JPS5970717A - Production of steel pipe having high collapsing strength - Google Patents

Abstract

PURPOSE:To improve the collapsing strength of a steel pipe by applying parallel load at two points having a specific central angle in the same section of a steel pipe in the direction opposite to each other from both opposed sides at the periphery of the pipe and subjecting the pipe to such loading over the entire length of the pipe and in the entire directions of the pipe diameter. CONSTITUTION:A pair of working jigs 2 having a sectional shape like a V block are placed to face each other in such a way that both edges 3 each having a V- shaped recess are pressed to a steel pipe 1. The jigs are then pressed from behind to apply parallel load P on the pipe 1. The pressing is executed for each of the directions D1, D2- in the pipe diameter at every other central angle 2theta within the same section of the pipe 1. The central angle 2theta ranges to 40-90 deg.. If such operation is carried out over the entire length of the pipe 1, the residual tensile strength in the circumferential direction on the inside surface of the pipe contributing to the improvement in the collapsing strength of the pipe 1 is assured.

Description

[Detailed Description of the Invention] The present invention relates to a method for manufacturing steel pipes with excellent collapse strength (strength against crushing due to external pressure), which is particularly important for oil well operations, and more specifically, it contributes to improving the collapse strength of pipes. This invention relates to a steel pipe processing method that can ensure circumferential tensile residual stress on the inner surface of the pipe.

In recent years, due to the tight oil and natural gas situation, there has been a marked trend toward deeper oil and natural gas wells, and in addition, there have been an increasing number of cases in which wet hydrogen sulfide is contained in the production gaff. For oil country tubular goods, there are also high demands regarding corrosion resistance and collapse strength.

However, the corrosion resistance and collapse strength of steel pipes are generally considered to be contradictory to each other.

To improve the crush and collapse strength, it is necessary to increase the yield strength, but an increase in the yield strength is usually accompanied by an increase in the tensile strength. For these reasons, it is essentially difficult to achieve both corrosion resistance and collapse strength, and it is difficult to achieve both corrosion resistance and collapse strength by simple means such as adjusting the composition of pipe materials. It would be impossible to deal with the change.

It can be said that there is a need for a method to improve the collapse strength δ independently of VC-(d) and corrosion resistance to meet such increasingly sophisticated requirements.

The following methods are currently known as this type of method.

■ Perform diameter reduction processing on steel pipes.

■ Omit straightener processing.

■ Perform straightener processing at warm temperature.

However, both of these methods have their own problems. First, (2) is a method in which the diameter reduction process increases only the yield strength in the circumferential direction of the tube, which is directly involved in improving the collapse strength, to a limited extent, but there is a problem with this diameter reduction method itself. In other words, as diameter reduction means, it has been considered to use segments that are divided into a large number of segments in the circumferential direction, but this creates a slight difference in the contact side of the segments in the circumferential direction of the tube. The rate of increase in yield strength varies in each part, making it impossible to expect a stable and effective improvement in collapse strength.

Next, the normal straightening process, which passes between the upper and lower chain-shaped rolls, causes the generation of compressive residual stress in the circumferential direction on the inner surface of the steel pipe and the decrease in yield strength due to the Uzinger effect, resulting in a deterioration of the collapse strength. The straightener process itself is omitted because of the view that it will lead to problems, but this is not a lie that requires advanced pipe manufacturing technology from the viewpoint of maintaining the quality of the steel pipe, and it may reduce the value of the finished product, especially for small diameter pipes. It is completely impossible to avoid it.

In addition, (2) is it possible to prevent the generation of compressive residual stress and decrease in yield strength of the steel pipe by performing the straightening process at a warm temperature? It requires processing at fairly high temperatures, making it economically viable.

In addition, including the above-mentioned item (2), measures to prevent the occurrence of compressive residual stress in copper pipes are not proactive measures, and it cannot be denied that they have little effect on their own.

As described above, none of the conventionally known methods of increasing collapse strength independently of corrosion resistance can be said to be sufficient.

