JP2564311B2 - Steel pipe welding method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a high-efficiency and high-quality welding method for preventing defects occurring at the end of a UOE steel pipe, that is, a straight seam submerged arc welded steel pipe.

[Conventional technology]

When manufacturing a straight seam welded steel pipe, there is a problem that weld end cracking occurs. Prevent this end crack,
It is well known to mount a so-called discard plate called a tab plate 13 at the start and end of welding of a steel pipe as shown in FIG. 9 for the purpose of performing the welding process smoothly and with high quality. The tab plate is generally attached by welding such as carbon dioxide arc welding.

Since the tab plate is removed after the welding of the steel pipe is completed, it takes a lot of time to remove the tab plate when firmly attached or when a large tab plate is used, which hinders the productivity factory. Also, the consumption of welding materials and tab plate materials is large. Therefore, from the standpoint of production, it is desirable that the tab plate be as small as possible, and it is most preferable that it can be performed without welding in order to obtain an ideal production process.

FIG. 2 shows the rate of occurrence of terminal cracks with respect to the wall thickness of the steel pipe when the tab plate is welded and attached and when the tab plate is not attached. The number of cracks generated is the ratio of the number of cracked pipes to the total number of welded pipes expressed in%. It can be seen from FIG. 2 that the occurrence of cracks depends on the wall thickness of the steel pipe, and that the tab plate has the effect of suppressing the weld end cracking of the steel pipe, and the wider the width, the higher the effect. It is natural that welding of tab plates is considered to be essential in the conventional method, and caution is required for thinner pipes.

FIG. 3 schematically shows an example of a typical end crack 3 generated near the pipe end 4 when the welding bead 2 is placed on the inner surface of the steel pipe 1 with the welding direction facing the pipe end. Occurs parallel to the weld line 5.

In the case of butt welding of plates, there is a so-called "rotational deformation" of the welded portion, so-called means for restraining horizontal displacement.
-3309. This kind of means is effective when the amount of bending deformation is small, such as in the case of single-sided welding of thick plates, but when complex bending deformation is the main cause of distortion, such as in steel pipes, that is, when bending resistance is the main prevention factor. Can not be expected to be effective. That is, seam welding of steel pipes has a mechanism that is essentially different from butt welding of plates.

[Problems to be solved by the invention]

In order to put into practice a process that can improve productivity by omitting tab plate attachment, it is necessary to prevent terminal cracking near the pipe end. Therefore, the cause and conditions of the weld end cracking of the steel pipe were clarified based on the detailed behavioral investigation of the thermoelastic-plastic deformation of the steel pipe.

First, it was found that the form of cracks was high-temperature (solidification) cracks from observations such as fracture surface observation.

This is the cracking that occurs when a strain exceeding the so-called intrinsic critical strain leading to cracking acts in the more or less specific embrittlement temperature range of the weld metal, for example, the solidification temperature or the range from the solidification temperature to about 100 ° C lower temperature. Is. Therefore, to completely prevent this crack, use weld metal with a large intrinsic strain (low crack sensitivity).

The generated strain is reduced or the generation of strain is prevented.

It is already well known that these two measures are effective. The above is contrary to the requirement of high performance, so free design is not always allowed.

From the industrial point of view, the above measures are good, but it is obvious that this cannot be achieved effectively without knowing the nature of distortion (size, direction, place, timing) to be prevented. This is the reason why the complete effect has not been obtained until now in preventing cracking of the steel pipe. That is, in the ordinary steel pipe manufacturing process, thermo-elasto-plastic deformation of the pipe due to welding heat occurs three-dimensionally, and it is difficult to specify the strain that should be prevented. In order to break this wall, the present inventor used a method such as the finite element method and investigated in detail the deformation mode of the steel pipe during seam welding and the behavior of the strain (displacement) caused thereby.

As a result, the cause of cracking at the weld end of the steel pipe was investigated, and a welding method capable of preventing it was developed, and the present proposal was made here.

