JPH07314251A - Steel pipe threading method - Google Patents

Abstract

(57) [Abstract] [Purpose] The present invention relates to a thread cutting method for a steel pipe such as an oil well pipe having a special seal portion at the pipe end. [Structure] In the method of performing thread cutting by finishing grinding the inner surface of a steel pipe having a special seal portion at the pipe end using a pre-processing machine and then finishing grinding the outer surface using a thread cutting machine,
When the steel pipe P whose inner surface has been ground by the pre-processing machine is carried into the threading machine 10, the mandrel 13 with the distance sensor 15 attached is inserted into the pipe end to measure the distance to the inner surface, and based on the measured distance value. The centering device 20 is controlled by the centering device 20 to center the steel pipe P, and then the external surface finish cutting is performed by the thread cutting machine 10, so that the external surface finish cutting without center deviation can be performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread cutting method for a steel pipe such as an oil well pipe having a special seal portion at the pipe end.

[0002]

2. Description of the Related Art Conventionally, oil well pipe screws used for oil drilling and the like have extremely strict requirements in terms of manufacturing and applications, and therefore API screw joints and the like have been developed. However, oil wells in recent years have become deeper, and joint strength and airtightness are required to be improved more than API threaded joints.Therefore, the joints have more metal-to-metal seals, and the thread shape is square and A joint with a Teflon ring inserted is being developed.

As shown in FIG. 4, for example, as shown in FIG. 4, a screw of an oil country tubular good having a special seal portion has an inner surface seal portion 2 provided from an end surface 1a of a pipe end 1 of a steel pipe P to an inner surface 1b and an outer surface seal provided on an outer surface 1c. External surface 1c as in part 3
And the threaded portion 4 provided on the. In the case where the cutting is performed while rotating the steel pipe in the axial direction of such a screw using a lathe type thread cutting machine, conventionally, it has been a 7-pass process as shown in FIG. That is, (a) the cutting tool 6 attached to the holder 5
a step of cutting the end surface 1a of the pipe end 1 using a, and further forming the rough seal portion 2a on the inner surface 1b thereof, (b) cutting tool 6
a step of forming a rough seal portion 3a on the outer surface 1c of the pipe end 1 using b, and then processing the screw lower taper outer diameter portion 3b,
(c) a step of cutting the coarse screw 4a on the screw lower taper outer diameter portion 3b using the cutting tool 6c, (d) a step of finishing the inner surface 1b of the pipe end using the cutting tool 6d, (e) a cutting tool 6e A step of simultaneously finishing the inner and outer surface seal parts 2 and 3 by using (f)
7 passes of the step of finishing the threaded portion 4 twice using the cutting tool 6f.

However, in this lathe method, as described above, a total of 6 kinds of cutting tools are selected one by one with a turret (not shown) for each step, attached to the holder 5, and used in order for cutting. Therefore, it takes a lot of time to rotate and stop the steel pipe for each pass, and to handle the steel pipe. Therefore, it takes a long time to form a screw for each steel pipe, resulting in poor screw forming efficiency.

As one of means for solving such a drawback of the lathe method, a tool rotating type thread cutting machine for rotating a tool by fixing a pipe has been adopted in recent years. In the case of this tool rotation type, as shown in FIG.
Using a pre-processing machine 7 provided with a and 8a and a thread cutting machine 8,
The above-mentioned steps (a), (b), (d) and (e) for finishing the inner surface seal portion 2 are performed by the pre-processing machine 7, and the remaining (c) and (e) for the outer surface seal portion 3 and Generally, the step (f) is divided into two steps, that is, a screw cutting machine 8 is used. This is because it is difficult to attach the cutting tools required for each cutting to one threading machine, and it is more advantageous to divide it into two steps in terms of productivity and cost. This is due to the reason. In this cutting method, it goes without saying that balancing the processing times of the pre-processing machine 7 and the thread cutting machine 8 is an important requirement for improving productivity.

