JPH04331886A - Method of fastening pipe joint - Google Patents

Abstract

PURPOSE:To efficiently and precisely fasten a pipe joint by detecting a timing just before the torque for screwing a pipe into a coupling abruptly increases, and by controlling the fastening in accordance with a degree of rotation of the pipe after the detection, relative to the coupling. CONSTITUTION:In a special thread joint for fastening an oil well pipe, a male thread part 3 of a pipe 1 is screwed into a female thread part 4 of a coupling 2. Further, a seal part 7 is given by metal contact between the front end part 5 and the pipe 1 and a torque shoulder part of the coupling 2. In this case, a timing just before a torque for screwing the pipe 1 into the coupling 2 abruptly increases is detected. Further, the fastening is controlled in accordance with a degree of rotation of the pipe, relative to the coupling after the time of the detection. Accordingly, it is possible to efficiently carry out the fastening, and to ensure a contact surface pressure required for obtaining a leakage resistance, irrespective of a friction coefficient, thereby it is possible to enhance the reliability during use of the oil well pipe.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for fastening oil country tubular goods used in oil and gas extraction using special threaded joints.

0002

[Background Art] In recent years, with the depletion of resources and advances in drilling technology, the development of oil and gas wells has been proceeding under higher temperature and higher pressure environments. The characteristics are also becoming more difficult. Conventionally, API (American Petro
leum Institute, American Petroleum Institute)
Threaded joints such as standard round screws and buttress screws are widely used, but problems have arisen in terms of leak resistance and mechanical strength under high temperature and high pressure. Demand is on the rise.

FIG. 2 shows an example of a typical special screw joint.
Figure 3 shows an API standard round screw joint. In the case of API standard threaded joints, sealing is performed between the male threaded part 3 of the pipe 1 and the female threaded part 4 of the coupling 2, whereas in the case of special threaded joints, the sealing is performed between the pipe tip 5 and the torque shoulder part of the coupling 2. Sealed by metal contact between 6 and 6. Therefore, in the tightening work of the special threaded joint, the pipe tip 5 and the torque shoulder part 6 of the coupling 2 start contact at the seal part 7 shown by the arrow near the right shoulder of the pipe tip 5 in this figure. Thereafter, it is necessary to continue the tightening operation until the surface pressure necessary to ensure leak resistance is generated at this contact portion. Incidentally, such tightening work is performed not only in drilling wells for oil and gas, but also in cases where a coupling is attached to the end of a pipe at a pipe manufacturing factory and the pipe is shipped.

[0004] To prevent seizure of contact parts during tightening,
Normally, the entire surface or part of the male threaded part 3, female threaded part 4, pipe tip 5, and torque shoulder part 6 is coated with a film such as zinc phosphate, and before tightening, a coating of grease called a compound, zinc, Usually, a lubricant containing lead or the like as a main component is applied to each of these parts.

[0005]

By the way, the general method for tightening these special threaded joints is to use a torque control method in which after applying a compound, the joint is set in a tightening machine and tightened to a predetermined torque value. The tightening torque value and the contact surface pressure generated at the seal part have a monotonically increasing relationship as shown in Figure 4 (a), and the necessary surface pressure can be obtained by tightening to the appropriate torque value, but for some reason. If the coefficient of friction between the male threaded part 3, female threaded part 4, pipe tip 5, and torque shoulder part 6 changes, this effect is not reflected in the tightening torque, so even if the tightening torque is the same, There was no guarantee that the surface pressure of the seal would be constant.

Furthermore, the coefficient of friction varies depending on the type of compound applied, the amount applied, the coating conditions on the threaded surface or sealing surface, the roughness of the machined surface of the threaded surface, etc., and the environmental conditions such as temperature and humidity during tightening work. It is rather normal for the friction coefficient to change; when the friction coefficient is larger than the standard value, sufficient contact surface pressure cannot be obtained, and conversely, when the friction coefficient is smaller than the standard value, it is usually an overtightening condition called overtorque. As a result, the seal portion 7 or the pipe tip portion 5 and the torque shoulder portion 6 are significantly plastically deformed. With the conventional fixed target torque method, not only was it impossible to maintain a constant surface pressure at the sealing part, but there was also the risk of leakage from the pipe joint due to insufficient surface pressure.

An object of the present invention is to provide a method for tightening a special threaded joint that eliminates the above-mentioned problems.

[0008]

[Means for Solving the Problems] The present invention detects the timing immediately before a sudden increase in torque with respect to the rotation of the pipe relative to the coupling when tightening a threaded joint for oil country tubular goods, and detects the timing immediately before the torque suddenly increases relative to the rotation of the pipe relative to the coupling, and It is characterized by controlling the tightening state by the amount of rotation.

