μ is selected for the chemical conversion treatment film, and a thickness of 7.5 μ or more and 40 μ or less is selected for the metal plating film. Further, the metal plating film may be provided as a two-layer film instead of a regular layer.

After the underlayer made of the nitride layer of the present invention is applied, the joint part made of alloy steel having a high Cr content is treated by the conventional treatment method in which the underlayer is not removed. There is no problem even if the surface treatment film layer is applied under the conditions.

As described above, in the present invention, high Cr
Due to the effect of forming an underlayer consisting of a nitriding layer on the surface of the alloy steel containing, it is easy to form the above-mentioned various surface-treated coatings with excellent adhesion and strength of the coating, so it has excellent galling resistance. You can get the joint of the steel pipe.

[0021]

A steel pipe joint manufactured from a Cr-containing steel containing 10% or more of Cr, and a high Cr alloy steel in which Ni, Mo, etc. are added to the steel pipe joint is subjected to nitriding treatment in a molten salt bath.
The passivation film containing Cr oxide on the surface is melted and removed, and the Cr removal reaction proceeds, and the surface layer is a nitride layer containing iron nitride as a main component, and the inner layer is composed of iron nitride and chromium nitride. A nitride layer is formed.

The iron nitride layer formed on this surface has a very general surface cleaning and cleaning property as compared with the surface of a high Cr content alloy steel in which a passivation film containing Cr oxide is easily formed. A chemical conversion treatment film or Cu, Zn, Sn, Ni which has excellent adhesion and film strength easily by activation treatment.
Such a plated film is uniformly formed. As a result, the galling resistance of the steel pipe joint is significantly improved. In addition, since the nitrided layer formed on the steel surface has excellent wear resistance, the effect of preventing seizure resistance of the seal part due to contact between the metal parts of the steel pipe joint part is effective even after the surface treatment film is consumed. Add more to the part.

[0023]

[Example] Cr content of each composition shown in Table 1 is 10
% Of high Cr content steel pipe joints made of steel,
That is, the coupling 1 (joint member) and the pin 2 shown in FIG.
With respect to the (steel pipe tip joint portion), only the coupling 1 or the coupling 1 and the pin 2 are subjected to the nitriding treatment according to the method of the present invention with respect to the screw portion 3 and the metal-metal seal portion 4 constituting each joint portion. A steel pipe joint having a base layer and a surface treatment coating layer was prepared and subjected to an evaluation test.

[0024]

[Table 1] In the evaluation test, the coupling material and the pin 2 are fitted to each other as shown in FIG. After that, it is made up by a tightening machine with a torque of 1230 kg · m, and thereby slides while applying a high surface pressure to the screw portion 3 and the metal-metal seal portion 4 of the coupling 1 and the pin 2 of FIG. Let

After that, the coupling 1 and the pin 2 are rotated in the opposite directions at the time of make-up by the tightening machine to break out.

After breaking out, the coupling 1
Also, the threaded portion 3 and the sealed portion 4 of the pin 2 are observed, and the presence or absence of peeling of the surface treatment film and galling is investigated.

If there is no peeling or galling or if it is mild, the coupling 1 and the pin 2 are fitted again, and make-up is performed under the same conditions by the above-mentioned tightening machine.

Example 1 The tip of a coupling 1 having an inner diameter of 4.5 inches and a pin 2 having a size corresponding to the coupling 1 made of the test steel A was heated in the atmosphere at a temperature of 250 ° C. for 10 minutes, After removing oil and fat on the surface, 20% NaCN-15% KCN-17.5
% NaCNO-17.5% KCNO-10 % Na 2 CO
In ₃ -20% K ₂ CO ₃ made of a molten salt bath, 450
A heating nitriding treatment was performed at 30 ° C. for 30 minutes, and the mixture was cooled in an oil bath. After degreasing the nitriding machine by solvent degreasing, 0.0
A weak alkaline aqueous solution containing 5% of Ti colloid performed at room temperature for 10 seconds immersion, F ^- concentration 140 containing
Using a g / l Mn phosphate-based chemical conversion treatment bath at 95 ° C.-10
A chemical conversion treatment was performed for a minute to prepare an evaluation machine according to the method of the present invention. The treatment of the present invention was applied to the screw portion 3 and the metal seal portion 4, respectively.

A nitriding layer 7.5μ and a Mn-phosphate treated coating 14μ were obtained.

