JPH03157594A - Clamping control method for special joint with shoulder seal - Google Patents

Abstract

PURPOSE:To aim at the optimization of clamping torque by clamping a special joint system, consisting of a joint with an internal thread on an inner circumferential surface and a pipe with an external thread on the outer circumferential surface, as long as the setting time as detecting a shoulder touch, in such a control method as clamping the internal thread to the external thread after being screwed in. CONSTITUTION:A special joint 1 is thread-joined by an internal thread 2 installed on a double-end inner circumferential surface and an external thread 4 threaded on each outer circumferential surface of pipes 3a, 3b, through which it is metal-sealed. This is a control method that clamps this special joint 1 after each end of these pipes 3a, 3b performs a shoulder touch with a shoulder part 6, setting the clamping time of clamping torque of thread part + shoulder seal. Next, thread clamping takes place as detecting the shoulder touch and, after detection of the shoulder touch, these threads are clamped as long as the setting time, and when this time elapses, the clamping is over. In consequence, since a proper contact pressure is given to the shoulder seal part, stable clamping can be done.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tightening control method for a special joint having a shoulder seal, which is used, for example, to connect oil country tubular goods.

[Conventional technology]

For example, when joining oil country tubular goods with good sealing properties, a special joint 1 is used as shown in FIG. This special joint 1 has a female screw 2 and a pipe 3a provided on the inner peripheral surface of both ends thereof.
, 3b and a male screw 4 threaded on the outer peripheral surface thereof, and the sealing is performed by a metal seal. As shown in the partially enlarged view of Fig. 2, the metal seal portion is located at the contact point 5 between the inner circumferential surface of the special joint l and the outer circumferential surface of the pipe 3&.
It has two seal parts: a circumferential seal at , a shoulder seal at the end of the female screw inside the special joint 1, and a shoulder seal at the end of the pipe 3a. It is constructed to be completely sealed.

FIG. 3 is a graph showing characteristics of changes in tightening torque of a special joint having such a shoulder seal. In the drawings, each symbol is defined as follows.

A: Tightening torque of the threaded part, B: Tightening torque of the shoulder seal of the threaded part, C: Shoulder touch, D: Tightening completed.

As shown in the drawing, after tightening the special joint l to the pipes 3a and 3b with torque (A) and creating a shoulder touch (C) where the joint shoulder 6 and the pipe end come into contact, the tightening torque (B
), it rises rapidly from the shoulder touch as shown in Figure 3.

Conventionally, in tightening control of special joints characterized by changes in tightening torque, a method has been adopted in which a reference tightening torque is set and tightening is terminated when this reference tightening torque is exceeded.

[Problem to be solved by the invention]

FIG. 4, FIG. 5, and FIG. 6 are graphs showing the relationship between tightening torque and tightening amount in a special joint having a shoulder seal. As shown in FIGS. 4 to 6, the shoulder touch in the special joint is not constant. Because of these variations in shoulder touch, conventional special joint tightening control methods have the following problems.

(1) ■Tightening is terminated when the reference tightening torque is exceeded, so the sum of the torque (A) up to the shoulder touch and the torque (B) from the shoulder touch to the end of tightening is constant.

■ Torque (A) up to shoulder touch changes depending on the tightening allowance of the screw.

(2) From (2) and (2), when the torque (A') is high as in the case of FIG. 5, the torque (Bo) is low and sufficient surface pressure is not applied to the sealing surface.

(2) When the torque (A") is low as in the case of FIG. 6, the torque (B") becomes high, causing deformation of the sealing surface.

(3) As a result, the torque (B) cannot be managed using the conventional tightening control method. (The surface pressure of the shoulder seal cannot be managed.) As a control method for a special joint with a shoulder seal to solve the above-mentioned problem, shoulder touch torque is detected and tightening control is performed based on the detected shoulder touch torque. The present inventors have disclosed a method of obtaining appropriate contact pressure at the shoulder seal portion by this method in Japanese Patent Laid-Open No. 63-229272.

FIG. 7 shows a block diagram of a tightening control device related to a conventional method of controlling a special joint having a shoulder seal. In the drawings, reference numeral 10 denotes a torque detector, and the torque detector IO detects the tightening torque of the special joint 1 shown in FIGS. 1 and 2. 11 is a sampling time setter, 12 is a sampling means for sampling the tightening torque detected by the torque detector 10 at fixed time intervals, 13 is a storage means for storing the tightening torque sampled by the sampling means 12, 14 is a subtracter, 15 is sampling means 1
2 is a sampling number output means for outputting the number of times of sampling, 16 is an adder, I7 is a reference value setter, 18 is a comparator, 19 is an AND circuit, and 20 is a counter.

The operation of controlling the tightening of the special joint 1 by the control device configured as described above will be explained based on the tightening torque and tightening time characteristics shown in FIG. 8 and the flowchart shown in FIG. 9.

First, the torque detector 10 detects the tightening torque when tightening the special joint 1 and the pipe 3a, and the sampling means 12
(step 31). The sampling means 12 receives the sampling signal every minute time Δ set in the sampling time setting device 11, samples the tightening torque every sampling time Δ, and stores the sequentially sampled tightening torque in the storage means 13 and the subtractor. I4 (step 32). The subtracter 14 calculates the sum of the difference ΔT between the tightening torque sent from the sampling means 12 and the tightening torque at the time of the previous sampling stored in the storage means 13, and calculates the sum ΣΔT, that is, the tightening torque, every predetermined sampling number n. The difference in tightening torque at each time n·Δ is sent to the comparator 18 (step 34
).

