JP2010255710A - Method of tightening special screw joint for oil well pipe - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To propose a method of improving seal performance at a sealing nose part to the maximum without changing the thickness of the sealing nose part in a special screw joint having a taper screw part, a seal part and a shoulder part. <P>SOLUTION: The relationship of the revolutions and torque of the special screw joint is detected real-time. Based on the detected relation of the revolutions and torque, an inclination of torque is obtained by dividing a torque increment by a revolution increment. Fastening is stopped at the time when the inclination of torque shows the maximum value while monitoring the inclination of torque and then the inclination of torque decreases from the maximum value by a predetermined value. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a tightening method capable of enhancing the sealing performance of a special threaded joint for oil well pipes to the limit.

In recent years, wells that are easy to develop at a low depth have decreased, and oil wells that are deeper and have higher temperatures and pressures have increased. Also, more well shaped oil wells such as slanted wells and horizontal wells are increasing. Along with this, special threaded joints for oil well pipes with improved sealing performance have been developed.
The structure of a special threaded joint for oil well pipes (also simply referred to as a special threaded joint or coupling) is shown in FIG. The special threaded joint 2 has a taper thread part 3, a seal part 4 and a shoulder part 5, and the sealing performance is such that the seal part 4 and the shoulder part 5 of the special threaded joint 2 are formed at the pipe end of the oil well pipe. This is achieved by tightening until the tip of the male pin 1 comes into metal-metal contact (Patent Documents 1, 2, and 3).

In FIG. 3A, the seal nose portion thickness H is a value obtained by adding the radial thicknesses of the respective portions of the seal portion 4 and the shoulder portion 5, and is an important dimension on the seal of the special screw joint 2. is there. Further, the amount of screw interference (= d ₁ -d ₂ , d ₁ : screw diameter of pin 1, d ₂ : screw diameter of coupling 2) is also important as well as the seal of the special screw joint 2. The amount of interference is defined by the screw diameter in the vicinity of the center of the length of the complete screw portion indicated by the arrow with *.

  The special threaded joint having such a structure is tightened based on the detected relationship between the rotational speed and the torque while detecting the relationship between the rotational speed and the torque in real time. At that time, the relationship between the detected rotational speed and torque is generally as shown by a solid line in FIG. That is, screw interference starts at point O, and after a screw interference region (between OA) where the torque increases linearly, a seal interference region (between AB) and then a shoulder interference region (between BC) appear. The slope of the straight line (= torque increment / rotation speed increment) in the seal interference area (between AB) is larger than the screw interference area (between OA), and the straight line slope in the shoulder interference area (between BC) Special threaded joints are designed to be larger than the interference zone (between AB). In the relationship between the rotation speed and torque of the special threaded joint, a value obtained by dividing the torque increment by the rotation speed increment is referred to as a torque gradient. In FIG. 4, point A is referred to as a seal interference start point, point B as a shoulder interference start point, and point C as a yield start point.

  Here, in the conventional method, based on the relationship between the detected rotation speed and torque, the tightening stop position is set to an intermediate optimum torque in the shoulder interference area (between BCs) that does not exceed the yield start point C. Therefore, as shown in FIG. 5, when the screw interference torque increment is increased by increasing the screw interference amount, the seal torque TF ′ at the seal nose portion is small in the screw interference torque increment. It becomes smaller than the seal torque TF at the seal nose portion, and the sealing performance at the seal nose portion becomes insufficient. The increase in screw interference torque also occurs due to unpredictable factors such as screw interference abnormality, lubricant deterioration, and foreign matter contamination. The seal torques TF and TF ′ at the seal nose portion correspond to the amount of torque increase from the seal interference start point A or A ′ to the optimum torque (see FIG. 5).

  By the way, as means for improving the sealing performance at the seal nose portion, a method of increasing the optimum torque, increasing the seal nose portion thickness H, and the like can be considered.