The inventors of the present invention need to overcome this situation.In the past, we have been conducting intensive research on effective measures to increase the collapse strength of steel pipes, but in the course of our research, we have investigated the residual stress in the circumferential direction of the inner surface of the pipe. We found a useful relationship existing between the collapse strength of steel pipes. In other words, the relationship shown in Fig. 1 is the above residual stress (σR) multiplied by i on the compression side (what is the negative sign in the figure? The expression of compressive stress will be based on this below). - As said, it has a negative effect on collapse strength, but on the tensile side, when the stress value is 0.15 times or less of yield strength (σy), it actually contributes to improving collapse strength. It has also been confirmed that this relationship is universal and holds true regardless of the strength level/L'1 of the steel pipe and other conditions.The inventors focused on this relationship shown in Figure 1. As a result of repeated experiments and studies on methods for stably obtaining the optimal tensile residual stress in the circumferential direction of the inner surface of tubes for collapse strength, in particular tube processing methods, we have succeeded in completing the present invention shown below. .

In other words, the gist of the present invention is to apply parallel loads in opposite directions from opposite sides of the tube periphery to two points on the outer surface of the tube that are shifted by 40 to 90 degrees at the tube center angle in the same cross section of the steel tube. The present invention provides a method for manufacturing a high-collapse strength steel blind, which is characterized in that the compression process under load is carried out in all directions of the tube diameter or in each specific direction of the tube diameter, and is carried out over the entire length of the tube. By applying this method, it is possible to impart a desired circumferential tensile residual stress to the inner surface of the tube, and therefore, the above-mentioned tensile residual stress of 0.15 times or less of the yield strength shown in Fig. 1 can be produced. The collapse strength can be effectively improved.

The stress distribution in the tube cross section when the same cross section of the tube is compressed by simultaneously applying a parallel load (2) to four points (G) on the outer periphery of the tube in the form shown in FIG. 2 can be considered as follows.

The point on the inner surface of the tube (the position of @ is the parallel load (P) [F]
A line in the pipe radial direction (9
) is defined by the central angle (b) taken from this, then when this α is in the range of 0 to the concentric angle (of) representing the position of the point of action (G), m Moment regarding the point (M/) (ri) is given by the following equation (1).

-! ! ! -! −-1((π-2θ)sinθ-2cos
θ)=c <Q...-(1) PD π Here, D=outer diameter of the tube C: constant Also, the above moment CM in the range of α-θ~2, 2)
It can be found by the following formula.

According to the above equations (1) and (2), it is possible to know the distribution of moments as shown in Figure 3. This figure shows an example of the case of θ--, line (branch)
At point (8) on the inner surface of the tube through which the bending moment passes, the bending moment is a negative value, and therefore the stress on the inner surface of the tube exhibits tension at that position.On the other hand, at the point (g) which is 90° misaligned at the center angle from point A, the bending moment is a negative value. The bending moment takes a positive value and the stress on the inner surface of the tube becomes compressive.

In this case, the absolute value of the compressive stress (σB) near point B exceeds the tensile stress (σA) at point A, that is, −σB+>
If the condition of σA is satisfied, it is possible to compressively yield the inner surface of the tube near point B. Therefore, if this compressive yield is applied to the entire circumference of the inner surface of the tube, the inner surface of the tube in the tensile direction This allows residual stress to be generated.

Here, satisfying the above 1σB+>σA means that the moment at a point on the inner surface of the tube near point B (Mλ) is expressed by the following formula, M, 2-(-M/)>O... ( 3) is satisfied.

The example of θ-2 shown in Figure 3 is nothing but a case that satisfies this equation (3), but here, as an index representing the range around point B on the inner surface of the tube that satisfies equation (3), point B is Introducing the central angle φ) taken with reference to the line (3) in the pipe radial direction passing through , β can be determined as follows. That is, by substituting equations (1) and (2) into equation (3) above, equation (4) below can be obtained.

−((yr−2θ)Sinθ−2cosθ) +si,
nα−5inθ〉0π 5i−nα＞ (j−!−s inθ)−4−cos
θ ・・・・・・(4) π π This represents the relationship between the central angle (which indicates the point of action of the load [F]) and α for which the relationship in (3) above holds. On the other hand, the limit α that satisfies the condition (3) is now tentatively α
If it is expressed as l, then between αl and β, β---
αl ・・・・・・(5)(5
) holds true. By combining both equations (4) and (5) with δ, α
By eliminating , the relationship between θ and β can be derived.

