JPS5850386A - Screw 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 threaded joint for oil country tubular goods in which a groove is cut in a coupling and a sealing resin ring is inserted and filled into the groove in order to ensure desired sealing performance.

Conventionally, in this type of threaded joint, in order to seal between the pipe body 1 and the coupling 2 as shown in Fig. 1, a resin ring R1 made of Teflon or the like is usually placed inside the coupling thread. Either the resin ring R2 was inserted into the cut-up part at the back, or the resin ring R2 was inserted near the cut-up part of the fully threaded part of the tube body.

However, in the case of the former resin ring R1, when the joint is tightened, the resin ring R1 flows out from the incomplete thread In addition, the resin ring that flows out expands the coupling 2 outward and shrinks the tube body 1 inward, so the metal-to-metal There is also the problem that the original surface pressure of the seal part MS decreases, making it impossible to maintain the airtightness of the seal part MS, and stress in the coupling and the tube body also increases.

On the other hand, in the case of the resin ring R2, in order to insert and fill the resin ring, an insertion groove G2 is further cut in the thin-walled part of the coupling 2, so that excessive stress is applied to the coupling 2 when the joint is tightened. Note that the insertion grooves Gl and G2 are usually 10 to 2.0 times the thread pitch and 1 to 2 times deeper than the thread pitch line for the insertion grooves Gl and G2. mN and samurai.

Furthermore, conventionally, little consideration has been given to the degree of filling (compressibility) when inserting and filling resin rings. However, in reality, if the resin ring is not properly inserted and filled into the groove, the blood pressure necessary to prevent leakage cannot be created between the resin ring and the screw. If the resistance becomes too large, an excessive tightening torque will be required, which will reduce tightening workability, and furthermore, the resin ring will protrude from the groove, resulting in a situation similar to the above.

The present invention was proposed as a result of studies to comprehensively solve the above-mentioned problems.The purpose of the present invention is to provide sufficient sealing performance, eliminate the risk of damage due to force, pulling, etc., and eliminate the possibility of tightening. An object of the present inventor is to provide a threaded joint for oil country tubular goods that requires a relatively small torque.The present inventor investigated the insertion and filling position of the resin ring and the degree of insertion and filling into the groove from various angles, and found that the desired performance could be achieved. In order to achieve this goal, we have discovered that these are extremely important elements, and have completed the present invention.

That is, the present invention provides a threaded joint for oil country tubular goods in which a groove is cut in a tubular ring and a sealing resin ring is inserted and filled into the groove.A. The insertion position of the resin ring, which has been abraded at a distance from the pipe end, is (a) on the complete thread side from the complete thread to incomplete thread transition part at the innermost part of the coupling thread, and (b) the transition in item (a). The distance from the part to the fully threaded side shall not exceed twice the thread pitch. (a) Area compression ratio: 2.5% to 15%; (b) Height compression ratio: 15% to 30%.

Next, the present invention will be described in further detail with reference to the drawings.

Figure 2 shows the transition between incomplete thread and complete thread thread (boundary part) when a resin ring is not inserted (NO) for couplings of various outer diameter sizes with different weights or wall thicknesses. ) When an insertion groove is formed at the center of the resin ring and the resin ring is inserted (Ll), the thread is two threads closer to the complete thread side than the transition part from the incomplete thread to the complete thread, which is an embodiment of the present invention.
4) When inserting a resin ring by forming an insertion groove at the location (L
2) Circumferential stress 6”t in the metal-to-metal seal portion of the coupling (Figure (a))
, and the difference in surface pressure of the same seal portion.

According to FIG. 2, the insertion of the resin ring increases the circumferential stress 6t, but the threaded joint according to the present invention (L2
In line), the stress 6t is smaller than the conventional example and is preferable.
In addition, by inserting the resin ring, the surface pressure at the metal-to-metal seal part decreases compared to the case where it is not inserted (No), but the amount of decrease is as follows in the threaded joint of the present invention.
It is found that the amount is less than that of the conventional example and does not impede sealing performance.

