JPS6054241A - Upset working method of steel pipe - Google Patents

Abstract

PURPOSE:To manufacture efficiently an upset pipe having a high quality by determining the upper limit value of a thickness increasing rate of every ratio of a thickness of a pipe end part and its outside diameter, and executing a compressing operation so that the thickness increasing rate becomes below the upper limit value, when executing an upset working of the pipe end part. CONSTITUTION:At every ratio t/D value of a pipe end part thickness (t) and an outside diameter D, a ratio of the original thickness and the final thickness, namely, a thickness increasing rate is calculated. On the other hand, by a chart and expressions I , II, a critical thickness increasing rate alpha1cr of the first shot and a critical thickness increasing rate alpha2cr of the second shot are derived. In this way, an upset working is executed so that the thickness increasing rate in each shot becomes within a range of the ciritical thickness increasing rates alpha1cr, alpha2cr.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an upset processing method for increasing the thickness of a steel pipe by compressing it in the axial direction.

Generally, long pipe bodies such as oil country tubular goods are manufactured using a large number of tj4. It is configured by connecting pipes.

If the pipe end is threaded in order to connect the steel pipe with a coupling, there is a risk that that part will become thinner by the machining allowance and its strength will decrease. In order to prevent a decrease in strength, a tubular body called Abcera 1-tube is used, which has a thickened portion formed by so-called ablets at the end of the tube.

To briefly explain the upset processing method, Fig. 1 (
A>(B) is a schematic diagram showing the so-called external ablation processing, in which the end of the steel pipe 1 is locally heated to a high temperature by an induction heating method, etc., and a part of the inner diameter is made smaller than the outer diameter of the steel pipe 1. restraining the end of the steel pipe 1 with a large split die 2;
In this state @'c, the heated tube end is compressed in the axial direction by a punch 3 having a shaft portion having the same diameter as the inner diameter of the steel tube 1, thereby inflating the tube end and increasing the thickness toward the outer circumference.

Furthermore, FIGS. 2(A) and 2(B) are schematic diagrams showing the so-called internal absera machining. Using a punch 5 with a thinner shaft, the tube end is locally heated and restrained by the splitting die 4 and compressed in the axial direction by the punch 5, thereby increasing the thickness toward the inner circumference.

When performing such upset processing, it is known that the quality and productivity are greatly affected by the processing schedule 1, that is, the number of shots J3 and the thickness increase rate.

Here, the number of shots is the number of compression operations performed to obtain the final wall thickness, and the wall thickness increase rate is the increase rate of tube end wall thickness per shot α = (L l -to) /1o
(jo: wall thickness immediately before compression operation, tl: wall thickness after compression operation). However, when processing a steel pipe with a large thickness increase, it is difficult to achieve the desired wall thickness with a single compression operation, so
It is necessary to determine the rate of increase in thickness per shot. Therefore,
From the viewpoint of energy saving and productivity, it is advantageous to reduce the number of shots and increase the rate of increase in thickness, but if the rate of increase in thickness is increased, the end of the tube may buckle and deform. There is a risk that wrinkles and dents may occur on the inner and outer circumferential surfaces, resulting in a decrease in quality.

This invention was made in view of the above circumstances, and it is possible to efficiently manufacture a high-quality upset J-tube.
The purpose of this invention is to provide an upset processing method that can save energy.

In other words, the inventors of the present invention have carried out extensive experiments and RTL+ research, and have found that the flaws at the tube end are caused by buckling deformation of the tube end due to compressive force in the axial direction, and the degree of this is different from that at the tube end. It has been found that the rigidity of the tube end is greatly affected by the rigidity of the tube end, and therefore the rigidity of the tube end depends on its dimensions, that is, its wall thickness and outer diameter. This invention was made based on the above-mentioned knowledge, and it was found that the wall thickness of the tube end before the compression operation a is different depending on the outer diameter. The upper limit of the thickness increase rate in each compression operation is determined from the viewpoint of the degree of wrinkling, etc. for each ratio to the outer diameter of the steel pipe to be compressed, and the thickness increase rate in each compression operation is less than or equal to the upper limit value. By performing each compression operation so that

The knowledge that led to this invention and the method of this invention will be explained in more detail below.

Figure 3 is a diagram showing the occurrence of wrinkle defects when the ratio of wall thickness [to outer diameter 1] (t/D) is changed while the rate of increase in thickness to the outside surface is constant. In FIG. 3, short thin lines indicate the locations where wrinkles occur and their depths. Third
As is clear from the results shown in the figure, when the t/D value is large, there are fewer crease defects, and therefore when t/Dla is large, t
For 14 pipes, it seems that there is no problem in increasing the rate of increase in thickness per 1 shot.