Compound grease is applied to the metal seal portion 4 of the coupling 1 and the pin 2, and a surface pressure of 2000 kg / cm ² is applied to the seal portion 4 while repeating make-up and breakout of the joint portion. I did a test. As a result of repeating the test 10 times, baking of the seal portion and generation of rust were extremely small, and the result was very good.

Comparative Example 1 The tip of the coupling 1 and the pin 2 having an inner diameter of 4.5 inches prepared from the test steel A was degreased with a hydrogen degreasing agent,
Then, after pickling with 10% H ₂ SO ₄ at a temperature of 60 ° C. for 60 seconds, Mn phosphate was carried out under the same conditions as in Comparative Example 1,
It was set as Comparative Example 1.

It was impossible to form a Mn phosphate treated film.

Example 2 Coupling 1 having an inner diameter of 5.5 inches made of test steel C was degreased with a hydrogen degreasing agent to obtain (15% Na
CNO-40% KCNO-10% Na 2 CO 3 -35%
In a K ₂ CO ₃ ) system bath, a heat nitriding treatment was performed at 590 ° C. for 30 minutes, and the mixture was cooled in a vacuum atmosphere. The nitriding machine was degreased with a solvent, pickled in a 20% H ₂ SO ₄ aqueous solution at 50 ° C. for 20 seconds, and a current density of 7.
A Zn plating layer was provided on the screw portion 3 and the metal seal portion 4 by electrolytic treatment (50 ° C.) at 5 A / dm ² for 380 seconds to prepare an evaluation machine according to the method of the present invention.

The nitriding layer 25.5 μ and the Zn plating layer 12
got μ.

In the same manner as in Example 1, compound grease was applied, and while applying a surface pressure of 2500 kg / cm ² to the seal portion 4, the joint portion was repeatedly tested for make-up and breakout. The test was repeated 10 times, and the result was that the sealing part was extremely free from seizure and rusting, and was very good.

When making up,
A lubricant equivalent to API Bu1 5A2 Sect2 is applied to the screw portion 3 and the seal portion 4 of the coupling 1 and the pin 2, and the pin is rotated at a speed of 1 to 3 rpm with respect to the coupling for make-up and breakout. It was

COMPARATIVE EXAMPLE 2 A coupling 1 having an inner diameter of 7 inches, which was prepared by using the steel C to be tested, was degreased with a solvent, and then in a 20% H ₂ SO ₄ aqueous solution at 50 ° C.
A pickling treatment for 60 seconds was performed, and under the same conditions as in Example 2, Z
An n-plated layer was provided on the screw portion 3 and the metal seal portion 4 to make Comparative Example 2.

A Zn plated layer 12μ was obtained.

As a result of performing an evaluation test under the same conditions as in Example 2, the Zn plating layer was peeled off in the fourth test repeatedly, and baking and smashing were remarkably generated in the fifth test.

Example 3 A coupling 1 having an inner diameter of 7 inches prepared by using the test steel B was degreased with a solvent, and then (15% NaCN-20% KCN was used.
-15% NaCNO-10% KCNO- 20% Na 2 C
In _{O 3 -10% K 2 CO 3} ) based bath, 550 ° C., subjected to heat nitriding treatment for 20 minutes, then cooled in an oil bath. The nitriding machine was subjected to solvent degreasing, pickling treatment in a 15% H ₂ SO ₄ aqueous solution at room temperature for 10 seconds, and then an organic acid-based Sn plating bath (trade name; Ronastan bath) was used to obtain a current density of 10 A. /
An Sn plating layer was provided on the methane seal portion 4 by electrolytic treatment (room temperature) at dm ² for 300 seconds to prepare an evaluation machine.

A nitriding layer 15μ and an Sn plating layer 15μ were obtained.

In the same manner as in Example 1, compound grease was applied, and while applying a surface pressure of 3000 kg / cm ² to the seal portion 4, the joint portion was repeatedly tested for make-up and breakout. The test was repeated 10 times, and the result was that the sealing part was extremely free from seizure and rusting, and was very good.

Comparative Example 3 Coupling 1 having an inner diameter of 7 inches prepared using test steel B was degreased with a solvent and then pickled in a 15% H ₂ SO ₄ aqueous solution for 10 seconds. A Sn plating layer was provided on the metal seal portion 4 under the conditions of, and Comparative Example 3 was obtained.

