JPS6283586A - Oil well pipe joint having excellent sealing property - 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] "Objective of the invention" (Industrial application field) In recent years, the depth of wells that produce natural gas and crude oil has reached as much as 10,000 meters underground (depending on the amount of injection). The invention relates to a pipe joint for oil country tubular goods inserted vertically into such deep wells.

(Conventional OCTG) A huge number of OCTG are installed vertically into deep wells, and these OCTG are connected in series using integral type pipe fittings or coupling type pipe fittings.

FIG. 5 is a front view showing a Campling-type pipe joint laid sideways and partially cut away. Oil country tubular joints of this type must withstand the effects of external compressive force due to earth pressure and pressing force on the inner circumferential surface due to internal fluid, and must also have reliable airtightness to ensure that internal fluid never leaks. It is strictly required to have one. Therefore, a configuration as shown in FIG. 6 is adopted.

FIG. 6 is an enlarged view of the part indicated by the arrow in FIG. 2 is a diagram showing a state at a certain point in time. As shown in the figure, the tip b1 of the pin b and the inner part of the box a are formed in a tapered shape that corresponds to each other, and normally, the minimum outer diameter of the tip b1 of the pin b is the box a. It is formed slightly larger than the maximum inner diameter of the inner part a1 at a.

Therefore, when the oil country pipe B and the coupling A (see Fig. 5) are tightened, the tip end bl of the pin b is moved along the tapered inner circumferential surface a3 whose diameter is gradually reduced from the cut end at the deep part a1 of the box a. is inserted while being reduced in diameter. Therefore, a main seal portion with high surface pressure metal-to-metal contact is formed between the tapered outer peripheral surface b3 of the pin b and the tapered inner peripheral surface of the box a. In addition, the annular tip end of pin b is flush with the pipe axis at an angle of about 100 degrees (slanted) to the pipe axis direction, just like the tip of the shaft, so the tightening of the OCTG B and coupling A is completed. Sometimes, a metal-to-metal sub-seal with high surface pressure contact is formed between the tip annular surface of the pin b and the inner annular surface a4 of the box a. The oblique force generated when retightening causes the annular surface of the distal end of pin b to expand in the direction of its outer periphery. Also runs a business.

By the way, as mentioned above, the number of OCTGs B vertically installed in a deep well is enormous, and accordingly, the number of couplings A is also enormous.Therefore, each pipe joint has OCTGs B A strong tensile charge is applied in the direction of the tube axis due to the accumulation of force and weight of 7 pulling A.For this reason, in the past, measures such as pinching the neck part of the pipe joint and improving the standard chevron shape were used. However, a small gap still occurred in the main seal part and the sub-seal part, and the internal fluid sometimes leaked from the small gap.Therefore, as shown in Fig. 5, the screw part on the box a side of the pipe joint or A Teflon ring C was fitted into the threaded portion on the pin b side to assist in sealing action.

(Problems to be Solved by the Invention) When the pin b and the box a are screwed together, it is necessary to uniformly increase the contact pressure of the Teflon ring C against both over the entire circumference. Therefore, during tightening, the Teflon ring C was designed to flow and deform largely along the threaded portion of the pipe joint. For this reason, the Teflon ring C was required to have fluidity against the deformation and toughness to prevent breakage during tightening. However, if the fluidity or toughness is too large, if there is a local gap between pin b and box a, the Teflon ring C will flow unevenly into the gap, and the specified contact surface There were times when I couldn't get enough pressure. In this way, Teflon ring C had to satisfy conflicting demands regarding fluidity and toughness.

On the other hand, in deep wells that extend from several thousand meters to 17 meters underground, the temperature atmosphere in the deep parts of the wells reaches an extremely high temperature of 400 to 500 degrees Celsius. However, the Teflon ring C has a melting point of 3
The temperature is as low as around 00°C, and the usable conditions, in other words, the usable depth range in a well, are narrowly limited. Furthermore, even if it is within the usable temperature range of 300°C or less, the compressive creep strength and compressive yield stress of Teflon Ring C cannot be said to be sufficient, and these values are particularly susceptible to thermal cycles, and the sealing material Its reliability was extremely poor. It should be noted that sealing materials used in oil country tubular joints are required to have the ability to immediately fill gaps that widen due to increases in tensile load or ambient temperature.

