JPS60218424A - Production of steel pipe having high collapsing strength - Google Patents

Abstract

PURPOSE:To obtain a steel pipe having extremely high collapsing strength in a method for heating the hardened and tempered steel pipe to a prescribed temp. and working the pipe by using 4 pieces a set of specific rolls in place of a strainer in specific working of said pipe. CONSTITUTION:A hardened and tempered steel pipe 1 is applied with compressive load P at 4 points on the outside circumference thereof by means of 4 pieces a set of parallel rolls 21, 22, 31, 32 in the >=3 positions apart from each other in the axial direction of the pipe under the temp. conditions of >=300 deg.C and below the tempering temp. The pipe 1 is thus acted with bending force and is subjected to the working to generate required deformation in the specific diametral direction of the pipe and to rotate at least half the pipe around the axis of the pipe while maintaining the deformation. The roll load is thereafter gradually removed under rotation of the pipe by maintaining the specified change rate of the above-described deformation with respect to said rotation and setting the rotating amt. of the pipe in the process of removing the load at >=1 rotations. Such operation is subjected to the overall length of the pipe. The yield strength, out of roundness and the residual stress distribution in the inside surface of the pipe are thus respectively improved and the collapsing strength is improved.

Description

[Detailed description of the invention]

<Industrial Application Field> The present invention relates to a method for manufacturing high-column strength steel pipes with excellent 7717 strength (strength against crushing due to external pressure), which is particularly important for oil country tubular products. <Prior art> In recent years, there has been a remarkable trend toward deeper oil wells due to the tight oil situation, and this has led to an increased demand for oil country tubular goods with high strength. To achieve this, a method is needed to comprehensively increase the strength of the steel pipe by improving the shape, strengthening the material, etc. during the manufacturing process of steel pipes.Currently, the following two methods are known as methods of this type. It is being First of all, as a method for straightening the roundness and bending of steel pipes, the general method is to straighten the υ curve V and to a certain degree of roundness by passing the pipe cold between several pairs of slanted rolls. After this, a method is carried out in which the outer diameter drawing process is performed using drawing rolls arranged horizontally and vertically alternately to further improve the roundness. Therefore, based on the idea that cold straightener processing leads to the generation of compressive residual stress in the circumferential direction on the inner surface of the tube and a decrease in yield strength, the strength of the quenched and tempered steel tube'fI is reduced.
: By heating to a temperature above 800℃ and below the tempering temperature and passing it through warm straightener processing, the generation of the compressive residual stress is suppressed and the decrease in yield strength is prevented, resulting in a corrugated shape.
There is a method to improve the strength of the base. However, although this method can improve the yield strength, the roundness that can be secured is limited to 0.4% at most, and it cannot be expected to achieve more than that, and the residual stress distribution is not sufficient. Strong steel pipes cannot be obtained. ■ The temperature condition of the quenched and tempered steel pipe supplied to the straightener processing in (■) above is set to a high temperature of 450°C or higher to further improve the residual stress distribution and achieve a high co-efficiency.
There is a way to obtain high-strength steel pipes. However, this method is expensive due to high-temperature processing, and is subject to constraints from the economical point of view of high cost.
There is a problem in that it cannot be applied to steel pipes that are tempered at temperatures lower than 0°C. As described above, none of the conventionally known methods for increasing the strength of 3717 can be said to be sufficient as an earthwork. <Object of the Invention> The present invention improves the roundness of the pipe, the yield strength, and the residual stress distribution in the circumferential direction on the inner surface of the pipe all at once, which are factors that influence the Cobbus strength, and achieves a higher degree of collapse than conventional methods. The object of the present invention is to provide a method for manufacturing a high-coherence-strength steel pipe that can increase strength and at the same time straighten curvature. <Structure of the invention> That is, the present invention uses a quenched and tempered steel pipe, and
At a temperature of 0°C or higher and lower than the tempering temperature, a compressive load is applied to four locations on the outer circumference by a set of four parallel rolls at three or more locations apart from each other in the tube axis direction to bend the tube. A force is applied to the pipe to produce the required deformation in a specific pipe diameter direction, and while this deformation is maintained, the roll is rotated at least half a turn around the pipe axis, and then this roll load is removed while the pipe is rotating. The rate of change in the amount of deformation is kept constant, and the amount of rotation of the pipe during the unloading process is set to one revolution or more, and this operation is carried out gradually so that the compressive load applied by the rolls extends over the entire length of the pipe. The main subject of this paper is a method for manufacturing high-strength steel pipes that are characterized by The method of the present invention aims to improve the pipe yield strength, roundness, and residual stress distribution on the inner surface of the pipe, which are factors that influence the core strength, and to improve the steel strength by combining these effects. . Hereinafter, the method of the present invention will be explained in detail by dividing it into yield strength, roundness, and residual stress distribution on the inner surface of the tube, and including reasons for improvement in each item and reasons for limiting each requirement. ■ Yield strength The yield strength has been determined by the inventors' numerous experiments.
