JPS59126191A - Pipe joint for oil well pipe - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] The present invention relates to a pipe joint for oil country tubular goods that is vertically inserted deep underground in order to extract natural gas and crude oil produced underground, and in particular, the joint is repeatedly screwed in and unscrewed. The present invention relates to a pipe joint that has greatly improved the possibility of being used for reverse use.

The depth of the wells that produce all the crude oil is several thousand meters, and in recent years the depth has been increasing further to reach 10,000 meters. A huge number of oil country tubular goods are installed vertically to extract crude oil from such wells, and they are all connected by pipe joints. The most important requirements for such pipe fittings are to withstand strong tensile loads and to maintain reliable airtightness.The above requirements for pipe fittings are the depth of the well! 7) It goes without saying that things get tougher as you get older. The various types of pipe joints that have been proposed over the years speak volumes about this fact. Rpchi, Japanese Patent Publication No. 35-7630, Japanese Patent Publication No. 41-1742, Japanese Patent Publication No. 45-18096, Japanese Patent Publication No. 52-27367, as well as US Patent No. 2907589, US Patent No. 2980451
The pipe joints described in this patent and US Pat. No. 2,992,019 are such examples. Among these conventional pipe joints, the most basic one is shown in FIG.

The pipe joint shown in Fig. 1 includes a coupling A having a cylindrical appearance, a pipe C screwed onto both ends of the coupling A,
It is composed of C. 1fUl of coupling A
It usually heats up from both ends as you go deeper in the axial direction. In the A, P, and ■ standards, the inner diameter is reduced with a taper.A buttress-type internal thread is carved into the inner diameter, and an annular shoulder B is formed on the inner peripheral wall of the central part, which protrudes around the axis. There is. On the other hand, each of the tubes C9C has a male thread cut into its end to be screwed into the female thread of the coupling Al7)ljiJ. FIG. 2 shows an enlarged view of the screwed state of the coupling A and the pipe C on the left side of FIG. 1. As seen in Figure 2, beyond the part of the pipe C where the male thread is cut off (on the right side), there is an unthreaded lip in an area corresponding to 1.5 to 3 threads. There is. On the outer circumferential surface of this lip part, there is a mark that follows the male thread in the previous stage. A tapered, flat outer circumferential sealing surface D1 is formed, and an over-ring-shaped tip seal [fnD2 with an angle of about 100° relative to the axis of the tube C] is formed at its tip. On the other hand, there is also a 1/
There is a part with no thread with a 16 taper,
An inner seal surface B1 corresponding to the outer seal IkJ of the lip portion and an abutment seal curved horse corresponding to the tip seal surface D2 are formed. And pipe C and coupling A
When the screws are strongly tightened, the outer seal surface D8 and the inner seal surface B□ and the tip seal curve D2 and the abutment seal surface B2 will contact each other and form a metal surface to metal surface. An airtight seal is obtained.

The basic structure of conventional pipe joints is as described above, but when the depth of the well increases to @L degree, tensile strength and reliable sealing performance become difficult. Due to the reinforcement, the threaded connection between the pipe C and the coupling A tends to be excessively tightened. If it is over-tightened, remove the outer cylinder seal and inner seal!
1]]B1, and the tip seal surface D2 and the abutting seal direction B
A type of galling, called galling, occurs between the wells and the sealing effect, which actually impairs the sealing effect.Also, when the well becomes extremely deep, the tubes and couplings used As the number of tubes and couplings becomes enormous, there is a growing desire to reuse used tubes and couplings in other new wells from the perspective of saving materials. and couplings may not be subjected to reuse.

In view of the conventional problem described in 01J, the present invention prevents as much as possible the occurrence of galling on the metal-to-metal sealing surface even when screwing is performed excessively, thereby increasing the tensile strength. The purpose of this invention is to provide a pipe joint that has excellent sealing properties and can be reused. The invention will be explained below based on embodiments shown in the drawings.