This function is controlled by the shape recovery property of the material forming the sealing material. Therefore, the shape restorability of Teflon forming the Teflon ring C was investigated as shown in FIG. First, assuming the contact surface pressure between pin b and box a, a predetermined compressive force was applied to Teflon to generate stress, and the strain recovery rate was measured when the compressive stress was gradually unloaded. . In addition, the measurement was performed using Teflon at 20°C.
The test was carried out while being held at . As a result, a high value of approximately 15% was measured, which corresponds to a compressive stress of 3.5Kgf.
This value is limited to an extremely low stress region from /md to O, and this value could hardly be expected when high contact surface pressure is applied, such as when pin b and box a are aligned. Moreover, as mentioned above, Teflon has an extremely poor compressive yield stress of 5Kgf/*d or less, so the compressive stress is 3.5Kgf/vat in the first place.
The fact that it was not possible to add additional light is also an important drawback that cannot be overlooked. Furthermore, in addition to these drawbacks, the Teflon ring C also has the drawback that it must be replaced with a new one every time the oil country pipe B and the cassop ring A are unscrewed.

The present invention was made in view of the above circumstances, and is capable of achieving high reliability in sealing performance without being affected by strong tensile loads or high-temperature atmospheres, and also allows easy screwing and unscrewing. It is an object of the present invention to provide a novel oil country tubular joint (hereinafter referred to as the oil country tubular goods joint of the present invention) with excellent sealing properties that can be repeated many times.

"Structure of the Invention" (Means for Solving the Problems) The gist of the oil country tubular joint of the present invention is that a metal-to-metal seal is formed between the outer circumferential surface of the tip of the pin and the inner circumferential surface of the deep part of the box. The oil well pipe joint is provided with a seal ring made of a shape memory alloy interposed in the seal portion, and the reverse transformation point temperature of the shape memory alloy is lower than the temperature in a deep oil well environment, The degree of shape recovery of the lower seal ring is larger than the degree of deformation of the pin and box so that it expands in the radial direction around the tube axis.

In this specification, the term "shape memory effect alloy" refers to an alloy that has a thermoelastic martensitic transformation, and its characteristic is that it deforms when an external force is applied to the original shape below the reverse transformation temperature, and Even when removed, the deformed shape is maintained substantially, and when the deformed shape is heated above the reverse transformation point temperature, it exhibits a shape memory effect in that it returns to its original shape. On the other hand, at a temperature higher than the reverse transformation point, even if the material is greatly deformed by an external force, it exhibits pseudoelastic behavior in which it returns to its original shape when the external force is removed. Typical shape memory alloys include Ni-Ti alloy and Au-Cd.
Examples include alloys, Cu-Zn alloys, and the like.

(Function) The seal ring is made of 9 alloy, and when exposed to an environment with a temperature higher than the reverse transformation temperature,
Due to shape recovery, the deformation is enlarged to a degree greater than the degree of deformation of the pin and box.

The seal ring is interposed between the outer peripheral surface of the tip of the bottle and the inner peripheral surface of the inner part of the box, and the direction of expansion deformation due to the shape recovery is along the radial direction around the tube axis of the bottle and the box. It is set as follows. In other words, the seal ring expands and deforms both in the direction of decreasing its inner diameter and in the direction of increasing its outer diameter. Therefore,
When the oil country pipe joint of the present invention is inserted vertically into the deep interior of an oil well, the seal rings will press against each other the outer circumferential surface of the tip of the bottle and the inner circumferential surface of the deep part of the box. For this reason, even if a tapered gap is formed in the sealing portion consisting of the outer circumferential surface of the tip of the pin and the inner circumferential surface of the inner part of the box due to an increase in tensile load, the seal against the bottle and box will be sealed. The rings are in close contact with each other, and the sole properties are not impaired. Moreover, the shape memory alloy that forms the seal ring recovers its shape along the radial direction and exhibits pseudoelastic behavior when exposed to a temperature higher than its reverse transformation temperature. Even when the tapered gap gradually expands, this expansion variation is quickly followed to ensure that the predetermined pressing state does not loosen at all times. In addition, the oil country tubular joint of the present invention does not cause permanent deformation of the seal ring when the pin and box are screwed together, and does not substantially deform even if screwed together and unthreaded many times. Needless to say.