An Sn plating layer of 15μ was obtained.

For comparison, the coupling 1 or the threaded portion 3 of the coupling 1 and the pin 2 and the metal-metal seal portion 4 were carried out without providing an underlayer by the nitriding treatment in the method of the present invention. A steel pipe joint provided with a surface treatment coating layer was prepared under the same conditions as in the example, and the galling resistance was investigated by the same evaluation method as above.

As a result of performing an evaluation test under the same conditions as in Example 3, peeling of the Sn plating layer occurred in the second repeated test, and seizure and rusting occurred remarkably in the seal portion 4 in the third test.

Example 4 Coupling 1 having an inner diameter of 7 inches prepared from test steel B was solvent degreased and shot with glass beads (particle size # 10).
0, pressure 5 hgf / cm ² , 60 seconds) after pretreatment,
(25% NaCN-10% KCN-25% NaCNO-
_{10% KCNO-20% Na 2} CO 3 -10% K 2 CO
₃ ) Heat nitriding treatment was performed at 570 ° C. for 15 minutes in a molten salt bath of the system and cooled in an oil bath. The nitriding machine was degreased with a hydrogen degreasing agent, followed by pickling in a 10% H ₂ SO ₄ aqueous solution (room temperature-30 seconds), and then a base Ni plating layer and a Cu sulfate plating bath using a modified Watts bath. Cu plating was applied to each of the screw portion 3 and the metal seal portion 4 to prepare an evaluator according to the method of the present invention. Note that Ni
The plating was performed at a current density of 5 A / dm ² for 60 seconds, and the Cu plating was performed at a room temperature of 5 A / dm ² for 975 seconds.

Nitriding layer 10μ and Ni undercoat layer 1μ
And a Cu plating layer 18μ were obtained.

By the evaluation test, the occurrence of goring (baking and rustling) in the metal-metal seal portion 4 and the number of repetitions of make-up and break-out were investigated.

In the same manner as in Example 1, while applying compound grease and applying a surface pressure of 3000 kg / cm ² to the seal portion 4, the joint portion was repeatedly tested for make-up and breakout. The test was repeated 10 times, and the result was that the sealing part was extremely free from seizure and rusting, and was very good.

Comparative Example 4 Similarly, the coupling 1 having an inner diameter of 7 inches prepared by using the sample steel B was degreased with a solvent, and after pickling with 10% H ₂ SO ₄ at room temperature for 30 seconds, the same as Example 4. Under the conditions of Ni
The plated layer and the Cu plated layer are connected to the screw part 3 and the metal seal part 4.
And provided as Comparative Example 4.

Underlying Ni plating layer 1 μ and Cu plating layer 18
got μ.

As a result of conducting an evaluation test under the same conditions as in Example 4, peeling of the Cu plating layer occurred in the sixth test, and seizure resistance and rusting occurred remarkably in the seal part in the seventh test.

From these results, in the high Cr content steel pipe joint portion provided with the underlayer and the various surface treatment layers by the nitriding treatment based on the method of the present invention, the seizure resistance of the metal-metal seal portion is improved and crease resistance is improved. Occurrence is unlikely to occur, and the galling resistance is remarkably excellent.

[0055]

EFFECTS OF THE INVENTION By the method for forming a surface treatment film on a steel pipe joint portion made of a high Cr content alloy steel according to the present invention, a nitriding film formed on the surface of the steel at the same time as the removal of the Cr oxide-containing passivation film. Due to the effect of the underlying layer containing an iron layer as a main component, a uniform chemical conversion treatment film or metal plating film having excellent film adhesion and film strength can be easily formed.
It is possible to improve the baking resistance in the steel pipe joint portion and prevent the occurrence of rust.

That is, by applying the treatment method of the present invention, it becomes possible to manufacture a steel pipe joint portion made of a high Cr content alloy steel having excellent galling resistance.

[Brief description of drawings]

FIG. 1 shows a joint constituent member to which the present invention is applied.

FIG. 2 shows an assembled structure of each joint component.

[Explanation of symbols]

1 Coupling 2 Steel pipe tip 3 Screw 4 Metal-metal seal

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[Procedure amendment]

[Submission date] September 5, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Detailed explanation of the invention

[Correction method] Change

[Correction content]

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coupling joint for connecting oil country tubular goods used for crude oil or natural gas mining.

