JPH06221475A - Tightening method for oil well pipe thread joint - Google Patents

Abstract

PURPOSE:To obtain an efficient tightening method by calculating the remaining number of turns necessary to secure an objective delta toque value by use of the torque values at a first and a second bent points in an actual joint torque/turn value and torque values in a reference joint after the second bent point obtained in advance. CONSTITUTION:A first bent point from a first region into a second region and a second bent point from the second region into a third region are determined byfirst obtaining the tightening torque/turn values in a reference joint and then obtaining the tightening torque/turn values in tightening an actual joint successively and comparing them with the reference values. Accordingly, before entering the third region where the torque starts to increase rapidly with advance in the number of turns, the tightening toque quantity occurring in the first and second regions and the necessary delta torque quantity are obtained, so that the number of turns is calculated from a specified tightening torque/turn value in the third region. A final tightening torque value is thus set anew.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fastening method for fastening oil well pipes used for mining oil and gas with pipe joints.

[0002]

2. Description of the Related Art The depth of an oil well reaches several thousand meters, and in recent years,
It is about to reach 10,000 meters. Although the number of oil well pipes that are vertically inserted into such an oil well is enormous, they are all connected in series by pipe joints. Such pipe joints are subjected to various harsh forces such as an axial tensile force due to the weight of the pipe and the pipe joint itself, a ground pressure exerted from the periphery to the outer peripheral surface, and a pressing force exerted by the internal fluid on the inner peripheral surface. To work.

It goes without saying that these forces become more severe as the oil well depth increases. A pipe joint that can be used under such severe conditions is required to withstand a large tensile load and at the same time have a reliable sealing property.

As a joint for oil country tubular goods, API (Amer
ican Petroleum Institute (American Petroleum Institute) standard threaded joints such as round threads and buttress threads are generally used, but special threaded joints superior to API standard threads tend to be used to meet the above requirements. .

FIG. 2 shows an API-standard round screw joint portion, and FIG. 3 shows a typical special screw joint portion. In the case of the API standard threaded joint, sealing is performed between the male threaded portion 3 of the pipe 1 and the female threaded portion of the coupling 2. On the other hand, in the special threaded joint, a seal portion is provided in the non-threaded portion of the joint, and the pipe tip portion 5 and the seal portion 7 of the coupling 2 are brought into metal contact with each other to ensure the sealing property. Therefore, when tightening the special threaded joint, the pipe tip 5
After the seal portion 7 of the coupling 2 starts contacting with each other, it is necessary to continue the tightening work until the surface pressure necessary to secure the sealing property is generated at this contact portion. The torque from the start of contact of the seal portion to the end of tightening is called delta torque. As shown in FIG. 4, the surface pressure and the delta torque are in a close relationship, and in order to secure the sealing property, the pipe 1 and the coupling 2 are required until a proper delta torque is secured.
It is important to tighten. The torque generated before the seal portions start contacting each other is called shoulder torque. The value of the shoulder torque fluctuates as shown in FIG. 5 depending on the magnitude of the interference between the male screw and the female screw.

For the tightening work of the special screw joint, a grease called a compound, a lubricant containing zinc, lead or the like as a main component is used for the male screw portion 3, the female screw portion 4, the pipe tip portion 5,
After applying to all or part of the torque shoulder portion 6,
It is common to set it on a tightening machine and tighten it to a predetermined torque value. Such tightening work is performed not only in the oil field but also when the pipe manufacturing factory ships with the coupling attached to the pipe end.

An example of the tightening torque / turn curve of the special threaded joint is shown in FIG. As shown in the figure, in the first half, the tightening torque gradually increases as the pipe turns.
In the latter half, the torque sharply increases as the number of turns increases, and beyond the proper tightening torque range, the joint itself plastically deforms and becomes unusable. Therefore, conventionally, when tightening a special screw joint, a predetermined delta torque is set from the viewpoint of sealing property and a tightening torque range is set from the viewpoint of plastic deformation of the joint itself. The tightening torque range is a range in which the necessary delta torque value satisfying the predetermined sealing property can be secured and the problem of plastic deformation does not occur even when the diameter of the male screw or the female screw changes within the tolerance and the shoulder torque changes. As the diameter of the tubing becomes smaller, the shoulder torque value becomes relatively larger and the range tends to become narrower.

[0008]

However, the prior art has the following problems. That is, in the latter half of tightening, the torque sharply increases with respect to the turn, and this is done in a short time, so it is difficult to secure the required delta torque and stop within the final target torque range from the viewpoint of tightening stop accuracy of the tightening machine. There was As one of the measures,
Considering the responsiveness of the tightening machine stop, it may be possible to set the machine to issue a stop command early considering the torque amount (overshoot amount) from the stop command until the machine actually stops. However, if the estimated overshoot amount is too large, the required delta torque will be insufficient. Further, if this estimate is too small, the final target torque range may be exceeded and the joint itself may be plastically deformed, and there was a problem in mechanical accuracy and responsiveness. As another measure, there is a method of reducing the tightening speed, but it is considered that a new problem will occur in terms of productivity.