(Example) The present invention will be described below based on drawings showing examples thereof.

FIG. 1 shows the oil country pipe joint of the present invention.
FIG. 3 is a partial cross-sectional view showing a state in which the box L and the box L are screwed together. As shown in the figure, the most important parts of the oil country pipe joint of the present invention are the outer peripheral surface 23 of the tip of the pin 2 and the inner peripheral surface 1 of the inner part of the box 1.
A seal ring 3 made of a shape memory alloy is interposed in the main seal portion formed by a.

In this example, N1-T+gold alloy was used as the shape memory alloy forming the seal ring 3.

As mentioned above, the Ni-Ti alloy is known as a typical shape memory alloy, and generally contains Ti in an atomic percent range of 48 to 52%. The N1Ji alloy has the property of recovering to a memorized shape by heating, and it has been found that the higher the heating temperature, the greater the shape memory effect (shape recovery force). Also Ni-
Among Ti alloys, especially those containing 49.8 atomic percent Ti, the compressive stress (virtual contact surface pressure) is gradually unloaded in the temperature range below the reverse transformation temperature, that is, the temperature range below about 92°C. Eventually, 20Kg during the unloading process.
The strain is recovered by 7 to 10% in the stress range from f/- to O. Furthermore, in addition to the strain recovery rate due to the shape memory effect, when the heating temperature is in a temperature range equal to or higher than the reverse transformation point temperature of the Ni-Ti alloy, the unloading process of compressive stress occurs as shown in FIG. 40K inside
Within the high stress region from gf/- to 30Kg4/-,
It exhibits a pseudoelastic behavior in which it quickly recovers as much as 5% strain. For reference, ICr-AM, for example, is commonly used as a material for forming the pin 2 and the box l.

It goes without saying that low alloy steel does not have a shape memory effect or pseudoelastic behavior, but the elastic strain recovery rate also increases from 70 Kgf/ad to 5 during the unloading process of compressive stress.
This Ni-Ti alloy shows only 0.4% in the stress region of Kgf/s+/, and the compressive yield stress of this Ni-Ti alloy is 20K.
gf/Iad, and this value is more than sufficient for the strength of the sealing material.

Table 1 compares the mechanical properties of this Ni-Ti alloy with those of Teflon and glass fiber-containing Teflon. As can be seen from Table 1, this Ni-Ti alloy has a high tensile strength.

The elongation, compressive yield stress, Young's modulus, and melting point are all acceptable as a sealing material for oil country tubular joints, and they cannot be compared with Teflon or glass fiber-filled Teflon.
-The coefficient of thermal expansion in the Ti alloy is small, and at the same time the lCr-! which forms the pin 2 and the box l! 4M
o The value is almost similar to that of low alloy steel. Therefore, this Ni-T
Even if the i-alloy is subjected to extreme thermal cycling, it will not create any gap between the pin 2 or the box l due to the difference in thermal expansion. Furthermore, Ni shown in Table 2
-Ti alloy shows 49.8% Ti in atomic percent.

