JP2000314489A - Steel pipe screw joint for oil well pipe - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steel pipe screw joint for an oil well pipe to prevent deterioration of sealing ability due to the increase of a doping pressure. SOLUTION: In a steel pipe screw joint for an oil well pipe provided with a metal seal part 6 and a thread 3 connected thereto, a groove 8 short-circuiting roots on both sides of a thread is formed on one or both of the coupling 2 side and the pin 1 side of the thread. This constitution prevents the increase in a doping pressure by spreading the air gap of the thread and ensures sealing ability.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a threaded joint for a steel pipe for an oil country tubular good, which is used for mining resources such as oil and gas and is required to have a leak resistance.
The present invention relates to a steel pipe threaded joint for oil country tubular goods in which the thread structure is improved. In the present invention, the "oil well pipe" refers to a pipe that is built in a mining hole (oil well, gas well, etc.) for an energy resource fluid (oil, natural gas, etc.) and is used for pumping the energy resource fluid.

[0002]

2. Description of the Related Art In recent years, the depth of oil wells, gas wells, etc., has increased from several thousand meters to one
Oil well pipes to be built in such oil wells, gas wells, etc., which are going to reach a depth of 10,000 meters, are assembled by connecting a huge number of steel pipes in series by coupling.

[0003] At the connecting portion of the oil country tubular good, an axial tensile force due to the weight of the steel pipe and the coupling, a ground pressure exerted from the periphery to the outer peripheral surface, a pressing force on the inner peripheral surface by the fluid flowing inside, and the like. Needless to say, various types of severe forces act, and these forces become more severe as the depth of the well increases. Therefore, the connection portion is required to have a performance capable of withstanding a strong tensile load (tensile strength) and a performance of reliably sealing a fluid (sealability; synonymous with leak resistance).

[0004] In order to ensure these performances, the connecting portion is conventionally constituted by a steel pipe threaded joint having a structure as shown in FIG. In FIG. 3, a steel pipe having a threaded end is referred to as a pin. The pin 1 has a tapered outer periphery at the distal end, a male screw 1a engraved on the tapered surface thereof, and a pin-side sealing portion 4 having a convex conical surface following the male screw 1a at the distal end side. Reference numeral 2 denotes a coupling. The coupling 2 has a female screw 2a formed on the inner peripheral surface thereof so as to be screwable with the male screw 1a. A coupling-side seal portion 5 (having a convex portion on a part thereof) is provided. A metal seal portion 6 is formed by the pin-side seal portion 4 and the coupling-side seal portion 5 that come into metallic contact with each other, and a screw portion 3 is formed by the male screw 1a and the female screw 2a that are screwed together. That is, the steel pipe threaded joint has the metal seal portion 6 and the thread portion 3 connected thereto.

[0005] In such a steel pipe threaded joint, the tensile strength is maintained at a predetermined value by optimizing the thread shape, thread pitch, etc. of the threaded portion, and the sealing performance is reduced to a predetermined torque T as shown in FIG. The steel pipe threaded joint is tightened and a predetermined contact surface pressure P is generated in the metal seal portion 6 connected to the steel pipe thread joint, thereby ensuring the predetermined level.

[0006]

The threaded joint of a steel pipe is usually applied with a lubricant called a compound to its thread portion and metal seal portion prior to the tightening. This compound is extruded in a spiral shape along the screw path due to the gradual reduction of the screw gap (gap between the male and female screws) as the screwing progresses during tightening. However, if the size of the screw gap is too small, the compound cannot be sufficiently discharged, and the trapped compound has a pressure called dope pressure. In particular, as shown in FIG. 5, when the dope pressure in the dope pool 7 near the metal seal portion 6 increases, a force F for reducing the contact surface pressure of the metal seal portion 6 acts, and as a result, sufficient sealing performance is obtained. I will not be able to.

An object of the present invention is to solve the above problem and to provide a threaded joint for a steel pipe for an oil country tubular good, in which the deterioration of sealing properties due to an increase in dope pressure is prevented.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention is directed to a steel pipe threaded joint for oil country tubular goods having a metal seal portion and a threaded portion connected to the metal seal portion, the coupling side and the pin side of the threaded portion. A threaded joint for a steel pipe for oil country tubular goods, wherein a groove for short-circuiting thread valleys on both sides of the thread in the pipe axis direction is provided in one or both of the threads.

