JPS61218892A - 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 "Field of Industrial Application" The present invention relates to a pipe joint for oil country tubular goods used to extract crude oil, natural gas, etc. from deep underground. It relates to a device with a resin ring inserted and attached for holding.

``Conventional technology'' The depth of oil wells is several thousand meters, and in recent years has been reaching 10,000 meters. A huge number of oil country tubular goods are installed vertically in such oil wells, and they are all connected in series by pipe joints. Such pipe fittings are subject to axial tensile force due to the weight of the pipe and pipe fitting themselves, ground pressure exerted on the outer circumferential surface from the surroundings, pressing force on the inner circumferential surface due to internal fluid, etc.
Various harsh forces come into play. It goes without saying that these forces become even more severe as the depth of the oil well increases. Pipe fittings that can be used under such harsh conditions must be able to withstand enormous tensile loads and at the same time be reliable. It is required to have good airtight performance. Therefore, many proposals have been made in the past in order to meet the above requirements.

As for tensile load resistance, good results have been obtained by improving the shape, pitch, etc. of the threads in the joint. On the other hand, with regard to airtightness, a technique is generally known in which a metal-to-metal seal is provided by forming a tapered lip in the unthreaded portion of the joint.

By the way, metal-to-metal seals have a problem of seizure during fastening. The seal part usually contains 100
A high surface pressure of ~150 kr/'w2 is applied, and if there is insufficient lubrication during fastening, the seal part is likely to seize. When this seize occurs, the airtight performance will be impaired and the internal fluid will leak. A technique has also been proposed in which high lubricity is ensured and seizure is prevented by forming a metal coating, chemical conversion coating, resin coating, etc. on the metal-to-metal seal portion.

However, the airtightness may still be insufficient, and in order to maintain airtightness in the unlikely event that the metal-to-metal seal part seizes or has surface flaws, a fourth
A pipe joint for oil country tubular goods as shown in the figure was proposed. FIG. 4 is a partial half-sectional view showing a state in which the tube body 2 is fastened to the female screw member 1. A metal-to-metal seal portion 3 is provided at the joint portion of the joint. The female screw member 1 has an annular groove 4 provided around the screw portion 1a, and a resin ring 5 inserted into the annular groove 4. The resin ring 5 is made of a fluorine-based resin such as Teflon, and is formed to be slightly larger than the annular groove 4. Male screw part 2a carved in tube body 2
When the resin ring 5 is screwed into the female thread member 1 and tightened and rotated, the resin ring 5 is simultaneously deformed and compressed by the threaded part of the male threaded part 2a, and Rel! The gap between the child member 1 and the tube body 2 is filled. Therefore, even if the internal fluid leaks from the metal-to-metal seal portion 3 into the joint joint, the resin ring 5 can prevent the fluid from leaking to the outside. In addition, since the resin ring 5 is the main sealing member in a pipe joint that does not have a metal body metal seal part 3, it was a very important issue how to improve the airtight performance of the resin ring 5. Φ "Problem to be Solved by the Invention" Conventionally, the annular groove 5 was circumferentially formed by turning, and its surface roughness was about 12J4Rmax. On the other hand, the surface roughness of the male threaded portion 2a of the tube body 2 is smaller than the surface roughness of the annular groove 4, and is approximately 6uaRsiax. In addition, the male thread part 2a
A lubricant is applied to the parts before they are screwed together.

Therefore, since the coefficient of friction between the resin ring 5 and the surface of the annular groove 4 is larger than the coefficient of friction between the resin ring 5 and the pipe body 2, the resin ring 5 is attached to the annular groove 4 when the joint is fastened.
There was little slippage and rotation in the annular groove 4, and it deformed smoothly along the shape of the threaded portion within the annular groove 4, and was filled in a good condition. [See FIG. 5 (8)] However, such a good condition was obtained only when the steel pipe was manufactured using a material such as carbon steel or low alloy steel.

Recently, with the deterioration of the oil well environment, high-alloy steel with excellent corrosion resistance is increasingly being used for oil country tubular goods, and new problems have arisen here.