As shown in FIG. 2, the seal ring 3 is formed into an annular shape by cutting or powder metallurgy processing a Ni-Ti alloy. The cross-sectional shape of the seal ring 3 is a parallelogram, as shown in FIG. On the other hand, a fitting stepped portion 1b having a size in which the seal ring 3 is just fitted is bored in the inner peripheral surface 1a of the box l. Further, the fitting step portion 1b is -
It is provided on the circumferential surface 1c that is formed so as to be recessed toward the outer circumferential direction. Therefore, when the pin 2 is inserted and tightened into the box l in which the seal ring 3 is installed in the fitting step lb, a clearance is created between the seal ring 3 and the outer peripheral surface 1a of the tip of the pin 2. There is. This clearance is a measure to prevent galling (seizure) of the main seal portion when the pin 2 and box 1 are tightened.

By the way, before the seal ring 3 is fitted into the fitting groove 1b of the box 1, it is necessary to memorize the enlarged shape. Therefore, in this example, when manufacturing the seal ring 3 from a Ni-Ti alloy by cutting or powder metallurgy as described above, the outer shape of the seal ring 3 was set to the expanded shape (this ). Then, the seal ring 3 in the original shape is loaded into an appropriate mold in an atmosphere at a temperature below the reverse transformation point temperature, and compressed in the direction of enlarging the inner diameter dimension and the direction of reducing the outer diameter dimension. inset dlb
It was deformed into a shape that fits perfectly. In addition, when setting the original shape of the seal ring 3, the inner diameter dimensions must be taken into consideration so that the clearance to the outer peripheral surface 1a of the tip of the pin 2 can be filled and sufficient contact surface pressure can be exerted. Moreover, it is preferable to apply appropriate heat treatment or the like after the seal ring 3 is compressed and deformed.

The usage conditions of the oil country tubular joint of the present invention thus constructed will be explained. When pin 2 and box 1 are mechanically tightened to a specified torque in an atmosphere below the reverse transformation point temperature of the shape memory alloy, the metal-to-metal main seal and sub-seal provide the same perfect sealing action as before. It is rare. Further, in this state, the sole ring 3 remains in no contact with the outer peripheral surface 2a of the tip end of the pin 2. Assume that the oil country tubular joint of the present invention is inserted vertically into a well, and as a result of increased tensile load, a tapered gap is generated in the main seal portion between the pin 2 and the box l. In this state, when the temperature atmosphere surrounding the oil country tubular joint of the present invention rises above the reverse transformation point salinity of the shape memory alloy (the reverse transformation temperature in a Ni-Ti alloy with 49.8% Ti atomic percent is 92°C), this As the temperature rises, the seal ring 3 develops a shape memory effect and expands and deforms in the radial direction of the pin 2 and box 1 in an attempt to recover its original shape. Therefore, the seal ring 3 is in a state in which the force to restore its shape is blocked by the pin 2 and the box 1, and internal strain is accumulated. Therefore, the seal ring 3 maintains a close contact state with the pin 2 and the box l with high mutual contact surface pressure. In addition, the seal ring 3 exhibits pseudo-elastic behavior when the oil country tubular joint of the present invention is surrounded by an atmosphere where the temperature is above the reverse transformation point temperature of the α alloy. In other words, while maintaining a high contact pressure due to the shape memory effect, the contact pressure of the seal ring 3 with respect to the pin 2 and box 1 sometimes tends to decrease dramatically due to an increase in tensile load, a rise in ambient temperature, etc. In such a case, the pseudoelastic behavior immediately recovers the decrease in contact surface pressure as described above,
It comes to follow the enlargement fluctuation of the gap between pin 2 and box l. Table 2 shows the results of testing the airtightness of the oil country tubular joint of the present invention. Additionally, Table 3 shows the results of testing the airtightness of conventional oil well pipe joints equipped with only Teflon rings. As is clear from a comparison between Table 2 and Table 3, the oil well pipe joint of the present invention has a power consumption of at least 7 kgf/
It can withstand an internal pressure close to mj, and can sufficiently overcome the internal pressure of 6.2 Kgf/I, which is generally required for oil well pipe joints. On the other hand, with conventional oil well pipe fittings, the amount of pressure is only 3 kgf depending on the internal surface roughness of the groove where the Teflon ring is installed.
Leakage was confirmed even at an internal pressure of /-. As can be seen from this, when installing a Teflon ring, the inner surface of the Teflon ring groove must be finished to a predetermined roughness, which requires more time and effort for processing such as sandblasting and knurling.

