JPH10267175A - Screw joint for steel pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a screw joint which fits a box having a male screw and a female screw which correspond to inner and outer sides of a pipe, a sealing face, and a shoulder face so as to expand a proper torque range by forming solid lubricant on a metal contact face and forming a thickness of solid lubricant film of a screw load flank face to a specific value. SOLUTION: As the most preferable screw shape in the case where solid lubricant is used, a coupling crest face 11 is in contact with a load flank face 12, a stapping flank face 13 and a coupling route are not in contact with a pin crest 14, and lubrication treatment is applied to a coupling female screw side. A solid lubrication film on a shoulder face and the screw load flank face 12 is formed to be extremely thin so that its thickness is 5 μm or less, or a solid lubrication film is formed on a metal contact face other than the screw load flank face 12 and the shoulder face. Consequently, it is possible to obtain a pipe screw joint which can improve final torque resistance, can expand a scope of proper tightening torque, and is very excellent industrially.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a threaded joint for oil country tubular goods in which a solid lubricant is used for a specific part of a joint component.

[0002]

2. Description of the Related Art Generally, oil country tubular goods such as casings and tubing used for oil drilling are fastened by screw joints. Recently, oil wells and gas wells have been deepened, and premium joints having a metal contact portion in particular in terms of sealing properties have been actively used. In addition, horizontal wells aimed at improving the efficiency of excavating crude oil have also become extremely prosperous, and in such oil wells, the torsional strength of joints has been required more than ever before.

On the other hand, it has been pointed out that heavy metal powder contained in compound grease used when fastening oil country tubular goods threaded joints leads to environmental pollution in the environment. Particularly, in the North Sea and Alaska, metal powder is contained in compound in the compound. Grease that does not contain glycerol has been used. Further, it is necessary to warm the compand grease when it is used in extreme cold, and it is desired that the grease application and cleaning actions themselves be omitted from the viewpoint of work efficiency. In addition, the adverse effect of grease on the performance in use has been pointed out, and measures have been taken in designing the joint (Japanese Patent Laid-Open No.
JP-A-3-21048).

[0004]

In order to drastically solve such a problem, Japanese Patent Application Laid-Open Nos. 61-136087 and 8-103724 have been proposed. The primary purpose of compand grease is to prevent seizure during fastening of the joint, and in that sense, the solid lubricant exhibited performance equal to or higher than compand grease. However, the solid lubricant has a new problem that the fastening torque varies.

[0005]

Means for Solving the Problems In order to solve the problems with the solid lubricant as described above, the inventors have intensively developed and as a result, the metal contact portion using the solid lubricant instead of the compound grease, the shoulder, and the like. An object of the present invention is to provide a threaded joint for oil country tubular goods having a portion, with the aim of improving final torque resistance and expanding an appropriate fastening torque range. The gist of the invention is as follows: (1) A threaded joint which fits a pin having a male screw, a sealing surface, and a shoulder surface on the outside of a tube and a female screw, a sealing surface, and a shoulder having a corresponding pin on the inside of the tube. 3. The threaded joint for steel pipe according to claim 1, wherein a solid lubricant is formed on the metal contact surface, and a thickness of the solid lubricant film on the screw load flank surface is reduced to 5 μm or less.

(2) In a screw joint in which a pin having a male screw, a sealing surface, and a shoulder surface on the outside of a tube and a female screw, sealing surface, and a shoulder surface corresponding to the pin on the inside of the tube are fitted, a metal contact surface is provided. A threaded joint for steel pipes, wherein a solid lubricant is formed, and the thickness of the solid lubricant film on the screw load flank surface and the shoulder surface is reduced to 5 μm or less.

(3) In a screw joint in which a pin having a male screw, a sealing surface, and a shoulder surface on the outside of the tube and a female screw, a sealing surface, and a shoulder surface corresponding to the pin on the inside of the tube are fitted, a screw load flank surface is provided. A threaded joint for steel pipes wherein a solid lubricant film is formed on a metal contact surface other than the metal contact surface.

(4) In a screw joint in which a pin having a male screw, a seal surface, and a shoulder surface on the outside of the tube and a female screw, a seal surface, and a shoulder having a corresponding pin on the inside of the tube are fitted, a screw load flank surface is provided. And a threaded joint for steel pipes, wherein a solid lubricant film is formed on a metal contact surface other than the shoulder surface.

