JPH07100773A - Method for determining tightening state of pipe joint with shoulder seal - Google Patents

Abstract

PURPOSE:To detect the tightening disorder in the abnormal biting, galling, cross thread, and seal part plastic deformation, as for a pipe coupling having a shoulder seal. CONSTITUTION:In the tightened state judging method for a pipe coupling having a shoulder seal, at least one is selected beforehand from among the shoulder torque, shoulder turn, shoulder slope, delta torque, delta turn, delta slope, final slope and the torque drop, as the management index corresponding to each judgement item, for each judgement item of the abnormal biting, gauling, cross thread, and the seal part plastic deformation. Then, the management range value is previously determined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for determining a tightened state of a pipe joint having a shoulder seal, which is used for connecting oil country tubular goods and the like.

[0002]

2. Description of the Related Art Conventionally, there is a pipe joint having a shoulder seal as a pipe joint screwed and fastened to a pipe end. As shown in FIG. 1, this pipe joint 1 is provided with a screw fitting portion 3 that is screwed with a pipe 2, and has a shoulder seal portion 4 that performs a sealing action by contact with an end surface of the pipe 2 inside thereof. There is.

FIG. 2 is a diagram showing the relationship between the number of turns of the pipe joint 1 and the torque. In the pipe joint 1, first, the interference of the screw fitting portion 3 starts to increase the tightening torque, and when the interference of the shoulder seal portion 4 then starts, the torque increases further rapidly. In FIG. 2, T _S is the shoulder torque corresponding to the interference starting point P1 of the shoulder seal portion 4, R
_S is a shoulder turn corresponding to the interference starting point P1 of the shoulder seal portion 4, T _F is a final torque upon completion of tightening, R _F is a final turn upon completion of tightening, and T _D is a final torque from T _F to shoulder torque T. It is the delta torque minus _S.

Normally, in a taper screw such as a round or buttress specified by API, the final torque and the final turn are indicators for controlling the quality of the tightened state. However, in the case of a special joint having a shoulder seal, in consideration of the characteristics shown in FIG. 2, for example, delta torque is used as a control index as described in JP-A-63-229272, or
Shoulder torque, as described in 4-839887 publication,
The shoulder turn is used as a management index.

[0005]

However, in the prior art in which the delta torque is used as a management index, or the shoulder torque and the shoulder turn are used as management indexes, there is a tightening problem due to deviation of the basic dimensions of the screw such as standoff and taper. (Poor sealing, poor fitting force) can be detected, but foreign matter is caught, goring, cross thread,
Tightening defects due to plastic deformation of the seal cannot be detected.

An object of the present invention is to make it possible to detect, in a pipe joint having a shoulder seal, abnormal tightening, a galling, a cruz thread, and a tightening defect such as plastic deformation of a seal portion.

[0007]

DISCLOSURE OF THE INVENTION According to the present invention, when a pipe joint having a shoulder seal portion which performs a sealing action by contact with a pipe end face inside is screwed and fastened to a pipe end, foreign matter is caught, goring, For each of the judgment items of cross thread and plastic deformation of seal part, shoulder torque, shoulder turn, shoulder slope, delta torque, delta turn, delta slope, final slope, torque drop as the management index corresponding to the judgment item. In addition to pre-selecting one or more selected from among the
For at least one of each judgment item of the galling, the cross thread, and the plastic deformation of the seal portion, the detected value of the management index corresponding to the judgment item is compared with the management range value, and the quality of the judgment item is judged. This is a tightening state determination method.

[0008]

[Operation] Table 1 shows the shoulder torque T _S , shoulder turn R _S , shoulder slope S _S , and delta torque T _S.
D , Delta Turn R _D , Delta Slope S _D , Final Slope S _F , Torque Drop T _DR
It shows which of the judgment items such as poor fitting force, poor sealing property, foreign matter entrapment, goring, cross thread, plastic deformation of seal portion, and defective screw element contributes to detection. ◯ indicates that there is an effect, and △ indicates that the effect is small but there is a possibility of detection. In addition, in the judgment items in Table 1, *
The combinations indicated by the marks are outside the scope of the present invention.

[0009]

[Table 1]

Here, the management range values (upper and lower limit values) of the management index corresponding to each judgment item are obtained in advance by theoretical calculation, experiment, etc. for each size, standard, and screw type, and charts, functional formulas, etc. It is stored in the form of.

Each management index is defined as follows (FIG. 3). (1) Shoulder torque T _S Torque corresponding to the interference start point P1 of the shoulder seal part

(2) Shoulder turn R _{S The} number of turns corresponding to the interference start point P1 of the shoulder seal portion

(3) Shoulder slope S _S Torque change rate with respect to turn in the interference area of the screw fitting portion before the interference start point P1 of the shoulder seal portion

(4) Delta torque T _D Torque obtained by subtracting the shoulder torque T _S from the final torque T _F at the time of completion of tightening

(5) Delta turn R _{D The} number of turns obtained by subtracting the shoulder turn R _S from the final turn R _F at the completion of tightening.

