JPS59129723A - Production of high squeezing strength seam welded steel tube - Google Patents

Abstract

PURPOSE:To obtain an electric welded steel tube having high squeezing strength without heat treatment by sizing the tube at a prescribed total drawing rate in succession to water cooling after seam welding then setting and finishing the tube with Turk's heads. CONSTITUTION:A seam welded steel tube T is fed from the right to the left by pinch roll stands 1, 2, and th weld zone of the tube T is cooled to around room temp., in a cooler 3. The tube T is finished to a specified size by sizing stands 4-7. The sizing in this case is accomplished at 1.0-3.5% total drawing rate and at the total drawing rate in the prior art (about 0.2-0.6%) or above. More specifically, the outside diameter of the tube T is successively reduced and the tube is finished to the roundness having a prescribed outside diameter in the final stand 7. The tube T finished in the stands 4-7 is finished straightforward by Turk's heads 9, 10 whereby the intended high squeezing type electric welded steel tube is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing an electric resistance welded steel pipe with high crushing strength.

In recent years, gas and oil wells have tended to become deeper and deeper, and the demand for high collapse type oil country tubular goods has been increasing year by year. ERW steel pipes have higher dimensional accuracy than seamless steel pipes, and have a fine-grained structure that gives them high strength, making them suitable for highly crushed oil country tubular goods. However, since the forming of ERW steel pipes, the sizing process to make the pipe a constant diameter and perfect circle, and the straightening process to make the pipe straight, it is necessary to avoid the generation of compressive residual stress on the inner surface of the pipe. I can't. This residual stress acts to reduce the crushing strength of the electric resistance welded steel pipe. It has been known for a long time that residual stress can be reduced by heat treatment, but heat treatment requires a large amount of cost. Further, in some cases, the yield stress of the tube decreases due to heat treatment, which causes a problem in that the crushing strength decreases.

This invention was made to solve the above-mentioned problems in manufacturing high-pressure crush type ERW steel pipes, and provides a method for manufacturing ERW steel pipes with high crushing strength without heat treatment. It is to be.

In the manufacturing method of the ERW steel pipe of this invention, the pipe is water-cooled after seam welding, and then the pipe is processed at a total drawing rate (the drawing rate of the total of all stands) of 1.
．． Sizing at 0-3.5% and then finishing the tube by straightening it with a Turk's head.

Here, finishing the tube means finishing the tube-making process without subjecting the straightened tube to heat treatment for stress relief.

As mentioned above, in sizing, by setting the total reduction rate to 1.0 to 3.5%, which is more than twice that of the conventional one, it is possible to reduce the compressive residual stress on the inner surface of the tube generated in the process before sizing. Further, by using a Turk's head during straightening, straightening can be performed without generating almost any residual stress. Therefore, an electric resistance welded steel pipe with high crushing strength can be obtained without performing heat treatment to remove residual stress. Also, by omitting heat treatment,
The manufacturing cost of high crush type ERW steel pipes can be greatly reduced.

The present invention will be described in detail below.

In order to improve the crushing strength, it is necessary to reduce the compressive residual stress on the inner surface of the tube, and it is known to heat-treat the tube for this purpose. However, if heat treatment is performed, the yield strength of the tube will decrease, and the crushing strength will also decrease accordingly.

Therefore, in the present invention, the compressive residual stress generated on the inner surface of the pipe during the pipe making process is reduced, and heat treatment is omitted.

In this invention, in order to reduce the residual stress in the sizing 7, contrary to conventional wisdom, the total drawing ratio is made significantly large. That is, the conventional total sizing error rate is about 0.2 to 0.6%, but in the present invention, it is set to 10 to 3.5 percent, which is more than double this. It is not clear why the residual stress decreases with such a large total drawing ratio, but when sizing is performed at a large total drawing ratio, a large tensile stress is added to the inner surface of the pipe, and the compressive residual stress generated in the process before sizing is This is expected to decrease.

FIG. 1 is an example of a graph showing the relationship between the total proofreading rate of sizing and the internal compressive residual stress immediately after sizing. In the figure,
Symbol A indicates the conventional method, and symbol B indicates the range of the total aperture ratio of the present invention. It is clear from the figure that the residual stress decreases as the total reduction ratio increases, as shown by the force 1.

In this invention, the total sizing error rate is limited to a range of 10 to 3.5 factors. It is determined from the value of residual stress that is allowable in order to obtain the practically necessary crushing strength at the lower limit of 10. In addition, when 1.0% is replaced with residual stress, it is equivalent to 15K ring, and this residual stress is equivalent to %d in crushing pressure of 40%, which is required for the production of high-pressure steel pipes [Hl, 0% sizing reduction ratio]. is necessary. 3.5% of the upper limit, the first
As is clear from the figure, this was decided taking into consideration that when the drawing ratio is too steep, the rate of reduction in residual stress is small and that pipe VCore flaws are more likely to occur.