FIG. 3 is an enlarged cross-sectional view showing the main structure of the first embodiment of the pipe joint according to the present invention. A buttress based on the A, P, ■ standards with a predetermined taper on the outer eight curves of the pipe 1 A male thread 1a of the mold is engraved, a lip part 2 without a thread is formed at the end, an outer peripheral sealing surface 3 is formed on the outer peripheral surface of the lip part 2, and a tip seal []J is formed toward the distal end of the lip part 2. ] 4 are provided respectively. On the other hand, the coupling 6 is also provided with a female thread 6a corresponding to the male thread 1a, and near the shoulder 7 there is an inner seal surface 8 corresponding to the outer seal surface 3 and a tip seal 113. An abutment sealing surface 9 corresponding to the sealing surface 4 is provided. These things are no different from conventional pipe joints. The pipe joint according to the present invention is significantly different from the conventional one in that a stepped surface 5 is provided at the part where the male thread 1a of the pipe 1 transitions from the cut-off part near the tip to the outer peripheral sealing surface 3. Correspondingly, a receiving surface 10 is provided at a portion where the female thread 6a of the coupling 6 transitions from the cut-off portion nearer to the inner circumferential seal 1f118K. The stage surface 5 and the stage surface 10 are as follows:
When the screwing of the pipe 1 into the coupling 6 reaches its limit, the grains come into contact with each other and act as a stopper. This prevents the lip portion 2 of the tube 1 from entering further into the coupling 6.

FIG. 4 is a schematic diagram showing the dimensional relationship of various parts of the tube 1 in the vicinity of the lip portion 2. The bump surface 5 is the inner pipe wall 1b.
The step lid 81 with respect to the outer sealing surface 3 is normally 1.5 m or more. This step amount S is also limited by the wall thickness of the unbroken portion of the pipe 1, which is usually set to be 25 inches or less. The tip sealing surface 4 of the lip portion 2 is in the shape of an oarpart with respect to the tube inner wall surface 1b, and the angle θ thereof is usually about 10ff'. The tip thickness t of the lip portion 1 is three cycles or more. is desired.

If it is less than 3 tan, when tightening the screw,
If the elastic deformation limit is exceeded and permanent deformation occurs, there is a risk that the blood pressure required for the seal may not be obtained. Needless to say, the tip thickness t is also limited by the wall thickness of the main body of the tube 1, and as with the step amount 6, it is usually set to 25% or less. The length l of the lip portion 2 is 1.5 to 3 times the tip thickness t.

If it is less than 1.5 times, the deformation resistance during screw tightening will be high, so the outer seal surface 3 and the tip seal [f]
4, galling is likely to occur. On the other hand, if it exceeds 3 times, it becomes easy to deform and therefore it becomes difficult to maintain the blood pressure necessary for sealing. Thickness 7.72rra
In the case of a pipe of n, the step amount 8 is 2. Osw, tip thickness t is 4
゜0tan,') The protrusion length l is in the order of 10. It goes without saying that the dimensional relationship of the various parts near the shoulder 7 in the coupling 6 corresponds to the dimensions of the respective parts near the lip capital 2, so we will not go into details here. Although the above precision finishing is required, the bottom of the stopper shape can be finished with a normal lathe, so the processing is extremely simple.
A pipe fitting according to the present invention made as described above, a pipe 1
When screwing and tightening the coupling 6, first, they are temporarily tightened by hand tightening, and then tightening is performed by power tightening with a specified torque.