[0002]

2. Description of the Related Art The joint portion used to connect oil country tubular goods is
Rotating and tightening the joint part consisting of the screw part formed at the tip of the oil country tubular good and the taper part formed at the base of the oil well pipe, the screw part that engages with this screw part, and the joint member that forms the tapered part at the tip. A high surface pressure is generated on the contact surfaces of the two taper portions to form a metal-metal seal portion to maintain a perfect sealing property.

However, since this joint is repeatedly slid at a high surface pressure at the time of make-up and break-out, seizure and rustling occur with the pipe material,
This hinders the sealing property. For this reason, for example, as described in Japanese Patent Publication No. 12995/1989, generally, a chemical conversion film is formed on the screw portion and the metal-metal seal portion by various chemical conversion treatments, or Cu, Z.
Soft metals such as n and Pb, or Fe, Ni, Co,
Plating of Pt, etc. is applied to prevent seizure and rusting. That is, the galling between the joint portion of the oil country tubular good and the joint member is prevented.

On the other hand, in recent years, high pressure steel oil well pipes made of high alloy steel in which 10% or more of high Cr content steel and further Ni, Mo, etc. are added to increase pressure resistance have come to be used. .

In performing the chemical conversion treatment or alloy plating on the joint portion of the oil well pipe having such a high Cr content,
There is a passivation film containing Cr oxide on the surface of the joint part, which hinders the chemical conversion treatment or plating process to form a uniform film, which causes insufficient galling resistance. There is.

Therefore, when applying a surface treatment layer to the oil well pipe joint portion made of such a high Cr content alloy steel, the passivation film made of oxide on the surface of the Cr steel is removed by strong pickling, and activation is performed by a strike plating method or the like. Treated,
Furthermore, in order to improve the adhesion between the plating layer and Cr steel, a Ni plating layer is provided, and Cu plating or Z
A method of performing n plating or the like is usually adopted.

That is, in order to provide a surface treatment layer having excellent galling resistance of a seal portion due to contact between metals in an oil well pipe joint portion of a high Cr content steel alloy, it is extremely necessary to provide a high Cr content steel joint portion. Since it is necessary to form a surface-treated film having excellent adhesion, the complicated treatment process is required as described above, which is extremely disadvantageous in terms of productivity and cost. Further, in the conventional treatment method, since hydrogen is exposed to a hydrogen gas generating atmosphere in the activation treatment process by strong pickling and strike plating for removing oxides containing Cr, hydrogen intrusion into the high Cr alloy steel does not occur. It is unavoidable, and as a result, there is a problem that embrittlement of the steel pipe joint may occur.

Further, by the chemical conversion treatment with manganese phosphate, which has been conventionally performed to prevent seizure of the joint portion of a steel pipe and generation of rusting, good adhesion is obtained with respect to the steel plate containing high Cr of 10% or more. It is known that it is extremely difficult to form a film uniformly.

[0009]

The problem to be solved by the present invention is to solve the above-mentioned conventional high Cr content steel containing 10% or more, and further to this, a high Cr content steel pipe pipe joint portion containing Ni, Mo or the like. In order to solve the problems caused by the above-mentioned conventional means, a high Cr content steel pipe joint portion having a surface-treated coating having excellent coating adhesion, coating strength and galling resistance, and a surface treatment method thereof are provided. It is a thing.

[0010]

DISCLOSURE OF THE INVENTION The present invention provides a coating layer for preventing seizure and rusting on a sliding portion of a joint of an oil country tubular good made of an alloy steel having a high Cr content with a Cr content of 10% or more. When performing the surface treatment for imparting, a nitriding treatment is performed as a base treatment to form a nitride layer, and then a chemical conversion treatment or metal plating is performed.

The processing of the present invention is performed by a joint portion used for connecting oil country tubular goods, that is, a joint portion formed of a threaded portion formed at the tip of the oil country tubular goods and a taper portion formed at the base thereof, and the threaded portion and the screw portion. It may be applied to both the threaded portion to be fitted and the joint member having a tapered portion at the tip thereof, or may be applied to either one of them, particularly to the joint member.

Therefore, the nitriding treatment, which is the essence of the present invention,
After removing oils and fats attached during the manufacturing process of the joint portion, it is performed using a molten salt bath containing a nitrogen compound.

