JP2007232012A - Threaded joint for oil well pipe - Google Patents

Abstract

A threaded joint for an oil well pipe capable of reducing variation in shoulder torque is provided.
A male-side pin and a female-side box to be screw-coupled, each having a screw portion, a seal portion and a shoulder portion successively connected to the tip end side of the screw portion, at locations corresponding to each other. In the threaded joint for oil pipes, at least one taper changing point is provided in the length region of at least one of the screw portion 3 on the pin 1 side and the box 2 side, and the vicinity of the center of the screw portion length region by the taper changing point Thus, the pin screw portion and the box screw portion are preferentially brought into contact with each other.
[Selection] Figure 3

Description

  The present invention relates to an oil well pipe threaded joint, and more particularly to an oil well pipe threaded joint with reduced shoulder torque variation.

In recent years, oil wells and gas wells that are easy to develop have decreased, and wells at higher depths and higher temperatures and pressures have increased. In addition, with the progress of drilling technology, wells with more complicated shapes such as inclined wells and horizontal wells are increasing. Along with this, requirements for threaded joints of oil well pipes, such as airtightness under complex loads such as tension, compression, internal / external pressure, and bending, are becoming increasingly sophisticated. (Non-Patent Document 1)
As shown in FIG. 1, the threaded joint for an oil well pipe includes a male pin 1 and a female box (or coupling) 2 to be screw-coupled, and a thread portion 3 is provided at a position where both of them correspond to each other. And a seal portion 4 and a shoulder portion 5 that are successively connected to the distal end side of the screw portion 3. A taper screw is machined into the thread portion 3, and a taper of the taper screw is usually a constant linear taper throughout the entire length of the thread portion 3.

  There are various combinations of pin taper (taper thread taper on the pin 1 side) and box taper (taper thread taper on the box 2 side) depending on the required specifications of the threaded joint. FIG. 1 shows a taper setting example in which the pin taper is larger than the box taper. Depending on the attribute of the cutting process, in addition to the complete thread 31A, the thread 3 on the pin 1 side is formed with an incomplete thread 31B in which the thread gradually decreases toward the pin root. The screw diameter measurement position is normally taken near the center of the length of the complete screw portion 31A, and the screw interference amount (box screw diameter) with the screw diameter at this position as a representative value is the basis of the design.

  In general, when the taper screw joint is tightened, the relationship between the turn (the number of tightening rotations) and the torque is as shown by a solid line or a broken line in FIG. That is, at the point O, screw interference between the pin and the box starts and the torque starts to increase. Next, seal interference participates at point A (or A 'point), and the torque increase rate increases. Furthermore, shoulder interference participates at point B (or B 'point), and the torque increase rate further increases. This tightening is stopped when the torque reaches the optimum torque (specified tightening torque value). A point at which shoulder interference starts (for example, point B or B ′) is referred to as a shoulder point, and a torque value at the shoulder point is referred to as a shoulder torque.

If the shoulder torque is too high and the difference from the optimum torque is small, the shoulder portion is not sufficiently tightened, and the sealing performance of the threaded joint becomes insufficient. Therefore, for example, a shoulder torque upper limit as shown by a dotted line in FIG. 2 is set, and the screw interference amount is designed so that the shoulder torque does not exceed the shoulder torque upper limit. In other words, the shoulder torque upper limit is set from the viewpoint that the torque from there to the optimum torque is the minimum necessary torque (or the safety factor multiplied by this) that is applied to the shoulder to ensure sealing performance. Is done.
JFE Technical Report No. 9 (August 2005) p.46-50

  However, during the tightening test, the shoulder point (point B) is not necessarily located below the dotted line (shoulder torque upper limit line) as shown by the solid line in FIG. 2 (the shoulder torque does not exceed the shoulder torque upper limit). Not limited to this, the shoulder point (B ′ point) is positioned above the dotted line (shoulder torque upper limit) as shown by the broken line in FIG. 2 (the shoulder torque exceeds the shoulder torque upper limit). There is a problem. This is presumably because the shoulder torque varies greatly.

  An object of the present invention is to solve the above-mentioned problems and to provide a threaded joint for oil country tubular goods that can reduce variation in shoulder torque.

The inventor obtained the following knowledge as a result of repeated studies to solve the above problems.
(A) The taper of the conventional thread part is taken so that it may become constant throughout the thread part length. Therefore, even if the designed screw interference amount at the screw diameter measurement position is the same, the actual screw interference amount varies depending on the combination of the pin taper and the box taper. For example, in the taper setting example shown in FIG. 1, the actual screw interference amount at the incomplete screw portion is considerably larger than the designed screw interference amount. In this case, as shown by the broken line in FIG. 2, the maximum torque (torque at point A ′) due to only screw interference increases, and the shoulder torque (torque at point B ′) increases accordingly, exceeding the upper limit of the shoulder torque. May occur.