[0006]

However, when rough cutting is performed by the pre-processing machine 7 and finish cutting is performed by the thread cutting machine 8, the steel pipe P
The center of the cutting portion is likely to be displaced, and this displacement causes the centers of the inner surface sealing portion 2 and the outer surface sealing portion 3 to be displaced, resulting in uneven thickness. If there is this uneven thickness, as shown in FIG. 8, when the coupling C is tightened, a stepped portion D occurs. When the fluid flows, the stepped portion D causes a vortex or the like at that portion, which causes a problem such as shortening the life of the steel pipe.

In order to prevent the uneven thickness, a centering device 9 for centering the steel pipe P is usually provided between the threading machine 8 and the chuck 8a as shown in FIG. As shown in FIGS. 7 (a) and 7 (b), this centering device 9 includes a steel pipe P with three arms 9a, 9b and 9c.
The uncut portion of is clamped. However, in such a centering device 9, since centering is performed on the basis of the outer surface of the steel pipe P, the center of the inner surface cutting portion is displaced depending on which part of the steel pipe P the arms 9a to 9c contact. There is a problem that it will occur.

For such a center deviation, for example, as disclosed in Japanese Unexamined Patent Publication (Kokai) No. 5-192818, a chamfering machine horizontally performs rough outer surface cutting over a predetermined length, and a horizontal outer cutting portion thereof. There is a method of centering by clamping with a centering chuck on the threading machine side.
However, even in the case of this method, there is an error that occurs because a large rigidity cannot be given due to restrictions such as the space occupied by the centering device itself. Further, there remains a problem that the outer center does not match the inner center.

An object of the present invention is to provide a method for threading a steel pipe, which solves the problems of the prior art as described above.

[0010]

SUMMARY OF THE INVENTION According to the present invention, a steel pipe having a special seal portion at the pipe end is finish-ground by a pre-processing machine, and then an outer surface is finish-ground by a threading machine for thread cutting. In the method to be performed, when the steel pipe whose inner surface is ground by the pre-processing machine is carried into the thread cutting machine, the distance to the inner surface is measured by inserting a mandrel equipped with a distance sensor in the tube end, and the measured distance value. A method for threading a steel pipe is characterized in that after the steel pipe is centered on the basis of the above, finish cutting of the outer surface is performed.

[0011]

[Operation] According to the present invention, when a steel pipe having an inner surface finished and cut by a pre-processing machine is carried into a threading machine, the steel pipe is measured according to a value of a distance to the inner surface measured by a distance sensor attached to a mandrel. Since the centering position is adjusted, it is possible to prevent the center deviation when finishing cutting the outer surface of the thread cutting machine.

[0012]

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 shows an outline of a thread cutting machine used in the present invention. (A) is a side view and (b) is AA.
FIG. In the figure, 10 is a threading machine used in the present invention, and a die head 12 is rotatably held in a threading machine body 11. A mandrel 13 is attached to the center of the die head 12, and a tool block 14 for setting a cutting tool is attached to the periphery of the mandrel 13. In addition, around the mandrel 13, four, for example, optical distance sensors
15 are installed vertically and horizontally symmetrically. A linear slide 16 is attached to the threading machine main body 11 so that it can be moved forward and backward on the guide 17 in the arrow F direction.

A centering device 20 used in the present invention is composed of a pair of left and right centering device bodies 21, 21. A chuck 22 for clamping the steel pipe P is provided in the centering device main body 21 so as to be freely taken in and out in the horizontal direction, and is further vertically movable by an elevating device 23. As the lifting device 23, a hydraulic cylinder or an electric motor is suitable.