In other words, high-alloy steel has lower seizure resistance than the low-alloy steel or carbon steel grade products that were used for oil country tubular goods until then.Therefore, as a measure to prevent seizure, copper, etc. are added to the female thread member 1 side. Metal plating is applied to the tube body 2 side so that the lubricant is easily retained on the surface (the surface roughness is set to 10mRma).
Sandblasting was performed to give a roughness of about x. In the above state, the coefficient of friction between the resin ring 5 and the male threaded portion 2a is larger than the coefficient of friction between the resin ring 5 and the annular part 14. Therefore, the resin ring 5 cannot smoothly deform along the shape of the threaded portion of the tube body 2, and slides and rotates with respect to the annular groove while being integrated with the male threaded portion 2a. It will be pushed deep into the member 1. Therefore, a portion 5a of the resin ring 5 leaks into the gap between the tube body 2 and the female screw member 1 (see FIG. 5)], and furthermore, a gap is created between the resin ring 5 and the annular groove 4. As can be seen from these figures, the resin ring 5 is strongly (compressed) in the short direction of the tube body 2 within the annular groove 4, and when the degree of outflow of the part 5a is severe, The resin ring 5 may even get caught in the threaded part and be broken. In such a state, the surface pressure exerted by the resin ring 5 on the tube body 2 and the female threaded member 1 becomes uneven and inappropriate. , the leakage prevention effect is impaired.Furthermore, the outflow portion 5a of the resin ring 5 acts to reduce in diameter with respect to the tube body 2 and to expand in diameter with respect to the female screw member 1, so that the leakage of internal fluid is prevented. Moreover, for the same reason, in products with a metal-to-metal seal, the sealing performance of this part may be deteriorated (i.e.,
While the dimensions of the tube fitting egg part are the same for both male and female parts, the metal-to-metal seal part is designed with a slight difference in diameter so that the female part is the male part, thereby increasing the surface pressure and ensuring sealing performance. However, due to the above-mentioned action, the difference in diameter at the time of needle setting tends to be erased, and in some cases, the difference in diameter is reversed and sealing performance is lost. Furthermore, in such a state, the tightening resistance between the resin ring 5 and the tube body 2 becomes large (which increases the tightening torque), resulting in a disadvantage that an excessive tightening torque is required and the work efficiency deteriorates.

"Means for Solving the Problems" The present inventors have made extensive research efforts to solve the above problems. As a result, we came to the following findings.

■ In conventional turning of an annular groove, simply increasing the surface roughness cannot prevent the inserted resin ring from sliding and rotating. This is because the direction of the unevenness formed by turning is the direction of sliding and rotation. It is thought that this is because sufficient frictional resistance cannot be imparted to the resin ring since it coincides with the above.

■ If the surface roughness of the annular groove exceeds 100100JJIIR, there is a risk that the airtight performance of the pipe joint will be reduced. In addition, the tolerance range of the shape and dimensions of the annular groove will be exceeded, and A
This is not desirable because it results in a product that deviates from PI standards, etc.

(2) In order to prevent the resin ring from rotating within the annular groove, a surface roughness of at least 20 mRsax is required.

The configuration of the present invention was determined based on the above findings. That is, a feature of the present invention is that a resin ring for maintaining airtightness is inserted into an annular groove provided around the threaded part of a female thread member of an oil country pipe joint, and the surface roughness of the annular groove surface is set to 20 to 20. 100
It was set as mRsax.

"Function" The present invention improves the surface roughness of the annular groove surface by 20 to 100 JJI.
IRsax prevents the inserted resin ring from slipping and rotating within the annular groove, being pushed toward the back of the tube in the spiral direction, or protruding from the annular groove and causing counterflow. It disappears.

"Example" The pipe joint for oil country tubular goods according to the present invention is mainly used for those made of elevated metal steel. As shown in FIG. 1, an annular groove 4 is provided around a threaded portion 1a of a female threaded member 1 of a pipe joint for oil country tubular goods, but this is done by turning or other means as in the past. The dimensions of the annular groove are usually 1.0 to 2.
0 times, and the depth is 1.5 to 2.0 times the screw thread height.

In order to prevent the resin ring inserted into the annular groove 4 from sliding and rotating, the annular groove surface 4a has a surface roughness of 20 to 100 J.
JIR■ax unevenness is provided. The formation of this unevenness is
This is done by knurling or sandblasting.

2 and 3 are drawings in which the annular groove 4 is viewed from the front. As described above, if the direction of the unevenness of the annular groove surface 4a coincides with the direction of sliding rotation of the resin ring, as shown in FIG. 3, the sliding rotation cannot be sufficiently prevented.

Furthermore, even if there are only irregularities provided in the axial direction of the tube as shown in FIG. There is a possibility that the condition may be biased. Therefore, the unevenness is the second [m(al to (
As shown in cl, it is desirable to have a shape in both the vertical and horizontal directions, a mesh shape, or an irregular shape without directionality.

Table 1 shows the experimental results comparing the airtight performance of the product of the present invention and the conventional product.

The conditions for the airtight experiment were as follows.

Pipe ■ Outer diameter 139.7m Wall thickness 7.72 Dragon material
API standard N-80 yield point
56 kgf7m' specified pipe body yield pressure 620 k
gf/Ryu 2 surface treatment Sandblasting surface roughness 10 mRs+ax height 1.6, m terminal pitch
5.08m Taber 1/16 (Margin below, continued on next page) Pipe body ■ Outer diameter 177.6m Wall thickness 9.20 Kamo material
API standard C-95 yield point
67 kgf/Tsuru 2 standard pipe body yield pressure 690 k
gf/Tsuru 2 surface treatment Sandblasting surface roughness 10 4Rmax screw thread height
1.6 Crane screw pitch 5
．． 08 Tsuru Taper ゛ 1/16 Female screw member material API standard C-95 surface treatment
Copper plating annular groove width 7.6 fl annular groove depth
2.5 Tsuru tightening conditions rotation speed 5 rp-tightening torque Tube E 900kg-m Tube U 1200kg
-m Resin ring material Teflon ring width 6.2 Thickness
2. O fin (hereinafter referred to as blank space) Table 1 In Table 1, the flow state of the resin ring is the result of observations made by performing a tightening and unfastening experiment of a pipe joint.