  (B) In order to suppress the variation in the actual screw interference amount with respect to the designed screw interference amount due to the combination of the pin taper and the box taper as described above, the entire thread length of at least one of the pin side and the box side It is effective to distribute a plurality of different tapers in each section so that the pin screw portion and the box screw portion are preferentially in contact with each other in the vicinity of the center of the screw portion length region.

This invention is made | formed based on the said knowledge, The summary is as follows.
(1) It has a male pin and a female box to be screw-coupled, and has a screw portion and a seal portion and a shoulder portion successively connected to the tip end side of the screw portion at locations where both of them correspond to each other. In the oil well pipe threaded joint, at least one taper changing point is provided in at least one of the thread lengths on the pin side and the box side, and the pin threaded part is located near the center of the thread length by the taper changing point. A threaded joint for oil country tubular goods characterized in that the box threaded portion is preferentially in contact.

  (2) The threaded joint for oil country tubular goods according to (1), wherein the number of taper changing points is one or two.

  According to the present invention, since the screw interference amount near the center of the thread length region can be made larger than that near both ends, the shoulder torque variation due to the combination of the pin and the taper of the box can be suppressed, and the shoulder It is possible to effectively prevent the occurrence of problems exceeding the torque upper limit.

  An embodiment of the present invention will be described with reference to a taper setting example (corresponding to Example No. 1 of the present invention in Table 1) shown in FIG. In this example, the thread length area on the pin 1 side and the thread length area on the box 2 side are divided into three sections, L1, L2, and L3, at the common points on both sides of the pin 1 and box 2. Divide each section into three sections of “small”, “standard”, and “large” taper (the tolerance ranges of different levels do not overlap) as shown in the figure, and the screw part 3 of the pin 1 and the screw of the box 2 The part 3 is preferentially contacted in the vicinity of the center of the thread length region.

  In this example, pin 1 and box 2 each have a taper change point (two on each side of the pin side and box side) at the positions of the L1 / L2 division point and L2 / L3 division point that are common to each other. However, the present invention is not limited to this, and the position of the taper change point in the thread length region may be set to a different position on the pin side and the box side, and the number of taper change points is the pin side and the box side. The taper change point may be provided only on either the pin side or the box side.

  However, increasing the number of taper change points unnecessarily does not increase the effect of suppressing variations in shoulder torque, but only incurs the disadvantage of complicating thread cutting. Whether it is provided on only one or both, the number is preferably 1 to 2 on each side. However, in the case where the taper change points are provided only on either the pin or the box, it is more preferable that the number of taper change points on the side to be provided is two.

  Conventionally, the screw diameter measurement position for obtaining the designed screw interference amount is located near the center of the complete screw portion 31A as shown in FIG. 1, but in the present invention, the actual screw interference amount and the design are determined. In order to minimize the error from the above screw interference amount, the screw diameter measurement position is set at the center of the length portion of the screw portion where the pin screw portion and the box screw portion preferentially contact to increase the screw interference amount. It is important to take it near (in the example of FIG. 3, near the center of the L2 ward).

Threaded joints for oil pipes were manufactured under various taper setting conditions shown in Table 1 (a plurality of conditions in which the combination of pin taper and box taper is different), and a tightening test was performed. A torque vs. turn curve having a transition pattern similar to that in FIG. 2 is measured for each condition, and the shoulder torque to optimum torque ratio obtained from the measurement results is shown in FIG.
As shown in FIG. 4, in the conventional example, No. 4 (combination of pin taper “large” and box taper “small”) has a large variation tendency that the shoulder torque is significantly larger than the others. In the invention example, such variation is remarkably reduced, and a shoulder torque lower than that in the conventional example is obtained under any taper combination condition.

  As is apparent from this result, according to the present invention, the variation in shoulder torque due to the combination of the pin taper and the box taper is remarkably reduced, and the occurrence of a malfunction exceeding the upper limit of the shoulder torque can be effectively prevented.

It is a schematic sectional drawing which shows one of the prior art examples of the threaded joint for oil country pipes. It is a schematic diagram which shows transition of the torque with respect to a threaded joint fastening turn. It is a schematic diagram which shows one example of embodiment of this invention. It is a graph which shows the relative level of the shoulder torque of this invention example and a prior art example.

Explanation of symbols

1 pin 2 box (or coupling)
3 Screw part 4 Seal part 5 Shoulder part
31A Full thread
31B Incomplete thread

Claims (2)

  An oil well pipe screw comprising a male-side pin and a female-side box to be screw-coupled, and having a screw part, a seal part and a shoulder part successively connected to the tip side of the screw part at a position where both of them correspond to each other The joint has at least one taper change point in at least one of the thread length regions on the pin side and the box side, and the pin screw portion and the box screw portion in the vicinity of the center of the thread length region by the taper change point. And oil well pipe threaded joints characterized by preferential contact.   2. The threaded joint for oil country tubular goods according to claim 1, wherein the number of taper changing points is 1-2.

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