JPH0128645B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method of manufacturing an electric resistance welded steel pipe. Generally, steel pipes used for oil wells, etc. are formed from a steel band into a tubular shape, electrical resistance welded, locally heated with a post annealer, rounded with a sizer roll, and then passed through a straightening machine. It is becoming straighter. In the case of such a steel pipe, if the amount of bending of the steel pipe exceeds a permissible limit, thread cutting operations on the steel pipe become extremely difficult, and troubles occur during oil well drilling work and the like. Therefore, the precision required for the finished dimensions of steel pipes, especially their straightness, has become more stringent as, for example, oil wells become deeper. That is, the maximum allowable bending amount of steel pipes for oil wells is set to be several millimeters or less in a fixed length pipe such as 40 feet long. However, when using conventional manufacturing methods, especially API (American Petroleum Institute) standards J-55, K-
In high-strength ERW steel pipes for oil wells such as 55 and N-80,
As shown in FIG. 1, a blank pipe 1 having a length L may be bent by a maximum bending amount H, and it is necessary to straighten the bend in the blank pipe 1 using a straightening machine in a subsequent process. However, it is extremely difficult to select the roll setting conditions required for this straightening, resulting in problems such as decreased productivity due to an increase in straightening work time, and decreased shape and dimensional accuracy due to poor straightening. An object of the present invention is to provide a method for manufacturing an electric resistance welded steel pipe that can stably manufacture an electric resistance welded steel pipe with good shape and dimensional accuracy. In order to achieve the above object, the present invention provides an electric resistance welded steel tube in which a blank tube is formed by welding both edges of a bent steel strip, and the blank tube is formed to a fixed diameter with a sizer roll. In the manufacturing method, when the diameter including the welded part of the raw pipe is the vertical diameter of the raw pipe, and the diameter perpendicular to the above-mentioned vertical diameter of the raw pipe is the horizontal diameter of the raw pipe, the horizontal diameter of the raw pipe before entering the sizer roll is The blank pipe is pre-deformed by side rolls before entering the sizer rolls so that the ratio r (longitudinal diameter/horizontal diameter) of the longitudinal diameter to the diameter is 1.04≦r≦1.10. The present invention will be explained in more detail below. First, the principle behind the establishment of the present invention will be explained. That is, in manufacturing an electric resistance welded steel pipe, a blank tube is formed by welding both edges of a bent steel band, and the blank tube is formed to a fixed diameter using a sizer roll. The area around the welded part of the raw pipe has a different strength and structure compared to other parts due to welding and subsequent heat treatment using a post annealer, and inevitably some residue remains in the circumferential direction of the welded part. This causes non-uniform stress distribution and non-uniform residual stress in the longitudinal direction due to processing strain difference between the edge part (corresponding to the welded part) and the part 180 degrees opposite during upstream forming. This results in bending based on the longitudinal residual stress difference at each position. Therefore, the present invention applies plastic deformation of bending and unbending to the welded part of the raw pipe before entering the sizer roll by using side rolls 10 shown in FIG. 2, thereby making the cross section of the raw pipe vertically elongated. Therefore, by actively deforming the welded part of the raw pipe in the sizer roll and the part 180 degrees opposite to it in the longitudinal direction, the residual stress distribution in the longitudinal direction of the pipe after the sizer is made uniform, and bending is prevented. In the present invention, the diameter direction of the raw pipe including the welded part is defined as the longitudinal direction, and the diameter thereof is defined as the longitudinal diameter). In other words, API standard N-80, outer diameter 114.3, which is typical for high-tensile oil well steel pipes.
In the production of ERW steel pipes with a wall thickness of 6.35 mm, changes in the ratio r (b/a) of the vertical diameter b to the horizontal diameter a of the raw pipe before entering the sizer roll, and the welded part after the sizer roll forming. The relationship between the residual stress difference Δσ in the longitudinal direction of the base material and the relationship determined by the cutting method is shown in FIG. 3. According to FIG. 3, it is recognized that when the ratio r is 1.04 or more, the residual stress difference Δσ becomes approximately zero, and the residual stress distribution becomes approximately uniform. Furthermore, when the above ratio exceeds 1.10, the residual stress difference △σ becomes approximately zero and the residual stress distribution becomes approximately uniform; It has been recognized that this causes difficulty in the rolling process and makes the raw pipe more susceptible to roll flaws. By the way, the example shown in FIG. 3 has the strictest tolerance for bending among the electric resistance welded steel pipes manufactured by the applicant.