Is there a diagram of this relationship in Figure 4?
It can be seen that β>0 only in the range θ>20°. This also shows that if the load application point (G) is set at a position where θ is 20° or more, compressive yield on the inner surface of the tube can be obtained without fail.

Therefore, based on the method of the present invention, the compression process using the parallel load is performed in all directions of the tube diameter or in each specific tube diameter direction, thereby causing compression yielding of the inner surface of the tube over the entire circumference. A tensile residual stress can be applied in the circumferential direction of the inner surface of the tube. In this case, the magnitude of the circumferential tensile residual stress applied to the inner surface of the pipe can be controlled to a desired level by adjusting the above θ and the applied load (D), and therefore the above tensile residual stress can be adjusted to the optimum level for the collapse strength. It's what you can get.

The method of the present invention involves moving the loaded state according to the present invention as shown in FIG. 2 in the pipe circumferential direction while maintaining its shape.
By moving it to the original axially symmetrical position (180° inverted position), compression processing is performed in all directions of the pipe diameter.
Alternatively, the same load condition as shown in FIG.
...There are things that appear every time. In this latter case ('
)') l'j: Based on the relationship shown in Figure 4 above, taking into account the range of β determined by θ, it is determined that the compressive yield of the inner surface of the tube can be ensured throughout the entire circumference. Bye.

In the present invention, θ is 20° or more (2θ: 40° or more)
The reason for limiting θ to 45° or less (2θ: 90° or less) is obvious from the above explanation of the effect.
This is because it is practically difficult to apply the parallel load (e) when the angle θ exceeds 45°, and (2) the generation of stress in the linear direction takes a short time to avoid, considering practicality.

In addition, in the method of the present invention, the center angles (θ) (B) u that are opposite to each other in FIG. 2 do not necessarily have to be the same,
It is sufficient that θ on each side independently satisfies the condition of 20° and θ<45°.

The method of the invention can be specifically implemented in a wide variety of ways. Here are 2.3 examples.

■ A pair of machining jigs (2) having a block-like cross-sectional shape as shown in FIG. 6 are used facing each other.

Pinch both edges (3) of the ■-shaped recess of the jig (2) (1)
By applying pressure from behind, a parallel load CP) is applied in the form shown in Figure 2. Within the same cross section of this compression processing operation 'fx'tt, the pipe diameter direction (D/) (D co) at a predetermined angle (γl)
...I come every time to give alms. This (γ/) is the range from 0 to the range 0 of the inner surface of the tube where compression yields in one processing, shown in Figure 5 (γ), and δ in Figure 4, to the range of compressive yield of the inner surface of the tube over the entire circumference. decide so that it is achieved. In thermal theory, this processing may be performed continuously in the circumferential direction, in which case a roller (4) is incorporated into the tube contacting edge of the jig (2) as shown in FIG. It is recommended that the tube (1) be smoothly moved relative to the tube (1) in the circumferential direction in the pressurized state. Needless to say, it may be the pipe or the jig that is rotated during processing.

In this method, a jig is used that is long enough to machine the entire length of the pipe, or a jig with a short length is used to machine the pipe sequentially from one end of the pipe to the other in unit length increments. By adding processing, the entire length of the pipe can be processed.

■ As shown in Figure 8, a set of two parallel fixed coaxial rolls (5) (5) are arranged in the required number of tandems, and the roll axis (T) of each stage passes between the rolls. The pipes (1) are inclined at appropriate angles to each other in a plane perpendicular to the pipe (1), and the pipe (1) is fed between the opposing rows/I/(5) and (5) to pass through. This method is characterized by the fact that the entire length and circumference of the tube is compressed all at once by moving the tube in the axial direction, and it can be said to be a highly efficient method suitable for continuous production of tube fins. Regarding the number of rolls to be installed and the inclination angle of the row/low axis of each stage, the concept is exactly the same as (γ/) in the previous section, and β in Fig. 4 is determined.
can be decided based on.

In this method, each roll is actively driven to
It is reasonable to use it for driving. However, from the pure point of view of processing, there is no particular difference whether the drive is driven or not, so even if a means for driving the tube is provided separately, and the rolls are simply rotated as the tube travels, There is no problem.