That is, the nitriding layer for achieving the object of the present invention can be formed by the nitriding treatment by the heat treatment under the condition that the bath temperature of the molten salt bath is 400 to 700 ° C.
In this treatment, if the temperature of the molten salt bath is less than 400 ° C, it is difficult to form a uniform nitride layer on the surface of the high Cr content alloy steel, and if the treatment temperature exceeds 700 ° C,
Evaporation of the molten salt bath is remarkable, and it is industrially difficult to perform stable nitriding treatment. Therefore, the nitriding treatment in the present invention is performed by heat treatment in a molten salt bath having a molten salt bath temperature of 400 to 700 ° C, preferably 450 to 600 ° C.

Therefore, the thickness of the nitride layer needs to be 1 μm to 30 μm in order to achieve the above-mentioned object of the present invention. The thickness of the nitride layer is 1μ
When the amount is less than the above, the nitride layer has many defects and does not have a function as a base layer for stably obtaining a surface-treated layer having good adhesion. Further, if the thickness exceeds 30 μ, the function and effect of the underlayer are saturated and it is economically disadvantageous. Rather, this nitrided layer has a high hardness, and therefore, if the thickness thereof is excessively increased, the material of the high Cr content alloy steel deteriorates, which is not preferable. Therefore, the thickness of the nitride layer in the present invention is limited to 1 to 30 μ thickness, preferably 5 to 20 μ thickness.

The bath composition of the molten salt and the treatment time for obtaining the nitrided layer are not particularly limited. For example, as the treatment bath composition, (A) NaCN 25% KCN 10% NaCNO 25% A molten salt bath containing a nitrogen compound such as KCNO 10% Na ₂ CO ₃ 20% K ₂ CO ₃ 10% (B) NaCNO 10% KCNO 45% Na ₂ CO ₃ 10% K ₂ CO ₃ 35% is used. At the same time, the processing is carried out for the processing time selected in accordance with the applied condition or size of the joint portion, the processing temperature and the like.

In the present invention, prior to the nitriding treatment in the molten salt bath, the surface of the high Cr content alloy steel is cleaned beforehand by mechanical means such as grit blasting and glass bead shot. It is possible to shorten the formation time of the nitride layer.

Next, as the surface treatment after forming the underlayer made of the nitrided layer, chemical conversion treatment with manganese phosphate, which has been conventionally performed for improving the galling resistance of the steel pipe joint portion, Cu, Zn, Corresponding to the intended function of the metal plating of Sn, Ni, etc., they are arbitrarily applied. That is, the method for applying each of these surface treatment layers to the underlying layer made of a nitride layer is not specified at all, and a known metal-plating method such as a manganese phosphate treatment method and an electroplating method is applied.

The thickness of this surface treatment layer is as follows.
Generally, a thickness of 5 μ to 25 μ is selected for the chemical conversion treatment film, and a thickness of 7.5 μ or more and 40 μ or less is selected for the metal plating film. Further, the metal plating film may be provided as a two-layer film instead of a single layer.

After the underlayer made of the nitride layer of the present invention is applied, the joint part made of alloy steel having a high Cr content is treated by the conventional treatment method in which the underlayer is not removed. There is no problem even if the surface treatment film layer is applied under the conditions.

As described above, in the present invention, high Cr
Due to the effect of forming an underlayer consisting of a nitriding layer on the surface of the alloy steel containing, it is easy to form the above-mentioned various surface-treated coatings with excellent adhesion and strength of the coating, so it has excellent galling resistance. You can get the joint of the steel pipe.

[0021]

A steel pipe joint manufactured from a Cr-containing steel containing 10% or more of Cr, and a high Cr alloy steel in which Ni, Mo, etc. are added to the steel pipe joint is subjected to nitriding treatment in a molten salt bath.
The passivation film containing Cr oxide on the surface is melted and removed, and the Cr removal reaction proceeds, and the surface layer is a nitride layer containing iron nitride as a main component, and the inner layer is composed of iron nitride and chromium nitride. A nitride layer is formed.

The iron nitride layer formed on this surface is a very general surface cleaning and activation as compared with the surface of a high Cr alloy steel in which a passivation film containing Cr oxide is easily formed. By the chemical treatment, a chemical conversion treatment film or a plating treatment film such as Cu, Zn, Sn, and Ni which is excellent in film adhesion and film strength can be easily and uniformly formed. as a result,
The galling resistance of the steel pipe joint is significantly improved. In addition, since the nitrided layer formed on the steel surface has excellent wear resistance, the effect of preventing seizure of the seal portion due to contact between the metal parts of the steel pipe joint part is maintained even after the surface treatment film is consumed. To give more.