As Power Tight is tightened, the outer sealing surface 3 of the lip portion 2 is tightly fitted to the inner sealing surface 8 of the coupling 6, and as the mutual contact area gradually increases, the surface pressure also increases. 0 As a result, the lip s2 is slightly bent and deformed in the axial direction of the tube 1, and stress due to blood pressure is accumulated within the lip portion 2. As the tightening progresses further, the tip seal surface 4 comes into contact with the abutting seal surface 9 of the shoulder 7. When this state is reached, the tightening torque rapidly increases, and the outer circumferential seal surface 3 vs. the inner circumferential seal surface 8 and The aging blood pressure of the tip seal surface 4 versus the abutment seal 9 also increases rapidly. Figure 5 shows an outer diameter of No. 7' (190°5rrrI).
n), as the tightening by Power Tight progresses for the entire pipe with a wall thickness of 7.72 m, the tightening shows the state in which the torque and the surface pressure of the sealing surface change. In the figure, the top line is a torque curve for tightening, the dashed-dotted line is a blood pressure curve of the sealing surface of a conventional pipe joint, and the broken line is a blood pressure curve of a pipe joint according to the invention. In this figure, the characteristic difference between the conventional pipe joint and the pipe joint according to the present invention is that in the conventional pipe joint, after the tip sealing surface 4 contacts the abutment sealing surface 9, the blood pressure curve shows a steep rise line. In contrast, in the case of the pipe joint according to the present invention, after the tip seal surface 4 abuts in the abutting seal direction 9, the step surface 5
After the receiving surface 10 comes into contact with the receiving surface 10 and plays the role of a stopper, the surface pressure curve suddenly bends, and even if excessive tightening is performed, the blood pressure will rise, which is necessary to ensure a seal. The goal is to maintain a constant optimal blood pressure. Incidentally, the surface pressure 6oKgfA2 in the same figure is the minimum blood pressure value necessary to ensure a seal at the target pipe joint, which is 120Kgf/1.
rva" is a dangerous blood pressure value at which galling may occur. According to this, in conventional pipe fittings, when the specified tightening is performed, it indicates that the dangerous blood pressure value at which galling may occur has already been reached. During tightening work, the point in time when the torque reaches the specified value is determined visually and the Power Tight tightening is stopped without missing this timing, but if this timing is incorrect, galling will occur immediately. , the pipe joint is not only unusable, but also impossible to reuse.With the pipe joint according to the present invention, such dangers are completely eliminated.

In the present invention, the reason for providing a stopper portion that comes into contact with each other near the outer circumferential sealing surface and the inner circumferential sealing surface of the pipe joint is that in the case of a threaded joint of a pipe under the same conditions, normally, Tensile strength is largely controlled by the amount of torque during tightening, but sealing performance is not necessarily controlled only by the amount of torque; in many cases, it is determined by the blood pressure between the sealing surfaces. This is based on the knowledge that the blood pressure is not necessarily higher and better; if it is excessive, galling will occur, which will actually impair the sealing performance. It is.

FIG. 6 shows the main structure of a second embodiment of the pipe joint according to the present invention. This failed embodiment differs from the first failed embodiment in that the stopper portion is constituted by an inclined step surface 5' and an inclined step receiving surface 10'. Its slope is
As in the case of the tip sealing surface 4, the angle with respect to the pipe inner wall surface was set to 10 (after r@iJ.)
As the screw tightening progresses and the outer peripheral sealing surface 3 comes to be tightly fitted into the inner peripheral sealing surface 8, the portion near the tip of the lip portion 2 tends to bend in the axial direction of the tube 1. Then, when the tip seal surface 4 comes into contact with the abutment seal surface 9, since both the tip seal surface 4 and the abutment seal surface 9 form an inclined surface, the lip portion that was once bent in the axial direction The portion near the tip of the tube 2 receives deformation force in the direction away from the axis of the tube 1 along the inclined surface, and the stress accumulated in the lip portion 2 when it was already bent in the axial direction is compounded. In addition, the tip end portion of the lip portion 2 is strongly pressed against the inner circumferential sealing surface 8, thereby ensuring the sealing effect. However, the action as shown in C will occur at the base of the lip portion 2 in the case where the step surface 5 and the step surface 10 are provided perpendicularly to the inner wall surface of the tube 1 as shown in FIG. (The part near the bumper surface 5) is not as good as that. Therefore, when looking at the entire abutment surface between the outer circumferential sealing surface 3 and the inner circumferential sealing surface 8, the surface pressure tends to become uneven. Therefore, in the second embodiment shown in FIG. 6, the stopper part is composed of an inclined step surface 5' and an inclined step direction 10'. Also, a deforming force is applied in a direction away from the axis of the tube 1, so that blood pressure is uniformly distributed over the entire outer circumferential sealing surface 3 and inner circumferential sealing surface 8.