(6) Delta slope S _D Torque change rate with respect to turn in the shoulder seal part interference area after the interference start point P1 of the shoulder seal part

(7) Final slope S _F Torque change rate with respect to turn immediately before completion of tightening

(8) Torque drop T _{DR The} amount of torque drop that drops stepwise in the interference area of the screw fitting area before the interference start point P1 of the shoulder seal section.

A corrected delta torque T _D '(FIG. 3) may be used as the delta torque in (4) above.

[0020]

[Example] As a result of investigating the tightening state of a special joint having a 7 "x 29 LDS, API 5CT-L80 shoulder seal, a tightening pattern as shown in Fig. 4 was obtained. Tightening stop control here As the method, a method of matching the final torque T _F with the target torque was adopted, and the values in Table 2 were given as the management range values of each management index.

[0021]

[Table 2]

According to the method of the present invention, conventional tightening torque management and delta torque management, such as poor fitting force and poor sealing performance, can also detect tightening problems other than the judgment items for which the problems could be detected. Becomes

For example, FIG. 5 shows the tightening situation when foreign matter is caught in the threaded portion. However, since the load on the screw fitting portion becomes large, the shoulder slope S _S deviates from the upper limit of the control range value. Therefore, by managing this, it becomes possible to detect the foreign matter biting into the screw portion.

Further, FIG. 6 shows the tightening condition when a hard foreign matter is caught in the seal portion. Since the torque sharply rises due to the interference of the foreign matter, the delta slope S _D deviates from the upper limit of the control range value. . Further, the delta turn R _D goes out of the lower limit of the control range value. By managing these, it becomes possible to detect the foreign matter biting into the seal portion.

It is also possible to detect the occurrence of galling in the screw portion and the seal portion in the same manner. FIG. 7 shows a tightening situation in the case where a cross thread is generated and the original screw fitting is corrected. In the process of increasing the shoulder torque T _S , there is a portion where the torque drops stepwise, and abnormality can be detected by managing the torque drop amount T _DR and the shoulder slope S _S variation.

FIG. 8 shows the tightening situation when the plastic deformation of the seal portion occurs. The torque increase immediately before the completion of tightening is moderated by the plastic deformation, and the final slope S _F deviates from the lower limit of the control range value.

As described above, it is possible to reliably and easily detect the tightening defect such as foreign matter biting failure, goring, cross thread, and plastic deformation of the seal portion, which could be found only by the operator's chart and the actual product confirmation. Became.

[0028]

As described above, according to the present invention, in a pipe joint having a shoulder seal, it is possible to detect a tightening defect such as abnormal biting, galling, cruz thread, and plastic deformation of the seal portion.

[Brief description of drawings]

FIG. 1 is a schematic view showing a main part of a pipe joint having a shoulder seal.

FIG. 2 is a torque chart when tightening a pipe joint having a shoulder seal.

FIG. 3 is a schematic diagram showing the definition of a management index in the present invention.

FIG. 4 is a schematic diagram showing a tightening pattern obtained according to an embodiment of the present invention.

FIG. 5 is a schematic diagram showing a tightening pattern when foreign matter is caught in a screw part.

FIG. 6 is a schematic diagram showing a tightening pattern when a hard foreign matter is caught in the seal portion.

FIG. 7 is a schematic diagram showing a tightening pattern when a cross thread occurs.

FIG. 8 is a schematic diagram showing a tightening pattern when a plastic deformation of the seal portion occurs.

[Explanation of symbols]

T _S Shoulder Torque R _S Shoulder Turn S _S Shoulder Slope T _D Delta Torque R _D Delta Turn S _D Delta Slope S _F Final Slope T _DR Torque Drop

Claims (1)

[Claims] 1. When a pipe joint having a shoulder seal portion, which performs a sealing action by contact with the pipe end surface, is screwed and fastened to the pipe end, foreign matter is caught, galling, cross thread, and plastic deformation of the seal portion. For each of the judgment items of, as a management index corresponding to the judgment item, one or more selected from shoulder torque, shoulder turn, shoulder slope, delta torque, delta turn, delta slope, final slope, and torque drop. In addition to selecting items in advance, determine the control range value in advance, and for at least one of the determination items of foreign matter entrapment, goring, cross thread, and plastic deformation of seal part, detect the detected value of the management index corresponding to the determination item. It is characterized by comparing the management range value and judging whether the judgment item is good or bad. Tightening state determination method of the pipe joint having a shoulder seal that.