JPH10196264A - Threaded fittings for oil country tubular goods - Google Patents

Abstract

(57) [Problem] To provide a threaded joint for oil country tubular goods having a sufficient leak resistance performance even when a use environment temperature is 250 to 400 ° C. SOLUTION: This is a threaded joint for an oil country tubular good having a pin portion 1a having an external thread 1aa and a box portion 2a having an internal thread 2aa. Set the threaded joint body to Cr: 0.4-1.0
% By weight, Mo: 0.1 to 1.5% by weight Cr-Mo steel, and at least one of the fitting portions of the pin portion 1a and the box portion 2a is treated with phosphoric acid.
Perform zinc plating or copper plating.

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 an oil country tubular good used for exploration and production of natural gas and crude oil produced from underground. The present invention relates to a threaded joint suitable for performing the above.

[0002]

2. Description of the Related Art Screw joints are widely used as a technique for connecting oil country tubular goods used in exploration and production of natural gas fields and oil fields. This threaded joint has a pin at one end of the pipe,
There are an integra system in which a box portion is formed at the other end to connect the tubes, a coupling in which two box portions are formed, and a coupling system in which a tube having pin portions at both ends is connected.

[0003] In both of the above-mentioned methods, there are a number of combinations of the seal portion and the torque shoulder portion. An example of the coupling method is shown in FIG. In the example shown in FIG. 1, a male pipe 1 provided at an end of a steel pipe 1 is provided.
At the tip of the pin portion 1a having an aa portion, a taper-shaped sealless threadless portion 1b is provided, and the coupling 2 has a female portion 2aa which is screwed to the male screw 1aa provided at both ends. The portion is provided with a tapered seal-forming screwless portion 2b fitted to the screwless portion 1b, and a seal portion is formed by fitting the two screwless portions 1b, 2b together.

On the other hand, regarding the shape of the screw, a trapezoidal screw conforming to the API as shown in FIG. 2, a rugged screw as shown in FIGS. 3 (a) and 3 (b), a hook screw as shown in FIG. There are many types, such as a round screw as shown in FIG.

[0005]

Among these, API standard trapezoidal screws and round screws use a sealant at the time of tightening, and leakage resistance is achieved by sealing the sealant interposed between the male screw and the female screw. Operating temperature is 250 ℃
In this case, most of the sealant is gasified, the viscosity of the sealant is lost, a gap is formed between the male screw and the female screw, and a leak occurs when an internal pressure is applied.

Therefore, a special screw having a metal seal has begun to be widely adopted in place of a trapezoidal screw or the like conforming to the API standard. (Stress relaxation) works to eliminate the surface pressure of the metal seal portion, and a leak occurs when an internal pressure is applied.

[0007] The present invention has been made in view of the above-mentioned conventional problems, and has an operating environment temperature of 250 to 400 ° C.
Even so, an object of the present invention is to provide a threaded joint for oil country tubular goods having a sufficient leak resistance performance.

[0008]

In order to achieve the above-mentioned object, in the threaded joint for oil country tubular goods according to the present invention, the threaded joint body has a Cr content of 0.4 to 1.0% by weight and a Mo content of 0.1 to 0.1%. 1.
It is made of 5% by weight of Cr-Mo steel, and at least one of the pin portion and the fitting portion of the box portion is subjected to a phosphoric acid treatment, a zinc plating treatment, or a copper plating treatment. And the threaded joint body is Cr-M
By using o-steel, Cr and Mo work to preserve the strength with respect to the use environment temperature, and the degree of relaxation is reduced. By subjecting at least one of the fitting portions to a phosphoric acid treatment, a zinc plating treatment, or a copper plating treatment, a good solid lubrication state is obtained even in a temperature range of 250 to 400 ° C.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION A threaded joint for oil country tubular goods according to the present invention is a threaded joint for oil country tubular goods having a pin part having a male thread and a box part having a female thread.
r: 0.4 to 1.0% by weight, Mo: 0.1 to 1.5% by weight made of Cr-Mo steel, and at least one of a fitting part in a pin part and a box part,
Phosphoric acid treatment, zinc plating treatment or copper plating treatment is performed.

[0010] The surface pressure generated in the metal seal portion of the threaded joint depends on the shrink-fitting effect of the pin portion and the box portion. That is, the pin portion generates a compression hoop stress, and the box portion generates a tensile hoop stress. Therefore, in a high-temperature environment, the hoop stress acting on the pin portion and the box portion is reduced, and as a result, the surface pressure generated in the metal seal portion also decreases. However, the Cr-Mo steel has a function of preserving the strength of Cr and Mo with respect to a use environment temperature.
It has been found that the degree of relaxation is remarkably reduced when the content is 1.0 to 1.0% by weight and Mo is 0.1 to 1.5% by weight. Therefore, in the present invention, the threaded joint body is made of Cr:
It is to be made of Cr-Mo steel of 0.4 to 1.0% by weight and Mo: 0.1 to 1.5% by weight.