This is the result of a research study for materials with the highest grade (strength), and bending can be suppressed for materials of other grades and sizes as long as they satisfy the r value of 1.04 to 1.10 shown in FIG. That is, the occurrence of bending can be suppressed if the r value other than the one illustrated in FIG. 3 is at least within the range of the r value shown in FIG. Therefore, in the present invention, pre-deformation is applied by the side rolls 10 so that the ratio r becomes 1.04≦r≦1.10, and then the sizer roll is used to form the fixed diameter, thereby preventing the occurrence of bending. This made it possible to prevent this. Accordingly, in the present invention, pre-deforming the raw tube means compressing the nearly perfect circular raw tube in the width direction of the tube to flatten it into an elongate shape and "ellipse" it. The purpose is to provide a deformation as shown in FIG. This deformation is given by the side rolls 10, and some parts of the raw pipe (parts A and B in Fig. 6)
Part) Plastically deforms and maintains a vertically elongated elliptical shape even after passing through the side rolls 10. In the present invention, the side rolls apply plastic deformation to the raw pipe so that the ratio r of (longitudinal diameter/horizontal diameter) after processing (after passing) by the side rolls is 1.04≦r≦1.10, and the raw pipe is shaped into an ellipse. It is something that becomes. Here, the significance of pre-deforming the raw pipe before entering the sizer roll is that by deforming the raw pipe vertically before entering the sizer roll, the welded part and the
The objective is to actively deform (bending and extending) the 180-degree opposing portions in the longitudinal direction, and to minimize the difference in processing strain between the two portions received in the upstream process (before the side rolls). FIG. 7 shows a schematic diagram of the modification. Even if the circumferential length of the raw pipe on the sizer roll entry side is approximately the same, the deformation within the sizer roll bite differs depending on whether the raw pipe on the sizer roll entrance side is vertically elongated or not. Taking FIG. 7 as an example, when a raw pipe having a vertical diameter b1 enters the sizer roll, this raw pipe comes into contact with the roll at a position ld in front of the center of the roll and is deformed. At this time, the raw pipe undergoes drawing deformation in the circumferential direction, and at the same time, the welded part and its 180-degree opposing part undergo bending deformation and elongation deformation in the longitudinal direction within the roll bite. This processing deformation serves to suppress bending of the raw pipe. Moreover, if the amount of processing deformation is small,
The processing strain difference between the two parts that occurred in the upstream process is not reduced, and as a result, the residual stress in both parts remains large, resulting in bending of the pipe after the sizer roll. The present invention has been made with attention to this point, and as will be described in detail later, by increasing the amount of longitudinal deformation of both parts of the sizer roll, the difference in processing strain between the two parts is reduced, and This makes it possible to equalize the residual stress in both parts, thereby suppressing bending of the tube after the sizer roll. In addition, in Fig. 7, K is the welded part, and L is the welded part.
is the 180 degree opposing portion, α is the bite angle, R is the roll throat radius, b1 is the vertical diameter of the sizer roll inlet pipe, b2 is the vertical diameter of the sizer roll outlet pipe, and ld is the projected contact length between the roll and the material. Figure 8 shows the occurrence of pipe bending in the conventional method,
This figure shows the circumferential distribution of the longitudinal processing strain (longitudinal elongation strain at the center of the plate thickness) that causes this, and its relationship with the generation of residual strain. Here, the residual stress is calculated based on a stress-strain relational expression. Considering that the residual stress is within the elastic stress, the residual stress is in a proportional relationship with the residual strain, and exhibits the same tendency as the residual strain shown in FIG. Generally, when forming ERW steel pipes,
Since the edge part is stretched during the forming process compared to the 180-degree opposing part, the weld part tends to have a convex bend, but welding with a squeeze roll adds a concave bend to the weld part, and depending on the degree of this, a convex bend or a concave bend can occur. . When this bending occurs, the cause is always the longitudinal processing strain (extension strain) as shown in Figure 8, which has a deviation in the pipe circumferential direction, especially at the edge (weld) and the 180-degree opposing part. As a result, a residual strain is generated, and a residual stress that is proportional to the residual strain as described above is generated, and the tube is bent. As mentioned above, the present invention aims to suppress bending of the pipe by reducing the relative difference in the longitudinal processing strain in the circumferential direction of the pipe, especially between the welded part and the 180-degree opposing part, and by reducing the generated residual stress. The