Reference numeral 30 denotes a centering control device, which is a distance sensor.
It has a function of inputting the measurement signal from 15 and performing arithmetic processing to control the chuck 22 and the lifting device 23 of the centering device 20. The centering operation of the device of the present invention will be described below. When the steel pipe P roughly ground from a pre-processing machine (not shown) is fed into the thread cutting machine 10, the steel pipes P are horizontally projected from the centering device bodies 21 and 21 in the centering device 20 by chucks 22 and 22 from both sides. Clamp P. As shown in FIG. 2, the threading machine 10 is moved forward, the tip of the mandrel 13 is inserted into the tip portion 1 of the steel pipe P, and stopped at a predetermined position on the inner surface 1b of the pipe end.
Measure the vertical and horizontal distances to the inner wall surface of the pipe. If the rod 18 for hydraulic operation is attached to the tip of the mandrel 13 and the mandrel 13 is fixed by contacting the inner wall surface of the pipe during the measurement, the measurement accuracy is not impaired. These distance measurement values are input to the centering control device 30 and compared with a preset allowable value. Then, if all the measured distance values are within the allowable values, the process directly proceeds to the finishing cutting step. However, if a distance measurement value exceeding the allowable value is obtained, it is judged that there is a center deviation, and the centering control device 30 outputs a position correction signal according to the deviation and the centering device main body 21, 21 is clamped. Adjust the position. That is, in the case of vertical displacement, it is corrected by adjusting the strokes of the lifting devices 23, 23, and in the case of horizontal displacement, it is corrected by adjusting the strokes of the chucks 22, 22. After that, the process proceeds to the finishing cutting process.

Using the device of the present invention, the outer diameter: 244.5 mmφ ×
When a special screw was cut on a steel pipe P with dimensions of wall thickness; 11.99 mmt x length: 12000 mmL, the uneven thickness of the seal parallel part is as shown in Fig. 3 mean value x _AV is 0.10 mm, standard deviation σ is 0.
A distribution of 05 mm was obtained. These values are the average value x _AV ; 0.23 mm, standard deviation σ; 0.10 mm in the conventional example shown in FIG.
It can be seen that it is significantly improved compared to.

Although the optical sensor is used as the distance sensor 15 in the above embodiment, the present invention is not limited to this. For example, a linear gauge combined with a differential transformer may be used. Good. Further, although the number of the distance sensors 15 is four, the number of the distance sensors 15 may be one as long as it can simultaneously measure the vertical and horizontal distances of the steel pipe.

[0017]

As described above, according to the present invention,
When the steel pipe with the inner surface finished and cut by the pre-processing machine is loaded into the threading machine, the distance to the inner wall surface of the pipe is measured using the distance sensor attached to the mandrel, and the centering position of the steel pipe is adjusted according to the measured value. As a result, it is possible to perform the outer surface finish cutting without the center deviation of the steel pipe in the thread cutting machine, and it is possible to improve the quality of the product.

[Brief description of drawings]

FIG. 1 shows an outline of a thread cutting machine used in the present invention, (a) is a side view, and (b) is a front view taken along the line AA.

FIG. 2 is an explanatory diagram showing a measurement state of the inner surface of the pipe.

FIG. 3 is a characteristic diagram showing a frequency of occurrence of uneven thickness.

FIG. 4 is a partial cross-sectional view showing the shape of a special screw of an oil country tubular good.

FIG. 5 is an explanatory diagram showing a conventional threading process for an oil country tubular good.

FIG. 6 is an arrangement view showing a configuration of a conventional tool rotary type thread cutting machine.

7 (a) is a front view and FIG. 7 (b) is a side view showing an outline of a conventional centering device.

FIG. 8 is a side sectional view showing a state in which a coupling is attached to a special screw.

[Explanation of symbols]

 1 Pipe End 1b Inner Surface 10 Thread Cutting Machine 11 Thread Cutting Machine Main Body 12 Die Head 13 Mandrel 15 Distance Sensor 20 Centering Device 21 Centering Device Main Body 22 Chuck 23 Lifting Device 30 Centering Control Device P Steel Pipe

Claims (1)

[Claims] 1. A method of performing thread cutting by finishing grinding an inner surface of a steel pipe having a special seal portion at a pipe end by using a pre-processing machine, and then finishing grinding an outer surface by using a thread cutting machine. At the time when the steel pipe whose inner surface was ground by the above was carried into the threading machine, a mandrel with a distance sensor was inserted into the pipe end to measure the distance to the inner surface, and after centering the steel pipe based on the measured distance value. A method for threading a steel pipe, characterized by performing finish cutting on the outer surface.