When local sticking occurs due to fitting of the pin portion and the box portion, a leak starts from the sticking portion. In addition, sealant is 2
At a high temperature of 50 ° C. or higher, most of the gas is gasified, and the same situation occurs in the metal seal portion of the special joint. Therefore, in a high temperature environment of 250 ° C. or more,
It becomes a solid lubrication state instead of a liquid lubrication state. Therefore, in the present invention, at least one of the fitting portions is subjected to appropriate phosphoric acid treatment, zinc plating treatment, or copper plating treatment as solid lubrication. The reason is that they do not melt even at 250 to 400 ° C., and their hardness is Hv = 115 for zinc plating and Hv = 115 for copper plating.
This is because it is relatively small at 96. Also, the phosphoric acid treatment is effective for rust prevention and seizure resistance.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a threaded joint for oil country tubular goods of the present invention will be described.
An explanation will be given based on the results of experiments conducted to confirm the effect. With the following specifications, a threaded joint of the coupling type having the configuration shown in FIG. 1 was manufactured by variously changing the material of the threaded joint body and the surface treatment applied to the fitting portion of the pin portion and the box portion. As a result of performing a leak test as described below using these threaded joints, as shown in Tables 1 and 2 below, no leak occurred in the case of the threaded joint of the present invention example (Table 1). However, in the case of the comparative example (Table 2), all leaks occurred.

That is, the leak test used in this experiment
It is to check whether a leak has occurred through the following steps (1) to (4). After tightening the pipe and the coupling with the lubricant (compound) on the screw part with a torque of 1863 kg · m, loosen them. Repeat the above operation.

[0014] A lubricant (compound) is applied to the screw portion.
Attach the pipe and coupling with a torque of 1518kgm
tighten. About 2500p at 350 ° C (critical temperature of steam)
si (176 kg / cm ^Two) Pressure steam is enclosed in the tube
This state is maintained for 12 hours and the lubricant (compound
Gasification).

At 350 ° C., tension and compression are repeated 5 cycles at a stress of 85% of the standard minimum yield stress. Tensile and compressive cycles are repeated at room temperature and a pressure of 2500 psi with a stress of 95% of the standard minimum yield stress.

[Specifications of Screw Joint] Outer diameter of pipe body: 177.8 mm Wall thickness of pipe body: 10.36 mm Outer diameter of coupling: 194.5 mm Thread shape: trapezoidal thread (BTC) Thread pitch: 5.08mm

[0017]

[Table 1]

[0018]

[Table 2]

Next, using the same threaded joint as in the above-mentioned leak test, the pin portion of the pipe before and after the heating test was repeated at the temperature of 350 ° C. at a stress of 85% of the standard minimum yield stress for 5 cycles of tension and compression. Table 3 and Table 4 below show the results obtained by measuring the amount of reduction in the outer diameter of the seal portion in.

[0020]

[Table 3]

[0021]

[Table 4]

From Tables 3 and 4, in the threaded joint of the present invention example (Table 3), the reduction in the outer diameter of the seal portion at the pin portion of the pipe before and after the heating experiment was smaller than that in the comparative example (Table 4). It can be seen that it has decreased significantly. Therefore, from the results, it is clear that in the threaded joint of the example of the present invention, the decrease in the surface pressure in the seal portion is small, and the degree of relaxation is reduced.

[0023]

As described above, the threaded joint for oil country tubular goods of the present invention has a sufficient leak resistance even when the operating environment temperature is 250 to 400 ° C. Therefore, since no leakage occurs, the press-fitting of steam can be performed as predetermined, and the efficiency of recovering highly viscous oil increases.

[Brief description of the drawings]

FIG. 1A is a front view partially showing the structure of a coupling type oil country tubular good threaded joint, and FIG. 1B is an enlarged view of a main part of FIG.

FIG. 2 is a view showing the shape of a trapezoidal screw conforming to the API standard.

FIGS. 3A and 3B are diagrams each showing a shape of a rugged screw;

FIG. 4 is a view showing the shape of a hook screw.

FIG. 5 is a view showing a shape of a round screw.

[Explanation of symbols]

 1a Pin part 1aa Male screw 2a Box part 2aa Female screw

Claims (1)

[Claims] In a threaded joint for oil country tubular goods having a pin part having a male thread and a box part having a female thread, the threaded joint main body has a Cr content of 0.4 to 1.0% by weight and a Mo content of 0.4 to 1.0%.
It is made of 1-1.5% by weight of Cr-Mo steel, and at least one of the pin portion and the fitting portion of the box portion is subjected to a phosphoric acid treatment, a zinc plating treatment or a copper plating treatment. Screw joints for oil country tubular goods.