[0023]

[Example] Cr content of each composition shown in Table 1 is 10
% Of high Cr content steel pipe joints made of steel,
That is, the coupling 1 (joint member) and the pin 2 shown in FIG.
With respect to the (steel pipe tip joint portion), only the coupling 1 or the coupling 1 and the pin 2 are subjected to the nitriding treatment according to the method of the present invention with respect to the screw portion 3 and the metal-metal seal portion 4 constituting each joint portion. A steel pipe joint having a base layer and a surface treatment coating layer was prepared and subjected to an evaluation test.

[0024]

[Table l] In the evaluation test, the coupling material and the pin 2 are fitted to each other as shown in FIG. After that, a tightening machine is used to make up a predetermined torque value according to the coupling diameter, so that the coupling 1 shown in FIG.
Then, the threaded portion 3 and the metal-metal seal portion 4 of the pin 2 are slid while applying a high surface pressure.

After that, the coupling 1 and the pin 2 are rotated in the direction opposite to that at the time of make-up by the tightening machine to break out.

After breaking out, the coupling 1
Also, the threaded portion 3 and the seal portion 4 of the pin 2 are observed to investigate the peeling state of the surface-treated film and the occurrence of galling.

Is there no peeling of the coating or galling?
Alternatively, in the case of a slight case, the coupling 1 and the pin 2 are fitted again, and make-up is performed under the same conditions by the above-mentioned tightening machine.

As described above, the evaluation material according to the method of the present invention was evaluated by repeating the above test up to 10 times until peeling of the coating or galling occurred.

When making up,
A lubricant (compound grease) equivalent to API Bul 5A2 Sect2 is applied to the screw portion 3 and the seal portion 4 of the coupling 1 and the pin 2, and the makeup,
Breakout pin 1-3r against coupling
It was rotated at a speed of pm.

For comparison, the coupling 1, or the screw portion 3 and the metal seal portion 4 of the coupling 1 and the pin 2 are not provided with an undertreatment layer by the nitriding treatment in the method of the present invention. A steel pipe joint provided with a surface treatment coating layer under the same conditions as in the example was prepared as a comparative material and subjected to the same evaluation test as above.

Example 1 The tip of a coupling 1 having an inner diameter of 4.5 inches and a pin 2 having a size corresponding to the coupling 1 made of the test steel A was heated at a temperature of 250 ° C. for 10 minutes in the atmosphere, After removing oil and fat on the surface, 20% NaCN-15% KCN-17.5
% NaCNO-17.5% KCNO-10% Na ₂ CO
In ₃ -20% K ₂ CO ₃ made of a molten salt bath, 450
A heating nitriding treatment was performed at 30 ° C. for 30 minutes, and the mixture was cooled in an oil bath. After degreasing the nitriding material by solvent degreasing, 0.0
Performed at room temperature for 10 seconds immersed in a weak alkaline aqueous solution containing 5% of Ti colloid, F ^- containing concentration 14
Using a 0 g / l Mn phosphate-based chemical conversion treatment bath at 95 ° C. −1
A chemical conversion treatment was performed for 0 minutes to prepare an evaluation material according to the method of the present invention. The treatment of the present invention is applied to the threaded portion 3 and the metal seal portion 4 at the tip of the coupling 1 and the pin 2, respectively, and the nitriding layer 7.5 μ and Mn phosphate are applied to them.
A two-layer coating consisting of 14 μm of the treated coating layer was formed.

Apply compound grease to the metal seal portion 4 of the coupling 1 and the pin 2, and apply a torque value of 64
Make-up was performed under the condition of 0 kg · m, and the joint part was repeatedly tested for make-up and break-out. As a result of repeating the test 10 times, although the surface of the Mn phosphate coating layer was slightly peeled off, the occurrence of galling (sealing of the seal portion, generation of rustle) was extremely small, which was very good.

COMPARATIVE EXAMPLE 1 The tip of the coupling 1 and pin 2 having an inner diameter of 4.5 inches prepared from the test steel A was degreased with an aqueous degreasing agent,
Then, after pickling with 10% H ₂ SO ₄ at a temperature of 60 ° C. for 60 seconds, Mn phosphate treatment was performed under the same conditions as in Comparative Example 1 to obtain Comparative Example 1.

