JP2005337469A - Screw joint for oil well pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a screw joint for an oil well pipe which requires a small increase in cost without any decrease in the scope of applications, and can obtain a critical torque value exceeding previous limits. <P>SOLUTION: The screw joint for the oil well pipe comprises a pin 1 on the male side and a coupling 2 on the female side which are screw-connected. Then the screw joint for the oil well pipe has a screw part 3, a seal part 4 and a shoulder part 5A at the position where the pin and the coupling correspond with each other. The seal part is stretched in sequence on the end side of the screw part, and the shoulder part is at the end of the seal part. Then a coating or a lubricant 7 such as elastomer, which makes the coefficient of the friction of the shoulder part higher than that of the screw part and the seal part, is applied only to the shoulder part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a threaded joint for oil well pipes, and more particularly to a threaded joint for oil well pipes that can maintain fluid leakage resistance even when a high tightening torque is applied. Here, the oil well pipe means a pipe used for an oil well or a gas well.

  In recent years, the number of oil wells or gas wells that dig the bottom of the well diagonally or horizontally is increasing in order to reduce drilling costs and improve productivity. At this time, a protective tube material called a liner may be pushed in as a casing at the bottom of the well while rotating. This rotational force is transmitted from the upper part of the well. In this case, the joint portion of the pipe material on the way also receives torque accompanying the rotation. As a joint portion of the pipe material in the middle, a threaded joint (hereinafter referred to as a metal-metal seal portion) including a pin provided with a male screw and a coupling provided with a female screw screwed into the male screw (hereinafter referred to as a metal-metal seal portion). Often used as a special screw.)

  In general, when a special screw is tightened, the relationship between the number of rotations and the torque is as shown in FIG. That is, at the point A, the torque begins to increase as the interference of the screw portion begins. Next, at point B, the interference of the metal-metal seal portion (hereinafter simply referred to as the seal portion) starts and the rate of increase in torque (the amount of increase in torque per turn) increases. Further, at point C, a portion called a shoulder portion begins to interfere, but with this interference, the torque starts to increase rapidly. When the torque reaches a predetermined final tightening target torque, the tightening is stopped.

  At this time, if the final tightening torque is too high (more precisely, the torque acting on the shoulder portion is too high), for example, as shown in FIG. 4, the corresponding shoulder portion 5 of the coupling 2 and / or the pin 1. Begins to plastically deform. As a result, the seal portion 4 does not maintain its original shape and the sealing performance cannot be maintained.

  The torque value when the shoulder portion begins to plastically deform as described above (point D in FIG. 3) is referred to as a limit torque value. Since the final tightening target torque can be set larger as the limit torque value is higher, the sealing performance is better. As a method for increasing the limit torque value, for example, a method of increasing the thickness of the shoulder portion is known, such as a swage type special screw shown in FIG.

  However, in order to increase the thickness of the shoulder portion, it is necessary to reduce the diameter of only the distal end of the threaded tube before threading. In order to reduce the diameter, it is necessary to add a process, and there is a problem that the cost is greatly increased. Moreover, since the inner diameter of the shoulder portion is inevitably reduced when the diameter reduction is performed, there is a problem that the outer diameter of the pipe or tool inserted into the screw joint has to be reduced, and the application range of the screw joint is narrowed. there were. Further, since the inner diameter of the shoulder portion cannot be made smaller than the limit for drift specified by the API, there is a problem in that there is a limit to the torque increase.

  An object of the present invention is to provide a threaded joint for oil country tubular goods that solves the above-described problems and can obtain a limit torque value that exceeds a conventional limit without increasing the cost and reducing the application range.

  The present invention comprises a male-side pin and a female-side coupling to be screw-coupled, and a screw portion, a seal portion sequentially connected to the tip side of the screw portion, and the seal portion, both of which correspond to each other An oil well pipe threaded joint having an end shoulder part, wherein only the shoulder part is provided with a film or a lubricant that makes the shoulder part have a higher coefficient of friction than the thread part and the seal part. It is a threaded joint.

  In the present invention, the shoulder portion is further provided at one or more positions different from the shoulder portion at the end of the seal portion, and the shoulder portion at the end of the seal portion or at one or more positions different from the shoulder portion. Any one or two or more of these may be coated with the film or lubricant.

  In the present invention, it is preferable to provide a compound reservoir for accumulating a compound or a lubricant used for lubricating the screw portion and the seal portion.

  According to the present invention, the limit torque value can be increased without reducing the inner diameter of the shoulder portion, so that the increase in cost is small and the application range is not narrowed, and a limit torque value exceeding the conventional limit can be obtained.

  The screw joint of the present invention is similar to the above-described special screw. With special screws, the torque when tightened is proportional to the product of the contact resistance and the friction coefficient of the pin and coupling accompanying the deformation of the screw. Therefore, if the friction coefficient is increased, a high torque is generated even with the same deformation amount.

    When tightening an oil well pipe, a compound having the performance specified in API 5A2 of API (American Petroleum Institute) is generally applied to prevent screw galling. The friction coefficient of this compound is about 0.05. is there. Although other compounds may be used, many compounds have a coefficient of friction within a range of about 0.05 × (0.8 to 1.2). Furthermore, in recent years, a lubricant having a component system different from that of a compound has been developed. However, the coefficient of friction falls within the same range as that of a compound.