On the other hand, the reference value setter 17 is preset with a reference value ΔT0 for detecting tightening torque that rapidly increases after shoulder touch torque is generated.
0 is also sent to comparator 18. The comparator 18 compares the difference in tightening torque for each sampling number n sent from the adder 16 with the reference value ΔT sent from the reference setting device 17, and when the difference in tightening torque becomes larger than the reference value ΔT0, That is, when shoulder touch torque is generated and the tightening torque starts to increase rapidly, a high level signal is sent to the AND circuit 19 (step 35). Note that when the difference in tightening torque is smaller than the reference value ΔT0, the counter 20 is always reset to zero (step 36).

When the output signal from the comparator 18 is sent to the AND circuit 19, the number of samplings sent from the sampling number output means 15 is outputted to the counter 20, and the counter 20 counts the number of samplings after the shoulder touch torque Ts is generated (step 37). When the count number of this counter 20 reaches a predetermined set value, the counter 2
0 to the tightening drive device (not shown) (step 38) to stop tightening the special joint 1 (
Step 39) According to the conventional method described above, by detecting the fluctuating shoulder touch torque and performing tightening control based on the detected shoulder touch torque, an appropriate contact pressure is obtained at the shoulder seal portion of the special joint. Stable tightening can be performed.

The present invention was also made to solve quality control problems in tightening special joints, such as loosening due to insufficient surface pressure and seal surface deformation due to excessive surface pressure. It is an object of the present invention to provide a method for controlling the tightening of a special joint having a shoulder seal, which is capable of applying a tightening torque.

[Means to solve the problem]

The present invention provides a joint in which a female thread is threaded on the inner peripheral surface of both ends over the entire circumference thereof, and a shoulder portion is provided at the end of the female thread;
It consists of a tube with a male screw threaded on the outer circumferential surface, and the female screw of the joint is screwed into the male screw of the tube and tightened, and the end of the tube touches the shoulder part and then further tightened. The special joint tightening control method is characterized in that a time period from the time of shoulder touch to stopping tightening is set, the joint is tightened while detecting the shoulder touch, and the joint is further tightened for the set time from the shoulder touch point. It is something that you have.

Next, the present invention will be explained with reference to the drawings.In order to control the torque from the time of shoulder touch to the end of tightening, detection of shoulder touch is necessary. Regarding this shoulder touch detection method, the above-mentioned conventional example (
JP-A-63-229272) will be used, so the description will be omitted.

The control method from when the shoulder touch is detected to when the tightening is finished is as follows.

■ Set the tightening time for the tightening torque of the threaded shoulder seal.

■ Tighten while detecting shoulder touch.

■ After the shoulder touch is detected (after the shoulder touch detection signal is output), the tightening is continued for a set time, and when the set time has elapsed since the shoulder touch, the timer outputs a stop signal to finish tightening the screw shoulder seal.

FIG. 10 is a graph showing the amount of torque increase after a shoulder touch performed by the method of the present invention.

Even if the shoulder touch varies as shown in Figure 10,
The amount of torque increase after the shoulder touch is constant.

Note that the tightening stop time is preferably set at 0.1 seconds using a timer.

As a result, even if the shoulder touch varies, the amount of increase in torque after the shoulder touch remains constant, and appropriate torque can be applied.

FIG. 11 is a graph showing the amount of torque increase after a shoulder touch when tightening a special joint performed by a conventional tightening control method.

As shown in FIG. 11, there are various fluctuations in the torque increase after the shoulder touch.

〔Effect of the invention〕

As explained above, according to the present invention, tightening is performed while detecting fluctuating shoulder touches, and the amount of torque increase after the detected shoulder touch is held constant, thereby applying appropriate contact pressure to the shoulder seal portion of the special joint. This provides industrially useful effects such as stable tightening and good quality control.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing a special joint having a shoulder seal according to the present invention, Fig. 2 is a partial sectional view showing the seal portion of the special joint shown in Fig. 1, and Fig. 3 is a diagram showing the tightening torque of the special joint. Graphs showing the characteristics of changes; Figures 4, 5, and 6 are graphs showing the relationship between tightening torque and tightening amount in special joints; Figure 7 is tightening control according to the conventional tightening control method for special joints. Device block diagram, No. 8
The figure shows a graph showing the tightening torque and tightening time characteristics showing the operation when performing tightening control of a conventional special joint.
FIG. 9 is a flowchart showing the operation when performing conventional tightening control of a special joint, and FIGS. 1θ and 11 are graphs showing the amount of increase in tightening torque after a shoulder touch. In the drawings, l...-special joint, 28. -Female screw, 3a, 3b...tube, 4--male screw, 501. Contact point, 6.-.Shoulder, 10-) Lubricant detector, 11 +++ Sampling time setter, 12-9. Sampling means, 13, -Storage means, 14-.-Subtractor, 15-0. sampling number output means, 16-0. Adder, 17--Reference value setter, 189. - Comparator, 19 - AND circuit, 20..., counter.

Claims (1)

[Claims] 1. Consisting of a joint with female threads threaded around the entire circumference on the inner peripheral surface of both ends and a shoulder portion at the end of the female thread, and a pipe with male threads threaded on the outer peripheral surface, A method for controlling the tightening of a special joint, which comprises screwing the female thread of the joint into the male thread of the pipe, tightening the joint, and further tightening after the end of the pipe comes into shoulder contact with the shoulder, and the method includes tightening the joint from the point of shoulder contact. A method for controlling the tightening of a special joint having a shoulder seal, the method comprising: setting a time until stopping the joint, tightening the joint while detecting a shoulder touch, and further tightening for the set time from the point of shoulder touch.