[0009]

FIG. 1 is a partial sectional view of a threaded steel pipe joint according to an embodiment of the present invention. In FIG. 1, reference numeral 8 denotes a groove, and the same or corresponding members as those in the conventional example of FIG. FIG. 2 is a sectional view of the coupling 2 showing the entire groove 8 of the present embodiment. As shown in FIGS. 1 and 2, in this embodiment, a groove 8 that short-circuits the thread valleys on both sides of the thread in the tube axis direction is provided in the thread on the coupling side of the thread. By providing such a groove 8, the screw portion gap forming the discharge path of the compound is enlarged,
The dope pressure generated at the time of tightening is more reliably reduced than in the conventional case having no groove. Therefore, the contact surface pressure of the metal seal portion 6 is maintained at a high level, and the sealing performance is significantly improved.

In the present invention, the number of grooves may be singular or plural as long as there is no problem in the rigidity of the thread portion, and the side on which the grooves are provided may be the pin side instead of the coupling side in this embodiment. Alternatively, both the coupling side and the pin side may be used. Further, the sectional shape of the groove is not particularly limited.

[0011]

EXAMPLE The threaded steel pipe joint of the present invention was applied to a connection part of an oil country tubular good corresponding to API standard L80 (steel pipe part: outer diameter 88.9 mm × wall thickness 6.452 mm). For the metal seal part of this joint, the pin side seal part is defined as taper angle: 1/10, length: 10.2 mm, seal diameter: 84.02 mm, and the corresponding coupling side seal part is taper angle: 1/100. 10, convex surface seal length ×
The seal radius R was defined as 5.1 mm x 76 mm, and the seal diameter was 83.69 mm.

Sample A prepared as an embodiment of the present invention
As shown in FIGS. 1 and 2, a single groove 8 having the same depth as the female screw 2a is machined in the inner periphery of the coupling 2 in the axial direction. Further, as a comparative example, a sample B without groove processing was also prepared as in the related art. Samples A and B were each 500
Tighten with a torque of kg · m, and then apply an axial tensile load of 76.1
ton (axial stress 50.6 kgf / mm ² corresponding to 90% SMYS)
And a gas internal pressure of 740 kg / cm ² (corresponding to 90% SMYS) were applied, and the presence or absence of leakage was inspected. as a result,
Although a leak occurred in Sample B, no leak occurred in Sample A, confirming the effect of improving the sealability according to the present invention.

[0013]

As described above, according to the present invention, there is an excellent effect that the compound discharge property at the time of tightening is improved and a threaded steel pipe threaded joint for oil country tubular goods having much better leak resistance than the conventional one can be obtained.

[Brief description of the drawings]

FIG. 1 is a partial sectional view of a steel pipe threaded joint showing an example of the present invention.

FIG. 2 is a cross-sectional view of the coupling showing the entire groove of the example shown in FIG. 1;

FIG. 3 is a partial sectional view showing a conventional example of a threaded steel pipe joint.

FIG. 4 is an explanatory diagram of a contact surface pressure generating mechanism.

FIG. 5 is an explanatory view of deterioration of sealing property due to high doping pressure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pin 1a Male screw 2 Coupling 2a Female screw 3 Screw part 4 Pin side seal part 5 Coupling side seal part 6 Metal seal part 7 Dope accumulation 8 Groove

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takaaki Toyooka 1-1-1, Kawasaki-cho, Handa-shi, Aichi F-term in the Chita Works of Kawasaki Steel Corporation (reference) 3H013 JA01

Claims (1)

[Claims] 1. A threaded joint for a steel pipe for an oil country tubular good having a metal seal portion and a thread portion connected to the metal seal portion, a thread on one or both of a coupling side and a pin side of the thread portion, and a thread on both sides of the thread portion. A threaded joint for a steel pipe for oil country tubular goods, wherein a groove for short-circuiting a valley in a pipe axis direction is provided.