However, almost no Mn phosphate-treated film was formed, and as a result of performing an evaluation test under the same conditions as in Example 1, seizure and rusting, ie, galling remarkably occurred in the second repeated test. did.

Example 2 Coupling 1 having an inner diameter of 5.5 inches prepared from test steel C was degreased with an aqueous degreasing agent to obtain (15% Na
CNO-40% KCNO-10% Na 2 CO 3 -35%
In a K ₂ CO ₃ ) system bath, heat nitriding treatment was performed at 590 ° C. for 30 minutes, and cooling was performed in a vacuum atmosphere. The nitriding material was solvent-degreased, pickled in a 20% H ₂ SO ₄ aqueous solution at 50 ° C. for 20 seconds, and then a current density of 7.
The Zn plating layer was provided on the screw portion 3 and the metal seal portion 4 of the coupling 1 by electrolytic treatment (50 ° C.) at 5 A / dm ² for 380 seconds, and the nitriding treatment layer 2 was formed by the method of the present invention.
An evaluation material having 5.5 μ and a Zn plating layer 12 μ was formed.

Compound grease was applied in the same manner as in Example 1 to make up under the condition of a torque value of 770 kg · m, and the joint part was repeatedly tested for make up and breakout. As a result of repeating the test 10 times, only a very small amount of the surface of the Zn plating layer was peeled off, the seizure of the seal portion and the generation of rusting were extremely small, and the galling resistance was very good.

COMPARATIVE EXAMPLE 2 A coupling 1 having an inner diameter of 7 inches, which was prepared by using the steel C to be tested, was degreased with a solvent, and then in a 20% H ₂ SO ₄ solution at 50 ° C.
A pickling treatment was performed for 60 seconds, and a Zn plating layer having a plating thickness of 12 μ was provided on the screw part 3 and the metal seal part 4 of the coupling 1 under the same conditions as in Example 2 to make Comparative Example 2.

As a result of performing an evaluation test under the same conditions as in Example 2, the Zn plating layer was peeled off at the fourth test of the repeated test, and seizure and musing, that is, galling remarkably occurred at the fifth test.

Example 3 A coupling 1 having an inner diameter of 7 inches prepared by using a test steel B was degreased with a solvent, and then (15% NaCN-20% KCN was used.
-15% NaCNO-10% KCNO- 20% Na 2 C
In _{O 3 -10% K 2 CO 3} ) based bath, 550 ° C., subjected to heat nitriding treatment for 20 minutes, then cooled in an oil bath. The nitriding material was subjected to solvent degreasing, pickling treatment in a 15% H ₂ SO ₄ aqueous solution at room temperature for 10 seconds, and then an organic acid-based Sn plating bath (trade name: Ronastan bath) was used to obtain a current density I0A.
A Sn plating layer was provided on the screw portion 3 and the metal seal portion 4 of the coupling 1 by electrolytic treatment (room temperature) for 300 seconds at / dm ² to form a two-layer coating of the nitriding layer 15μ and the Sn plating layer 15μ. An evaluation material was created. , Compound grease was applied in the same manner as in Example 1 to obtain a torque value of 126.
Make-up was performed under the condition of 0 kg · m, and the joint part was repeatedly tested for make-up and break-out. The result of repeating the test 10 times was Sn.
Only a small amount of the surface of the plating layer was peeled off, and the seizure and rusting of the seal portion were extremely small, that is, the galling was extremely small and good.

Comparative Example 3 Coupling 1 having an inner diameter of 7 inches prepared using test steel B was degreased with a solvent and then pickled in a 15% H ₂ SO ₄ aqueous solution for 10 seconds. Under the above conditions, a Sn plating layer having a plating thickness of 15 μ was provided on the metal seal portion 4 of the coupling 1 to obtain Comparative Example 3.

As a result of performing an evaluation test under the same conditions as in Example 3, peeling of the Sn plating layer occurred in the second repeated test, and at the third test, galling (seizure and rust) remarkably occurred in the seal portion 4. did.