It was confirmed that even in the process of the present invention, in which a compressed cart is roll-loaded at four opposing positions on the outer periphery of the tube, it is possible to improve the yield strength through warm working, similar to the conventional method. In the present invention, the temperature conditions for warm working are limited as described above because if the yield strength is lower than 300°C, sufficient improvement in yield strength cannot be obtained and improvement in coffee strength cannot be expected. An example of the relationship between and processing temperature is shown in Figure 1.As seen in the figure, yield strength is low and insufficient at temperatures below 9300°C. It has been found that the roundness can be effectively improved by implementing the following method instead of roll compression processing at two opposing positions on the outer circumference.In other words, in the same cross section of the steel pipe, A set of four parallel rolls applies a compressive load to four locations on the outer circumferential surface of the pipe to produce the required deformation in a specific pipe diameter direction, and while maintaining this amount of deformation, the roll is rotated at least half a turn around the pipe axis υ. After that, the roll load is gradually removed by keeping the rate of change of the amount of deformation constant with respect to the rotation while the tube is rotating, and by setting the amount of tube rotation in the unloading process to one rotation or more. This is a method of carrying out the compression process and the conditions for the subsequent unloading in this method.As shown in Fig. 2, four parallel rolls (21
) (2 pieces) (8/) (8J) When a pressure wire load (7) is applied by roll at four opposing positions on the outer circumference of the pipe, the stress distribution of the pipe is as follows: tensile stress at point A on the inner surface of the pipe, tensile stress at point B The point is compressive stress,
Point A on the outer surface of the tube is compressive stress, and point B' is tensile stress. Therefore, when the tube (1) rotates in the direction indicated by the arrow, the stress at point A on the inner surface of the tube (←) due to the rotation is tensile ( JE), compression (
The period of this stress fluctuation is the bar of the above (goods). In this case, the stress (σ) to strain (ε) hysteresis at the point A is as shown in Figure 4. By the way, since the pipe material hardens or softens during processing, the load amplitude remains constant. When the load is controlled, the hysteresis becomes unstable9, and at some points the plastic strain shifts to the tensile side, as shown in Figure 5(a), and at other points, the hysteresis becomes unstable.
As shown in the figure (Figure 1), a phenomenon of movement toward the compression side occurs, and the shape of the tube deteriorates as the stress is repeated (that is, as the tube rotates).On the other hand, the amount of deformation due to the load If the load is controlled to keep it constant, the maximum and minimum values of strain in each part will be approximately constant, and hysteresis will occur regardless of whether the pipe material hardens or softens (see Figure 6) or (1). ), the average strain is approximately 0.
Therefore, the shape of the tube does not deteriorate due to repeated stress. In addition, in removing the compressive load while rotating the tube,
In terms of work efficiency, it is desirable that the unloading speed be as fast as possible, but for example, if the number of revolutions of the pipe during the unloading period is 1 revolution,
If the load is unloaded with a constant load reduction amount, a positive or negative residual strain of 0 will always occur at some position on the tube circumference, as shown in FIG. 7(a). On the other hand, when the load is unloaded while keeping the rate of change in the amount of deformation due to the load constant, the residual strain (R') that occurs as shown in Figure 7 (1)) has a large absolute value compared to the residual strain 0. becomes smaller. In order to improve the roundness of the pick tube and process it in a short period of time, it is necessary to unload the tube while keeping the rate of change in deformation constant as described above. If the rotation kJii of the tube in the above-mentioned compression process is not more than half a turn, the compression process will not be performed over the entire circumference of the tube, and the roundness correction effect will be insufficient. Furthermore, unless the amount of tube rotation during the unloading process is one rotation or more, the degree of improvement in roundness will be low, and the result will be the same as that of conventional straightener processing. FIG. 8 is a diagram showing the relationship between the tube rotation speed and the tube roundness in the above-mentioned unloading process, which was obtained by surprise. From the relationship in the figure, it is not sufficient if the tube rotation speed during the unloading process is less than 1 rotation.