Hereinafter, the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram showing a joint fastening state between a make-up torque and a turn number curve during the joint fastening. As shown in this figure, a torque is generated by the frictional resistance of the screw portion or the seal portion according to the fitting of the joint, and the torque rapidly increases simultaneously with the contact with the shoulder portion. The torque at this time is called a shoulder torque. The contact of the shoulders gives the seal interference allowance and the screw interference allowance on the drawing, and this is the minimum index indicating that the fastening is completed successfully in the premium joint.

When the fastening torque finally reaches the recommended make-up torque value, the fastening is completed. For some types of joints, the shoulder absorption torque (ΔT) from the shoulder torque to the final torque must be substantially controlled. However, when a solid lubricant is used, the shoulder torque greatly varies compared to the grease fastening, and the shoulder torque also varies greatly due to machining tolerance, so a final torque that can always obtain the shoulder torque was selected. In this case, as shown in FIG. 2, it was found that the shoulder absorption torque became too large for the joint having the shoulder torque of the lower limit value of the variation, and the shoulder portion and the seal portion suffered fatal plastic deformation.

[0011] The problem of plastic deformation due to such over-torque is also the make-up using conventional grease, but the frictional resistance, that is, the variation in shoulder torque is not so large. As a reason for this, as shown in FIG. 3, it has been clarified that the grease pressure generated at the thread interface stabilizes the torque at a low level. On the other hand, as shown in FIG. 4, it was also found that when only the solid lubricant was provided, the variation in the friction coefficient (0.05 to 0.15) appeared as the variation in the torque as it was. Therefore, when fastening a joint using only a solid lubricant,
It has been found that it is necessary to improve the torque resistance more than before.

Therefore, it has been noted that the fastening torque up to the shoulder torque is mainly generated at the screw portion, while the shoulder absorption torque is generated by the reaction force generated at the shoulder and the load flank surface of the screw portion. . Since the frictional resistance can be approximated by Coulomb's law of friction, the generated torque T
Is T = μN where μ is a coefficient of friction and N is a reaction force. Therefore, it is understood that the shoulder absorption torque can be increased by increasing the friction coefficient μ. However, μ is closely related to seizure, and generally, increasing μ means that seizure resistance is deteriorated. In order to solve these conflicting problems at the same time, as shown in FIG. 5, solid lubricant is not applied to the load flank surface 6 of the screw, or even if it is applied, the solid lubricant is thinned to an unavoidable level in the construction, It has been found that a solid lubricating film may be formed.

Based on such findings, the thickness of the solid lubricant film on the load flank surface or the load flank surface and the shoulder surface of the screw according to the present invention was formed as thin as 5 μm or less. The reason for setting the thickness of the solid lubricant film on the load flank surface or the load flank surface and the shoulder surface of the screw to 5 μm or less is that if the thickness exceeds 5 μm, the final torque resistance aimed at by the present invention is improved. In addition, it is not possible to increase the appropriate fastening torque range. Note that a preferable range is 1 to 3 μm.

[0014]

FIG. 5 is a block diagram according to the present invention. FIG. 5A is a diagram showing an assembly configuration of a joint component, FIG. 5B is an enlarged view of the screw portion 3, and FIG.
(C) is an enlarged view of the shoulder contact surface 4. As shown in FIG. 5 (a), seizure may occur on all the sliding surfaces of the pin 2 and the box 1, but is most likely to occur on the sealing surface 5 where the surface pressure is high in oil well pipe joints. As shown in FIGS. 5B and 5C, the crest root surface 7 and the shoulder contact surface 4 of the screw are formed. Most surface pressure on the load flank surface occurs only for a small sliding distance after the shoulder abutment, and almost the same surface pressure generated on the shoulder is applied to the load flank surface of each thread. To be distributed,
Despite being a contact surface, seizure of the load flank surface is extremely unlikely to occur. Therefore, even if the solid lubricant is not applied to the road flank surface, the surface is not substantially burned. On the other hand, if the solid lubricant is not applied to the load flank surface, the frictional resistance increases and the final torque resistance can be expected to improve.

A coupling is shown as an example of a construction method in which a solid lubricant is not formed on the load flank surface or is formed very little even if it is attached as in the present invention. FIG.
FIG. 3 is a diagram showing a coating method in normal construction. As shown in FIG. 6, in a normal construction, the coupling is rotated and sprayed at an angle radially while being attached to the screw surface, the seal surface, and the shoulder surface, and the left and right sides are exchanged for uniformity. On the other hand, FIG. 7 shows a method commonly used in the present invention that makes it difficult to adhere to the load flank surface. In other words, masking one side to prevent the resin from adhering, and always moving the spray gun from the back of the coupling to the front, enough for the seal surface, shoulder surface, and screw crest surface where seizure is likely to occur. However, since the load flank does not have a large angle with respect to the angle of incidence of the spray, the resin hardly adheres to the load flank.