[Means for solving problems]

INDUSTRIAL APPLICABILITY The present invention is a technique applied to seam welding of a UOE steel pipe in the pipe axial direction. (1) Prior to welding, within a certain region of the pipe end of the steel pipe,
A bending deformation restraining force that keeps the curvature of the steel pipe constant is applied to the steel pipe.

(2) This area is 30 from the end of welding toward the anti-welding direction.
Within 0 mm, it is an area within 150 mm on each side of the welding line that sandwiches the welding line.

(3) Next, seam welding is performed, and after the welded portion is cooled, the deformation restraining force is released.

This is the technical means of problem solving.

[Action]

In the following, in order to simplify the description, the inner surface welding of the pipe will be described as an example.

According to the research conducted by the present inventor, it has been found that the steel pipe is extremely characteristically deformed by welding, and the bending deformation of the weld metal is extremely large as compared with the deformation of the flat plate by welding. Fourth
One example is schematically shown in the figure. FIG. 4 illustrates the displacement of the pipe end on the welding end side when seam welding of one steel pipe is performed. The displacements in the figure are magnified 10 times in the vertical direction for emphasis.

Before welding (welding length 0%), the cut end of the welding end (pipe end) 4 is almost a perfect circle. The pipe end is gradually flattened until the welded length reaches 70% of the total welded length, and as a result, the weld metal 2 undergoes bending deformation 15 in the opening direction and its amount gradually increases. If the weld length exceeds 70%, a sharp bending behavior 15a occurs.

Such a bending deformation is an angular shape Δδ with the welding line 5 as the axis.
Can be revealed by measuring. For example, as shown in FIG.
It can be measured by combining and dial gauge 7.

An example of bending deformations 15 and 15a sandwiching the weld metal 2 obtained by the measuring method shown in FIG. 5 is shown in FIG.

FIG. 6 shows the measurement results at the pipe end, but until just before welding reaches the measurement point (point A), the shape of the end face of the steel pipe is flattened, and bending deformation is added in the direction in which the weld metal 2 opens.
However, when the welding reaches the vicinity of the pipe end, the deformation of the end face is changed to the bending deformation in the direction in which the weld metal 2 is closed. It is considered that this is because the seam portion temporarily protrudes outward in the radial direction due to thermal expansion in the vicinity of the weld line and the shape of the end surface becomes convex.

The bending deformation in the direction in which the weld metal 2 closes becomes maximum when passing through the welding point (point B), and immediately thereafter, the bending deformation 15a in the direction in which the weld metal 2 opens suddenly reaches C. At this time, cracking occurs.

That is, it was found that the occurrence of the sudden bending deformation for opening the weld metal 2 in the open bending deformation 15a portion indicated by the white arrow in FIG. 6 almost completely corresponds to the occurrence of cracking.

Therefore, it is clear that preventing this sudden bending deformation 15a is an essential method for preventing cracking. However, what is important is how to implement this method efficiently.

Then, we used computer simulation again, examined various restraint methods, and found the following method by the test in the actual pipe. That is, in seam welding of the steel pipe 1 in the pipe axial direction, in the region surrounded by 300 mm from the welding end end 4 of the pipe toward the inside of the pipe and 150 mm on both sides in the pipe circumferential direction with the welding line 5 in the center, Welding line 5 generated by welding thermal stress
A bending deformation restraining force that suppresses the bending deformations 15 and 15a of the steel pipe with the axis of rotation as the axis of rotation is applied at two or more constraint points, and cracks may occur if welding is performed with the curvature of the steel pipe kept constant within the above region. Highly efficient and high quality steel pipe welding is possible.

Note that this method can naturally be applied to welding from the outer surface of the steel pipe.

As described in the embodiments, a clamper or the like is an example of the restraint means.

 Next, the basis of the present invention will be described.