non-uniform distribution of longitudinal processing strain in the circumferential direction is controlled by a sizer roll. FIG. 9 and FIG. 10 are diagrams illustrating the principle of uniformizing the longitudinal strain distribution of the raw pipe in the sizer roll in the method of the present invention in comparison with the conventional method. Figure 9A is a diagram showing the longitudinal strain distribution of the raw tube before the sizer roll in the conventional forming method, and Figure 9B is a diagram showing the longitudinal strain distribution applied to the raw tube by the sizer roll in the conventional forming method. , Figure 9C is a diagram showing the strain distribution in the longitudinal direction of the raw tube after the sizer roll in the conventional forming method and the residual strain distribution based on it, and Figure 10A is a diagram showing the longitudinal direction of the raw tube before the sizer roll in the method of the present invention. A diagram showing the strain distribution. Figure 10B is a diagram showing the longitudinal strain distribution applied to the raw pipe by the sizer roll in the method of the present invention. Figure 10C is a diagram showing the longitudinal direction of the raw pipe after the sizer roll in the method of the present invention. Diagram showing directional strain distribution and residual strain distribution based on it, No. 11
The figure is a stress-strain diagram showing the change in strain difference after applying equal strain to two parts where there is already a strain difference. In addition, in FIGS. 9 and 10, W indicates a welded portion, and 180 degrees indicates a 180-degree opposing portion. That is, FIG. 9A and FIG. 10A show an example of the longitudinal strain distribution in the raw pipe before the sizer roll. As described above, the strain in the longitudinal direction of the raw pipe before the sizer roll is non-uniform due to the forming and welding in the upstream process. For this reason, the raw pipe bends as described above. Therefore, as shown in FIGS. 9B and 10B, it is considered to apply elongation strain in the longitudinal direction of the raw pipe by processing with a sizer roll to make the uneven strain distribution in the above-mentioned upstream process uniform. As mentioned above, the method of the present invention focuses on this point, and the sixth roll is made in the side roll before the sizer roll.
By making the raw tube oval as shown in the figure,
By increasing the longitudinal elongation strain at the part 180 degrees opposite the welded part during sizer roll forming, and making the circumferential distribution of the longitudinal strain of the tube after the sizer roll uniform, as shown in Figure 10C. , the residual strain and ultimately the residual stress are reduced and made uniform at the same time. Therefore, the key point of the strain equalization principle of the present invention is that if a large strain in the same direction is applied to a raw pipe with a difference in strain, the difference in strain will decrease. FIG. 11 explains the reason by modeling a stress-strain diagram. That is, in FIG. 11, A0 is a point corresponding to the welded part of the raw pipe, and B0 is a point corresponding to the 180-degree opposing part, and it is assumed that there is already a strain difference Δε0=1% between the two. (a) When a small processing strain of ε1=0.86% is added to A0 and B0 above, B0 passes through B1 and reaches B2, and A0
passes through A1 and reaches A2 (=A0). After adding this machining strain ε1, the strain difference △ε1 between A2 and B2 is
This decreases to only 0.86%. (b) For (a) above, ε2=2ε1=1.72 for A0 and B0.
When a large processing strain of % is applied, B0 passes through B0'' and reaches B3, and A0 passes through A0'' and reaches A3. After adding this processing strain ε2, the strain difference Δε2 between A3 and B3 decreases to 0.71%. According to (a) and (b) above, there is already a strain difference between the two
When equal strain is applied to two portions, as the strain is increased, the difference in strain between the two portions can be reduced and made more uniform according to the present invention. Note that this is due to the work hardening characteristics of the material. FIG. 4 is a plan view showing the front stage of an electric resistance welded steel pipe manufacturing line to which the present invention is applied, and FIG. 5 is a side view showing the rear stage of the same manufacturing line. That is, as shown in FIG. 4, the steel strip 11A is sequentially formed into a cylindrical shape by the breakdown rolls 12 and the side cluster rolls 13 in the early and middle stages of forming, and then
After being rolled down in the circumferential direction of the pipe by tandem-type fine pass rolls 14 as finishing forming rolls to form edge portions 11E, they are passed through seam guide rolls 15, and both edge portions 11E are welded by squeeze rolls 16. , it becomes the raw pipe 11B.
As shown in FIG. 5, the raw pipe 11B is locally heat-treated at the welded part by a post annealer 17, passes through an air cooling zone, a water cooling zone 18, the aforementioned side rolls 10, and a sizer roll 19. After that, it is cut and continues to pass through a straightening machine 20 to become a product. Table 1 shows the results of the above embodiment in comparison with the manufacturing results based on the conventional method.