Conventional limits

0.4%] It can be seen that one or more revolutions are required to obtain excellent roundness of 0.8% or less. ■ Residual stress distribution on the inner surface of the tube The present inventors have previously conducted various studies on ridges to improve the strength of the tube. found a relationship. In other words, it was confirmed that the residual stress distribution on the inner surface of the tube, which is not on the compression side but slightly on the tensile side, greatly contributes to improving the strength of the tube. Furthermore, in order to obtain a residual stress distribution state in the circumferential direction on the inner surface of the tube that is preferable for the strength of the steel tube, compressive loads are applied to four locations on the outer circumference of the steel tube in the same cross section to cause deformation in a specific tube radial direction. We found that it is effective to perform compression processing in all directions of the pipe diameter. In other words, if the pipe processing and unloading operation is performed based on the method of the present invention, it is possible to turn the compressive residual stress in the circumferential direction generated on the inner surface of the tube into the tensile side, and the desired circumferential direction can be applied to the inner surface of the tube. By applying tensile residual stress, the collapse strength can be improved. FIG. 9 shows a steel pipe that has been subjected to cold straightener processing using the conventional method to generate a compressive residual stress of -20 to -40 on the inner surface of the pipe.
'X 100%, however, D is the original outer diameter d is the outer diameter after processing)
The relationship between the degree of working and the residual stress on the inner surface of the tube is shown in an example in which the sample material was compressed with various changes, and then unloaded at a tube rotation speed of 1.25 rotations during the unloading process. It is a graph. As shown in the figure, -20 to -40 occurred in the sample material by 9f.
The compressive residual stress of /yd gradually decreases as the workability increases.At a workability of 1.5%, the compressive residual stress turns to the tensile side, and at 1.5% or more, the residual stress distribution becomes stable in tension. I can see that I started to keep it. <Example> The method of the present invention will be specifically explained below based on the drawings. FIG. 10 is a process diagram schematically showing the method of the present invention, and as shown, the steel leaves the tempering furnace (4)! The material (1) is maintained at a temperature of 300υ or more and less than the tempering temperature in a heat insulating furnace (5), and then sent to the next processing device (6). FIGS. 11(a) and 11(b) are a front view and a side view showing an example of an apparatus for carrying out the processing according to the present invention. In the figure, (6 / Part 1
The rolls are arranged in tandem at predetermined intervals in the axial direction of the parallel rolls. The stand number of (6/) (6J) (6J) corresponds to the subscript of each symbol. One stand structure will be described below, taking the first nutand (61) as an example. Ⅱ:/F In (6/), (7) is the housing, and there are two standing pillars (8/) (8 pieces) (8J x 8g) and their heads set up at appropriate intervals on both the left and right sides. It consists of a head member αO that is horizontally suspended between the parts. The head member α1 is the above-mentioned standing pillar (8/) (8,2) (87X8
It is supported by a total of four hydraulic cylinders αυ installed on the outside of the casing, and its height can be adjusted. In such a housing (7), there are a set of two upper parallel rows /I/(2/) (2 pieces) and a set of two lower parallel rows 1 (8/) (8, 2). ) with two sets of parallel row I
L/ is provided. Upper parallel roll (2/) (2
J) is supported from above via a block a3 by an upper horizontal member (6) horizontally suspended vertically movably on the four pillars of the housing (7), and the lower parallel row IL/(8/)(8 Ko)
is similarly supported from below via a block α0 by a lower horizontal member α4 which is vertically movably suspended horizontally on the four pillars of the housing (7). And the ozmo parallel c2-/I/(2/)(2J) and (8/)(8,2) are arranged opposite each other,
The steel pipe (1) to be straightened is held in the center of its arrangement in parallel with the rolls and sandwiched between the parallel rolls from both sides so that compressive loads can be applied to four locations on the outer surface of the pipe. The upper horizontal member (2) is approached by the head member QO of the housing (7) via the load detector αQ, and changes its position up and down as the head member αO moves. The load detector detects the roll load applied to the aoIIi tube (1). Further, the lower horizontal member α4 is supported by the base αη of the housing (7) via a launch mechanism, for example, a hydraulic ram device θ frame, and the rod α of the hydraulic ram device is extended and retracted by the housing (7). It can move up and down along the pillar. (20/) is a displacement detector that detects the distance between the upper parallel row tL7 (2/) (2 pieces) and the lower parallel row /' (8/) (8J). This is connected to the controller of the hydraulic ram system via an amplifier 12υ. (20 pieces) is a displacement detector that detects the displacement of the interval between the lower horizontal member a4 and the Bene force. The structure of each stand is as described above, but three stands with this structure (67X 6 pieces) (6J)
between u and w4 tube holding position (6) of the stand (indicated by the position of the tube axis) between the first stand (6/) and the third stand (
63] and parallel low/' (2/X2JX8