The present invention is applied to a straight seam steel pipe in the pipe axis direction. For example, it is considered that the generated strain is different in spiral steel pipes and the like, and that the method of the present invention as it is may not be sufficiently effective. Welding end 4 in the axial direction of the steel pipe 1.
From the inside of the pipe to the region of 300 mm, and the welding point was sandwiched in the center and the constraint point was limited to the region of 150 mm on both sides in the pipe circumferential direction, even if the region outside of this was constrained by any bending deformation constraint force. This is because the distance from the welding line and its end is too long to prevent the bending deformation 15 of the opening.

As described above, as a jig for satisfying the above condition, a so-called clamper 9 type jig for sandwiching the pipe end 4 as shown in FIG. 1 is considered as the simplest example. Of course, the jig for restraining the pipe end is not limited to this, and for example, the clamping of the pipe end 4 by the mold 11 as shown in FIG. 7 is performed with the high strength belt 12 as shown in FIG. Tightening of the tab plate 13 that is normally used as shown in Fig. 9
Welding 14 and other methods are possible.

In the method using the die, the equipment becomes large in scale, the workability is poor, and in order to restrain the bending deformation, it is necessary to compress the die until the outer peripheral portion of the steel pipe comes into close contact with the die without a gap. It is not preferable in terms of higher efficiency.

The method using a belt is a means of preventing open bending deformation which is a cause of cracking because the pipe cross-sectional shape can change freely due to the property of being able to deform corresponding to the steel pipe shape which is the original property of the belt. I won't.

The method of welding the tab plate 13 of may have an effect close to the method of the present invention, but since a tab plate having a thickness equal to the thickness of the steel pipe is used for ensuring quality, in the case of a thin steel pipe, the tab plate is used. The bending deformation resistance of the plate is small, the bending deformation restraining force becomes insufficient, and the effect of suppressing the strain applied to the weld metal in the pipe may not be obtained in some cases, and in many cases cracking cannot be completely prevented.

〔Example〕

An X-shaped groove was provided in the axial direction of a UOE pipe having a wall thickness of 7 mm and an outer diameter of 700 mm, and the inner surface of the pipe was welded by three-electrode submerged arc welding (SAW) with a welding heat input of 20 kJ / cm.

In the groove on the outer surface side of the pipe, a temporary welding bead, which was previously CO ₂ welded under the condition of 2.5 kJ / cm, is continuously provided to prevent the pipe from freely opening.

The restraint jig uses a clamper 9 of the type shown in FIG.
As shown in FIG. 11, the bending deformation restraint force is generated at this time by fixing one arm 9a of the restraint jig with the restraint jig fixing jig 18 and adding a bending torque of 20 kgf · m to the other side. The amount of angular displacement 17 was measured and determined. The crack occurrence rate was calculated by (number of crack occurrences) / total number of welds × 100%, and in this example, the crack occurrence rate was 500 units.

Example 1 No tab plate and no restraint (Comparative example 1) When a tab plate (width 300 mm) was welded (Comparative example 2) As shown in FIG. 11, the bending deformation restraining force 16 was 20 kgf · m. Bending deformation Δθ is 0.5 degrees, with a restraint jig of the shape shown in Fig. 1, at the position 20mm from the pipe end, sandwiching the welding line, both sides
FIG. 10 shows a comparison of the opening angle deformation behaviors under the three conditions when the width of 150 mm was constrained (Example 1). Table 1 shows the crack generation rate corresponding to this, and it can be seen that the crack generation is completely prevented under the conditions of the embodiment.

Examples 2 to 7 Table 2 shows a constraint jig as shown in Fig. 1 having a bending deformation constraint force of 0.5 degree or less with respect to a torque of 20 kgf · m, and the constraint point interval is 50 around the welding line. ~ 450mm,
In addition, the occurrence rates of cracks are shown in comparison when the depth distance from the pipe end is changed to 20 to 500 mm.

All of Examples 2 to 7, which are within the scope of the present invention, were able to prevent cracking. On the other hand, cracks are generated in Comparative Examples 3 to 8 which deviate from this.