Straightening is performed subsequent to the above sizing.

Conventionally, straightening has been carried out using a rotary straightener having a plurality of slanted rolls. However, in this invention, J: correction is performed on the Turk's head.

In rotary straighteners, the tube is straightened by roll offset and crush, which tends to generate large residual stress. On the other hand, in the present invention, the Turkshead VC,r pipe is bent in a direction perpendicular to the pipe axis to make the pipe straight. Therefore, the tangential stress in the inner circumferential direction of the pipe hardly occurs, so that the residual stress immediately after sizing is maintained as is. In other words, the internal compressive residual stress remains almost unchanged before and after straightening.

FIG. 2 is an example of a diagram showing differences in residual stress due to different straightening methods. As can be seen from this figure (η), when straightening is performed using a rotary straightener, the internal compressive residual stress increases significantly (approximately three times).

On the other hand, if correction is performed using a Turk's head, the residual stress will hardly change.

Next, the method of the present invention will be explained in more detail along with an apparatus for carrying out the method.

FIG. 3 is a side view showing a part of the pipe making apparatus.

Tube T [Sent from right to left. Although not shown on the right side of the figure, an uncoiler 9 forming stand, a seam welding machine, etc. are arranged. Further, on the left side of the figure, a traveling cutting machine, a chamfering machine, and a hydraulic testing machine (all not shown) are arranged.

As shown in the drawing, a cooling device 3, sizing stands 4°5, 6, 7, Turk's heads 9, 10, and an ultrasonic flaw detector 12 are arranged in this order between the pinch roll stand 1°2.

The pinch roll stands 1 and 2 apply thrust to the pipe T whose joints are welded, and feed the pipe T from right to left. Pipe T is cooling device 3
The weld is cooled to near room temperature.

Next, the pipe '14I is finished to a constant diameter using four sizing stands 4 to 7. Each sizing stand 4-7
It is a double rolling mill with oval or round holes, and the rolling rolls 8 are arranged alternately at right angles between the stands. The outer diameter of the tube Tfi is sequentially reduced in pressure, and the final stand 7
It is finished into a perfect circle with a predetermined outer diameter.

The pipe T finished to a constant diameter on sizing stands 4 to 7 is finished straight using a Turk's head 9vl (lc).

Each Targis head 9, 10i and four rolls 1 spaced apart by 90 degrees form a runland hole shape equal to the outside diameter of the tube. The position of the roll 11 of the second Turk's head 10 (center position of the groove) is fixed, whereas the position of the roll 11 of the first Turk's head 9 (center position of the groove) is fixed. It can be moved and adjusted vertically and laterally (perpendicular to the plane of the paper in the drawing).

Once the forming apparatus (not shown) and the sizing stands 4 to 7 are installed, the direction and magnitude of the bend of the tube T at the exit side of the final sizing stand 7 are fixed. By applying bending to the tube TVr by the Turk's heads 9 and 10 to cancel out this bending, the tube T can be finished straight.

The direction and magnitude of the required bending is as per Turkshead 9.1.
It is obtained by adjusting the relative position between 0 and 0.

Here, an experimental example showing the effects of this invention will be given.

Table 1 shows the pipe diameter s)/2II, inner thickness 0. The figure shows a comparison of the crushing pressures of '304'' electric resistance welded steel pipes manufactured under various sizing and straightening conditions vCx.

As far as differences in sizing and straightening conditions are concerned, the crushing pressure is increased by at least 10% in the present invention. (Comparison of Samples A and F) Since heat treatment is performed in the conventional method, the crushing pressure is about 530 to 590 K9/crl.

[Brief explanation of the drawing]

Fig. 1 is a graph showing an example of the relationship between the total sizing proofing rate and internal compressive residual stress, Fig. 2 is a diagram showing an example of the relationship between the straightening method and internal compressive residual stress, and Fig. 3 is a graph showing an example of the relationship between the correction method and internal compressive residual stress. 1 is a schematic side view of an apparatus for carrying out the method; FIG. 1.2...Pinch roll, 3...Cooling device, 4-7
...Sizing stand, 9.10...Turks head, T...tube. Patent applicant and patent attorney Tomoyuki Yafuki. (is force) 1 person) Figure 1 Iwano 2゛Metal exchange rate ('A); ゛S 2 is 1

Claims (1)

[Claims] In the production of ERW steel pipes, the pipe is water-cooled after seam welding, and then the pipe is sized with a total reduction rate of 1.0 to 3.5%, and then the pipe is straightened and finished using a Turk's head. Manufacturing method of type ERW steel pipe.