) (8) in the opposite direction, that is, in the vertical direction in the figure, by a required amount. This is to apply a bending force to the steel pipe (1) for straightening the bend, and the setting of the pipe holding position (N) is based on the upper and lower parallel rolls by the hydraulic cylinder αυ and the hydraulic ram device Ql. (2/) (2
j) (8/) This is done by adjusting the storage position of (8 pieces) (detected by displacement detectors (20 pieces)). That is, in the apparatus for carrying out the method of the present invention, the tube holding positions (8) are set so as to be alternately shifted in units of stands in the direction facing the parallel rolls. Although not shown, the apparatus for carrying out the method of the present invention includes a tube (
In order to carry out the transfer and rotation of the tube axis in step 1), a conventional transfer device and a rotation device are used together. The operations for improving yield strength, roundness, straightening bends, and improving residual stress distribution on the inner surface of a tube performed using the processing apparatus of the present invention configured as described above are as follows. In other words, the steel pipe (1) maintained at a predetermined temperature condition in the insulating furnace (5) is placed in eight stands (6/) (6 x 6 J).
In between and each stand there is an upper parallel roll (
2/) (2J) and the lower parallel roll (8/) (8λ), and extend the end of the hydraulic ram device (g) to lower the lower horizontal member α. At the same time, push up the lower parallel row /' (8/) (8J) and remove the pipe (
1) Apply a compressive load by rolling. This roll load is carried out so that the compressive load becomes the set load while watching the load detector α・. After causing the required deformation in the pipe (1), the load is applied based on the detected value of the displacement detector (20/). While performing feedback control to maintain the amount of deformation, the tube (1) can be rotated around the tube axis by at least half a turn or more. After that, the unloading operation of the roll load is carried out, and the unloading operation is also carried out in such a way that the rate of change in the amount of deformation with respect to the rotation of the pipe is kept constant based on the detected value of the displacement detector (20/). This is done by setting the amount of tube rotation during the unloading process to one rotation or more while performing feedback control. After the above-mentioned processing and unloading steps are completed, the pipe (1) is sent in the axial direction with one pitch being slightly shorter than the length of the rolls, and the same straightening operation is performed, and by repeating the steps +111, the entire length of the pipe is straightened. conduct. In this way, processing according to the method of the present invention,
If unloading is performed, yield strength, roundness, and residual stress inside the tube can be improved as will be described later. In this case, the tube (1) spanning between 8 nuts (6/x6 pieces) (63) is rotated and receives the required bending force due to the displacement of the tube holding position (A) between the nuts. As a result, a sufficient effect can be expected in terms of correction of wrinkles. <Effects of the Invention> Next, examples of the present invention will be described. Outer diameter 177.8”I, wall thickness 9 with chemical composition shown in Table 1
．． Using two-dimensional quenched and tempered steel pipes, they were subjected to a rolling process using several pairs of slanted rolls under a temperature condition of 300°C or higher and lower than the tempering temperature, and then placed vertically and horizontally alternately. Conventional test tubes were obtained by drawing the outside diameter by drawing crawl and improving the strength by various types of warm straightener processing. Table 1 Next, a high collapse strength steel pipe was manufactured by the method of the present invention using the above test pipe as a raw material. That is, after the material is quenched and tempered, it is sent to a processing device shown in FIG. 11 with each parallel roll having a length of 850M under a temperature condition of 300° C. or higher and lower than the tempering temperature, and the tube is rotated once at various processing degrees. Compression processing was performed, and after that, the number of revolutions of the tube was increased to 1.255 revolutions, and unloading was performed at a constant rate of change of the tube-shaped hold. Next, the pipe was transferred in the pipe axial direction at a pitch of aoox, and the same compression processing and unloading operations were repeated.The processing operation was performed over the entire length of the pipe to obtain a test pipe according to an example of the present invention. For each test tube of the conventional example and the present invention example, the yield strength,
Roundness, residual stress on the inner surface of the tube, and bending were measured. Each measurement result will be explained below. Regarding the yield strength, - the average value of the conventional example was 86.4 # ru, while the average value of the example of the present invention was 89.2 t
By applying the method of the present invention, a yield strength comparable to that of a conventional warm nutretona-processed pipe was obtained. FIG. 12 is a graph showing the results of measuring roundness. In the figure, the circle mark indicates the roundness of the conventional example, and the mark e indicates the roundness of the present invention example.While the conventional example is approximately 0.4%,
In the examples of the present invention, the roundness is at an extremely high level of 0.2% or less for all of the working ratios of 0.6, 1.0%, and 1.4%. Regarding the residual stress distribution on the inner surface of the tube, in all conventional examples compressive residual stress was observed, approximately -20 to -40 kg.