Examples 8 to 9 Table 3 shows that when the clamper 9 shown in Fig. 1 is used and the constraint point (position of the clamp bolt 10) is set to 300 mm and the position 20 mm from the pipe end is constrained, the torque is 20 kgf · m. This is an example in which the bending deformation restraining force of the jig is changed so that the bending deformation becomes 2, 0.5 and 0.1 degrees. Although there is a tendency for the cracking rate to increase a little when the binding force becomes smaller, the tremendous effect of the present invention can be seen by comparing without the tab plate, that is, in comparison with the cracking rate in Table 1.

Example 4 This example shows an example in which the present method is applied to outer surface welding. First
As shown in Fig. 12, three-electrode submerged arc welding with a welding heat input of 20 kJ / cm was performed from the outer surface side in the pipe axis direction of a pipe having an outer diameter of 700 mm and a wall thickness of 7 mm. The groove was V and the backing material 20 was applied from the inside. In addition, a small temporary bead (2.5 kJ / cm, CO ₂ welding) 19 was previously placed in the V groove to prevent the opening of the pipe.
In the comparative example, no restraint was performed, the tab plate (300 mm width, 7 mm) was attached, and the restraint method of the present invention (same conditions as in Example 1) was performed. The result The results are shown in Table 4. It can be seen that the method of the present invention has a sufficient effect on external surface welding.

〔The invention's effect〕

ADVANTAGE OF THE INVENTION According to this invention, the tab plate used at the time of completion | finish of the welding of a pipe can be eliminated, the efficiency of welding can be improved significantly, and the labor-saving effect by automation is also large.

In addition, the ability to prevent cracks is optimal for UOE steel pipes for line pipes, which require high quality, and contributes greatly to ensuring safety, and can be expected to improve pending production.

In addition, it is possible to apply generally known high-strength weld metal with high susceptibility to cracking and high alloy weld metal to steel pipe welding,
We can supply high-performance steel pipes to a wide range of industrial fields.

[Brief description of drawings]

FIG. 1 is a perspective view of an example of a pipe end clamp jig suitably used for carrying out the method of the present invention, and FIG. 2 is a graph showing the relationship between the wall thickness of a steel pipe and the number of cracks at the end of welding. Fig. 3 is a schematic diagram of a typical end crack, Fig. 4 is an explanatory diagram showing the deformation behavior of a steel pipe due to welding (10 times displacement is displayed), and Fig. 5 is an explanation showing a method for measuring angular deformation due to flattening of a steel pipe. FIG. 6 is a graph showing a typical example of angular displacement sandwiching a welding line in a steel pipe cross section, FIG. 7 is a perspective view showing a steel pipe fixing mold example, and FIG. 8 is a perspective view showing a pipe end tightening belt example. FIG. 9 is a perspective view showing an example of attaching a tube end tab plate, FIG. 10 is a graph showing an example of preventing angular displacement according to the present invention, FIG. 11 is a sectional view showing a method for measuring bending restraining force, and FIG. It is a perspective view showing an example of application to outer surface welding. 1 …… Steel pipe, 2,2a …… Welding metal 3 …… End cracking 4 …… Pipe end (welding end) 5,5a …… Welding line 6 …… Welding position 7 …… Dial gauge 8 …… Fixed fixing Tool 9 …… Clamper, 10 …… Clamp bolt 9a …… Restriction jig, 11 …… Mold 12 …… High-strength belt 13 …… Tab plate 14 …… Welding part 15,15a …… Bending deformation 16 …… Bending torque 17 …… Angular displacement 18 …… Restricting jig Fixing jig 19 …… Temporary bead 20 …… Backing material

Claims (1)

(57) [Claims] 1. When performing seam welding of a UOE steel pipe in the axial direction of the pipe, the steel pipe is welded within a region of 300 mm or less in the anti-welding direction from both ends of the weld line within 150 mm on both sides in the pipe circumferential direction. A method for welding a steel pipe, which comprises applying a bending deformation restraining force for maintaining a constant curvature, then performing seam welding, and releasing the deformation restraining force after cooling the welded portion.