FIG. 4 is a diagram showing the results of experiments conducted based on such predictions. In the experiment whose results are shown in Fig. 4, the wrinkle depth (ratio of large wrinkle flaw depth to Abcera 1~thickness) when the thickness increase rate to the outer surface was changed was calculated for steel pipes with different t/D values. were measured. As is clear from the results shown in FIG. 4, it was confirmed that if the t/D value is large by 1, the wrinkle depth can be kept shallow even if the thickness increase rate is increased.

As mentioned above, the stiffness f of the tube m section! In other words, the larger the ratio of wall thickness t to outer diameter (t/D), the less likely wrinkles are to occur and the shallower the depth. It has been found that the rate of increase in thickness within a range that does not particularly cause the increase in thickness depends on the t/D value, and that the rate of increase in thickness can be increased as the t/D value is large.

By the way, it is preferable that there be no wrinkle defects due to Absela 1 processing, but since screw processing is applied to the thickened part that has been subjected to abhit processing, wrinkle defects may be removed due to thread processing, so there may be some wrinkle defects. Wrinkle defects are acceptable.

As mentioned above, the degree of edge flaws differs depending on the thickness increase rate for each t/D value, and the smaller the t/D value and the greater the thickness increase rate, the more noticeable they become. If the permissible limit for wrinkle defects is determined based on the relationship with processing, the critical thickness increase rate for each L/l) value is uniquely determined. Fifth
The figure is a one-line diagram showing the critical thickness increase rate for each L/D value obtained in this way, and the broken line in Fig. 5 shows the case of so-called external absera], and the solid line shows the case of internal upset. . For external ablets, the critical thickness increase rate α1c for each shot
r, α and C are given by the following equations (1) and (2) from the broken lines in FIG.

1 shot]・[l marginal thickness increase rate αiCrαtcr=f
(t/D) - (1) 2 shots] - Critical eye thickening rate α
2CI−α2cr= (1+α1c, r) [1+ f
(□) ].

(2) In the case of inner surface upset, the critical thickness increase rate for each stain 1 can be determined based on the solid line in FIG.

As mentioned above, it has been found that the critical thickness increase rate at which wrinkle defects are within the allowable limit is determined as a function of the t/D, and this invention is based on this knowledge, and the present invention is based on the above-mentioned limit. This is a method of processing Abcera 1 to within the range of the thickness increase rate.

By the way, when performing upset processing, it is necessary to determine the number of shots in addition to the thickness increase rate, and the procedure will be explained below.

First, in determining the number of shots, the ratio of the original wall thickness of the tube end to the final wall thickness to be obtained, that is, the wall thickness increase rate, is calculated, and the critical wall thickness increase rate for each shot is calculated from Figure 5 and the above formula. Then, calculate the number of shots required to reach the critical thickness increase rate at which the ratio to the thickness increase rate is 1 or less. The number of shots thus calculated is the required number of shots. Further, the thickness increase rate of each shop 1 to 1 is determined so that the ratio to each marginal thickness increase rate is approximately constant. Therefore, for example, in the case of external upsetting machining where the number of shots is 2, it is given by equation (3).

α1 α2 αIey α2hi (αler 〈α2〈α2er)・
(3) By the way, the present invention is not limited to the outer abseller 1-, but can be applied to both the inner surface upset and the inner and outer double-sided abseller 1-. Figure 6 shows a generalized flowchart. 1 First, indicate the numbers 1 to 1, set the J variable 1 to 1, and obtain the outer wall thickness increase rate α and the inner wall thickness increase rate β as the wall thickness of the original tube. Add π1 from the final thickness. Next, the critical thickness increase rate on the outer surface side and the inner surface side in the shot indicated by the above-mentioned variable is calculated. The calculation can be performed using a curve not shown in FIG. 5 and a mathematical formula based thereon. Calculate the sum of the ratios of the thickness increase rate and the critical thickness increase rate, and repeat the calculation of the critical thickness increase rate and the value until the K value becomes 1 or less, and then calculate the value until the K value becomes 1 or less. The number of repetitions until the number of shots is reached is the number of shots. Next, from the number of shots obtained as described above, the thickness increase rate for each shot is calculated so that the ratio of the thickness increase rate to the critical thickness increase rate is approximately constant. In this way, the number of shots and the rate of increase in thickness for each shot can be determined.