[Table] In other words, Table 1 shows the raw pipes before entering the sizer roll in the manufacture of high-strength oil well steel pipes of API standards N-80, J-55, and K-55 with an outer diameter of 114.3 mm and a wall thickness of 6.35 mm. For the conventional method, r=
1.01 to 1.02, and for the method of the present invention, r=
This is a result showing the average maximum amount of bending obtained when setting the value to 1.05 to 1.08. In addition, in the above conventional method, setting r = 1.01 to 1.02 is not an intentional setting, but the raw pipe before entering the sizer roll, that is, after forming, welding, and post-annealing, is usually approximately r = 1.01 to 1.02, and unless special upstream processing is added, r = 1.05 to 1.08 does not normally occur. According to Table 1, it is recognized that the average maximum amount of bending per 12 m of standard length is significantly reduced by implementing the method of the present invention. That is, according to the method of the present invention as described above,
By applying pre-deformation to the raw pipe before it enters the sizer roll, the longitudinal residual stress distribution at each position in the circumferential direction of the raw pipe after sizer roll forming is made uniform, and local bending moments are prevented from occurring. This makes it possible to suppress the occurrence of bending. Here, the method of the present invention has a strength of API
It is particularly effective for high-strength electric resistance welded steel pipes for oil wells of J-55 or higher according to the standard, that is, those with a yield strength (0.5% elongation) of 38.7 Kg/mm ² or more and a tensile strength of 52.7 Kg/mm ² or more, and the steel pipe material It is recognized that the higher the strength, the greater the effect. However, the present invention is of course also effective when applied to ERW steel pipes with lower strength than the above standards.
It is also possible to improve the dimensional accuracy, piping, and installation accuracy of steel pipes for uses other than oil wells, such as ERW steel pipes for gas and water supplies, ERW steel pipes for boilers, and ERW steel pipes for materials. As described above, the present invention provides a method for producing an electric resistance welded steel pipe, in which a raw pipe is formed by welding both edges of a bent steel band, and the raw pipe is formed to a fixed diameter using sizer rolls. When the diameter including the welded part of the raw pipe is the vertical diameter of the raw pipe, and the diameter perpendicular to the above vertical diameter of the raw pipe is the horizontal diameter of the raw pipe, the vertical diameter with respect to the horizontal diameter of the raw pipe before entering the sizer roll is ratio of diameters r
So that (vertical diameter / horizontal diameter) is 1.04≦r≦1.10,
It is designed to apply pre-deformation by side rolls to the raw pipe before it enters the sizer rolls. Therefore, it is possible to stably manufacture an electric resistance welded steel pipe with good shape and size accuracy.

[Brief explanation of drawings]

Fig. 1 is a front view showing a general pipe bent in the longitudinal direction, Fig. 2 is a front view showing a pre-deformed state given to the raw pipe by the side rolls in the present invention, and Fig. 3 is a front view showing the state of pre-deformation given to the raw pipe by the side rolls in the present invention, and Fig. 3 is before entering the sizer roll in the present invention. Figure 4 is a plan view showing the front stage of the ERW steel pipe production line to which the present invention is applied; A side view showing the subsequent stage. FIG. 6 is a schematic diagram showing the state of pre-deformation of the tube with the side rolls according to the present invention. FIG. 7 is a schematic diagram showing the drawing process of the tube with the sizer roll. FIG. A schematic diagram showing the relationship between processing strain, residual stress, and bending. Figure 9A is a diagram showing the longitudinal strain distribution of the raw tube before the sizer roll in the conventional forming method. Figure 9B is a diagram showing the longitudinal strain distribution of the raw tube before the sizer roll in the conventional forming method. Figure 9C is a diagram showing the longitudinal strain distribution applied to the raw tube in the conventional forming method, and Figure 10A is a diagram showing the longitudinal strain distribution of the raw tube after sizer rolls in the conventional forming method and the residual strain distribution based on it. 10B is a diagram showing the longitudinal strain distribution of the raw pipe before the sizer roll in the method of the present invention, and FIG. 10B is a diagram showing the longitudinal strain distribution applied to the raw pipe by the sizer roll in the method of the present invention. C is a diagram showing the strain distribution in the longitudinal direction of the raw tube after sizer rolling in the method of the present invention and the residual strain distribution based thereon, and Figure 11 shows the strain after applying equal strain to two parts where there is already a difference in strain. It is a stress-strain diagram showing a change in difference. 10...Side roll, 11A...Strip plate, 11
B...Main pipe, 16...Squeeze roll, 19...
Sizer roll.

Claims (1)

[Claims] 1. In a method for manufacturing an electric resistance welded steel pipe in which a blank pipe is formed by welding both edges of a bent steel strip, and the blank pipe is formed to a fixed diameter using sizer rolls, the welded portion of the blank pipe is When the diameter including the vertical diameter is the vertical diameter of the raw pipe, and the diameter perpendicular to the vertical diameter of the raw pipe is the horizontal diameter of the raw pipe, the ratio r (vertical diameter) of the vertical diameter to the horizontal diameter of the raw pipe before entering the sizer roll is /lateral diameter) is 1.04≦r
A method for manufacturing an ERW steel pipe, characterized in that pre-deformation is applied to the raw pipe by side rolls before entering the sizer rolls so that ≦1.10.