Incidentally, as a conventional method for processing pipes, a method using a chain-shaped roll for the purpose of straightening the pipe has been used, but in this method, the pipe (1) is placed at opposing positions on the outer circumferential surface as shown in Figure 9. If the shape is such that it receives a concentrated load (g), tensile stress is applied to point (2) on the inner surface of the pipe at the location where the load is applied, and at the same time, point CB) i is shifted by 90 degrees at the central angle from point A. /c compressive stress is generated respectively. However, in this case, the absolute value of the tensile stress at point A always exceeds the compressive stress at point B, regardless of the conditions. In other words, the aforementioned lσB
It is completely impossible to obtain a mechanical form that satisfies l>σA.

Next, the effects of implementing the present invention will be described.

Outer diameter 17'1. having the chemical composition shown in Table 1. FDg;
.

Processing based on the present invention was applied to a tuning piece with a wall thickness of 18.54*jl and a length of 500 mm (yield strength: 66, 2 #f/w*2).

Table 1 (wt%) Processing was carried out using the pair of jigs shown in Fig. 7 as shown in Fig. 6, and continuous processing in the circumferential direction while rotating the pipe by the method described in (■) above. Depends on how you do it.

The jig used had a length that exceeded the total length of the target pipe, which was 50,011 ff, and therefore the entire length of the pipe could be processed in one process. The 2θ halo in FIG. 2 was 0°.

FIG. 10 is a plot of the load applied during the above machining (the applied load value per unit length of 9) and the residual stress value in the circumferential direction of the inner surface of the tube caused by the machining.

As is clear from the figure, in the method of the present invention, it is possible to apply a circumferential tensile residual stress to the inner surface of the tube, and by adjusting the applied load ■, the tensile residual stress value can be adjusted to a range of o, 15σy, which is preferable for collapse strength. (indicated by σ in the figure).

As a comparative example, we will briefly describe the case of straightener machining using the pin-shaped rolls shown in Fig. 9. As shown in Fig. 11, the crush amount, in other words, the applied load (
P) (see FIG. 9) is set, residual stress in the compressive direction always occurs in the circumferential direction KU of the tube inner surface, and no residual stress in tension is obtained.

As is clear from the above explanation, the method of the present invention is capable of >14
<v?
- It can be said to be effective when applied to the production of oil country tubular goods, which requires high collapse strength as well as corrosion resistance.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the effect of residual stress in the circumferential direction on the inner surface of the tube on the strength of the tube, Fig. 2 is a schematic diagram illustrating compression processing based on the present invention, and Fig. 3 is the inner surface of the tube during compression processing. FIG. 4 is a graph showing the relationship between θ and β in the method of the present invention. FIG. 7 is a front view showing a preferred example of a jig used for the above compression process, and FIG. 8 is another example of a specific means for performing the above compression process. FIG. 9 is a diagram for explaining the mechanical relationship during conventional straightener processing, and FIG. 10 is a diagram showing the load of residual stress in the circumferential direction of the pipe inner surface when the method of the present invention is applied. Figure 11 shows the relationship between the crush amount and the residual stress in the circumferential direction of the inner surface of the tube after the conventional straightener processing. , 2: Machining jig, 4: Roll, 5: Coaxial fixed type vs. roll Applicant: Sumitomo Metal Industries, Ltd. Figure 6 Figure 11 Voluntary procedure amendment band Commissioner of the Patent Office Kazuo Wakasugi 2. Name of the invention: High collapse strength Manufacturing method for steel pipes 3, relationship with the amended case Patent applicant address 5-15 Kitahama, Higashi-ku, Osaka Name (21)
1) Sumitomo Metal Industries, Ltd. Representative Norifumi Kumagai 4 Agent 6 Contents of the amendment in the "Detailed Description of the Invention" column of the specification to be amended (1) It is stated on page 8, line 12 of the specification. 4θ "sinα>(--1)sinθ+4-cO8θ...
(Corrected to April π π.

Claims (1)

[Claims] (1) On the same cross section of a steel pipe, compression processing is performed in which parallel loads in opposing directions are applied from opposite sides of the pipe periphery to two points on the outer surface of the pipe that are offset by 40 to 90 degrees at the center angle of the pipe. A method for producing a high collapse strength steel pipe, which is characterized in that the process is performed in all directions of the pipe diameter or in each specific pipe diameter direction, and is applied over the entire length of the pipe.