Below is a specific example of an extroverted abset.

Original tube outer diameter D-88,9III11 wall thickness t = 6.
45111111, Ablet outer diameter -101.8mm
C will be explained using the case of C as an example.

■ Thickening rate α, β α= (101,L-88,9)Total 2÷6.45 x
100=100(%) (β-0 because the outer surface is 1-) ■ Critical thickness increase rate α1cV-1βicr-1 c2=f (t/D) =f (6,45/88.
9) = 60 (%) (-, - intertwined with the broken lines in Figure 5) ■ K value = α/αxcy- = 100/60 #1.67 >
1■ Calculate /- to the critical thickness increase rate α again: i=2 α2CA−−(1+αtcr ) (1+f ((10α1cr)t/D)) −1 = (1+ 0.6> (1+f (1 ,6x6.45
/88.9) ) -1 = (10.6) (1→ 0,68) -15=
, 1.69 (°,° From Figure 5 t (0,116) = 0.68
>■ K value is −α/α2 (, r = 100/169−0.59
< 1 ■ Determination of the number of shots Since i = 2, 2 shots] ~ ■ 1st shot for sieving of thickness increase rate in each shot αl-αxL = 100x4 = 36% (Z) cr 2 shots] ~ α2 = The number of shots and the thickness increase rate for each shot obtained as described above are the values n calculated based on the critical thickness increase rate at which wrinkle defects are within the allowable limit. If Absela 1~ is processed according to the number of shots and the thickness increase rate,
It is possible to efficiently manufacture an upset tube with no particular problems in terms of quality.

In addition, in the above explanation, the case was shown in which the critical thickness increase rate was calculated for each ratio (L/D) between the wall thickness and the outer diameter of the steel pipe, which is the raw material, but the rigidity of the pipe end depends on the wall thickness and the inner diameter. The same result can also be obtained by expressing the ratio of the wall thickness to the inner diameter, so in this invention, instead of using the t/D value, the limit increase in thickness for each ratio of the wall thickness to the inner diameter is used. You can lower the rate.

Furthermore, in the above embodiment, the ratio of the thickness increase rate in each compression operation to the critical thickness increase rate is constant, but as is clear from the above explanation, each If the thickness increase rate in the compression operation is less than the critical thickness increase rate, wrinkles will be within the allowable range, so the compression operation should be performed so that the ratio of the thickness increase rate in each compression operation to the critical thickness increase rate is constant. It is not necessarily necessary to do so.

As explained above, the method of the present invention is capable of calculating the critical thickness increase rate at which wrinkle flaws at the pipe end are within the allowable range, and performs abulet processing at a thickness increase rate within the range of the critical thickness increase rate. Therefore, the method of the present invention not only does not cause wrinkles that would impair the quality of the final product, but also allows the abulet processing to be performed at as high a thickness increase rate as possible within that range. Since high-quality applet tubes can be efficiently produced and the number of shots, that is, the number of compression operations can be kept to the minimum necessary, energy can be saved.

[Brief explanation of drawings]

Figure 1 (A>(B) is a schematic cross-sectional view showing the process of external upsetting); Figures 2 (A) and (B) are schematic cross-sectional views showing the process of internal upsetting; Figure 3 is thickening. Figure 4 shows the relationship between the outer wall thickness increase rate and the wrinkle depth as a function of wall thickness and outer diameter. Figure 5 is a correlation diagram showing the relationship between the critical thickness increase rate and the ratio of wall thickness to outer diameter for both external and internal upsets. Flowchart 1 to show the procedure. 1... Steel pipe, 2.4... Split die, 3.5...
Punch, T...thickness, D...outer diameter. Applicant Kawasaki Steel Co., Ltd. Agent Patent Attorney Yutaka [U Takehisa (one idiot) 1st (A) 2nd (A) Figure (B)

Claims (2)

[Claims] (1) When performing abset processing, which thickens the end of a heated steel pipe by compressing it in the axial direction, the thickness of the end of the pipe immediately before the compression operation and the outer diameter of the steel pipe are An applet for a steel pipe characterized in that an upper limit value of the thickness increase rate is determined for each ratio, and the tube end is compressed to increase the thickness so that the thickness increase rate in each compression operation is equal to or less than the upper limit value. Processing method. (2) The pipe end portion is compressed to increase the thickness so that the ratio of the thickness increase rate to the upper limit value in each compression operation is a substantially constant value of 1 or less. The described steel pipe upset processing method.