In determining the flow state of the resin ring, Fig. 5 (a
＞, a good condition is defined as no flow, and as shown in the same figure ('b), a part 5a of the resin ring 5 has flowed out,
A state in which there is no gap between the ring groove 4 and the annular groove 4 is defined as a small flow state, and as shown in FIG.
a flows out into the gap between the tube body 2 and the female screw member 1, and
A state in which a gap was created between the annular groove 4 and the annular groove 4 was defined as a high flow state.

In addition, in the airtightness test, in order to evaluate the airtightness of only the resin ring 5, a drill hole 6 was drilled in the metal-to-metal seal portion 3 of the tube body 2, and nitrogen gas was pumped into the sealed steel tube. Then, the pumping pressure when nitrogen gas leaked outside the pipe joint was measured.

(See Figure 6) As is clear from Table 1, in the product of the present invention, no part of the resin ring leaks into the threaded part, or even if it does, it is extremely small. . Also,
Significant improvement in airtight performance is observed compared to conventional products. With conventional products, the leakage of nitrogen gas is 30% with pipe body ■.
0 kgf/cm2, 250 kgf for pipe body ■
/ am2, but in the product of the present invention, the pumping pressure of nitrogen gas exceeds the specified tube body yield pressure (620 kgf for tube body ■)
/cIA', the pipe body ■ maintains airtightness even when the pressure reaches a high pressure of 690 kgf/12). In particular, the improvement in large-diameter tube bodies is remarkable, with a value of 2.7 times or more.

The type of pipe joint for oil country tubular goods according to the present invention may be either a coupling type or an integral type. Also, depending on the degree of airtightness required and the type of oil country tubular goods, it may or may not have a metal-to-metal seal, and even if multiple resin rings are inserted. Of course, the tubular body and female screw member are not limited to those made of commonly used high alloy steel, but may also be made of low alloy steel or carbon steel. The surface treatment method for the annular groove is not limited to knurling and sandblasting, but it is also possible to process it by electrical discharge machining or laser machining.0 Surface treatment only needs to be applied to the bottom surface of the annular groove.
In order to increase the radial frictional resistance of the resin ring, it is more effective if the annular groove side surface is also provided with irregularities.

Further, in the embodiment, Teflon was used as the material for the resin ring, but it is not limited to fluorine-based resins, and other synthetic resins with excellent heat resistance and corrosion resistance may be used.

"Effects of the Invention" As described above, the present invention provides a surface roughness of 20 to 100 JJI of the annular groove provided around the threaded part of the female threaded member of the pipe joint.
By using IR ax, the resin ring inserted into the annular groove will not slip and rotate when the tube is tightened, and will not be biased towards the feeding direction of the tube within the annular groove. , the resin ring can be smoothly deformed along the shape of the threaded portion of the tube. Moreover, a part of it will not flow out to the threaded portion. Therefore, the resin ring satisfactorily fills the gap between the tube body and the female screw member, so that the airtight performance is significantly improved and unnecessary stress is not exerted on the tube body and the female screw member. Furthermore, since it reduces the tightening resistance of the tube body, it eliminates the need for excessive tightening torque and improves work efficiency. In particular, it is effective for oil country tubular goods made of high-alloy steel, so it is effective for oil wells in corrosive environments, which have been difficult to mine up to now.

[Brief explanation of drawings]

FIG. 1 is an enlarged partial sectional view showing an embodiment of the present invention, and FIG.
Figures (a) to (C1 are drawings showing the annular groove surface of the oil country pipe joint according to the present invention, and Figure 3 (al and 'b) is
1 is a diagram illustrating a conventional annular groove surface and an unsuitable surface shape; FIG. 4 is a half-sectional view showing a conventional oil country pipe joint;
FIG. 5 (Ml to TCI are drawings explaining the deformed state of the resin ring, and FIG. 6 is a drawing showing the test method for airtight performance. l--Female thread member 1a...-Thread part 4 - Annular groove 4a - Annular groove surface 5 Resin ring Patent applicant Sumitomo Metal Industries Co., Ltd. Agent Patent attorney 1) Toshihiko (a) (b) (c) Figure 2 (a) ( b)

Claims (1)

[Claims] 1. A pipe joint for oil country tubular goods in which a resin ring for maintaining airtightness is inserted into an annular groove provided around the threaded portion of a female thread member, the surface roughness of the annular groove being 20 to 100 μm.
A pipe joint for oil country tubular goods characterized by Rmax.