[0009]

[Operation] Fig. 1 shows an example of the torque-turn curve of the special threaded joint according to the present invention. The torque increases gradually up to point A, but at point A, pipe 1 turns (rotates).
The torque starts to increase rapidly. Starting from point B, where the increase in torque becomes even more rapid and the graph changes to an almost vertical straight line, the area to the left of point A in the diagram is area I, the area between points A and B is area II, and the area to the upper right of point B. will be called region III. The relationship between each region and the pipe joint is that in region I, only the male threaded part 3 of the pipe and the female threaded part 4 of the coupling are in contact, and the pipe tip 5 and the torque shoulder part 6 of the coupling are in contact with the seal part 7. Point A is where contact starts near the seal portion 7, and point B is where contact is started on the entire surface other than the seal portion 7.

Tightening of the special threaded joint means tightening the pipe tip 5 and the torque shoulder 6 from the design concept of this joint.
This is to press the contact pressure against each other with a predetermined contact pressure, and ensuring leak resistance is all about managing the control level of this contact pressure. Region I is important for controlling contact pressure
I and region III. As mentioned above, it is difficult to control the contact surface pressure of the seal portion 7 in these areas by torque, and in the present invention, the amount of rotation of the pipe relative to the coupling, that is, the number of turns, is used instead of torque. I made it.

FIG. 4 shows the relationship between the torque and turn in regions II and III and the seal surface pressure. (a)
As shown in (b), even if the torque is constant, there will be a large difference in the seal surface pressure due to the effect of the friction coefficient.
), it can be seen that if the turn is the control target, there will be no variation in the seal surface pressure. Therefore, in the present invention,
Detect point A in Figure 1, that is, the timing immediately before the sudden increase in torque with respect to the rotation of the pipe relative to the coupling, and turn the pipe with the total amount of rotation of the pipe relative to the coupling in regions II and III counted from that point, that is, the number of turns. Let it be the control amount. The specific target value of this turn control amount varies depending on the specifications, dimensions, etc. of the special threaded joint, and must be determined individually through experiments and analysis.

0012

[Example] Table 1 shows the results of a tightening and gas leak test performed using a special threaded joint for oil country tubular goods that conforms to API standard L80, has an outer diameter of 88.9 mm, and a wall thickness of 6.45 mm.

[0013]

[Table 1]

[0014] Test number 1 is for standard conditions, and the type of compound, amount of application, temperature at the time of tightening, etc. match the specifications of this special threaded joint. Tightening torque 400kg
-m, the turn control amount was 0.070. No leak was observed in a gas leak test to evaluate the gas leak resistance of this joint. In test numbers 2 to 6, tightening was performed using the conventional torque control method with slight changes in conditions such as compound type, amount of application, and temperature during tightening from the standard conditions, and in test numbers 3 and 4, the friction coefficient was It is estimated that it has become smaller. On the other hand, in test numbers 2, 5, and 6, the friction coefficient was too high, and the target torque value was reached in a considerably small number of turns, resulting in insufficient contact surface pressure of the seal part 7, and in test numbers 5 and 6, the gas leak test A leak has occurred.

Test numbers 7 to 11 applied the turn control method according to the present invention, and due to variations in the friction coefficient, the tightening torque was 3 compared to the standard condition of 400 kg-m.
The weight varies from 52kg-m to 472kg-m, but since the number of turns is controlled, it is presumed that the contact pressure generated at the seal part is maintained at a constant level, and the gas leak test results are also good. Met.

[0016]

[Effects of the Invention] According to the present invention, the tightening work between the coupling and the pipe can be performed efficiently, and the leak resistance is improved without being affected by fluctuations in the coefficient of friction due to the structure, dimensions, condition, etc. of the coupling or the pipe. Remarkable effects were obtained, such as ensuring the necessary contact surface pressure and improving reliability when using oil country tubular goods.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between pipe rotation speed and tightening torque for a coupling according to the present invention.

FIG. 2 is a sectional view showing a special threaded joint according to the present invention.

FIG. 3 is a cross-sectional view showing a threaded joint according to the API standard according to the prior art.

FIG. 4 is a graph showing the relationship between torque, turn control amount, and seal surface pressure when tightening a pipe joint.

[Explanation of symbols]

1 Pipe 2 Coupling 3 Male thread part 4 Female thread part 5 Pipe tip 6 Torque shoulder part 7 Seal part

Claims (1)

[Claims] [Claim 1] In tightening a threaded joint for oil country tubular goods,
A method for tightening a pipe joint, characterized by detecting the timing immediately before a sudden increase in torque with respect to the rotation of the pipe relative to the coupling, and controlling the tightening state based on the amount of rotation of the pipe relative to the coupling from that point on.