Figure 3 shows the changes in the circumferential stress 6t and axial stress 6z acting on the outer surface of the coupling at the resin ring insertion site in the case where the resin ring is not inserted (No) and when the resin ring is inserted. This is what is shown. and (a
) The figure shows the case where the resin ring is inserted in the above-mentioned position L2 according to the present invention, and (b) the figure shows the case where the resin ring is inserted in the L1 position, compared with fidgeting and no resin ring inserted (NO). Shown below. According to Fig. 3, by inserting the resin ring at any position, the circumferential stress 6t increases as shown by the hatched part in the figure, but the axial stress 6''Z increases, but the absolute value is 6t. It turns out that /JX is small compared to .

Therefore, it is clear that when inserting the resin ring, it is not necessary to consider the stress in the axial direction, and it is sufficient to pay attention to the stress in the circumferential direction. Also, from the same figure, the closer the insertion position of the resin ring is to the coupling end, the more
It is shown that the amount of increase in circumferential stress 6rt is large.

Figure 4 shows the stress at the coupling end Le, the stress at the L1 position, and the stress at the L2 position regarding the enormous circumferential stress 6L, which is clear from the results shown in Figure 3. This is what we investigated. As can be seen from the figure, the circumferential stress generated in the coupling is greatest at the thinnest end of the coupling, and at the L2 position it is smaller than, but approximately the same as, the circumferential stress. The stress at the L+ position is quite small for the and combs. Therefore, even if the resin ring is inserted at any of the positions of Ll and L2, the stress is smaller than the stress at the end of the coupling, so there is no need to increase the wall thickness of the coupling. As a result, even if the resin ring is inserted into the L2 position according to the present invention, there is no risk of damage to the coupling.

Note that the stress in the circumferential direction of the coupling, when no resin ring is inserted, draws the distribution curve of the 6 t o line in Figure 5, and when the resin ring is inserted, the stress in the circumferential direction at the insertion site is dtL. Draw a line distribution curve. Therefore, the apex of the distribution curve line 6tL is the distribution curve line t. There will be no problem if the level is lower than point 9, which corresponds to the coupling end position of , but if point PIl! If the coupling exceeds the level of
Although it is lower than the level, the resin ring can be inserted without changing the specifications of the spring body (7).

As described above, the insertion position of the resin ring is (a) closer to the complete thread than the transition part between complete thread and incomplete thread at the innermost part of the coupling screw, and (b) closer to the fully threaded side from the transition part. If the distance l does not exceed twice the thread pitch, the filling performance of the resin ring will be improved, and the deterioration of sealing performance due to the resin ring flowing out can be reliably prevented. Since the reduction in surface pressure at the metal-to-metal seal portion is suppressed to a minimum, there is no deterioration in sealing performance, and since stress in the coupling is also taken into consideration, there is no damage to the coupling.

On the other hand, in terms of obtaining the desired sealing performance, the insertion position of the resin ring as well as the degree of filling of the resin ring are important factors. Therefore, various experiments were conducted to find a suitable filling degree. As shown in Fig. 6, a resin ring R with an initial thickness of b and width a of Width A
When inserted into the insertion groove G and tightened the joint, when the distance between the bottom of the insertion groove G and the pitch circle of the screw (insertion groove depth) is B, the height compression ratio and area compression ratio are as follows. O Height compressibility ratio HR=1-- x b Figure 7 shows a leakage test method for resin rings, in which the spiral teeth 30 at the center of the tube member 10 and the tube member 2o are , and also has threaded portions 10a, 1 corresponding to an actual threaded joint.
0a is formed in the tube member 10, a resin ring R is inserted into the insertion groove G formed in the tube member 20, and various loads Q are applied to the outer surface of the tube member 20 to change the degree of filling (compressibility) of the resin ring. At the same time, water pressure is applied to check for leakage from the pipe member 10.20. We also conducted a leakage test using an actual joint, and the test results are shown in Figure 8. In FIG. 8, it can be seen that the higher the area compression ratio AR, the higher the leakage resistance. However, according to actual joint tests, when the area compression ratio A5 exceeds 15%, the torque when tightening the joint becomes
It has been found that the amount increases by about 20% compared to the case where no resin ring is inserted, and the variation is also large. Moreover, since the resin ring flows between the threads and the leakage resistance does not improve much, it is desirable that the area compression ratio A6 be 15% or less. If the Al1 content is less than 2.5%, the desired high scratch resistance cannot be obtained.

