JPH0155836B2 - - Google Patents

Description

[Detailed description of the invention]

"Industrial Field of 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.
This relates to a female screw member in which a resin ring for maintaining airtightness is inserted and mounted. “Conventional technology” The depth of oil wells is several thousand meters, and in recent years the depth has been increased to 10,000 meters.
is also about to be reached. A huge number of oil country tubular goods are installed vertically into such oil wells, and they are all connected in series by pipe joints. Such pipe fittings are subject to various severe forces, such as 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, and pressing force on the inner circumferential surface due to internal fluid. act. Needless to say, these forces become more severe as the depth of the oil well increases. Pipe joints that can be used under such severe conditions are required to withstand enormous tensile loads and at the same time have reliable 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. However, regarding the metal-to-metal seal portion, there was a problem of seizure during fastening. A high surface pressure of 100 to 150 Kg/mm ² is normally applied to the seal portion, and if lubrication is insufficient during fastening, seizure is likely to occur in the seal portion. When this seizure occurs, the airtight performance is impaired and internal fluid leaks. Therefore, a technique has been proposed in which high lubricity is ensured and seizure is prevented by forming a metal coating, a chemical conversion coating, a resin coating, or the like on the metal-to-metal seal portion. However, the airtightness may still be insufficient, and in order to maintain airtightness even in the unlikely event that the metal-to-metal seal portion is sewn or surface flaws occur, the A pipe fitting for oil country tubular goods as shown 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, and 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
The material is a fluororesin such as Teflon, and the groove is slightly larger than the annular groove 4. Pipe body 2
When the male threaded part 2a carved in is screwed into the female threaded member 1 and tightened and rotated, the resin ring 5 receives a deformation action and a compression action at the same time by the threads of the male threaded part 2a. At the same time, the gap between the female screw 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, in pipe fittings that do not have a metal-to-metal seal part 3, the resin ring 5
Since the resin ring 5 is the main sealing member, how to improve the airtight performance of the resin ring 5 has been a very important issue. "Problems to be Solved by the Invention" Conventionally, the annular groove 5 was formed by turning, and its surface roughness was approximately 12 μm Rmax. 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 surface, and is approximately 6 μm Rmax. Furthermore, a lubricant is applied to the male threaded portion 2a prior to screwing. Therefore, the coefficient of friction between the resin ring 5 and the surface of the annular groove 4 is greater than the coefficient of friction between the resin ring 5 and the tubular body 2, so that the resin ring 5 does not touch 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 threads within the annular groove 4, and was filled in a good condition. [See FIG. 5a] However, such a good condition was only obtained 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 has been increasingly used for oil country tubular goods, and new problems have arisen here.
That is, high-alloy steel has low seizure resistance, unlike the low-alloy steel or carbon steel grade products that have been used for oil country tubular goods to date. Therefore, as a measure to prevent seizure, the female screw member 1 side is plated with metal such as copper, and the pipe body 2 side is sandblasted to a surface roughness of about 10 μm Rmax so that the lubricant is easily retained on the surface. was being carried out. In the above state, the coefficient of friction between the resin ring 5 and the male threaded portion 2a is greater than the coefficient of friction between the resin ring 5 and the annular groove 4. Therefore, the resin ring 5 cannot be smoothly deformed along the shape of the thread of the tube body 2, and slides and rotates with respect to the annular groove while being integrated with the male thread part 2a. It will be pushed deep into the member 1. Therefore, a part 5a of the resin ring 5 flows into the gap between the tube body 2 and the female screw member 1 [FIG. 5b], and furthermore,
A gap is created between the resin ring 5 and the annular groove 4 [FIG. 5c]. As can be seen from these figures, the resin ring 5 is strongly compressed in the annular groove 4 in the direction of the spiral movement of the tube body 2, and when a portion 5a of the ring 5 leaks out to a large degree, the resin ring 5 is compressed into the threaded portion into which the resin ring 5 is screwed. It may even get stuck and break.
In such a state, the surface pressure exerted by the resin ring 5 on the tube body 2 and the female screw member 1 becomes uneven and inappropriate, and the leakage prevention effect is impaired. In addition, since the outflow portion 5a of the resin ring 5 acts to contract in diameter with respect to the tube body 2 and to expand in diameter with respect to the female screw member 1, there is a possibility that internal fluid may leak out.
Furthermore, for the same reason, in those having a metal-to-metal seal portion, the sealing performance of this portion also deteriorates. In other words, while the dimensions of the male and female pipe fitting threads are the same, the metal-to-metal seal is designed with a slight difference in diameter so that the female part is the male part, thereby increasing the surface pressure and sealing. However, due to the above-mentioned action, the difference in diameter at the time of design 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 resin ring 5 and the tube body 2
Since the tightening resistance increases, an excessive tightening torque is required, which has the disadvantage of reducing work efficiency. "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 slipping and rotating. This is thought to be because the direction of the unevenness formed by turning coincides with the direction of sliding rotation, making it impossible to provide sufficient frictional resistance to the resin ring. If the surface roughness of the annular groove exceeds 100 μm Rmax, there is a risk that the airtight performance of the pipe joint will be reduced. Furthermore, the tolerance range of the shape and dimensions of the annular groove will be exceeded, resulting in a product that deviates from API standards, etc., which is undesirable. In order to prevent the resin ring from rotating within the annular groove, a surface roughness of at least 20 μm Rmax 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 portion 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. The Rmax was set at 100 μm. "Operation" The present invention improves the surface roughness of the annular groove surface by 20 to 100μ.
m Rmax, so the inserted resin ring may slip and rotate within the annular groove, be pushed toward the back of the tube in the spiral direction, or protrude from the annular groove and cause meat flow. disappears. "Example" The oil country pipe joint according to the present invention is mainly applied to those made of high alloy steel. As shown in FIG. 1, a threaded portion 1a of a female threaded member 1 of a pipe joint for oil country tubular goods
An annular groove 4 is provided around the periphery, which is conventionally done by turning or other means. The annular groove usually has a width of 1.0 to 2.0 times the thread pitch and a depth of 1.5 to 2.0 times the thread height. In order to prevent the resin ring inserted into the annular groove 4 from sliding and rotating, the annular groove surface 4a is provided with a surface roughness of 20 to 100 μm.
Rmax 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. 3a, 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. 3b,
The resin ring may be pushed deep into the annular groove 4 in the spiral direction of the tube, resulting in uneven filling. Therefore, as shown in FIGS. 2a to 2c, the unevenness is desirably in both the vertical and horizontal directions, in a mesh shape, or in 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. Tube outer diameter 139.7mm Wall thickness 7.72mm Material API standard N-80 Yield point 56Kgf/mm ² Specified tube body yield pressure 620Kgf/mm ² Surface treatment Sandblasting Surface roughness 10μm Rmax Thread height 1.6mm Thread pitch 5.08mm Taper 1 /16 Pipe body Outer diameter 177.6mm Wall thickness 9.20mm Material API standard C-95 Yield point 67Kgf/mm ² Specified tube body yield pressure 690Kgf/mm ² Surface treatment Sandblasting Surface roughness 10μm Rmax Thread height 1.6mm Thread pitch 5.08mm Taper 1/16 Female thread member Material API standard C-95 Surface treatment Copper plating Annular groove width 7.6 mm Annular groove depth 2.5 mm Tightening conditions Rotation speed 5 rpm Tightening torque Tube 900Kg・m Tube 1200Kg・m Resin ring Material Teflon Ring width 6.2mm Ring thickness 2.0mm