JP-A-6-270072 Japanese Patent Application Laid-Open No.7-100773 Japanese Unexamined Patent Publication No. 2007-232012

However, when tightening until the shoulder part of the special threaded joint comes into contact with the tip of the male pin, if the optimum torque is simply increased with the aim of improving the sealing performance at the seal nose part, the seal nose part There is a danger that excessive plastic deformation occurs and the sealing performance at the seal nose portion becomes insufficient.
In addition, when the seal nose portion thickness H is increased in order to improve the sealing performance at the seal nose portion, the diameter of the pipe end of the oil well pipe is reduced and the subsequent operation is performed as the seal nose portion thickness H is changed. There arises a problem that additional processing such as performing stress-relieving annealing of the pipe end having a reduced diameter is required in the manufacturing process of the oil well pipe.

  Therefore, the present invention solves the above-mentioned problems of the prior art, and in a special threaded joint having a taper screw part, a seal part and a shoulder part, the sealing performance at the seal nose part without changing the seal nose part thickness. The purpose of this is to propose a tightening method that can raise the limit to the maximum.

  The inventor performs numerical analysis (FEA) by the finite element method or the actual tightening test for each material and size of the special screw joint in advance until the yield torque of the special screw joint is exceeded. It has been found that by grasping the amount of plastic deformation, the sealing performance at the seal nose can be enhanced to the limit, and the present invention has been made based on this finding.

That is, the present invention is as follows.
1. A method for tightening a special threaded joint having a taper thread part, a seal part, and a shoulder part, wherein when the shoulder part of the special threaded joint comes into contact with the tip of the male pin, the rotational speed of the special threaded joint And the torque in real time, and based on the detected relationship between the rotational speed and the torque, the torque increment is divided by the rotational speed increment to obtain the torque slope, and the torque slope is monitored while monitoring the torque slope. A tightening method for a special threaded joint for oil well pipes, wherein the tightening is stopped when a maximum value is exhibited and then the torque gradient decreases by a predetermined value from the maximum value.
2. A numerical analysis (FEA) by the finite element method or the actual tightening test is performed for each material and dimension of the special threaded joint until the yield torque of the special threaded joint is exceeded, and for each material and dimension of the special threaded joint. A predetermined value to be reduced from the maximum value of the torque gradient is determined. The tightening method of the special threaded joint for oil country tubular goods described in 2.

  According to the present invention, the sealing performance at the seal nose portion of the special threaded joint can be enhanced to the utmost, and even when the required torque is high.

It is a characteristic view which shows the relationship between the rotation speed and torque by this invention method. It is a characteristic view explaining the example of analysis of the method of this invention by the numerical analysis (FEA) by a finite element method. (A) is principal part sectional drawing which shows the structure of the special threaded joint to which this invention is applied, (b) is a schematic diagram explaining the screw interference amount in design. It is a characteristic view which shows the relationship between the rotation speed and torque by a conventional method. It is a characteristic view when the increment of the screw interference torque is large and small according to the conventional method.

First, according to the required torque, the special threaded joint has a special threaded joint material, dimensions and design screw interference amount (= d ₁ -d ₂ , d ₁ : screw diameter of pin 1, d ₂ : coupling 2 Set the appropriate screw diameter. A case for increasing the screw diameter d ₁ of the pin 1, there is a case to reduce the thread diameter d ₂ of the coupling, if the thread interference with the same, increment of thread interference torque is the same.

  Next, after grasping the amount of plastic deformation at the seal nose for each material and size of the special thread joint designed and manufactured, the special thread joint is tightened. In other words, numerical analysis (FEA) by the finite element method or actual tightening test is performed until the yield torque of the special threaded joint is exceeded for each material and dimension of the special threaded joint. A predetermined value to be reduced from the maximum value of the torque gradient is determined. The maximum value of the torque gradient is generated in the vicinity of the yield start point C as shown in FIG. Here, the numerical value analysis (FEA) by the finite element method or the actual tightening test is performed for each material and size of the special threaded joint because the predetermined value that decreases from the maximum value of the torque gradient is the material of the special threaded joint This is because each dimension varies.

  As described above, the method of the present invention detects the amount of plastic deformation at the seal nose for each material and size of the special threaded joint, and then detects the relationship between the rotational speed and torque of the special threaded joint in real time. On the other hand, based on the relationship between the detected rotational speed and torque, the torque increment is divided by the rotational speed increment to obtain the torque slope, and the torque slope shows the maximum value while monitoring the torque slope. The tightening is stopped when the inclination of the angle decreases by a predetermined value from the maximum value (see FIG. 1). That is, according to the method of the present invention, the tightening is stopped when the inclination of the torque is reduced from the maximum value by a predetermined value based on the relationship between the detected rotational speed and the torque.