FIG. 7 shows the main structure of a third embodiment of the pipe joint according to the present invention. In this embodiment, the outer circumferential sealing surface is divided into an outer circumferential sealing surface 3' near the base and an outer circumferential sealing surface 3'' near the tip, and a gap between the outer circumferential sealing surface 3' near the base and the outer circumferential sealing surface 3'' near the tip. An inclined step surface 5' is provided on the bottom.

In general, the ends of tubes are likely to come into contact with other objects during tube transportation, tube connection operations, and other operations. As a result, there is a risk that the seal portion may be damaged, but in the case of such a two-stage seal structure, even if the tip seal surface 4 or the outer seal surface 3'' near the tip is damaged, the inclined impact Since the stepped surface 5' and the outer circumferential sealing surface 3' near the base can sufficiently cover the deterioration of sealing performance due to damage, a sealing effect with a higher guarantee rate can be obtained.
Since the contact load near the lip portion 2 and the shoulder portion 7 can be distributed to the two-stage sealing surface, the zero-order pipe joint according to the present invention also has the effect of suppressing the occurrence of galling. The test results are explained based on comparison with conventional pipe fittings. Table 1 shows the configuration conditions of pipe fittings.
Table 2 shows the test conditions and test results. 1st
In the table, A in the model column is the first embodiment of the present invention (see Figure 3)
B is the same as the second example (see Figure 6).
C is that of the third embodiment (see Figure 7) Table 1 As is clear from Table 2, the pipe fitting according to the present invention The torque that causes galling when tightening is more than double, and when tightening with the specified torque at the ridge where galling occurs, the number of times it is tightened back is also 2.
It has more than doubled.

As described above, the present invention not only has good workability in screwing and tightening pipe joints, and there is no risk of galling due to over-tightening, but also greatly expands the possibility of reuse and saves materials. This will greatly benefit the oil extraction industry, which is highly desired.

[Brief explanation of the drawing]

Fig. 1 is a partial cross-sectional schematic diagram showing the basic structure of a conventional pipe joint, Fig. 2 is an enlarged sectional view of the left side of Fig. 1, and Fig. 3 is a partial cross-sectional diagram showing the basic structure of a conventional pipe joint. FIG. 4 is a schematic diagram for explaining the dimensional relationship of each part near the lip portion in FIG. 3;
Fig. 5 is a graph showing changes in the torque curve and blood pressure curve when the pipe joint according to the present invention is tightened with Power Tight, Fig. 6 is a sectional view showing the main structure of the second embodiment, and Fig. 7
The figure is a sectional view showing the main structure of the third embodiment. 1... Pipe 2... Lip s 3... Outer periphery sealing surface 4... Tip sealing surface 5... Thrust surface 6... Coupling 7... Shoulder part 8... Inner periphery Seal surface 9...
・Abutting seal surface 10...Supporting surface Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 1 Fig. 5 □ The bevel is attached with 7 lines of torque, 1--6 lines of surface pressure of VC are attached. Itinerary Figure 6 Figure 7

Claims (1)

[Claims] 1. In a threaded joint for oil country tubular goods, a lip portion having a tapered outer periphery sealing surface and a tip sealing surface is formed at the end of the pipe with a male thread carved thereon, and a female thread is carved therein to be screwed into the front piping. A shoulder portion having an inner seal surface and an abutting seal surface corresponding to the outer seal surface and the tip seal surface is formed in the inner deep part of the coupling, A pipe joint for oil country tubular goods, characterized in that stopper portions that abut each other are formed.