(Margins below) Continued on next page Table 2〉 Table 3〉 (Study of another aspect) The fitting groove for the seal ring 3 is the outer peripheral surface 2a of the tip of the pin 2.
It may be provided on the side, or may be provided on both the outer peripheral surface 2a of the tip of the pin 2 and the inner peripheral surface 1a of the box 1. Further, the seal ring 3 may be installed anywhere within the main seal portion of the pin 2 and the box l; for example, a fitting groove for a Teflon ring may be bored in the center of the main seal portion. Good, of course.
The shape memory alloy forming the seal ring is not limited to the Ni4i alloy, and further sealing effects can be expected if a Teflon ring is also used.

As described above, the detailed configuration and shape of the oil country tubular joint of the present invention can be changed as appropriate depending on the embodiment.

"Effects of the Invention J As is clear from the above explanation, according to the oil country tubular joint with excellent sealing properties according to the present invention, the seal ring formed of the shape memory alloy moves in the radial direction as the ambient temperature rises. Since the pin and box are designed to expand and deform, the pin and box are designed to maintain high contact pressure at all times, and the tapered gap between the pin and box has a limited expansion range to some extent. Therefore, the contact surface pressure tends to increase as the ambient temperature rises.In other words, in the oil country pipe joint of the present invention, the higher the ambient temperature, the more effective the sealing action becomes, and the internal fluid will not leak. In contrast, in conventional oil country joints, the contact surface pressure of the Teflon ring against the pin or box reaches its maximum value when the pin and box are tightened, and then increases due to the increase in the applied tensile load and the atmospheric temperature. As the size increases, the size of alloy 9 continues to decrease.In general, alloy 9 is not very strong against external forces such as bending and tension, and is insufficient to be used as a forming material for oil country pipe joints themselves. In addition, there is a risk that the cost will rise.Therefore, in the oil country pipe fitting of the present invention, in order to solve these problems, shape memory alloys are locally used in appropriate locations, and the shape memory alloy is used only as a sealing material. In addition, the strength of the oil well pipe joint is addressed by using the same material as before, such as lCr-%Mo low alloy steel.In other words,
This means that even in conventional oil country tubular joints, the effects of the present invention can be obtained by simply improving the fitting steps or grooves for the seal ring.

[Brief explanation of drawings]

Fig. 1 is a partial sectional view showing the screwed state of the pin and box in the oil country pipe joint of the present invention, Fig. 2 is a perspective view showing the seal ring, and Fig. 3 is the stress showing the strain recovery rate in the Ni-Ti alloy. - Strain curve, Figure 4 is a stress-strain curve showing the recovery rate of strain in a Teflon ring, Figure 5 is a partially cutaway front view of a conventional oil country tubular joint, and Figure 6TI! J is an enlarged cross-sectional view of a part of the oil country tubular joint in FIG. 5. 1... Box 1a... Inner peripheral surface 2...
・Pin 2a...Tip outer circumferential surface 3...Seal ring Patent applicant Sumitomo Kinryo Industries Co., Ltd. Representative Patent attorney 1) Toshihiko Figure 1 Figure 2 Figure 3 Distorted turning rod ('/, ) Figure 4

Claims (1)

[Claims] 1. An oil well pipe joint in which a metal-to-metal seal is formed between the outer peripheral surface of the tip of the pin and the inner peripheral surface of the inner part of the box,
A seal ring made of a shape memory alloy is interposed in the seal portion, and the reverse transformation point temperature of the shape memory alloy is lower than the temperature in the deep oil well environment, and the seal ring in the deep oil well environment is An oil country pipe joint with excellent sealing performance, characterized in that the degree of shape recovery is greater than the degree of deformation of the pin and box and expands in the radial direction around the pipe axis.