[0016]

The present invention will be specifically described below with reference to examples. As a test material, a premium joint of L-80 material having an outer diameter of 3-1 / 2 ゛ was subjected to a phosphate treatment as a base treatment, MoS ₂ was used as a solid lubricant, and this was coated using polyamideimide as a binder. . Both sides of the coupling were constructed in each way, one was tested and the other cross section was observed. Table 1 shows the results determined from the observation results and the film thickness obtained from the electromagnetic film thickness meter. Here, the seizure is a visually determined result, and the limit torque value is shown in FIG.
According to the method.

[0017]

[Table 1]

In Table 1, No. 9-No. Reference numeral 11 denotes a typical prior art example. When a solid lubricating film is applied to the seal surface to improve the lubricity of the seal surface where seizure is most likely to occur, the solid lubricant adheres to the shoulder surface and the screw load flank surface. As a result, the frictional resistance decreases, and as a result, the limit torque value decreases. On the other hand, when the solid lubricating film was not adhered to the screw-loaded flank surface, or even if it was adhered, the amount was 5 μm or less. 1 to No. 8, the limit torque is improved. Further, the effect is further enhanced by avoiding the adhesion to the shoulder surface. Focusing only on the limit torque, when the entire metal contact surface was thinned (No. 12), the limit torque was increased, but seizure occurred on the seal portion and the screw portion crest surface, and it became unusable.

FIG. 8 is a diagram showing the effect of the present invention in relation to the reduction rate of the seal interference allowance and the shoulder absorption torque. Here, the vertical axis indicates the ratio of the remaining seal interference to the initial seal interference. It is considered that the point where the interference margin starts to decrease rapidly is considered to be the limit value of the shoulder absorption torque, and there is a possibility that the sealing performance cannot be secured for a torque larger than this. While the torque limit was 6,000 Nm in the conventional method in which the lubricant was applied to the load flank surface, the final torque limit according to the present invention was remarkably improved to 8500 Nm. By consciously avoiding the adhesion of the resin containing the solid lubricant to the load flank surface, it was found that the shoulder absorption torque was improved by nearly 30%, and that no seizure occurred on any of the contact surfaces. .

Although it is effective to improve the torque resistance of the joint, it is effective to intentionally avoid the solid lubricant from adhering to not only the load flank surface of the screw but also the shoulder surface. When the torque increases, seizure on the shoulder surface is concerned. In this case, phosphate treatment, nitriding treatment, iron plating,
By performing processing with lubricating ability on its own, such as shot blasting and sand blasting, seizure is the most severe,
On the sealing surface and screw crest route surface, the adhesion of resin coating containing solid lubricant can be further improved, and even on the shoulder surface, which may be seized depending on the joint size and tightening torque, and the load flank surface of the screw, a certain degree of Seizure resistance can be ensured, and the final torque resistance can be increased.

The present invention relates to a type of solid lubricant, a type of resin,
Type of surface treatment is not intended to specify a method, other MoS ₂ mentioned in the examples as a solid lubricant, WS ₂ or PTFE is preferred. The resin is preferably an epoxy-based or furan-based resin in addition to a polyimide-based resin such as polyamideimide.

Next, the relationship between the screw shape and the present invention will be described.
FIG. 9 is a diagram showing an example of a screw shape and a coating position. FIG. 9A shows a case in which a solid lubricant is used, and the coupling female screw side is lubricated in a thread shape considered to be the most suitable. In this case, the coupling crest surface (thread surface) 11 and the load flank surface 12 are in contact, and the stamping flank surface 13 and the coupling root-pink rest space 14 are not in contact. The advantage of this combination is that when solid lubricant is applied to the coupling, the solid lubricant does not easily adhere to the coupling root surface (screw bottom surface). There is no fear. Further, even if the screw design is such that the crest surface and the root surface are in contact at the same time, the same effect is exhibited because the solid lubricant adheres to the coupling crest surface thicker than the root surface. The opposite is true when lubrication is performed on the pin side, but usually various combinations are preferable because the processing on the coupling side is easy.