[Table] In Table 1, the flow state of the resin ring is the result of observation by conducting a tightening and loosening experiment of a pipe joint.
In determining the flow state of the resin ring, the fifth
As shown in figure a, a good condition is defined as no flow, and figure b
As shown in FIG. A state in which a portion 5a of the fluid flows out into the gap between the tube body 2 and the female screw member 1, and a gap is created between the annular groove 4 and the annular groove 4 is defined as a large flow state. In addition, for the airtightness test, the resin ring 5
In order to evaluate the airtight performance of the pipe, a drill hole 6 was drilled in the metal-to-metal seal part 3 of the pipe body 2, and nitrogen gas was pumped into the sealed steel pipe, and nitrogen gas leaked outside the pipe fitting. The pumping pressure at that time was measured.
(See FIG. 6) As is clear from Table 1, in the product of the present invention, no part of the resin ring leaks into the threaded portion, or even if it does, it is extremely small. Additionally, compared to conventional products, a significant improvement in airtightness was observed. With conventional products, nitrogen gas leakage is 300Kgf/cm ² from the pipe body.
This occurs at 250 Kgf/cm ² in the pipe body, but in the case of the product of the present invention, the pumping pressure of nitrogen gas is equal to the specified pipe body descending pressure (620 Kgf/cm ² in the pipe body, 620 Kgf/cm ² in the pipe body). Airtightness is ensured even at high pressures. In particular, the improvement in large-diameter pipes is remarkable, with a value of more than 2.7 times. In addition, the type of pipe joint for oil country tubular goods according to the present invention is as follows:
It is possible to use either a coupling type or an integral type. Furthermore, depending on the degree of airtightness required and the type of OCTG, it may or may not have a metal-to-metal seal, and multiple resin rings may be inserted and installed. It's okay. The tubular body and the female screw member are not limited to those made of high alloy steel, but of course may 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 electric discharge machining and laser machining can also be used. The surface treatment may be applied to the bottom surface of the annular groove, but it is more effective if the side surfaces of the annular groove are also provided with irregularities in order to increase the radial frictional resistance of the resin ring. 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 the annular groove provided around the threaded part of the female threaded member of the pipe joint.
By setting Rmax to 100 μm, the resin ring inserted into the annular groove will not slip and rotate when the tube is tightened, nor will it be biased toward the inner part of the tube in the direction of spiral movement within the annular groove. , the resin ring can be smoothly deformed along the shape of the thread of the tube body. Moreover, it will not flow out to some of the threaded parts. Therefore, the resin ring fills the gap between the tube body and the female screw member in a good condition, 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. It is particularly 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, FIGS. 2 a to c are drawings showing the annular groove surface of the oil country pipe joint according to the present invention, and FIGS. 3 a and b
1 is a drawing showing a conventional annular groove surface and an unsuitable surface shape. Fig. 4 is a half-sectional view showing a conventional oil country pipe joint, Figs. be. DESCRIPTION OF SYMBOLS 1... Female screw member, 1a... Thread part, 4... Annular groove, 4a... Annular groove surface, 5... Resin ring.

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, and the surface roughness of the annular groove is 20 to 100 μm Rmax. A pipe fitting for oil country tubular goods that is characterized by the following.