  The tightening of the special screw is a severe tightening, and particularly the seal portion is exposed to a high surface pressure. Therefore, it is indispensable to use the above compound or lubricant.

  The screw part has a much smaller surface pressure in the ideal state than the seal part, but in actual manufacturing, local stress concentration occurs due to the difference in dimensions such as the lead and coupling between the pin and coupling, and tightening. The possibility of goling cannot be denied. Therefore, it is indispensable to use the above compound or lubricant as well as the seal portion.

  On the other hand, the shoulder portion has a feature that the contact area is much larger than that of the seal portion and generally has processing accuracy equivalent to that of the seal portion, so that the contact stress is substantially smaller than other portions. .

  The present invention has been made in consideration of the conditions that bring about this feature. A conventional compound or lubricant is applied to the seal portion and the screw portion, and a film or lubricant that increases the coefficient of friction is applied only to the shoulder portion. It is something to be applied. Since the shoulder portion has substantially better galling resistance than other portions, there is no problem even if the friction coefficient is increased.

  For the application of coatings or lubricants that increase the coefficient of friction, a thin film of high-viscosity material such as elastomer (friction coefficient: about 0.1 to 0.2) is applied or applied, or the same as this. It is advisable to apply a lubricant having a friction coefficient as high as possible.

  By the way, in the special screw, in addition to the shoulder portion at the end of the seal portion, it may be provided at one or two or more positions different from this. For example, FIG. 2 shows an example in which shoulder portions 5B, 5C, and 5D are provided at the tip, middle, and base end positions of the screw portion 3 different from the shoulder portion 5A at the end of the seal portion 4, respectively. . In such a case, the coating object or the lubricant for increasing the friction coefficient may be only the shoulder portion 5A at the seal end, but if necessary, any one or more of the other shoulder portions may be used. It is preferable to add to the construction object.

  Also, depending on the shape of the special screw, when tightening, the conventional compound or lubricant applied to the seal part and screw part flows into the shoulder part coated with a film or lubricant that increases the friction coefficient, and the friction of the shoulder part The coefficient may decrease and the limit torque value may not increase sufficiently. In such a case, for example, as shown in FIG. 1, a compound reservoir 6 for storing a compound (or a lubricant) used for lubricating the screw portion 3 and the seal portion 4 may be provided. Thereby, the compound (or lubricant) pushed out by interference of the screw part or the seal part at the time of tightening preferentially accumulates in the compound reservoir 6 having a smaller passage resistance than other parts, and this is the shoulder part. Inflow to 5A (or 5B) can be effectively prevented. The position where the compound reservoir is provided is the position between the screw portion 3 and the seal portion 4 in FIG. 1, but is not limited to this. Any number of these may be used, and the number thereof is not particularly limited.

  In addition, in FIG. 1, the example which applied the elastomer to the shoulder part 5A of the seal | sticker part end was shown.

  Two of the special threaded joints with the same material and dimensions (outer diameter 4.5 inches) were extracted at random. This threaded joint has a shoulder portion only at the end of the seal portion. One of the two extracted parts is 45 mm of API 5A2 equivalent compound (friction coefficient 0.05) on the screw part, seal part, and shoulder part at the end of the seal part. Apply the same compound to the screw part and the seal part in the same way, and apply elastomer (friction coefficient 0.10) to the shoulder part at the end of the seal part to a uniform thickness. Example. The compound and the elastomer were applied to the pins.

  The screw joints of the comparative example and the example were subjected to a tightening test and the limit torque value was measured. As a result, the limit torque value was 150 in the example and improved from the comparative example when viewed as a relative value with the comparative example being 100.

  INDUSTRIAL APPLICABILITY The present invention can be used for industries that mine underground resources such as oil and natural gas using oil well pipes.

It is sectional drawing which shows preferable embodiment of this invention. It is sectional drawing which shows an example of the special screw which has a shoulder part in a seal | sticker part edge and other positions. It is a graph which shows the relationship between the rotation speed and torque when tightening a special screw. It is sectional drawing which shows the mode of the plastic deformation of a shoulder part. It is sectional drawing which shows an example of a swage type special screw.

Explanation of symbols

1 Pin 2 Coupling 3 Screw part 4 Seal part 5, 5A, 5B, 5C, 5D Shoulder part 6 Compound reservoir 7 Film or lubricant for increasing the coefficient of friction

Claims (3)

  It consists of a male-side pin and a female-side coupling that are screw-coupled, and a screw part, a seal part that is successively connected to the tip side of the screw part, and a shoulder part at the end of the seal part. A threaded joint for oil country tubular goods, wherein a film or a lubricant that makes a friction coefficient of the shoulder part higher than that of the threaded part and the seal part is applied only to the shoulder part.   Furthermore, it has a shoulder part at one or two or more positions different from the shoulder part of the seal part end, and either one of the shoulder part of the end of the seal part or one or more shoulder parts different from this. 2. The threaded joint for oil country tubular goods according to claim 1, wherein the coating or lubricant is applied to only two or more.   3. A threaded joint for oil country tubular goods according to claim 1, further comprising a compound reservoir for storing a compound or a lubricant used for lubricating the screw portion and the seal portion.

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