On the other hand, FIG. 9B shows another example of the screw shape and the coating position. As shown in FIG. 9 (b), when the load flank surface 12 has a negative angle, the load flank surface 12 can be used even in a normal spraying method.
There is practically no solid lubricant adhesion to the
The present invention includes that the solid lubricant is not applied to the load flank surface 12 regardless of the screw shape.
FIG. 9C is a diagram showing still another example of a screw shape and a coating position. As shown in FIG. 9C, this is an example of a screw shape in which the load flank surface 12 and the stamping flank surface 13 are in contact with each other. Also in this case, the torque resistance is increased by avoiding the adhesion of the solid lubricant to the load flank surface 12, and is included in the present invention.

In the present invention, the position of the coating is specified on the condition that it has a metal contact, a threaded portion and a substantial shoulder, and is not specified for each shape. For example, as shown in FIG. 10, even if there is no shoulder on the coupling side, and the pin tips simultaneously abut each other, there is a substantial effect of the shoulder, the substantial solid on the load flank surface 12. If there is no lubricating film, it is included in the present invention. Also, A
Even when a seal portion is provided on the inner surface and a shoulder portion is provided on the outer surface, as in the case of the EL casing of PI, torque resistance can be improved by not performing lubrication on the load flank surface 12, and is included in the present invention. Further, in a joint in which a resin ring is attached to a screw interface or a pin tip for sealing purpose or corrosion resistance purpose, a metal contact portion, a shoulder portion, and a screw portion are included in the present invention in addition to the resin ring.

[0025]

As described above, in the threaded joint according to the present invention, the thickness of the solid lubricating film on the thread load flank surface and the shoulder surface is formed extremely thin to 5 μm or less.
An industrially superior pipe screw joint that can improve the final torque resistance and expand the appropriate fastening torque range by forming a solid lubricating film on the metal contact surface other than the screw load flank surface and the shoulder surface. Can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a joint fastening state between a make-up torque and a turn number curve during joint fastening.

FIG. 2 is an explanatory diagram of deformation of a joint due to overtorque.

FIG. 3 is a diagram showing a variation in torque due to tightening using grease.

FIG. 4 is a diagram showing variations in torque due to tightening using a solid lubricant.

FIG. 5 is a configuration diagram according to the present invention.

FIG. 6 is a view showing a coating method in normal construction.

FIG. 7 is a diagram showing a coating method according to the present invention.

FIG. 8 is a view showing the effect of the present invention in the relationship between the reduction rate of the seal interference allowance and the shoulder absorption torque.

FIG. 9 is a diagram showing an example of a screw shape and a coating position.

FIG. 10 is a view showing an example of an applied joint according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Box 2 Pin 3 Screw part 4 Shoulder part 5 Seal part 6 Load flank surface 7 Coupling thread 8 Coupling screw bottom 9 Stamping flank 10 Coating containing solid lubricant 11 Coupling screw-pin screw contact surface 12 Load flank surface 13 Stapling flank surface 14 Coupling screw bottom-Pin thread surface

Claims (4)

[Claims] 1. A threaded joint in which a pin having a male screw, a sealing surface, and a shoulder surface on the outside of a pipe and a female screw, a sealing surface, and a box having a corresponding shoulder on the inside of the pipe are fitted. Lubricant is formed and the thickness of the solid lubricant film on the screw load flank is 5μ.
A threaded joint for steel pipes characterized by being formed thinner than m. 2. A threaded joint in which a pin having an external thread, a sealing surface, and a shoulder surface on the outside of a tube and a box having a female screw, a sealing surface, and a shoulder surface corresponding to the pin on the inside of the tube are fitted. A threaded joint for steel pipes, wherein a lubricant is formed and a solid lubricant film thickness on a thread load flank surface and a shoulder surface is formed as thin as 5 μm or less. 3. A threaded joint in which a pin having an external thread, a sealing surface, and a shoulder surface on the outside of a tube and a female screw, a sealing surface, and a box having a shoulder surface corresponding to the pin on the inside of the tube are fitted, except for the screw load flank surface. A threaded joint for steel pipes, wherein a solid lubricant film is formed on the metal contact surface of the above. 4. A screw joint in which a pin having a male screw, a sealing surface, and a shoulder surface on the outside of a tube and a box having a female screw, a sealing surface, and a shoulder surface corresponding to the pin on the inside of the tube are fitted. A threaded joint for steel pipes, wherein a solid lubricant film is formed on a metal contact surface other than a shoulder surface.