f/wIO value, but in the example of the present invention, the processing degree is 1
．． When tensile residual stress was obtained at 5% or more, the yield strength and roundness were improved, and the collatooth strength was improved by a maximum of 15% due to the improvement in the residual stress distribution on the inner surface of the tube. In addition, when measuring the curvature using the method specified in the API standard, the conventional example and the present invention example had approximately the same value of 4'.
B wVm was shown. As is clear from the above description, the method of the present invention makes it possible to produce steel pipes with extremely high collar strength, which is impossible to achieve with conventional methods, and also makes it possible to improve the roundness and straighten curvature of steel pipes at the same time. The method of the present invention is economically advantageous compared to the conventional method because it can be carried out at the same time in the process, and it is also much more effective than the conventional method especially in terms of roundness. It can be said that this method is extremely practical, especially as a manufacturing method for oil country tubular goods for deep wells.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between processing temperature and yield strength, Figure 2 is a graph showing the relationship between processing temperature and yield strength.
The figure is a cross-sectional view showing a state in which a compressive load is applied to the tube by the method of the present invention, and Figure 3 is a point A on the inner surface of the tube in Figure 2 when the tube is rotated once while maintaining the amount of deformation due to the compressive load. Figure 4 is a diagram showing the stress-strain hysteresis at the point A, and Figures 5 (a) and (b) are the changes at the point A when the load amplitude is constant. Figures 6(a) and (b) are diagrams showing the stress-strain hysteresis at point A when the load is maintained constant. Figure 7 shows the stress-strain hysteresis at point A. (a) shows the residual strain that occurs when unloading with a constant load reduction amount, and Figure 7 (in Figure 7) shows the residual strain that occurs when unloading with a constant rate of change in deformation due to load. Figure 8 is a graph showing the relationship between tube rotation speed and roundness during the unloading process, Figure 9 is a graph showing the relationship between working degree and residual stress on the tube inner surface, and Figure 10 is a graph showing the relationship between tube rotation speed and roundness during the unloading process. Process diagram, Figure 11 (a)
(B) is an explanatory diagram showing an example of a processing device that performs the method of the present invention ((A) is a front view, (B) is a side view, and FIG. 12 is a measurement of roundness of conventional example and the example of the present invention. This is a graph showing the results. l: Steel pipe, 2t, 2w, Bl+8.2: Low Ibi, 4:
Tempering kettle, 5: Heat retention furnace, 6.6/, 6.2, 67: Processing equipment, 7: Housing, 81, 8, 8J, 8g: Vertical column, IO = head member, 11: Hydraulic cylinder, 12 : Upper horizontal member, 1B, 15 Niblock, 14: Lower horizontal member, 16: Load detector, 17: Bake, 18: Hydraulic ram device, 19: Rod, 20/, 20J: Displacement detector,
zl: yin y - Applicant Sumitomo Metal Industries Co., Ltd. Representative Patent Attorney Shigeru Katamoto 1 Figure 4 Figure 5 (CI) (b) (Q) ” 1'21 (b)

Claims (1)

[Claims] (1) Using a steel pipe that has been quenched and tempered, it is rolled at four locations on the outer periphery using four IM parallel rolls at three or more locations spaced apart from each other in the tube axis direction under a temperature condition of at least ao'ot; and below the tempering temperature. A compressive load is applied to the tube by a roll to apply a bending force to the tube, and the required deformation is caused in a specific tube diameter direction, and while this amount of deformation is maintained, the tube is rotated at least half a turn around the tube axis, and then After that, the roll load is gradually removed by keeping the ashing rate of the deformation constant with respect to the rotation while the tube is rotating, and by setting the tube rotation amount in the unloading process to one rotation or more. A method for manufacturing high-collapse strength steel pipes, characterized in that compressive loads are applied over the entire length of the pipes.