For example, in the example described later, numerical analysis (FEA) by the finite element method is performed, and a predetermined value that is decreased from the maximum value of the torque gradient is set to the maximum value of the torque gradient × 0.1.
On the other hand, in the conventional method, based on the relationship between the detected rotational speed and torque, the fastening stop position is set to an intermediate optimum torque in the shoulder interference area (between BCs) that does not exceed the yield start point C.

  FIG. 2 is a characteristic diagram comparing the sealing performance at the seal nose portion by tightening until the shoulder portion of the special screw joint comes into contact with the tip portion of the male pin in the above-described method of the present invention and the conventional method. According to the method of the present invention, after performing numerical analysis (FEA) by the finite element method and grasping the amount of plastic deformation at the seal nose portion, the torque gradient is maximized based on the relationship between the detected rotational speed and torque. Since the tightening is stopped when the pressure drops by a predetermined value, the area of the seal area where the contact surface pressure of unit circumference is generated is more than 10% wider than the conventional method, and the seal in the seal nose portion It turns out that the nature is high.

The method of the present invention was applied to a 110 ksi grade oil well pipe (13% Cr steel) having an outer diameter of 100 mm and a wall thickness of 12.6 mm. As a result of designing and manufacturing a special threaded joint for fastening to the male pin 1 formed on the pipe end of the oil well pipe, and performing a tightening test on the actual product, the yield torque was optimal torque × 1.4 N · m.
Further, as a result of numerical analysis (FEA) by the finite element method, after reaching the yield torque in the relationship between the rotational speed and torque of the special threaded joint, the special threaded joint is rotated about 0.05 times (= 0. (05 x 360 degrees = 18 degrees) Even if tightened by tightening, there is no problem with the sealing performance at the seal nose, and after reaching the yield torque, tightening the special screw joint more than 0.05 rotations will result in a seal It was found that the sealing performance at the nose portion was lowered. From this result, after reaching the yield torque, the predetermined value to be decreased from the maximum value of the torque gradient was set to the maximum value of the torque gradient × 0.10 based on the relationship between the detected rotational speed and the torque.

When the method of the present invention is applied based on the above results, as shown in FIG. 1, the torque increase amount a from the yield start point C can be set to a = yield torque × 0.05 N · m, and the seal nose portion Thus, it was possible to improve the sealing performance at the seal nose portion to the maximum while preventing excessive plastic deformation.
On the other hand, the tightening stop position of the special screw joint according to the conventional method is the time when the optimum torque is reached, and a sufficient margin is expected so that plastic deformation does not occur in the seal nose portion.

d Screw diameter of ₁ pin d ₂ Screw diameter of coupling H Seal nose thickness a Increase amount of torque from yield start point C b Increase torque due to increase in seal nose thickness A Points A and A ′ Seal interference start point B, B 'point Shoulder interference start point C, C' point Yield start point 1 Pin 2 Special screw joint or coupling 3 Screw part 4 Seal part
5 Shoulder TF, TF 'Seal torque at seal nose

Claims (2)

A method for tightening a special threaded joint having a taper thread part, a seal part, and a shoulder part, and when tightening until the shoulder part of the special threaded joint comes into contact with the tip of the male pin,
The relationship between the rotation speed and torque of the special screw joint is detected in real time, and the torque gradient is calculated by dividing the torque increment by the rotation speed increment based on the detected rotation velocity and torque relationship, and the torque gradient is monitored. However, the tightening method of the special threaded joint for oil well pipes is characterized in that the tightening is stopped when the torque gradient exhibits a maximum value and then the torque gradient decreases by a predetermined value from the maximum value. A numerical analysis (FEA) by the finite element method or the actual tightening test is performed for each material and dimension of the special threaded joint until the yield torque of the special threaded joint is exceeded, and for each material and dimension of the special threaded joint. 2. The method for tightening a special threaded joint for oil country tubular goods according to claim 1, wherein a predetermined value to be reduced from a maximum value of the torque gradient is determined.

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