Regarding the height compression ratio H2, it can be seen that the higher the height compression ratio, the better the leakage resistance for the same area compression ratio. However, as shown in Fig. 9, if the height compression ratio H is too large, there will be no gap for the resin ring to flow into the threaded trough when it is pressed in at the threaded part, and the resin ring will be pushed out of the insertion groove. Protruding.

Not only is it not possible to obtain a predetermined area compression ratio (region Z), but the stress in the coupling increases, which may lead to breakage. On the other hand, if the height compression ratio 1 is too small, as shown in FIG. 8, it will not be possible to obtain the desired cutting resistance. In view of this, it is desirable that the height compression ratio H3 is 15 to 30%. The results shown in FIG. 9 are for an example in which the distance between the thread surface and the pitch circle is 0.79 mm (thus, the thread height is 15 stm).

On the other hand, for the couplings of oil country tubular screw joints of various sizes, a Teflon resin ring is compressed within the above range at the position of 1 to 2 threads by screwing out from the incomplete thread to complete thread transition part to the fully threaded side. The joints were filled according to the ratio, the joints were actually fastened, and the stresses in the couplings were investigated, and a leakage test was conducted on the fastened joints. As a result, good results were obtained in terms of stress and sealability, confirming that the threaded joint of the present invention is extremely effective.

As can be inferred from the above explanation, the resin ring may be inserted not only in one place but also in multiple places on each side of the coupling. , which is within the scope of the invention.

(11) For example, another resin ring may be inserted into the fully threaded portion of the coupling. However, when inserting and filling other resin rings, the degree of filling (compressibility) within the above range should be satisfied.

As described in detail below, according to the present invention, since the insertion position of the resin ring and its filling degree are specified, the sealing performance can be improved, and damage to the puller ring due to force can be prevented. Furthermore, the required tightening torque can be minimized.

[Brief explanation of the drawing]

Figure 1 is a sectional view showing the conventional resin ring insertion position, Figure 2
Figures 4 to 4 are correlation diagrams showing the mechanical changes associated with insertion of couplings of various sizes, Figure 5 is a stress distribution diagram that acts on the coupling when the resin ring is not inserted, and Figure 6 is the definition of compressibility. Fig. 7 shows the leakage test system of the resin ring, (a) shows the shape of the teeth, (b) shows the cross-sectional view, and Fig. 8 shows the compressibility of the resin ring. The correlation diagram with pressure and FIG. 9 are characteristic diagrams regarding height compression ratio. (12) 1..Pipe body 2..Coupling R1, Rz -R.
・Resin ring' et al. 5th week 6th:-J 7th door (a)

Claims (1)

[Claims] (1) A threaded joint for oil country tubular goods in which a groove is cut in the coupling and a sealing resin ring is inserted and filled into the groove. The inserting position of the resin ring, which has been pre-heated at a distance from the end of the pipe body, shall be (a) on the fully threaded side of the transition area between the fully threaded and incomplete threads at the innermost part of the pulling thread, and (b) as specified in (a). The distance from the transition part to the fully threaded side shall not exceed twice the thread pitch. (a) Area compression ratio 2.5% to 15%, (b)
A threaded joint for oil country tubular goods characterized by a height compression ratio of 15% to 30%.