The present invention provides a method for tightening an oil country tubular goods threaded joint that is efficient in this respect.

The present invention prevents the necessary delta torque from becoming insufficient when the oil country tubular goods are fastened with a pipe joint, and prevents the joint itself from being plastically deformed beyond the final target torque range. However, it is an object of the present invention to provide an efficient tightening method for a special screw joint.

[0011]

As a result of repeated research and studies on the tightening method of special threaded joints, the present inventor can divide the torque / turn curve into four regions, and [tightening torque / turn] for each region. It was found that the value of (the torque increase rate) is closely related to the interference of the screw or the seal part, and further research has shown that in the tightening method of the special screw joint, (1) the torque is increased due to the interference between the male screw and the female screw. The first [tightening torque / turn] curve region that occurs and the second torque that occurs when the seal portion of the pipe tip contacts the seal portion of the coupling
[Tightening torque / turn] curve area, the third [Tightening torque / turn] curve area in which torque is generated by the contact of the torque shoulder, and the fourth [Tightening torque / turn] curve in which the joint itself is plastically deformed by excessive tightening. The value of the third [tightening torque / turn] curve is obtained in advance for the reference joint having the torque / turn curve region, and (2) the [tightening torque / turn] curve is set when the actual joint is tightened. Find the first [tightening torque /
The first turn point that transitions from the [turn] curve area to the second [tightening torque / turn] curve area is passed, and then the second
It is acknowledged that the second inflection point transitioning from the [Tightening torque / turn] curve area of to the third [Tightening torque / turn] curve area has passed, and at each point of the first and second inflection points. After obtaining the torque value, (3) determine the remaining number of turns necessary to secure the target delta torque value at the final tightening stage of the actual joint at each of the first and second inflection points. The torque value and the value of the third [tightening torque / turn] curve are used for calculation, and (4) the actual well joint is tightened at this calculated number of turns to efficiently form an oil well pipe threaded joint. Successfully tightened.

[0012]

The present inventor conducted a detailed investigation on the torque / turn curve during tightening of the special threaded joint, and confirmed that the value of [tightening torque / turn] was closely related to the interference of the screw or the seal part. did it. It was revealed that the torque / turn curve can be classified into four regions by the value of [tightening torque / turn], that is, the slope of the curve, as shown in FIG.

The first region is a portion where torque is generated by the interference between the female screw and the male screw, and the inclination of the curve is affected by the interference or friction of the screws. In the second region, the seal portion at the tip of the pin is used. It was found that the torque is generated by contact with the seal portion of the coupling, and the inclination is affected by the interference or frictional state of the seal portion.
The third region is a portion where the torque rapidly increases as the number of turns increases due to the contact of the torque shoulder portion. Inclination of the third area [tightening torque / turn]
It has been found that, as compared with the first and second regions, the joint has almost the same design, size and grade. The fourth region is a portion where the joint itself plastically deforms due to excessive tightening, and it is necessary to finish tightening before reaching this range.

When the special threaded joint was tightened a number of times under the same compound condition and the value of [tightening torque / turn] was taken into consideration, the following three things were also clarified.

1) In the first and second regions, the value of [tightening torque / turn] is the interference of screws or seals,
Although it varies depending on the coating conditions of the screw surface or the sealing surface, the finished surface roughness, the environmental conditions such as the temperature during tightening work, etc., the fluctuation amount is small.

2) In the third region, the value of the machining [tightening torque / turn] of the screw tip or the torque shoulder portion is a constant value.

3) The value of [tightening torque / turn] increases as the first area → the second area → the third area.

Using the results of the above examination, the [tightening torque / turn] value of the reference joint is obtained in advance, and the [tightening torque / turn] value during actual fastening of the joint is sequentially obtained and compared. Thus, it was found that the transition point from the first region to the second region (first refraction point) and the transition point from the second region to the third region (second refraction point) can be determined. From this, before being tightened into the third region where the torque sharply increases with the increase in the number of turns, the first and the second
Since the tightening torque amount and the required delta torque amount generated in the area of can be obtained, the tightening amount (number of turns) is calculated from the value of [tightening torque / turn] specified in the range of the third area. It was found that the final tightening torque value can be reset.

API grade L to which the method of the present invention has been applied
Fig. 1 shows an example of the tightening results for a special threaded joint with a diameter of 80, an outer diameter of 88.9 mm, and a wall thickness of 6.45 mm. By using the method of the present invention, it has become possible to reduce the defective rate to 30% or less of the conventional one as compared with the conventional one.