Example 4 Coupling 1 having an inner diameter of 7 inches prepared using test steel B was degreased with a solvent and shot with glass beads (particle size # 10).
0, pressure 5 hgf / cm ² , 60 seconds) after pretreatment,
(25% NaCN-10% KCN-25% NaCNO-
10% KCNO-20% Na ₂ CO ₃ -10% K ₂ CO
₃ ) Heat nitriding treatment was performed at 570 ° C. for 15 minutes in a molten salt bath of the system and cooled in an oil bath. The nitriding material is degreased with an aqueous degreasing agent, pickled in a 10% H ₂ SO ₄ aqueous solution (room temperature-30 seconds), and then a base Ni plating layer and a Cu sulfate plating bath using a modified Watt's bath are used. Cu plating by means of threading 3 and metal seal 4 of coupling 1
And an evaluation material by the method of the present invention was prepared. For Ni plating, the current density was 5 A / dm ² for 60 seconds, and for Cu plating, the current density was 5 A / dm ² for 975 seconds.
Electrolysis treatment was performed at room temperature.

By this treatment, an evaluation material consisting of a nitriding layer 10 μ, a Ni undercoat layer 1 μ, and a Cu plating layer 18 μ was prepared.

Compound grease was applied in the same manner as in Example 1 and make-up was performed under the condition of a torque value of 1260 kg · m, and the joint part was repeatedly tested for make-up and breakout. As a result of repeating the test 10 times, only a small amount of the surface of the Cu plating layer was peeled off, and the occurrence of seizure and rustle was extremely small.
No occurrence of goring was observed.

Comparative Example 4 Similarly, the coupling 1 having an inner diameter of 7 inches prepared by using the sample steel B was degreased with a solvent and after pickling with 10% H ₂ SO ₄ at room temperature for 30 seconds, the same as Example 4. Under the conditions of Ni
A plating layer 1 μ and a Cu plating layer 18 μ were provided on the screw portion 3 and the metal seal portion 4 of the coupling 1, respectively, and a comparative example 4
And

An evaluation test was conducted under the same conditions as in Example 4. As a result, the Cu plating layer was peeled off at the sixth test repeatedly, and baking and rusting occurred remarkably at the seal part at the seventh test, and the galling resistance was deteriorated. .

From these results, in the high Cr content steel pipe joint portion which is provided with the underlayer and various surface treatment layers by the nitriding treatment based on the method of the present invention, the seizure resistance of the metal-metal seal portion is improved and crease resistance is reduced. Occurrence is unlikely to occur, and the galling resistance is remarkably excellent.

[0048]

EFFECTS OF THE INVENTION By the method for forming a surface treatment film on a steel pipe joint portion made of a high Cr content alloy steel according to the present invention, a nitriding film formed on the surface of the steel at the same time as the removal of the Cr oxide-containing passivation film. Due to the effect of the underlying layer containing an iron layer as a main component, a uniform chemical conversion treatment film or metal plating film having excellent film adhesion and film strength can be easily formed.
It is possible to improve seizure resistance in the steel pipe joint portion and prevent the occurrence of rust.

That is, by applying the treatment method of the present invention, it becomes possible to manufacture a steel pipe joint portion made of a high Cr content alloy steel having a very excellent galling resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Haruyuki Nagayoshi, Inventor Haruyuki Nagayoshi 1-1, Tobata-cho, Tobata-ku, Kitakyushu, Fukuoka (72) Innovator Toshiharu Sakamoto, Tobata-ku, Kitakyushu, Kitakyushu, Fukuoka Town No. 1-1 Shin Nippon Steel Co., Ltd. Yawata Works (72) Inventor Seijun Higuchi 1-15-1, Nihonbashi, Chuo-ku, Tokyo Inside Parkerizing Co., Ltd. Japan (72) Ryusuke Inoue Chuo-ku, Tokyo Nihonbashi 1-151-1 Nihon Parkerizing Co., Ltd. (72) Inventor Tsuneo Nakaizumi 1-151-1 Nihonbashi, Chuo-ku, Tokyo Nihon Parkerizing Co., Ltd.

Claims (2)

[Claims] 1. A joint structure of an oil country tubular good made of a high Cr content alloy steel having a Cr content of 10% or more, wherein a metal-sealing portion including at least a screw portion has an iron nitride underlayer,
Oil well pipe fittings that have a seizure prevention film formed on the underlying layer. 2. An oil well in which a joint portion of an oil well pipe made of an alloy steel having a high Cr content of 10% or more with a Cr content is immersed in a nitriding molten bath and then surface-treated to prevent seizure. Pipe fittings and their surface treatment methods.