[0020]

[Example] API grade L80, outer diameter 88.9 mm, wall thickness 6.45
Using special mm mm threaded joints, a tightening experiment and a gas leak test were carried out for the purpose of securing an appropriate delta torque to maintain the gas sealability and investigating whether the joint itself was deformed. Table 1 shows the inclinations of the first to third regions and the experimental results regarding the above-mentioned reference joint. In Table 1, based on the method of the present invention, first, second
In the present invention example No. in which the delta torque value and the final tightening torque value are regulated in an appropriate range by sequentially obtaining the remaining necessary delta torque while comparing the value of [tightening torque / turn] in the area of and the same value of the reference joint. No leak occurred in any of 1 to 10. On the other hand, Comparative Examples Nos. 11 to 20 may cause a leak because the method of the present invention was not used. In No.l2, the overshoot amount was estimated too much from the standpoint of the stopping accuracy of the tightening machine, so the delta torque became insufficient and a leak was confirmed in the gas leak test. In No. 19, the joint itself was plastically deformed due to a delay in stopping the tightening machine, and a leak occurred in the gas leak test.

[0021]

[Table 1]

That is, according to the present invention, (1) the first [tightening torque / turn] curve region where torque is generated by the interference between the male screw and the female screw, and the seal portion at the tip of the pipe contact the seal portion of the coupling. A second [tightening torque / turn] curve area in which torque is generated by
Reference joint having a third [tightening torque / turn] curve area in which torque is generated by contact of the torque shoulder portion and a fourth [tightening torque / turn] curve area in which the joint itself plastically deforms due to overtightening About the 3rd [tightening torque / turn] curve, (2) [tightening torque / turn] curve at the time of actual tightening of the joint, and the 1st [tightening torque / turn] curve The first bending point passing from the curved region to the second [tightening torque / turn] curved region is passed, and further from the second [tightening torque / turn] curved region to the third
[Tightening torque / turn] curve area
After confirming that the inflection point has passed and obtaining the torque value at each of the first and second inflection points, (3) secure the target delta torque value at the final tightening stage of the actual joint. The remaining number of turns required for is calculated using the torque value at each point of the first and second inflection points and the value of the third [tightening torque / turn] curve, and (4 ) The tightening work can be performed efficiently by finishing the tightening of the actual joint with the calculated number of turns.

Before calculating the number of turns in the above (3), the value of [tightening torque / turn] after the second inflection point in the torque / turn curve of the actual joint is
It may be possible to confirm that it agrees with the value obtained in advance for the reference joint in (1).

[0024]

As described above, according to the present invention, when the oil country tubular goods are fastened by the pipe joint, the necessary delta torque is prevented from becoming insufficient, and the final target torque range is exceeded so that the joint itself is It is possible to prevent plastic deformation and obtain an efficient tightening method for a special screw joint.

[Brief description of drawings]

FIG. 1 is a diagram showing a tightening failure rate when a tightening method according to the method of the present invention is used, in comparison with a conventional method.

FIG. 2 is a cross-sectional view showing a threaded joint portion of API standard relating to a conventional technique.

FIG. 3 is a cross-sectional view showing a special screw joint portion according to the present invention.

FIG. 4 is a diagram showing a relationship between delta torque and seal portion surface pressure.

FIG. 5 is a diagram showing a relationship between a screw interference amount and a shoulder torque.

FIG. 6 is a diagram showing a relationship between a turn (rotation) and tightening torque during tightening.

FIG. 7 is a diagram showing a relationship between a turn (rotation) and tightening torque during tightening.

[Explanation of symbols]

 1 Pipe 2 Coupling 3 Male Threaded Part 4 Female Threaded Part 5 Pipe Tip Part 6 Torque Shoulder Part 7 Sealed Part

Claims (1)

[Claims] 1. A method for tightening an oil well pipe threaded joint, wherein the first [tightening torque / turn] curve region where torque is generated by the interference between the male screw and the female screw, and the seal portion of the pipe tip contacts the seal portion of the coupling. The second [tightening torque / turn] in which torque is generated by
A curved region, a third [tightening torque / turn] curved region in which torque is generated by the contact of the torque shoulder portion, and a fourth [tightening torque / turn] curved region in which the joint itself plastically deforms due to excessive tightening. The value of the third [tightening torque / turn] curve is obtained in advance for the reference joint having the above. When the actual joint is tightened, the [tightening torque / turn] curve is obtained, and the first [tightening torque / turn] curve is obtained. ] A first inflection point passing from the curved region to the second [tightening torque / turn] curved region has passed, and further, from the second [tightening torque / turn] curved region to the third [tightening torque / turn] curved region After confirming that the second inflection point transitioning to No. 1 has passed, and obtaining the torque value at each point of the first inflection point and the second inflection point, The remaining number of turns required to secure the target delta torque value at the final tightening stage is determined by the torque value at each of the first and second inflection points and the third [tightening torque / turn] curve. And the value of, and tightening of the actual joint is completed with this calculated number of turns.